Dissertations / Theses on the topic 'Modal analysis'
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Potgieter, Brendon Ryan. "Experimental modal analysis and model validation of antenna structures." Thesis, Stellenbosch : University of Stellenbosch, 2010. http://hdl.handle.net/10019.1/5423.
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Thesis (MScEng (Mechanical and Mechatronic Engineering))--University of Stellenbosch, 2010.ENGLISH ABSTRACT: Numerical design optimisation is a powerful tool that can be used by engi- neers during any stage of the design process. Structural design optimisation is a specialised usage of numerical design optimisation that has been adapted to cater speci cally for structural design problems. A speci c application of structural design optimisation that will be discussed in the following report is experimental data matching. Data obtained from tests on a physical structure will be matched with data from a numerical model of that same structure. The data of interest will be the dynamic characteristics of an antenna structure, focusing on the mode shapes and modal frequencies. The structure used was a scaled, simpli ed model of the Karoo Array Telescope-7 (KAT-7) antenna structure. Experimental data matching is traditionally a di cult and time-consuming task. This report illustrates how optimisation can assist an engineer in the process of correlating a nite element model with vibration test data.
AFRIKAANSE OPSOMMING: Numeriese ontwerp-optimisering is 'n kragtige ingenieurshulpmiddel wat ty- dens enige stadium in die ontwerpsproses ingespan kan word. Strukturele ontwerp-optimisering is 'n gespesialiseerde gebruik van numeriese ontwerp- optimisering wat aangepas is om spesi ek van diens te wees by die oplos van strukturele ontwerpsprobleme. 'n Spesi eke toepassing van strukturele ontwerp-optimisering wat in hierdie verslag bespreek sal word, is eksperi- mentele datakorrelasie. Data afkomstig van toetse op 'n siese struktuur sal gekorreleer word met data afkomstig van 'n numeriese model van die selfde struktuur. Die data van belang is die dinamiese eienskappe van 'n anten- nastruktuur, spesi ek die modusvorme en modale frekwensies. Die betrokke struktuur wat gebruik is, is 'n vereenvoudigde skaalmodel van die Karoo Array Telescope-7 (KAT-7) antennastruktuur. Eksperimentele datakorrelasie is, tradisioneel gesproke, 'n moeilike en tydro- wende taak. Hierdie verslag sal illustreer op watter wyse optimisering 'n inge- nieur van hulp kan wees in die proses om 'n eindige elementmodel met vibrasietoetsdata te korreleer.
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Kolhatkar, Shashank C. "Modal analysis of a robot arm using the finite element analysis and modal testing /." Online version of thesis, 1989. http://hdl.handle.net/1850/10623.
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Lanier, Prather Jonathan. "Stereovision Correction Using Modal Analysis." Thesis, Virginia Tech, 2010. http://hdl.handle.net/10919/31662.
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Presently, aerial photography remains a popular method for surveillance of landscapes, and its uses continually grow as it is used to monitor trends in areas such as plant distribution and urban construction. The use of computer vision, or more specifically stereo vision, is one common method of gathering this information. By mounting a stereo vision system on the wings of an unmanned aircraft it becomes very useful tool. This technique however, becomes less accurate as stereo vision baselines become longer, aircraft wing spans are increased, and aircraft wings become increasingly flexible. Typically, ideal stereo vision systems involve stationary cameras with parallel fields of view. For an operational aircraft with a stereo vision system installed, stationary cameras can not be expected because the aircraft will experience random atmospheric turbulence in the form of gusts that will excite the dominate frequencies of the aircraft.
A method of stereo image rectification has been developed for cases where cameras that will be allowed to deflect on the wings of an fixed wing aircraft that is subjected to random excitation. The process begins by developing a dynamic model the estimates the behavior of a flexible stereo vision system and corrects images collected at maximum deflection. Testing of this method was performed on a flexible stereo vision system subjected to resonance excitation where a reduction in stereo vision distance error is shown. Successful demonstration of this ability is then repeated on a flying wing aircraft by the using a modal survey to understand its behavior. Finally, the flying wing aircraft is subjected to random excitation and a least square fit of the random excitation signal is used to determine points of maximum deflection suitable for stereo image rectification. Using the same techniques for image rectification in resonance excitation, significant reductions in stereo distance errors are shown.Master of Science
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McDonald, Steven. "Operational modal analysis, model updating, and seismic analysis of a cable-stayed bridge." Thesis, University of British Columbia, 2016. http://hdl.handle.net/2429/56633.
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The Port Mann Bridge is currently one of the longest cable-stayed bridges in North America and the second widest bridge in the world. It is a cable-stayed bridge consisting of 288 cables, two approach spans made of concrete box girders and precast deck panels, and a main span consisting of steel girders and cross beams with precast deck panels. This work sets out to accomplish three main goals: study the dynamic behaviour of the Port Mann Bridge, calibrate the finite element model, and study the effects of model updating using a seismic analysis. The dynamic behaviour of the Port Mann Bridge’s main span is studied using experimental data from field ambient vibration tests and from a structural health monitoring network. A finite element model is created by importing a version of the structural designer’s model and editing it based on design drawings. In order to assess what parameters would be feasible to calibrate, a sensitivity analysis is carried out using various material properties and boundary conditions. The model is then updated to match the experimental analysis results by varying multiple parameters. Finally, the calibrated model is compared to the original model by completing a linear time history analysis. A suite of ground motions were selected and scaled to match specific points on the response spectrum corresponding to the first few periods of the structure. Multiple critical locations are monitored in the time history analysis, and data from these locations are compared before and after calibration to examine the effect of model updating. The study concludes that model updating has a large effect on the predicted seismic behaviour of the bridge, which proves the importance of calibrating finite element models and maintaining physically meaningful parameters. It also shows that having a structural health monitoring program is very important for current and future research endeavours.Applied Science, Faculty of
Civil Engineering, Department of
Graduate
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Hanson, David Mechanical & Manufacturing Engineering Faculty of Engineering UNSW. "Operational modal analysis and model updating with a cyclostationary input." Awarded by:University of New South Wales. School of Mechanical and Manufacturing Engineering, 2006. http://handle.unsw.edu.au/1959.4/31199.
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This thesis addresses the problem of identifying the modal properties of a system based only on measurements of the system responses. This situation is frequently encountered in structural dynamics and is particularly relevant for systems where the in-service excitation is not artificially reproducible. The inherent non-linearities in these systems mean that the modal properties estimated using traditional input/output techniques will be different to those exhibited in operation. A common example from the literature is an aircraft in flight where the modal properties are heavily influenced by the operating point, i.e. the combination of load, speed, altitude etc., at which the aircraft is travelling. The process of identifying the modal properties of systems in-service is called Operational Modal Analysis (OMA). Not knowing the input complicates the analysis. Most of the techniques in the literature overcome the lack of knowledge about the unmeasured excitations by assuming they are both spatially and frequentially white, i.e. of equal magnitude and with a flat autospectrum. This thesis presents a new technique for OMA which relaxes these constraints, requiring only that the system is excited by a so called cyclostationary input with a unique cyclic frequency, and that the log spectrum of the second order component of this input is frequentially smooth, as will be explained. Such systems include vehicles with internal combustion engines as the vibration from such an engine exhibits cyclostationary statistics. In this thesis, the technique is applied to a laboratory test rig and a passenger train both using an artificial input, and to a race car using the engine as the excitation. By combining cyclostationary signal processing and the concept of the cepstrum, the technique identifies the resonances and anti-resonances in the transfer functions between each response and the cyclostationary source. These resonances and antiresonances can be used to regenerate Frequency Response Functions (FRFs) and it is shown how the unknown scaling of the system can be recovered by employing finite element model updating in conjunction with this regeneration. In addition, the contribution made to model updating by the anti-resonances is also investigated. Finally, the potential of OMA to inform a model updating process is demonstrated using an experimental case study on a diesel railcar.
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Wicks, Matthew L. "A modal analysis method for a lumped parameter model of a dynamic fluid system." Thesis, This resource online, 1993. http://scholar.lib.vt.edu/theses/available/etd-07292009-090406/.
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Gutierrez-Wing, Enrique Simon. "Modal analysis of rotating machinery structures." Thesis, Imperial College London, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.409293.
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Chan, Kin Lung. "Modal analysis of elliptic waveguide junctions." Thesis, University of Hull, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.389728.
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Mahdi, Hassan Hamoodi. "Vibrational modal analysis of rotating machines." Thesis, University of Hertfordshire, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.303391.
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Archibald, Charles Mark. "Parametric spatial modal analysis of beams." Diss., Virginia Tech, 1993. http://hdl.handle.net/10919/37278.
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Modal analysis is the experimental characterization of the dynanlical behavior of a structure. Recent advances in laser velocimetery have made available to the experimentalist a rich, new source of vibration data. Data can now be obtained from many different spatial locations on a structure. A method is presented to use this new data for the analysis of beams. Two approaches are investigated: minimum residual methods and boundary condition methods. The minimum residual approaches include autoregressive methods and non-linear least squares techniques. Significant contributions to sample rate considerations for parametric sinusoidal estimation resulted from this research. The minimum residual methods provide a good connection between the measured data and the fitted model. However, they do not yield a true modal decomposition of the spatial data. The boundary condition approach provides a complete modal model that is based on the spatial data and is completely compatible with classical beam theory. All theoretical constraints are included in the procedure. Monte Carlo investigations describe the statistical characteristics of the methods. Experiments using beams validate the methods presented. Advantages and limitations of each approach are discussed.Ph. D.
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You, You, and Daxin Chen. "Modal Analysis on a MIMO System : For an asphalt roller CC1200." Thesis, Blekinge Tekniska Högskola, Institutionen för maskinteknik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:bth-10998.
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Impact hammer is the current modal testing way in Dynapac testing department. Due to highly damped characteristic of big construction machines, there are a few weaknesses for modal testing when using hammer, such as short response time, limited frequency resolution, poor quality of frequency response functions. Therefore, a more advanced excitation equipment is needed to improve the measurement quality. The object for this study is to compare two different measuring methods. The thesis will show a comparison between the hammer testing and the shaker MIMO testing compared with analytical model in a highly damped system. It will also give a reference for further highly damped modal analysis and budgetary assessment to decide the budget expenditure. Result from shaker testing shows a little better correlation than hammer testing compared with FEM model. While the correlation between FEM model and measurement is bad due to many reasons, such as many local modes that can not excited, lack of excitation points, unexpected noise and error from the measurement. While considering the compared results obtained from this machine for now, a simpler structure experiment is suggested to be carried on in the future. Shorter length of stinger can be used to enable higher amplitude of force to excite the property on this machine.
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Aluri, Srinivas. "Updating low-profile FRP deck FE model using experimental modal analysis." Morgantown, W. Va. : [West Virginia University Libraries], 2006. https://eidr.wvu.edu/etd/documentdata.eTD?documentid=4656.
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Thesis (M.S.)--West Virginia University, 2006.Title from document title page. Document formatted into pages; contains vi, 76 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 60-61).
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Baldwin, Mark W. "Modal Analysis Techniques in Wide-Area Frequency Monitoring Systems." Diss., Virginia Tech, 2008. http://hdl.handle.net/10919/26522.
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The advent of synchronized wide-area frequency measurements obtained from frequency disturbance recorders and phasor measurement units has presented the power industry with special opportunities to study power system dynamics. I propose the use of wide-area frequency measurements in identifying system disturbances based on power system post-event modal properties.
In this work, power system dynamics are examined from an internal system energy viewpoint. Since an electric power system is composed of coupled rotating machines (large generators) which have air gap magnetic fields that are essentially static, or quasi-static, the power system may be modeled as a system with energy stored in quasi-static magnetic fields. The magnetic fields in the machines do change with time but may be modeled as static as far as wave propagation is concerned. The dynamic model that I develop treats this magnetic energy specifically as potential energy. Each rotating machine also contains an inertia due to the mass and motion of its rotor train and so each machine contains a rotational kinetic energy. Thus the internal system energy for a power system dynamic model may be considered to be contained in potential (magnetic) and kinetic (rotating mass) energies. This notion of internal energy lends itself to the use of a state-space model where each system state is associated with either a kinetic energy or a potential energy. An n-machine system would have a total of 2n states and would thus be a 2n-th order system. For many power system disturbances, I postulate that a linearized version of this model may be used to examine system natural response in terms of frequency and phasor measurements. The disturbances that I will investigate include generator and line outages. For any particular outage, the power system exhibits a very specific natural response in terms of its kinetic and potential energies. Kinetic energy in the system is directly related to each specific machine's rotational speed. I propose that the kinetic energy corresponds directly with bus frequencies through a linear transformation. Likewise magnetic field energy in each machine corresponds directly with a torque angle. The potential energy in the system thus corresponds directly with bus angles through a linear transformation.
The primary focus of this work is on frequency deviation modal characteristics – specifically damped oscillation frequencies, mode shapes, and damping ratios. This work presents how specific disturbances on a power system will lead to specific oscillation frequencies in the deviation quantities and that these oscillation frequencies may be used to identify the disturbance. The idea of disturbance identification stems out of previous work done in locating disturbances by using a distributed parameter (DP) model of an electric power system. This DP model, which assumes a wave-like motion of frequency and phase quantities, was used to locate disturbances via a triangulation method. This present work, instead of using a DP model of the power system, assumes lumped parameters and focuses on disturbance identification strictly via modal characteristics – particularly oscillation frequency in the frequency deviations. This model is not concerned with geographic location but focuses on system topology, loading, and machine mass as lumped parameters. Advantages of disturbance identification include mainly reliability enhancements but can also be used in marketing applications.
The state-space model used to realize this theory is verified via simulation using small, "academic" systems which should prove useful in classroom settings. Additionally the model is verified on a larger test system in order prove its validity and potential usefulness on large power systems.Ph. D.
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Serbichenko, Daria. "Modal analysis of time-dependent structures using Derictional Derivatives." Thesis, Ecole centrale de Nantes, 2019. http://www.theses.fr/2019ECDN0059.
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Dans un grand nombre de domaines, l'analyse modale de structures est une composante capitale du dimensionnement. Pour l'identification des fréquences et modes propres, les logiciels de calcul éléments finis sont maintenant souvent utilisés et offrent des réponses rapides et satisfaisantes dans une grande majorité de cas. Cependant, lorsqu'une structure possède une géométrie qui varie au cours du temps ou alors lorsqu'une fissure se propage dans cette structure, les méthodes classiques employées peuvent être contraignantes et consommatrice de temps CPU (remaillage, résolution itérative de problèmes aux valeurs propres...), surtout si l'on veut suivre l'évolution des solutions propres.Dans ces travaux de doctorat, une méthode originale est proposée afin d’améliorer la gestion de l’analyse modale de structures subissant des changements de forme au cours du temps. Celle-ci est basée sur les dérivées directionnelles et sur la méthode X-FEM. En effet, les dérivées directionnelles permettent de prédire l’évolution des solutions propres entre deux configurations temporelles de la structure et X-FEM permet de s’affranchir des contraintes liées au maillage de chacune des configurations. Grâce à des critères spécifiquement développés, la méthodologie a été testée pour des cas de problèmes plans et axysymétrique. Les résultats obtenus en regard des méthodes classiques et les conclusions qu’elles peuvent amener, permettent de voir les nombreux avantages de l’outil que nous avons proposéIn many industrial fields, modal analysis of structures is a primary key during the design. Finite Element Method is often used to identify both natural frequencies and shapes, offering quick and satisfactory answers in most cases. However, when a structure possesses a time-dependent geometry or if the structure is subjected to a crack propagation, the standards methods used can be constraining. They can also be CPU time consuming (due to remeshing, iterative solving of eigenvalue problems…), especially if one wants to track the evolution of the eigensolutions.In this research work, an original method is proposed to improve the management of finding the evolution of eigensolutions in case of time-dependent structures. This methology is based on the combination of directional derivatives and X-FEM. The directional derivatives allow to estimate the evolution of the eigensolutions between two configurations of the structure and X-FEM overcomes the constraints related to mesh generation of each configuration. Through specific developed criteria, the methodology has been tested for cases of plane and axisymmetric problems. The results obtained in comparison to the standard modal analyses and the conclusions that they can bring, highlight the advantages of the numerical tool that we proposed
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Zhou, Wenliang. "Multivariate analysis in vibration modal parameter identification /." View online ; access limited to URI, 2006. http://0-digitalcommons.uri.edu.helin.uri.edu/dissertations/AAI3248248.
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Saad, Mohamed Shawky. "Problems in selective modal analysis and control." College Park, Md. : University of Maryland, 2007. http://hdl.handle.net/1903/6882.
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Thesis (Ph. D.) -- University of Maryland, College Park, 2007.Thesis research directed by: Electrical Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Thurston, Michael G. "Modal analysis of a computer disk drive /." Online version of thesis, 1988. http://hdl.handle.net/1850/10139.
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Zheng, Ming M. Eng Massachusetts Institute of Technology. "Modal pushover analysis for high-rise buildings." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/82829.
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Thesis (M. Eng.)--Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 2013.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 50).
Pushover analysis is a nonlinear static analysis tool widely used in practice to predict and evaluate seismic performance of structures. Since only the fundamental mode is considered and the inelastic theorem is imperfect for the conventional pushover analysis, a modified Modal Pushover Analysis (MPA) is proposed by researchers. In this thesis, the theories of dynamics for single-degree-of-freedom (SDOF) and multiple-degree-of-freedom (MDOF) are introduced, including elastic analysis and inelastic analysis. The procedures and equations for time history analysis, modal analysis, pushover analysis and modal pushover analysis are discussed in detail. Then an 8-story height model and a 16-story height model are established for analysis. The pushover analysis is conducted for each equivalent SDOF system, and by combination of the distribution of 1 mode, 2 modes and 3 modes, the responses of modal pushover analysis are obtained. The results of pushover analysis and modal pushover analysis are compared with those of time history analysis. The results of the analysis show that the conventional pushover analysis is mostly limited to low- and medium-rise structures in which only the first mode is considered and where the mode shape is constant. The modal pushover analysis is shown to have a superior accuracy in evaluation of seismic demands for higher buildings, especially for story drift ratios and column shears. With this in mind, some design recommendations and areas of future work are proposed in the conclusion.
by Ming Zheng.
M.Eng.
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Martell, Raymond F. "Investigation of Operational Modal Analysis Damping Estimates." University of Cincinnati / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1291147391.
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Busseti, Gabriele. "Modal and Fatigue Analysis of the Stratotimer." Thesis, KTH, Lättkonstruktioner, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-262042.
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Fatigue analysis of the printed circuit boards (PCBs) of an avionic instrument has been analyzed. The natural frequency and transmissibility has been estimated through analytical approach and finite element approach with Solid- Works and experimentally. Fatigue analysis damage has been obtained with three methods: Steinberg Stress approach, Steinberg Relative Displacement approach and Dirlik method. The analysis indicates that the solder that holds the CPU on the control unit is critical for the fatigue life. The results show that each method is far from the critical CDI value of 0:7 and therefore the design could be optimized.En utmattningsanalys har utförts av ett kretskort (printed circuit board” PCB) i en avioniskt kronograf, kallad Stratotimer. Egenfrekvenser och överföring har uppskattats analytiskt, nummeriskt med finita element i SolidWorks samt experimentellt. Utmattningsrisk har predikterats med tre metoder: Steinbergs spänningskriterium, Steinbergs relativa förskjutningskriterium och Dirlikmetod. Analysen indikerar att den lödning som håller fast CPUn på kontrollenheten är kritisk för utmattningslivet. Resultaten från de ollika metoderna skiljer sig något men samtliga metoder indikerar en stor marginal till det kritiska design indexet (CDI) på 0,7. Därmed bör det finnas utrymme för optimering av Stratotimern.
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Drexel, Michael V. "Modal parameter identification using mode isolation." Diss., Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/17239.
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Zhou, Shi Huang. "Operational modal decomposition approach for MDOF structures using multi-channel response measurements." Thesis, University of Macau, 2018. http://umaclib3.umac.mo/record=b3950681.
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Buke, Fatih. "An Investigation On The Application Of Operational Modal Analysis." Master's thesis, METU, 2006. http://etd.lib.metu.edu.tr/upload/2/12607529/index.pdf.
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Modal parameter identification of a structure is done through modal testing and modal analysis using various system identification methods. These methods employ linear input-output relationships to extract the modes of a structure.
There are cases where laboratory testing of a structure is not possible or information about the structure under operating conditions is seeked. A set of techniques called Operational Modal Analysis have been developed for modal parameter identification in operating conditions of a structure. These techniques use only response measurements to extract the modes.
The aim of this study is to investigate the applicability and use of three selected time-domain methods adapted to operational modal analysis. The algorithms are programmed in Matlab©environment, and various cases are evaluated using computer simulations for each method. Two of the selected methods are evaluated on a laboratory scale test setup.
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Swaminathan, Balakumar. "Operational Modal Analysis Studies on an Automotive Structure." University of Cincinnati / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1277155789.
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Marudachalam, Kannan. "An attempt to quantify errors in the experimental modal analysis process." Thesis, This resource online, 1992. http://scholar.lib.vt.edu/theses/available/etd-08142009-040508/.
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Kaya, Huseyin. "Experimental Modal Analysis Of A Steel Grid Frame." Master's thesis, METU, 2004. http://etd.lib.metu.edu.tr/upload/3/12604710/index.pdf.
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In this study, experimental modal analysis was studied. Experimental modal analysis includes modal testing, modal parameter estimation and calibration. For this purpose a 4 span skewed steel frame was constructed in Structural Mechanics Laboratory of Civil Engineering Department of METU. The model was transported to Vibration and Acoustic Laboratory of Mechanical Engineering Department of METU. The tests were conducted by cooperation with Vibration and Acoustics Laboratory. Due to lack of experimental modal analysis software in Structural Mechanics Laboratory, modal parameter estimation and finite element updating softwares were written in Matlab platform. The written softwares were executed on the data obtained from modal testing.
15 reasonable modes are extracted from the FRFs that are obtained from modal testing. 59.23 percent consistency is found for the nominal modal comparison. At the end of calibration process 76.14 percent consistency is achieved between the experimental results and analytical results.
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Shimizu, Kenji. "Application of modal analysis to strongly stratified lakes." University of Western Australia. Faculty of Engineering, Computing and Mathematics, 2009. http://theses.library.uwa.edu.au/adt-WU2009.0079.
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Modal analysis for strongly stratified lakes was extended to obtain a better understanding of the dynamics of the basin-scale motions. By viewing the basin-scale motions as a superposition of modes, that have distinct periods and three-dimensional structures, the method provides a conceptual understanding for the excitation, evolution, and damping of the basin-scale motions. Once the motion has been decomposed into modes, their evolution and energetics may be extracted from hydrodynamic simulation results and field data. The method was applied to Lake Biwa, Japan, and Lake Kinneret, Israel, and used for a theoretical study. The real lake applications showed that winds excited basin-scale motions that had a surface layer velocity structure similar to the wind stress pattern. Three-dimensional hydrodynamics simulations of Lake Biwa indicated that most of the energy input from winds was partitioned into the internal waves that decayed within a few days. The gyres, on the other hand, received much less energy but dominated the dynamics during calm periods due to their slow damping. Analyses of field data from Lake Kinneret suggested that the internal waves, excited by the strong winds every afternoon, were damped over a few days primarily due to bottom friction. Theoretical investigations of damping mechanisms of internal waves revealed that bottom friction induced a velocity anomaly at the top of the boundary layer that drained energy from the nearly inviscid interior by a combination of internal wave cancelling and spin-down. These results indicate that gyres induce long-term horizontal transport near the surface and internal waves transfer energy from winds to near-bottom mixing. Modal structure of dominant basin-scale internal waves can induce large heterogeneity of nearbottom mass transfer processes. The method presented here provides a tool to determine how basin-scale motions impact on biogeochemical processes in stratified lakes.
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Shen, Zhongxiang. "Modal expansion analysis of monopole and microstrip antennas." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0009/NQ30645.pdf.
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Elizalde, Siller Hugo Ramon. "Non-linear modal analysis methods for engineering structures." Thesis, Imperial College London, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.419886.
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Johnston, Mark. "Static and modal analysis of wind turbine towers." Thesis, De Montfort University, 1999. http://hdl.handle.net/2086/4184.
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Wake, Richard Neil. "Detection of cracks in cylinders using modal analysis." Thesis, University of Newcastle Upon Tyne, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.321302.
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Eow, Andy Khai Siang. "Quantitative multi-modal analysis of pediatric focal epilepsy." Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/34110.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2005.Includes bibliographical references (p. 101-103).
For patients with medically refractive focal epilepsy, surgical intervention to remove the epileptic foci is often the last alternative for permanent cure. The success of such surgery is highly dependent on the doctor's ability to accurately locate the epileptogenic region during the pre-surgical planning and evaluation phase. Hence the goal of this project is to provide an end-to-end quantitative analysis pipeline that fuses an array of imaging modalities including magnetic resonance imaging (MRI), diffusion tensor MRI, positron emission tomography (PET), single-photon emission computerized tomography (SPECT) as well as EEG data to build patient-specific head models and to compute prior probability maps of epileptic hotspots for more accurate EEG source localization. By improving the ability to accurately locate these epileptogenic seizure sources, patients can benefit tremendously from accurate surgical resection and consequently have a better chance for complete seizure free recovery.
by Andy Khai Siang Eow.
S.M.
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Yamashita, Nelson N. "Modal analysis of a cylindrical dielectric-loaded cavity." Thesis, Massachusetts Institute of Technology, 1987. http://hdl.handle.net/1721.1/14832.
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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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Venturella, Michael Anthony. "Modal Analysis of the Ice-Structure Interaction Problem." Thesis, Virginia Tech, 2008. http://hdl.handle.net/10919/31749.
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In the present study, the author builds upon the single degree of freedom ice-structure interaction model initially proposed by Matlock, et al. (1969, 1971). The model created by Matlock, et al. (1969, 1971), assumed that the primary response of the structure would be in its fundamental mode of vibration. In order to glean a greater physical understanding of ice-structure interaction phenomena, it was critical that this study set out to develop a multi-mode forced response for the pier when a moving ice floe makes contact at a specific vertical pier location. Modal analysis is used in which the response of each mode is superposed to find the full modal response of the entire length of a pier subject to incremental ice loading. This incremental ice loading includes ice fracture points as well as loss of contact between ice and structure. In this model, the physical system is a bottom supported pier modeled as a cantilever beam. The frequencies at which vibration naturally occurs, and the mode shapes which the vibrating pier assumes, are properties which can be determined analytically and thus a more precise picture of pier vibration under ice loading is presented. Realistic conditions such as ice accumulation on the pier modeled as a point mass and uncertainties in the ice characteristics are introduced in order to provide a stochastic response. The impact of number of modes in modeling is studied as well as dynamics due to fluctuations of ice impact height as a result of typical tidal fluctuations. A Poincaré based analysis following on the research of Karr, et al. (1992) is employed to identify any periodic behavior of the system response. Recurrence plotting is also utilized to further define any existing structure of the ice-structure interaction time series for low and high speed floes. The intention of this work is to provide a foundation for future research coupling multiple piers and connecting structure for a comprehensive ice-wind-structural dynamics model.Master of Science
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Davis, Ivan Christopher. "Damage Detection in Aluminum Cylinders Using Modal Analysis." Thesis, Virginia Tech, 2002. http://hdl.handle.net/10919/34317.
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Many studies have attempted to detect structural damage by examining differences in the frequency response functions of a structure before and after damage. In an experimental setting, this variation can not be attributed solely to the addition of damage. Other sources of variation include testing and structure variation. Examples of testing variation include the error introduced by modal parameter extraction, measurement noise, and the mass loading of the accelerometer. Structure variability is due to slight differences in the supposedly identical structures. Dimensional tolerancing is one example.
This study began with six "identical" undamaged aluminum cylinders, of which three were later damaged to varying extents. The frequency response functions of the undamaged and damaged cylinders were measured. Also, the frequency response function of the same undamaged cylinder was measured multiple times to investigate testing variation. The contributions of testing, cylinder, and damage variation to the differences between cylinder responses was elucidated by specifically examining their frequency response functions in two ways: comparing the natural frequencies and directly investigating the entire frequency response function. The curvature of the frequency response functions was then used to determined the presence, location, and severity of the imparted damage.Master of Science
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Prater, Glen. "Complex modal analysis of nonproportionally damped continuous beams /." The Ohio State University, 1988. http://rave.ohiolink.edu/etdc/view?acc_num=osu14875974241363.
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Uwajambo, Pacifique, and Nisha Thakur. "Numerical and Experimental Modal Analysis of CNC Machine." Thesis, Blekinge Tekniska Högskola, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:bth-21652.
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Numerical and Experimental Modal Analysis of RAW CNC milling machine was performed in this project. The RAW CNC machine's lightweight, easy assembling, and operation features make it a good choice for hobbyists and professionals. As the machine is subjected to vibration during the milling process, the work is intended to study the machine's dynamic behaviour through Finite Element Method (FEM) in the first stage, followed by validating it with Experimental Modal Analysis (EMA). The simulation and experimentation are focused on X and Y-axis. In the first stage, the inventor model of the machine was created and then simulated in COMSOL Multi-physics and Nastran by extracting mode shapes and frequencies. In the second stage, experimentation was carried out in the laboratory for both axes separately. Through the EMA, the four resonance frequencies and their mode shape were determined and compared with the simulated FEM modal. The result showed the first lowest frequency for the x-axis in experimental modal had a bit more deviations than finite element simulation, which raised the need for estimation of possible causes of error. However, the deviation range between experimental and FEM simulation is below 16.68%, which was acceptable for all other modes. From the analysis, the Y-axis beams were the weakest part of the machine. Finally, methods for improving the model was recommended, which could be applied in future models to increase the stiffness of the machine.
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Tremaine, Kellie Michelle. "MODAL ANALYSIS OF COMPOSITE STRUCTURES WITH DAMPING MATERIAL." DigitalCommons@CalPoly, 2012. https://digitalcommons.calpoly.edu/theses/823.
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The purpose of this study is to develop an analytical solution for modal analysis of actively damped orthotropic composite plates in bending and to verify it with experimental analysis.
The analytical modal analysis solution for composite plate dynamics is derived using Euler theory. This analysis applies to structures with orthotropic lamina of uniform material properties at any lamination angle. The bending-extensional coupling can be neglected for plates that are symmetric or approximately symmetric, which allows an exact solution for natural frequency and mode shape to be obtained. An exact solution can be found for natural vibration and in general.
The active control is modeled analytically by combining the Lagrange equation with the Ritz Assumed Mode method. This analysis produces a generalized coordinate vector that correlates the assumed mode to the particular amplitude of a particular case. The kinetic energy dissipated by the piezoelectric actuator from the system over one oscillation can be calculated from the generalized coordinate vector and the assumed mode. The equivalent damping ratio of the active control system is calculated as the ratio between the kinetic energy absorbed by the piezoelectric actuator from the system in one oscillation and the maximum strain energy of the system during that oscillation.
A point mass on the plate, such as an accelerometer mass, can also be modeled as a single layer of uniform mass, that is an isotropic layer, by equating the potential energy of the point mass with the potential energy of the uniform mass layer. It is important to note that the mass of the isotropic layer is frequency dependent, and it has no effect on the plate stiffness.
The analytical model is validated by comparison to experimental work. The samples studied were aluminum and composite plates of various lengths. The active control predictions were also validated using previous experimental work completed at California Polytechnic State University in San Luis Obispo. These cases included active control of an aluminum beam with a patch of piezoelectric material and an aluminum sailplane with a patch of piezoelectric material.
Results indicate that while the analytical mode solutions are in good agreement with the experimental results, they are also systematically higher than the experimental results. The analytical active control solutions match previous work when the piezoelectric effects are linear. The main result of adding an active control system is approximately a 5-10% increase in modal frequencies and a 200-800% increase of damping ratio.
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XHIXHA, ELONA. "PASSIVE METHOD FOR DYNAMIC CHARACTERIZATION OF SOIL AND BUILDINGS." Doctoral thesis, Università di Siena, 2017. http://hdl.handle.net/11365/1013203.
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The research followed consist mainly on the use of passive methods for dynamic characterization of soil and building. Local Seismic Response of the construction site and Calibration of FE model of a reinforced concrete building have been performed. Passive seismic measurements have been acquired by two portable seismographs synchronized by each other with GPS antenna. Subsequently, structural verifications (global structural response) have been realized using once the response spectrum estimated from Local Seismic Response and once from technical standards. Finally, confronts between results have been realized at the aim to evaluate the importance of local seismic response of soil.
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Wang, Yaolun. "Vibrational measurement techniques applied on FE-model updating." Thesis, Linnéuniversitetet, Institutionen för maskinteknik (MT), 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-45213.
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In this thesis, the dynamics of two plates overlapping and connected by three bolts are studied. The data collected in the test are used in modal analysis. The vibrational test and the modal analysis were made using an LMS system. Hammer excitation is used for the tests. The main purpose of this thesis is to study how the suspensions affect the extracted eigenfrequencies and modal dampings. In this thesis, more than 10 suspensions were examined. Another objective in this thesis work is to build an FE-model. This model is made using the software Abaqus. To improve the reliability of the FE-model, a set of reliable experimental data is used to calibrate the model. The calibrated FE-model, using the measurement data, has a dynamic behavior close to the measurement data.
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Altunel, Fatih. "Model Updating Of A Helicopter Structure Using A Newly Developed Correlation Improvement Technique." Master's thesis, METU, 2009. http://etd.lib.metu.edu.tr/upload/2/12611300/index.pdf.
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Numerical model usage has substantially increased in many industries. It is the aerospace industry that numerical models play possibly the most important role for development of optimum design. However, numerical models need experimental verification. This experimental verification is used not only for validation, but also updating numerical model parameters. Verified and updated models are used to analyze a vast amount of cases that structure is anticipated to face in real life.
In this thesis, structural finite element model updating of a utility helicopter fuselage was performed as a case study. Initially, experimental modal analyses were performed using modal shakers. Modal analysis of test results was carried out using LMS Test.lab software. At the same time, finite element analysis of the helicopter fuselage was performed by MSC.Patran &Nastran software. v Initial updating was processed first for the whole helicopter fuselage then, tail of the helicopter was tried to be updated. Furthermore, a new method was proposed for the optimum node removal location for getting better Modal Assurance Criterion (MAC) matrix. This routine was tried on the helicopter case study and it showed better performance than the Coordinate Modal Assurance Criterion (coMAC) that is often used in such analyses.
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Tbaileh, Ahmad Anan. "Power System Coherency Identification Using Nonlinear Koopman Mode Analysis." Thesis, Virginia Tech, 2014. http://hdl.handle.net/10919/49261.
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In this thesis, we apply nonlinear Koopman mode analysis to decompose the swing dynamics of a power system into modes of oscillation, which are identified by analyzing the Koopman operator, a linear infinite-dimensional operator that may be defined for any nonlinear dynamical system. Specifically, power system modes of oscillation are identified through spectral analysis of the Koopman operator associated with a particular observable. This means that they can be determined directly from measurements. These modes, referred to as Koopman modes, are single-frequency oscillations, which may be extracted from nonlinear swing dynamics under small and large disturbances. They have an associated temporal frequency and growth rate. Consequently, they may be viewed as a nonlinear generalization of eigen-modes of a linearized system. Koopman mode analysis has been also applied to identify coherent swings and coherent groups of machines of a power system. This will allow us to carry out a model reduction of a large-scale system and to derive a precursor to monitor the loss of transient stability.Master of Science
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Moloney, Christopher W. "Visual and analytical characteristics for the identification of complex modes." Thesis, Georgia Institute of Technology, 2003. http://hdl.handle.net/1853/16337.
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Zaki, Bassem R. "A modified approach to improve the robustness of the algorithm of mode isolation." Thesis, Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/17563.
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Mendonça, Willy Roger de Paula [UNESP]. "Estudo e implementação do método de Ewins-Gleeson para identificação de parâmetros modais." Universidade Estadual Paulista (UNESP), 2007. http://hdl.handle.net/11449/97093.
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Estruturas e máquinas em regime operacional usualmente são submetidas a carregamentos dinâmicos ocasionados por vibração. Este fenômeno é em grande parte prejudicial, tendo em vista que podem causar falhas por fadiga, ruídos indesejáveis, etc. Com objetivo de minimizar e avaliar níveis de vibração em sistemas estruturais, técnicas de modelagem teórica e experimental vêm sendo utilizadas com freqüência. Dentre diferentes técnicas aplicadas à avaliação do comportamento dinâmico de estruturas, a análise modal figura como uma das principais.O presente trabalho tem como objetivo implementar um método de identificação de parâmetros modais no domínio da freqüência, de estruturas com vários graus de liberdade (MDOF). O método foi implementado em um ambiente computacional de baixo custo. O programa desenvolvido possibilita através de suas interfaces gráficas identificar os parâmetros modais de dados experimentais de uma estrutura metálica ensaiada, simular os modos de vibrar identificados da estrutura e permite de forma pratica que os usuários com poucos conhecimentos em análise modal interajam com todo o processo de análise dos dados experimentais.
Structures and machines in operational regime are usually submitted to dynamic loads caused by vibration. This phenomenon is largely harmful, considering can cause cracks for fatigue, undesirable noises, etc. With objective of minimize and evaluate vibration levels in structural systems, techniques of theoretical and experimental modeling have been used frequently. Among different techniques applied to the evaluation of the dynamic behavior of structures, the modal analysis present as one of the main. The present work has as objective implements a method of identification of modal parameters in the domain of the frequency to structures with multi degrees of freedom (MDOF). The method should be implemented in a low cost software. The developed software had made possible through their graphic interfaces to identify the modal parameters of experimental data of a rehearsed metallic structure, to simulate the modes of vibration identified and make possible users with few knowledge in modal analysis interact with the whole the process of analysis of the experimental data.
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Rossetto, Gustavo Dalben. "Contribuição a teoria e pratica da analise modal acustica experimental." [s.n.], 2001. http://repositorio.unicamp.br/jspui/handle/REPOSIP/265319.
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Orientador: Jose Roberto de França ArrudaDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica
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Resumo: Neste trabalho uma geometria simples (cavidade retangular) é usada para o estudo da metodologia aplicada na análise modal acústica. Modelos analítico e numérico são desenvolvidos para a comparação com os resultados experimentais. Três tipos de dispositivos de excitação do sistema acústico foram construídos. Um baseado num pistão conectado a um shaker, e outros dois usando um alto-falante do tipo driver. O primeiro atuador usando o driver é similar ao modelo desenvolvido por um projeto europeu, onde um tubo flexível com uma terminação instrumentada com um microfone é usado para a condução da excitação acústica. O segundo atuador baseado no uso do driver também usa um tubo flexível, mas este é instrumentado com dois microfones em sua terminação. O comportamento destes dois últimos atuadores em termos de aceleração de volume (essencial para a análise modal acústica experimental) e de potência ativa (necessária para Análise Estatística de Energia Experimental) sendo injetados no meio são investigados. A análise modal experimental da cavidade retangular é realizada e um método que utiliza a transformada de Fourier espacial multidimensional do campo de pressão medido é proposto para-a construção do campo de deslocamento de partícula para a visualização do modo acústico
Abstract: In the present work, a simple geometry (rectangular shallow cavity) is used to investigate the acoustic modal analysis methodology. Analytical and numerical models are developed for the comparison with the experimental results. Three types of excitation devices were constructed. One based on a shaker-driven piston and the other two using a driver loudspeaker. The first actuator based on a driver loudspeaker is similar to a model developed by an EEC project, where a flexible tube with a socket, instrumented with one microphone, at its termination is used to conduct the sound excitation. The second actuator based on a driver loudspeaker alse uses a flexible tube, but it is instrumented with two microphones in its socket instead of one. The behavior of these last two actuators in terms of volume acceleration (essential in the acoustic modal analysis) and active power (necessary for the Experimental Statistical Energy Analysis) being injected into the medium are investigated. The experimental modal analysis of the rectangular cavity is performed and a method using multi-dimensional spatial Fourier transforms of the array of pressure measurements is proposed for the construction of the partic1e displacement field for acoustic mode shape visualization
Mestrado
Mecanica dos Sólidos e Projeto Mecanico
Mestre em Engenharia Mecânica
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Wang, Zhenhong. "Power flow analysis of engineering structure using substructure techniques." Thesis, University of Southampton, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.270373.
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Peng, Ya-Yi, and 彭爗毅. "The Manufacturing and Modal Analysis of Micro Electrostatic Modal Actuators." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/39977842756443862338.
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碩士華梵大學
機電工程研究所
93
A novel electrostatic micro modal actuator adopted the orthogonality of the mode shape of the microstructure is created. By using the design of the shape of the modal electrode, the stability of the actuator can be improved and the driving voltage can be reduced by controlling the actuated modes precisely. In the analysis in this investigation, the equations of motion considering the effect of the coupling between the flexibility and the electrostatic field of the micro actuator are developed. The modal equations derived by the modal expansion indicate that distributed electrostatic modal actuators can be realized through the constructed correctly modal electrodes and the specific excited mode. The developed electrostatic modal actuator can reduce the driven voltage and eliminate the spillover phenomenon. Since, the stiffness, the dynamic properties, and the stability of the system can be affected by the changes of the electric field, the effect of the electrostatic field and the shape of the electrode on the actuator are also investigated. The experimental modifications of the modes caused by different shapes of the actuators are examined by using the time-average holographic micro-scope laser interferometer. The analytical model considering the coupling effect between the structure and electrostatic field can be established in the form of the linear periodically time-varying function and the relationship between the full field mode and the driven voltage can be obtained.
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Lou, Jr-Cheng, and 盧志誠. "Modal Analysis of Ring Gyroscope." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/32321031944747373417.
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碩士國立臺灣大學
應用力學研究所
97
Research of Gyro has been developed for many years. It is used on airplane、ship and satellite for military affairs a long time ago then now it is applied to car or game industry and kinds of gyro evolved from rotor gyro into vibrating gyro or fiber gyro. The paper primarily study vibrating gyro because that can improve restrictions of rotor gyro including life and time of switch. There are all kinds of vibrating gyro include tuning fork gyro, rod gyro and hemispheres, and in this paper, the study main apply metallic ring which is driven and sense by piezoelectric material. So it can make the vibrating gyro vibrate without input signal and restrain vibrating in the node which can use force-balance method to check angular velocity between voltages in the future. According to experiment result, it can make sure the first natural frequency of the vibrating ring-gyro and design feedback circuit to let the ring vibrate without inputting signal in the first natural frequency and restrain to vibrate in the node. From the result, the metallic ring can achieve my demands. It must improve signal in the circuit and reduce affect from noise which will make for sensing angular velocity between voltages with force-balance method in the future.