Ces travaux de thèse portent sur l’étude expérimentale et numérique des réponses vibratoires non linéaires des structures mécaniques. Les études expérimentales menées au CEA/CESTA montrent que la réponse des structures assemblées à des sollicitations vibratoires est souvent très fortement dépendante du niveau d’excitation. Ces résultats expérimentaux ne peuvent pas être reproduits en simulation avec la méthode de simulation vibratoire linéaire classique. L’objectif de ces travaux est de proposer et de mettre en place des méthodes expérimentales et numériques pour étudier ces réponses non-linéaires. Cet objectif passe par l’étude de maquettes d’essai sujettes aux mêmes phénomènes vibratoires non-linéaire que les objets d’étude industriels du CEA/CESTA. Au niveau expérimental, les développements se basent sur les installations et logiciels industriels. Au niveau simulation, les méthodes de simulation vibratoire non-linéaires et les techniques numériques avancées développées depuis de nombreuses années dans le monde académique sont utilisées dans le contexte industriel du CEA/CESTA. Le premier objet d’étude est une poutre métallique bi-encastrée. Cette structure présente une réponse vibratoire non-linéaire d’origine géométrique. La structure est modélisée avec des conditions aux limites non-idéales et sa réponse vibratoire est simulée par trois méthodes (développement multi- échelles, méthode de balance harmonique et méthode de tir). Ces résultats de simulation sont comparés entre eux et avec l’expérience. La maquette d’étude au cœur de ces travaux de thèse est un assemblage présentant des interfaces frottantes : la maquette ✭✭Harmonie ✮✮. De nombreux essais vibratoires sont réalisés sur cette maquette afin d’identifier ses modes de résonance et ceux de ses composants, d’étudier l’évolution de la réponse vibratoire de l’assemblage due au frottement et enfin de mesurer le mouvement vibratoire local dans la zone de frottement. Un modèle numérique de cette structure est ensuite réalisé. Ce modèle est réduit par une méthode de sous-structuration puis des relations non-linéaires de frottement sont introduites au niveau des liaisons frottantes. La réponse vibratoire non-linéaire du modèle obtenu est simulée grâce à la méthode de balance harmonique couplée à des algorithmes de condensation et de continuation. Des comparaisons essai-calcul sont présentées pour les réponses globales et pour les mouvements locaux des liaisons. / This PhD work deals with the experimental and numerical study of mechanical structures’ nonlinear vibration response. Experimental studies led at the CEA/CESTA show that jointed structures vibration responses are often strongly dependent on the excitation level. These experimental results cannot be simulated using the classical linear vibration simulation method. This work aims at proposing and implementing experimental and numerical methods to study nonlinear responses. This objective involves the study of test structures subject to the same non-linear vibratory phenomena as CEA/CESTA industrial structures. Experimentally, developments are based on industrial facilities and softwares. Numerically, nonlinear vibration simulation methods and advanced numerical techniques that have been developed for many years in academia are applied in the CEA/CESTA industrial context. The first test structure is a clamped-clamped steel beam. This structure has a geometric nonlinear behavior. The structure is modeled with non-ideal boundary conditions and its frequency response is simulated using three different simulation methods (method of multiple scales, the harmonic balance method and a shooting method). These simulation results are compared one with each other and with experimental results. The test structure at the heart of this work is an assembly with friction joints named “Harmony”. Many vibration tests are carried out to identify its resonance modes and those of its components, to study the evolution of the vibration response due to friction and finally to measure the local vibrational movement in the friction zone. A numerical model is then developed. This model is reduced using a substructuring method and then in the friction zone, linear joints are replaced by nonlinear friction models. The nonlinear vibration response of this reduced model is simulated using the harmonic balance method coupled with condensation and continuation algorithms. Test-simulation comparisons are presented both for global responses and for local joints movements.

Master of Science / Department of Civil Engineering / Hani G. Melhem / This study reports the results of an analytical, experimental and a numerical study (proof of concept study) on a proposed method for extracting the pseudo-free-vibration response of a structure using ambient vibration, usually of a random nature, as a source of excitation to detect any change in the dynamic properties of a structure that may be caused by damage. The structural response contains not only a random component but also a component reflecting the dynamic properties of the structure, comparable to the free vibration for a given initial condition. Structural response to the arbitrary excitation is recorded by one or several accelerometers with a desired data-collection frequency and resolution. The free-vibration response of the structure is then extracted from this data by removing the random component of the response by the method proposed in this study. The features of the free-vibration response of the structure extracted by a suitable method, namely Fast Fourier Transform (FFT) in this study, can be used for change detection. Possible change of the pattern of these features is dominantly linked to the change in dynamic properties of the system, caused by possible damage. To show the applicability of the concept, besides an analytical verification using Newmark’s linear acceleration method, two steel portal frames with different flexural stiffness were made in the steel workshop of the structural laboratory for an experimental study. These structures were also numerically modeled using a finite element software. A wireless accelerometer with a sampling frequency rate of 2046 Hz was affixed on the top of the physical structure, at the same location where the acceleration was recorded for the corresponding numerical model. The physical structure was excited manually by an arbitrary hit and the response of the structure to this excitation, in terms of the acceleration on the top of the structure, was recorded. The pseudo-free-vibration response was extracted and transferred into frequency domain using FFT. The frequency with the largest magnitude which is the fundamental frequency of the structure was traced. This was repeated for several independent excitations and the fundamental frequencies were observed to be the same, showing that the process can correctly identify the natural frequencies of the structure. Similarly, the numerical model was excited and for several base excitation cases, the fundamental frequencies were found to be the same. Considering the acceptable accuracy of the results from the two numerical models in simulating the response of their corresponding physical models, additional numerical models were analyzed to show the consistency and applicability of the proposed method for a range of flexural stiffness and damping ratio. The results confirm that the proposed method can precisely extract the pseudo-free-vibration response of the structures and detect the structural frequencies regardless of the excitation. The fundamental frequency is tied to the stiffness and a larger stiffness leads to a higher frequency, as expected, regardless of the simulated ambient excitation.

Content of this work is oriented on mechanical testing of PWB. Deals with standards related to mechanical testing and quality evaluation of PWB. This works is engaged into industry standards, for example IPC or JEDEC. Studies principle and methods of chosen vibration tests. Further aim of this work is vibration fundamentals of PWB assembly. This work describes some research studies, which were conducted in past years and dealt with vibration stress issues. Shows individual factors, which has effect on vibration response of DPS and its destruction, like component position, acceleration difference between component and substrate, around temperature or material constants. In practical part was chosen method of vibration test and experiment in Labview programming interface was performed to verify these findings from vibration theory.

No description available.

This PhD dissertation experimentally characterized the vibration amplitude, frequency, and energy associated with ambulance travel and defined the relationship of the vibration to safety, comfort and care of ambulance patients. Average vertical vibration amplitudes of .46 to 2.55 m/sec2 were recorded in the patient compartment of four ambulances over four road surfaces at three speed settings. Power spectrum analysis of the data revealed that the vibration energy and resulting vertical acceleration forces were concentrated in the .1 to 6 Hz range. Relationships between the measured ambulance vibration and the impact of whole body vibration on human physiology and performance were quantified. It was found that the accelerations measured in the ambulances were in excess of what is considered to be a normal human comfort level. Furthermore, the vibration measured was in a spectrum which could present physical impediments to optimum task performance for the on-board medical team. Phase portrait analysis combined with the power spectrum data revealed the presence of nonlinearities, stochastic fluctuations and time delays inherent in the data. The ambulance vibration data was then used to create a unique analytical model and library of forcing functions corresponding to the vehicles, road surfaces and vehicle speeds that were tested. Using the example of a vibration absorbing force plate fit over an existing ambulance floor, it was demonstrated how the model and forcing functions could be used to develop a control law equation to select parameters for active control of vibration to produce sustainable regions of patient safety, comfort and care.

No description available.

Recent progresses by the aircraft industry in the development of a quieter supersonic transport have opened the possibility of overland supersonic flights, which are currently banned by aviation authorities in most countries. For the ban to be lifted, the sonic booms the aircraft generate at supersonic speed must be acceptable from a human-perception point of view, in particular inside buildings. The problem of the transmission of sonic booms inside buildings can be divided in several aspects such as the external pressure loading, structure vibration, and interior acoustic response. Past investigations on this problem have tackled all these aspects but were limited to simple structures and often did not account for the coupled fluid-structure interaction. A more comprehensive work that includes all the effects of sonic booms to ultimately predict the noise exposure inside realistic building structures, e.g. residential houses, has never been reported. Thus far, these effects could only be investigated experimentally, e.g. flight tests. In this research, a numerical model and a computer code are developed within the above context to predict the vibro-acoustic response of simplified building structures exposed to sonic booms, at low frequency. The model is applicable to structures with multiple rectangular cavities, isolated or interconnected with openings. The response of the fluid-structure system, including their fully coupled interaction, is computed in the time domain using a modal-decomposition approach for both the structural and acoustic systems. In the dynamic equations, the structural displacement is expressed in terms of summations over the "in vacuo" normal modes of vibration. The interior pressure is expressed in terms of summations over the acoustic modes of the rooms with perfectly reflecting surfaces (hard walls). This approach is simple to implement and computationally efficient at low frequency, when the modal density is relatively low. The numerical model is designed specifically for this application and includes several novel formulations. Firstly, a new shell finite-element is derived to model the structural components typically used in building construction that have orthotropic characteristics such as plaster-wood walls, floors, and siding panels. The constitutive matrix for these types of components is formulated using simple analytical expressions based on the orthotropic constants of an equivalent orthotropic plate. This approach is computationally efficient since there is no need to model all the individual subcomponents of the assembly (studs, sheathing, etc.) and their interconnections. Secondly, a dedicated finite-element module is developed that implements the new shell element for orthotropic components as well as a conventional shell element for isotropic components, e.g. window panels and doors. The finite element module computes the "in vacuo" structural modes of vibration. The modes and external pressure distribution are then used to compute modal loads. This dedicated finite-element module has the main advantage of overcoming the need, and subsequent complications, for using a large commercial finite-element program. Lastly, a novel formulation is developed for the fully coupled fluid-structure model to handle room openings and compute the acoustic response of interconnected rooms. The formulation is based on the Helmholtz resonator approach and is applicable to the very low frequency-range, when the acoustic wavelength is much larger than the opening dimensions. Experimental validation of the numerical model and computer code is presented for three test cases of increasing complexity. The first test structure consists of a single plaster-wood wall backed by a rigid rectangular enclosure. The structure is excited by sonic booms generated with a speaker. The second test structure is a single room made of plaster-wood walls with two double-panel windows and a door. The third test structure consists of the first room to which a second room with a large window assembly was added. Several door configurations of the structure are tested to validate the formulation for room openings. This latter case is the most realistic one as it involves the interaction of several structural components with several interior cavities. For the last two test cases, sonic booms with realistic durations and amplitudes were generated using an explosive technique. Numerical predictions are compared to the experimental data for the three test cases and show a good overall agreement. Finally, results from a parametric study are presented for the case of the single wall backed by a rigid enclosure. The effects of sonic-boom shape, e.g. rise time and duration, and effects of the structure geometry on the fluid-structure response to sonic booms are investigated. / Ph. D.

abstract: One type of assistive device for the blind has attempted to convert visual information into information that can be perceived through another sense, such as touch or hearing. A vibrotactile haptic display assistive device consists of an array of vibrating elements placed against the skin, allowing the blind individual to receive visual information through touch. However, these approaches have two significant technical challenges: large vibration element size and the number of microcontroller pins required for vibration control, both causing excessively low resolution of the device. Here, I propose and investigate a type of high-resolution vibrotactile haptic display which overcomes these challenges by utilizing a ‘microbeam’ as the vibrating element. These microbeams can then be actuated using only one microcontroller pin connected to a speaker or surface transducer. This approach could solve the low-resolution problem currently present in all haptic displays. In this paper, the results of an investigation into the manufacturability of such a device, simulation of the vibrational characteristics, and prototyping and experimental validation of the device concept are presented. The possible reasons of the frequency shift between the result of the forced or free response of beams and the frequency calculated based on a lumped mass approximation are investigated. It is found that one of the important reasons for the frequency shift is the size effect, the dependency of the elastic modulus on the size and kind of material. This size effect on A2 tool steel for Micro-Meso scale cantilever beams for the proposed system is investigated. / Dissertation/Thesis / Doctoral Dissertation Systems Engineering 2019

<p>This thesis reports on a numerical and experimental investigation of the unsteady loading of high solidity vertical axis wind turbines (VAWTs). Two-dimensional, unsteady Reynolds averaged Navier-Stokes simulations of a small scale, high solidity, H-type Darrieus vertical axis wind turbine revealed the dominant effect of dynamic stall on the power production and vibration excitation of the turbine. Operation of the turbine at low blade speed ratios resulted in complex flow-blade interaction mechanisms. These include; dynamic stall resulting in large scale vortex production, vortex impingement on the source blade, and significant flow momentum extraction.</p> <p>To validate the numerical model, a series of full-scale experimental wind tunnel tests were performed to determine the aerodynamic loading on the turbine airfoils, vibration response behaviour, and wake velocity. In order to accomplish this, a complex force measurement and wireless telemetry system was developed. During the course of this investigation, high vibration response of the turbine was observed. This resulted in conditions that made it difficult or impossible to measure the underlying aerodynamic loading. A vibration mitigation methodology was developed to remove the effect of vibration from the measured aerodynamic forces. In doing so, an accurate and complete measurement of the aerodynamic loading on the turbine blades was obtained.</p> <p>Comparison of the two-dimensional numerical model results to the experimental measurements revealed a considerable over-prediction of the turbine aerodynamic force and power coefficients, and wake velocity. From this research, it was determined that the three-dimensional flow effects due to the finite aspect ratio of the turbine and blades, as well as parasitic losses, could be accounted for through the application of inlet velocity and turbine height correction factors. In doing so, the two-dimensional numerical model results could be properly scaled to represent the three-dimensional flow behaviour of the turbine prototype. Ultimately, a validated VAWT design tool was developed.</p> / Doctor of Philosophy (PhD)