| Acta Mechanica Sinica |
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| Acta Mechanica Sinica--2011, 27 (2) Published: 18 April 2011 |
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| Aerodynamics of indirect thrust measurement by the impulse method |
| C.K. Wu H.X. Wang X. Meng X. Chen W.X. Pan |
| Abstract |
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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...
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| On the unsteady motion and stability of a heaving airfoil in ground effect |
| J. Molina X. Zhang |
| Abstract |
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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...
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| Computation of the stability derivatives via CFD and the sensitivity equations |
| G.D. Lei Y.X. Ren |
| Abstract |
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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...
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| Large eddy simulation of vertical turbulent jets under JONSWAP waves |
| J. Lu L.L. Wang H.W. Tang H.C. Dai |
| Abstract |
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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...
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| 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 |
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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.
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| Numerical simulation of pedestrian flow past a circular obstruction |
| Y.Q. Jiang R.X. Liu Y.L. Duan |
| Abstract |
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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 ...
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| Exact solutions for the flow of second grade fluid in annulus between torsionally oscillating cylinders |
| A. Mahmood S. Parveen N.A. Khan |
| Abstract |
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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...
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| 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 |
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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...
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| Magnetohydrodynamic peristaltic flow of a hyperbolic tangent fluid in a vertical asymmetric channel with heat transfer |
| S. Nadeem S. Akram |
| Abstract |
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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...
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| Energy dissipation and contour integral characterizing fracture behavior of incremental plasticity |
| Q.L. He L.Z. Wu M. Li H.B. Chen |
| Abstract |
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$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...
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| Perturbed magnetic field of an infinite plate with a centered crack |
| F. Qin Y. Zhang Y.N. Liu |
| Abstract |
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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...
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| 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 |
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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...
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| A passive-biped model with multiple routes to chaos |
| F. Farshimi M. Naraghi |
| Abstract |
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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...
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| Stability and Hopf bifurcation of a delayed ratio-dependent predator-prey system |
| W.Y. Wang L.J. Pei |
| Abstract |
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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...
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| Interaction of subway LIM vehicle with ballasted track in polygonal wheel wear development |
| L. Li X.B. Xiao X.S. Jin |
| Abstract |
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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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