Experimental Dynamic Substructuring Analysis and Design Strategies for Vehicle Development Maarten van der Seijs Experimental Dynamic Substructuring Analysis and Design Strategies for Vehicle Development PROEFSCHRIFT ter verkrijging van de graad van doctor aan de Technische Universiteit Delft, op gezag van de Rector Magnificus prof. ir. K. C. A. M. Luyben, voorzitter van het College voor Promoties, in het openbaar te verdedigen op donderdag 16 juni 2016 om 12:30 uur door Maarten Vincent VAN DER SEIJS werktuigkundig ingenieur geboren te Heiloo, Nederland. Dit proefschrift is goedgekeurd door de promotor: Prof. dr. ir. D. J. Rixen copromotor: Dr. ir. D. de Klerk Samenstelling promotiecommissie: Rector Magnificus voorzitter Prof. dr. ir. D. J. Rixen Technische Universiteit Delft / TU München, promotor Dr. ir. D. de Klerk Technische Universiteit Delft, copromotor Onafhankelijke leden: Prof. dr. P. Avitabile University of Massachusetts Lowell Prof. dr. A. T. Moorhouse University of Salford Prof. dr. ir. N. B. Roozen Katholieke Universiteit Leuven Prof. dr. ir. J. W. Verheij Voormalig hoogleraar Technische Universiteit Eindhoven Prof. dr. ir. E. G. M. Holweg Technische Universiteit Delft Prof. dr. ir. J. L. Herder Technische Universiteit Delft, reservelid Copyright © 2016 by Maarten van der Seijs – All rights reserved – No part of the material protected by this copyright notice may be reproduced or utilised in any other form or by any other means, electronic or mechan- ical, including photocopying, recording or by any information storage and retrieval system, without the prior permission of the author. ISBN 978-94-6186-671-4 An electronic version of this dissertation is available at http://repository.tudelft.nl/. Printed by: Gildeprint, Enschede Cover art by: Thijs ten Brummelhuis Author email: [email protected] Abstract Experimental Dynamic Substructuring – Analysis and Design Strategies for Vehicle Development – Sound and vibration have a defining influence on our perception of product quality. They are especially well-known aspects in the automotive industry; a branch which sees, be- sides safety and driving comfort, ever-increasing expectations of the acoustic experience. After all, a smooth and silent driving experience appeals to a feeling of premiumness, a connotation no longer reserved to the top segment in the industry. While traditional com- bustion engines are gradually getting replaced by hybrid or full-electric drive-lines, other electromechanical (so-called mechatronic) systems make their entrance. As a consequence, the sound experience shifts from low-frequent engine roar to high-frequent humming and whining — a yet unfamiliar experience that calls for redefinition of the soundscape. To sup- port such change, it is necessary that sound and vibration aspects can be considered in an early phase of development by means of simulations. This poses a true challenge: although state-of-art numerical modelling techniques can simulate the low-frequent dynamics fairly well, they often fail to provide reliable answers for the higher acoustic frequency range. This thesis presents techniques that aim to implement measurements of structural dyna- mics and active vibration sources into development processes. By characterising the pass- ive and active dynamics of yet available components by means of measurements and com- bining those with numerical models, a hybrid simulation emerges that may provide an- swers to high-frequent problems in an early phase of development. This hybrid simulation is facilitated by use of Experimental Dynamic Substructuring: a methodology that determ- ines structural dynamic aspects of complete products based on individually measured com- ponents. Part one of this thesis presents a variety of methods for simulation and substructuring that form the basic toolbox for generation, analysis, coupling and decoupling of dynamic mod- els. Pivotal is the experimental approach, which means that dynamic models are obtained from measurements rather than numerical modelling efforts. To transform such measure- ments into a model that is compatible for coupling with other (numerical) models, the vir- tual point transformation is proposed. This method considers measured responses and ap- plied forces around (user-chosen) points as locally rigid displacements and forces. Doing so, every connection point of a component can be described by three translations and three rotations with respect to a global reference frame, perfectly suited for substructuring. At the same time, the quality of the measurement and transformed frequency response func- tions can be quantified objectively using the proposed consistency functions. Altogether, the virtual point method bridges the gap between experimental and numerical modelling activities and enables us to exploit substructuring effectively for complex high-frequency systems. Part two presents a comprehensive study of Transfer Path Analysis (TPA); a collection of methods that contemplate a vibration problem as a source, transmission and receiver. A general framework for TPA is presented by re-interpreting eleven methods from the per- spective of substructuring. It is shown that these methods can be categorised into three iii families, that in turn differ in the nature of characterisation of the source. The component- based TPA is regarded the most promising family, which allows to characterise a source independent of the environment in which it has been measured. The vibrations of the act- ive source can be replaced by equivalent force spectra that, multiplied with the (simulated) FRFs of the assembled vehicle, predict what this source would sound like in the vehicle. Several practical methods are discussed to determine such equivalent forces: from forces measured against a blocked boundary, using free velocities, based on measurements on a compliant test bench or using the so-called in-situ and pseudo-forces methods. For further generalisation, a notation is presented that governs the abovementioned principles and fa- cilitates the application and comparison of component-based TPA methods. In particular, it is shown that controllability and observability — concepts adopted from control theory — are strongly related to TPA; proper understanding of these principles yields interesting opportunities for analysis and simulation. The developed methods have been applied to analyse the vibrations of the electric power- assisted steering (EPS) system, which is reported on in part three. It is demonstrated that the virtual point transformation is able to determine accurate FRFs in a frequency range up to 6000 Hertz. Substructuring is applied to simulate the FRFs of a vehicle by applying the principle of substitute coupling, which employs a substitute beam during measurement in the vehicle to represent the dynamic effects of the steering system to couple. For the pur- pose of characterisation of the steering system’s excitations, several testing environments are discussed: a stiff test bench, more compliant test benches and the vehicle itself. Each configuration is accompanied by a specific method for source characterisation, for which it is demonstrated that the equivalent forces are indeed an environment-independent de- scription of the active excitations of the steering system. It is shown that these forces can be used for the prediction of sound and vibrations in the vehicle. The presented applica- tions offer, with understanding of substructuring and TPA theory, insights in the practical aspects of the methodology. This opens interesting opportunities for early-phase develop- ment of sound and vibration. iv Samenvatting Experimentele Dynamische Substructurering – Strategieën voor Analyse en Ontwerp in Voertuigontwikkeling – Trillingen en geluid hebben een bepalende invloed op onze perceptie van productkwaliteit. Het zijn met name bekende aspecten in de automobielindustrie; een markt waarin, naast veiligheid en rijcomfort, ook steeds hogere eisen worden gesteld aan de akoestische erva- ring. Immers, een geruisloze rijervaring appelleert aan een gevoel van premiumness, iets dat niet meer alleen is weggelegd voor het topsegment van de industrie. Terwijl de tradi- tionele verbrandingsmotor gaandeweg plaats maakt voor hybride of volledig elektrische aandrijflijnen, doen andere elektrisch-mechanische (zogeheten mechatronische) systemen hun intrede. Hiermee verschuift de geluidservaring van laagfrequent motorgebrom naar hoogfrequent zoemen en fluiten — een nu nog onbekende ervaring die vraagt om herde- finitie van het klankprofiel. Om zulke veranderingen te ondersteunen is het noodzakelijk dat trillingen en geluid in een vroege fase van ontwikkeling kunnen worden beschouwd door middel van simulaties. Hierin schuilt een grote uitdaging: hoewel de hedendaagse numerieke modellerings¬technieken goed in staat zijn om het laagfrequente dynamische gedrag te simuleren, bieden zij voor het hogere akoestische frequentiebereik nog geen be- trouwbaar antwoord. Dit proefschrift presenteert technieken die erop gericht zijn om metingen aan structuurdy- namica en actieve trillingsbronnen te implementeren in ontwerpprocessen. Door de passie- ve en actieve eigenschappen van reeds beschikbare onderdelen door middel van metingen te karakteriseren en deze te combineren met numerieke modellen, ontstaat een hybride simulatie die in een vroege fase van ontwikkeling antwoorden kan bieden voor hoogfre- quente dynamische problemen. Deze hybride simulatie is mogelijk door gebruik te maken van Experimentele Dynamische