bluuebunny/crossref_metadata_2025 huggingface dataset:
Destabilizing Effect of In-Plane Magnetic Field on Panel Flutter
Authors: Lin Chun-Bo
Published: May 2011

Destabilizing effect of magnetic damping on the supersonic panel flutter is investigated. The linear piston theory is available to formulate the air force at high Mach numbers. A plate in supersonic flow can be stabilized by reducing the compression force perpendicular to the flow. However, once the dynamic pressure parameter exceeds some critical value, the time rate of motion becomes complex then the flutter occurs. In this paper, the strength of in-plane magnetic field to reduce the panel flutter under higher dynamic pressure parameter is determined. Due to the complexity in finding the exact solution of plate motion, Galerkin solution with different terms of truncation is adopted herein. Therefore, the exact solution can be obtained by using the four-term solution as an initial value. The most attractive feature is that the supersonic flutter can be avoided efficiently through the application of in-plane magnetic field.
Green's Function for a Point Heat Source in an Anisotropic Body Containing an Elliptic Hole or a Rigid Inclusion
Authors: Wang Chung-Hao , Chao Ching-Kong
Published: May 2011

The thermoelastic problem associated with a point heat source embedded in an anisotropic body containing an elliptic hole or a rigid inclusion is considered in this paper. By using the formalism of Stroh [1], the approach of analytic function continuation and the technique of conformal mapping, the expression for the temperature, displacements and stress functions is expressed in explicit matrix form. The present derived solutions are also valid for some special problems such as a crack or a rigid line inclusion if one lets the minor axis of the ellipse approach to zero. The stress intensity factors induced by a point heat source are also obtained.
EndoFEM Studies in the Mode I Stable Crack Growth of Fatigue Precracked CT Specimen
Authors: Lee C.F. , Lee K.L.
Published: May 2011

In this paper, the EndoFEM incorporated with a node duplicated and then unloaded crack extension methodology, is employed to produce the CT specimen of A1 2024-T3 with initial fatigue crack and then to simulate its stable crack growth under Mode I condition. Using the experimental P-LLD data, the P-Δa diagram can be estimated by the effective compliance method. This results in a further simulation of crack extending procedures which can obtain the stress-plastic strain distributions of growing crack front and their crack opening profiles, CTOD and CTOA vs. Δa Diagram, COD and COA measured at 5 positions behind the original crack tip vs. Δa diagram. The results mentioned above have excellent agreements with results of related experiments and other computational simulations.

In consequence, the paper proposes a single fracture parameter of crack growth which can be casted in the future studies of EndoFEM simulation: (1) Within the crack initiation range whose crack extension rates da/dP has the lowest constant value, the COA measured at 0.5mm behind the original crack tip is takes as 5°; (2) Within the stable crack growth region whose crack extension rates are nonlinearly and monotonically increasing with finite values, the COA measured at 1mm behind the current crack tip is also taken as 5°.
Heat Transfer of an Electrically Conducting Viscoelastic Fluid Over a Stretching Sheet
Authors: Liu I-C. , Kong C.-H.
Published: May 2011

The solutions for flow and heat transfer in a steady laminar boundary layer flow are presented analytically for an electrically conducting viscoelastic fluid, subject to a transverse uniform magnetic field, past a semi-infinite stretching sheet. The temperature profiles and thermal characteristics at the wall are drawn and tabulated for selected parameters with prescribed surface temperature (PST) and prescribed surface heat flux (PHF) conditions. We also give the asymptotic solutions for temperature when the Prandtl number is very large. It is found that the inclusion of Joule heating has a significant influence on the thermal characteristics at the wall and the wall heat transfer strongly depends on the Prandtl number Pr as well as the Eckert number Ec. The heat flow may transfer from the fluid to the wall when Ec is large rather than from wall to the fluid when Ec is small. A physical argument about the thermal characteristics at the wall is proposed.
Wrinkling of a Debonded Initially Compressed Si1−XGex Film
Authors: Fedorchenko A. I. , Wang A.-B. , Mashanov V. I. , Cheng H.-H.
Published: May 2011

A compressively strained pseudomorphic Si1−xGex film being debonded from Si substrate by selective etching forms wrinkles with a uniform space periodicity. The present study provides experimental evidences and a theoretical model for the wrinkling process. To allow large deflection, non-linear Von Karman plate theory is employed. The amplitude and wavelength of wrinkles are determined by minimizing the total free energy of a debonded wrinkled film. The wrinkling analysis has shown that the amplitude and wavelength of wrinkled film are an outcome of a subtle compromise between bending energy, and normal and shearing components of the stretching energy. The wave number nondimentionalized over the depth of etch is a function of the membrane strain of a bonded film, Poisson's ratio, and the nondimensional film thickness.
Prediction of Cutting Forces in Milling Stainless Steels using Chamfered Main Cutting Edge Tool
Authors: Chang C.-S.
Published: May 2011

To study the cutting forces, the carbide tip's surface temperature, and the mechanism of secondary chip and main chip formation of face milling stainless steel with a chamfered main cutting edge has been investigated. Theoretical values of cutting forces were calculated and compared to the experimental results with SUS 304 stainless steel plate as a workpiece material. Force data from these tests were used to estimate the empirical constants of the mechanical model and to verify its prediction capabilities. A comparison of the predicted and measured forces shows good agreement. A preliminary discussion is also made for the design of special tool holders and their geometrical configurations. Next, the tips mounted in the tool holders are ground to a chamfered width and the tool dimensions are measured by using a toolmaker microscope.
Spatiotemporal Intermittency Measurements in a Gas-Phase Near-Isotropic Turbulence Using High-Speed Dpiv and Wavelet Analysis
Authors: Yang T. S. , Shy S. S. , Chyou Y. P.
Published: May 2011

Recently, Shy and his co-workers developed a new turbulent flow system that used a pair of counter-rotating fans and perforated plates to generate stationary near-isotropic turbulence, as verified by LDV measurements, for the study of premixed turbulent combustion processes. This paper evaluates for the first time the correlations between spatial and temporal properties of small-scale intermittency in such a fan-stirred near-isotropic turbulence. These spatiotemporal properties are obtained simultaneously via high-speed digital particle image velocimetry together with wavelet analyses. It is found that the wavelet energy spectra in the inertial range of near-isotropic region all exhibit a slope of nearly −5/3 which spans at least from 3Hz to 100Hz. Characteristic scales, including the integral time and length scales, Taylor microscales, and viscous dissipation scales, are identified without the use of Taylor hypothesis. Thus, a direct evaluation of Taylor hypothesis in near-isotropic turbulence with zero mean velocity can be made. From variations of the flatness factor, equivalent to the 4th order velocity structure function, in the spatial and time domains, it is found that the characteristic spatial and temporal intermittent scales of intense vorticity structures in the dissipation range of the fan-stirred near-isotropic turbulence occur around 5 ∼ 8η and τk, respectively, where η and τk are the Kolmogorov length and time scales. These results are useful for further study of particle settling in turbulence, a problem of both engineering and geophysical interest.
Dielectric and Mechanical Loading Effects of a Fluid on Lamb Waves Propagating in an Immersed Piezoelectric Plate
Authors: Yang C.-H. , Lai Y.-A.
Published: May 2011

This research is focused on exploring the fluid loading effects on the dispersion curves of Lamb modes propagating in a piezoelectric plate. A theoretical treatment based on a partial wave analysis is developed to model the dispersion curves of Lamb modes propagating in an X-LiNbO3 plate loaded by a fluid with combined mechanical/dielectric properties. In particular, the mode-shifting characteristics caused by the fluid loading as a function of the propagation orientation are illustrated with numerical examples. Finally, for the case of water as an immersing fluid, individual attributions of the mechanical and dielectric loading effects causing the mode-shifting are analyzed. It is found that the dielectric loading effect dominates the mode-shifting while the mechanical density loading can be neglected while Lamb waves propagate in an X-LiNbO3 plate immersing in water. The current results provides useful information for the applications of acoustic plate mode (APM) devices used in liquid sensor applications.
Broadband Dispersion Behaviors of Wedge Waves Propagating Along Large-Angled Wedges
Authors: Yang C.-H. , Tsai K.-Y.
Published: May 2011

Broadband dispersion behaviors of wedge waves traveling along large-angled wedges are investigated with a laser ultrasound technique. Wedge waves are guided acoustic waves propagating along wedge tips. Until now, no elasticity-based close-form solution is available for the prediction of dispersion behavior of wedge waves. By assuming the wedge as a thin plate with variable thickness, McKenna obtained a theoretical approximation for the prediction of dispersion relation of truncated wedges within limited apex angle and bandwidth. The current research provides experimental data on wideband dispersion spectra of wedge waves traveling along large-angled wedges. It is found that the thin plate theory is accurate only within a small wavenumber regime. Also, a limiting behavior in the large wavenumber regime the ASF dispersion spectra are found to approach the Rayleigh wave speed.
Forming Limits Prediction of the Sheet Metal Forming Process by the Energy-Based Damage Model
Authors: Yeh H.-Y. , Cheng J.-H.
Published: May 2011

An energy-based damage model is proposed and applied to predict the fracture initiation of the sheet metal forming process. The fracture mechanism is investigated through the plastic energy dissipation. The concepts of the damaging work and the fracture energy are proposed for the quantitative description of damage evolution and crack initiation. The developed formulations are implemented into the finite element program ABAQUS to simulate the biaxial stretching of sheet metals and to predict the fracture strains. The material parameter needed in the damage model for fracture prediction is determined by the stress-strain history of the uniaxial tensile test. The forming limits for aluminum alloy sheets under various strain paths are predicted by the present approach and then compared to the measured data quoted from the literatures [1,2]. Good agreements are found between this study and the previous results.
On the Almansi-Michell Problems for an Inhomogeneous, Anisotropic Cylinder
Authors: Lin H.-C. , Dong S.B.
Published: May 2011

A semi-analytical finite element (SAFE) method is presented for constructing solutions for an arbitrarily loaded cylinder, whose cross-section is general in terms of its shape and the number of distinct, perfectly bonded elastic, rectilinear anisotropic materials. The surface traction and body force loads need to be expressed in a power series of the axial coordinate. Linear three-dimensional theory is used. For a homogeneous isotropic cylinder, it is known as the Almansi-Michell problem, and the SAFE analysis herein is an extension to inhomogeneous, anisotropic bodies. By SAFE, the cross-section is discretized. The displacement field is expressed by interpolation functions over the cross-section and by analytical functions axially. The method herein is an extension of the authors' previous method cylinder with a general cross-section. Herein, the SAFE solution procedure is given and numerical examples will be presented.
Equivalent Fixed-Base Model for Soil-Structure Interaction Analysis
Authors: Chen C.-H. , Hsu S.-Y.
Published: May 2011

This paper is to investigate the effects of Soil-Structure Interaction (SSI) on the dynamic response of a soil-structure system. An ideal model with a simple structure supported on elastic half space is utilized to derive the factor FSSIthat can completely represent the effects of SSI. This factor is able to characterize both the change of predominant frequency and damping ratio of the system when compared to the conventional rigid-base type structural analysis. Based on that, an Equivalent Fixed-Base (EFB) model, which takes the effects of SSI into account, can be constructed. The Hualien field test results are then used to verify the applicability of the proposed EFB model.
Master Curve of Creep in Polymeric Off-Axis Composite Laminates
Authors: Hu H-W.
Published: May 2011

An approach to establish a master curve for effective creep compliances of polymeric off-axis composites with various fiber orientations was presented. Carbon/epoxy composite IM7/977–3 was used to fabricate four types of off-axis specimens and then subjected to momentary creep tests after a period of initial aging. Creep compliance and elastic compliance were separated from the total compliance. Using one-parameter creep potential theory, creep compliances were transformed to effective creep compliances. After choosing a proper value for the one-parameter, all effective creep compliances with various off-axis fiber orientations were superposed into a master curve. This master curve enables us to obtain creep compliance with any off-axis fiber orientation by testing only one off-axis specimen.
Numerical Simulations of a Miscible Drop in a Spinning Drop Tensiometer
Authors: Chen Ching-Yao , Liu K.-T.
Published: May 2011

The present investigation addresses the estimation of the unconventional effective interfacial tension (EIT), the so-called Korteweg stress, for a miscible interface. Two independent characteristic estimations are calculated: (1) the measurement based on a Spinning Drop Tensiometer (SDT) commonly applied in an immiscible situation, and (2) the theoretical predication involving an unknown physical constant (Korteweg constant) and detailed concentration distributions. Excellent agreements between these two estimations are found. By demonstrating the excellent agreement between these two proposed measurements, the applicability of a SDT for measuring miscible EIT is numerically verified. This numerical conclusion provides a possible simple method for further estimations of currently unknown physical constants.
Nondestructive Evaluation of In-Isolation Pile Shaft Integrity by Wigner-Ville Distribution
Authors: Ni S.-H. , Charng J.-J. , Lo K.-F.
Published: May 2011

The Wigner-Ville Distribution is a new numerical analysis tool for signal process technique in the time-frequency domain and it can offer assistance and enhance signal characteristics for better resolution both easily and quickly. Time-frequency transform can describe how a spectrum of signals changes with time owing to defects and boundary conditions. In this study, five single pre-cast concrete piles have been tested and evaluated by both sonic echo method and Wigner-Ville distribution (WVD). The appropriateness of time-frequency domain analysis is discussed. Furthermore, two difficult problems in nondestructive evaluation problems are discussed and solved: the first one is with a pile with slight defect, whose necking area percentage is less than 10%, and the other is a pile with multiple defects. The results show that WVD can not only recognize the characteristics easily, but also locate the defects more clearly than the traditional pile integrity testing method.
Mechanics of Matrix Cracking in Bonded Composites
Authors: Chiang Y.-C.
Published: May 2011

In this paper, a general matrix cracking model including the effect of fiber/matrix debonding in the crack wake is developed for a unidirectional fiber reinforced composite. The debonding mechanics is incorporated into matrix cracking model by treating the crack-wake debonding as a particular crack propagation problem along the interface. Then, the closed-form analytical solution of the critical stress for the onset of widespread matrix cracking is derived, based on the analysis of steady state crack growth in the matrix. The fracture mechanics approach adopted in the present analysis is compared with the analysis in which the crack-wake debonding mechanics was modeled by energy balance approach. The conditions for attaining no-debonding and debonding as onset of widespread matrix cracking are discussed in terms of the interfacial properties of debond toughness and frictional shear stress. The theoretical results are compared with experimental data that are available in the literature.
Failure Probabilities of Reinforced Concrete Square Pile Caps
Authors: Lu W.-Y.
Published: May 2011

An analytical model for determining the shear strength of concrete pile caps under the failure mode of diagonal-compression originally based on the softened strut-and-tie model is proposed. The failure probabilities of reinforced concrete pile caps are investigated by Monte Carlo method. The results indicate that the proposed model can accurately predict the shear strength of the pile caps. The distribution of the failure probabilities for pile caps designed to ACI 318-02 Appendix A and the proposed design method are more uniform than that designed to the ACI 318-99. The ACI 318-99 is very conservative and cannot provide a consistent safety for pile caps design. It is suggested that the procedures in the ACI 318-02 Appendix A should be moved to the main body of ACI 318-02 and the proposed design method should be incorporated into the current reinforced concrete pile cap design methods.
Velocity-Vorticity Formulation for 2D Natural Convection in an Inclined Cavity by the DQ Method
Authors: Lo D. C. , Liao T. , Young D. L. , Gou M. H.
Published: May 2011

The aim of this paper attempts to apply the differential quadrature (DQ) method for solving two-dimensional natural convection in an inclined cavity. The velocity-vorticity formulation is used to represent the mass, momentum, and energy conservations of the fluid medium in an inclined cavity. We employ a coupled technique for four field variables involving two velocities, one vorticity and one temperature components. In this method, the velocity Poisson equation, continuity equation, vorticity transport equation and energy equation are all solved as a coupled system of equations so as to we are capable of predicting four field variables accurately. The main advantage of present approach is that coupling the velocity and the vorticity equations allows the determination of the boundary values implicitly without requiring the explicit specification of the vorticity values at the boundary walls. A natural convection in a cavity with different angle of inclinations for Rayleigh number equal to 103, 104, 105 and 106 and H/L aspect ratios varying from 1 to 3 is investigated. It is shown that with the use of the present algorithm the benchmark results for temperature and flow fields could be obtained using a coarse mesh grid.
Morphological Instabilities in Time Periodic Crystallization
Authors: Chung C. A. , Chien W. Z. , Hsieh Y. H.
Published: May 2011

A linear stability analysis is performed on the interface that forms during directional solidification of a dilute binary alloy in the presence of time-periodic growth rates. The basic state, in which the flat crystal-melt interface advances at a steady rate with an oscillation superimposed, is solved analytically by expanding the governing equations in terms of the assumed-small amplitude of modulation. We find that there is a frequency window of stabilization, in which the Mullins-Sekerka instability can be stabilized synchronously. Outside of the window, large input frequencies may destabilize the Mullins-Sekerka mode. The subharmonic mode, which occurs with small wave numbers, is stabilized with increasing the frequency. As for the modulation amplitude, larger amplitude tends to reduce the synchronous mode while enhance the subharmonic mode.
Entropy Generation of Free Convection Film Condensation From Downward Flowing Vapors onto a Cylinder or Sphere
Authors: Dung S. C. , Tzeng S. H. , Yang S. A.
Published: May 2011

This study aims at analyzing entropy generation rate of saturated vapor flowing slowly onto and condensed on an isothermal sphere/horizontal cylinder. We derive an expression for entropy generation, which accounts for the resultant action of specified irreversibilities of film-wise condensation outside a cylinder/sphere. The result shows that local entropy generation rate increases with Brinkman group parameters. As Rayleigh group parameters increase, dimensionless heat transfer coefficient is enhanced, but entropy generation number is augmented too. Heat transfer irreversibility dominates over the film flow friction irreversibility in the upper half of a sphere, and vice versa for the lower half of a sphere. As for a cylinder, heat transfer irreversibility dominates over film flow friction irreversibility except around the middle way of streamwise length for the cases of Brinkman group parametersBr/ ψ≥ 0.75.
Experimental Study of Coal Pyrolysis and Gasification in Association with Syngas Combustion
Authors: Chen W.-H. , Chen J.-C. , Tsai C.-D. , Du S.-W.
Published: May 2011

Coal pyrolysis and gasification incorporating synthesis gas (syngas) combustion are investigated experimentally in the present study. Two different coals are considered; one pertains to high-volatile bituminous and the other low-volatile one. For the pyrolysis, using thermogravimetry in association with mass spectrometry reveals that the concentrations of CO and CO2 increase with increasing temperature, whereas those of H2 and CH4 undergo increase followed by decrease. Regarding the gasification, the formations of the four gases between the two different coals are similar. However, when the reaction temperature is relatively low such as 800°C, carbon reactivity of the low-volatile coal decays in a significant way. Furthermore, with the reaction temperature of 1000°C the entire gasification histories of the two coals can be divided into five periods in accordance with syngas combustion. They are initiated, growing, rapidly decaying, progressively decaying, and frozen periods, sequentially. The flame is wrinkled in the growing and rapidly decaying periods where the reaction strength is much higher than that near extinction. When the reaction temperatures are 800 and 900°C, the growing and rapidly decaying periods tend to wither. Recognizing the syngas combustion characteristics, one is capable of figuring out the coal gasification process in more detail.
Effect of Interface Anisotropy on Elastic Wave Propagation in Particulate Composites
Authors: Hasheminejad S. M. , Maleki M.
Published: May 2011

The scattering of time harmonic plane longitudinal and transverse elastic waves in a composite consisting of randomly distributed identical isotropic spherical inclusions embedded in an isotropic matrix with anisotropic interface layers is examined. The interface region is modeled as a spherically isotropic shell of finite thickness with five independent elastic constants. The Frobenius power series solution method is utilized to deal with the interface anisotropy and the effect of random distribution of particulates in the composite medium is taken into account via a recently developed generalized self-consistent multiple scattering model. Numerical values of phase velocities and attenuations of coherent plane waves as well as the effective elastic constants are obtained for a moderately wide range of frequencies, particle concentrations, and interface anisotropies. The numerical results reveal the significant dependence of phase velocities and effective elastic constants on the interface properties. They show that interface anisotropy can moderately depress the effective phase velocities and the elastic moduli, but leave effective attenuation nearly unaffected, especially at low and intermediate frequencies. Limiting cases are considered and good agreements with recent solutions have been obtained.
A Factorization Algorithm for Wave Propagation in Periodic Structures with Application to Torsional Waves in an Infinite Cylinder
Authors: Barone R.C.A. , Kaul R.K.
Published: May 2011

In this paper we introduce a fundamentally new concept in the field of wave-propagation in periodic structures. We show that a phenomenal amount of simplification can be achieved by using symmetry arguments. Problems which ordinarily lead to (2n × 2n) determinantal eigenvalue equations, can effectively be reduced to two (n × n) determinantal equations. We state the final result in the form of a factorization theorem and then with the help of a simple problem, we show the superiority of this new result over the traditional methods of solution.
Vibration and Buckling Analyses of Beams by the Modified Differential Quadrature Method
Authors: Chou Y.-T. , Choi S.-T.
Published: May 2011

In this paper the modified differential quadrature method (MDQM) is proposed for static and vibration analyses of beams. Modified weighting matrices are developed and a new formulation process is presented for incorporating boundary conditions such that the numerical error induced by using the δ-method in the original DQM is reduced. The present method is applied to various beam problems, such as static deflections of Euler beams, buckling loads of columns, and free vibrations of Timoshenko beams. Numerical results of the present method are shown to have excellent accuracy when compared to exact values and are more accurate than those obtained by the original DQM. The accuracy and efficiency of the present method have been demonstrated.
Vibration Control of a Beam Using the Nearly Optimal Control Algorithm with a Disturbance Force Observer
Authors: Wang Der-An , Huang Yii-Mai
Published: May 2011

Active vibration control of a flexible beam subjected to arbitrary, unmeasurable disturbance forces is investigated in this paper. The concept of independent modal space control is adopted. Both the feedforward and feedback control is implemented here to reduce the beam vibration. Because of the existence of the disturbance forces, the feedforward control is applied by employing the idea of force cancellation. A modal space disturbance force observer is then established in this paper to observe the disturbance modal forces for the feedforward control. For obtaining the feedforward and feedback control gains with the optimal sense, the nearly optimal control law is derived, where the modal disturbance forces are regarded as additional states. The vibration control performances and the asymptotic properties of the control law are discussed.
Biomechanical Analysis of Wrist Loading During Lifting Tasks
Authors: Chou P. H. , Chou Y. L. , Wei H. C. , Ho C. S. , Jiang S.S.
Published: May 2011

This study develops a kinematic/kinetic model to evaluate the effect of different handle angles on wrist loading during lifting task. An imaged-based motion analysis system is used to study the movement pattern, force and moment of the wrist joint among nine different handle angles. Six CCD cameras were used to record 3-D trajectories of limb-mounted markers based on the laboratory coordination system as defined by an 8-marker cube. Euler angles are used to describe the orientation of a distal segment reference frame relative to a proximal segment reference frame. Each segment of the upper extremities is regarded as a uniform rigid body with six degrees of freedom. The resultant loading of the wrist joints was determined using an inverse dynamic procedure.

This study indicates that tool handles can be designed or selected to reduce manual loading and the potential for injury during tool use. The mean curve of joint force and moment provided consultations and understandings of the wrist loading during lifting task. In this study, handles that kept the wrist joints in a dorsiflexed and radial deviated position, showed significant reduction in stresses around the surrounding soft tissue.
A Modified Gaussian Integration Scheme in Element Free Method
Authors: Sheng Jopan , Wang Chung-Yue , Shen Kuo-Jui
Published: May 2011

In this paper, a modified numerical integration scheme is presented that improves the accuracy of the numerical integration of the Galerkin weak form, within the integration cells of the analyzed domain in the element-free methods. A geometrical interpretation of the Gaussian quadrature rule is introduced to map the effective weighting territory of each quadrature point in an integration cell. Then, the conventional quadrature rule is extended to cover the overlapping area between the weighting territory of each quadrature point and the physical domain. This modified numerical integration scheme can lessen the errors due to misalignment between the integration cell and the boundary or interface of the physical domain. Some numerical examples illustrate that this newly proposed integration scheme for element-free methods does effectively improve the accuracy when solving solid mechanics problems.
Fluid Flow and Heat Transfer in Duct Fan Flows with Top-Wall Rectangular-Wing Turbulators
Authors: Chen T. Y. , Chen Y. H.
Published: May 2011

Fluid flow and heat transfer in duct fan flows with a 90° rectangular-wing turbulator, mounted on the top duct wall, were experimentally studied and compared with the bottom-wall turbulator results. Threecomponent velocities were measured to characterize the flow structures and to obtain near-wall flow parameters. Temperatures on heat transfer surfaces were measured to obtain Nusselt number distributions. Results show that the turbulator has the effect to increase the near-wall axial mean velocity, axial vorticity and turbulent kinetic energy, and, consequently, augment the heat transfer. The axial mean velocity and axial vorticity play an influential role on the heat transfer distributions for the flows across the top-wall and bottom-wall turbulators, respectively.
Heat and Mass Transfer for Electrical Conducting Mixed Convection with Radiation Effect for Viscoelastic Fluid Past a Stretching Sheet
Authors: Hsiao K.-L.
Published: May 2011

In this study, an analysis has been performed for heat and mass transfer of a steady laminar boundarylayer flow of an electrically conducting fluid with radiation effect of second grade subject to suction and to a transverse uniform magnetic field past a stretching sheet. Parameters Gr, Gc, Nr, M, Sc represent the dominance of the buoyant effect, radiative effect, magnetic effect and mass transfer effect which have presented in governing equations, respectively. The similar transformation and the finite-difference method have been used to analyze the present problem.
Near-Tip Field and the Associated Path-Independent Integrals for Anisotropic Composite Wedges
Authors: Wu Kuang-Chong
Published: May 2011

The asymptotic fields in an elastic anisotropic composite wedge are considered for a wide range of boundary conditions. It is shown that the eigenfunctions for the near-field and far-field are dual as they are generated by the same set of eigenvalues in general. If the boundary conditions on the wedge faces are the same, an additional eigenfunction may appear in the far-field. Moreover the dual eigenfunctions are used to derive path-independent integrals that relate the near-field to the far-field.
Manipulating Tumble and Swirl Flows in Cylinder of a Motored Four-Valve Engine by Inlet Deflection Valve
Authors: Huang R. F. , Yu J. H. , Yeh C.-N.
Published: May 2011

Effects of the inlet-stream deflection on the temporal and spatial evolution processes of the in-cylinder flow structures (tumble/swirl) and turbulence intensities in the symmetry and diametral planes of a motored four-valve, four-stroke engine are diagnosed by using a particle image velocimeter. The inception, establishment, and evolution of the tumbling/swirling vortical flow structures during the intake and compression strokes in the engine cylinder with/without inlet-stream deflection are depicted and compared. Quantitative strengths of the rotating vortical flow motions are presented by dimensionless parameters (tumble and swirl ratios) which can represent the mean angular velocity of the vortices in the target plane. The turbulence intensity is calculated by using the measured time-varying velocity data. The results show that by deflecting the inlet air-stream the tumble and swirl ratios of the in-cylinder flow are appreciably increased by about 0.1 and the turbulence intensity is increased by about 5 ∼ 10%.
Dispersion Control in Nano-Channel Systems Using a Genetic Algorithm
Authors: Kamali R. , Movahed S.
Published: May 2011

There has been a growing interest in developing the miniaturized fluidic devices for transportation, separation and detection of bio-samples. In many of these phenomena electrokinetic effects play an important role. Studies show that in fabricating these devices, if long channels are used, separation efficiency can be improved. In these devices, turns must be induced to integrate a long channel within the small area of a single chip. But these turns can cause a serious dispersion that can result in degraded separation quality. The present study shows that the dispersion in the channel can be reduced by using an optimized distribution for ζ-potential near the turns. A computer code based on the genetic algorithm has been developed to study the dispersion in L-shape and U-shape turns.
A Study on Pushover Analysis of Frame Structure Infilled with Low-Rise Reinforced Concrete Wall
Authors: Lai M. -C. , Sung Y. -C.
Published: May 2011

This paper focused on the pushover analysis of a frame structure infilled with low-rise reinforced concrete (RC) wall. The softening model of concrete as well as the elastoplastic model of reinforcement was considered in the analysis associated with the equilibrium and compatibility conditions. Accordingly, the shear load-deformation relationship of the wall subjected to monotonic lateral load can be analyzed through the proposed analysis procedure. Based on the relationship obtained, we employed a single equivalent structural strut represented by a nonlinear axial member, acting in the diagonal direction of the frame, in simulating the infilled RC wall to simplify the framed wall model. As a result, the sequential pushover analysis of the whole structure could be performed easily and efficiently based on the realistic procedure proposed.

To validate the proposed approach, reported results from the cyclic loading tests of fifteen specimens were adopted for the correlation. Based on the correlation, it is found that this study can provide an acceptable result of the pushover analysis and give an insight into progressive failure consequence of the framed wall structure. The proposed procedure simplifying the structural model helps the practical engineers get a higher efficiency while performing seismic evaluation and retrofit design of the high-redundancy frame structure with numerous infilled low-rise RC walls.
Investigation of Effect of Endpoint Constraint on Time-Line Cubic Spline Interpolation
Authors: Tsai T.-L. , Chen J.-Y.
Published: May 2011

In this study, the effects of various endpoint constraints, including the first derivative, natural, quadratic, and not-a-knot endpoint constraints, on the time-line cubic spline interpolation are examined by solving the advection-diffusion equation with constant and variable velocities, and the viscous Burgers equation. The natural endpoint constraint could produce large numerical diffusion. The quadratic endpoint constraint can decrease the numerical diffusion from the natural endpoint constraint, but it could trigger large numerical oscillation. The first derivative endpoint constraint with higher-order central difference approximation has better simulated results than the natural and quadratic endpoint constraints. It can significantly reduce not only the numerical diffusion produced by the natural endpoint constraint, but also the numerical oscillation caused by the quadratic endpoint constraint. The applicability of the time-line cubic spline interpolation together with the not-a-knot endpoint constraint is limited, since the computational instability is caused while the Courant number is greater than unity. Therefore, as far as accuracy and applicability are concerned, the first derivative endpoint constraint with higher-order central difference approximation rather than the commonly used natural endpoint constraint should be a better choice for the time-line cubic spline interpolation.
Ribbing Instability Analysis of Forward Roll Coating
Authors: Lie K. N. , Chiu Y. M. , Jang J. Y.
Published: May 2011

The ribbing instability of forward roll coating is analyzed numerically by linear stability theory. The velocity ratio of two rolls is fixed to be 1/4 for practical surface coating processes. The base flows through the gap between two rolls are solved by use of powerful CFD-RC software package. A numerical program is developed to solve the ribbing instability for the package is not capable of solving the eigenvalue problem of ribbing instability. The effects of the gap between two rolls, flow viscosity, surface tension and average roll velocity on ribbing are investigated. The criterion of ribbing instability is measured in terms of critical capillary number and critical wave number. The results show that the surface coating becomes stable as the gap increases or as the flow viscosity decreases and that the surface coating is more stable to the ribbing of a higher wave number than to the ribbing of a lower wave number. The effect of average roll velocity is not determinant to the ribbing instability. There are optimum and dangerous velocities for each setup of rolling process.
Heat Transfer and Friction Characteristics Optimization with Compound Turbulators in Roughened Ducts
Authors: Kamali R. , Binesh A. R.
Published: May 2011

The use of artificial roughness or turbulence promoters on a surface is an effective technique to enhance the rate of heat transfer of the fluid flowing in a duct. In this study, a computer code has been developed to perform a numerical simulation for optimizing the shape of two-dimensional channel with periodic ribs mounted on the bottom wall to enhance turbulent heat transfer. The Reynolds-Averaged Navier-Stokes analysis is used as a numerical technique and the SST k-(ω) turbulent model with near-wall treatment as a turbulent model. The simulations were performed for two rib shapes, trapezoidal with decreasing height in the flow direction with and without grooves between the ribs. The results are validated by comparing with existing experimental data and semi-empirical correlations. The Reynolds number, pitch-to-rib high ratio and relative groove position are chosen as design variables. The effects of roughness parameters on Nusselt number and friction factor have been discussed and the conditions for the best performance have been determined and presented.
The Consistence Between the Stokes Wave Theory and General Wave Theory
Authors: Liu C.-M. , Hwung H.-H. , Yang R.-Y.
Published: May 2011

The consistence between the Stokes wave theory and general wave theory is examined in this study. As well known, the nonlinear terms of Stokes wave are generated by the self-interaction of first-order wave. On the other side, using the general wave theory one can also obtain the nonlinear solutions according to the interaction of n waves with the same amplitude, frequency and phase. It is found that the inconsistence between these two wave trains arises due to the subharmonic effects included in general wave theory but not considered in the Stokes theory. In conclusion, these two theories are substantially different unless the Bernoulli constants are properly chosen for mathematical equivalence.
Time-Dependent Poiseuille Flows of an Elasto-Viscoplastic Fluid with Hypoplastic Effects
Authors: Fang C.
Published: May 2011

An evolution equation for the Cauchy stress tensor is proposed, taking into account the elastic, viscous and plastic characteristics of complex fluids. Hypoplasticity, in particular, is incorporated to model the plastic features. The model is applied to investigate time-dependent Poiseuille flows between two parallel plates to simulate non-Newtonian behavior of complex rheological fluids. Results show that while different degrees of elastic and viscous features can be indexed by varying the values of the model parameters, hypoplasticity is capable of simulating the plastic characteristics. The fluid tends to be divided into different parallel layers as hypoplastic effects enhance gradually. Applications of the model may be found in geomorphic fluid motions involved granular materials.
Thermo-Acoustic Instability Simulation in Gas Turbine
Authors: Akbari N. , Mehdizadeh N. S.
Published: May 2011

The main aims of this research are, at first, combustion instability study based on equivalence ratio oscillation, and, secondly, investigation various frequency modes of combustion instability, taking combustion chamber geometry into account. Considering the configuration of the simulated combustion chamber, excitation probability of the longitudinal modes is higher than that of transversal modes. The reason of this fact is that the resonance frequency values of the longitudinal modes are less than those of transversal modes. So, the most important frequency mode, during combustion instability, is the first longitudinal mode. In this paper thermo-acoustic instability model is utilized for pre-mixed gas turbines combustion chamber, founded on equivalence ratio oscillation. For this purpose Lieuwen method is developed in order to attain the phase difference between pressure and heat release oscillations. Results concluded from combustion instability simulation for the first longitudinal mode, considering its importance, are compared with experimental data and good agreement is observed.
Nonlinear Aerodynamic Effects on Transonic Flap Buzz, Tail Flutter and Limit-Cycle Oscillations of Two-Dimensional Wing-Flap-Tail Configurations
Authors: Cheng J.-C.
Published: May 2011

The transonic tail flutter and flap buzz under the wing-flap-tail configurations are analyzed utilizing a dynamic grid capability of unstructured Euler solver coupled with an appropriate aeroelastic solver. From the results, the presence of a forewing, either stationary or oscillating, has significant effect on the tail flutter characteristics. In particular, the tail motion may be in resonance with the oscillating wing before the onset of flutter, which is dangerous to the tail structure because of the large amplitude oscillations. Besides, a complicated aerodynamic and aeroelastic interference of the tail have been found due to the unsteady disturbance which is a strong variability of flow structure induced by the buzz of the flap. In the high transonic flow regime, the flap buzz with limit-cycle oscillations does occur, and the influence induced by the tail is not important. The increasing restoring force at the pivot where the flap joints with the wing will reduce the flap oscillations that improves the effect of the flap buzz.
The Rheology of Blood Flow in a Branched Arterial System with Three-Dimensional Model: A Numerical Study
Authors: Hsu C.-H. , Vu H.-H. , Kang Y.-H.
Published: May 2011

Blood flow rheology is a very complex phenomenon. Hemodynamics owns Newtonian or non-Newtonian characteristic is still debatable. Recently, studies related to blood tend to classify blood as non-Newtonian fluid. In this research, power law, Casson and Carreau which are being the most popular non-Newtonian models are applied to investigate the hemodynamics variables that influence formation of thrombosis and predict damageability to blood cell. The branched arterial system is simplified as T-junction geometry and the computational fluid dynamics software Fluent 6.2 with finite volume method is utilized to analyze the blood flow rheology in cases of continuous and pulsatile flow. The analysis results are compared with that of Newtonian model and give out very interesting hemodynamics predictions for each model. The size of recirculation zone is different from each model that is observed significantly. The wall shear stress of Carreau model gets the highest value, 14% in case of continuous flow and around 17% in pulsatile case bigger than that of Newtonian model. The results of pulsatile flow show that the Newtonian model is closed to power law model while the Casson model is similar to the Carreau model.
Constructing Poisson and Dissipative Brackets of Mixtures by using Lagrangian-to-Eulerian Transformation
Authors: Chen K.-C.
Published: May 2011

This paper aims to construct the bracket formalism of mixture continua by using the method of Lagrangian- to-Eulerian (LE) transformation. The LE approach first builds up the transformation relations between the Eulerian state variables and the Lagrangian canonical variables, and then transforms the bracket in Lagrangian form to the bracket in Eulerian form. For the conservative part of the bracket formalism, this study systematically generates the noncanonical Poisson brackets of a two-component mixture. For the dissipative part, we deduce the Eulerian-variable-based dissipative brackets for viscous and diffusive mechanisms from their Lagrangian-variable-based counterparts. Finally, the evolution equations of a micromorphic fluid, which can be treated as a multi-component mixture, are derived by constructing its Poisson and dissipative brackets.
Topology Optimization of Elastic-Plastic Structures
Authors: Leu L. J. , Huang C. W. , Chou J. J.
Published: May 2011

The evolutionary structural optimization method is improved and extended to elastic-plastic topology optimization for the first time. An adaptive rejection ratio is proposed to control the number of removal elements without destroying the symmetric pattern in each evolution. Two performance indices suitable for elastic-plastic topology optimization are also proposed and examined. The performance indices can be used to investigate the material efficiency of structures in different evolutionary stages, and to serve as stop criteria in the evolutionary process. Moreover, an interactive special purpose computer analysis and graphics system is developed to visualize the topology in the evolutionary process. Finally, the effects of yield stress, Young's modulus, and the prescribed displacement in an elastic-plastic analysis on the obtained topology are discussed.
Pressure Analysis of Platform Screen Door Subjected to a Moving Train in Mass Rapid Transport Underground Station
Authors: Chun Lin-Jye , Chiang Yuan-Ching , Ting Chun-Chin , Ma Rong-Hua , Chen Sih-Li
Published: May 2011

This paper analyzes the pressure distribution on the platform screen door (PSD) subjected to a moving train running through a station in the tunnel. The advantages of adopting PSD design are to reduce the cooling load and the construction cost in mass rapid transport underground station. However, as the moving train enters or leaves the station, the PSD will face a long-term wind oscillation pressure force. For the safety design, dynamic simulation is requisite for the analysis of pressure force exerted on the PSD. The present study uses the commercial code PHOENICS to simulate dynamically the pressure and velocity distribution on the platform screen door. The results show that the maximum pressure on the platform screen door occurs at 6 m behind the front platform end with the values of 1,457 and 942 Pa, as the train moving speeds are 80km/hr and 65km/hr respectively. It is also indicated that the ratio of the different maximum pressures exerted on the PSD has a linear relationship with the square of train speed ratio for two different train speeds.