Acta Mechanica Sinica
     Acta Mechanica Sinica
  Acta Mechanica Sinica--2011, 27 (2)   Published: 18 April 2011
Review
On the generalized Cauchy function and new Conjecture on its exterior singularities
Th.Y. Wu
Abstract
This article studies on Cauchy’s function f (z) and its integral, (2πi)J[ f (z)] =C f (t)dt/(t z) taken along a closed simple contour C, in regard to their comprehensive properties over the entire z = x + iy plane consisted of the simply connected open domain D+ bounded by C and the pen domain D utside C. (1)...
Research papers
Aerodynamics of indirect thrust measurement by the impulse method
C.K. Wu H.X. Wang X. Meng X. Chen W.X. Pan
Abstract
The aerodynamic aspects of indirect thrust measurement by the impulse method have been studied both experimentally and numerically. The underlying basic aerodynamic principle is outlined, the phenomena in subsonic, supersonic and arc-heated jets are explored, and factors affecting the accuracy of the method are studied and discussed. Results show that the impulse method is reliable for indirect thrust measurement if certain basic requirements are met, and a simple guideline for its proper...
On the unsteady motion and stability of a heaving airfoil in ground effect
J. Molina X. Zhang
Abstract
This study explores the fluid mechanics and force generation capabilities of an inverted heaving airfoil placed close to a moving ground using a URANS solver with the Spalart-Allmaras turbulence model. By varying the mean ground clearance and motion frequency of the airfoil, it was possible to construct a frequency-height diagram of the various forces acting on the airfoil. The ground was found to enhance the downforce and reduce the drag with respect to freestream. The unsteady motion in...
Computation of the stability derivatives via CFD and the sensitivity equations
G.D. Lei Y.X. Ren
Abstract
The method to calculate the aerodynamic stability derivates of aircrafts by using the sensitivity equations is extended to flows with shock waves in this paper. Using the newly developed second-order cell-centered finite volume scheme on the unstructured-grid, the unsteady Euler equations and sensitivity equations are solved simultaneously in a non-inertial frame of reference, so that the aerodynamic stability derivatives can be calculated for aircrafts with complex geometries. Based on t...
Large eddy simulation of vertical turbulent jets under JONSWAP waves
J. Lu L.L. Wang H.W. Tang H.C. Dai
Abstract
The effect of random waves on vertical plane turbulent jets is studied numerically and the mechanism behind the interaction of the jet and waves is analyzed. The large eddy simulation method is used and the $\sigma $-coordinate system is adopted. Turbulence is modeled by a dynamic coherent eddy model. The $\sigma $-coordinate transformation is introduced to map the irregular physical domain with a wavy free surface and an uneven bottom onto a regular computational domain. The fractional s...
Modeling of drag reduction in turbulent channel flow with hydrophobic walls by FVM method and weakly-compressible flow equations
L. Li M.S. Yuan
Abstract
In this paper the effects of hydrophobic wall on skin-friction drag in the channel flow are investigated through large eddy simulation on the basis of weakly-compressible flow equations with the MacCormack's scheme on collocated mesh in the FVM framework. The slip length model is adopted to describe the behavior of the slip velocities in the streamwise and spanwise directions at the interface between the hydrophobic wall and turbulent channel flow. Simulation results are presented by ana...
Homotopy analysis solutions for the asymmetric laminar flow in a porous channel with expanding or contracting walls
X.H. Si L.C. Zheng X.X. Zhang Y. Chao
Abstract
In this paper, the asymmetric laminar flow in a porous channel with expanding or contracting walls is investigated. The governing equations are reduced to ordinary ones by using suitable similar transformations. Homotopy analysis method (HAM) is employed to obtain the expressions for velocity fields. Graphs are sketched for values of parameters and associated dynamic characteristics, especially the expansion ratio, are analyzed in detail.
Numerical simulation of pedestrian flow past a circular obstruction
Y.Q. Jiang R.X. Liu Y.L. Duan
Abstract
In this paper, a revisiting Hughes' dynamic continuum model is used to investigate and predict the essential macroscopic characteristics of pedestrian flow, such as flow, density and average speed, in a two dimensional continuous walking facility scattered with a circular obstruction. It is assumed that pedestrians prefer to walk a path with the lowest instantaneous travel cost from origin to destination, under the consideration of the current traffic conditions and the tendency to avoid ...
Exact solutions for the flow of second grade fluid in annulus between torsionally oscillating cylinders
A. Mahmood S. Parveen N.A. Khan
Abstract
The velocity field and the associated shear stress corresponding to the torsional oscillatory flow of a second grade fluid, between two infinite coaxial circular cylinders, are determined by means of the Laplace and Hankel transforms. At time $t=0$, the fluid and both the cylinders are at rest and at $t=0^+$, cylinders suddenly begin to oscillate around their common axis in a simple harmonic way having angular frequencies $\omega_1$ and $\omega_2$. The obtained solutions satisfy the gov...
A continuum traffic flow model with the consideration of coupling effect for two-lane freeways
D.H. Sun G.H. Peng L.P. Fu H.P. He
Abstract
A new higher-order continuum model is proposed by considering the coupling and lane changing effects of the vehicles on two adjacent lanes. A stability analysis of the proposed model provides the conditions that ensure its linear stability. Issues related to lane changing, shock waves and rarefaction waves, local clustering and phase transition are also investigated with numerical experiments. The simulation results show that the proposed model is capable of providing explanations to some...
Magnetohydrodynamic peristaltic flow of a hyperbolic tangent fluid in a vertical asymmetric channel with heat transfer
S. Nadeem S. Akram
Abstract
In the present paper we discuss the magnetohydrodynamic (MHD) peristaltic flow of a hyperbolic tangent fluid model in a vertical asymmetric channel under a zero Reynolds number and long wavelength approximation. Exact solution of the temperature equation in the absence of dissipation term has been computed and the analytical expression for stream function and axial pressure gradient are established. The flow is analyzed in a wave frame of reference moving with the velocity of wave. The ex...
Energy dissipation and contour integral characterizing fracture behavior of incremental plasticity
Q.L. He L.Z. Wu M. Li H.B. Chen
Abstract
$J^{\rm ep} $-integral is derived for characterizing the fracture behavior of elastic-plastic materials. The $J^{\rm ep}$-integral differs from Rice's $J$-integral in that the free energy density rather than the stress working density is employed to define energy-momentum tensor. The $J^{\rm ep}$-integral is proved to be path-dependent regardless of incremental plasticity and deformation plasticity. The $J^{\rm ep}$-integral possesses clearly clear physical meaning: (1) the value $J_{\rm...
Perturbed magnetic field of an infinite plate with a centered crack
F. Qin Y. Zhang Y.N. Liu
Abstract
Deforming a cracked magnetoelastic body in a magnetic field induces a perturbed magnetic field around the crack. The quantitative relationship between this perturbed field and the stress around the crack is crucial in developing a new generation of magnetism-based nondestructive testing technologies. In this paper, an analytical expression of the perturbed magnetic field induced by structural deformation of an infinite ferromagnetic elastic plate containing a centered crack in a weak exte...
Bauschinger and size effects in thin-film plasticity due to defect-energy of geometrical necessary dislocations
Z.L. Liu Z. Zhuang X.M. Liu X.C. Zhao Y. Gao
Abstract
The Bauschinger and size effects in the thin-film plasticity theory arising from the defect-energy of geometrically necessary dislocations (GNDs) are analytically investigated in this paper. Firstly, this defect-energy is deduced based on the elastic interactions of coupling dislocations (or pile-ups) moving on the closed neighboring slip plane. This energy is a quadratic function of the GNDs density, and includes an elastic interaction coefficient and an energetic length scale L. By inco...
A passive-biped model with multiple routes to chaos
F. Farshimi M. Naraghi
Abstract
This paper presents a new passive-biped model consisting of a simplest walking model beneath an upper body, with no kinematic constraint. The upper body is attached to the legs with a linear torsional spring. The model is a passive dynamic walker, so it walks down a slope without energy input. The governing equations of motion are derived and simulated for the parameter analysis purposes. Simulation results reveal some different routes to chaos that have not been observed in previous mode...
Stability and Hopf bifurcation of a delayed ratio-dependent predator-prey system
W.Y. Wang L.J. Pei
Abstract
Since the ratio-dependent theory reflects the fact that predators must share and compete for food, it is suitable for describing the relationship between predators and their preys and has recently become a very important theory put forward by biologists. In order to investigate the dynamical relationship between predators and their preys, a so-called Michaelis-Menten ratio-dependent predator-prey model is studied in this paper with gestation time delays of predators and preys taken into c...
Interaction of subway LIM vehicle with ballasted track in polygonal wheel wear development
L. Li X.B. Xiao X.S. Jin
Abstract
This paper develops a coupled dynamics model for a linear induction motor (LIM) vehicle and a subway track to investigate the influence of polygonal wheels of the vehicle on the dynamic behavior of the system. In the model, the vehicle is modeled as a multi-body system with 35 degrees of freedom. A Timoshenko beam is used to model the rails which are discretely supported by sleepers. The sleepers are modeled as rigid bodies with their vertical, lateral, and rolling motions being considere...
 
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