bluuebunny/crossref_metadata_2025 huggingface dataset:
Parallel Computation of Turbulent Flows Using Equation Decomposition Scheme
Authors: Jaw Shenq-Yuh , Wang Alpha Y.
Published: May 2011

A problem independent, equation decomposition scheme of parallel computation is adopted and tested using a two-dimensional turbulent channel flow. The incompressible Navier-Stokes equations, incorporated with the SIMPLEC algorithm and a two-layer turbulence model, were distributed to four nodes of IBM SP2 parallel machine using the PVM software and solved simultaneously. The computation domain and the interior iteration loop for the solution of every transport equation is the same, load balancing among different machines is automatically satisfied. Since all the transport equations and the flow field was solved and updated simultaneously, the solutions obtained from the equation decomposition scheme at each time step were more accurate than those obtained from a unit process code, which in turn sharply reduced the required convergence time steps. Without modifying any of the solution algorithm, or tuning the computer code, the rate of convergence speeds up more than four times by invoking four nodes of parallel machines using the equation decomposition scheme.
Numerical Investigation of Flow Around Bluff Bodies
Authors: Tsai Chou-Jiu , Chen Ger-Jyh
Published: May 2011

In this study, fluid flow around bluff bodies are studied to examine the vortex shedding phenomenon in conjuction with the geometrical shapes of these vortex shedders. These flow phenomena are numerically simulated. A finite volume method is employed to solve the incompressible two-dimensional Navier-Stokes equations. Thus, quantitative descriptions of the vortex shedding phenomenon in the near wake were made, which lead to a detailed description of the vortex shedding mechanism. Streamline contours, figures of lift coefficent, and figures of drag coefficent in various time, are presented, respectively, for a physical description.
Dynamic Green's Function for SH-Wave in Multi-Dipping Layers Embedded in a Half-Space
Authors: Teng Tsung-Jen , Chai Juin-Fu , Yeh Chau-Shioung
Published: May 2011

In this paper, the recursive T-matrix formalism is developed to determine the dynamic Green's function for SH-wave in the multi-dipping layers with arbitrary shape embedded in a half-space. In each layer, the wave field generated by a harmonic line load can be separated into two parts: the source term and the complementary part. The source term is exactly the Green's function for SH-wave in two-dimensional half-space, and the complementary part which causes the SH-wave to satisfy the boundary conditions at the interface is determined by the wave function expansion method. Using the polar coordinates, the basis functions are constructed by Bessel typed cylindrical functions, and their orthogonality conditions at the corresponding interfaces can be derived by means of Betti's third identity. Applying the conditions of continuity at the interface, the recursive T-matrix formalism is developed for determining the expansion coefficients of the complementary part from the associated source dependent constants.
Chaotic Behavior of an Inelastic Beam
Authors: Yeh Jiin-Po
Published: May 2011

The dynamical system considered in this paper is an inelastic beam whose supports are subjected to a harmonic excitation. This paper first explores whether the system has chaotic motion. The appearance of the irregular time history, strange attractor on the Poincaré map as well as period-doubling bifurcation phenomenon strongly indicates that chaos indeed exist in this system. After finding the chaos phenomenon, this paper continues to investigate the relationship between the decay time of the autocorrelation function and the largest Lyapunov exponent. The Poincaré mapping points are chosen to be the sampled function of the discrete autocorrelation function. It's found that a power model of regression analysis can fit with good accuracy the data points, which are composed of the mapping times for the autocorrelation to decay into the square of the mean of the Poincaré points and the corresponding largest Lyapunov exponent.
Blowing/Suction Effect on Combined Convection in Stagnation Flow Over a Vertical Plate Embedded in a Porous Medium
Authors: Yih K.A.
Published: May 2011

Blowing/suction effect on steady two-dimensional laminar combined convection owing to the stagnation flow against a vertical flat plate with linear wall temperature with distance in a saturated porous medium is numerically analyzed. The nonlinear coupled boundary-layer equations were transformed and the resulting ordinary differential equations were solved by Keller box method. Numerical results for the local friction coefficient and the local Nusselt number are presented for various parameters. In general, it is observed that in the buoyancy assisting (opposing) flow both the local friction coefficient and the local Nusselt number increase (decrease) because of the increase of buoyancy parameter, blowing/suction parameter and permeability parameter. The local Nusselt number becomes nearly constant when Ω is very small (pure fluid flow) and Ω is very large (pure Darcy flow).
On the Viscous Models for Wave Propagation in Solid Loaded with Viscous Liquid
Authors: Chang M.-P. , Wu T.T.
Published: May 2011

Recently, in the fields of biosensing and nondestructive of materials, there are increasing interests on the investigations of the surface wave propagation in fluid loaded layered medium. Several different models for the elastic coefficients of viscous liquids are usually adopted in the investigations. The purpose of this paper is to study the variations of choosing different viscous liquid models on the dispersion and attenuation of waves in liquid loaded solids. In the paper, a derivation of the elastic coefficients of a viscous liquid based on the Stokes' assumption is given first. Then, for the hypothetical solid assumption of a viscous liquid, the associated wave equations and expressions of the stress components for different viscous liquid models utilized in the literatures are given. Finally, dispersion and attenuation of waves in a viscous liquid loaded A1 half space and a SiC plate immersed in a viscous liquid are calculated and utilized to discuss the differences among these four different models.
Evaluation of Interlaminar Shear Stress by Strain Measurements on Laminate Surfaces
Authors: Lee C.Y. , Huang C.C.
Published: May 2011

For most composite structures, because of the uncertainty in some design variables, it is not possible to predict precisely the stresses during design stage. Therefore, monitoring the structural responses in service becomes crucial for structure with concerns, e.g., the composite panels on an airplane, etc. In this study, the strains at neighboring points of the interested location on surfaces of the laminate, along with the classical laminate theory and the higher-order shear deformation theory, are used to predict the interlaminar shear stresses in the cross-ply laminate. Several numerical examples using the simulated surface strains are employed to evaluate the accuracy of the proposed technique. It is found that the approach using the higher-order shear deformation theory has improved accuracy for the analysis of thick symmetric laminate over the approach using the classical laminate theory.
Some Nonlinear Features of the Squeeze-Film Problem
Authors: Lei U. , Chen Chia-Han
Published: May 2011

The nonlinear features of the squeeze-film problem between two parallel long strips driven by the relative harmonic oscillation of the strips is studied via the regular perturbation and numerical calculation for ∈ < 1 and σ = O(1)- O(103), where ∈ is the dimensionless amplitude of the oscillation, and σ is the squeeze number. The fluid film behaves as a (nonlinear) spring for large σ and as a (nonlinear) damper for small σ, which are qualitatively similar to the linear analysis. However, a steady state force is generated even though the driving mechanism is purely oscillatory due to the nonlinear effect. Furthermore, the dimensionless quasi-steady rate of energy dissipation within one cycle of the plate oscillation, E, is not zero (zero for linear analysis), and is maximized at σ ≈ 10. Also the rate of increase of E with ∈ is greater than ∈2. The present study may be helpful for the design of some accelerometers and vibration absorbers.
Optimal Allocation of Heat Transfer Area for a Heat Engine
Authors: Hsieh Y. C. , Chiou J. S.
Published: May 2011

For an endoreversible heat engine operates steadily between two fixed temperatures, Bejan found the engine's best performance can be obtained if the total thermal conductance is evenly divided for hot-end and cold-end heat exchangers. In this study, a heat by-pass model is used to represent the losses due to internal irreversibilities, and the more general formulations are derived for both the optimal area allocation and the maximum thermal efficiency. The results calculated from the present formulations when there is no internal irreversibility(a special case) are consistant with that obtained by Bejan.
Heat Conduction in Dissimilar Anisotropic Media with Bonding Defects/Interface Cracks
Authors: Shiah Y. C. , Yang R.-B. , Hwang P.-W.
Published: May 2011

As an essential foundation for the associated thermoelasticity analysis in the boundary element method (BEM), this article proposes an expedient, yet powerful, approach to analyze the heat conduction in multiply jointed anisotropic media with bonding defects/interface cracks. The direct domain mapping technique (DDM) is applied to treat a domain consisting of dissimilar anisotropic sub-regions in the potential theory of BEM. The heat transfer across a crack is modeled with a gap conductance equation specially formulated for the BEM analysis. Two numerical examples are provided as illustrations of the validity and the applicability of this proposed scheme.
Method of Fundamental Solutions for Stokes' First and Second Problems
Authors: Hu S. P. , Fan C. M. , Chen C. W. , Young D. L.
Published: May 2011

This paper describes the applications of the method of fundamental solutions (MFS) as a mesh-free numerical method for the Stokes' first and second problems which prevail in the semi-infinite domain with constant and oscillatory velocity at the boundary in the fluid-mechanics benchmark problems. The time-dependent fundamental solutions for the semi-infinite problems are used directly to obtain the solution as a linear combination of the unsteady fundamental solution of the diffusion operator. The proposed numerical scheme is free from the conventional Laplace transform or the finite difference scheme to deal with the time derivative term of the governing equation. By properly placing the field points and the source points at a given time level, the solution is advanced in time until steady state solutions are reached. It is not necessary to locate and specify the condition at the infinite domain such as other numerical methods. Since the present method does not need mesh discretization and nodal connectivity, the computational effort and memory storage required are minimal as compared to the domain-oriented numerical schemes. Test results obtained for the Stokes' first and second problems show good comparisons with the analytical solutions. Thus the present numerical scheme has provided a promising mesh-free numerical tool to solve the unsteady semi-infinite problems with the space-time unification for the time-dependent fundamental solution.
Extraction of Frequency Dependent Macromodels for Mems Squeezed-Film Damping Effects
Authors: Joseph Yang Yao-Joe , Chien Chih-Ming , Kamon Mattan , Rabinovich Vladimir L. , Gilbert John R.
Published: May 2011

In this paper, an efficient macromodel extraction technique for dynamical MEMS gas damping effects is presented. The technique applies an Arnoldi-based model-order-reduction algorithm to generate low-order macromodels from a FEM approximation of the governing equation of the squeeze-film fluidic damping effect, the Reynolds equation. We demonstrate that this approach is more than 100 times efficient than previous approaches, which solve the Reynolds equation using transient finite-element/finite-difference methods. The generated gas-damping macromodels can be easily inserted into system-level modeling packages, such as SPICE, Saber and Simulink, for transient and frequency coupled-domain analysis. We also demonstrated that the simulated results are in good agreement with experimental results for various MEMS devices.
The Stationary Values of Young's Modulus For Monoclinic and Triclinic Materials
Authors: Ting T. C. T.
Published: May 2011

The stationary values (maximum, minimum, saddle point) of Young modulusE(n) for a general anisotropic elastic materials is studied. The general results are then spcialized for monoclinic materials. Equations that provide the directionnfor a stationary value are given. Some have an explicit solution. Other may require a numerical computation. The equations that required numerical solutions are two coupled polynomials of degree no more than four.
Clarifying Low-Frequency Variatoions Phenomenon Using a Novel Mode Decomposition Method
Authors: Wang C.-T.
Published: May 2011

Low-frequency variations in wake flow are complex and many aspects of its behavior remain poorly understood. A mode decomposition method developed by Huang et al is utilized herein because it can decompose any complicated data set into a finite number of intrinsic modes without distorting their original characteristics. The results of decomposition analysis of the measured base pressure signals reveal that a finite number of various kinds of flow structure modes, with their own characteristic time scales, coexist with the residue that exhibits most of the low-frequency variations in flow at Re = 11760 and 31600, respectively. As the Reynolds number increases, the decomposition method yields more components. Results also show exactly the vortex shedding structure in an intrinsic mode and the low-frequency variations that appear in the residue during vortex shedding process.
A Study of Duct Flow Passing in a Horizontal Channel with a Cylinder Source Adjacent to Planar Boundary
Authors: Wang L. W. , Kung Y. C. , Lin K. H. , Sung S. H. , Wu C. Y.
Published: May 2011

The purpose of the present study is to investigate laminar fully developed flow in a horizontal rectangular channel with a cylinder solutal source adjacent to planar boundary. The boundaries in this experiment include four cases:

(A) Cylinder is cathode and top plate is anode;

(B) Cylinder is anode and top plate is cathode;

(C) Cylinder is cathode and bottom plate is anode;

(D) Cylinder is anode and bottom plate is cathode.

The influences of the mass transfer rate and the boundary types between the sources have also been investigated. An experimental investigation of mixed convection mass transfer between a cylinder and a plate mass source with an electrochemical system is carried in a horizontal rectangular channel. The working fluid here is CuSO4 + H2SO4 + H2O. The shadowgraph technique is used to visualize the flow and to determine the nature and effect of solutal driven secondary flows in a horizontal channel. The ranges of the parameters in the work are Pr = 7, Ar = 1, Sc = 1700 ∼ 2400, Re = 50 ∼ 200 (Red= 12.5 ∼50), Grm = 9.45 × 105, d/H = 0.25, h/d=0, 3.
Hygrothermal Effect on Deformations of QFN Electronic Packaging
Authors: Tsai M. Y. , Huang C. H. , Huang C. Y.
Published: May 2011

The hygrothermal-mechanical behavior of a quad flat non-lead (QFN) package without a chip inside is investigated experimentally and numerically. The present study is focused on understanding the effect of the inherent hygrothermal behaviors of epoxy molding compound (EMC) on the deformations of QFN package. Prior to studying the package, the coefficient of moisture expansion for the EMC is measured experimentally. Full-field moiré and Twyman-Green interferometries are used for measuring the real-time in-plane and out-of-plane deformations of the specimen, respectively, under thermal and moisture loading. In addition, the finite element and theoretical analyses are adopted for validating the experimental observations and further understanding the hygrothermal mechanics of the specimen. The coefficient of moisture expansion of the EMC was experimentally obtained to be about 0.2. The experimental results of the full-field deformations of the specimen, due to temperature, moisture and a combination of both, are presented. The experimental observations are validated by the finite element and theoretical analyses. It was observed that the maximum moisture-induced deformation (strain) can be up to as large as 50% of the thermal deformation (strain) caused by ΔT = 50°C for the specimen. As a result, neglecting moisture-induced deformations (strains) would cause the significant amount of error in thermal deformation (strain) measurement of plastic packages. Furthermore, the present study has laid down the fundamental mechanics and approaches for the QFN packaging structural design and analysis in terms of hygrothermal effects.
Deflection Form Factors of Worm and Worm Gear
Authors: Chung M. Y. , Shaw D.
Published: May 2011

In this study, a simplified method for evaluating amount of deflection for the tooth of worm and worm gear under loading is proposed. In a previous study, the plate theory was used for the approximation. However, it was found that the deflection of gear tooth using the plate theory was far from the actual value, and that the values from 3D FE analyses were closer to the actual value than from the plate theory. However, the FE analysis process starting from the CAD model to the final analysis results is complicated and too time-consuming. Therefore, the form factors are needed to facilitate simple but accurate results for the design purpose. In this study, the equations of form factors obtained from the results of plate theory and the 3D FEM, are developed. Since the worm gear assembly has various tooth geometries, the moment of inertia and the deflection of tooth geometry are different. Therefore, tooth geometries with trapezoid and involute forms are investigated.
A Study on the Safety of the Shear Capacity Design of Reinforced Concrete Beam-Column Joints
Authors: Lu W.-Y.
Published: May 2011

The shear failure probabilities of reinforced concrete beam-column joints have been investigated by Monte Carlo method. The theoretical shear strength of joints is based on the softened strut-and-tie model proposed by Hwang and Lee (2002). The random variables included in this study are the strengths of concrete, the ultimate compression strain of concrete, the strengths of reinforcement, the dimensions of cross-section, and the model error of theoretical shear strength of joints. The shear failure probabilities of joints with SD 280 flexural reinforcement in the beams designed using the ACI Code are all higher than 0.04. The joints designed according to the softened strut-and-tie model are safer than those designed according to the ACI Code. The shear failure probabilities of exterior joints are higher than those of interior joints. The shear failure probabilities of joints with SD 280 flexural reinforcement in the beams are higher than those of joints with SD 420 flexural reinforcement.
Application of Biot Theory in Analyzing the Sound Insulation Characteristic of Honeycomb Sandwich Panels
Authors: Wang C.-N. , Tang M.-J. , Tse C.-C.
Published: May 2011

The purpose of this paper is to apply Biot theory on analyzing honeycomb core to investigate the sound insulation characteristics of honeycomb sandwich panels. At first, the honeycomb core was regarded as a porous material and the sandwich panel is made of layered media. Thus Biot theory developed for fluid saturated porous material is adopted to analyze the waves propagated in honeycomb core. Then the transfer matrix for waves propagated between two ends of each panel is established. The combination of these related matrices can be conducted on evaluating the sound propagation characteristic in the layered media. The comparison of the transmission loss between the available experimental measurements and numerical predictions shows that the present method is reliable. With the present method, the numerical results reveal that the coincident frequency decreases apparently as the thickness of core increases. Therefore, the transmission loss is also increased in the analyzed frequency range. Further, the effect of core density and cell size are also investigated.
Studying Three-Dimensionality of Vortex Shedding Behind a Circular Cylinder with Mems Sensors
Authors: Tu J. K. , Miau J. J. , Wang Y. J. , Lee G. B. , Lin C.
Published: May 2011

Experiments were made with 14 MEMS sensors situated along the span of a circular cylinder whose aspect ratio was 5. The signals of the MEMS sensors were sampled simultaneously as flow over the cylinder at Reynolds numbers of 104. The results of Wavelet analysis of the signals indicate that the percentage of time during which strong three-dimensionality of vortex shedding was detected is about 10%.As noted, strong three-dimensionality took place when the fluctuating amplitude of the signals was severely modulated and the vortex shedding frequency reduced appeared abnormally high or low. Further noted was that the addition of a splitter plate of 0.5 or one diameter in length behind the circular cylinder was not able to suppress the three-dimensionality of the flow.
Effects of Structural Behavior on Electromagnetic Resonance Frequency of a Superconducting Radio Frequency Cavity
Authors: Lin M.-C. , Wang Ch. , Chang L.-H. , Yeh M.-K. , Kao F.-S.
Published: May 2011

During operation, a superconducting radio frequency cavity is cooled down to below critical superconducting temperature by liquid helium. Thus it is under external pressure by liquid helium while an ultrahigh vacuum inside. Being a niobium-made shell structure, the SRF cavity's shape and consequently the electromagnetic resonance frequency are sensitive to external load variations. A CESR-III 500MHz superconducting radio frequency cavity is illustrated to investigate this relationship. A simulation that links the calculations on mechanical structure and radio frequency electromagnetic field with the finite element code ANSYS® is demonstrated herein. The changes of electromagnetic resonance frequency associated with external loads and mechanical properties of niobium are studied systematically. A complete understanding on the mechanism is thus achieved. The computed results also indicate that the electromagnetic resonance frequency increases as the cavity is either cooled to cryogenic temperature or stretched longitudinally, while the reduction of the helium vessel pressure also raises the resonance frequency. Besides, the electromagnetic resonance frequency shift is ruled by the coefficient of thermal expansion when the cavity is cooled from room temperature to liquid helium temperature. Young's modulus and thickness of the cavity wall dominate the structure stiffness and thus also affect the frequency shift.
Physical Aging in Long Term Creep of Polymeric Composite Laminates
Authors: Hu H. W.
Published: May 2011

This paper presents a complete approach to characterize physical aging in long term creep of composite laminates using short term creep test. Carbon/epoxy composite IM7/977−3 was use to make the coupon specimens of unidirectional fiber orientation and symmetrical laminates. Creep tests were conducted on the specimens to obtain momentary compliances at isothermal conditions. Physical aging in elastic and in creep compliances were modeled respectively. Momentary creep compliances in various aging times were shifted to superpose a reference curve by introducing shift factors for both relaxation time and shape factor of a power law model. Linear relations between shift factors and aging time in log-log scale were found and defined as shift rates. By using reference curve associated with the shift rates, momentary creep compliance in any given aging time can be predicted. By introducing a time dependent shift factor, momentary creep compliance can be modified and turned into an effective time model, which can successfully predict the long term creep of composite laminates at isothermal aging. This approach only requires the test data of momentary creep, and no material properties in each lamina are needed.
Evaluation of Nonlinear System Parameters by Stochastic Spectral Method
Authors: Chang T.-P. , Liu M.-F.
Published: May 2011

A stochastic spectral method is proposed to estimate the nonlinear parameters of a system subjected to random excitation. Sometimes, it is impossible to measure the excitation process; therefore, estimation must then be based on the response measurement only, in conjunction with a stochastic model of the excitation. The concept of this method is to establish an objecting function involving the unknown parameters through frequency domain analysis, and then we can minimize the objecting function to estimate the unknown parameters by using standard nonlinear optimization algorithm. Finally, the validation of the proposed method is accomplished through many simulations and it can be concluded that the proposed method is applicable to a variety of different problems.
A Study on Mass Transfer in the Cathode Gas Channel of a Proton Exchange Membrane Fuel Cell
Authors: Jeng K.-T. , Wen C.-Y. , Anh L. D.
Published: May 2011

A two-dimensional, transient mathematical model for the mass transfer of a reactant gas in the cathode gas channel of a PEMFC is developed. This model accounts concurrently for gas flow and multicomponent species (oxygen, water vapor and nitrogen) transport in the gas channel at specified cell current densities. The governing equations along with the boundary and initial conditions are solved numerically by using finite-difference methods. The numerical results show that the oxygen and water vapor concentrations in the gas channel are strong functions of stoichiometry. However, at a fixed stoichiometry, the current density has only a slight influence on the concentration variations. The fully-developed Sherwood number for oxygen mass transfer in the gas channel was found to be 6.0, which agrees well with the Sherwood number estimated from the correlation between mass and heat transfer. The current mathematical model and numerical results are confirmed by the experimental verification of the location of first appearance of liquid water at the channel/GDL interface.
Train-Induced Vibration Control of Simple Beams Using String-Type Tuned Mass Dampers
Authors: Yau J.-D.
Published: May 2011

Since a long-term oscillation of a tuned mass damper (or TMD) in vibration control may impair the spring stiffness of the TMD, this phenomenon will directly down-tune the target frequency of the TMD. For this reason, this study intends to present a string-type tuned mass damper (or STMD) with an adjustable tuning frequency to mitigate the resonant response of a simple beam due to moving loads. The STMD device is installed inside the inner room of a bridge box girder and is composed of a distributed spring-dashpot-mass with a stretched string. Considering a linear beam-STMD model, a generalized two-degrees-of-freedom system is employed to determine the optimum tuning frequency condition and parameters of the STMD in vibration control. Compared with a traditional TMD device, the proposed STMD has the advantage of being adjustable in tuning frequency. From the numerical examples, the results indicate that the proposed STMD is a potential vibration control device in suppressing the train-induced vibration of railway bridges. Even though the tuning frequency of the STMD down-deviate from the target one by 10%, the control effectiveness of such a detuning STMD can still achieve about 90% as that of an optimal STMD by tuning its frequency to fit the optimum tuning frequency condition presented in this study.
The Effect of Flow Velocity on Microcantilever-Based Biosensors
Authors: Wu M.-C. , Chang J.-S. , Wu K.-C. , Lin C.-H. , Wu C.-Y.
Published: May 2011

This work focuses on studying the effect of flow velocity on microcantilever-based biosensor by numerical simulation. The microcantilever sensors used in detecting biomolecules have attractive advantages like cost efficiency, real-time and ability of fabricating in array. Both rectangular and triangular shapes of a general model of microcantilever beam are considered. Several important physical phenomena are obtained. Comparing with the first order Langmuir theory, we have calculated the effect on the reactive rate, produced concentration, the distribution of concentration and deflection in the z axis by solving these physical coupled problem involving flow field, concentration field and chemical reaction on the reaction surface. It is found numerically that the transportation of analyte, reactive rate, the distribution of concentration and deflection in the z axis are all effected by changing the flow velocity. The result has shown that flow velocity is an important factor for this biosensor.
Hybrid Flux-Splitting Finite-Volume Scheme for the Shallow Water Flow Simulations with Source Terms
Authors: Guo W.-D. , Lai J.-S. , Lin G.-F.
Published: May 2011

The extension of the hybrid flux-splitting finite-volume (HFF) scheme to the shallow water equations with source terms is presented. Based on the monotonic upstream schemes for conservation laws (MUSCL) method, the scheme is second-order-accurate both in space and time. An accurate and efficient surface gradient method (SGM), in conjunction with the HFF scheme, is adopted for the discretization of source terms, including the bed slopes and friction slopes. The resulting scheme has several desirable properties: ease of implementation, satisfaction of entropy condition, sharp shock resolution and preservation of well-balancing. The HFF scheme with SGM is verified through the simulations of steady transcritical flow over a hump and steady flow over an irregular bed. Besides, the effects of the limiter functions, the grid sizes and the Manning roughness coefficients on the simulated results are investigated for the steady transcritical flow problems. Using the laboratory measurements, the scheme is also applied to the dam-break flows: with an adverse slope, with a triangular hump, and with a constriction. Furthermore, the HFF scheme is employed in the simulation of typhoon flood flow with natural-irregular river topography to demonstrate the practical engineering application. The results show good agreements compared with the exact solutions, the experimental data and the field measurements.
Drag Force on a Sphere Moving in Low-Reynolds-Number Pipe Flows
Authors: Lee S.-H. , Wu Tzuyin
Published: May 2011

In this paper, the drag force on a sphere moving constantly along the centerline of a circular pipe filled with viscous fluid (the falling-sphere problem) under low Reynolds number condition is investigated via numerical calculation. The incompressible Navier-Stokes equations are formulated in a pseudocompressibility form. The numerical scheme makes use of finite-volume method and the numerical flux terms are evaluated using the Total-Variation Diminishing (TVD) strategy commonly applied to the compressible flow. Steady solution is obtained by marching (iterating) in time until the artificial time derivative of pressure term in the continuity equation drops to zero.

In the calculation, six different Reynolds number (Re) ranging from 0.1 to 1 and seven different pipe-to-sphere diameter ratios (D/d) ranging from 5 to 40 are selected to study the pipe-wall effect. In each case, the drag force on the sphere is evaluated and the results are compared with the existing approximate theoretical values derived from correcting the Stokes' formula. Both results agree in trend, but with noticeable deviation in values, particularly for cases with large pipe-to-sphere diameter ratios. The deviation is due to the fact that theoretical values were based on the solution to the linearized Navier-Stokes equations (Stokes' creeping-flow equations), while the fully nonlinear form of the Navier-Stokes equations are adopted in the present calculations. Finally, a least-square regression technique is applied to collapse the calculated results into a single expression exhibiting the functional relationship between the drag force, Reynolds number (Re), and the pipe-to-sphere diameter ratio (D/d).
Steady Motion of a Finite Granular Mass in a Rotating Drum
Authors: Tai Y.C. , Hutter K. , Gray J. M. N. T.
Published: May 2011

The Savage-Hutter (SH) theory (1989) of dense granular avalanche flow uses an earth pressure coefficient Kx which depends on the internal angle of friction and the bed friction angle but assumes different values in diverging and converging flows. So the earth pressure coefficient is undefined when the strain rate ∂u/∂x changes sign. Steady plane flow of a finite mass of a cohesionless granular material in a permanently rotating drum admits an exact solution of the SH-equations at ∂u/∂x = 0 provided the value for Kx is prescribed. However, avalanche profiles depend on the values of Kx. Experiments on avalanche shapes in steady rotating drums offer therefore a possibility to identify the value of Kx at zero strain rate.
Reflections on Nonlinear Dynamics of Machines and Structures
Authors: Moon Francis C.
Published: May 2011

In this short note a comparison is made between the methodology of nonlinear analysis in machine systems versus structural systems. Because of strong nonlinearities in machines with parts in relative motion, chaotic-like dynamics are more likely to occur in complex multi-body machines than in structural systems. Furthermore, it is conjectured that well designed machines have evolved to where a small amount of chaos is always present and is sometimes desired.
Natural Vibrations of Repetitive Structures
Authors: Wang Dajun , Wang C.-C.
Published: May 2011

Natural vibration frequencies and modes of repetitive structures, including symmetric, periodic, linking structures, are considered in this work. By using the repetition of the identical parts, we reduce the eigenvalue problem of the structure to a set of eigenvalue problems of lower dimensions associated with the parts. Special forms and properties of the modes of natural vibrations are observed.
Investigations of Thermo-Acoustic Instabilities by Direct Acoustic Admittance Measurements
Authors: Chen Tzeng-Yuan , Chen Man-Ge
Published: May 2011

This research applied the method of direct acoustic admittance measurement to investigate effects of the flame character and the burner acoustic admittance on the flame-driving behavior. The acoustic admittance data were obtained by directly measuring the amplitudes of pressure and velocity oscillations, and the phase relations between the pressure and velocity oscillations. Results of this research reveal that the flame-driving characteristic is mainly dominated by the nonreactive burner admittance not the flame. Whether the flame is to drive or damp the acoustic field is detcrmined by the acoustic admittance of the burner system. The flame equivalence ratio plays a role mainly in determining the magnitude of the flame driving/damping.
Creeping Flow Relative to a Porous Spherical Shell
Authors: Chen Ming-Da , Li Wang-Long
Published: May 2011

In this study, the problem of creeping flow relative to an isolated porous spherical shell has been examined. The Brinkman-extended Darcy equations and the Stokes' equations are utilized to model the flow in the porous region (shell region) and free fluid region (inside the core and outside the shell), respectively. The stress jump boundary conditions at the porous media/free fluid interfaces are included and the exact solution has been found. The drag experienced by the porous shell has been discussed for various jump parameters and shell thickness.
Importance of Nonreactive Burner Acoustic Admittance on Thermo-Acoustic Instability
Authors: Chen Tzeng-Yuan , Chen Chien-Pang
Published: May 2011

The importance of nonreactive acoustic admittance at a burner exit plane on the flame-driving characteristic was discussed using the measured phase difference between the velocity and pressure oscillations, and the acoustic wave structure inside the duct. Also, the flame-driving characteristics were investigated by flame radiation measurements, and results were compared with those obtained previously from admittance studies. Results show that the comparisons are in good agreement. Also, the flame-driving characteristics are closed related to the acoustic wave structure at the burner exit plane, and could be qualitatively predicted by knowing the imaginary part of nonreactive burner acoustic admittance.
Three-Dimensional Finite Element Analysis of Frictional Contact for Belt Transmission Systems
Authors: Shieh Chyuan-Jau , Chen Wen-Hwa
Published: May 2011

This work presents a rigorous three-dimensional finite element procedure to analyze belt transmission systems. The frictional contact behavior between the belt and the pulley, which accounts for the power loss of the system and the wear of the belt, is investigated in detail. In addition to adopting the transformation matrix to satisfy the geometric conditions on the contact surfaces, the proposed procedure also uses the modified elements with incremental Wilson displacement modes to improve the accuracy due to bending at the end zones of the contact area for the belt. To demonstrate the accuracy and feasibility of the proposed procedure, the analyses for flat and V belt drives are carried out. Excellent correlations between the calculated results and referenced theoretical/experimental solutions are found. The influences of friction coefficients on the deformation, normal and tangential contact forces on the contact surfaces are studied as well. Those will be helpful for the estimation of wear properties and operation efficiency for belt transmission systems.
Peculiar Appearance of Nearly Symmetrical Tidal Flooding Time Along the Western Coast of Taiwan
Authors: Juang Wen-Jye , Lin Ming-Chung , Liou Wen-Jiunn
Published: May 2011

During the past several decades, nearly symmetrical tidal appearances, both the time of high water elevation and the tidal range, were noted along the western coast of Taiwan. Research corresponding to anomalous amplifications of tidal range have been well studied by Lin, et al. [1,2], but the particular symmetrical tidal appearance of high water time has not yet been clarified. In this paper, we firstly apply a harmonic analysis to tidal data compiling. Based on the results, the important symmetric appearances of high water time and tidal range can be located. Emphasis is given on the investigation of symmetrical distribution of high water time by superposing two progressive waves that interfere on a topographic shelf with specific width. A conceptual configuration of co-oscillating standing tides is proposed to demonstrate the symmetrical tidal range distributing in the space domain and oscillating in the time domain.
3C Duct Design Method
Authors: Shiu Huan-Ruei , Ou Feng-Chu , Chen Sih-Li
Published: May 2011

A new 3C duct design method is proposed for designing a high quality, energy-efficiency cost-effective air duct system. It not only considers the demand of volume flow rate, but also takes into consideration a number of issues including system pressure balance, noise, vibration, space limitation and total system cost. This new method comprises three major calculation procedures: initial computer-aided design (CAD), computer-aided simulation (CAS) and correction processes (CP). An example is presented in this study to understand the characteristics of 3C method. It shows that 3C duct design method provides a simple computation procedure for an optimum air duct system. It also shortens the design schedule, prevents human calculation errors, and reduces the dependence on designer experience. In addition to apply in a new duct system design, 3C duct design method is also a powerful design tool for the expansion of an existing duct system.
A Hybrid Method for Analyzing the Dynamic Responses of Cavities or Shells Buried in an Elastic Half-Plane
Authors: Yeh Chau-Shioung , Teng Tsung-Jen , Shyu Wen-Shinn , Tsai I-Chang
Published: May 2011

In this paper, based on a variational formalism which originally proposed by Mei [1] for infinite elastic medium and extended by Yeh, et al. [2,3] for elastic half-plane, a hybrid method which combines the finite element and series expansion method is implemented to solve the diffraction of plane waves by a cavity buried in an elastic half-plane. The finite domain which encloses all inhomogeneities including the cavity can be easily formulated by finite element methods. The unknown boundary data obtained by subtracting the known free fields from the total fields which include the boundary nodal displacements and tractions at the interface between the finite domain and the surrounding elastic half-plane are not independent of each other and can be correlated through a series representation. Due to the continuity condition at the interface, the same series representation is still valid for the exterior elastic half-plane to represents the scattered wave. The unknown coefficients of this series are treated as generalized coordinates and can be easily formulated by the same variational principle. The expansion function of the series is composed of basis function. Each basis function is constructed from the basis function for an infinite plane by superimposing an additional homogeneous reflective term to satisfy both traction free conditions at ground surface and radiation conditions at infinity. The numerical results are made against those obtained by boundary element methods, and good agreements are found.
Numerical Study of Inlet and Geometry Effects on Discharge Coefficients for Liquid Jet Emanating From a Plain-Orifice Atomizer
Authors: Yeh Chun-Lang
Published: May 2011

A computational model for flow in a plain-orifice atomizer is established to examine the inlet and geometry effects on discharge coefficients. The volume of fluid (VOF) method with finite volume formulation was employed to capture the liquid/gas interface. A continuum Surface Force (CSF) model was adopted to model the surface tension. The body-fitted coordinate system was used to facilitate the configuration of the atomizer. The influences of the inlet chamfer angle, the orifice length/diameter ratio, the Reynolds number, and the inlet turbulence intensity are analyzed. It is found that the optimum discharge coefficient occurs at a chamfer angle of about 50°. The discharge coefficient at first increases with the increase in the orifice length/diameter ratio and then it decreases. The discharge coefficient increases with the increase in the Reynolds number up to Re = 40000, after which it remains sensibly constant. The influence of the inlet turbulence intensity on discharge coefficient is not significant, especially for a longer orifice.
The Theoretical and Experimental of Tube Drawing With Floating Plug for Micro Heat-Pipes
Authors: Wang C.-S. , Wang Y.-C.
Published: May 2011

This work presents a novel mathematical model, formed by modifying the conventional Slab Model, to predict the behaviors of tube drawing with a floating plug in the hollow copper tubes. FEM and experimentation are employed to verify the analytical solution. The model incorporates some parameters, including as die semi-angle, plug semi-angle, friction coefficient and wall thickness reduction ratio. The Self Lock Effect is simulated using FEM, and the effect is useful in estimating the critical drawing force. The results of this work reveal that the new model is more accurate than the conventional Slab Model especially at reduction ratios of up to 40%.
Study on an Improved Shock Absorber Used in the Oil Test Pipe Under Impact Load
Authors: Wang Y. X. , Cui Z. J. , Hu H. P. , Yin C. C. , Chen C. Y.
Published: May 2011

Performance of an improved shock absorber designed for absorbing and isolating the oil test pipe vibration is researched in this paper. 3D finite element model is established for the analysis of the shock absorber system accurately by the FEA software ANSYS/LS-DYNA. Numerical simulations show that the effect of the shock absorber can be greatly improved by optimizing the plastic material parameter. In the practice petroleum well test, the new designed shock absorber showed good shock absorption effect and no damage on the detecting instruments was observed even after ten times loading.
Comparison of Fatigue Tensile Properties of Scrimp-Gfrp and Hlup-Gfrp
Authors: Lin H.-J. , Liao C.-I
Published: May 2011

Seemann Composites Resin Infusion Molding Process (called SCRIMPTM for short) is a resin transfer molding process which is commonly used in the manufacture of yachts. Fiber-Reinforced Plastic (called FRP for short) manufactured by using SCRIMP has higher fiber-volume-content than that manufactured by using Hand Lay-Up Process (called HLUP for short). In general, the tensile strength and fatigue strength are used to compare the tensile properties of SCRIMP-FRP and HLUP-FRP. In this paper, another viewpoint of comparison is used to compare their tensile properties, especially their fatigue tensile properties. Experiments on the fatigue life and damage phenomena in SCRIMP-FRP and HLUP-FRP were performed. Experimental results show that if the same fibers are used in SCRIMP-FRP and HLUPFRP, SCRIMP-FRP will be much thinner than HLUP-FRP and few air bubbles exist inside SCRIMP-FRP. Although SCRIMP-FRP has higher tensile strength than HLU-FRP, the tensile forces they can bear are approached. That means, processes do not affect the tensile load carrying capacities of FRP. However, SCRIMP-FRP exhibits shorter fatigue life than HLUP-FRP. The reason for that is discussed in this paper and qualitative analysis is performed to explain the author's contentions.
Dissipation Improvement of MUSCL Scheme for Computational Aeroacoustics
Authors: Lin San-Yin , Shih Sheng-Chang , Hu Jen-Jiun
Published: May 2011

An upwind finite-volume scheme is studied for solving the solutions of two dimensional Euler equations. It based on the MUSCL (Monotone Upstream Scheme for Conservation Laws) approach with the Roe approximate Riemann solver for the numerical flux evaluation. First, dissipation and dispersion relation, and group velocity of the scheme are derived to analyze the capability of the proposed scheme for capturing physical waves, such as acoustic, entropy, and vorticity waves. Then the scheme is greatly enhanced through a strategy on the numerical dissipation to effectively handle aeroacoustic computations. The numerical results indicate that the numerical dissipation strategy allows that the scheme simulates the continuous waves, such as sound and sine waves, at fourth-order accuracy and captures the discontinuous waves, such a shock wave, sharply as well as most of upwind schemes do. The tested problems include linear wave convection, propagation of a sine-wave packet, propagation of discontinuous and sine waves, shock and sine wave interaction, propagation of acoustic, vorticity, and density pulses in an uniform freestream, and two-dimensional traveling vortex in a low-speed freestream.