Computer-Aided Engineering Methodologies for Robust Automotive NVH Design (Simulatiemethoden voor robuust vibro-akoestisch ontwerp van voertuigen)

Dit proefschrift bespreekt het gebruik van numerieke methoden ( Computer-Aided Engineering - CAE) voor het simuleren en voorspellen van het trillingsgedrag en de akoestiek van voertuigen, meer bepaald in de automobielindustrie. De Eindige Elementen Methode (EEM) is een veelgebruikt hulpmiddel bij numerieke ontwerpvalidatie in het laagfrequente gebied. Voor nauwkeurige voorspellingen bij hogere frequenties moeten de eindige elementen verder verfijnd worden, hetgeen teveel rekenkracht vergt. Bovendien wordt het effect van onzekerheden en variabiliteiten op het voertuiggedrag groter met toenemende frequentie. Om deze effecten te voorspellen, dienen vele varianten van het nominale voertuig te worden berekend. Tenslotte is er in de industrie behoefte aan simulatieresultaten reeds in de vroege conceptfase van het ontwerpproces, reeds voordat het eerste CAD-ontwerp wordt gemaakt. Traditionele Eindige Elementen-modellen kunnen juist pas worden vervaardigd op basis van dit eerste CAD-ontwerp.De bovengenoemde uitdagingen vormen het kader van het onderzoek in dit proefschrift. Zo werd het effect van onzekerheden op frequentieresponsievoorspellingen onderzocht, hetgeen leidde tot een nieuwe efficiënte methode ( Short Transformation Method - STM) voor de klasse van structuren met monotone invloed van parameteronzekerheden. Ook werd gekeken naar het effect van ontbrekende laspunten op het dynamisch systeemgedrag. Het streven naar efficiëntere variantenberekeningen leidde tot een nieuwe koppelingsmethode van substructuren ( Wave-Based Substructuring - WBS). Met een golfgebaseerde koppeling verkrijgt men een kleinere beschrijving van de koppeling; dit maakt het mogelijk om de substructuren efficiënt te reduceren tot een modaal model. Het kleinere systeemmodel dient dan als basis voor lokale variantenberekeningen. Tenslotte werd een nieuwe CAE-methode toegepast in de vroege conceptfase van de ontwikkeling van de carrosserie. Deze methode maakt het mogelijk om balkstructuren en balkverbindingen compact te beschrijven en modificaties hiervan efficiënt door te rekenen. Het nut van de bijdragen in deze dissertatie in het voertuig ontwerpproces is aangetoond d.m.v. toepassingen op realistische modellen uit de voertuigindustrie.status: publishe

Robust design and optimization in vibro-acoustic engineering

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Advanced Vehicle Body Concept Modeling Approach Using Reduced Models of Beams and Joints

The paper presents a vehicle body concept modeling methodology based on reduced models of beams, joints and panels. The aim of the approach is to enable accurate Noise, Vibration and Harshness (NVH) simulations of the vehicle Body in White (BIW) already in the initial phases of the vehicle design process, when the detailed geometry information has not yet become available. In the presented approach, concept models of beams and joints are created, respectively, by means of a geometric analysis of beam-member cross-sections and a static analysis of joints FE models that results in an efficient matrix formulation. Concept panels are modeled by coarsening the original FE mesh. Improvements to the approach are proposed through the introduction of a new connection element, so-called “RBE2.5”, which permits to refine the modeling of shell-based beam and joint ends, leading to more accurate joint matrix formulation. Furthermore, a new optimization process has been worked out, which allows taking into account the discontinuities of the original beam-like structure sections.. The proposed approach has been validated by using an industrial case study, for which the beam, joint and panel concept methodology has been used in combination with a substructuring technique to create an efficient and accurate vehicle BIW model. More specifically, simplified models of beams, joints and panels of the upper region of the vehicle BIW are created, while the bottom part has been reduced by means of MacNeal‟s Method.status: publishe

A reliability analysis approach to improve the fatigue life of a vehicle knuckle

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NVH optimization methodologies based on bead modification analysis in vehicle body design

Poster - ISMA 2010 Poster Session, 20 Sept. 2010 ; ID PAPER = 522status: publishe

Subcomponent modelling of input parameters for Statistical Energy Analysis by using a Wave Based Boundary Condition

This paper presents a new and efficient method to calculate point mobilities from subcomponents of a full structure. Subcomponent modelling is a commonly used method to gain information on the dynamic behaviour of complex assembly structures using smaller and more efficient models. For instance, point mobility calculations on subcomponent level are used to obtain more accurate input parameters for statistical energy analysis (SEA) models. A full system analysis is often too computationally expensive, so normally only individual subcomponents of the structure are extracted and analysed. This procedure yields a large reduction in computational effort, but also often results in a substantial loss of accuracy. This is due to the use of an approximation of boundary conditions to represent the eliminated remainder part of the structure, i.e. the full structure except the subcomponent at hand. Commonly, these boundary conditions are simplified by assuming clamped, free or simply supported edges. However, this is a huge simplification and may introduce large errors, especially in the low- and mid-frequency ranges. Earlier work has shown that a more accurate description of the boundary conditions can be achieved by describing the interface dynamics by a combination of so-called dynamic waves. In this paper, the method is developed further and a more robust and efficient wave extraction procedure is presented. An industrial body in white BIW is used as a test case and results are presented for three different cases. The results show that the wave-based boundary condition for point impedance calculations from a subcomponent model gives more accurate results than the results obtained with free or clamped boundary conditions.status: publishe

NVH optimization methodologies based on bead modification analysis in vehicle body design

In the automotive industry, Computer-Aided Engineering (CAE) methods are increasingly used to predict the various functional performance attributes (noise and vibration, crashworthiness, etc.) and to adapt the design based on the outcome of virtual simulations, such as numerical Finite Element (FE) models. The framework presented in this work is aimed at testing and validating methodologies for NVH optimizations, based on structural modifications that affect the global structural dynamic behaviour in order to reduce the structure born noise radiated in vehicle cavities. From the full FE model of a vehicle, mainly consisting out of thin-walled panels (modelled by shell elements), first a critical component is identified which is then subjected to structural modifications. Bead patterns are created by merely acting on the FE mesh nodal positions according to Mesh Morphing. The combination between Wave-Based Substructuring (WBS) and an Acoustic Transfer Vector (ATV) approach allows fast and accurate NVH predictions, enabling efficient modification approaches and optimizations. The proposed procedure is applied on a case study FE model resembling a simplified vehicle from which the spare wheel panel is selected as critical component. A WBS-reduced representation is achieved, where the panel is still in FE representation enabling modifications on it, while the remainder is reduced. The main innovation introduced in this framework comprises the optimization of the vehicle interior vibro-acoustics by making use of a structural optimization software - running purely structural analyses - in combination with an acoustic analysis tool for calculating the ATVs. Two different methodologies have been worked out, based on two strategies for bead pattern optimization. Finally, the optimized components are evaluated in terms of interior Sound Pressure Level (SPL) and manufacturability.8th EC RTN "Smart Strcutures" Workshop. Institute of Sound and Vibration Research (ISVR). Nov 25-26, 2010. Southampton (UK)status: publishe

Strategies of fuzzy uncertaintly modelling applied on a static analysis of a car-body

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Structural reliability analysis of a car front cradle with multiple design criteria

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On the use of a novel wave based boundary condition for efficient subcomponent point impedance calculations

Subcomponent modelling is a commonly used method to gain information on the dynamic behaviour of complex assembly structures using smaller and more efficient models. For instance point mobility calculations on subcomponent level are used to obtain more accurate input parameters for Statistical Energy Analysis (SEA) models. A full system analysis is often too computationally expensive, so normally only individual subcomponents of the structure are extracted and analysed. This procedure yields a large reduction in computational effort, but also often results in a substantial loss of accuracy. This is due to the use of an approximation of (virtual) boundary conditions to represent the eliminated remainder part of the structure, i.e. the full structure except the subcomponent at hand. Commonly, these boundary conditions are simplified by assuming clamped, free or simply supported edges. However, this is a huge simplification and may introduce large errors. Earlier work has shown that a more accurate description of the boundary conditions can be achieved by using a combination of so-called dynamic waves. In this paper, the method is developed further and a more efficient wave extraction procedure is presented.status: publishe