For a bi-linear SDOF system subjected to a specific wave form of the ground acceleration, the unique yielding pseudo spectral acceleration and spectral displacement (Say, Sdy) together with various inelastic responses (Sai, Sdi) can be obtained via nonlinear time history analyses, respectively, by tuning the different levels of peak ground acceleration as various input ground motions. Meanwhile, the corresponding elastic responses (Sae, Sde) of a linear SDOF system with the identical mass, viscous damping and elastic stiffness as those of the bi-linear one can also be determined through linear time history analyses under the same excitations. The proposed NSAD format shown on the diagram of the elastic force ratio, Ω=Sae/Say I Say, versus the ductility ratio, (μ= (Sdi/Sdy), is a dimensionless plot of the seismic demands suitable to the engineers who are familiar with the conventional force-based design using linear structural analysis. In this paper, more than two hundred ground motions recorded in the Chi-Chi earthquake, Taiwan (1999) were chosen as the seismic inputs for the establishment of the NSAD format. The characteristics and applications of the NSAD format on the performance-based seismic design of the bridge structures were discussed, and realistic procedures for the methodology were proposed.

The results obtained shows that the NSAD format can help the engineers evaluate the multiple-level seismic demands not only with a well precision but also with a great convenience.

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.

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.

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.

No-moving-parts valves (NMPV) pumps produce the net volume flow due to the difference of pressure resistances between forward and reverse flow of a microchannel structure. NMPV has been developed by a number of research groups. However, most of NMPV in these studies are designed and based on steady state flow conditions. Little data is available regarding the NMPV in unsteady flow conditions. In this study, the performances of NMPV under both steady and unsteady flow conditions are investigated numerically. The NMPV used in this study is a diffuser-type microchannel with diffuser angle of 20° because of its outstanding production of net volume flow. By a series of numerical simulations, some useful results would be addressed for the performance of NMPV micropumps. First, Reynolds number confirmed by steady analysis should be greater than 10 (Re > 10) for the NMPV pumps to be more effective. Second, an optimal Strouhal number with maximum net volume flow rate is found at St = 0.013 for the unsteady flow condition. In addition, the relation between the driving pressure amplitude and net volume flow rate with a linear behavior found was helpful to the performance of the micropump system. According to these findings, it was easy for users to operate and design of NMPV micropumps.

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.

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.

This article analyzes the performance of a piezoelectric energy harvester in the flexural mode for scavenging ambient vibration energy. The energy harvester consists of a piezoelectric bimorph plate with a variable width. A theoretical study is performed and the computational results show that the output power density increases initially, reaches a maximum, and then decreases monotonically with the increasing width, underscoring the importance for the width design of the scavenging structure. Further analysis indicates that the peak of output power density is determined by both the bimorph deformation amplitude and the efficiency in scavenging-energy. The analysis for this simplified model piezoelectric harvester provides a framework for further development on design guidelines for piezoelectric energy harvesters of optimal performance.

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.

Time-reversal mirror (TRM) was recently developed for underwater communication system application. This technique has been introduced as an approach to compensate for signal distortion due to multiple path effect in ocean waveguide. TRM is used in this paper for sending a message signal in ocean waveguide, received at time-reversal-array (TRA), and retransmitted to the dynamic ocean environment with an internal solitary wave. The focal structures obtained from different simulating cases are used for bidirectional transmission expediency, and the TRA is used as the relay-line or trunked radio. Ocean waveguide characteristic effects on acoustical properties are also shown in this paper, and focal structure in different ocean environments is analyzed to provide an optimal approach to underwater communication systems and for physical insight's interests.

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.

This study proposes an efficiently evolutionary algorithm, termed IGA-LS, which combines an intelligent genetic algorithm (IGA) with a gradient-based local search (LS). The IGA performs a crossover operation and uses a fractional factorial design to determine the optimal combination of design variables. That is, in the proposed IGA, the chromosomes of children are generated via an intelligent crossover process with factorial experiments after the execution of the selection operation of the GA. This gene mating process differs from that of the traditional GA, in which each chromosome of child exchange genes randomly. The gradient-based optimization approach seeks feasible and usable directions in which to minimize a specified objective function. The initial conditions are provided by the IGA in each generation. Therefore, the IGA-LS offers fast convergence and high numerical accuracy. Several multi-modal test functions are introduced herein to examine the algorithmic capacity and efficiency of finding the global optima. Moreover, the proposed IGA-LS algorithm is applied to optimize the design of a supersonic wing planform for supersonic airplane. The objective function is to minimize the drag during supersonic cruising. From the numerical results, the presented algorithm outperforms the traditional GA, the micro-GA and the intelligent GA in terms of convergence rate and value of the optimal function.

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.

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.

This paper is to present the design and development of a piezoelectric actuator for SPM in ultrahigh vacuum (10−7∼10−9 Torr). The measuring probe is installed on a precise scanning actuator, which is further driven by a fast approaching actuator. The precise scanning actuator composed of a piezo-tube with segmented electrodes can realize 3-D precise scanning motions at subnanometer level to move the measuring probe over the measured surface. Because of its stable and smooth actuating behavior, the inchworm actuating principle is selected for the fast approaching actuator, which is build up with two controllable clamping devices and an actuating device. Diverse flexure mechanisms are applied in the actuator to attain frictionless guiding and recovery functions. To realize balanced clamping forces on the scanning tube, each clamping device is integrated with a fine regulating mechanism for clamping force. By applying the theoretical model and the finite element analysis, the relations between force and deflection inside the actuator were investigated to validate its function. The developed actuator has sustained the severe baking and pumping process, and their function and performance were verified experimentally in ultrahigh vacuum.

In the paper, the degenerate kernels and Fourier series expansions are adopted in the null-field integral equation to solve bending problems of a circular beam with circular holes. The main gain of using degenerate kernels in integral equations is free of calculating the principal values for singular integrals. An adaptive observer system is addressed to fully employ the property of degenerate kernels for circular boundaries in the polar coordinate. After moving the null-field point to the boundary and matching the boundary conditions, a linear algebraic system is obtained without boundary discretization. The unknown coefficients in the algebraic system can be easily determined. The present method is treated as a “semi-analytical” solution since error only attributes to the truncation of Fourier series. Stress concentration is also our concern. Finally, several examples, including two holes and four holes, are given to demonstrate the validity of the proposed method. The results are compared with those of Naghdi and Bird and Steele. Also, the position where the maximum concentration factor occurs is examined. The present formulation can be extended to handle beam problems with arbitrary number and various positions of circular holes by using the developed general-purpose program.

The paper investigates the hydromagnetic stability theory of a thin electrically conductive fluid film flowing down along the outside surface of a vertical cylinder. The long-wave perturbation method is employed to solve for generalized kinematic equations with free film interface. The normal mode approach is used to compute the stability solution for the film flow. The modeling results display that the degree of instability in the film flow is further intensified by the lateral curvature of cylinder. This is somewhat different from that of the planar flow. It is also observed that by increasing the effect of the magnetic field and increasing the radius of the cylinder the film flow can become relatively more stable as traveling down along the vertical cylinder.

This paper adopts a three-dimensional (3D) finite element method to simulate the injection molding of organic 3D stacked-chip assemblies. The geometry model of the assembly is simplified to a five-layered structure of stacked-chips with no solder bumps. The injection molding process incorporates 3D stacked-chip packaging and encapsulation techniques, and comprises primarily of multi-layer cavity-filling and reactive-thermosetting curing processes. The current investigation considers the effects of specifying different entrances on the resultant flow fronts, air-traps, and weld-lines. In general, the present results confirm the value of performing numerical simulations of the 3D stacked-chip packaging process to support the injection molding CAE approaches which are commonly applied nowadays to improve the packaging assembly design and to facilitate the rapid set up of mass-production conditions. The simulation results indicate that the best packaging results are obtained when the melt is introduced either at the center of the periphery side of the stacked-chip modulus or at its corner.

In this paper, the band structures of Lamb waves in the two-dimensional phononic-crystal plates are calculated and analyzed based on the plane wave expansion method. The phononic-crystal plates are composed of an array of circular crystalline iron cylinders embedded in the epoxy matrix. Square lattice and triangular lattice are analyzed and discussed, respectively. For the square lattice, two complete band gaps exist, and a narrow pass band between the complete band gaps separates them apart. For the triangular lattice, a wide complete band gap existing with the ratio of gap width to midgap frequency Δω/ωm equal to 72% is found. Furthermore, the influence of the plate thickness is crucial for band structures of Lamb waves. Tuning plate thickness can shift the pass bands effectively, and band shifting causes the variation of the width of complete band gap and its opening and closure.

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 parameters Br / ψ≥ 0.75.