bluuebunny/crossref_metadata_2025 huggingface dataset:
Realizing Potential: Building Regional Organizing Capacity in Polycentric Urban Regions
Authors: Meijers Evert , Romein Arie
Published: July 2003

Regional planning for and in polycentric urban regions may entail certain competitive potentialities over a stand-alone development of their individual cities or city-regions. These potentialities relate to the pooling of resources, complementarities and spatial diversity. It seems that planners are increasingly aware of these potentialities as in several European countries attempts are made to identify such polycentric regional systems of formerly independent and distinct cities that are located close to each other, often building on increasing functional relationships between them. This article argues, however, that in order actually to exploit the theoretical potential planning for polycentric urban regions has, one needs to do more than just identify a polycentric system on the map. Rather, an active building of regional organizing capacity is needed - that is, the ability to regionally co-ordinate developments through a more or less institutionalized framework of co-operation, debate, negotiation and decision-making in pursuit of interests at the regional scale - to shape a polycentric urban region's competitive advantages. This need for regional organizing capacity may sound obvious, but in practice successful examples of proclaimed polycentric urban regions developing networks for regional co-ordination and action are rather thin on the ground. Basing our argument on evidence from four polycentric urban regions in North West Europe, it was found that the building of regional organizing capacity is conditioned by a number of spatialfunctional, political-institutional and cultural factors. Major constraints in the examined regions include institutional fragmentation, an internal orientation of key persons and the lack of identification with the region at large.
A Continuum Damage Theory with Rotation Gradients
Authors: Wang Gang-Feng , Yu Shou-Wen , Feng Xi-Qiao
Published: July 2003

Deformation and damage evolution of materials often involve localization in some small regions, where the strain gradients and the interaction between defects are of significance. A phenomenological continuum damage theory with rotation gradient effects is presented in this paper based on the theory of couple stresses. The constitutive relations are formulated for centrosymmetrically isotropic materials and linear anisotropic materials. To illustrate the application of the present theory, the deformation and damage of a thin film/substrate system is investigated. It is found that the strain gradients exert a considerable influence on the damage distribution and failure behavior near an interface.
Failure Prediction of Aluminum Laser-Welded Blanks
Authors: Chien W. Y. , Pan J. , Friedman P. A.
Published: July 2003

The formability of aluminum-3% magnesium laser-welded blanks manufactured by 3kW YAG laser welding process is investigated in this paper. Previous experimental results showed that shear failure occurs in the welds of these blanks during tensile testing with the weld line perpendicular to the tensile axis. In order to further understand the failure in these blanks under uniaxial and biaxial straining conditions, finite element computations under generalized plane strain conditions are conducted to understand the effects of weld geometry and strength on the shear failure. The results indicate that the average plastic stress-strain behavior of the weld should be softer than that in the base metal in the direction perpendicular to the weld line. The results also show that the weld geometry has significant effects on strain localization in the weld under the tensile loading perpendicular to the weld line. The stress-strain histories of the material elements of the weld metal in tensile specimens obtained from the finite element computation are used for a failure/localization analysis. The imperfection approach of Marciniak and Kuczynski is employed to examine the failure/localization in the weld of the tensile specimens. The failure/localization analysis is based on an elastic-viscoplastic constitutive law that accounts for the potential surface curvature, material plastic anisotropy, material rate sensitivity and softening due to nucleation, growth and coalescence of microvoids. The material imperfection parameters for void nucleation and growth are obtained by fitting the results of the failure/localization analysis to those of the uniaxial tensile tests. The material imperfection parameters are then used to predict the failure strains of the blanks under biaxial straining conditions based on the stress-strain histories of the material elements obtained from finite element computations under generalized plane strain conditions. The results indicate that the forming limits of the blanks under plane strain tension and equal biaxial tension are reduced significantly when compared with that under uniaxial tension. Finally, a finite element simulation of the welded sheet under uniaxial tension is carried out with consideration of void nucleation and growth for all the material elements in the weld. Our computational results indicate that without consideration of the failure/localization analysis presented in this paper, an unrealistically high volume fraction for void nucleation must be assumed in our finite element simulation of the tensile tests in order to match the failure strains observed in the uniaxial tensile tests.
A Unified Viscoplastic Fatigue Damage Model for 63Sn-37Pb Solder Alloy Under Cyclic Stress Control
Authors: Yang X. J. , Chow C. L. , Lau K. J.
Published: July 2003

A damage coupling viscoplastic model is developed to predict fatigue life of solder alloy 63Sn-37Pb under stress control. The viscoplastic flow rule chosen employs a hyperbolic sine function. A damage evolution equation is formulated based on three distinct material deformation behaviors: (i) stress rate independent damage evolution; (ii) stress rate dependent cyclic damage evolution; and (iii) stress rate dependent ductile damage evolution. The cyclic stress testing with different stress waveforms was first conducted to investigate their progressive viscoplastic deformations of the solder alloy. The investigation reveals that the material constants used in the model can be adequately determined from the results of standard creep tests. The constitutive model is validated by comparing the predicted and measured ratchetting results of the solder alloy under different forms of stress cycling. The proposed model is found to be capable of satisfactorily describing the viscoplastic deformation and ratchetting failure behaviors of the solder alloy under the conditions of the cyclic stress loading.
An Anisotropic Damage Model for Ductile Metals
Authors: Hammi Y. , Horstemeyer M. F. , Bammann D. J.
Published: July 2003

An anisotropic ductile damage description is motivated from fracture mechanisms and physical observations in Al-Si-Mg aluminum alloys with second phases. Ductile damage is induced by the classical process of nucleation of voids at inclusions, followed by their growth and coalescence. These mechanisms are related to different microstructural and length scale parameters like the fracture toughness, the void size, the intervoid ligament distance, etc. The classical thermodynamic constraints of irreversible processes with material state variables are used to model the tensorial damage evolution coupled to the Bammann-Chiesa-Johnson (BCJ) rate-dependent plasticity. The damage-plasticity coupling is based on the effective stress concept, assuming the total energy equivalence, and written through a deviatoric damage effect tensor on the deviatoric part and through the trace of the second rank damage tensor on the hydrostatic part. The damage rate tensor is additively decomposed into a nucleation rate tensor, a void growth rate scalar, and a coalescence rate tensor. The induced damage anisotropy in mainly driven by the nucleation, which evolves as a function of the absolute value of the plastic strain rate tensor. Finally, some experimental data of cast A356 aluminum alloy are correlated with predictive void-crack evolution to illustrate the applicability of the anisotropic damage model.
On the Thermal Buckling Response of Shear-Flexible All-Edge Clamped Rectangular Plates
Authors: Al-Khaleefi Abdulateef M. , Kabir Humayun R. H.
Published: July 2003

Using an analytical approach, we investigate a thermal stability response for a rectangular plate with all-edge clamped boundary conditions. We consider the first-order shear deformation theory that utilizes shear flexible response, in order to obtain three highly coupled governing partial differential equations in three unknowns: one transverse displacement, and two independent rotations of the normal. The solution functions are assumed in the form of double Fourier series that satisfy the boundary conditions, as well as the partial differential equations. The results obtained from the analytical solution are compared with available finite element solutions. These analytically obtained results can be capitalized to check the accuracy of various approximate methods.
A Damage Analysis of Steel-Concrete Composite Beams Via Dynamic Methods: Part I. Experimental Results
Authors: Morassi Antonino , Rocchetto Luigi
Published: July 2003

This paper is an experimental investigation on damage-induced changes in modal parameters of steel-concrete composite beams subject to small vibrations. Dynamic tests have been performed on two pairs of composite beams, whose connections have different linear densities, and three damage configurations for each beam have been analyzed. Damage was induced by removing concrete around some elements connecting the steel beam and the reinforced concrete slab and consequently causing a lack of structural solidarity between the two beams. Experiments revealed that: (i) unlike axial frequencies, flexural frequencies show a rather high sensitivity to damage and therefore can be considered as a valid indicator upon a diagnostic analysis; (ii) induced damage causes the nodes of flexural vibration modes to displace towards the damaged area; (iii) in addition to hindering relative sliding on the concrete-steel interface, the elements connecting the slab and the metallic beam play a key role in reducing transversal motions between the two beams. These experimental results were crucial to outline an accurate analytical model of the dynamic behavior of composite beams with damaged connectors and to formulate a diagnostic problem from dynamic test data. Part II of this research will deal with mechanical modeling of damaged composite beams and damage identification.
A Damage Analysis of Steel-Concrete Composite Beams Via Dynamic Methods: Part II. Analytical Models and Damage Detection
Authors: Dilena Michele , Morassi Antonino
Published: July 2003

This paper is the second part of an experimental-analytical investigation on the dynamic behavior of damaged steel-concrete composite beams. In the first part of the research, we presented and discussed the experimental results of a comprehensive series of dynamic tests performed on composite beams with damage in the connection. Experimental observations suggested the formulation of a composite beam analytical model, where the strain energy density of the connection also includes an energy term associated to the occurrence of relative transversal displacements between the reinforced concrete slab and the steel beam. A comparison with experimental results shows that the model enhances accuracy in describing the undamaged state of composite beams and that it is also appropriate to accurately predict the dynamic behavior under damaged conditions. A damage detection technique based on the measurement of variation in the first flexural frequencies was then applied to the suggested model and gave positive results.
Adaptive Output Feedback Force Control of a Cantilever Beam Using a Piezoelectric Actuator
Authors: Yim W. , Singh S. N.
Published: July 2003

In this paper, we treat the question of force control and stabilization of a flexible beam using a piezoceramic actuator using only output feedback. It is assumed that there are unstructured model uncertainties, including the beam parameters, the contact surface stiffness, and the number of vibration modes in the model, and only force measurement is used for the contact force control. The controller has the structure of an inverse (a feedback linearizing) control system. In order to compensate for the unknown function in the inverse control law arising from the uncertainties in the model, its estimate is constructed by a high-gain observer. Simulation results are presented which show robust force trajectory control and stabilization in the closed-loop system in the presence of unstructured uncertainties. Furthermore, it is observed that stability and trajectory tracking are preserved in the presence of measurement noise.
A Multidisciplinary Analysis of Tail Buffeting Alleviation Using Streamwise Fences
Authors: Sheta Essam F.
Published: July 2003

A multidisciplinary analysis of vertical tail buffeting and buffeting alleviation of generic fighter aircraft is conducted. This complex multidisciplinary problem is solved for the fluid dynamics, structure dynamics, fluid-structure coupling, and grid deformation using a computing environment that controls the temporal synchronization of the data transfer between the analysis modules. The generic fighter aircraft consists of a sharp-edged delta wing with an aspect ratio of one and a swept-back, flexible, vertical twin tail with a taper ratio of 0.23. Twin streamwise fences are located at the 30% chord-station of the delta wing. The fences are used to alter the vortical flow and to delay the onset of vortex breakdown above the delta wing, in order to alleviate the twin-tail buffeting. The effect of the geometrical shape of the fences on the buffeting responses is investigated. The performance of the fences over a wide range of high angles of attack is also investigated. The trapezoidal configuration of the fences at a taper ratio of 0.7 produced the most favorable results. The results indicated that the fences are effective in reducing the aeroelastic loads and responses, especially at angles of attack less than 30°.
Direct Adaptive Control of Underwater Vehicles using Neural Networks
Authors: Kim Myung-Hyun , Inman Daniel J.
Published: July 2003

A direct adaptive neural network controller is developed for a model of an underwater vehicle. A radial basis neural network and a multilayer neural network are used in the closed-loop to approximate the nonlinear vehicle dynamics. No prior off-line training phase and no explicit knowledge of the structure of the plant are required, and this scheme exploits the advantages of both neural network control and adaptive control. A control law and a stable on-line adaptive law are derived using the Lyapunov theory, and the convergence of the tracking error to zero and the boundedness of signals are guaranteed. A comparison of the results with different neural network architecture is made, and the performance of the controller is demonstrated by computer simulations.
Robust Kalman-Filter-Based Frequency-Shaping Optimal Active Vibration Control of Uncertain Flexible Mechanical Systems with Nonlinear Actuators
Authors: Chen Shinn-Horng
Published: July 2003

In this paper, we present a time-domain control methodology, called the robust Kalman-filter-based frequency-shaping optimal feedback (KFBFSOF) control method. Using this method, we treat the active vibration control (or active vibration suppression) problem of flexible mechanical systems under simultaneously high-frequency unmodeled dynamics, residual modes, linear time-varying parameter perturbations in both the controlled and residual parts, noises (input noise and measurement noise), noise uncertainties and actuator nonlinearities. Two robust stability conditions are proposed for the flexible mechanical system, which is controlled by a KFBFSOF controller and subject to mode truncation, noise uncertainties, actuator nonlinearities and linear structured time-varying parameter perturbations simultaneously. The advantage of the presented KFBFSOF control methodology is that it can make the controlled closed-loop system have both good robustness at high frequencies and good performance at low frequencies. Besides, the proposed robust stability criteria guarantee that the designed KFBFSOF controller can make the controlled flexible mechanical system avoid the possibilities of instability induced by both spillover and time-varying parameter perturbations. Two examples are given to illustrate the application of the presented control methodology to the active vibration control problems of a simply-supported flexible beam and of a flexible rotor system.
Active Vibration Control with State Feedback in Woodcutting
Authors: Chen Y. , Wang X. G. , Sun C. , Devine F. , De Silva C. W.
Published: July 2003

Circular saws are widely used in wood processing for applications ranging from primary lumber manufacturing to furniture industry and home workshops. They directly contribute to production problems such as poor cutting accuracy, poor surface quality, short tool life, high noise levels, and excessive raw material wastage. Vibration of the saw blade during woodcutting has been identified as a key reason for poor wood recovery. In fact, about 12% of the raw material in woodcutting ends up as sawdust due to excessive sawing gap. Efficient wood sawing is being pursued with the objective of mitigating these problems; particularly, to reduce saw blade vibration and sawdust. In this paper, we present active control of saw blade vibration using linear quadratic Gaussian (LQG) control. We outline a test rig that has been developed for our experimental investigation. The system configuration is described and the control problem is formulated. The experimental procedure for identification of a system model is described. The implementation of the LQG control scheme is outlined, and typical results from the experimental control system are presented and discussed. The developed controller is shown to be very effective in the present application, as evident from the results that have been obtained. In particular, the amplitude of the saw blade vibration has been reduced by 66% on average using active control, compared to cases with no control. Also, the cutting gap (kerf) has been reduced by 25%, from 2.00 mm to 1.50 mm, through active control. In terms of 1995 prices, this would correspond to an increased revenue of $640,000 per year for a mill producing 100 MM fbm of lumber annually.
Robust Estimation-Based Control of Chaotic Behavior in an Oscillator with Inertial and Elastic Symmetric Nonlinearities
Authors: Al-Qaisia A. A. , Harb A. M. , Zaher A. A. , Zohdy M. A.
Published: July 2003

In this paper, we study the dynamics of a forced nonlinear oscillator with inertial and elastic symmetric nonlinearities using modern nonlinear, bifurcation and chaos theories. The results for the response have shown that, for a certain combination of physical parameters, this oscillator exhibits a chaotic behavior or a transition to chaos through a sequence of period doubling bifurcations. The main objective of this paper is to control the chaotic behavior for this type of oscillator. A nonlinear estimation-based controller is proposed and the transient performance is investigated. The design of the parameter update mechanism is analyzed while discussing ways to extend its performance to further account for other types of uncertainties. We examine robustness problems as well as ways to tune the controller parameters. Simulation results are presented for the uncontrolled and controlled cases, verifying the effectiveness and the capability of the proposed controller. Finally, a discussion and conclusions are given with possible future extensions.
Slow Passage through Resonance in Mathieu's Equation
Authors: Ng Leslie , Rand Richard , O'Neil Michael
Published: July 2003

We investigate slow passage through the 2:1 resonance tongue in Mathieu's equation. Using numerical integration, we find that amplification or de-amplification can occur. The amount of amplification (or de-amplification) depends on the speed of travel through the tongue and the initial conditions. We use the method of multiple scales to obtain a slow flow approximation. The Wentzel-Kramers-Brillouin (WKB) method is then applied to the slow flow equations to obtain an analytic approximation.
Vibration Characteristics of Fibrous Composites with Damage
Authors: Nayfeh Adnan H. , Abdelrahman Wael G.
Published: July 2003

A micromechanical model is developed in order to study the vibration characteristics of fibrous composites with damage. Damage is taken in the form of either a broken fiber or a matrix crack normal to the fiber direction. The unidirectionally reinforced periodic composite, when vibrating in the longitudinal (fiber) direction, is modeled as a concentric cylindrical system subjected at its outer boundaries to vanishing radial displacement and shear stress. Guided by the symmetry and the fiber-matrix interface continuity conditions, an approximate radial dependence of some of the field variables is first assumed. The two-dimensional field equations that hold in both the fiber and the matrix, together with their interface conditions, are then reduced to a quasi-one-dimensional system which automatically satisfies all interface and boundary conditions. The simplified model is applied to the study of the vibration characteristics of the composite with and without damage. The cases of broken fibers and cracked matrix are treated by invoking stress-free conditions at the crack faces. The dependence of the resonance frequencies and mode shapes on the nature and location of the damage is exploited. Significant reduction in the values of resonance frequencies can be realized for damage located close to the center of the composite system.
Control Reconfiguration Based on Hierarchical Fault Detection and Identification for Unmanned Underwater Vehicles
Authors: Ni Lingli , Fuller Chris R.
Published: July 2003

Unmanned underwater vehicles (UUVs) have been developed for various applications in ocean engineering. When failures occur to UUVs and result in abnormal operations, the only solution is to abort from the mission due to lack of fault tolerance. The purpose of this study is to investigate a method by which UUVs can continue to operate acceptably following failure occurrences. Based on a unique hierarchical fault detection and identification, this paper presents a control reconfiguration scheme with multiple sliding-mode controllers for each of the hypothesized failure modes from a discrete set [θ1, θ2,..., θ n], which depict the failure status of actuators and sensors. The reconfigured control is a probability weighted average of all the elemental control signals. We apply this method to the steering subsystem of the Naval Postgraduate School (NPS) UUV with simulated rudder and/or sensor failures. The results show that both the heading angle and the steering track have been properly compensated.
A New Approach to the Stability Analysis of Boost Power-Factor-Correction Circuits
Authors: Mazumder Sudip K. , Nayfeh Ali H.
Published: July 2003

We analyze the stability of a boost power-factor-correction (PFC) circuit using a hybrid model. We consider two multi-loop controllers to control the power stage. For each closed-loop system, we treat two separate cases: one for which the switching frequency is approaching infinity and the other for which it is finite but large. Unlike all previous analyses, the analysis in this paper investigates the stability of the converter in the saturated and unsaturated regions of operation. Using concepts of discontinuous systems, we show that the global existence of a smooth hypersurface for the boost PFC circuit is not possible. Subsequently, we develop conditions for the local existence of each of the closed-loop systems using a Lyapunov function. In other words, we derive the conditions for which a trajectory will reach a smooth hypersurface. If the trajectories do not reach the sliding surface, then the system saturates. As such, the stability of the period-one orbit is lost. Using the conditions for existence and the concept of equivalent control, we show why, for the second closed-loop system, the onset of the fast-scale instability occurs when the inductor current approaches zero. For this system, we show that the onset of the fast-scale instability near zero-inductor current occurs for a lower line voltage. Besides, when the peak of the line voltage approaches the bus voltage, the fast-scale instability may occur not only at the peak but also when the inductor current approaches zero. We develop a condition which ensures that the saturated region does not have any stable orbits. As such, a solution that leaves the sliding surface (if existence fails) cannot stabilize in the saturated region. Finally, we extend the analysis to the case in which the converter operates with a finite but large switching frequency. As such, the system has two fundamental frequencies: the switching and line frequencies. Hence, the dynamics of the system evolve on a torus. We show two different approaches to obtaining a solution for the closed-loop system. For the second closed-loop system, using the controller gain for the current loop as a bifurcation parameter, we show (using a Poincaré map) the mechanism of the torus breakdown. If the mechanism of the torus breakdown is known, then, depending on the post-instability dynamics, a designer can optimize the design of the closed-loop converter.
Nonlinear Analysis of Parallel Dc-Dc Converters
Authors: Mazumder Sudip K. , Nayfeh Ali H. , Boroyevich Dushan
Published: July 2003

We develop analytic methodologies for stability analysis of a parallel dc-dc converter using its switching model, discrete model (based on nonlinear map) and averaged model. We use these methodologies to investigate the dynamics of an interleaved and a synchronized parallel dc-dc buck converter. Using the switching and discrete models we show the mechanism and boundaries of fast-scale and slow-scale instabilities. We show the difference in mechanism of fast-scale instability between the interleaved and a synchronized converter. The averaged model does not show this difference. It also differs considerably (from the other two models) in prediction of instability boundaries.
A Benchmark Control Problem for Supercavitating Vehicles and an Initial Investigation of Solutions
Authors: Dzielski John , Kurdila Andrew
Published: July 2003

At very high speeds, underwater bodies develop cavitation bubbles at the trailing edges of sharp corners or from contours where adverse pressure gradients are sufficient to induce flow separation. Coupled with a properly designed cavitator at the nose of a vehicle, this natural cavitation can be augmented with gas to induce a cavity to cover nearly the entire body of the vehicle. The formation of the cavity results in a significant reduction in drag on the vehicle and these so-called high-speed supercavitating vehicles (HSSVs) naturally operate at speeds in excess of 75 m s-1. The first part of this paper presents a derivation of a benchmark problem for control of HSSVs. The benchmark problem focuses exclusively on the pitch-plane dynamics of the body which currently appear to present the most severe challenges. A vehicle model is parametrized in terms of generic parameters of body radius, body length, and body density relative to the surrounding fluid. The forebody shape is assumed to be a right cylindrical cone and the aft two-thirds is assumed to be cylindrical. This effectively parametrizes the inertia characteristics of the body. Assuming the cavitator is a flat plate, control surface lift curves are specified relative to the cavitator effectiveness. A force model for a planing afterbody is also presented. The resulting model is generally unstable whenever in contact with the cavity and stable otherwise, provided the fin effectiveness is large enough. If it is assumed that a cavity separation sensor is not available or that the entire weight of the body is not to be carried on control surfaces, limit cycle oscillations generally result. The weight of the body inevitably forces the vehicle into contact with the cavity and the unstable mode; the body effectively skips on the cavity wall. The general motion can be characterized by switching between two nominally linear models and an external constant forcing function. Because of the extremely short duration of the cavity contact, direct suppression of the oscillations and stable planing appear to present severe challenges to the actuator designer. These challenges are investigated in the second half of the paper, along with several approaches to the design of active control systems.
Payload Pendulation Reduction Using a Variable-Geometry-Truss Architecture with LQR and Fuzzy Controls
Authors: Dadone Paolo , Lacarbonara Walter , Nayfeh Ali H. , Vanlandingham Hugh F.
Published: July 2003

We investigate the feasibility of a variable-geometry truss (VGT) based architecture for suppressing payload pendulations in ship-mounted cranes. The VGT assembly is conceived to be retrofitted onto the boom tip of ship-mounted cranes. A simplified planar model is developed. A control point along the cable hoisting the payload is constrained to move along a straight path with a given control input (acceleration) imparted via the actuators embedded in the VGT assembly. Control laws based on either linear quadratic or fuzzy control methodologies are developed in order to minimize an assigned cost functional. Their effectiveness is compared through extensive numerical simulations. The performance of the VGT architecture and associated control laws is analyzed when the crane is subject to the most severe combination of resonant excitations: a primary resonant roll excitation at the natural frequency of the controlled system, and a principal-parametric resonant heave excitation, both corresponding to sea state three and higher. The proposed strategy exhibits enough control authority over the system dynamics, greatly reducing the severe and undesirable resonant pendulations caused by the ship motions in a broad-band frequency range. Moreover, its disturbance-rejection capabilities are exerted with feasible control efforts, which are localized in the segment of the crane where they are needed.
Roll Stabilization by Passive Anti-Roll Tanks Using an Improved Model of the Tank-Liquid Motion
Authors: Youssef Khaled S. , Mook Dean T. , Nayfeh Ali H. , Ragab Saad A.
Published: July 2003

Roll motion is an undesirable feature of the behavior of a ship in rough seas, and so it is natural to consider ways of reducing it. The most common devices for increasing roll damping are bilge keels. However, the effectiveness of keels is limited, and anti-roll tanks and fins are used when more control is required. Moreover, unlike keels, anti-roll tanks can be used when the ship is not underway. Our objective is to develop design procedures for passive tanks for roll reduction in rough seas. To this end, we develop an improved model of the passive tank-liquid motion in this paper. This tank consists of U-shaped tubes placed side by side along the length of the ship. The equations of six-degrees-of-motion (6DOF) that govern the tank-liquid are coupled with those that govern the 6DOF motion of the ship, and all of the equations are integrated simultaneously in the time domain using the Large Amplitude Motion Program (“LAMP”). LAMP is a three-dimensional time-domain simulation of the motion of ships in waves. The unstabilized and stabilized roll motions of a S60-70 ship with forward speed and beam waves have been analyzed. For high-amplitude waves, the variation of the roll angle with the encounter-wave frequency exhibits typical nonlinear phenomena: a shift in the resonance frequency, multi-valued responses, and jumps. The performance of passive tanks on a S60-70 ship with forward speed is investigated in an irregular sea with different encounter-wave directions. It is found that passive anti-roll tanks tuned in the nonlinear range are very effective in reducing the roll motion. The effect of the tank mass and distribution of tank tubes on the performance of the tank system is studied. Also, it is found that passive anti-roll tanks are very effective in reducing the roll motion in sea state five of a ship whose pitch frequency is nearly twice its roll frequency.
Dynamics and Control of Cranes: A Review
Authors: Abdel-Rahman Eihab M. , Nayfeh Ali H. , Masoud Ziyad N.
Published: July 2003

We review crane models available in the literature, classify them, and discuss their applications and limitations. A generalized formulation of the most widely used crane model is analyzed using the method of multiple scales. We also review crane control strategies in the literature, classify them, and discuss their applications and limitations. In conclusion, we recommend appropriate models and control criteria for various crane applications and suggest directions for further work.
Small Oscillations and Stability of a Thick Highly Elastic Slab
Authors: Usmani S. A.
Published: July 2003

The problem of small oscillations of a thick slab superimposed on a finite biaxial deformation subject to both dead and hydrostatic lateral loads is investigated. A general frequency equation is derived from which specific results are deduced for both slender and stubby slabs. The question of the stability of a thick plate is studied with the aid of a kinetic stability criterion. The results for a special case are compared with others in the literature. Upon the introduction of certain effective Lamé moduli, correspondence with the work of others is established, and some existing discrepancies are explained. Some results for the disputed problem of stability in equibiaxial finite deformation are presented.
On The Elliptic Balance Method
Authors: Elías-Zúñiga Alex
Published: July 2003

In many practical situations a pair of coupled, damped, homogeneous nonlinear ordinary differential equations model the dynamical behavior of mechanical systems. For example, these equations arise during the process of studying the mechanical response of systems such as strings, beams, absorbers, plates, and so on. In general, the exact solution of this sort of equation is unknown and hence, numerical integration, perturbation techniques or geometrical methods have been applied to obtain their approximate solution. A large number of studies of the nonlinear behavior of such systems have been made using perturbation techniques; however, the vast majority have dealt with weakly nonlinear systems, i.e. with small values of the nonlinear parameter ε or the damping parameter ν. The objective of this work is to apply a novel perturbation technique developed by Elías-Zúñiga, called the Elliptic Balance Method (EBM), to obtain the approximate solution of nonlinear two-degree-of-freedom systems. Two examples are presented to compare the EBM solution with numerical integration. The first is related to a damped, nonlinear system with two degrees of freedom that describes the dynamical behavior of a viscohyperelastic simple shear suspension system with an undamped linear absorber, and the second is related to a proposed damped, nonlinear mechanical model. It will be shown that its amplitude-time response can be accurately described by the EBM solution even for moderate values of the damping coefficients νi and the nonlinear parameter ε.
Mechanoelectrical Phenomena In Ionic Polymers
Authors: Shahinpoor Mohsen
Published: July 2003

Ion containing polymers display certain spectacular mechanoelectrical phenomena when suitably composited with a conductor phase such as a metal, a conductive polymer or graphite—sometimes called ionic polymer conductor composites. When subjected to a dynamic electric field they deform dynamically (actuation), and if dynamically deformed they generate a dynamic electric field (transduction or sensing). Here, we present a description of these phenomena in the linear regime, and in steady-state conditions using the standard Onsager formulation. We describe the underlining principle of ionic polymer-metal composite actuation/sensing phenomena using linear irreversible thermodynamics. When static conditions are imposed, a simple description of the mechanoelectric effect is possible based upon two forms of transport: ion transport (with a current density, J) and electro-osmotic solvent transport (with a flux, Q). The conjugate forces include the electric field, E, and the pressure gradient, -▿ p. We also present some estimates on the Onsager coefficients.
The Graves Condition for Incompressible Finite Elasticity
Authors: Mac Sithigh G. P.
Published: July 2003

The Graves and Weierstrass necessary conditions for minimizers are of central importance in the study of elastic materials that can undergo a change of phase. Proofs of these results applicable to the case of unconstrained materials abound. For the case of an incompressible material, however, only partial results have been established. Here, a complete proof is given.
A Pressurized Spherical Elastomeric Membrane Undergoing Temperature Induced Scission and Crosslinking
Authors: Myers Kristin , Wineman Alan
Published: July 2003

When an elastomeric material is held at a fixed state of stretch at a sufficiently high temperature, macromolecular network junctions undergo time-dependent scission and the applied force relaxes with time. The affected molecules recoil and crosslink to form a new network that is stress-free in a new reference configuration. A constitutive equation that accounts for this process as the elastomer undergoes a time-dependent deformation has been presented elsewhere. This constitutive equation is used to study the response of a pressurized spherical elastomeric membrane at a temperature high enough for the scission-crosslinking process to occur. It is shown that the membrane diameter increases with time. Moreover, there can be a finite time when the membrane diameter increases at an infinite rate, i.e. there is “runaway inflation”. This event depends on the elastic properties of the molecular networks, the rate of scission, the rate of formation of new networks, and the history of the increase in the membrane diameter. Numerical results are presented that illustrate these phenomena.
Analysis of the Air-damping Effect on a Micromachined Beam Resonator
Authors: Zhang Chuanli , Xu Guanshui , Jiang Qing
Published: July 2003

An analysis of the air-damping effect on the frequency response of a micromachined beam resonator is presented. The motion of the beam is analyzed based on the linear elastic beam theory. The air drag to the beam vibration is characterized based on the Oseen solution of the drag force acting on an infinite long cylinder that moves in incompressible viscous fluids at low Reynolds numbers. The conditions for the validation of this characterization are discussed. The analytical results show that air-damping generally shifts the resonant frequency downward and degrades the quality factor, and that this effect increases as the dimension of the beam decreases. The dependence of this effect on the dimension of the beam is illustrated. The presented analysis provides a simplified analytical approach to estimate the length-scale-dependent air-damping effect for designing high-performance micromachined beam resonators.
Fracture Criteria for Pre-stressed and Pre-polarized Piezoelectric Crystals
Authors: Baesu Eveline , Soós Eugen
Published: July 2003

Griffith's notion of energy-release rate is extended to the linearized incremental theory of pre-stressed and pre-polarized piezoelectric crystals under suitable restrictions on the pre-existing fields.
Application of Transfer Functions to the Thermal Processing of Sweet and Sour Cherries Preserves: Influence of Particle and Container Sizes
Authors: Márquez C. A. , Salvadori V. O. , Mascheroni R. H. , De Michelis A.
Published: July 2003

The conditions of thermal processing of fruit preserves packed in transparent glass containers have great importance from the point of view of the final product appearance. Process simulation can allow to predict the quality of the product and its possible degradation. This work applied the transfer function method to simulate the pasteurisation of whole sweet and sour cherries canned in glass containers, with a 25 °Brix sucrose solution as covering liquid, and the predicted results were experimentally tested. The influence of fruit and container diameters on the treatment times was analysed. Kinetic models for enzyme degradation were coupled to the prediction model as examples of the possibilities of optimising the whole pasteurisation process. The accuracy (average error in predicted temperatures: 2.1%) of the simulation method was satisfactory for practical purposes, its use resulted simple and fast, and it allowed adjusting of pasteurisation times, even during the process.
Combined Effect of Modified Atmosphere Packaging and Addition of Lycopene Rich Tomato Pulp, Oregano and Ascorbic Acid and Their Mixtures on the Stability of Beef Patties
Authors: Sánchez-Escalante A. , Torrescano G. , Djenane D. , Beltrán J. A. , Roncalés P.
Published: July 2003

Beef patties were treated with ascorbic acid, oregano extract, lycopene rich tomato pulp (LRTP) and their mixtures, packaged in modified atmosphere and stored at 2°C. Lipid oxidation (TBARS formation), metmyoglobin formation, psychrotrophic bacterial counts and sensory odour and discolouration were analyzed throughout 20 days of storage. TBA values of beef patties containing oregano were the lowest ( p < 0.05); those containing ascorbic acid and LRTP alone were also significantly lower ( p < 0.05) than the control. The formation of surface metmyoglobin was significantly delayed ( p < 0.05) by the addition of oregano alone and its mixtures with ascorbic acid and/or LRTP. Psychrotrophic bacterial counts were significantly lower ( p < 0.05) in patties treated with 500 ppm oregano. Sensory colour and odour characteristics of beef patties were in agreement with the results of lipid and pigment oxidation. The antioxidant ability of oregano was dependent on the concentration; the presence of 500 ppm extended the shelf life of beef patties by about 8 days. LRTP alone exerted a limited antioxidant effect, while its combination with oregano resulted in a reduction of the antioxidative effect of the latter.
Note: Inhibition of Pathogenic Bacteria by Essential Oils at Different Concentrations
Authors: Özkan G. , Sağdiç O. , Özcan M.
Published: July 2003

The antimicrobial effect of 11 selected Turkish spice essential oils was investigated against seventeen pathogenic bacteria. The antimicrobial activity of the essential oils of six spices (cumin, fennel, laurel, mint, marjoram, oregano, pickling herb, sage, savory, thyme (black) and thyme) was tested at four concentrations (0.2, 0.4, 1 and 2%) on various microorganisms ( E. aerogenes, E. coli, E. coli O157:H7, K. pneumoniae, P. vulgaris, S. enteritidis, S. gallinarum, S. typhimurium, S. aureus, Y. enterocolitica, A. hydrophila, C. xerosis, M. luteus, M. smegmatis, E. feacalis, P. aeruginosa and P. fluorescens). All preparations showed antibacterial activity against at least one or more bacteria. The inhibitory effect of the essential oils was evaluated through paper disc diffusion method. In general, the essential oils at 1 and 2% levels were effective. The most active essential oils were marjoram, thyme and oregano. According to the results, the studied essential oils potentially might be used as antibacterial agents to prevent the spoilage of food products, although further research is needed.
Effect of Sodium Lauryl Sulphate on the Texture of Sponge Cake
Authors: Gujral Hardeep Singh , Rosell C. M. , Sharma S. , Singh Sukhprit
Published: July 2003

Sponge cake was prepared by adding sodium lauryl sulphate (SLS), an anionic surfactant, to egg albumen during the mixing stage at levels of 0, 0.05, 0.1 and 0.2% on flour weight basis. The rheology of the cake batter was studied and texture of sponge cake crumb was measured on an Instron universal testing machine. Increasing levels of SLS lowered the specific gravity, surface tension, consistency coefficient and air bubble diameter. The cake volume increased with increasing levels of SLS. Texture profile analysis of cake crumb revealed that increasing SLS levels lowered crumb firmness and cohesiveness. Storage of cake crumb for up to 10 days at room temperature revealed that crumb containing SLS remained softer and that SLS may be involved in preventing starch retrogradation.
Note: Characterization of Yeast Strains on the Basis of Autolytic Activity and Volatile Compounds
Authors: Barcenilla J. M. , Martín-Álvarez P. J. , Vian A. , Gonzalez R.
Published: July 2003

Autolytic activity and the production of several major volatile compounds were studied for a set of 18 commercial and non-commercial Saccharomyces cerevisiæ strains isolated from sparkling wine, cider and sherry fermentations. No correlation was found between the autolytic capacity of the strains and isobutanol production levels, in contrast with results published by other authors for a limited number of S. cerevisiæ strains. The 18 strains were classified in three groups by cluster analysis; the variables that best discriminated the groups were related with autolysis, with a limited effect of the volatile compounds. All the commercial sparkling wine second fermentation strains appeared in the same group, which was characterized by the release of high amounts of proteins under conditions of accelerated autolysis. This could probably be explained by an indirect selection for efficient autolysis for these commercial strains. Most sherry and cider isolates appeared in a single group. Interestingly, one strain isolated from cider fermentation is grouped with sparkling wine commercial strains.
Physicochemical Properties of Quinoa Extrudates
Authors: Doğan H. , Karwe M. V.
Published: July 2003

Response surface methodology (RSM) was used to analyse the effect of temperature, screw speed, and feed moisture content on physicochemical properties of quinoa extrudates. A three-level, three-variable, Box-Behnken design of experiments was used. The experiments were run at 16-24% feed moisture content, 130-170°C temperature, and 250-500 rpm screw speed with a fixed feed rate of 300 g/min. Second order polynomials were used to model the extruder response and extrudate properties as a function of process variables. Responses were most affected by changes in feed moisture content and temperature, and to a lesser extent by screw speed. Calculated specific mechanical energy (SME) values ranged between 170-402 kJ/kg which were lower than those observed for other cereals, most likely due to high (7.2%) fat content of quinoa. High levels of feed moisture alone, and in combination with high temperature, resulted in poor expansion. The best product, characterised by maximum expansion, minimum density, high degree of gelatinization and low water solubility index, was obtained at 16% feed moisture content, 130°C die temperature, and 375 rpm screw speed, which corresponds to high SME input. It was demonstrated that the pseudo-cereal quinoa can be used to make novel, healthy, extruded, snack-type food products.
Thermodynamic Analysis of Water Vapour Sorption of Edible Starch Based Films
Authors: Bertuzzi M. A. , Armada M. , Gottifredi J. C.
Published: July 2003

Moisture sorption isotherms of high amylose corn starch (HACS) films at 5, 25, 35 and 45 °C within an approximate water activity ( aw) range of 0.11-0.85 were obtained using a static gravimetric method. HACS films fitted a type III BET model at all temperatures studied. Water sorption process in high amylose based films was exothermic within the range of water activities investigated. There was a continuous decrease of the affinity between film sorbed structure with moisture as water content increased. Negative values of Δ G in the whole range of moisture content studied were indicative of a spontaneous process. The entropy curve exhibited a well-defined minimum corresponding at the completion of the monolayer.