Vibration generated from various sources (engine, road surface, tires, exhaust, etc.) should be considered in the design of a car body. These vibrations travel through transfer systems (drivetrain, suspension, body, etc.) to the steering wheel, seats and other areas where it is detected by the passengers of the vehicle. Transmission routes must be studied and efforts made to keep transfer systems from amplifying vibration and to absorb it instead. Since the superior vibration transfer system is the car body, finite element analysis and experimental vibration analysis are performed on car body-in-white. Body vibration analysis entails understanding and improving the body&rsquo / s dynamic characteristics that act as vibration transfer channels. In the previous study, a finite element model has been created for a car body-in-white available in Automotive Laboratory (Mechanical Engineering Department, Middle East Technical University, Ankara) and its natural frequencies and mode shapes have been determined using finite element analysis software. In this study, vibration tests have been performed on actual car body-in-white. Frequency response functions between 34 response locations and force application point have been measured. Using these frequency response functions, natural frequencies and mode shapes of the body-in-white have been determined. Finite element analysis and experimental results have been compared to evaluate the finite element model reliability.

Vibration testing of structures constitutes a crucial step in design and commissioning of engineering structures. The focus here is on simulating field conditions in a laboratory so that detailed investigations of the structural behavior under various future load scenarios can be carried out. A major enabling technology in recent years in this field of study, especially, in the context of earthquake engineering, and automotive testing, has been the development of servo-hydraulic actuation systems, which form the principal component of test facilities, such as, multi-axes shake tables for testing building structures under earthquake loads, multi-post testrigs for testing vehicles subjected to road loads, and reaction-wall based test systems for simulating horizontal effects of earthquake loads on building structures. These systems have enabled the conduct of systematic studies on simulation of nonlinear structures under transient loads, simulation of multi-component and spatially varying random loads, and combining numerical and experimental methods with a view to avoid scaling while testing small scale critical components of large built-up structures. The investigations reported in this thesis are in this area of research and are primarily aimed at exploring the potential of servo-hydraulic test systems to address a few intricate issues related to performance assessment of engineering vibrating systems. A broad-based overview of goals of experimental approaches in vibration engineering, including dynamic system characterization and performance assessment, is presented in Chapter 1. Also discussed are the brief details of vibration testing methods developed in the context of earthquake engineering (including quasi-static test, effective force test, shake table test, combined effective force and shake table test, various versions of pseudo-dynamic test, and real-time substructuring) and automotive vehicle testing (including input excitation based methods and response based methods). The discussion notes the remarkable success witnessed in combining mathematical methods and experimental techniques especially in problems of characterization of dynamic system properties. Similar success, however, is observed to be not wide-spread in the context of development of test methods aimed at performance assessment of vibrating systems. The review culminates with the identification of the following three problems to be tackled in the present thesis: (a) development of efficient experimental procedures to estimate time varying reliability of structures under multi-component earthquake loads and similar analysis of vehicle structures under spatially varying random road loads; the focus here is on achieving sampling variance reduction in estimating the reliability; (b) development of experimental procedures to determine optimal cross-power spectral density models of partially specified multi-component random loads so as to produce the highest and lowest response variance in a specified response variable; the focus here is on seismic tests of asymmetric structures under partially specified multi-component earthquake loads, and on characterizing optimal correlations between two parallel tracks which maximize or minimize the vehicle response; and (c) development of a modified pseudo-dynamic test procedure, to incorporate additional components in numerical and experimental modeling in terms of an augmented linearized variational equation, so as to assess and contain propagation of numerical and experimental errors. The subsequent three chapters of the thesis tackle these questions and in doing so the thesis makes the following contributions: (A) Inspired by the Girsanov transformation based Monte Carlo simulation method for estimating time-variant component reliability of vibrating systems, an experimental test procedure, which incorporates the Girsanov transformation step into its folds, has been developed to estimate the time-variant system reliability of engineering systems. The two main ingredients of application of this strategy consists of determination of a control vector, which is artificially introduced to facilitate reduction in sampling variance, and the formulation of the Radon-Nikodym derivative, which serves as the correction to be introduced in order to compensate for the addition of the artificial control. (B) In problems of response analysis of structures subjected to random earthquake loads and vibration of vehicles running on rough roads, it may not be always feasible to completely specify the external actions on the structures. In such situations, it is of interest to determine the most favorable and the least favorable responses, along with the models for missing information in the inputs which produce the extreme responses. The present study, again inspired by existing analytical solutions to this problem, develops an experimental procedure to characterize the optimal excitation models and associated responses. (C) In the context of PsD testing of nonlinear structure to earthquake loads, a refinement in the test procedure involving the treatment of a linearized variational equation is proposed. This has led to the estimation of the evolution of global error norm as test proceeds with time. The estimates of error thus obtained have been used to decide upon altering the time step of integration.

As the industry is being reshaped concentrically around sustainability, the consumption of fossil fuels is targeted to decrease day by day. As a consequence of that, a righteous rise of electricity as energy source prevails in different branches of industry. It results for electric vehicle components to increase in size and weight which in fact were relatively smaller on conventional fossil fuel driven vehicles e.g. trucks. Every component weighing more than two kilograms is classified as a large component by Scania and these large electric components uncovers the need of evaluation of established testing methods in terms of their validity. This thesis project was carried out at Scania, Södertälje, and deals with the investigation on vibration testing methods that are currently used in different fields of engineering and identification of potentially applicable ones at Scania in testing large components. A case study on the stiffness of an individual component is performed to assess its impact on alteration of eigenfrequencies. Few case studies based on empirical tests as well as finite element method simulations on certain large components, i.e. high voltage junction box and battery packs, are performed with respect to their vibration behaviours while undergoing Scania’s established vibration testing spectra. Investigation into the vibration behaviour on dependence on measurement locations were performed. Additionally, rudimentary case studies are conducted on thermal loads during vibration testing, thermal dwell time, and required energy to oscillate large components at certain levels. How thermal features of the component are affected due to its size is noted. / Den senaste tekniska paradigmen inom fordonsindustrin är fokus på minskning av beroende på fossila bränslen, högre energisnålhet och en ökad hållbarhet och effektivitet i produktionsprocessens alla delar. Detta och de stora genombrotten i batteritekniken hade som påföljd att utvecklingen av fordon riktades mot elektrifiering av alla fordon. Elmotorer har sedan tidigare funnit sin tillämpning på mindre maskiner i inomhusmiljöer som t.ex. palldragare och lasttruckar. För tyngre applikationer som t.ex. personbilar och lastbilar ställs det helt nya krav på komponenternas storlek och prestanda, vilket leder till de elektriska komponenternas högre vikt. Scania, som vill vara ledande inom denna omställning, klassificerar alla komponenter med större vikt än 2 kg som stora komponenter. De stora elektriska komponenterna skapar ett behov att utvärdera de aktuella testmetoderna och verifiera deras validitet. Det här magisterexamensarbetet har genomförts på Scania i Södertälje och handlar om undersökning av vibrationstestningsmetoderna som nuförtiden används i olika teknikområden samt identifiering av de eventuellt applicerbara metoderna för provning av stora elektriska komponenter. En fallstudie genomfördes gällande en individuell komponent och påverkan på dess egenfrekvenser med varierande styvhetskonstanter. Dessutom genomfördes några andra fallstudier utgående från empiriska tester samt simuleringar med hjälp av finita elementmetoden på vissa stora komponenter såsom högspänningsförgreningsdosa och batteripacken. Vibrationsprov genomfördes genom att utsätta komponenterna för Scanias nuvarande vibrationstestningsspektrum. Även vibrationsbeteendet beroende på positionen av mättningspunkterna har undersökts. Utöver det utfördes fallstudier angående termiska belastningar under vibrationstestning, tid för värmeöverföring samt energibehovet för att oscillera stora komponenter på förbestämda accelerationsnivåer. Inverkan av komponenternas storlek på deras värmeöverföringsegenskaper noterades.

Existing methods of evaluating the structural system of a building after a seismic event consist of removing architectural elements such as drywall, cladding, insulation, and fireproofing. This method is destructive and costly in terms of downtime and repairs. This research focuses on removing the guesswork by using forced vibration testing (FVT) to experimentally determine the health of a building. The experimental structure is a one-story, steel, bridge-like structure with removable braces. An engaged brace represents a nominal and undamaged condition; a dis-engaged brace represents a brace that has ruptured thus changing the stiffness of the building. By testing a variety of brace configurations, a set of experimental data is collected that represents potential damage to the building after an earthquake. Additionally, several unknown parameters of the building’s substructure, lateral-force-resisting-system, and roof diaphragm are determined through FVT. A suite of computer models with different levels of damage are then developed. A quantitative analysis procedure compares experimental results to the computer models. Models that show high levels of correlation to experimental brace configurations identify the extent of damage in the experimental structure. No testing or instrumentation of the building is necessary before an earthquake to identify if, and where, damage has occurred.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / This work presents contributions to the sinusoidal acceleration control of electrodynamic shakers applied in vibration testing. Considering the importance of sine tests to identify critical frequencies of operation and to determine mechanical weakness in the specified performance of specimens, vibration controllers are designed to reproduce the amplitude and the frequency of the reference acceleration specifically at the interface between the shaker and the structure under test. Two distinct approaches are considered to solve the control problem: time domain control, where the acceleration instantaneous value is adjusted to track the sinusoidal reference, and frequency domain control, in which only the amplitude or the root mean square value of the acceleration is compensated to follow the reference magnitude. The solutions developed based on these two different approaches are implemented in a digital control platform and experimentally evaluated. The development of vibration controllers is complemented by contributions to the study of the shaker dynamic model, as well as to the instrumentation applied to measure and feedback the acceleration and to the voltage control of switching-mode power amplifiers designed to drive the shaker. Regarding the vibration machine dynamic model, a method is proposed to experimentally identify the mechanical parameters of a two degrees of freedom system that represents the suspension resonance and the finite armature stiffness of the electrodynamic shaker. A procedure is developed to design and implement charge mode preamplifiers and signal conditioning circuits for piezoelectric accelerometers. A robust model reference adaptive algorithm is applied to control the output voltage of an industrial switching-mode power amplifier. The experimental analysis of the adaptive controller considers not only the improvements on the power amplifier performance, but also the of impact over the behavior of a commercial digital vibration control system. / Este trabalho apresenta contribuições ao controle de aceleração senoidal de vibradores eletrodinâmicos utilizados em ensaios de vibração. Considerando a importância de testes com aceleração senoidal para identificar freqüências críticas de operação e determinar a resistência de materiais e estruturas, são desenvolvidos controladores para a máquina de vibração com o propósito de garantir que a amplitude e a freqüência da aceleração imposta à estrutura sob teste correspondam aos valores de referência. Na solução do problema, admitem-se duas abordagens distintas: controle no domínio do tempo, onde o valor instantâneo da aceleração é ajustado para seguir a referência senoidal, e controle no domínio da freqüência, no qual apenas a amplitude ou o valor eficaz da aceleração é regulado conforme a magnitude de referência. As técnicas propostas com base nestas abordagens são implementadas numa plataforma de controle digital e avaliadas experimentalmente. O desenvolvimento dos controladores de vibrações é complementado por contribuições ao estudo do modelo dinâmico do vibrador, à instrumentação aplicada para realimentar a aceleração e ao controle da tensão de amplificadores de potência que utilizam inversores com modulação por largura de pulso para acionar a máquina. Com relação ao modelo do vibrador, é descrito um método que permite determinar experimentalmente os parâmetros mecânicos de um modelo com dois graus de liberdade, o qual representa o comportamento da máquina devido à suspensão e à rigidez finita da armadura. Um procedimento de projeto e realização prática de pré-amplificadores de carga e de um circuito de condicionamento para acelerômetros piezoelétricos é apresentado. Um algoritmo adaptativo robusto por modelo de referência é avaliado no controle da tensão de saída de um amplificador industrial projetado para excitar o enrolamento da armadura do vibrador. A análise experimental do impacto do controlador adaptativo é realizada considerando não apenas a melhoria no desempenho do amplificador, mas também em termos dos reflexos na performance de uma plataforma comercial de controle de ensaios de vibrações.

Master's thesis deals with implementation of a control system for an electrodynamic exciter. Patent and literature research with focus on applicable control methods is performed. Then, description of the methods applicable in the system identification, as well as types of the signals used in the vibration testing are discussed. The practical section is dedicated to the analysis of available hardware resources, design, assembly and verification of a control system for an electrodynamic exciter equipped with piezoelectric accelerometer and components of National Instruments.

Space industry has been booming in the recent times, investments have not justbeen made on satellites and launch vehicles but also on space sustainability. Spaceindustry has its users in national agencies, private commercial agencies, academia andexperimental organisations. Smallsats and cubesats are one of the most interestingdomains in space industry today. This has led to pure research and astonishinginnovations in this domain to enable lower costs, lower mass, increased orbital period,better accessibility and global impact. Development of sustainable products requiresthe system to qualify a certain standard set up in the industry. This standard ensuresthat the system safely completes its mission up in space. The problem described byGomSpace Sweden concerns one of their ongoing products, a cold gas propulsionunit which is suitable for a typical 6U cubesat called ESA6DOF. In large, the productconsists of a structure, two propellant tanks, one plenum tank, piping, electronics andsix thrusters. Qualification of this propulsion system module involves the system toundergo a random vibration test according to ECSS standards. This thesis work shallbe focused on setting up the structure needed to perform random vibration simulationsin COMSOL. This step is done to primarily iterate the design to make it robust enoughto sustain loads during flight and also to avoid any physical damages during testingcampaign. Followed by performing the actual random vibration test at a facility usingthe assembled ESA6DOF propulsion module. Finally, this ends with validating thesimulation results with that of testing. / Rymdindustrin har blomstrat den senaste tiden. Investeringar har inte bara gjortspå satelliter och bärraketer utan också på hållbarhet i rymden. Rymdindustrinhar sina användare i nationella organisationer, privata kommersiella organisationer,universitetsvärlden och forsknings organisationer. Smallsats och cubesats är tvåav de mest intressanta domänerna inom rymdindustrin idag. Detta har letttill grundforskning och häpnadsväckande innovationer inom detta område för attmöjliggöra lägre kostnader, lägre massa, ökad omloppstid, bättre tillgänglighetoch global påverkan. Utveckling av hållbara produkter kräver att systemet möteren viss standard uppsatt i branschen. Denna standard säkerställer att systemetsäkert slutför sitt uppdrag uppe i rymden. Problemet som beskrivs av GomSpaceSweden gäller en av deras pågående produkter, en kallgasdrivenhet lämplig för entypisk 6U cubesat kallad ESA6DOF. I stort består produkten av en struktur, tvådrivmedelstankar, en plenumtank, rörledningar, elektronik och sex finjusterarraketer.Kvalificeringen av denna framdrivningssystemmodul innebär att systemet genomgåren slumpmässig vibration enligt ECSS-standarder. Detta examensarbete harfokuserat på att sätta upp den struktur som behövs för att utföra slumpmässigavibrationssimuleringar i COMSOL. Detta steg gjordes för att i första hand itereradesignen för att göra den robust nog att tåla belastningar under flygning och ävenför att undvika fysiska skador under testkampanjen. Efter detta utfördes det faktiskaslumpmässiga vibrationstestet på en anläggning med den sammansatta ESA6DOF-framdrivningsmodulen. Avslutningsvis utfördes validering av simuleringsresultatenmot testresultaten.

The purpose of this study was to examine the effect of bottom chord extensions on deflections and vibration characteristics of joist supported floor systems when joist bottom chord extensions are installed. To understand the effect of bottom chord extensions on deflections, natural frequency, damping, mode shape and effective mass, extensive analytical and experimental studies were conducted on single span and three span joist supported laboratory footbridges with different bottom chord extension configurations. Finite element computer models were created to simulate and compare the results of stiffness and vibration tests. Testing was done with a) the bottom chord extensions in-place before the concrete was placed, b) with all or part of the bottom chord extensions removed, and c) after the bottom chord extensions had been reinstalled with jacking for the single span footbridge and without jacking for the three-span footbridge. Results from the stiffness tests indicate that re-installing the bottom chord extensions to the joists of the single span footbridge with cured concrete with the center of the span raised helps to reduce the uniform load deflections to some extent, but not as much as placing the bottom chord extensions before the concrete placement. Likewise, for the three span footbridge, placing the bottom chord extensions before the concrete placement is observed to be a better solution. Results from the dynamic tests indicate that the effect of bottom chord extensions on the single span footbridge is consistent for natural frequency, 20 psf live load deflections, sinusoidal excitations with high amplitudes, quarter point heel drop excitations, walking excitations, and effective mass values. The effect of bottom chord extensions on the three span footbridge is consistent for the natural frequency and 20 psf deflections. However, the FRF (Frequency Response Function) peaks of chirp, heel drop, sinusoidal excitations, accelerations from walking data, and the MEScope and Finite Element model effective mass results do not follow a common trend. It can be concluded that even though the footbridge was stiffened by the bottom chord extensions, that does not necessarily mean that the acceleration levels, and hence the frequency response function peaks, decrease. However, bottom chord extensions do increase the natural frequencies for all the three governing bending modes. / Ph. D.

Monte Carlo simulation techniques have emerged as widely accepted computing tools in tackling many problems in modern structural mechanics. Apart from developments in computational hardware, which have undoubtedly made simulation strategies practically feasible, the success of Monte Carlo simulations has also resulted equally significantly from the methodological developments aimed at controlling sampling variance of the Monte Carlo estimates. The study reported in the present thesis is aimed at developing and validating Monte Carlo simulation based approaches with inbuilt variance reduction capabilities to deal with problems of time variant reliability modeling, random vibration testing, and updating reliability models for statically/dynamically loaded instrumented structures. The relevant literature has been reviewed in Chapter 1. Time variant reliability analysis of randomly parametered and randomly driven non-linear vibrating systems has been tackled by combining two Monte Carlo variance reduction strategies into a single framework (Chapter 2). The first of these strategies is based on the application of the Girsanov transformation to account for the randomness in dynamic excitations and, the second approach is fashioned after the subset simulation method to deal with randomness in system parameters. A novel experimental test procedure to estimate the reliability of structural dynamical systems under excitations specified via random process models has been proposed (Chapter 3). The samples of random excitations to be used in the test are modified by the addition of an artificial control force. An unbiased estimator for the reliability is derived based on measured ensemble of responses under these modified inputs based on the tenets of Girsanov’s transformation. The study observes that an acceptable choice for the control force (that can reduce the sampling variance of the estimator) can be made solely based on experimental techniques. This permits the proposed procedure to be applied in the experimental study of time variant reliability of complex structural systems which are difficult to model mathematically. Illustrative example consists of a multi-axes shake table study on bending-torsion coupled, geometrically non-linear, five-storey frame under uni/bi-axial, non-stationary, random base excitation. The first order reliability method (FORM) and inverse FORM have been extended to handle the problem of updating reliability models for existing, statically loaded structures based on measured responses (Chapter 4). The proposed procedures are implemented by combining Matlab based reliability modules with finite element models residing on the Abaqus software. Numerical illustrations on linear and non-linear frames are presented. A solution strategy within the framework of Monte Carlo simulation based dynamic state estimation method and Girsanov’s transformation for variance reduction has been developed to tackle the problem of updating the reliability of instrumented structures based on measured response under random dynamic loading (Chapter 5). For linear Gaussian state space models, the solution is developed based on continuous version of the Kalman filter, while, for non-linear and (or) non-Gaussian state space models, bootstrap particle filters are adopted. Results from laboratory testing of an archetypal five storey bending-torsion coupled frame under seismic base motions form the basis of one of the illustrative examples. A set of three annexures contain details of numerical methods for discretizing Ito’s differential equations (Annexure 1), working of the Girsanov transformation through Kolmogorov’s equations (Annexure 2) and tools for interfacing Matlab and Abaqus codes (Annexure 3).

<p>    </p> <p>Additive manufacturing (or 3D printing) is one of the manufacturing processes which is currently being explored for its applicability under space boundary conditions, also known as in-space manufacturing. The space boundary conditions specifically affect material properties which in turn affect the printability of materials in space. Printing of soft materials in space is a novel application and the intent of this research was to print the softest of materials: edible materials, as a case study. 3D food printing is a novel food delivery method of using food products to either reproduce as a more aesthetically pleasing product or to print more nutrient-diverse foods. Launch of payload carrier and the boundary conditions of low Earth orbit including a vacuum environment, microgravity, temperature fluctuations, etc. These conditions make printing difficult, and my thesis is to overcome the boundary conditions (except microgravity) using a 3D soft material printer operating within a CubeSat. A CubeSat is a small satellite usually launched as an auxiliary payload used for basic Earth observation and radio communication. The printer must be able to survive launch and operation conditions, print within a simulated space environment, and adhere to the American Society for Testing and Materials (ASTM) specific definition of additive manufacturing. The 3D soft material printer was designed, fabricated, and tested using space and CubeSat boundary conditions for determining optimal design. Testing conditions including: (1) printing under Earth conditions showing it follows ASTM standards, (2) surviving NASA standards for vibration testing for microsatellites under launch conditions, (3) completing a print under a vacuum setting. The results of the testing would prove a small microsatellite could print in the vacuum of space and survive launch parameters. Further work would provide insight into the design of food printers being readily available in smaller sizes and its operability in microgravity condition. </p>