Acta Mechanica Sinica
     Acta Mechanica Sinica
  Acta Mechanica Sinica--2015, 31 (1)   Published: 20 January 2015
REVIEW PAPER
Modeling ocean wave propagation under sea ice covers Hot!
Xin Zhao, Hayley H. Shen, Sukun Cheng
Abstract

Operational ocean wave models need to work globally, yet current ocean wave models can only treat ice covered regions crudely. The purpose of this paper is to provide a brief overview of ice effects on wave propagation and different research methodology used in studying these effects. Based on its proximity to land or sea, sea ice can be classified as: landfast ice zone, shear zone, and the marginal ice zone. All ice covers attenuate wave energy. Only long swells can penetrate deep into an ic...

FLUID MECHANICS
The spatial-temporal evolution of coherent structures in log law region of turbulent boundary layer
Xiao-Bo Zheng, Nan Jiang
Abstract

The spatial-temporal evolution of coherent structures (CS) is significant for turbulence control and drag reduction. Among the CS, low and high speed streak structures show typical burst phenomena. The analysis was based on a time series of three-dimensional and three-component (3D-3C) velocity fields of the flat plate turbulent boundary layer (TBL) measured by a Tomographic and Time-resolved PIV (Tomo TRPIV) system. Using multi-resolution wavelet transform and conditional sampling method, we...

Lagrangian statistics in isotropic turbulent flows with deterministic and stochastic forcing schemes
Jin-Cai Chen, Guo-Dong Jin, Jian Zhang
Abstract

Artificial input of energy into the flow is necessary to create and maintain a statistically stationary isotropic turbulence for sampling in studying the statistics. Due to the nonlinear coupling among different Fourier modes through the triadic interaction, whether or not various forcing schemes affect the statistics in turbulence is an important and open question. We present detailed comparison of Lagrangian statistics of fluids particles in forced isotropic turbulent flows in 1283...

A general solution for Stokes flow and its application to the problem of a rigid plate translating in a fluid
Xiang-Yu Li, Si-Cong Ren, Qi-Chang He
Abstract

A general solution for 3D Stokes flow is given which is different from, and more compact than the existing ones and more compact than them in that it involves only two scalar harmonic functions. The general solution deduced is combined with the potential theory method to study the Stokes flow induced by a rigid plate of arbitrary shape translating along the direction normal to it in an unbounded fluid. The boundary integral equation governing this problem is derived. When the plate is ellipti...

Effect of the size and pressure on the modified viscosity of water in microchannels
Zhao-Miao Liu, Yan Pang
Abstract

The phenomenon that flow resistances are higher in micro scale flow than in normal flow is clarified through the liquid viscosity. Based on the experimental results of deionized water flow in fused silica microtubes with the inner radii of 2.5 μm, 5 μm, 7.5 μm, and 10 μm, respectively, the relationship between water flow velocity and pressure gradient along the axis of tube is analyzed, which gradually becomes nonlinear as the radius of the microtube decreases. From the correlatio...

A dynamic coupling numerical model for pollutant transport under wave condition
Yong Li, Mian Lin, Zhen Wang
Abstract

In order to study the diffusion, migration, and distribution of pollutants among overlying water-body and porous seabed under wave conditions, a dynamic coupling numerical model is proposed. In this model, the coupling between wave field of overlying water-body and seepage of porous bed, the capture and release of pollutants in porous media, and the transport process between the two different regions are taken into account. We use the unified equations for pressure correction and pollutant co...

The effect of single-horn glaze ice on the vortex structures in the wake of a horizontal axis wind turbine
Zhe-Yan Jin, Qiao-Tian Dong, Zhi-Gang Yang
Abstract

The present study experimentally investigated the effect of a simulated single-horn glaze ice accreted on rotor blades on the vortex structures in the wake of a horizontal axis wind turbine by using the stereoscopic particle image velocimetry (Stereo-PIV) technique. During the experiments, four horizontal axis wind turbine models were tested, and both "free-run" and "phase-locked" Stereo-PIV measurements were carried out. Based on the "free-run" measurements, it ...

The asymptotic solution of particle growth in the convective undercooled melt driven by a biaxial straining flow
Ming-Wen Chen, Xiu-Min Liu, Zhen-Chao Yang, Zi-Dong Wang
Abstract

A dynamical system of particle growth in the convective undercooled melt driven by a biaxial straining flow is modeled. A uniformly valid asymptotic solution for the interface evolution in particle growth is obtained by means of the multiple variable expansion method. The analytical solution as a function of both azimuth angle and polar angle shows that the interface shape of particle growth in the biaxial straining flow is significantly deformed by the biaxial straining flow. The biaxial str...

SOLID MECHANICS
Extension of covariant derivative (I): From component form to objective form
Ya-Jun Yin
Abstract

This paper extends the covariant derivative under curved coordinate systems in 3D Euclid space. Based on the axiom of the covariant form invariability, the classical covariant derivative that can only act on components is extended to the generalized covariant derivative that can act on any geometric quantity including base vectors, vectors and tensors. Under the axiom, the algebra structure of the generalized covariant derivative is proved to be covariant differential ring. Based on the power...

Extension of covariant derivative (II): From flat space to curved space
Ya-Jun Yin
Abstract

This paper extends the classical covariant derivative to the generalized covariant derivative on curved surfaces. The basement for the extension is similar to the previous paper, i.e., the axiom of the covariant form invariability. Based on the generalized covariant derivative, a covariant differential transformation group with orthogonal duality is set up. Through such orthogonal duality, tensor analysis on curved surfaces is simplified intensively. Under the covariant differential transform...

Extension of covariant derivative (III): From classical gradient to shape gradient
Ya-Jun Yin
Abstract

This paper further extends the generalized covariant derivative from the first covariant derivative to the second one on curved surfaces. Through the linear transformation between the first generalized covariant derivative and the second one, the second covariant differential transformation group is set up. Under this transformation group, the second class of differential invariants and integral invariants on curved surfaces is made clear. Besides, the symmetric structure of the tensor analys...

A novel robust design method for improving stability of optimized structures
Ming-Jie Cao, Hai-Tao Ma, Peng Wei
Abstract

It is known that structural optimization may lead to designs of structures having low stability and sometimes even kinematically unstable designs. This paper presents a robust design method for improving the stability of optimized structures. A new approach is proposed, in which certain perturbation loads are introduced and the corresponding compliance is added to the objective function as a penalization. The stability of the optimized structures can thus be improved substantially by consider...

BIOMECHANICS
Hierarchical model for strain generalized streaming potential induced by the canalicular fluid flow of an osteon
Xiao-Gang Wu, Wei-Lun Yu, Hai-Peng Cen, Yan-Qin Wang, Yuan Guo, Wei-Yi Chen
Abstract

A hierarchical model is developed to predict the streaming potential (SP) in the canaliculi of a loaded osteon. Canaliculi are assumed to run straight across the osteon annular cylinder wall, while disregarding the effect of lacuna. SP is generalized by the canalicular fluid flow. Analytical solutions are obtained for the canalicular fluid velocity, pressure, and SP. Results demonstrate that SP amplitude (SPA) is proportional to the pressure difference, strain amplitude, frequency, and strain...

An improved correlation of the pressure drop in stenotic vessels using Lorentz's reciprocal theorem
Chang-Jin Ji, Kazuyasu Sugiyama, Shigeho Noda, Ying He, Ryutaro Himeno
Abstract

A mathematical model of the human cardiovascular system in conjunction with an accurate lumped model for a stenosis can provide better insights into the pressure wave propagation at pathological conditions. In this study, a theoretical relation between pressure drop and flow rate based on Lorentz's reciprocal theorem is derived, which offers an identity to describe the relevance of the geometry and the convective momentum transport to the drag force. A voxelbased simulator V-FLOW VOF3D, where...

Skin temperature oscillation model for assessing vasomotion of microcirculation
Yuan-Liang Tang, Ying He, Hong-Wei Shao, Irina Mizeva
Abstract

It has been proved that there exists a certain correlation between fingertip temperature oscillations and blood flow oscillations. In this work, a porous media model of human hand is presented to investigate how the blood flow oscillation in the endothelial frequency band influences fingertip skin temperature oscillations. The porosity which represents the density of micro vessels is assumed to vary periodically and is a function of the skin temperature. Finite element analysis of skin temper...

 
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