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).

This paper proposes a robust Kalman-filter-based optimal model-following control (OMFC) methodology for actively suppressing the vibration of the mechanical structure system, which is modeled by the modal force technique (MFT) and subjects to both disturbance/noise uncertainties and linear structured time-varying parameter perturbations. The proposed method can not only avoid the problem of how to choose appropriate weighting matrices in the quadratic cost function of the linear quadratic Gaussian (LQG) control but also make the controlled closed-loop system to have desired system response characteristics. Besides, this paper also presents a robust stability criterion to guarantee that the designed controller can keep the controlled mechanical structure system from the possibility of time-varying-parameter-perturbation-induced instability. An example of L-shaped cantilever beam structure system is employed to demonstrate the application of the proposed method and the use of the robust stability criterion. Numerical simulation is performed to evaluate the improvement of the vibration response.

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.

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.

Adopting the DEFORM software for the finite element analysis, this study simulated steady-state plastic deformation of the sheet at the roll-gap during asymmetrical sheet rolling. Using FEM code DEFORM, the effects of roll speed ratio, roll radius ratio, friction factor ratio upon the curvature of the rolled product and rolling force were systematically discussed. With a view to verifying the validity of the study simulated, a series of experiments on asymmetrical cold sheet rolling using Aluminum sheet as specimen are carried out. The comparisons between numerical and experimental results show good agreement. Therefore, this numerical model using DEFORM software can offer useful knowledge for designing the pass-schedule of asymmetrical sheet rolling.

The solidification of a phase change material (PCM), exemplified by a molten metal, in a thick-walled container is analyzed in this paper. The effects of natural convection and several important controlling parameters are investigated extensively. These parameters include the initial temperature of the PCM, external cooling conditions, thickness and thermal properties of the wall, and the thermal contact resistance at the PCM/wall interface. Two representative configurations are examined in this study. A modified version of the enthalpy formulation in which the sensible heat is separated from the latent heat, is employed to construct the energy equation for the PCM. Vorticity-stream-function approach is adopted for solving the flow field. The governing equations pertinent to the problem are discretized by the weighting function scheme and finally solved by the SIS (Strongly Implicit Solver) algorithm. It is demonstrated that for both configurations natural convection has prominent effect on the temperature distribution of the liquid phase of the PCM; however, the effect of natural convection on the shape of the solid/liquid interface and the overall solid fraction is case dependent. It is also shown that the above-mentioned controlling parameters have a direct impact on the solidification process. Specifically, an increase in the Biot number (from 1 to infinity) and the thermal diffusivity of the mold (from 0.8 to 5) enhances the solidification rate. Reverse effect was found for the other controlling parameters.

The dynamic Green's function due to an impulse in an infinite anisotropic medium under anti-plane deformation is derived by the method of Smirnov [1] for two-dimensional wave equation. The Green's function is inversely proportional to the time t and an effective dynamic shear modulus. It is shown that the tractions on the planes passing through the source point vanish identically. Based on the free-space Green's function, the Green's functions for wedges, semi-infinite media and strips are obtained.

Experiments are performed to study the unsteadiness of rectangular cavity flows at Mach 0.325, 0.620 and 0.818. Typical characteristics of mean surface pressure distributions show a slight pressure variation near the front face, a local peak surface pressure ahead of the rear corner and a low pressure at immediate downstream of the cavity. Larger peak pressure and pressure variation near the cavity rear face are observed as the length-to-depth ratio increases. Surface pressure fluctuation distribution shows an increase toward the cavity rear face and reaches a peak value. At further downstream locations, the level of surface pressure fluctuation approaches the value of incoming flow. The amplitude of peak surface pressure fluctuation is associated with length-to-depth ratio and reaches the maximum at length-to-depth ratio of 8.60. This is considered due to intermittent switching between open- and closed-cavity flows. Higher moments of surface pressure signal at immediate downstream of the cavity show a similar trend. More negative skewness coefficient and larger deviation of flatness coefficient indicate the presence of more large negative events, which is mainly corresponding to mass removal process (breath-out phase). This unsteady mass flow is more pronounced at higher Mach number.

An efficient boundary weight function method for the determination of mode I stress intensity factors in a three-dimensional cracked body with arbitrary shape and subjected to arbitrary loading is presented in this study. The functional form of the boundary weight functions are successfully demonstrated by using the least squares fitting procedure. Explicit boundary weight functions are presented for through cracks in rectangular finite bodies. If the stress distribution of a cut out rectangular cracked body from any arbitrary shape of cracked body subjected to arbitrary loading is determined, the mode I stress intensity factors for the cracked body can be obtained from the predetermined boundary weight functions by a simple integration. Comparison of the calculated results with some solutions by other workers from the literature confirms the efficiency and accuracy of the proposed boundary weight function method.

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.

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°.

Based on the weight function theory and Hutchinson's technique, the analytic form of the toughness change near a crack-tip is derived. The inhomogeneity toughening is treated as an average quantity calculated from the mean-field approach. The solutions are suitable for the composite materials with moderate concentration as compared with Hutchinson's lowest order formula. The composite has the more toughened property if the matrix owns the higher value of the Poisson ratio. The composite with thin-disc inclusions obtains the highest toughening and that with spheres always provides the least effective one. For the microcrack toughening, the variations of the crack shape do not significantly affect the toughness change if the Budiansky and O'Connell crack density parameter is used. The explicit forms for three types of the void toughening and two types of the microcrack toughening are also shown.

The problem of a stable stratified fluid heated by a point source of heat at various depths is treated in this paper. A hot plume is formed with a series of layer around and above it. Quantitative estimates for the criterion of onset of doubly diffusive instability are obtained in this work. The linear differential system governing stability is then solved. The results show that the stationary onset of this doubly diffusive problem caused by a point source may be led to a similar form of small-gap Taylor- Couette problem.

This paper describes a model using boundary element and finite element methods for the solution of three-dimensional incompressible viscous flows in slow motion, using velocity-vorticity variables. The method involves the solution of diffusion-advection type vorticity equations for vorticity whose solenoidal vorticity components are obtained by solving a Poisson equation involving the velocity and vorticity components. The Poisson equations are solved using boundary elements and the vorticity diffusion type equations are solved using finite elements and both are combined. Here the results of Stokes flow with very low Reynolds number, in a typical cavity flow are presented and compared with other model results. The combined BEM-FEM model has been found to be efficient and satisfactory.

To study the performance and estimate the oscillating bearing loads of a twin screw air compressor, a theoretical model is proposed in this paper. Based on the model, a computer simulation program is developed and effects of different design parameters such as rotor profile, geometric clearance, oil injected position, oil temperature, oil flow rate and other operational conditions are investigated. Output variables such as bearing loads, specific power, compression efficiency, volumetric efficiency, discharge temperature are obtained. Some of the results are then compared with experimentally measured data, and good agreements are found between the simulation results and the measured data.

This paper develops a method to re-evaluate the reliability of a structure after a period of service. System identification is performed on the structure to identify the current properties of the structure. The Bayesian approach is adopted to modify the prior distributions of the properties based on the identification results. Then, reliability analysis is performed on the structure using the updated distributions of the properties. Sensitivity analysis is also performed to attain the maintenance strategy.

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.

A new computational procedure is developed to solve the external field problems of the incompressible viscous flows. The method is able to solve the infinite boundary value problems by extracting the boundary effects coming from the finite computational domain. The present method is based on the projection method of the Navier-Stokes equations. We use three-step explicit finite element method to solve the momentum equation of the flow motion. The external field solver of the boundary element is used to treat the pressure Poisson equation. The arbitrary Lagrangian-Eulerian method is employed to deal with the moving boundary, such as wind-structure interaction problems. For illustration of the present numerical code, a vortex-induced cross-flow oscillations of a circular cylinder mounted on an elastic dashpot-spring system is considered. The phenomena of the beat, lock-in, and resonance are revealed in the Reynolds number range between 100 and 110, which are much narrower than the previous studies.

This paper uses a simple model, the lumped single-degree-of-freedom system on rigid mat foundation, to investigate the effects of soil-structure interaction on the dynamic response of a soil-structure system. Based on that, the key parameters affecting the natural frequency of a soil-structure system can be easily identified and be used to assess the effects of soil-structure interaction. Accordingly, it was used to simulate the dynamic response of the forced vibration tests conducted at Hualien, Taiwan. Results obtained show that the simple model can predict the field responses very satisfactorily.

The stress-strain relationship of the sand and asphalt concrete materials is one of the most important research subjects in the past, and many conctitutive laws for these materials have been proposed in the last two decades. In this study, the Vermeer plasticity model is modified and used to predict the behavior of the sand and asphalt concrete materials under different stress path conditions. The results show that the predictions and test results agree well under different stress path conditions. However, the orignal Vermeer model can not predict the stress-strain behavior of the asphalt concrete. Finally, the modified Vermeer plasticity model is incorporated with the pavement rutting model to predict the rut depth of pavement structure under traffic loadings.