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1
Lee, Jongsoo. "Facet model optic flow and rigid body motion." Diss., Virginia Polytechnic Institute and State University, 1985. http://hdl.handle.net/10919/53885.
Повний текст джерелаАнотація:
The dissertation uses the facet model technique to compute the optic flow field directly from a time sequence of image frames. Two techniques, an iterative and a non-iterative one, determine 3D motion parameters and surface structure (relative depth) from the computed optic flow field. Finally we discuss a technique for the image segmentation based on the multi-object motion using both optic flow and its time derivative.
The facet model technique computes optic flow locally by solving over-constrained linear equations obtained from a fit over 3D (row, column, and time) neighborhoods in an image sequence. The iterative technique computes motion parameters and surface structure using each to update the other. This technique essentially uses the least square error method on the relationship between optic flow field and rigid body motion. The non-iterative technique computes motion parameters by solving a linear system derived from the relationship between optic flow field and rigid body motion and then computes the relative depth of each pixel using the motion parameters computed. The technique also estimates errors of both the computed motion parameters and the relative depth when the optic flow is perturbed.Ph. D.
2
Schestowitz, Samuel. "Unifying models and registration : a framework for model-based registration and non-rigid registration assessment." Thesis, University of Manchester, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.509887.
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3
Lin, Cong. "Non-rigid visual object tracking with statistical learning of appearance model." Thesis, University of Macau, 2017. http://umaclib3.umac.mo/record=b3691900.
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4
Black, Christopher Lee Carleton University Dissertation Engineering Aerospace. "CF-18 tail buffet prediction based on rigid model pressure data." Ottawa, 1993.
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5
Hall, Anthony R. "The Pseudo-Rigid-Body Model for Fast, Accurate, Non-Linear Elasticity." BYU ScholarsArchive, 2013. https://scholarsarchive.byu.edu/etd/3869.
Повний текст джерелаАнотація:
We introduce to computer graphics the Pseudo-Rigid-Body Mechanism (PRBM) and the chain algorithm from mechanical engineering, with a unified tutorial from disparate source materials. The PRBM has been used successfully to simplify the simulation of non-linearly elastic beams, using deflections of an analogous spring and rigid-body linkage. It offers computational efficiency as well as an automatic parameterization in terms of physically measurable, intuitive inputs which fit naturally into existing animation work flows for character articulation. The chain algorithm is a technique for simulating the deflection of complicated elastic bodies in terms of straight elastic elements, which has recently been extended to incorporate PRBM beam-elements in three dimensions. We present a new, mathematically equivalent optimization of the 3D PRBM chain algorithm, from its former asymptotic complexity of O(n^2) in the number of elements n, to O(n). We also extend an existing PRBM for combined moment-force loads to 3D, where the existing 3D PRBM chain algorithm was limited to 3D PRBM elements for a moment-only load. This optimization and extension are validated by duplicating prior experimental results, but substituting the new optimization and combined-load elements. Finally, a loose road-map is provided with several key considerations for future extension of the techniques to dynamic simulations.
6
Fedotov, IA, AD Polyanin, and MY Shatalov. "Theory of Free and Forced Vibrations of a Rigid Rod Based on the Rayleigh Model." Pleaides Publishing LTD, 2007. http://encore.tut.ac.za/iii/cpro/DigitalItemViewPage.external?sp=1001012.
Повний текст джерелаАнотація:
We consider one-dimensional longitudinal vibrations
of a rigid rod with a nonuniform cross-section,
fixed at its ends with lumped masses and springs. The
cross-section inertia effects are taken into account on
the basis of the Rayleigh theory. The equation of
motion and the boundary conditions are derived from
Hamilton’s variational principle. The characteristic
equation is constructed and the eigenvalues for the harmonic
vibrations of the rod are calculated. It is shown
that the eigenvalues are bounded from above. Two
types of the orthogonality of the eigenfunctions corresponding
to the eigenvalues are discussed. The Green
function is constructed for the problem of forced vibrations
of the rod governed by a linear fourth-order partial
differential equation, which involves mixed derivatives.
Exact solutions of the rod vibration problems are found
for rods with constant and conical cross-sections.
Rigid isotropic waveguides are often used for generating,
transmitting, and amplifying mechanical vibrations,
for example, in acoustic transducers. Theoretical
investigation of acoustic, mechanical, and electromagnetic
waveguides is usually based on the analysis of
second-order wave equations. This approach is justified
in descriptions of the wave propagation in relatively
thin and long rigid rods. As was shown by Rayleigh [1],
the error due to the neglect of the transverse motion of
the rod is proportional to the square of the ratio of the
characteristic section radius to the length of the rod
(aspect ratio). For a more accurate analysis of the longitudinal
vibrations of a relatively thick and short rod,
the rod deformation in the transverse direction must also be taken into account. The approach to the analysis
of the vibrations of a thick and short rod used in this
study is based on the theory of longitudinal vibrations
of a rod, in which the effects due to the transverse
motion are taken into account (the corresponding mathematical
model is called the Rayleigh rod). The equation
of motion and the boundary conditions for the onedimensional
longitudinal vibrations of the Rayleigh rod
with variable cross section and ends fixed by means of
lumped masses and springs are derived from Hamilton’s
variational principle. As a result, we arrive at a linear
fourth-order partial differential equation with variable
coefficients, which involves mixed derivatives.
Previously, approximate analytical methods, such as
the Galerkin method [2] and the method based on the
expansion of the solution in a power series in the Poisson
coefficient [3], were used for solving this equation.
The frequencies of the natural vibrations of a cylindrical
rod with rigidly fixed ends were determined in [4,
pp. 159, 160]. In this study we use the method of the
separation of variables based on the exact solutions of
the equations of motion of the Rayleigh rod, which
makes it possible to construct the Green function. A
similar approach to an analysis of the longitudinal
vibrations of stepped rigid waveguides described by
second-order wave equations was applied in [5, 6].
7
Fischli, Simon. "Simulation of wrist kinematics on the basis of a rigid body spring model." Thesis, Kingston, Ont. : [s.n.], 2007. http://hdl.handle.net/1974/668.
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8
Khanse, Karan Rajiv. "Development and Validation of a Tool for In-Plane Antilock Braking System (ABS) Simulations." Thesis, Virginia Tech, 2015. http://hdl.handle.net/10919/56567.
Повний текст джерелаАнотація:
Automotive and Tire companies spend extensive amounts of time and money to tune their products through prototype testing at dedicated test facilities. This is mainly due to the limitations in the simulation capabilities that exist today. With greater competence in simulation, comes more control over designs in the initial stages, which in turn lowers the demand on the expensive stage of tuning. The work presented, aims at taking today's simulation capabilities a step forward by integrating models that are best developed in different software interfaces. An in-plane rigid ring model is used to understand the transient response of tires to various high frequency events such as Anti-Lock Braking and short wavelength road disturbances. A rule based ABS model performs the high frequency braking operation. The tire and ABS models have been created in the Matlab-Simulink environment. The vehicle model has been developed in CarSim. The models developed in Simulink have been integrated with the vehicle model in CarSim, in the form of a design tool that can be used by tire as well as vehicle designers for further tuning of the vehicle functional performances as they relate to in-line braking scenarios. Outdoor validation tests were performed to obtain data from a vehicle that was measured on a suspension parameter measuring machine (SPMM) in order to complement this design tool. The results of the objective tests performed have been discussed and the correlations and variations with respect to the simulation results have been analyzed.Master of Science
9
Yildiz, Ersan. "Lateral Pressures On Rigid Retaining Walls : A Neural Network Approach." Master's thesis, METU, 2003. http://etd.lib.metu.edu.tr/upload/1264415/index.pdf.
Повний текст джерелаАнотація:
Lateral pressures on non-yielding walls due to surface strip loads were
investigated considering the non-linear stress-strain behaviour of the soil by finite
element analyses. Data obtained from the finite element analyses were used to
train neural networks in order to obtain a solution to assess the total lateral thrust
and its point of application on a non-yielding wall due to a strip load. A 2-layered
backpropogation type neural network was used. An artificial neural network
solution was obtained, as a function of six parameters including the shear strength
parameters of the soil ( cohesion and angle of friction ). The effects of each input
parameter on the lateral thrust and point of application were summarized and the
results were compared with the conventional linear elastic solution.
10
Jones, Garrett D. "Semi-rigid towing model for analysis of maneuvering in the horizontal plane." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2001. http://handle.dtic.mil/100.2/ADA397072.
Повний текст джерелаАнотація:
Thesis (M.S. in Mechanical Engineering) Naval Postgraduate School, Sept. 2001.Thesis advisor, Papoulias, Fotis A. "September 2001." Includes bibliographical references (p. 47). Also Available in print.
11
Daum, Volker Gerhard [Verfasser], and Joachim [Akademischer Betreuer] Hornegger. "Model-Constrained Non-Rigid Registration in Medicine / Volker Daum. Betreuer: Joachim Hornegger." Erlangen : Universitätsbibliothek der Universität Erlangen-Nürnberg, 2012. http://d-nb.info/102359742X/34.
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12
Evans, Benjamin Scott. "Model based techniques for use by automated systems handling non-rigid materials." Thesis, University of Bristol, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.261355.
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13
Majors, Benjamin. "Development of a Rigid Body Computational Model for Investigation of Wrist Biomechanics." VCU Scholars Compass, 2010. http://scholarscompass.vcu.edu/etd/2319.
Повний текст джерелаАнотація:
The wrist is one of the most complex joints in the human body. As such, the wrist joint is difficult to model due to the number of bones involved and its intricate soft tissue interactions. Many studies have attempted modeling the wrist previously; however, the majority of these studies simplify the joint into two-dimensions or idealized mechanical joints to reduce the complexity of the simulation. While these approaches still yield valuable information, the omission of a third-dimension or geometry defined movements limits the models’ usefulness in predicting joint function under non-idealized conditions. Therefore, the goal of this study was to develop a computational model of the wrist joint complex using commercially available software, whereby joint motion and behavior is dictated by highly accurate three-dimensional articular contact, ligamentous constraints, muscle loads, and external perturbations only. As such, a computational model of the human wrist was created using computed tomography (CT) images of a cadaver right upper extremity. Commercially available medical imaging software and three-dimensional computer aided design (CAD) software were used to reconstruct the osteoarticular surfaces and accurately add soft tissue constraints, as well as calculate kinematic motion simulations. The model was able to reproduce physiologic motion including flexion/extension and radial/ulnar deviation. Validation of the model was achieved by comparing predicted results from the model to the results of a published cadaveric experiment that analyzed wrist function under effects of various surgical procedures. The model was used to replicate the exact testing conditions prescribed for the experiment, and the model was able to accurately reproduce the trends and, in many instances, the magnitudes of the range of motion measurements in the study. Furthermore, the model can now be used to predict the magnitudes for the joint contact forces within the wrist as well as the tension developed in ligaments in hopes locating potential areas of concern after these surgical procedures have been conducted, including further development of arthritis in the wrist and ligament breakdown.
14
Brown, Matthew Lee. "Dynamics of Rigid Fibers in a Planar Converging Channel." Diss., Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/6894.
Повний текст джерелаАнотація:
The influence of turbulence on the orientation state of a dilute suspension of stiff fibers at high Reynolds number in a planar contraction is investigated. High speed imaging and
LDV techniques are used to quantify fiber orientation distribution
and turbulent characteristics. A nearly homogenous, isotropic grid
generated turbulent flow is introduced at the contraction inlet.
Flow Reynolds number and inlet turbulent characteristics are
varied in order to determine their effects on orientation
distribution. The orientation anisotropy is shown to be accurately
modelled by a Fokker-Planck type equation. Results show that
rotational diffusion is highly influenced by inlet turbulent
characteristics and decays exponentially with convergence ratio.
Furthermore, the effect of turbulent energy production in the
contraction is shown to be negligible. Also, the results show
that the flow Reynolds number has negligible effect on the
development of orientation anisotropy, and the influence of
turbulence on fiber rotation is negligible for $mathrm{Pe_r}>$
10. It was concluded that inertia induced fiber motion played a
negligible role in the experiments.
15
Boyle, Cameron. "A Closed-Form Dynamic Model of the Compliant Constant-Force Mechanism Using the Pseudo-Rigid-Body Model." BYU ScholarsArchive, 2003. https://scholarsarchive.byu.edu/etd/53.
Повний текст джерелаАнотація:
A mathematical dynamic model is derived for the compliant constant-force mechanism, based on the pseudo-rigid-body model simplification of the device. The compliant constant-force mechanism is a slider mechanism incorporating large-deflection beams, which outputs near-constant-force across the range of its designed deflection. The equation of motion is successfully validated with empirical data from five separate mechanisms, comprising two configurations of compliant constant-force mechanism. The dynamic model is cast in generalized form to represent all possible configurations of compliant constant-force mechanism. Deriving the dynamic equation from the pseudo-rigid-body model is useful because every configuration is represented by the same model, so a separate treatment is not required for each configuration. An unexpected dynamic trait of the constant-force mechanism is discovered: there exists a range of frequencies for which the output force of the mechanism accords nearer to constant-force than does the output force at static levels.
16
Frey, Norman W. "Development of a rigid ring tire model and comparison among various tire models for ride comfort simulations." Connect to this title online, 2009.
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17
She, Yu. "Optimization of Pseudo-Rigid-Body Models for Accurately and Efficiently Predicting Dynamics of Compliant Mechanisms." The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu15414414341246.
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18
Thornton, D. A. "Computational human rigid body model with applications to landing falls and injury prevention." Thesis, Swansea University, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.639234.
Повний текст джерелаАнотація:
A three-dimensional computational human body model, named CHRIS (Computational Human Rigid-Body Impact Simulator), was developed to study the mechanical behaviour of the body in low and high acceleration environments. CHRIS is constructed from 15 rigid ellipses, which are connected by 14 kinematic joints, and has 34 degrees of freedom (DOF). Various human limbs and joints can be attached to CHRIS, so as to determine stresses and strains in specific body regions during impacts. Within this thesis a three-dimensional knee joint and lower leg are connected to CHRIS, and the stresses within the ligaments and bones are analysed. Biological materials, present within the human body, generally consist of an elastin ground substance and bundles of collagen fibres. Subsequently, hyperelastic transversely isotropic constitutive models are employed in this thesis. Bone is modelled using a general transversely isotropic hyperelastic function, which recovers the linear transversely isotropic constitutive matrix in the linear regime. Soft biological materials, such as tendons and ligaments, exhibit a high degree of stiffening for lower strains; thus, an exponential based function is used to stimulate this phenomenon. Although, soft biomaterials fundamentally display viscoelastic material properties, the time-dependent effects can be neglected when studying short impacts; hence, a purely hyperelastic response is sufficient. In the future, it is hoped that this research will prove to be a valuable tool in the automobile and aerospace industries, where the ability to predict injuries within the human body (and thus design safety systems) would be of use.
19
Yevsieiev, V. V., S. Miliutina, and V. E. Salieva. "Flexible and flex-rigid printed circuit boards basic characterastics for parametric model development." Thesis, ДРУКАРНЯ МАДРИД, 2016. http://openarchive.nure.ua/handle/document/8850.
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20
Spratley, Edward. "The Design and Validation of a Computational Rigid Body Model of the Elbow." VCU Scholars Compass, 2009. http://scholarscompass.vcu.edu/etd/1998.
Повний текст джерелаАнотація:
The use of computational modeling is an effective and inexpensive way to predict the response of complex systems to various perturbations. However, not until the early 1990s had this technology been used to predict the behavior of physiological systems, specifically the human skeletal system. To that end, a computational model of the human elbow joint was developed using computed topography (CT) scans of cadaveric donor tissue, as well as the commercially available software package SolidWorks™. The kinematic function of the joint model was then defined through 3D reconstructions of the osteoarticular surfaces and various soft-tissue constraints. The model was validated against cadaveric experiments performed by Hull et al and Fern et al that measured the significance of coronoid process fractures, lateral ulnar collateral ligament ruptures, and radial head resection in elbow joint resistance to varus displacement of the forearm. Kinematic simulations showed that the computational model was able to mimic the physiological movements of the joint throughout various ranges of motion including flexion/extension and pronation/supination. Quantitatively, the model was able to accurately reproduce the trends, as well as the magnitudes, of varus resistance observed in the cadaveric specimens. Additionally, magnitudes of ligament tension and joint contact force predicted by the model were able to further elucidate the complex soft-tissue and osseous contributions to varus elbow stability.
21
Marmaduke, Andrew Robert. "A Simple Coarse-Grained Model of a Carbon Nanotube Forest Interacting with a Rigid Substrate." University of Akron / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=akron1430418484.
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22
ZHOU, FENGFENG. "MODEL-BASED SIMULATION OF STEEL FRAMES WITH ENDPLATE CONNECTIONS." University of Cincinnati / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1119316578.
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23
Davies, Samuel Ingraham 1980. "3D model-based pose estimation of rigid objects from a single image for robotics." Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/99817.
Повний текст джерелаАнотація:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2015.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 167-170).
We address the problem of finding the best 3D pose for a known object, supported on a horizontal plane, in a cluttered scene in which the object is not significantly occluded. We assume that we are operating with RGB-D images and some information about the pose of the camera. We also assume that a 3D mesh model of the object is available, along with a small number of labeled images of the object. The problem is motivated by robot systems operating in indoor environments that need to manipulate particular objects and therefore need accurate pose estimates. This contrasts with other vision settings in which there is great variability in the objects but precise localization is not required. Our approach is to find the global best object localization in a full 6D space of rigid poses. There are two key components to our approach: (1) learning a view-based model of the object and (2) detecting the object in an image. An object model consists of edge and depth parts whose positions are piece-wise linear functions of the object pose, learned from synthetic rendered images of the 3D mesh model. We search for objects using branch-and-bound search in the space of the depth image (not directly in the Euclidean world space) in order to facilitate an efficient bounding function computed from lower-dimensional data structures.
by Samuel I. Davies.
Ph. D.
24
Lyon, Scott M. "The pseudo-rigid-body model for dynamic predictions of macro and micro compliant mechanisms /." Diss., CLICK HERE for online access, 2003. http://contentdm.lib.byu.edu/ETD/image/etd219.pdf.
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25
Lyon, Scott Marvin. "The Pseudo-Rigid-Body Model for Dynamic Predictions of Macro and Micro Compliant Mechanisms." BYU ScholarsArchive, 2003. https://scholarsarchive.byu.edu/etd/82.
Повний текст джерелаАнотація:
This work discusses the dynamic predictions of compliant mechanisms using the Pseudo-Rigid-Body model (PRBM). In order to improve the number of mechanisms that can be modeled, this research develops and identifies several key concepts in the behavior of beam segments where both ends are fixed to a rigid body (fixed-fixed flexible segments). A model is presented, and several examples are discussed. The dynamic behavior of several compliant segments is predicted using the PRBM and the results are compared to finite element analysis and experimental results. Details are presented as to the transient behavior of a typical uniform rectangular cross section beam. The results of this study are extended and applied to compliant planar mechanisms. It is shown by comparison with finite element analysis and experimental results that the PRBM is a good model of the physical system's dynamic behavior. The method is also demonstrated for use with compliant microelectromechanical (MEMS) systems.
26
McErlain-Naylor, Stuart A. "The effect of joint compliance within rigid whole-body computer simulations of impacts." Thesis, Loughborough University, 2017. https://dspace.lboro.ac.uk/2134/33495.
Повний текст джерелаАнотація:
In high impact human activities, much of the impact shock wave is dissipated through internal body structures, preventing excessive accelerations from reaching vital organs. Mechanisms responsible for this attenuation, including lower limb joint compression and spinal compression have been neglected in existing whole-body simulation models. Accelerometer data on one male subject during drop landings and drop jumps from four heights revealed that peak resultant acceleration tended to decrease with increasing height in the body. Power spectra contained two major components, corresponding to the active voluntary movement (2 Hz 14 Hz) and the impact shock wave (16 Hz 26 Hz). Transfer functions demonstrated progressive attenuation from the MTP joint towards the C6 vertebra within the 16 Hz 26 Hz component. This observed attenuation within the spine and lower-limb joint structures was considered within a rigid body, nine-segment planar torque-driven computer simulation model of drop jumping. Joints at the ankle, knee, hip, shoulder, and mid-trunk were modelled as non-linear spring-dampers. Wobbling masses were included at the shank, thigh, and trunk, with subject-specific biarticular torque generators for ankle plantar flexion, and knee and hip flexion and extension. The overall root mean square difference in kinetic and kinematic time-histories between the model and experimental drop jump performance was 3.7%, including ground reaction force root mean square differences of 5.1%. All viscoelastic displacements were within realistic bounds determined experimentally or from the literature. For an equivalent rigid model representative of traditional frictionless pin joint simulation models but with realistic wobbling mass and foot-ground compliance, the overall kinetic and kinematic difference was 11.0%, including ground reaction force root mean square differences of 12.1%. Thus, the incorporation of viscoelastic elements at key joints enables accurate replication of experimentally recorded ground reaction forces within realistic whole-body kinematics and removes the previous need for excessively compliant wobbling masses and/or foot-ground interfaces. This is also necessary in cases where shock wave transmission within the simulation model must be non-instantaneous.
27
Lehnert, Christopher. "Locally weighted learning methods for non-rigid robot control." Thesis, Queensland University of Technology, 2015. https://eprints.qut.edu.au/82358/1/Christopher_Lehnert_Thesis.pdf.
Повний текст джерелаАнотація:
This thesis develops a novel approach to robot control that learns to account for a robot's dynamic complexities while executing various control tasks using inspiration from biological sensorimotor control and machine learning. A robot that can learn its own control system can account for complex situations and adapt to changes in control conditions to maximise its performance and reliability in the real world. This research has developed two novel learning methods, with the aim of solving issues with learning control of non-rigid robots that incorporate additional dynamic complexities. The new learning control system was evaluated on a real three degree-of-freedom elastic joint robot arm with a number of experiments: initially validating the learning method and testing its ability to generalise to new tasks, then evaluating the system during a learning control task requiring continuous online model adaptation.
28
Palomba, Ilaria. "State estimation in multibody systems with rigid or flexible links." Doctoral thesis, Università degli studi di Padova, 2016. http://hdl.handle.net/11577/3427127.
Повний текст джерелаАнотація:
In the multibody field the design of state observers proves useful for several tasks, ranging from the synthesis of control schemes and fault detection strategies, to the identication of uncertain parameters. State observers are designed to obtain accurate estimates of unmeasurable or unmeasured variables. Their accuracy and performance depend on both the estimation
algorithms and the system models. Indeed, on the one hand the estimation algorithms should be able to cope with multibody system (MBS) nonlinearities. On the other, MB models should be suitable to state estimation, i.e. accurate and computationally efficient.
In order to obtain the best results, it has been necessary to develop dierent approaches for rigid-link and flexible-link MBSs.
In the case of rigid-link MBSs, state observers based on nonlinear kinematic models (i.e. kinematic constraint equations) have been developed. When compared to dynamic models, kinematic models present some relevant advantages. In particular, they are less complex and much less aected
by uncertainty. Additionally, though kinematics-based observers do not require force and torque measurements (often dicult to gather) as inputs, they can be successfully employed for estimating unknown forces: to this purpose a novel two-stage approach is proposed in this dissertation.
As far as modeling flexible-link MBSs is concerned, it is more complicated and makes the implementation of kinematics-based observers impossible, since it is not possible to decouple kinematics from dynamics easily. Furthermore, the so called ne motion of such systems is typically described through a large number of elastic coordinates, which in turns leads to high
model dimensions, and to very inefficient, if not impossible to synthesize, state observers. In order to address this issue, firstly, a new strategy has been developed to keep model dimensions to a minimum. Such a strategy leads to a signicant reduction in the size of the models, which, in turns, provide an appropriate representation of the system dynamics in a frequency range of interest. The availability of reduced-dimension but accurate models for flexible-link MBSs poses the way to the synthesis of more efficient observers provided that a suitable estimation algorithm is chosen.
This thesis also collects results from a large number of numerical and experimental tests carried out to validate the intermediate and nal outcomes of the theoretical investigations.Nello studio e nella progettazione di meccanismi e manipolatori (comunemente detti sistemi multibody MB) la sintesi di stimatori dello stato diviene un requisito indispensabile in molteplici applicazioni avanzate, quali ad esempio la fault detection, l'identicazione dei parametri, la sintesi di controllori, o il controllo attivo delle vibrazioni. Gli stimatori dello stato sono progettati per ottenere delle accurate stime di variabili non misurabili o non misurate. Le prestazioni di uno stimatore dipendono tanto dalla scelta di un opportuno algoritmo di stima, che deve essere capace di fronteggiare le nonlinearità dei sistemi MB, quanto dalla modellazione adottata per i sistemi stessi. In particolare, quest'ultima deve essere adatta al processo di stima, nel senso che deve fornire una descrizione accurata del sistema fisico ma al contempo essere efficiente computazionalmente. Al fine di ottimizzare le prestazioni degli stimatori sono stati sviluppati degli approcci di stima diversicati per i sistemi MB a membri rigidi ed a membri flessibili. In riferimento ai sistemi MB a membri rigidi è stato sviluppato un approccio di stima che rafforza significativamente il ruolo delle equazioni di chiusura cinematiche. Infatti esse, rispetto ai modelli dinamici sino ad ora ampiamente utilizzati, presentano alcuni vantaggi tra cui la minore complessità ed incertezza. Questo nuovo approccio permette non solo di ottenere stime dello stato più accurate ma anche di affrontare con successo il problema della stima delle forze incognite attraverso una formulazione del tutto innovativa, chiamata approccio a due stadi ("two-stage approach"). Per quanto concerne la modellazione dei sistemi MB a membri flessibili, essa presenta criticità alquanto diverse dal precedente ambito di indagine, tra cui la difficoltà di disaccoppiare l'analisi cinematica da quella dinamica, che impedisce l'adozione di un approccio cinematico per la stima delle variabili di stato, e le elevate dimensioni dei modelli che usualmente non permettono la sintesi di stimatori computazionalmente efficienti. Tali criticità hanno imposto preliminarmente lo sviluppo di una nuova strategia per la riduzione dei modelli dinamici non lineari configurazione-varianti dei sistemi MB a membri flessibili. Questa nuova strategia di riduzione permette di ottenere dei modelli dinamici di dimensioni significativamente ridotte, ma ugualmente capaci di descrivere accuratamente la dinamica dei sistemi MB a membri flessibili in un intervallo di frequenze d'interesse. La disponibilità di tali modelli ridotti ha reso possibile la successiva implementazione di più efficienti stimatori dello stato anche nonlineari. Nel presente lavoro di tesi sono inoltre raccolti i numerosi risultati derivanti da test sia numerici che sperimentali condotti per dimostrare la validità degli sviluppi teorici discussi.
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Bediz, Mehmet. "A computer simulation study of a single rigid body dynamic model for biped postural control." Thesis, Monterey, California. Naval Postgraduate School, 1997. http://hdl.handle.net/10945/8136.
Повний текст джерелаАнотація:
Approved for public release; distribution is unlimitedExisting kinematics models for humans cannot simulate movement beyond geometric constraints. On the other hand, complex dynamics models are computationally expensive for real time computer graphics applications in Virtual Environments(VE). To be able to create a more realistic, real time, and computationally efficient human model, a simple dynamic model needs to be developed. The approach taken in this thesis was to develop a single rigid body dynamic human model with massless legs. Instead of a Lagrangian model, which complicates the calculations exponentially as the complexity of the system increases, the Newton-Euler method was chosen to derive system differential equations. Linear state feedback was used for postural control. As part of this research, a previous realistic looking human model is further developed. The major conclusion of this thesis is that a single rigid body dynamic model can be used for simulation of postural control. The simulation results contained in this thesis show that such a modeling technique could be used to cause a detailed kinematic representation of a human figure to move in a smooth and realistic way without resorting to complexity of a multi-link dynamic model
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Monteiro, Azevedo Nuno Miguel. "A rigid particle discrete element model for the fracture analysis of plain and reinforced concrete." Thesis, Heriot-Watt University, 2003. http://hdl.handle.net/10399/1134.
Повний текст джерелаАнотація:
Concrete is regarded as a skeleton of aggregate particles of various sizes, almost in direct contact with each other. The cement matrix acts as a filler and adhesive enabling the structure to be able to carry tensile stresses. A 2D circular rigid discrete element formulation based on the Discrete Element Method has been adopted. Random assemblies of particles based on a given sieve analysis can be generated enabling the simulation of the concrete structure at the meso-level. Contact models that are able to transmit moments through the contact plane have been implemented, namely, a developed contact model adopting more than one contact point at the contact plane. The steel reinforcement has been modelled with 1D beam finite elements or with 1D rigid discrete elements that interact with the discrete rigid particles through contact interfaces. Softening has been introduced into the microlevel constitutive equations. The traditional DEM has been enhanced with a boundary wall driven by force algorithm, an adaptive global damping algorithm and an arc-length control algorithm increasing the range of applicability and the performance of the model. The behavior of a double notched plain concrete specimen is investigated. Comparison of results in terms of crack patterns and load displacement relationships up to the peak load with both experimental and numerical results obtained using a lattice beam element formulation showed good agreement. The performance of the developed DEM model has also been evaluated for uniaxial tension, uniaxial compression and tensile splitting tests. The developed model showed good agreement in terms of peak strength, fracture localization and crack patterns. Finally the interaction between the stiffness of the reinforcement normal to the plane of cracking and the shear stiffness due to aggregate interlock is investigated. Good comparisons in terms of shear force and shear displacement relationships for a given crack width and reinforcement stiffness were obtained with known experimental data
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Chandra, Harish. "Differential Model and Impact Response of a Flexible Beam Attached to a Rigid Supporting Structure." University of Akron / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=akron1207948250.
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Sun, Shaohua. "Lung nodule registration in CT scans using a Semi-Rigid model and enhanced simulated annealing /." May be available electronically:, 2007. http://proquest.umi.com/login?COPT=REJTPTU1MTUmSU5UPTAmVkVSPTI=&clientId=12498.
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Sabbagh, Lamis Marlyn Kenedy. "Study of rigid solids movement in a viscous fluid." Thesis, Montpellier, 2018. http://www.theses.fr/2018MONTS103/document.
Повний текст джерелаАнотація:
Cette thèse est consacrée à l’analyse mathématique du problème du mouvement d’un nombre fini de corps rigides homogènes au sein d’un fluide visqueux incompressible homogène. Les fluides visqueux sont classés en deux catégories: les fluides newtoniens et les fluides non newtoniens. En premier lieu, nous considérons le système formé par les équations de Navier Stokes incompressible couplées aux lois de Newton pour décrire le mouvement de plusieurs disques rigides dans un fluide newtonien visqueux homogène dans l’ensemble de l’espace R^2. Nous montrons que ce problème est bien posé jusqu’à l’apparition de la première collision. Ensuite, nous éliminons tous les types de contacts pouvant survenir si le domaine fluide reste connexe à tout moment. Avec cette hypothèse, le système considéré est globalement bien posé. Dans la deuxième partie de cette thèse, nous montrons la non-unicité des solutions faibles au problème d’interaction fluide-solide 3D, dans le cas d’un fluide newtonien, après collision. Nous montrons qu’il existe des conditions initiales telles que nous pouvons étendre les solutions faibles après le temps pour lequel le contact a eu lieu de deux manières différentes. Enfin, dans la dernière partie, nous étudions le mouvement bidimensionnel d’un nombre fini de disques immergés dans une cavité remplie d’un fluide viscoélastique tel que des solutions polymériques. Les équations de Navier Stokes incompressible sont utilisées pour modéliser le solvant, dans lesquelles un tenseur de contrainte élastique supplémentaire apparaît comme un terme source. Dans cette partie, nous supposons que le tenseur de contrainte supplémentaire satisfait la loi différentielle d’Oldroyd ou sa version régularisée. Dans les deux cas, nous prouvons l’existence et l’unicité des solutions fortes locales en temps du problème considéréThis thesis is devoted to the mathematical analysis of the problem of motion of afinite number of homogeneous rigid bodies within a homogeneous incompressible viscous fluid. Viscous fluids are classified into two categories: Newtonian fluids, and non-Newtonian fluids. First, we consider the system formed by the incompressible Navier-Stokes equations coupled with Newton’s laws to describe the movement of several rigid disks within a homogeneous viscous Newtonian fluid in the whole space R^2. We show the well-posedness of this system up to the occurrence of the first collision. Then we eliminate all type of contacts that may occur if the fluid domain remains connected at any time. With this assumption, the considered system is well-posed globally in time. In the second part of this thesis, we prove the non-uniqueness of weak solutions to the fluid-rigid body interaction problem in 3D in Newtonian fluid after collision. We show that there exist some initial conditions such that we can extend weak solutions after the time for which contact has taken place by two different ways. Finally, in the last part, we study the two-dimensional motion of a finite number of disks immersed in a cavity filled with a viscoelastic fluid such as polymeric solutions. The incompressible Navier–Stokes equations are used to model the flow of the solvent, in which the elastic extra stress tensor appears as a source term. In this part, we suppose that the extra stress tensor satisfies either the Oldroyd or the regularized Oldroyd constitutive differential law. In both cases, we prove the existence and uniqueness of local-in-time strongsolutions of the considered moving-boundary problem
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Woodcock, Cassandra. "The Design and Validation of a Computational Rigid Body Model for Study of the Radial Head." VCU Scholars Compass, 2013. http://scholarscompass.vcu.edu/etd/3277.
Повний текст джерелаАнотація:
Rigid body modeling has historically been used to study various features of the elbow joint including both physical and computational models. Computational modeling provides an inexpensive, easily customizable, and effective method by which to predict and investigate the response of a physiological system to in vivo stresses and applied perturbations. Utilizing computer topography scans of a cadaveric elbow, a virtual representation of the joint was created using the commercially available MIMICS(TM) and SolidWorks(TM) software packages. Accurate 3D articular surfaces, ligamentous constraints, and joint contact parameters dictated motion. The model was validated against two cadaveric studies performed by Chanlalit et al. (2011, 2012) considering monopolar and bipolar circular radial head replacements in their effects on radiocapitellar stability and respective reliance upon lateral soft tissues, as well as a comparison of these with a novel anatomic radial head replacement system in an elbow afflicted with the “terrible triad” injury. Rigid body simulations indicated that the computational model was able to accurately recreate the translation of forces in the joint and demonstrate results similar to those presented in the cadaveric data in both the intact elbow and in unstable injury states. Trends in the resulting data were reflective of the average behavior of the cadaveric specimens while percent changes between states correlated closely with the experimental data. Information on the transposition of forces within the joint and ligament tensions gleaned from the computational model provided further insight into the stability of the elbow with a compromised radial head.
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Welch, Charles Robert. "A full-engulfment engineering model, and its experimental and numerical verification, for the response of a rigid body to ground-shock." Diss., This resource online, 1993. http://scholar.lib.vt.edu/theses/available/etd-09192008-063134/.
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Turkmen, Haydar Kursat. "An Experimental Study Into Bearing Of Rigid Piled Rafts Under Vertical Loads." Phd thesis, METU, 2008. http://etd.lib.metu.edu.tr/upload/3/12609420/index.pdf.
Повний текст джерелаАнотація:
In this study, the load bearing behavior of piled raft foundations is investigated performing laboratory and field tests. Piled raft foundation of a multi storey building was also instrumented and monitored in order to study the load sharing mechanism of piled raft foundations.
A small reinforced concrete piled raft of 2.3 m square supported by four mini piles at the corners was loaded and contribution of the raft support up to 41 % of the total load was observed. The soil was stiff fissured Ankara clay with no ground water.
A building founded on a piled raft foundation was instrumented and monitored using earth pressure cells beneath the raft during its construction period. The foundation soil was a deep graywacke highly weathered at the upper 10 m with no ground water. The proportion of load that was carried by the raft was 21 to 24 % of the total load near the edge and 44 to 56 % under the core.
In the laboratory tests, model aluminum piles with outerinner diameters of 2218 mm and a length of 200 mm were used. The raft was made of steel plate with plan dimensions of 176 mm x 176 mm and a thickness of 10 mm. The model piles were instrumented with strain gages to monitor pile loads. Model piled raft configurations with different number of piles were tested. The behavior of a single pile and the plain raft were also investigated. The soil in the model tests was half and half sand &ndashkaolinite mixture. It has been observed that when a piled raft is loaded gradually, piles take more load initially and after they reach their full capacity additional loads are carried by raft. The proportion of load that was carried by the raft decreases with the increasing number of piles and the load per pile is decreased. Center, edge and corner piles are not loaded equally under rafts. It has been found that rafts share foundation loads at such levels that should not be ignored.
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León, Alejandro. "A pseudo-rigid-body model for spherical mechanisms : the kinematics and elasticity of a curved compliant beam." [Tampa, Fla.] : University of South Florida, 2007. http://purl.fcla.edu/usf/dc/et/SFE0002272.
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León, Alejandro. "A pseudo-rigid-body model for spherical mechanisms: The kinematics and elasticity of a curved compliant beam." Scholar Commons, 2007. http://scholarcommons.usf.edu/etd/2259.
Повний текст джерелаАнотація:
This thesis improves a previous kinematic analysis and develops the elastic portion of the analysis of a curved compliant beam. This analysis is used to develop a Pseudo-Rigid-Body Model for the curved compliant beam. The Pseudo-Rigid-Body Model consist of kinematic and elastic parameters which can be used to simplify the computation of the large deflections of the beam as it undergoes spherical motion. The kinematic parameters that are developed are the characteristic radius, Gamma*length, the parametric angle coefficient, c_theta, and the kinematic parametrization limit, Capital_theta_max(Gamma). The elastic parameters developed are the stiffness coefficient, K_theta, and the elastic parameterization limit, Capital_theta_max(K). Additionally, curve fit parameters are developed which enable the calculation of the stress in curved beam as it deflects.
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Chimento, Jairo Renato. "A 3-D Pseudo-Rigid-Body Model for Rectangular Cantilever Beams with an Arbitrary Force End-Load." Scholar Commons, 2014. https://scholarcommons.usf.edu/etd/4993.
Повний текст джерелаАнотація:
This dissertation introduces a novel three-dimensional pseudo-rigid-body model (3-D PRBM) for straight cantilever beams with rectangular cross sections. The model is capable of capturing the behavior of the neutral axis of a beam loaded with an arbitrary force end-load. Numerical integration of a system of differential equations yields approximate displacement and orientation of the beam's neutral axis at the free end, and curvatures of the neutral axis at the fixed end. This data was used to develop the 3-D PRBM which consists of two torsional springs connecting two rigid links for a total of 2 degrees of freedom (DOF). The 3-D PRBM parameters that are comparable with existing 2-D model parameters are characteristic radius factor (mean: γ = 0.8322), bending stiffness coefficient (mean: KΘ = 2.5167) and parametric angle coefficient (mean: cΘ = 1.2501). New parameters are introduced in the model in order to capture the spatial behavior of the deflected beam, including two parametric angle coefficients (means: cΨ = 1.0714; cΦ = 1.0087). The model is verified in a few locations using ANSYSTM and its use in the design of compliant mechanisms is illustrated through spatial compliant versions of crank slider and double slider mechanisms.
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Espinosa, Diego Alejandro. "Moment-dependent pseudo-rigid-body models for beam deflection and stiffness kinematics and elasticity." [Tampa, Fla] : University of South Florida, 2009. http://purl.fcla.edu/usf/dc/et/SFE0002943.
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Ahlman, Ove. "To infinity and back : Logical limit laws and almost sure theories." Licentiate thesis, Uppsala universitet, Algebra och geometri, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-223166.
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Almeida, João Francisco Coelho Mateus Martins de. "Internationalization project - Logoplaste in the Turkish market." Master's thesis, NSBE - UNL, 2014. http://hdl.handle.net/10362/11824.
Повний текст джерелаАнотація:
A Work Project, presented as part of the requirements for the Award of a Masters Degree in Management from the NOVA – School of Business and EconomicsThis thesis project aims to be a successful instrument for Logoplaste’s management team if they received a proposal to invest in the Turkish market. In the project I studied not only Logoplaste’s value chain but also its competitive advantages and how the company can handle them in order to be successful in this market. Moreover, it contains a careful analysis of the Turkish market that helps to understand how the market accepts Foreign Direct Investment and also to understand if there are attractive business opportunities for Logoplaste.
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Halverson, Peter Andrew. "Modeling, Design, and Testing of Contact-Aided Compliant Mechanisms in Spinal Arthroplasty." BYU ScholarsArchive, 2010. https://scholarsarchive.byu.edu/etd/2168.
Повний текст джерелаАнотація:
Injury, instrumentation, or surgery may change the functional biomechanics of the spine. Spinal fusion, the current surgical treatment of choice, stabilizes the spine by rigid fixation, reducing spinal mobility at the cost of increased stress at adjacent levels. Recently, alternatives to spinal fusion have been investigated. One such alternative is total disc replacements. The current generation of total disc replacements (TDRs) focuses on restoring the quantity of motion. Recent studies indicate that the moment-rotation response and axis of rotation, or quality of motion (QOM), may have important implications in the health of adjacent segments as well as the health of the surrounding tissue of the operative level. This dissertation examines the use of compliant mechanism design theory in the design and analysis of spinal arthroplasty devices. Particularly, compliant mechanism design techniques were used to develop a total disc replacement capable of replicating the normal moment-rotation response and location and path of the helical axis of motion. Closed-form solutions for the device's performance are proposed and a physical prototype was created and evaluated under a modified F1717 and a single-level cadaveric experiment. The results show that the prototype's QOMclosely matched the selected force-deflection response of the specified QOM profile. The use of pseudo-rigid-body modeling to evaluate the effects of various changes on motion at adjacent segments is also investigated. The ability to model biomechanical changes in the spine has traditionally been based on animal models, in vitro testing, and finite element analysis. These techniques, although effective, are costly. As a result, their use is often limited to late in the design process. The pseudo-rigid-body model (PRBM) developed accurately predicted the moment-rotation response of the entire specimen and the relative contribution of each level. Additionally, the PRBM was able to predict changes in relative motion patterns of the specimen due to instrumentation.
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Siramdasu, Yaswanth. "Discrete Tire Model Application for Vehicle Dynamics Performance Enhancement." Diss., Virginia Tech, 2015. http://hdl.handle.net/10919/74394.
Повний текст джерелаАнотація:
Tires are the most influential component of the vehicle as they constitute the only contact
between the vehicle and the road and have to generate and transmit forces necessary for
the driver to control the vehicle. The demand for the tire models are increasing due to
the need to study the variations of force generation mechanisms due to various variables
such as load, pressure, speed, and road surface irregularities. Another need from the vehicle
manufactures is the study of potential incompatibilities associated with safety systems such
as Anti-lock Braking System (ABS) and Electronic Stability Control (ESC) and tires. For
vehicle dynamic simulations pertaining to the design of safety systems such as ABS, ESC
and ride controllers, an accurate and computationally efficient tire model is required. As
these control algorithms become more advanced, they require accurate and extended validity
in the range of frequencies required to cover dynamic response due to short wavelength road
disturbances, braking and steering torque variations. Major thrust has been provided by the
tire industry to develop simulation models that accurately predict the dynamic response of
tires without the use of computationally intensive tools such as FEA.
The objectives of this research are
• To develop, implement and validate a rigid ring tire model and a simulation tool
to assist both tire designers and the automotive industry in analyzing the effects of
tire belt vibrations, road disturbances, and high frequency brake and steering torque
variations on the handling, braking, and ride performances of the vehicle.
• To further enhance the tire model by considering dynamic stiffness changes and temperature dependent friction properties.
• To develop, and implement novel control algorithms for braking, stability, and ride
performance improvements of the vehiclePh. D.
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Koseoglu, Ahmet. "A Finite Element Model For Partially Restrained Steel Beam To Column Connections." Master's thesis, METU, 2013. http://etd.lib.metu.edu.tr/upload/12615736/index.pdf.
Повний текст джерелаАнотація:
In the analyses of steel framed structures it is customary to assume the beam to column connections as either fully rigid which means that all moments are transferred from beam to column with negligible rotation or ideally pinned that resists negligible moment. This assumption is reasonable for some types of connections. However when considering steel connections such as bolted-bolted double web angle connections it can be seen that the behavior of these connections is in between the two extreme cases. Thus a third connection type, namely semi rigid or partially restrained connection, is introduced. However this type of connection exhibits such a nonlinear behavior that modeling this behavior necessities a substantial effort. Moreover to perform a performance based analyses the true behavior of these connections should be incorporated as part of the modeling effort. Several researches dealing with these two topics have been undertaken in literature. Despite these efforts, modeling of the moment rotation behavior of these connections still requires improvement especially under cyclic loading conditions. In addition to this, performing an analysis with existing elements incorporating semi-rigid connections as a spring attached to beam ends is not practical because of the fact that displacement based formulation increases meshing significantly which requires substantial computational power.
In this study a hysteretic (quadra-linear) moment rotation model considering pinching, damage and possibility of residual moment capacity is developed. The behavior is calibrated via experimental data available in the literature. Furthermore a force based macro element considering spread inelastic behavior along the element is presented. With this element several connections located anywhere along the beam could be incorporated in the analysis with less degree of freedom with respect to displacement based elements. Moreover the macro element model can be used in conjunction with corotational formulation for the capture of nonlinear geometric effects.
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Logan, Philip James. "A Planar Pseudo-Rigid-Body Model for Cantilevers Experiencing Combined Endpoint Forces and Uniformly Distributed Loads Acting in Parallel." Scholar Commons, 2015. http://scholarcommons.usf.edu/etd/5730.
Повний текст джерелаАнотація:
This dissertation describes the development and effectiveness of a mathematical model used to predict the behavior of cantilever beams whose loading conditions include parallel combinations of evenly distributed loads and endpoint forces. The large deflection of cantilever beams has been widely studied. A number of models and mathematical techniques have been utilized in predicting the endpoint path coordinates and load-deflection relationships of such beams. The Pseudo-Rigid-Body Model (PRBM) is one such method which replaces the elastic beam with rigid links of a parameterized pivot location and torsional spring stiffness. In this paper, the PRBM method is extended to include cases of a constant distributed load combined with a parallel endpoint force. The phase space of the governing differential equations is used to store information relevant to the characterization of the PRBM parameters. Correction factors are also given to decrease the error in the load-deflection relationship and extend the angular range of the model, thereby further aiding compliant mechanism design. The calculations suggest a simple way of representing the effective torque caused by a distributed load in a PRBM as a function of easily calculated model parameters.
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Tamrakar, Swaraj. "Analytical Model Study of Flow Through Trapezoidal, Half-Trapezoidal and Rectangular Channels with Submerged and Un-submerged Rigid Cylinders." OpenSIUC, 2014. https://opensiuc.lib.siu.edu/theses/1380.
Повний текст джерелаАнотація:
For this study, two analytical models were developed for predicting the depth-averaged velocity distribution (U) in trapezoidal, half-trapezoidal and rectangular channels with submerged and unsubmerged rigid cylinders. The first model uses linear superposition of momentum defects (MDS) and mass conservation, and is referred to as the MDS model. The second model uses linear superposition of velocity defects (VDS) and mass conservation, and is referred to as the VDS model. For implementing either the VDS or MDS model, a criterion is required for considering the wake created by an individual cylinder to be fully dissipated (i.e., a cutoff criterion). Also, implementing the MDS model requires numerical integration. Analyses were conducted to identify suitable cutoff criterion and an appropriate subinterval size for the numerical integration. Data from a physical model study conducted in a flume with a half-trapezoidal channel section was used to calibrate and validate the models. Data from a physical model study conducted in a rectangular channel section was also used to validate the model. Predicted values of U from the VDS and MDS models were within the range of ± 20 % of the trapezoidal channel section validation data. The models failed to accurately predict U for the rectangular channel section data. It is concluded that the models developed herein should be used only for half-trapezoidal channel sections. With respect to the trapezoidal channel section validation data, the MDS model yields a sum of squared errors that is 36% less than that yielded by the VDS model. Therefore, the MDS model is regarded as the best model overall for computing U in half-trapezoidal channel sections.
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Stapasolla, Tayron Zilli. "Análise experimental e numérica da relação entre deformação e aceleração em dutos rígidos submetidos a ensaio de fadiga por ressonância." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2018. http://hdl.handle.net/10183/186151.
Повний текст джерелаАнотація:
O crescimento da produção de petróleo offshore traz consigo a demanda por tubulações para escoamento de hidrocarbonetos capazes de conciliar elevada resistência mecânica, elevada resistência à corrosão e baixo peso estrutural. Para tal, após o projeto mecânico, faz-se necessária a qualificação dessas estruturas por intermédio de ensaios mecânicos. Um dos métodos de teste em risers rígidos que alia baixos custos em equipamentos à rapidez de execução é o teste de fadiga por ressonância. Usualmente, este tipo de teste é controlado através do nível de deformação lido por extensômetros instalados na região central da amostra. Contudo, o tempo de instalação e a fragilidade dos sensores acabam por aumentar significativamente o tempo total de teste. Portanto, o presente estudo propõe que o controle do teste seja feito por intermédio dos níveis de aceleração no centro do tubo, uma vez que acelerômetros são mais robustos e mais fáceis de instalar. Assim, o trabalho traz uma correlação numérica e experimental entre os níveis de deformação e aceleração no centro de tubos submetidos a testes de fadiga por ressonância. Foram realizados testes nas amostras sem água, com água, e com pressão interna de 200 Bar. Foi constatado que a relação entre a aceleração e a deformação no centro das amostras para frequências próximas à frequência de ressonância é linear. Além disso, as diferenças observadas entre os resultados experimentais e os numéricos variaram de 0,13% a 14,73%. Em conclusão, o modelo numérico apresentou resultados consistentes em grande parte dos casos estudados, o que evidencia a viabilidade de implementação do sistema de controle por aceleração. Para tal, foram apresentadas sugestões de melhoria para aplicação em testes futuros, a fim de otimizar a uniformidade dos resultados e completar a validação do modelo numérico.The development of offshore oil production implies the demand of pipelines for the hydrocarbon flow, which are capable of combining high mechanical and corrosion resistance with low structural weight. For this, after the mechanical design, it is required to qualify these structures by means of mechanical tests. One method of test for rigid risers that combines low equipment costs with quick execution is the resonance fatigue test. Usually, this type of test is controlled by strain levels obtained by strain gauges installed at the pipe center. However, the installation lead time and the sensors fragility increase significantly the overall test time. Therefore, the present study proposes that the test controlling system could be performed by means of the acceleration levels at the middle of the sample, since accelerometers are more robust and the installation is simpler. Thus, this work brings a numerical and experimental relationship between strain and acceleration levels at the center of pipes submitted to resonance fatigue test. Tests were performed on the samples without water, with water, and with internal pressure of 200 Bar. It was found that the relationship between strain and acceleration at the center of the samples is linear for frequencies near the resonant frequency. In addition, the differences between experimental and numerical results ranged from 0.13% to 14.73%. In conclusion, the numerical model presented consistent results in most of the studied cases, which evidences the feasibility of implementing the acceleration controlling system. For this purpose, improvement suggestions for application in future tests were presented in order to optimize the uniformity of the results and to complete the numerical model validation.
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Kim, Shinwoong. "Experimental study on wave bending moments of a zero-speed rigid containership model in regular, irregular, and equivalent design waves." Electronic Thesis or Diss., Ecole centrale de Nantes, 2023. http://www.theses.fr/2023ECDN0001.
Повний текст джерелаАнотація:
La thèse vise à étudier les mouvements et les chargements internes d’un modèle de porte-conteneur rigide formé de 9 segments dans des vagues extrêmes. L’étude est principalement expérimentale et est réalisée avec une maquette sans vitesse d’avance dans une houle de face et une houle oblique (-120 degrés). L’étude aboutit à des résultats soulignant l’importance de la prendre en compte les aspects non linéaires des vagues et des réponses structurelles correspondantes.Dans des conditions de mer de face, trois types de vagues sont testés. Des vagues régulières sont utilisées pour s’assurer que le modèle se comporte de manière similaire à la campagne précédente effectuée avec la même maquette. Une approche de type Monte Carlo avec un certain nombre de réalisations de 2 heures 30 de vagues irrégulières est ensuite utilisée pour construire des données de référence. Enfin, des vagues equivalentes de design (EDW) sont générées pour vérifier, en particulier, la faisabilité d’une approche EDW irrégulière appelée First Order Reliability Method (FORM). Un algorithme numérique FORM couplé avec le solveur HOSNWT est développé et validé par rapport aux résultats Monte Carlo. Les caractéristiques géométriques des signaux EDW et VBM ainsi que leurs statistiques sont étudiées. L’étude vise peut-être deux quantités. Le premier est la hauteur de crête de la vague dans un scénario de vague seule, et le second est le VBM du modèle segmenté. L’utilisation du solveur de génération d’onde non linéaire HOS-NWT, permet une validation croisée avec la mesure expérimentale car les vagues générées sont comparables. Dans la condition de vagues obliques, l’étude est limitée aux vagues régulières avec différentes cambrure de vagues afin de fournir des données de référence pour les futures études. L’effet de non-linéarité des vagues sur les moments de flexion horizontaux et verticaux des vagues avec une cambrure variable est démontréThe present thesis aims to study the motions and the internal loads of a 9-segmented rigid containership model in extreme waves. The study is mainly experimental and is carried out on a zero-speed model in a 180-degree head sea and a -120 degree oblique sea. The study leads to results highlighting the importance of the consideration of nonlinear wave descriptions and corresponding nonlinear structural responses.In head sea conditions, three wave approaches are considered. Regular waves are used to ensure that the model behaves similar to the earlier campaign. A Monte Carlo approach with a number of full scale 2h30 irregular wave realizations is used to have reference data. Finally, irregular equivalent design waves (EDW) are studied to check, in particular, the feasibility of one irregular EDW approach called First Order Reliability Method.A numerical algorithm coupling with the HOS-NWT for the FORM EDW is developed and the validation compared to the Monte Carlo results is performed in terms of geometrical characteristics of the EDW and IW signals along with their statistics. The study targets mainly two quantities. The first is the wave crest in a wave-only scenario, and the second is the VBM of the segmented model. The use of the HOSNWT, a nonlinear wave generation solver, enables cross-validation with experimental measurement.In the oblique wave condition, the study is limited to regular waves with various wave steepness with the intent to provide reference data for future benchmark studies. The wave nonlinearity effect on the horizontal and vertical wave bending moments with varying steepness is shown
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Shaheed, Rawaa. "3D Numerical Modelling of Secondary Current in Shallow River Bends and Confluences." Thesis, Université d'Ottawa / University of Ottawa, 2016. http://hdl.handle.net/10393/34922.
Повний текст джерелаАнотація:
Secondary currents are one of the important features that characterize flow in river bends and confluences. Fluid particles follow a helical path instead of moving nearly parallel to the axis of the channel. The local imbalance between the vertically varying centrifugal force and the cross-stream pressure gradient results in generating the secondary flow and raising a typical motion of the helical flow. A number of studies, including experimental or mathematical, have been conducted to examine flow characteristics in curved open channels, river meanders, or confluences. In this research, the influence of secondary currents is studied on the elevation of water surface and the hydraulic structures in channel bends and confluences by employing a 3D OpenFOAM numerical model.
The research implements the 3D OpenFOAM numerical model to simulate the horizontal distribution of the flow in curved rivers. In addition, the progress in unraveling and understanding the bend dynamics is considered. The finite volume method in (OpenFOAM) software is used to simulate and examine the behavior of secondary current in channel bends and confluences. Thereafter, a comparison between the experimental data and a numerical model is conducted. Two sets of experimental data are used; the data provided by Rozovskii (1961) for sharply curved channel, and the dataset provided by Shumate (1998) for confluent channel.
Two solvers in (OpenFOAM) software were selected to solve the problem regarding the experiment; InterFoam and PisoFoam. The InterFoam is a transient solver for incompressible flow that is used with open channel flow and Free Surface Model. The PisoFoam is a transient solver for incompressible flow that is used with closed channel flow and Rigid-Lid Model. Various turbulence models (i.e. Standard k-ε, Realizable k-ε, LRR, and LES) are applied in the numerical model to assess the accuracy of turbulence models in predicting the behaviour of the flow in channel bends and confluences. The accuracies of various turbulence models are examined and discussed.