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1
Sladojevic, Ivan. "Forced response analysis of aero-elastically coupled mistuned bladed discs". Thesis, Imperial College London, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.438210.
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Hutton, Timothy M. "Innovative Forced Response Analysis Method Applied to a Transonic Compressor". Wright State University / OhioLINK, 2003. http://rave.ohiolink.edu/etdc/view?acc_num=wright1074801945.
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White, Alex. "A quantitative analysis of hemodynamic forces on cellular response". Thesis, University of Sheffield, 2013. http://etheses.whiterose.ac.uk/5695/.
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Mechanical forces are known to be important in various physiological and pathological processes, including the development of atherosclerosis. In particular it is believed that abnormal shear stress, transduced by the vascular endothelium, is particularly important in promoting atherogenesis. However, it is still unclear to what extent the precise details of the mechanical environment to which the vascular endothelium is subjected affect its response. Therefore, a novel flow-bioreactor system has been developed which is capable of subjecting endothelial cells cultured in vitro to various mechanical parameters at similar levels to those applied in vivo. The fluid dynamics within the flow-bioreactor system has been analysed computationally to accurately quantify the mechanical forces experienced by cells cultured within the flow-bioreactor system, and a validation of the computational model used has been performed to ensure the accuracy of the results of the computational fluid dynamics analysis. The flow bioreactor system has been used to subject human endothelial cells to physiologically realistic mechanical forces for up to 24 hours. The cells were shown to realign in the direction of the shear stress and elongate in response to the application of WSS, consistent with the results shown both in other mechanical models and in vivo. A computational image processing programme has been developed to accurately quantify the morphology of cells. Quantitative analysis using this programme showed that the degree of realignment and elongation was significantly dependent on the local cell density. The enabling technologies developed during this project may help with future work aimed at elucidating the features of the mechanical environment which are important in promoting or suppressing atherogenesis.
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Dolasa, Anaita Rustom. "Computer-Aided Design Software for the Undamped Two-Dimensional Static and Dynamic Analysis of Beams and Rotors". Thesis, Virginia Tech, 1999. http://hdl.handle.net/10919/32283.
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The objective of this research work was to develop a design tool to analyze and design undamped beam and rotor systems in two dimensions. Systems modeled in two dimensions, such as beams with different moments of inertia, could produce varying responses in the each direction of motion. A coupling between the vertical and horizontal motions also exists in rotor systems mounted of fluid film bearings.
The computer program called 2DBEAM has been developed to model and provide analyses of such systems in two dimensions. The tool has been based on an existing design package, BEAM9, which in its present state provides the response of beams and rotors in one plane of motion. The 2DBEAM program has the capability of performing the static response, free vibration, forced dynamic response, and frequency response analyses of a system.
The Transfer Matrix Method has been used in the development of the software and an explanation of the method is included in this thesis. Mathematical problems and solutions encountered while developing 2DBEAM are also documented in this study. The code has been tested against analytical and published solutions for the types of analysis mentioned above and on coupled and uncoupled system models.Master of Science
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Griffin, Timothy R. "Computer-Aided Design Software for Torsional Analysis". Thesis, Virginia Tech, 1998. http://hdl.handle.net/10919/36548.
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The goal of this research has been the development of an effective design tool for torsional analysis. In the hopes of achieving this goal the computer program, Torsion 1, has been created. This torsional transfer matrix program provides the user with the ability to easily model multi-rotor systems using a simple user-interface. The program is capable of modeling such components or system characteristics as continuously distributed mass, viscous and structural damping, vibration absorbers, and gear meshes with gear tooth flexibility. The analysis capabilities of the program include forcedresponse and free-vibration analyses. The forced-response analysis module is capable of determining a system’s response to a static or harmonic torsional load. The free-vibration analysis module allows is capable of determining the eigenvalues and eigenvectors for damped and undamped systems. This thesis includes an explanation of the multi-rotor transfer matrix technique employed in Torsion 1. The derivation of transfer matrices for visco-elastic vibration absorbers, pendulum absorbers, flexible gear meshes, and planetary gear trains are included in this work. Finally, the validity of the program results is verified with a set of benchmark examples.Master of Science
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Romanov, Artyom. "Investigation and development of low-fidelity analytical models for forced response, flutter and distortion propagation analysis". Thesis, Imperial College London, 2013. http://hdl.handle.net/10044/1/24425.
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The study describes a methodology for the analysis and design of turbomachinery components at low-fidelity level. This methodology is part of a broad, object-oriented environment developed at the Rolls-Royce VUTC. The approach described in this thesis is applicable to any axial turbomachinery configuration, however, main emphasis is made on compressors. The purpose of the research is to provide the opportunity to perform forced response, flutter and other unsteady analysis without the need for the expensive CFD runs. This is particularly demanded in the early stages of the aero-engine design process or in any other cases when the detailed information of the engine is not yet available, however, a broad unsteady parametric analysis based on the existing information is needed. The model uses a linearized form of the mass, momentum and energy budgets to relate small changes in the state of the gas at several positions in the machine to known disturbances at inlet or outlet, or to known changes in the geometry. The chosen approach allows usage of an arbitrary gas model without the assumption of constant gas properties. It also provides a straightforward way to obtain a steady-state solution in a minimal amount of iterations and to evaluate the exact values of the characteristic slopes. The unsteady solution methodology represents an extended and improved Semi-Actuator Disc model. The major improvements are the real geometry application, ability to handle rotating bladerows, loss models implementation and the cascade impedance model. As the solver is linearized, the harmonic perturbations are assumed to have small amplitude compared to the steady-state data and relatively long wavelength, compared to the blade measurements. Thus contributions of several perturbation sources may be superimposed within the model. The model has a block-wise structure, where every block represents a blade or an empty duct. Non-reflecting boundary conditions are applied to the blocks boundary interfaces together with a thought-through method for the angular frequency scattering. This allows assembling a multi-bladerow domain with both rotating and stationary bladerows for the unsteady analysis. A great deal of effort has been made to connect the system to a modern and general representation of the engine geometry. This data is then used to set up the domain geometry with minimal assumptions, thus considering the changes in areas, radii and the slope of the annulus. The complex blade profile information is accessible at any moment during the computation, thus allowing using a chosen set of loss and deviation models. The model uses the same geometry database as used for the CFD and FE analysis, however, any geometry data may be overridden on demand. The model has been validated on a variety of data, from the previous publications, for forced response and flutter and from alternative solvers for distorted casings. The agreement between the calculated results and the reference data is very satisfactory, with nearly exact match for a series of idealized cases. The improvements introduced in this approach, such as cascade impedance model and the loss and deviation model package extend and complete several statements made in previous publications regarding the effect of total pressure loss and presence of the passage end reflections. The model is also validated against more complex reference cases, such as 3D CFD simulation of the LP turbine blade flutter, providing a good estimation of the damping curve slope in the low-ND region. Having a tip clearance loss model, the non-uniform casing simulations have been setup for evaluation of the relationship between the unsteady mass flow and pressure ratio perturbations. A thorough literature survey is made on the previous publications of the similar subject. The survey reviews a series of the modular systems for the axial turbomachinery analysis and then continues with the investigation of semi-empirical closures for the total pressure loss and outlet flow deviation modelling. The latter two play an essential role in this research as their implementation provides more realistic results, comparable to the heavy CFD runs. Greater part of the survey is devoted to the previous publications on various approaches for 1D and 2D unsteady turbomachinery modelling. The research completes with a thorough discussion of the features implemented and the results achieved, concluding with several future work proposals for the eventual further extension of the model as well as its applicability as a keystone for possible construction of a higher-fidelity solver. The primary programming object-oriented environment chosen for the model implementation is C++ with some parts written in FORTRAN.
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Zheng, Zhijun. "The analytical force prediction and dynamic response analysis of the Bristol H25A compressor". Thesis, This resource online, 1995. http://scholar.lib.vt.edu/theses/available/etd-01102009-063019/.
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Shrestha, Santosh. "A COMPARATIVE STUDY OF EQUIVALENT LATERAL FORCE METHOD AND RESPONSE SPECTRUM ANALYSIS IN SEISMIC DESIGN OF STRUCTURAL FRAMES". OpenSIUC, 2019. https://opensiuc.lib.siu.edu/theses/2561.
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Equivalent Lateral Force Method (ELF) and Response Spectrum Analysis (RSA) are the two most popular methods of seismic design of structures. This study aims to present a comparative study of the two methods using hand-calculated approach as well as computer analysis according to ASCE 7-10 Standards. The two methods have been compared in terms of base shear and story forces by analyzing various models for different number of stories and different support conditions. It was found that ELF gives conservative results in comparison to RSA. This result was more obvious in case of four-story frames. Hence, for structures of increased elevation, the analysis from ELF may not be sufficient.
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Chasparis, Filippos. "Vortex-induced motions of marine risers : straked force database extraction & transient response analysis". Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/50570.
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Thesis (S.M. in Mechanical Engineering and Naval Architecture and Marine Engineering)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2009.Includes bibliographical references (p. 55-58).
In part I of the thesis, we extend a methodology to extract a VIV hydrodynamic database from field data to accommodate partially straked cylinders. There are two databases, each consisting of the lift and added mass coefficients as functions of reduced velocity and amplitude of response; the first for the bare part of the riser, and the second for the straked part. First, the program VIVA together with nominal force databases obtained from laboratory hydrodynamic experiments is used in order to get an initial prediction of the riser response under a particular flow profile. The nominal databases are then altered in a systematic way until the new VIVA predicted response best matches the measured field response, thus resulting in optimal databases. In part II of the thesis, we show using experimental data on a model riser that lock-in of long flexible risers placed in sheared or uniform cross-flows is a much richer phenomenon than lock-in of flexibly-mounted rigid cylinders under similar conditions. In particular, we find that the frequency content of the riser response may be either narrow-banded around a single dominant frequency (Type I response) or distributed along a relatively broad range of frequencies (Type II response). Distinct transition from Type I to Type II response, and vice versa, can occur several times within a single experimental record. Type I responses reveal features of a quasi-periodic oscillation, often accompanied by large 3rd harmonic components in the acceleration and strain signals, increased correlation length, stable riser trajectories, and monochromatic traveling or standing waves.
(cont.) Type II responses, on the other hand, are characterized by features of chaotic oscillation with small or non-existent 3rd harmonic components in the acceleration and strain signals, reduced correlation length, and a continuous spectrum.
by Filippos Chasparis.
S.M.in Mechanical Engineering and Naval Architecture and Marine Engineering
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Garafolo, Nicholas Gordon. "AN EXPERIMENTAL INVESTIGATION OF MULTIPLE MODE EXCITATION OF AN INTEGRALLY BLADED DISK". University of Akron / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=akron1164047919.
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Gagne, Anton. "Effects of Asymmetry and Other Non-Standard Excitations on Structural Dynamic Forced Response Analysis of Turbomachinery Flow-Path Components". Thesis, KTH, Kraft- och värmeteknologi, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-154623.
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A recent paper explored a potential deficiency in the single frequency harmonic response structural dynamic analysis approach typically used to assess a resonant condition in turbomachinery flow path components. This deficiency is prevalent in supersonic flow conditions when non-adjacent stages are present. The previous investigation demonstrated other excitation sources present in complex or supersonic flows could be missed using the typical analysis approach, in some cases leading to large under-prediction of structural response when compared with a baseline transient analysis. This paper presents the results of a follow on study, in which the inclusion of these effects in dynamic analyses is investigated. A representative rotor was created and analyzed for forced response characteristics when individual and combined unsteady content was present. A simple shell and beam 2D model was used to study the forced response behavior using transient and harmonic analyses. The results showed a significant contribution from non-integer forcing as well as from certain integer order forcing. A 3D model was also created for future analysis but did not display the sideband characteristics similar to flow seen in the previous investigation.
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Kapp, Ashley. "An analysis of restructuring and work design used by manufacturing organisations in response to changing global forces". Thesis, Port Elizabeth Technikon, 2004. http://hdl.handle.net/10948/145.
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Due to the continual increase in competitive pressure from international organisations, it has become necessary to assess the degree of transformational change within South African organisations to overcome the effect of global forces. Transformation was investigated in terms of organizational restructuring and the various work designs that are utilised by organisations to deal with the effect of global forces. To examine the main problem, three sub-problems were identified. The first sub-problem that had been identified dealt with the extent of which global forces impacted on the business environment. It was investigated by evaluating various economic, technological and sociopolitical forces. From the results it may be concluded that global forces have a large impact on the local business environment. The second sub-problem looked at the degree to which work designs assisted organisations to manage the effect of global forces. It was evident that the flexible types of work designs were more readily utilised to optimise productivity and employee moral. Finally, the third sub-problem investigated the various structures that organisations could adopt to deal with the effect of global forces. Organisational structures were analysed in terms of customer orientation, fulfilment of company objectives and the types of structures that are used within organisations. The results showed that 75% of the sample population believed that their organisational structures co-ordinated all activities within their organisations. Feedback on the type of structures that were used by organisations revealed that various types are being used.
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Eshun, Kow Okyere. "Quantification of the Effects of Soil Uncertainties on Nonlinear Site Response Analysis: Brute Force Monte Carlo Approach". University of Akron / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=akron1367510751.
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Zhang, Zhi y Zhi Zhang. "Analytical Investigation of Inertial Force-Limiting Floor Anchorage System for Seismic Resistant Building Structures". Diss., The University of Arizona, 2017. http://hdl.handle.net/10150/625385.
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This dissertation describes the analytical research as part of a comprehensive research program to develop a new floor anchorage system for seismic resistant design, termed the Inertial Force-limiting Floor Anchorage System (IFAS).
The IFAS intends to reduce damage in seismic resistant building structures by limiting the inertial force that develops in the building during earthquakes. The development of the IFAS is being conducted through a large research project involving both experimental and analytical research. This dissertation work focuses on analytical component of this research, which involves stand-alone computational simulation as well as analytical simulation in support of the experimental research (structural and shake table testing).
The analytical research covered in this dissertation includes four major parts:
(1) Examination of the fundamental dynamic behavior of structures possessing the IFAS (termed herein IFAS structures) by evaluation of simple two-degree of freedom systems (2DOF). The 2DOF system is based on a prototype structure, and simplified to represent only its fundamental mode response. Equations of motions are derived for the 2DOF system and used to find the optimum design space of the 2DOF system. The optimum design space is validated by transient analysis using earthquakes.
(2) Evaluation of the effectiveness of IFAS designs for different design parameters through earthquake simulations of two-dimensional (2D) nonlinear numerical models of an evaluation structure. The models are based on a IFAS prototype developed by a fellow researcher on the project at Lehigh University.
(3) Development and calibration of three-dimensional nonlinear numerical models of the shake table test specimen used in the experimental research. This model was used for predicting and designing the shake table testing program.
(4) Analytical parameter studies of the calibrated shake table test model. These studies include: relating the shake table test performance to the previous evaluation structure analytical response, performing extended parametric analyses, and investigating and explaining certain unexpected shake table test responses.
This dissertation describes the concept and scope of the analytical research, the analytical results, the conclusions, and suggests future work. The conclusions include analytical results that verify the IFAS effectiveness, show the potential of the IFAS in reducing building seismic demands, and provide an optimum design space of the IFAS.
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Harrison, Stella y Siri Nöjd. "Influence of Foundation Modelling on the Seismic Response of a Concrete Dam". Thesis, KTH, Betongbyggnad, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-300448.
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It is of great importance to ensure the structural safety of dams during earthquakes since a failure may cause catastrophic consequences. Conventional computation of the structural response of dams is based on a simplified approach where the foundation is considered as massless. However, recent developments have produced several new analysis methods that consider the foundation mass, modelled with absorbing boundaries and free-field forces. These newer methods are intended to simulate the seismic structural response more accurately, optimize the design and minimise future unnecessary reparations. The aim of the thesis was to investigate the influence of foundation modelling in seismic time history analyses. This was done by comparing the established massless foundation approach to two approaches with foundation mass and free-field forces included; the analytical approach presented by Song et al. (2018) and the direct FE approach by Løkke (2018). Both the efficiency of the seismic wave propagation simulation and the structural response of the dam were of interest, and points on the dam and foundation were studied to accurately compare these modelling approaches. The time history analyses showed that the massless approach corresponded perfectly with the ideal theoretical velocity at the foundation surface when studying only the foundation block, as expected. The analytical and direct FE however, differed slightly from the theoretical value but still gave an accurate representation. Both methods using free-field forces obtained equivalent and realistic structural responses when studying the dam-reservoir-foundation model. The massless method however,strongly overestimated the dam response and was therefore found to not capture the actual behavior of the dam accurately, despite modifications such as increased material damping in the concrete. Additionally, another aim was to analyse the influence of modelling in 2D versus 3D for determining the dynamic characteristics of the dam such as natural frequencies and eigenmodes of the dam. These frequency analyses were made using models with and without foundation mass considered and was compared to experimental data.The massless 3D model was found to be the most effective modelling approach for deriving the dynamic characteristics of the dam since the use of a 3D model was necessary in order to study the behaviour of the whole dam and post-processing was simpler when using the massless model.Det är nödvändigt att säkerställa dammars säkerhet mot jordbävningar i design-processen eftersom ett dammbrott kan få katastrofala konsekvenser. Traditionellt används förenklade beräkningar där dammens strukturella respons beräknas med en berggrund där bergets massa är försummad. Den senaste tiden har flera nya analysmetoder tagits fram, som tar hänsyn till bergets massa och är modellerade med absorberande randvillkor och free-field forces. De nyare metoderna förväntas modellera de seismiska krafterna mer exakt för att optimera designen och minimera onödiga reparationer. Syftet med projektet var att undersöka inverkan från olika metoders sätt att beakta berggrunden vid seismiska analyser. Det utfördes genom att jämföra den etablerade masslösa metoden med två metoder som beaktar bergmassan och free-fieldforces; den analytiska metoden av Song et al. (2018) och Direct FE-metoden av Løkke (2018). Både effektiviteten i den seismiska vågutbredningssimuleringen och dammens strukturella respons var av intresse. Modelleringsmetoderna jämfördes genom att studera punkter på både dammen och berget. När enbart berggrunden studerades med den masslösa metoden så erhölls, som förväntat, god överenstämmelse med den ideala teoretiska hastigheten på bergsytan. De analytiska och Direct FE metoderna skiljde sig marginellt från det teoretiska värdet men gav fortfarande en korrekt hastighet på bergsytan. Vid analys av modeller med dam och reservoar inkluderade, gav metoderna som använde free-field forces ekvivalenta och realistiska strukturella responser. Den masslösa metoden däremot, överskattade kraftigt dammens respons och ansågs därför inte modelleradet verkliga beteendet hos dammen på ett korrekt sätt, trots modifieringar med ökad materialdämpning i betongen. Ett annat syfte var att analysera påverkan av modellering i 2D kontra 3D för att bestämma dammens dynamiska egenskaper, som egenfrekvenser och egenmoder. Dessa frekvensanalyser gjordes med hjälp av modeller som både beaktade och försummade bergets massa, och jämfördes med experimentella data. Den masslösa 3D-modellen visade sig vara den mest effektiva modelleringsmetoden för att erhållade dynamiska egenskaperna hos dammen. Det eftersom en 3D-modell var nödvändig för att studera hela dammens beteende och hantering av utdata var förenklad vid användning av den masslösa modellen.
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Yuan, Peng. "MODELING, SIMULATION AND ANALYSIS OF MULTI-BARGE FLOTILLAS IMPACTING BRIDGE PIERS". UKnowledge, 2005. http://uknowledge.uky.edu/gradschool_diss/310.
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The current design code governing bridge structure resistance to vessel impact loads in the U.S. is the American Association of State Highway and Transportation Officials' (AASHTO) Guide Specification and Commentary for Vessel Collision Design of Highway Bridges. The code stipulated method, based on Meir-Dornberg's equivalent static load method, is usually not warranted because of insufficient data on the impact load histories and wide scatter of the impact force values. The AASHTO load equations ignore certain fundamental factors that affect the determination of impact forces and bridge dynamic responses. Some examples of factors that are omitted during standard impact force analysis are: impact duration, pier geometry, barge-barge and barge-pier interactions, and structural characteristics of bridges.
The purpose of this research is to develop new methods and models for predicting barge impact forces on piers. In order to generate research information and produce more realistic flotilla impact data, extensive finite element simulations are conducted. A set of regression formulas to calculate the impact force and time duration are derived from the simulation results. Also, a parametric study is performed systematically to reveal the dynamic features of barge-bridge collisions. A method to determine the quasi upper bound of the average impact force under any given scenarios is preposed. Based on the upper bounds of the average impact forces, an impact spectrum procedure to determine the dynamic response of piers is developed. These analytical techniques transform the complex dynamics of barge-pier impact into simple problems that can be solved through hand calculations or design charts. Furthermore, the dependency of the impact forces on barge-barge and barge-pier interactions are discussed in detail. An elastoplastic model for the analysis of multi-barge flotillas impacting on bridge piers is presented. The barge flotilla impact model generates impact force time-histories for various simulation cases in a matter of minutes. The results from the proposed model are compatible with the respective impact time-histories produced by an exhuaustive finite element simulation.
All of the proposed methods and loading functions in this study are illustrated through design examples. Accordingly, the research results may help engineers to enhance bridge resistance to barge impacts and also lead to economic savings in bridge protection design.
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Moore, Alyssa Nicole. "An Engagement Bout Analysis of the Effects of Effort". Thesis, University of North Texas, 2017. https://digital.library.unt.edu/ark:/67531/metadc1011796/.
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Operant response rate can be viewed as bouts, periods of alternating engagement and disengagement with ongoing schedules of reinforcement. Relatively few studies have examined the role of force and effort on engagement bouts. Moreover, those examining effort have used switch closure devices to define the response. Switch closures tend to overestimate the effect of effort because increasing the force requirement excludes low-force responses that previously activated the switch. In the present study, we examined the effects of effort using a force transducer, which allows us to record criterion responses that meet the force requirement and subcriterion responses that do not. The current study was conducted using four male Sprague Dawley rats. Each rat was run through a series of four conditions, each with a different combination of variable interval schedules (VI 30s, VI 120s) and force requirements (5.6g, 32g). Log survivor analyses of bout structure showed that increased force requirements decreased the rate of bout initiations. Additionally, when log-survivor functions were computed using only criterion responses, shifts in the function were less extreme than when all measured responses were used; the latter finding suggests exclusion of "subcriterion" responses in prior work has overestimated the effects of force on bout structure
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Trippas, Dries. "Motivated reasoning and response bias : a signal detection approach". Thesis, University of Plymouth, 2013. http://hdl.handle.net/10026.1/2853.
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The aim of this dissertation was to address a theoretical debate on belief bias. Belief bias is the tendency for people to be influenced by their prior beliefs when engaged in deductive reasoning. Deduction is the act of drawing necessary conclusions from premises which are meant to be assumed as true. Given that the logical validity of an argument is independent of its content, being influenced by your prior beliefs in such content is considered a bias. Traditional theories posit there are two belief bias components. Motivated reasoning is the tendency to reason better for arguments with unbelievable conclusions relative to arguments with believable conclusions. Response bias is the tendency to accept believable arguments and to reject unbelievable arguments. Dube et al. (2010) pointed out critical methodological problems that undermine evidence for traditional theories. Using signal detection theory (SDT), they found evidence for response bias only. We adopted the SDT method to compare the viability of the traditional and the response bias accounts. In Chapter 1 the relevant literature is reviewed. In Chapter 2 four experiments which employed a novel SDT-based forced choice reasoning method are presented, showing evidence compatible with motivated reasoning. In Chapter 3 four experiments which used the receiver operating characteristic (ROC) method are presented. Crucially, cognitive ability turned out to be linked to motivated reasoning. In Chapter 4 three experiments are presented in which we investigated the impact of cognitive ability and analytic cognitive style on belief bias, concluding that cognitive style mediated the effects of cognitive ability on motivated reasoning. In Chapter 5 we discuss our findings in light of a novel individual differences account of belief bias. We conclude that using the appropriate measurement method and taking individual differences into account are two key elements to furthering our understanding of belief bias, human reasoning, and cognitive psychology in general.
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Henry, Emily Brooke. "Stochastic Modeling of Geometric Mistuning and Application to Fleet Response Prediction". Wright State University / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=wright1421095761.
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Timorian, Safiullah. "Investigation for the analysis of the vibrations of quasi-periodic structures". Thesis, Bourgogne Franche-Comté, 2020. http://www.theses.fr/2020UBFCD002.
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Dans cette thèse, la définition et les effets de la quasi-périodicité dans la structure périodique sont étudiés. Plus important encore, l'analyse de la présence de faibles irrégularités dans les structures périodiques et de son impact significatif sur les réponses vibroacoustiques des systèmes élastiques est abordée. Dans la littérature, il a déjà été montré qu'un panneau sandwich optimisé par rapport aux performances vibroacoustiques et doté de propriétés aléatoires ajoutées du noyau pouvait présenter des caractéristiques de bande d'arrêt dans certaines gammes de fréquences. Par conséquent, une cible supplémentaire peut consister à encadrer la propriété susmentionnée sous la méthode des éléments finis vagues (WFEM) afin d’aboutir à certaines directives de conception. Dans ce travail, (1) sont présentées des études numériques de l'analyse vibrationnelle de faisceaux finis, périodiques et quasi-périodiques 1D. Le contenu traite des modèles d'éléments finis de faisceaux axés sur l'analyse spectrale et les réponses forcées amorties. La quasi-périodicité est définie en appelant la séquence de Fibonacci pour construire les variations affectées (géométrie et matériau) le long de la plage du modèle d'éléments finis dans une direction. De même, la même plage est utilisée comme une super unité cellulaire avec WFEM pour analyser les systèmes périodiques infinis. (2) La méthode de variation avec un algorithme développé est également considérée pour rechercher le déséquilibre géométrique d'impédance le plus efficace des cellules unitaires pour le contrôle des vibrations. (3) Des études numériques et des mesures expérimentales sur des réseaux bidimensionnels périodiques et quasi périodiques sont ainsi effectuées. Les validations expérimentales sont effectuées en comparant le réseau quasi-périodique simulé en utilisant la modélisation WFEM avec un prototype fabriqué par usinage laser. Les principaux résultats montrent que, en considérant à la fois les ondes élastiques longitudinales et de flexion dans les faisceaux 1D, les gammes de fréquences correspondant aux bandes interdites sont étudiées. Dans les structures 2D, les caractéristiques des ondes du réseau quasi-périodique introduisent la possibilité de concevoir des bandes d'arrêt de fréquence plus larges dans les gammes de basses fréquences. Elles présentent certains éléments novateurs et pourraient être prises en compte pour la conception de filtres structurels et le contrôle des propriétés des ondes élastiques. Les résultats obtenus dans cette thèse montrent que le faisceau avec les caractéristiques de Fibonacci et les panneaux avec les caractéristiques de Thue-Morse peuvent améliorer les performances en termes d’atténuation sans pénalité de poids, ce qui peut être un avantage pour les méta-matériauxIn this thesis, the definition and effects of quasi-periodicity in periodic structure are investigated. More importantly, the presence of irregularity in periodic structures and its significant impact in vibroacoustic responses of elastic systems are analyzed. In the extant literature, it has already shown that a sandwich panel, optimized for vibroacoustic performance with added random properties of the core, can exhibit stop band characteristics in some frequency ranges. Therefore, an additional target can exist in framing the abovementioned property under the Wave Finite Element Method (WFEM) for resulting in some design guideline. In this paper, (1) the numerical stud- ies of the vibrational analysis of 1D finite, periodic, and quasi-periodic beams are presented. The paper's content deals with the finite element models of beams focusing on spectral analysis and the damped forced responses. The quasi-periodicity is defined by invoking the Fibonacci sequence for building the assigned variations (geometry and material) along the span of the finite element model in one direction. Similarly, the same span is used as a super unit cell with WFEM for analyzing the infinite periodic systems. (2) The method of variation with a developed algorithm is also considered to find the most efficient geometrical impedance mismatch behavior of unit cells for vibration control. (3) Numerical studies and experimental measurements on 2D periodic and quasi-periodic lattices are thus performed. Experimental validations are performed by comparing the quasi-periodic lattice simulated by using WFEM modelling, with a prototype manufactured by laser machin- ing. Based on the major findings, and considering both longitudinal and flexural elastic waves in 1D beams, the frequency ranges corresponding to band gaps are investigated. In the 2D structures, the wave characteristics in the quasi-periodic lattice introduce the possibility of designing wider fre- quency stop bands in low frequency ranges, and presents some elements of novelty; moreover, they can be considered for designing structural filters and controlling the properties of elastic waves. The results obtained in this study show that the beam with Fibonacci characteristics and panels with Thue- Morse characteristics can improve performances in terms of attenuation level without weight penalty, which can be an asset for metamaterials
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Albannai, Humaid Ali Mohammad. "Combating the trafficking of women in the United Arab Emirates : a critical analysis of the United Arab Emirates legal response in the context of international law". Thesis, Brunel University, 2018. http://bura.brunel.ac.uk/handle/2438/17141.
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The United Arab Emirates (UAE) is a key destination and transit country for human trafficking. Human trafficking is a complex international criminal enterprise that supplies humans for many different forms of forced labour and commercial sexual exploitation. It has devastating effects on its victims. Theories suggest that human trafficking is strongly linked to migration, which would explain why it has become an urgent issue for the UAE, since its massive influx of migrants seeking a better life and economic circumstances, are habitually lured to the UAE and subjected to exploitation by traffickers. It is a situation that in recent years has tarnished the UAE's reputation to the international community and its wealthy investors. It is for all of these reasons that this thesis is concerned with human trafficking in the UAE, with a special focus on the trafficking of women, as well as the legal mechanisms and initiatives created to combat this scourge. At the heart of this investigation is Federal Law No. 51 which marked a pivotal moment for the UAE, as it was a law specifically designed to address trafficking on its territory. However, as with laws drafted by the international community, there exist difficulties with how trafficking should be construed, and with how traffickers and trafficked victims should be treated in order to effectively eliminate this crime. Ultimately, the research highlights the importance and benefits of a victim-centred human rights based approach, as opposed to the pervasive crime control one, which includes ensuring that victims are genuinely protected and fully rehabilitated to re-enter society. In addition, the research provides crucial insights from Islamic law and principles that raise significant implications for understanding how the trafficking in women should be conceptualised and dealt with in modern-day Muslim societies such as the UAE.
22
Majdoub, Fida. "Innovative measurement of ultra-low friction : analysis of dynamic free responses characterized by damped oscillatory motion". Phd thesis, Ecole Centrale de Lyon, 2013. http://tel.archives-ouvertes.fr/tel-01001752.
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Réduire l'énergie générée par le frottement et dissipée dans les systèmes mécaniques réels est un des challenges actuels en tribologie. Ce point représente une importance toute particulière dans le domaine des transports terrestres. En réponse à cette nécessité, les constructeurs automobiles se concentrent sur la réduction de la consommation d'énergie en sélectionnant des lubrifiants et des matériaux appropriés d'une part et les systèmes mécaniques performants d'autre part. Grâce à leurs propriétés physiques et tribologiques en termes de réduction de la friction et de l'usure, les couches minces de DLC (Diamond-like Carbon) sont considérées comme l'une des solutions. Le comportement tribologique de couches minces de ta-C (carbone amorphe très dur dépourvu d'hydrogène) et de a-C:H (carbone amorphe hydrogéné) est ici exploré. D'autre part, des "lubrifiants verts" et des additifs participant aussi à la réduction du frottement et de l'usure sont testés. Ces essais sont effectués dans différentes conditions en utilisant une nouvelle méthodologie expérimentale. Le tribomètre dynamique oscillant développé au LTDS possède la capacité de quantifier avec une très grande précision et sans recourir à une quelconque mesure de force, des niveaux de frottement faibles (dans la gamme 10 - 5 à 10 - 2), et permet en plus d'identifier différentes contributions du frottement. Dans un premier temps, une loi de frottement linéaire a été utilisée afin d'évaluer deux contributions de frottement. La première, μ0 est le coefficient transitoire de frottement quand la vitesse s'annule au changement de direction (du type frottement de Coulomb). La seconde, μ1, est une contribution dépendante de la vitesse de glissement. Ensuite, une étude numérique a été réalisée en appliquant une loi de frottement quadratique afin de mieux comprendre l'aspect dynamique des réponses libres. Cela nous a permis d'étudier numériquement la décroissance d'amplitude des oscillations déterminée grâce à la méthode de moindres carrés. Nous nous intéressons aussi à l'étude des formes de l'enveloppe de ces oscillations en relation avec le modèle de frottement. Les résultats numériques et expérimentaux pour les lois de frottement linéaire et quadratique sont ensuite comparés. En complément, nous avons mesuré la force tangentielle correspondant aux tribosystèmes testés. Finalement, nous avons étudié numériquement un système dynamique masse-ressort à un degré de liberté, modélisé par la loi de frottement LuGre. Cette loi est décrite par le phénomène d'hystérésis et l'effet de décalage de temps qui ont été détectés expérimentalement. Les résultats expérimentaux obtenus avec le tribomètre oscillant montrent qu'ils sont qualitativement comparables à ceux obtenus en configuration classique cylindre-plan, travaillant à vitesse de glissement constante. Dans tous les cas, les résultats montrent la supériorité du tribosystème ta-C/ta-C dans la réduction du frottement μ0. De plus, les résultats numériques et expérimentaux sont cohérents. Cette étude montre qu'une loi de frottement quadratique est capable de décrire correctement toutes les formes d'enveloppes obtenues expérimentalement : droite, convexe, concave et une combinaison des formes convexe et concave.
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Brown, Jeffrey M. "Reduced Order Modeling Methods for Turbomachinery Design". Wright State University / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=wright1229962254.
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Gurcay, Melih. "Human Interventions On Wetlands And Their Long Term Impacts On Human Well-being A Study Of Kizilirmak Delta Case, Samsun, Turkey". Thesis, METU, 2009. http://etd.lib.metu.edu.tr/upload/2/12611408/index.pdf.
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Acknowledging the necessity of a detailed understanding of the dynamics and contributions of wetlands in decision making processes, this research aims to identify the trade-offs between human interventions and human well-being in wetlands. Being one of the thirteen Ramsar Sites of Turkey and providing various ecosystem functions, Kizilirmak Delta was determined as the case study area of the research. Following the literature review on wetlands and their valuation, an assessment framework was developed for analyzing the trade-offs in the Kizilirmak Delta. Following this framework, first the importance, values and functions of the delta were defined by evaluation of its ecological, socio-cultural and economic structures and function analysis. Then, the pressures on the delta and their impacts were analyzed through DPSIR (Driving forces, Pressures, State, Impacts and Responses) Framework by action analysis. Finally, the trade-offs in the delta were calculated in monetary terms through valuation of the functions of the delta. Because of time and data constraints only a small portion of the functions of the delta was quantified in monetary terms. Calculated functions of the delta provide 753.531.772 TL worth of services that constitutes the 34 % of total GDP of the delta. This value was accepted as the cost of trade-offs in the delta, because the pressures on the delta would result in the loss of this value.
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Sitte, David. "Odezva atypického vertikálního rotoru vodní turbíny na buzení nevývažkem oběžného kola a nevývažkem rotoru generátoru". Master's thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2021. http://www.nusl.cz/ntk/nusl-443737.
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This master’s thesis deals with the dynamic behaviour of vertical Francis turbine, which is atypical its shaft length. In the first part of thesis, there is theoretic research of water turbine, which is followed by derivation of equations for the Stodola rotor. The second part deals with the creation of the turbine shaft in 1D and 3D. A modal analysis was performed in the ANSYS Workbench software, based on which the Campbell diagram is created and it was determined the critical speed. And the harmonic analysis from which was determined the forces response in radial bearings, amplitude of deviation in radial direction in the turbine impeller and the generator and the axial displacement located in turbine impeller and axial bearing. 1D and 3D solutions were compared between themselves.
26
Jakel, Roland. "Linear Dynamic System Analyses with Creo Simulate – Theory & Application Examples, Capabilities, Limitations –". Universitätsbibliothek Chemnitz, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-qucosa-225992.
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1. Einführung in die Theorie dynamischer Analysen mit Creo Simulate 2. Modalanalysen (Standard und mit Vorspannung) 3. Dynamische Analysen einschließlich Klassifizierung der Analysen; einige einfache Beispiele für eigene Studien (eine Welle unter Unwuchtanregung und ein Ein-Massen-Schwinger) sowie etliche Beispiele größerer dynamischer Systemmodelle aus unterschiedlichsten Anwendungsbereichen 4. Feedback an den Softwareentwickler PTC (Verbesserungsvorschläge und Softwarefehler) 5. Referenzen1. Introduction to dynamic analysis theory in Creo Simulate 2. Modal analysis (standard and with prestress) 3. Dynamic analysis, including analysis classification, some simple examples for own self-studies (shaft under unbalance excitation and a one-mass-oscillator) and several real-world examples of bigger dynamic systems 4. Feedback to the software developer PTC (enhancement requests and code issues) 5. References
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Yumer, Mehmet Ersin. "On The Non-linear Vibration And Mistuning Identification Of Bladed Disks". Master's thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/3/12611498/index.pdf.
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Forced response analysis of bladed disk assemblies plays a vital role in rotor blade design and has been drawing a great deal of attention both from research community and engine industry for more than half a century. However because of the phenomenon called &lsquomistuning&rsquo
, which destroys the cyclic symmetry of a rotor, there have been several difficulties related to forced response analysis ever since, two of which are addressed in this thesis: efficient non-linear forced response analysis of mistuned bladed disks and mistuning identification. On the nonlinear analysis side, a new solution approach is proposed studying the combined effect of non-linearity and mistuning, which is relatively recent in this research area and generally conducted with methods whose convergence and accuracy depend highly on the number of degrees of freedom where non-linear elements are attached. The proposed approach predicts nonlinear forced response of mistuned bladed disk assemblies considering any type of nonlinearity. In this thesis, special attention is given to the friction contact modeling of bladed disks which is the most common type of nonlinearity found in bladed disk assemblies. In the modeling of frictional contact a friction element which enables normal load variation and separation of the contact interface in three-dimensional space is utilized. Moreover, the analysis is carried out in modal domain where the differential equations of motions are converted to a set of non-linear algebraic equations using harmonic balance method and modal superposition technique. Thus, the number of non-linear equations to be solved is independent of the number of non-linear elements used. On the mistuning identification side, a new method is enclosed herein which makes use of neural networks to assess unknown mistuning parameters of a given bladed disk assembly from its assembly modes, thus being suitable for integrally bladed disks. The method assumes that a tuned mathematical model of the rotor under consideration is readily available, which is always the case for today&rsquo
s realistic bladed disk assemblies. A data set of selected mode shapes and natural frequencies is created by a number of simulations performed by mistuning the tuned mathematical model randomly. A neural network created by considering the number of modes, is then trained with this data set for being used to identify mistuning of the rotor from measured data. On top of these, a new adaptive algorithm is developed for harmonic balance method, several intentional mistuning patterns are investigated via excessive Monte-Carlo simulations and a new approach to locate, classify and parametrically identify structural non-linearities is introduced.
28
Janošková, Lenka. "Dynamická analýza konstrukce zatížené seismickým zatížením". Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2013. http://www.nusl.cz/ntk/nusl-226464.
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In this diploma thesis the seismic load on two different models is solved – the first model is a beam hall and the second model is a multistory building. The calculation of seismic load was performed according to standard ČSN EN 1998-1 (Eurocode 8) using the response spectrum analysis and the method of equivalent static forces (substi-tute load). For the combination of seismic responses in different directions are used SRSS and CQC rules. Models and calculations were solved in a student’s version of program RFEM 4.10 (Ing. Software Dlubal, s.r.o.). The comparison of mentioned methods in each models, also the comparison of combinative rules in calculation and the final evaluation of seismic responses on both of models are the subject of this thesis.
29
Hokeš, Filip. "Statická a dynamická analýza předpjaté mostní konstrukce". Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2014. http://www.nusl.cz/ntk/nusl-226802.
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The main objective of the thesis is to perform static and dynamic analysis of prestressed concrete bridge structures in computational system ANSYS. For the analysis was chosen footbridge over the river Svratka in Brno. In relation to this topic are solved various types of modeling prestress at a finite element level. Before analyzing the footbridge is analyzed in detail the static system and the corresponding final geometry of the structure. Knowledge of the functioning of the static system is used to build the computational model of the structure, on which is subsequently performed static and dynamic analysis.
30
Burberi, Corrado. "CFD strategy for the aerodynamic and aeromechanic design and verification of axial compressor for gas turbine engines". Doctoral thesis, 2021. http://hdl.handle.net/2158/1238621.
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This thesis proposes a CFD strategy for the aerodynamic and aeromechanic design and verification of axial compressor for gas turbine engines characterized by a combined use of steady and unsteady numerical simulations in order to significantly increase the design accuracy keeping industrial design time requirements.In particular, the stall margin prediction and the forced response assessment are the key aspects of this procedure. An unsteady analysis of the whole compressor is capable of predicting a stall margin comparable to the measured one and, at the same time, of evaluating the complete blade forcing spectrum on each row from the unsteady solution. The spatial decomposition theory introduced in this thesis applied to the overall unsteady aerodynamic forcing allows to separate the contributions of the different nodal diameters. The proposed improved use of the Interference Diagram is able to detect additional possible resonances in the operating range of turbomachines trying to avoid many unexpected vibrations during compressor validation tests.
31
Peruzzi, Lorenzo. "Aeromechanical characterization strategy for high pressure steam turbines". Doctoral thesis, 2018. http://hdl.handle.net/2158/1127996.
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The thesis deals with a viable strategy of aeromechanical characterization of steam turbine blades for high pressure stages for industrial application
In the first part of the work, the effects related to the fludo-structure interaction for the evaluation of aerodynamic damping are taken into consideration. In the second part the effects of the multi-row environment for the evaluation of the forcing effect of the adjacent stators on the rotor blade are studied.
In confirmation of the strategy developed in the first part of the thesis, the work ends with the evaluation of aerodynamic damping in multi-rows environment, taking into consideration not only the unsteadiness related to the blade modeshape, but also those due to the interaction of wakes and potential fields of the stators adjacent to the rotor blade under examination.
32
HSIU-CHI-LAI y 賴秀吉. "Identification of Parameters in Vibration System Combining Wavelet Analysis with Forced Response". Thesis, 2001. http://ndltd.ncl.edu.tw/handle/49313447998079210236.
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碩士國立中正大學
機械系
89
Abstract This thesis addresses the identification of linear dynamic systems. Two approaches based on wavelet analysis are studied. The first method relies on a special relationship between system parameters ( such as natural frequency and damping ratio) and the Morlet wavelet transform of the system’s forced response. It can only be applied to linear time invariant systems. The other method is based on the representation of system’s responses by the Haar basis. It can be used to identify both time invariant and time —varying systems. Both approaches are verified numerically and experimentally. For the approach of Morlet wavelet transform, it is shown that the identification error depends strongly on system’s damping ratio. The identification errors are kept less than 5% for the systems with damping ratio of less than . When the damping ratio is greater than , the method will fail. Comparisons with conventional Fourier techniques indicate that the present method is superior in two cases: noisy systems and multi-DOF systems. Due to the property of multi-resolution, the wavelet approach can automatically filter out the high-frequency noise in the input and output data, leading to better identification. On the other hand, there is a tunable parameter in the Morlet wavelet, which can adjust the frequency resolution. Therefore, in the identification of multi-DOF systems, by Morlet wavelet transform, we can adjust the frequency resolution so that at different scaling parameters, the wavelet transforms correspond to different modal responses. The associated mode frequency and damping ratio can thus be identified. This is especially useful when two modes are closed coupled. Fourier techniques usually give bad identification results for multi-DOF systems with strongly coupled modes. For the approach of Haar basis, it is shown that this approach is equally applicable to time-invariant or time-varying systems. It utilizes several unique properties of Haar basis. First, the Haar basis is orthogonal and very easy in computations. Second, both the integration and multiplication of Haar basis functions can also be expanded in Haar basis. The coefficients of the Haar basis representation admit a recursive form. With those properties, one can transform the governing state equation into an algebraic equation in Haar basis. Together with the techniques of Kronecker product and least square, the unknown system parameters or the coefficients of the unknown time-varying functions can be obtained. The identification accuracy depends on the number of Haar basis functions used to approximate the system responses and unknown functions. Although more bases require more computations, the easy computation of Haar basis allows for the used of large number of bases. Thus, good identification results can be obtained easily.
33
Otterson, Timm. "An analysis of the wind-forced response of Conception Bay using a reduced-gravity numerical model /". 1992. http://collections.mun.ca/u?/theses,67730.
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Biagiotti, Sara. "Development of an integrated procedure for aerodynamic and aeromechanic design of gas turbine engines". Doctoral thesis, 2021. http://hdl.handle.net/2158/1239475.
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The objective of this work is focused on the development of an integrated procedure for the aerodynamic and aeromechanic design of axial gas turbines blade rows. The methodology is based on steady and unsteady CFD simulations, which are used to evaluate the aerodynamic performance, aerodynamic damping and forcing functions which excite the turbine blade rows. FEM analyses are also rpovided to obtain natural frequencies and mode shapes, which are input data to calculate the aerodynamic damping (by means of flutter computations) and the forced response analysis of the component under investigation.
35
Li, Larry y 李育霖. "Analysis of Wind Power Spectrum and Structural Response Subjected to Along-wind Force". Thesis, 1996. http://ndltd.ncl.edu.tw/handle/47051964173377684630.
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Yang, Ming-Lun y 楊明倫. "Dynamic response analysis of a rotating Rayleigh beam with periodically radial and axial forces". Thesis, 2005. http://ndltd.ncl.edu.tw/handle/81461412012747002502.
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碩士國立中央大學
機械工程研究所
93
This paper formulates the processing of the lathe. In this process, a turning tool moves along the workpiece repeatedly. It could be seem as a periodically moving load which includes radial motion-dependent force and axial tension and compression distributed forces. To analyze the dynamic response of the workpiece after numerous turning cycles, those external forces are periodic functions in the forms of Fourier series. A rotating Rayleigh beam with periodically radial and axial forces was considered. The governing equations were derived by Hamilton's principle and expressed in a dimensionless form. The equation of motions was turned into discrete equations by Galerkin's method. For each mode, the stability of the rotating beam was analyzed by the method of multiple scales and Floquet theory. The differential equations were also solved by Runge-Kutta method. The phenomena of stability analysis and spectrum analysis are discussed. Finally, the time responses of the beam are showed and discussed.
37
Huang, Teng-Wei. "Exploring item response theory in forced choice psychometrics for construct and trait interpretation in cross-cultural context". Diss., 2011. http://hdl.handle.net/10500/5159.
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This thesis explores item response theory (IRT) in the Personal Profile Analysis (PPA)
from Thomas International. The study contains two parts (Part 1 and Part II) for which
two sample groups were collected. For Part I of the research 650 participants were
collected via the old form (CPPA25/C7) in the Beijing office of Thomas International in
China (male=323, Female=267, missing=60). Part II of the research used the
amended form in the same area and collected a sample of 307 (male=185, female=119,
missing=3).
The study postulates that IRT methods are applicable to forced-choice psychometrics.
The results of Part I showed that the current CPPA form functions, to some extent,
according to PPA’s original constructs. Part I of the research identified 16 items that
need to be amended (called Amend A in this research). The amended form was
returned to China for the collection of samples for Part II, and the results are deemed
acceptable.
The study concludes with a research protocol for PPA-IRT research generated from the
current research. The research protocol suggests four levels of analysis for forced
choice (FC) psychometrics, namely: 1. Textual analysis, 2. Functional analysis, 3.
Dynamic analysis, and 4. Construct analysis.Psychology
M.A. (Psychology)
38
Peng, Yong-Geng y 彭詠耕. "Analysis on Nonlinear Responses of a Mooring Ship System under the Action of Environmental Forces". Thesis, 2008. http://ndltd.ncl.edu.tw/handle/38375366991432663651.
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碩士國立臺灣大學
工程科學及海洋工程學研究所
96
In the present study, a numerical model is developed for simulating the dynamic responses of a mooring ship system under the action of waves and winds. In the mooring system, a mooring ship, elastic catenary mooring lines and elastic fenders are considered. A linear strip method is applied to formulate the 6-DOF ship motions, but the interacting nonlinear forces of the mooring lines and fenders make the equations of motion nonlinear and have to be solved in time domain step by step. A series of numerical simulation has been conducted for investigating the nonlinear responses dependence on wave length, wave height, wave direction, wind speed and wind direction. Through the simulation, the time histories of ship motion, tension forces of mooring lines, and reacting forces of fender are obtained, and the characteristics of the nonlinear responses of a mooring ship system are discussed.
39
(6635912), Eimar A. Sandoval Vallejo. "Undrained Seismic Response of Underground Structures". Thesis, 2019.
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Underground structures must be able to support static overburden loads, as well as to accommodate additional deformations imposed by seismic motions. Progress has been made in the last few years in understanding the soil-structure interaction mechanisms and the stress and displacement transfer from the ground to the structure during a seismic event. It seems well established that, for most tunnels, the most critical demand to the structure is caused by shear waves traveling perpendicular to the tunnel axis. Those waves cause distortions of the cross section (ovaling for a circular tunnel, and racking for a rectangular tunnel) that result in axial forces (thrusts) and bending moments. While all this has been well-studied for structures placed in linear-elastic ground, there is little information regarding the behavior of buried structures placed in nonlinear ground, especially under undrained conditions, i.e., when excess pore pressures generate and accumulate during the earthquake.
Two-dimensional dynamic numerical analyses are conducted to assess the seismic response of deep circular tunnels located far from the seismic source, under drained or undrained loading conditions. It is assumed that the liner remains elastic and that plane strain conditions apply.
A new cyclic nonlinear elastoplastic constitutive model is developed and verified, to simulate the nonlinear behavior and excess pore pressures accumulation with cycles of loading in the ground. The results of the numerical analyses show negligible effect of input frequencies on the normalized distortions of a tunnel for input frequencies smaller than 5 Hz (the distortions of the tunnel are normalized with respect to those of the free field); that is, for ratios between the wavelength of the seismic input and the tunnel opening larger than about eight to ten. The results also show that undrained conditions, compared with drained conditions, tend to reduce deformations for flexible liners and increase them for stiffer tunnels, when no accumulation of pore pressures with cycles of loading is assumed. However, when pore pressures increase with the number of cycles, the differences in distortions between drained and undrained loading are reduced, i.e., the normalized distortions increase for flexible and decrease for stiff tunnels, compared to those with drained conditions.
Undrained loading produces larger thrust in the liner than drained loading for stiff tunnels with flexibility ratio F ≤ 2.0.
For more flexible tunnels with F > 2.0, the behavior is the opposite, i.e., smaller axial forces are obtained for undrained loading than for drained loading. Including excess pore pressure accumulation does not introduce significant changes in the axial forces of the liner, irrespective of the flexibility of the tunnel, compared to those obtained from undrained loading without pore pressure accumulation.
The drainage loading condition (drained or undrained) or the magnitude of the free-field excess pore pressures during undrained loading do not affect the normalized bending moments for flexible tunnels, with F ≥ 2. For stiffer tunnels, with F < 2, the normalized bending moments increase from drained to undrained loading, and with the free field excess pore pressures.
It is found that the tunnel’s response is determined by the load on the liner, or by the distortions of the cross section, depending on the flexibility ratio. For stiff structures, with F ≤ 2.0, important axial forces and bending moments are produced in the structure, with larger magnitudes for the undrained case; while the distortions of the cross section are very small. When the tunnel becomes more flexible, the loading on the liner decreases, but the distortions of the cross section start to be important. For flexible structures with initial F ≥ 10 (for the cases investigated), the performance is largely determined by the distortions of the cross section, while the axial forces and bending moments are almost negligible. Such distortions are drastically affected by the drainage loading condition and by the magnitude of pore pressures in the free field.
40
Gusella, Federico. "On the mechanical behavior of steel rack connections and its influence on the seismic response of industrial storage systems". Doctoral thesis, 2019. http://hdl.handle.net/2158/1166359.
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Steel storage pallet racks are commonly used worldwide to store goods on pallets and represent complex and challenging structures to design. The main racking system is denoted as “selective steel storage pallet rack”. These racking systems are one pallet deep and are separated by aisles, allowing for each pallet, stored on horizontal beams, to be always accessible. Selective racks behave like bracing system in cross-aisle direction, with uprights connected by diagonal bracings, while in down-aisle direction, bracings are usually not installed to make palletised goods always accessible. Therefore, in down-aisle direction racks behave like moment resisting frames (MRFs) whose stability and seismic resistance depend on the performance of beam-to-column connections. This Thesis is motivated by the need to increase the knowledge about the mechanical behavior of rack joints, investigating how it is affected by structural details and design parameters, and its effect on the global seismic response of rack systems. This is not only a very interesting and challenging problem from a scientific point of view, but it can also have a very large economic impact.
The proposed goal is achieved through: experimental tests, carried out on full-scale boltless rack joints to identify their non-linear moment-rotation curve under monotonic and cyclic loading; the development of a theoretical model to simulate experimental curves of joints; probabilistic analyses to highlight the influence of uncertainties in material strength and geometrical features on the mechanical performance of joints; and finally the development of a numerical model, capable to describe the pinching in hysteresis loops of connections and its effect on the seismic response of industrial storage systems.
To obtain the moment-rotation curve of rack connections and to evaluate how it is affected by structural details, a set of full-scale joints are tested at the Structures and Material Testing Laboratory of the Department of Civil and Environmental Engineering of the University of Florence. In the first part of the Thesis, results of monotonic and cyclic tests are presented. Some joints are also equipped with additional bolts, which could represent an effective solution to improve the seismic response of steel storage pallet racks. Experimental testing is useful to get information about the semi-rigid behavior and ductility of beam-column joints. Nevertheless, despite the success and popularity of experimental testing, tests can be expensive and time-consuming, therefore current state-of-art models for traditional steel joints are based on the Component Method (CM). The CM approach can be applied to any kind of connections because the joint is modeled theoretically as an assembly of components with an elasto-plastic or rigid force-displacement relationship. A mechanical model based on the CM is developed and used to analytically evaluate the non-linear structural response of rack beam-column joints. The accuracy of the proposed approach is checked by the comparison with experimental results.
To explore the impact of the component structural details and the uncertainty in steel mechanical properties and geometrical features, a Monte Carlo simulation of rack connection assemblies is also performed. For the development of simulations, statistical properties of material random variables are assumed on experimental results, the variability in geometric tolerances are assumed in accordance with current standard code requirements and the structural response of rack joints is modeled using the proposed mechanical model based on the CM.
Finally, experimental tests showed a non-negligible pinching in the cyclic moment-rotation curve of rack connections, with a reduction of energy dissipation. This structural behavior is expected to influence the seismic response of rack systems and it is investigated in the last chapter of the Thesis. A simplified Finite Element (FE) numerical model is proposed for the analysis of steel storage pallet racks under cyclic loads, considering the pinching in the joint hysteresis loop. The effectiveness of the proposed model is its fast tuning and easily implementation in commercial software packages, commonly used for non-linear seismic vulnerability analyses. For a deeper understanding of the pinching effect, a case-study is discussed, comparing two models of joints differing in the modeling of the degradation of the rotational stiffness. Results highlight that a non-liner dynamic analysis with the proposed pinching model, which describes the effective non-linear elasto-plastic behavior of rack joints, is suggested to obtain a seismic vulnerability assessment of industrial storage systems on the safe side.
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Chen, Chia-Hung y 陳家泓. "Effects of Damping Properties of Restored Teeth on Loading Response－Analysis of a Viscoelastic Finite Element Model under Dynamic Force". Thesis, 2008. http://ndltd.ncl.edu.tw/handle/79893365944358164152.
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碩士臺北醫學大學
牙醫學系碩博士班
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Loading response of restored teeth can be expressed by fracture resistance. Fracture resistance of restored teeth was found to correlate to bonding strength of restorative materials and the amount of remained tooth structure. However, the exact effect of the restorative materials on the loading response of restored teeth was still not discussed. Damping effect of a structure is associated with the degree of damage when the structure was sustained to a sudden impact. In our in vitro study, the damping ratios of teeth with and without restoration were detected and compared. Human maxillary premolars were chosen and prepared as Black’s Class I cavity (with geometry of 4x4x4 mm). The tested teeth were divided into three catalogues which restored with amalgam, glass ionomer, and composite resin, respectively. Modal testing was used to measure the damping ratios of the teeth before and after restorations. The mean damping ratio of the teeth before restorations is 0.120±0.020. The damping ratio of teeth restored with amalgam demonstrated a statistically lower value (0.081±0.022) than those of teeth restored with glass ionomer (0.106±0.024, p<0.05) and composite resin (0.111±0.020, p<0.05). These values were then input into a 3-D finite element model to calculate its viscoelastic response when subjected to a dynamic load. In the finite element analysis of this study, the change of maximum stress of models with and without damping properties was compared. The change ratio of the model with amalgam restoration (0.20%) was higher than those of teeth without restoration (0.11%), with glass ionomer restoration (0.12%) and with composite resin restoration (0.10%). The maximal equivalent stress of the point in buccal cusp near distal cervical area before and after restoration was compared. The values of teeth were 9.58 MPa (original), 8.15 MPa (amalgam restoration), 11.59 MPa (glass ionomer restoration), and 9.77 MPa (glass ionomer restoration). Our results demonstrated that different restorative materials have different damping properties. In addition, the damping properties really affect the loading response of the restored teeth. Accordingly, we suggest that the damping effects should be took into account when choosing restorative materials.
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CAO, DENG-GAO y 曹登皓. "Non-linear and non-gaussian stochastic analysis for the dynamic responses of offshore structures to morison-type wave-current forces". Thesis, 1990. http://ndltd.ncl.edu.tw/handle/14751405527250286018.
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Whyte, Angela C. "Placing blame or finding peace: a qualitative analysis of the legal response to rape as a war crime in the former Yugoslavia". Thesis, 2005. http://hdl.handle.net/1993/94.
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This thesis is a qualitative analysis of the international legal response to rape as war crime in the former Yugoslavia. Through the examination of the International Criminal Tribunal for the former Yugoslavia (ICTY) and the case law it has generated, this thesis addresses the question will the androcentric characteristics of law found in domestic rape cases be replicated at the international level? More specifically this thesis undertakes an examination which questions will international law be able to adequately amplify and listen to women voices, or will the women’s words be silenced by the rule of law? The following research is loosely informed by Carol Smart’s (1989) sociology of law theory combined with Liz Kelly’s (1988) notions of coping, resisting, and surviving. The purpose of using Kelly’s theory is to go beyond viewing women as inevitable victims of sexual assault. The methodological approach is both qualitative and inductive. It draws on data from the ICTY structure, Statute, Rules of Procedures and Evidence, case law and transcripts and women’s stories presented outside the legal realm.
The analysis reveals that while written law (including the interpretation and application of the law) is somewhat aware of the experiences of women, it falls short of adequately responding to the needs of women. A detailed look at the women’s stories of war revealed diverse experiences not captured in the legal realm. The women’s stories spoke of concerns beyond sexual assault and other crimes identified by the ICTY Statute. This thesis also introduces alternatives or complimentary approaches to law when dealing with war crimes. These alternatives include women’s local groups and truth commissions. This thesis also identifies the criminological relevance of studying war crimes (as defined by international law) and crimes of war and marks an important step in understanding rape and war from a criminological perspective.February 2005