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Matrix Optimization for Testing by Interaction of Virtual And Test Environments

Periodic Reporting for period 2 - MOTIVATE (Matrix Optimization for Testing by Interaction of Virtual And Test Environments)

Reporting period: 2018-12-01 to 2020-05-31

Simulation of structural behaviour is a key part of the design and operation of safety critical engineering infrastructure. It is used to support design choices and to inform decisions about the servicing and operation of engineering structures and machines. It is common practice to establish confidence in predictions from computer models used in simulation by comparing them to measurements obtained from physical tests on prototypes. These physical tests are often expensive and time-consuming to conduct, which can place them on the critical path in the development of new designs, e.g. of aircraft. Recent advances in measurement technology allow fields of measurements of the deformation of large-scale structures to be obtained during physical tests; however, the effective use of this ‘big data’ presents both challenges and opportunities in the context of validating predictions of structural behaviour. The aim of the MOTIVATE project was to bring about a step change in the way simulations, or virtual tests, and physical tests are used together in an industrial environment to reduce the cost, risks and time associated with product development. The project objectives were:

i. to develop a robust and repeatable method for the quantification of uncertainties in measurements using digital image correlation in an industrial environment,
ii. to produce advanced structural test protocols with an associated methodology for validation of simulation data, and
iii. to deploy the validation methods and test protocols in a demonstration during a structural test case.

The project was a response to Innovation Action JTI-CS2-2016-CFP04-AIR-02-32 entitled 'Testing Matrix Optimisation by Interaction between Numerical Modelling & Innovative Non-Contact Measurement Technology' within Work Package B 3.3.2 of Technology Stream B3: Advanced Integrated Structures in the ITD Airframe of the Clean Sky Joint Technology Initiative. Specifically, the intention was to improve and develop the existing methodologies for quantifying uncertainty in measurements of displacement and strain field, and in parallel, to progress and mature the current methodologies for correlating predicted and measured data fields in order to provide a simple-to-use and robust approach to validating computational models. Enabling technologies, which had been demonstrated in laboratory conditions during a series of EU FP 5 and 7 projects, including SPOTS [No. G6RD-CT-2002-00856]; ADVISE [No. 218595] and VANESSA [No. NMP3-SA-2012-319116], have been refined, developed and transitioned into the industrial environment and demonstrated in a structural test on an aircraft subcomponent (a 1 sq.m fuselage panel) and on an aircraft -scale (a cockpit section) at the Topic Manager’s site [Airbus in Toulouse]. The outcomes of the project are:

A. A methodology for the validation of simulation tools in structural mechanics;
B. A procedure for the quantification of measurement uncertainty in digital image correlation;
C. Protocols and best practice for validation methodology for subcomponents; and
D. Test cases demonstrating 'double-blind' deployment of protocols and implementation of validation methodology.

In conclusion, the robust protocols for validation will enhance confidence and credibility in computational simulations of structures, and thus, enable light-weight, more reliable, elegant designs to be brought to the marketplace faster and at lower costs by reducing the number of tests required to develop high fidelity models of new designs of aircraft structures. Light-weight, elegant structures are essential in realising the EU and Clean Sky environmental and other goals.
In more detail the technical results of the project are:

A. A methodology for the validation of simulation tools in structural mechanics including a new validation metric which quantifies the probability that a field of predictions belongs to the same population as a field of measurements given a quantified measurement uncertainty;
B. A new procedure for the quantification of measurement uncertainty in digital image correlation (DIC) for use in industrial environments which can be implemented for any DIC system using a calibration target and provides fields of uncertainty describing the measurement uncertainty for the displacement components measured in the field of view of the system;
C. Protocols and best practice for validation methodology applicable to subcomponents described in a good practice guide and summarised in a flowchart that is incorporated in a Graphical User Interface (GUI) to aid the test engineer in the implementation of the methodology, and which allows the consideration of historical data for validation as well as the standard approach of conducting tests specifically for the purpose of validation; and
D. Test cases, at the sub-component and aircraft level, demonstrating 'double-blind' deployment of protocols and implementation of the validation methodology. The aircraft-scale industrial demonstrator comprised a full-scale front nose section of an aircraft fuselage and included the implementation of the procedure for quantification of measurement uncertainty, the use of the best practice guide and flowchart, and the evaluation of the predictions using the new validation metric.

Three manuscripts for publication in archived journals have been prepared based on the implementation of the new method for quantification of measurement uncertainty, the implementation of the validation protocol and metric on a sub-component (fuselage panel), and the demonstration of the new technologies on the full-scale aircraft fuselage. In addition, 13 presentations have been made at 7 conferences, 12 blog posts have been produced, 4 workshops have been organised, and 3 videos posted in the project website at www.engineeringvalidation.org.

It was decided that commercial exploitation of the new technologies was neither appropriate nor viable; and, hence, exploitation is being pursued through its incorporation in pre-standard documentation. Work is underway to produce a CEN Technical Report.
The new method for quantifying measurement uncertainties within a measurement volume in an industrial environment represents a significant advance over existing methods by providing an elegant, easy-to-use process which yields fields of uncertainty that capture all sources of error and is applicable to all DIC systems. It supports the use of the probabilistic validation metric which is the first to allow quantification of the comparison between fields of predictions and measurements based on describing the fields using feature vectors. Additional work has been performed to advance image decomposition so that irregularly-shaped data fields can be decomposed and compared using a generic approach. The incorporation of these advances into a validation protocol and flowchart that permits consideration of historical data and provides guidance on their implementation in industrial environments is a significant step beyond the current laboratory-orientated procedures. Hence, the project outcomes represent a significant and generic advance and maturation in the technologies and methodologies used to validate computational models of structures and this will benefit a wide range of industrial sectors through support for the rapid introduction of disruptive technologies such as novel structural concepts, by enabling high-fidelity simulations.
Composite image showing demonstrations on subcomponent at EMPA and on aircraft fuselage.
Composite image showing KOM, test at EMPA and new validation flowchart