bluuebunny/crossref_metadata_2025 huggingface dataset:
Evaluation of Thermal Energy Storage Devices for Advanced Solar Dynamic Systems
Authors: Crane Roger A. , Bharadhwaj Gannesh
Published: June 2008

The work described herein addresses the thermal performance of three concepts for thermal energy storage as applied to solar dynamic applications. It is recognized that designs providing large thermal gradients or large temperature swings during orbit are susceptible to early mechanical failure. Concepts incorporating heat pipe technology may encounter operational limitations over sufficiently large ranges. By reviewing the thermal performance of basic designs the relative merits of the basic concepts are to be compared. In addition, the effect of thermal enhancement and metal utilization as applied to each design provides a partial characterization of the performance improvements to be achieved by developing these technologies.
An Analytical Examination of Methods for Improving the Performance of Desiccant Cooling Systems
Authors: Collier R. K. , Cohen B. M.
Published: June 2008

The conventional Pennington Cycle desiccant cooling system offers a clear opportunity for heat-actuated air conditioning. However, efforts to translate this opportunity into commercially viable hardware have not been successful. The performance of the hardware has been inadequate, resulting in excessive solar collector requirements or, in the case of gas-fired equipment, uneconomical use of natural gas. Two methods for improving the coefficient of performance (COP) of these systems are: (1) the addition of inert heat capacity to the desiccant matrix, and (2) “staging” the regeneration air stream. An analysis is presented in this paper which explains the benefits and drawbacks of these methods based upon the wave nature of the heat and mass transfer processes occurring within the desiccant bed. The results indicate that the best overall system performance is obtained by staging the regeneration process while minimizing the amount of inert heat capacity.
Distinctive Properties of Tubular Solar Chemical Reactors
Authors: Meirovitch Eva
Published: June 2008

Concentrated sunlight can be stored in the chemical bond by activating an endothermic reaction. This novel concept has been implemented recently with solar power captured in a central receiver equipped with chemical reactors. The related theory, presented in this report, singles out this interactive radiative-chemical system as distinctively stable thermodynamically, resilient to perturbations, internally regulatory and self-corrective. None of the thermochemical devices conceived so far bear all these attributes.
A Simple Structure for Bilateral Transparent Teleoperation Systems With Time Delay
Authors: Alfi Alireza , Farrokhi Mohammad
Published: June 2008

This paper presents a simple structure design for bilateral teleoperation systems with uncertainties in time delay in communication channel. The goal is to achieve complete transparency and robust stability for the closed-loop system. For transparency, two local controllers are designed for the bilateral teleoperation systems. One local controller is responsible for tracking the master commands, and the other one is in charge of force tracking as well as guaranteeing the stability of the closed-loop system in the presence of uncertainties in time delay. The stability analysis will be shown analytically for two cases: (I) the possibly stability and (II) the intrinsically stability. Moreover, in Case II, in order to generate the proper inputs for the master controller in the presence of uncertainties in time delay, an adaptive finite impulse response (FIR) filter is designed to estimate the time delay. The advantages of the proposed method are threefold: (1) stability of the closed-loop system is guaranteed under some mild conditions, (2) the whole system is transparent, and (3) design of the local controllers is simple. Simulation results show good performance of the proposed method.
Robust Unknown Input Observer for Nonlinear Systems and Its Application to Fault Detection and Isolation
Authors: Mondal S. , Chakraborty G. , Bhattacharyya K.
Published: June 2008

A robust unknown input observer for a nonlinear system whose nonlinear function satisfies the Lipschitz condition is designed based on linear matrix inequality approach. Both noise and uncertainties are taken into account in deriving the observer. A component fault detection and isolation scheme based on these observers is proposed. The effectiveness of the observer and the fault diagnosis scheme is shown by applying them for component fault diagnosis of an electrohydraulic actuator.
Discrete-Time Control of Linear Time-Periodic Systems
Authors: Kalender S. , Flashner H.
Published: June 2008

A discrete-time control design approach for periodically time-varying systems is introduced. The method employs a period-to-period (point-mapping) formulation of the system’s dynamics and a parametrization of the control input to obtain an equivalent time-invariant discrete-time representation of the system. The representation is generalized to include sampling within the period and varying sampling rates in different feedback loops. The proposed formulation allows for the design of feedback control laws using established discrete-time control methodologies. In this paper, dead-beat and optimal control laws with state- or output-feedback control are presented. An example of a multivariable control design for double inverted pendulum with periodic forcing is used to illustrate the proposed approach.
Coexistence Phenomenon in Autoparametric Excitation of Two Degree of Freedom Systems
Authors: Recktenwald Geoffrey , Rand Richard
Published: June 2008

Coexistence phenomenon refers to the absence of expected tongues of instability in parametrically excited systems. In this paper we obtain sufficient conditions for coexistence to occur in the generalized Ince equation: (1+a1cost+a2cos2t)v¨+(b1sint+b2sin2t)v˙+(δ+c1cost+c2cos2t)v=0 The results are applied to the stability of motion of a nonlinear normal mode, the x-mode, in a class of conservative two degree of freedom systems.
Continuum Modeling of a Slewing ISAT (Innovative Space Antenna Technology)
Authors: Salehian Armaghan , Cliff Eugene M. , Inman Daniel J.
Published: June 2008

A simple approach is presented herein for obtaining the equivalent continuum model of an ISAT (Innovative Space Antenna Technology) truss structure in order to find the free vibration solutions for different coordinates of vibration. Kinetic and potential energy expressions are written in terms of the strain components of the elements and the nodal velocities. The Lagrangian approach is employed to find the governing partial differential equations of the structure which for the bending degrees of freedom lead to an equivalent Timoshenko beam. Finally, the physical characteristics of the continuum model are written in terms of the material and geometrical properties of the truss, which provide a simple tool for comparing dynamic characteristics of lattices with different properties. The natural frequencies are found for each of the bending, longitudinal, and torsional coordinates of vibration and are compared to those of a FEM solution for the purpose of validation. The analytical model shows very high accuracy in prediction of the natural frequencies of the original truss.
Vibration Analysis of Rotating Asymmetric Structures
Authors: Shen I. Y. , Kim Hyunchul
Published: June 2008

This paper is to develop a unified algorithm to analyze vibration of spinning asymmetric rotors with arbitrary geometry and complexity. As a first approximation, the effects of housings and bearings are not included in this analysis. The unified algorithm consists of three steps. The first step is to conduct a finite element analysis on the corresponding stationary rotor to extract natural frequencies and mode shapes. The second step is to represent the vibration of the spinning rotor in terms of the mode shapes and their modal response in a coordinate system that is rotating with the spinning rotor. Through use of the Lagrange equation, one can derive the modal equation of motion. To construct the equation of motion explicitly, the results from the finite element analysis will be used to calculate the gyroscopic matrix, centrifugal stiffening (or softening) matrix, and generalized modal excitation vector. The third step is to solve the equation of motion to obtain the modal response, which, in turn, will lead to physical response of the rotor for a rotor-based observer or for a ground-based observer through a coordinate transformation. Finally, application of the algorithm to rotationally periodic rotors indicates that Campbell diagrams of the rotors will not only have traditional forward and backward branches as in axisymmetric rotors, but also have secondary resonances caused by higher harmonics resulting from the mode shapes. Calibrated experiments were conducted on an air bearing spindles carrying slotted circular disks to verify the theoretical predictions in the ground-based coordinates.
Finite Element Analysis of the Geometric Stiffening Effect Using the Absolute Nodal Coordinate Formulation
Authors: Garci´a-Vallejo Daniel , Sugiyama Hiroyuki , Shabana Ahmed A.
Published: June 2008

In this paper, the limitations of the linear elasticity finite element solutions in describing the coupling between the extensional and bending displacements are discussed. The fact that incorrect unstable solutions are obtained for models with more than one finite element using the linear elasticity theory motivates the analytical study of the rotating beam presented in this paper. It is shown, as documented in the literature, that the instability of the incorrect solution is directly related to the singularity of the stiffness matrix, and such an instability occurs when the angular velocity reaches the first bending fundamental frequency of the beam. The increase in the number of finite elements only leads to an increase of the critical speed. Crucial in the analysis presented in this paper is the fact that the mass matrix and the form of the elastic forces obtained using the absolute nodal coordinate formulation remain the same under orthogonal coordinate transformation. The absolute nodal coordinate formulation, in contrast to conventional finite element formulations, does account for the effect of the coupling between bending and extension. A similar concept can be incorporated into the finite element floating frame of reference formulation in order to introduce coupling between the axial and bending displacements. Nonetheless, when the linear theory of elasticity is used and no special measures are taken to account for the coupling effect as proposed in the literature, there always exists a critical velocity regardless of the number of finite elements used.
Theoretical and Numerical Investigation of a Special Case of a Rotating Chain: The Helicoseir Problem
Authors: Yoo Wan-Suk , Dmitrochenko Oleg , Mun Sang-Hyuk , Lee Hyun-Woo
Published: June 2008

A physically simple but mathematically cumbrous problem of rotating heavy chain with one fixed top point is studied. Nonlinear partial differential equations of motion in 3D case are derived as well as ones for 2D shapes of relative equilibrium. The equations are found very complicated and solved numerically. A linear case of small displacements is analyzed in terms of Bessel functions. The qualitative and quantitative behaviour of the problem is discussed with the help of bifurcation diagram. Dynamics of the two-dimensional model near the equilibrium positions is studied with the help of simulation using the absolute nodal coordinate formulation (ANCF); the equilibriums are found unstable. The reason of instability is explained using a variational principle. Analysis of 3D motion in the rotating frame shows that Coriolis inertia forces can stabilize the motion. 3D numerical simulation using ANCF shows that the spatial motion of the helicoseir is stable and looks like self-excited oscillations near the flat instable configurations that were obtained before.
Study on Tool Wear and Vibration Characteristics in Micro Drilling Operation
Authors: Tang Ying , Ji Yuan
Published: June 2008

This paper presents studies on micro drilling operation, which refers to manufacturing of micro-holes with diameters less than 0.5 mm. Wear process of micro drill and its influence on machined hole quality and vibration characteristics in micro drilling operation were investigated through extensive experimentation with 0.29mm diameter twists drills drilling into plain carbon steel. Vibration signals collected from the micro drilling experiments were analyzed using time and frequency techniques. Characteristic parameters of vibration signatures: statistical measures of the time domain and averaged spectral amplitude at specified bands of the frequency domain were found very sensitive to drill wear and breakage.
Solution of Systems of Linear Delay Differential Equations Via Lambert Functions
Authors: Maghami Asl Farshid , Ulsoy A. Galip
Published: June 2008

A new analytic approach to obtain the complete solution for systems of delay differential equations (DDE) based on the concept of Lambert functions is presented. The similarity to the concept of the state transition matrix in linear ordinary differential equations enables the approach to be used for general classes of linear DDE’s in matrix form. The solution is in the form of an infinite series of modes written in terms of Lambert functions. Results are presented for stability criteria for the individual modes, free response, and forced response in the context of specific examples. This new approach is also applied to the problem of chatter stability in a machining operation on a lathe. The results, since they are only for individual modes, and there are an infinite number of them, represent a necessary condition for system stability.
Knowledge Based Design Method for Fibre Metal Laminate Fuselage Panels
Authors: Vermeulen B. , van Tooren M. J. L. , Peeters L. J. B.
Published: June 2008

Fibre Metal Laminates (FML) are a member of the hybrid materials family, consisting of alternating metal layers and layers of fibres embedded in a resin. Improved damage resistance and tolerance result in a significant weight and maintenance cost reduction compared to aluminium. FML also give the aircraft engineer additional design freedom, such as local tailoring of laminate properties. However, experience has shown that FML’s provide the aircraft manufacturer with many challenges as well. With increasing complexity of the structure, requirements from different disciplines within the engineering process will start to interfere, resulting in conflicts. This article discusses the current engineering process of FML fuselage panels as applied at Stork/Fokker Aerospace (FAESP). A case study is presented, clarifying the current design process and the way requirements start to interfere during the engineering process. A new approach based on Knowledge Engineering is discussed, implementing knowledge from engineers from all disciplines in an early stage of the design process. An automated design approach for FML fuselage panels is presented, using the same design parameters as the current approach. Because of the high complexity of the design, requirements start to conflict. Fulfilling all requirements with a traditional engineering approach results in an iterative and time consuming process. Automation of the design process, integrating knowledge and requirements from all disciplines, results in a fast and transparent design approach.
Integrated Vehicle Dynamic Control Through Coordinating Control of Steering and Suspension System
Authors: Chen Wuwei , Xiao Hansong , Liu Liqiang , Zu Jean W.
Published: June 2008

This paper addresses the problem of integrated control of Electrical Power Steering System (EPS) and Active Suspension System (ASS). Through integrating EPS with ASS, a full car dynamic model is established. Based on the integrated model, a random sub-optimal control strategy based on output feedback is designed to fulfill the integrated control of both EPS and ASS. The characteristics of the integrated control system are analyzed using Matlab/Simulink and a series of comparisons are made with the system without control and the ASS-only/EPS-only system. The simulation results show that the integrated control scheme can not only enhance the steering quality, but also significantly isolate the road excitation. Moreover, the integrated control system has a great improvement on anti-roll and anti-pitch abilities. The proposed research provides a theoretical solution for simultaneously improving the multiple vehicle performance indices including maneuverability, handling stability, ride comfort, and safety.
Quantum Chaos and Quantum Fractals With Atoms and Photons in a Microcavity
Authors: Uleysky M. Yu. , Prants S. V.
Published: June 2008

Nonlinear dynamics in the fundamental interaction between a two-level atom with recoil and a quantized radiation field in a high-quality microcavity is studied. We consider the strongly coupled atom-field system as a quantum-classical hybrid with dynamically coupled quantum and classical egrees of freedom. We show that, even in the absence of any other interaction with environment, the coupling of quantum and classical degrees of freedom provides the emergence of classical dynamical chaos from quantum electrodynamics. It manifest itself in the atomic external degree of freedom as a random walking of an atom inside a cavity with a prominent fractal-like behavior and in the quantum atom-filed degrees of freedom as a sensitive dependence of atomic inversion on small variations in initial conditions. It is shown that dependences of variance of quantum entanglement and of the maximum Lyapunov exponent on the detuning of the atom-field resonance correlate strongly. This result provides a quantum-classical correspondence in a closed physical system.
Performance Analysis of a Cascaded Rectangular-Triangular Fin Using Maple
Authors: Aziz A.
Published: June 2008

The present paper treats the finned array problem using the symbolic algebra package in Maple. The use of Maple not only alleviates the tedium of algebraic manipulation, but its powerful numerical and graphical capabilities allow numerical results to be tabulated or portrayed graphically. To illustrate the effectiveness of Maple, a configuration consisting of a rectangular fin cascaded with a triangular fin is considered. The problem formulation has three distinctive features. First, a convective boundary condition is imposed at the base of the fin unlike the constant base temperature condition that is commonly used. Second, the model allows the thermal conductivities of the rectangular and the triangular sections to be different. Prior studies of a finned array have all assumed the thermal conductivity to be the same throughout the structure. Third, the convection heat transfer coefficient for the triangular part, i.e. h1, is taken to be different from that of the rectangular part, i.e. h2. Previously reported analyses have assumed a uniform h for all the surfaces of the structure. The paper demonstrates that the use of Maple allows new and challenging problems in heat conduction to be introduced in both the undergraduate and graduate heat transfer courses.
On the Computation of Degrees-of-Freedom: A Didactic Perspective
Authors: Pennestri` E. , Cavacece M. , Vita L.
Published: June 2008

Some didactic issues associated with the computation of degrees-of-freedom (d.o.f.) are herein discussed. In particular the paper reports different definitions and methodologies of computation of this important parameter. It is also proposed an analytical approach to the d.o.f. computation of planar figures subjected to unilateral constraints. Mechanisms with variable kinematic structure are included in the present analysis. Some ambiguities in the d.o.f. definition are pointed out.
Design of Fuzzy Logic Controller for Four Wheel Steering System
Authors: Ozatay Evren , Unlusoy Samim Y. , Yildirim Murat A.
Published: June 2008

Integration of the driver’s steering input together with the four-wheel steering system (4WS) in order to improve the vehicle’s dynamic behavior with respect to yaw rate and body sideslip angle is possible with intelligent vehicle dynamics control systems. The goal of this study is to develop a fuzzy logic controller for this purpose. In the first stage of the study, a three-degree of freedom nonlinear vehicle model including roll dynamics is developed. The Magic Formula is applied in order to formulate the nonlinear characteristics of the tires. In the design of the fuzzy logic controller, a two-dimensional rule table is created based on the error and on the change in the error of sideslip angle, which is to be minimized. Fuzzy logic controlled model is then compared with front wheel steering vehicle and the vehicles having different control strategies that have previously been studied in literature. Simulations indicate that fuzzy logic controlled vehicle can provide zero body sideslip angle in transient motion and quick response in terms of yaw rate during steady state cornering and lane change maneuvers.
Modal Parameter Identification of Time-Varying Systems Using the Time-Varying Multivariate Autoregressive Model
Authors: Liu Lilan , Liu Hongzhao , Wu Ziying , Yuan Daning , Li Pengfei
Published: June 2008

A new time-varying multivariate autoregressive (TVMAR) model method for modal parameter identification of linear time-varying (TV) systems with multi-output is introduced. Besides, a modified recursive least square method based on the traditional one is presented to determine the coefficient matrices of the TVMAR model. In the proposed method, multi-dimensional nonstationary response signals of the vibrating system can be processed simultaneously. Not only the TV modal frequency and damping ratio of the system, but also the changing behavior of the mode shape in the course of vibration are identified by the proposed procedure. Numerical simulations, in which a three-degree-of-freedom system with TV stiffness is respectively subjected to impulse excitation and white noise excitation, are presented. The validity and accuracy of the method are demonstrated by the good simulation results.
On Tolerance Information Extraction of Feature Model in Automotive Engine CAPP System
Authors: Yuguo Sun
Published: June 2008

A generative automotive engine CAPP (Computer-Aided-Process Planning) system based on Oracle database was developed. A practical tolerance information communication solution between the CAD and CAPP system was proposed and realized in an independent file schema. A parametrical cylinder head model based on manufacturing feature was created to meet the requirements of the CAPP system feature recognizing. The data structure of the tolerance information in the Pro/ENGINEERING database was presented. A Pro/TOOLKIT program was developed to extract the model’s tolerance information automatically. The tolerance information extracted was then organized with EXPRESS language and imported into the CAPP system database Oracle.
Thermal Effects on the Natural Frequency of Nonlinear, Co-Rotating Disks
Authors: Luo Albert C. J. , Saniei Nader , Harp William Ray
Published: June 2008

Thermal effects on the natural frequency for the nonlinear free vibration of co-rotating disks are investigated for non-uniform temperature distributions relative to airflow induced by disk rotation. The natural frequencies for symmetric and asymmetric responses of a 3.5 inch diameter computer memory disk are calculated. When the disk is heated, its stiffness becomes larger for the two lowest nodal diameter numbers and smaller for the other nodal diameter numbers. It implies that the vibration of heated, rotating disks for the higher nodal diameter numbers may be induced more easily than the cooled one.
Force Product Criteria of Sliding Motions in a Forced Linear Oscillator Including Dry Friction
Authors: Luo Albert C. J. , Gegg Brandon C.
Published: June 2008

In this paper, the switching conditions for sliding motions in a periodically, forced linear oscillator with dry friction are obtained analytically. The generic mappings for the friction-induced oscillator are introduced. From the generic mappings, the corresponding criteria for the sliding motions are presented through the force product conditions. The analytical prediction of the onset and vanishing of the sliding motions is illustrated. Finally, numerical simulations of sliding motions are carried out to verify the analytical prediction.
The Characteristic Experiment Analysis of the Giant Magnetostrictive Actuator
Authors: Sun Huagang , Yuan Huiqun , Wen Bangchun
Published: June 2008

In this paper through the characteristic experiment of the giant magnetostrictive actuator, the relation between the magnetostrictive strain and the electric current under the different pre-stress is achieved. And the experiment formula between the maximal magnetostrictive strain and the pre-stress under the maximal electric current is founded. The optimal working pre-stress is established through the analysis to the data of the experiment. Then the characteristic of the magnetostrictive actuator under the optimal working pre-stress is discussed, and the experiment formula between the magnetostrictive strain and the electric current is founded. And, the 3-D interpolation curve of the magnetostrictive coefficient, pre-stress, and the electric current is achieved through the multidimensional interpolation. Last, magnetostrictive coupling coefficient is measured. Through the analysis of the experiment, some characteristics about the magnetostrictive strain, pre-stress, and the electric current have been established.
The Number of Real Zeros of the Single Parameter Mittag-Leffler Function for Parameter Values Between 1 and 2
Authors: Hanneken John W. , Vaught David M. , Narahari Achar B. N.
Published: June 2008

The single parameter Mittag-Leffler function, which is a generalization of the exponential function, occurs naturally in the solution of physical problems involving fractional calculus and its zeros play a significant role in the dynamic solutions. It is known that the Mittag-Leffler function has a finite number of real zeros in the range of parameter values between 1 and 2, which is quite relevant for many physical problems. However, the number of real zeros for a given parameter value in this range is not known. An iteration formula for calculating the number of real zeros of the Mittag-Leffler function for any value of the parameter in the range between 1 and 2 is presented.
Ride Comfort Values of Four Korean Cars in Highways
Authors: Park Dong-Woon , Yoo Wan-Suk , Kim Min-Seok , Hong Kyung-Tae , Hong Keum-Shik
Published: June 2008

Vibrations on the floor in a car are transmitted to the foot, hip, and back from the seat. Human body recognizes these vibrations, but the sensitivity for each vibration is different. To evaluate these vibrations, RMS(root mean square) of accelerations, VDV(vibration does value), percent vibration, and SEAT (Seat Effective Amplitude Transmissibility) value are commonly used. For the SEAT value calculation, the PSD (Power Spectral Density) of the accelerations at the seat and the PSD of the floor are used with the frequency weighting function. If the SEAT value is less than 1, the vibration level on the seat is less than the floor, which means seat is effective to reduce the vibration. In this paper, four types of cars, i.e., a small size car of 1300cc gasoline engine, a mid-size car of 1800 gasoline engine, a full-size luxurious car of 3600cc gasoline engine, and a SUV (sport utility vehicle) of 2900 diesel engine are used and compared ride comforts using SEAT values. Experiments were carried on a highway near the suburb of Busan metro-politan city in South Korea. To compare ride comforts, the SEAT values in dynamic state are compared. Several air cells are installed in the seat cushion to improve seat comfort and to adjust seat properties by changing the air pressure. From the real car experiments, optimum air cell pressure depending on the vehicle speeds and road conditions are recommended.
A New Method for Multi-Fault Diagnosis of Rotor System
Authors: Jing Jian Ping , Meng Guang
Published: June 2008

A Blind Source Separation (BSS) based new method for multi-fault diagnosis of rotors is presented. The statistic variable based decorrelation approach is employed to analyze the signals of the rotors with crack and rub-impact, crack and oil-whirl multi-faults, the typical features of the frequency spectrum of each fault of the rotor are separated out. The separated results show that (1) the BSS technique is helpful to the multi-fault diagnosis of a rotor system. (2) Due to the signals in the same direction at different locations of a rotor is correlative in some extent, if the observed points are not chosen properly, the separated accuracy will be affected greatly. The analysis shows that: for a one shaft rotor, choosing the signals in x, y direction at a same point of a rotor will lead to a better separated result. (3) If want to applying the BSS to practical diagnosis of rotor system, some efforts and works still need to be done.
Chaos in the Quasiperiodically Forced Helmholtz-Duffing Oscillator With Two-Well Potential
Authors: Lou Jing-Jun , Zhu Shi-Jian , He Qi-Wei
Published: June 2008

The chaotic dynamics of the quasiperiodically excited Helmholtz-Duffing oscillator with two-well potential was investigated. The condition of the existence of homoclinic orbit in the corresponding Hamiltonian system was presented which is asymmetrical resulting from the asymmetry restoring force. It was found that the mechanism for chaos is transverse homoclinic tori and it is illustrated how transverse homoclinic tori give rise to chaos for the Helmholtz-Duffing oscillator with multi-frequency periodic forces. The criterion for the existence of chaos was given utilizing a generalization of the Melnikov’s method. The region in parameter space where chaotic dynamics may occur was given. It was also demonstrated that increasing the number of forcing frequencies increases the area in parameter space where chaotic behavior can occur.
Applications of Acoustic Rhinometry in the Modeling of Living Human Nasal Cavity Based on CT Scan
Authors: Liu Yingxi , Zhang Jun , Sun Xiuzhen
Published: June 2008

Acoustic rhinometry can quantify upper airway condition of air draft by drawing a graph plotting the distance from the nostril vs. the cross-sectional area. Some decrease on the graph corresponds to the typical anatomic structures of human nasal cavity. The 3-dimensional, computing fluid dynamic model of the same person was developed based on computed tomography scans. The veracity of the CFD model were valued by contrasting the relevant areas of stenosis site between the model and the AR graph. The aim in this study is to make clear how to use an AR to help improve and enrich the CFD model with the information of graph acquired from the measurement. The combination of AR and CT can be used to establish a living human nasal cavity model with higher significant information content.
Degradation Assessment for Machinery Prognostics Using Hidden Markov Models
Authors: Qiu Hai , Liao Haitao , Lee Jay
Published: June 2008

Degradation detection and recognition of degradation pattern are crucial to the successful deployment of prognostics. A machine degradation process is known to be stochastic instead of deterministic. Recognizing the degradation pattern needs helps from stochastic and probabilistic models. Among various stochastic approaches. Hidden Markov Models (HMMs) have been proven to be very effective in modeling both dynamic and static signals [1]. In this paper, aiming to providing a guideline of how to effectively and efficiently use the HMMs to assess degradation for various machinery prognostic applications, three different approaches of applying the HMMs are reviewed and compared. It demonstrates that depending on the varieties of applications, available prior knowledge, and characteristics of degradation processes, those three implementation approaches perform differently. A full understanding of the strengths and weaknesses of each deployment approach is extremely important in order to effectively utilize this powerful tool for system degradation assessment.
Passive Balancing for Rotor Systems Using Pendulum Balancers
Authors: Horvath Roland , Flowers George T. , Fausz Jerry
Published: June 2008

An analytical, numerical and experimental investigation of the dynamic behavior of a passive balancing system is presented. Due to the system constraints and dynamic characteristics, this system is capable of combined static and dynamic mass balancing. This work is an extension of previous studies in which ball-balancing systems were used to reduce harmful vibration caused by radial perturbation in the principal axis of inertia. In the present research, the imbalance compensation problem is divided into axial and radial components. A spherical suspension was applied at the rotational axis that allows the rotating disk to tilt, thus eliminating coupled dynamic centrifugal forces caused by the axial mass imbalance. In a fashion similar to earlier ball balancing systems, in this study the balancing balls were replaced by two single pendulums suspended in the geometrical axis of a disk in order to compensate for radial unbalance. The governing equations are developed, which results in a set of cross-coupled nonlinear differential equations, which are analyzed in detail. An experimental study is also conducted to validate and test the conclusions of the analysis and simulation work.
The Application of Cell Mapping Method to High-Dimensional Nonlinear System
Authors: Yu Xiang , Zhu Shi-Jian , Liu Shu-Yong
Published: June 2008

After analyzing the inefficiency of the conventional Cell Mapping Methods in global analysis for high-dimensional nonlinear systems, several principles should be followed for these methods’ implementations in high-dimensional systems are proposed in this paper. Those are: appropriate selection of investigating plane, reduction of data size, and projection of attractors to the investigating plane. According to these, the idea of dynamic array is introduced to the method of Point Mapping Under Cell Reference (PMUCR) to improve computing efficiency. The comparison of the CPU time between the applications of this modified method to a 2-dimensional system and to a 4-dimensional one is carried out, and the results confirm this modified method can be utilized to analyze high-dimensional systems effectively. Finally, as examples, the periodic and chaotic motions of a coupled Duffing system are investigated through this method and some diagrams of global characteristics are presented.
Study on the Response of Flexible Joint Coupled With Unbalanced Rotor
Authors: Zhang Zhen-Zhong , Zhao Cun-Sheng , Zhu Shi-Jian
Published: June 2008

The dynamic response of the flexible joint with unbalanced rotor was analyzed. The mathematical model was investigated and simplified and the unbalanced system was found to be with periodic coefficient. The stability conditions of the periodic solution were simply derived from existing conclusions. And a method for an approximate steady solution was presented. The validity was confirmed by the simulation.
Comprehensive Method of Chaotic Vibration Identification
Authors: Liu Shu-Yong , Yu Xiang , Zhu Shi-Jian
Published: June 2008

When the parameters are in a special range, the response of a nonlinear vibration system is chaotic, which is different from the classical regular response such as primary, super-, sub-, ultra-sub-harmonic resonances. Because the chaotic time series looks like random signal, the characteristics of the chaos cannot be identified from the time history. This paper presents a comprehensive method to identify the chaotic vibration. The attractor of the system is reconstructed in the phase space, and thus the characteristics of the chaotic signal are reflected by the attractor. If the attractor is regular, the response may be periodic. If the topologic structure of the phase diagram is very complicate, the attractor is strange, that is, the system may be in a chaotic state. Correlation dimension and Lyapunov exponent are calculated to prove the conclusions above. It is clear that if the correlation dimension is fraction and the Lyapunov exponent is positive, the measured signal is chaotic. The difference between chaotic signal and noise is studied as well Results show that the comprehensive method can be applied to identify the chaotic vibration efficiently.
Induction Motor Fault Detection and Diagnosis Using Artifical Neural Networks
Authors: Mechefske Chris K. , Li Lingxin
Published: June 2008

This paper investigates induction motor fault detection and diagnosis using Artificial Neural Networks (ANN). The ANN techniques include feedforward backpropagation networks (FFBPN) and self organizing maps (SOM), used individually and in combination. Common induction motor faults such as bearing faults, stator winding fault, unbalanced rotor and broken rotor bars are considered. The ANNs were trained and tested using dynamic measurements of stator currents and mechanical vibration signals. The effects of different network structures and the training set sizes on the performance of the ANNs are discussed. This study shows that, while the feedforward ANNs give satisfactory results and the SOMs can classify the type of motor fault during steady state working conditions, using a combination of SOM and FFBPN techniques yields superior fault detection and diagnostic accuracy. In addition, incipient motor fault detection has been investigated. The above results show that improved induction motor maintenance strategies may be possible through the use of comprehensive on-line induction motor condition monitoring and fault diagnosis systems.
Dry Friction Induced Attractivity of Equilibrium Sets in Mechanical Multibody Systems
Authors: Leine Remco I. , van de Wouw Nathan
Published: June 2008

The dynamics of mechanical systems with dry friction elements, modelled by set-valued force laws, can be described by differential inclusions. The switching and set-valued nature of the friction force law is responsible for the hybrid character of such models. An equilibrium set of such a differential inclusion corresponds to a stationary mode for which the friction elements are sticking. The attractivity properties of the equilibrium set are of major importance for the overall dynamic behaviour of this type of systems. Conditions for the attractivity of the equilibrium set of linear MDOF mechanical systems with multiple friction elements are presented. These results are obtained by application of a generalisation of LaSalle’s principle for differential inclusions of Filippov-type. Besides passive systems, also systems with negative viscous damping are considered. For such systems, only local attractivity of the equilibrium set can be assured under certain conditions. Moreover, an estimate for the region of attraction is given for these cases. The results are illustrated by means of a 2DOF example.
Estimation of Metabolical Costs for Human Locomotion
Authors: Schiehlen Werner , Ackermann Marko
Published: June 2008

Metabolical energy is the chemical energy consumed by skeletal muscles to generate force. This quantity is useful to understand the comfort of human gait and to evaluate, in terms of effort required, the performance of devices or therapies designed to improve gait quality of persons presenting gait disorders. Firstly, this paper presents the frequently used estimations of energy expenditure based lonely on joint torques and mechanical costs obtained by inverse dynamics of passive and active walking devices. Secondly, a more advanced approach is discussed consisting of modeling the musculoskeletal system with Hill-type phenomenological muscle models and computing the metabolical expenditure adopting expressions recently proposed in the literature. As an example a musculoskeletal model of the lower limb in the sagittal plane consisting of thigh, shank and foot with three degrees of freedom and actuated by eight muscles is considered. This model is used to estimate metabolical costs for known normal gait kinematical data obtained in a gait analysis laboratory.
On Preliminaries of 3D Solid Reconstruction Using Auxiliary Views
Authors: Mishra Amitesh , Saxena Anupam
Published: June 2008

In this paper is proposed a method to reconstruct a solid from given two or three orthographic views along with any number of primary auxiliary views based on the combination of wireframe and volumetric approaches. None of the existing works in automatic reconstruction of solids from two dimensional orthographic views have addressed auxiliary views in detail. Polyhedral approximation of cylindrical, conical, toroidal and spherical surfaces is considered. The algorithm presented, entails the construction of the basic wire-frame from given standard views using the wire-frame approach. The projections in the auxiliary views on the basic orthographic views are swept along the projection lines to form the primitives. These primitives are glued to the basic wire-frame to construct the final solid. Numerous examples are presented in this paper to demonstrate the versatility of the proposed method which can handle partial standard and auxiliary views as well.
Nonlinear Energy Pumping With Strongly Nonlinear Coupling: Identification of Resonance Captures in Numerical and Experimental Results
Authors: Gourdon E. , Coutel S. , Lamarque C. H. , Pernot S.
Published: June 2008

The present work aims to study the effect of a nonlinear energy sink (NES) with relatively small mass on the dynamics of a coupled system under impulsion with free oscillations. The process of energy transfer is governed by structure of damped nonlinear normal modes of the system. In particular the energy pumping occurs if the nonlinear normal mode is quickly broken down with rather abrupt decrease of both amplitudes, i.e. a bifurcation (brutal change of frequency) is associated with the breakdown of the resonant regime of vibrations. The theoretical effects are experimentally verified with a mechanical experiment which confirms the above results by using a small building model. To identify those frequency migrations, a new wavelet-based methodology, namely quasi-continuous wavelet method, is used.
An Approach for Compensation of Geometric Faults in Machine Tools
Authors: Rudolf Christian , Wauer Jo¨rg , Munzinger Christian , Fleischer Ju¨rgen
Published: June 2008

Geometric faults in parts of machine tools with parallel kinematics lead to stresses in the structure and deflections of the tool center point, reducing the quality of the workpiece. Improving the design of machine tools can reduce these influences. In this paper an approach to compensate the influence of geometric faults in parallel kinematics based on the design of an adaptronic strut is introduced. The strut is divided in two halves and two piezoelectric transducers are implemented in between them, used as sensor and actuator, respectively. A preliminary design of the adaptronic strut is presented. The problems of measuring low-frequency signals using piezoelectric transducers are considered in the design. Finally, a primary analytical model of the dynamical behavior of the adaptronic compensation unit is presented. The strut and its connection to the surroundings are regarded as a flexible multibody system, the equations of motion are derived using linear graph theory. Some simulation results are presented.
MRI Scanner Vibration and Acoustic Noise
Authors: Mechefske Chris K.
Published: June 2008

To characterize the vibration properties as well as the acoustic noise properties of the gradient coil, a finite element (FE) model was developed using the dimensional design specifications of an available gradient coil insert and the concentration of the copper windings in the coil. This FE model was then validated using experimentally collected vibration data (experimental modal testing of the gradient coil in a free-free state (no boundary constraints)). Based on the validated FE model, boundary conditions (supports) were added to the model to simulate the operating condition when the gradient coil insert is in place in an MRI machine. Vibration analysis results from the FE model were again validated through experimental vibration testing, this time with the gradient coil insert installed in the MRI scanner and excited using swept sinusoidal time waveforms. The simulation results from the computational acoustic noise model were also validated through experimental noise measurement from the gradient coil insert in the MRI scanner using swept sinusoidal time waveform inputs. Comparisons show that the FE model predicts the vibration properties and the computational acoustic noise model predicts the noise characteristic properties extremely accurately.
Orbit Motion Tracking Control for Rotating Machine With Magnetic Suspensions
Authors: Sun Guangyoung
Published: June 2008

Conventional use of active magnetic bearings (AMB) focuses on keeping a rotor centered at the zero reference. In this research, a control algorithm is developed for an alternate task of tracking high-bandwidth sinusoidal targets: whirling and conical motions. To increase robustness to the parametric uncertainty and the nonlinearity of inherent AMB dynamics, the sliding mode control is developed based on an original nonlinear AMB model with an uncertain magnetic force constant. Performance indices, such as the I2R power loss, the tracking error and the phase lag, are compared for the two target motions, and they are also utilized to find an optimal bias current of the actuators. Simulation results show that the rotor follows the two high-bandwidth large motion targets with low tracking error and phase lag in the presence of parametric uncertainty. Orbit motion tracking control has a variety of potential applications in rotating machinery such as active rotating stall control, in which seal clearance is required to follow a sinusoidal dynamic motion.
Numerical Approximation of Bilinear Control of the Schroedinger Equation
Authors: Kime Katherine A.
Published: June 2008

We consider the one-dimensional Schroedinger equation in which the control is a time-dependent rectangular potential barrier/well. This is a bilinear control problem, as the potential multiplies the state. Differential geometric methods have been used to treat the bilinear control of systems of finitely many ODEs, and have been applied to the Schroedinger equation (quantum systems). In this paper we will calculate, using MATLAB, explicit controls which steer localized initial data to localized terminal data. These will be obtained using the Crank-Nicolson approximation, in which both space and time are discretized. If one semi-discretizes, in space, one obtains a bilinear control problem for a system of finitely many ODEs. One may pass from the semi-discretized system to Crank-Nicolson using the trapezoid rule. Thus the controls we calculate may be used to construct approximations to controls for the system of ODEs.
Closed Boundary Offset From the Medial Axis
Authors: Zhang Feiqi , Faddis Terry
Published: June 2008

Closed boundary orthogonal offset has been a default function in many CAD systems and has applications in manufacturing engineering such as toolpath generation and computer science fields such as image processing. Most current solutions to this function are limited to the single boundary inputs composed of linear segments and circular arcs. This paper describes a novel method to generate the approximate offsets of closed boundaries directly from the associated medial axis. The method accepts both single boundaries and multi-connected boundaries as input. The local and global intersection problems are entirely avoided. An extended discrete medial axis transform construction algorithm for multi-connected boundaries is introduced. The associated tree structure storing the medial axis data is generated along with the medial axis. The discrete characteristic of the medial axis construction method also gives the offset method the advantageous potential to handle B-spline inputs.