2012 Vol. 33, No. 7

Display Method:
Propagation of Plane P-Waves at the Interface Between an Elastic Solid and an Unsaturated Poroelastic Medium
CHEN Wei-yun, XIA Tang-dai, CHEN Wei, ZHAI Chao-jiao
2012, 33(7): 781-795. doi: 10.3879/j.issn.1000-0887.2012.07.001
Abstract(1349) PDF(882)
A linear viscoporoelastic model was developed to describe the problem of reflection and transmission of an obliquely incident plane Pwave at an interface between an elastic solid and an unsaturated poroelastic medium in which the solid matrix was filled with two weakly coupled fluids (liquid and gas). The expressions for the amplitude reflection coefficients and amplitude transmission coefficients were derived using the potential method. The present derivation was subsequently applied to study the energy conversions among the incident, reflected and transmitted wave modes. It was found that the reflection coefficients and transmission coefficients in the forms of amplitude ratios and energy ratios are functions of incident angle, liquid saturation, frequency of incident wave and elastic constants of the upper and lower media. The numerical computations are performed graphically, and the effects of the incident angle, frequency and liquid saturation on the amplitude and energy reflection and transmission coefficients are respectively discussed. It was verified that during transmission process there was no energy dissipation at the interface.
Analysis of Main Shock of Thrust Fault Earthquake by Catastrophe Theory
PAN Yue, ZHAO Zhi-gang
2012, 33(7): 796-811. doi: 10.3879/j.issn.1000-0887.2012.07.002
Abstract(1218) PDF(841)
The relationship between work and energy increment of thrust fault system with quasistatic deformation can be decomposed into two parts, i.e. the relationship between work and energy increment of volume strain energy and that of deviation stress energy,which was analyzed by using method of catastrophe theory. The research indicates that the characteristics displayed by fold catastrophe model can appropriately describe the earthquake generation condition, the evolvement process of main shock of thrust fault earthquake and some important earthquake effects as well. The bigger the surrounding press of surrounding rock is, the bigger the maximum principal stress is. The smaller the incidences of the potential thrust fault surface are, the smaller the rate between the tangential stiffness of surrounding rock and the slope is, which is at inflexion point on the softened zone of fault shearing strength curve. Thus when earthquake occurrs, the larger the elastic energy releasing amount of surrounding rock is, i.e. the larger the intensity of earthquake is. The larger the half distance of fault dislocation is.The larger the displacement amplitude of surrounding rock end face is. Fracturing, expanding of the fault rock body and releasing of volume strain energy of surrounding rock while earthquake occurrs enhance the foregoing earthquake effects together.
Bifurcation on the Synchronous Full Annular Rub of a Rigid-Rotor Elastic-Support System
ZHANG Hua-biao, CHEN Yu-shu, LI Jun
2012, 33(7): 812-827. doi: 10.3879/j.issn.1000-0887.2012.07.003
Abstract(1678) PDF(1114)
Aero engine rotor system was simplified to be an unsymmetrical-rigid-rotor with nonlinear-elasticsupport based on its characteristics. Governing equations of the rubbing system obtained from Lagrange equation were solved by averaging method to find the bifurcation equations. Then, according to the two-dimensional constraint bifurcation theory, transition sets and bifurcation diagrams of the system with and without rubbing were given to study the influence of system’s eccentric and damping on the bifurcation behaviors, respectively. Finally, according to Liapunov stability theory, the stability region of steady-state rubbing solution and the boundary of static bifurcation and Hopf bifurcation were determined to discuss the influence of system parameters on the evolution of system’s motion. The research results may provide some references for the design of aero rotor systems.
An Integrated Numerical Model for Vegetated Surface and Saturated Subsurface Flow Interaction
2012, 33(7): 828-844. doi: 10.3879/j.issn.1000-0887.2012.07.004
Abstract(1224) PDF(880)
The construction of an integrated numerical model was presented to deal with interactions between vegetated surface and saturated subsurface flows. The numerical model was built up by integrating previously developed quasi-three-dimensional vegetated surface flow model with a two-dimensional saturated groundwater flow model. The vegetated surface flow model was constructed by coupling the explicit finite volume solution of the two-dimensional shallow water equations (SWE) with the implicit finite difference solution of Navier-Stokes equations (NSE) for vertical velocity distribution. The subsurface model was based on the explicit finite volume solution of twodimensional saturated groundwater flow equations (SGFE). The ground and vegetated surface water interaction was achieved by the introduction of source-sink terms into the continuity equations. Two solutions were tightly coupled in a single code. The integrated model was applied to four test cases and the results were satisfactory.
MHD Flow and Mass Transfer of a Chemically Reactive Upper Convected Maxwell (UCM) Fluid Past a Porous Surface
K.Vajravelu, K.V.Prasad, A.Sujatha, Chiu-on NG
2012, 33(7): 845-855. doi: 10.3879/j.issn.1000-0887.2012.07.005
Abstract(1190) PDF(813)
The MHD flow and mass transfer of an electrically conducting upper convected Maxwell fluid at a porous surface in the presence of a chemically reactive species was studied. The governing nonlinear partial differential equations along with the appropriate boundary conditions were transformed into nonlinear ordinary differential equations, and were solved numerically by the Keller-Box method. The effects of various physical parameters on the flow and mass transfer characteristics were presented graphically and discussed. It is observed that the order of the chemical reaction is to increase the thickness of the diffusion boundary layer. Also, the mass transfer rate strongly depends on the Schmidt number and the reaction rate parameter. Furthermore, available results in the literature are obtained as a special case.
LES of Fluid Mixing in a Tee With a Sintered Porous Medium
WANG Yong-wei, LU Tao, JIANG Pei-xue, CHENG Peng-fei, WANG Kui-sheng
2012, 33(7): 856-867. doi: 10.3879/j.issn.1000-0887.2012.07.006
Abstract(1031) PDF(835)
Mixing processes of hot and cold fluids in a tee with and without sintered copper spheres were simulated by FLUENT using the large-eddy simulation (LES) turbulent flow model and the sub-grid scale (SGS) Smagorinsky-Lilly (SL) model with buoyancy. Comparisons of the numerical results of the two cases with and without sintered copper spheres show that the porous medium significantly reduces the velocity and temperature fluctuations, because the porous medium can effectively restrict the fluid flow and enhance heat transfer. The porous media obviously increase the pressure drop in the main duct. The porous medium reduces the PSD of the temperature fluctuations in the frequency range from 1 Hz to 10 Hz.
On Similarity Solutions to the Viscous Flow and Heat Transfer of Nanofluid Over Nonlinearly Stretching Sheet
M.A.A.Hamad, M.Ferdows
2012, 33(7): 868-876. doi: 10.3879/j.issn.1000-0887.2012.07.007
Abstract(1618) PDF(866)
The boundary-layer flow and heat transfer in a viscous fluid containing metallic nanoparticles over a nonlinear stretching sheet was analyzed. The stretching velocity was assumed to vary as a power function of the distance from the origin. The governing partial differential equation and auxiliary conditions were reduced to coupled nonlinear ordinary differential equations with the appropriate corresponding auxiliary conditions. The resulting non-linear ODEs were solved numerically. The influences of various relevant parameters, namely, the Eckert number Ec,the solid volume fraction of the nanoparticles and the nonlinear stretching parameter n were discussed and comparison with published results was presented. Different types of nanoparticles were studied. It was noted that the behavior of the fluid flow was changed with the change of the nanoparticles type.
Unsteady Mixed Convective Heat Transfer of Two Immiscible Fluids Confined Between a Long Vertical Wavy Wall and a Parallel Flat Wall
J.C.Umavathi, LIU I-chung, M.Shekar
2012, 33(7): 877-895. doi: 10.3879/j.issn.1000-0887.2012.07.008
Abstract(1175) PDF(730)
An analysis on the combined effects of thermal and mass convection of viscous incompressible, immiscible fluids through a vertical wavy wall and a smooth flat wall was performed. The dimensionless governing equations were perturbed into: mean part (zeroth order) and a perturbed part (first order). The first order quantities were obtained by perturbation series expansion for short wavelength, in which terms of exponential order arise. Analytical expressions for the zeroth order, first order and the total solutions were obtained.The numerical computations were presented graphically to show salient features of the fluid flow and heat transfer characteristics. Separate solutions were matched at the interface by using suitable matching conditions. The shear stress and the Nusselt number were also analyzed for different variations of the governing parameters. It is observed that Grashof number, viscosity ratio, width ratio and conductivity ratio promote the velocity parallel to the flow direction. A reversal effect is observed for the velocity perpendicular to the flow direction.
A New Simple Exact Penalty Function for Constrained Minimization
ZHENG Fang-ying, ZHANG Lian-sheng
2012, 33(7): 896-906. doi: 10.3879/j.issn.1000-0887.2012.07.009
Abstract(1421) PDF(845)
By adding one variable for equality or inequality constrained minimization problems, a new simple exact penalty function was proposed, namely, the new exact penalty function did not contain the gradients of the objective function and constraint functions. Under mild assumptions, the local minimizer of the penalty function is the local minimizer of  primal problem, when the penalty parameter is sufficiently large.