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- Model of inflatable structure/fluid interaction for variable leading edge
- Yuewen Jiang Zhengyin Ye Zhengke Zhang
- 2010, 42(1): 1-7. DOI: 10.6052/0459-1879-2010-1-2008-386
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- Research on statistic characteristic of near-wall turbulence
- Honglin Xiao Jisheng Luo
- 2010, 42(1): 8-14. DOI: 10.6052/0459-1879-2010-1-2008-593
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- Numerical studies on flows around a flexiblly wiggling hydrofiol
- Guoyi He Xing Zhang Shuguang Zhang
- 2010, 42(1): 15-22. DOI: 10.6052/0459-1879-2010-1-2008-570
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- The nonlinear water wave equations with full dispersion
- Jin Hong Zhili Zou
- 2010, 42(1): 23-34. DOI: 10.6052/0459-1879-2010-1-2008-080
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- Experimental study of crescent wave without wind driving
- Yalong Zhou Zhili Zou
- 2010, 42(1): 35-43. DOI: 10.6052/0459-1879-2010-1-2008-143
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- Dynamic interaction between waves and poroelastic seabed with boundary layer effects
- 2010, 42(1): 44-50. DOI: 10.6052/0459-1879-2010-1-2008-227
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- Leaky rayleigh wave at the interface between inviscid fluid and solid
- Xiao Chen
- 2010, 42(1): 51-55. DOI: 10.6052/0459-1879-2010-1-2007-563
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- he analytical solutions of thick-walled cylinder of softening material and its stability
- Youquan Yin
- 2010, 42(1): 56-64. DOI: 10.6052/0459-1879-2010-1-2008-440
- Asbtract ( 1445 ) PDF (1259KB) ( 499 )
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- Equivalences of the generalized viscoelastic models and their inherent properties
- Xiaohua Huang Xiating Feng Bingrui Chen
- 2010, 42(1): 65-73. DOI: 10.6052/0459-1879-2010-1-2008-128
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- discontinuous galerkin method for discontinuous temperature field problems
- Donghuan Liu Xiaoping Zheng Yinghua Liu
- 2010, 42(1): 74-82. DOI: 10.6052/0459-1879-2010-1-2009-003
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- Area coordinates and b-net method for quadrilateral spline elements
- Juan Chen Chongjun Li Wanji Chen
- 2010, 42(1): 83-92. DOI: 10.6052/0459-1879-2010-1-2008-501
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- Influence of the stress path on dilatancy of soils and its modeling
- Ding Luo Zhiwei Gao Yangping Yao
- 2010, 42(1): 93-101. DOI: 10.6052/0459-1879-2010-1-2008-484
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- The biomechanical study of the subsequent injury of an acl deficient knee
- Jie Yao Yubo Fan Ming Zhang Deyu Li He Gong
- 2010, 42(1): 102-108. DOI: 10.6052/0459-1879-2010-1-2008-526
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- Numerical study on the effect of the floating mass transducer on middle ear sound transmission
- Houguang Liu Na Ta Zhushi Rao
- 2010, 42(1): 109-114. DOI: 10.6052/0459-1879-2010-1-2008-519
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- Experimental and theoretical analysis of intelligent control for structural nonlinear vibration
- Luyu Li Gangbing Song Jinping Ou
- 2010, 42(1): 115-121. DOI: 10.6052/0459-1879-2010-1-2008-355
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- xistence condition of one-dimensional self-similar motion of ideal gas
- Xiaoming Lai Baomin Bian Ling Yang Anzhi He
- 2010, 42(1): 122-126. DOI: 10.6052/0459-1879-2010-1-2008-576
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- A new method for location leak in long-distance pipeline
- Junhua Li Wenbai Liu Li Cui Zhaochen Sun
- 2010, 42(1): 127-131. DOI: 10.6052/0459-1879-2010-1-2008-222
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- Tensile fatigue damage and its mechanism of stitched composite laminates
- Xiaoquan Cheng Kun Yang Renwei Hu Jian Zou
- 2010, 42(1): 132-137. DOI: 10.6052/0459-1879-2010-1-2009-028
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- A study on the two second-order strain gradient theories
- Jie Zhao Wanji Chen Bin Ji
- 2010, 42(1): 138-145. DOI: 10.6052/0459-1879-2010-1-2008-517
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18 January 2010, Volume 42 Issue 1

Research paper

The paper presents the interactive motion equation of
inflatable structure in flow. The inflatable structure is used in the
technique of a variable leading edge for high lift. The interaction between
structure and fluid is a typically aeroelastic problem. The motion equation is
obtained through the analytic solution of an infinitesimal element in the
discrete membrane. Coupled with Navier--Stokes equation, the aeroelastic
equation was solved with time-marching methods, and the aerodynamic
characteristics of NACA 63-212 airfoil with the inflatable leading edge
(ILE) were obtained. From the results, the ILE technique has been applied to
significantly increase the stall angle of attack and lift coefficient.
The values of stall angle of attack and maximum lift coefficient were
enhanced to be 30 percent and 22 percent, respectively. In addition, the
deformation of ILE greatly influenced the flow around the airfoil while the
elastic coefficient of material was low. The inflatable structure near the
suck peak deformed clearly, and this hump could induce the separation in
advance.

Channel turbulence is simulated by large eddy simulation
(LES), and turbulent databases of channel flows at different Reynolds
numbers are established. Then, the mean velocity distribution, Reynolds
stress and root-mean-square (RMS) velocity distribution are obtained.
Furthermore the problem of the wall law is discussed. Meanwhile, a rule of
Reynolds stress, energy of velocity fluctuations and RMS velocity with
different Reynolds number is presented along with quantitative formula.

Fishes often use a wiggling motion to generate propulsion for swimming. The wiggling motion can be modeled by a progressive wave. In the present study, an immersed boundary method is used to simulate the flows around the wiggling hydrofoil NACA 65-010 at low Reynolds numbers, and the effects of Reynolds numbers on the propulsion generation are investigated. It is observed that, as the Reynolds number ranges from 1 to 200, both the thrust coefficient and the propulsion efficiency increase with the increase of the Reynolds number, while the power efficiency decreases. Especially in the ranges of the Reynolds number smaller than 20, the lift, thrust and power coefficients exhibit a large change. With the increase of the Reynolds number, the flow patterns around the wiggling foils become more complex: the vorticity becomes more intensive near the trailing edge and the wiggling foil produces reversed von Karman vortex streets to generate propulsion.

A 2D nonlinear water wave model with full dispersion is
developed. The model is based on the nonlinear kinematic and dynamic free
surface boundary conditions and is expressed in terms of free surface
elevation $\eta $ and the velocity potential $\phi _\eta $ at the free
surface. The derivation of the equations is accurate to third order in
nonlinearity and keeps exact dispersion. The mild slope assumption is
adopted and the derived equations can be seen as the extention of the mild
slope equation of Berkhoff (1972) to the nonlinear and irregular wave case.
The corresponding numerical scheme is presented, and the special attention
is paid on the treatment of the integration terms in the equations. The
validation of the model is made by simulating the first and second order
Stokes waves and the nonlinear evolution of wave groups, the advantage of
the model is shown by the good prediction of amplitude dispersion and
four-wave resonant interaction for the wave group evolution.

Experiment study on crescent waves was performed without
wind driving. L2-type crescent waves wereobtained in the experiment, as
well as other two new types of three-dimensional wave patterns. The time
series and amplitude spectra characteristics of generated crescent waves
were analysized, and wave lengths of transverse waves and wave heights of
L2-type crescent waves were discussed.

Dynamic interaction between waves and poroelastic seabed
is investigated in relation to the boundary layer near the seabed. Potential
theory is applied to describe the wave field and a boundary layer
modification is considered. The deformation of the seabed is governed by
Biot's consolidation theory. Stress and velocity continuity at the interface
will be coupled with the wave motion and the relevant seabed response. Under
the assumptions of small amplitude waves and small deformation of the
seabed, an analytical solution is obtained and shown to be in good agreement
with field data. The conditions under which wave-seabed interaction becomes
significant are also discussed.

The leaky Rayleigh wave, an inhomogeneous surface wave,
exists at the interface between a fluid half space and a solid half space.
The secular equation of leaky Rayleigh wave is derived and the formulas of
particle displacement and stress distributions in the inviscid fluid and the
isotropic solid are presented. The characteristics of leaky Rayleigh waves,
the particle displacement and stress distributions in the fluid and solid
are investigated with numerical results using those equations. The effect of
the fluid-solid density ratio on the velocity and attenuation of leaky
Rayleigh wave and its particle displacement and stress distributions in the
fluid and the solid is analyzed numerically. The leaky Rayleigh wave is
non-dispersive and attenuate with propagetion distance. Its velocity and
attenuation increase with the fluid-solid density ratio. The fluid-solid
density ratio has significant effect on the vertical displacement but little
on horizontal displacement in the solid half space. The fluid-solid density
ratio also dramatically effects on the vertical normal stress and shear
stress but little on horizontal normal stress in the solid half space. The
theory is promising to be explored to nondestructive testing and evaluation
with leaky Rayleigh wave.

The constitutive law of elastoplastic material being
simplified to three-line model (elastic-linear softening plastic-residual
ideal plastic model), and the material obeying Tresca yield criteria and
associated flow rule, the analytical solutions of thick-walled cylinder
subject to internal pressure $p$ were derived in the paper. The result shows
that the yield stress in the softening plastic region is the inverse square
of radial coordinate $r$.
Firstly, the pressure $p$ was taken as generalized force, the displacement $u$
taken as generalized displacement, and the thick-walled cylinder taken as a
whole system. On the basis of the solutions the stability problem of
thick-walled cylinder was then discussed. The $p$-$u$ curve of balance path was
drawn, on which each point denotes a balance state. The slope of the tangent
line for each point can be considered the stiffness of thick-walled
cylinder. The extreme value of generalized force is the critical point on
the curve, and the critical point separates the curve into two sections: the
section before the critical point is stable, and the stiffness is positive;
the section after the point is unstable, and the stiffness is negative. When
the generalized force reaches the critical point, the displacement increases
quickly and the system loses its stability, while ideal plastic thick-walled
cylinder loses its stability only when the plastic region penetrates through
the whole cylinder. Therefore, the failure mechanism is completely
different: the former belongs to extreme value point destabilization, and
the latter belongs to strength failure. That is to say, the bearing capacity
has different mechanical meanings.

The equivalences of generalized viscoelastic models and
their inherent properties are investigated. The creep compliance of the
generalized Maxwell model is difficult to obtain due to its parallel
connection. However, a method by using Laplace transform is proposed in the
present paper to solve this problem and a theoretical expression is
obtained. The equivalence of the generalized Maxwell model and the Kelvin
chain is proved and the conversion relations of the parameters between these
two models are also derived. Moreover, an inherent property of the
generalized viscoelastic model proved here is that relaxation times and
delay times are mutually interlaced, and the former is always greater than
the latter when the spectrums of relaxation time and delay time are placed
in order. This property is also the imperative condition when the
generalized viscoelastic model is applied to describe the rheological
behavior of materials in engineering. As special instances of the
equivalence of the generalized Maxwell model and the Kelvin chain, there are
the equivalence between the Wiechert model and the generalized Zhong-cun
model, the Generalized Jeffreys model and the Generalized N-K model, the
Maxwell chain and the Generalized Kelvin model. Finally, the proposed method
is demonstrated by an example.

A discontinuous Galerkin (DG) finite element method for
the discontinuous temperature field problems is presented. The DG method
uses discontinuous interpolation functions on the element boundaries, and
the discontinuous effect is considered by the penalty function techniques,
in which the numerical flux and the stabilization term are adopted at the
interface. By substituting the numerical flux at the imperfect contact
interface with the definition of the thermal contact resistance, and
eliminating the stabilization term, the present DG method can easily and
accurately capture the temperature jump caused by thermal contact
resistance. Compared with the continuous Galerkin method, the present DG
method also has higher computational efficiency in capturing the peak value
of the heat flux of the local high gradient temperature field. Numerical
examples also show that the present DG method is a novel numerical method
for solving the coupling problems between the temperature and stress field
caused by thermal contact resistance.

In general, there are two types of quadrilateral
isoparametric elements, Serendipity type and Lagrangian type. The S-type
elements only possess low order completeness, and are sensitive to mesh
distortions. The L-type elements possess high order completeness, but
include interior nodes. By using numerical integrations due to isoparametric
transformation, the overall stiffness matrix may remain singular. In this
paper, a kind of quadrilateral spline elements are constructed by using
triangular area coordinates interpolation and B-net method. These spline
elements have property of conformality, and are insensitive to mesh
distortions. The 8 and 12-node quadrilateral elements are represented by
bivariate splines of degree 2 and 3, respectively. The two elements possess
2 and 3 order completeness in Cartesian coordinates, higher than the
corresponding isoparametric elements with the same nodes. Some numerical
examples are employed to evaluate the performance of the proposed elements.
The results show that the new spline elements present higher precision and
efficiency in comparison with other quadrilateral elements.

One of the most important characteristics of soil is its
dilatancy in which plastic volumetric strain occurs during shearing. The
influence of stress path on the dilatancy of soils is systematically
analyzed in this paper with the asymptote state model proposed by authors et
al (Luo et al, 2009), in which the part coupling effect between the plastic
volumetric strain and plastic shear strain is assumed firstly. The
comparisons are carried out between the test results of the dilatancy and
the model predictions of the original Cam-Clay model, the modified Cam-Clay
model, the unified hardening model (Yao et al, 2008) and our proposed model.
The comparisons results demonstrate that the asymptote state model can
describe the effect of the stress path on the dilatancy of soils in a better
way in the stress-strain and strength behaviors of soils.

Meniscus and ligament ruptures are common in anterior
cruciate ligament (ACL) deficient knee. The mechanism of injuries is still
unclear, and was mainly inferred from ex vivo experiments and clinical
studies. In this study, a three dimensional finite element model of knee
joint was reconstructed from magnetic resonance images. The geometry data of
the knee from literature was used to validate the model. Tibial displacement
and in situ force in ACL in response to the anterior tibial loads were
calculated and coincided with the published experimental data. The
simulations of the models with and without ACL were performed under anterior
tibial loads and axial tibial loads at 0$^\circ$ and 30$^\circ$ flexion. Our results
suggest that ACL deficiency could lead to abnormal stress distribution: the
stress near the posterior insertion of the medial meniscus increased
significantly; the changes of the stress in the lateral meniscus, posterior
cruciate ligament and collateral ligaments depended on the loads and the
flexion angles. This study may help to explain the higher subsequent injury
rate of ACL-deficient knee, and to predict the injury risk positions in the
joint. Furthermore, this model could shed some light on the mechanism of ACL
injuries and the treatments.

To overcome some inherent problems in conventional hearing
aids, such as low gain at high frequencies, discomfort, and acoustic
feedback, floating mass type for middle ear implant system are currently
under development. The floating mass transducer (FMT) is the most important
component of these devices. For the purpose of investigating the effect of
the FMT to middle ear sound transmission, a middle ear finite element model
with FMT clamped was constructed. This model was built based on a complete
set of computerized tomography section images of a healthy volunteer's left
ear by reverse engineering technology. The validity of this model was
confirmed by comparing the motion of the tympanic membrane and stapes
footplate obtained by this model with published experimental measurements on
human temporal bones. The result shows that FMT produces mass loading effect
prominently at high frequencies, the force required to drive the incus to
the equivalent of 100\,dB SPL is about 8.9 dynes, and placing the clamp point
of the FMT close to the incudostapedial joint enhances the driving effect.

Experimental verification of structural dynamics and
control strategies is essential for theoretical and numerical study, but
only the linearity of the structures was studied in the existing model
tests. Therefore, recently there has been an increasing interest in research
of establishing experimental model for structural nonlinear vibration. In
this paper, MagnetoRheological (MR) rotary brake is used to mimic the
plastic hinge of structure so as to analyze structural nonlinear vibration.
By means of adjusting the input voltage to MR rotary brakes, different
nonlinear behaviors can be detected. Moreover, the dynamical neural network
and adaptive fuzzy sliding mode control have been experimentally verified
under different nonlinear behaviors by incorporating MR damper into this
experimental model. Experimental results show that the structural nonlinear
vibration model which is established in this paper can be recovered to
initial state without any cost after nonlinear vibration tests. In addition,
different nonlinear behaviors can be achieved by changing the input voltage
to MR rotary brakes. The intelligent control algorithms are experimentally
verified to be suitable for control of structural nonlinear vibration.

Study news

The extension criterion of ideal gas self-similarity motion is not very
complete. Hydrodynamic equations are made dimensionless, and then we obtain
the basic characteristic quantities solutions of ideal gas one-dimensional
self-similarity differential equations described by relative coordinate \xi
and distance r. All of them have the same form Y ( \xi ,r ) =
y ( \xi ) r^{C_Y }, which means that characteristic quantities for
every certain \xi are spatial scale-invariant according to r. It is proved
that the spatial scale-invariant is the existence condition of
one-dimensional ideal gas self-similarity motion.

For the long-distance pipeline based mainly on frictional
head loss, it is necessary to locate the leak point after the leak appears.
The researchers have developed many methods for position leak during the
past of a few years, such as pressure gradient method, inverse transient
method, etc. These methods have their respective advantages and
disadvantages for long-distance pipeline. The pressure gradient method is
suitable to the pipeline of hydraulic grade line varied linearly. The leak
location in the inverse transient method is firstly assumed. Therefore, a
new method for location of the leakage points has been developed with the
combination of the pressure gradient method and the inverse transient method
in this paper. In this scheme, the coefficients of the friction resistance
before and after the leakage points, and the coefficients of the leakage
flow, are taken as the optimizing control variables, and the difference of
water head between the calculated values by waterhammer equations and the
measured values at measured sites are utilized as the objective function.
The coefficients of the friction resistance before and after the leakage
points are optimized through the genetic algorithm, based on which the
iterative method is used to locate the leakage points.
To verify the new method, the experiment in a water pipe with a length of
48.775m and a diameter of 53mm was set up in the hydraulics laboratory of
Dalian University of Technology. The pipeline is made of iron pipe, and is
connected to the pump at the upstream end and the water flume at the
downstream end. The error value of mean location in this method is about
4%, compared with the experimental data. The experimental results show
that the method is quite feasible and efficient to locate the leak in
long-distance pipeline.

Stitched laminate is a new kind of composite structure to
improve the interface strength of composite. But the in-plane properties of
the laminate may reduce because there are local fiber bending in the
laminate plane and in the thickness direction, and the damage induced by the
stitching threads. A lot of researches have been carried out on the
properties of laminates to push this material into engineering applications,
such as in-plane tension and compression, compression after impact,
hygrothermal properties, etc. But few studies have been performed on
stitched composite fatigue properties. The aim of this paper is to
comprehend the fatigue damage development and mechanism of stitched
laminates under tensile loads. The material of the laminates was uni-weave
T300/QY9512 stitched in 0^\circ direction. Un-stitched laminates were studied
for comparison with the stitched laminates.
Experimental study was carried out on the fatigue performance of stitched
and non-stitched composite laminate. The finite element models were
established to obtain the stress or strain distributions in the laminates.
The mechanism of tensile fatigue damage origination and propagation of
stitched laminates was analyzed. The results show that the tensile fatigue
damage origination and propagation mechanisms of laminates have been changed
by stitching. The stress concentration of in-plane stress \sigma_{x} and
interlaminar shear stress near the stitching node plays an important role in
damage origination and propagation. Stress concentration of interlaminar
stress at the free sides has effect on fatigue performance of stitched
laminates. The stress concentration of interlaminar stress at the free sides
is the main reason that causes fatigue damage and its propagation of
non-stitched laminates.

There are various strain gradient theories derived from
phenomenal theory and nonlocal continuum mechanics. Meanwhile, there are two
popular second-order strain gradient theories in which strain gradient term
was introduced into the constitutive law with positive and negative signs
respectively. In this paper, these two theories are discussed in the aspect
of formula derivation, energy expression, and application fields. By using
the 18-DOF triangle strain gradient plan element (RCT9+RT9) and axisymmetric
element (BCIZ+ART9) which can pass C^{0\hbox{-}1} patch test, the elastic
pull-out processes of the reinforced concrete bond specimen and the
deformation of a cantilever beam are simulated to compare the limitation of
the two theories in the analysis of microstructures.