EFFECT OF THE MAGNETIC FIELD ON THE PULSATILE FLOW THROUGH A RIGID TUBE

This study presents the effect of the magnetic field with constant intensity on the pulsatile flow through a rigid tube. Basing on the experimental results, the influence of the magnetic field on the blood viscosity is considered The analytic solution of the pulsatile flow through a rigid tube under constant magnetic field intensitier and the effect of the magnetic field on the velocity distribution, flow and impedance in a rigid tube are given. this investigation is valuable for understanding the influence of the magnetic field on the blood circulation.

Effects of Rigid Vegetation on the Turbulence Characteristics in Sediment-Laden Flows

The effects of rigid vegetation on the turbulence characteristics were experimentally studied in the interior water flume. An ADV was used to determine the three dimensional turbulent velocities in clear water flow without vegetation, sediment-laden flow without vegetation, sediment-laden flow with submerged vegetation and sediment-laden flow with non-submerged vegetation. By experimental and theoretical analysis, the effects of rigid vegetation on the distribution of averaged velocities, turbulence intensities and Reynolds stress were summarized. In sediment-laden flow with submerged vegetation, the averaged stream wise velocities above the top of vegetation fit well with the log distribution low. The three-dimensional turbulence intensities increase from the bottom until they reach the maximum at the top of the vegetation. The method to calculate the shear velocity with the maximum of the Reynolds stress is recommended. In sediment-laden flow with non-submerged vegetation, the turbulence problems cannot be explained by theory of bed shear flow. The average velocities, turbulence intensities and Reynolds stress approximate uniformly distributed along vertical direction.

MOTION AND DEFORMATION OF VISCOUS DROP IN STOKES FLOW NEAR RIGID WALL

A boundary integral method was developed for simulating the motion and deformation of a viscous drop in an axisymmetric ambient Stokes flow near a rigid wall and for direct calculating the stress on the wall. Numerical experiments by the method were performed for different initial stand-off distances of the drop to the wall, viscosity ratios, combined surface tension and buoyancy parameters and ambient flow parameters. Numerical results show that due to the action of ambient flow and buoyancy the drop is compressed and stretched respectively in axial and radial directions when time goes. When the ambient flow action is weaker than that of the buoyancy the drop raises and bends upward and the stress on the wall induced by drop motion decreases when time advances. When the ambient flow action is stronger than that of the buoyancy the drop descends and becomes flatter and flatter as time goes. In this case when the initial stand-off distance is large the stress on the wall increases as the drop evolutes but when the stand-off distance is small the stress on the wall decreases as a result of combined effects of ambient flow, buoyancy and the stronger wall action to the flow. The action of the stress on the wall induced by drop motion is restricted in an area near the symmetric axis, which increases when the initial stand-off distance increases. When the initial stand-off distance increases the stress induced by drop motion decreases substantially. The surface tension effects resist the deformation and smooth the profile of the drop surfaces. The drop viscosity will reduce the deformation and migration of the drop.

Numerical investigation of velocity distribution of turbulent flow through vertically double-layered vegetation

The velocity structures of flow through vertically double-layered vegetation(VDLV)as well as single-layered rigid vegetation(SLV)were investigated computationally with a three-dimensional(3D)Reynolds stress turbulence model,using the computational fluid dynamics(CFD)code FLUENT.The detailed velocity distribution was explored with a varying initial Froude number(Fr),with consideration of the steady subcritical flow conditions of an inland tsunami.In VDLV flows,the numerical model successfully captured the inflection point in the profiles of mean streamwise velocities in the mixing-layer region around the top of short submerged vegetation.An upward and downward movement of flow occurred at the positions located just behind the tall and short vegetation,respectively.Overall,higher streamwise velocities were observed in the upper vegetation layer due to high porosity,with Pr=98%(sparse vegetation,where Pr is the porosity),as compared to those in the lower vegetation layer,which had comparatively low porosity,with Pr=91%(dense vegetation).A rising trend of velocities was found as the flow passed through the vegetation region,followed by a clear sawtooth distribution,as compared to the regions just upstream and downstream of vegetation where the flow was almost uniform.In VDLV flows,a rising trend in the flow resistance was observed with the increase in the initial Froude number,i.e.,Fr?0.67,0.70,and 0.73.However,the flow resistance in the case of SLV was relatively very low.The numerical results also show the flow structures within the vicinity of short and tall vegetation,which are difficult to attain through experimental measurements.

Effect of Mixed Vegetation of Different Heights on Open Channel Flows

Vegetation of different heights commonly grows in natural rivers, canals and wetlands and affects the biodiversity and morphological process. The role of vegetation has drawn great attention in river ecosystems and environmental management. Due to the complexity of the vegetated flow, most previous research focuses on the effect of uniformed one-layered vegetation on the flow structure and morphological process. However, less attention was paid to the impact of the mixing vegetation of different heights, which is more realistic and often occurs in natural riverine environments. This paper aims to investigate the effect of mixing three-layered vegetation on flow characteristics, particularly the velocity distrbution, via a novel experiment. Experiments were performed in a titling water flume fully covered with vegetation of three heights (10, 15 and 20 cm) arranged in a staggered pattern, which is partially submerged. Velocities at different positions along a half cross-section were measured using a mini propeller velocimeter. Observed results showed that the velocity has a distinct profile directly behind vegetation and behind the vegetation gap. The overall profile has two distinct reflections about ? below or near the top of short vegetation (h): the velocity remains almost constant in the bottom layer ( h) the velocities directly behind the middle after short vegetation increase much faster than those directly behind the short after tall vegetation. The finding in this study would help river riparian and ecosystem management. .

生态浮床布设下明渠水流结构及阻力特性试验研究

生态浮床已广泛运用于城市河道净化工程,但浮床布设改变了原河道断面水流结构,增加水流阻力,可能降低河道行洪能力。现有研究主要针对浮床水动力学特性分析,而关于浮床引起的水流阻力变化定量研究较少。为此,通过水槽试验研究了浮床刚性植物在10、20、30 cm三种淹没深度及平行、交错两种布置方式的组合工况下对水槽断面水流结构产生的影响。由于传统的曼宁公式无法直接用于浮床覆盖区糙率系数的求解,基于等效断面原理增加浮床阻力项,求解浮床覆盖区综合糙率与刚性植物附加糙率。结果表明,淹没深度越大,浮床阻水效果越强;交错布置方式比平行布置方式更增加水流阻力;浮床刚性植物在平行布置条件下断面综合糙率在0.381~0.417之间,交错布置条件下断面综合糙率在0.397~0.427之间,断面综合糙率随植物淹没深度和布置方式的变化而变化。

舰船复合材料轴振动能量传递特性研究

针对舰船复合材料传动轴减振机理尚不清晰的问题,文中构建了某舰船复合材料轴仿真模型,基于功率流法分析了复合材料轴振动能量传递特性,并在此基础上进一步探究了钢法兰-复合材料刚柔耦合界面匹配参数和轴段内复合材料铺层方式对振动能量传递的影响规律。最后通过复合材料传动轴模态试验和振动传递试验验证了仿真模型的准确性。结论如下:刚柔耦合界面对于振动能量抑制有着显著作用,其振动能量的传递随接触面积的增大而降低,而弹性模量比仅影响传动轴固有频率;随着铺层角度的减小及铺层数量的增加,复合材料轴段隔振性能逐渐增加。

江河流域水量分配方案研究——以建溪流域为例

为落实最严格水资源管理制度,强化水资源刚性约束,促进江河流域水资源的合理配置,实现水资源可持续利用,提出了制定江河流域水量分配方案的一般方法及需要重点关注的要素。以建溪流域为例,详细分析了建溪流域水量分配的制定过程,以各省区用水总量控制指标为约束,综合考虑流域经济社会发展情况及现状用水关系,通过水资源供需平衡调算,提出了建溪流域各省区河道外水量分配方案。在此基础上,总结提出了制定水量分配方案需要遵循的“公开、公平、公正”原则,以及落实水量分配需要践行的“调度手段、监测手段、制度手段”,为促进流域水资源节约和合理配置、满足新时期流域水资源管理要求提供参考。

掠海导弹触水滑跳运动特性数值模拟研究

水面滑跳运动是一种飞行体在近水面运动时底部反复触水并被弹起的运动过程,该运动方式可以提高远程对海打击导弹在末端近水面无动力运动时的航程和机动能力。为研究导弹的水面滑跳运动特性,通过求解非定常Navier-Stokes方程和Realizable k-ε湍流模型,结合重叠网格技术,采用VOF方法捕捉空气和水之间的自由液面变化,通过六自由度方程模拟刚体运动,对典型导弹外形水面滑跳运动过程进行模拟研究,给出并分析了导弹一次水面滑跳过程的运动参数和表面压力变化。结果表明:根据水面滑跳过程中导弹姿态和相对水面位置的变化特点,可将导弹水面滑跳运动过程分为入水前空中飞行段、第1次触水弹起段、近水面滑行段、第2次触水滑行段、滑跳出水飞行段5个阶段;第1次触水过程中,船尾段受到水面冲击被迅速弹离水面,同时使弹体低头,导弹整体仍向下朝水面运动;第2次触水过程中,导弹下表面大面积拍击水面,不仅产生较大的水面冲击力,且产生使弹体抬头的力矩,在向上冲击力和抬头力矩作用下,导弹被抬升滑跳出水面。船尾收缩段产生的抬头力矩及导弹前端触水处产生的冲击载荷共同作用使得导弹完成水面滑跳过程。

改进型BCM-100H丙烯聚合催化剂在Horizone装置应用及高性能产品开发

原BCM-100H催化剂生产较高MFR(熔体流动速率)产品时聚合物细粉较多,不利于装置运行。本文考察了改进型BCM-100H催化剂在Horizone装置的工业应用,并与原催化剂及进口催化剂进行对比;使用该催化剂首次在该装置上开发3个高MFR高刚性高抗冲共聚产品K8740H、KH39M和KH75M。结果表明:改进后BCM-100H催化剂活性,氢调敏感性,共聚能力等性能基本不变;聚合物粉料中≤0.15 mm细粉减少约80%,聚合物等规指数(绝对值)提高0.5%,优于进口催化剂;K8740H弯曲模量和常温冲击强度分别是1.36 GPa和8.51 kJ·m^(-2),优于进口同类产品;KH39M和KH75M弯曲模量和冲击强度分别是1.57 GPa,6.00 kJ·m^(-2)和1.59 GPa,5.84 kJ·m^(-2),优于国产同类产品;对助剂进行了筛选优化,可将产品弯曲模量提高5%~10%。产品弯曲模量和冲击强度分别达到1.72 GPa和5.72 kJ·m^(-2),超过进口同类牌号水平。

具有深腔结构的刚挠结合板制作方法探讨

印制电路板(PCB)需要在有限的空间内集成更多的功能模块,因此有一种相应的深腔设计。但深腔制作存在深度控制精度差、工艺流程复杂及制作难度高等问题。以一种具有深腔结构的有机发光二极管(OLED)模组刚挠结合板为研究对象,通过解析关键制程工艺、关键控制点,以及对比不同工艺优缺点的方式,对深腔结构的制作难点进行分析,重点介绍了深腔加工的关键制作技术。

某水电站水轮机超出力运行研究

针对某水电站常年弃水量大、弃水时间长现象,本文采用数值仿真计算,在不改动电站设备的前提下,对该电站水轮机展开超出力运行研究,分析其水轮机超出力运行的可行性。通过选取3种超出力工况,对其进行流场分析,得出在3种超出力工况下运行时,水轮机内部流态良好;同时分析3种工况下的空化性能,并结合电站实际运行情况,得出3种工况下运行机组空化性能满足要求;通过计算最大载荷下超出力工况的压力脉动与刚强度,得出机组稳定性良好且转轮刚强度符合设计要求。

内燃动车组动力包刚柔耦合双层隔振系统动力学建模及参数影响分析

动力包系统为内燃动车组的重要组成部分,其隔振性能直接关系到动车组的运行安全性及乘坐舒适性。针对动力包刚柔耦合双层隔振系统,提出了一种基于子结构频响函数综合的动力包刚柔耦合双层隔振系统建模方法。该方法将动力包系统分为发电机组、散热器机组、公共构架和车体地板子结构,通过2次频响函数综合建立了公共构架B-基础D综合体和机组刚体的频响函数表达式,大大提升了建模效率与计算速度,对工程计算和设计具有重要的价值。通过与ABAQUS软件中有限元频响结果进行对比,验证了该方法的正确性与计算精度。以某型内燃动车组动力包系统为研究对象,利用该建模方法,结合动力包系统实际隔振设计需求,研究了子结构质量比、子结构刚度、子结构阻尼、各级隔振器刚度及阻尼等参数对动力包系统隔振性能的影响规律,为内燃动车组动力包隔振系统设计及优化提供了理论支撑。

湿地刚性植物对水流结构影响的三维数值模拟

针对有植被的湿地水流问题的复杂性,基于VOF表面跟踪技术下的RNGk-ε模型,采用有限体积法和PISO算法建立了数值模拟方法,通过对同一来流情况下三种不同株径的刚性植物群的数值计算,分析了植物带前、带中、带后典型断面的纵、横向水面线变化及流场。结果表明,随植物的生长,不同断面水流的水位、平均流速与植物的株径均有密切关系,利用模型计算的结果与实验值吻合较好,该方法用于模拟湿地刚性植物对水流的作用行之有效。

刚性沉水植被水流的流速垂向分布

水流速度分布是植被水流动力学研究的基础问题之一。含有沉水植物的水流由于植被阻力的作用,其流速的垂向分布与不含水生植物的水流相比,具有很大的差异;在形态各异植被的影响下,其流动十分复杂,很难得到流速分布的解析表达式。在"圆柱型"植被流速分布的基础上,通过有限解析法逐段分析含有沉水植被水流的动力特性,考虑了沉水植被的垂向形态变化对植间水流的影响,得到了任意形状植被水深范围内的水流流速分布。通过与室内试验数据的比较分析,所用方法得到的结果与试验数据吻合很好,能够准确地反映植被间水流流速的垂向变化,并具有更为广泛的适用性。

一种新型圆锥式节流阀口的特性分析

本文分析了用于水压传动的二级圆锥式节流阀口的刚度特性、流量系数等问题,与一级节流阀口相比,二级节流阀口有较大的优越性。

折减荷载法分析刚性桩复合地基路基绕流滑动稳定性

针对整体滑动稳定安全系数满足规范要求的刚性桩复合地基路基仍然可能滑塌的事实,对刚性桩复合地基路基绕流滑动稳定分析开展了研究。基于对桩土作用力的研究,对桩土作用力进行了简化处理,提出了折减荷载法用于刚性桩复合地基绕流滑动稳定分析。工程实例表明刚性桩复合地基路基需要分析绕流滑动稳定性,折减荷载法简单实用。

刚性桩复合地基路基绕流滑动稳定分析

针对整体滑动稳定性满足规范要求的部分刚性桩复合地基路基发生滑塌的现实,分析了刚性桩复合地基路基可能的破坏模式,指出桩间荷载较大且桩间土软弱时可能会发生绕流滑动破坏,对刚性桩复合地基路基建议同时进行整体滑动稳定分析、绕流滑动稳定性分析和毁桩验算等。分析了刚性桩对滑动体的作用力并给出了相应的计算方法,通过对路堤荷载进行折减处理以及将桩周摩擦力转换至加固区地基土重度等措施,提出了绕流滑动稳定分析简化方法。工程实例表明,该方法合理可行。基于刚性桩复合地基路基绕流滑动稳定分析,对路基下刚性桩复合地基设计提出了建议。

基于Fluent的明渠水流三维数值模型验证

基于Tominaga和Nezu等人的矩形明渠试验模型数据,利用Fluent软件,分别采用刚盖假定方法和VOF方法,模拟明渠自由水面,对比研究不同宽深比条件下的明渠水流特性。通过分析研究得到:与刚盖假定法得到的模拟值相比,VOF模拟值更接近试验值,且VOF方法模拟得到数据显示在宽深比小于5时,垂线最大流速出现在相对水深0.6～0.8的范围内,这与传统理论研究也是相符合的。

刚性挡土墙主动土压力颗粒流模拟

将土体离散为具有滑动连接模型的刚性条块,用颗粒流PFC2D程序数值从细观力学角度模拟了墙体平移(T)、绕墙底转动(RB)和绕墙顶转动(RT)位移模式下不同位移大小时刚性挡土主动土压力分布。模拟结果表明:刚性挡墙主动土压力非线性分布、墙土间外摩擦角和土体剪切角或内摩擦角对土压力有很大影响;墙体绕顶部转动时,大约0.3倍墙高以上的主动土压力大于静止土压力产生土拱效应;模拟计算值与模型试验实测数据吻合比较好,具有一定的理论价值。