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See detailMultiphysic topology optimization of electromechanical micro-actuators considering pull-in effect
Lemaire, Etienne ULg; Van Miegroet, Laurent ULg; Schoonjans, Thibaut et al

in Proceedings of the IVth European Conference on Computational Mechanics (ECCM 2010) (2010)

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See detailAPPLICATION DE L’OPTIMISATION DE FORME ET DE TOPOLOGIE A LA CONCEPTION INNOVANTE D’EJECTEURS POUR UN CONCASSEUR MAG’IMPACT
Van Miegroet, Laurent ULg; Lemaire, Etienne ULg; Duysinx, Pierre ULg

Report (2009)

La recherche concerne l'application des techniques d'optimisation de forme et de topologie à la conception innovante des ejecteurs du concasseurs MAG'IMPACT.

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See detailSensitivity in shape optimization of complex 3D geometries using level sets and non-conforming finite elements
Duysinx, Pierre ULg; Van Miegroet, Laurent ULg

Conference (2009, September)

For the last 20 years shape optimization has been stocking to penetrate industrial and real-life applications, whereas topology optimization was experiencing a fast growing soar and extensions to various ... [more ▼]

For the last 20 years shape optimization has been stocking to penetrate industrial and real-life applications, whereas topology optimization was experiencing a fast growing soar and extensions to various applications. By the way there is still a great interest in shape optimization because of the intrinsic capability of shape description to facilitate considering complex problems involving local stress and manufacturing constraints for instance. The level set description proposed by Osher and Sethian (1988) opened new perspectives to handle variable boundaries as in shape optimization. The implicit description of the geometrical entities allows for a more friendly and flexible manipulation of the geometry and overcome some restrictions related to the explicit approach of the geometry used in CAD systems: for example it is possible to reduce the topological complexity by removing or merging geometric entities (i.e. holes can merge or disappear) without degenerating the model, which was major restriction of shape optimization. A few years ago, the level set method was nicely complemented by the XFEM (eXtended Finite Element Method) proposed by Moes et al (1999). This approach greatly reduces the difficulty of considering time-variable boundaries and complex geometries by using non-conforming meshes. This is definitively an advantage to circumvent the so-called velocity field to carry out shape sensitivity and mesh relocation difficulties, especially with thin walled structures or 3D designs. The present research is continuing along and extending works by Duysinx et al (2006) and Van Miegroet and Duysinx (2007) to consider shape optimization based on a parametric level set description and XFEM. The work that is carried out in a common research project EFCONICO sponsored by the Walloon Region of Belgium aims at extending preliminary results 3 D structure and complex geometries, increasing the reliability of the method, enhancing the performances using advanced mesh generators as Gmsh, etc. In particular the paper presents new theoretical developments and their numerical implementation in sensitivity analysis with respect to parametric design variable of level sets. The developments are illustrated with numerical applications dealing with complex shape applications involving 3D geometries and the boundary conditions along design variable boundaries. [less ▲]

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See detailInfluence of the material model on local pull-in in electromechanical microdevices topology optimization
Lemaire, Etienne ULg; Van Miegroet, Laurent ULg; Duysinx, Pierre ULg et al

in PLATO-N International Workshop - Extended Abstracts (2009, September)

The appearance of local pull-in modes has been noticed during electromechanical microdevices topology optimization. The goal of the present research is to study the influence of material properties ... [more ▼]

The appearance of local pull-in modes has been noticed during electromechanical microdevices topology optimization. The goal of the present research is to study the influence of material properties (mechanical and electrical) modeling for intermediate densities to see if an appropriate choice allows avoiding such local modes. At first, a simple 1D model is developed to study the influence of the material properties interpolation. Finally, we evaluate if the conclusions from the 1D model can help to prevent the appearance of local modes for a 2D topology optimization problem. [less ▲]

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See detailDynamic analysis and preliminary design of twin-cylinder engines for clean propulsion systems
Louvigny, Yannick ULg; Vanoverschelde, Nicolas; Janssen, Guy et al

Conference (2009, July 02)

Facing environmental and energy challenges, automotive industry has to improve the fuel economy of vehicles and to reduce their polluting emissions. In this particular context, small twin-cylinder engines ... [more ▼]

Facing environmental and energy challenges, automotive industry has to improve the fuel economy of vehicles and to reduce their polluting emissions. In this particular context, small twin-cylinder engines regain interest for using in urban cars or as prime movers in hybrid electric cars. One difficulty with engine having few cylinders (three or less) comes from the balancing of the inertia forces created by the moving parts. Several models (from simple analytical model to complex flexible multibody simulation) of different configurations of twin-cylinder engine are developed. These models allow computing the inertia forces and moments generated by the engines and computing the strains and stresses of engine components. An important step is the engine balancing by modification of the crankshaft counterweights or by addition of balance shafts. The effect of the gas pressure on the balancing and on the component’s strains and stresses is also modelled. At the end, a comparison of the different configurations of twin-cylinder engine is provided [less ▲]

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See detailEco-efficiency methodology of Hybrid Electric Vehicle based on multidisciplinary multi-objective optimization
Nzisabira, Jonathan; Louvigny, Yannick ULg; Christiaens, Sébastien et al

in Proceeding of the 8th World Congress on Structural and Multidisciplinary Optimization (2009, June 01)

The eco-efficiency concept of clean propulsion vehicles aims at is simultaneously reducing the fuel consumption and environment pollutants impact (Eco-score) without decreasing the vehicle performances ... [more ▼]

The eco-efficiency concept of clean propulsion vehicles aims at is simultaneously reducing the fuel consumption and environment pollutants impact (Eco-score) without decreasing the vehicle performances and other user satisfaction criteria. Based on a simulation model in ADVISOR, one can evaluate the performances, the emissions and then the Ecoscore and the User Satisfaction for different driving scenarios. To establish a rationale methodology for conducting the eco-efficiency design of electric and hybrid vehicles, we adopt a multidisciplinary optimization approach while minimizing / maximizing both Ecoscore and User satisfaction objective functions. The proposed approach is then illustrated on the case study of the comparison of different mild parallel hybrid buses (hybrid electric vehicle (HEV) and hybrid hydraulic vehicle (HHV) by highlighting the effect of different energy storage systems (batteries, ultra capacitors, hydraulic system), mechanical and electric components sizes upon the optimized hybrid design. The optimization results show that the hybrid electric buses using ultra capacitors have almost the same performances as those using batteries, while the HHV technology can compete with HEV because of the hydraulic components low cost and recyclability if possibly using of water as motor/pump fluid. [less ▲]

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See detailOn the use of a truly–mixed formulation in topology optimization with global stress–constraints
Bruggi, Matteo; Duysinx, Pierre ULg

in Proceeding of the 8th World Congress on Structural and Multidisciplinary Optimization (2009, June)

The work refers to the field of topology optimization for bidimensional structures and addresses the case in which global stress–constraints are considered to improve final designs. Most of the previous ... [more ▼]

The work refers to the field of topology optimization for bidimensional structures and addresses the case in which global stress–constraints are considered to improve final designs. Most of the previous research tackles this topic relying on classical displacement–based finite elements where stresses are recovered via post–processing techniques. The work conversely investigates the use of a truly–mixed formulation where stresses are independent variables of the problem while displacements play the secondary role of Lagrangian multiplier. The implemented discretization is based on a composite triangular element whose features may be advantageously exploited in stress–constrained topology optimization. The discretization is checkerboard–free and allows to tackle topology optimization with element–based constraints without introducing any additional filtering technique. The high accuracy in the evaluation of the average stresses is expected to improve the efficiency of the numerical procedure, especially in the case of a single global constraint that has to govern the whole domain. The adopted discretization also passes the robustness condition even in the case of incompressible materials and this allows to menage strength constraints also for rubber–like components. Basing on these ideas, numerical investigations are carried out to test preliminary applications of the truly–mixed technique coupled with topology optimization and global stress–constraints. To handle the well–known singularity problem, that affects the constraints imposition, an alternative scheme is herein adopted instead of a classical "–relaxation. An example where a homogenous stress distribution is expected is firstly tested, having the aim of pointing out the main features of the proposed procedure. Afterwards, numerical simulations address a classical L–shaped specimen, pointing out pros and cons of the approach. [less ▲]

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See detail3D Shape Optimization with X-FEM and a Level Set Constructive Geometry Approach
Van Miegroet, Laurent ULg; Duysinx, Pierre ULg

in Proceeding of the 8th World Congress on Structural and Multidisciplinary Optimization (2009, June)

This paper extends previous work on structural optimization with the eXtended Finite Element Method (X-FEM) and the Level Set description of the geometry. The proposed method takes advantage of fixed mesh ... [more ▼]

This paper extends previous work on structural optimization with the eXtended Finite Element Method (X-FEM) and the Level Set description of the geometry. The proposed method takes advantage of fixed mesh approach by using an X-FEM structural analysis method and from the geometrical shape representation of the Level Set description. In order to allow the optimization of complex geometries represented with a Level Set description, we apply here a Constructive Solid Geometry (CSG) approach with the Level Set geometrical representation. Hence, this extension allows to optimize any boundary of the structure that is defined with a coumpound Level Set. Design variables are the parameters of basic geometric primitives which are described with a Level Set representation and/or the control points of the NURBS curves that act as the definition of an advanced Level Set primitive. The number of design variables of this formulation remains small whereas global (i.e. compliance or eigenfrequency) and local constraints (i.e. stresses) can be considered. Our results illustrate that fixed grid optimization with X-FEM coupled to a Level Set geometrical description is a promising technique to achieve structural shape optimization. [less ▲]

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See detailMicrostructure design with generalized shape optimization based on level set geometrical description and XFEM
Qiu, Kepeng; Duysinx, Pierre ULg; Zhang, Wei-Hong et al

(2009, May)

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See detailPreliminary design of twin-cylinder engines for hybrid electric vehicle applications
Louvigny, Yannick ULg; Christiaens, Sébastien; Duysinx, Pierre ULg

Conference (2009, March 10)

Most of HEV are built using existing engines. These engines have been developed for conventional car and are not especially tailored for HEV. The objectives of this work are to establish general ... [more ▼]

Most of HEV are built using existing engines. These engines have been developed for conventional car and are not especially tailored for HEV. The objectives of this work are to establish general requirements placed on an ICE for a HEV application, to draw the main characteristics of the engine and to find the best configuration of twin-cylinder ICE to motorize an HEV. The twin-cylinder engine offer interesting perspectives in the field of HEV thanks to its small size, low weight and low cost. [less ▲]

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See detailComparison of Ultra Capacitors, Hydraulic Accumulators and Batteries Technologies to Optimize Hybrid Vehicle Ecoefficiency
Nzisabira, Jonathan; Louvigny, Yannick ULg; Duysinx, Pierre ULg

in Proceeding of 2nd IEEE Int. Conference of Power Engineering, Energy, and Electric Drives (2009, March)

The main objective of vehicle powertrain hybridization is to improve the fuel consumption and environment pollutants impact (Eco-score) without decreasing the vehicle performances and other user ... [more ▼]

The main objective of vehicle powertrain hybridization is to improve the fuel consumption and environment pollutants impact (Eco-score) without decreasing the vehicle performances and other user satisfaction criteria. The Eco efficiency is a global index which accounts for both environmental impacts and user satisfaction. The Hybrid vehicles ability to overcome these two requirements depends on the optimal choice of their key mechanical, electric or hydraulic components. Some energy storage systems like ultra capacitors and hydraulic system are environmentally friendly and meet some user satisfaction criteria like daily cost, security, short charge/discharge duration and long life service. On the contrary, others like batteries have some times a environmental impact mitigate. The objective of this study is to establish a comparison between HEV (hybrid electric vehicle) and HHV(hybrid hydraulic vehicle) configuration by highlighting the effect of different energy storage systems (batteries, ultra capacitors, hydraulic system), mechanical and electric components sizes (engine, motors) upon the optimized HEV design taking care of both Eco-score and User satisfaction for different driving scenarios. The approach is formulated as a multidisciplinary optimization problem. At first, the HEV and HHV are modeled and simulated using ADVISOR (advanced vehicle simulator) with respect to several driving situations. Then emissions can be determined and the Ecoscore indicator can be calculated. User Satisfaction can be evaluated based on performance criteria extracted from ADVISOR simulation and on simple evaluation tools relying on the state-of-the art of technological information for safety, reliability and daily cost. The design problem is stated as follows: select mechanical, electric or hydraulic components (e.g. engine, motor and energy storage system sizes) to minimize the Ecoscore indicator and to maximize user satisfaction criteria subject to catalogue constraints on the choice of the components. The approach is illustrated on applications dealing with mild parallel hybrid buses. Results show that the hybrid electric buses using ultra capacitors have almost the same performances as those using batteries. However, the preferred choice would go towards super capacities because they have other appreciable properties compared to the batteries: the very high lifetime, high efficiency of charge and discharge and no polluting recyclability. Despite a smaller fuel saving than a HEV, the HHV technology has a chance to compete with HEV because of the hydraulic components low cost (industrial maturity), no pollutants recyclability due to the possible using of water as motor/pump fluid. HHV technology is a possible alternative in niche markets such as urban buses; bin-lorries or heavy urban delivery vehicles. [less ▲]

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See detailTopology Optimization of Structural Components: A Multibody Dynamics-Oriented Approach
Bruls, Olivier ULg; Lemaire, Etienne ULg; Duysinx, Pierre ULg et al

in Proceedings of the Multibody Dynamics ECCOMAS Conference (2009)

This work addresses the topology optimization of structural components embedded in multibody systems with large amplitude motions. Generally, topology optimization techniques consider that the structural ... [more ▼]

This work addresses the topology optimization of structural components embedded in multibody systems with large amplitude motions. Generally, topology optimization techniques consider that the structural component is isolated from the rest of the mechanism and use simplified quasi-static load cases to mimic the complex loadings in service. In contrast, this paper proposes an optimization procedure based on the dynamic simulation of the full multibody system with large amplitude motions and elastic deflections. We show that the simulation model, which involves a nonlinear finite element formulation, a time integration scheme and a sensitivity analysis, can be efficiently exploited in an optimization loop. The method is applied to truss structural components. Each truss is represented by a separate structural universe of beams with a topology design variable attached to each one. A SIMP model (or a variant of the power law) is used to penalize intermediate densities. The optimization formulation is stated as the minimization of the mean compliance over a time period or as the minimization of the mean tip deflection during a given trajectory, subject to a volume constraint. In order to illustrate the benefits of the integrated design approach, the case of a two degrees-of-freedom robot arm is developed. [less ▲]

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See detailMultiphysic topology optimization of electromechanical microdevices considering pull-in voltage using an electrostatic force filter
Lemaire, Etienne ULg; Duysinx, Pierre ULg; Rochus, Véronique ULg

in Proceeding of the 8th World Congress on Structural and Multidisciplinary Optimization (2009)

Electrostatic actuation is often used in microsystems as it is relatively easy to implement and provides a short response time. However, because of the non-linearity of electrostatic forces, these devices ... [more ▼]

Electrostatic actuation is often used in microsystems as it is relatively easy to implement and provides a short response time. However, because of the non-linearity of electrostatic forces, these devices may suffer from an unstable behavior called pull-in effect. Previous work of the authors intended to delay pull-in effect by maximizing pull-in voltage studying a simplified problem where the optimization domain was purely mechanical. The present paper generalizes the approach by considering a multiphysic optimization domain. However, the generalization of the optimization problem is not straightforward as local pull-in modes appear after a few optimization iterations. Therefore, the paper investigates several solutions to prevent the appearance of local pull-in modes. [less ▲]

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See detailKinematical Optimization of Closed-Loop Multibody Systems
Collard, Jean-François; Duysinx, Pierre ULg; Fisette, Paul

in Botasso, Carlo (Ed.) Multibody Dynamics - Computational Methods and Applications (2009)

Applying optimization techniques in the field of multibody systems (MBS) has become more and more attractive considering the increasing development of computer resources. One of the main issues in the ... [more ▼]

Applying optimization techniques in the field of multibody systems (MBS) has become more and more attractive considering the increasing development of computer resources. One of the main issues in the optimization of MBS concerns closed-loop systems which involve non-linear assembly constraints that must be solved before any analysis of the system. The addressed question is: how to optimize such closed-loop topologies when the objective evaluation relies on the assembly of the system? The authors have previously proposed to artificially penalize the objective function when those assembly constraints cannot be exactly fulfilled. However, the method suffers from some limitations especially due to the difficulty to get a differentiable objective function. Therefore, the key idea of this paper is to improve the penalty approach. Practically, instead of solving the assembly constraints, their norm is minimized and the residue is taken as a penalty term instead of an artificial value. Hence, the penalized objective function becomes differentiable throughout the design space, which enables the use of efficient gradient-based optimization methods such as the sequential quadratic programming (SQP) method. To illustrate the reliability and generality of the method, two applications are presented. They are related to the isotropy of parallel manipulators. The first optimization problem concerns a 3-dof Delta robot with 5 design parameters and the second one deals with a more complex 6-dof model of the Hunt platform involving 10 design variables. [less ▲]

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See detailTopology and generalized shape optimisation: why stress constraints are so important?
Duysinx, Pierre ULg; Van Miegroet, Laurent ULg; Lemaire, Etienne ULg et al

in International Journal of Simulation & Multidisciplinary Design Optimization (2008), 2(4), 253-258

The paper continues along the work initiated by the authors in taking into account stress constraints in topology optimization of continuum structures. Revisiting some of their last developments in this ... [more ▼]

The paper continues along the work initiated by the authors in taking into account stress constraints in topology optimization of continuum structures. Revisiting some of their last developments in this field, the authors point out the importance of considering stress constraints as soon as the preliminary design phase, that is, to include stress constraints in the topology optimization problem in order to get the most appropriate structural lay-out. Numerical applications that can be solved using these new developments make possible to exhibit interesting results related to the specific nature of strength based structural lay out for maximum strength compared to maximum stiffness. This particular character of stress design is clearly demonstrated in two kinds of situations: once several load cases are considered and when unequal stress limits in tension and compression are involved. [less ▲]

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See detailComparison of Ultra capacitors and Batteries Technologies to Optimize Hybrid Electric Vehicle Efficiency
Nzisabira, Jonathan; Louvigny, Yannick ULg; Duysinx, Pierre ULg

in Proceedinbg of 3rd European Symposium on Supercapacitors and Application (ESSCAP08) (2008, November)

The acceptance of Electric and Hybrid Electric Vehicle is related to their eco-efficiency, i.e. their ability to both reduce environmental impact while also providing a sufficient user satisfaction. The ... [more ▼]

The acceptance of Electric and Hybrid Electric Vehicle is related to their eco-efficiency, i.e. their ability to both reduce environmental impact while also providing a sufficient user satisfaction. The objective of this study is to provide a rationale design tool based on a multidisciplinary optimization approach to support the design of hybrid electric powertrain to simultaneously maximize user satisfaction complex criteria and minimize the Eco-score. In order to carry out the optimization problem efficiently the approach makes use of metamodeling techniques in order to save computation time in the optimization process that is driven by a Genetic Algorithm. The approach is applied to highlight the effect of different energy storage systems (batteries v.s. ultra capacitors) upon the optimized HEV design taking care of both Eco-score and User satisfaction. In the selected application that is a heavy urban bus with a mild hydrid electric powertrain, the ultra capacitors are slightly superior to NiMH batteries when emphasizing the Ecoscore criterion. [less ▲]

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See detailDesign of mechanism components using topology optimization and flexible multibody simulation
Bruls, Olivier ULg; Lemaire, Etienne ULg; Eberhard, Peter et al

in Proceedings of the 8th World Congress on Computational Mechanics (2008, July)

This work addresses the topology optimization of structural components embedded in multibody systems with large amplitude motions. For example, in deployable space structures, piston engines, automotive ... [more ▼]

This work addresses the topology optimization of structural components embedded in multibody systems with large amplitude motions. For example, in deployable space structures, piston engines, automotive suspensions, robots and high-speed machine-tools, the articulated components undergo large displacements and elastic deformations, and are subject to transient loads and nonlinear dynamic effects. The performance of such systems often depends on the mechanical design in a non-intuitive way. <br />Several researchers have addressed the optimization of the geometric parameters of mechanisms and also of the connectivity of mechanisms made of rigid members. In contrast, topology optimization techniques are often based on continuum mechanics assumptions, and usually aim at optimizing the layout of an isolated structural component under the assumption of small displacements and small deflections. In order to apply topology optimization to mechanism components, one may consider that each structural component is isolated from the rest of the mechanism and use simplified quasi-static load cases to mimic the complex loadings in service. However, two main drawbacks are associated with this approach. Firstly, defining the equivalent load cases is a rather difficult task, which is often based on trials and errors and which requires some expertise. Secondly, topology optimization is often sensitive to loading conditions, especially for multiple load cases and stress constraints, so that the optimal character of the resulting design becomes questionable if the loading is approximative. For these reasons, in order to obtain better optimal layouts, this paper proposes an optimization procedure based on dynamic simulations of the full flexible multibody system. <br />For this purpose, the nonlinear finite element approach is selected for the modelling and the simulation of the flexible multibody system. The present work is thus similar to the usual approach used in topology optimization in which the continuum domain is discretized into finite elements. The nonlinear finite element formalism accounts for both large rigid-body motions and elastic deflections of the structural components. The design variables are classically density-like parameters associated to a power law interpolation of effective material properties for intermediate densities, also known as Simply Isotropic Material with Penalization (SIMP). <br />The nonlinear equations of motion are solved using a generalized-alpha time integration scheme, and the sensitivity analysis of mechanical responses is based on a direct differentiation method. The efficient solution of the optimization problem relies on the sequential convex programming concept at the core of the CONLIN software. <br />In the present study, the method is applied to various types of mechanical systems. Firstly, planar mechanisms with truss structural components are considered. Each truss is represented by a structural universe of beams with a topology design variable attached to each one. Secondly, the discussion is extended to similar mechanisms with 3D motions. Finally, the topology optimization of spatial bodies represented by 3D finite element meshes is considered. [less ▲]

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See detailShape optimization of electromechanical microsystems for prescribed "capacitance-voltage" curve
Clément, Fabien; Rochus, Véronique ULg; Lemaire, Etienne ULg et al

in Proceedings of the 8th World Congress on Computational Mechanics (2008, July)

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