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OptimizationThroughSimulation A Summary of the recentNAFEMS France Seminar

Didier Large, NAFEMS France

The seminar "Optimization by Simulation" chaired by Yves Tourbier,Director of Advanced Research at Renault, brought together morethan 90 participants in Paris on Tuesday, May 30th.

Optimization has become an essential part of the design process, it hasemerged and flourished in all areas of physics and at all projectmilestones. Embedding optimization upstream at the design stage isessential as it allows the right decisions to be made as soon as possible.Optimisation is also used in the dimensioning process and to set atechnical definition on performance objectives throughout projectplanning. Deciding what is the best solution, the best compromise, addsadditional expense upfront but reduces the number of design iterations.Optimization accompanies innovation, composite materials are a goodexample of this: their cost can be prohibitively high so that they can onlybe competitive if materials are minimised and new forms explored.

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In the introduction Yves Tourbier of Renault presentedtheir 5-10 year roadmap by major areas of optimizationboth at the upstage design phase and in thedimensioning process. Topological optimization tools andparametric methods were explored in particular detail.Renault example case studies were presented, whichidentified the optimization categories and listed theassociated R & D needs. In particular, these indicatedthat the post-optimization plans had been eliminatedthrough studies on upstream manufacturing processes.The pressure on development cycles limits the time spenton optimization, which requires the use of new numericalmethods and new algorithms using artificial intelligence.There are some areas such as crash simulation in theautomotive industry that still remain a major challengefor optimization methods. The objective is to have asingle 3D CAD definition and a single 3D multidisciplinarysimulation model. With model sizes constantly increasingHPC resources even at Renault are constantly beingsaturated even with continual investment. The HPCdemand imposed by optimization makes it necessary touse automatic reduction and parameterizationtechniques. Deployment of new tools and methods takestime, which makes it necessary to move from the currentuse of optimization tools (for dimensioning, problemcorrection, failure detection and recalibration ofbehaviour laws) to support the decision-making processby enlarging the field to be explored, automating themanual processes (pre-post processing) and varying theparameters (CAD-Morphing) available by improving thequality of the models.

Like its competitor Boeing, Airbus has also created anoptimization centre. Stephane Grihon said there weresimilarities between the approach in Airbus and that inRenault. He presented a multi-fidelity approachexploiting the reduction of models for optimization indimensioning of aircraft structures by reviewing the newtools available. One of these tools is PRESTO, for therapid sizing of structures with the possibility of changingin real time a thousands of parameters such as the typeof materials. Other tools have been developed inpartnership with Dassault Systèmes for topologicaloptimization, with Datadvance for big data around theAirbus’ common environment called ISAMI (ImprovedStructural Analysis through Multidisciplinary Integration)or MyShape, a tool to support 3D printing.

Benoit Guillaume of the Quality and EngineeringDepartment at PSA Group indicated how optimisation haschanged the design process through concrete examples.Optimization upstream of the design is still not verywidespread but is undergoing strong development.Topological optimization is now pushed to the extremeand the optimization of the additive manufacturingprocesses deeply impacts the traditional methods withapplications for tooling, prototype parts or parts forvehicle style and customization.

Romain Charrier of Renault presented a new methoddeveloped in collaboration with the IRT SystemX called

ReCUR which allows the engineer to limit the number ofcalculations using model reduction. For the optimizationof a crash case, more than 50 parts and 37 thicknessparameters must be taken into account. With theclassical design method, the number of computationalexperiments varies between 3 and 10 times the numberof variables. The ReCUR method has demonstrated itsreliability and efficiency, taking into account the "carryover" of parts that can be modified without any additionaldevelopment costs. The ultimate goal is to obtain betteraccuracy of the input data and apply the method to thequalitative variables.

Romain Soulier of Enginsoft presented an exampleshowing the influence of design parameters on theperformance of a totally new 3l V6 engine for the newMaserati produced for FCA (Fiat-Chrysler Automobiles).The multi-objective optimization focuses on the torquetime, the braking torque, the fuel consumption includingthe emission constraints, the air-fuel mixture and thenoise.

Nicolas Louis of Valeo Systèmes Thermiques and LaurentLastugue of Intes France presented a multimodaloptimization project (topological and parametric) of anengine air inlet module based on multi-physicssimulations. The new anti-pollution standards requireengines of lesser displacement with equivalentperformance, which often leads to the use of aturbocharger which in turn increases the airtemperature. Valeo ST have developed a new conceptcalled "Charge Air Cooler" which integrates in a singlecomponent various functions including the air manifold(AIM), water cooler, valves, sensors and supports. Thesimulation of the AIM is complex because it uses CFD,structural calculations, materials, extended temperatureand frequency ranges, small part sizes and smallthicknesses. A specific and innovative method was put inplace, validated and applied during this project tosimulate a system in the context of thermal shock.

A multimodal optimization on an industrial demonstratorwas carried out with the PERMAS code of Intes. Thismulti-physics demonstrator includes a very fine model(> 60 million cells), thermal shock conditions derivedfrom CFD simulations, dynamics, cyclic pressure loadingand complex parametrization (2,200 parameters and650,000 topological elements). Thanks to the resultsobtained and the information they provided, decision-making is facilitated in a number of areas (cost,robustness, lifetime, etc.), which is a real added value ofnumerical simulation.

Jérôme Pasquiet of Safran Engineering Servicespresents several real use cases of topologicaloptimization based on Altair's Optistruct tool fordesigning aeronautical supports and fittings for additivemetallic laser beam fabrication (LBM). The first caseconcerns replacing a titanium alloy support machined intwo parts, welded and riveted by a single piece createdwith additive manufacturing. The process consists in

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making a mass optimization (25% improvement) withseveral safety factors, then creating polyNURBS for therationalization of so-called "bionic" forms. The optimizedsolution met the certification criteria. The other twocases concerned an aluminum or titanium fitting and asupport either in a network of bars or in a "lattice" typestructure (cellular materials). The weight improvement isbetween 20 and 35%.

Prof. Francisco Chinesta of Ecole Centrale de Nantespresented his vision of the future of optimization bysimulation and in particular advanced tools for real-timesimulation based on virtual abacuses and mass data. Itpresents the advantages of the PGD (Proper GenerationDecomposition) method, which can be used in manyfields such as solid mechanics, CFD, electromagnetism,structural mechanics or stamping to solve largemultidimensional models. An example developed with theIRCAD of Strasbourg proposes parameterization of ahuman liver with only four combinations of distortion.

The presentation by Professor Pierre Duysinx of theUniversity of Liège (Belgium) dealt with problems relatedto the optimization of parts produced in metallic additivemanufacturing, which introduces new constraints to betaken into account in topological optimization. The mainones are the undesired effects to be verified by the finiteelements calculation a posteriori, the technicallimitations (concentration of maximum heat), constraintsof design (minimum-maximum size, minimum space) oraesthetic aspects. Progress is possible to limit theaddition of supports (self-supporting structures), thedetection of material deflection problems in overhangingangles, the choice of lattice-type structures, thermomechanical analysis for prediction of residual stresses,and the development of meta-models to optimizecomputation time.

Michael Bruyneel of GD Tech Engineering explained theconstraints associated with the optimization of reinforcedfibre composite structures with thin walls. He discussedthe parameters to be used for the topologicaloptimization of composite parts and the methods used tosolve the models. The main parameters are theorientation of the fibres, the thickness and the shape ofthe folds, the stacking, the characteristics of thematerials and the lamination phenomena. Questions thatwere posed included which optimization strategy should

we adopt, is there a unique solution, and should thepriority be the decomposition of problems or the focus onconstraints.

Denis Espinassou of the CETIM (Technical Centre ofMechanical Industries) presented a method of multi-leveloptimization of low-cost and high-speed thermoplasticcomposites manufactured by QSP® process (QuiltedStratum Design) developed with ONERA. It consists ofidentifying economical "preforms" that are easy todevelop, composed of multi-patches and designed toanticipate the deformation due to forming. Simpleflattening induces economic preforms. The multi-leveloptimization consists of a first step of macroscopicoptimization with distribution of the thicknesses andtaking into account the rigidity of the distribution, then amesoscopic phase with identification of the stacks. Theexpected improvements include the automation of initialzoning, accounting for rupture and replacing drapingplans with patching plans by integrating the economiccriteria.

Fabrice Poirion of ONERA presented the recent results ofthe application of a multi-objective optimization methodunder uncertainty and its application to a sandwich typeplate.

Finally, Benedikt Eck of Faurecia described a method ofreducing the faults in composite parts by simulation andoptimization. The increasing use of composite partsresults in greater design freedom but a higher cost ofmaterials. The "formability" of fabrics must be controlledby optimizing the manufacturing process to avoidwrinkling, limiting falls of material and thus optimizingthe cost of the parts produced. This is done at FaureciaComposites by the automated linking of the threemechanical simulation processes plus the resin transfermoulding (RTM) estimator and cost estimation. The samemesh is used for product and process simulation. Usingthe RTM estimator process compared to the standardsolver saved 96% in set time and 46% in optimizationtime by reducing the cost estimate from a few days to animmediate result.

The presentations from this event will be available toNAFEMS members in the coming weeks atnafe.ms/2uQyPMS �