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Mid-frequency vibro-acoustic modelling tools / Innovative CAE methodologies to strengthen European competitiveness

Periodic Report Summary - MID-MOD (Mid-frequency vibroacoustic modelling tools / Innovative CAE methodologies to strengthen European competitiveness)

Project context and objectives:

The lack of Computer-aided engineering (CAE) tools for mid-frequency issues forms the target for this collaborative project. In this project a well-balanced consortium of both academic and industrial partners will develop robust CAE tools, applicable for the analysis of mid-frequency noise and vibration problems. In a second stage, these tools will be applied on industrial problems, filling the currently existing gap. A third important aspect of the project is the dissemination of mid-frequency analysis and modelling skills throughout the European Union (EU) engineering community to spread crucial knowledge and skills in strengthening EU transportation vehicle competitiveness.

A first objective of the proposed project is the development of innovative solutions for the modelling and simulation of vibroacoustic transport problems in the mid-frequency range, in this way filling crucial gaps in the state-of-the-art and state-of-the-use of vibroacoustic modelling. Milestones 1 and 2 correspond to this first objective.

Milestone 1 involves a profound comparative study between five deterministic technologies (wave based method, fast multipole method, domain decomposition method, stabilised method and higher order wave based integration schemes) which are currently most promising with respect to their applicability for industrial vibroacoustic problems in the mid-frequency range. MID-MOD research activities involve studies towards what is needed to lift these technologies out of their academic environment and to apply them for real-life engineering problems in the transportation industry. Problems, for which currently industrial CAE tools are lacking.

Milestone 2 involves a similar comparative study, but instead of approaching the mid-frequency range from below using deterministic approaches, this time five high-frequency probabilistic methodologies are studied (stochastic boundary elements, wave based finite elements, component modal approach, spectral finite elements and point mobility approach).

Secondly, these innovative methodologies will be validated extensively with respect to component level, subsystem level and, finally, full vehicle level validations. As such, the industrial partners will be trained in the use of the novel methodologies and can increase their competitiveness by obtaining state-of-the-art knowledge of their application. Two important real-life validation cases are considered:

- the evaluation of body - noise - transfer - functions (interior validation case);
- the assessment of pass-by-noise (exterior validation case).

The goals of the proposed project are depicted briefly as triple digit performance improvements'. Such improvements will become apparent in the following quantifiable targets:

- the reduction of solution times: pursuing 'over-night' calculation times, i.e. starting the simulation at office closing time and having the results the morning after;
- the enlargement of the applicable frequency range: bridging the mid-frequency gap for interior transportation applications (i.e. the 200 Hz - 1 kHz gap) and increasing the upper frequency limit of exterior calculations (i.e. going from the 500 Hz octave band to the 4 kHz octave band);
- increasing the prediction accuracy in the low-, mid- and high-frequency range: pursuing a 3 dB absolute accuracy;
- the reduction of computational loads, i.e. both Central processing unit (CPU), times as well as memory and disk space requirements such that (networks of) conventional office desktop personal computer (PC)s may be applied for numerical;
- tools for Noise, vibration, and harshness (NVH) evaluation to become available not only for the expert analyst, but also for the design engineer to support early-design stage decisions based on a multi-attribute optimisation including NVH.

Milestone 3 involves the above described validation strategy, applied to truck applications, milestone 4 comprises the validation of the innovative methodologies for automotive applications, while milestone 5 is related to their validation for interior rail applications.

A third important objective is the dissemination of the innovative mid-frequency research results within the broad European engineering community. The dissemination will be a crucial point in training a sufficient number of people with the proper vibroacoustic skills. Milestone 6 corresponds to this third objective.

Additionally, milestone 7 addresses the intermediate project report and milestone 8 the final project report. They will provide a valuable overview of both MID-MOD technological innovations and MID-MOD industrial validation studies, which will form a reference work for the consortium partners with respect to mid-frequency vibroacoustic issues.

Project results:

The work performed so far, in the project during the first half, can be summarised as follows:

WP1: Enhanced deterministic techniques
The feasibility of the enhanced deterministic methods and the current status is being investigated and research on new and more industry oriented applications is ongoing in close cooperation with Work package (WP)s 3-7. All initially foreseen deliverables are finished. One additional deliverable D1.7 was defined and is on schedule to be delivered - on schedule.

The participating partners have established joint cooperation activities, as is illustrated by the numerous joined publications. In task 1.1 research is performed to investigate the applicability of the wave based method towards industrial problems. Task 1.2 focuses on overcoming the non-uniqueness problem in boundary element schemes. The 'Non-uniqueness problem' refers to the fact that the boundary element method fails to provide a unique solution for exterior problems at frequencies corresponding to internal resonances. This problem becomes even more critical at higher frequencies with the increasing modal density inside the cavity. In task 1.2 a new strategy, which consists of imposing Robin boundary condition only on certain percentage of elements, has been developed and tested with some academic and industrial numerical validation cases. This allows to mitigate the non-uniqueness problem without drastically increase the computational cost. In task 1.3 domain decomposition methods, such as wave based sub-structuring and stabilised Finite element method (FEM)s are investigated while task 1.4 focuses on advanced integration schemes and efficient equivalent fluid descriptions for modelling porous materials.

All partners involved in WP1 are working in solid and frequent interaction. The developments have been reported in 6 deliverables and several joined conference and journal publications. The developed methodologies are now in the process of being validated, together with the approaches of WP2, in the application WPs 3-7.

WP2: Enhanced energy based methods
Research ongoing and the cooperation between users (industry) and developers (universities) have started in good pace - deliverables are being written - on schedule.

A Stochastic boundary element method (SBEM) is being developed with the aim of lowering the application range of probabilistic methods. The SBEM formulation, initially developed for academic structures, within MID-MOD has been extended and completed to deal with hybrid problems, to be coupled with FEM, and it has been extended to three-dimensional (3D) formulation. Examples of these applications are presented in detail in deliverable D2.1: two- and three-dimensional acoustic and vibroacoustic applications. By means of these applications the SBEM has been tested to deal with industrial applications in acoustic and hybrid vibroacoustic coupled analysis.

The formulation is still in its development process and thus UNIFI intends to continue working and researching on it. The long term objective at UNIFI is to develop a stochastic acoustic tool which can easily interact with commercial software like Matlab, Nastran and Virtual Lab to deal with interior 2D and 3D acoustic applications characterised by random parameters. The development of the method has been presented at MID-MOD workshop within the Graz ISNVH 2010 conference and will be presented at a boundary element conference in the United Kingdom in September. Work in MID-MOD is based on both finite element calculations, a wave method (Waveguide FE) and SEA and it springs from a long term commitment to the modelling of porovisco elastic materials.

WP3: Interior truck applications
Application scenarios are being developed and investigated - good pace in the planning activities - on schedule.

WP3 involves an extensive numerical / experimental validation campaign and is set-up to evaluate the performance of the methodologies for the analysis of interior acoustic truck problems. WP3 is progressing on schedule. The work plan has been agreed between all partners and described into detail in D3.1 'Interior truck applications - problem definition'. WP3 technical plan is available and has been agreed by all WP3 partners:

WP3 deliverable D3.1 'Problem definition' has been finalised by LMS:

Technical progress - recent and ongoing activities (status June 2010):
- LMS has performed pre-test on truck floor (Nastran FE model);
- SIMR has cut remaining ends from floor (in line with pre-test);
- SIMR are performing the floor component testing;
- IKA are finalising definition of construction of concrete cab - final geometry is being defined.

Planning of future activities:
- 2010: Finalise all experimental testing; finalise nominal model preparation up to subsystem level. Results to be reported in D3.2 - measurement database by month 24 (due Dec 2010).
- 2011: Update BCs in full system model; focus on simulation methodology validation. Results to be reported in D3.3 - validation report by month 33 (due Oct 2011).

WP4: Exterior truck applications
Application scenarios are being developed and investigated. Good pace in the planning activities - on schedule.

The definition phase within WP4 is about to be finished and the modelling and testing phases are already begun. The FMBEM with the 'Internal impedance method' developed in WP1 will be applied to predict the acoustic radiation and emission of a truck Muffler in the mid-frequency range. The validity of the results will be evaluated using experimental results. The definition of the problem is reported in deliverable D4.1.

WP5: Interior car applications
Application scenarios are being developed and investigated. Good pace in the planning activities - on schedule.

Model of the cavity for WP5 is distributed for the application. Test campaign started at CRF on the vehicle that will be dismantled step by step - first experimental results for P / dQ / dt expected for the end of September. VW is starting up the measurement campaigns (detailed planning presented). The definition of the problem is reported in deliverable D5.1.

WP6: Exterior car applications
Application scenarios are being developed and investigated. Good pace in the planning activities - on schedule.

The definition phase within WP6 is in its finalisation phase and the modelling and testing phases are just begun. The FMBEM with the 'Internal impedance method' developed in WP1 will be applied to predict the acoustic radiation and emission of a signal horn in the mid-frequency range. The modelling complexity will increase from the component level (acoustic emission of the horn itself) to the sound radiation of the signal horn located in the engine bay, as prescribed by standards CEE 70 / 388 and ECE No28. The validity of the results will be evaluated using experimental results. The definition of the problem is reported in deliverable D6.1.

WP7: Interior rail applications
Application scenarios are being developed and investigated, Good pace in the planning activities - on schedule.

Work is progressing according to plan, and component and sub-system levels have been defined. The definition of the problem will be reported in deliverable D7.1.

WP8: Summary and guidelines
Work is starting up - on schedule.

UNIFI is involved in the preparation of D8.1 deliverable 'Comparative report on enhanced deterministic methods' and D8.2 deliverable 'Comparative report on enhanced energy based methods'.

The cooperation within the consortium is good and the partners are actively contributing to the creation of the public documents which will contribute to the dissemination of MID-MOD results and to increase the interest towards the methodologies developed and tested.

WP9: Transfer of knowledge and dissemination
Homepage is up and running - development courses and workshops are being planned by the WP leader - on schedule.

The amount of conferences attended, and the number of written and accepted journal papers is steadily increasing, and is already now above 20. Professional course to be held during Q4 2010 in Southampton (place to be finally decided).

WP10: Management
ongoing - on schedule.

Consortium meetings, reporting activities and homepage updating, all in order.

Potential impact:

Noise and vibration have a very large impact on the competitiveness of transportation vehicles, not only driven by the increasing customer demand for vibroacoustic comfort, but also by the tightening legal regulations regarding noise and vibration emissions and immissions. Since noise and vibration as functional performance attributes often conflict with other attributes, such as weight and CO2 emission, concurrent design and analysis procedures are required. Such processes involve multi-attribute optimisation and are facilitated by the use of CAE tools. Also, there is an increasing trend towards virtual prototyping to reduce costs and development times. As a result, good CAE tools are essential in modern vehicle design.

Ideally CAE tools would be applicable in the whole frequency range of interest, which is the audio-frequency range. In practice specific methods are applicable in a limited frequency region. A class of deterministic 'low frequency' methods is both well developed and well established. At 'high frequencies' energy based methods are valuable, but less well-established. There is however a 'mid-frequency' gap in current modelling capabilities: too high for deterministic and too low for energy based tools. This is important, since it strongly affects product performance and competitiveness.

The lack of CAE tools for mid-frequency issues forms the target for this collaborative project. In this project a well-balanced consortium of both academic and industrial partners will develop robust CAE tools, applicable for the analysis of mid-frequency noise and vibration problems. In a second stage, these tools will be applied on industrial problems, filling the currently existing gap. A third important aspect of the project is the dissemination of mid-frequency analysis and modelling skills throughout the EU engineering community to spread crucial knowledge and skills in strengthening EU transportation vehicle competitiveness.

List of websites: http://mid-mod.eu/