泄洪闸中墩在水脉动压力作用下的动力分析

分析了飞来峡水利枢纽泄流闸中墩的动力特性及在两条脉动水压力波形作用下的动力反应，分析结果为：闸墩结构的基频为２．０４ＨＺ，从振型型态图上看，闸墩振动特性类似厚板一端固定的动力特性，在两条脉动水压力波形作用下，其动力反应的脉动压力均方根σ为最大，作用水体范围也较大，并在整个水体视为同一脉动压力的计算条件下，得出了闸墩各部位应力σｙ分布状况，以上结果可为闸墩设计者考虑脉功影响时提供参考。     

黑麇峰抽水蓄能电站尾水管压力脉动试验

尾水管压力脉动对水泵水轮机组的安全稳定运行和发电效益有非常重要的影响。对黑麋峰电站2号机组,采用在直锥段内部安放传感器的方式,在变转速空载、变负荷等多种工况下测定尾水管压力脉动在波形及频谱上的变化规律。结果表明,变转速工况下压力脉动相对幅值随转速升高而升高,变负荷工况下压力脉动相对幅值变化总趋势是随负荷增大而减小;部分负荷下的尾水管内压力脉动相对幅值范围为0.85%~5.6%;不同负荷情况下,尾水管内频率成分不同,在较低负荷下,尾水管内低频成分较多,以叶片过流频率(45 Hz)为主频;在接近额定负荷时,尾水管内主要频率为叶片过流频率及其倍频。     

水力机械锯齿波压力脉动探讨

本文首先论述了锯齿波在水力机械的压力脉动和振动波形中大量存在,说明了对其进行深入研究的必要性。然后分析了锯齿波压力脉动产生的两大可能原因,其一是涡带空腔及周围自由涡带来的压力速升速降或空化空腔快速收缩-膨胀带来的冲击,其二是大幅值压力波在传播过程中因密度变化而产生的波形畸变;而对于尾水管涡带压力脉动而言,其主要原因是前者。在对锯齿波压力脉动进行快速傅里叶分析时,会分析出与主频压力脉动频率呈整数倍关系的所谓倍频分量,其实是一种假象。     

高含沙泄洪水流的荷载特性试验研究

高含沙水流特性已有较多研究,但主要针对河道中的高含沙渐变水流开展的,而对高含沙河流高坝枢纽泄洪水流荷载特性的研究较少,本文开展了孔板消能工高含沙水流的时均压力和脉动压力特性研究。试验共研究了含沙量从0至300 kg/m~3,流速从1.78 m/s至3.73 m/s,共28组不同工况。结果表明:高含沙泄洪水流的时均和脉动压力的沿程分布规律与清水相同,但幅值变化规律存在差异,相同流速条件下时均压力幅值随含沙量的增加而增加,而脉动压力幅值受含沙量和流速条件的双重影响,随含沙量的增加呈现出先增加后减小的趋势;脉动压力概率密度分布符合正态;频率分布范围受水流条件影响随流速的增加而增加,其中低频分量随含沙量的增加而增加。根据试验结果,提出了高含沙泄洪水流荷载计算的修正方法,该方法对于高含沙枢纽的工程设计有重要参考价值。     

自振空化射流冲击压力脉动特性实验研究

自振空化射流是利用瞬态流和水声学原理调制而成的一种新型射流，本文研究了自振空化射流在常压及围压下的压力脉动特性及其参数影响规律。研究结果表明，在实验条件下各种风琴管喷嘴的压力脉动存在最优喷距，无因次最优喷距都在8～14范围内，风琴管自振空化射流的冲击压力脉动峰值和脉动幅度分别比普通喷嘴高37％和24％；最大脉动幅度并不出现在射流轴心，而是偏离轴心一段径向距离；随着围压的增加，脉动峰值压力随着喷距的衰减速度明显加快，而脉动炳室基本不随围压、压降和喷距的变化而变化，保持在1.38KHz左右。     

脉动压力在板块缝隙中传播衰变机理研究

探讨高坝下游水垫塘内脉动压力在底板缝隙水介质中的传播机理,分析缝隙粗糙程度及堵塞程度对脉动压力传播的衰变影响,进一步阐明脉动压力在水垫塘底板破坏中的作用。基于一维瞬变流模型和特征线法,同时考虑缝隙通道的阻滞作用,对脉动压力在缝隙中的传播进行数值模拟,得出单体板块入口端瞬时感应到低频余弦脉动压力干扰波、出口端分别为盲端和自由端时,不同堵塞系数下底板缝隙中点处的点脉动压力时间过程。分析得出:缝隙中点处的脉动压力是由低频干扰波和由于缝隙中类似于水击的水力瞬变引起的高频波的叠加。受缝隙通道阻滞作用,脉动压力的高频脉动分量在短时间内迅速衰变,时间过程曲线趋于与干扰波同频率的余弦曲线。     

辐条控制技术对竖井贯流泵马鞍区水力特性影响的数值模拟

基于非定常雷诺时均(URANS)方法,采用曲率修正的SST k-ω湍流模型,对竖井贯流泵内部流场进行非定常计算,研究辐条控制技术对不同工况下竖井贯流泵水力性能以及水泵叶轮进口流场和压力脉动特性的影响。结果表明:在设计工况下,辐条控制技术对竖井贯流泵的水力性能和叶轮进口流场、压力脉动特性的影响不大;在马鞍区工况下,竖井贯流泵叶轮前进水流道的轴向速度降低,速度环量增大,并随着流量减小而产生大范围回旋流,造成进水流道堵塞,引起低频压力脉动幅值增大;辐条控制技术可有效抑制回旋流的强度,提高叶轮入流的均匀度,降低压力脉动幅值,有效改善竖井贯流泵马鞍区工况的水力性能。     

跌坎对消力池水力特性影响的试验研究

为研究跌坎在底流消能中的作用,依托某工程水力学模型,研究了跌坎对消力池内水流流态、临底流速及脉动压强的影响。结果表明:在来流量一定的情况下,随着跌坎高度的增加,消力池内流态会由底流依次演变为淹没混合流及淹没面流流态。加设跌坎可显著降低消力池前半段的临底流速,且跌坎越高,最大临底流速降幅越大,跌坎对消力池后半段的临底流速基本无影响;跌坎对脉动压强影响较大,随跌坎高度的增加,最大脉动压强先增大后减小;加设跌坎后,脉动压强和临底流速沿程先增大后减小,且脉动压力和临底流速的最大值位置基本在同一区域。     

叶片数对高比转速离心泵固液两相非定常流的影响

为了探索叶片数在固液两相流条件下对高比转速离心泵非定常特性的影响情况,利用ANSYS CFX软件,采用Mixture多相流模型,对4种不同叶片数离心泵的固液两相湍流进行了非定常数值模拟,分析了叶片数对固液两相流离心泵瞬时扬程、压力、压力脉动及径向力的影响。研究结果表明：① 随着叶片数量的增多,固液两相流离心泵的瞬时扬程增大,波动频率变快,蜗壳内及隔舌处的压力值越来越大,波动频率变快,脉动幅值反而越来越小,叶轮上的径向力会减小,隔舌处的径向力会增大;② 不同叶片数的固液两相流离心泵蜗壳内及隔舌处的压力脉动主频均出现在其叶频处;③ 叶片数为5时,是蜗壳的内压力值和压力脉动幅值增减速度快慢的分界点,也是叶轮上及隔舌处径向力大小增减速度快慢的分界点。     

基于高压脉动水力压裂的脉动波传播机理研究

脉动水力压裂技术是一项具有广阔前景的增渗新技术。当前脉动压裂过程中传播机理研究较少,为更好地研究脉动压裂增压效果与裂缝中传播机理,指导脉动水力压裂施工。该文基于波动方程和湍流模型,编制计算程序,建立模拟井下压力传播物理模型和类地层边界条件,研究了脉动压裂传播机理。计算结果表明:该模拟条件下,脉动波传播特征与实验结果具有较高吻合度,得出以下三个结论:(1)脉动压裂能够获得比静载压裂更高压力,提高压力值约30%;矩形脉动波比正弦脉动波与锯齿脉动波能够获得更高压力,提高压力约20%。(2)矩形脉动波压力值从波谷阶跃到波峰产生"水锤效应"明显,利于提高流体压力。(3)脉动压裂压力波衰减满足线性对数关系:y=-A·ln(x)+B,y为压力值,x为传播距离,A和B为常数系数;传播过程中脉动水力能量主要消耗在近井壁地带。研究成果有利于指导优化脉动水力压裂工艺参数。     

波流相互作用下沿垂向的水流结构及其实验验证

本文研究了波流相互作用情形下波浪对水平流速沿垂向分布的影响。作者从Navier Stokes方程出发，用涡动粘滞系数模型来封闭波流相互作用下的流动方程，提出了一个求解整个水深内的断面流速分布的方法。理论计算与实验结果基本一致。     

局部狭窄动脉内血流动力学环境的动态数值研究

为了定量研究局部狭窄动脉内的血流动力学环境,进而寻求其与动脉粥样硬化发生发展的关联,本文推导并建立了针对该问题的差分数值求解体系。推导了控制方程在特定坐标系空间的表达,给出了适当的边界条件。最后选择猪的颈动脉为研究对象,利用高频电磁流量探头和压力探头在体测量了入口段一个心动周期的血流量、压力等数据。利用这些测量数据作为求解体系的输入数据,心动周期内局部狭窄动脉内的各种血流动力学数据被细致求解,心动周期不同时期的流场、轴向速度分布、壁面切应力被详细显示并作了生理层面的分析。     

A HEMODYNAMIC MODEL AND A MATHEMATICAL METHOD TO CALCULATE THE DYNAMICS INDEX FOR CEREBRAL CIRCULATION

The dynamics indexes,playing an important role in the cerebral circulation,will be changed significantly compared with their normal range in many cerebrovascular disease.The geometrical parameters of cerebrovascular may be detected by DSA or MRA scan,but the hemodynamic parameters,such as,blood flow,artery resistance and compliance must be calculated by building hemodynamics model. The cerebral circular system that has four entrances for blood flow(two carotid and two vertebral arteries)and three communicating arteries is much different from the systematic ststem which has only one entrance,ic.,the aortic.The purpose of this study is to set up a hemodynamics model with lumped parameters to describe the cerebral circulation.From this model,we get its governing equations and present a new method to calculate the hemodynamics indexes in clinical application.     

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 )     

圆柱容器内流经环形填充层流动的研究

本文对圆柱容器内流经环形填充层的流动进行了分析,导得了基本运动方程,并进行了实验研究。计算结果与实验结果符合得比较好。研究表明,结构型式、中心通道与环形通道面积比、填充层自身的阻力系数以及圆柱容器的长径比,对于流经填充层的径向流速沿轴向的分布都有影响。     

LARGE EDDY SIMULATION FOR PLUNGING BREAKER WAVE

1 .　INTRODUCTIONInthenear shoreregion ,aswavespropagateintoshallowwater ,theprocessofshoalingleadstotheincreaseofwaveheight ,however ,thisprocesscannotcontinue ,andatacertain positionthewavebreaks .Inpractice ,breakingwavesarepow erfulagentsforgeneratingturbulence ,whichplaysanimportantroleinmostofthefluiddynamicalprocessesthroughoutthesurfzone ,suchaswavetransformation ,generationofnear shorecurrent ,diffusionofmaterials ,andsedimenttransporta tion .Manynumericalstudieshavebeenconductedt…     

Comparison of blood rheological models in patient specific cardiovascular system simulations

Newtonian, Quemada and Casson blood viscosity models are implemented in order to simulate the rheological behavior of blood under pulsating flow conditions in a patient specific iliac bifurcation. The influence of the applied blood constitutive equations is monitored via the wall shear stress(WSS) distribution, magnitude and oscillations, non-Newtonian importance factors, and viscosity values according to the shear rate. The distribution of WSS on the vascular wall follows a pattern which is independent of the rheological model chosen. On the other hand, the WSS magnitude and oscillations are directly related to the blood constitutive equations applied and the shear rate. It is concluded that the Newtonian approximation is satisfactory only in high shear and flow rates. Moreover, the Newtonian model seems to overestimate the possibility for the formation of atherosclerotic lesions or aneurysms at sites of the vascular wall where the WSS are oscillating.     

Revisiting study on Boussinesq modeling of wave transformation over various reef profiles

To better understand the complex process of wave transformation and associated hydrodynamics over various fringing reef profiles, numerical experiments were conducted with a one-dimensional （1D） Boussinesq wave model. The model is based on higher-order Boussinesq equations and a higher-accuracy finite difference method. The dominant energy dissipation in the surf zone, wave breaking, and bottom friction were considered by use of the eddy viscosity concept and quadratic bottom friction law, respectively. Numerical simulation was conducted for a wide range of wave conditions and reef profiles. Good overall agreement between the computed results and the measurements shows that this model is capable of describing wave processes in the fringing reef environment. Numerical experiments were also conducted to track the source of underestimation of setup for highly nonlinear waves. Linear properties （including dispersion and shoaling） are found to contribute little to the underestimation; the low accuracy in nonlinearity and the ad hoc method for treating wave breaking may be the reason for the problem.     

FORMATION AND INFLUENCING FACTORS OF FREE SURFACE VORTEX IN A BARREL WITH A CENTRAL ORIFICE AT BOTTOM

Based on the Navier-Stokes equations with considering the effect of the Coriolis force, the finite volume method was employed to discretize the governing equations, the SIMPLE method was adopted to solve the discretized equations, and the flow field in a barrel with an outlet at the center of the bottom was simulated. The numerical results agree well with the experimental data. From the Lagrangian, the relations among the acceleration, the Coriolis force and the viscosity force were analyzed. The results show that the Coriolis force is the major factor that causes the formation of the vortex. The flow fields in the flume under different incoming flow conditions were numerically simulated using the software Fluent. The numerical simulations show good agreement with the experiments for the shape and position of the vortex.