bluuebunny/crossref_metadata_2025 huggingface dataset:
On the Creation of a Unified Modeling Language Based Collaborative Virtual Assembly/Disassembly System
Authors: Mo Jianzhong , Chu Chi-Cheng , Prabhu B. S. , Gadh Rajit
Published: June 2008

Design For Assembly/disassembly (DFA) allows systematic evaluations and analysis of product assembly and disassembly during the product design stage with the goal of reducing assembly costs, improving quality and shortening time to market. These evaluations include assemblability, disassemblability, part accessibility, and part layout [1]. With the growing availability and widespread use of high bandwidth network and Virtual Reality (VR) technologies, the issues involved with product assembly, disassembly may be addressed and resolved effectively in a collaborative virtual environment over the Internet. In this paper, an analysis on the framework and definition of a collaborative virtual assembly and disassembly system, called Motive3D [2, 3], is introduced and examined using Unified Modeling Language (UML) [4]. UML is an Object Management Group’s (OMG) standard for object-oriented analysis and software design method, which allows specifying, constructing, visualizing, and documenting a distributed software-intensive system. Carrying out systematic analysis on the Motive3D system using UML, we believe that it expedites system development and will be possible to expedite the product design cycle and enable the assembly and disassembly process over Internet, and thus reduce the assembly and disassembly process bottlenecks.
Minimum Height Packing for Layered Manufacturing Using an Extended Pattern Search Algorithm
Authors: Aladahalli Chandankumar , Cagan Jonathan , Shimada Kenji
Published: June 2008

This paper introduces an approach to solve the minimum height layout problem for layered manufacturing using a pattern search based algorithm called Extended Pattern Search. In the batch processing of several components in a typical layered manufacturing run, it is efficient in terms of cost and time to build the components after packing their 3D models such that the maximum height of the components is minimized. 3D component layout based on a pattern search algorithm provides a framework to accomplish such minimum height packing. A method to determine the objective function weights for a class of problems is also provided. Finally error minimizing build directions are incorporated in the 3D layout framework by imposing suitable spatial orientation constraints on individual components.
Process Planning for Embedding Flexible Materials in Multi-Material Prototypes
Authors: Hatanaka Motohide , Cutkosky Mark R.
Published: June 2008

We describe a set of techniques to permit the fabrication of multi-material layered prototypes with embedded flexible components such as reinforcing fibers, fabrics and electrical wiring. The main challenges are to maintain the shapes of the flexible elements during processing and to control precisely the geometries of adjacent regions of part material without either damaging the flexible elements or being hindered by them. The solutions involve sequences of controlled deposition and/or removal of part material and sacrificial “buffer” material. Functional considerations concerning strength and fatigue life may induce additional constraints on the processing sequence. Where conventional material removal is impractical, we present a new approach involving a hybrid of photolithography and shape deposition manufacturing. Alternative methods of achieving similar functions without cross-boundary embedding can ease fabrication and even improve performance. Design and process selection guidelines have been composed based on fabrication experience.
Solution of Topology Embryonic Graph and Topology Graph for Unified Planar-Spatial Mechanisms
Authors: Yi Lu , Leinonen Tatu
Published: June 2008

An analysis matrix approach for solving an isomeric topology embryonic graph and a digital group approach for solving an isomeric topology graph of a unified planar-spatial mechanism are presented and the relative theory is discussed. Firstly, all binary links are removed from each acceptable linkage system with different degrees of freedom, many analysis matrixes are constructed, and many topology embryonic graphs of the mechanism are derived. Secondly, from an acceptable multi-element link combination of planar or spatial mechanisms, a rule for determining the isomeric topology embryonic graphs and an unreasonable topology embryonic graph is obtained. Thirdly, by considering the degree of freedom of the mechanism and the configuration of a planar or spatial mechanism, the number of binary links is determined. Finally, all removed binary links are rearranged systematically back into an isomeric topology embryonic graph, and the acceptable topology graphs of the mechanism are derived by using a digital group approach. Some illustrations show that the two approaches are simple and effective tools and can be employed to synthesize both planar and spatial mechanisms.
Rapidly Re-Configurable Mold Manufacturing of Free-Form Objects
Authors: Kelkar Aditya , Koc Bahattin , Nagi Rakesh
Published: June 2008

This paper describes geometric algorithms for manufacturing freeform objects using a re-configurable mold system. The proposed process involves a mold block, with n faces, in which the mold cavity is formed. Each face of the mold block holds a uniform grid of pins, which are used to approximate the part surfaces. The geometric algorithms presented in this paper analyze the part and determine the face of mold block from which the part model is approximated best using the pins from that face. By moving these pins in and out of the mold block, the shape of the mold cavity can be configured dynamically to suit the changes in the part geometry. Since the proposed process approximates free-form objects with discrete pins, a surface-error calculation method is also developed to control the accuracy. Computer implementation and examples are also provided in this paper.
Numerical Continuation Methods and Bifurcation Analysis Applied to Multibody System Dynamics
Authors: Meijaard J. P.
Published: June 2008

It is shown how a standard public-domain program for the numerical continuation of stationary and periodic solutions of dynamical systems, and of their bifurcations, can be used to analyse the behaviour of solutions of the equations of motion for a multibody system. The equations of motion are derived with the aid of a symbolic multibody program. From these, the variational equations and the derivatives with respect to parameters can be easily obtained with the underlying algebraic manipulation routines. The analysis procedure is illustrated in the example of a double pendulum, where some results can be checked against analytically derived results.
Biaxial Vibrations of an Elasto-Plastic Beam With a Prescribed Rigid-Body Rotation
Authors: Dibold M. , Gerstmayr J. , Irschik H.
Published: June 2008

In the present work, the development of plastic strains in a flexural beam is studied. The beam is modeled as a Bernoullieuler beam, where large rigid-body rotations and biaxial bending in the small strain regime are studied. The deformation is split into the spatial deformation of a hinged-hinged beam and the movement of the second support. Neglecting axial displacements of the beam, this support moves on a sphere. In the present paper, the latter motion is considered as prescribed. The beam thus is assumed to possess only flexural degrees-offreedom. Such a problem is frequently to be encountered in machine dynamics or robotics. We assume the stiffness of the beam to be considerably lowered due to catastrophic environmental influences, such that the deformations relative to the rigid-body motion, albeit small, reach the plastic regime. The equations of motion are derived by Hamilton’s principle. The potential energy follows from the internal energy due to the elastic part of the deformation and the potential due to gravity. Plastic strains are treated according to the theory of eigenstrains, which act as sources of self-stress upon the linear elastic beam. The biaxial deflections are discretized in space by means of Legendre polynomials. The plastic strains are discretized over length, height and width of the beam by small plastic cells. The plastic strains are computed in every time-step by a suitable iterative procedure. An implicit midpoint rule, which preserves the total energy of the system, is used for integration of the equations of motion. Linear elastic/perfectly plastic behavior is exemplarily treated in a numerical study.
Use of Plasticity Theory in Flexible Multibody System Dynamics
Authors: Sugiyama Hiroyuki , Shabana Ahmed A.
Published: June 2008

The objective of this investigation is to develop a general nonlinear finite deformation formulation for the elastic-plastic analysis of flexible multibody systems. The Lagrangian plasticity theory based on J2 flow theory is used to account for the effect of plasticity in flexible multibody dynamics. In addition, it is demonstrated that the principle of objectivity that is an issue when existing finite element formulations using ratetype constitutive equations are used can be fully satisfied when the stress and strain rate are directly calculated in the Lagrangian descriptions using the absolute nodal coordinate formulation employed in this investigation. This is attributed to the fact that, in the finite element absolute nodal coordinate formulation, the position vector gradients can completely define the state of rotation and deformation within the element. As a consequence, the numerical algorithm used to determine the plastic deformations such as the Radial Return Algorithm becomes much simpler when the absolute nodal coordinate formulation is used as compared to existing finite element formulations that employ incrementally objective algorithms. Several numerical examples are presented in order to demonstrate the use of the formulations presented in the paper.
Estimation of Partial Frequency Response Functions of a Parametrically Excited Flexible Multibody System
Authors: Prothmann Thorsten , Sachau Delf
Published: June 2008

Flexible multibody system simulation allows for fast and adequate investigation of the dynamics of mechanical systems. But in case of a system response with large deformations the time response does not uncover the causes, i. e. the resonances of the system. The identification of the systems eigenfrequencies gives more insight in resonance phenomena, but in case of periodic time-variant systems the often used snap-shot-eigenfrequencies do not reveal the real system dynamics, which has to be described by more than only one frequency response function. Based on the formulation of a flexible multibody system and the theory of ordinary linear periodic differential equations, partial frequency response functions, describing the real characteristics of a periodic system, are calculated and compared to the snapshot-frequency response functions.
Heart Composite Material Model for Stress-Strain Analysis
Authors: Hu Zhenhua , Metaxas Dimitris , Axel Leon
Published: June 2008

Mechanical properties of the myocardium have been investigated intensively in the past four decades. Due to the non-linearity and history dependence of myocardial deformation, many complex strain energy functions have been used to describe the stress-strain relationship in the myocardium. These functions are good at fitting in-vitro experimental data from myocardial stretch testing into strain energy functions. However, it is difficult to model in-vivo myocardium by using strain energy functions. In a previous paper [1], we have implemented a transversely anisotropic material model to estimate in-vivo strain and stress in the myocardium. In this work, the fiber orientation is updated at each time step from the end of diastole to the end of systole; the stiffness matrix is recalculated using the current fiber orientation. We also extend our model to include residual ventricular stresses and time-dependent blood pressure in the ventricular cavities.
Dynamic Analysis and Contact Modeling for Two Dimensional Media Transport System
Authors: Cho H. J. , Bae D. S. , Choi J. H. , Suzuki Takashi
Published: June 2008

In this paper, two dimensional dynamics analysis of media transport systems is presented by using multibody dynamic methods. Even though there are many requests for the dynamic analysis and design of media transport system from industry, there have been no clear solutions for the design and analysis methods at early stage. Therefore most engineers in industries have depended on trial and error techniques, which is very tedious and inefficient technologies. In this investigation the flexible sheet are modeled by multi-rigid bodies interconnected by revolute joints and rotational spring damper force elements. The contacts, between sheet and roller, and guides, are defined by using compliant contact force analysis. The proposed methods illustrated in this investigation have good agreement with experimental results and proved that it is very efficient tool comparing to previous trial and error methods.
An Efficient Method for Contact/Impact Problems in Multibody Systems: Topologies With Many Loops
Authors: Anderson Kurt S. , Sadowski Michael J. A.
Published: June 2008

This paper presents an algorithm for the efficient numerical analysis and simulation of contact/impact problems in modest to heavily constrained multi-rigid-body dynamic systems. The algorithm can accommodate the spatial motion of general multirigid-body systems containing arbitrarily many closed loops in O(n+m) operations overall for systems containing n generalized coordinates, and m independent algebraic constraints. The presented method uses a generalized momentum balance approach to determine the velocity jumps which take place across impacts in such constrained multibody dynamic systems. The presented method does not suffer from the performance (speed) penalty encountered by most other momentum balance methods given its O(n + m) cost, and exact direct embedded consideration of the all constraints. Due to these characteristics, the presented algorithm offers superior computing performance relative to other methods in situations involving both large n and m.
Impact and Bifurcation of Flexible Multibody Systems
Authors: Zahariev Evtim V.
Published: June 2008

In the paper, the process of loss of stability of multibody systems and structures is analyzed. A novel approach is presented and applied as for the statically loaded spatial systems so for analysis of dynamic response of systems imposed on impact. The analysis is based on solution of the dynamic equations and eigenvalue problem of systems, and of resultant motion simulation. The flexible systems are discretized using the method of finite elements. The dynamic equations are derived with respect to the relative coordinates of the finite elements. Large flexible deflections due to loss of stability are simulated. The initial forms of the possible deformations are defined by the eigenvectors computed solving the eigenvalue problem for the system stiffness matrix. The critical forces and system deflections obtained due to percussive forces and impact are then analyzed. Examples of bifurcation of beam and beam structure imposed on compulsive motion, percussive forces and impact are presented.
Formulation of Multibody Dynamics as Complementarity Problems
Authors: Trinkle J. C.
Published: June 2008

Multibody systems with rigid bodies and unilateral contacts are difficult to simulate due to discontinuities associated with gaining and losing contacts and stick-slip transitions. Methods for simulating such systems fall into two categories: penalty methods and complementarity methods. The former calculate penetration depths of virtual rigid bodies at every time step and compute restoring forces to repair penetrations, while the latter assume that the bodies are truly rigid and compute contact forces that prevent penetration from occurring at all. In this paper, we are concerned with complementarity methods. We present an instantaneous formulation of the equations of motion of multi-rigid-body systems with frictional contacts as a complementarity problem. The unknowns in this formulation are accelerations and forces at the contacts. Since it is known that this model does not always admit a finite solution, it is problematic to use it directly in an integration scheme. This fact motivates the discrete-time formulation presented second. Although the discrete-time formulation also takes the form of a complementarity problem, it does not suffer from non-existence, and thus it is suitable for simulation. Numerical results are compared to the exact solution for a sphere initially sliding, then rolling, on a horizontal plane.
Dynamic Modeling of a Flexible Cantilever Beam: An Experimental Technique
Authors: Megahed S. M. , Nada A. A.
Published: June 2008

This paper describes an investigation of real time dynamic modeling method for a flexible cantilever beam, as an approximation of a robot flexible link, using experimental measurement techniques. The beam is equipped with a number of strain gauges to measure the corresponding nodal flexibilities and using them to obtain its real-time dynamic model. Two methods are proposed; the 1st method is based on approximating the beam deflection by a 4th order polynomial curve while the 2nd one is based on the solution of its Eulerbernoulli equation. The polynomial constants are obtained by real-time estimation using the readings of the strain gauges. These readings are used to estimate the beam temporal solution in the 2nd method. The error in the beam tip deflection is reduced to 0.01% by relocating the last strain gauge at 12.5% instead of 30% from its tip. Both methods show good agreement with the general beam theory and results.
Spatial Joint Constraints in Flexible Multibody Systems Using the Absolute Nodal Coordinate Formulation
Authors: Sugiyama Hiroyuki , Escalona Jose´ L. , Shabana Ahmed A.
Published: June 2008

This paper is concerned with the formulation and computer implementation of spatial joint constraints and generalized forces using the large deformation absolute nodal coordinate formulation. Unlike the floating frame of reference formulation that employs a mixed set of absolute reference and local elastic coordinates, in the absolute nodal coordinate formulation, global displacement and slope coordinates are used. The nonlinear kinematic constraint equations and generalized force expressions are expressed in terms of the absolute global displacements and slopes. In particular, a new formulation for the sliding joint between two very flexible bodies is developed. A contact parameter is introduced as an additional new variable in order to facilitate the formulation of this sliding joint. Numerical examples are presented in order to demonstrate the use of the formulations developed in the paper.
Dynamic Modeling of High-Speed Flexible Links
Authors: Liu Jinyang , Hong Jiazhen
Published: June 2008

In this paper, the dynamic modeling of high-speed flexible links is studied. By using a stretch variable, the foreshortening deformation is introduced to the longitudinal deformation of each link, therefore, the geometric stiffening effect is naturally taken into account. The equations of motion of flexible links are obtained based on the virtual work principal. Simulation of a high-speed double-link system shows the stiffening effect on large overall motions as well as deformation of the flexible multibody system. Furthermore, the applicability of the conventional modeling method without consideration of the stiffening effect is also discussed.
Multibody Dynamics and Vibration Analysis for Railcar Wheelset Design Studies
Authors: Schiehlen Werner , Claus Holger
Published: June 2008

This paper presents design studies and dynamic analyses of a railway passenger coach. The wheelset excitations are deterministic due to polygonalization generating noise in ICE passenger coaches and stochastic due to track irregularities. The strength of conventional wheelsets against vibrations due to polygonalized wheels is investigated. Radialelastic wheels reduce the unsprung mass and isolate the bogie frame and carbody from the medium and high frequency excitation caused by the wheel/rail interaction. A parameter optimization of such wheels leads to considerably reduced carbody vibrations. Stability tests are performed for various parameter sets of radialand lateralelastic wheels. The results show that designs with increased bending stiffness and improved parameters are feasible, and guarantee the stability of the wheelset motion as well as a noise reduction.
Three-Dimensional Multibody Tracked Vehicle Modeling and Simulation
Authors: Sandu Corina , Freeman Jeffrey S.
Published: June 2008

Off-road vehicles have broad areas of application (in agriculture, in the construction industry, in the transport industry, in the military, in the U.S. space programs, in the oil and gas industry). A large segment of the off-road vehicles is made up by the tracked vehicles. The purpose of this study is to develop and implement an independent vehicle model. The vehicle model is general, in the sense that it is not restricted to a specific vehicle; it can model vehicles with varying numbers of road wheels, or different suspension characteristics It can be used, together with a track model, to analyze several types of tracked vehicles. A recursive dynamics formulation approach is used to model the vehicle. All the computations are performed in relative coordinates. The kinematic formulation of the model is presented, as well as the dynamic analysis, including the external and the internal applied forces. Dynamic settling simulations of the vehicle model on several types of soil are presented. The vehicle model presented in this study serves as a support, to help testing and comparing different track models and track-terrain interaction formulations.
Neuro-Fuzzy Control of Smart Flexible Mechanisms
Authors: Smaili Ahmad , Mrad Fouad , Maamoun Hadi
Published: June 2008

This paper presents an analytical investigation in which a controller based on Adaptive Neuro-Fuzzy Inference System (ANFIS) is designed and implemented to control the vibrations of a flexible mechanism system with smart coupler link. The most dominant vibration mode of the mechanism is identified and the controller is then designed to reduce the effect of this mode on the response of the mechanism system. The proposed control algorithm is implemented on a mechanism system with a thin plate-type piezoceramic actuator bonded to the coupler link surface at the high strain location corresponding to the dominant mode. Simulation results showed the capability of the proposed ANFIS controller to reduce the coupler link mid point amplitudes by nearly 60%.
Multibody Dynamics of the 2 Sections Flexible Ladder Model Extending and Retracting Each Other
Authors: Fujita Katsuhisa , Koike Katsutoshi , Shiono Yasuhiro , Koseki Takuro
Published: June 2008

A ladder of the ladder truck with lift mechanism often generates a lot of vibrations at the time of the lift operation. The lift operation includes the extending and retracting motions, the ascending and descending motions, and the turning motion. In this paper, the simulation analysis of the dynamic behavior for the 2 sections flexible ladder which can extend and retract each other is described. We make the dynamic analytical model of the 2 sections flexible ladder using multibody dynamics though we have already reported the simulation analysis of the 2 sections ladder composed of a rigid and a flexible ones. A coupled equation of motion of the 2 sections flexible ladder is derived using the differential algebraic equation (DAE). Performing the numerical simulation studies taking the dimensions of the 2 sections flexible ladder model parameters, the physical meaning of the dynamic behavior at the time of extending and retracting motions between 2 ladder sections is discussed comparing with the former reported results for the 2 sections ladder composed of a rigid and a flexible ones. Moreover, the validity of our proposed simulation method is investigated comparing with the experimental results partially.
Recursive Method for the Dynamic Analysis of Open-Loop Flexible Multibody Systems
Authors: Hwang Yunn-Lin
Published: June 2008

The main objective of this paper is to develop a recursive method for the dynamic analysis of open-loop flexible multibody systems. The nonlinear generalized Newton-Euler equations are used for flexible bodies that undergo large translational and rotational displacements. These equations are formulated in terms of a set of time invariant scalars, vectors and matrices that depend on the spatial coordinates as well as the assumed displacement fields, and these time invariant quantities represent the dynamic coupling between the rigid body motion and elastic deformation. The method to solve for the equations of motion for open-loop systems consisting of interconnected rigid and flexible bodies is presented in this investigation. This method applies recursive method with the generalized Newton-Euler method for flexible bodies to obtain a large, loosely coupled system equations of motion. The solution techniques used to solve for the system equations of motion can be more efficiently implemented in the vector or digital computer systems. The algorithms presented in this investigation are illustrated by using cylindrical joints that can be easily extended to revolute, slider and rigid joints. The basic recursive formulations developed in this paper are demonstrated by two numerical examples.
Comparison of Fractional and Integer Order Control of an Hexapod Robot
Authors: Silva Manuel F. , Machado J. A. Tenreiro , Lopes Anto´nio M.
Published: June 2008

This paper studies the dynamics of foot-ground interaction and the performance of integer and fractional order controllers in multi-legged locomotion systems. For that objective the robot prescribed motion is characterized in terms of several locomotion variables. Moreover, to compare the system performance, we formulate six performance measures of the walking robot namely, the mean absolute power, the mean power dispersion, the mean power lost in the joint actuators, the mean force of the interface body-legs per walking distance and the mean square error of the hip and foot trajectories. A set of model-based experiments reveals the influence of the different controller implementations in the proposed indices.
Preshaping Command Inputs for 2nd Generation CRONE Control: Application on an Instrumented DC Motor Bench
Authors: Melchior Pierre , Poty Alexandre , Orsoni Bruno , Oustaloup Alain
Published: June 2008

Shaping command input or preshaping is used for reducing system oscillation in motion control. Desired systems inputs are altered so that the system finishes the requested move without residual oscillation. This technique, developed by N.C. Singer and W.P. Seering, is used for example in the aerospace field, in particular in flexible structure control. This paper presents the study of ZV shaper for explicit fractional derivative systems (generalized derivative systems). A robustness study of ZV shaper is then presented and applied to improve second generation CRONE control response time. Results in simulation and on a DC motor bench are given.
Fractional Order Dynamics in the Trajectory Planning of Redundant and Hyper-Redundant Manipulators
Authors: Duarte Fernando B. M. , Machado J. A. Tenreiro
Published: June 2008

Redundant manipulators have some advantages when compared with classical arms because they allow the trajectory optimization, both on the free space and on the presence of obstacles, and the resolution of singularities. For this type of arms the proposed kinematic control algorithms adopt generalized inverse matrices but, in general, the corresponding trajectory planning schemes show important limitations. Motivated by these problems this paper studies the pseudoinverse-based trajectory planning algorithms, using the theory of fractional calculus.
Fractional Calculus Model of the Semilunar Heart Valve Vibrations
Authors: El-Shahed Moustafa
Published: June 2008

The objective of this paper is to solve the equation of motion of semilunar heart valve vibrations. The vibrations of the closed semilunar valves were modeled with a Caputo hactional derivative of order α. With the help of Laplace transformation, closed-form solution is obtained for the equation of motion in terms of Mittag-Leffler function. An alternative Method for Semi-differential equation, when α = 0.5, is examined using MATHEMATICA. The simplicity of these solutions makes them ideal for testing the accuracy of numerical methods. This solution can be of some interest for a better fit of experimental data.
Averaging for Oscillations With Light Fractional Order Damping
Authors: Wahi Pankaj , Chatterjee Anindya
Published: June 2008

We apply the method of averaging to study small, possibly nonlinear perturbations to a harmonic oscillator, particularly including fractional derivative damping. The averaging procedure here corresponds to the general or aperiodic case, and requires evaluation of Fresnel type integrals. We also describe a conceptually simple numerical scheme which can be used to verify the accuracy of the averaged equations. Systems studied are a linear, fractionally damped oscillator, a van der Pol type oscillator with a limit cycle, and a weakly nonlinear system forced sinusoidally near resonance. The averaged dynamics closely matches the full numerical solution in each case. It is discussed, in light of the averaged equations, why fractional damping is not equivalent to some simple effective traditional damping.
H2 Norm of Fractional Differential Systems
Authors: Malti Rachid , Aoun Mohamed , Cois Olivier , Oustaloup Alain , Levron Franc¸ois
Published: June 2008

The H2 norm, or the impulse response energy, of fractional differential explicit systems is computed, and complements Astro¨m’s algebraic formula for classical rational systems.
A New Discretization Method for Fractional Order Differentiators via Continued Fraction Expansion
Authors: Chen YangQuan , Vinagre Blas M. , Podlubny Igor
Published: June 2008

In this contribution, to discretize the fractional order differentiators in continuous time domain, a new IIR (infinite impulse response) type digital fractional order differentiator (DFOD) is proposed by using a new family of first order digital differentiators expressed in the second order IIR filter form. The integer first order digital differentiators are obtained by the stable inversion of the weighted sum of Simpson integration rule and the trapezoidal integration rule. The distinguishing point of the proposed DFOD lies in an additional tuning knob to compromise the high frequency approximation accuracy.
The Fractional Fourier Transform and Its Applications to Image Representation and Beamforming
Authors: Yetik I. S¸amil , Kutay M. Alper , Ozaktas Haldun M.
Published: June 2008

The ath order fractional Fourier transform operator is the ath power of the ordinary Fourier transform operator. We provide a brief introduction to the fractional Fourier transform, discuss some of its more important properties, and concentrate on its applications to image representation and compression, and beamforming. We show that improved performance can be obtained by employing the fractional Fourier transform instead of the ordinary Fourier transform in these applications.
Initial Condition Problems of Fractional Viscoelastic Equations
Authors: Fukunaga Masataka , Shimizu Nobuyuki
Published: June 2008

The 2nd order differential equation with fractional derivatives describing dynamic behavior of a single-degree-of-freedom viscoelastic oscillator, referred to as fractional viscoelastic equation (FVE), is considered. Some types of viscoelastic damped mechanical systems may be described by FVE. The differential equation with fractional derivatives is often called the fractional differential equation (FDE). FDE can be solved for zero initial values, but it can not generally be solved for non-zero initial values. How to solve the problem is one of the key issues in this field. This is called “Initial condition (value) problems” of FDE. In this paper, initial condition problems of FVE are solved by making use of the prehistory functions of unknowns which are specified before the initial instance (referred to as the initial functions) starts. Introduction of initial functions into FDE reflects the physical state in giving the initial values. In this paper, several types of initial function are used to solve unique solutions for a type of FVE (referred to as FVE-I). The solutions of FVE-I are obtained by means of both numerical and analytical methods. Implication of the solutions to viscoelastic material will also be discussed.
Application of Fractional Derivatives to Modeling the Quasi-Static Response of Polyurethane Foam
Authors: Deng Rong , Davies Patricia , Bajaj Anil K.
Published: June 2008

A fractional derivative model of dissipative effects is combined with a nonlinear elastic model to model the response of polyurethane foam in quasi-static compression tests. A system identification method is developed based on a separation of the elastic and viscoelastic parts of the response, which is possible because of symmetries in the imposed deformation timehistory. Simulations are used to evaluate the proposed identification method when noise is present in the response. The system identification technique is also applied with some success to experimental data taken from several compression experiments on two types of polyurethane foam blocks.
Stability Investigation of a Two-Link 3DOF Rotational Pendulum
Authors: Horvath Roland , Flowers George T. , Overfelt Ruel A.
Published: June 2008

A numerical and experimental investigation of the dynamic behavior of a two-link, 3 degree of freedom (DOF) rotational pendulum is presented. This work extends previous studies of two-link 2DOF rotational pendulum systems in which the links were connected to each other and to the main driver by 1 DOF pinned joints. In the present study, an additional degree of freedom is added in which the first link is connected to the main driver shaft by a 2DOF cardanic joint. The two links are still connected by a pinned joint. It is observed that such systems have inherent zones of instability. A stable zone and an unstable zone, separated by a specific critical angular velocity, were identified. If the rotational speed is under this critical value, the mechanical system shows asymptotic stability. For rotational speeds above this value, the system shows instability around a static bifurcation.
A New Modeling Technique and Control System Design of a Flexible Rotor Supported by Active Magnetic Bearings for Motion and Vibration Control
Authors: Ichihara Mitsuhiro , Shida Hideo , Sagane Takahito , Tajima Hiroshi , Saigou Muneharu , Seto Kazuto
Published: June 2008

This paper proposed a new modeling technique and control system design of a flexible rotor using active magnetic bearings (AMB) for motion and vibration control. The purpose of the research was to pass through a critical speed and achieve high-speed rotation. To achieve this, it is necessary to control both vibration and motion. Even though reduced order physical model [1] that we used before is available technique in expressing vibration, this technique cannot express motion. Thus we propose an extended reduced order physical model [2] that can simultaneously express motion and vibration. Further, by using the model we apply the design of a new controller that combined proportional integral derivative (PID) with linear quadratic (LQ) control to a flexible rotor. The procedure we propose is verified by simulations as being effective for a flexible rotor.
Experimental Study on Vibration Properties and Control of Squeeze Mode MR Fluid Damper-Flexible Rotor System
Authors: Wang Jianxiao , Meng Guang , Hahn Eric
Published: June 2008

A squeeze mode MR fluid damper used for rotor vibration control is designed and manufactured, and the unbalance response properties and control method of a single-disk flexible rotor system supported by the damper are studied experimentally. It is found from the study that the magnetic pull force can decrease both the first critical speed and the critical amplitude; the oil film reaction force can decrease the amplitude at the undamped critical speeds, but increase the amplitude in a speed range between two undamped critical speeds. For the rotor system supported by a journal bearing and an MR fluid damper, it is possible to appear oil film instability as the increasing of the control current. The damper may have the best effect to make the vibration minimize within the range of all working speed by using on-off control method. The research show that the squeeze mode MR fluid damper has the advantages such as simple structure, clearly effectiveness, quick response, etc., and this kind of damper has a promising potential future in vibration control of flexible rotor systems.
Nonlinear Free Vibration of a Rotor Shaft System With Viscoelastically Supported Bearings
Authors: Shabaneh N. , Zu J. W.
Published: June 2008

This paper investigates the dynamic analysis of a single-rotor shaft system with nonlinear elastic bearings at the ends mounted on viscoelastic suspension. A Timoshenko shaft model is utilized to incorporate the flexibility of the shaft; the rotor is considered to be rigid and located at the mid-span of the shaft. A nonlinear bearing pedestal model is assumed which has a cubic nonlinear spring and linear damping characteristics. The viscoelastic supports are modeled using the Kelvin-Voigt model. Free vibration is investigated based on the direct multiple scales method of one-to-one frequency-to-amplitude relationship using third order perturbation expansion. The results of the nonlinear analysis show that a limiting value of the internal damping coefficient of the shaft exists where the trend of the frequency-response curve switches.
An Efficient Algorithm for Blade Loss Simulations Using a High Fidelity Ball Bearing and Damper Model
Authors: Sun Guangyoung , Kaushik Nikhil , Palazzolo Alan B. , Provenza Andrew J. , Lawrence Charles , Carney Kelly
Published: June 2008

This paper presents a novel approach for blade loss simulation of an aircraft gas turbine rotor mounted on rolling element bearings with squeeze film dampers. The modal truncation augmentation (MTA) method provides an efficient tool for modeling this large order system with localized nonlinearities in the ball bearings. The gas turbine engine, which is composed of the power turbine and gas generator rotors, is modeled with 38 lumped masses. A nonlinear angular contact bearing model is employed, which has ball and race degrees of freedom and uses a modified Hertzian contact force between the races and balls. This combines a dry contact force and an equivalent viscous damping force. Prediction of the maximum contact load and the corresponding stress on an elliptical contact area between the races and balls is made during the blade loss simulations. A finite-element based squeeze film damper (SFD), which determines the pressure profile of oil film and calculates damper forces for any type of whirl orbit, is developed, verified, and utilized in the simulations. The new approach is shown to provide efficient and accurate predictions of whirl amplitudes, maximum contact load and stress in the bearings, transmissibility, the maximum and minimum damper pressures and amount of unbalance force for incipient oil film cavitation.
Stress and Strain Tensors in Granular Medium Application to Masonry Structures
Authors: Chetouane Brahim , Bohatier Claude , Dubois Fre´de´ric , Vinches Marc
Published: June 2008

The general framework of the present paper is the modeling of stone work, subject to dynamic loads. In this study, a masonry structure is considered as a collection of rigid blocks, linked together by Coulomb’s type friction laws. We define on such a granular medium, a stress tensor and a macroscopic strain tensor, on an elementary cell. The definition of these tensors allows us to get, locally, an average information on this granular medium.
Constraint Stabilization for Time-Stepping Approaches for Rigid Multibody Dynamics With Joints, Contact, and Friction
Authors: Anitescu Mihai , Miller Andrew , Hart Gary D.
Published: June 2008

We present a method for achieving geometrical constraint stabilization for a linear-complementarity-based time-stepping scheme for rigid multibody dynamics with joints, contact, and friction. The method requires the solution of only one linear complementarity problem per step. The method depends on an adjustable parameter γ, but the constraint stabilization effect is shown to hold for any γ ∈ (0,1]. Several examples are used to demonstrate the constraint stabilization effect.
Reduction of Structural Dynamics Models Having Nonlinear Damping
Authors: Kim Jihwan , Burton T. D.
Published: June 2008

The purpose of this work has been to explore the suitability of significantly reduced order structural dynamics models for simulation of nonlinear response of structures. In this paper oscillator chains having nonlinear damping and linear stiffness are considered. Both non-smooth and smooth nonlinear damping will be discussed for the case of isolated nonlinear damping and for the case of many equal nonlinear damping elements distributed throughout the structure. Most of the results to be shown will address the accuracy with which significantly reduced order models (e.g., 5, 10 and 20 DOF reduced models of a 1,000 DOF system) simulate the free oscillation decay caused by the nonlinear damping. The model reduction employed utilizes an “exact-for-the-linear-case” linear state transformation to eliminate slave coordinates, yielding a reduced model containing only specified master degrees of freedom. The ultimate objective of this work is to develop efficient, sufficiently accurate models that can be integrated numerically to determine response of very large nonlinear structures in situations for which numerical integration over reasonably long times is needed. The results obtained here are promising: even drastically reduced models provide accurate simulation of the oscillation decay for both smooth and non-smooth nonlinearity.
Joint Parameters Identification of a Structure With Large Number of Discrete Joints
Authors: Wang J. H. , Chuang S. C.
Published: June 2008

The joint parameters of a structure with a large number of discrete joints generally are very difficult to identify accurately. The difficulty is due to the fact that the dynamic behavior of a structure becomes more complex with more number of joints. A new identification method which uses the measured frequency response functions (FRFs) to identify the joint parameters is proposed in this work to overcome this difficulty. The new method uses an error function to select different best data to identify different joints so that the accuracy of the identification can be improved. The accuracy of the new method and other two traditional methods is compared in this work. The results show that the accuracy of the proposed new method is far better than other two previous methods. The proposed new method has special advantage when (1) the number of joints is large, (2) the orders of magnitude of the joint parameters are different significantly.
Component Mode Synthesis Using Nonlinear Normal Modes
Authors: Apiwattanalunggarn Polarit , Shaw Steven W. , Pierre Christophe
Published: June 2008

This paper describes a methodology for developing reduced-order dynamic models of nonlinear structural systems that are composed of an assembly of component structures. The approach is a nonlinear extension of the fixed-interface component mode synthesis technique developed for linear structures by Hurty and modified by Craig and Bampton. Specifically, the case of nonlinear substructures is handled by using fixed-interface nonlinear normal modes. These normal modes are constructed for the various substructures using an invariant manifold approach, and are then coupled through the traditional linear constraint modes (i.e., the static deformation shapes produced by unit interface motions). A simple system is used to demonstrate the proof of concept and show the effectiveness of the proposed procedure. Simulations are performed to show that the reduced-order model obtained from the proposed procedure outperforms the reduced-order model obtained from the classical fixed-interface linear component mode synthesis approach. Moreover, the proposed method is readily applicable to large-scale nonlinear structural systems.
System Identification of Mistuned Bladed Disks From Traveling Wave Response Measurements
Authors: Feiner D. M. , Griffin J. H. , Jones K. W. , Kenyon J. A. , Mehmed O. , Kurkov A. P.
Published: June 2008

A new approach to modal analysis is presented that allows the modes and natural frequencies of a mistuned bladed disk to be determined from its response to a traveling wave excitation. The resulting modes and natural frequencies are then used as input to a system identification method to determine the bladed disk’s mistuning while it is rotating. This capability is useful since it provides a basis for determining blade frequencies under engine operational conditions and could help monitor the health of the engine.
Reliability-Based Optimal Design of Fluid Filled Tanks Under Seismic Excitation
Authors: Theodosiou C. , Aichouh P. , Natsiavas S. , Papadimitriou C.
Published: June 2008

This work integrates developments in simplified dynamic modeling of unanchored fluid-filled tanks, stochastic modeling of earthquake loading time histories, probabilistic structural analysis tools, cost analyses, and multi-criteria optimal design formulations for the design optimization of unanchored fluid-filled cylindrical tanks operating in an uncertain seismic environment. An appropriate simplified mechanical model is developed which includes effects from the sloshing at the liquid free surface, the soil flexibility and the separation of the base plate of the tank from its foundation, which occurs during strong ground motion. A class of stochastic processes with frequency content and time-varying intensity characteristics determined by seismological parameters is used to model the earthquake loading time history. The reliability of the cylindrical tank against failure of the shell structure is computed using latest developments in efficient Monte Carlo simulation methods. A multi-criteria design optimization methodology is then used to obtain the optimal design characteristics of the tank system that meet cost and reliability constrains. Issues related to reliability estimation and optimization are addressed. The methodology is useful for optimally designing fluid-filled structures that operate in a seismic environment to withstand earthquakes with minimal social and economical losses during the lifetime of the structure.