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1
Yi, Tong Yong 1955. "Structural Identification Based on Vibration Data for Flexible and Rigid Multibody System Dynamics." Diss., The University of Arizona, 1996. http://hdl.handle.net/10150/565568.
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2
Yamashita, Hiroki. "Flexible multibody dynamics approach for tire dynamics simulation." Diss., University of Iowa, 2016. https://ir.uiowa.edu/etd/2297.
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The objective of this study is to develop a high-fidelity physics-based flexible tire model that can be fully integrated into multibody dynamics computer algorithms for use in on-road and off-road vehicle dynamics simulation without ad-hoc co-simulation techniques. Despite the fact detailed finite element tire models using explicit finite element software have been widely utilized for structural design of tires by tire manufactures, it is recognized in the tire industry that existing state-of-the-art explicit finite element tire models are not capable of predicting the transient tire force characteristics accurately under severe vehicle maneuvering conditions due to the numerical instability that is essentially inevitable for explicit finite element procedures for severe loading scenarios and the lack of transient (dynamic) tire friction model suited for FE tire models. Furthermore, to integrate the deformable tire models into multibody full vehicle simulation, co-simulation technique could be an option for commercial software. However, there exist various challenges in co-simulation for the transient vehicle maneuvering simulation in terms of numerical stability and computational efficiency. The transient tire dynamics involves rapid changes in contact forces due to the abrupt braking and steering input, thus use of co-simulation requires very small step size to ensure the numerical stability and energy balance between two separate simulation using different solvers.
In order to address these essential and challenging issues on the high-fidelity flexible tire model suited for multibody vehicle dynamics simulation, a physics-based tire model using the flexible multibody dynamics approach is proposed in this study. To this end, a continuum mechanics based shear deformable laminated composite shell element is developed based on the finite element absolute nodal coordinate formulation for modeling the complex fiber reinforced rubber tire structure. The assumed natural strain (ANS) and enhanced assumed strain (EAS) approaches are introduced for alleviating element lockings exhibited in the element. Use of the concept of the absolute nodal coordinate formulation leads to various advantages for tire dynamics simulation in that (1) constant mass matrix can be obtained for fully nonlinear dynamics simulation; (2) exact modeling of rigid body motion is ensured when strains are zero; and (3) non-incremental solution procedure utilized in the general multibody dynamics computer algorithm can be directly applied without specialized updating schemes for finite rotations. Using the proposed shear deformable laminated composite shell element, a physics-based flexible tire model is developed. To account for the transient tire friction characteristics including the friction-induced hysteresis that appears in severe maneuvering conditions, the distributed parameter LuGre tire friction model is integrated into the flexible tire model. To this end, the contact patch predicted by the structural tire model is discretized into small strips across the tire width, and then each strip is further discretized into small elements to convert the partial differential equations of the LuGre tire friction model to the set of first-order ordinary differential equations. By doing so, the structural deformation of the flexible tire model and the LuGre tire friction force model are dynamically coupled in the final form of the equations, and these equations are integrated simultaneously forward in time at every time step.
Furthermore, a systematic and automated procedure for parameter identification of LuGre tire friction model is developed. Since several fitting parameters are introduced to account for the nonlinear friction characteristics, the correlation of the model parameters with physical quantities are not clear, making the parameter identification of the LuGre tire friction model difficult. In the procedure developed in this study, friction parameters in terms of slip-dependent friction characteristics and adhesion parameter are estimated separately, and then all the parameters are identified using the nonlinear least squares fitting. Furthermore, the modified friction characteristic curve function is proposed for wet road conditions, in which the linear decay in friction is exhibited in the large slip velocity range. It is shown that use of the proposed numerical procedure leads to an accurate prediction of the LuGre model parameters for measured tire force characteristics under various loading and speed conditions. Furthermore, the fundamental tire properties including the load-deflection curve, the contact patch lengths, contact pressure distributions, and natural frequencies are validated against the test data. Several numerical examples for hard braking and cornering simulation are presented to demonstrate capabilities of the physics-based flexible tire model developed in this study.
Finally, the physics-based flexible tire model is further extended for application to off-road mobility simulation. To this end, a locking-free 9-node brick element with the curvature coordinates at the center node is developed and justified for use in modeling a continuum soil with the capped Drucker-Prager failure criterion. Multiplicative finite strain plasticity theory is utilized to consider the large soil deformation exhibited in the tire/soil interaction simulation. In order to identify soil parameters including cohesion and friction angle, the triaxial soil test is conducted. Using the soil parameters identified including the plastic hardening parameters by the compression soil test, the continuum soil model developed is validated against the test data. Use of the high-fidelity physics-based tire/soil simulation model in off-road mobility simulation, however, leads to a very large computational model to consider a wide area of terrains. Thus, the computational cost dramatically increases as the size of the soil model increases. To address this issue, the component soil model is proposed such that soil elements far behind the tire can be removed from the equations of motion sequentially, and then new soil elements are added to the portion that the tire is heading to. That is, the soil behavior only in the vicinity of the rolling tire is solved in order to reduce the overall model dimensionality associated with the finite element soil model. It is shown that use of the component soil model leads to a significant reduction in computational time while ensuring the accuracy, making the use of the physics-based deformable tire/soil simulation capability feasible in off-road mobility simulation.
3
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.
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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.
4
Stemple, Timothy J. "Dynamics and Control of Flexible Multibody Structures." Diss., Virginia Tech, 1998. http://hdl.handle.net/10919/30407.
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The goal of this study is to present a method for deriving
equations of motion capable of modeling the controlled
motion of an open loop multibody structure comprised of an
arbitrary number of rigid bodies and slender beams. The
procedure presented here for deriving equations of motion
for flexible multibody systems is carried out by means of
the Principle of Virtual Work (often referred to in the
dynamics literature as d'Alembert's Principle). We first
consider the motion of a general flexible body relative to
the inertial space, and then derive specific formulas for
both rigid bodies and slender beams. Next, we make a small
motions assumption, with the end result being equations for
a Rayleigh beam, which include terms which account for the
axial motion, due to bending, of points on the beam central
axis. This process includes a novel application of the
exponential form of an orthogonal matrix, which is ideally
suited for truncation. Then, the generalized coordinates and
quasi-velocities used in the mathematical model, including
those needed in the spatial discretization process of the
beam equations are discussed. Furthermore, we develop a new
set of recursive relations used to compute the inertial
motion of a body in terms of the generalized coordinates and
quasi-velocities. This research was motivated by the desire
to model the controlled motion of a flexible space robot,
and consequently, we use the multibody dynamics equations to
simulate the motion of such a structure, providing a
demonstration of the computer program. For this particular
example we make use of a new sequence of shape functions,
first used by Meirovitch and Stemple to model a two
dimensional building frame subjected to earthquake
excitations.Ph. D.
5
Mantikas, Nikolaos. "Dynamics of large flexible multibody structures in space." Thesis, University of Southampton, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.396146.
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Chen, Jiunn-Liang. "Dynamics and control of structurally flexible multibody systems." Case Western Reserve University School of Graduate Studies / OhioLINK, 1992. http://rave.ohiolink.edu/etdc/view?acc_num=case1056383298.
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Park, Jungho 1958. "Uncoupling of rigid-flexible multibody equations of motion using node annexation method." Diss., The University of Arizona, 1997. http://hdl.handle.net/10150/282519.
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This study presents the node annexation method for modeling kinematic joints between rigid and flexible bodies of rigid-flexible multibody systems. Each node of a flexible body is assumed to have lumped mass and three translational degrees of freedom, resulting in a diagonal mass matrix. Based on the node annexation method, both the nodal- and the modal-coordinate formulations for rigid-flexible multibody dynamics are developed. Conventionally rigid-to-flexible-body joints are treated as kinematic constraints using the Lagrange multiplier method. The formulations based on kinematic constraint method yield coupled equations of motion which have the difficulties associated with modal truncation. On the other hand, the node annexation method transfers the inertia and force effect of connected nodes of a flexible body to the connected rigid body. The mass matrix of the resultant equations of motion consists of two different kind of sub-matrices: one is rigid-body sub-system matrix containing the inertia of both rigid bodies and connected nodes of the flexible body and another is flexible-body sub-system matrix containing the inertia of free nodes of the flexible body. Since there is no off-diagonal terms coupling the sub-matrices, the node annexation method allows the division of the equations of motion into smaller sub-system equations. The node annexation method not only provides computational efficiency but also fundamentally eliminates any kinematic error at rigid-to-flexible-body joints. In addition, the node annexation method preserves the uncoupled nature of modal coordinates, allowing a mathematically justified modal truncation. Computer simulations are performed using a vehicle model with a flexible car body. The simulation results show computational advantage over the kinematic constraint method.
8
Rodriguez, Jesus. "Modeling of complex systems using nonlinear, flexible multibody dynamics." Diss., Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/12344.
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9
Leyendecker, Sigrid. "Mechanical integrators for constrained dynamical systems in flexible multibody dynamics." [S.l.] : [s.n.], 2006. http://deposit.ddb.de/cgi-bin/dokserv?idn=980411912.
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Roberts, David Thomas. "Assessment of finite element approximations for nonlinear flexible multibody dynamics." Thesis, Massachusetts Institute of Technology, 1991. http://hdl.handle.net/1721.1/42506.
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Moore, Brian M. "Flexible multibody dynamics and control of the bifocal relay mirror." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2003. http://library.nps.navy.mil/uhtbin/hyperion-image/03Dec%5FMoore.pdf.
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Thesis (Aeronautical and Astronautical Engineer and M.S. in Astronautical Engineering)--Naval Postgraduate School, December 2003.Thesis advisor(s): Brij N. Agrawal, Marcello Romano. Includes bibliographical references (p. 59). Also available online.
12
Choi, Jou-Young. "Flexible multibody analysis of thin structures with actuated components." Diss., Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/12532.
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Tuzun, Aydin. "Large Deformation Analysis Of Flexible Multibody Systems." Phd thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12614821/index.pdf.
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Large displacement and large strain problems of mechanical systems can be solved mainly by four methods. These are Floating Frame of Reference, Incremental Finite Element, Large Rotation Vector and Absolute Nodal Coordinate Formulations (ANCF). Due to exact rigid body representation, simple mass matrix structure and non-incremental formulation, ANCF is more convenient in analyzing flexible multibody systems. However, it is limited to problems with regular boundaries, currently.
The aim of the thesis is to improve the current ANCF in order to handle various problems with irregular boundaries. For this purpose, firstly meshfree ANCF has been developed to analyze flexible multibody systems. Verification of the developed meshfree formulation has been performed for beam type structures and accurate results have been obtained. Then, &ldquoANCF with Virtual Element Mapping Method&rdquo
has been proposed to overcome the boundary problems of the current formulations. The proposed method has been implemented to plane stress, plane strain, plate/shell and 3D solid finite elements. Verification of the proposed method has been performed by using the patch test problems available in the literature. Besides, it has been verified by various flexible multibody problems with large deformations. Additionally, shape function polynomials for thin plate assumption have been derived. It is observed that developed formulations and methods can be useful not only for flexible multibody systems but also for structural mechanics problems subjected to large deformations and/or rotations. The proposed methods and formulations are more efficient than the current formulations in the literature due to extended shape limits of finite elements.
14
Ibrahim, Ahmed El-Hady M. "Mathematical modelling of flexible multibody dynamics with application to orbiting systems." Thesis, University of British Columbia, 1988. http://hdl.handle.net/2429/28840.
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A relatively general formulation for the governing equations of motion, applicable to a large class of flexible multibody systems, is developed using a concise matrix format. The model considered consists of a number of arbitrarily connected flexible deployable members forming branched and closed loop configurations. Joints between bodies are permitted up to six degrees of freedom in translation and rotation. To be effective, the matrix-Lagrangian formulation necessitates development of the kinetic energy expression in a quadratic form in terms of the system velocities. The mass matrix associated with such a quadratic form is known for simple systems such as a collection of point masses, a group of connected rigid bodies, and a discretized flexible structure. However, for a multibody system, where the contributing forces arise from system's translation, rotation, elasticity, deployment, and their interactions, such an expression is not available. To fill this gap, multibody kinematics is developed in terms of the elements of the geometry matrix,
which uniquely describes the configuration of branched systems. The characteristic dynamical quantities, i.e., elements of the mass matrix, are identified and the formulation is approached in an increasing order of complexity. The concept of specified and generalized coordinates together with established procedures of analytical dynamics lead to characteristic
quantities ( Lagrangian, Hamiltonian, etc. ) and finally result in governing equations of motion which are new to the multibody dynamics. To account for flexibility in a consistent
manner, a second-degree nonlinear displacement field is permitted. Alternatively, a linear displacement field can be used if the nonlinear terms up to the fourth-degree are preserved in the strain energy. An algorithm for calculating the stiffness matrix of a flexible element is developed, where terms up to the third-degree of nonlinearity in displacement are retained.
Application of this versatile formulation is illustrated through a set of examples of contemporary interest. They pertain to a spacecraft comprising of a central rigid body with attached flexible appendages. The configuration corresponds to a large class of present and planned communication satellites. It can also represent the Space Shuttle based deployment
of beam and plate type appendages aimed at scientific experiments or construction of the proposed Space Station. The system static equilibrium and stability are discussed. A computer code is developed and specialized to the specific cases in hand. Typical results of an extensive parametric study are presented for two particular situations :
(i) the Space Shuttle based deployment of a beam or a plate type structural member;
(ii) the configuration similar to the Waves In Space Plasma (WISP) experiment jointly proposed by Canada and the U.S.A.
The problems are analyzed systematically, through progressive introduction of complexity,
to help appreciate interactions between librational dynamics, flexibility, deployment, inertia parameters, orbit eccentricity, initial conditions, appendage orientation, etc. The information is fundamental to the missions concerned and essential to help develop appropriate
control strategies.Applied Science, Faculty of
Mechanical Engineering, Department of
Graduate
15
Jayasuriya, Arachige Tilak A. "Dynamics of unbalanced rotors on rigid and flexible bearings." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0016/MQ48062.pdf.
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Goyal, Anmol [Verfasser], and Bernd [Akademischer Betreuer] Simeon. "Isogeometric Shell Discretizations for Flexible Multibody Dynamics / Anmol Goyal. Betreuer: Bernd Simeon." Kaiserslautern : Technische Universität Kaiserslautern, 2015. http://d-nb.info/107154747X/34.
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Shi, Pengfei. "Flexible multibody dynamics, a new approach using virtual work and graph theory." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0008/NQ32856.pdf.
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Min, Byung No. "Object-oriented modeling for the dynamics of tree-topological flexible multibody systems." Thesis, McGill University, 2002. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=19569.
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Obtaining equations of motion is quite demanding but indispensable for the simulation of a multibody system, especially in space applications. This thesis is devoted to establishing a dynamics formalism and modeling tool in the framework of the objectoriented method for flexible multibody systems in a tree topology. In order to manage the modular construct as well as to take the material flexibility of body into account, the formulations are based on the Euler-Lagrange method in conjunction with the natural orthogonal complement of the kinematic constraint matrix. The elements constituting the dynamics of multibody mechanical systems are identified under the standard mathematical formats. They are embodied into distinct object modules equipped with characteristic variables and operations. A general flexible body is decomposed into several components with the kinematics and kinetics objects, while various types of articulation are delimited as the joint objects. The free-floating condition is represented by a special joint object having six degrees of freedom. A dynamics model is achieved by the interconnection of the object modules according to the relationships for data flow. A recursion formula, in conjunction with the lower body index representation, systematically evaluates the natural orthogonal complement matrix, which leads to a minimal set of equations of motion. The proposed method has been implemented to yield a practical modeling tool. It is validated through various simulation cases. The results match with the solutions of explicit formulations as well as the outputs from a sophisticated functional simulation facility. Additional simulations are performed with the incorporation of a control scheme.
19
Sänger, Nicolas [Verfasser]. "Elemente für die Dynamik flexibler Mehrkörpersysteme. Elements for flexible multibody dynamics / Nicolas Sänger." Siegen : Universitätsbibliothek Siegen, 2011. http://d-nb.info/1017180997/34.
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Moghadasi, Ali [Verfasser], and Robert [Akademischer Betreuer] Seifried. "Contributions to topology optimization in flexible multibody dynamics / Ali Moghadasi ; Betreuer: Robert Seifried." Hamburg : Universitätsbibliothek der Technischen Universität Hamburg-Harburg, 2019. http://d-nb.info/1190723743/34.
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21
Ricci, Stefano <1982>. "Model reduction techniques in flexible multibody dynamics with application to engine cranktrain simulation." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2013. http://amsdottorato.unibo.it/5882/1/ricci_stefano_tesi.pdf.
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The development of a multibody model of a motorbike engine cranktrain is presented in this work, with an emphasis on flexible component model reduction.
A modelling methodology based upon the adoption of non-ideal joints at interface locations, and the inclusion of component flexibility, is developed: both are necessary tasks if one wants to capture dynamic effects which arise in lightweight, high-speed applications.
With regard to the first topic, both a ball bearing model and a journal bearing model are implemented, in order to properly capture the dynamic effects of the main connections in the system: angular contact ball bearings are modelled according to a five-DOF nonlinear scheme in order to grasp the crankshaft main bearings behaviour, while an impedance-based hydrodynamic bearing model is implemented providing an enhanced operation prediction at the conrod big end locations.
Concerning the second matter, flexible models of the crankshaft and the connecting rod are produced. The well-established Craig-Bampton reduction technique is adopted as a general framework to obtain reduced model representations which are suitable for the subsequent multibody analyses. A particular component mode selection procedure is implemented, based on the concept of Effective Interface Mass, allowing an assessment of the accuracy of the reduced models prior to the nonlinear simulation phase. In addition, a procedure to alleviate the effects of modal truncation, based on the Modal Truncation Augmentation approach, is developed. In order to assess the performances of the proposed modal reduction schemes, numerical tests are performed onto the crankshaft and the conrod models in both frequency and modal domains.
A multibody model of the cranktrain is eventually assembled and simulated using a commercial software. Numerical results are presented, demonstrating the effectiveness of the implemented flexible model reduction techniques. The advantages over the conventional frequency-based truncation approach are discussed.
22
Ricci, Stefano <1982>. "Model reduction techniques in flexible multibody dynamics with application to engine cranktrain simulation." Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2013. http://amsdottorato.unibo.it/5882/.
Full textAbstract:
The development of a multibody model of a motorbike engine cranktrain is presented in this work, with an emphasis on flexible component model reduction.
A modelling methodology based upon the adoption of non-ideal joints at interface locations, and the inclusion of component flexibility, is developed: both are necessary tasks if one wants to capture dynamic effects which arise in lightweight, high-speed applications.
With regard to the first topic, both a ball bearing model and a journal bearing model are implemented, in order to properly capture the dynamic effects of the main connections in the system: angular contact ball bearings are modelled according to a five-DOF nonlinear scheme in order to grasp the crankshaft main bearings behaviour, while an impedance-based hydrodynamic bearing model is implemented providing an enhanced operation prediction at the conrod big end locations.
Concerning the second matter, flexible models of the crankshaft and the connecting rod are produced. The well-established Craig-Bampton reduction technique is adopted as a general framework to obtain reduced model representations which are suitable for the subsequent multibody analyses. A particular component mode selection procedure is implemented, based on the concept of Effective Interface Mass, allowing an assessment of the accuracy of the reduced models prior to the nonlinear simulation phase. In addition, a procedure to alleviate the effects of modal truncation, based on the Modal Truncation Augmentation approach, is developed. In order to assess the performances of the proposed modal reduction schemes, numerical tests are performed onto the crankshaft and the conrod models in both frequency and modal domains.
A multibody model of the cranktrain is eventually assembled and simulated using a commercial software. Numerical results are presented, demonstrating the effectiveness of the implemented flexible model reduction techniques. The advantages over the conventional frequency-based truncation approach are discussed.
23
Ribaric, Adrijan Petar. "Orientation Invariant Characteristics of Deformable Bodies in Multibody Dynamics." Diss., The University of Arizona, 2012. http://hdl.handle.net/10150/238644.
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In multibody systems, mechanical components (bodies) can be assumed rigid (non-deformable), if their deformation is negligible. For components with non-negligible deformations several methods were developed to represent their deformation. The most widely used method is the floating frame of reference. In this formulation the deformable body is represented by a finite element model whose deformation is described with respect to a local body-fixed frame. Unfortunately, finite element models can include many degrees-of-freedom, which stand in contradiction to the requirements of multibody dynamics. System truncation is therefore inevitable to support computational efficiency. The use of modal data in representing a deformable body is well understood in the multibody community. By truncating modes associated with higher frequencies, the total degrees-of-freedom of the deformable body can be reduced while preserving its dynamic eigen-properties. However, since the finite element model may be in contact with other moving bodies, the reduction technique needs to address the issue of moving boundary conditions. The component mode synthesis reduction methods are such techniques that describe the deflection of all the nodes as a superposition of different types of modes. However, it is limited in the fact that the nodes in contact need to remain in contact throughout a simulation. In some applications these nodes may change, i.e. a node that is in contact with another body or the ground at one instant may become free at the next instant. The present methodologies in multibody modeling of a deformable body with modal data have not yet addressed the issue of changing contact nodes. This research highlights the usefulness of orientation invariant characteristics of some deformable bodies. It proposes to define orientation invariant degrees-of-freedom of the reduced model in Eulerian space, while the remaining degrees-of-freedom are defined in Lagrangian space. In some circumstances, this approach can resolve the issue of changing contact nodes. The combination of Eulerian and Lagrangian formulation for component mode synthesis reduced finite element models is a new concept in deformable multibody dynamics.
24
Das, Manabendra. "Aeroelastic Analysis of Rotor Blades Using Three Dimensional Flexible Multibody Dynamic Analysis." Diss., The University of Arizona, 2008. http://hdl.handle.net/10150/195601.
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This study presents an approach based on the floating frame of reference method to model complex three-dimensional bodies in a multibody system. Unlike most of the formulations based on the floating frame of reference method, which assume small or moderate deformations, the present formulation allows large elastic deformations within each frame by using the co-rotational form of the updated Lagrangian description of motion. The implicit integration scheme is based on the Generalized-alpha method, and kinematic joints are invoked in the formulation through the coordinate partitioning method. The resulting numerical scheme permits the usage of relatively large time steps even though the flexible bodies may experience large elastic deformations. A triangular element, based on the first order shear deformable theory, has been developed specifically for folded plate and shell structures. The plate element does not suffer from either shear or aspect-ratio locking under transverse and membrane bending, respectively. A stiffened plate element has been developed that combines a shear deformable plate with a Timoshenko beam. A solid element, that utilized the isoparametric formulation along with incompatible modes, and one-dimensional elements are also included in the element library. The tools developed in the present work are then utilized for detailed rotorcraft applications. As opposed to the conventional approach of using beam elements to represent the rotor blade, the current approach focuses on detailed modeling of the blade using plate and solid elements. A quasi-steady model based on lifting line theory is utilized to compute the aerodynamic loads on the rotor blade in order to demonstrate the capabilities of the proposed tool to model rotorcraft aeroelasticity.
25
Liu, Chih-Hsing. "A finite element based dynamic modeling method for design analysis of flexible multibody systems." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/39605.
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This thesis develops a finite element based dynamic modeling method for design and analysis of compliant mechanisms which transfer input force, displacement and energy through elastic deformations. Most published analyses have largely based on quasi-static and lump-parameter models neglecting the effects of damping, torsion, complex geometry, and nonlinearity of deformable contacts. For applications such as handling of objects by the robotic hands with multiple high-damped compliant fingers, there is a need for a dynamic model capable of analyzing the flexible multibody system. This research begins with the formulation of the explicit dynamic finite element method (FEM) which takes into account the effects of damping, complex geometry and contact nonlinearity. The numerical stability is considered by evaluating the critical time step in terms of material properties and mesh quality. A general framework incorporating explicit dynamic FEM, topology optimization, modal analysis, and damping identification has been developed. Unlike previous studies commonly focusing on geometry optimization, this research considers both geometric and operating parameters for evaluation where the dynamic performance and trajectory of the multibody motion are particularly interested. The dynamic response and contact behavior of the rotating fingers acting on the fixed and moving objects are validated by comparing against published experimental results. The effectiveness of the dynamic modeling method, which relaxes the quasi-static assumption, has been demonstrated in the analyses of developing an automated transfer system involved grasping and handling objects by the compliant robotic hands. This FEM based dynamic model offers a more realistic simulation and a better understanding of the multibody motion for improving future design. It is expected that the method presented here can be applied to a spectrum of engineering applications where flexible multibody dynamics plays a significant role.
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Parsa, Kourosh. "Dynamics, state estimation, and control of manipulators with rigid and flexible subsystems." Thesis, McGill University, 2003. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=83089.
Full textAbstract:
Kinematically redundant manipulators composed of a rigid-link, rigid-joint robot and a structurally flexible arm on top of which the former is located constitute a new paradigm of long-reach manipulation systems. In order to have the end-effector of such a system faithfully follow a preplanned path, one should be able to reliably monitor the motions of the flexible submanipulator due to its elastic deformations. To this end, it is proposed that redundant point-acceleration measurements made on the rigid-robot base be used in an extended Kalman filter to estimate the flexural states of the flexible submanipulator. More specifically, this is done by processing the above-mentioned acceleration data in a novel pose and twist estimation technique, formulated in this thesis, to obtain those of the tip of the flexible arm; the pose and the twist data are then utilized as the measured outputs for the observer. Of course, the state-output relations should be linearized; the linearization is performed in closed-form.The mathematical models of the flexible and the rigid submanipulators are derived separately, each through the premultiplication of the transpose of the kinematic-constraint matrix by the assembled set of the link Lagrange equations; this matrix is the natural orthogonal complement of the kinematic-constraint wrench. Obviously, the reaction wrench acting between the rigid-robot base and the end-effector of the flexible submanipulator couples the two sets of dynamics equations. This wrench can be determined by substituting the twist-rate of the base, i.e., its angular and translational accelerations, into the dynamics equations of the rigid submanipulator and, subsequently, solving them. Then, considering the wrench as a time-dependent input for the flexible arm, we take the flexible-arm dynamics as the modelled dynamics in the observer. The reduced-order dynamics helps dramatically reduce the required floating-point operations within the observer.
Two redundancy-resolution techniques, namely, rigid-link redundancy resolution and flexible-link redundancy resolution, are discussed. Whereas the former assumes all the links to be rigid, the latter takes the flexibility effects into account. In both approaches, the self-motion of the system is computed so as to minimize the forces exciting its lowest "modal coordinates" while imposing a proportional damping on the flexural dynamics.
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Moberg, Stig. "Modeling and Control of Flexible Manipulators." Doctoral thesis, Linköpings universitet, Reglerteknik, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-60831.
Full textAbstract:
Industrial robot manipulators are general-purpose machines used for industrial automation in order to increase productivity, flexibility, and product quality. Other reasons for using industrial robots are cost saving, and elimination of hazardous and unpleasant work. Robot motion control is a key competence for robot manufacturers, and the current development is focused on increasing the robot performance, reducing the robot cost, improving safety, and introducing new functionalities. Therefore, there is a need to continuously improve the mathematical models and control methods in order to fulfil conflicting requirements, such as increased performance of a weight-reduced robot, with lower mechanical stiffness and more complicated vibration modes. One reason for this development of the robot mechanical structure is of course cost-reduction, but other benefits are also obtained, such as lower environmental impact, lower power consumption, improved dexterity, and higher safety. This thesis deals with different aspects of modeling and control of flexible, i.e., elastic, manipulators. For an accurate description of a modern industrial manipulator, this thesis shows that the traditional flexible joint model, described in literature, is not sufficient. An improved model where the elasticity is described by a number of localized multidimensional spring-damper pairs is therefore proposed. This model is called the extended flexible joint model. The main contributions of this work are the design and analysis of identification methods, and of inverse dynamics control methods, for the extended flexible joint model. The proposed identification method is a frequency-domain non-linear gray-box method, which is evaluated by the identification of a modern six-axes robot manipulator. The identified model gives a good description of the global behavior of this robot. The inverse dynamics problem is discussed, and a solution methodology is proposed. This methodology is based on the solution of a differential algebraic equation (DAE). The inverse dynamics solution is then used for feedforward control of both a simulated manipulator and of a real robot manipulator. The last part of this work concerns feedback control. First, a model-based nonlinear feedback control (feedback linearization) is evaluated and compared to a model-based feedforward control algorithm. Finally, two benchmark problems for robust feedback control of a flexible manipulator are presented and some proposed solutions are analyzed.
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Schmitt, Alexander Georg [Verfasser], and Robert [Akademischer Betreuer] Seifried. "Real-time simulation of flexible multibody systems in vehicle dynamics / Alexander Georg Schmitt ; Betreuer: Robert Seifried." Hamburg : Universitätsbibliothek der Technischen Universität Hamburg-Harburg, 2019. http://d-nb.info/1200058712/34.
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Akbulut, Burak. "Attitude Control Of Multiple Rigid Body Spacecraft With Flexible Hinge Joints." Master's thesis, METU, 2009. http://etd.lib.metu.edu.tr/upload/2/12611079/index.pdf.
Full textAbstract:
Control algorithm is developed for a satellite with flexible appendages to achieve a good pointing performance. Detailed modeling activity was carried out that consists of sensor and actuator models, disturbances and system dynamics. Common hardware found in the spacecraft such as reaction wheels, gyroscopes, star trackers etc. were included in the model. Furthermore, the Newton-Euler method is employed for the derivation of multi-body equations of motion. Evaluation of the pointing accuracy with proper pointing performance metrics such as accuracy, jitter and stability during slew maneuvers are obtained through simulations. Control strategies are proposed to improve pointing performance.
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Oral, Gokhan. "Flexible Multibody Dynamic Modeling And Simulation Of Rhex Hexapod Robot With Half Circular Compliant Legs." Master's thesis, METU, 2008. http://etd.lib.metu.edu.tr/upload/12610137/index.pdf.
Full textAbstract:
The focus of interest in this study is the RHex robot, which is a hexapod robot that is capable of locomotion over rugged, fractured terrain through statically and dynamically stable gaits while stability of locomotion is preserved. RHex is primarily a research platform that is based on over five years of previous research. The purpose of the study is to build a virtual prototype of RHex robot in order to simulate different behavior without manufacturing expensive prototypes. The virtual prototype is modeled in MSC ADAMS software which
is a very useful program to simulate flexible multibody dynamical systems.
The flexible half circular legs are modeled in a finite element program (MSC
NASTRAN) and are embedded in the main model. Finally a closed loop
control mechanism is built in MATLAB to be able to simulate real
autonomous RHex robot. The interaction of MATLAB and MSC ADAMS
softwares is studied.
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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.
Full textAbstract:
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.
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Cebulla, Thomas [Verfasser], Heinz [Akademischer Betreuer] Ulbrich, and Carlo L. [Akademischer Betreuer] Bottasso. "Spatial Dynamics of Pushbelt CVTs: Model Enhancements to a Non-smooth Flexible Multibody System / Thomas Cebulla. Gutachter: Heinz Ulbrich ; Carlo L. Bottasso. Betreuer: Heinz Ulbrich." München : Universitätsbibliothek der TU München, 2014. http://d-nb.info/1050025792/34.
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Epple, Alexander. "Methods for increased computational efficiency of multibody simulations." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/26532.
Full textAbstract:
Thesis (Ph. D.)--Aerospace Engineering, Georgia Institute of Technology, 2009.Committee Chair: Olivier A. Bauchau; Committee Member: Andrew Makeev; Committee Member: Carlo L. Bottasso; Committee Member: Dewey H. Hodges; Committee Member: Massimo Ruzzene. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Mureithi, Njuki W. "An experimental study of the flow structure and dynamics of a flexible cylinder within an array of rigid cylinders subjected to water cross-flow /." Thesis, McGill University, 1988. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=61717.
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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.
Full textAbstract:
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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Luu, Quang Khanh [Verfasser], Dirk [Akademischer Betreuer] Söffker, and Tamara [Akademischer Betreuer] Nestorovic. "Stability-Oriented Dynamics and Control of Complex Rigid-Flexible Mechanical Systems Using the Example of a Bucket-Wheel Excavator / Quang Khanh Luu. Gutachter: Tamara Nestorovic. Betreuer: Dirk Söffker." Duisburg, 2015. http://d-nb.info/1066206376/34.
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Luu, Quang Khanh Verfasser], Dirk [Akademischer Betreuer] [Söffker, and Tamara [Akademischer Betreuer] Nestorovic. "Stability-Oriented Dynamics and Control of Complex Rigid-Flexible Mechanical Systems Using the Example of a Bucket-Wheel Excavator / Quang Khanh Luu. Gutachter: Tamara Nestorovic. Betreuer: Dirk Söffker." Duisburg, 2015. http://d-nb.info/1066206376/34.
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Lacoursière, Claude. "Ghosts and machines : regularized variational methods for interactive simulations of multibodies with dry frictional contacts." Doctoral thesis, Umeå University, Computing Science, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-1143.
Full textAbstract:
A time-discrete formulation of the variational principle of mechanics is used to provide a consistent theoretical framework for the construction and analysis of low order integration methods. These are applied to mechanical systems subject to mixed constraints and dry frictional contacts and impacts---machines. The framework includes physics motivated constraint regularization and stabilization schemes. This is done by adding potential energy and Rayleigh dissipation terms in the Lagrangian formulation used throughout. These terms explicitly depend on the value of the Lagrange multipliers enforcing constraints. Having finite energy, the multipliers are thus massless ghost particles. The main numerical stepping method produced with the framework is called SPOOK.
Variational integrators preserve physical invariants globally, exactly in some cases, approximately but within fixed global bounds for others. This allows to product realistic physical trajectories even with the low order methods. These are needed in the solution of nonsmooth problems such as dry frictional contacts and in addition, they are computationally inexpensive. The combination of strong stability, low order, and the global preservation of invariants allows for large integration time steps, but without loosing accuracy on the important and visible physical quantities. SPOOK is thus well-suited for interactive simulations, such as those commonly used in virtual environment applications, because it is fast, stable, and faithful to the physics.
New results include a stable discretization of highly oscillatory terms of constraint regularization; a linearly stable constraint stabilization scheme based on ghost potential and Rayleigh dissipation terms; a single-step, strictly dissipative, approximate impact model; a quasi-linear complementarity formulation of dry friction that is isotropic and solvable for any nonnegative value of friction coefficients; an analysis of a splitting scheme to solve frictional contact complementarity problems; a stable, quaternion-based rigid body stepping scheme and a stable linear approximation thereof. SPOOK includes all these elements. It is linearly implicit and linearly stable, it requires the solution of either one linear system of equations of one mixed linear complementarity problem per regular time step, and two of the same when an impact condition is detected. The changes in energy caused by constraints, impacts, and dry friction, are all shown to be strictly dissipative in comparison with the free system. Since all regularization and stabilization parameters are introduced in the physics, they map directly onto physical properties and thus allow modeling of a variety of phenomena, such as constraint compliance, for instance.
Tutorial material is included for continuous and discrete-time analytic mechanics, quaternion algebra, complementarity problems, rigid body dynamics, constraint kinematics, and special topics in numerical linear algebra needed in the solution of the stepping equations of SPOOK.
The qualitative and quantitative aspects of SPOOK are demonstrated by comparison with a variety of standard techniques on well known test cases which are analyzed in details. SPOOK compares favorably for all these examples. In particular, it handles ill-posed and degenerate problems seamlessly and systematically. An implementation suitable for large scale performance and accuracy testing is left for future work.
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Martz, Yannick. "Modélisation et commande de systèmes d'entraînement de bandes flexibles : nouvelles approches à l'aide des éléments finis." Thesis, Strasbourg, 2017. http://www.theses.fr/2017STRAD016.
Full textAbstract:
Les systèmes d'entraînement de bandes flexibles sont utilisés dans la production d'une très grande variété de produits du quotidien mais également dans la métallurgie et dorénavant pour la production des nouvelles technologies. L'amélioration des systèmes industriels d'entraînement de bandes est un problème difficile car ils sont de grande dimension, non-linéaires, à paramètres variant et incertains. Ils possèdent un fort couplage entre les différentes parties (mécanique et commande) à cause de la bande qui relie les éléments. Il faut donc améliorer la chaîne de production par une approche pluridisciplinaire. Les objectifs sont de maîtriser les paramètres clés de ces systèmes afin de garantir les cadences de production et les précisions demandées de plus en plus importantes. Il faut également réduire les défauts les plus récurrents, notamment les plis de bande. Or jusqu'à présent seuls des modèles 1D étaient utilisés. Ils sont indispensables pour la synthèse de commande et les études fréquentielles mais ne permettent pas d'étudier des phénomènes complexes tels que les plis de bande. Une nouvelle approche d'étude de ces systèmes est développée. Dans un premier temps, des améliorations de structures de commandes sont proposées. Dans un second temps un modèle 3D par éléments finis utilisant un algorithme de dynamique multicorps flexibles est développé et utilisé pour étudier les plis de bande par comparaison à la théorie classique de prédiction de ces défauts. Dans un troisième temps un simulateur complet est développé comprenant le modèle 3D mécanique par élément finis couplé à la partie commande (co-simulation)Roll-to-Roll systems are used in the manufacturing of a wide variety of everyday products as well as in metallurgy and for the manufacturing of new technologies. The improvement of Roll-to-Roll systems is a difficult problem because they are large, non-linear, with varying and uncertain parameters. They have a coupling between the different parts (mechanical and control) with the help of the web connecting the elements. It is therefore necessary to improve the process line through a multidisciplinary approach. The objectives are to master the key parameters of these systems in order to guarantee the manufacturing rates and the more important accuracies requested. It is also necessary to reduce or remove the most recurring defects such as web wrinkles. Until now, only 1D models were used. They are essential for control synthesis and frequency studies but they do not allow to study complex phenomena such as web wrinkles. A new approach for studying these systems is developed. First, improvements of control structures are proposed. Secondly, a 3D finite element model using a flexible multibody dynamics algorithm is developed, used in this work to study web wrinkles and compared to the classical prediction theory of these defects. Finally, a complete simulator is developed including the mechanical 3D model by finite element coupled to the control part (co-simulation)
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Nandihal, Paramanand Vivekanand. "Dynamics of rigid-flexible multibody systems." Thesis, 2018. http://localhost:8080/iit/handle/2074/7765.
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Zhao, Zhicheng. "Dynamics of a general flexible multibody system." 1992. http://hdl.handle.net/1993/29500.
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Yeh, Chun-tien. "Dynamics and control of a rigid/flexible manipulator." Thesis, 1992. http://hdl.handle.net/1957/37233.
Full textAbstract:
Control of high-speed, light-weight robotic
manipulators is a challenge because of their special
dynamic characteristics. In this work, a two-stage
control algorithm for the position control of flexible
manipulators is proposed. First, the more complex,
flexible robot system is replaced by a simplified
hypothetical rigid body system (HRRA) with off-line
trajectory planning. This reduces the complexity of the
controller design for the flexible robotic arm. A
parameter-optimization approach was adopted to minimize
the difference between these two models in this stage.
Also, a comparison of computational efficiency is made
among the methods of calculus-of-variations, dynamic-programming,
and the proposed parameter-optimization. At
the second stage, simple linear state feedback
controllers, based on the simplified hypothetical rigid
body model, are proposed to control the actual robotic
system. With the feedback gains selected properly by the
pole-placement and linear quadratic methods, the results
show satisfactory achievement of the motion objectives.
The algorithm is implemented for a two-link
rigid/flexible robotic arm, and the results indicate that
the procedure is capable of providing effective control
with much simpler computational requirements than those
of procedures published previously.Graduation date: 1992
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Khude, Naresh Nilkanth. "Modal analysis of a helicopter wing-pylon structure using flexible multibody dynamics." 2006. http://etd.utk.edu/2006/KhudeNaresh.pdf.
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Leyendecker, Sigrid [Verfasser]. "Mechanical integrators for constrained dynamical systems in flexible multibody dynamics / Sigrid Leyendecker." 2006. http://d-nb.info/980411912/34.
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Findlay, Everett. "Investigation of Active Vibration Suppression of a Flexible Satellite using Magnetic Attitude Control." Thesis, 2011. http://hdl.handle.net/1807/30593.
Full textAbstract:
The problem of attitude control of a flexible satellite using magnetic attitude control is investigated. The work is motivated by JC2Sat - a joint CSA and JAXA mission whose main purpose is a proof of concept of two satellites performing differential drag formation flying. The impact of additional flexible drag panels (of various sizes) on the attitude control is assessed. JC2Sat's attitude control system consists of three perpendicular magnetorquers and one reaction/bias-momentum wheel. Four Linear Quadratic Regulator controllers are compared, ranging in complexity from being time-invariant and assuming a rigid satellite, to being periodic and actively suppressing panel vibrations. These include the first controllers which use magnetic attitude control to actively suppress vibrations, and where the periodic vibration suppression controller is able to guarantee asymptotic stability of the linearized system. It was found that for larger panels, the controllers which actively suppressed the vibrations outperformed those that did not.
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Wang, Ding-Qin, and 王鼎欽. "A Simulation of Conjugated Polymer with Rigid Segments and Flexible Links through All-Atom and Coarse-Grained Molecular Dynamics Methods." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/88737983856391933648.
Full textAbstract:
碩士國立臺灣大學
高分子科學與工程學研究所
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We developed a coarse-grained force field for the Poly(p-biphenylene terephthalate)-O9 alternating copolymer which consist of biphenyl group and ester group in main-chain and lateral alkyl chain in side chain, respectively. We adopted iterative Bozeman inversion method to develop a coarse-grained force field connecting with all-atom molecular dynamics. The force field contains intra- and inter-molecular interactions including bonds, angles, dihedral angles, and nonbonded terms. Through comparison of RDF, bond length distribution, angle distribution, and dihedral angle distribution are fitted between all-atom and coarse-grained molecular dynamics to comprehend the mapping results. The results indicated the disordered and locally ordered packing are revealed in mapping of single chain and 4 chains, respectively. Otherwise, the dihedral angle parameter is the most important parameter to affect the chain conformation and packing behavior. Besides, the incompatibility between main-chain and side-chain help the PBpT-O9 to pack into ordered morphology. Finally, the effective coarse-grained force field parameters are obtained to describe the realistic polymer chain.
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Bondoky, Karim. "A Contribution to Validation and Testing of Non-Compliant Docking Contact Dynamics of Small and Rigid Satellites Using Hardware-In-The-Loop Simulation." 2020. https://tud.qucosa.de/id/qucosa%3A73251.
Full textAbstract:
Spacecraft (S/C) docking is the last and most challenging phase in the contact closure of two separately flying S/C. The design and testing of S/C docking missions using software-multibody simulations need to be complemented by Hardware-In-The-Loop (HIL) simulation using the real docking hardware. The docking software multibody simulation is challenged by the proper modeling of contact forces, whereas the HIL docking simulation is challenged by proper inclusion of the real contact forces. Existing docking HIL simulators ignore back-reaction force modeling due to the large S/C sizes, or use compliance devices to reduce impact, which alters the actual contact force. This dissertation aims to design a docking HIL testbed to verify docking contact dynamics for small and rigid satellites by simulating the real contact forces without artificial compliance.
HIL simulations of docking contact dynamics are challenged mainly by:
I. HIL simulation quality: quality of realistic contact dynamics simulation relies fundamentally on the quality of HIL testbed actuation and sensing instrumentation (non-instantaneous, time delays, see Fig. 1)
II. HIL testbed design: HIL design optimization requires a justified HIL performance prediction, based on a representative HIL testbed simulation (Fig. 2), where appropriate simulation of contact dynamics is the most difficult and sophisticated task.
The goal of this dissertation is to carry out a systematic investigation of the technically possible HIL docking contact dynamics simulation performances, in order to define an appropriate approach for testing of docking contact dynamics of small and rigid satellites without compliance and using HIL simulation. In addition, based on the investigations, the software simulation results shall be validated using an experimental HIL setup.
To achieve that, multibody dynamics models of docking S/C were built, after carrying out an extensive contact dynamics research to select the most representative contact model. Furthermore, performance analysis models of the HIL testbed were built. In the dissertation, a detailed parametric analysis was carried out on the available models’ design-spaces (e.g., spacecraft, HIL testbed building-blocks and contact dynamics), to study their impacts on the HIL fidelity and errors (see Fig. 1). This was done using a generic HIL design-tool, which was developed within this work. The results were then used to identify the technical requirements of an experimental 1-Degree-of-Freedom (DOF) HIL testbed, which was conceived, designed, implemented and finally utilized to test and validate the selected docking contact dynamics model.
The results of this work showed that the generic multibody-dynamics spacecraft docking model is a practical tool to model, study and analyze docking missions, to identify the properties of successful and failed docking scenarios before it takes place in space.
Likewise, the 'Generic HIL Testbed Framework Analysis Tool' is an effective tool for carrying out performance analysis of HIL testbed design, which allows to estimate the testbed’s fidelity and predict HIL errors.
Moreover, the results showed that in order to build a 6DOF HIL docking testbed without compliance, it is important to study and analyze the errors’s sources in an impact and compensate for them. Otherwise, the required figure-of-merits of the instruments of the HIL testbed would be extremely challenging to be realized.
In addition, the results of the experimental HIL simulation (i.e., real impacts between various specimen) serve as a useful contribution to the advancement of contact dynamics modeling.
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Das, Prashant. "Unsteady Two Dimensional Jet with Flexible Flaps at the Exit." Thesis, 2016. https://etd.iisc.ac.in/handle/2005/2752.
Full textAbstract:
The present thesis involves the study of introducing passive exit flexibility in a two dimensional starting jet. This is relevant to various biological flows like propulsion of aquatic creatures (jellyfish, squid etc.) and flow in the human heart. In the present study we introduce exit flexibility in two ways. The first method was by hinging rigid plates at the channel exit and the second was by attaching deformable flaps at the exit. In the hinged flaps cases, the experimental arrangement closely approximates the limiting case of a free-to-rotate rigid flap with negligible structural stiffness, damping and flap inertia; these limiting structural properties permitting the largest flap openings. In the deformable flaps cases, the flap’s stiffness (or its flexural rigidity EI) becomes an important parameter. In both cases, the initial condition was such that the flaps were parallel to the channel walls. With this, a piston was pushed in a controlled manner to form the starting jet. Using this arrangement, we start the flow and visualize the flap kinematics and make flow field measurements. A number of parameters were varied which include the piston speed, the flap length and the flap stiffness (in case of the deformable flaps).
In the hinged rigid flaps cases, the typical motion of the flaps involves a rapid opening with flow initiation and a subsequent more gradual return to its initial position, which occurs while the piston is still moving. The initial opening of the flaps can be attributed to an excess pressure that develops in the channel when the flow starts, due to the acceleration that has to be imparted to the fluid slug between the flaps. In the case with flaps, additional pairs of vortices are formed because of the motion of the flaps and a complete redistribution of vorticity is observed. The length of the flaps is found to significantly affect flap kinematics when plotted using the conventional time scale L/d. However, with a newly defined time-scale based on the flap length (L/Lf ), we find a good collapse of all the measured flap motions irrespective of flap length and piston velocity for an impulsively started piston motion. The maximum opening angle in all these impulsive velocity program cases, irrespective of the flap length, is found to be close to 15 degrees. Even though the flap kinematics collapses well with L/Lf , there are differences in the distribution of the ejected vorticity even for the same L/Lf .
In the deformable flap cases, the initial excess pressure in the flap region causes the flaps to bulge outwards. The size of the bulge grows in size, as well as moves outwards as the flow develops and the flaps open out to reach their maximum opening. Thereafter, the flaps start returning to their initial straight position and remain there as long as the piston is in motion. Once the piston stops, the flaps collapse inwards and the two flap tips touch each other. It was found that the flap’s flexural rigidity played an important role in the kinematics. We define a new time scale (t ) based on the flexural rigidity of the flaps (EI) and the flap length (Lf ). Using this new time scale, we find that the time taken to reach the maximum bulge (t* 0.03) and the time taken to reach the maximum opening (t* 0.1) were approximately similar across various flap stiffness and flap length cases. The motion of the flaps results in the formation of additional pairs of vortices. Interestingly, the total final circulation remains almost the same as that of a rigid exit case, for all the flap stiffness and flap lengths studied. However, the final fluid impulse (after all the fluid had come out of the flap region) was always higher in the flap cases as compared to the rigid exit case because of vorticity redistribution. The rate at which the impulse increases was also higher in most flap cases. The final impulse values were as large as 1.8 times the rigid exit case. Since the time rate of change of impulse is linked with force, the measurements suggest that introduction of flexible flaps at the exit could result in better propulsion performances for a system using starting jets.
The work carried out in this thesis has shown that by attaching flexible flaps at the exit of an unsteady starting jet, dramatic changes can be made to the flow field. The coupled kinematics of the flaps with the flow dynamics led to desirable changes in the flow. Although the flaps introduced in this work are idealized and may not represent the kind of flexibility we encounter in biological systems, it gives us a better understanding of the importance of exit flexibility in these kinds of flows.
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Das, Prashant. "Unsteady Two Dimensional Jet with Flexible Flaps at the Exit." Thesis, 2016. http://hdl.handle.net/2005/2752.
Full textAbstract:
The present thesis involves the study of introducing passive exit flexibility in a two dimensional starting jet. This is relevant to various biological flows like propulsion of aquatic creatures (jellyfish, squid etc.) and flow in the human heart. In the present study we introduce exit flexibility in two ways. The first method was by hinging rigid plates at the channel exit and the second was by attaching deformable flaps at the exit. In the hinged flaps cases, the experimental arrangement closely approximates the limiting case of a free-to-rotate rigid flap with negligible structural stiffness, damping and flap inertia; these limiting structural properties permitting the largest flap openings. In the deformable flaps cases, the flap’s stiffness (or its flexural rigidity EI) becomes an important parameter. In both cases, the initial condition was such that the flaps were parallel to the channel walls. With this, a piston was pushed in a controlled manner to form the starting jet. Using this arrangement, we start the flow and visualize the flap kinematics and make flow field measurements. A number of parameters were varied which include the piston speed, the flap length and the flap stiffness (in case of the deformable flaps).
In the hinged rigid flaps cases, the typical motion of the flaps involves a rapid opening with flow initiation and a subsequent more gradual return to its initial position, which occurs while the piston is still moving. The initial opening of the flaps can be attributed to an excess pressure that develops in the channel when the flow starts, due to the acceleration that has to be imparted to the fluid slug between the flaps. In the case with flaps, additional pairs of vortices are formed because of the motion of the flaps and a complete redistribution of vorticity is observed. The length of the flaps is found to significantly affect flap kinematics when plotted using the conventional time scale L/d. However, with a newly defined time-scale based on the flap length (L/Lf ), we find a good collapse of all the measured flap motions irrespective of flap length and piston velocity for an impulsively started piston motion. The maximum opening angle in all these impulsive velocity program cases, irrespective of the flap length, is found to be close to 15 degrees. Even though the flap kinematics collapses well with L/Lf , there are differences in the distribution of the ejected vorticity even for the same L/Lf .
In the deformable flap cases, the initial excess pressure in the flap region causes the flaps to bulge outwards. The size of the bulge grows in size, as well as moves outwards as the flow develops and the flaps open out to reach their maximum opening. Thereafter, the flaps start returning to their initial straight position and remain there as long as the piston is in motion. Once the piston stops, the flaps collapse inwards and the two flap tips touch each other. It was found that the flap’s flexural rigidity played an important role in the kinematics. We define a new time scale (t ) based on the flexural rigidity of the flaps (EI) and the flap length (Lf ). Using this new time scale, we find that the time taken to reach the maximum bulge (t* 0.03) and the time taken to reach the maximum opening (t* 0.1) were approximately similar across various flap stiffness and flap length cases. The motion of the flaps results in the formation of additional pairs of vortices. Interestingly, the total final circulation remains almost the same as that of a rigid exit case, for all the flap stiffness and flap lengths studied. However, the final fluid impulse (after all the fluid had come out of the flap region) was always higher in the flap cases as compared to the rigid exit case because of vorticity redistribution. The rate at which the impulse increases was also higher in most flap cases. The final impulse values were as large as 1.8 times the rigid exit case. Since the time rate of change of impulse is linked with force, the measurements suggest that introduction of flexible flaps at the exit could result in better propulsion performances for a system using starting jets.
The work carried out in this thesis has shown that by attaching flexible flaps at the exit of an unsteady starting jet, dramatic changes can be made to the flow field. The coupled kinematics of the flaps with the flow dynamics led to desirable changes in the flow. Although the flaps introduced in this work are idealized and may not represent the kind of flexibility we encounter in biological systems, it gives us a better understanding of the importance of exit flexibility in these kinds of flows.
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Shinde, Sachin Yashavant. "Creation of an Orderly Jet and Thrust Generation in Quiescent Fluid from an Oscillating Two-dimensional Flexible Foil." Thesis, 2012. http://etd.iisc.ac.in/handle/2005/3160.
Full textAbstract:
In nature, many of the flapping wings and fins in swimming and flying animals have various degrees of flexibility with strong and coupled solid-fluid interactions between the structure and the fluid. In most cases, the wing structure, the flow and their interactions are complex. This thesis experimentally investigates a ‘simple’ fluid-flexible foil interaction problem: flow generated by a pitching foil with chordwise flexibility.
To explore the effect of flexibility on the flow, we study the flow generated in quiescent water (the limiting case of infinite Strouhal number) by a sinusoidally pitching rigid symmetrical NACA0015 foil to which is attached a 0.05 mm thick chordwise flexible polythene flap at the trailing edge. The chordwise length of flap is 0.79 c, where c = 38 mm is the chord length of the rigid foil; span of the foil and flap is 100 mm. Detailed particle image velocimetry (PIV) and flow visualization measurements have been made for twelve cases, corresponding to three pitching amplitudes, ±10◦,± 15◦, ±20◦, and four frequencies, 1, 2, 3 and 4 Hz for each amplitude.
For most of these cases, a narrow coherent jet aligned along the center-line, containing a reverse B’enard–K´arm´an vortex street, and a corresponding unidirectional thrust are generated. This thrust is similar to the upward force generated during hovering, but motion of our foil is much simpler than the complex wing kinematics found in birds and insects; also the thrust generation mechanism seems to be different. In our case, the thrust is from a coordinated pushing action of the rigid foil and the flexible flap. Control volume analysis reveals the unsteady nature of thrust generation. In this intricately coupled flow generation problem, chordwise flexibility is found to be crucial in producing the coherent jet. In this thesis, we explore in detail the physics of jet flow produced by the foil with a flexible flap, and identify the importance of flexibility in flow generation. Flap motion ensures appropriate spatial and temporal release of vortices, and also imparts them convective motion, to obtain the staggered pattern that produces the jet. To describe the fluid-flap interaction, we conveniently characterize the flap through a non-dimensional stiffness, ‘effective stiffness’ (EI)∗ of the flap, that captures the effects of both the flap properties as well as the external forcing. With the same flap by changing the pitching parameters, we cover a fairly large (EI)∗ range varying over nearly two orders of magnitude. However, we observed that only moderate (EI)∗ (~0.1 - 1) generates sustained narrow, orderly jet. We provide thrust estimates useful for the design of flapping foil thrusters/propulsors. Although this study has only indirect connections with the hovering in nature, it may be useful in understanding the role of flexibility of bird and insect wings during hovering.
In contrast, a foil with a rigid trailing edge produces a weak jet whose inclination changes continually with time. This meandering is observed to be random and independent of the initial conditions over a wide range of pitching parameters.