两种人工机械心瓣启闭过程的ALE有限元分析*

本文采用任意拉格朗日-欧拉(ALE)有限单元法,将血液视为不可压缩粘性流体,同时将人工机械瓣简化为定轴转动刚体,建立了机械心瓣/血液耦合运动的二维计算模型。在此基础上。计算了顺向人工机械瓣(DDM)的开闭过程,并与St.Jude瓣(SJM)进行了对比。由本文研究可得以下主要结论:1.DDM瓣与SJM相比,开启较为迅速,关闭则较为柔和。2.DDM瓣的峰值回流量较之SJM瓣小。本文研究表明DDM瓣由于更好利用了天然心瓣的关闭机理,而具有较高的耐久性潜力。     

人工机械心瓣启闭过程的ALE有限元分析

本文采用任意拉格朗日－欧拉（ＡＬＥ）有限单元法，将血液视为不可压缩粘性流体，同时将人工机械瓣简化为定轴转动刚体，建立了机械心瓣－血液耦合运动二维计算模型，解决了人工机械瓣启闭过程的计算问题．对Ｓｔ．Ｊｕｄｅ瓣启闭过程的数值分析表明：１．Ｓｔ．Ｊｕｄｅ瓣启闭过程包括四个阶段，即：Ⅰ．开启相；Ⅱ．开启保持相；Ⅲ．关闭相；Ⅳ．关闭保持相．２．Ｓｔ．Ｊｕｄｅ瓣关闭时回流明显，伴有显著水击效应．３．在启闭过程中，高剪力区位于两瓣叶间及瓣环附近．本文的研究突破了以非耦合的方法研究心瓣启闭过程的局限性．     

人工机械瓣／血液耦合系统瞬态有限元分析

本文将人工机械心瓣／血液耦合系统作为研究对象，采用有限元法，分析了热解碳、钛合金钢、钴－铬合金钢及陶瓷四种材料机械瓣关闭状态下受突加阶梯压力荷载时的瞬态动力行为。结果表明，人工机械瓣态动力行为近乎刚性，寻致瓣叶上产生较高冲击压力，减小机械瓣的弹性模量，可以降低瓣／血液耦合系统的冲击压力。     

心脏后负荷对瓣膜功能影响的数值模拟(Ⅰ)

为了研究心脏和瓣膜的功能特性,我们建立心室、瓣膜和后负荷等物理模型,从而分别导出描述这三部分的基本方程,并在生理、病理参数变化范围内耦合求解所导出的基本方程.在此基础上,心脏后负荷各参量的变化对心脏射血、瓣膜开启以及瓣膜功能的影响情况将在另文详尽讨论.     

房地产企业成长能力的作用机理研究

房地产企业成长是一项复杂的系统工程.分别从空间、时间和内涵视角对房地产企业成长能力的作用机理进行探究.利用隐喻研究法、结合企业基因理论等,阐明成长能力对房地产企业成长的协同作用和演化机理,在内涵视角上,研究每个具体子能力作用于企业成长的微观作用机理.通过问卷调查,进行实证研究.研究表明:房地产企业的持续成长需要各个成长能力协同作用,而且不同成长阶段,成长能力的作用程度不尽相同,能力束实现了不同阶段的跃迁.     

萃取剂有机相中微乳状液的形成及其对萃取机理的影响

本文通过对环烷酸-仲辛醇-煤油这一重要萃取体系的研究,首次提出并证明了皂化某些典型的酸性萃取剂(如羧酸类,酸性磷萃取剂类等)是微乳状液的形成过程。而皂化后的萃取剂萃取稀土或二价金属离子,则是微乳状液的破乳过程.文中强调了水在萃取过程中的重要作用及其在萃取前后存在状态的变化,从而为萃取机理的研究提出了新的途径.这有助于了解萃取反应的真实过程,以及萃取中经常发生的乳化,出现第三相和萃取剂的溶解损失等现象.文中还讨论了关于环烷酸与稀土的萃合物的组成及萃取机理研究方法中存在的问题.     

带有N策略,启动时间和服务台故障的M/M/1排队的均衡策略

本文考虑带有N策略,启动时间和服务台故障的M/M/1排队的顾客的策略行为.当系统为空时服务台关闭,并且只有当系统中的顾客数达到一个给定的阈值时才会被激活,启动时间服从指数分布.服务台在工作时可能会故障,一旦发生故障,它立即被维修,维修的时间服从指数分布.我们得到了不同状态的均衡到达率并且给出了均衡社会收益函数.最后对均衡到达率和均衡社会收益进行了数值研究.     

我国食品安全问题中人为故意行为作用机理路径研究

食品安全关乎国计民生.现阶段,我国食品安全问题凸显,其中人为因素是食品安全事件频发的主要原因.以"掷出窗外网"收集的2004-2013年间全国范围内的1117条食品安全事件为研究对象,分别提炼出了作坊与正规企业中人为故意导致食品安全事件的主要作用机理路径,研究发现,这些事件的作用机理路径均服从幂律分布,且这些事件发生的时间间隔时间序列具有长程相关性.最后,给出了相应的风险防控对策.     

凝析气田压力曲线特征分析

本文采用一个带汇项的流动方程描述了凝析气井在压力大于最大凝析压力时的压力时间变化特征.根据Duhamel叠加原理建立了反映凝析作用的汇项;引入了描述这一汇项的两个新的物理参数:凝析强度R_D和凝析弛豫时间λ_D.由汇项在流动方程中的作用,给出了凝析作用影响井口压力的定量表述,阐明了凝析作用影响井口压力的机理.本文给出了这一流动方程外边界条件为无限大、内边界以定产量生产情况下的解析解.本文的结论可用于试井理论.     

自媒体时代网络推手参与下的负面网络舆论传播及治理研究——基于三方博弈视角

自媒体时代,纷繁复杂的网络信息填补着公众的碎片化时间,公众的注意力成为相关利益主体争夺的宝贵资源,网络推手应运而生,在负面网络舆论传播中有强大影响,成为治理网络舆论重要的研究对象.运用演化博弈方法构建了当事人、网络推手和监管者三方行为主体的博弈模型,对模型求解分析与数值仿真,研究各主体策略行为对负面网络舆论传播的作用机理,继而提出治理对策.通过对网络推手参与下负面舆论传播作用机理和影响因素的分析,有针对性的提出了降低负面舆论传播的监管成本、提高监管者的处罚力度、提高负面舆论传播成本、限制网络推手舆论传播收益等治理手段的具体措施.研究有助于有效治理负面网络舆论传播,净化网络空间.     

Modeling and numerical simulation of fluid flow induced by the sutureless 3F-Enable aortic valve

Diseases of the aortic valve belong to the most common health problems. The aortic valve maintains the blood flow in one direction and serves to prevent retrograde flow from aorta to the left ventricle. To date, new bio-prosthetic, suturless heart valves have been designed. The purpose of the present study is therefore to evaluate their influence on hemodynamics in the cardiovascular system. Especially the blood flow in the vicinity of the aortic valve, in the sinus of Valsalva and the ascending aorta becomes on importance from the fluid dynamical point of view. The three-dimensional geometrical model is generated after segmentation of CT data of the 3F-Enable aortic valve prosthesis. A set of simulations with different initial velocity profiles and pulse frequencies has been created to examine the transient behavior of the fluid flow and the heart valve prosthesis. The function of heart valve system, however, involves an analysis of fluid-structure interaction to predict the motion of leaflets. Hence, the separation of the soft tissue and the hard nitinol-based frame is carried out. The results reveal pressure and velocity distributions as well as normal and shear stresses acting on the wall of the prosthesis and aorta. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

The critical cross-section of a vortex

Summary This paper discusses the problem of critical-flow cross-sections in vortex flows. It is shown that there are two different types of vortex flows, A-type and B-type vortices (say). An A-type vortex approaches its critical flow state as its cross-sectional area increases and departs from the critical state as the cross-sectional area is decreased. This property is associated with the particular dependence of total pressure and circulation on the stream function, and it holds for both subcritical and supercritical A-type vortices. On the other hand, both subcritical and supercritical B-type vortices approach their critical flow states as their cross-sectional areas are decreased and depart from their critical states for increasing cross-sectional area. As was shown by Benjamin, setting the first variation of the flow force with respect to the stream function equal to zero leads to Euler's equation of motion. The second variation also vanishes if the corresponding flow state is critical. In this case the sign of the third variation decides whether the flow is an A-type or a B-type vortex. Within the framework of inviscid-fluid flow theory the type of a vortex is preserved unless vortex breakdown occurs. Making use of the knowledge that vortex flows are controlled by two different types of critical-flow cross-sections a variety of vortex flow phenomena are investigated, including the two types of inlet vortices that are observed upstream of jet engines, the behavior of vortex valves, the flow characteristics of liquid-fuel atomizers and the bath tub vortex.     

Investigation on the effect of trailing edge ejection on a turbine cascade

This paper presents a detailed experimental and numerical investigation for a turbine cascade with different trailing edge ejection. The numerical simulation is based on Three-Dimensional Navier–Stokes equations coupled with an effective ejection model, where a high resolution non-oscillatory scheme, LU-SGS implicit algorithm and Baldwin-Lomax turbulence model are employed. The experiments presented in this paper focused on a transonic turbine cascade performance with different ejection to validate the numerical simulation results. The results show that the blowing ratio has a small effect on the Mach number distribution and exit flow angle with two slot types. However the energy loss coefficient increases initially, and subsequently has a decrease tendency with the increasing of blowing ratio. The ejection from the symmetry slot blows away the vortex at the blade trailing edge and strengthens the mixing between the wake and main flow. The ejection from the pressure side cutback only clears up the vortex near the slot surface, and has small effect on the flow field near the trailing edge.     

Analysis of hydrodynamic losses for various types of aortic valves

Conclusions The creation of an automated computer-controlled hydraulic stand made it possible to measure the main hydrodynamic parameters of the flow through the investigated HVP and to determine the coefficients of Eq. (2) of fluid flow in the test chamber of the stand. The coefficients found can serve as a criterion of a comparative assessment of the hydrodynamics of HVPs. An analysis of the coefficients showed that the main contribution to pressure losses across ball and disc valves is made by viscous and convective effects. An analysis of inertial losses confirmed the presence of oscillations of the ball closing elements of the AKCh-3-06 valve around the props of the stroke limiters and made it possible to assess them quantitatively. For leaflet valves the contribution of inertial losses to the total pressure losses is more considerable than in the case of disc and ball valves both in the regime of an increase of power of the output and in the regime of a constant power. The mechanical properties of the material of leaflet valves have an effect on the hydrodynamic characteristics. The advantage of the investigated leaflet valves consists not only in that they have smaller total hydraulic losses compared with the other valves, but also in that they provide a high amplitude of pulsations of the blood stream in the case of insufficient contractility of the heart.Translated from Mekhanika Kompozitnykh Materialov, No. 3, pp. 506–512, May–June, 1985.     

Numerical simulation of the interaction between vortex ring and bubble plume

In present paper a three-dimensional Vortex-In-Cell method with two-way coupling effect was developed to study the bubble plume entrainment by a vortex ring. In this method the continuous flow was calculated by the three-dimensional Vortex-In-Cell method and the bubbles are tracked through bubble motion equation. Two-way coupling effect between continuous flow and dispersed bubbles is considered by introducing a vorticity source term, which is induced by the change of void fraction gradient in each computational cell. After validated by the comparison between experimental measurements and simulation results for the motion of vortex rings and the rising velocity of bubble plume, present method is implemented to simulate the interaction between an evolving vortex ring and a rising bubble plume. It was found that there is little effect of the bubble entrainment to the total circulation of vortex ring while the effect of bubble entrainment to the vortex ring structure is quite obvious. The bubble entrainment by the vortex ring not only changed the vorticity distribution in the vortex structure, but also displaced the positions of the vortex cores. The vorticity in the lower vortex core of the vortex ring decreases more than that in the upper vortex core of the vortex ring while the vortex core in the upper part of the vortex ring is displaced to the center of vortex ring by the entrained bubbles. Smaller bubbles are easier to be entrained by the large scale vortex structure and the transportation distance is in inverse proportion to bubble diameter.     

漩涡合并过程中颗粒运动的数值模拟

漩涡合并不仅影响着流场的演化,还制约着颗粒相的运动．基于涡团分裂合并机制,以一种改进的涡核扩散方法(CCSVM)计算了二相流中的漩涡合并与演化,在此基础上采用单颗粒轨道模型计算、分析了漩涡合并过程中的颗粒运动轨迹．研究结果表明:漩涡合并过程中的颗粒轨迹是一条螺旋线,并且保持与漩涡相同的旋转方向,合并后的漩涡中心即为达到稳定状态后的环状颗粒群中心;合并时间与环量初始值、漩涡半径与涡心距比值的初始值有关;特定条件下,颗粒群中会生成一条拉伸的尾迹,尾迹的产生与黏度系数、颗粒与漩涡的相对位置、合并漩涡环量的不对称性有关．     

Forward

Tatsien LI Fanghua LIN Guiqiang CHEN Xiaoming WANG Professor Andrew Majda is one of the most prominent applied mathematicians in the world. He is well-known for both his seminal theoretical contributions to partial differential equations and his diverse and fundamental contributions to many applied areas such as scattering theory, shock waves, combustion, incompressible flow, vortex motion, turbulent diffusion and atmosphere ocean science.     

A free boundary problem for the Navier–Stokes equations with measure data

The existence of a weak solution of an initial boundary-value problem for the plane nonstationary Navier–Stokes equations with Radon measure data on the free boundary, is established. The problem may be considered as a model of the blood flow around the heart valves. An inverse problem is studied, it allows us to find the boundary forces acting on the valve from the observed values of the velocity of the fluid in a fixed subregion.     

Vortex soliton with axial flow

Our recent works on vortex soliton with axial flow are reviewed. At first, the relationship between the equation of motion of a vortex with axial flow derived by Fukumoto and Miyazaki and the integrable equation derived by Wadati, Konno, and Ichikawa is shown. Later the equation has been solved by the inverse scattering method. Using soliton solutions two experiments of vortex filament done by Hopfinger et al. and Maxworthy et al. are analyzed in order to estimate the effect of axial flow. It is found that the effect is large for both experiments. Transport of momentum and angular momentum and sound generation by vortex soliton are investigated. It is found that collision of two solitons gives rise to very enhanced interference of the sound pressure.Department of Physics, College of Science and Technology, Nihon University, Chiyoda-ku, Tokyo 101, Japan. College of Engineering, Chubu University, Kasugai-shi 487, Japan. Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 99, No. 2, pp. 329–336, May, 1994.