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Dissertations / Theses on the topic 'Forced responce'

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Published: 10 March 2023

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1

Raouf, Raouf A. "Nonlinear forced response of circular cylindrical shells." Thesis, Virginia Polytechnic Institute and State University, 1985. http://hdl.handle.net/10919/101255.

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A combination of the Galerkin procedure and the method of multiple scales is used to analyze the nonlinear forced response of circular cylindrical shells in the presence of internal (autoparametric) resonances. If ωf and af denote the frequency and amplitude of a flexural mode and ωb and ab denote the frequency and amplitude of the breathing mode, the steady-state response exhibits a saturation phenomenon when ωb ≈ 2wf if the shell is excited by a harmonic load having a frequency Ω near ωb. As the amplitude f of the excitation increases from zero, ab increases linearly whereas af remains zero until a threshold is reached. This threshold is a function of the damping coefficients and ωb -2wf. Beyond this threshold, ab remains constant (i.e., the breathing mode saturates) and the extra energy spills over into the flexural mode. In other words, although the breathing mode is directly excited by the load, it absorbs a small amount of the input energy (responds with a small amplitude) and passes the rest of the input energy into the flexural mode (responds with a large amplitude).
M.S.
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2

Metelues, Francis Gabriel. "The Knee Response during Squats with Heels Up and Down." University of Toledo / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1388574269.

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3

Seybert, Jacob. "A New Item Response Theory Model for Estimating Person Ability and Item Parameters for Multidimensional Rank Order Responses." Scholar Commons, 2013. http://scholarcommons.usf.edu/etd/4942.

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The assessment of noncognitive constructs poses a number of challenges that set it apart from traditional cognitive ability measurement. Of particular concern is the influence of response biases and response styles that can influence the accuracy of scale scores. One strategy to address these concerns is to use alternative item presentation formats (such as multidimensional forced choice (MFC) pairs, triads, and tetrads) that may provide resistance to such biases. A variety of strategies for constructing and scoring these forced choice measured have been proposed, though they often require large sample sizes, are limited in the way that statements can vary in location, and (in some cases) require a separate precalibration phase prior to the scoring of forced-choice responses. This dissertation introduces new item response theory models for estimating item and person parameters from rank-order responses indicating preferences among two or more alternatives representing, for example, different personality dimensions. Parameters for this new model, called the Hyperbolic Cosine Model for Rank order responses (HCM-RANK), can be estimated using Markov chain Monte Carlo (MCMC) methods that allow for the simultaneous evaluation of item properties and person scores. The efficacy of the MCMC parameter estimation procedures for these new models was examined via three studies. Study 1 was a Monte Carlo simulation examining the efficacy of parameter recovery across levels of sample size, dimensionality, and approaches to item calibration and scoring. It was found that estimation accuracy improves with sample size, and trait scores and location parameters can be estimated reasonably well in small samples. Study 2 was a simulation examining the robustness of trait estimation to error introduced by substituting subject matter expert (SME) estimates of statement location for MCMC item parameter estimates and true item parameters. Only small decreases in accuracy relative to the true parameters were observed, suggesting that using SME ratings of statement location for scoring might be a viable short-term way of expediting MFC test deployment in field settings. Study 3 was included primarily to illustrate the use of the newly developed IRT models and estimation methods with real data. An empirical investigation comparing validities of personality measures using different item formats yielded mixed results and raised questions about multidimensional test construction practices that will be explored in future research. The presentation concludes with a discussion of MFC methods and potential applications in educational and workforce contexts.
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4

Lauer, Ira Edwin. "Studies of wood pallet response to forced vibration." Thesis, This resource online, 1991. http://scholar.lib.vt.edu/theses/available/etd-12232009-020354/.

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5

Hultman, Hugo. "Validation of Forced Response Methods for Turbine Blades." Thesis, KTH, Kraft- och värmeteknologi, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-172144.

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6

Moffatt, Stuart. "Forced response prediction for industrial gas turbine blades." Thesis, Durham University, 2006. http://etheses.dur.ac.uk/2692/.

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A highly efficient aeromechanical forced response system is developed for predicting resonant forced vibration of turbomachinery blades with the capabilities of fully 3-D non-linear unsteady aerodynamics, 3-D finite element modal analysis and blade root friction modelling. The complete analysis is performed in the frequency domain using the non linear harmonic method, giving reliable predictions in a fast turnaround time. A robust CFD-FE mesh interface has been produced to cope with differences in mesh geometries, and high mode shape gradients. A new energy method is presented, offering an alternative to the modal equation, providing forced response solutions using arbitrary mode shape scales. The system is demonstrated with detailed a study of the NASA Rotor 67 aero engine fan rotor. Validation of the forced response system is carried out by comparing predicted resonant responses with test data for a 3-stage transonic Siemens industrial compressor. Two fully-coupled forced response methods were developed to simultaneously solve the flow and structural equations within the fluid solver. A novel closed-loop resonance tracking scheme was implemented to overcome the resonant frequency shift in the coupled solutions caused by an added mass effect. An investigation into flow-structure coupling effects shows that the decoupled method can accurately predict resonant vibration with a single solution at the blade natural frequency. Blade root-slot friction damping is predicted using a modal frequency-domain approach by applying linearised contact properties to a finite element model, deriving contact Droperties from an advanced semi-analytical microslip model. An assessment of Coulomb and microslip approaches shows that only the microslip model is suitable for predicting root friction damping.
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7

Smythe, Caitlin J. (Caitlin Jeanne). "Forced response predictions in modern centrifugal compressor design." Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/32454.

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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2005.
Includes bibliographical references (p. 119-120).
A computational interrogation of the time-averaged and time-unsteady flow fields of two centrifugal compressors of nearly identical design (the enhanced, which encountered aeromechanical difficulty, and production, which did not encounter any such difficulty) is undertaken in an effort to establish a causal link between impeller-diffuser interactions and the forced response behavior of the impeller blades. Through comparison of time- averaged flow variable and performance estimates with test rig data, the three- dimensional, unsteady, Reynolds-averaged Navier-Stokes flow solver (MSU Turbo) used in this interrogation is found to be adequate to the task of distinguishing the flow fields of the two centrifugal compressor designs. Thus, it is found that MSU Turbo can be a useful tool in comparing the unsteady flow fields in different centrifugal compressors. In addition, through comparisons of MSU Turbo/ ANSYS® estimates of strain with measured peak strain, MSU Turbo is also found to have the potential, as part of a CFD/ ANSYS® system, for serving as a predictive tool for forced response behavior in centrifugal compressors. Differences are found in the unsteady flow fields of the two compressors. The fluctuations over time of the unsteady blade loading on the enhanced impeller blades are greater than those on the production impeller blades. In the vaneless space, on each annular plane (from the impeller exit to the diffuser inlet), at a given spanwise location, the enhanced compressor has both a greater spatial variation in pressure and a higher average static pressure than the production compressor. At the diffuser inlet, there are differences in the time-averaged incidence angle distributions of the two compressors.
(cont.) Based on the observations delineated above, it is hypothesized that the differences in the time-averaged incidence angle distributions are the source of the differences in the pressure field that propagates upstream into the impeller passage, where these differences affect the unsteady blade loading. The differences in the unsteady blade loading then lead to the observed forced response behavior in the two designs.
by Caitlin J. Smythe.
S.M.
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8

Holzinger, Felix. "Development of a Concept for Forced Response Investigations." Thesis, Virginia Tech, 2009. http://hdl.handle.net/10919/46074.

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Striving to improve performance and lower weight of aircraft engines, modern compressor blades become thinner and lighter but higher loaded resulting in an increased vulnerability towards flutter. This trend is further aggravated through blisk designs that diminish structural damping and therewith flutter margin. Modern 3D wide-chord blade designs result in complex structural behaviors that add to the difficulty of correctly predicting flutter occurrence. To counteract above tendencies by driving the physical understanding of flutter and thereby helping to improve aero engine design tools, free flutter as well as forced response will be investigated in the 1.5 stage transonic compressor at TU Darmstadt. Aim of the forced response campaign is to determine the system damping in the stable compressor regime. Hence a novel excitation system capable of dynamically exciting specific rotor blade modes is needed. It is aim of the present work to find a promising concept for such a system. In the present work, the requirements for an excitation system to be used in the TUD compressor are defined with respect to achievable frequency, phase controllability, transferred excitation level, mechanical robustness, integrability and cleanliness. Different excitation system concepts, i.e. oscillating VIGVs, rotating airfoils, tangential and axial air injection are investigated numerically. An evaluation of the results obtained through 2D numerical studies proposes axial air injection as the most favorable concept.
Master of Science
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9

Rattray, Andrew. "Platelet response to haemodynamic shear forces." Thesis, University of Liverpool, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.367819.

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10

Wouters, Emiel Frans Maria. "Bronchial response in COPD measured by forced oscillation technique." Maastricht : Maastricht : Rijksuniversiteit Limburg ; University Library, Maastricht University [Host], 1987. http://arno.unimaas.nl/show.cgi?fid=5376.

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11

Green, Jeff. "Controlling Forced Response of a High Pressure Turbine Blade." Doctoral thesis, Stockholm, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4043.

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12

Sbardella, Luca. "Simulation of unsteady turbomachinery flows for forced response predictions." Thesis, Imperial College London, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.341913.

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13

Guillard, Victor. "Study of the Fan Forced Response due to Crosswind." Thesis, KTH, Aerodynamik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-163900.

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Structures of an aircraft engine are not completely rigid. Therefore when they are subjected to aerodynamic loading, those structures will deform elastically and their shape will change, especially fan blades because of their size. Those elastic deformations and change in load can, depending on structural and flow characteristics, lead to stability problems and cause an excessive fatigue of the structure decreasing its lifetime or in the worst case, break the structure. Consequently it is necessary to study the engine response to aerodynamic loads to design it to prevent those problems and to simplify the certification. A way to do it is to use Computational Fluid Dynamics (CFD) calculations to predict behaviors and better explain phenomena. Today, the trend for turbofans in order to decrease their fuel consumption is to increase their bypass ratio so their fan diameter as well and consequently increase potential elastic deformations, and to shorten the length of the engine air intake to decrease the engine mass but therefore the flow homogeneity also. In these conditions, the crosswind has an increasing impact on turbofan engines because it can create instabilities on the fan blades. Therefore it is important to develop a method to predict the fan behavior under crosswind with a numerical simulation. The present study thus aims to develop a robust and accurate methodology which from a given crosswind speed predicts the displacement of a fan blade to characterize the fan forced response under crosswind. Computations will be made on a high-bypass turbofan engine where such phenomena can occur and which was tested. Thus computed results will be compared to test results.
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14

Garnaud, Xavier. "Modes, transient dynamics and forced response of circular jets." Palaiseau, Ecole polytechnique, 2012. https://theses.hal.science/tel-00740133/document.

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La stabilité linéaire des jets axisymétriques est étudiée dans un contexte global, c'est à dire en prenant en compte sans approximation la géométrie et le non-parallélisme de l'écoulement. Afin de caractériser le "mode préféré" du jet observé expérimentalement et numériquement, différentes analyses ont été mises en oeuvre. Une conjecture étant que ces structures à une résonance entre des perturbations extérieures et le mode propre le moins atténué, une analyse modale de l'écoulement a tout d'abord été effectuée. Cette étude a demandé la mise au point d'une méthode numérique spécifique pour pouvoir traiter les écoulements compressibles de manière efficace. Cependant, les résultats ont montré qu'une représentation modale n'est pas adaptée pour décrire la dynamique des écoulements stable dominés par l'advection. Des modèles simplifiés permettant de mieux comprendre les limites de cette approche sont présentés. Cette dynamique peut cependant être caractérisée par le calcul des perturbations optimales et du forçage harmonique optimal. Cette dernière approche reproduit de manière robuste les observations expérimentales concernant la fréquence et la structure spatiale du "mode préféré". La structure de ce paquet d'onde global est interprétée comme provenant de la coopération entre différentes familles de modes locaux. L'analyse présentée dans cette thèse montre que le "mode préféré" du jet ne vient pas de la résonance d'un mode propre, mais qu'il s'agit en fait d'une pseudo-résonance
The linear stability of axisymmetric jets is studied in a global frame- work, such that the geometry and the non-parallelism of the base flow are fully accounted for. In order to characterize the "preferred mode" of the jet, which is consistently observed in experiments and numerical simulations, different types of analyses are carried out. As a well-known conjecture ascribes the existence of this "preferred mode" to a resonance between external noise and the least-stable eigenmode, a modal study is first performed. This analysis prompted the development of a new numerical method allowing an efficient treatment of compressible flows; however, the results indicate that a modal representation is not well-suited for a description of the dynamics of convection-dominated stable flows. Studies of simplified model problems are presented that underpin this conclusion. Instead, the instability dynamics of such flows are characterized in a consistent manner in terms of optimal initial perturbations and optimal harmonic forcing. The latter approach robustly reproduces experimental observations with regard to the frequency and the spatial structure of the jet "preferred mode". Furthermore, the results allow an interpretation of this global wavepacket structure as a cooperation of different families of local instability modes. The present analysis demonstrates that the "preferred mode" does not arise from resonance with an eigenmode, but rather is to be interpreted as a pseudo-resonance
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15

PHADKE, RAHUL A. "A MICROSLIP SUPERELEMENT FOR FRICTIONALLY-DAMPED FORCED RESPONSE PREDICTIONS." University of Cincinnati / OhioLINK, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1085760663.

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16

Wilson, Emma. "Force response of locust skeletal muscle." Thesis, University of Southampton, 2010. https://eprints.soton.ac.uk/190857/.

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The force response of the locust hind leg extensor muscle to input excitation pulses is modelled. Despite the processes behind muscle contraction being well established, no broadly valid method of modelling skeletal muscle exists. Studies that compare the merits of existing models are extremely scarce and researchers make various assumptions in order to simplify the complex, nonlinear behaviour of the muscle. Locusts provide an opportunity to develop a muscle model in a simpler system, that will still show similar properties to that of mammalian muscles. In developing a model previous work is considered, and complexity is introduced in the experimental conditions in stages. This meant a model could be built up in parts. This approach reduces the need for questionably valid assumptions. The main focus of this work is modelling activated isometric muscle. Experimental data was collected by stimulating the extensor muscle and measuring the force generated at the tibia. In the first instance the response to individual stimulus pulses is modelled. This is extended to develop a predictive model capable of estimating the isometric force response to general pulse train inputs. In developing the model, data was fit to existing models, and from this an improved isometric model developed. The effect of changing the isometric muscle length is considered. Commonly changing the muscle length is assumed to just scale the force response. This assumption is poor. The dynamics of the force response were found to be modifed by the change in muscle length, and the isometric model adapted to include this dependency. Results related to the non-isometric behaviour are also presented. Passive muscle is usually just modelled over the lengthening period, however, the whole stretch-shorten cycle is considered here. A model, adapted from the standard linear model, is developed to describe the passive force response.
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17

Litvin, Melanie Ann. "Comparing Response Frequency and Response Effort in Reinforcer Assessments with Children with Autism." Thesis, University of North Texas, 2005. https://digital.library.unt.edu/ark:/67531/metadc849638/.

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Reinforcer assessments have largely relied on the use of progressive ratio (PR) schedules to identify stimuli that function as reinforcers. PR schedules evaluate the reinforcing efficacy of a stimulus by measuring the number of responses produced in order to access a stimulus as the number of required responses increases. The current evaluation extends the literature on reinforcer assessments by measuring responding under a progressive force (PF) schedule, in addition to progressive ratio requirements. We compared responding under PR and PF schedules with two children with autism using a multielement design embedded within a reversal experimental design. Results were mixed and implications for further development of reinforcer assessment methods (particularly PF schedules) are discussed.
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18

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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19

Stapelfeldt, Sina Cornelia. "Advanced methods for multi-row forced response and flutter computations." Thesis, Imperial College London, 2013. http://hdl.handle.net/10044/1/24824.

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This thesis presents the formulation and validation of a novel time-accurate method for the computation of forced response and flutter in multiple blade row turbomachinery. Advanced gas turbine and aeroengine designs require unsteady computational methods to predict aeroelastic behaviour and prevent the occurrence of flutter or forced response which could ultimately lead to engine failure. Currently, time-accurate schemes can successfully represent unsteady flows across multiple blade rows if the domain encompasses the full circumference. However, the large domain size and range of time scales involved make this approach very expensive and unfeasible during the design cycle. More efficient methods take advantage of the inherent time-space periodicity in turbomachines to reduce the computational domain to a single bladed passage per row. These single-passage multi-row methods successfully model unsteadiness due to rotor-stator interaction or blade vibration by applying phase-lagged boundary conditions. However, they are limited to assemblies without passage-to-passage variations in the time-averaged flow field. In multi-stage turbomachinery, where the interaction of rows with unequal blade counts in the same frame of reference creates steady circumferential variations, single-passage methods cannot be applied as no phase-shifted temporal periodicity exists between adjacent passages. Similarly, it is not possible to represent non-axisymmetries such as inlet distortions or stagger profiles using a single passage approach. The time-domain Fourier method presented in this thesis models multi-row non-axisymmetric flows on a reduced number of passages. In order to capture stationary variations, the flow inside several discrete passages, which are located at different circumferential positions, is solved using a time-accurate scheme. Boundary conditions at the azimuthal and inter-row surfaces are approximated from a time-space Fourier series and couple the individual passages. The method is validated for several applications including low engine order forcing in an aerodynamically mistuned assembly and rotor-rotor interaction. It is demonstrated that, within the limit of the Fourier approximation, the resulting solution is equivalent to the full circumference solution and requires only a fraction of the computational resources.
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20

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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21

Chen, Jin-Jae. "Prediction of periodic forced response of frictionally constrained turbine blades /." The Ohio State University, 1999. http://rave.ohiolink.edu/etdc/view?acc_num=osu1488187763847997.

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22

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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23

Lamouroux, Julien. "Aeroelastic forced response of a bladed drum from a low pressure compressor." Thesis, KTH, Kraft- och värmeteknologi, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-183376.

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The purpose of this master thesis is to provide a reliable methodology to predict the forced response of a monoblock bladed drum from a low pressure compressor. Pre-test forced response calculations have already been made at Techspace Aero in 2013. Now that experimental data are available, the methodology has to be adapted to ensure the best numerical-experimental correlation possible. The final goal is that, at the end of the thesis, engineers at Techspace Aero will be able to launch reliable forced response simulations within a short amount of time. For the sake of confidentiality, some data are not revealed, such as the engine name, some numerical values (forced response, aerodynamic damping, frequency of the mode etc…) and axis scales. In this paper, the study focuses on the forced response of a rotor blade from the first stage under the excitation from the upstream stator. The mode under investigation is the 2S2, the one that responded during the experiment. The TWIN approach is used to compute the forced response of the rotor blade. With this approach, a steady stage computation has first to be carried on as an initialization. Then two unsteady computations are necessary. The first, without blade motion, will provide the excitation aerodynamic forces. The aerodynamic damping will be extracted from the second one, where the motion of the blade is imposed on a given eigenmode. The forced response can then be computed with these two results and some additional structural data.  The results will be compared to the experimental value.
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24

Laumert, Björn. "Numerical Investigation of Aerodynamic Blade Excitation Mechanisms in Transonic Turbine Stages." Doctoral thesis, KTH, Energy Technology, 2002. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3417.

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With the present drive in turbomachine engine developmenttowards thinner and lighter bladings, closer spaced blade rowsand higher aerodynamic loads per blade row and blade, advanceddesign criteria and accurate prediction methods for vibrationalproblems such as forced response become increasingly importantin order to be able to address and avoid fatigue failures ofthe machine early in the design process. The present worksupports both the search for applicable design criteria and thedevelopment of advanced prediction methods for forced responsein transonic turbine stages. It is aimed at a betterunderstanding of the unsteady aerodynamic mechanisms thatgovern forced response in transonic turbine stages and furtherdevelopment of numerical methods for rotor stator interactionpredictions.

The investigation of the unsteady aerodynamic excitationmechanisms is based on numerical predictions of thethree-dimensional unsteady flow field in representative testturbine stages. It is conducted in three successive steps. Thefirst step is a documentation of the pressure perturbations onthe blade surface and the distortion sources in the bladepassage. This is performed in a phenomenological manner so thatthe observed pressure perturbations are related to thedistortion phenomena that are present in the blade passage. Thesecond step is the definition of applicable measures toquantify the pressure perturbation strength on the bladesurface. In the third step, the pressure perturbations areintegrated along the blade arc to obtain the dynamic bladeforce. The study comprises an investigation of operationvariations and addresses radial forcing variations. With thehelp of this bottom-up approach the basic forcing mechanisms oftransonic turbine stages are established and potential routesto control the aerodynamic forcing are presented.

For the computation of rotor stator interaction aerodynamicsfor stages with arbitrary pitch ratios a new numerical methodhas been developed, validated and demonstrated on a transonicturbine test stage. The method, which solves the unsteadythree-dimensional Euler equations, is formulated in thefour-dimensional time-space domain and the derivation of themethod is general such that both phase lagged boundaryconditions and moving grids are considered. Time-inclination isutilised to account for unequal pitchwise periodicity bydistributing time co-ordinates at grid nodes such that thephase lagged boundary conditions can be employed. The method isdemonstrated in a comparative study on a transonic turbinestage with a nominal non integer blade count ratio and anadjusted blade count ratio with a scaled rotor geometry. Thepredictions show significant differences in the blade pressureperturbation signal of the second vane passing frequency, whichwould motivate the application of the new method for rotorstator predictions with non-integer blade count ratios.

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25

Breslavsky, Ivan, Marco Amabili, and Mathias Legrand. "Circular Cylindrical Shell Made of Neo-Hookean-Fung Hyperelastic Material Under Static and Dynamic Pressure." Thesis, NTU "KhPI", 2016. http://repository.kpi.kharkov.ua/handle/KhPI-Press/24767.

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The present study is devoted to the investigation of static and dynamic behavior of the three-layered composite shell made of hyperelastic material. Such a shell can be considered as a model of human aorta. Since soft biological materials are essentially nonlinear even in the elasticity zone, not only geometrical, but also physical nonlinearity should be taken into account. The physical nonlinearity of soft biological tissues is usually modeled by certain hyperelastic law. The law chosen for this study is the combination of the Neo- Hookean law, which describes the isotropic response at small strains, and Fung exponential law, that models the stiff anisotropic response of the collagen fibers at larger strains. Each of three shell layers has its own hyperelastic constants set. These constants are determined basing on experiential data [1]. The straindeflection relations are modeled with higher-order shear deformation theory [2]. Initially, the shell is preloaded with static pressure. Since the defection in our study is large we use the expression for pressure as a follower load [3]. The static problem is solved with the help of the local models method [4]. Afterwards, the free and forced dynamical response of the preloaded shell is studied both in vacuo and with still fluid inside. The modes of interest are the first axisymmetric mode and mode with two half-waves in circumferential direction (so-called collapse mode). It is found that static pressure decreases the dynamic nonlinearity and it is quite weak. At the same time, the presence of fluid makes the softening nonlinearity stronger as in case of shells of conventional material [5].
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26

Jackson, Zane Steven. "Arterial remodeling in response to hemodynamic and axial forces." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp05/NQ63690.pdf.

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27

Hardy, Michael Stuart Anthony. "The response of flexible pavements to dynamic tyre forces." Thesis, University of Cambridge, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.385406.

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28

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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29

Hall, Ashley K. "Examination of Something Else as a Response Alternative in Forced-Choice Questions." University of Toledo / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1415117471.

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30

Svenkeson, Adam. "How Cooperative Systems Respond to External Forces." Thesis, University of North Texas, 2014. https://digital.library.unt.edu/ark:/67531/metadc500014/.

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Cooperative interactions permeate through nature, bringing about emergent behavior and complexity. Using a simple cooperative model, I illustrate the mean field dynamics that occur at the critical point of a second order phase transition in the framework of Langevin equations. Through this formalism I discuss the response, both linear and nonlinear, to external forces. Emphasis is placed on how information is transferred from one individual to another in order to facilitate the collective response of the cooperative network to a localized perturbation. The results are relevant to a wide variety of systems, ranging from nematic liquid crystals, to flocks and swarms, social groups, and neural networks.
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31

Turner, Darryl A. "Force And Electromyographic Responses To Ergometer Rowing." Thesis, Edith Cowan University, Research Online, Perth, Western Australia, 2000. https://ro.ecu.edu.au/theses/1544.

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During many athletic events, fatigue influences the physiological and biomechanical characteristics of performance. For optimal performance in events such as rowing, athletes must maintain a skilfully co-ordinated movement technique. The ability to produce high force outputs during repetitive contractions is influenced by fatigue and dependent on a number of factors including neuromuscular activities. Neuromuscular activation may be expressed by amplitude and frequency characteristics of the electromyographic signal (EMG) sample from the muscle. During sustained isometric contractions, changes in EMG characteristics are related to changes in force, which may be useful in monitoring the fatigue process (Basmajian, 1974: De Luca, 1985). However, the force-EMG relationship is not as clear when applied lo dynamic contractions such as those in rowing performance. The central objective of this thesis is to assess the application of EMG in relation to biomechanical and physiological responses to rowing tasks. In particular, EMG characteristics of the quadriceps muscle in relation to total force output during a typical self-pace rowing ergometer performance. In order to reach the objective, five studies were undertaken in a systematic order. The studies had specific purposes, which included establishing force/torque-EMG relationships under controlled conditions and evaluating the transfer of force or torque output and EMG characteristics to less controlled performance conditions that were influenced by fatigue, pacing strategy, or both. In this investigation, trials (N – 117) were conducted on three ergometers affording varying levels of control over muscle length, contraction velocity, and muscle contribution to force output. Subjects (a – 11) that participated were selected from trained rowing crews. Trials were performed on an isokinetic dynamometer with analogue outputs of angular rotation and torque recorded. In addition, trials were performed on a leg-only ergometer and a standard rowing ergometer with performance outcomes recorded using a potentiometer to measure handle position and a strain gauge to measure force output. Bipolar surface electrodes were used to record EMC activity of the rectus femoris and vastus latcralis during all contractions. Biomechanical and EMO data were recorded on a data acquisition system (Amlab). Results validated the force/torque-rmsEMG relationship during non-fatiguing isometric, isokinetic, and dynamic contractions. During fatiguing contractions performed on the rowing ergometer, strength of the force/torquc-rmsEMG relationship was reduced and subject responses varied widely. Under the same condition, handle force and mean power frequency (MPF) of the vastus luteralis muscle showed a positive correlation. which might therefore be used to monitor fatigue during simulated rowing performance. EMG analysis was more appropriate when the exercise protocol was similar to that used during performance. Finally, a constant-pace strategy significantly reduced force loss and was associated with qualitative muscle activation changes that potentially might improve performance outcome. In conclusion, EMG analysis is constrained by methodological and confounding factors during dynamic exercise. Nevertheless EMG provides an insight into neural activation strategies during rowing fatigue and may be a useful tool for monitoring co-ordinated muscle activity and for devising strategies to improve performance.
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32

Li, Sinan. "Laser speckle contrast detection of acoustic radiation force response." Thesis, Imperial College London, 2015. http://hdl.handle.net/10044/1/34931.

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Light and ultrasound are both non-ionizing radiations, ideal for biomedical applications. Recent studies on combining ultrasound and light for biomedical imaging show new promises in improving imaging quality and/or providing complementary imaging contrast. Among a variety of the imaging modalities that simultaneously use ultrasound and light, this work focuses on optical detection of tissue responses to acoustic radiation force (ARF). The applications include optical shear wave elastography and ultrasound modulated optical tomography. The first half of the thesis provides a systematic study on tracking shear waves in optical turbid media using CCD-based laser speckle contrast analysis. The theory, simulation and experiment are developed and cross-validated. The simulation quantitatively relates CCD speckle contrast signal with shear waves, providing useful information to understand the underlying physics. In addition, multiple shear waves are tracked using laser speckle contrast detection. Results show that two counter-propagating shear waves produce a modulation pattern in the optical signal, and the modulation pattern was suggested by simulation as a result of the dual shear wave interference. Shear wave speed measurements in phantoms suggest that the dual shear wave approach is more accurate than the single shear wave approach as that the standard deviation of the speed measurement is reduced by a factor of at least 2. The the dual shear wave approach also provides a reduced boundary effect. Both factors suggest that the dual shear wave approach should improve the accuracy of elasticity measurements. In the second half of the thesis, instead of detecting ARF response in the late phase, the study is motivated by detecting ARF response in the early stage for enhancement of ultrasound modulation of light. A pilot study on incorporating perfluorocarbon-based phase change contrast agent with ultrasound modulated optical tomography is explored. To understand the phase transition process, a quantitative measurement of acoustic nanodroplet vapourisation is developed. A preliminary result also showed that a single ultrasound burst can simultaneously vaporise the nanodroplets and sonify the converted microbubbles to provide additional ultrasound modulation of light. This additional light modulation was shown to increase the laser speckle contrast signal detected on a CCD camera.
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33

Isegawa, Miho. "Development of polarizable force field with charge response kernel." 京都大学 (Kyoto University), 2009. http://hdl.handle.net/2433/126573.

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34

Litvin, Melanie A. "Comparing Response Frequency and Response Effort in Reinforcer Assessments with Children with Autism." Thesis, University of North Texas, 2016. https://digital.library.unt.edu/ark:/67531/metadc849638/.

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Reinforcer assessments have largely relied on the use of progressive ratio (PR) schedules to identify stimuli that function as reinforcers. PR schedules evaluate the reinforcing efficacy of a stimulus by measuring the number of responses produced in order to access a stimulus as the number of required responses increases. The current evaluation extends the literature on reinforcer assessments by measuring responding under a progressive force (PF) schedule, in addition to progressive ratio requirements. We compared responding under PR and PF schedules with two children with autism using a multielement design embedded within a reversal experimental design. Results were mixed and implications for further development of reinforcer assessment methods (particularly PF schedules) are discussed.
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35

Böe, Erik. "NATOs nye konsepter, NATO Response Force og Combined Joint Task Force - i et maritimt perspektiv." Thesis, Försvarshögskolan, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:fhs:diva-1658.

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Bakgrunnen for innføringen av CJTF-konseptet, og dermed innslag av multinasjonale enheter, varreduksjoner i de alliertes nasjonale styrkestrukturer. Dessuten er flernasjonale styrker blitt mer vanlige bådei internasjonale fredsstøtteoperasjoner og for å løse mer tradisjonelle allierte oppgaver.Det er viktig å kunne se sammenhengen mellom NATOs nye deployeringskonsepter. Tidligere hadde ikkeNATO et system som ivaretok de prosesser og aktiviteter som var nødvendige i perioden fra krisen var etfaktum til en CJTF var operativ. NRF er ment å skulle fylle dette tomrommet.Den forsvars- og sikkerhetspolitiske utviklingen er, og har vært, preget av mange begivenheter. NATOstilnærming til Europa, European Security and Defence Identity, og EUs militære fokusering, EuropeanSecurity and Defence Policy, er begge viktige milepæler for ulike nasjoners militære fokusering.Sammen med nye operasjonsområder og tilhørende konfliktskala, ulike konfliktløsere og nasjonersalliansetilhørighet, vil jeg belyse tre valgte lands maritime evne og villighet til å delta internasjonalt iNATOs nye konsepter.Sverige – på tross av sitt medlemskap i EU, en stadig tilnærming til NATO samt satsning på kystnæreoperasjonskonsepter – har tydelige begrensninger. Den politiske viljen er ikke alltid like presis og dethersker en for stor diskrepans mellom mål og midler. Norge har med sitt NATO medlemskap opparbeidetseg verdifull erfaring, de har en velutviklet konseptuel basis, men må være observant sin marginale flåtepark.Storbritannia – som en europeisk stormakt og foregangsland på mange områder – har gjentatte gangerdemonstrert evne, politisk vilje og handlekraft.
Avdelning: ALB - Slutet Mag 3 C-uppsHylla: Upps. ChP 02-04
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36

Moyroud, François. "Fluid-structure integrated computational methods for turbomachinery blade flutter and forced response predictions /." Stockholm : Tekniska högsk, 1998. http://www.lib.kth.se/abs98/moyr1214.pdf.

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37

Harre, Thomas David Andrew. "Human Trafficking For Forced Labour At Sea: An Assessment Of New Zealand's Response." Thesis, University of Canterbury. Law, 2013. http://hdl.handle.net/10092/8377.

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The fishing industry is worth approximately $1.4 billion annually to the New Zealand economy, making seafood New Zealand's fifth largest export earner, and giving the industry as a whole a position of high importance to New Zealand. All is not well however. Recent events have exposed a sordid underside to this industry involving the abuse of labour of foreign fishermen at the hands of Korean boat owners, chartered by New Zealand companies to fish New Zealand waters. Since the introduction of the quota management system in the 1980s, the New Zealand fishing industry has had problems relating to the exploitation of migrant workers. In some instances, this exploitation appears to be manifested in the form of human trafficking. Adopting a socio-legal methodology, this thesis examines the facts that support claims of human trafficking of economically vulnerable fishers from countries such as Indonesia and the Philippines into New Zealand, where they are required to work in exploitative conditions upon foreign charter vessels in New Zealand's exclusive economic zone. Having established the argument for the existence of human trafficking in New Zealand's territory (a claim which has been consistently downplayed or denied by government officials) this thesis then examines the evolving nature of the legal obligations that have been placed upon the New Zealand government by international law. Combining these international obligations with standards of best practice that have been derived from an examination of three other jurisdictions - Australia, the United Kingdom and the United States of America - into a set of benchmark criteria, this thesis concludes with a critical assessment of the New Zealand anti-trafficking framework by these standards.
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38

Walton, Edward James. "Forced response of a centrifugal compressor stage due to the impeller-diffuser interaction." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/87485.

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Thesis: S.M., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2014.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 135-136).
The unsteady pressure field experienced by a centrifugal compressor stage can be dominated by of the impeller-diffuser interaction. The energy of the unsteady field, under certain aerodynamic and structural conditions, is capable of forcing the rotating impeller blades to vibrate excessively to the point of failure, better known as a high cycle fatigue (HCF) failure. This thesis seeks to identify the physical mechanisms that set the forced response amplitude of an impeller due to the impeller-diffuser interaction. The centrifugal stage researched is comprised of a stationary discrete passage diffuser and an unshrouded rotating impeller with both main and splitter blades. The forced response of two splitter blade modes are computed for a variety of structural boundary conditions and unsteady loadings to elicit the driving physical mechanisms. The findings indicate that the forced response is enhanced when the excitation frequency matches a component's natural frequency, the characteristic wavelength of the unsteady loading matches that of the structural vibration mode, the resonance occurs at high speed, and when modal displacement exists at the impeller blade's trailing edge. The findings also suggest that modal coupling of blade and disk dominant modes leads to high sensitivity of the forced response to small variations in airfoil and disk backwall thickness. Identification of blade-disk couplings are described using a simplified SAFE (Singh's Advanced Frequency Evaluation) diagram. The forced response of taut strings, Bernoulli-Euler beams, and a two mass-spring system are also utilized to elicit how the physical mechanisms act on the impeller's forced response. The Bernoulli-Euler beam model suggests that a mismatch of the forcing wavelength to the structural wavelength by 50% will reduce the forced response amplitude by at least 75%. Finally, a decision tree is proposed to assess the relative resonant risk of impeller modes to the diffuser excitation by identifying which of the physical mechanisms may be the dominant driver of the forced response.
by Edward James Walton.
S.M.
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39

Moyroud, François. "Fluid-structure integrated computational methods for turbomachinery blade flutter and forced response predictions." Lyon, INSA, 1998. http://www.theses.fr/1998ISAL0101.

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Les ensembles disque-aubes des turbomachines modernes sont amenés à satisfaire des critères stricts en termes de stabilité aéroélastique et de réponse forcée. L'objectif de cette thèse est d'utiliser et de développer des techniques de modélisation, capables de prédire le phénomène de flottement et de quantifier les amplitudes de résonance des aubages de turbomachine. Pour le flottement, deux méthodes d'analyse aéroélastique sont considérées: la méthode énergétique (approche fluidestructure non-couplée) et le schéma de couplage modal (approche fluide-structure couplée). Ces modèles ont été installés dans le code de calcul STRUFLO qui offre des outils d'interface performants pour coupler divers codes de calcul. Des méthodes spécifiques sont utilisées afin de combiner plusieurs types d'analyses fluide et structure, et ainsi de progresser dans le sens d'un traitement général des interactions fluide-structure. A cet effet, le schéma de couplage modal est adapté pour être compatible avec des analyses modales d'aube seule ainsi que des analyses modales d'ensemble disque-aubes avec ou sans symétrie cyclique. Un maillage d'interface est utilisé pour résoudre les problèmes liés à l'incompatibilité des maillages fluide et structure à l'interface et une méthode d'interpolation/extrapolation permet de transférer les modes de vibration d'aube et les champs de pression instationnaire, du maillage structure au maillage aérodynamique et vice versa. Le désaccordage structure est l'une des caractéristiques pouvant considérablement modifier la stabilité aéroélastique et les amplitudes de résonance des aubages. A cet effet, deux méthodes de réduction ont été étudiées afin d'autoriser des analyses modales et de réponse forcée d'ensemble disque-aubes complet. Les techniques développées sont appliquées à l'étude des comportements dynamiques, aérodynamiques et aéroélastiques du fan transonique NASA Rotor 67, d'un fan transonique avec nageoires et d'un fan subsonique à large corde
The lightweight, high performance bladed-disks used in today's aeroengines must meet strict standards in terms of aeroelastic stability and resonant response characteristics. The research presented in this thesis is directed toward improved prediction and understanding of blade flutters and forced response problems in turbomachines. To address the blade flutter problem, two aeroelastic analysis methods are considered: the energy method (fluid-structure uncoupled approach) and the modal aeroelastic coupling scheme (fluid-structure coupled approach). The two methods have been implemented in the STRUFLO master code which is designed to provide fluid-structure interfaces for a library of structural and flow solvers. Especially tailored methods are used to couple or interface a wide range of structural and aerodynamic analyses. First, the modal aeroelastic coupling scheme is extended to deal with single blade, cyclic symmetric and full assembly modal analyses as weil as single and multiple blade passage unsteady aerodynamic analyses. Second, an interfacing grid technique is proposed to circumvent problems due to the presence of non-conforming fluid and structural grids at the interface. Finally, a grid-to-grid interpolation/extrapolation scheme is used to transfer blade mode shapes and blade surface unsteady pressures from the structural grid to the aerodynamic grid and vice versa. One structural characteristic of bladed-disks that can significantly impact bath on the aeroelastic stability and the resonant response is that of structural mistuning. With this respect, two reduction methods have been developed to perform full assembly modal analyses and forced response analyses. Various numerical applications are proposed to illustrate the applicability of the above mentioned methods including structural dynamic, aerodynamic and aeroelastic analyses of the NASA Rotor 67 unshrouded transonic fan, a shrouded transonic fan and a subsonic wide chard fan
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40

Piraccini, Matteo. "Prediction and measurement of forced response of a composite blade undergoing nonlinear vibration." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2015. http://amslaurea.unibo.it/8491/.

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The main objective of this project is to experimentally demonstrate geometrical nonlinear phenomena due to large displacements during resonant vibration of composite materials and to explain the problem associated with fatigue prediction at resonant conditions. Three different composite blades to be tested were designed and manufactured, being their difference in the composite layup (i.e. unidirectional, cross-ply, and angle-ply layups). Manual envelope bagging technique is explained as applied to the actual manufacturing of the components; problems encountered and their solutions are detailed. Forced response tests of the first flexural, first torsional, and second flexural modes were performed by means of a uniquely contactless excitation system which induced vibration by using a pulsed airflow. Vibration intensity was acquired by means of Polytec LDV system. The first flexural mode is found to be completely linear irrespective of the vibration amplitude. The first torsional mode exhibits a general nonlinear softening behaviour which is interestingly coupled with a hardening behaviour for the unidirectional layup. The second flexural mode has a hardening nonlinear behaviour for either the unidirectional and angle-ply blade, whereas it is slightly softening for the cross-ply layup. By using the same equipment as that used for forced response analyses, free decay tests were performed at different airflow intensities. Discrete Fourier Trasform over the entire decay and Sliding DFT were computed so as to visualise the presence of nonlinear superharmonics in the decay signal and when they were damped out from the vibration over the decay time. Linear modes exhibit an exponential decay, while nonlinearities are associated with a dry-friction damping phenomenon which tends to increase with increasing amplitude. Damping ratio is derived from logarithmic decrement for the exponential branch of the decay.
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41

Wu, Tenghu. "Modeling biomechanical responses of cells to external forces." Thesis, University of British Columbia, 2015. http://hdl.handle.net/2429/54153.

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For many cells, their biomechanical properties are important to their biofunctions. This thesis contains three computational studies of cellular dynamics under mechanical deformation. When infected by malaria, infected red blood cells (iRBCs) become less deformable and tend to block microcapillaries. Microfluidic channels have been used to investigate the deformability of iRBC at different infection stages. In my first project, I applied a discrete iRBC model to simulate the traverse of iRBCs through a microfluidic channel and investigated the progressive loss of the cell deformability due to three factors: the membrane stiffening, the cell surface-volume ratio reduction, and the parasite growing inside the cell. The results indicate that the growth of the parasite clusters play the most significant role in causing the channel blockage. Recent experiments have investigated the response of neutrophils after passing through microfluidic channels. The results indicate that neutrophils may be activated by mechanical deformation. Mechanical deformation causes disassembly of the cytoskeletal network of the neutrophils, which results in a sudden drop of the cell elastic modulus (termed fluidization). The fluidization is followed by either activation of the neutrophils with formation of pseudopods or uniform recovery of the cytoskeletal network without pseudopod formation. The former only occurs when the neutrophils' transit rate is slow. I proposed a chemo-mechanical model for the fluidization and activation processes, based on the polarization of the Rac protein through a wave-pinning mechanism. The model captures the main features of the experimental observation. The third project investigates the response of smooth muscle cells to transient stretch-compress (SC) and compress-stretch (CS) maneuvers. Prior experimental results indicate that the transient SC maneuver causes a sudden fluidization of the cell while the CS maneuver does not. To understand this asymmetric behavior, I built a biomechanical model to probe the response of stress fibers to the two maneuvers. The model couples the cross-bridge cycle of myosin motors with a viscoelastic Kelvin-Voigt element. Simulation results point to the sensitivity of the myosin detachment rate to tension as the cause for the asymmetric response of the stress fiber to the CS and SC maneuvers.
Applied Science, Faculty of
Chemical and Biological Engineering, Department of
Graduate
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42

Mohammed, Ali Hjaji. "Steady State Response of Thin-walled Members Under Harmonic Forces." Thèse, Université d'Ottawa / University of Ottawa, 2013. http://hdl.handle.net/10393/24013.

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The steady state response of thin-walled members subjected to harmonic forces is investigated in the present study. The governing differential equations of motion and associated boundary conditions are derived from the Hamilton variational principle. The harmonic form of the applied forces is exploited to eliminate the need to discretize the problem in the time domain, resulting in computational efficiency. The formulation is based on a generalization of the Timoshenko-Vlasov beam theory and accounts for warping effects, shear deformation effects due to bending and non-uniform warping, translational and rotary inertial effects and captures flexural-torsional coupling arising in asymmetric cross-sections. Six of the resulting seven field equations are observed to be fully coupled for asymmetric cross-sections while the equation of longitudinal motion is observed to be uncoupled. Separate closed form solutions are provided for the cases of (i) doubly symmetric cross sections, (ii) monosymmetric cross-sections, and (iii) asymmetric cross-sections. The closed-form solutions are provided for cantilever and simply-supported boundary conditions. A family of shape functions is then developed based on the exact solution of the homogeneous field equations and then used to formulate a series of super-convergent finite beam elements. The resulting two-noded beam elements are shown to successfully capture the static and dynamic responses of thin-walled members. The finite elements developed involve no special discretization errors normally encountered in other finite element formulations and provide results in excellent agreement with those based on other established finite elements with a minimal number of degrees of freedom. The formulation is also capable to predict the natural frequencies and mode-shapes of the structural members. Comparisons with non-shear deformable beam solutions demonstrate the importance of shear deformation effects within short-span members subjected to harmonic loads with higher exciting frequencies. Comparisons with shell element solution results demonstrate that distortional effects are more pronounced in cantilevers with short spans. A generalized stress extraction scheme from the finite element formulation is then developed. Also, a generalization of the analysis procedure to accommodate multiple loads with distinct exciting frequencies is established. The study is concluded with design examples which illustrate the applicability of the formulation, in conjunction with established principles of fatigue design, in determining the fatigue life of steel members subjected to multiple harmonic forces.
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43

Baldauf, Joerg Franz. "Implementing flexible response : the US, Germany, and NATO's conventional Forces." Thesis, Massachusetts Institute of Technology, 1987. http://hdl.handle.net/1721.1/14849.

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44

Payer, Florent. "Prédiction et analyse du phénomène de réponse forcée : application à un cas de compresseur haute pression." Phd thesis, Ecole Centrale de Lyon, 2013. http://tel.archives-ouvertes.fr/tel-01063776.

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L'enjeu de cette thèse est d'améliorer la compréhension et la prédiction du phénomène de réponse forcée des aubages de turbomachines en situation de résonance. L'étude a été menée au moyen de simulations numériques U-RANS 3D et en s'appuyant sur le compresseur d'essai ERECA, dédié au phénomène de réponse forcée. Pour prédire les amplitudes de vibration des aubages excités aérodynamiquement, la méthode de prédiction la plus répandue consiste à effectuer séparément un calcul d'excitation et un calcul d'amortissement aérodynamique ; on parle alors de calcul découplé. C'est cette méthode qui a été mise en œuvre dans un premier temps. Les calculs d'excitation et d'amortissement aérodynamiques ont été comparés individuellement aux résultats d'essais. Pour cela une méthode de traitement du signal fréquence/amplitude a été développée dans le but d'extraire l'amortissement et l'excitation des résultats d'essais. Les analyses des simulations ont permis de mieux comprendre les mécanismes d'excitation et d'amortissement aérodynamique. On a ainsi pu montrer que le phénomène d'interaction rotor/stator s'apparente par son caractère discontinu à une percussion périodique. Quant au phénomène d'amortissement, il se caractérise par le bilan des contributions de chaque zone d'échange d'énergie sur la paroi de l'aubage. En outre, les amplitudes vibratoires calculées à partir de cette méthode sont très proches des valeurs d'essais. Toutefois, cette procédure de calcul requiert la mise en œuvre de 2 calculs instationnaires différents et ne permet pas à l'heure actuelle d'être utilisée dans un cycle de conception. Dans le but de simplifier et d'améliorer la qualité de prédiction des analyses de réponse forcée, la méthode du couplage dynamique a été mise en œuvre et évaluée. Avec cette méthode, l'aubage répond librement aux sollicitations engendrées par le fluide. Une fois le régime transitoire évacué, l'aubage oscille en régime permanent. Cette méthode permet donc de prédire une amplitude vibratoire à partir d'un seul calcul instationnaire. En revanche, le calcul s'avère bien plus onéreux que la méthode découplée de par l'existence du régime transitoire. Dans le but de rendre accessible cette méthode à un niveau industriel, deux méthodes d'accélération du calcul ont été mises en place. Les résultats obtenus sont très encourageants et devraient permettre de réduire drastiquement les temps de restitution des analyses de réponse forcée. A la connaissance de l'auteur, cette thèse constitue une étude inédite de comparaison entre méthode découplée et couplage dynamique, qui par ailleurs s'appuie sur des résultats d'essais dédiés exclusivement au phénomène de réponse forcée.
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45

Bardswell, Sonya Caroline. "The mechanism of the slow force response to myocardial stretch." Thesis, King's College London (University of London), 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.416416.

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46

OLIVEIRA, NATALIA DE BRITO. "BRAZILIAN AIR FORCE LOGISTICS IN RESPONSE OPERATIONS TO NATURAL DISASTERS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2015. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=25678@1.

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A crescente participação das Forças Armadas (FA) em cooperação com a Defesa Civil em situações de desastres naturais tem demonstrado a importância do aprofundamento e aprimoramento dos estudos da logística humanitária no campo militar. Sabendo que a excelência nos processos pode gerar economia dos recursos a serem mobilizados para alcançar as necessidades da população afetada, bem como a minimização do tempo de resposta, este estudo objetiva apresentar e analisar as atividades de resposta a desastres naturais desempenhadas pela Força Aérea Brasileira (FAB), sob a ótica da modelagem de processos. Para isso, realiza-se um estudo de caso pautado no mapeamento das atividades realizadas pela Aeronáutica com base nas legislações em vigor e com base na operação real de apoio às vítimas do desastre da região serrana fluminense em 2011, considerada uma das maiores tragédias climáticas ocorridas no Brasil. Simultaneamente, é conduzida uma comparação de adequação ao padrão em relação à literatura acadêmica. Os resultados deste trabalho apontam para processos realizados pela FAB que podem ser considerados na elaboração de uma doutrina específica relativa ao tema e ainda os processos não previstos nas legislações vigentes, os quais podem ser objeto de futuras pesquisas na FAB, além de sugerir a inclusão de processos não representados nos modelos de processos de resposta a desastre da literatura acadêmica. Com isso, almeja-se subsidiar futuras pesquisa no meio acadêmico sobre o tema, bem como contribuir para a elaboração de uma doutrina específica relativa a essas atividades, a fim de se obter uma maior eficácia e eficiência no apoio da FAB em missões humanitárias.
The growing participation of the Armed Forces (AF) in natural disasters situations has ratified the importance of deepening and improvement of studies in humanitarian logistics in the military field. Knowing that excellence in processes can generate savings of resources to be mobilized to meet the needs of the affected population as well as minimizing the response time, this study aims to present and analyze the response activities to natural disasters performed by the Brazilian Air Force (BRAF), from the perspective of process modeling. For this, a case study is carried out according to the mapping of activities performed by the BRAF based on the legislation in place and on a real operation of support to victims of a disaster in the mountainous region of Rio de Janeiro in 2011, considered one of the biggest climate tragedy in Brazil. Simultaneously, a pattern matching comparability in relation to the academic literature is conducted. The results of this study point to processes performed by the BRAF that can be considered in the preparation of a specific doctrine on the subject and to processes not considered in current legislation, which may be the subject of future research in the BRAF. It also suggests the inclusion of processes not represented in process models of disaster response in the academic literature. Thus, it aims to support future studies in academic research on the subject, as well as contribute to the development of a specific doctrine on these activities in order to achieve greater effectiveness and efficiency in the BRAF support for humanitarian missions.
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47

Plaks, Dmitriy Vital. "Dynamics of longitudinally forced bluff body flames with varying dilatation ratios." Thesis, Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/31767.

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Thesis (M. S.)--Aerospace Engineering, Georgia Institute of Technology, 2010.
Committee Chair: Tim Lieuwen; Committee Member: Jeff Jagoda; Committee Member: Suresh Menon. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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48

Myhre, Mikkel. "Numerical investigation of the sensitivity of forced response characteristics of bladed disks to mistuning." Licentiate thesis, KTH, Energy Technology, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-1639.

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Two state of the art finite element reduction techniquespreviously validated against the direct finite element method,one based on classical modal analysis and another based oncomponent mode synthesis, are applied for efficient mistunedfree vibration and forced response analysis of several bladeddisk geometries. The methods are first applied to two testcases in order to demonstrate the differences in computationalefficiency as well as to validate the methods againstexperimental data. As previous studies have indicated, nonoticeable differences in accuracy are detected for the currentapplications, while the method based on classical modalanalysis is significantly more efficient. Experimental data(mistuned frequencies and mode shapes) available for one of thetwo test cases are compared with numerical predictions, and agood match is obtained, which adds to the previous validationof the methods (against the direct finite element method).

The influence of blade-to-blade coupling and rotation speedon the sensitivity of bladed disks to mistuning is thenstudied. A transonic fan is considered with part span shroudsand without shrouds, respectively, constituting a high and alow blade-to-blade coupling case. For both cases, computationsare performed at rest as well as at various rotation speeds.Mistuning sensitivity is modelled as the dependence ofamplitude magnification on the standard deviation of bladestiffnesses. The finite element reduction technique based onclassical modal analysis is employed for the structuralanalysis. This reduced order model is solved for sets of randomblade stiffnesses with various standard deviations, i.e. MonteCarlo simulations. In order to reduce the sample size, thestatistical data is fitted to a Weibull (type III) parametermodel. Three different parameter estimation techniques areapplied and compared. The key role of blade-to-blade coupling,as well as the ratio of mistuning to coupling, is demonstratedfor the two cases. It is observed that mistuning sensitivityvaries significantly with rotation speed for both fans due toan associated variation in blade-to-blade coupling strength.Focusing on the effect of one specific engine order on themistuned response of the first bending modes, it is observedthat the mistuning sensitivity behaviour of the fan withoutshrouds is unaffected by rotation at its resonant condition,due to insignificant changes in coupling strength at thisspeed. The fan with shrouds, on the other hand, shows asignificantly different behaviour at rest and resonant speed,due to increased coupling under rotation. Comparing the twocases at resonant rotor speeds, the fan without shrouds is lessor equally sensitive to mistuning than the fan with shrouds inthe entire range of mistuning strengths considered.

This thesis’scientific contribution centres on themistuning sensitivity study, where the effects of shrouds androtation speed are quantified for realistic bladed diskgeometries. However, also the validation of two finite elementreduction techniques against experimental measurementsconstitutes an important contribution.

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49

Pham, Hoang. "A perturbation solution for forced response of systems displaying eigenvalue veering and mode localization." Diss., Georgia Institute of Technology, 1995. http://hdl.handle.net/1853/19120.

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50

Mata, Sanjay. "A fast generalized single-passage method for multi-blade row forced response and flutter." Thesis, Imperial College London, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.523742.

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