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 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.

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.

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 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.

Based the previously published model on the two-dimensional micromechanical fiber interaction framework of two-phase composites, effective transverse elastic properties of composites containing two types of randomly located yet unidirectionally aligned circular fibers are studied in this paper. Approximate local solutions for the interaction problem of two randomly located circular fibers of different elastic properties are presented. A fiber-reinforced composite material containing two extreme types of inclusions, voids and rigid fibers, is also investigated. Comparison with Hashin's variational bounds and Mori-Tanaka method, the current approach provides reasonably accurate predictions for three-phase composites. Finally, numerical simulation examples are implemented to demonstrate the capability of the proposed model.

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.

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 elastic-plastic microcontact model of a sphere in contact with a flat plate is developed in the present study to investigate the effect of surface roughness on the total contact area and contact load. From the study done by the finite element method, the dimensionless asperity contact area, average contact pressure, and contact load in the elastoplastic regime are assumed to be a power form as a function of dimensionless interference (δ/δec). The coefficients and exponents of the power form expressions can be determined by the boundary conditions set at the two ends of the elastoplastic deformation regime. The contact pressures evaluated by the present model are compared with those predicted by the Hertz theory, without considering the surface roughness and the reported model, including the roughness effect, but only manipulating in the elastic regime. The area of non-zero contact pressure is enlarged if the surface roughness is considered in the microcontact behavior. The maximum contact pressure is lowered by the presence of surface roughness if the contact load is fixed. Under a normal load, both the contact pressure and the contact area are elevated by raising the plasticity index for the surface of the same surface roughness.

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.

The modified Reynolds equation for power law fluid is derived from the viscous adsorption theory for thin film elastohydrodynamic lubrication (TFEHL). The differences between classical non-Newtonian EHL and non-Newtonian TFEHL are discussed. Results show that the proposed model can reasonably calculate the pressure distribution, the film thickness, the velocity distribution and the average viscosity under thin film lubrication. The thickness (δ), the viscosity (m1), and the flow index (n1) of the adsorption layer influence significantly the lubrication characteristics of the contact conjunction. Furthermore, the film thickness increases with the increase of n1 and the film thickness affected by m1 is greater than that affected by n1, but the effect of n1 produces a very small difference in the pressure distributions. In addition, the greater n1, the smaller the change of velocity distribution in the adsorption layer, and the greater the change of velocity distribution in the middle layer. The larger δ and n1, the larger the deviation on log (film thickness) vs. log (speed) produced in the very thin film regime. In the region of the flow index ratio between 1.0 and 1.3, the difference in film thickness is significant. When the flow index of the adsorption layer is 1.6 times greater than the flow index of the middle layer, the adsorption layer is generally looked upon as a “solid-like”.

Generally, the Force-State Mapping (FSM) is an effective method to identify the parameters of nonlinear joints provided that the joint model is exactly known in advance. However, the variation of the non-linear joints is so large that the mathematical models of non-linear joints generally are not known in advance. Therefore, the model and the parameters of a non-linear joint should be identified simultaneously in practice. In this work, a new identification procedure which was based on the FSM method in frequency domain was proposed to identify the mathematical model and parameters of a non-linear joint simultaneously. Generally, there are many feasible combinations of models and parameters which can satisfy the measurement data within an allowable range of error. In this work, an iteration procedure was used to update the feasible models to result in an optimal model with its parameters. The simulation results show that a proper mathematical model and accurate parameters can be identified simultaneously by the new procedure even that the measurement data are contaminated by noise.

This research proposes a straightforward and efficient method to optimize a sandwich monocoque car body with the developed equivalent shell element based on stiffness equivalence. The fact that stiffness rather than strength is dominant constraint for ordinary car body optimization is demonstrated. A simple but heavy flat chassis plate is utilized as upper bound, while an ideal monocoque is used as lower bound for an actual car body optimization. Convergence hours can be significantly reduced with the equivalent element and the initial-bounded method. A novel electric car body optimization is presented, fulfilling UltraLight Steel Auto Body (ULSAB) stiffness requirements and showing similar optimal weight results as a conventional approach with a much lower analysis time cost.

It is believed that a dynamic analysis is urgently required to provide a more reliable numerical method for seismic evaluation of a full system, which includes foundation, super structure, and ground in earthquake zones such as Taiwan and Japan. A centrifugal model test of pile foundation is simulated numerically using a three-dimensional finite-element model (3D-FEM) code in this study. In the numerical simulation, parameters of the sandy soils in tij model that are derived from accumulated experiences in static tests are first calibrated by centrifugal vibration tests of sandy ground. Model tests of a single pile foundation installed in grounds of same unit weight of soil as in the static tests are then simulated using the calibrated parameters. The numerical simulation resulted in a good agreement with the corresponding physical model tests. By comparing the computed and the observed results, one can find and confirm that it is necessary to employ an appropriate soil model to reproduce dynamic soil behavior due to major vibration. Representation of pile by beam element in the numerical analysis is applicable when attention is paid on the response acceleration of top of pile foundation, on soils at some distances to the pile foundation, and on bending moment of the pile in a stiffer ground. Equal-displacement boundary condition for two-side boundaries is proven to be efficient. To reduce the computation time, the assumption of a constant damping of viscous matrix is acceptable.

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.

The coalescent behaviors in collisions between two droplets respectively made of different alkanes, water and alkane, methanol and alkane, and ethanol and hexadecane were experimentally studied. The coalescent results between two droplets of different alkanes are qualitatively the same as that with the same material, which simply form a spherical droplet. However, it took time to have the concentration within the droplet to become uniformly distributed. The collision results of water and alkane droplets collision become slightly more complex, in most cases, the water droplet was either inserted into or adhesive to the hexadecane droplet while only insertion was observed if the target droplet was dodecane or heptane. The inserted water droplet tends to partially expose to the environment as the volume fraction of water is sufficiently high, say, ∼0.62 for hexadecane, > 0.70 for dodecane, and > 0.78 for heptane; and the limit is lowered with the decreasing of water or merged droplet size. For the cases of methanol and alkanes, and ethanol and hexadecane, the two colliding droplets were adhesive to each other in all the studies. Furthermore, in most conditions, air bubbles were observed immediately after the collisions, while only few or even none of them might be trapped within the final merged droplet.

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).

In this paper, an endochronic theory of cyclic viscoplasticy with damage is established based on the irreversible thermodynamics of continuous media with internal state variables containing an isotropic damage parameter. The constitutive equations derived have the same mathematical form as those of convectional endochronic theory without damage, except the effective stress with damage is used. This result coincides with the Lemaitre's statements of stain equivalence principle.

Using the experimental cyclic stress-strain curves of 63Sn/37Pb solder bars, corrected from the uniaxially constant displacement amplitude cyclic tests under MTS Tytron microtester, the computational results of cyclic stess-strain curves with several degrees of damage can reproduce the experimental data quite well. Based on compressive buckling appeared in the vicinity of the compressive end parts of the hysteresis loop, the critical values of damage are determined between 0.3 and 0.4.

The evolution equation of damage proposed in terms of the intrinsic damage time scale and its results in the modified Coffin-Manson LCF law can be extended in the future research for a statistical theory of life distribution under low cycle fatigue tests.

The behaviour of vortices induced by a single square cylinder in an oscillating flow was investigated. The flow patterns in the vicinity of square cylinders were visualized using an in-house numerical model. Meanwhile, force coefficients exerted on the square cylinder were determined numerically. In terms of various Keulegan-Carpenter (KC) numbers, it turns out that the flow patterns for an oscillating flow past a single cylinder can be divided into three modes: (i) no vortex, (ii) pairs of symmetric vortices, and (iii) asymmetric vortex shedding. Reynolds (Re) number did not affect the flow field apparently in this study. In addition, the in-line force coefficient decreases exponentially as KC increases. Spectrum analysis of in-line force coefficients for various KCs was provided. It can be found that the flow system was at a periodic state at small KC for the first two modes. Variations of the flow system from a periodic state to a highly nonlinear state in which asymmetric vortex shedding appeared were demonstrated for increasing KC. The relationship between the in-line force and KC was provided for future applications.

Tunnel stress path during excavation was investigated in the study scope. The triple-center section is commonly designated for highway tunnels, but the analytical solution of the stress state for a non-circular tunnel section with multiple bench excavations is difficult to obtain. Our investigation provides an algorithmic procedure which reliably evaluates stress adjustment of a bench excavation with respect to the three-dimensional state of stress. Evaluation of a safety factor at the tunnel face during advancement is performed following the stress path and principal stress space.