Dissertations / Theses: 'Frequency Response Function(FRF)'

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Vasudeva, Vikas. "Characterization of MEMS devices on the basis of their frequency response function (FRF)." abstract and full text PDF (free order & download UNR users only), 2007. http://0-gateway.proquest.com.innopac.library.unr.edu/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:1447635.

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Majba, Christopher. "A Review of Uncertainty Quanitification of Estimation of Frequency Response Functions." University of Cincinnati / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1346171022.

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Ozturk, Murat. "Finite Element Structural Model Updating By Using Experimental Frequency Response Functions." Master's thesis, METU, 2009. http://etd.lib.metu.edu.tr/upload/2/12610608/index.pdf.

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Initial forms of analytical models created to simulate real engineering structures may generally yield dynamic response predictions different than those obtained from experimental tests. Since testing a real structure under every possible excitation is not practical, it is essential to transform the initial mathematical model to a model which reflects the characteristics of the actual structure in a better way. By using structural model updating techniques, the initial mathematical model is adjusted so that it simulates the experimental measurements more closely. In this study, a sensitivity-based finite element (FE) model updating method using experimental frequency response (FRF) data is presented. This study bases on a technique developed in an earlier study on the computation of the so-called Mis-correlation Index (MCI) used for identifying the system matrices which require updating. MCI values are calculated for each required coordinate, and non-zero numerical values indicate coordinates carrying error. In this work a new model updating procedure based on the minimization of this index is developed. The method uses sensitivity approach. FE models are iteratively updated by minimizing MCI values using sensitivities. The validation of the method is realized through some case studies. In order to demonstrate the application of the method for real systems, a real test data obtained from the modal test of a scaled aircraft model (GARTEUR SM-AG19) is used. In the application, the FE model of the scaled aircraft is updated. In the case studies the generic software developed in this study is used along with some commercial programs.

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Johansson, Tim, and Magdalena Cwenarkiewicz. "Experimental Dynamic Substructuring of an Ampair 600 Wind Turbine Hub together with Two Blades : A Study of the Transmission Simulator Method." Thesis, Linnéuniversitetet, Institutionen för maskinteknik (MT), 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-53605.

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In this work, the feasibility to perform substructuring technique with experimental data is demonstrated. This investigation examines two structures with different additional mass‑loads, i.e. transmission simulators (TSs). The two structures are a single blade and the hub together with two blades from an Ampair 600 wind turbine. Simulation data from finite element models of the TSs are numerically decoupled from each of the two structures. The resulting two structures are coupled to each other. The calculations are made exclusively in the frequency domain. A comparison between the predicted behavior from this assembled structure and measurements on the full hub with all three blades is carried out. The result is discouraging for the implemented method. It shows major problems, even though the measurements were performed in a laboratory environment.

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Sharma, Akhil. "A New Multiple Input Random Excitation Technique Utilizing Pneumatic Cylinders." University of Cincinnati / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1470671978.

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Patwardhan, Rohit S. "Frequency Response and Coherence function estimation methods." University of Cincinnati / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1592169805143687.

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Schulte, Walter B. III. "The frequency response, impulse response, and transfer function of an ocean waveguide." Thesis, Monterey, California. Naval Postgraduate School, 2004. http://hdl.handle.net/10945/1516.

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Approved for public release, distribution is unlimited In this thesis, the ocean was modeled as a waveguide with an ideal pressure - release surface, and an ideal rigid bottom. The ocean waveguide was then treated as a linear, time - invariant, space - variant (TISV) filter or communication channel. The filter is time - invariant because no motion was modeled and because the properties of the ocean were assumed to be constant. The filter is space - variant because of the presence of the two boundaries, that is, the ocean surface and ocean bottom. This thesis investigates the ocean as a linear TISV filter by evaluating 1) the complex frequency response, 2) the impulse response, and 3) the transfer function of the ocean with respect to depth. It is shown that the TISV impulse response of the ocean contains information that can be used to help localize a target in range and whether the target is above or below the receiver. Computer simulation results were obtained by evaluating the three filter functions for several different test cases. Ensign, United States Navy

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Schulte, Walter B. "The frequency response, impulse response, and transfer function of an ocean waveguide /." Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2004. http://library.nps.navy.mil/uhtbin/hyperion/04Jun%5FSchulte.pdf.

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Thesis (M.S. in Applied Science (Signal Processing))--Naval Postgraduate School, June 2004. Thesis advisor(s): Lawrence J. Ziomek. Includes bibliographical references (p. 47). Also available online.

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Kim, Youngtae. "Spatial resolution limits for the reconstruction of acoustic source distribution by inverse techniques." Thesis, University of Southampton, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.274706.

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McCune, Robert E. "Identification of Continuous-Time and Discrete-Time Transfer Function Models from Frequency Response Measurements." Ohio University / OhioLINK, 1989. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1239731009.

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Hassan, Pour Dargah Mahmoud. "Effects of Shaker Impedance and Transducer Cross-Axis Sensitivity in Frequency Response Function Estimation." University of Cincinnati / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1342729500.

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Badri, Abdellatef E. O. "Performance improvement of MEMS accelerometers in vibration based diagnosis." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/performance-improvement-of-mems-accelerometers-in-vibration-based-diagnosis(f407deb3-6af5-476c-bbc7-c101873ced32).html.

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Vibration measurement and analysis has been an accepted method since decades to meet a number of objectives - machinery condition monitoring, dynamic qualification of any designed structural components, prediction of faults and structural aging-related problems, and several other structural dynamics studies and diagnosis. However, the requirement of the vibration measurement at number of locations in structures, machines and/or equipments makes the vibration measurement exorbitant if conventional piezoelectric accelerometers are used. Hence, there is a need for cheaper and reliable alternative for the conventional accelerometers. The Micro-Electro-Mechanical Systems (MEMS) accelerometers are one such cheap alternative. However, a significant deviation in the performance of the MEMS accelerometers has been observed in earlier research studies and also confirmed by this presented study when compared with well known conventional accelerometer. Therefore, two methods have been suggested to improve the performance of the existing MEMS accelerometers; one for correction in time domain and other in frequency domain. Both methods are based on the generation of a characteristic function (CF) for the MEMS accelerometer using well known reference accelerometer in laboratory tests. The procedures of both methods have been discussed and validations of these methods have been presented through experimental examples. In addition, a Finite Element (FE) model of a typical MEMS accelerometer has been developed and modal analysis has been carried out to understand the dynamics of capacitive type MEMS accelerometer and to identify the source of errors. It has been observed that the moving fingers behave like a cantilever beam while the fixed fingers showed rigid body motion. This cantilever type of motion seems to be causing non-parallel plates effect in the formed capacitors between moving and fixed fingers which results in errors in the vibration measurement. Hence, design modifications on finger shape have been suggested to remove the cantilever motion and results showed remarkable improvement. Moreover, the effect of using synchronous amplitude modulation and demodulation in the readout circuit has been studied. The experimental study showed that this circuit also introduces errors in amplitude and phase of the output signal compared with the input signal. Thus, in the new design of MEMS accelerometers, improvements in both mechanical design and electronic circuit are required.

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Deshpande, Anirudh Gururaj. "Parameter study of bodywork attachments influencing the chassis dynamics by vibration response analysis." Thesis, KTH, Maskinkonstruktion (Inst.), 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-232452.

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Bilindustrin är i ständig utveckling och är väl medvetna om de ökande kraven från kundermed avseende på körkomfort och körupplevelse. Lastbilar med tunga laster är ofta utrustademed en påbyggnad, till exempel en låda för pallar och gods, en sopsamlare eller en stödram förbärning av timmer. SCANIA Bodybuilding Center utvecklar riktlinjer för val av olika typer avkarosseri, dvs typ av stödram och antal , fästpunkter. Målet med detta arbete är att utvecklaen bättre förståelse för hur det stödjande ramverket och dess infästningar i en lastbil påverkarrammens dynamik och sedan föreslå förbättringar till dessa riktlinjer.Viktiga parametrar som påverkar chassisdynamiken identifierades och beskrivs från början.Fysisk vibrationstestning av chassiet och påbyggnadsram med fasthållningsfäste utfördes vidi testrigg på Scania R&D. Frekvensresponsfunktionerna från mätningarna användes för attbestämma modala parametrar. Olika test utfördes genom att ändra parametrarna och upptagningenav mätningarna. Testresultaten användes för att studera egenfrekvenser egna frekvenser,modifieringsformer och dämpning i systemet. Även en ny metod för att bygga en dynamiskfinit element (FE) modell eller chassi och påbyggnadsram är presenterad i denna undersökning.Modalanalys av chassi-påbygnadsramssystemet gjordes för att studera FEMs egna frekvenseroch modeformer. Den föreslagna metoden för koppling av chassit och delramen i FEM är kritisktbedömd genom att korrelera FE-simuleringen med de experimentella resultaten. Baserat på deutförda experimenten och den numeriska simuleringen föreslås från experiment och numerisksimulering, föreslås nya rekommendationer med avseende på påbyggnadsanslutningarnas konfigurationi lastbil. The automotive sector is continuously evolving and the companies are well aware of therising demands from customers with regard to driving comfort and experience. Trucks carryingheavy loads are often equipped with on-built bodywork, for example a box for pallets and goods, agarbage collector device or a supporting frame for carrying timber. SCANIA bodybuilding centredevelops guidelines for selecting different types of bodywork, i.e. the type of supporting frame,design and number of attachment brackets, attachment points. The purpose of this master thesisis to develop a better understanding of how the supporting frame and its attachments in a truckinfluence the chassis frame dynamics and to propose improvements to these guidelines.Major parameters influencing the chassis dynamics were identified and described from theoutset. Physical vibration testing of the chassis-subframe assembly was carried out at roadsimulator. The frequency response functions from the measurements were used to determinethe modal parameters. Several tests were performed by altering the parameters and recordingthe measurements. The results from the test cases were used to study and analyse the eigenfrequencies, mode shapes and damping in the system. Also, a new method to build a dynamicfinite element (FE) model of chassis and subframe is presented in this study. Modal analysisof the chassis-subframe assembly was done to study the eigen frequencies and mode shapes byFEM. The proposed method of coupling the chassis and the subframe is critically assessed bycorrelating the results from FE simulation with the experimental results. Based on the resultsfrom experiment and numerical simulation, new recommendations are proposed with regard tothe bodywork attachments’ configuration in the truck.

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Cobb, Richard E. "Confidence bands, measurement noise, and multiple input - multiple output measurements using three-channel frequency response function estimator." Diss., Virginia Polytechnic Institute and State University, 1988. http://hdl.handle.net/10919/53675.

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A three-channel Frequency Response Function (FRF) estimator is discussed and statistical relations developed. Methods for estimating the variance of the FRF magnitude and levels of uncorrelated content in the test signals are developed. FRF magnitude variance estimates allow ’confidence bands’ to be placed on FRF magnitude estimates, giving an indication of the variability of the result. Uncorrelated content estimates indicate sources and magnitudes of noise in the measurement system. Both Monte Carlo simulations and experimental work are used to verify the statistical and uncorrelated content estimates. Relations to extend the three-channel FRF estimator to multiple input-multiple output measurements are developed and verified through simulations. Ph. D.

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Schwartz, Jeffrey R. "An Experimental and Analytical Investigation of Dynamic Flow Response of a Fan Rotor with Distorted Inlet Flow." Thesis, Virginia Tech, 1999. http://hdl.handle.net/10919/44314.

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An experimental and analytical investigation was conducted to gain insight and ultimately predict the dynamic flow response of a fan rotor with inlet flow distortion. Rotor exit total pressure circumferential profiles were accurately predicted using frequency response functions derived from experimental rotor response data. Using these predicted profiles, an initial attempt was made at predicting the dynamic (distorted) stage characteristics of the test machine with promising results. The first step of this research was an experimental investigation to gather unsteady rotor response data. The steady three-dimensional inlet flow of an isolated rotor subjected to inlet distortion was obtained using a five-hole pneumatic prism probe. Exit flow dynamic wake data were obtained using a piggyback steady/unsteady total pressure probe in non-nulling mode. Inlet and exit data were collected for eighteen different combinations of distortion level, operating point, and measurement span. Frequency response functions were generated and then averaged for each operating regime, span, and distortion intensity, assuming the data to be stationary and ergodic. These 'generalized' FRF's were used to predict the rotor exit total pressure profile. These pressure profiles were then used in an initial attempt to predict the dynamic stage (distorted) characteristics of the test machine. Best predictions resulted when an FRF was used for individual operating regimes, defined with respect to rotor blade mean aerodynamic loading. Master of Science

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16

Thomas, Edward John. "A C++ class library capable of handling matrix, polynomial, transfer function, state space, and frequency response data types." Ohio : Ohio University, 1995. http://www.ohiolink.edu/etd/view.cgi?ohiou1178902180.

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Hall, Melissa A. "Characterization of Vibration Test Fixtures using Modal Analysis." University of Cincinnati / OhioLINK, 2021. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1627664784639955.

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Xu, Weiwei. "Effect of Bolted Joint Preload on Structural Damping." Scholar Commons, 2013. http://scholarcommons.usf.edu/etd/4794.

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Bolted joints are integral parts of mechanical systems, and bolt preload loss is one of the major failure modes for bolted joint structures. Understanding the damping and frequency response to a varying preload in a single-bolted lap-joint structure can be very helpful in predicting and analyzing more complicated structures connected by these joints. In this thesis, the relationship between the bolt preload and the natural frequency, and the relationship between the bolt preload and the structural damping, have both been investigated through impact hammer testing on a single-bolted lap-joint structure. The test data revealed that the bolt preload has nonlinear effects on the structural damping and on the natural frequency of the structure. The damping ratios of the test structure were determined to increase with decreasing preload. An increase in structural damping is beneficial in most engineering circumstances, for it will reduce the vibrational response and noise subjected to external excitations. It was also observed that the modal frequency increased with increasing preload, but remained approximately constant for preload larger than 30% in the bolt yield strength. One application for studying the preload effect is the detection for loose bolts in structures. The possibility of using impact testing for estimating preload loss has been confirmed, and the modal damping was determined to be a more sensitive indicator than the natural frequency in a single-bolted lap-joint structure.

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19

Chatterjee, Prateep. "A Computational Fluid Dynamics Investigation of Thermoacoustic Instabilities in Premixed Laminar and Turbulent Combustion Systems." Diss., Virginia Tech, 2004. http://hdl.handle.net/10919/11209.

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Lean premixed combustors have been designed to lower NOx and other pollutant levels in land based gas turbines. These combustors are often susceptible to thermo-acoustic instabilities, which manifest as pressure and heat release oscillations in the combustor. To be able to predict and control these instabilities, it is required that both the acoustics of the system, and a frequency-resolved response of the combustion process to incoming perturbations be understood. Currently, a system-level approach is being used widely to predict the thermoacoustic instabilities. This approach requires simple, yet accurate models which would describe the behavior of each dynamic block within the loop. The present study is directed toward using computational fluid dynamics (CFD) as a tool in developing reduced order models for the dynamics of laminar flat flames and swirl stabilized turbulent flames. A finite-volume based approach is being used to simulate reacting flows in both laminar and turbulent combustors. The study has been divided into three parts -- the first part involves the modeling of a self-excited combustor (the acoustics of the combustor are coupled with the unsteady heat release); the second part of the research aims to study the effect of velocity perturbations on the unsteady heat release rate from a burner stabilized laminar flat flame; the third and final part of work involves an extension of the laminar flat flame study to turbulent reacting flows in a swirl stabilized combustor, and study the effects on the turbulent heat release due to the velocity perturbations. A Rijke tube combustor was selected to study self-excited combustion phenomenon. A laminar premixed methane-air flat flame was stabilized on a honeycomb flame-stabilizer. The flame stabilizer was placed at the center of the 5 feet vertical tube. The position of the flame at the center of the tube leads to a thermoacoustic instability of the 2nd acoustic mode. The fundamental thermoacoustic frequency was predicted accurately by the CFD model and the amplitude was reasonably matched (for a flow rate of Q = 120 cc/s and equivalence ratio phi = 1.0). Other characteristics of the pressure power spectrum were captured to a good degree of accuracy. This included the amplitude modulation of the fundamental and the harmonics due to a subsonic pulsating instability. The flat flame study has been being conducted for Q = 200 cc/s and equivalence ratio phi = 0.75. The objective has been to obtain a frequency response function (FRF) of the unsteady heat release rate (output) due to incoming velocity perturbations (input). A range of frequencies (15 Hz - 500 Hz) have been selected for generating the FRF. The aim of this part of the study has been to validate the computational model against the experimental results and propose a physics based interpretation of the flame response. Detailed heat transfer modeling (including radiation heat transfer) and two-step chemistry models have been implemented in the model. The FRF generated has been able to reproduce the experimentally observed phenomena, like the low frequency pulsating instability occurring at 30 Hz. A heat transfer study has been conducted to explain the pulsating instability and a fuel variability study has been performed. Both the heat transfer study and the fuel variability study proved the role of heat transfer in creating the pulsating instability. The final part of the study involves simulation of reacting flow in a turbulent swirl stabilized combustor. The effect of velocity perturbations on the unsteady heat release has been studied by creating an FRF between the unsteady velocity and the unsteady heat release rate. A Large Eddy Simulation (LES) approach has been selected. A swirl number of S = 1.19 corresponding to a flow rate of Q = 20 SCFM with an equivalence ratio of phi = 0.75 have been implemented. Reduced reaction chemistry modeling, turbulence-chemistry interaction and heat transfer modeling have been incorporated in the model. The LES of reacting flow has shown vortex-flame interaction occurring inside the combustor. This interaction has been shown to occur at 255 Hz. The FRF obtained between unsteady velocity and unsteady heat release rate shows good comparison with the experimentally obtained FRF. Ph. D.

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20

Rufinelli, Marco. "Optimum Damping of Beam Vibrations Using Piezoceramic Transducers." Thesis, Virginia Tech, 2016. http://hdl.handle.net/10919/64936.

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In this thesis a piezo-electro-mechanical system, constituted of an aluminum beam with five piezoelectric patches glued on it, each of them shunted with an RL electrical circuit, has been numerically and experimentally investigated, in order to determine the optimal electric tuning parameters for vibration damping. A numerical code based upon Galerkin weighted-residual method is developed and the complete piezo-electro-mechanical system is designed, realized and finally tested by a standard modal testing technique. Comparisons between different shunting configurations of the system are given and finally the experimental data are compared with ones obtained by the developed numerical code in order to verify the accuracy of the latter. Master of Science

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21

Cierocka, Joanna, and Jiayue Tang. "Vibrational tests of preloaded rubber vibration isolators : A cam controlled displacement excitation." Thesis, Linnéuniversitetet, Institutionen för maskinteknik (MT), 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-53703.

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Vibrations are very common phenomenon. It influences structures and generates acoustic noise which might be harmful to human beings. The vibration isolator was invented to reduce the effect from vibrations. However, the behavior of rubber material, which many vibration isolators are made of, is hard to predict. Consequently, vibration tests are needed to obtain the dynamic properties of rubber isolator.In this case, a six-year old LORD 2204-5 rubber isolator provided by Atlas Copco was tested. The aim of this paper is to obtain the FRF (Frequency Response Function) diagram which can describe the property of the rubber material. Moreover, the influence of aging of rubber material on the dynamic properties was studied.As the vibration test should simulate the working environment of the isolators that are both a static load from the structure and a dynamic force from the engine, a new excitation method was designed. The camshaft with the shape of an epitrochoid induced the sinusoidal signal of the isolator and the frame transferred the static load from the hydraulic machine. The artificial aging was performed in a hot air oven in 90°C for 42 hours, which according to Arrhenius equation should be equivalent to six years of natural aging. The vibration isolator was tested again after being aged.The obtained data showed that the aging process decreased the stiffness of the material. The results were corresponding with other studies regarding aging of rubber.

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Cairns, Nicola J. "The feasibility of vibration analysis as a technique to detect osseointegration of transfemoral implants." Thesis, Queensland University of Technology, 2010. https://eprints.qut.edu.au/38874/1/Nicola_Cairns_Thesis.pdf.

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One of the main causes of above knee or transfemoral amputation (TFA) in the developed world is trauma to the limb. The number of people undergoing TFA due to limb trauma, particularly due to war injuries, has been increasing. Typically the trauma amputee population, including war-related amputees, are otherwise healthy, active and desire to return to employment and their usual lifestyle. Consequently there is a growing need to restore long-term mobility and limb function to this population. Traditionally transfemoral amputees are provided with an artificial or prosthetic leg that consists of a fabricated socket, knee joint mechanism and a prosthetic foot. Amputees have reported several problems related to the socket of their prosthetic limb. These include pain in the residual limb, poor socket fit, discomfort and poor mobility. Removing the socket from the prosthetic limb could eliminate or reduce these problems. A solution to this is the direct attachment of the prosthesis to the residual bone (femur) inside the residual limb. This technique has been used on a small population of transfemoral amputees since 1990. A threaded titanium implant is screwed in to the shaft of the femur and a second component connects between the implant and the prosthesis. A period of time is required to allow the implant to become fully attached to the bone, called osseointegration (OI), and be able to withstand applied load; then the prosthesis can be attached. The advantages of transfemoral osseointegration (TFOI) over conventional prosthetic sockets include better hip mobility, sitting comfort and prosthetic retention and fewer skin problems on the residual limb. However, due to the length of time required for OI to progress and to complete the rehabilitation exercises, it can take up to twelve months after implant insertion for an amputee to be able to load bear and to walk unaided. The long rehabilitation time is a significant disadvantage of TFOI and may be impeding the wider adoption of the technique. There is a need for a non-invasive method of assessing the degree of osseointegration between the bone and the implant. If such a method was capable of determining the progression of TFOI and assessing when the implant was able to withstand physiological load it could reduce the overall rehabilitation time. Vibration analysis has been suggested as a potential technique: it is a non destructive method of assessing the dynamic properties of a structure. Changes in the physical properties of a structure can be identified from changes in its dynamic properties. Consequently vibration analysis, both experimental and computational, has been used to assess bone fracture healing, prosthetic hip loosening and dental implant OI with varying degrees of success. More recently experimental vibration analysis has been used in TFOI. However further work is needed to assess the potential of the technique and fully characterise the femur-implant system. The overall aim of this study was to develop physical and computational models of the TFOI femur-implant system and use these models to investigate the feasibility of vibration analysis to detect the process of OI. Femur-implant physical models were developed and manufactured using synthetic materials to represent four key stages of OI development (identified from a physiological model), simulated using different interface conditions between the implant and femur. Experimental vibration analysis (modal analysis) was then conducted using the physical models. The femur-implant models, representing stage one to stage four of OI development, were excited and the modal parameters obtained over the range 0-5kHz. The results indicated the technique had limited capability in distinguishing between different interface conditions. The fundamental bending mode did not alter with interfacial changes. However higher modes were able to track chronological changes in interface condition by the change in natural frequency, although no one modal parameter could uniquely distinguish between each interface condition. The importance of the model boundary condition (how the model is constrained) was the key finding; variations in the boundary condition altered the modal parameters obtained. Therefore the boundary conditions need to be held constant between tests in order for the detected modal parameter changes to be attributed to interface condition changes. A three dimensional Finite Element (FE) model of the femur-implant model was then developed and used to explore the sensitivity of the modal parameters to more subtle interfacial and boundary condition changes. The FE model was created using the synthetic femur geometry and an approximation of the implant geometry. The natural frequencies of the FE model were found to match the experimental frequencies within 20% and the FE and experimental mode shapes were similar. Therefore the FE model was shown to successfully capture the dynamic response of the physical system. As was found with the experimental modal analysis, the fundamental bending mode of the FE model did not alter due to changes in interface elastic modulus. Axial and torsional modes were identified by the FE model that were not detected experimentally; the torsional mode exhibited the largest frequency change due to interfacial changes (103% between the lower and upper limits of the interface modulus range). Therefore the FE model provided additional information on the dynamic response of the system and was complementary to the experimental model. The small changes in natural frequency over a large range of interface region elastic moduli indicated the method may only be able to distinguish between early and late OI progression. The boundary conditions applied to the FE model influenced the modal parameters to a far greater extent than the interface condition variations. Therefore the FE model, as well as the experimental modal analysis, indicated that the boundary conditions need to be held constant between tests in order for the detected changes in modal parameters to be attributed to interface condition changes alone. The results of this study suggest that in a clinical setting it is unlikely that the in vivo boundary conditions of the amputated femur could be adequately controlled or replicated over time and consequently it is unlikely that any longitudinal change in frequency detected by the modal analysis technique could be attributed exclusively to changes at the femur-implant interface. Therefore further development of the modal analysis technique would require significant consideration of the clinical boundary conditions and investigation of modes other than the bending modes.

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Senturk, Sabri. "Experimental Determination Of Transfer Functions For A Car Body-in-white." Master's thesis, METU, 2004. http://etd.lib.metu.edu.tr/upload/12604899/index.pdf.

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

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Azarskov, V. N., O. U. Kurganskyi, O. V. Ermolaeva, and G. I. Rudyuk. "Structural Identification Algorithm Based on Results of Multidimensional Nonlinear Stabilization Plant Test." Thesis, Kyiv, "Osvita Ukrainy", 2015. http://er.nau.edu.ua/handle/NAU/28365.

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Scussel, Oscar. "On the use of Volterra series in structural dynamics : contributions from input-output to output-only analysis and identification /." Ilha Solteira, 2017. http://hdl.handle.net/11449/150506.

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Orientador: Samuel da Silva Resumo: Muitas aplicações da engenharia envolvem estruturas essencialmente não-lineares onde várias técnicas têm sido recentemente estudadas e investigadas por muitos pesquisadores. Dentre as várias abordagems, as que usam séries de Volterra têm apresentado propriedades úteis para fornecer um melhor entendimento para identificação e análise. Neste contexto, a presente tese propõem novas contribuições em como usar as séries de Volterra para caracterização, identificação e análise dinâmica de sistemas não-lineares usando sinais de entrada e saída e sinais somente de saída. Inicialmente, apresenta-se uma metodologia para análise de sistemas mecânicos não-lineares através das funções de resposta em frequência de alta-ordem (HOFRFs) e o conceito de HOFRFs estendidas com dados apenas de saída é introduzido e descrito em detalhes. Após isso, uma abordagem para identificação de sistemas não-lineares com base nas séries de Volterra através da expansão na base ortonormal de Kautz é proposta. Essa técnica permite identificar os seus núcleos mais facilmente e permite separar as contribuições dos termos lineares e não-lineares usando somente sinais de saída. Além disso, uma metodologia para análise modal de sistemas fracamente não-lineares sujeito a excitações com vários níveis de amplitude é também apresentada. A contribuição desse novo método reside no fato de que as HOFRFs são simplesmente estimadas como função das FRFs lineares. Basicamente, essa metodologia estende o conceito ... (Resumo completo, clicar acesso eletrônico abaixo) Abstract: Most recent engineering applications involve structures essentially nonlinear where several techniques have been recently studied and investigated by many researchers. Among them, the methods based on Volterra series expansion have presented powerful properties to provide a better understanding for identification and analysis. In this context, the present thesis proposes new contributions in how to use Volterra series for characterization, identification and dynamical analysis of nonlinear systems based on input and output signals and output-only signals. Initially, a methodology for analysis of nonlinear mechanical systems through higher-order frequency response functions (HOFRFs) is presented and the concept of extended HOFRFs based on output-only is introduced and described in detail. Afterwards, an approach for identification of nonlinear systems based on Volterra series through the expansion onto orthonormal Kautz basis is proposed. This technique allows to identify the Volterra kernels easily and enable to split the contribution of the linear and nonlinear terms using input-output as well as output-only signals. Furthermore, a methodology for modal analysis of weakly nonlinear systems under multilevel excitation is also proposed. The contribution of this new approach lies in the fact that HOFRFs are simply computed as functions of the linear FRFs. Basically, it extends the conventional experimental modal analysis methods in order to characterize and treat no... (Complete abstract click electronic access below) Doutor

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Scussel, Oscar [UNESP]. "On the use of Volterra series in structural dynamics: contributions from input-output to output-only analysis and identification." Universidade Estadual Paulista (UNESP), 2017. http://hdl.handle.net/11449/150506.

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Submitted by OSCAR SCUSSEL null (oscar.scussel@gmail.com) on 2017-04-29T13:57:37Z No. of bitstreams: 1 PhDThesisScussel.pdf: 4308679 bytes, checksum: 08a1260ebbd5cc5320910fff695b1037 (MD5) Approved for entry into archive by Luiz Galeffi (luizgaleffi@gmail.com) on 2017-05-03T16:39:39Z (GMT) No. of bitstreams: 1 scussel_o_dr_ilha.pdf: 4308679 bytes, checksum: 08a1260ebbd5cc5320910fff695b1037 (MD5) Made available in DSpace on 2017-05-03T16:39:39Z (GMT). No. of bitstreams: 1 scussel_o_dr_ilha.pdf: 4308679 bytes, checksum: 08a1260ebbd5cc5320910fff695b1037 (MD5) Previous issue date: 2017-03-27 Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Muitas aplicações da engenharia envolvem estruturas essencialmente não-lineares onde várias técnicas têm sido recentemente estudadas e investigadas por muitos pesquisadores. Dentre as várias abordagems, as que usam séries de Volterra têm apresentado propriedades úteis para fornecer um melhor entendimento para identificação e análise. Neste contexto, a presente tese propõem novas contribuições em como usar as séries de Volterra para caracterização, identificação e análise dinâmica de sistemas não-lineares usando sinais de entrada e saída e sinais somente de saída. Inicialmente, apresenta-se uma metodologia para análise de sistemas mecânicos não-lineares através das funções de resposta em frequência de alta-ordem (HOFRFs) e o conceito de HOFRFs estendidas com dados apenas de saída é introduzido e descrito em detalhes. Após isso, uma abordagem para identificação de sistemas não-lineares com base nas séries de Volterra através da expansão na base ortonormal de Kautz é proposta. Essa técnica permite identificar os seus núcleos mais facilmente e permite separar as contribuições dos termos lineares e não-lineares usando somente sinais de saída. Além disso, uma metodologia para análise modal de sistemas fracamente não-lineares sujeito a excitações com vários níveis de amplitude é também apresentada. A contribuição desse novo método reside no fato de que as HOFRFs são simplesmente estimadas como função das FRFs lineares. Basicamente, essa metodologia estende o conceito de métodos convencionais de analise modal experimental para caracterizar e tratar efeitos não-lineares. Os resultados via exemplos numéricos e experimentais apresentados ao longo da tese mostram as contribuições, benefícios e eficácia da proposta. Most recent engineering applications involve structures essentially nonlinear where several techniques have been recently studied and investigated by many researchers. Among them, the methods based on Volterra series expansion have presented powerful properties to provide a better understanding for identification and analysis. In this context, the present thesis proposes new contributions in how to use Volterra series for characterization, identification and dynamical analysis of nonlinear systems based on input and output signals and output-only signals. Initially, a methodology for analysis of nonlinear mechanical systems through higher-order frequency response functions (HOFRFs) is presented and the concept of extended HOFRFs based on output-only is introduced and described in detail. Afterwards, an approach for identification of nonlinear systems based on Volterra series through the expansion onto orthonormal Kautz basis is proposed. This technique allows to identify the Volterra kernels easily and enable to split the contribution of the linear and nonlinear terms using input-output as well as output-only signals. Furthermore, a methodology for modal analysis of weakly nonlinear systems under multilevel excitation is also proposed. The contribution of this new approach lies in the fact that HOFRFs are simply computed as functions of the linear FRFs. Basically, it extends the conventional experimental modal analysis methods in order to characterize and treat nonlinear effects. The results based on numerical and experimental examples presented along the thesis show the contributions, benefits and effectiveness of the proposal. FAPESP: 2012/09135-3 CNPq: 47058/2012-0 CNPq: 203610/2014-8

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Lima, Michelline Nery Azevedo. "Testes modais utilizando martelo instrumentado em estruturas de baixas freqüências naturais." Universidade Federal da Paraíba, 2006. http://tede.biblioteca.ufpb.br:8080/handle/tede/5322.

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Made available in DSpace on 2015-05-08T14:59:36Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 1565570 bytes, checksum: 641bee91a3e1ec7240272fff8310ca82 (MD5) Previous issue date: 2006-11-30 Coordenação de Aperfeiçoamento de Pessoal de Nível Superior In this work it is discussed the improvement in the modal test for obtaining the Frequency Response Function (FRF) in low natural frequency structures by using as exciter an instrumented hammer. There are two conflicting needs in this kind of test: on the one hand, the low natural frequencies of the structure, which are usually associated with low damping, demand long acquisition time so that good resolution in the spectrum may exist. On the other hand, the sampling rate must be increased to correctly catch the short duration signal of the hammer. This leads to an elevated number of points in the signal to be acquired, and there may eventually be limitation on such number of points when using spectrum analyzers in the acquisition and obtaining of the FRFs. Thus, in this work, the selective decimation technique explored for the improvement of the test. The work includes the construction of a prototype with two degrees of freedom (S2GL) to serve as case study for the tests enabling the theoretical and experimental Frequency Response Functions (FRF) to be compared, as well as adjusting the parameters of the model. The MATLAB programming language was used for obtaining the FRFs. The efficiency of the improvement applied was verified through the frequency spectra, in which it was observed significant resemblance between the non-decimated FRF with the acquisition having a high number of points, and the decimated FRF with smaller number of points and selected so that it could preserve the correct detection of the hammer signal. Neste trabalho discute-se o aprimoramento do teste modal para obtenção da Função Resposta em Freqüência (FRF) em estruturas de baixas freqüências naturais utilizando como excitador um martelo instrumentado. Há duas necessidades conflitantes neste tipo de teste: de um lado, as baixas freqüências naturais da estrutura, usualmente associadas com baixo amortecimento, requerem um tempo longo de aquisição para haver boa resolução no espectro. Por outro lado, a taxa de amostragem deve ser elevada para captar corretamente o sinal de curta duração do martelo. Isto leva a um número elevado de pontos no sinal a ser adquirido, havendo eventualmente limitação de tal número de pontos ao se utilizar analisadores de espectro na aquisição e obtenção das FRFs. Neste sentido, neste trabalho foi explorada a técnica de decimação seletiva para aprimoramento do teste. O trabalho inclui a construção de um protótipo com dois Graus de Liberdade (S2GL) para servir como objeto de estudo para os testes deste aprimoramento, permitindo assim, comparar as Funções Resposta em Freqüências (FRF) teóricas e experimentais, bem como ajustar os parâmetros do modelo. Utilizou-se da linguagem de programação MATLAB® para a obtenção das FRFs. A eficiência do aprimoramento empregado foi verificada através dos espectros de freqüência, onde observou-se uma significativa similaridade entre a FRF não decimada com a aquisição possuindo um número elevado de pontos e a FRF decimada com menor número de pontos e selecionada de modo a preservar a correta detecção do sinal do martelo.

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Dmitrijev, Jevgenij. "Dinaminio proceso perdavimo spyruokle tyrimas." Master's thesis, Lithuanian Academic Libraries Network (LABT), 2009. http://vddb.library.lt/obj/LT-eLABa-0001:E.02~2009~D_20090615_110052-83892.

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Magistro darbe tiriami dinaminio proceso perdavimo spyruokle ypatumai bei galimybės, ir kaip tą panaudoti spyruoklėmis vibroizoliuotų atramų diagnostikai. Buvo sukurta tyrimo metodika ir spyruoklės įėjimo ir išėjimo charakteristikoms gauti atitinkamas matavimo stendas. Naudojant impulsinio tipo signalą, buvo gautas sistemos savųjų virpesių spektras, taip pat sistema buvo žadinama vibratoriumi, siekiant ištirti ir įvertinti spyruoklės perdavimo funkciją esant nerezonansiniams dažniams. Analizuojant išmatuotas realizacijas, buvo išvesta perdavimo funkcija. Darbą sudaro 7 dalys: įvadas, literatūros apžvalga ir analizė, eksperimentiniai tyrimai, tyrimo rezultatai, rekomendacijos, išvados ir pasiūlymai, literatūros sąrašas. Darbo apimtis – 44 p. teksto be priedų, 41 iliustr., 31 bibliografiniai šaltiniai. Atskirai pridedami darbo priedai. Particulars of the problem of the dynamics transfer function of the spring and possibilities for diagnostics of the support bearings which are insulated from the external body by the resilient elements are developed in this article. During this research work the investigation methodology was found and suitable research stand was made as well. The impulse type input signal was submitted to the system to observe free oscillations in the stand. Also the system was excited by electromagnetic vibrator to research transfer function of the spring. Finally using the output and input signals at the spring ends the transfer function was derived. The thesis consists of 7 parts: introduction, rewiew of references and analisys, experimentation investigations, experimentation results, recommendations, conclusions and suggestions, the list of the references. Thesis consist of: 44 p. of text without appendixes, 41 pictures, 31 bibliographical entries. Appendixes included.

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Santos, Ariane Rebelato Silva dos. "Um estudo sobre reconstrução de carregamentos dinâmicos usando pseudo-inversa de Moore-Penrose." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2018. http://hdl.handle.net/10183/178493.

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Determinar as forças que estão agindo em um dado sistema é uma questão frequente em dinâmica estrutural, de modo que a reconstrução ou a identificação de carregamento se torna um importante problema de engenharia. Quando um sistema é exposto a um carregamento desconhecido e/ou não se é possível medir diretamente a força atuante nesse sistema, se torna necessária a utilização de métodos inversos. Esta metodologia consiste essencialmente na aplicação de cargas dinâmicas pontuais nos modelos de estudo e posterior recuperação de estimativas dessas cargas nos pontos de interesse. Na prática, há situações em que o número de pontos de interesse diferem do número de pontos testados, sendo assim, a matriz da função de resposta de freqüência (FRF) do sistema resulta retangular, fazendo-se necessário o uso da pseudo-inversa de Moore-Penrose. No presente trabalho, essa metodologia é aplicada a modelos númericos a fim de testar sua eficácia. Os resultados dos processos de reconstrução de carregamento dinâmico utilizando a presente metodologia foram obtidos a partir de aplicações analíticas e numéricas. Além disso, diretrizes para utilização da pseudo-inversa de Moore-Penrose na reconstrução de carregamento dinâmico são apresentadas ao final deste trabalho. Determining the forces acting on a given system is a frequent issue in structural dynamics, so that load reconstruction or load identification becomes an important engineering problem. When a system is exposed to an unknown load and/or if it is not possible to directly measure the force acting on that system, it is necessary to use inverse methods. This methodology consists essentially in the application of punctuals dynamics load in the study models and later recovery of estimates of these loads at points of interest. In practice, there are situations where the number of points of interest differ from the number of points tested, so the matrix of the frequency response function (FRF) of the system is rectangular, making it necessary to use the pseudo-inverse of Moore-Penrose. In the present work, this methodology is applied to numerical models in order to test their effectiveness. The results of the dynamic load reconstruction processes using the present methodology were obtained from analytical and numerical applications. In addition, guidelines for using Moore-Penrose pseudo-inverse in the dynamic load reconstruction are presented at the end of this work.

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Sismilich, Vladimír. "Vibrace při obrábění kovů – příčiny a jejich eliminace." Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2010. http://www.nusl.cz/ntk/nusl-229329.

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This diploma thesis is concerning about summarizing and describing types of vibrations, their causes and influences to the machining. The stable conditions of machining were pointed out. The experiment was conducted in which the frequency response function of specific milling machine was measured. Than the stability lobe diagram was constructed.

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Zanardo, Gabriele. "Structural Modification Approaches to Modal Design Optimisation of Vibrating Systems." Doctoral thesis, Università degli studi di Padova, 2011. http://hdl.handle.net/11577/3427526.

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This dissertation addresses the problem of assigning the desired dynamic behaviour to vibrating systems, with particular attention on the generality of the approaches proposed. The main focus of this work is in developing structural modification approaches ensuring the feasibility and the optimality of the computed solution. The proposed approaches are suitable for both the design of new mechanical systems, and the performance optimisation of existing ones. Three formulations are proposed: in the first, the original system is modelled by means of mass and stiffness matrices, while in the second the Frequency Response Functions of the original system are employed. The final formulation allows for discrete structural modification, by casting the structural modification problem as a mixed-integer non-linear optimisation problem. Compared with most of the approaches appearing in literature, one of the strengths of the approaches proposed is the capability to handle different design tasks. Also, the proposed approaches allow the modification of an arbitrary number of parameters (even in the presence of linear interrelated modifications) and of assigned vibration modes (regardless of their magnitude), as well as the possibility of dealing with mass and stiffness matrices with an arbitrary topology. To this purpose, the structural modification problem is formulated as a constrained inverse eigenvalue problem. The problem is constrained in the sense that a wide family of parameter constraints can be included in the formulations adopted in order to incorporate the physical constraints to the system modifications. Moreover, a regularization term biases the solution towards preferable modifications and assures good numerical conditioning. The problem is then solved within the frame of constrained convex optimisation, which ensures that a unique, and hence global, optimal and feasible solution exists and that it can be efficiently computed by means of reliable numerical algorithms. The effectiveness and the capabilities of the proposed approaches are demonstrated by firstly applying it to theoretical test cases and secondly through experiments on industrial and laboratory test cases. Such test cases involve lumped and distributed parameter modifications, as well as multimode and single mode assignments. In questa Tesi si affronta il problema di assegnare il comportamento dinamico desiderato a sistemi vibranti, e si dedica particolare attenzione alla generalità degli approcci proposti. Questo lavoro si concentra sullo sviluppo di approcci per il calcolo di modifiche strutturali che siano in grado di assicurare la realizzabilità fisica e l’ottimalità della soluzione calcolata. Gli approcci proposti sono adatti sia al progetto di nuovi sistemi meccanici, sia all’ottimizzazione delle performance di quelli esistenti. Vengono proposte tre formulazioni: nella prima il sistema originale é modellato per mezzo di matrici di massa e rigidezza, mentre nella seconda vengono impiegate le funzioni di risposta in frequenza (Frequency Response Functions). La terza formulazione prende in considerazione modifiche strutturali discrete, in quanto il problema delle modifiche strutturali viene formulato come un problema di ottimizzazione non-lineare mista-intera. In confronto agli approcci presenti in letteratura, uno dei punti di forza degli approcci proposti risiede nella capacità di poter affrontare obiettivi di progetto diversificati tra loro. Degna di nota é la modifica di un numero arbitrario di parametri (anche in presenza di modifiche tra loro linearmente correlate) e di modi di vibrare (a prescindere dalla loro normalizzazione), cosi pure la possibilità di trattare matrici di massa e rigidezza con topologia arbitraria. A tale fine, il problema di modifica strutturale viene formulato come un problema agli autovalori inverso vincolato. Il problema é vincolato nel senso che una ampia famiglia di vincoli sui parametri può essere introdotta nelle formulazioni adottate, per includere nel problema i vincoli fisici sulle modifiche del sistema. Inoltre, un termine di regolarizzazione permette di dirigere la soluzione verso modifiche preferenziali, ed assicura un buon condizionamento numerico. Il problema è risolto all’interno del contesto matematico dell’ottimizzazione convessa vincolata, che assicura l’esistenza di un’unica, e quindi globale, soluzione ottima realizzabile, e che tale soluzione sia calcolabile efficacemente per mezzo di algoritmi numerici consolidati ed affidabili. L’efficacia degli approcci proposti, e la loro capacità di fornire soluzioni realizzabili è stata dapprima dimostrata applicandoli dapprima su esempi teorici, e successivamente su test case industriali e da laboratorio. Tali test case includono sia modifiche di parametri concentrati che parametri distribuiti, così come l’assegnazione di uno o più modi di vibrare.

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Libardi, Ana Lúcia. "Técnicas de cancelamento de massa em análise modal experimental." Universidade de São Paulo, 2000. http://www.teses.usp.br/teses/disponiveis/18/18135/tde-11072018-120016/.

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Esta dissertação tem como objetivo principal o estudo das técnicas de cancelamento de massa, bem como suas aplicações em análise modal experimental. Estas técnicas são utilizadas na redução de determinados erros nos dados de resposta em frequência da estrutura sob estudo. Estes erros são por sua vez causados por fontes adicionais de inércia, tais como acelerômetros e transdutores de força, que são frequentemente utilizados nos ensaios para o levantamento das características dinâmicas da estrutura. As técnicas de cancelamento de massa estudadas neste trabalho são desenvolvidas a partir de uma modelagem das relações de entrada e saída no domínio da frequência, utilizando-se para tanto as Funções de Resposta em Frequência (FRF), bem como conceitos de subestruturação. Os modelos analíticos utilizados no problema de cancelamento de massa são também aplicados na geração de FRFs desconhecidas para a estrutura sob estudo, a partir de um subconjunto de FRFs medidas com massas adicionais acopladas à estrutura. Os métodos estudados são aplicados a dados obtidos através de simulações numéricas em sistemas discretos, bem como a dados experimentais provenientes de ensaios em estruturas simples. Resultados satisfatórios foram obtidos tanto a partir das simulações numéricas quanto na análise experimental para o problema de cancelamento de massa. Na obtenção de FRFs desconhecidas, verificou-se que os modelos teóricos conduzem a resultados satisfatórios em determinadas situações, e que o ruído encontrado em dados experimentais representa um fator detrimental na utilização das técnicas de cancelamento de massa para o propósito de gerar-se FRF desconhecidas a partir de FRF efetivamente medidas na estrutura sob estudo. The goal of this dissertation is to develop a study on mass cancellation techniques and their applications in experimental modal analysis. These techniques are commonly employed in the reduction of experimental errors on the structure\'s measured frequency response data. Such errors are in turn caused by extra masses such as accelerometer and force transducers, that are utilized on the measurement of the system\'s Frequency Response Functions (FRF). The mass cancellation techniques studied here are developed through frequency domain input and output relationships as well as substructuring concepts. The analytical models employed in the mass cancellation problem are also applied in obtaining unknown FRF from a subset of measured FRF that are measured with extra masses attached to the structure. The methods studied are applied to numerically simulated data from discrete systems, as well as to experimental data coming from modal tests performed on simple structures. Reasonably good results are obtained in either the numerical and experimental analysis for the mass cancellation problem. In obtaining unknown FRF data, it was verified that the models generated reasonable results in some circumstances, and that experimental noise is a major source of error in using these mass cancellation techniques for the purpose of obtaining unmeasured data from a subset of measured FRF.

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Wiberg, Niklas, and Jasmin Halilovic. "Train Induced Vibration Analysis of an End-frame Bridge : Numerical Analysis on Sidensjövägen." Thesis, KTH, Bro- och stålbyggnad, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-231911.

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Higher speeds and higher capacity will cause the Swedish rail network to be exposed to disturbing dynamic effects. Higher speeds cause higher vertical acceleration levels of the bridge deck. In this thesis, a numerical analysis of a three span end-frame bridge subjected to train induced vibrations is performed. The aim is to identify which structural components and boundary conditions that affect the dynamic behavior of the bridge. Furthermore, the influence of soil structure interaction (SSI) will be investigated as it may have contribution to the stiffness and damping of the structural system. In order to capture the dynamic response of the bridge, an analysis in the frequency domain was preformed where frequency response functions (FRF) and acceleration envelopes were obtained. For this purpose, a detailed FE-model in 3D was created. Three different cases were studied, model subjected to ballast, model subjected to soil and model subjected to both ballast and soil in coherence. A high speed load model (HSLM) was used to create simulation of train passages at different speeds and applied to all cases so that the bridge deck accelerations could be studied. A simplified 2D-model with impedance functions representing the soil-structure interaction was created to validate the results from the detailed 3D-model and for practical design purposes. The result of this numerical analysis showed that the vertical accelerations were within acceptable levels of the maximum allowed limits given in governing publications. Considering the surrounding soil, the results revealed an increase of the dynamic response in the midspan at resonant frequency. However, it was identified that this behavior is not explained by the influence of soil structure interaction but rather the change in boundary conditions of the end-shields. The same dynamic behavior was identified for the simplified 2D-model, with a slight underestimation of the vertical accelerations at resonance.

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Elgazzar, Hesham. "End-Shield Bridges for High-Speed Railway : Full scale dynamic testing and numerical simulations." Licentiate thesis, KTH, Bro- och stålbyggnad, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-204774.

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The increasing need for High-Speed Railway (HSR) to reduce the travelling time requires increasing research within this field. Bridges are main components of any railway network, including HSR networks, and the optimization of their design for this purpose would contribute to a faster and more cost effective development of the HSR network. The initial investment, the running and maintenance costs of the bridges can be decreased through better understanding of the their dynamic behaviour. This thesis studies the dynamic behaviour of end-shield railway bridges under HSR operation. 2D beam analysis is used to study the effect of the distribution of the train’s axle load. Relatively accurate 3D FE-models are developed to study the effect of Soil-Structure Interaction (SSI) and the dynamic response of the bridges. Modelling alternatives are studied to develop an accurate model. A full scale test of a simply supported Bridge with end-shields using load-controlled forced excitation was performed and the results were used to verify the theoretical models. A manual model updating process of the material properties of the 3D FE-model is performed using FRFs from the field measurements. A Simple 2D model is also developed, where a spring/dashpot system is implemented to simplify SSI, and updated to reproduce the field measured responses. The conclusions of the project emphasize the importance of SSI effects in the dynamic analysis of end-shield bridges for predicting their dynamic behaviour. The conclusions also show that the modelling of the surrounding soil and the assumption of the soil material parameters have significant effect on the dynamic response. Even the boundary conditions, bedrock level and the ballast on the railway track affects the response. The results also show that the bridge’s concrete section behaves as uncracked section under the studied dynamic loading. QC 20170403

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Eyring, Nicholas J. "Development and Validation of an Automated Directivity Acquisition System Used in the Acquisition, Processing, and Presentation of the Acoustic Far-Field Directivity of Musical Instruments in an Anechoic Space." BYU ScholarsArchive, 2013. https://scholarsarchive.byu.edu/etd/4004.

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A high spatial resolution acoustic directivity acquisition system (ADAS) has been developed to acquire anechoic measurements of the far field radiation of musical instruments that are either remote controlled or played by musicians. Building upon work performed by the BYU Acoustic Research Group in the characterization of loudspeaker directivity, one can rotate a musical instrument with sequential azimuthal angle increments under a fixed semicircular array of microphones while recording repeated notes or sequences of notes. This results in highly detailed and instructive directivity data presented in the form of high-resolution balloon plots. The directivity data and corresponding balloon plots may be shown to vary as functions of time or frequency. This thesis outlines the development of a prototype ADAS and its application to different sources including loudspeakers, a concert grand piano, trombone, flute, and violin. The development of a method of compensating for variations in the played amplitude at subsequent measurement positions using a near-field reference microphone and Frequency Response Functions (FRF) is presented along with the results of its experimental validation. This validation involves a loudspeaker, with known directivity, to simulate a live musician. It radiates both idealized signals and anechoic recordings of musical instruments with random variations in amplitude. The concept of coherence balloon maps and surface averaged coherence are introduced as tools to establish directivity confidence. The method of creating composite directivities for musical instruments is also introduced. A composite directivity comes from combining the directivities of all played partials to approximate what the equivalent directivity from a musical instrument would be if full spectral excitation could be used. The composite directivities are derived from an iterative averaging process that uses coherence as an inclusion criterion. Sample directivity results and discussions of experimental considerations of the piano, trombone, flute, and violin are presented. The research conducted is preliminary and will be further developed by future students to expand and refine the methods presented here.

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Cinarel, Dilara. "Vibration Isolation Of Inertial Measurement Unit." Master's thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12614069/index.pdf.

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Sensitive devices are affected by extreme vibration excitations during operation so require isolation from high levels of vibration excitations. When these excitation characteristics of the devices are well known, the vibration isolation can be achieved accurately. However, it is possible to have expected profile information of the excitations with respect to frequency. Therefore, it is practical and useful to implement this information in the design process for vibration isolation. In this thesis, passive vibration isolation technique is examined and a computer code is developed which would assist the isolator selection process. Several sample cases in six degree of freedom are designed for a sample excitation and for sample assumptions defined for an inertial measurement unit. Different optimization methods for design optimizations are initially compared and then different designs are arranged according to the optimization results using isolators from catalogues for these sample cases. In the next step, the probable designs are compared according to their isolator characteristics. Finally, one of these designs are selected for each case, taking into account both the probable location deviations and property deviations of isolators.

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Hofstetter, Marcel, and Nima Pashai. "Soil-structure interaction for traffic induced vibrations in buildings." Thesis, KTH, Bro- och stålbyggnad, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-233001.

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Major cities in Sweden experience a population growth, demanding innovative solutions regarding land exploitation for residential housing. One solution is to build closer to existing railway tracks, however difficulties arise regarding determining traffic induced vibrations from trains. This sometimes results in vibrations being too large in buildings regarding comfort, resulting in expensive measures taken as to reduce the vibrations. The scope of this thesis is to investigate the soil-structure interaction caused by traffic induced vibrations in buildings using ABAQUS FE software, where the aim is to partly investigate how a structure effects surrounding soil, partly to investigate which parameters of a structure has largest favorable impact on foundation vibrations. Major results include that ground vibrations at 2-4 meters parallel to a structure relative to the vibration source remain constant, independent on whether a house is present or not. Further results show that increasing the thickness of the foundation slab has a mitigating effect on the induced vibrations. The main conclusions of this thesis include that quadratic elements are superior to linear elements for dynamic analyses for soil, and that accelerometers should be placed at least 2-4 m next to an existing structure to obtain accurate measurements comparable to if no structure was present. Större städer i Sverige upplever en befolkningstillväxt, vilket resulterar i att kreativa lösningar måste introduceras gällande markexploatering för bostadshus. En sådan lösning är att bygga närmre befintlig järnväg, dock resulterar detta i svårigheter gällande att kvantifiera magnituden av trafikinducerade vibrationer i byggnadsfundament orsakade av tågtrafik. En konsekvens av detta är att vibrationsnivåerna i husen ibland blir för stora sett till komfortvibrationer, vilket resulterar i att dyra åtgärder måste tas för att minska vibrationerna. Denna avhandling syftar till att genom att använda ABAQUS FE-mjukvara utforska jord-strukturinverkan i hus orsakade av trafikvibrationer. Målet är delvis att undersöka hur byggnation påverkar omgivande markvibrationer, delvis att undersöka vilka parametrar som har störst gynnsam effekt gällande dämpning av trafikinducerade vibrationer. De viktigaste resultaten indikerar att markvibrationer 2-4 meter bredvid ett hus relativt vibrationskällan förblir oförändrade oberoende av om byggnation existerar eller ej, samt att en ökning av tjockleken av grundplattan resulterar i minskade fundamentvibrationer. Slutsatserna som presenteras är flera, däribland att kvadratiska element är mer beräkningseffektiva än linjära element för dynamiska analyser för jord, samt att accelerometrar bör placeras minst 2-4 m bredvid ett befintligt hus för att erhålla mätdata jämförbara med om ett hus inte skulle finnas på platsen.

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Hansell, Markus, and Panagiotis Tamtakos. "Dynamic analyses of hollow core slabs : Experimental and numerical analyses of an existing floor." Thesis, KTH, Bro- och stålbyggnad, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-278539.

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For intermediate floors in residential and office buildings, as well as in parking garages and malls, there is a wide use of hollow core concrete slabs in Sweden today. Hollow core slabs are precast and prestressed concrete elements with cylindrical-shaped voids extending along the length of the slab. These structural elements have the advantage compared to cast-in-situ concrete slabs that they have a high strength, due to the prestressing, and that the voids allow for a lower self-weight. Additionally, the voids allow for a reduction in the use of concrete material. These characteristics offer possibilities to build long-span floors with slender designs. However, a consequence of the slenderness of the slabs is that such floors have an increased sensitivity to vibrations induced by various dynamic loads. In residential and office buildings vibrations are primarily caused by human activity, and therefore concerns related to the serviceability of such floors are raised. These vibrations are often not related to problems with structural integrity, but rather to different aspects of comfort of the residents or workers. The aim of this thesis is to provide additional information regarding the dynamic behavior of hollow core floors. An experimental modal analysis has been performed on an existing floor in an office building. The dynamic properties in the form of natural frequencies, mode shapes, damping ratios and frequency response functions were derived and analyzed from these measurements. Subsequently, several finite element models were developed, aiming to reproduce the experimental dynamic behavior of the studied floor. The measurements initially showed some unexpected dynamic responses of the floor. For this reason, more advanced methods of signal analyses were applied to the data. The analyses showed that the slab has some closely spaced modes and that the modes of the floor are complex to a certain degree. The finite element models were studied with different configurations. In particular, the effect the model size, boundary conditions, material properties and potential structural discontinuities have on the dynamic response of the slab was studied. Sufficiently good agreement has been achieved between the experimental and numerical results in terms of natural frequencies and mode shapes. The acceleration amplitude responses of the numerical models were generally higher than the ones obtained from the measurements, which leads to difficulties in matching of the frequency response functions. Håldäck i betong används idag i stor utsträckning som bjälklag i bostads- och kontorsbyggnader, liksom i parkeringsgarage och köpcentra. Håldäcksbjälklag består av prefabricerade och förspända betongelement, med cylindriska hål som sträcker sig i plattans längsriktning. Dessa konstruktionselement har fördelen, jämfört med platsgjutna betongplattor, att de har en hög hållfasthet på grund av förspänningen och att hålen möjliggör en lägre egenvikt. Dessutom gör hålen att en mindre mängd betongmaterial behövs. Dessa egenskaper ger möjligheter att bygga golv med långa spännvidder och slank design. En konsekvens av slankheten är emellertid att sådana golv har en ökad känslighet för vibrationer som orsakas av olika dynamiska belastningar. I bostads- och kontorsbyggnader orsakas vibrationer främst av mänsklig aktivitet, och därför finns det en del oro relaterad till sådana golvs brukbarhet. Dessa vibrationer är oftast inte relaterade till frågor om strukturell integritet, utan snarare till olika aspekter av boendes eller arbetares känsla av komfort. Syftet med detta examensarbete är att bidra till kunskapen om håldäcksbjälklags dynamiska beteende. En experimentell modalanalys har utförts på ett befintligt golv i en kontorsbyggnad. De dynamiska egenskaperna i form av egenfrekvenser, modformer, dämpning och frekvenssvarsfunktioner erhölls och analyserades med hjälp av dessa mätningar. Därefter utvecklades flera finita element modeller för att reproducera det experimentellt uppmätta dynamiska beteendet hos det studerade golvet. Mätningarna visade initialt något oväntade dynamiska responser från golvet. Av denna anledning applicerades mer avancerade signalanalysmetoder på datan. Analyserna visade att plattan har några moder inom ett litet frekvensintervall och att moderna till en viss grad är komplexa. De finita element modellerna studerades med olika konfigurationer. I synnerhet studerades effekten av modellstorleken, randvillkoren, materialegenskaperna och potentiella strukturella diskontinuiteter på golvets dynamiska respons. Tillräckligt bra överensstämmelse har uppnåtts mellan de experimentella och numeriska resultaten i form av egenfrekvenser och modformer. Accelerationsamplituderna för de numeriska modellerna var i allmänhet högre än de som erhölls under mätningarna, vilket leder till svårigheter att matcha frekvenssvarsfunktionerna.

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Wickman, Erik. "Taluppfattbarhet med strupmikrofon." Thesis, Uppsala universitet, Signaler och System, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-353351.

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Contact microphones, especially throat microphones, have been developed to be used in environments with high background noises to improve the speech intelligibility in communication. They pick up vibrations from the surface they are attached to and are therefore less sensitive to sound and noise from the air. Comparison of the speech intelligibility with other types of microphones have previously been done by letting test persons examine the communication devices in question. This study examines the possibility to make use of the STI-method instead and therefore make a comparison faster, more cost-efficient and customizable. The thought is that if the relationship between speech signals and vibrations were known, it could be used to transform the STI test signal to vibrations and then use the STImethod to estimate the speech intelligibility for the chosen contact microphone. This study, containing 22 men and women, evaluated the vibrations at the most suitable locations on the head for contact microphones and compared it with the speech signal of the same test person. Frequency responses were calculated for all locations of the head and a more detailed study showed that the frequency response of the neck may be approximated as a second order lowpass filter with a cut-off frequency of about 300 Hz that attenuates speech signals with higher frequencies. Experiments were also done to measure the STI value of a throat microphone with the known relationship. However, the results pointed out several problems that needs to be addressed before a STI method can be performed successfully. The results from this study may also be used to deeper study the relationships between different vibrations resulting from speech signals and suggestions on how the performance of contact microphones may be improved are given.

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Chouaki, Amar. "Recalage de modèles dynamiques de structures avec amortissement." Cachan, Ecole normale supérieure, 1997. http://www.theses.fr/1997DENS0034.

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La maitrise de modèles de plus en plus complexes en mécanique est une préoccupation constante tant au niveau industriel qu'en recherche. Le problème auquel nous nous intéressons ici concerne le recalage de l'amortissement dans les modèles dynamiques de structures à partir de fonctions de réponses en fréquences. D'une manière plus générale, l'appréciation de la qualité d'un modèle est le problème central. Bien des propositions ont été faites mais peu ont une interprétation mécanique forte ; la méthode développée au LMT, depuis le début des années quatre vingt, est basée sur la notion d'erreur en relation de comportement. Après de récents développements (voir le rapport interne 150), cette approche tient compte des effets d'amortissement, et plus généralement des effets non-linéaires dus au comportement des matériaux. De plus, elle intègre tous type de résultats expérimentaux disponibles (statiques, forces et vibrations libres). L'étude présentée s'intéresse particulièrement à l'amortissement. Le recalage de l'amortissement dans le comportement dynamique des structures nécessite une représentation correcte de celui-ci. Son influence peut apparaitre tant au niveau structural qu'au niveau des liaisons entre sous-structures. La première partie de l'exposé concerne l'étude de la sensibilité de l'erreur en relation de comportement aux effets d'amortissement. Puis, dans une seconde partie, nous nous intéressons à l'influence du bruit de mesure sur le processus de recalage. Enfin, nous montrons sur différents exemples l'aptitude de la méthode à recaler l'amortissement et à l'identifier dans les liaisons entre sous-structures. Les modèles considérés sont linéaires et les résultats d'essais exploités sont de type fonctions de réponses en fréquences, incomplets et entaches de bruit de mesure.

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41

Seixas, Claudiner Mendes de. "Uma proposta de representação de sistemas de aterramento diretamente no domínio do tempo /." Ilha Solteira, 2017. http://hdl.handle.net/11449/151976.

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Orientador: Sérgio Kurokawa Resumo: Este trabalho apresenta uma proposta de representação de sistemas de aterramento elétrico diretamente no domínio do tempo, tendo como vantagem os benefícios da modelagem realizada no domínio da frequência, com os resultados fornecidos diretamente no domínio do tempo, sem passar por transformadas inversas (Laplace ou Fourier). Os modelos no domínio do tempo são facilmente inseridos nos softwares convencionais de análise transitória, onde as tensões e correntes são melhor compreendidas. A maior contribuição deste trabalho está no desenvolvimento de uma técnica capaz de representar o aterramento com elementos discretos e positivos de circuitos (resistores-R, capacitores-C e indutores-L). Assim, o circuito equivalente representativo do aterramento será sempre um circuito possível de ser implementado fisicamente. Nesta proposta o aterramento é inicialmente modelado no domínio da frequência, sua impedância harmônica é obtida e representada por meio de elementos discretos de circuitos (RLC) associados em série e/ou paralelo. Aterramentos constituídos por um eletrodo horizontal ou uma haste vertical foram representados por meio de aproximação usando o método dos mínimos quadrados (vector fitting), que permite obter a função racional equivalente à admitância do aterramento, a partir da qual são extraídos os ramos de circuitos e consequentemente o circuito equivalente. Apesar de ser possível representar uma infinidade de aterramentos, dependendo do comprimento e diâmetro do eletrodo/ha... (Resumo completo, clicar acesso eletrônico abaixo) Doutor

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Ambróz, Richard. "Analysis of Powertrain Acoustic Properties." Doctoral thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2012. http://www.nusl.cz/ntk/nusl-234137.

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Dizertačná práca rieši problematiku analýzy akustických vlastností pohonných jednotiek. V úvodnej časti je teoretický rozbor fyzikálnych princípov vibrácií a hluku a prehľad súčasného stavu riešenia problematiky v oblasti návrhu pohonných jednotiek. Vlastná časť práce popisuje konštrukčný návrh elektrodynamického budiča vibrácií, návrh hodnotenia výsledkov merania a taktiež spôsob spracovania výsledkov. Akustické vlastnosti sú hodnotené pomocou normálových rýchlostí kmitania povrchu. V závere práce sú prezentované ukážky využitia metódy v praktických príkladoch spojených s návrhom pohonnej jednotky. Celé riešenie predstavuje ucelený spôsob analýzy vhodný pre rýchle hodnotenie vplyvu konštrukčných úprav na akustické vlastnosti.

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Seixas, Claudiner Mendes de [UNESP]. "Uma proposta de representação de sistemas de aterramento diretamente no domínio do tempo." Universidade Estadual Paulista (UNESP), 2017. http://hdl.handle.net/11449/151976.

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Submitted by CLAUDINER MENDES DE SEIXAS null (claudiner2010@gmail.com) on 2017-10-21T02:06:24Z No. of bitstreams: 1 Tese_Claudiner_seixas_ac_dr_ilha.pdf: 3441885 bytes, checksum: 9e1f3e2ff82a0a8220457c535d4cea55 (MD5) Approved for entry into archive by Luiz Galeffi (luizgaleffi@gmail.com) on 2017-10-26T14:27:13Z (GMT) No. of bitstreams: 1 seixas_cm_dr_ilha.pdf: 3441885 bytes, checksum: 9e1f3e2ff82a0a8220457c535d4cea55 (MD5) Made available in DSpace on 2017-10-26T14:27:13Z (GMT). No. of bitstreams: 1 seixas_cm_dr_ilha.pdf: 3441885 bytes, checksum: 9e1f3e2ff82a0a8220457c535d4cea55 (MD5) Previous issue date: 2017-08-25 Este trabalho apresenta uma proposta de representação de sistemas de aterramento elétrico diretamente no domínio do tempo, tendo como vantagem os benefícios da modelagem realizada no domínio da frequência, com os resultados fornecidos diretamente no domínio do tempo, sem passar por transformadas inversas (Laplace ou Fourier). Os modelos no domínio do tempo são facilmente inseridos nos softwares convencionais de análise transitória, onde as tensões e correntes são melhor compreendidas. A maior contribuição deste trabalho está no desenvolvimento de uma técnica capaz de representar o aterramento com elementos discretos e positivos de circuitos (resistores-R, capacitores-C e indutores-L). Assim, o circuito equivalente representativo do aterramento será sempre um circuito possível de ser implementado fisicamente. Nesta proposta o aterramento é inicialmente modelado no domínio da frequência, sua impedância harmônica é obtida e representada por meio de elementos discretos de circuitos (RLC) associados em série e/ou paralelo. Aterramentos constituídos por um eletrodo horizontal ou uma haste vertical foram representados por meio de aproximação usando o método dos mínimos quadrados (vector fitting), que permite obter a função racional equivalente à admitância do aterramento, a partir da qual são extraídos os ramos de circuitos e consequentemente o circuito equivalente. Apesar de ser possível representar uma infinidade de aterramentos, dependendo do comprimento e diâmetro do eletrodo/haste combinado com determinadas resistividade e permissividade elétricas do solo, esse método pode não garantir que todos os elementos RLC sejam positivos. Por isso foi desenvolvido uma nova técnica e testada em aplicações com configurações de aterramento mais complexas (malhas). Essa técnica fornece resultados precisos e garante que todos os elementos RLC serão positivos. Sua validação foi realizada comparando os resultados propostos com os resultados obtidos pelo modelo de linha de transmissão (no caso de eletrodo/haste) e pelo modelo eletromagnético híbrido HEM (no caso das malhas). Essa técnica permite o uso de qualquer modelo capaz de fornecer a impedância harmônica, podendo ser aplicada a configurações genéricas de aterramento, o que a torna muito versátil e atrativa. This work presents a proposal to represent of electrical grounding systems directly in time domain, taking into account the benefits in frequency domain modelling, without employing inverse Laplace or Fourier transforms. The time domain models are easily inserted in conventional electromagnetic transient software, where voltages and currents are better understood. The main contribution of this work is the development of a technique that can represent grounding by discrete and positive circuits elements (R-resistors, C-capacitors and L-inductors). The representation of the grounding is an electric circuit, possible to be implemented physically. Grounding systems is initially modelled in the frequency domain, where its harmonic impedance is obtained and then represented by elements of circuit (RLC) made in series and/or parallel association. Grounding systems constituted by a horizontal electrode or a vertical rod were represented by means of an approximation using the method of the least squares (vector fitting). It reproduces the rational function equivalent to the admittance of the grounding, which branches of circuits are extracted, forming an equivalent circuit. Although it is possible to represent an infinity of groundings, depending on the length and diameter of the electrode / rod combined with certain electrical resistivity and permittivity of the soil, this technique may not guarantee that all RLC elements are positive. However, a new technique was developed and tested in more complex grounding systems (grids). This technique provides accurate results and ensures that all RLC elements will be positive. Its validation was performed comparing the proposed results with the results obtained by the TLM (Transmission Line Model) employed for the horizontal electrodes and vertical rods and by the HEM (Hybrid Electromagnetic Model) employed for grounding grids. This technique allows the use of any model capable of providing harmonic impedance, and can be applied to generic ground configurations, making it very attractive to electromagnetics transient analyses.

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Smigelski, Jeffrey Ralph. "Water Level Dynamics of the North American Great Lakes:Nonlinear Scaling and Fractional Bode Analysis of a Self-Affine Time Series." Wright State University / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=wright1379087351.

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Di, Renzo Antonio. "Sviluppo di metodologie per la qualifica di componenti mediante termoelasticità." Doctoral thesis, Università degli studi di Padova, 2007. http://hdl.handle.net/11577/3425002.

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The main subject of the thesis is the development of several methodologies aimed to qualify mechanical components through thermoelasticity. Such essay begins with the analysis of the thermoelastic method of measure. We come to develop a new measure methodology of stress maps on mechanical rotation components through two test cases; they show their application to the stress analysis on the joint of water meter and fan cooling.

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Heitz, Jean-François. "Propagation d'ondes en milieu non linéaire : applications à la reconnaissance des sols et au génie parasismique." Grenoble 1, 1992. http://www.theses.fr/1992GRE10120.

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La propagation d'ondes en milieu non lineaire est etudiee sur les plans theorique, experimental et numerique. Des applications touchant les domaines du genie parasismique et de la reconnaissance in situ des sols sont proposes. Apres un etat des connaissances acquises a ce jour sur le comportement du sol sous sollicitation dynamique, un modele de comportement viscoelastique non lineaire est introduit dans l'equation fondamentale de la dynamique. L'equation du mouvement du sol obtenue exhibe au second membre un terme de source contenant l'ensemble des termes caracteristiques lies a la non-linearite du sol. Une analyse dans l'espace des frequences montre que le comportement non lineaire deviatoire du sol est a l'origine de modifications du contenu spectral au cours de la propagation par rapport au contenu frequentiel de la sollicitation. Une methode iterative de resolution de l'equation du mouvement est utilisee. A chaque iteration, la solution est obtenue explicitement par l'utilisation de transformations fonctionnelles integrales appropriees. Deux essais dynamiques in situ en surface et en puits avec excitation harmonique sont interpretes sur la base de l'approche theorique precedente. Le premier essai a permis essentiellement de mettre en evidence in situ le comportement non lineaire du sol sous sollicitation sinusoidale. Pour le second essai, des calculs simulent la reponse du sol a distance du puits et une methode d'identification de parametres caracteristiques du comportement non lineaire du sol est proposee. Une autre application de l'approche theorique proposee permet d'etudier les effets de site unidimensionnels caracteristiques du comportement non lineaire d'un horizon de sol reposant sur un demi-espace et subissant une sollicitation transitoire de type sismiques. Une extension du calcul en configuration bidimensionnelle est ensuite proposee

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Huynh, Dung. "Damage detection in structures using frequency response function (FRF) data and finite element modelling." Thesis, 2003. https://vuir.vu.edu.au/15242/.

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This thesis presents a method to detect structural damage using frequency response function (FRF) data obtained from non-destructive vibration tests. The method is used to study cases of early structural damage in which there is no appreciable change in mass and damping. The resulting change in structural stiffness matrix is reflected in changes of FRF which can be exemplified by the evaluation of the damage location vector. This requires the dynamic stiffness matrix of the original undamaged structure and the frequency response curve of the currently damaged structure. In this thesis, the former is obtained from a finite element model of the virgin structure and the latter are obtained from an impact hammer test. The Damage Detection Algorithm will be used to detect simulated damage FRF data applied to a simple mass spring system, space truss structure and a plate structure and effects of noise. Both numerically simulated and experimentally measured noises are investigated. Experimental FRF data were obtained for a plate structure and used for detection of physical damage and comparisons made with the simulated data. Results show that the Damage Detection Algorithm can be used to successfully detect structure damage in situations where coordinate incompatibility and noise exists.

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Lamb, Matthew. "Monitoring the structural integrity of packaging materials subjected to sustained random loads." Thesis, 2011. https://vuir.vu.edu.au/16054/.

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During the distribution phase, packaged consignments are exposed to a variety of environmental hazards, such as vibrations, which, if excessively severe, may cause damage to or even destroy the product. The ability of packaging systems to withstand these dynamic loads is an important factor, since their function is not only to protect the product but also to ensure that damage to the package itself is not evidently apparent as this is likely to affect consumer confidence. Such concerns often result in the use of excessive packaging material and this is no longer acceptable. Therefore, engineered protective packaging systems need to be optimised. Such optimisation requires a suitable technique for continuously monitoring the structural integrity of the systems during laboratory based vibration testing.

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Lin, Yen Shiu, and 林彥旭. "Frequency Response Function of composite beam with viscoelastic layer." Thesis, 1998. http://ndltd.ncl.edu.tw/handle/90167963988653947510.

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碩士 國立臺灣大學 機械工程學系研究所 86 In this thesis, we investigate the dynamic characteristics of an elastic bea m completely covered by a viscoelastic layer both theoretically and experiment ally. The fourth-order differential equations of motion are derived for the tr ansverse vibration of thecomposite beam. Not only the transverse strain and st ress of the elastic and viscoelastic layer are included in the equation of mot ion,but also the longitudinal strain and stress are included. An eigenvaluepro blem corresponding to the differential equation is solved to obtainthe require d dynamic characteristics. Numerical analysis and experimental measurements i s illustrated by a cantilever beam in transverse vibration. Galerkin Method is used to find the eigen solution. The dynamic behavior of the composite beam is illustrated with frequency response functions.

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Kuo, Ku-Yu, and 郭家宇. "Application of Frequency Response Function in Building Structural Health Monitoring." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/49530437686448669558.

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碩士 國立交通大學 土木工程學系 99 A building structure may sustain damage either when subjected to severe loading like a strong earthquake or when its material deteriorates. The monitoring of the structural health (SHM) of buildings and civil infrastructure has attracted considerable interest in the last decade. Monitoring the structural health of a particular structural system involves a damage identification process that comprises detecting, locating, identifying type of, and estimating severity of, damage. Hence, a reliable, feasible, and economic SHM system is practical for building structures. The aim of this study attempts to utilize frequency response function (FRF) as index in SHM for locating and estimating severity of damage to building structures. First, a numerical study, based on SAP2000 software, is employed to create simulated damage cases including single and multi site(s) damage scenarios. Following, a novel FRF curvature method is developed and applied to locate damage. An ANN model is then utilized to evaluate the severity of damage for single-site cases. Finally, an experimental study is employed to verify the feasibility of the proposed FRF method. The simulation and experiment results expose that the proposed FRF index can locate damage correctly in single as well as multi site(s) damage and the ANN model can estimate the severity of damage for single-site damage cases acceptably.

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Dissertations / Theses on the topic 'Frequency Response Function(FRF)'

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