This paper presents a dynamic formulation of the boundary element method for stress and failure criterion analyses of anisotropic thin plates. The elastostatic fundamental solutions are used in the formulations and inertia terms are treated as body forces. The radial integration method (RIM) is used to obtain a boundary element formulationithout any domain integral for general anisotropic plate problems. In the RIM, the augmented thin plate spline is used as the approximation function. A formulation for transient analysis is implemented. The time integration is carried out using the Houbolt method. Integral equations for the second derivatives of deflection are developed and all derivatives of fundamental solutions are computed analytically. Only the boundary is discretized in the formulation. Numerical results show good agreement with results available in literature as well as finite element results.

The focal point of this paper is to uncover, by analyzing the higher order wave effect, an improved mechanism for space-constrained rectangular plenums using a simplified objective function in conjunction with a genetic (GA). Three kinds of rectangular mufflers hybridized with extended tubes will be assessed: Plenum A: A two-chamber plenum equipped with an extended tube; plenum B: A three-chamber plenum with two extended tubes; and plenum C: A two-chamber plenum equipped with three extended tubes. In order to shorten the numerical assessment, a simplified objective function (OBJ) is established using a boundary element model (BEM) in conjunction with the neural network model (NNM). To expediently approach an optimal plenum, the best OBJ will be numerically searched using a genetic algorithm (GA). However, before the GA operation is performed, the accuracy of the BEM is verified using analytical data. And, because the simplified objective function (OBJ) is seen to be in agreement with the BEM, the numerical cases of sound elimination relative to the various parameter sets and pure tones (300, 750, and 1300Hz) can be carried out.

Results reveal that the maximum value of the sound transmission loss (STL) can be accurately obtained at the desired frequencies. Additionally, the acoustical performance of the lower frequencies will be improved if the number of chambers and rectangular tubes are increased. However, the acoustical performance of the higher frequencies will decrease when the number of chambers and rectangular tubes are decreased. Consequently, the algorithms proposed in this study will efficiently develop optimal rectangular plenums with multiple rectangular extended tubes.

Upsetting is a typical test for determining the workability diagram. In most cases axisymmetric samples are used for such tests. However, the shape of samples may have a significant effect on the ductile fracture initiation. Therefore, a greater variety of sample geometry should lead to a more accurate shape of the workability diagram. A difficulty here is that a theoretical treatment of samples in which three-dimensional flow occurs is more difficult and time consuming as compared to axisymmetric samples under axisymmetric loading. This difficulty can be overcome in the case of the ductile fracture criterion based on the workability diagram and the average value of the triaxiality factor. In particular, if fracture occurs at free surfaces then it is sufficient to determine experimentally in-surface strains after several stages of the upsetting process, up to the initiation of ductile fracture. After that, the corresponding point of the workability diagram can be found by means of a simple analytical procedure and numerical integration. This approach is used in the present paper to correct the workability diagram using non-axisymmetric upsetting of five different samples made of steel. Some previous results are combined with the new results to obtain the workability diagram over a wide range of the triaxiality factor.

This paper presents an axisymmetric layerwise finite element formulation for dynamic analysis of laminated structures with embedded viscoelastic material whose constitutive behavior is represented by the Prony-generalized Maxwell series. To account the time dependence of the constitutive relations of linear viscoelastic materials, the incremental formulation in the temporal domain is used. Layerwise finite element has been shown to provide an efficient and accurate tool for the simulation of laminated structure. Most of the previous work on numerical simulation of laminated structures has been limited to elastic material behavior. Thus, the current work focuses on layerwise finite element analysis of laminated structures with embedded viscoelastic material. A computer code based on the presented formulation has been developed to provide the numerical results. The present approach is verified by studying its convergence behavior and comparing the numerical results with those obtained using the ABAQUS software. Finally, and as an application of the presented formulation, the effects of load duration on the dynamic structural responses of multilayered pavements are studied.

In this paper the transverse vibration characteristics of piezoceramic circular plates with V-notches are investigated theoretically through use of the Ritz's method incorporated with the defined equivalent constants. The Ritz's method is employed with two sets of admissible displacement functions, algebraic-trigonometric polynomials and corner functions, to guarantee convergence sufficiently and represent the stress singularity, respectively. Moreover, the equivalent constants derived by comparing the characteristic equations of transverse vibration between isotropic and piezoceramic disks are applied to suspend the electrical field consideration regarding the piezoelectricity. With the aid of theoretical analysis, the non-dimensional frequency parameters of transverse vibration modes for completely free V-notching circular plates are exhibited; in addition, the frequency variations depending on various notch angles and depths are explored. Numerical calculations using the finite element method (FEM) are performed and the results are compared with the theoretical analysis. It is shown that the resonant frequencies predicted by theoretical analysis and calculated by FEM are in good agreement.

Plastic packaging materials tend to absorb moisture from ambient environment and get swollen, this may raise hygro-stress in plastic electronic package and redistribute the internal stress. In this paper, we reviewed the dramatic deformation of a plastic package (Flip Chip Plastic Ball Grid Array-FCPBGA) due to moisture absorption first, then hygro-thermo-mechanical stress of the plastic package and its evolution during a period of three months were investigated with finite element method, user development was performed for this investigation. The finite element model was verified with hygro-thermal deformation of the FCPBGA measured with a 3-D moiré interferometry system. Following findings were obtained: A. Thermal stress field was changed a lot due to moisture absorption; B. Thermal stress of chip was released to some extent, but peal stress up to 62.2MPa occurred to the solder bump, thus the danger of Under Bump Metal (UBM) opening increased.

In the present work, a recently developed in-house 2D CFD code is used to study the effect of gas turbine stator blade roughness on various performance parameters of a two-dimensional blade cascade. The 2D CFD model is based on a high resolution flux difference splitting scheme of Roe (1981). The Reynolds Averaged Navier-Stokes (RANS) equations are closed using the zero-equation turbulence model of Baldwin-Lomax (1978) and two-equation Shear Stress Transport (SST) turbulence model. For the smooth blade, results are compared with experimental data to validate the model. Finally, a correlation between roughness Reynolds number and loss coefficient for both turbulence models is presented and tested for three other roughness heights. The results of 2D turbine blade cascades can be used for one-dimensional models such as mean line analysis or quasi-three-dimensional models e.g. streamline curvature method.

The present work studies the torsional instability of an elastic structure due to hydrodynamic loads into the water current. The structure applied here is a rectangular flat plate with an elastic axis in its mid-chord length. The elasticity in the structure is provided by torsion spring. The flat plate has only one degree of freedom which is rotation in pure yaw about its axis. Through the free vibration experiments, it is observed that as the current speed exceeds a critical velocity, the flat plate becomes unstable. Two different chord lengths are tested and the instability occurs for a chord base range of Reynolds number, 0.75 × 105 < Rec < 1.5 × 105. As a result of the instability, the flat plate begins to yaw about the elastic axis. The hydrodynamic moment acting on the flat plate is modeled by means of the flutter derivatives. As an identification technique to extract flutter derivatives, a curve fitting scheme called General Least-Square (GLS) theory is applied on the results of the free vibration experiments. The results confirm that the structure becomes dynamically unstable due to the hydrodynamic moment applied on it beyond the critical velocity. The super-critical Hopf bifurcation is also discussed in the light of the analysis.

The imaginary part of the Clausius-Mossotti factor, Ki, is crucial for quantitative particle/cell manipulation and characterization using travelling wave dielectrophoresis (twDEP) and electrorotation (ER). It can be measured rather easily using twDEP instead of using ER, as numerical calculation of the electric field and complicated devices are not needed for evaluating Ki using twDEP. However, the current single frequency twDEP method works only for particles/cells exhibiting negative dielectrophoresis (DEP), which is in general the case when cells are manipulated in physiological strength buffers with conductivity of order of 1S/m. In order to remove such a restriction, a modified twDEP method is proposed using dual frequency operation here capable of measuring the Ki spectra of particles/cells for the entire range of medium conductivity, irrespectively of whether the particles/cells exhibit positive or negative DEP. The success of the modified method relies on the adequate design of force balance between various forces in a designed micro channel, which was discussed in details. The method was validated, and demonstrated by measuring Ki spectra of three human cancer cells for medium conductivity from 0.01 ~ 1.2S/m. Both the method and the cell result find biomedical and other industrial applications.

This study presents the fluid temperature measurement at a 90-degree sharp bend inside a microchannel using molecule-based temperature sensor technique. This technique provides both detailed and global information for temperature investigation in microfluidic research. Rhodamine B was selected as the molecule-based temperature probe in the experiment to provide non-invasive and straightforward measurements. To resolve the luminescence deviation in the microscale temperature measurements introduced by the corner structure, in-situ calibration method and pixel-by-pixel correction were applied during the data reduction. The temperature measurement was performed in a 200μm wide, 67μm deep and 2cm long PDMS microchannel with a 90-degree sharp bend at the center. The temperature profile was measured at a Reynolds number of 27.66 using Rhodamine B in DI water while the bottom of channel was heated at 50°C. As revealed by the molecule-based temperature sensor, the temperature variation along the central line increased 2°C while passing the corner. Additionally, the lateral temperature distributions upstream of the corner show the temperature increase near the outer side of microchannel and decreased near the inner side. The velocity profiles around the 90-degree sharp bend were acquired to analyze the flow after corner. Secondary flow structure after the corner was observed in the velocity profiles along the depth of the microchannel. This study analyzes the thermal flow fields in the microchannel with a 90-degree sharp bend and reveals that regardless of the low Reynolds number, the flow mixing after the corner resulted in the increase of temperature downstream of the bend.

Micro milling operation is a fabrication process to create 3D parts from tens of micrometers to a few millimeters in size using a tool with diameter less than 1mm. Micro groove is one of the common features observed in the micro parts. The surface roughness of micro grooves plays an important role in their performance. Since most of the finishing processes could not be easily performed on the micro grooves, it is of extreme importance to find a relationship between micro milling parameters and the surface roughness profile. In this paper, in order to anticipate the profile and surface roughness of the groove floor a model is proposed based on the kinematic of cutting process and tool geometry. The effects of minimum chip thickness, elastic recovery, size effect and tool deflection are included in the model. Relationship between position of points on the floor surface of groove and kinematics of cutting process are derived. In next step, simulations of proposed model are performed in the ACIS environment. Finally, using the DOE method surface roughness is investigated stochastically. The simulated and measured surface roughnesses are compared together that confirm the validity of proposed model.