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.     

ANALYSIS OF PULSATILE FLOW IN THE PARALLEL-PLATE FLOW CHAMBER WITH SPATIAL SHEAR STRESS GRADIENT

The Parallel-Plate Flow Chamber (PPFC), of which the height is far smaller than its own length and width, is one of the main apparatus for the in-vitro study of the mechanical behavior of cultured vascular Endothelical Cells (ECs) exposed to fluid shear stress. The steady flow in different kinds of PPFC has been extensively investigated, whereas, the pulsatile flow in the PPFC has received little attention. In consideration of the characteristics of geometrical size and pulsatile flow in the PPFC, the 3-D pulsatile flow was decomposed into a 2-D pulsatile flow in the vertical plane, and an incompressible plane potential flow in the horizontal plane. A simple method was then proposed to analyze the pulsatile flow in the PPFC with spatial shear stress gradient. On the basis of the method, the pulsatile fluid shear stresses in several reported PPFCs with spatial shear stress gradients were calculated. The results were theoretically meaningful for applying the PPFCs in-vitro, to simulate the pulsatile fluid shear stress environment, to which cultured ECs were exposed.     

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.     

ANALYSIS OF OSCILLATORY BLOOD FLOW IN VARYING-AREA ELASTIC VESSEL

In this paper, by solving the fundamental e-quations of periodically oscillatory blood flow, the distributions of pressure gradient and blood velocity in varying-area e-lastic vessel were obtained, and then the wall shear stress and its gradient were calculated. As an example, the pulsatile blood flow in human carotid was analyzed and the effects of vessel taper angle on the distribution of wall shear stress and its gradient were discussed in detail. Numercial results show that the wall shear stress will enlarge when the taper angle increases. Meantime, no matter whether the vessel is converging or diverging, with the increase of the absolute value of taper angle, the amplitude of wall shear stress gradient will enlarge significantly.     

DRAG REDUCTION OF A CATIONIC SURFACTANT SOLUTION AND ITS SHEAR STRESS RELAXATION

In order to study the mechanisms of the turbulent frictional drag reduction by surfactant additives,the drag reduction,the shear viscosity and the shear stress relaxation were measured for solutions of a cationic surfactant cetyltrimethyl ammonium bromide (CTAB) with the same molar sodium salicylate as a counter-ion.It is found that the first step relaxation time decreases with increasing concentration and,thus,with the maximum drag-reducing rates,which indicates that the stiffness of the micellar structures with the first relaxation time,increases with the increase of the concentration of CTAB.Furthermore,for this surfactant,a viscoelastic property is necessary for reducing drag,while a stronger viscoelasticity characterized by a tail relaxation time does not necessarily mean a higher drag-reducing rate.     

BOTTOM SHEAR STRESS UNDER WAVE-CURRENT INTERACTION

The present work adopts the COHERENS-SWAN model developed by the first author through coupling three-dimensional hydrodynamic model （COHERENS） and third-generation wave model （SWAN）. Inside the COHERENS-SWAN, the SWAN is regarded as a subroutine and the time- and space-varying current velocity and surface elevation are obtained from the COHERENS. Wave-enhanced bottom shear stress, wave induced surface mixing length and wave dependent surface drag coefficient have been introduced into the COHERENS. Secondly, as wave-enhanced bottom shear stress （＂bottom shear stress＂ described as BSS sometimes in this article） is concerned, a modified bottom shear stress Grant and Madsen model which introduces random wave field is given and introduced to COHERENS-SWAN. COHERENS-SWAN is also adopted to simulate three-dimensional flow in the Yellow River Delta with wave-current co-existing. Four numerical experiments were given to study the effects of wave-current interaction on enhancing bottom shear stress. The simulated current velocities, wave height and wave period match well with field measurement data. The simulated significant wave height and wave period for the case with considering the effects of current can give better agreement with measurement data than the case without involving the effects of current. The introduction of random wave generates lower the bottom shear stress than the case without introducing it. There are obvious differences between bottom shear stress of two way interaction and one way interaction. Velocity field obtained by the COHERENS-SWAN is reasonable according to previous studies and measurements.     

APPLICATION OF MILES－HOWARD THEOREM TO STUDY THE INSTABILITY OF ATMOSPHERIC GRAVITY WAVES ON A HETEROGENEOUS ORTHOGONAL SHEAR FLOW

ＡＰＰＬＩＣＡＴＩＯＮ　ＯＦ　ＭＩＬＥＳ－ＨＯＷＡＲＤ　ＴＨＥＯＲＥＭ　ＴＯ　ＳＴＵＤＹ　ＴＨＥ　ＩＮＳＴＡＢＩＬＩＴＹ　ＯＦ　ＡＴＭＯＳＰＨＥＲＩＣ　ＧＲＡＶＩＴＹ　ＷＡＶＥＳ　ＯＮ　Ａ　ＨＥＴＥＲＯＧＥＮＥＯＵＳ　ＯＲＴＨＯＧＯＮＡＬ　ＳＨＥＡＲ...     

A NEW MEASURE FOR DIRECT MEASUREMENT OF THE BED SHEAR STRESS OF WAVE BOUNDARY LAYER IN WAVE FLUME

In this article, a shear plate was mounted on the bottom in a wave flume and direct measurements of the smooth and rough bed shear stress under regular and irregular waves were conducted with the horizontal force exerted on the shear plates by the bottom shear stress in the wave boundary layer. Under immobile bed condition, grains of sand were glued uniformly and tightly onto the shear plate, being prevented from motion with the fluid flow and generation of sand ripples. The distribution of the bottom mean shear stress varying with time was measured by examining the interaction between the shear plate and shear transducers. The relation between the force measured by the shear transducers and its voltage is a linear one. Simultaneous measurements of the bottom velocity were carried out by an Acoustic Doppler Velocimeter (ADV), while the whole process was completely controlled by computers, bottom shear stress and velocity were synchronously measured. Based on the experimental results, it can be concluded that (1) the friction coefficient groews considerably with the increase of the Reynolds number, (2) the shear stress is a function varying with time and linearly proportional to the velocity. Compared with theoretical results and previous experimental data, it is shown that the experimental method is feasible and effective, A further study on the bed shear stress under regular or irregular waves can be carried out. And applicability to the laboratory studies on the initiation of sediments and the measurement of the shear stress after sediment imigration.     

直剪试验中参数误差原因探讨

本文分析偏轴压力 ,复杂性的应力条件以及有效的剪切面积对参数的影响 ,得出 C,Φ的偏差趋势 ,指出直剪试验参数误差过大 ,建议尽量采用三轴仪进行强度试验。     

NUMERICAL INVESTIGATION OF THREE-DIMENSIONAL FLOW AND BED SHEAR STRESS DISTRIBUTION AROUND THE SPAN SHOULDER OF PIPELINE

1 .　INTRODUCTIONWhena pipelineis placedonanerodibleseabed ,freespanmaydevelopastheresultoflocalscourunderthepipeline .Oneofthemostimpor tantissuesinpipelinestabilitydesignistheevalua tionofthefreespanlengthandtherateatwhichthefreespandevelopsalongthespandirectionduetothescour .Bothfreespanlengthandtherateofscourdevelopmentdependonflowconditionsaroundthespanshoulders.Sincemostofthescourinvestigationsintheopenliteraturewereonthescourdepthorscourdevelopmentinthe perpendiculardirectionofpipe…     

负荷超声心动图检测冠心病冠状动脉病变部位的临床研究

目的 对比分析冠状动脉疾病(CAD)心绞痛患者多巴酚丁胺负荷超声心动图(DSE)时节段性室壁运动异常(RWMA)与冠状动脉造影(CAG)的结果,以分析和判断其相关的冠脉病变.方法 入选临床诊断或可疑CAD患者38例,静息二维超声心动图(2DE)检查未见RWMA,CAG为单支冠脉病变,并于CAG前1周内进行DSE试验.结果 缺血相关冠脉为左前降支(LAD)时累及前间隔中段,前壁基段、中段和心尖段,后间隔心尖段;缺血相关冠脉为左旋支(LCx)时累及侧壁基段、中段和后壁基段、中段例数居多;缺血相关冠脉为右冠状动脉(RCA)时累及下壁基段和中段例数居多.DSE检测出单支病变中LAD、LCx和RCA的敏感性依次为:78.9%,33.3%和70.0%.在LCx和RCA病变时后壁基段、中段RWMA的发生率比较差异无显著性(P＞0.05).结论 DSE试验对于判断心肌缺血的相关冠脉病变有一定的临床价值.     

EFFECTS OF VASCULAR ZERO STRESS STATE ON PULSATILE BLOOD FOLW

~~EFFECTS OF VASCULAR ZERO STRESS STATE ON PULSATILE BLOOD FOLW~~TheProjectsupportedbytheNationalNaturalScienceFoundationofChina .(No :19732 0 0 3;;1970 2 0 0 2 )     

THE INFLUENCE OF THE SECONDARY NORMAL STRESS DIFFERENCE OF VISCOELASTIC FLUID ON ECCENTRIC CAPSULE FLOW

ＴＨＥＩＮＦＬＵＥＮＣＥＯＦＴＨＥＳＥＣＯＮＤＡＲＹＮＯＲＭＡＬＳＴＲＥＳＳＤＩＦＦＥＲＥＮＣＥＯＦＶＩＳＣＯＥＬＡＳＴＩＣＦＬＵＩＤＯＮＥＣＣＥＮＴＲＩＣＣＡＰＳＵＬＥＦＬＯＷ￥ＰａｎＤａ－ｌｉｎ（ＧｕａｎｇｄｏｎｇＩｎｓｔｉｔｕｔｅｏｆｏｆＴｅｃ...     

NUMERICAL ANALYSIS OF THE NON-NEWTONIAN BLOOD FLOW IN THE NON-PLANAR ARTERY WITH BIFURCATION

A numerical analysis of non-Newtonian fluid flow in non-planar artery with bifurcation was performed by using a finite element method to solve the three-dimensional Navier-Stokes equations coupled with the non-Newtonian constitutive models, including Carreau, Cross and Bingham models. The objective of this study is to investigate the effects of the non-Newtonian properties of blood as well as curvature and out-of-plane geometry in the non-planar daughter vessels on the velocity distribution and wall shear stress. The results of this study support the view that the non-planarity of blood vessels and the non-Newtonian properties of blood are of important in hemodynamics and play a significant role in vascular biology and pathophysiology.     

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.     

加筋碎石土的抗剪强度特性研究

通过对比分析碎石土加筋前后高压大三轴饱和固结排水试验结果 ,研究碎石土加筋的抗剪强度特性。结果表明 :加筋碎石土复合体的应力 -应变 -体变关系仍然表现出不加筋碎石土的基本特性 ,加筋后的应力 -应变 -体变曲线比不加筋前显著提高 ,其本构关系可用邓肯 -张双曲线模型来描述。不论加筋与否 ,碎石土的加卸荷循环曲线基本都呈相互平行的直线。加筋增强了碎石土抵抗变形和破坏的能力 ,碎石土加筋的效果可以显著提高凝聚力 ,但对其内摩擦角影响很小。颗粒越粗硬 ,对提高强度、减小变形越有利。     

NONLINEAR INTERFACIAL CAPILLARY-GRAVITY WAVES IN SHEAR FLOW

In this paper,the capillary-gravity solitary waves in a two-fluid system withshear flow are theoretically investigated.Three cases are considered.For the first case(the nor-mal case),the KdV equation,with the effect of shear flow being taken into account,is derivedand it is found that there may exist single mode travelling solitary waves,slowly travelling soli-tary waves and even more slowly travelling solitary waves at some shear flow conditions.Thesecond case considered is that the fluid system is at the first kind critical condition.The modifiedKdV equation in which the cubic nonlinearity balances the dispersion is obtained and the solutionof mKdV solitary wave in shear flow is put forward.The third case is that the fluid system is atthe second kind critical condition.The generalized KdV equation with the effect of shear flowconsidered is given.It is shown that there exist normal and oscillatory solitary waves and thecondition of existence of oscillatory solitary waves are also presented.     

NUMERICAL STUDY ON THE VORTEX STRUCTURES IN THE WAKE OF AN OSCILLATING CIRCULAR CYLINDER IN A UNIFORM FLOW

ＮＵＭＥＲＩＣＡＬＳＴＵＤＹＯＮＴＨＥＶＯＲＴＥＸＳＴＲＵＣＴＵＲＥＳＩＮＴＨＥＷＡＫＥＯＦＡＮＯＳＣＩＬＬＡＴＩＮＧＣＩＲＣＵＬＡＲＣＹＬＩＮＤＥＲＩＮＡＵＮＩＦＯＲＭＦＬＯＷＬｕＸｉ－ｙｕｎ；ＴｏｎｇＢｉｎｇ－ｇａｎｇ；ＺｈｕａｎｇＬｉ－ｘｉａｎ...     

LAW OF BOUNDARY SHEAR IN OPEN RECTANGULAR CHANNELS WITHUNIFORM ROUGHNESS

In accordance with the characteristics of the rectangular prismatic channel, the flow in the channel was divided into two parts, the bed part and the wall part. On the basis of general principles of mechanics, the area relation between the bed part and the wall part was worked out. A formula for determining the shear acting on the bed and the walls in rectangular channels was derived, which has a simple form and is only related to the ratio of the breadth to the depth.The difference between the calculated value with the presented formula and the data published was illustrated to be less than that with other formulas, which shows that the formula is reasonable and can model the flow in the rectangular prismatic channel with higher accuracy and reliability.     

EFFECTS OF WAVE-CURRENT INTERACTIONS ON BOTTOM STRESS AND CURRENTS

1 .　INTRODUCTIONWave currentinteractionsareimportantforcalculationofeffectsofbedstressduetowindwaveactivityincoastalregions .Itisofsignifi cancetohavearobusttheoreticalbasisforsedi menttransportestimates ,beachevolutioncalcula tionsandconcomitant processesrelatedtothestudyofland seainteractionsincoastalareas.Inrecentyears ,therehasbeenincreasedinterestindevelopingmodelsthatcanresolvethenear bedre gion ,takingaccountofimpactsduetonear bedturbulencerelatedtowind waveactivity .Howev er ,how…