bluuebunny/crossref_metadata_2025 huggingface dataset:
The Angular Distribution of Diffuse Sky Radiance: An Assessment of the Effects of Haze
Authors: Rosen M. A.
Published: June 2008

The effects of haze on the angular distribution of the diffuse sky radiance are investigated by examining and comparing data for individual clear skies with and without haze, and for other selected sky types, and by modeling and comparing data for such skies. It is found that haze appears to affect the radiance distributions only for clear, partly cloudy, and lightly overcast skies, and that for clear skies, increasing haze increases the absolute sky radiance values. In addition, the radiance distributions for clear skies with haze are found to exhibit characteristics generally similar to those for the nonopaque overcast skies. However, it is also found that the normalized radiance distributions for clear skies with haze, which generally provide clearer illustrations of distribution shape than the absolute radiance distributions, exhibit slightly less intense circumsolar and horizon brightening components than do the normalized distributions for clear skies without haze. In general, a systematic, but complex, relationship appears to exist between haze and the distribution of the diffuse sky radiance. The results may prove useful to several disciplines, including the design of solar technologies.
Velocity Profiles of Liquid Flow Through Circular Tubes and How They Affect Flow Measurement
Authors: Goswami D. Yogi
Published: June 2008

This paper analyzes velocity profiles for flow through circular tubes in laminar, turbulent, and transition region flows and how they affect measurement by flow-meters. Experimental measurements of velocity profiles across the cross-section of straight circular tubes were made using laser doppler velocimetry. In addition, flow visualization was done using the hydrogen bubble technique. Velocity profiles in the laminar and the turbulent flow are quite predictable which allow the determination of meter factors for accurate flow measurement. However, the profiles can not be predicted at all in the transition region. Therefore, for the accuracy of the flowmeter, it must be ensured that the flow is completely in the laminar regime or completely in the turbulent regime. In the laminar flow a bend, even at a large distance, affects the meter factor. The paper also discusses some strategies to restructure the flow to avoid the transition region.
A Laser-Based Technique for Particle Sizing to Study Two-Phase Expansion in Turbines
Authors: Goswami D. Yogi , Hingorani S. , Mines Greg
Published: June 2008

Efficiency of binary power cycles can be improved by expanding the hydrocarbon working fluids through two-phase region in a turbine and exiting at saturated or superheated condition. This improvement can be achieved if there is no condensation during the expansion or if there is condensation, the droplet size is extremely small. In order to verify this, a particle sizing technique for extremely small particles in flow is needed. In this study, a laser-based technique is developed by which it is possible to detect particles as small at ten angstroms in size. The basis of the technique is that particles of size less than one third of the wavelength of the incident radiation will scatter according to Rayleigh scattering theory. According to this theory, the intensity of the scattered light will be the same in the forward as well as in the backward directions. Therefore, measurement of the scattered intensity at two or three different angles will confirm the presence of Rayleigh scattering. The size of the particles can, then, be calculated from the measured scattered intensity according to the Rayleigh scattering equation.
Nonminimum-Phase Phenomenon of PEM Fuel Cell Membrane Humidifiers
Authors: Chen Dongmei , Peng Huei
Published: June 2008

A membrane-based humidifier that uses cooling water of a fuel cell system to humidify the inlet air is modeled and analyzed in this paper. This four-state lumped model is simple and yet captures the humidification behavior accurately. A peculiar characteristic of this system is the fact that it exhibits nonminimum-phase (NMP) behavior. The reason the NMP behavior exists and the effect of system parameters on the location of the NMP zero are analyzed. A proportional control algorithm is proposed to reject the effect of system disturbances, and a feed-forward algorithm is developed to ensure proper humidifier operation under air flow rate changes. Because the NMP zero exists in the disturbance-to-output loop, the proposed algorithm was found to successfully eliminate the undershoot phenomena associated with the NMP zero. However, the disturbance-to-output loop is coupled with input-to-output loop, and the NMP zero could affect the feedback control design.
Robust Control of a Parallel- Kinematic Nanopositioner
Authors: Dong Jingyan , Salapaka Srinivasa M. , Ferreira Placid M.
Published: June 2008

This paper presents the design, model identification, and control of a parallel-kinematic XYZ nanopositioning stage for general nanomanipulation and nanomanufacturing applications. The stage has a low degree-of-freedom monolithic parallel-kinematic mechanism featuring single-axis flexure hinges. The stage is driven by piezoelectric actuators, and its displacement is detected by capacitance gauges. The control loop is closed at the end effector instead of at each joint, so as to avoid calibration difficulties and guarantee high positioning accuracy. This design has strongly coupled dynamics with each actuator input producing in multiaxis motions. The nanopositioner is modeled as a multiple input and multiple output (MIMO) system, where the control design forms an important constituent in view of the strongly coupled dynamics. The dynamics that model the MIMO plant is identified by frequency domain and time-domain identification methods. The control design based on modern robust control theory that gives a high bandwidth closed loop nanopositioning system, which is robust to physical model uncertainties arising from flexure-based mechanisms, is presented. The bandwidth, resolution, and repeatability are characterized experimentally, which demonstrate the effectiveness of the robust control approach.
An Optimal Control Approach to Minimizing Entropy Generation in an Adiabatic Internal Combustion Engine
Authors: Teh Kwee-Yan , Edwards Christopher F.
Published: June 2008

Entropy generation due to combustion destroys as much as a third of the theoretical maximum work that could have been extracted from the fuel supplied to an engine. Yet, there is no fundamental study in the literature that addresses the question of how this quantity can be minimized so as to improve combustion engine efficiency. This paper fills the gap by establishing the minimum entropy generated in an adiabatic, homogeneous combustion piston engine. The minimization problem is cast as a dynamical system optimal control problem, with the piston velocity profile serving as the control input function. The closed-form switching condition for the optimal bang-bang control is determined based on Pontryagin’s maximum principle. The switched control is shown to be a function of the pressure difference between the instantaneous thermodynamic state of the system and its corresponding equilibrium thermodynamic state at the same internal energy and volume. At optimality, the entropy difference between these two thermodynamic states is shown to be a Lyapunov function. In thermodynamic terms, the optimal solution reduces to a strategy of equilibrium entropy minimization. This result is independent of the underlying combustion mechanism. It precludes the possibility of matching the piston motion in some sophisticated fashion to the nonlinear combustion kinetics in order to improve the engine efficiency. For illustration, a series of numerical examples are presented that compare the optimal bang-bang solution with the nonoptimal conventional solution based on slider-crank piston motion. Based on the solution for minimum entropy generation, a bound for the maximum expansion work that the piston engine is capable of producing is also deduced.
Memoryless Adaptive Controller Design for Uncertain Polynomial Systems With Multiple Time Delays
Authors: Hua Chang-Chun , Wang Qing-Guo , Shi Peng , Guan Xin-Ping
Published: June 2008

The stabilization problem is investigated for a class of uncertain systems with multiple time-varying delays. The considered system includes the uncertain nonlinear time delay functions, whose bounds are in the form of polynomial-type functions with unknown coefficients. The system is decomposed into two subsystems based on the input matrix. For the first subsystem, a time delay dependent linear virtual control input is constructed. Then, a memoryless state feedback controller is designed based on backstepping method. By employing new Lyapunov–Krasovskii functional, we show that the closed-loop system is exponentially stable. Finally, simulations are conducted to verify the effectiveness of the proposed method.
Contact Analysis of the Rotor in a Variable Capacitance Micro-Motor
Authors: Zhang Wen-Ming , Meng Guang
Published: June 2008

The most widely known nonlinear phenomena in Micro-electro-mechanical systems (MEMS) are probably the contact instabilities. Contact problem is an important topic in the research of micro-motors. While the micro-motor is in operation, the rotor is intended to be in electrical contact with the ground plane, and the rotor and bearing hub form a pair of contact bodies. In the paper, a mathematic model is proposed to describe the contact process and two simplified contact finite element models of the rotor, bearing and ground plane are presented to simulate the contact. The effects on the contact stress, strain and pressure are analyzed in micro-scale. The rotor-to-bearing-hub and the hemispherical-bushing-on-ground-plane configurations finite element models (FEM) are established and the implementation of the contact problem is introduced to provide the numerical solutions acted as a guide to solution of contact problems in a variable capacitance micromotor. The numerical results of the contact stress, strain and pressure and the effects of the coefficient of friction and the surface roughness of the contact pairs on contact characteristics are studied and discussed in detail. It is indicated that the nonlinear effects should not be ignored and these results must be evaluated on a relative scale to compare different design options.
2:1:1 Resonance in the Quasiperiodic Mathieu Equation
Authors: Rand Richard , Morrison Tina
Published: June 2008

We present a small ε perturbation analysis of the quasiperiodic Mathieu equation: x¨+(δ+εcost+εcosωt)x=0 in the neighborhood of the point δ = 0.25 and ω = 0.5. We use multiple scales including terms of O(ε2) with three time scales. We obtain an asymptotic expansion for an associated instability region. Comparison with numerical integration shows good agreement for ε = 0.1. Then we use the algebraic form of the perturbation solution to approximate scaling factors which are conjectured to determine the size of instability regions as we go from one resonance to another in the δ-ω parameter plane.
Dynamics of Three Coupled Van der Pol Oscillators With Application to Circadian Rhythms
Authors: Rompala Kevin , Rand Richard , Howland Howard
Published: June 2008

In this work we study a system of three van der Pol oscillators, x, y and w, coupled as follows: x¨−ε(1−x2)x˙+x=εμ(w−x)y¨−ε(1−y2)y˙+y=εμ(w−y)w¨−ε(1−w2)w˙+p2w=εμ(x−w)+εμ(y−w) Here the x and y oscillators are identical, and are not directly coupled to each other, but rather are coupled via the w oscillator. We investigate the existence of the in-phase mode x = y for ε ≪ 1. To this end we use the two variable expansion perturbation method (also known as multiple scales) to obtain a slow flow, which we then analyze using the software products MACSYMA and AUTO. Our motivation for studying this system comes from the presence of circadian rhythms in the chemistry of the eyes. We model the circadian oscillator in each eye as a van der Pol oscillator (x and y). Although there is no direct connection between the two eyes, they are both connected to the brain, especially to the pineal gland, which is here represented by a third van der Pol oscillator (w).
Galloping Instabilities of Geometrically Nonlinear Nonshallow Cables Under Steady Wind Flows
Authors: Lacarbonara Walter , Paolone Achille , Vestroni Fabrizio
Published: June 2008

A geometrically exact mechanical model of nonshallow elastic cables subjected to aerodynamic forces generated by the mean wind velocity field is discussed. The linearization around the catenary configuration leads to the prediction of the critical galloping velocities and the critical modes accomplished employing the Routh-Hurwitz theorem. Then, the post-critical responses, past the pitchfork bifurcation occurring at the galloping critical condition, are constructed via an asymptotic treatment of the equations of motion. Bifurcation diagrams of the post-critical vibration amplitude for various sag-to-span ratios are computed to investigate the dependence of the post-critical galloping regime on the prestress level in the cable.
Fuzzy Estimation of Vehicle Speed
Authors: Oh Kyeung Heub , Hwang Jin Kwon , Song Chul Ki
Published: June 2008

The absolute longitudinal speed of a vehicle is estimated by using data from an accelerometer of the vehicle and wheel speed sensors of a standard 50-tooth antilock braking system. An intuitive solution to this problem is, “When wheel slip is low, calculate the vehicle velocity from the wheel speeds; when wheel slip is high, calculate the vehicle speed by integrating signal of the accelerometer.” The speed estimator weighted with fuzzy logic is introduced to implement the above concept, which is formulated as an estimation method. And the method is improved through experiments by how to calculate speed from acceleration signal and slip ratios. It is verified experimentally to usefulness o estimation speed of a vehicle. And the experimental result shows that the estimated vehicle longitudinal speed has only a 6 % worst-case error during a hard braking maneuver lasting a few seconds.
Discrete Fourier Series Approximation to Periodic Solutions of Autonomous Delay Differential Equations
Authors: Gilsinn David E.
Published: June 2008

This paper describes the algorithmic details involved in developing high-order Fourier series representations for periodic solutions to autonomous delay differential equations. Although the final approximate Fourier coefficients are computed by way of a nonlinear minimization algorithm, the steps to set up the objective function are shown to involve a sequence of matrix-vector operations. By proper coordination, these operations can be made very efficient so that high-order approximations can be obtained easily. An example of the calculations is shown for a Van der Pol equation with unit delay.
A Hybrid Multibody Model for Aircraft Occupant/Seat Cushion Crashworthiness Investigation
Authors: Beheshti Hamid Kh. , Lankarani Hamid M. , Gopalan Sivaraman
Published: June 2008

Seat cushion is in the primary load path between the seat and the occupant, and the potential for injuries to an occupant in an accident highly depends on it. The seat cushion is able to dissipate the kinetic energy due to impact in a controlled manner. Wide varieties of energy absorbing materials are used in aircraft interiors for occupant safety and ergonomic purposes. Flexible polyurethane foams are one among those used in seat cushions. Although comfort and aesthetics play an important role in the seat cushion design, safety is among the top criteria. Studies on seat cushions have demonstrated that the seat cushions generally amplify the lumbar/pelvis transmitted load to the occupant, making the seat cushion design further complicated for crashworthy design. The certification of seat cushion requires that their performance be demonstrated by dynamic full scale sled testing. Due to the high costs involved in dynamic testing, a mathematical hybrid multi-body model is developed in this study to simulate the dynamic responses of a bare iron seat, the seat cushion and the occupant represented by crash test dummy. The model is utilized to predict the lumbar load sustained when subjected to the FAR Part 23 and 25 dynamic test conditions for transport and general aviation category aircraft. The model is also used to determine the relative displacement and velocity of occupant against the seat pan. The results from the dynamic model are validated with full-scale sled tests performed at the National Institute for Aviation Research (NIAR), and hence can be utilized as a design tool for the selection of proper seat cushions.
Application of Parallel Computing to Joint-Disconnected Multibody Systems
Authors: Critchley James , McCullough Michael
Published: June 2008

In some areas of application, large multibody systems are encountered which are not completely coupled by kinematic constraints (joints). For these “joint-disconnected” systems, the generalized mass matrix is block diagonal and the coordinate accelerations associated with each block may be solved with independent dynamic inversions. In the absence of a complex (fully coupled) mass matrix, coupling through interaction forces becomes the dominant issue in parallel multibody solutions. An implementation which addresses these issues is described and evaluated on two current parallel platforms. The results demonstrate that inexpensive parallel resources can significantly improve the execution time.
The Different Effects of Damping on Dynamic Instability
Authors: Chiroiu Veturia , Donescu S¸tefania , Munteanu Ligia
Published: June 2008

In this paper we analyze certain mechanical systems, and the effect of damping on their stability. We focus on a category of systems which admit a strange behavior, such as the gyroscopic pendulum: when modeled as systems without damping they are stable and possess steady motions, but when small damping is introduced, the steady motions become randomly and unstable. The Meijaard stationary sliding model and the strength of damping concept are also discussed.
Modal Reduction of Mathematical Models of Biological Molecules
Authors: Li Aiqin , Dowell Earl H.
Published: June 2008

This paper reports a detailed study of modal reduction based on either linear normal mode(LNM) analysis or proper orthogonal decomposition(POD) for modeling a single α-D glucopyranose monomer as well as a chain of monomers. Also a modal reduction method combining POD and component modal synthesis(CMS) is developed. The accuracy and efficiency of these methods are reported. The focus of this study is to determine to what extent these methods can reduce the time and cost of molecular modeling and simultaneously provide the required accuracy. It has been demonstrated that a linear reduced order model(ROM) is valid for small amplitude excitation and low frequency excitation. It is found that a nonlinear ROM based on POD modes provides a good approximation even for large excitation while the nonlinear ROM using linear eigenmodes as the basis vectors is less effective for modeling molecules with a strong nonlinearity. The ROM based on CMS using POD modes for each component also gives a good approximation. With the reduction in the dimension of the system using these methods the computational time and cost can be reduced significantly.
A Longitudinal Force Model for Multibody Railroad Vehicle System Applications
Authors: Meng Quan , Heineman Jason R. , Shabana Ahmed A.
Published: June 2008

In this paper, a model is developed to analyze the longitudinal forces of interaction between the vehicles within a train consist. The track geometry is described in a preprocessor in terms of an arc length parameter. A single degree of freedom vehicle model is developed, in which the nonlinear equation of motion of the vehicle is expressed in terms of the track arc length using a velocity transformation. The velocity transformation matrix is obtained by expressing the Cartesian and angular velocities in terms of the time derivative of the arc length. Models are developed for representing; braking forces from a typical air brake system, coupler reactions from draft gear or end-of-car cushioning devices, and the rolling resistance acting on each vehicle. An example of a 10-car train is used to demonstrate the use of the formulations presented in this paper. Different simulation scenarios, including varying track configurations and brake failure, are presented.
Spatial Finite Element Formulation for the Pantograph/Catenary Systems
Authors: Seo Jong-Hwi , Sugiyama Hiroyuki , Shabana Ahmed A.
Published: June 2008

This paper describes a three-dimensional large deformation finite element formulation for the analysis of the multibody pantograph/catenary systems. The large deformation of the catenary is modeled using the three-dimensional finite element absolute nodal coordinate formulation. A non-generalized arc-length parameter is introduced in order to be able to formulate the joint between the catenary and pan-head and to accurately predict the location of the contact point. The resulting system of differential and algebraic equations formulated in terms of reference coordinates, finite element absolute nodal coordinates, and non-generalized arc-length and contact surface parameters are solved using computational multibody system algorithms. A method is also proposed to deal with the problem of the loss of contact between the pan-head and the catenary cable.
Modeling of Impact Dynamics of a Tennis Ball With a Flat Surface
Authors: Mohsin Jafri Syed Muhammad , Vance John M.
Published: June 2008

A model of impact of a tennis ball with a flat surface is developed based on a planar, two-mass, linear, four degree of freedom vibration system idealization. The impact is assumed to be incident on a flat surface with friction. The incident parameters of the ball include the centre of mass translational velocity, angle of impact with the surface and the incident angular spin of the ball. The linear, piecemeal vibration model predicts the corresponding rebound parameters of the tennis ball. The model also predicts the duration of contact of the tennis ball with the flat surface, the transition of motion of the tennis ball during contact with the ground from sliding to rolling contact, and the resulting contact forces developed between the tennis ball and the flat surface. The model is computationally efficient because the governing differential equations of motion are linear and their standard solutions can be easily implemented on a personal computer. Predictions of the rebound parameters from the model are compared with experimental findings on tennis balls which are incident on a flat surface with various angles, velocities and angular spins (zero spin, topspin and backspin). For selected parameters of the two-mass model, the comparisons show excellent agreement between the model and the measurements.
Multibody Dynamics and Competitiveness on the Company
Authors: Imanishi Etsujiro
Published: June 2008

This paper presents how the multibody dynamics is utilized in the company. In recent years, the advance evaluations considering the dynamics of the products become to be the mainstream on the design state in new product development. Moreover, the multibody dynamics is utilized to develop the advanced technology of the new products. As it becomes to be possible that the dynamics of the products is examined even in the design stage at the good accuracy by the progress of the multibody dynamics, the essential solutions and the quantitative evaluations can be carried out in the development of the new products. In the development of the completely new concept machine, the multibody dynamics is necessary to carry out the system optimization of the machine. In this paper, the activities using the multibody dynamics are introduced through the cases of the evaluation on the disorder winding of the wire rope in the tower crane, and the evaluation of the power consumption in the hydraulic excavator.
Efficient Placement of Strain Sensors of Plate Dynamics Based on Some Optimization Criteria
Authors: Di´az Iva´n Mun˜oz , Gonza´lez Emiliano Pereira , Lo´pez Cela Juan Jose´ , Feliu Batlle Vicente
Published: June 2008

This work presents two criteria for the optimal positioning of strain sensors on a cantilever thin plate, which has bending and torsional modes. The aim is to find an efficient placement of strain sensors in order to maximize the observability of the first N modes of vibration. To this end, we have developed two positioning criteria based on the von Mises equivalent strain, which is a unique representative value of a three-dimensional strain state. The sensors should be placed at points where this equivalent strain presents significant values for the dynamic plate behavior defined by the first N modes. Although these criteria are general and can be applied to any strain sensor, we intend to use fiber grating sensors as strain gauges taking advantage of their inherent characteristics in comparison with other sensors.
Visualizing Coherent and Fractal Structures in Numerical Experiments on Chaotic Advection in Fluids
Authors: Budyansky M. V. , Prants S. V.
Published: June 2008

We investigate typical mixing and fractal properties of chaotic scattering of passive particles in open hydrodynamic flows taking as an example a model two-dimensional incompressible flow composed of a fixed point vortex and a background current with a periodic component, the model inspired by the phenomenon of topographic eddies over mountains in the ocean and atmosphere. We have found, described and visualized a non-attracting invariant chaotic set defining chaotic scattering, fractality, and trapping of incoming particles. Geometry and topology of chaotic scattering have been studied and visualized. Scattering functions in the mixing zone have been found to have a fractal structure with a complicated hierarchy that has been described in terms of strophes and epistrophes. Mixing, trapping, and fractal properties of passive particles have been studied under the influence of a white noise with different amplitudes and frequency ranges. A new effect of clustering the particles in a noised flow has been demonstrated in numerical experiments.
Feedback Control of Stochastic Systems to Track Prespecified Probability Density Functions
Authors: Elbeyli Ozer , Sun J. Q.
Published: June 2008

We present a study of feedback controls of stochastic systems to track a prespecified probability density function (PDF). The moment equations of the response are used in the control design to illustrate the underlining issues. A hierarchical approach is proposed to design the control for tracking Gaussian and non-Gaussian PDFs. The control design approach is demonstrated with a simple example.
Dynamics and Path-Tracking Control of an Unmanned Bicycle
Authors: Chen Chih-Keng , Dao Thanh-Son
Published: June 2008

Due to its non-holonomic constraints and its highly unstable nature, the unmanned bicycle is difficult to be controlled for tracking a target path while retaining balance. As a result of the non-holonomic constraint conditions, the instantaneous velocity of the vehicle is limited to certain directions. Constraints of this kind occur under the no-slip condition. In this paper, the equations of motion describing the motions of the bicycle are developed using Lagrange’s equations for quasi-coordinates. Pure rolling without slip constraints between the ground and the two wheels are also considered in this model. Based on the developed equations of motion, two strategies for path-tracking control of an unmanned bicycle are proposed, compared and discussed.
Brake Squeal Noise Due to Disk Misalignment
Authors: Choi Yeon-Sun , Park Ju-Pyo
Published: June 2008

To understand brake squeal noise, the sound and vibration of an automobile brake system were measured using a brake dynamometer. The experimental results show that an important factor in squeal generation is the run-out due to disk misalignment. A three-degree of freedom model is developed for the brake system, where the run-out effect and nonlinear friction characteristic are included. A stability analysis of the model was also performed to predict the generation of squeal with the modification of the brake system. The results show that squeal generation is dependant on the run-out rather than the friction characteristic between pad and disk.
The R-Refinement Finite Element Analysis of Flexible Four-Bar Linkage
Authors: Kuo Y. L. , Cleghorn W. L. , Behdinan K.
Published: June 2008

The r-refinement of the finite element method locates the positions of nodes to increase accuracy based on a mesh with a given number of elements and a given set of nodal variables. To compare with the conventional refinements by increasing the number of nodal variables, the r-refinement does not increases computations but increase the accuracy of approximated solutions. This paper presents the application of the r-refinement on a flexible four-bar linkage, and provides the study of the effect of the r-refinement on the constant/periodical rotating speed and the discretization of the input link. The results are compared with those by increasing the number of elements.
Effect of Surface Roughness and Joint Material on Torque-Tension Relationship in Threaded Fasteners
Authors: Nassar S. A. , Sun T. S.
Published: June 2008

An experimental study is presented in order to investigate the effect of surface roughness on the torque-tension relationship in bolted assemblies. Three levels of surface roughness are considered for the fastener underhead and the joint surface; namely, low, medium, and high levels of surface roughness. The study is conducted for two joint materials, two fastener classes, and for coarse and fine threads. In this study, the torque-tension data is expressed in terms of the value of the nut factor as well as its scatter. The effect of the number of tightenings on surface roughness and on the torque-tension relationship is investigated as well. The surface roughness is measured before tightening, and after each loosening using a WYKO optical profiling system. An M12 fastener is used in this study. Both fine and coarse threads and fastener material Classes 8.8 and 10.9 for M12 fasteners are used in this study. The torque-tension data is analyzed for both steel and aluminum joints. The safety and reliability of bolted assemblies are mainly determined by the level and the stability of the clamp load provided by the initial tightening of the threaded fastener. The value of initial clamp load, which is achieved by a specific level of tightening torque, is highly sensitive to the friction torque components. This study provides an insight into the reliability of the existing engineering practices for estimating the clamp load level from the tightening torque. Hence, the findings of the study would help enhance the reliability and the safety of bolted assemblies, especially in critical applications.
Stability of Singularities of a Kinematical Chain
Authors: Lerbet Jean
Published: June 2008

Since few years, the geometry of singularities of kinematical chains is better known. Using both Lie group theory and concepts of differential or analytic geometry, we already classified these singularities according to the nature of the function f associated to the chain (f is a product of exponential mappings of a Lie group). In the most general case, the tangent cone at a singularity has been explicitely given. Here, a different (and more difficult) aspect of the problem is studied. The concrete realisation of a kinematical chain is never perfect. That means that the vectors of the Lie agebra defining the function f are not exactly those of the chain: they are deformed. What happens for the singularities in this case? Are they remaining or do they disappear during the deformation? First, the mechanical problem is analysed as this of the stability of the fuction f and mathematical tools concerning stable mappings are given. Stability of a mapping means that the orbit of f under the action of diffeomorphisms in the source and in the target is an open set and its infinitesimal equivalent formulation is noted the inf-stability. Then we prove that the set of singularities of first class itself is a sbmanifold and we analyse a condition of normal crossing of the restriction of f to its manifold of singularities. Applying a result of the general theory, the stability of f is analysed.
About the Links Between the Static and Dynamic Stabilities
Authors: Lerbet Jean , Absi Elie
Published: June 2008

The paper aims to present a new approach of the static stability of a structure and to compare it with spectral analysis (dynamic stability). Its is well-known that for conservative systems divergence (classical static instability) and flutter (classical dynamic instability) give same critical values of loads. It is well known too that for non conservative systems, particulary for undamped non conservative systems, (classical example of Beck column subjected to a follower force) the static approach fails: for all values of the force, the (non-symmetric) matrix of rigidity is regular. The only spectral analysis gives a critical value of the load. Introducing the concept of mixed perturbation of a structure, we propose a new criterion of (static) stability. We apply this criterion to the classical example previously cited (Beck column) and in a third part a general result about applications to flutter is proposed.
Modeling the Climber Fall Arrest Dynamics
Authors: Manin Lionel , Mahfoudh Jarir , Richard Matthieu , Jauffres David
Published: June 2008

Sports and mountaineering activities are becoming more and more popular. Equipment constructors seek to develop products and devices that are easy to use and that take into account all safety recommendations. PETZL and INSA have collaborated to develop a model for the simulation of displacements and efforts involved during the fall of a climber in the “safety chain”. The model is based on the classical equations of motion, in which climber and belayer are considered as rigid masses, while the rope is considered as a series of non-linear stiffness passing through several devices as brakes and runners. The main goal is to predict the forces in the rope and on the return anchor at the first rebound of the fall. Experiments were first performed in order to observe and determine the dynamic characteristics of the rope, and then to validate results stemming from simulations. Several fall configurations are simulated, and the model performs satisfactorily. It also provides a close approximation of the phenomena observed experimentally. The model enables the assessment of the existing equipments and the improved design of the future one.
Modular Add-On System for Vibration Control in Gantry Milling Machines
Authors: Za¨h Michael F. , Rashidy Haitham , Gra¨tz Florian
Published: June 2008

On the part of the manufacturer as well as the user, the notion of modular configurable machine tools gains increasing applause. It is almost evident that the need not only for configurable machine structures but also machining characteristics will be an incisive feature of the future machine tool. In this paper a concept for a modular add-on solution for active vibration damping of characteristic mode shapes of a three-axis milling machine is introduced. Although the developed concept was tailored to a specific case, it is generally valid for small to medium size gantry style machines. Furthermore, the paper discusses the realization of the concept and the actuator integration into the machine structure. Also, a pragmatic controller design is proposed using a modal formulation of the machine dynamics. The results of the FEM analysis and simulation will be presented. Experimental validation of the system is underway at the time and is not included in the paper. A major advantage of the presented study is its suitability for direct application in the industry.
Subharmonic Excitation for Electrically Actuated Microbeams
Authors: Nayfeh Ali H. , Younis Mohammad I.
Published: June 2008

We present analysis of the global dynamics of electrically actuated microbeams under subharmonic excitation. The microbeams are excited by a DC electrostatic force and an AC harmonic force with a frequency tuned near twice their fundamental natural frequencies. We show that the dynamic pull-in instability can occur in this case for an electric load much lower than that predicted with static analysis and the same order-of-magnitude as that predicted in the case of primary-resonance excitation. We show that, once the subharmonic resonance is activated, all frequency-response curves reach pull-in, regardless of the magnitude of the AC forcing. Our results show a limited influence of the quality factor on the frequency response. This result and the fact that the frequency-response curves have very steep passband-to-stopband transitions make the combination of a DC voltage and a subhormonic of order one-half a promising candidate for designing improved high-sensitive RF MEMS filters.
Hamilton’s Principle for Fluid-Structure Interaction and Applications to Reduced-Order Modeling
Authors: Gabbai Rene D. , Benaroya Haym
Published: June 2008

A general framework based on the extended Hamilton’s principle for external viscous flows is presented. The indicated method is shown to yield the correct governing equations and boundary conditions when applied to the problem (herein called the “model problem”) of vortex-induced oscillations of an elastically-mounted rigid circular cylinder with a transverse degree-of-freedom. The vortex shedding is assumed to be sufficiently correlated along the span of the cylinder that the flow can be taken as nominally two-dimensional. The incoming flow is assumed to be incompressible, steady, and uniform. The continuity equation results directly from the global mass balance law, thus avoiding its introduction via a Lagrange multiplier. The true strength of this framework lies in the fact that it represents a physically sound basis from which reduced-order models can be obtained. Some preliminary work on this reduced-order modeling applied to the model problem is described.
Fundamental Study on Contact Behavior of Ultrasonic Motor
Authors: Nakajima Daichi , Ozawa Tomoyuki , Maeda Takeshi , Tsukui Michio , Takatsuka Kohro , Yoshizawa Masatsugu
Published: June 2008

We discuss the contact behavior between the stator and the lining material that sticks to the rotor of an ultrasonic motor. The ultrasonic motor is powered by the vibration of the stator and operates with a frictional force between the stator and the lining material. Therefore, it is important to examine the mechanism of the contact behavior to improve the energy efficiency and durability of the ultrasonic motor. We propose a numerical technique using the finite element method to examine the contact behavior between the stator and the lining material. Then, we compare the numerical example with the theoretical solution proposed by L. A. Galin and confirm the validity of our technique. Moreover, on the basis of incremental theory, we use our technique to numerically examine the complex contact behavior of the non-contact zone, slip zone and stick zone in a non-rotating rotor.
On Self-Similarity as a Design Paradigm
Authors: Kormeier Thomas , Rudolph Stephan
Published: June 2008

Towards the future goal of providing a unified computer aided engineering design framework, engineering design languages are an already available option. Their application allows to formalize the computer aided design synthesis and analysis process. Design languages serve as a computable abstraction of design representation and synthesis processes by use of rule-based information processing mechanisms. In many design languages, recurrent rule patterns can be observed at various levels of abstraction in the synthesis processes. This gives rise to the existence hypothesis of generic patterns in such design information processing systems. As the abstraction of such a recurrent generic pattern, a self-similar design paradigm for design languages is introduced and investigated in this work. The self-similar design paradigm implies itself from a discussion on the nature of design problems and their solution implementation using design languages. The purpose of this self-similar design paradigm is to combine both top-down and bottom-up design sequences to form a consistent and recursive design process model. The self-similar design paradigm constitutes a theoretical framework for the thorough exploration of design spaces. It should be applicable on all abstraction levels of a design process. A comprehensive design methodology is developed by explaining how the self-similar design paradigm is reflected in the data abstraction and representation models which are both inherent to the design with design languages. As a conclusion, the completeness and the generality of the approach is investigated and discussed.
Constraint Formulation of Constant Velocity Joints to Estimate Joint Reaction Torque
Authors: Kim Min-Seok , Yoo Wan-Suk , Park Su-Jin , Kim Doo-Hyun
Published: June 2008

In multibody dynamic simulations, a powertrain system is usually modeled as one rigid body just transmitting forces and torques for simple modeling and application. With one body modeling for the powertrain system, it could not be determined the reaction forces and torques between components. Thus, in this paper, the constraint equation for the differential was modeled with an angular constraint between two rotation angles, and the constant velocity joint was newly formulated with kinematic constraint equations. Then, a powertrain model was developed including an engine, a torque converter, a differential, and constant velocity joints. A quasistatic torque map was considered for the engine modeling, and torque ratio and capacity factor are considered for the torque converter modeling. With the developed powertrain model, a dynamic simulation was carried to see dynamic response and reaction force occurred at the CV joint.
The Influence of Internal Damping on the Rotordynamic Stability of a Flywheel Rotor With Flexible Hub
Authors: Moreira Alfonso , Flowers George , Matras Alex , Balas Mark , Fausz Jerry
Published: June 2008

An investigation about the influence of internal damping on the rotordynamic stability of high-speed flywheel energy storage systems made from carbon fiber epoxy is presented. The research effort consists of simulation studies coupled with experimental testing and evaluation. Damping values obtained from composite beam samples and a composite rotor hub design are shown. The effect of vibration frequency on damping is examined and discussed. These parameters are then used in a series of simulation studies that examine the effects of internal damping on rotordynamic behavior. An experimental model has been developed to verify the conclusions made from the simulations. The experimental testing consisted of creating a prototype rig, characterizing the system parameters, applying these parameters to determine the expected critical speed and experimentally determine the actual critical speed. These results are presented and their implications for flexible hub flywheel designs discussed.
Geometric Surface Features Applied to Volumetric CAE Mesh Models
Authors: Chen Yifan , Tonshal Basavaraj , Saeed Ali
Published: June 2008

In this paper, we discuss a way to extend a geometric surface feature framework known as Direct Surface Manipulation (DSM) into a volumetric mesh modeling paradigm that can be directly adopted by large-scale CAE applications involving models made of volumetric elements, multiple layers of surface elements or both. By introducing a polynomial-based depth-blending function, we extend the classic DSM mathematics into a volumetric form. The depth-blending function possesses similar user-friendly features as DSM basis functions permitting ease-of-control of the continuity and magnitude of deformation along the depth of deformation. Practical issues concerning the implementation of this technique are discussed in details and implementation results are shown demonstrating the versatility of this volumetric paradigm for direct modeling of complex CAE mesh models. In addition, the notion of a model-independent, volumetric-geometric feature is introduced. Motivated by modeling clay with sweeps and templates, a model-independent, catalog-able volumetric feature can be created. Deformation created by such a feature can be relocated, reoriented, duplicated, mirrored, pasted, and stored independent of the model to which it was originally applied. It can serve as a design template, thereby saving the time and effort to recreate it for repeated uses on different models (frequently seen in CAE-based Design of Experiments study).
FEM Simulation and Life Optimization of Tandem Roller Thrust Bearing
Authors: Tibbits Patrick A.
Published: June 2008

Tandem thrust roller bearings carry high axial loads in rotary equipment such as mud pumps or extruders. Deflection of the bearing plates redistributes loads over rollers, and affects bearing life. In this study, solid finite elements modeled a shaft, housing and two stages of bearing plates. A line of spring elements represented each row of rollers. The stiffness of the line of spring elements modeled the stiffness of each roller/raceway non-Hertzian line contact. Modification of the spring element stiffness compensated for the compliance of the nodes of solid elements that modeled the bearing plates. This construct avoided computationally expensive surface-to-surface contact calculations. Further computational savings accrued from modeling the bearing and shaft assembly as axisymmetric. Program output included deflection of the bearing plates and a listing of spring element forces, which characterized the distribution of load over the length of the rollers. Bearings with optimized geometry had decreased maximum contact stress, more uniform distribution of contact stress over the length of each roller, and longer estimated rolling contact fatigue life.
A Web-Enabled Engineering Object Modeling Environment to Support Interoperability and Intelligent Services in Collaborative Design
Authors: Yang Q. Z. , Lu W. F.
Published: June 2008

Design collaboration is recognized as an effective approach in joint problem solving to achieve success of product development in distributed and heterogeneous environments. Design collaboration involves communication of design information, coordination of design activities, and negotiation of design conflicts between multi-disciplinary teams. To support these critical requirements in collaborative design, methodologies and software systems are needed. This paper shares our experience in the method and software development for a Web-enabled engineering object modeling environment. It presents our methods for interoperable and extensible design information modeling, for intelligent object behaviors embedment in CAD models, and for design information sharing across product lifecycle applications through a common vocabulary. The prototype implementation of the modeling environment provides standardized and localized engineering objects embedded with design semantics and intelligent behaviors for the information needs from multiple engineering software applications. The prototype also provides activity coordination and negotiation facilities through team setting, online visualization, live updating, conflict management, and messaging. Use scenarios are discussed in the paper.