STABILITY EIGENFUNCTIONS OF A BOUNDARY-LAYER FLOW OVER VISCOELASTIC COMPLIANT WALL

1 .　ＩＮＴＲＯＤＵＣＴＩＯＮＣｏｍｐｌｉａｎｔｓｕｒｆａｃｅｓａｒｅｃｕｒｒｅｎｔｌｙｆｉｎｄｉｎｇｍａｎｙａｐ ｐｌｉｃａｔｉｏｎｓｉｎｅｎｇｉｎｅｅｒｉｎｇ ,ｓｕｃｈａｓｔｈｅｒｅｄｕｃｔｉｏｎｏｆｓｋｉｎ ｆｒｉｃｔｉｏｎｏｎｍｏｖｉｎｇｖｅｈｉｃｌｅｓ ,ｔｈｅｖｉｂｒａｔｉｏｎｒｅｄｕｃｔｉｏｎｉｎｎａｖａｌｖｅｓｓｅｌｓ ,ａｎｄｔｈｅｎｏｉｓｅｓｈｉｅｌｄｉｎｇｉｎｓｏｎａｒａｒｒａｙｓ .Ｔｈｅｃｏｎｃｅｐｔｏｆｕｓｉｎｇａｃｏｍｐｌｉａｎｔｗａｌｌｔｏｒｅｄｕｃｅｓｋｉｎｆｒｉｃｔｉ…     

STUDY ON TURBULENCE FEATURES NEAR AN OSCILLATING CURVED WALL

In pursuit of possibly true turbulent characters and for exploring a change in turbulence structures near an oscillating flexible wall-curved surface, a sinusoidal oscillation mode was forced to a curved wall, whose vibrations disturbed the flow with an interacting effort between the fluid and the structure. The methodology used was the Large Eddy Simulation (LES) with fluid-structure interaction. The oscillating configuration was on a Fourier sinusoidal mode from the measurements of a Francis hydro turbine blade vibration. The effects of the vibration on the skin friction coefficient, vortices, turbulent coherent structures, and other statistical quantities were studied. The results showed that the streamwise velocity gradient along the normal direction and the normal velocity gradient along the spanwise direction were considerably increased within the viscous sublayer because of the oscillating wall, which additionally caused the low speed streaks to stay away from the wall and the high-momentum flows to be toward the wall. As a result, the streamwise vortices were much more elongated along the downstream to get an energy balance, and the wall skin friction coefficient or the wall friction velocity rose up.     

SYNERGY OF WALL SHEAR STRESS AND CIRCUMFERENTIAL STRESS IN STRAIGHT ARTERIES

The Wall Shear Stress （WSS） generated by blood flow and Circumferential Stress （CS） driven by blood pressure have been thought to play an important role in blood flow-dependent phenomena such as angiogenesis, vascular remodeling, and atherosgenesis. The WSS and CS in straight arteries were calculated by measuring the blood pressure, center-line velocity, wall thickness, and radius of vessels. The WSS and CS in the time domain were then decomposed into the amplitude and phase in the frequency domain. The CS amplitude to the WSS amplitude ratio （referred as stress ampli tude ratio, Zs ） and the phase difference between the CS and the WSS （referred as stress phase difference, SPA） in the fre quency domain were calculated to characterize the synergy of the CS and WSS. Numerical results demonstrated that the CS is not in phase with the WSS, a time delay in the time domain or a stress phase difference in the frequency domain between the WSS and the CS exists. Theoretical analysis demonstrated that the Zs and SPA are primarily determined by the local fac tors （blood viscosity, local inertial effects, local geometry, loeal elasticity） and the input impedance of whole downstream arterial beds. Because the arterial input impedance has been shown to reflect the physiological and pathological states of whole downstream arterial beds, the stress amplitude ratio Zs and stress phase difference SPA would be thought to be the appropriate indices to reflect the effects of states of whole downstream arterial beds on the local blood flow dependent phenomena such as angiogenesis, vascular remodeling, and atherosgenesis.     

THE EFFECTS OF PHYSIOLOGICAL FLOW WAVEFORM ON WALL SHEAR STRESS IN CAROTID BIFURCATION MODEL

Numerical models of carotid bifurcation were constructed using a combination of tuning-fork bifurcation and straight or curved common carotid. The different inlet velocity profiles of the common carotid were generated for Bloch flow waveform and Holdsworth flow waveform, respectively. The effects of the different flow waveform for the common carotid on Wall Shear Stress (WSS) and Oscillatory Shear Index (OSI) of carotid bifurcation were studied by CFD method. The results show that the physiological flow waveform of curved common carotid has a significant effect on OSI. In particular, the OSI on the outer walls of carotid sinus and external carotid becomes higher in the inward-curved common carotid for Holdsworth flow waveform. But, in both cases of low WSS and high OSI, the effects of flow waveforms are smaller than those of the curved common carotid. The study reveals that the exact knowledge of the physiological flow waveform, vascular geometry and inlet velocity profile is important for hemodynamic numerical simulation of artery bifurcation.     

LARGE EDDY SIMULATION OF THERMALLY-STRATIFIED TURBULENT CHANNEL FLOW WITH TEMPERATURE OSCILLATION ON THE BOTTOM WALL

Thermally-stratified shear turbulent channel flow with temperature oscillation on the bottom wall of the channel was investigated with the Large Eddy Simulation (LES) approach coupled with dynamic Sub-Grid-Scale (SGS) models. The effect of temperature oscillation on the turbulent channel flow behavior was examined. The phase-averaged velocities and temperature, and flow structures at different Richardson numbers and periods of the oscillation was analyzed.     

ON WALL SHEAR STRESS OF ARTERY

1 .　INTRODUCTIONTheendothelialcellslininginabloodvesselareexposedtotangentialstress (i.e .wallshearstress)offlowingviscousbloodonthearterialwall.Theyappeartoadapttheirmorphologyandfunctiontotheinvivohemodynamicenvironmentinwhichtheyreside .Oneofthemajoradvancesinvascularbiologyoverthelasttwodecadeshasshownthatamongvariousfactorsthatleadtovas cularremodelingandlocalizationofatherosclerosisinarteries ,theshearstressonthearterialwallisofgreatimportance .Certain patternsofthewallshearstressb…     

MARCHING CUBES BASED FRONT TRACKING METHOD AND ITS APPLICATION TO SOME INTERFACE INSTABILITY PROBLEMS

A front tracking method based on a marching cubes isosurface extractor,which is related filter generating isosurfaces from a structured point set,is provided to achieve sharp resolution for the simulation of non-diffusive interfacial flow.Compared with the traditional topology processing procedure,the current front tracking method is easier to be implemented and presents high performance in terms of computational resources.The numerical tests for 2-D highly-shearing flows and 3-D bubbles merging process are...     

NUMERICAL SIMULATION OF HYDRODYNAMIC CHARACTERISTICS ON AN ARC CROWN WALL USING VOLUME OF FLUID METHOD BASED ON BFC

In the present study, a new algorithm based on the Volume Of Fluid (VOF) method is developed to simulate the hydrodynamic characteristics on an arc crown wall. Structured grids are generated by the coordinate transform method in an arbitrary complex region. The Navier-Stokes equations for two-dimensional incompressible viscous flows are discretized in the Body Fitted Coordinate (BFC) system. The transformed SIMPLE algorithm is proposed to modify the pressure-velocity field and a transformed VOF method is used to trace the free surface. Hydrodynamic characteristics on an arc crown wall are obtained by the improved numerical model based on the BFC system (BFC model). The velocity field, the pressure field and the time profiles of the water surface near the arc crown wall obtained by using the BFC model and the Cartesian model are compared. The BFC model is verified by experimental results.     

NON-ZONAL BAROCLINIC INSTABILITY IN THE NORTH PACIFIC SUBTROPICAL COUNTERCURRENT

1 .　INTRODUCTIONSincethe 196 0sthesubtropicalcountercurrent(STCC)overthePacifichasbeenfoundtobeaneastwardcurrentexistingintheregion (14 0°E 170°W ,19°N 2 8°N) ,whichcontradictswiththeSver druptransporttheory (YoshidaandKidokoro196 7) ,ithasbecomeanimportanttopicinthephysicaloceanography (Cushman Roison 1984 ;Kubokawa 1997) .AokiandImawaki (1996 )andQiu (1999)foundthatintheSTCCregion ,theed dykineticenergyishigheroverthewesternsidethanovertheeasternside .Qiu (1999)discussedthe…     

NUMERICAL SIMULATION OF HORIZONTAL BUOYANT WALL JET

This article applies the realizable k-ε model to simulate the buoyant wall jet and gives the results of cling length,centerline trajectory and temperature dilutions at certain sections.The comparison between the numerical results and Sharp's experimental data indicates that the model is effective in estimating velocity distribution and temperature dilutions.The velocity profiles at the cental plane and z-plane both show a strong similarity at certain distance from the nozzle,and the distributions of velocity and temperature dilutions also exhibit a similarity along the axial direction at centerline in the near-field.Based on the results,the article gives the corresponding relationships between the distance and the dilutions of velocity and temperature,which is useful in predicting the behavior of the wall buoyant jet.     

NUMERICAL STUDY OF WALL WETTABILITIES AND TOPOGRAPHY ON DRAG REDUCTION EFFECT IN MICRO-CHANNEL FLOW BY LATTICE BOLTZMANN METHOD

The dynamics of two-phase flows with a constant driving force inside a micro-channel is studied by using the Lattice Boltzmann Method (LBM) and the Shan-Chen multiphase model in this article. Flow regimes under different wall wettabilities and over smooth and grooved geometric surfaces are investigated. It is found that flow behaviors are strongly affected by the wall wettability and topography. Our results show that the LBM is efficient and accurate, and has very good application prospect in the study of drag reduction of microscopic seepage of reservoir.     

THE IRREGULAR BREAKING WAVE FORCES ON VERTICAL WALL

A method for the calculation of total horizontal wave forces by irregular breaking waves on vertical wall was developed by authors, which was based on physical model test, dimensionless analysis and assessment of real construction. The methods for the determination of pressure distribution of horizontal forces on vertical wall as well as u-plift forces on the bottom of wall are also given. The comparison between calculated results by this method and samples of real construction are very well.     

FIRST ORDER WALL VORTICITY FORMULA UNDER IRREGULAR MESH

In the engineering applications, flow problems with complicated geometrical shape of boundaries are of ten happen. Their boundary conditions should be given in precisely when doing the simulation of these type of flows because the regions near to the boundaries generally play an important role on the defined solutions. Using the vorticity-stream function form of the N-S equations as governing equations in the flow field simulation with irregular mesh, the determining/calculating wall vorticity under irregular mesh is very important. In this paper, one first order formula of wall vorticity under irregular mesh was derived based on the 2-D Taylor expansion and was tested numerically through an example of a flow with the Z type, shape of boundaries. A satisfactory result was found which was compared with one obtained by FEM.     

THE STRUCTURE AND SCALE EFFECT OF WALL TURBULENT FLOW

In this paper the structure and scale effect of wall turbulence are investigated.Thecharacteristics of the turbulence structure in the wall region is described.The fact that the turbu-lence in whole flow field is controlled mainly by the structure of wall turbulence is demonstrat-ed.Discussion is concentrated on the scale effects of the streak structure,the vortex structureand the bursting frequency.     

SCOUR OF FINE SEDIMENT BY A TURBULENT WALL JET

ＳＣＯＵＲＯＦＦＩＮＥＳＥＤＩＭＥＮＴＢＹＡＴＵＲＢＵＬＥＮＴＷＡＬＬＪＥＴＬｉＷｅｎ－ｘｕｅ（ＩｎｓｔｉｔｕｔｅｏｆＨｙｄｒａｕｌｉｃＲｅｓｅａｒｃｈ，ＹｅｌｌｏｗＲｉｖｅｒＣｏｎｓｅｒｖａｎｃｙＣｏｍｍｉｓｓｉｏｎ，Ｚｈｅｎｇｚｈｏｕ，４５０００...     

SMW工法围护结构的设计

根据SMW工法的用途和特点,提出了该方法在围护工程中的设计计算理论和设计准则,总结出SMW工法的特点和优势,以便在今后的工程实践中更好的加以运用。     

增加挡墙稳定的措施

针对挡墙抗滑、抗倾、基底应力及偏心难以满足规范要求的情况，介绍几种增加挡墙稳定的措施。     

EXPERIMENTS ON HYDRODYNAMIC INTERACTION BETWEEN 3-D OVAL AND WALL

The boundary hydrodynamic interaction of a 3-D oval body was experimentally surveyed for different cases. The regression method was employed to find the experimental formulae of hydrodynamic coefficients relating to the attack angle, clearance to wall, and moving speed. The mechanism of interaction was discussed. The experimental results show that there exists a lifting effect, similar to wings in flow. The lifting effect is remarkable. The boundary hydrodynamic interaction of the small aspect ratio model is almost linearly dependent on the attack angle, but the effect of the moving speed of the body on the hydrodynamic coefficients is very small. The effect of clearance is related to the geometric shape. The boundary hydrodynamic interaction always enhances the lifting effect if the clearance is small.     

Kelvin-Helmholtz不稳定性和Rayleigh-Taylor不稳定性大变形发展阶段的数值模拟——(Ⅰ)数值方法和Rayleigh-Taylor不稳定性的数值模拟结果

本文对计算Kelvin-Helmholtz不稳定性和Rayleigh-Taylor不稳定性的离散涡方法进行了改进,并给出了Rayleigh-Taylor不稳定性的数值模拟结果。实际计算表明,改进措施不仅使方法模拟界面大变形的能力大大提高,而且使界面大变形阶段数值模拟的计算量大大减小。Rayleigh-Taylor不稳定性大变形阶段的数值模拟不仅重现了实验中所观察到的界面下垂端部的上卷等现象,还发现了上卷部分液滴溅出等一些新现象。     

EFFECT OF CIRCULAR TRANSDUCER SIZE ON WALL PRESSURE FLUCTUATION SIGNAL

ＥＦＦＥＣＴ　ＯＦ　ＣＩＲＣＵＬＡＲ　ＴＲＡＮＳＤＵＣＥＲ　ＳＩＺＥ　ＯＮ　ＷＡＬＬ　ＰＲＥＳＳＵＲＥ　ＦＬＵＣＴＵＡＴＩＯＮ　ＳＩＧＮＡＬＥＦＦＥＣＴＯＦＣＩＲＣＵＬＡＲＴＲＡＮＳＤＵＣＥＲＳＩＺＥＯＮＷＡＬＬＰＲＥＳＳＵＲＥＦＬＵＣＴＵＡＴＩＯＮ...