Final Report Summary - ULITES (Ultra-lightweight structures with integrated photovoltaic solar cells: design, analysis, testing and application to an emergency shelter prototype)
Executive Summary:
The work carried out by all the partners of uLites has allowed the design and construction of a real-scale prototype of a portable shelter structure for emergency situations. The main characteristics of the uLites prototype are:
- Standard available area (considering three tubes): 150 m2
- Weight: 250 kg/tube
- Folded volume: 0,75 m3/tube
- Average setup time: 1,25 hours
- Recommended personnel: 8 people
The set up lasts less than one hour to achieve a pressure of 20 mbar. To maintain the structure inflated 5-6 minutes of air inflation per day are sufficient. This inflation is automatically activated when pressure decreases below the 10mbar.The total energy consumption estimated is 251,4W/day
The main technological improvements achieved with the uLites prototype are:
1. BETTER PERFORMANCES than traditional inflatable structures:
o SUSTAINABLE Flexible photovoltaic SOLARPANEL modules are used on the shelter to minimize the energy requirements.
o LESS AIR LEAKAGE Leakage reduction from 2000m3/h to 0.038m3/h thank to the quality of PVC coating, the tangent tubes technology and the combination of welding and sewing manufacturing.
o NO NEED OF CONTINUOUS AIR IMPULSION A “mixed” system has been designed, which combines the energy storage by means of “pressure energy” and the use of batteries for the “extra” energy generated.
2. INNOVATIVE MATERIALS
o PHOTOVOLTAIC MEMBRANES: SOLARPANEL. Material characterization via uniaxial and biaxial tensile tests was performed.
o FLEXIBLE CARBON FIBER STRIPES: Development and testing of a new high-toughened thermosetting resin. 0.15-0.33mm thickness, some cm curvature radius. Creation and testing of new anchorage system.
3. INNOVATIVE SOLAR ENERGY SYSTEM
o SOLARPANELS Nominal power 80W
o 220Ah battery
4. NEW INTEGRATED DESIGN TOOL An integrated VIRTUAL WIND TUNNEL tool has been developed for the calculation and design of the shelter.
o Both CFD and FSI calculation.
o Atmospheric Boundary Layer Generator Module.
o User friendly integrated pre and post processing
The uLites team joined expertise in different areas, starting from the production and development of the materials (Reglass and Naizil), including the basic theoretical and practical knowledge for their more suitable applications (University of Padua) and the expertise in application and development of numerical algorithms (CIMNE and Technical University of Munich), up to the final design and construction phase (Buildair and SLRash).
An extended experimental campaign both on Naizil SOLARPANELS and Reglass carbon fibre stripes and anchorages was carried out at the University of Padua resulting in a careful assessment of the material properties of the new materials to be employed, providing crucial information for the future use of the new materials in practical applications. The Italian SMEs have worked closely to the uLites coordinator, Buildair, to integrate their innovative materials in Buildair inflatable structure. The outcome of this collaboration was the implementation of an improved manufacturing technology and of a novel energy storing and distribution system that improve considerably the performances of the inflatable structures.
On the other hand CIMNE and the Technical University of Munich, with the advice of SLRasch, have been developing an ambitious Virtual Wind Tunnel (VWT) tool. This is a virtual prototyping lab which allows the assessment of the coupled structural and aerodynamic performance of the new designs in a user friendly environment. The VWT include an Atmospheric Boundary Layer (ABL) generator module, a CFD code using advanced embedded technique based on Kratos Multiphysics (CIMNE) a CSD code based on Carat (TUM) a Human Interface based on GiD (CIMNE). This tool was validated by means of a series of benchmark tests and using the experimental results of a wind tunnel experimental campaign carried out at the University of Florence in CRIACIV laboratory.
Project Context and Objectives:
Every year several thousand people become homeless due to natural disasters as earthquakes, floods or wind storms, which periodically affect wide areas of the Earth. To face such situations emergency flying squads, national emergency squads and international organizations (military, red cross…), need to be able to quickly deploy temporary housing (mainly tents), facilities such as hospitals or headquarters, and infrastructures (roads, bridges, harbors) in different and adverse conditions. The importance and extent of such catastrophic events is unfortunately expected to rise over the next decades due to the impact of the global warming. While modern societies have limited power in preventing such exceptional events, they are expected to react in short time to any emergency situation, providing an efficient post-disaster intervention and reducing its economic and social impacts. In this sense, the present work aims to provide an answer to the increasing need for highly portable post disaster facilities, which could be satisfied by using temporary lightweight structures like tents, inflatable covers, portable warehouses or hangars.
The idea of uLites has been to leverage the large experience in design and construction of lightweight structures of two of the SMEs that participate in the consortium (BuildAir and Rasch) and to improve the efficiency of their products with the use of innovative materials and manufacturing techniques that can provide an enhanced performance while reducing some drawbacks. This was obtained with the joint work of all the partners of the uLites, providing their expertise to achieve the following objectives:
1. Creation, testing and patenting of new materials both for the carbon fibre stripes and the flexible photovoltaic cells (Reglass and Naizil with UniPD). The development, in recent years, of innovative lightweight materials opens new possibilities in the design and engineering applications of ultra-lightweight structures. On the material side, one of the main goals of the uLites project has been to foster the development and the practical applicability of the innovative materials which were developed by the SMEs in the consortium, namely the carbon fibre stripes (Reglass) and the polymeric fabric with embedded photovoltaic solar cells SOLARPANELS (patented by Naizil).
2. Optimization of the design process of inflatable structures (Buildair and SLRash with CIMNE and TUM). It is apparent that the classical experience-based approach towards the manufacturing of light-weight structures is no longer sufficient to be competitive, since it implies high costs in terms of testing expenses as well as a long iterative process. The maturity of numerical techniques both in Structural Mechanics and in Computational Fluid Dynamics (CFD), accompanied by the availability of affordable high-performance hardware, allows the use of virtual rapid-prototyping facilities (a Virtual Wind Tunnel) as realistic alternatives to traditional (time consuming and expensive) wind tunnel experiments.
3. Extended validation and testing of prototypes to create guidelines for future developments. The uLites partners has developed a series of performance tests and demonstrations benchmarks in order to have a quality check of the results and to facilitate take-up by the European market of the new technologies proposed
Project Results:
During the whole uLites project, the parallel work of the different partners has been organized and coordinated successfully. Both SMEs and RTDs have shown a great interest in the progresses of the project and in the results with an active and continuous cooperation.
The R&D objectives of uLites can be summarized in the following items:
1. Analysis of the state-of-the art in the market of lightweight structures and of innovative materials (WP1). For that purpose a preliminary patent search analysis was performed on M12 and has been updated on M20 and M24 showing no relevant changes.
2. Design of the emergency shelter prototype. First definition of the design of one module of the emergency shelter structure to be realized and definition of the load combination to be taken into account (WP1). This design was confirmed and detailed on M16 by the executive project of the emergency shelter (WP5 D5.1- D5.3).
The design of the structure for this project, thought as a modular emergency structure, has been done considering that the shape and the dimensions of the structure should be as standard as possible, in order to better compare the improvements due to the new power supply; the inclusion of photovoltaic cells, is also a relevant aspect since the structure design should be compatible with them; finally, as will be explained in the following points, the innovation also includes aspects related to the materials, such as lighter and more resistant materials or different manufacturing techniques to improve air-tightness of the tubes; the engine system should be also improved for a more sustainable use of the shelters.
The prototype built at the end of the project is a three tubes inflatable structure. The diameter of each tube is 2.50m the clear span width is 20m and the clear standard height is 10m. This shelter can be either closed or not with a front and back door depending on the need.
3. Concerning the innovative materials (WP1 and WP2) to be used in the prototype the following tasks have been achieved:
3.1. Definition of the material to be used (WP1). Polyester/PVC Type 2 seems to be the best choice for the good mechanical characteristics and the high tear strength. The carbon fiber stripes are a completely new material in the branch of tensile structures. These can replace traditional iron stripes providing a great flexibility with lower dimensions, lower weight and higher resistance. The use of a thermoplastic polyurethane resin leads to the possibility of welding stripes and membranes reducing the risk of cut in the stress concentration areas.
3.2. Definition of the parameters to be quantified before simulating the structure (WP2). In the case of photovoltaic membranes (Solarpanel) these are the stiffness of the membranes and their ultimate tensile strength (although this latter seems to be less important than the first). Finally the quantification of the strains compatible photovoltaic energy production should be made. On the other hand the fibre stripes need to be characterized in terms of their ultimate tensile strength and the ultimate strength of the anchorages.
3.3. Performing the experimental campaign on flexible SOLARPANEL modules (WP2). Specific procedures were defined and ad hoc devices were designed to allow testing the membranes with embedded photovoltaic cells since standard one could not be used (D2.5). Solarpanel, in fact, are produced with fixed modular dimensions (94×170 cm) and cannot be cut. On the contrary the “European Design Guide for Tension Structure – Tensinet 2004” defined standard uniaxial and biaxial test procedure to be executed on 50×50 cm specimens only.
Both tests on blank specimens and on specimens with solarpanel were carried on to analyse the influence of the photovoltaic module in the mechanical behaviour. During tests on Solarpanel, the photovoltaic cells are lightened and electricity production measured in order to evaluated which stress leads to failure of the cells. Preliminary numerical models were also built to evaluate the behaviour of the specimen during the experimental tests.
Tests were performed with the following steps:
First of all mounting of the specimen on the test frame; secondly imposition of a horizontal pretension (4% of the tensile strength) introduced using springs; after that, imposition of a vertical pretension (4% of the tensile strength) introduced using an hydraulic jack at the top of the test frame; later imposition of a cyclic vertical loading (4 cycles, up to the 20% of the tensile strength), using the hydraulic jack at the top of the test frame, to stabilize inelastic deformation and measure deformations and applied force.
The initial experimental campaign shows a premature rupture of the membranes even with low tensile loads: this was the consequence of the shape of the specimens, of the details introduced to impose a lateral pretension and to the imperfections of the cuts. To avoid these problems a optimization of the specimens to redefine the same in order not to affect to the experimental results has been performed. The new axial and biaxial tests show the problem has been overcome and gave promising results.
The results on specimens with Solarpanel pointed out how the transparent protective coating fully collaborates with the support membranes in bearing tensile loads. Specimens with Solarpanel had no increase of warp elastic modulus introducing a lateral pre-stress of 4000 N/m: this is due to the external protective coat, a uniform material whose modulus is not sensible to internal tensile stresses and which is much stiffer than support membrane. Uniaxial tests on specimens with Solarpanel showed values of tensile strength similar to the one of the blank specimens. As expected protective external coat seems not to give a contribution in terms of tensile strength because ultimate deformations of the supporting membrane are too large. Biaxial tests leaded both types of specimens to a premature failure because of stress concentrations and deviations due to the details and devices used to give lateral pretension: these, in fact, always originated the fractures. Finally, electricity production: was observed to be almost constant up to 22N/mm and above that stress level, decay was observed. Nevertheless both on uniaxial and biaxial tests power production were observed to be stable at different tensile stresses values in their serviceability range ([0; 20] N/mm).
3.4. Performing the experimental campaign on carbon fiber stripes (WP2 – D2.3 and D2.7).
A thermosetting polymer was used instead of a thermoplastic one because it manifests higher shear strength, reducing the risk of the delamination due to the frictional forces ensuring the restraints of the strip. In fact there have been made several attempts to find the best way to fabricate flexible ribbons with carbon fibre useful for this purpose. The main problem is due to the fact that carbon fibre stiffness is very high and the elongation at break is small. It is therefore quite difficult to redistribute the loads between the fibres and, furthermore, the possible curvature radius strongly increases with the ribbon thickness. The first idea was to embed the carbon fibres in a thermoplastic matrix in order to have high flexibility also with relative important thickness but the results of this test were not acceptable both for the poor shear strength of the resin and poor bonding with the fibres. Second idea has been to use an epoxy thermosetting resin with very thin ribbon thickness. The behaviour was better but the curvature radius was still too high and the ribbon very delicate and fragile.
After some other tests a new high-toughened thermosetting resin has been developed which has given very interesting results, leading to a good ribbon in 2 thicknesses: 0.15 and 0.3 mm with small curvature radius high resistance and acceptable toughness. Moreover two external layers made with a woven-nonwoven carbon fibre mat were introduced, conferring to the ribbons a higher stability against the undesired phenomena of separation of the tensed carbon fibres. This new ribbon is the one used in experimental campaign. The tests on the carbon fibre stripes consist in loading the specimens with a uniaxial tensile force thanks to an imposed elongation. To perform the test, Galdabini’s Sun 60 machine was used. To avoid any unexpected effect producing oscillation, the velocity of elongation was set low enough to represent a quasi-static condition in the test. Values that were used are 1.0 ÷ 2.0 mm/min. In order to connect specimens (anchorages, see below) to the test machine, specific forks were provided. Two different kinds of stripes were produced by Reglass: a strip with dimensions 14̇x0.15 mm and one with dimensions 14×0.3 mm. Evaluating the percentage ratio between the area of carbon fibres and the area of the whole section of the strip it has been defined a ‘theoretical value’ of the strength equal to 5290 N for the 0.15 thick strip and 10580 N for the 0.30 thick one. To increase the tensile strength the stripes will be placed side by side winding them together on the same anchorage.
3.5. The anchorages design was the result of the following requirements: compact size and ease of assembly to allow transportability, high strength to resist the tensile force deriving by the stripes, and scalability to be easily adaptable to the dimension of the stripes.
Two different anchorages were designed to perform tensile tests since the stripes require an extremely high level of flexibility and the compact size of the connections. A solution with a deviator (T1) and one with a wedge (T2) were tested.
The anchorage type T1 is composed by a steel cylinder on which to coil the strip and a diverter to realign tensile force with the central pin. These two components are joined by two plates that transmit the moment due to the deviation of the stripes on the diverter. This anchorage exploits friction between the strip and the cylinder in order to transmit traction from the first to the pin. The anchorage type T2 is composed by a wedge on which to coil the strip and to be inserted in a case to transmit tensile force to the central pin. Two plates close the wedge and the case. This anchorage exploits friction between the strip, the wedge and the contact wall of the case in order to transmit traction from the first to the case and so to the central pin.
In both cases a preliminary numerical analysis by means of a finite element model in non-linear regime were carried out to evaluate the strength of the anchorage previous to the experimental campaign detailed in D2.3.
It was observed that the anchorage T1 worked as expected whereas T2 seems to be very sensitive to imperfections due to the laser cut that leads to excessive local stress concentrations damaging the ribbons.
To limit this problem the anchorages have been produced in milled steel to reduce imperfections and “deformable” spikes made of plastic material (HDPE) were adopted. New tests have been performed obtaining a higher effectiveness of the anchor. As explained above, the desired value of tension to be carried by the stripes in the application (inflatable shelter) will be reached placing the stripes side by side winding them together on the same anchorage.
3.6. Connection between membranes and carbon fibre stripes
Two different connections systems were tested: sliding stripes contained in proper continuous cases made with the same material of the membrane and welded on the upper chord of the tubes composing the structure (a sort of hoop connected to the ground) and stripes connected directly to the membrane thanks to a high strength double-sided tape in order to allow load transmission between membrane and stripes. This latter connection system was seen to be not suitable for the uLites prototype since it manifests a highly non uniform distribution of shear stress and a very high sensitivity to the irregularity of the PVC surface. Both this aspects caused a premature breakage of the specimen. In the case of the sliding case the behaviour is better but the total strength observed is lower than the double of the single string strength. This might be the consequence of the scale of the experiment that does not allow the load device to guarantee the perfect alignment of the tensile force applied by the hydraulic jack. This connection type is suitable for the construction of the prototype providing a proper safety factor in the structural analysis to be adopted.
4. Concerning the creation of a Virtual Wind Tunnel (VWT), the following objectives have been achieved:
4.1. Definition of the design strategy (WP1 D1.5). Use of Davenport’s wind load chain in designing the wind loads on the structure, which define the fundamental loading to be taken into account in the design of the software for the VWT.
4.2. Definition of the essential input parameters to be taken into account in the simulation (WP3 D3.1). The possibility of analysing the wind spectra and especially the mean wind velocity at a given height considering the turbulent characteristics of the wind (i.e. corresponding to the target wind spectra), was seen to be an essential requirement for the design tool. The definition of a terrain roughness or the specification of a terrain category was also considered essential in order to a valuable response. These essential input parameters are required for the generation of physically meaningful wind fields in the so-called atmospheric boundary layer, where the building structures are situated. Within this project an Atmospheric Boundary Layer generation module (ABL) (D3.3) was developed and implemented. Numerical Wind Field Generation is to synthesize the turbulent part of the wind (the fluctuations) according to particular constraints, in order to have series of space/time-varying velocities that can be used as inlet boundary condition in CWE problems. Although random turbulence, or a “white noise”, although might fulfil the required wind intensity, they fail to comply with the physical requirements of the wind inlet condition. Besides containing the wrong distribution of energy (wrong spectrum), it lacks spatial and temporal coherence that real-wind turbulence has; causing the generated fluctuations to vanish immediately in Navier Stokes solver. Therefore, methods to produce more complex “noise” should be found to allow the fluctuating part of the numerical wind to represent realistic wind turbulence, and to be able to survive in the CFD environment. The ABL-generator tool was developed according to the wave-superposition-based method of J. Mann and was successfully validated (D3.4 D3.5). Since ABL is based on a method that has a stochastic nature, the straightforward approach to validate it is through examining the statistics of its product. This was checked by sampling the fluctuations at a chosen set of coordinates (i.e. obtaining synthesized wind turbulence time-series) and analysing them. Moreover a parametric study on the generator was carried out too. The validation of the ABL was completed using the data measured in the Physical wind tunnel tests performed on the rigid model (presented later) and confirm the validity of the tool.
The ABL package produces velocity fields which have length and time scales that model real-life winds scales, i.e. not wind-tunnel flow scales. Therefore, for a valid comparison for Atmospheric Boundary Layer effects on structures, a geometrical scale in the range (1:150-1:250) and a velocity scale in the range (1-5) should be used, keeping in mind the Reynolds number independency. This independency was experimentally proven in the wind tunnel experiments. Also, scaled up simulations were performed and have shown good agreement with the wind tunnel results for ABL flows (D3.5).
The guidelines to use the ABL were finally created (D3.6) considering different set of available data.
4.3. Implementation in the fluid code (Kratos) of a geometrical tool to embed the structural geometry in the fluid mesh (WP4 D4.5). This is done employing a modified finite element space which includes discontinuity along one surface. “Virtual nodes” are inserted in the finite elements where these are cut by the structure.
4.4. Implementation of the interface for the simulation codes (D4.1 D4.2).
The virtual wind tunnel is composed of different modules that should be coupled together. For this purpose a coupling tool has been adopted and customized to work with the structural code (Carat) and the CFD code (Kratos). The two modules have been interfaced using the Empire coupling tool and its API has been used for the definition of the communication between the different modules.
EMPIRE is designed and implemented for solving general multiphysics problems with n-code co-simulation. The customized interface is characterized by:
• Flexibility: co-simulation in a general scenario is available, since an arbitrary number of simulation codes and arbitrary connections among them are allowed.
• Modularity: partitioned strategy is used to apply existing simulation codes; the simulation codes are connected by Emperor; communication interface is provided in the library EMPIRE API; object oriented programming with C++ is used to implement EMPIRE.
• Efficiency: communication is realized by using MPI; efficient mortar method is implemented for mapping data between non-matching grids; methods are implemented to accelerate co-simulation, e.g. extrapolation and relaxation.
• Usability: co-simulation is set up in a single file (input XML file of Emperor); simulation codes in all C-compatible languages can link to the library EMPIRE API; various filters are provided for data operations including mapping, extrapolation and relaxation
A customization of the Empire was carried on and both Kratos and Carat were modified in order to allow the following design flow-chart:
1. Define the Structural Model (Carat)
2. Identify the coupling surface
3. Identify the inlet and generate a statistically appropriate inlet condition (virtual atmospheric boundary layer)
4. Transfer to Kratos the triangularized coupling surface together with the dimensions of the fluid domain to be considered (fluid domain will be box-shaped)
5. Construct the box fluid domain and eventually refine it locally in the vicinity of the structure. (to be performed internally by Kratos)
6. Transfer inlet conditions to the Kratos by suitable mapping operation
7. Solve the fluid domain using an embedded approach (Kratos)
8. Map pressure forces to the structure and displacements to the fluid (Empire)
9. Solve structural domain (Carat)
4.5. Implementation and validation of a graphical user interface (GUI) (D4.3 D4.4). Each of uLites solvers (CARAT and KRATOS) is modular. This motivates the use of GiD (http://www.gidhome.com) as a pre/post-processing tool. GiD allows defining an interactive graphical user interface used for the definition, preparation and visualization of all the data related to a numerical simulation. This data includes the definition of the geometry, materials, conditions, solution information and other parameters. The program can generate a mesh suitable for several numerical methods and write the information for a numerical simulation program in its desired format.
The program works, when defining the geometry, in a similar way to a Computer Aided Design (CAD) software. All materials, conditions and solution parameters can be defined on the geometry itself, separately from the mesh as the meshing is only done once the problem has been fully defined. The advantages of this are that, using associative data structures, modifications to the geometry can be made and all other information will automatically be updated and ready for the analysis run.
Full graphic visualization of the geometry, mesh and conditions is available for comprehensive checking of the model before the analysis run is started. More comprehensive graphic visualization features are provided to evaluate the solution results after the analysis run. This post-processing user interface can also be customized depending on the analysis type and the results provided.
In order to allow GiD to input to a modular code (CARAT or KRATOS), a so called “problem type” was implemented and included.
4.6. Validation of the VWT (D3.2 D3.4 D3.5 D4.5 D4.6 D5.3).
A series of validation examples to be used to check the virtual wind tunnel performance (D3.2) and beginning of the validation tests was defined. Both tests on simple geometries and tests on building like geometries have been taken into account and were used to test the automatic inlet generation module (D3.4,D3.5) the CFD code (D4.5) the geometrical tool to embed the structural geometry into the fluid solver (D4.5) and the complete VWT (D4.6 D4.7 D5.3).
A wind tunnel experimental campaign was carried out to provide validation data for the VWT. Both a rigid model and a flexible one were tested considering different positions and orientations of the structure with respect to the inlet direction as well as considering, in the case of the aeroelastic module, the possible presence of an obstacle of the same scale as the structure, in front of it. The purpose of these experiments was not the analysis of the real prototype structure; in this case, the scaling of material properties would have been extremely complicated if not impossible, but to test the good performance of the VWT in scale 1:1 (D3.5 D4.6).
On the other hand the real scale prototype was also simulated with the VWT to predict its response to the worst wind scenarios (D5.3).
After this tests were performed an estimation of the money and time saving of numerical tests vs physical one can be made for the specific case. The wind tunnel tests cost approximately 50.000Euros considering the cost of the model constructions, the hours of laboratory, the men/months and the duration is approximately 1 month. In the case of numerical simulation the estimated costs for performing the same cases is 15.000Euros considering one engineer working one months for pre and post processing issues and including the calculation hours to be rent to run the simulations in large clusters and the time is approximately one months. It is worth mentioning that in numerical modelling no scale effect should be taken into account allowing a 1:1 scaled analysis of the real case.
4.7. Guidelines for the use of the VWT lab (D4.7) All the steps to be followed to download and install the VWT were presented and a step-by-step tutorial was written so to allow SMEs’ partners to get in touch with the tool.
5. Design and Construction of the ulites emergency shelter prototype.
5.1. Improvement of air-tightness (WP5 D5.1). Different types of fabrics have been considered, with more/less resistance features, different coating, physical properties, and so on. Since the key point in this structure is the air-tightness, the candidate materials to be used are those that have a good PVC coating, which make the tubes air-tight and also easier to weld during the manufacturing process. On the other hand, these fabrics become a little heavier, increasing the total weight of the structure compared to previous hangars done by Buildair.
An innovative manufacturing process combining welding and sewing has been tested. The combination of both methods is ideal to achieve a manufacturing method that allows welding only the critical parts that require air-tightness in an easy manner. Then sewing is used on more complex parts that are not easy to close with the welding machine. Thanks to this procedure some kind of air-tight inner chamber can be manufactured with an independent closing envelope where needles does not affect the air-tightness. The structure manufactured consists of 3 independent tubes instead of a whole module of 3 tubes (the standard Build air technology). These tubes are positioned tangent one to another with the idea of increasing the length of the hangar with less number of tubes and, therefore, less energetic requirements to inflate them. The tubes are connected between them with high-resistance zippers. This fact allows having a very simple modular structure, in which the required length can be easily obtained just adding or removing one or more tubes. The tests show that the leakage is very low (of about 0,038 m3/h, compared to values of 2000 m3/h that some of previous structures used to have)
5.2. Development and testing of an innovative Energy system to improve sustainability (D5.1). A “mixed” system has been designed, which combines the energy storage by means of “pressure energy” and the use of batteries for the “extra” energy generated. The idea comes from the difficulty of finding blowers that have reduced energy consumption (with competitive prices) that are able to support the structure erected continuously, together with the big amount of solar panels required. With this combined system, with less photovoltaic cells and less powerful blowers, a balanced system can be defined to make the structure work with minimum power consumption and lower expenses. The definitive system is formed by a low power blower, which is supplied by a battery with enough capacity to make the first set-up inflation and ensure the maintenance of the pressure during the use of the emergency shelter. All this comes together with 3 flexible photovoltaic panels integrated on the structure, one on each of the 3 tubes, the ones that will charge the battery. It will also include a control system for the monitoring of the pressure and the management of the blower and valves to make it work when required. Considering all the previous requirements and features of the elements that form the system, the energetic needs estimation was the following: First set-up and weekly inflation - we estimated 1 hour of use of the blower per week to inflate the structure up to its maximum pressure (20 mbar) - Consumption = 1100 W/day. Pressure maintenance - between 5-6 minutes per day the rest of the days of the week will be used to maintain the structure within the admissible limits (10-20 mbar) - Consumption = 110 W/day. Total consumption = 1760 W/week (251,4 W/day)
5.3. Inclusion of the Solarpanels (D5.1 D5.4 D5.5). To obtain the minimum number of solar panels needed the Solar Peak Hours (HSP) was calculated. This is used to define the solar radiation that will receive the photovoltaic cells in the place they will be set. Considering the prototype was to be built in Barcelona in winter, the hypotheses for the calculation of the HSP were the following: Location: Barcelona Month: December (worst case) Inclination: 0º (not optimal). The inclination of the cells is determined by their positioning on the hangar. The structure has several anchoring points to try to optimize this position. The problem is that the positioning of the structure can be determined by so many different reasons and an optimal orientation might not be possible (and operative). That is why the hypothesis made is to place the cells on the top of the hangar, at an approximate angle of 0º. According to all these hypotheses, we obtain a value of HSP = 1,61. With this value, together with the energetic requirements and the Solarpanel technical feature, the number of flexible photovoltaic cells needed is 3, connected in parallel. The way to fix these cells to the structure is done with buttonholes on the cells’ support and on the structure, tied with ropes.
5.4. Inclusion of the new carbon fibre stripes (D5.1 D5.4 D5.5) Integrating the carbon fibre stripes in the inflatable structure needs a special set-up procedure, since it is not as easy to handle as a textile strap. The idea is to introduce the carbon-fibre stripes inside a membrane case (like a pocket), in a way that they are free to slide inside it. The membrane gives no contribution on carrying the tensile load. This element would replace the textile straps along the perimeter of at least one tube of the shelter prototype. The total number of carbon-fibre stripes for each tube is 4, grouped in pairs, which can be done with the anchorages designed. The idea of using carbon-fibre stripes in an inflatable structure is a new concept. The characteristics of this material, together with the interaction with the large structure of this project, lead us to think about its fragility if it is bended excessively. Particular care should therefore be taken during the set-up procedure of the structure. There in fact, does not seem very compatible with the treatment of the carbon-fibre material, and there might be a risk of breakage.
5.5. Construction of the prototype (D5.1 D5.4 D5.5) The prototype was successfully built in December 2014 and tested in two different phases: one phase in December 2014 testing all the parts of the structure separately inside Buildair’s factory, and a second phase at the beginning of January 2015 performing a real deployment test in the exterior of the factory testing the whole structure with all the parts together. After these tests, the results confirmed the expectations in many ways.
During the first tests phase, the three tubes composing the prototype were inflated separately, lying on the ground, in order to check the real air-tightness of them and to confirm the blower calibration. In general the results were very positive, since 2 out of 3 tubes showed to keep the required pressure (between 10 and 20 mbar) for much more than 24 hours, without needing any inflation. One of them was even tested during several days, achieving more than 2 days without requiring inflation. Unluckily, one of the tubes (the first that was manufactured) showed several air-leakages that could not allow reaching the objective. This fact allows us to show the difficulty in the manufacturing process, which needs to be checked very accurately. Having taken this into account, the other two tubes were manufactured in a more accurate way, as the improved results confirmed the problem was overcome. The first tube was then checked and repaired to improve its behaviour.
Another test was performed to check the time needed to inflate one tube until reaching the maximum pressure of 20 mbar. Only 12 minutes are required for one tube, so for the whole structure of 3 tubes we would probably need between 30 and 45 minutes (original estimation 1 hour). The time required to increase the pressure of one tube from 10 to 20 mbar was also checked. This is just 20-25 seconds for one tube, so for 3 tubes will be around 1-2 minutes (original estimation 5-6 minutes).
During the second tests phase, a real use was tested, confirming the tests performed before inside the factory. The 2 satisfactory tubes showed that were able to withstand erected without requiring inflation at least for more than 24 h. The other repaired tube was able to keep the pressure during the day but not during the night. This fact also shown that the temperature gradient between day and night is very important for these low-pressure air-tight structures, involving and increase/decrease of pressure of more than 30-40 mbar (initial inflation pressure is 20 mbar). We checked that when we inflated the tubes at 9AM at a pressure of 20 mbar, at midday we reached pressures over 60 mbar in some tubes, while at night it decreased down to 6-7 mbar. Studying carefully this fact will allow us to design an automatic control system to optimize the number of inflations thanks to doing it at the perfect time of the day, according to the temperature gradients. Regarding the required inflation time estimated, the whole structure was erected in just 25 minutes (a bit less than expected), and the re-inflation procedure between 10 and 20 mbar was less than 2 minutes as expected. Moreover, the system does not produce any relevant noise pollution since it is very silent.
Other tests were performed with the photovoltaic system, showing that the efficiency of the flexible solar cells is very influenced by the curvature they take when placed on the structure and also the incidence angle of the sun. We tried to put them on different positions and angles to find the optimal ones. These tests showed the importance of orientation of the structure and the cells, which has to be studied in detail depending on the season of the year and the place where the structure is going to be set-up. Finally, an important part was the connection between the cells. Initially thought in parallel, we changed to series to increase the voltage necessary to charge the battery, since the non-optimal orientation generated and insufficient voltage. Doing it in this way, the tests showed that thanks to the low-energy requirement of the structure to inflate, the cells could charge the battery after the first set-up in order to maintain the structure erected during the following days without problems.
Finally, the use of carbon fibre stripes to anchor the structure was proven to work well.
So, in conclusion, the designed structure confirmed the expectations in many ways and also helped the team to learn and understand better how it works in order to add improvements to this product for its future use.
To conclude, no relevant deviations from Annex I have been identified. Moreover considering the appraisal of technical and non-technical risks stated in the uLites proposal (Table 1.4.1) we can hopefully said that no relevant problems have appeared during the uLites. Nevertheless is worth mentioning that the consortium has been intensively busy with the technical work during the uLites with no sufficient time to fully exploit its results and organize demonstration activities. These are planned to be carried out in the near future.
SMEs’ OPINIONS at the end of uLites
BUILDAIR
Buildair, thank to the uLites project, could design an innovative manufacturing process for its inflatable structures with optimized performances and minimized air losses as largely explained in the reports. Moreover, the inclusion of photovoltaic membranes and the deriving minimization of consumption opened to Buildair new markets such as humanitarian, military and emergency. Therefore the collaboration with the partners of the consortium represented a good chance to improve the technical quality and to innovate the products of the company.
Finally the availability of a user friendly and validated computational tool for design and verification of the structures represent a relevant step forward with respect to the competitors in the sector of inflatable structure.
REGLASS
Reglass took part in the uLites project with the aim of create a new product (carbon fibre strips) that in the medium term could represent a sound and convenient solution for the realization of high performances tensile elements. The strict and satisfying collaboration with the University of Padova laid the foundations for the development and optimization of the products (strips and anchorages) directing our efforts towards real improvements. Our goal for the next future is to improve mechanical properties of strips and anchorages and ease of usage; once this goal will be reached the production will be organized and industrialized in order to enter the market. Moreover we think that the further developments will make the carbon fibre strips suitable for multiple purposes, not only for civil engineering applications.
NAIZIL
Naizil participated in the uLites project with the purpose of characterize the mechanical properties of Solarpanel, a new kind of flexible photovoltaic cell directly embedded to a supporting textile membrane. Collaboration with University of Padua allowed us to define a test procedure able to reach our purpose thanks to a continuous interchange of results and opinions with our RTD partner. Now that Solarpanel has been tested and characterized it can found real utilization into the market. Its uniqueness, in our opinion, makes it suitable for several applications concerning the renewable energy sources and its applicability also as a structural component will be the key for a possible large usage also to realize classical tensile structures. Our goal in the short and mid-term will be the launch and presentation of Solarpanel as the ideal solution for structure with special requirements (energy production for emergency situations) and for a new way of exploiting common tensile structures. This can help Naizil to overcome actual financial troubles and bring it back to be a leader company in Italy and in Europe in the supplying of innovative membranes for lightweight structures.
Collaboration with University of Padua during the project was continuous and was the key to achieve a fully positive project results
SL-RASCH
The main objective of SL Rasch was the developement, industrialization of the virtual wind tunnel and the virtual prototyping lab and the validation with aero-elastic wind tunnel models
- SL Rasch´s field of activity: design and engineering of large convertible membrane structures which are beyond the current state-of-the-art of engineering. Therefore it is absolutely necessary to apply computational tools for their design because current wind tunnel technology is limited.
- There has been a great step undertaken by the ULITES consortium to make a virtual wind tunnel available. It is already applied by SL Rasch for their projects.
- Furthermore the outcomes of ULITES (results, publications) and the collaboration with international recognized scientific institutions (TUM, CIMNE) in the field of numerical simulation is used as reference with regards to the requests of the proof engineering consulting companies in the SL Rasch projects
- Very close collaboration and fruitful technical discussions with R&D partners, especially TUM and CIMNE
- Further outcomes of ULITES like application of photovoltaic cells on membrane structures and application of carbon fiber cables are regarded to be applied also in future projects
RTDs' OPINIONS at the end of uLites
CIMNE
The participation of CIMNE to the uLites project has represented a good opportunity to strengthen existing collaboration with the partners of the consortium and to establish a new network of possible partners for the future. Actually we have already presented more than one proposal to H2020 with some of the partners of the uLites.
The specific benefit from CIMNE side was the realization of a virtual wind tunnel tool (together with TUM) that put together the expertise and the research results of the team for a practical engineering purpose.
During the uLites a numerical vs experimental validations campaign was successfully started and will hopefully continue and be completed in the near future with the partners from CRIACIV.
The main drawback, not directly related to uLites but to the Capacities programme was identified in the short time given for the project. This limited the possibility of exploiting more deeply the RTDs results.
TUM
Benefits that TUM got from ulites:
1- Improvement of the ABL generator to make it capable of modeling very low frequencies satisfying better Kaimal spectra of natural wind.
2- Wind-tunnel tests have provided good validation examples to which further methods and different implementations can be benchmarked.
3- Gaining more experience in the FSI modeling of membrane problems.
4- A new network of experts in different fields is established, which can further enrich research activities.
UNIPD
The participation of University of Padova as RTD member of uLites team has been satisfactory both in terms of work done (tests on new materials, direct contact with SME’s world and their know how) and of possible future developments (applications of new materials, numerical wind tunnel, design of inflatable structures, …). In particular we had the occasion of taking contact with innovative materials that represents, if properly applied, the next future of lightweight structures.
Cooperation with SMEs has been close and effective, also in copying the difficulties encountered during the execution of the tests. Interchange of information between partners and availability in discussing and “producing” solutions to the problems made the collaboration fruitful also in view of further future collaborations
Potential Impact:
The principal outcome of the project is represented by a innovative emergency shelter structure for which a new design has been developed and a prototype presented. In order to achieve this goal a number of sub-products have been generated, namely membrane with embedded photovoltaic cells, flexible carbon-fibre stripes and a virtual wind tunnel acting as simulation software for computer aided design.
The emergency shelter to be developed represents a new, lighter and more practical way to provide a temporary refuge to people who become homeless due to natural catastrophic events or social and geo-politic crises, than common refuges. In fact the integration of photovoltaic cells, combined with the improvement in the sealing of the structures, and the use of power-storage devices (e.g. batteries) for having available power during night time, make these continuum low pressure inflatable structures largely independent in terms of electric energy supply. The name “continuum” comes from the fact that traditionally these structures need to be connected permanently to a power source due to the big amount of air losses.
These continuum low pressure inflatable structures have been widely used worldwide since many years, with several applications in different target business sectors (e.g. aeronautics, defence / military, industrial, humanitarian aid, corporate events). These provide valuable advantages (light weight, big ratio storage volume / folded volume, easy anchorage to terrain without need of foundation works, short lead times, etc.) over other competitor structures (e.g. light metallic structures, tensile structures, presostatic structures, high pressure inflatable structures). However, for some specific uses, some of the intrinsic characteristics of the low pressure inflatable structures (e.g. energy supply dependency, continuous power consumption) make them difficult or even unfeasible to be used (e.g. in areas without any available power supply, or when power sources are expensive or difficult to be obtained or transported).
The integration of the solar cells into the uLites shelters, provides these structures with outstanding added values such as portability improvement, energetic autonomy, or negligible power consumption, which will allow them to compete with the competitor structures on the previously referred uses. This will introduce the SMEs to new notable customers as national emergency management agencies, humanitarian organization, Red Cross, armies, etc
On the other hand the experimental campaign on both Solarpanels and carbon fibre stripes is an important added value in the creation of a reliable shelter since the comprehensive behaviour of these materials has been analytically analysed and classified, not just empirically tested.
It is worth mentioning that carbon-fibre stripes open a new area of the market since, nowadays, there are applications of this material to civil structures, but these are never used as material to produce stays, wires, cables or stripes bringing the ulites’ SMEs to be pioneers in that field.
The creation of a simulation software that acts as a Virtual Wind Tunnel (form finding, structural analyses, wind tunnel simulation and fluid-structure interaction) represents a useful instrument for the innovative design of membrane structures. The development and validation of such software tool allow the study of a larger number of design alternatives allowing a wider design space to be explored and more optimal solutions to be found.
Finally it should be noticed that there is an intrinsic trans-national impact in the uLites project. The cooperation between the SMEs and the RTD will allow the SMEs to open to international markets where the other SMEs are already introduced therefore increasing their commercial network.
From the client point of view, the solar panels inflatable structures would have an impact on both purchase price & operative costs:
• Purchase price: The increase in price due to the inclusion of the solar panels would be around 15% of the current prices.
• Operative costs: Using the photovoltaic solar panels, the following costs could be eliminated
o Power consumption: Currently, the power consumption for the inflatable structures (although depends on the size and environmental conditions) would be around 0.5-1% of the purchase price per year. Assuming a amortization period of 5 years, such power consumption can represent 2.5-5% of the purchase price.
o Alternative emergency power supply sources purchase: The purchase price of the emergency power supply sources like generators (also depending on the size and environmental conditions), could be around 4-6% of the purchase price.
So, the operative savings (negligible or null power consumption + no need to purchase alternative power supply source) would represent 6.5-11% of the purchase price, which would almost compensate completely the price increase due to the use of the solar panels. However, the improvement can not only be measured in terms of price, but also considering that new market targets can be reached
IMPACT ON SMES GROWTH:
BuildAir: By participating in the uLites project, BuildAir expects to gain access to the emergency and fast-deployment cover markets, while enabling the use of new technology in the markets where it already competes. In particular, structures with the capability of generating solar energy would be extremely useful in the field of inflatable structures, which is BuildAir’s main area of expertise, allowing significant savings or even a surplus of energy.
The improvements in the manufacturing procedures and the innovative energy system designed for the uLites shelter will be widely used in Buildair products.
The technology developed will be used as the starting point for other H2020 proposals that are going to be submitted.
Additionally, access to the Virtual Wind Tunnel tool allow for a reduction of design time and costs, as well as ensure that the structures developed comply with the most demanding wind and weather conditions.
Naizil: The opportunity to be involved in the uLites project brought the possibility to continue the study on the behaviour of SOLARPANEL in terms of installation’s systems, different applications, specific simulation’s tests in different conditions (stress strain, load, wind, temperature).
Reglass: Reglass’ could develop an innovative and lightweight carbon fibre stripe of acceptable cost for fixed and flexible structures. One of the focal points of the research has been the realization and test of the joints and anchorage system between the carbon cable and the metal end which has to sustain the entire load and has to be absolutely safe.
SL-Rasch: The results of uLites will significantly expand the recent market of RASCH thanks to the development and validation of the Virtual Wind Tunnel during the uLites project. This will allow a faster evaluation of the potential of new designs in preliminary design stages and can allow a quick response to customer requests.
DISSEMINATION ACTIVITIES AND EXPLOITATION
Concerning the dissemination activities, the partners of Ulites have published 3 papers in JCR journals and are actually preparing other 5 papers to be submitted in the next months (table A1). The partners actively participated to International conferences presenting the results of the uLites, this is demonstrated by the 15 proceedings in international conferences (table A1). A monograph was also published.
Two doctorate courses of 2 ECTS have been organized by CIMNE at the Technical University of Munich. In this courses the recent advances in FSI solvers developed in the uLites where presented (Table A2). The Kratos Workshop, organized in the framework of an international conference on the recent advances of GiD pre and post process tool, was an occasion to present to an international audience the Virtual Wind Tunnel as an available opensource tool inside Kratos multiphysics (Table A2).
A Flyer summarizing the main innovative feature of the ulites was created and distributed among possible stakesholders. Around 200 flyers have been distributed.
A ulites group was created in linkedin https://www.linkedin.com/groups?home=&gid=8238318&trk=groups_most_recent-h-logo and a Wikipedia page is going to be created once the multimedia material regarding the construction of the prototype will be available.
A description of the project has been added to the Linkedin Community, linked to the involved researchers and with a link to the uLITES webpage
It’s to be noted that the uLites concept (ultra-lightweight structures with integrated photovoltaic solar cells) and added values (portability improvement, absence of energy supply dependency, reduced power consumption) have been commented during trade fairs on which some of the partners have exhibited or attended, with the aim to record the feedback from potential customers to this new technology. The result could not be better: many potential clients (especially from Defence / Military sector) consider this product as fully attractive, and the previously enumerated added values as outstanding. The improvement in portability and the elimination of energy supply dependency are key factors for many clients to consider very positively the ultra-lightweight structures.
For every business sector, direct communications have been performed with potential clients, who already know some of the project partners due to previous contacts:
- Aeronautics:
o MRO organizations (Lufthansa Technik, Delta, Iberia, British Airways, Air France-KLM, Avianca, ABS Jets, Jet Aviation, etc.)
o Aircraft manufacturers (Airbus, Boeing, Bombardier, etc.)
o Airlines (e.g. same as MRO organizations, plus Ryanair, Easyjt, etc.)
o Airports worldwide
- Defence / Military:
o Armies / Air Force (e.g. Spanish, Colombian, Polish)
o Spanish Guardia Civil
o Spanish Unidad Militar de Emergencias
o Protezione Civile Italiana
- Companies:
o Acciona
o Abengoa
o OHL
o Navantia
o Alava Ingenieros
- Humanitarian Aid:
o International Committee Red Cross
o United Nations High Commissioner for Refugees
o Medics Sans Frontieres
List of Websites:
http://www.cimne.com/websasp/ulites/
The work carried out by all the partners of uLites has allowed the design and construction of a real-scale prototype of a portable shelter structure for emergency situations. The main characteristics of the uLites prototype are:
- Standard available area (considering three tubes): 150 m2
- Weight: 250 kg/tube
- Folded volume: 0,75 m3/tube
- Average setup time: 1,25 hours
- Recommended personnel: 8 people
The set up lasts less than one hour to achieve a pressure of 20 mbar. To maintain the structure inflated 5-6 minutes of air inflation per day are sufficient. This inflation is automatically activated when pressure decreases below the 10mbar.The total energy consumption estimated is 251,4W/day
The main technological improvements achieved with the uLites prototype are:
1. BETTER PERFORMANCES than traditional inflatable structures:
o SUSTAINABLE Flexible photovoltaic SOLARPANEL modules are used on the shelter to minimize the energy requirements.
o LESS AIR LEAKAGE Leakage reduction from 2000m3/h to 0.038m3/h thank to the quality of PVC coating, the tangent tubes technology and the combination of welding and sewing manufacturing.
o NO NEED OF CONTINUOUS AIR IMPULSION A “mixed” system has been designed, which combines the energy storage by means of “pressure energy” and the use of batteries for the “extra” energy generated.
2. INNOVATIVE MATERIALS
o PHOTOVOLTAIC MEMBRANES: SOLARPANEL. Material characterization via uniaxial and biaxial tensile tests was performed.
o FLEXIBLE CARBON FIBER STRIPES: Development and testing of a new high-toughened thermosetting resin. 0.15-0.33mm thickness, some cm curvature radius. Creation and testing of new anchorage system.
3. INNOVATIVE SOLAR ENERGY SYSTEM
o SOLARPANELS Nominal power 80W
o 220Ah battery
4. NEW INTEGRATED DESIGN TOOL An integrated VIRTUAL WIND TUNNEL tool has been developed for the calculation and design of the shelter.
o Both CFD and FSI calculation.
o Atmospheric Boundary Layer Generator Module.
o User friendly integrated pre and post processing
The uLites team joined expertise in different areas, starting from the production and development of the materials (Reglass and Naizil), including the basic theoretical and practical knowledge for their more suitable applications (University of Padua) and the expertise in application and development of numerical algorithms (CIMNE and Technical University of Munich), up to the final design and construction phase (Buildair and SLRash).
An extended experimental campaign both on Naizil SOLARPANELS and Reglass carbon fibre stripes and anchorages was carried out at the University of Padua resulting in a careful assessment of the material properties of the new materials to be employed, providing crucial information for the future use of the new materials in practical applications. The Italian SMEs have worked closely to the uLites coordinator, Buildair, to integrate their innovative materials in Buildair inflatable structure. The outcome of this collaboration was the implementation of an improved manufacturing technology and of a novel energy storing and distribution system that improve considerably the performances of the inflatable structures.
On the other hand CIMNE and the Technical University of Munich, with the advice of SLRasch, have been developing an ambitious Virtual Wind Tunnel (VWT) tool. This is a virtual prototyping lab which allows the assessment of the coupled structural and aerodynamic performance of the new designs in a user friendly environment. The VWT include an Atmospheric Boundary Layer (ABL) generator module, a CFD code using advanced embedded technique based on Kratos Multiphysics (CIMNE) a CSD code based on Carat (TUM) a Human Interface based on GiD (CIMNE). This tool was validated by means of a series of benchmark tests and using the experimental results of a wind tunnel experimental campaign carried out at the University of Florence in CRIACIV laboratory.
Project Context and Objectives:
Every year several thousand people become homeless due to natural disasters as earthquakes, floods or wind storms, which periodically affect wide areas of the Earth. To face such situations emergency flying squads, national emergency squads and international organizations (military, red cross…), need to be able to quickly deploy temporary housing (mainly tents), facilities such as hospitals or headquarters, and infrastructures (roads, bridges, harbors) in different and adverse conditions. The importance and extent of such catastrophic events is unfortunately expected to rise over the next decades due to the impact of the global warming. While modern societies have limited power in preventing such exceptional events, they are expected to react in short time to any emergency situation, providing an efficient post-disaster intervention and reducing its economic and social impacts. In this sense, the present work aims to provide an answer to the increasing need for highly portable post disaster facilities, which could be satisfied by using temporary lightweight structures like tents, inflatable covers, portable warehouses or hangars.
The idea of uLites has been to leverage the large experience in design and construction of lightweight structures of two of the SMEs that participate in the consortium (BuildAir and Rasch) and to improve the efficiency of their products with the use of innovative materials and manufacturing techniques that can provide an enhanced performance while reducing some drawbacks. This was obtained with the joint work of all the partners of the uLites, providing their expertise to achieve the following objectives:
1. Creation, testing and patenting of new materials both for the carbon fibre stripes and the flexible photovoltaic cells (Reglass and Naizil with UniPD). The development, in recent years, of innovative lightweight materials opens new possibilities in the design and engineering applications of ultra-lightweight structures. On the material side, one of the main goals of the uLites project has been to foster the development and the practical applicability of the innovative materials which were developed by the SMEs in the consortium, namely the carbon fibre stripes (Reglass) and the polymeric fabric with embedded photovoltaic solar cells SOLARPANELS (patented by Naizil).
2. Optimization of the design process of inflatable structures (Buildair and SLRash with CIMNE and TUM). It is apparent that the classical experience-based approach towards the manufacturing of light-weight structures is no longer sufficient to be competitive, since it implies high costs in terms of testing expenses as well as a long iterative process. The maturity of numerical techniques both in Structural Mechanics and in Computational Fluid Dynamics (CFD), accompanied by the availability of affordable high-performance hardware, allows the use of virtual rapid-prototyping facilities (a Virtual Wind Tunnel) as realistic alternatives to traditional (time consuming and expensive) wind tunnel experiments.
3. Extended validation and testing of prototypes to create guidelines for future developments. The uLites partners has developed a series of performance tests and demonstrations benchmarks in order to have a quality check of the results and to facilitate take-up by the European market of the new technologies proposed
Project Results:
During the whole uLites project, the parallel work of the different partners has been organized and coordinated successfully. Both SMEs and RTDs have shown a great interest in the progresses of the project and in the results with an active and continuous cooperation.
The R&D objectives of uLites can be summarized in the following items:
1. Analysis of the state-of-the art in the market of lightweight structures and of innovative materials (WP1). For that purpose a preliminary patent search analysis was performed on M12 and has been updated on M20 and M24 showing no relevant changes.
2. Design of the emergency shelter prototype. First definition of the design of one module of the emergency shelter structure to be realized and definition of the load combination to be taken into account (WP1). This design was confirmed and detailed on M16 by the executive project of the emergency shelter (WP5 D5.1- D5.3).
The design of the structure for this project, thought as a modular emergency structure, has been done considering that the shape and the dimensions of the structure should be as standard as possible, in order to better compare the improvements due to the new power supply; the inclusion of photovoltaic cells, is also a relevant aspect since the structure design should be compatible with them; finally, as will be explained in the following points, the innovation also includes aspects related to the materials, such as lighter and more resistant materials or different manufacturing techniques to improve air-tightness of the tubes; the engine system should be also improved for a more sustainable use of the shelters.
The prototype built at the end of the project is a three tubes inflatable structure. The diameter of each tube is 2.50m the clear span width is 20m and the clear standard height is 10m. This shelter can be either closed or not with a front and back door depending on the need.
3. Concerning the innovative materials (WP1 and WP2) to be used in the prototype the following tasks have been achieved:
3.1. Definition of the material to be used (WP1). Polyester/PVC Type 2 seems to be the best choice for the good mechanical characteristics and the high tear strength. The carbon fiber stripes are a completely new material in the branch of tensile structures. These can replace traditional iron stripes providing a great flexibility with lower dimensions, lower weight and higher resistance. The use of a thermoplastic polyurethane resin leads to the possibility of welding stripes and membranes reducing the risk of cut in the stress concentration areas.
3.2. Definition of the parameters to be quantified before simulating the structure (WP2). In the case of photovoltaic membranes (Solarpanel) these are the stiffness of the membranes and their ultimate tensile strength (although this latter seems to be less important than the first). Finally the quantification of the strains compatible photovoltaic energy production should be made. On the other hand the fibre stripes need to be characterized in terms of their ultimate tensile strength and the ultimate strength of the anchorages.
3.3. Performing the experimental campaign on flexible SOLARPANEL modules (WP2). Specific procedures were defined and ad hoc devices were designed to allow testing the membranes with embedded photovoltaic cells since standard one could not be used (D2.5). Solarpanel, in fact, are produced with fixed modular dimensions (94×170 cm) and cannot be cut. On the contrary the “European Design Guide for Tension Structure – Tensinet 2004” defined standard uniaxial and biaxial test procedure to be executed on 50×50 cm specimens only.
Both tests on blank specimens and on specimens with solarpanel were carried on to analyse the influence of the photovoltaic module in the mechanical behaviour. During tests on Solarpanel, the photovoltaic cells are lightened and electricity production measured in order to evaluated which stress leads to failure of the cells. Preliminary numerical models were also built to evaluate the behaviour of the specimen during the experimental tests.
Tests were performed with the following steps:
First of all mounting of the specimen on the test frame; secondly imposition of a horizontal pretension (4% of the tensile strength) introduced using springs; after that, imposition of a vertical pretension (4% of the tensile strength) introduced using an hydraulic jack at the top of the test frame; later imposition of a cyclic vertical loading (4 cycles, up to the 20% of the tensile strength), using the hydraulic jack at the top of the test frame, to stabilize inelastic deformation and measure deformations and applied force.
The initial experimental campaign shows a premature rupture of the membranes even with low tensile loads: this was the consequence of the shape of the specimens, of the details introduced to impose a lateral pretension and to the imperfections of the cuts. To avoid these problems a optimization of the specimens to redefine the same in order not to affect to the experimental results has been performed. The new axial and biaxial tests show the problem has been overcome and gave promising results.
The results on specimens with Solarpanel pointed out how the transparent protective coating fully collaborates with the support membranes in bearing tensile loads. Specimens with Solarpanel had no increase of warp elastic modulus introducing a lateral pre-stress of 4000 N/m: this is due to the external protective coat, a uniform material whose modulus is not sensible to internal tensile stresses and which is much stiffer than support membrane. Uniaxial tests on specimens with Solarpanel showed values of tensile strength similar to the one of the blank specimens. As expected protective external coat seems not to give a contribution in terms of tensile strength because ultimate deformations of the supporting membrane are too large. Biaxial tests leaded both types of specimens to a premature failure because of stress concentrations and deviations due to the details and devices used to give lateral pretension: these, in fact, always originated the fractures. Finally, electricity production: was observed to be almost constant up to 22N/mm and above that stress level, decay was observed. Nevertheless both on uniaxial and biaxial tests power production were observed to be stable at different tensile stresses values in their serviceability range ([0; 20] N/mm).
3.4. Performing the experimental campaign on carbon fiber stripes (WP2 – D2.3 and D2.7).
A thermosetting polymer was used instead of a thermoplastic one because it manifests higher shear strength, reducing the risk of the delamination due to the frictional forces ensuring the restraints of the strip. In fact there have been made several attempts to find the best way to fabricate flexible ribbons with carbon fibre useful for this purpose. The main problem is due to the fact that carbon fibre stiffness is very high and the elongation at break is small. It is therefore quite difficult to redistribute the loads between the fibres and, furthermore, the possible curvature radius strongly increases with the ribbon thickness. The first idea was to embed the carbon fibres in a thermoplastic matrix in order to have high flexibility also with relative important thickness but the results of this test were not acceptable both for the poor shear strength of the resin and poor bonding with the fibres. Second idea has been to use an epoxy thermosetting resin with very thin ribbon thickness. The behaviour was better but the curvature radius was still too high and the ribbon very delicate and fragile.
After some other tests a new high-toughened thermosetting resin has been developed which has given very interesting results, leading to a good ribbon in 2 thicknesses: 0.15 and 0.3 mm with small curvature radius high resistance and acceptable toughness. Moreover two external layers made with a woven-nonwoven carbon fibre mat were introduced, conferring to the ribbons a higher stability against the undesired phenomena of separation of the tensed carbon fibres. This new ribbon is the one used in experimental campaign. The tests on the carbon fibre stripes consist in loading the specimens with a uniaxial tensile force thanks to an imposed elongation. To perform the test, Galdabini’s Sun 60 machine was used. To avoid any unexpected effect producing oscillation, the velocity of elongation was set low enough to represent a quasi-static condition in the test. Values that were used are 1.0 ÷ 2.0 mm/min. In order to connect specimens (anchorages, see below) to the test machine, specific forks were provided. Two different kinds of stripes were produced by Reglass: a strip with dimensions 14̇x0.15 mm and one with dimensions 14×0.3 mm. Evaluating the percentage ratio between the area of carbon fibres and the area of the whole section of the strip it has been defined a ‘theoretical value’ of the strength equal to 5290 N for the 0.15 thick strip and 10580 N for the 0.30 thick one. To increase the tensile strength the stripes will be placed side by side winding them together on the same anchorage.
3.5. The anchorages design was the result of the following requirements: compact size and ease of assembly to allow transportability, high strength to resist the tensile force deriving by the stripes, and scalability to be easily adaptable to the dimension of the stripes.
Two different anchorages were designed to perform tensile tests since the stripes require an extremely high level of flexibility and the compact size of the connections. A solution with a deviator (T1) and one with a wedge (T2) were tested.
The anchorage type T1 is composed by a steel cylinder on which to coil the strip and a diverter to realign tensile force with the central pin. These two components are joined by two plates that transmit the moment due to the deviation of the stripes on the diverter. This anchorage exploits friction between the strip and the cylinder in order to transmit traction from the first to the pin. The anchorage type T2 is composed by a wedge on which to coil the strip and to be inserted in a case to transmit tensile force to the central pin. Two plates close the wedge and the case. This anchorage exploits friction between the strip, the wedge and the contact wall of the case in order to transmit traction from the first to the case and so to the central pin.
In both cases a preliminary numerical analysis by means of a finite element model in non-linear regime were carried out to evaluate the strength of the anchorage previous to the experimental campaign detailed in D2.3.
It was observed that the anchorage T1 worked as expected whereas T2 seems to be very sensitive to imperfections due to the laser cut that leads to excessive local stress concentrations damaging the ribbons.
To limit this problem the anchorages have been produced in milled steel to reduce imperfections and “deformable” spikes made of plastic material (HDPE) were adopted. New tests have been performed obtaining a higher effectiveness of the anchor. As explained above, the desired value of tension to be carried by the stripes in the application (inflatable shelter) will be reached placing the stripes side by side winding them together on the same anchorage.
3.6. Connection between membranes and carbon fibre stripes
Two different connections systems were tested: sliding stripes contained in proper continuous cases made with the same material of the membrane and welded on the upper chord of the tubes composing the structure (a sort of hoop connected to the ground) and stripes connected directly to the membrane thanks to a high strength double-sided tape in order to allow load transmission between membrane and stripes. This latter connection system was seen to be not suitable for the uLites prototype since it manifests a highly non uniform distribution of shear stress and a very high sensitivity to the irregularity of the PVC surface. Both this aspects caused a premature breakage of the specimen. In the case of the sliding case the behaviour is better but the total strength observed is lower than the double of the single string strength. This might be the consequence of the scale of the experiment that does not allow the load device to guarantee the perfect alignment of the tensile force applied by the hydraulic jack. This connection type is suitable for the construction of the prototype providing a proper safety factor in the structural analysis to be adopted.
4. Concerning the creation of a Virtual Wind Tunnel (VWT), the following objectives have been achieved:
4.1. Definition of the design strategy (WP1 D1.5). Use of Davenport’s wind load chain in designing the wind loads on the structure, which define the fundamental loading to be taken into account in the design of the software for the VWT.
4.2. Definition of the essential input parameters to be taken into account in the simulation (WP3 D3.1). The possibility of analysing the wind spectra and especially the mean wind velocity at a given height considering the turbulent characteristics of the wind (i.e. corresponding to the target wind spectra), was seen to be an essential requirement for the design tool. The definition of a terrain roughness or the specification of a terrain category was also considered essential in order to a valuable response. These essential input parameters are required for the generation of physically meaningful wind fields in the so-called atmospheric boundary layer, where the building structures are situated. Within this project an Atmospheric Boundary Layer generation module (ABL) (D3.3) was developed and implemented. Numerical Wind Field Generation is to synthesize the turbulent part of the wind (the fluctuations) according to particular constraints, in order to have series of space/time-varying velocities that can be used as inlet boundary condition in CWE problems. Although random turbulence, or a “white noise”, although might fulfil the required wind intensity, they fail to comply with the physical requirements of the wind inlet condition. Besides containing the wrong distribution of energy (wrong spectrum), it lacks spatial and temporal coherence that real-wind turbulence has; causing the generated fluctuations to vanish immediately in Navier Stokes solver. Therefore, methods to produce more complex “noise” should be found to allow the fluctuating part of the numerical wind to represent realistic wind turbulence, and to be able to survive in the CFD environment. The ABL-generator tool was developed according to the wave-superposition-based method of J. Mann and was successfully validated (D3.4 D3.5). Since ABL is based on a method that has a stochastic nature, the straightforward approach to validate it is through examining the statistics of its product. This was checked by sampling the fluctuations at a chosen set of coordinates (i.e. obtaining synthesized wind turbulence time-series) and analysing them. Moreover a parametric study on the generator was carried out too. The validation of the ABL was completed using the data measured in the Physical wind tunnel tests performed on the rigid model (presented later) and confirm the validity of the tool.
The ABL package produces velocity fields which have length and time scales that model real-life winds scales, i.e. not wind-tunnel flow scales. Therefore, for a valid comparison for Atmospheric Boundary Layer effects on structures, a geometrical scale in the range (1:150-1:250) and a velocity scale in the range (1-5) should be used, keeping in mind the Reynolds number independency. This independency was experimentally proven in the wind tunnel experiments. Also, scaled up simulations were performed and have shown good agreement with the wind tunnel results for ABL flows (D3.5).
The guidelines to use the ABL were finally created (D3.6) considering different set of available data.
4.3. Implementation in the fluid code (Kratos) of a geometrical tool to embed the structural geometry in the fluid mesh (WP4 D4.5). This is done employing a modified finite element space which includes discontinuity along one surface. “Virtual nodes” are inserted in the finite elements where these are cut by the structure.
4.4. Implementation of the interface for the simulation codes (D4.1 D4.2).
The virtual wind tunnel is composed of different modules that should be coupled together. For this purpose a coupling tool has been adopted and customized to work with the structural code (Carat) and the CFD code (Kratos). The two modules have been interfaced using the Empire coupling tool and its API has been used for the definition of the communication between the different modules.
EMPIRE is designed and implemented for solving general multiphysics problems with n-code co-simulation. The customized interface is characterized by:
• Flexibility: co-simulation in a general scenario is available, since an arbitrary number of simulation codes and arbitrary connections among them are allowed.
• Modularity: partitioned strategy is used to apply existing simulation codes; the simulation codes are connected by Emperor; communication interface is provided in the library EMPIRE API; object oriented programming with C++ is used to implement EMPIRE.
• Efficiency: communication is realized by using MPI; efficient mortar method is implemented for mapping data between non-matching grids; methods are implemented to accelerate co-simulation, e.g. extrapolation and relaxation.
• Usability: co-simulation is set up in a single file (input XML file of Emperor); simulation codes in all C-compatible languages can link to the library EMPIRE API; various filters are provided for data operations including mapping, extrapolation and relaxation
A customization of the Empire was carried on and both Kratos and Carat were modified in order to allow the following design flow-chart:
1. Define the Structural Model (Carat)
2. Identify the coupling surface
3. Identify the inlet and generate a statistically appropriate inlet condition (virtual atmospheric boundary layer)
4. Transfer to Kratos the triangularized coupling surface together with the dimensions of the fluid domain to be considered (fluid domain will be box-shaped)
5. Construct the box fluid domain and eventually refine it locally in the vicinity of the structure. (to be performed internally by Kratos)
6. Transfer inlet conditions to the Kratos by suitable mapping operation
7. Solve the fluid domain using an embedded approach (Kratos)
8. Map pressure forces to the structure and displacements to the fluid (Empire)
9. Solve structural domain (Carat)
4.5. Implementation and validation of a graphical user interface (GUI) (D4.3 D4.4). Each of uLites solvers (CARAT and KRATOS) is modular. This motivates the use of GiD (http://www.gidhome.com) as a pre/post-processing tool. GiD allows defining an interactive graphical user interface used for the definition, preparation and visualization of all the data related to a numerical simulation. This data includes the definition of the geometry, materials, conditions, solution information and other parameters. The program can generate a mesh suitable for several numerical methods and write the information for a numerical simulation program in its desired format.
The program works, when defining the geometry, in a similar way to a Computer Aided Design (CAD) software. All materials, conditions and solution parameters can be defined on the geometry itself, separately from the mesh as the meshing is only done once the problem has been fully defined. The advantages of this are that, using associative data structures, modifications to the geometry can be made and all other information will automatically be updated and ready for the analysis run.
Full graphic visualization of the geometry, mesh and conditions is available for comprehensive checking of the model before the analysis run is started. More comprehensive graphic visualization features are provided to evaluate the solution results after the analysis run. This post-processing user interface can also be customized depending on the analysis type and the results provided.
In order to allow GiD to input to a modular code (CARAT or KRATOS), a so called “problem type” was implemented and included.
4.6. Validation of the VWT (D3.2 D3.4 D3.5 D4.5 D4.6 D5.3).
A series of validation examples to be used to check the virtual wind tunnel performance (D3.2) and beginning of the validation tests was defined. Both tests on simple geometries and tests on building like geometries have been taken into account and were used to test the automatic inlet generation module (D3.4,D3.5) the CFD code (D4.5) the geometrical tool to embed the structural geometry into the fluid solver (D4.5) and the complete VWT (D4.6 D4.7 D5.3).
A wind tunnel experimental campaign was carried out to provide validation data for the VWT. Both a rigid model and a flexible one were tested considering different positions and orientations of the structure with respect to the inlet direction as well as considering, in the case of the aeroelastic module, the possible presence of an obstacle of the same scale as the structure, in front of it. The purpose of these experiments was not the analysis of the real prototype structure; in this case, the scaling of material properties would have been extremely complicated if not impossible, but to test the good performance of the VWT in scale 1:1 (D3.5 D4.6).
On the other hand the real scale prototype was also simulated with the VWT to predict its response to the worst wind scenarios (D5.3).
After this tests were performed an estimation of the money and time saving of numerical tests vs physical one can be made for the specific case. The wind tunnel tests cost approximately 50.000Euros considering the cost of the model constructions, the hours of laboratory, the men/months and the duration is approximately 1 month. In the case of numerical simulation the estimated costs for performing the same cases is 15.000Euros considering one engineer working one months for pre and post processing issues and including the calculation hours to be rent to run the simulations in large clusters and the time is approximately one months. It is worth mentioning that in numerical modelling no scale effect should be taken into account allowing a 1:1 scaled analysis of the real case.
4.7. Guidelines for the use of the VWT lab (D4.7) All the steps to be followed to download and install the VWT were presented and a step-by-step tutorial was written so to allow SMEs’ partners to get in touch with the tool.
5. Design and Construction of the ulites emergency shelter prototype.
5.1. Improvement of air-tightness (WP5 D5.1). Different types of fabrics have been considered, with more/less resistance features, different coating, physical properties, and so on. Since the key point in this structure is the air-tightness, the candidate materials to be used are those that have a good PVC coating, which make the tubes air-tight and also easier to weld during the manufacturing process. On the other hand, these fabrics become a little heavier, increasing the total weight of the structure compared to previous hangars done by Buildair.
An innovative manufacturing process combining welding and sewing has been tested. The combination of both methods is ideal to achieve a manufacturing method that allows welding only the critical parts that require air-tightness in an easy manner. Then sewing is used on more complex parts that are not easy to close with the welding machine. Thanks to this procedure some kind of air-tight inner chamber can be manufactured with an independent closing envelope where needles does not affect the air-tightness. The structure manufactured consists of 3 independent tubes instead of a whole module of 3 tubes (the standard Build air technology). These tubes are positioned tangent one to another with the idea of increasing the length of the hangar with less number of tubes and, therefore, less energetic requirements to inflate them. The tubes are connected between them with high-resistance zippers. This fact allows having a very simple modular structure, in which the required length can be easily obtained just adding or removing one or more tubes. The tests show that the leakage is very low (of about 0,038 m3/h, compared to values of 2000 m3/h that some of previous structures used to have)
5.2. Development and testing of an innovative Energy system to improve sustainability (D5.1). A “mixed” system has been designed, which combines the energy storage by means of “pressure energy” and the use of batteries for the “extra” energy generated. The idea comes from the difficulty of finding blowers that have reduced energy consumption (with competitive prices) that are able to support the structure erected continuously, together with the big amount of solar panels required. With this combined system, with less photovoltaic cells and less powerful blowers, a balanced system can be defined to make the structure work with minimum power consumption and lower expenses. The definitive system is formed by a low power blower, which is supplied by a battery with enough capacity to make the first set-up inflation and ensure the maintenance of the pressure during the use of the emergency shelter. All this comes together with 3 flexible photovoltaic panels integrated on the structure, one on each of the 3 tubes, the ones that will charge the battery. It will also include a control system for the monitoring of the pressure and the management of the blower and valves to make it work when required. Considering all the previous requirements and features of the elements that form the system, the energetic needs estimation was the following: First set-up and weekly inflation - we estimated 1 hour of use of the blower per week to inflate the structure up to its maximum pressure (20 mbar) - Consumption = 1100 W/day. Pressure maintenance - between 5-6 minutes per day the rest of the days of the week will be used to maintain the structure within the admissible limits (10-20 mbar) - Consumption = 110 W/day. Total consumption = 1760 W/week (251,4 W/day)
5.3. Inclusion of the Solarpanels (D5.1 D5.4 D5.5). To obtain the minimum number of solar panels needed the Solar Peak Hours (HSP) was calculated. This is used to define the solar radiation that will receive the photovoltaic cells in the place they will be set. Considering the prototype was to be built in Barcelona in winter, the hypotheses for the calculation of the HSP were the following: Location: Barcelona Month: December (worst case) Inclination: 0º (not optimal). The inclination of the cells is determined by their positioning on the hangar. The structure has several anchoring points to try to optimize this position. The problem is that the positioning of the structure can be determined by so many different reasons and an optimal orientation might not be possible (and operative). That is why the hypothesis made is to place the cells on the top of the hangar, at an approximate angle of 0º. According to all these hypotheses, we obtain a value of HSP = 1,61. With this value, together with the energetic requirements and the Solarpanel technical feature, the number of flexible photovoltaic cells needed is 3, connected in parallel. The way to fix these cells to the structure is done with buttonholes on the cells’ support and on the structure, tied with ropes.
5.4. Inclusion of the new carbon fibre stripes (D5.1 D5.4 D5.5) Integrating the carbon fibre stripes in the inflatable structure needs a special set-up procedure, since it is not as easy to handle as a textile strap. The idea is to introduce the carbon-fibre stripes inside a membrane case (like a pocket), in a way that they are free to slide inside it. The membrane gives no contribution on carrying the tensile load. This element would replace the textile straps along the perimeter of at least one tube of the shelter prototype. The total number of carbon-fibre stripes for each tube is 4, grouped in pairs, which can be done with the anchorages designed. The idea of using carbon-fibre stripes in an inflatable structure is a new concept. The characteristics of this material, together with the interaction with the large structure of this project, lead us to think about its fragility if it is bended excessively. Particular care should therefore be taken during the set-up procedure of the structure. There in fact, does not seem very compatible with the treatment of the carbon-fibre material, and there might be a risk of breakage.
5.5. Construction of the prototype (D5.1 D5.4 D5.5) The prototype was successfully built in December 2014 and tested in two different phases: one phase in December 2014 testing all the parts of the structure separately inside Buildair’s factory, and a second phase at the beginning of January 2015 performing a real deployment test in the exterior of the factory testing the whole structure with all the parts together. After these tests, the results confirmed the expectations in many ways.
During the first tests phase, the three tubes composing the prototype were inflated separately, lying on the ground, in order to check the real air-tightness of them and to confirm the blower calibration. In general the results were very positive, since 2 out of 3 tubes showed to keep the required pressure (between 10 and 20 mbar) for much more than 24 hours, without needing any inflation. One of them was even tested during several days, achieving more than 2 days without requiring inflation. Unluckily, one of the tubes (the first that was manufactured) showed several air-leakages that could not allow reaching the objective. This fact allows us to show the difficulty in the manufacturing process, which needs to be checked very accurately. Having taken this into account, the other two tubes were manufactured in a more accurate way, as the improved results confirmed the problem was overcome. The first tube was then checked and repaired to improve its behaviour.
Another test was performed to check the time needed to inflate one tube until reaching the maximum pressure of 20 mbar. Only 12 minutes are required for one tube, so for the whole structure of 3 tubes we would probably need between 30 and 45 minutes (original estimation 1 hour). The time required to increase the pressure of one tube from 10 to 20 mbar was also checked. This is just 20-25 seconds for one tube, so for 3 tubes will be around 1-2 minutes (original estimation 5-6 minutes).
During the second tests phase, a real use was tested, confirming the tests performed before inside the factory. The 2 satisfactory tubes showed that were able to withstand erected without requiring inflation at least for more than 24 h. The other repaired tube was able to keep the pressure during the day but not during the night. This fact also shown that the temperature gradient between day and night is very important for these low-pressure air-tight structures, involving and increase/decrease of pressure of more than 30-40 mbar (initial inflation pressure is 20 mbar). We checked that when we inflated the tubes at 9AM at a pressure of 20 mbar, at midday we reached pressures over 60 mbar in some tubes, while at night it decreased down to 6-7 mbar. Studying carefully this fact will allow us to design an automatic control system to optimize the number of inflations thanks to doing it at the perfect time of the day, according to the temperature gradients. Regarding the required inflation time estimated, the whole structure was erected in just 25 minutes (a bit less than expected), and the re-inflation procedure between 10 and 20 mbar was less than 2 minutes as expected. Moreover, the system does not produce any relevant noise pollution since it is very silent.
Other tests were performed with the photovoltaic system, showing that the efficiency of the flexible solar cells is very influenced by the curvature they take when placed on the structure and also the incidence angle of the sun. We tried to put them on different positions and angles to find the optimal ones. These tests showed the importance of orientation of the structure and the cells, which has to be studied in detail depending on the season of the year and the place where the structure is going to be set-up. Finally, an important part was the connection between the cells. Initially thought in parallel, we changed to series to increase the voltage necessary to charge the battery, since the non-optimal orientation generated and insufficient voltage. Doing it in this way, the tests showed that thanks to the low-energy requirement of the structure to inflate, the cells could charge the battery after the first set-up in order to maintain the structure erected during the following days without problems.
Finally, the use of carbon fibre stripes to anchor the structure was proven to work well.
So, in conclusion, the designed structure confirmed the expectations in many ways and also helped the team to learn and understand better how it works in order to add improvements to this product for its future use.
To conclude, no relevant deviations from Annex I have been identified. Moreover considering the appraisal of technical and non-technical risks stated in the uLites proposal (Table 1.4.1) we can hopefully said that no relevant problems have appeared during the uLites. Nevertheless is worth mentioning that the consortium has been intensively busy with the technical work during the uLites with no sufficient time to fully exploit its results and organize demonstration activities. These are planned to be carried out in the near future.
SMEs’ OPINIONS at the end of uLites
BUILDAIR
Buildair, thank to the uLites project, could design an innovative manufacturing process for its inflatable structures with optimized performances and minimized air losses as largely explained in the reports. Moreover, the inclusion of photovoltaic membranes and the deriving minimization of consumption opened to Buildair new markets such as humanitarian, military and emergency. Therefore the collaboration with the partners of the consortium represented a good chance to improve the technical quality and to innovate the products of the company.
Finally the availability of a user friendly and validated computational tool for design and verification of the structures represent a relevant step forward with respect to the competitors in the sector of inflatable structure.
REGLASS
Reglass took part in the uLites project with the aim of create a new product (carbon fibre strips) that in the medium term could represent a sound and convenient solution for the realization of high performances tensile elements. The strict and satisfying collaboration with the University of Padova laid the foundations for the development and optimization of the products (strips and anchorages) directing our efforts towards real improvements. Our goal for the next future is to improve mechanical properties of strips and anchorages and ease of usage; once this goal will be reached the production will be organized and industrialized in order to enter the market. Moreover we think that the further developments will make the carbon fibre strips suitable for multiple purposes, not only for civil engineering applications.
NAIZIL
Naizil participated in the uLites project with the purpose of characterize the mechanical properties of Solarpanel, a new kind of flexible photovoltaic cell directly embedded to a supporting textile membrane. Collaboration with University of Padua allowed us to define a test procedure able to reach our purpose thanks to a continuous interchange of results and opinions with our RTD partner. Now that Solarpanel has been tested and characterized it can found real utilization into the market. Its uniqueness, in our opinion, makes it suitable for several applications concerning the renewable energy sources and its applicability also as a structural component will be the key for a possible large usage also to realize classical tensile structures. Our goal in the short and mid-term will be the launch and presentation of Solarpanel as the ideal solution for structure with special requirements (energy production for emergency situations) and for a new way of exploiting common tensile structures. This can help Naizil to overcome actual financial troubles and bring it back to be a leader company in Italy and in Europe in the supplying of innovative membranes for lightweight structures.
Collaboration with University of Padua during the project was continuous and was the key to achieve a fully positive project results
SL-RASCH
The main objective of SL Rasch was the developement, industrialization of the virtual wind tunnel and the virtual prototyping lab and the validation with aero-elastic wind tunnel models
- SL Rasch´s field of activity: design and engineering of large convertible membrane structures which are beyond the current state-of-the-art of engineering. Therefore it is absolutely necessary to apply computational tools for their design because current wind tunnel technology is limited.
- There has been a great step undertaken by the ULITES consortium to make a virtual wind tunnel available. It is already applied by SL Rasch for their projects.
- Furthermore the outcomes of ULITES (results, publications) and the collaboration with international recognized scientific institutions (TUM, CIMNE) in the field of numerical simulation is used as reference with regards to the requests of the proof engineering consulting companies in the SL Rasch projects
- Very close collaboration and fruitful technical discussions with R&D partners, especially TUM and CIMNE
- Further outcomes of ULITES like application of photovoltaic cells on membrane structures and application of carbon fiber cables are regarded to be applied also in future projects
RTDs' OPINIONS at the end of uLites
CIMNE
The participation of CIMNE to the uLites project has represented a good opportunity to strengthen existing collaboration with the partners of the consortium and to establish a new network of possible partners for the future. Actually we have already presented more than one proposal to H2020 with some of the partners of the uLites.
The specific benefit from CIMNE side was the realization of a virtual wind tunnel tool (together with TUM) that put together the expertise and the research results of the team for a practical engineering purpose.
During the uLites a numerical vs experimental validations campaign was successfully started and will hopefully continue and be completed in the near future with the partners from CRIACIV.
The main drawback, not directly related to uLites but to the Capacities programme was identified in the short time given for the project. This limited the possibility of exploiting more deeply the RTDs results.
TUM
Benefits that TUM got from ulites:
1- Improvement of the ABL generator to make it capable of modeling very low frequencies satisfying better Kaimal spectra of natural wind.
2- Wind-tunnel tests have provided good validation examples to which further methods and different implementations can be benchmarked.
3- Gaining more experience in the FSI modeling of membrane problems.
4- A new network of experts in different fields is established, which can further enrich research activities.
UNIPD
The participation of University of Padova as RTD member of uLites team has been satisfactory both in terms of work done (tests on new materials, direct contact with SME’s world and their know how) and of possible future developments (applications of new materials, numerical wind tunnel, design of inflatable structures, …). In particular we had the occasion of taking contact with innovative materials that represents, if properly applied, the next future of lightweight structures.
Cooperation with SMEs has been close and effective, also in copying the difficulties encountered during the execution of the tests. Interchange of information between partners and availability in discussing and “producing” solutions to the problems made the collaboration fruitful also in view of further future collaborations
Potential Impact:
The principal outcome of the project is represented by a innovative emergency shelter structure for which a new design has been developed and a prototype presented. In order to achieve this goal a number of sub-products have been generated, namely membrane with embedded photovoltaic cells, flexible carbon-fibre stripes and a virtual wind tunnel acting as simulation software for computer aided design.
The emergency shelter to be developed represents a new, lighter and more practical way to provide a temporary refuge to people who become homeless due to natural catastrophic events or social and geo-politic crises, than common refuges. In fact the integration of photovoltaic cells, combined with the improvement in the sealing of the structures, and the use of power-storage devices (e.g. batteries) for having available power during night time, make these continuum low pressure inflatable structures largely independent in terms of electric energy supply. The name “continuum” comes from the fact that traditionally these structures need to be connected permanently to a power source due to the big amount of air losses.
These continuum low pressure inflatable structures have been widely used worldwide since many years, with several applications in different target business sectors (e.g. aeronautics, defence / military, industrial, humanitarian aid, corporate events). These provide valuable advantages (light weight, big ratio storage volume / folded volume, easy anchorage to terrain without need of foundation works, short lead times, etc.) over other competitor structures (e.g. light metallic structures, tensile structures, presostatic structures, high pressure inflatable structures). However, for some specific uses, some of the intrinsic characteristics of the low pressure inflatable structures (e.g. energy supply dependency, continuous power consumption) make them difficult or even unfeasible to be used (e.g. in areas without any available power supply, or when power sources are expensive or difficult to be obtained or transported).
The integration of the solar cells into the uLites shelters, provides these structures with outstanding added values such as portability improvement, energetic autonomy, or negligible power consumption, which will allow them to compete with the competitor structures on the previously referred uses. This will introduce the SMEs to new notable customers as national emergency management agencies, humanitarian organization, Red Cross, armies, etc
On the other hand the experimental campaign on both Solarpanels and carbon fibre stripes is an important added value in the creation of a reliable shelter since the comprehensive behaviour of these materials has been analytically analysed and classified, not just empirically tested.
It is worth mentioning that carbon-fibre stripes open a new area of the market since, nowadays, there are applications of this material to civil structures, but these are never used as material to produce stays, wires, cables or stripes bringing the ulites’ SMEs to be pioneers in that field.
The creation of a simulation software that acts as a Virtual Wind Tunnel (form finding, structural analyses, wind tunnel simulation and fluid-structure interaction) represents a useful instrument for the innovative design of membrane structures. The development and validation of such software tool allow the study of a larger number of design alternatives allowing a wider design space to be explored and more optimal solutions to be found.
Finally it should be noticed that there is an intrinsic trans-national impact in the uLites project. The cooperation between the SMEs and the RTD will allow the SMEs to open to international markets where the other SMEs are already introduced therefore increasing their commercial network.
From the client point of view, the solar panels inflatable structures would have an impact on both purchase price & operative costs:
• Purchase price: The increase in price due to the inclusion of the solar panels would be around 15% of the current prices.
• Operative costs: Using the photovoltaic solar panels, the following costs could be eliminated
o Power consumption: Currently, the power consumption for the inflatable structures (although depends on the size and environmental conditions) would be around 0.5-1% of the purchase price per year. Assuming a amortization period of 5 years, such power consumption can represent 2.5-5% of the purchase price.
o Alternative emergency power supply sources purchase: The purchase price of the emergency power supply sources like generators (also depending on the size and environmental conditions), could be around 4-6% of the purchase price.
So, the operative savings (negligible or null power consumption + no need to purchase alternative power supply source) would represent 6.5-11% of the purchase price, which would almost compensate completely the price increase due to the use of the solar panels. However, the improvement can not only be measured in terms of price, but also considering that new market targets can be reached
IMPACT ON SMES GROWTH:
BuildAir: By participating in the uLites project, BuildAir expects to gain access to the emergency and fast-deployment cover markets, while enabling the use of new technology in the markets where it already competes. In particular, structures with the capability of generating solar energy would be extremely useful in the field of inflatable structures, which is BuildAir’s main area of expertise, allowing significant savings or even a surplus of energy.
The improvements in the manufacturing procedures and the innovative energy system designed for the uLites shelter will be widely used in Buildair products.
The technology developed will be used as the starting point for other H2020 proposals that are going to be submitted.
Additionally, access to the Virtual Wind Tunnel tool allow for a reduction of design time and costs, as well as ensure that the structures developed comply with the most demanding wind and weather conditions.
Naizil: The opportunity to be involved in the uLites project brought the possibility to continue the study on the behaviour of SOLARPANEL in terms of installation’s systems, different applications, specific simulation’s tests in different conditions (stress strain, load, wind, temperature).
Reglass: Reglass’ could develop an innovative and lightweight carbon fibre stripe of acceptable cost for fixed and flexible structures. One of the focal points of the research has been the realization and test of the joints and anchorage system between the carbon cable and the metal end which has to sustain the entire load and has to be absolutely safe.
SL-Rasch: The results of uLites will significantly expand the recent market of RASCH thanks to the development and validation of the Virtual Wind Tunnel during the uLites project. This will allow a faster evaluation of the potential of new designs in preliminary design stages and can allow a quick response to customer requests.
DISSEMINATION ACTIVITIES AND EXPLOITATION
Concerning the dissemination activities, the partners of Ulites have published 3 papers in JCR journals and are actually preparing other 5 papers to be submitted in the next months (table A1). The partners actively participated to International conferences presenting the results of the uLites, this is demonstrated by the 15 proceedings in international conferences (table A1). A monograph was also published.
Two doctorate courses of 2 ECTS have been organized by CIMNE at the Technical University of Munich. In this courses the recent advances in FSI solvers developed in the uLites where presented (Table A2). The Kratos Workshop, organized in the framework of an international conference on the recent advances of GiD pre and post process tool, was an occasion to present to an international audience the Virtual Wind Tunnel as an available opensource tool inside Kratos multiphysics (Table A2).
A Flyer summarizing the main innovative feature of the ulites was created and distributed among possible stakesholders. Around 200 flyers have been distributed.
A ulites group was created in linkedin https://www.linkedin.com/groups?home=&gid=8238318&trk=groups_most_recent-h-logo and a Wikipedia page is going to be created once the multimedia material regarding the construction of the prototype will be available.
A description of the project has been added to the Linkedin Community, linked to the involved researchers and with a link to the uLITES webpage
It’s to be noted that the uLites concept (ultra-lightweight structures with integrated photovoltaic solar cells) and added values (portability improvement, absence of energy supply dependency, reduced power consumption) have been commented during trade fairs on which some of the partners have exhibited or attended, with the aim to record the feedback from potential customers to this new technology. The result could not be better: many potential clients (especially from Defence / Military sector) consider this product as fully attractive, and the previously enumerated added values as outstanding. The improvement in portability and the elimination of energy supply dependency are key factors for many clients to consider very positively the ultra-lightweight structures.
For every business sector, direct communications have been performed with potential clients, who already know some of the project partners due to previous contacts:
- Aeronautics:
o MRO organizations (Lufthansa Technik, Delta, Iberia, British Airways, Air France-KLM, Avianca, ABS Jets, Jet Aviation, etc.)
o Aircraft manufacturers (Airbus, Boeing, Bombardier, etc.)
o Airlines (e.g. same as MRO organizations, plus Ryanair, Easyjt, etc.)
o Airports worldwide
- Defence / Military:
o Armies / Air Force (e.g. Spanish, Colombian, Polish)
o Spanish Guardia Civil
o Spanish Unidad Militar de Emergencias
o Protezione Civile Italiana
- Companies:
o Acciona
o Abengoa
o OHL
o Navantia
o Alava Ingenieros
- Humanitarian Aid:
o International Committee Red Cross
o United Nations High Commissioner for Refugees
o Medics Sans Frontieres
List of Websites:
http://www.cimne.com/websasp/ulites/
