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Dissertations / Theses on the topic 'Modal dynamic analysis'
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Wicks, Matthew L. "A modal analysis method for a lumped parameter model of a dynamic fluid system." Thesis, This resource online, 1993. http://scholar.lib.vt.edu/theses/available/etd-07292009-090406/.
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XHIXHA, ELONA. "PASSIVE METHOD FOR DYNAMIC CHARACTERIZATION OF SOIL AND BUILDINGS." Doctoral thesis, Università di Siena, 2017. http://hdl.handle.net/11365/1013203.
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The research followed consist mainly on the use of passive methods for dynamic characterization of soil and building. Local Seismic Response of the construction site and Calibration of FE model of a reinforced concrete building have been performed. Passive seismic measurements have been acquired by two portable seismographs synchronized by each other with GPS antenna. Subsequently, structural verifications (global structural response) have been realized using once the response spectrum estimated from Local Seismic Response and once from technical standards. Finally, confronts between results have been realized at the aim to evaluate the importance of local seismic response of soil.
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McLean, Jayse Clifton. "Modal Analysis of the Human Brain Using Dynamic Mode Decomposition." Thesis, North Dakota State University, 2020. https://hdl.handle.net/10365/31804.
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The human brain is the most important organ of the human body. It controls our thoughts, movements and emotions. For that reason, protecting the brain from harm is of the utmost importance but to protect the brain, one must first understand brain injuries. Currently, observations and criteria involving brain injury are focused around acceleration and forces. However, the brain is poorly understood in the frequency domain. This study uses finite element analysis to simulate impact for 5 different impact angles. Then a numerical technique called dynamic mode decomposition is used to extract modal properties for brain tissue in regions near the corpus callosum and brain stem. Three modal frequencies were identified with frequency ranges of (44-68) Hz, (68-155) Hz, and (114-299) Hz. Additionally, it was observed that impact angle, displacement direction, and region of the brain have a significant impact on the modal response of brain tissue during impact.
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Iglesias, Angel Moises. "Investigating Various Modal Analysis Extraction Techniques to Estimate Damping Ratio." Thesis, Virginia Tech, 2000. http://hdl.handle.net/10919/35890.
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Many researchers have devoted their work to the development of modal analysis extraction techniques in order to obtain more reliable identification of the modal parameters. Also, as a consequence of all this work, there are some other works devoted to the evaluation and comparison of these methods in order to find which one is the most reliable method with respect to certain characteristics. In this thesis the Rational Fraction Polynomial (RFP) Method, the Prony or Complex Exponential Method (CEM), the Ibrahim Time Domain (ITD) Method, and Hilbert Envelope Method are used to evaluate how the accuracy of the damping ratio is affected with respect to various parameters and conditions. The investigation focuses in the estimation of damping ratio because among the modal parameters, it is the most difficult to model. Each method is evaluated individually in order to understand how the damping ratio estimation is affected with respect to each method when the characteristics of the FRF are changed. Also, they are compared to show that, in general, the Rational Fraction Polynomial Method is a more reliable method than the other methods. To investigate this, a simulated analytical data and an experimental data are processed to estimate the modal parameters, but focusing in the damping ratio. For the simulated analytical data the damping ratio's percent of error were calculated. The highest damping ratio's percent of error of the RFP was 0.0073501%. In the other hand, for the CEM, ITD, and Hilbert Envelope Method their highest damping ratio's percent of error were 83.02%, 99.82%, and 4.077%, respectively.<br>Master of Science
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Lin, Rongming. "Identification of the dynamic characteristics of nonlinear structures." Thesis, Imperial College London, 1991. http://hdl.handle.net/10044/1/46888.
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Fu, Gen. "Full Field Reconstruction Enhanced With Operational Modal Analysis and Compressed Sensing for General Dynamic Loading." Diss., Virginia Tech, 2021. http://hdl.handle.net/10919/103741.
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In most applications, the structure components have to be tested under different loading conditions before being placed in operation. A reliable and low cost measuring technique is desirable. However, most currently employed measuring approaches can only provide the structural response at several discrete locations. The accuracy of the measurements varies with the location and orientation of the sensors. Practically, it is not possible to place sensors at all the critical locations for different excitations. Therefore, an approach that derives the full field response using a limited set of measured data is desirable. In contrast to experimental full field measurement techniques, the expansion approach involves analytically expanding the limited measurements to all the degrees of freedom of the structure. Among all the analytical methods, the modal expansion method is computationally efficient and thus more suitable for real time expansion of measured data. In this method, the full-field response is approximated by the linear combination of mode shapes. In previous studies, the modal expansion method is limited by errors from mode aliasing, inaccuracy of the calculated mode shapes and the noise in measurements.
In order to overcome these limitations, the modal expansion method is enhanced by mode selection and error compensation in this study. First, the key parameters used in modal expansion method were analyzed using a cantilever beam model and a method for optimal placement of sensors was developed. A mode selection method and error compensation method based on operation modal analysis and adaptive compressed sensing techniques were then developed to reduce the effects of mode aliasing, mode shape inaccuracy and measurement noise. The developed approach was further tested virtually using a numerical model of rotor 67. The numerical model was created using a two-way coupled fluid structure interaction technique. By developing these methods, the enhanced modal expansion approach can provide full field response for structures under different load conditions. Compared to the traditional modal expansion method, it can expand the data with high noise and under general dynamic loading.<br>Doctor of Philosophy<br>Accurate knowledge of the strain and stress at critical locations of a given structure is crucial when assessing its integrity. However, currently employed measuring approaches can only provide the structural response at several discrete locations. Practically, it is not possible to place sensors at all the critical locations for different excitations. Therefore, an approach that derives the full field response using a limited set of measured data is desirable. Compared to experimental full field measurement techniques, the expansion approach is focused on analytically expanding the limited measurements to all the degrees of freedom of the structure. Among all the analytical methods, the modal expansion method is computationally efficient and thus more suitable for real-time expansion of measured data. The current modal expansion method is limited by errors from mode aliasing, inaccuracy of the mode shapes, and the noise in measurements. Therefore, an enhanced method is proposed to overcome these shortcomings of the modal expansion. The following objectives are accomplished in this study: 1) Develop a method for optimal placement of sensors for modal expansion; 2) Eliminate the mode aliasing effects by determining the significance of participated modes using operational modal analysis techniques; 3) Compensate for the noise in measurements and computational model by implementing the compressed sensing approach. After accomplishing these goals, the developed approach is able to provide full field response for structures under different load conditions. Compared to the traditional modal expansion method, it can expand the data under dynamic loading; it also shows promise in reducing the effects of noise and errors. The developed approach is numerically tested using fluid-structure interaction model of rotor 67 fan blade.
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Shutty, Michael Allen. "Dynamic modeling and modal analysis of an air-to-air missile." Thesis, Monterey, California. Naval Postgraduate School, 1991. http://hdl.handle.net/10945/25858.
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Approved for public release; distribution is unlimited.<br>The P-3 Orion patrol airplane has a need for air-to-air missile system for defense against enemy aircraft on its long-range missions. In response to this need, the Naval Air Test Center was tasked in 1989 to conduct a P-3/AIM-9 (Sidewinder) integration program. In support of this program, a vibration test stand was established at NPS, and a ground vibration characterization was conducted to determine if a potential flutter problem existed..
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Woon, Christopher Earle. "The effects of ambient temperature variations on structural dynamic characteristics." Thesis, This resource online, 1995. http://scholar.lib.vt.edu/theses/available/etd-12172008-063258/.
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Åkesson, Henrik. "Active control of vibration and analysis of dynamic properties concerning machine tools." Licentiate thesis, Karlskrona : Blekinge Institute of Technology, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:bth-00360.
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Vibration in internal turning is a problem in the manufacturing industry. Vibrations appear under the excitation applied by the material deformation process during the machining of a workpiece. In order for a lathe to perform an internal turning or boring operation, for example, in a pre-drilled hole in a workpiece, it is generally required that the boring bar should be long and slender; therefore extra sensitive to vibrations. These vibrations will affect the result of machining, in particular the surface finish, also the tool life may be reduced. As a result of tool vibration, severe acoustic noise frequently occurs in the working environment. This thesis comprises three parts and the first part presents a method for active control of boring bar vibration. This method consists of an active boring bar controlled by, for example, an analog controller. The focus lies on the analog controller and the advantages that may be obtained from working in the analog domain. The controller is a lead-lag compensator with digitally controlled parameters, such as gain and phase. However, signals remain in the analog domain. In addition, the analog controller is compared with a digital adaptive controller and it is found that both controllers yield an attenuation of the vibration by up to 50 dB. The second part of this thesis concerns the dynamic properties of a clamped boring bar used by the industry. In order to design a robust controller for a certain system, knowledge about the system's dynamic properties is required. On the workshop floor, a boring bar is dismounted and remounted, and reconfiguration of boring bars will alter the dynamic properties of the clamped boring bar. The dynamic properties of a standard boring bar and an active boring bar for a number of possible clamping conditions, as well as for a linearized clamping have been investigated based on an experimental approach. Also simple Euler-Bernoulli modeling of clamped boring bars incorporating simple non-rigid models of the boring bar clamping are investigated. Initial simulations of nonlinear SDOF systems have been carried out: one with a signed squared stiffness and one with a cubic stiffness. The purpose of these simulations was to identify a nonlinearity that introduces a similar behavior in the SDOF system dynamics as the nonlinear behavior observed in the dynamic properties of a clamped boring bar. The third and final part of this thesis focuses on vibration analysis methods in engineering education. A signal analyzer (which is a commonly used instrument in signal processing and vibration analysis) was made accessible via the Internet. Assignments were developed for students to learn and practice vibration analysis on real signals from a real setup of a relevant structure; a clamped boring bar. Whilst the experimental setup was fixed, the instrument and sensor configuration nonetheless enable a variety of experiment, for example: excitation signal analysis, spectrum analysis and experimental modal analysis.
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Geeves, S. S. "Dynamic equivalents for power system stability studies combining modal analysis and coherency." Thesis, Imperial College London, 1985. http://hdl.handle.net/10044/1/37702.
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Koricherla, Manindra Varma. "An experimental modal analysis of an Lithium-ion Battery using Dynamic Excitation." University of Akron / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=akron1502476407014686.
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SHARMA, AMIT. "DYNAMIC CHARACTERISTICS OF A SHAFT-UNIVERSAL JOINT SYSTEM." University of Cincinnati / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1148001333.
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Hadian, Mohammad Jafar. "Modal interactions in the dynamic response of isotropic and composite plates." Diss., Virginia Tech, 1991. http://hdl.handle.net/10919/39785.
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Hamilton's principle and a third-order shear-deformation theory are used to derive a set of five coupled partial-differential equations governing the nonlinear response of composite plates. The reduction of these equations by using classical plate theory is discussed and the corresponding partial-differential equations governing both rectangular and circular plates are derived.
Generalized Levy-type solutions are obtained for the problem of linear free vibrations and linear stability of shear-deformable cross-ply laminated plates. The governing equations are transformed into a set of first-order linear ordinary-differential equations with constant coefficients. The general solution of these equations is obtained by using the state-space concept. Then, the application of the boundary conditions yields equations for the natural frequencies and critical loads. However, a straightforward application of the state-space concept yields numerically ill-conditioned problems as the plate thickness is reduced. Various methods for overcoming this problem are discussed. An initial-value method with orthonormalization is selected. It is shown that this method not only yields results that are in excellent agreement with the results in the literature, but it also converges fast and gives all the frequencies and buckling loads regardless of the plate thickness. Further It is shown that the application of classical plate theory to thick plates yields inaccurate results. The influence of modal interactions on the response of harmonically excited plates is investigated in detail. The case of a two-to-one autoparametric resonance in shear-deformable composite laminated plates is considered. Four first-order ordinary-differential equations describing the modulation of the amplitudes and phases of the internally resonant modes are derived using the averaged Lagrangian when the higher mode is excited by a primary resonance. The fixed-point solutions are determined using a homotopy algorithm and their stability is analyzed. It is shown that besides the single-mode solution, two-mode solutions exist for a certain range of parameters. It is further shown that in the multi-mode case the lower mode, which is indirectly excited through the internal resonance may dominate the response. For a certain range of parameters, the fixed points lose stability via a Hopf bifurcation, thereby giving rise to limit cycle solutions. It is shown that these limit-cycles undergo a series of period-doubling bifurcations, culminating in chaos.
Finally, the case of a combination resonance involving the first three modes of axisymmetric circular plates is studied. The method of multiple scales is used to determine a set of ordinary-differential equations governing the modulation of phases of the modes involved and that the excited mode is not necessarily the dominant one.
Furthermore, it is shown that for a choice of parameters the multi-mode response loses stability through a Hopf bifurcation, resulting in periodically or chaotically modulated motions of the plate.<br>Ph. D.
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Diagne, Ibrahima. "Dynamic Analysis and Control of Multi-machine Power System with Microgrids: A Koopman Mode Analysis Approach." Diss., Virginia Tech, 2017. http://hdl.handle.net/10919/84546.
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Electric power systems are undergoing significant changes with the deployment of large-scale wind and solar plants connected to the transmission system and small-scale Distributed Energy Resources (DERs) and microgrids connected to the distribution system, making the latter an active system. A microgrid is a small-scale power system that interconnects renewable and non-renewable generating units such as solar photo-voltaic panels and micro-turbines, storage devices such as batteries and fly wheels, and loads. Typically, it is connected to the distribution feeders via power electronic converters with fast control responses within the micro-seconds. These new developments have prompted growing research activities in stability analysis and control of the transmission and the distribution systems. Unfortunately, these systems are treated as separated entities, limiting the scope of the applicability of the proposed methods to real systems. It is worth stressing that the transmission and distribution systems are interconnected via HV/MV transformers and therefore, are interacting dynamically in a complex way. In this research work, we overcome this problem by investigating the dynamics of the transmission and distribution systems with parallel microgrids as an integrated system . Specifically, we develop a generic model of a microgrid that consists of a DC voltage source connected to an inverter with real and reactive power control and voltage control. We analyze the small-signal stability of the two-area four-machine system with four parallel microgrids connected to the distribution feeders though different impedances. We show that the conventional PQ control of the inverters is insufficient to stabilize the voltage at the point-of-common coupling when the feeder impedances have highly unequal values. To ensure the existence of a stable equilibrium point associated with a sufficient stability margin of the system, we propose a new voltage control implemented as an additional feedback control loop of the conventional inner and outer current control schemes of the inverter. Furthermore, we carry out a modal analysis of the four-machine system with microgrids using Koopman mode analysis. We reveal the existence of local modes of oscillation of a microgrid against the rest of the system and between parallel microgrids at frequencies that range between 0.1 and 3 Hz. When the control of the microgrid becomes unstable, the frequencies of the oscillation are about 20 Hz. Recall that the Koopman mode analysis is a new technique developed in fluid dynamics and recently introduced in power systems by Suzuki and Mezic. It allows us to carry out small signal and transient stability analysis by processing only measurements, without resorting to any model and without assuming any linearization.<br>Ph. D.
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Araujo, Cleudmar Amaral de. "Modelagem de sistemas dinamicos atraves da sintese modal de componentes." [s.n.], 1998. http://repositorio.unicamp.br/jspui/handle/REPOSIP/264966.
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Orientador: Paulo Roberto Gardel Kurka<br>Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica<br>Made available in DSpace on 2018-07-23T18:37:28Z (GMT). No. of bitstreams: 1
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Previous issue date: 1998<br>Resumo: Uma das principais técnicas de modelagem mixta de sistemas complexos ou de grande porte é a técnica de síntese modal. Os vários métodos de síntese modal propostos são formulados sob dois pontos de vista distintos, ou seja, considerando-se o sistema sem amortecimento ou com amortecimento geral. Além disso, surgem inerentes dificuldades na
aplicação da metodologia de síntese modal na análise experimental. Neste trabalho é proposto uma técnica de síntese modal generalizada aplicada em sistemas sem amortecimento ou com amortecimento geral. O método utiliza um superconjunto modal de flexibilidade residual, cuja principal aplicação é na síntese modal experimental. O método utiliza um processo de remontagem das subestruturas que otimiza as equações finais da síntese. Propõe-se, também, um novo procedimento, definido como critério de eliminação automática de modos (CEA), que define um índice de qualidade para os modos das subestruturas, indicando quais serão aqueles mais apropriados para serem mantidos nas bases modais. Todas as metodologias propostas no trabalho foram implementadas em um software denominado Programa STRUCT. O método foi testado através de quatro exemplos de simulação. Foi feita uma validação experimental através de uma estrutura construída em escala reduzida, que visa representar um modelo esquemático e simplificado de uma asa de avião com um tanque de combustível fixado em sua extremidade. Além disso, foi também construído o modelo de elementos finitos da estrutura, com a finalidade de ajustar os modelos analítico e experimental<br>Abstract: Modal Synthesis is one of the main techniques for the modelling of complex or large sized system's. Two approaches for modal synthesis might be formulated those which considers the behaviour of undamped system's and those where the effects of generalized damping is apprised. Further to those consideration comes the application of the modal synthesis techniques in experimental modal analysis. The present work proposes a generalized modal synthesis procedure for damped and undamped system's. The method uses a residual flexibility superset which is applied to the experimental modal analysis. A methodology for
assembling adjacent substructures is also proposed which represents an important step towards the obtention of more accurate final results. Another important procedure introduced is that of automatic selection of modes to be kept in the modal base of the residual flexibility superset, defining a quality index for the modes of each substructure. AlI methodologies have been implemented in the form of the STRUCT software. Results of four numerical simulation and a practical application have been included to illustrate the performance of the methodologies. Finite element models have also been developed for the practical application (Combination of aircraft wing and fuel tank models) for performance comparison purposes<br>Doutorado<br>Mecanica dos Solidos<br>Doutor em Engenharia Mecânica
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Capraro, Ilaria. "Operational Modal Analysis: the CEME Skywalk at UBC, Vancouver." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2012. http://amslaurea.unibo.it/4240/.
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Slender and lighter footbridges are becoming more and more popular to meet the transportation demand and the aesthetical requirements of the modern society. The widespread presence of such particular structures has become possible thanks to the availability of new, lightweight and still capable of carrying heavy loads material .
Therefore, these kind of structure, are particularly sensitive to vibration serviceability problems, especially induced by human activities. As a consequence, it has been imperative to study the dynamic behaviour of such slender pedestrian bridges in order to define their modal characteristics.
As an alternative to a Finite Element Analysis to find natural frequencies, damping and mode shape, a so-called Operational Modal Analysis is a valid tool to obtain these parameters through an ambient vibration test.
This work provides a useful insight into the Operational Modal Analysis technique and It reports the investigation of the CEME Skywalk, a pedestrian bridge located at the University of British Columbia, in Vancouver, Canada.
Furthermore, human-induced vibration tests have been performed and the dynamic characteristics derived with these tests have been compared with the ones from the ambient vibration tests. The effect of the dynamic properties of the two buildings supporting the CEME Skywalk on the dynamic behaviour of the bridge has been also investigated.
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Harat, Robert Oliver. "Dynamic investigation of vibratory screen response in a FEM environment." Diss., University of Pretoria, 2020. http://hdl.handle.net/2263/79583.
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Effective models of vibratory screens which can capture the true response characteristics are crucial in the understanding of faults and failures which occur in vibratory screens. However, the current available models are usually simplified and have limited validation to that of a physical screen.
Much research has been conducted to optimise the screening efficiency of screens. The optimisation includes screen geometry, material processing of the screen and the dynamic response of the screen. These investigations have not been furthered to investigate the effects of different faults on the dynamic response of a vibratory screen.
To model a vibratory screen which can replicate the dynamics of a physical vibratory screen it is important to create a model with enough complexity to capture the dynamics of the screen. The model of the screen was validated using both modal analysis and the transient response of the screen.
The modal analysis was used to ensure that the physical characteristics of the model are consistent with that of the physical screen. Once this was completed, the second validation aimed to investigate if the model of the screen could capture transient faults which are measured experimentally. It was found that it was not possible to conclusively determine if the finite element methods model could Finally, an intelligent method was used to distinguishing between different faults and classifying them accordingly. The intelligent method was also trained using the FEM data and then used to classify the physical screen data.<br>Dissertation (MEng)--University of Pretoria, 2020.<br>Mechanical and Aeronautical Engineering<br>MEng<br>Unrestricted
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Bose, Mrinal Kanti. "NON-CLASSICAL DAMPING PROPERTIES AND MODAL CORRELATION COEFFICIENT FOR DYNAMIC ANALYSIS OF STRUCTURES." NCSU, 2001. http://www.lib.ncsu.edu/theses/available/etd-20010305-150413.
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<p>BOSE, MRINAL KANTI. Non-Classical Damping Properties and Modal Correlation Coefficient for Dynamic Analysis of Structures. (Under the direction of Abhinav Gupta and Ajaya Gupta.)The seismic response of secondary systems depends, in addition to their uncoupled dynamic characteristics, on the interaction with primary structures supporting them. This dissertation presents a verification study of the formulations to evaluate the seismic response of non-classically damped building-piping systems by modal synthesis approach. The existing studies consider only simple representative primary-secondary systems. No real-life like coupled system such as building-piping was used in these studies. Further, the majority of simple systems considered in these studies do not represent realistic coupled systems with significant effect of non-classical damping as they have either high values of mass ratios or systems with detuned modes.In this dissertation, different configurations of simple representative systems as well as real-life like building-piping systems are considered. Responses obtained from modal superposition time history analyses as well as response spectrum analyses are compared with the corresponding responses obtained by Brookhaven National Laboratory from the direct integration time history analyses. Modal superposition time history analyses results and direct integration time history analyses results are almost identical. The mean and standard deviation of responses from response spectrum analyses are close to the corresponding values evaluated using direct integration time history analysis. In addition to the verification results, a detailed discussion is also presented on the significance of non-classical damping. It is shown that the effect of non-classical damping is significant in systems that have nearly tuned modes and sufficiently small values of modal mass ratios. It is also illustrated that composite modal damping is an alternate form of classical damping that can result in incorrect responses in non-classically damped systems. Possible reasons for numerical and modeling differences that can occur in real-life like building-piping system are identified and their effect on the dynamic characteristics of the coupled system is illustrated.In the response spectrum method, the maximum modal responses are combined using an appropriate formulation for the modal correlation coefficient. This dissertation presents a new formulation which is based on the observation that the response spectrum method is a design method such that the statistical values of responses evaluated from multiple time history analyses should be close to the corresponding values obtained from the response spectrum method. Results from a numerical study using several real earthquake records are used to develop the new formulation. Different expressions are proposed for combining modal responses that have same algebraic sign and for those that have opposite algebraic signs.<P>
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Suliman, Ridhwaan. "A quadratic non-linear elasticity formulation for the dynamic behaviour of fluid-loaded structures." Thesis, University of Cambridge, 2018. https://www.repository.cam.ac.uk/handle/1810/277824.
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This work details the development and implementation of a numerical model capable of solving strongly-coupled fluid-structure interaction problems involving long thin structures, which are common multi-physics problems encountered in many applications. In most fluid-structure interaction problems the deformation of the slender elastic bodies is significant and cannot be described by a purely linear analysis. We present a new formulation to model these larger displacements. By extending the standard modal decomposition technique for linear structural analysis, the governing equations and boundary conditions are updated to account for the leading-order non-linear terms and a new modal formulation with quadratic modes is derived. The quadratic modal approach is tested on standard benchmark problems of increasing complexity and compared with analytical and full non-linear numerical solutions. Two computational fluid-structure interaction approaches are then implemented in a partitioned manner: a finite volume method for discretisation of both the fluid and solid domains and the quadratic modal formulation for the structure coupled with a finite volume fluid solver. Strong-coupling is achieved by means of a fixed-point solver with dynamic relaxation. The fluid-structure interaction approaches are validated and compared on benchmark problems of increasing complexity and strength of coupling between the fluid and solid domains. Fluid-structure interaction systems may become unstable due to the interaction between the fluid-induced pressure and structural rigidity. A thorough stability analysis of finite elastic plates in uniform flow is conducted by varying the structural length and flow velocity showing that these are critical parameters. Validation of the results with those from analytical methods is done. An analysis of the dynamic interactions between multiple finite plates in various configurations is also conducted.
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Kahraman, Engin. "Investigation Of The Dynamic Properties Of Plate-like Structures." Master's thesis, METU, 2011. http://etd.lib.metu.edu.tr/upload/12613703/index.pdf.
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This study presents the investigation and the verification of the modal parameters of a plate-like structure by using different modal analysis methods. A fin-like structure which is generally used in aircraft is selected as a subcategory of a plate-like test structure.
In the first part of the thesis, the natural frequencies and the corresponding mode shapes of the fin are extracted by Finite Element Analysis method. Classical Modal Analysis and Testing methods comprising both impact hammer and modal shaker applications are then applied in order to obtain the modal parameters such as<br>resonance frequencies, mode shapes and damping ratios.
In the second part, a recent modal analysis technique, Operational Modal Analysis, is also applied in the laboratory environment. Since Operational Modal Analysis method does not require any information of input forcing, the fin structure is tested under both mechanical and acoustical types of excitations without measuring the given input forces.
Finally, Operational Modal Analysis and Testing is also performed under various flow conditions generated in the wind tunnel which may simulate the real operating environment for the fin structure. The modal parameters extracted under these flow conditions are then compared with the previously obtained Finite Element, Classical and Operational Modal Analyses results.
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CABBOI, ALESSANDRO. "Automatic operational modal analysis: challenges and applications to historic structures and infrastructures." Doctoral thesis, Università degli Studi di Cagliari, 2014. http://hdl.handle.net/11584/266404.
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The core of the work turns around the capability to automate Operational Modal Analysis methods for permanent dynamic monitoring systems. In general, the application of OMA methods requires an experienced engineer in experimental dynamics and modal analysis; in addition, a lot of time is usually spent in manual analysis, necessary to ensure the best estimation of modal parameters. Those features are in contrast with permanent dynamic monitoring, which requires algorithms in order to efficiently manage the huge amount of recorded data in short time, ensuring
an acceptable quality of results. Therefore, the use of parametric identification methods, like SSI methods, are explored and some recommendations concerning its application are provided. The identification process is combined with the automatic interpretation of stabilization diagrams based on a damping ratio check and on modal complexity inspection. Finally, a clustering method for the
identified modes and a modal tracking strategy is suggested and discussed. The whole procedure is validated with a one-month and a one-year set of "manually-identified" modal parameters. This constitutes a quite unique set of validation data in the literature. Two monitoring case studies are studied: a railway iron arch bridge (1889) and a masonry bell-tower (XII century). Within this framework, classical and new strategies to handle the huge amount of recorded and identified data are proposed and compared for structural anomaly detection. The classical strategies
are mainly based on the inspection of any irreversible frequency variation. To such purpose, it is mandatory an extensive correlation study with environmental and operational factors which affect the frequency of the vibration modes. Conversely, one of the proposed strategy aims to use alternative dynamic features that are not sensitive to environmental factors, like mode shape or
modal complexity, instead of frequency parameters in order to detect any structural anomaly. In addition, a further strategy has the goal to eliminate the environmental-induced effects on frequency without the knowledge and the measurements of such factors. The procedure is mainly based on the combination of a simple regression model with the results obtained by a Principal Component
Analysis. Furthermore, two automated Operational Modal Analysis (OMA) procedures are compared for Structural Health Monitoring (SHM) purposes: the first one is based on SSI methods, while the second one involves a non-parametric technique like the Frequency Domain Decomposition method
(FDD). In conclusion, a model updating strategy for historic structures using Ambient Vibration Test
and long term monitoring results is presented. The main goal is to integrate the information provided by a FE model with those continuously extracted by a dynamic monitoring system, basing so any detection of structural anomalies on the variation of the uncertain structural parameters.
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Ruggiero, Eric John. "Active Dynamic Analysis and Vibration Control of Gossamer Structures Using Smart Materials." Thesis, Virginia Tech, 2002. http://hdl.handle.net/10919/32299.
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Increasing costs for space shuttle missions translate to smaller, lighter, and more flexible satellites that maintain or improve current dynamic requirements. This is especially true for optical systems and surfaces. Lightweight, inflatable structures, otherwise known as gossamer structures, are smaller, lighter, and more flexible than current satellite technology. Unfortunately, little research has been performed investigating cost effective and feasible methods of dynamic analysis and control of these structures due to their inherent, non-linear dynamic properties. Gossamer spacecraft have the potential of introducing lenses and membrane arrays in orbit on the order of 25 m in diameter. With such huge structures in space, imaging resolution and communication transmissibility will correspondingly increase in orders of magnitude.
A daunting problem facing gossamer spacecraft is their highly flexible nature. Previous attempts at ground testing have produced only localized deformation of the structureâ s skin rather than excitation of the global (entire structureâ s) modes. Unfortunately, the global modes are necessary for model parameter verification. The motivation of this research is to find an effective and repeatable methodology for obtaining the dynamic response characteristics of a flexible, inflatable structure. By obtaining the dynamic response characteristics, a suitable control technique may be developed to effectively control the structureâ s vibration. Smart materials can be used for both active dynamic analysis as well as active control. In particular, piezoelectric materials, which demonstrate electro-mechanical coupling, are able to sense vibration and consequently can be integrated into a control scheme to reduce such vibration. Using smart materials to develop a vibration analysis and control algorithm for a gossamer space structure will fulfill the current requirements of space satellite systems. Smart materials will help spawn the next generation of space satellite technology.<br>Master of Science
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Degirmenci, Can. "Dynamic Pull Analysis For Estimating The Seismic Response." Master's thesis, METU, 2006. http://etd.lib.metu.edu.tr/upload/12607833/index.pdf.
Full textAbstract:
The analysis procedures employed in earthquake engineering can be classified as linear static, linear dynamic, nonlinear static and nonlinear dynamic. Linear procedures are usually referred to as force controlled and require less analysis time and less computational effort. On the other hand, nonlinear procedures are referred to as deformation controlled and they are more reliable in characterizing the seismic performance of buildings. However, there is still a great deal of unknowns for nonlinear procedures, especially in modelling the reinforced concrete structures.
Turkey ranks high among all countries that have suffered losses of life and property due to earthquakes over many centuries. These casualties indicate that, most regions of the country are under seismic risk of strong ground motion. In addition to this phenomenon, recent studies have demonstrated that near fault ground motions are more destructive than far-fault ones on structures and these effects can not be captured effectively by recent nonlinear static procedures.
The main objective of this study is developing a simple nonlinear dynamic analysis procedure which is named as &ldquo<br>Dynamic Pull Analysis&rdquo<br>for estimating the seismic response of multi degree of freedom (MDOF) systems. The method is tested on a six-story reinforced concrete frame and a twelve-story reinforced concrete frame that are designed according to the regulations of TS-500 (2000) and TEC (1997).
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Jakel, Roland. "Linear Dynamic System Analyses with Creo Simulate – Theory & Application Examples, Capabilities, Limitations –." Universitätsbibliothek Chemnitz, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-225992.
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1. Einführung in die Theorie dynamischer Analysen mit Creo Simulate 2. Modalanalysen (Standard und mit Vorspannung) 3. Dynamische Analysen einschließlich Klassifizierung der Analysen; einige einfache Beispiele für eigene Studien (eine Welle unter Unwuchtanregung und ein Ein-Massen-Schwinger) sowie etliche Beispiele größerer dynamischer Systemmodelle aus unterschiedlichsten Anwendungsbereichen 4. Feedback an den Softwareentwickler PTC (Verbesserungsvorschläge und Softwarefehler) 5. Referenzen<br>1. Introduction to dynamic analysis theory in Creo Simulate 2. Modal analysis (standard and with prestress) 3. Dynamic analysis, including analysis classification, some simple examples for own self-studies (shaft under unbalance excitation and a one-mass-oscillator) and several real-world examples of bigger dynamic systems 4. Feedback to the software developer PTC (enhancement requests and code issues) 5. References
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Haoyu, C. (Chen). "A preliminary study of micro-gestures:dataset collection and analysis with multi-modal dynamic networks." Master's thesis, University of Oulu, 2017. http://jultika.oulu.fi/Record/nbnfioulu-201706022490.
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Abstract. Micro-gestures (MG) are gestures that people performed spontaneously during communication situations. A preliminary exploration of Micro-Gesture is made in this thesis. By collecting recorded sequences of body gestures in a spontaneous state during games, a MG dataset is built through Kinect V2. A novel term ‘micro-gesture’ is proposed by analyzing the properties of MG dataset. Implementations of two sets of neural network architectures are achieved for micro-gestures segmentation and recognition task, which are the DBN-HMM model and the 3DCNN-HMM model for skeleton data and RGB-D data respectively. We also explore a method for extracting neutral states used in the HMM structure by detecting the activity level of the gesture sequences. The method is simple to derive and implement, and proved to be effective. The DBN-HMM and 3DCNN-HMM architectures are evaluated on MG dataset and optimized for the properties of micro-gestures. Experimental results show that we are able to achieve micro-gesture segmentation and recognition with satisfied accuracy with these two models. The work we have done about the micro-gestures in this thesis also explores a new research path for gesture recognition. Therefore, we believe that our work could be widely used as a baseline for future research on micro-gestures.
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Moshiri, Farzad, Bahareh Mobasher, and Issa Osama Talib. "Detection of defects in timber using dynamic excitation and vibration analysis." Thesis, Växjö University, School of Technology and Design, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:vxu:diva-5444.
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<p>This thesis evaluates the possibility to detect natural defects, such as knots, in timber boards using dynamic excitation test and ABAQUS software. In the study the edgewise bending direction were compared with axial direction. Dynamic excitation and modal analysis were used to extract the natural frequencies of several sound and artificially defected boards with the help of Signalcalc. Mobylizer software. By using the first edgewise natural frequency, modulus of elasticity (MOE) was calculated. An ABAQUS 2D Finite Element model was utilized to model the board and to extract the frequencies for the six first mode shapes in both axial and edgewise directions. The extracted frequencies from the model were compared with the frequencies from the tests. The analytical and experimental results, from the homogeneous boards, in edgewise direction has similar frequency variations. The defects in the timber boards decreased the natural frequencies. The bending modes with more curvature at the location of the artificial defect displayed more frequency deviation in that mode. The variation in response frequencies for uniform and defected boards was more noticeable in edgewise bending modes than in longitudinal modes.</p>
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Allahverdiyev, Rovshan. "Effects of beam configuration on dynamic properties and seismic performances of multi-storey frame building models." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2020.
Find full textAbstract:
The present study aims at comparing the dynamic properties and seismic performances offered by reinforced concrete frame structures characterised by different beams distribution.
Multi-storey regular frame buildings are considered as reference structures. Different models are then developed according to various layout of the beams (x-direction is the longitudinal direction, whilst y-direction is the transversal one): (1) beams placed along the x-direction at the odd storeys and placed along the y-direction at the even storeys; (2) beams placed along the y-direction at the odd storeys and placed along the x-direction at the even storeys; (3) and (4) alternating beams every two storeys; (5) beams placed along the x-direction at all storeys; (6) beams placed along the y-direction at all storeys; (7) complete three-dimensional frame with beams placed along both the x- and the y-direction at all storeys. In all models, smaller perimeter beams are placed along the direction orthogonal to the one of the main beams.
Modal analysis has been conducted to evaluate the influence of beams distribution on the period of vibration. Response spectrum and time-history dynamic analyses have been carried out to assess the effects of beams distribution on the base shear and base bending moments, top-storey displacements, interstorey displacements and floor accelerations.
On the contrary of what could be expected, the results indicate that structures with beams alternating every storey do not behave unfavorably with respect to the complete three-dimensional frames. In more detail, two effects may be clearly recognized: one associated to the period and one associated to the static scheme. The former acting basically on the base shear; the latter acting mainly on the base bending moment. The understanding of the influence of beams distribution on frame structures is useful when dealing with seismic vulnerability assessment of existing buildings and design of new buildings.
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Mohammed, Usman Ali. "Analysis of Parameters Affecting Modal Frequencies in Bolted Joint Connections." University of Cincinnati / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1535709260529555.
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Nádvorník, Vít. "Dynamické vlastnosti obrobku při soustružení." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2016. http://www.nusl.cz/ntk/nusl-241875.
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The contens of master thesis is theoretical analysis of vibrations during turning and possibillity to eliminate them, measure dynamic compliance and modal paramteters. The goal of experimental part is to determine the effect of material and type of clamping for three shafts at natural frequency, mode shape and dynamic compliance. Using these results we can optimized cutting parameters and to better overcome vibration during machining.
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Reynolds, Thomas Peter Shillito. "Dynamic behaviour of dowel-type connections under in-service vibration." Thesis, University of Bath, 2013. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.608327.
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This study investigated the vibration serviceability of timber structures with dowel-type connections. It addressed the use of such connections in cutting-edge timber structures such as multi-storey buildings and long-span bridges, in which the light weight and flexibility of the structure make it possible that vibration induced by dynamic forces such as wind or footfall may cause discomfort to occupants or users of the structure, or otherwise impair its intended use. The nature of the oscillating force imposed on connections by this form of vibration was defined based on literature review and the use of established mathematical models. This allowed the appropriate cyclic load to be applied in experimental work on the most basic component of a dowel-type connection: a steel dowel embedding into a block of timber. A model for the stiffness of the timber in embedment under this cyclic load was developed based on an elastic stress function, which could then be used as the basis of a model for a complete connector. Nonlinear and time-dependent behaviour was also observed in embedment, and a simple rheological model incorporating elastic, viscoelastic and plastic elements was fitted to the measured response to cyclic load. Observations of the embedment response of the timber were then used to explain features of the behaviour of complete single- and multiple-dowel connections under cyclic load representative of in-service vibration. Complete portal frames and cantilever beams were tested under cyclic load, and a design method was derived for predicting the stiffness of such structures, using analytical equations based on the model for embedment behaviour. In each cyclic load test the energy dissipation in the specimen, which contributes to the damping in a complete structure, was measured. The analytical model was used to predict frictional energy dissipation in embedment, which was shown to make a significant contribution to damping in single-dowel connections. Based on the experimental results and analysis, several defining aspects of the dynamic response of the complete structures, such as a reduction of natural frequency with increased amplitude of applied load, were related to the observed and modelled embedment behaviour of the connections.
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Konjerla, Krishna Chaitanya. "FRF Based Experimental – Analytical Dynamic Substructuring Using Transmission Simulator." Thesis, KTH, MWL Marcus Wallenberg Laboratoriet, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-198535.
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In dynamic substructuring, a complex structure is divided into multiple substructures that can be analysed individually and these individual component responses are coupled together to obtain the global response of the whole structure. Dynamic substructuring can be performed on substructure models that are identified either experimentally or analytically. For dynamic substructuring to be successful, it is very essential to have the precise information of the connection points or the interfaces between the substructures. The method has been extensively used with analytical models in most of the available standard finite element software packages where the information about all degrees of freedom is known. However, it is difficult to get the information about all connection degrees of freedom from the measurements and experimental substructuring is thus limited in its use compared to analytical substructuring. In order to overcome these difficulties, the Transmission Simulator method commonly also known as Modal Constraints for Fixture and Subsystem method can be used. In this method, an additional fixture called Transmission Simulator which is available both physically and analytically, is attached to the substructures at the interfaces and their respective responses are measured. The substructures could be analytical as well as experimental. The coupling is done by constraining the transmission simulator on the substructures to have the same motion and the effect of the transmission simulator is later removed from the coupled structure by subtracting the analytical transmission simulator model. This method has been successfully implemented for Component Mode Synthesis and Frequency Based Substructuring for structures with multiple connection points at a single location. In this thesis work, frequency response function based experimental–analytical dynamic substructuring using the transmission simulator is performed on a rear subframe and rear differential unit assembly of a Volvo XC90 car where the differential unit is connected to the subframe at three locations. The aim of this work is to verify the Transmission Simulator Method for multiple location connection points using the frequency response functions and build confidence on the methodology in order to be used for future work at Volvo Car Corporation.
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Savini, Gabriel. "A numerical program for Railway vehicle-track-structure dynamic interaction using a modal substructuring approach." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2011. http://amslaurea.unibo.it/2098/.
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This work presents a program for simulations of vehicle-track and vehicle-trackstructure
dynamic interaction . The method used is computationally efficient in the
sense that a reduced number of coordinates is sufficient and doesn’t require high
efficiency computers.
The method proposes a modal substructuring approach of the system by modelling
rails , sleepers and underlying structure with modal coordinates, the vehicle
with physical lumped elements coordinates and by introducing interconnection elements
between these structures (wheel-rail contact, railpads and ballast) by means
of their interaction forces.
The Frequency response function (FRF) is also calculated for both cases of track
over a structure (a bridge, a viaduct ...) and for the simple vehicle-track program;
for each case the vehicle effect on the FRF is then analyzed through the comparison
of the FRFs obtained introducing or not a simplified vehicle on the system.
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Armengol, Llobet Joaquim. "Application of modal interval analysis to the simulation of the behaviour of dynamic systems with uncertain parameters." Doctoral thesis, Universitat de Girona, 2000. http://hdl.handle.net/10803/7743.
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Els models matemàtics quantitatius són simplificacions de la realitat i per tant el comportament obtingut per simulació d'aquests models difereix dels reals. L'ús de models quantitatius complexes no és una solució perquè en la majoria dels casos hi ha alguna incertesa en el sistema real que no pot ser representada amb aquests models. Una forma de representar aquesta incertesa és mitjançant models qualitatius o semiqualitatius. Un model d'aquest tipus de fet representa un conjunt de models. La simulació del comportament de models quantitatius genera una trajectòria en el temps per a cada variable de sortida. Aquest no pot ser el resultat de la simulació d'un conjunt de models. Una forma de representar el comportament en aquest cas és mitjançant envolupants. L'envolupant exacta és complete, és a dir, inclou tots els possibles comportaments del model, i<br/>correcta, és a dir, tots els punts dins de l'envolupant pertanyen a la sortida de, com a mínim, una instància del model. La generació d'una envolupant així normalment és una tasca molt dura que es pot abordar, per exemple, mitjançant algorismes d'optimització global o comprovació de consistència. Per aquesta raó, en molts casos s'obtenen aproximacions a l'envolupant exacta. Una aproximació completa però no correcta a l'envolupant exacta és una envolupant sobredimensionada, mentre que una envolupant correcta però no completa és subdimensionada. Aquestes propietats s'han estudiat per diferents simuladors per a sistemes incerts.
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Haji, Zyad. "Dynamic analysis and crack detection in stationary and rotating shafts." Thesis, University of Manchester, 2016. https://www.research.manchester.ac.uk/portal/en/theses/dynamic-analysis-and-crack-detection-in-stationary-and-rotating-shafts(2e9dcab4-685d-4c20-8f9d-55b6892b8149).html.
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The sustainability, smooth operation and operational life of rotating machinery significantly rely on the techniques that detect the symptoms of incipient faults. Among the faults in rotating systems, the presence of a crack is one of the most dangerous faults that dramatically decreases the safety and operational life of the rotating systems, thereby leading to catastrophic failure and potential injury to personnel if it is undetected. Although many valuable techniques and models have been developed to identify a crack (or cracks) in stationary and rotating systems, finding an efficient technique (or model) that can identify a unique vibration signature of the cracked rotor is still a great challenge in this field. This is because of the unceasing necessity to develop high performance rotating machines and driving towards significant reduction of the time and cost of maintenance. Most of the crack identification techniques and models in the available literature are based on vibration-based methods. The main idea of the vibration-based method is that the presence of a crack in a rotor induces a change in the mass, damping, and stiffness of the rotor, and consequently detectable changes appear in the modal properties (natural frequencies, modal damping, and mode shapes). Among all these modal properties, the choice of the modal natural frequency change is more attractive as a tool for crack identification. The changes in natural frequencies due to a crack can be conveniently measured from just a few accessible points on the cracked rotor. Furthermore, measuring the natural frequencies does not require expensive measuring instruments, and the natural frequency data is normally less contaminated by experimental noise. However, the change that a crack induces in the natural frequencies is usually very small and can be buried in the ambient noise. Moreover, the natural frequencies are not affected if the crack is located at the nodes of modes or far from the location of inertia force and out-of-unbalance force that the disc generates in the shaft. To overcome these problems (or limitations), therefore, this study is conducted using the idea of the roving mass (roving disc in rotor case). The modal natural frequencies are used for the identification and location of cracks of various severities at different locations in both stationary and rotating shafts. The fundamental idea of the roving disc is that an extra inertia force is traversed along the cracked rotor to significantly excite the dynamics of the rotor near the crack locations. In other words, the location of a crack can be anywhere on the shaft which is contrary to the developed techniques in the available literature in which the location of a crack should be close to the disc. Along with the roving disc idea, three crack identification techniques are developed in this study using the natural frequencies of the cracked and intact shafts. Each of these techniques has its merits and limitations for crack identification. These techniques are implemented using data that are numerically generated by the finite element method based on the Bernoulli-Euler shaft elements and experimentally validated in the laboratory environment. The numerical and experimental results clearly demonstrate the capability of the suggested approach for the identification and location of cracks in stationary and rotating shafts.
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RAVIZZA, Gabriele. "Modal dynamic identification of civil structures via inverse analysis based on Heterogeneous Data Fusion and post-processing." Doctoral thesis, Università degli studi di Bergamo, 2021. http://hdl.handle.net/10446/183099.
Full textAbstract:
The present Doctoral Thesis belongs to the Scientific-Disciplinary Sector of Mechanics of Solids and Structures (ICAR/08 - Scienza delle Costruzioni), and falls within the broader research field of Structural Health Monitoring (SHM), with specific reference to the civil engineering context.
Nowadays, SHM-based approaches and the attached development of consistent numerical modeling, with related model updating, may constitute fundamental tools to pursue the goal of engineering structural safety, preventing possible causes of damage that may even lead to structural failure.
In particular, this research work proposes complementary post-processing approaches to address the issue of noise cleaning on dynamic structural response signals typically encountered in structural engineering applications (specifically, acceleration and displacement signals). Two approaches are mainly presented, especially aiming at enhancing displacements response signals, since they are commonly affected by higher levels of noise, also due to the low-cost monitoring instrumentation that may possibly be employed. Heterogeneous Data Fusion (HDF) procedures, which involve a Kalman Filter (KF)-based implementation, are primarily investigated, by integrating data acquired from different types of sensors, so that the resulting information turns out to be characterized by a lower degree of uncertainty. A denoising approach is also inspected, as the process through which a source signal may be reconstructed, starting from a recorded, noise-affected one, by removing its noisy part, without losing the useful information incorporated within it.
A HDF procedure and a denoising approach are then combined within an integrated strategy, in an effort to enhance the reliability of the monitoring process, for assessing the health conditions of bridges.
Aspiring at providing a comprehensive research framework on these topics, both synthetic response signals and real response signals are considered, as well as signals displaying a different nature (non-stationary vs. stationary). These processed response signals are finally employed toward modal identification purposes, for extracting the modal properties of the monitored structure.<br>The present Doctoral Thesis belongs to the Scientific-Disciplinary Sector of Mechanics of Solids and Structures (ICAR/08 - Scienza delle Costruzioni), and falls within the broader research field of Structural Health Monitoring (SHM), with specific reference to the civil engineering context.
Nowadays, SHM-based approaches and the attached development of consistent numerical modeling, with related model updating, may constitute fundamental tools to pursue the goal of engineering structural safety, preventing possible causes of damage that may even lead to structural failure.
In particular, this research work proposes complementary post-processing approaches to address the issue of noise cleaning on dynamic structural response signals typically encountered in structural engineering applications (specifically, acceleration and displacement signals). Two approaches are mainly presented, especially aiming at enhancing displacements response signals, since they are commonly affected by higher levels of noise, also due to the low-cost monitoring instrumentation that may possibly be employed. Heterogeneous Data Fusion (HDF) procedures, which involve a Kalman Filter (KF)-based implementation, are primarily investigated, by integrating data acquired from different types of sensors, so that the resulting information turns out to be characterized by a lower degree of uncertainty. A denoising approach is also inspected, as the process through which a source signal may be reconstructed, starting from a recorded, noise-affected one, by removing its noisy part, without losing the useful information incorporated within it.
A HDF procedure and a denoising approach are then combined within an integrated strategy, in an effort to enhance the reliability of the monitoring process, for assessing the health conditions of bridges.
Aspiring at providing a comprehensive research framework on these topics, both synthetic response signals and real response signals are considered, as well as signals displaying a different nature (non-stationary vs. stationary). These processed response signals are finally employed toward modal identification purposes, for extracting the modal properties of the monitored structure.
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Mejri, Seifeddine. "Identification et modélisation du comportement dynamique des robots d'usinage." Thesis, Clermont-Ferrand 2, 2016. http://www.theses.fr/2016CLF22688/document.
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La robotisation des procédés d’usinage suscite l’intérêt des industriels en raison du grand espace de travail et le faible coût des robots par rapport aux machines-outils conventionnelles et la possibilité d’usiner des pièces de formes complexes. Cependant, la faible rigidité de la structure robotique favorise le déclenchement de phénomènes dynamiques liés à l’usinage sollicitant le robot en bout de l’outil qui dégradent la qualité de surface de la pièce usinée. L’objectif de ces travaux de thèse est de caractériser le comportement dynamique des robots en usinage. Ces travaux ont suivi une démarche en trois étapes : La modélisation d’un premier modèle considéré de référence où le robot est au repos. Ensuite l’identification du comportement dynamique du robot en service. Enfin, l’exploitation des modèles dynamiques du robot en vue de prédire la stabilité de coupe. L’originalité de ces travaux porte sur le développement des méthodes d’identification modale opérationnelles. Elles permettent d’intégrer les conditions réelles d’usinage et d’élaborer des modèles plus précis que le premier modèle de connaissance sans être biaisés par l’effet des harmoniques de rotation de l’outil. Enfin, des préconisations sur le choix de configurations du robot et sur la direction des forces d’excitation sont proposées pour assurer la stabilité de la coupe lors de l’usinage robotisé<br>Machining robots have major advantages over cartesian machine tools because of their flexibility, their ability to reach inaccessible areas on a complex part, and their important workspace. However, their lack of rigidity and precision is still a limit for precision tasks. The stresses generated by the cutting forces and inertia are important and cause static and dynamic deformations of the structure which result in problems of workpiece surface. The aim of the thesis work is to characterize the dynamic behavior of robots during machining operation. This work followed a three-step approach : Modeling a first model considered as a reference where the robot is at rest. Then the identification of the dynamic behavior in service. Finally, the prediction of the cutting stability using the robot dynamic model. The originality of this work is the development of new operational modal identification methods. They integrate the machining conditions and result into a more accurate model than the first model of reference without being biased by harmonics. Finally, guidlines of robot’s configurations and excitation forces’ direction are proposed to ensure the robotic machining stability
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Valo, Lukáš. "Simulační analýza vibrací turbodmychadla." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2019. http://www.nusl.cz/ntk/nusl-401530.
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The master thesis deals with computational modeling of a turbocharger vibrations and and assessment of influnce of passive dynamic vibration absorber on vibrations of actuator bracket. The use of dynamic vibration absorber was summarized in the research study. The analysis were performed using finite element method in ANSYS. Several computational models of turbocharger were created with different ways of modeling bolted joints between turbocharger parts. Modal analysis of each model was performed and the results were compared. For the selected model, the response to the kinematic excitation from the internal combustion engine for two load conditions was calculated using harmonic analysis. A simple model of vibration dynamic absorber was applied to the turbocharger model with reduced degrees of freedom and its influnce on vibrations of actuator bracket was investigated. Significant decrease of the maximum acceleration amplitude was achieved in a given frequency range when absorber parameters were optimized.
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Kosaraju, Nikhil Maharshi. "Dynamic Analysis of an Automotive Power Transfer unit : Towards prediction of TE and housing vibrations." Thesis, KTH, Maskinkonstruktion (Avd.), 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-259683.
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This work describes the use of Multi-Body Simulation (MBS) to create a virtual prototype of a geared drive called Power transfer unit (PTU). PTU is a subsystem of the all-wheel drive driveline responsible for transfer of power between front and rear axles in an Automobile. The objective of the developing the prototype is to simulate the dynamic behavior of the PTU. Focus is on predicting the gear transmission error(TE) and gearbox housing vibration level. A Hypoid gear set, bearings, tubular shaft and housing are the major components in the PTU. This work is carried out at GKN Automotive which specializes in development of Automotive All wheel drive systems. When developing such geared systems one important characteristic analyzed is the noise and vibration it generates. And for companies like GKN it is desirable to predict these characteristics as early as possible for two reasons, to avoid late design changes and to speed up the product development cycle. To achieve this, a validated virtual model which is computationally efficient is desired. The methodology followed contains of two facets, development of the MBS model and validation of the developed model with physical testing. An integrated MBS-FEM approach is used, an FE modal reduction technique is used to create flexible components with which a virtual prototype is built and simulated in an MBS tool MSC ADAMS c . Gear contact and bearings are defined using an analytical approach which considers the nonlinear stiffness and damping. A dynamic analysis and system level modal analysis is performed to predict the TE, housing vibrations and PTU modal parameters. Experimental modal analysis and physical testing on test rig are performed to measure the actual values of the above predicted outputs. Parameters like damping, contact stiffness of the model are then tuned to achieve correlation. When comparing test and prediction, close correlation is seen in the TE and for housing vibration a similar trend is observed with some deviations. Predicted TE is heavily dependent on gear contact parameters. On the modal parameter comparison, a correlation of five modes and mode shapes below 2500Hz is seen which shows the validity of the MBS model. Parameter studies are performed to study the effect of bearing damping and preload on housing vibrations and TE. It is observed that an optimum value of preload and damping is essential to avoid unnecessary vibrations. In conclusion, the model with some fine tuning of damping parameters can be used for virtual noise and vibration analysis of the PTU.<br>Detta arbete beskriver anv¨andningen av beräkningsmetoden Multi-Body Simulation (MBS) för att skapa en virtuell prototyp av en vinkelväxel (Power Transfer Unit, PTU ). PTU är ett delsystem för fyrhjulsdrift som har funktionen att överföra kraft mellan fram- och bakaxlar i en bil. Målet med att utveckla modellen är att simulera PTUns dynamiska beteende. Fokus ligger på att beräkna vinkelväxelns transmissionsfel och vibrationsnivåer på växellådans hus. De vikitgaste komponenterna i PTUn är hypoidväxeln med kronhjul och pinjong, röraxel, lager och hus. Detta arbete har utförts på GKN Automotive som är specialiserade på utveckling av drivsystem för fyhjulsdrivna bilar. Ljud och vibrationer är viktiga egenskaper att ta hänsyn till under utvecklingen. För företag som GKN är det önskvärt att kunna beräkna dessa egenskaper så tidigt i projektet av två skäl: dels för att undvika sena konstruktionsförändringar och dels att påskynda produktutvecklingscykeln. För att uppnå detta behövs en validerad virtuell modell som är beräkningseffektiv. Den metod som använts innehåller två delar: utveckling av MBS-modellen och validering av den utvecklade modellen med fysisk testning. En integrerad MBS-FEM -mettod har använts. Det innebär att en FE-modal reduktionsteknik andvänds för att skapa flexibla komponenter med vilka en virtuell prototyp byggs och simuleras i ett MBS-verktyg (MSC ADAMS (c) ). Lager och kuggkontakt i växeln definieras med hjälp av en analytisk metod som beaktar den olinjära styvheten och dämpningen. En dynamisk analys och modalanalys på systemnivå har utförts för att beräkna TE, husvibrationer och PTUns modala parametrar. Experimentell modalanalys och testning i rigg gjorts för att mäta motsvarande värden som har beräknats. Parametrar som dämpning och kontaktstyvhet har sedan justerats för att uppnå korrelation. Vid jämförelse av test och förutsägelse ses en god korrelation i TE och för husvibrationer observeras en liknande trend, med vissa avvikelser. Beräknat TE är starkt beroende på parametrar för kuggkontakten i växeln. Vid jämförelse av modala parametrar ses en god korrelation under 2500 Hz mellan fem moder i mätning och beräkning vad gäller frekvens och modform, vilket visar MBS-modellens giltighet. Parameterstudier har utförts för att studera effekten av lagerdämpning och förbelastning på TE och husvibrationer. Ett optimalt värde på förbelastning och dämpning är viktigt för att undvika onödiga vibrationer. Sammanfattningsvis kan modellen med viss finjustering av dämpningsparametrar användas i virtuell ljud- och vibrationsanalys av PTU.
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Level, Pascal. "Contribution à l'élaboration d'une stratégie de calcul en dynamique des grandes structures : Développement et intégration des méthodes de réanalyse modale." Valenciennes, 1989. https://ged.uphf.fr/nuxeo/site/esupversions/ddd3277b-ac0d-4f10-a671-4f9e5d5af490.
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Etude de cinq méthodes de réanalyse modale, évitant le calcul direct des nouvelles solutions propres après modification de la structure; implantation numérique et calculs d'essai. Détermination de la meilleure méthode (méthode de partition des matrices de modification)
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Bleichner, Noah G. "A Comparative Study on Seismic Analysis Methods and the Response of Systems with Classical and Nonclassical Damping." DigitalCommons@CalPoly, 2020. https://digitalcommons.calpoly.edu/theses/2219.
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This thesis investigated the application of seismic analysis methods and the response of idealized shear frames subjected to seismic loading. To complete this research, a Design Basis Earthquake (DBE) for a project site in San Luis Obispo, CA, and five past earthquake records were considered. The DBE was produced per the American Society of Civil Engineers’ Minimum Design Loads for Buildings and Other Structures (ASCE 7-10) and used for application of the Equivalent Lateral Force Procedure (ELFP) and Response Spectrum Analysis (RSA). When applying RSA, the modal peak responses were combined using the Absolute Sum (ABS), Square-Root-of-the-Sum-of-Squares (SRSS), and Complete Quadratic Combination (CQC) method.
MATLAB scripts were developed to produce several displacement, velocity, and acceleration spectrums for each earthquake. Moreover, MATLAB scripts were written to yield both analytical and numerical solutions for each system through application of Linear Time History Analysis (THA). To obtain analytical solutions, two implicit forms of the Newmark-beta Method were employed: the Average Acceleration Method and the Linear Acceleration Method.
To generate a comparison, the ELFP, RSA, and THA methods were applied to shear frames up to ten stories in height. The system parameters that impacted the accuracy of each method and the response of the systems were analyzed, including the effects of classical damping and nonclassical damping models. In addition to varying levels of Rayleigh damping, non-linear hysteric friction spring dampers (FSDs) were implemented into the systems. The design of the FSDs was based on target stiffness values, which were defined as portions of the system’s lateral stiffness. To perform the required Nonlinear Time History Analysis (NTHA), a SAP2000 model was developed. The efficiencies of the FSDs at each target stiffness, with and without the addition of low levels of viscous modal damping are analyzed.
It was concluded that the ELFP should be supplemented by RSA when performing seismic response analysis. Regardless of system parameters, the ELFP yielded system responses 30% to 50% higher than RSA when combing responses with the SRSS or CQC method. When applying RSA, the ABS method produced inconsistent and inaccurate results, whereas the SRSS and CQC results were similar for regular, symmetric systems. Generally, the SRSS and CQC results were within 5% of the analytical solution yielded through THA. On the contrary, for irregular structures, the SRSS method significantly underestimated the response, and the CQC method was four to five times more accurate. Additionally, both the Average Acceleration Method and Linear Acceleration Method yielded numerical solutions with errors typically below 1% when compared with the analytical solution.
When implemented into the systems, the FSDs proved to be most efficient when designed to have stiffnesses that were 50% of the lateral stiffness of each story. The addition of 1% modal damping to the FSDs resulted in quicker energy dissipation without significantly reducing the peak response of the system. At a stiffness of 50%, the FSDs reduced the displacement response by 40% to 60% when compared with 5% modal damping. Additionally, the FSDs at low stiffnesses exhibited the effects of negative lateral stiffness due to P-delta effects when the earthquake ground motions were too weak to induce sliding in the ring assemblies.
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Althoff, Eric C. "Detailed and Simplified Structural Modeling and Dynamic Analysis of Nuclear Power Plant Structures." The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1492642525831339.
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IBISEVIC, AIDA, and HASANHÜSEYIN UGUR. "Numerical and experimental dynamic analyses of Hägernäs pedestrian bridge : Including seasonal effects." Thesis, KTH, Bro- och stålbyggnad, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-254550.
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Wood as a construction material has in recent years increased, in particular concerningpedestrian bridges. By utilizing wood, the ecological footprint can be reduced,and the material can be designed to comply with the increasing aesthetic demandbridge designers are facing. However, as the material weighs little with respect toits bearing capacity, combined with design becoming more slender, human inducedvibrations are becoming a problem.Having this in mind, the objective of the thesis is to conduct a case study on anexisting timber pedestrian bridge and assess its dynamic parameters by means ofexperiential testing and numerical modelling. The case study concerns the Hägernäsbridge, an arch bridge located in Hägernäs, Täby. The thesis also considers seasonaleffects by conducting experiments on two separate occasions. In addition, the thesisevaluates influencing parameters on the dynamic behaviour by conducting a sensitivityanalysis. To aid the above mentioned objective, a literature review coveringsimilar type of analysis is conducted. The literature review also studies the seasonaleffect, mainly from the asphalt layer, as its stiffness contribution is temperaturedependant.The results from the dynamic parameters showed that not all modes fall above therecommended values concerning damping ratio (with values above 1-1.5%). However,all modes fulfill design criteria concerning the magnitude of the natural frequencies.Furthermore, results showed that the natural frequencies are highly temperaturedependant. The measured values during warm weather (+17C) resulted in lowervalues than those from the cold weather experiment (-10C). Moreover, the greatestdifference, by 21% was on the 1st transverse mode and the lower difference was onthe 1st vertical mode, that decreased by merely 5%. Moreover, the damping ratiowas calculated and it was not possible to find any correlation between warm andcold temperature. Instead, decreased temperature caused some modes to increase indamping ratio and others to decrease. The most affected mode was once again the1st transverse mode which increased by 146% going from warm to cold temperature
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Brol, Kellen Aparecida. "Modelagem de estrutura de suporte." [s.n.], 2011. http://repositorio.unicamp.br/jspui/handle/REPOSIP/263808.
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Orientador: Katia Lucchesi Cavalca<br>Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica<br>Made available in DSpace on 2018-08-17T18:55:49Z (GMT). No. of bitstreams: 1
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Previous issue date: 2011<br>Resumo: Uma máquina rotativa é composta por muitos componentes interconectados, que atuam em conjunto e a influência mútua ocasiona uma grande variedade de fenômenos durante seu funcionamento. Os modelos matemáticos visam simular o comportamento dinâmico destes sistemas, com o objetivo de representar uma condição real, e para ser útil na previsão da resposta do sistema. Esse tipo de informação pode ser aplicado na solução de problemas durante a fase de projeto, e, além disso, pode servir como entrada em modelos baseados nas técnicas de diagnósticos de falhas. Neste caso, um modelo computacional robusto permite um "design" otimizado, redução de custos e melhoria da confiabilidade. O objetivo deste trabalho é observar a influência da estrutura de suporte ou fundação no comportamento dinâmico de uma estrutura através dos métodos de impedância mecânica e coordenadas modais, sendo neste último caso, aplicando a redução modal e análise de sensibilidade qualitativa da mesma na influência da resposta dinâmica do sistema. A fundação é responsável pelo suporte do rotor, através da interconexão com os mancais. Os mancais transmitem à fundação, as forças causadas pelo movimento do rotor, como no desbalanceamento e vice-versa. Os modos de vibrar da fundação são excitados no intervalo de freqüência do rotor são também transmitidos através dos mancais de volta ao rotor. O método de coordenadas mistas usualmente considera o amortecimento estrutural proporcional e, portanto, ele representa o sistema em coordenadas modais desacopladas. Assim, foi verificada a igualdade entre os métodos de análise considerando todos os modos; para a combinação de modos reduzidos foi determinado o número mínimo de modos que representam a estrutura de suporte com amortecimento proporcional e não proporcional e a maneira como o amortecimento ficava acoplado ao sistema; e no caso do método das coordenadas mistas com uma fundação experimental de entrada, determinou-se o número mínimo de modos quando acoplados ou desacoplados ao sistema e tipo de amortecimento estrutural da fundação<br>Abstract: A rotating machine is composed by many interconnected components that work together and therefore they influence each other causing a wide range of phenomena during operation. The mathematical models allow to simulate the dynamic behavior of these systems in order to represent the reality, and, then, to be useful in predicting the system response. Such information can be applied to solve problems during the design phase, and, moreover, it can be the input to model based on failure diagnosis techniques. In this case, a robust computational model also enables the design optimization, cost reduction and reliability improvement. The objective of this work is to observe the support structure, or foundation, influence in the dynamic behavior of a structure through the methods of mechanical impedance and modal coordinates, and in the latter case, applying the reduced modal and sensitivity analysis of the same qualitative influence on the system dynamics response. The foundation is responsible for supporting the rotor, through interconnection with the bearings. The bearings transmit the foundation forces caused by the rotor movement, as those due to the mass imbalance, and vice versa. The vibration modes of the foundation are excited in the rotor frequency range also transmitted through the bearings back into the rotor. The coordinate method usually considers the mixed proportional structural damping, and therefore it represents the system in modal coordinates uncoupled. Thus was established the equality between the analysis methods for all modes; for the reduced modes combination was determined the minimum modes number that represent the support structure with proportional damping and non-proportional damping and the way that was connected to the system; and in the case the mixed coordinates method with a experimental foundation input, it was determined the minimum modes number when coupled and uncoupled system and the type of foundation structural damping<br>Mestrado<br>Mecanica dos Sólidos e Projeto Mecanico<br>Mestre em Engenharia Mecânica
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Gillet, Guillaume. "Simply supported composite railway bridge: a comparison of ballasted and ballastless track alternatives : Case of the Banafjäl Bridge." Thesis, KTH, Bro- och stålbyggnad, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-36359.
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Petersson, Viktor, and Andreas Svanberg. "Operational modal analysis and finite element modeling of a low-rise timber building." Thesis, Linnéuniversitetet, Institutionen för byggteknik (BY), 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-105208.
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Timber is a building material that is becoming more common and of interest for use in high-rise buildings. One of the reasons is that timber requires less energy input for the manufacturing process of the material compared to non-wood based materials. When designing high- rise timber buildings it is of great significance to understand the dynamic behavior of the structure. One method to obtain the dynamic properties is to use Operational Modal Analysis, which is based on the structural response from operational use. Finite element (FE) analysis is a tool which can be used for dynamic analysis for large structures. In this study an Operation Modal Analysis (OMA) was conducted on a four-story timber building in Växjö. A finite element model was created of the same building using commercial FE packages. Based on the mode shapes and natural frequencies obtained from the OMA, the FE model was fine-tuned. The purpose of this thesis is to gain knowledge of which parameters that might have a significant role in finite element modelling for a structural dynamic analysis. The aim is to develop a finite element model that accurately simulates the dynamic behavior of the tested building. It was shown from the result that is possible with an enough detailed FE model to capture the dynamic behaviour of a structure. The parameters that had the largest effect on the result can be pointed to the mass and the stiffness of the structure.<br>Trä är ett byggnadsmaterial som börjar bli allt mer vanligt och är av intresse att använda som stommaterial för höga byggnader. En anledning till detta är att det krävs mindre energi i tillverkningsfasen för trä jämfört med stål och betong. Vid dimensionering av höga träbyggnader är det essentiellt att förstå byggnadens dynamiska egenskaper. För att ta fram en byggnads dynamiska egenskaper kan en metod som benämns Operational Modal Analysis (OMA) tillämpas vilken baseras på byggnadens rörelser vid daglig användning. Finita element (FE) metoden är ett verktyg som kan användas vid dynamisk analys för större byggnader. I detta arbete genomfördes en OMA för ett fyravåningshus med trästomme beläget i Växjö. Genom användning av kommersiella FE-mjukvaror togs en finita element modell av samma byggnad fram. Baserat på de egenfrekvenser och egenmoder erhållna från OMA, uppdaterades FE-modellen därefter. Syftet med detta arbete är att erhålla kunskap kring vilka parametrar som har betydelse vid FE-modellering med hänsyn till dynamisk analys. Syftet är även att validera den prototyp av datainsamlingsenhet som använts vid fältmätningen. Målet med arbetet är att ta fram en FE-modell som på ett korrekt sätt beskriver den testade byggnadens dynamiska beteende. Resultatet av arbetet påvisar att med en tillräckligt detaljerad FE-modell är det möjligt att erhålla en byggnads dynamiska egenskaper. De parametrar som har störst inverkan på resultatet är byggnadens styvhet och inkluderad massa.
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Kosta, Tomislav. "Meshfree Modeling of Vibrations of Mechanical Strctures." FIU Digital Commons, 2013. http://digitalcommons.fiu.edu/etd/1032.
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In this work, a pioneering application of the Solution Structure Method (SSM) for structural dynamics problems is presented. Vibration analysis is an important aspect of any design-analysis cycle for which reliable computational methods are required. Unlike many meshfree methods, SSM is capable of {\it exact treatment of all prescribed boundary conditions}. In addition, the method is capable of using basis functions which do not conform to the shape of the geometric model. Together, this defines an unprecedented geometric flexibility of the SSM.
This work focused on the development of numerical algorithms for 2D in-plane and 3D natural vibration analysis and 2D in-plane dynamic response. The convergence and numerical properties of the method were evaluated by comparing meshfree results with those obtained using traditional Finite Element Analysis implemented in Solidworks and ANSYS.
The numerical experiments presented in this work illustrate that the Solution Structure Method possesses good convergence and in some cases, such as geometries with partially fixed boundaries, this method converges much more rapidly than traditional FEA. Finally, in addition to complex boundary conditions, this method can easily handle complex geometries without losing favorable convergence properties.
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Santos, Cody Joshua. "Dynamic Testing for a Steel Truss Bridge for the Long Term Bridge Performance Program." DigitalCommons@USU, 2011. https://digitalcommons.usu.edu/etd/894.
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Under the direction of the Federal Highway Administration the Long Term Bridge Performance Program (LTBP) selected Minnesota Bridge number 5718 as a pilot bridge for evaluation. This program focuses on the monitoring of bridges for a 20-year period to understand the structural behavior over time due to the various loads and weathering. In monitoring this bridge a better understanding can be acquired for the maintenance issues related to the nation's deteriorating bridge infrastructure.
Bridge Number 5718, which is located just outside of Sandstone Minnesota, is a steel truss bridge that spans the Kettle River. Constant monitoring of the bridge along with periodic testing of the bridge will allow for the collection of data over a 20-year period. The focus of this work is to establish a baseline for the bridges characteristics through nondestructive dynamic testing. Later tests will be compared to these results and changes can then be tracked.
In order to perform the required testing, two electromagnetic shakers were used to produce the excitation. The bridge was also outfitted with an array of velocity transducers to allow for the response to be recorded. The data was then used to extract the resonant frequencies, mode shapes, and damping ratios. A modal assurance criterion was also performed to solidify the findings. These parameters define the structural identity of the bridge. Through performing these tests the database that is being collected under the Long Term Bridge Performance Program will be used to better the overall health and safety of the nation's bridges.
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Glovina, Filip. "Zavěšený most přes rychlostní komunikaci R52." Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2012. http://www.nusl.cz/ntk/nusl-225504.
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This work deals with statics and dynamics analysis of stayed cable bridge and design of supporting structure according to limit states. The work contains of static calculation, drawing documentation and visualization.
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Ur-Rashid, Md Masud. "Characterization of Dynamic Elastic Modulus and Damping Property of CNx Coating Material by Experimental Modal Analysis and Finite Element Approach." Thesis, KTH, Industriell produktion, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-138868.
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Free-layer hard or soft coating material can be used for enhancing the inherent damping capacity (energy dissipation ability) of a structure under cyclic bending deformation. This may help to attenuate the vibration amplitude at the resonance frequency. In this study, dynamic mechanical and damping properties of a carbon based (CNx) coating material have been investigated. For determining the material properties of this coating, two samples (600 μm and 800 μm thick carbon nitride (CNx) film layers) were produced and deposited onto two internal turning tools by using the plasma enhanced chemical vapor deposition (PECVD) process. The deposition process was conducted at the room temperature with the magnetron sputtering of a copper and a subsequent graphite target plate in a highly ionized plasma and reactive environment of Ar, N2 and C2H2 gases. Eigen frequencies and system loss factors of the uncoated and coated tools were extracted, for the first two fundamental bending modes (mode X and mode Y), from the ‘drive point’ measurements of free hanging impact tests at the free-free boundary condition. Modulus of elasticity and loss factor of the coating material has been deduced through the comparison between the eigen frequencies and resonance amplitudes of the identical bending modes extracted from the experimental and analytical frequency response functions. The results obtained from the experimental modal analyses and the iterative finite element analyses show that, compared to the substrate, the flexural stiffness and the damping capacity of the coated tools have increased notably. The resonant frequencies of the coated samples have been shifted to the higher frequency levels, and the frequency response acceleration amplitudes have been attenuated dramatically. Elastic modulus and loss factor range of the coating material have been found to be in the range of 32.5 GPa to 49.1 GPa and 0.004 to 0.0245 respectively. Comparison between the analytical frequency response functions of the CNx coating material and 3M-112 viscoelastic material coated samples (for 800 μm film thickness) has anticipated that the coating material has higher loss modulus (energy dissipation ability) as opposed to the viscoelastic material. Scanning electron microscope images of the cross-section of a coated sample have revealed that the frictional energy losses between the interfaces of the carbon-nitride columnar micro-structures dominate the inherent damping mechanism of the coating material. Voids and porosities, present between the columnar clusters, further increase the energy dissipation ability of the coating material by enhancing the interface slippage mechanism during the cyclic bending deformation.
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Hall, Braydon Day. "The Dynamic Analysis of a Composite Overwrapped Gun Barrel with Constrained Viscoelastic Damping Layers Using the Modal Strain Energy Method." DigitalCommons@USU, 2013. https://digitalcommons.usu.edu/etd/1972.
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The effects of a composite overwrapped gun barrel with viscoelastic damping layers are investigated. Interlaminar stresses and constrained layer damping effects are described. The Modal Strain Energy method is developed for measuring the extent to which the barrel is damped. The equations of motion used in the finite element analysis are derived. The transient solution process is outlined. Decisions for selected parameters are discussed. The results of the finite element analyses are presented using the program written in FORTRAN. The static solution is solved with a constant internal pressure resulting in a calculated loss factor from the Modal Strain Energy Method. The transient solution is solved using the Newmark-Beta method and a variable internal pressure. The analyses conclude that strategically placed viscoelastic layers dissipate strain energy more effectively than a thick single viscoelastic layer. The optimal angle for maximizing the coefficient of mutual influence in a composite cylinder is not necessarily the optimal angle when viscoelastic layers are introduced between layers.