bluuebunny/crossref_metadata_2025 huggingface dataset:
Local Hierarchical Grid Refinement for Analysis Using Structured Grids
Authors: Kumar Ashok V. , Burla Ravi K.
Published: July 2010

Structured grids with regular shaped uniform elements are easy to generate automatically and have been used in extended finite element approaches to avoid mesh generation difficulties. But the grid or mesh should ideally have higher resolution in areas where the solution has large gradients. In this paper a technique for refinement of structured grids is presented that allows refinement of the grid without violating compatibility requirements by using solution structures constructed using approximate step functions. Essential boundary conditions are applied using implicit boundary method, which allows boundary conditions to be imposed even when there are no nodes on the boundary. This grid refinement technique is evaluated using two dimensional elasticity problems that involve stress concentration.
A Least-Squares Galerkin Split Finite Element Method for Compressible Navier-Stokes Equations
Authors: Kumar Rajeev , Dennis Brian H.
Published: July 2010

A novel finite element method is proposed that employs a least-squares method for first-order derivatives and a Galerkin method for second order derivatives, thereby avoiding the need for additional unknowns required by a pure LSFEM approach. When the unsteady form of the governing equations is used, a streamline upwinding term is introduced naturally by the least-squares method. Resulting system matrix is always symmetric and positive definite and can be solved by iterative solvers like pre-conditioned conjugate gradient method. The method is stable for convection-dominated flows and allows for equal-order basis functions for both pressure and velocity. The stability and accuracy of the method are demonstrated in the context of compressible flows by results of few compressible benchmark problems solved using low-order C0 continuous elements.
Using Multiple Open-Source Low-Cost Unmanned Aerial Vehicles (UAV) for 3D Photogrammetry and Distributed Wind Measurement
Authors: Jensen Austin M. , Morgan Daniel , Chen YangQuan , Clemens Shannon , Hardy Thomas
Published: July 2010

Small, low-cost unmanned aerial vehicles (UAV) has made data acquisition more convenient and accessible for many applications. Using multiple UAVs (a coven) brings even more advantages like redundancy and distributed information. The objective of this paper is to show how a coven of UAVs can help two applications: measuring wind and 3D photogrammetry.
Switched Stiffness Vibration Controllers for Fluidic Flexible Matrix Composites
Authors: Lotfi-Gaskarimahalle Amir , Rahn Christopher D.
Published: July 2010

This paper investigates semi-active vibration control using Fluidic Flexible Matrix Composites (F2MC) as variable stiffness components of flexible structures. The stiffness of F2MC tubes can be dynamically switched from soft to stiff by opening and closing an on/off valve. Fiber reinforcement of the F2MC tube changes the internal volume when externally loaded. With an open valve, the fluid in the tube is free to move in or out of the tube, so the stiffness is low. When the valve is closed, the high bulk modulus fluid resists volume change and produces high stiffness. The equations of motion of an F2MC-mass system is derived using a 3D elasticity model and the energy method. The stability of the unforced dynamic system is proven using a Lyapunov approach. To capture the important system parameters, nondimensional full order and reduced order models are developed. A Zero Vibration (ZV) state switch technique is introduced that suppresses vibration in finite time, and is compared to conventional Skyhook semiactive control. The ITAE performance of the controllers is optimized by adjusting the open valve flow coefficient. Simulation results show that the optimal ZV controller outperforms the optimal Skyhook controller by 13% and 60% for impulse and step response, respectively.
Improved Sensitivity and Reliability Analysis of Nonlinear Euler-Bernoulli Beam Using a Complex Variable Semi-Analytical Method
Authors: Jin Weiya , Dennis Brian H. , Wang Bo Ping
Published: July 2010

The semi-analytical method (SAM) has been reported serious accuracies in sensitivity analysis of structural elements such as frame, beam, plate elements because the finite difference method (FDM) used in the SAM is sensitive to the step size. The proposed semi-analytical complex variable method (SACVM) adopts the complex variable method (CVM) to avoid the accuracy problem and maintain the computational efficiency of the SAM. Various methods have been developed to improve the accuracy of the SAM in linear structural problems. However, a few methods address this accuracy problem for nonlinear cases. The paper applies the SACVM to a geometrical nonlinear Euler-Bernoulli beam to obtain the accurate sensitivity of finite element response. As an example application, the SACVM sensitivities are used to compute the reliability index of a defined limit state function for the nonlinear beam. The results reveal that the SACVM can always compute response sensitivity and system reliability consistently, accurately and efficiently. The method is also computationally efficient as it employs a semi-analytical approach. The SACVM is easily applicable and only requires minor modifications to existing finite element codes, therefore it has great application in practical problems.
Fault Parameter Identification for Model Based Prognostics of a Ball Bearing With an Outer Race Defect
Authors: Kappaganthu Karthik , Nataraj C. , Samanta Biswanath
Published: July 2010

This paper deals with identifying the fault parameters of a rotor-bearing system with an outer race defect. The fault parameters can then be used for prognostics. The faults in the bearing are modeled as pits in the outer race of a bearing in a rotorbearing system with four degrees of freedom. Discrete wavelet transforms are used to obtain the energy and entropy features of the rotor-bearing system. The relationship between the features and the fault parameter is studied. Particle swarm optimization is used to generate an optimal set of features. This optimal feature set is used to train an artificial neural network to determine the amount of fault in the system.
Low-Frequency Pulse Width Modulation Design for HVAC Compressors
Authors: Burke William , Auslander David
Published: July 2010

This paper discusses the design of low-frequency pulse width modulation for heating ventilation and air conditioning (HVAC) compressors. HVAC units are traditionally controlled using nonlinear control techniques like hysteresis control. Using a very long pulse width, this method can treat an on/off air conditioner or heat pump compressor as a variable input for which traditional linear (or nonlinear) controls can be applied. The key advantage of this method is direct control over the compressor power using tunable saturation. Power control is especially useful when considering load management and real time energy pricing.
An Approach to Determine the Test Intervals for CBM
Authors: Chen Zhong-Zhe , Huang Hong-Zhong , Liu Yu , Miao Qiang , Ren Pei-Yu
Published: July 2010

In this paper, reduction factor, which describes the degree of service age reduction resulting from the preventive maintenance, is introduced into a condition-based maintenance strategy. The model determining the sequential test intervals is formulated under the constraint that the probability that the failure has not test successfully within each test interval should be less than a fixed threshold. The failure risk of deteriorating system can be reduced via shortening test interval. The effectiveness of the presented methods is illustrated via a numerical case.
Mobile Agent Based Integration Framework for Flexible Dynamic Job Shop Scheduling
Authors: Cao Hua-Jun , Chou Yu-Cheng , Cheng Harry H.
Published: July 2010

Although production scheduling has been extensively studied, it is limited in the scope of applications. A mobile agent based flexible dynamic scheduling framework is presented in this article as a scheme to integrate various scheduling models, approaches, and algorithms, and flexibly and autonomously adapt the disturbances in the shop floor. Therefore, such a mobile agent based framework can help expand the scope of applications in the production scheduling field. In this framework, there are three kinds of main agents, including order data agent, scheduling model agent, and cell data agent. The order and cell data agents are designed to acquire dynamically calculated and formatted data from the systems and devices. The scheduling model agent is designed to obtain the optimal solution for distributed manufacturing cells to achieve high performance, such as minimizing the energy consumption. Devices, such as machine tools, are integrated into the framework through intelligent embedded terminals, which can be used by human operators or triggered by sensors to acquire the real-time processing data and on-the-spot conditions. A C based multi-agent platform, which is called Mobile-C, is adopted to develop the mobile agents for real-time and resource constrained applications with interface to hardware in different execution environments. A computational experiment of energy-saving scheduling based on generic algorithm is presented to validate the proposed mobile agent-based dynamic scheduling framework.
Flexible Dynamic Task Allocation in Cooperative Mission-Based Robotic Systems
Authors: Nestinger Stephen S. , Cheng Harry H. , Chen Bo
Published: July 2010

Mission-based multi-robot systems (MRS) require the ability to quickly adapt to different missions while maintaining the innate advantages of cooperation and fault tolerance. This requires a flexible architecture capable of adapting to real-time changes in the system while dynamically assigning tasks to available drones. The provided mobile agent-based dynamic task allocation architecture enables non-centralized methods for allocating tasks to a heterogeneous system of mobile robots. The architecture utilizes three types of intelligent software agents including a mobile task agent, stationary control agent, and a mobile behavior agent. A mobile task agent is used to automatically collect the next available task and communicates with the on-board stationary control agent in order to complete the desired task. A mobile behavior agent is used to automatically gather the robot specific behaviors necessary to execute the low-level reactive control system required for the task. A case study involving border patrolling demonstrates the feasibility of the dynamic task allocation architecture. A simple yet effective wall-following behavior algorithm is given.
Supervisory Control of Dynamical Systems With Uncertain Time Delays
Authors: Song Bo , Sun Jian-Qiao
Published: July 2010

This paper presents a study of controlling dynamical systems with uncertain and varying time delays. We apply the supervisory control algorithm to handle uncertainties in time delay. The hysteretic switching rule selects control gains out of the set of pre-determined optimal feedback gains for certain time delays in a range with known lower and upper bounds. The criterion is to judge when the system stays stable for any gains being selected and has a smaller switching index when the uncertain time delay varies in a known interval. A linear time-invariant system is used as an example to demonstrate the theoretical work.
An Object-Space Based Machining Simulation in Milling: Part 2 — By Toroidal Surface
Authors: Aras Eyyup
Published: July 2010

This is the second part of a two-part paper presenting an efficient parametric approach for updating the in-process workpiece represented by the Z-map. With the Z-map representation, the machining process can be simulated by intersecting z-axis aligned vectors with cutter swept envelopes. In this paper the vector-envelope intersections are formulized for the toroidal section of a fillet-end mill which may be oriented arbitrarily in space. For a given tool motion a toroidal surface generates more than one envelope. In NC machining because the torus is considered as one of the constituent parts of a fillet-end mill, only some parts of the torus envelopes, called contact envelopes, can intersect with Z-map vectors. In this paper an analysis is developed for separating the contact-envelopes from the non-contact ones. When a fillet-end mill has an orientation along the vertical z-axis of the Cartesian coordinate system, which happens in 2 1/2 and 3-axis machining, the number of intersections between a Z-map vector and the swept envelope of a toroidal section of the fillet-end mill is maximum one. For finding this single intersection point one of the numerical root finding methods, i.e. bisection, can be applied to the nonlinear function obtained from vector-envelope intersections. On the other hand when a fillet-end mill has an arbitrary orientation, the number of intersections can be more than one and therefore the numerical root finding methods cannot be applied directly. Therefore for addressing those multiple intersections, a system of non-linear equations in several variables, obtained by intersecting a Z-map vector with the envelope surface of the toroidal section of a fillet-end mill, is transformed into a single variable non-linear function. Then developing a nonlinear root finding analysis which guarantees the root(s) in the given interval, those intersections are obtained.
The Initialization Response of Linear Fractional-Order Systems With Ramp History Functions
Authors: Hartley Tom T. , Lorenzo Carl F.
Published: July 2010

In this paper, the distinction between an operator’s historical initial condition function, the consequential initialization function of the operator, and the resulting initialization response of an entire system, is discussed. The paper then presents the initialization responses for fractional-order systems that have specifically had arbitrarily-long ramp displacements in negative time.
Different Types of Instabilities and Complex Dynamics in Fractional Reaction-Diffusion Systems
Authors: Gafiychuk Vasyl , Datsko Bohdan
Published: July 2010

In this article we analyze a influence of possible instabilities on pattern formations in the reaction-diffusion systems with fractional derivatives. The results of qualitative analysis are confirmed by numerical simulations. The main attention is paid to two models: a fractional order reaction diffusion system with Bonhoeffer-van der Pol kinetics and to Brusselator model.
Contact Dynamics With Onset of Plasticity in Probing Nanoscale Thin Solid Films by AFM and Nanoindentation
Authors: He Xiaoling
Published: July 2010

This study is focused on the nanoscale AFM/nanoindentation probing tip dynamics in scratching and indenting thin solid films of nanoscale. A model is developed to identify bifurcation conditions that define the stick-slip oscillation patterns of the AFM tip. The model incorporates the inelastic deformation in the contact dynamics. The study reveals that the local energy fluctuations as a function of the inelastic deformation, defect formation, material properties and contact parameters determine the stick-slip behavior of the AFM tip. In addition, the transient variation of the localized function at the adhesion junction makes the response nonlinear. By quantifying the relation between the bifurcation parameters and the oscillation behavior, this model prescribes the complex adhesion dynamics of the contacting solids at nanoscale. Specifically, the model identified the stick-slip behavior in relation to the inelastic deformation and the local potential variations, which enables the model to justify the experimental observations and the molecular dynamics simulation of the adhesion/ friction dynamics at the nanoscale contact.
Response-Only Frequency-Domain Method for Structural Damage Detection
Authors: Zhong Shuncong , Oyadiji S. Olutunde
Published: July 2010

This paper proposes a response-only method in frequency domain for structural damage detection by using the derivative of natural frequency curve of beam-like structures with a traversing auxiliary mass. The approach just uses the response time history of beam-like structures and does not need the external source of force excitation. The natural frequencies of a damaged beam with a traversing auxiliary mass change due to change in flexibility and inertia of the beam as the auxiliary mass is traversed along the beam. Therefore the auxiliary mass can enhance the effects of the crack on the dynamics of the beam and, therefore, facilitating locating the damage in the beam. That is, the auxiliary mass can be used to probe the dynamic characteristic of the beam by traversing the mass from one end of the beam to the other. However, it is impossible to obtain accurate modal frequencies by the direct operation of the Fast Fourier Transform of the response data of the structure because the frequency spectrum can be only calculated from limited sampled time data which results in the well-known leakage effect. A spectrum correction method is employed to estimate high accurate frequencies of structures with a traversing auxiliary mass. In the present work, the modal responses of damaged simply supported beams with auxiliary mass are computed using the Finite Element Analysis. The graphical plots of the natural frequencies versus axial location of auxiliary mass are obtained. The derivatives of natural frequency curve can provide crack information for damage detection of beam-like structures. However, it is suggested that the derivative do not go beyond the third derivative of natural frequency curves to avoid the difference approximation error which will be magnified at higher derivative. The sensitivity of crack index for different noise, crack depth, auxiliary mass and damping ratio are also investigated. The simulated result demonstrated the efficiency and precision of the response-only frequency-domain method which can be recommended for the real application in structural damage detection.
Investigation of Degradation Signature for Hard Disk Drives Using Vibration and Acoustic Emission Sensors
Authors: Zeid Ibrahim , Kamarthi Sagar , Bagul Yogesh
Published: July 2010

The hard disk drive (HDD) is a critical component of any computer system. The performance of a computer system largely depends on the performance and health of its HDD. This paper investigates degradation signatures for the estimation of remaining useful life and the assessment of health of a HDD. Most of the mechanical faults in a HDD results in head-disk collision or friction. As a HDD ages, it may experience gradual damage to the head and scratches on the disk. One can expect that changes in the condition of head and disk may result in comparable changes in the characteristics of HDD vibration and acoustic emission signals. Based on this premise, this research conducted experiments on HDDs subject to accelerated deterioration. HDDs are monitored through vibration and acoustic emission sensors. Extracting features from these sensor signals, HDD degradation signatures are created. The results indicate that though degradation signatures exhibit a gradual trend with HDD aging, accurate assessment remaining useful life and health are not possible using these degradation signatures. Poor signal to noise ratio is the main impediment in this approach. The conclusion is that the best vibration and acoustic sensors available for this application are neither sensitive nor selective enough to capture the changes in the head and the disk of an aging HDD.
Numerical Investigation of Abradable Coating Wear Through Plastic Constitutive Law: Application to Aircraft Engines
Authors: Legrand Mathias , Pierre Christophe
Published: July 2010

In the field of turbomachines, better engine performances are achieved by reducing possible parasitic leakage flows through the closure of the clearance distance between blade tips and surrounding casings. Together with new technologies involving higher casing conicity for improved compression rates, direct contact is now considered as part of aircraft engines normal life. In order to avoid possibly catastrophic scenarios due to high contact efforts between the rotating and static components, implementation of abradable coatings has been widely recognized as a robust solution offering several advantages: reducing potential damage to the incurring blade as well as adjusting operating clearances, in-situ, to accept physical contact events. Nevertheless, the process of wear undergone by abradable coatings is not well understood and its consequences are still under investigation. In the present work, its macroscopic behavior is numerically approximated through a piecewise linear plastic constitutive law which allows for real time access to the current abradable layer profile. First results prove convergence in time and space of the proposed approach and show that the frequency content of the blade response is clearly affected by the presence of abradable coatings. It seems that opening the clearance between the blade tip and the casing during wear leads to large amplitudes of motion far from the usual linear conditions provided by the well-known Campbell diagrams.
Design and Implementation of Sensing and Estimation Software in AggieNav, a Small UAV Navigation Platform
Authors: Coopmans Calvin , Chao Haiyang , Chen YangQuan
Published: July 2010

Small UAV performance is limited by the sensors and software filters used in the navigational systems. Several solutions of various complexity and cost exist, however no ready-made solutions exist for a high-accuracy, low-cost UAV system. Presented is the design (low-level system as well as high-level extended Kalman filter) for a specifically designed small-UAV navigation platform, AggieNav.
Parameter Sensitivity Analysis of Rotating Beams in Frequency Domain
Authors: Ansari Masoud , Esmailzadeh Ebrahim , Jalili Nader
Published: July 2010

Many mechanical rotating systems can be modeled as a cantilever beam attached to a rotating substrate. Vibratory beam gyroscopes are good examples of such systems. They consist of a rotating beam with a tip mass, attached to a rotating base. Due to the base rotation, the governing partial differential equations of the system are coupled, and hence, the system undergoes coupled torsional-bending vibrations. The coupling effect complicates the frequency analysis of the system, especially in determining the system characteristic equation. Many investigators have chosen to use the assumed mode method in their analysis of such systems instead of extracting the exact mode shapes of the system. In spite of all these difficulties, this paper addresses the exact frequency analysis of such systems and presents a closed-form frequency characteristic equation and evaluates the accurate values of the natural frequencies. The application of the proposed method is not limited to the system at hand, as it can be utilized for analyzing general systems with coupled governing equations of motion. Having analyzed a closed-form frequency equation has two valuable advantages: a) it can serve as the basis for the subsequent time-domain analysis; and b) it can be very essential in developing control strategies. In this study a thorough sensitivity analysis is performed to determine the effects of different parameters on the natural frequencies of the coupled vibrating system. The proposed method reveals some interesting findings in the systems which were difficult, if not impossible, to be revealed by the assumed mode method commonly utilized in many research work reported recently in literature.
Electromechanical Modeling of the Low Frequency MEMS Energy Harvester
Authors: Karami M. Amin , Inman Daniel J.
Published: July 2010

An analytical electromechanical model is proposed to predict the deflection, voltage and the power output a proposed low frequency micro harvesting structure. The high natural frequencies of the existing designs of MEMS vibrational energy harvesters are serious drawbacks. A zigzag design is proposed to overcome this limitation. The mode shapes of the free vibration problem are first calculated together with the natural frequencies of the structure. The piezoelectric direct and reverse effect equations together with the electrical equations are used to relate the voltage output of the structure to the base vibrations magnitude and frequency. The closed form solution of the continuous electromechanical vibrations precisely gives the power output as a function of base acceleration spectrum. The usefulness of the design is proved by the significant increase of the power output from the same base accelerations, providing a method of designing a MEMS harvester with low natural frequency.
Design of a New Type of Eddy Current Damper With Increased Damping Density
Authors: Zuo Lei , Scully Brian , Nayfeh Samir
Published: July 2010

Eddy current dampers have advantages of no mechanical contact, high reliability and stability, but also suffer from the disadvantage of large mass and packing size. In this paper we present a new type of eddy current damper with remarkable high efficiency and compactness. Instead of orienting the magnetic field in a uniform direction, we split the magnetic field into multiple ones with alternative directions so as to reduce the electrical resistance of the eddy current loops and thus to increase the damping force. Experimental results demonstrate that an eddy current damper of 100 × 150 × 140 mm3 has a damping coefficient nearly 3000 Ns/m. The damping density [Ns/m/m3] and dimensionless damping constant are 3–7 times higher than those in literature.
Modeling and Analysis Support for Complex Deformable Systems Interfacing With Crack-Prone Systems
Authors: Ma Jianfeng , Summers Joshua David , Joseph Paul F.
Published: July 2010

In this paper, we describe a meshless integral method based on the regularized boundary integral equation to model and simulate complex deformable systems interfacing with crack-prone systems that traditional interconnected Finite Element Method (FEM) has difficulty addressing. This method is an improved version of Local Boundary Integral Equation with the following enhancements: (1) the subtraction method is used to remove the strong singularity in the local integral equation making the new method practical and accurate; (2) a special numerical integration scheme is employed for the calculation of integrals with weak singularity to further improve accuracy; and (3) the collocation method is employed to enforce essential boundary conditions, while the natural boundary conditions are incorporated in the system governing equation and require no special handling. This method has been used to analyze linear elasticity, elastoplasticity with small deformation, and elastoplasticity with large deformation. This meshless method offers the following advantages over other candidate meshless algorithms: ease of imposing essential boundary conditions, elimination of a background mesh, numerical stability, and high accuracy. We detail the requisite future work to use this meshless method for modeling and simulating complex deformable systems interfacing with crack-prone systems.
On the Usage of Dynamic Vibration Absorbers for Reduction of Forced Vibrations of a System of Coupled Rigid Bodies
Authors: Chebanov Dmitry , Kovalev Alexander M. , Bolgrabskaya Irina A. , Shcherbak Vladimir F.
Published: July 2010

In this paper we study the problem of neutralizing the forced vibrations of a chain of heavy rigid bodies coupled by one-degree-of-freedom joints using dynamic vibration absorbers. Each absorber is modeled by a system that has a constant mass and is capable of making instantaneous changes in its stiffness. We propose and analyze several strategies for introducing the absorbers that differ from each other by the number of absorbers attached and the way they are positioned on the chain links. In particular, we suggest a way to choose the parameters of the absorbers so that their controlled motion totally compensates the effect of the external perturbations.
Improvement of Degeneracy for Hybrid Transducer
Authors: Ting Yung , Tan Le Ba , Hariyanto Gunawan , Hou Bing-Kuan , Thang Lang Van , Chen Cheng-Yu , Son Tran Thai
Published: July 2010

In this paper, a new design of hybrid transducer consisting of individual longitudinal and torsional vibrators is investigated. Degeneracy approach for searching the same resonant frequency of both the longitudinal and torsional ceramic vibrators is the primary task of hybrid transducer design. In this study, a new structure is proposed so that a range of degeneracy can be found, which provides more possible configuration design of the longitudinal and torsional vibrators. A case study is presented to demonstrate the structure design and the approach of degeneracy. Also, an optimal design of large torque is achieved based on the searched range of degeneracy. With the determined driving frequency for both the longitudinal and torsional vibrators, simulation is carried out to verify the function and performance of the transducer.
Distributed Sensing Signals of Truncated Conical Shells With Clamped-Free Boundary Conditions
Authors: Li H. , Chen Z. B. , Tzou H. S.
Published: July 2010

In aerospace structures, vehicles, civil structures, conical shells are used to support a part or connect different parts, such as spacecraft adaptors, fixtures of machine tools. This type of structures has the possibility of vibration isolation. The final purpose of the on-going research is to isolate the supported part from the vibration transferred from the other end. As a phase of the research, the present paper emphasizes on the distributed sensing signals and modal voltages of the truncated conical shell. To simulate free vibrations of supported part, one end of the truncated conical shell is clamped and the other end is free. The piezoelectric patches are attached on top skin of the shell along diagonal helical line. This paper presents an analytical procedure of sensing of truncated conical shell supporting a mass. The displacement functions satisfying the special boundary conditions are given. Based on the thin-shell theory and Donnel-Mushtari-Valsov theory, sensing equations of the piezoelectric stripes are derived. The sensing signals consist of four components, i.e. sensing signals due to meridional and circular membrane strains, meridional and circular bending strains. These components are studied separately to show their distributions to the sensing signals. Finally, a case study is carried out using a sample truncated conical shell model with laminated piezoelectric stripes.
Web-Based Data Inquiry and Real-Time Control of Structural Health Monitoring Sensor Networks
Authors: Chen Bo , Liu Wenjia , Wang Jinjiang , Slepak Justin
Published: July 2010

This paper presents a Web-based data inquiry and real-time control of sensor’s operating mode for structural health monitoring sensor networks. The main objective of the presented system is to provide a Web interface for real-time sensor data visualization, sensor-level damage diagnosis, and control of sensor’s operating mode. Web services are available both on distributed sensor nodes and a data repository machine. Users can request Web pages hosted on the sensor nodes or the data repository machine by specifying corresponding sensor IDs. The ability of directly accessing data on sensor nodes via internet allows users to monitor a structure’s performance in a timely manner. The damage diagnosis algorithms implemented on the sensor nodes help users to assess the structural health conditions without the need of transmitting sensor data to a central data station. The presented system also provides the capability of dynamically changing sensor’s operating mode through the Web interface. This feature greatly enhances the flexibility of the system to accommodate different sensing needs and achieve a long lifespan. The system has been tested in the Laboratory to validate its capabilities.
Unified Approach for Holonomic and Nonholonomic Systems Based on the Modified Hamilton’s Principle
Authors: Kamiya Keisuke , Morita Junya , Mizoguchi Yutaka , Matsunaga Tatsuya
Published: July 2010

As basic principles for deriving the equations of motion for dynamical systems, there are d’Alembert’s principle and the principle of virtual power. From the former Hamilton’s principle and Langage’s equations are derived, which are powerful tool for deriving the equation of motion of mechanical systems since they can give the equations of motion from the scalar energy quantities. When Hamilton’s principle is applied to nonholonomic systems, however, care has to be taken. In this paper, a unified approach for holonomic and nonholonomic systems is discussed based on the modified Hamilton’s principle. In the present approach, constraints for both of the holonomic and nonholonomic systems are expressed in terms of time derivative of the position, and their variations are treated similarly to the principle of virtual power, i.e. time and position are fixed in operation with respect to the variations. The approach is applied to a holonomic and a simple nonholonomic systems.
Approach to Compute the Lyapunov Characteristic Exponents for Continuous Dynamical Systems of Dimension Four
Authors: von Bremen Hubertus
Published: July 2010

In this paper an existing general method for accurately computing the Lyapunov Characteristic Exponents of continuous dynamical systems will be implemented for systems of dimension four. Previously, this approach has only been implemented for systems up to dimension three. A numerical example illustrating the accuracy of the implementation is presented.
Dual Approach for Electromechanical Coupling in MEMS
Authors: Rochus Ve´ronique , Golinval Jean-Claude , Geuzaine Christophe
Published: July 2010

In this paper we present an approach for the computation of coupled electromechanical problems in micro-electromechanical systems based on a vector potential formulation of the electrostatic problem. This formulation is the dual of the scalar potential approach commonly used in the literature. We present an analytic derivation of the force computed using this dual method based on the virtual work principle, and compare the primal and dual approaches on the finite element solution of simple two-dimensional test-cases.
Viscoelastic Damping Effect on Brake Squeal Noise
Authors: Chevallier Gael , Renaud Franck , Dion Jean-Luc
Published: July 2010

Brake squeal remains a widespread cause for discomfort in automobiles. Manufacturers overcome this problem by adding damping materials in their systems. The purpose of this work is to take into account the damping in the modeling. As the materials exhibit a viscoelastic behavior, the authors chose to model the damping with the Generalized Maxwell model. Moreover, the authors have tested their method on a detailed Finite Element-model of a brake system. To compute the complex poles of the model, the authors have established a state-space formulation of the viscoelastic model with a new assumption that allows one to reduce the number of states. Making the computation on the whole model is rather difficult due to the number of Degrees Of Freedom, the model is thus reduced on a basis constituted with the eigenvectors of the undamped model. Several results are also presented and discussed as the observed phenomena are rather different from the results obtained with undamped systems.
A Tire Model for Off-Highway Vehicle Simulation and Comfort Evaluation
Authors: Langer Thomas H. , Hansen Michael R. , Ebbesen Morten K. , Mouritsen Ole O̸.
Published: July 2010

Manufacturers of construction machinery are challenged to accommodate legal requirements on the vibration exposure associated with their products. Hence, the ability to evaluate ride comfort by virtual prototyping is needed. One of the derived necessities is a modeling approach that can handle big off-road tires on irregular terrain and even the passing of sharp corner obstacles. In this paper a simple tire model combining the well known slip theory and a displaced volume approach is presented. A non-gradient optimization routine is applied for parameter identification by minimizing the difference between simulated data and experimental data obtained from a full vehicle model passing a set of well defined obstacles. The two most important deviations have been identified as frequency and force amplitude response because comfort is computed as a frequency weighted acceleration of the operator. Based on the obtained agreement between simulated and measured results the tire model is considered as well suited for comfort evaluation and, subsequently, reliable model based design.
Modeling of Spinning Solar Sail by Multi Particle Model and Its Application to Attitude Control System
Authors: Funase Ryu , Sugita Masayuki , Mori Osamu , Tsuda Yuichi , Kawaguchi Junichiro
Published: July 2010

In this paper, the attitude motion and attitude control strategy of spinning solar sail are discussed. As the spinning type solar sail does not have any rigid structure to support its membrane, the impulsive torque by the RCS can introduce oscillatory motion of the membrane. Thus, an “oscillation free” attitude controller is needed, which takes into account the flexibility of the membrane and avoid unnecessary oscillatory motion. First, the dynamics model and numerical model were introduced, and the validity of these models and dominant out-of-plane membrane vibration mode is examined by membrane vibration experiment and comparison between both models. Then, based on the analysis of the dynamics of torque-free motion, it was shown that a spinning solar sail has three oscillation modes of nutation, one of which is equal to the spinning rate of the spacecraft. The dominancy of each nutation mode was analytically and numerically discussed. Then, we discussed the spin axis maneuver control using conventional RCS. It was analytically shown that continual impulsive torque synchronizing the spin rate can excite nutation velocity and that a controller is needed to damp the nutation while controlling the spin axis at the same time. The authors proposed new controller named Flex-RLC and improved one. Their effectiveness was verified by numerical simulations using precise multi-particle numerical model which can express higher order oscillatory motion of the flexible membrane, and it was found that the proposed method can control the attitude of spinning solar sail while drastically reduces the nutation velocity compared with conventional control logic. So, it can be said that the proposed method is promising fast and stable controller for spinning solar sail.
Determining the Optimum Number of RFID Readers for Efficient Asset Tracking
Authors: Oztekin Asil , Mahdavi Pajouh Foad , Kong Zhenyu , Bukkapatnam Satish T. S.
Published: July 2010

This paper aims to determine the optimum number of RFID readers and their placement for asset tracking. To achieve this goal, an optimization model based on location set covering problem (LSCP) is established. It is implemented in a healthcare facility and the required number of readers for full coverage was determined under certain constraints. This paper is a foremost study which utilizes an enhanced LSCP model for determining the number of RFID readers and their locations. The methodology is original in that it analyzes the tradeoff between cost effectiveness and overall RFID system performance, and provides possible decision guidance to optimize the RFID system. It is vital for healthcare providers to locate crucial assets in the shortest possible time, particularly in emergency situations where human lives are at risk. Hence, increasing the overall RFID system performance will definitely have a valuable effect on real time information sharing, thereby decreasing related search time for crucial assets.
Free Vibration Analysis of Rotating Tapered Bresse-Rayleigh Beams Using the Differential Transformation Method
Authors: Jackson Dominic R. , Oyadiji S. Olutunde
Published: July 2010

The free vibration characteristics of a rotating tapered Rayleigh beam is analysed in this study. First, the strain-displacement relationship for the rotating beam is formulated and used to derive the kinetic and strain energies in explicit analytical form. Second, Hamilton’s variational principle is used to derive the governing differential equation of motion and the associated boundary conditions. Third, the Differential Transformation Method (DTM) is applied to reduce the governing differential equations of motion and the boundary conditions to a set of algebraic equations from which the frequency equation is derived. Next, a numerical algorithm implemented in the software package Mathematica is used to compute the natural frequencies of vibration for a few paired combinations of clamped, pinned and free end conditions of the beam. Also, the variation of the natural frequencies of vibration with respect to variations in the rotational speed, hub radius, taper ratio and the slenderness ratio is studied. The results obtained from the Bresse-Rayleigh theory are compared with results obtained from the Bernoulli-Euler and Timoshenko theories to demonstrate the accuracy and relevance of their application.
A Modal Approach for Chaotic Vibrations of a Drillstring
Authors: Mongkolcheep Kathira , Palazzolo Alan , Ruimi Annie , Tucker Randall
Published: July 2010

The purpose of this paper is to present a methodology to predict vibrations of drilllstrings for oil recovery service. The paper extends a previous model in the literature to include drill collar flexibility utilizing a modal coordinate condensed, finite element approach. The nonlinear effects of drillstring / borehole contact, friction and quadratic damping are included. Bifurcation diagrams are presented to illustrate the effects of speed, friction, stabilizer gap and drill collar length on chaotic vibration response. A study is conducted on factors for improving the accuracy of Lyapunov Exponents to predict the presence of chaos. This study considers the length of time to steady state, the number and duration of linearization sub-intervals, the presence of rigid body modes and the number of finite elements and modal coordinates. The results may be helpful for computing Lyapunov exponents of other types of nonlinear vibrating systems with many degrees of freedom.
Damping Enhancement in Printed Circuit Boards With Potting Materials or Microfibrous Metallic Cloth
Authors: Hyatt Nesha , Black Meagan , Dean Robert , Flowers George , Grantham Brian , Garner Russ
Published: July 2010

As a result of the relatively low intrinsic damping in printed circuit boards, vibration and shock loading may excite vibration modes that lead to vibration-induced damage of the PCB and attached components. An investigation of techniques to enhance the damping in printed circuit boards is conducted. Experimental evaluation of the effects of several damping treatments was performed. Of particular interest were the effects of potting materials and microfibrous metallic cloth sandwich configurations. The results from different configurations for each type of treatment are compared and the results discussed. An overall summary of the results is presented and conclusions/observations are discussed.
Review of Recent Developments in Composite Material for Aerospace Applications
Authors: Shue Bruce , Moreira Alfonso , Flowers George
Published: July 2010

Advanced materials are a key element in the development of modern aerospace vehicles and composites are one of the most promising types of such materials. They tend to be significantly lighter than their metal counterparts, while possessing impressive strength and performance characteristics. This paper describes recent work and developments in three major types of composite materials — polymer matrix composite (PMC), metal matrix composite (MMC), and ceramic matrix composite (CMC). Recent work in nanocomposites, which is particularly applicable to polymer matrix and metal matrix composites is also presented and discussed. In addition, some recent work in composite material damping is discussed and a modeling strategy for amplitude dependent damping is developing based upon heuristic modeling considerations and experimental testing results.
Comment on “Observational and Model Evidence for Positive Low-Level Cloud Feedback”
Authors: Broccoli Anthony J. , Klein Stephen A.
Published: July 2010

Clement
et al
. (Reports, 24 July 2009, p. 460) provided observational evidence for systematic relationships between variations in marine low cloudiness and other climatic variables and found that most current-generation climate models were deficient in reproducing such relationships. Our analysis of one of these models (GFDL CM2.1), using more complete model output, indicates better agreement with observations, suggesting that more detailed analysis of climate model simulations is necessary.
Response to Comment on “Observational and Model Evidence for Positive Low-Level Cloud Feedback”
Authors: Clement Amy C. , Burgman Robert , Norris Joel R.
Published: July 2010

Broccoli and Klein argue for additional diagnostics to better assess the simulation of cloud feedbacks in climate models. We agree, and here provide additional analysis of two climate models that reveals where model deficiencies in cloud simulation in the Northeast Pacific may occur. Cloud diagnostics from the forthcoming Climate Model Intercomparison Project 5 should make such additional analyses possible for a large number of climate models.
Small Peptides Switch the Transcriptional Activity of Shavenbaby During
Drosophila
Embryogenesis
Authors: Kondo T. , Plaza S. , Zanet J. , Benrabah E. , Valenti P. , Hashimoto Y. , Kobayashi S. , Payre F. , Kageyama Y.
Published: July 2010

Transcription On and sORF

Eukaryotic transcriptomes include numerous RNAs that are presumed noncoding because they include only short open reading frames (sORFs). However, some sORF RNAs actually produce small peptides with unknown activity. Now

Kondo
et al.

(p.
336
; see the Perspective by

Rosenberg

) report the function of peptides containing 11 to 32 amino acids that are encoded by the gene
polished-rice
(
pri
).
pri
triggers N-terminal truncation of the transcription factor Shavenbaby that controls epidermal differentiation in
Drosophila
. Following
pri
expression, Shavenbaby is converted from a transcriptional repressor to an activator. Thus, sORF peptides can control transcriptional programs during embryonic development.
Performance-Based Data in the Study of STEM Ph.D. Education
Authors: Feldon David F. , Maher Michelle A. , Timmerman Briana E.
Published: July 2010

Performance-based assessments of student skill development can help inform decisions about improving graduate education.
When Still Waters Ran Deep
Authors: Kiefer Thorsten
Published: July 2010

Near the end of the last ice age, the Pacific appears to have played a bigger role in forming deep ocean waters than it does today.
A Volunteer Army for Science
Authors: Rea Donald G. , Nielsen Katherine M.
Published: July 2010

Late last year, President Obama announced an “Educate to Innovate” campaign to increase the engagement and performance of America's students in science, technology, engineering, and mathematics (STEM). The United States has more than a million scientists and engineers over 60 years of age with bachelor's degrees or higher, and nearly 600,000 doctoral students and 50,000 postdoctoral trainees in STEM fields. Existing volunteer programs prove that if the government were to dedicate new federal resources, tens of thousands of volunteers could be recruited from these groups and trained to help the United States achieve its national goals.