Modeling Blood Flow in Veins of Uniform Properties (Giraffe Jugular Vein)

This paper models the giraffe’s jugular veins as a uniform collapsible tube from a rigid skull. The equations governing one-dimensional steady flow through such a tube for various conditions have been developed. The effects of inertial and inclination angles that have not been discussed previously have been included. It has been shown that different flows for a uniform tube (vein) are possible. However, this flow matches that of a jugular vein which is supercritical, and the steady solution has been given by the balance between the driving forces of gravity and the viscous resistance to the flow at the right atrium of the heart must be sub-critical for a fixed right-atrium pressure which means that an elastic jump is required to return the flow to sub-critical from the supercritical flow upstream this type of relationship gives rise to flow limitation at the same time given any right atrium fixed pressure there exists a maximum flow rate which when exceeded the boundary conditions of the flow do not hold boundary conditions at the right atrium are not satisfied hence making the steady flow impossible this mechanism of flow limitation is slightly different from the other one in that causes airways through forced expiration from the observation made it is clearly shown that there is an intravascular pressure difference with a change in height.

Experiments on two-phase flow in hydraulic jump on pebbled rough bed:Part 2–Bubble clustering

A survey on bubble clustering in air–water flow processes may provide significant insights into turbulent two-phaseflow.These processes have been studied in plunging jets,dropshafts,and hydraulic jumps on a smooth bed.As a first attempt,this study examined the bubble clustering process in hydraulic jumps on a pebbled rough bed using experimental data for 1.70<Fr_(1)<2.84(with Fr_(1) denoting the inflow Froude number).The basic properties of particle grouping and clustering,including the number of clusters,the dimensionless number of clusters per second,the percentage of clustered bubbles,and the number of bubbles per cluster,were analyzed based on two criteria.For both criteria,the maximum cluster count rate was greater on the rough bed than on the smooth bed,suggesting greater interactions between turbulence and bubbly flow on the rough bed.The results were consistent with the longitudinal distribution of the interfacial velocity using one of the criteria.In addition,the clustering process was analyzed using a different approach:the interparticle arrival time of bubbles.The comparison showed that the bubbly flow structure had a greater density of bubbles per unitflux on the rough bed than on the smooth bed.Bed roughness was the dominant parameter close to the jump toe.Further downstream,Fr_(1) predominated.Thus,the rate of bubble density decreased more rapidly for the hydraulic jump with the lowest Fr_(1).

Experiments on two-phase flow in hydraulic jump on pebbled rough bed:Part 1–Turbulence properties and particle chord time and length

This study reported and discussed turbulence characteristics,such as turbulence intensity,correlation time scales,and advective length scales.The characteristic air–water time scale,including the particle chord time and length and their probability density functions(PDFs),was investigated.The results demonstrated that turbulence intensity was relatively greater on a rough bed in the roller length,whereas further downstream,the decay rate was higher.In addition,the relationship between turbulence intensity and dimensionless bubble count rate reflected an increase in turbulence intensity associated with the number of entrained particles.Triple decomposition analysis(TDA)was performed to determine the contributions of slow and fast turbulent components.The TDA results indicated that,regardless of bed type and inflow conditions,the sum of the band-pass(T'_(u))and high-pass(T″_(u))filtered turbulence intensities was equal to the turbulence intensity of the raw signal data(T_(u)).T″_(u) highlighted a higher turbulence intensity and larger vorticities on the rough bed for an identical inflow Froude number.Additional TDA results were presented in terms of the interfacial velocity,auto-and cross-correlation time scales,and longitudinal advection length scale,with the effects of low-and high-frequency signal components on each highlighted parameter.The analysis of the air chord time indicated an increase in the proportion of small bubbles moving downstream.The second part of this research focused on the basic properties of particle grouping and clustering.

Analysis of Nonlinear Stochastic Systems with Jumps Generated by Erlang Flow of Events

In this paper we consider the stochastic systems with jumps (random impulses) generated by Erlang flow of events that lead to discontinuities in paths. These systems may be used in various applications such as a control of complex technical systems, financial mathematics, mathematical biology and medicine. We propose to use a spectral method formalism to the probabilistic analysis problem for the stochastic systems with jumps. This method allows to get a solution of the analysis problem in an explicit form.

Second-order slip MHD flow and heat transfer of nanofluids with thermal radiation and chemical reaction

The effects of the second-order velocity slip and temperature jump boundary conditions on the magnetohydrodynamic （MHD） flow and heat transfer in the presence of nanoparticle fractions are investigated. In the modeling of the water-based nanofluids containing Cu and A1203, the effects of the Brownian motion, thermophoresis, and thermal radiation are considered. The governing boundary layer equations are transformed into a system of nonlinear differential equations, and the analytical approximations of the solutions axe derived by the homotopy analysis method （HAM）. The reliability and efficiency of the HAM solutions are verified by the residual errors and the numerical results in the literature. Moreover, the effects of the physical factors on the flow and heat transfer are discussed graphically.

HOMEOMORPHISM FLOWS FOR NON-LIPSCHITZ SDES DRIVEN BY LVY PROCESSES

In this article, homeomorphism flows for non-Lipschitz stochastic differential equations driven by Levy processes are studied.

低弗劳德数条件下尾坎坡度对消力池内流场结构的影响

低水头、大流量条件下泄洪,易形成低弗劳德数水流,对下游河床和边坡造成冲刷风险。基于某水利枢纽工程,采用数值模拟的方法,应用RNG k-ε数值模型,研究了不同尾坎坡度体型下消力池内低弗劳德数水跃的流场特征。研究结果表明:低弗劳德数来流条件下,消力池内形成的淹没式水跃沿水流方向可分为核心区、发展区和回流区;核心区在水深方向上按流速特性又分为射流内层、射流外层、旋滚内层和旋滚外层;不同尾坎坡度的消力池中,均遵循时均压强沿程增大、临底流速自收缩断面后沿程减小的规律;尾坎坡度变陡会使得水跃的旋滚起始断面向上游移动,旋滚终止断面向下游移动,从而使得旋滚长度增大;当尾坎坡度为1∶3时,尾坎斜坡段临底流速梯度为0,当尾坎坡度小于1∶3时,尾坎斜坡段临底流速梯度为负,当坡度大于1∶3时,流速梯度为正,其原因是尾坎坡度变陡使得尾坎对水体的阻力在平行于尾坎坡面方向的分量减小,从而使得流速梯度逐渐增大。研究成果可为类似工程中消力池的设计选型提供参考。

某工程泄水建筑物泄洪雾化范围计算分析

为了减少泄洪雾化带来的工程影响和损失,笔者结合工程实例,根据理论公式对表孔溢洪洞、泄洪冲沙洞在不同水位下的雾化范围进行估算,并依据估算结果提出针对性工程设计建议。结果表明:表孔溢洪洞在校核洪水位下雾化影响范围最大;该工程的厂区虽位于强暴雨区横向影响范围以外,但处于雾流降雨区范围之内,设计时需考虑雾化对厂区电气设备带来的不利影响;出口边坡局部位于强暴雨区和雾流降雨区范围内,需对边坡进行加固处理并采取表面防护措施,确保边坡运行安全稳定。计算成果可为工程布置、设计提供理论支撑。

血流限制下低强度增强式跳跃训练干预功能性踝关节不稳的效果

目的 探讨血流限制下低强度增强式跳跃训练(LI-PJT+BFR)对功能性踝关节不稳(FAI)大学生的下肢动态姿势控制的影响。方法 2023年3月至5月,招募西安体育学院FAI大学生40例,随机分为高强度增强式跳跃训练(HI-PJT, n=14)组、低强度增强式跳跃训练(LI-PJT, n=13)组和LI-PJT+BFR组(n=13),各组完成相应的干预训练,共6周。干预前后,采用无线遥感表面肌电测试仪测量胫骨前肌、腓骨长肌、腓肠肌外侧头、臀大肌、股外侧肌、股二头肌和半腱肌最大自主等长收缩(MVIC)和单腿下落(SLL)时肌电均方根值(RMS),采用Y平衡和坎伯兰踝关节不稳问卷(CAIT)进行评定。结果 干预后,除LI-PJT组腓骨长肌、臀大肌、股二头肌和半腱肌MVIC和RMS,LI-PJT+BFR组腓骨长肌RMS外,各组其余肌肉MVIC和RMS均较干预前提高(t> 2.218, P <0.05);3组中,除腓骨长肌外,LIPJT组各肌肉MVIC和RMS均最低(F> 3.262, P <0.05);各组Y平衡各方向评分和综合分均提高(t> 2.485,P <0.05),3组中LI-PJT组最低(F> 5.042, P <0.05);各组CAIT评分显著改善(t> 5.227, P <0.001),3组中LI-PJT组最低(F=4.640, P <0.05)。结论 LI-PJT+BFR可改善功能恢复期FAI大学生下肢动态姿势控制能力,效果与HI-PJT相似。

反汇编工具中间接跳转表求解算法分析与测试

二进制反汇编是困难的,但是对于提高二进制软件的安全性至关重要.造成二进制反汇编比较困难的一大原因是编译器为了提高效率会在二进制代码中引入很多间接跳转表.为了求解间接跳转表,主流反汇编工具采用了各种策略.然而,这些策略的具体实现以及策略的效果不得而知.为了帮助研究人员理解反汇编工具的算法实现以及性能,首先系统总结反汇编工具求解间接跳转表的策略;然后构建自动化测试间接跳转表框架,基于该框架,可以大规模地生成关于间接跳转表的测试集(包含2410455个跳转表);最后,在该测试集上,对反汇编工具求解间接跳转表的性能进行评估,并人工分析反汇编工具的每个策略引入的错误.另外,得益于针对反汇编工具算法实现的系统性总结,发现6个反汇编工具实现上的bugs.

Computational simulations of near-continuum gas flow using Navier-Stokes-Fourier equations with slip and jump conditions based on the modal discontinuous Galerkin method

Blunt-body configurations are the most common geometries adopted for non-lifting re-entry vehicles.Hypersonic re-entry vehicles experience different flow regimes during flight due to drastic changes in atmospheric density.The conventional Navier-Stokes-Fourier equations with no-slip and no-jump boundary conditions may not provide accurate information regarding the aerothermodynamic properties of blunt-bodies in flow regimes away from the continuum.In addition,direct simulation Monte Carlo method requires significant computational resources to analyze the near-continuum flow regime.To overcome these shortcomings,the Navier-Stokes-Fourier equations with slip and jump conditions were numerically solved.A mixed-type modal discontinuous Galerkin method was employed to achieve the appropriate numerical accuracy.The computational simulations were conducted for different blunt-body configurations with varying freestream Mach and Knudsen numbers.The results show that the drag coefficient decreases with an increased Mach number,while the heat flux coefficient increases.On the other hand,both the drag and heat flux coefficients increase with a larger Knudsen number.Moreover,for an Apollo-like blunt-body configuration,as the flow enters into non-continuum regimes,there are considerable losses in the lift-to-drag ratio and stability.

基于动脉自旋标记的睡眠剥夺大脑血流灌注特点

目的探讨睡眠剥夺与正常睡眠状态下大脑血流灌注特点的差异。资料与方法2020年10月—2021年12月在西安市各高校中招募50例受试者。使用精神运动警觉性任务(PVT)收集持续性注意力行为学数据。采用动脉自旋标记技术比较睡眠剥夺后与正常睡眠后的相对脑血流量(rCBF),分析两种状态下差异脑区的rCBF与PVT脱漏频次差值的相关性。结果与正常睡眠后相比,睡眠剥夺后双侧背外侧前额叶、双侧顶上小叶、左侧眶部额中回、双侧颞中回、右侧中央后回、双侧角回的血流灌注显著减低,而双侧丘脑、左侧楔前叶、右侧内侧前额叶、左侧后扣带回、左侧颞下回的血流灌注明显增高(FDR校正,P<0.05,团块大小≥20体素)。左侧背外侧前额叶及右侧顶上小叶的rCBF变化与PVT脱漏频次差值呈负相关(r=-0.56,P<0.001;r=-0.64,P<0.001),左侧楔前叶的rCBF变化与PVT脱漏频次差值呈正相关(r=0.72,P<0.001)。结论默认网络、额顶网络及丘脑相关脑区血流灌注异常改变可能是睡眠剥夺后持续性注意力下降的重要神经机制。

Hydraulic jump and choking of flow in pipe with a change of slope

This paper investigates hydraulic jumps in sloping pipes by means of wall-resolved large eddy simulation(LES).The purpose is to achieve an improved understanding of jump behaviours driven by pipe discharge and slope.The LES model predicts the hydraulic jump as a 3-D two-phase flow,with air as the gas phase and water as the liquid phase.The predictions yield instantaneous velocity and pressure fields as well as fluid volume fraction.The instantaneous flow variables allow ensemble averages,which quantify the internal structures and integral properties of the hydraulic jump.The predicted instantaneous velocity shows spectra in consistency with the well-known Kolmogorov−5/3 law.The ensemble averages of air and water velocities,free-surface profile,roller length and aeration length,compare well with available experimental data.The jump behaviours are complex.Some aspects such as free-surface fluctuation and jump-toe oscillation resemble the classical hydraulic jump on horizontal floors.Others like the 3-D distributions of core jet,vorticity and aeration are much more complicated.Depending on the pipe discharge and slope,the resulting jump can be a complete or an incomplete jump.The incomplete hydraulic jump causes choked flow downstream.This has severe consequences on drainage conditions in sewer pipes laid on sloping terrain.This paper proposes using the Okubo-Weiss parameter as a new way to subtly delineate the region of hydraulic jump.It is much more efficient and less ambiguous,compared with traditional visual inspections.

Analogy Between Hydraulic Jump in Films Formed by Impinging Liquid Jet and Critical Flow in Internal Flows

Formulated are simple models for the flow in liquid film, formed by impinging jet, and a two-phase downward flow in pipe. The models are based on simplified equations of mass, momentum and energy. The solutions of such conservation equations may have regular points belonging to one integral curve only as well as turning points can be found amongst them, which refer to extreme values in the appropriate co-ordinate system. The solutions can also have singular points belonging to none or more than one integral curve. Both the turning and singular points have a clear physical meaning. They could be linked to critical flow conditions in the pipe flow or to the so-called hydraulic jump. Analogy existing between critical conditions in the pipe and the flow of liquid films formed by the liquid jet have been shown in the paper.

台阶式溢洪道各流况的消能特性

在斜坡角度θ=19°的台阶式溢洪道上,变化其来流量、台阶高度及相对坝高等条件,对跌落水流、过渡水流及滑行水流,下游消力池形成临界水跃的跃前、跃后消能率进行了对比试验研究。试验结果表明,在试验条件范围内,以上三种流态的消能率差别甚小,总消能率最大可达95%左右,其中跃前的消能率占85%以上。

U形渠道机翼形量水槽水跃数值模拟与试验研究

量水槽是灌区常见的特设量水设备,而槽后水力特性是判断其选型是否合理的重要指标之一。以某小型灌区末级灌溉渠系改造工程为原型,针对两种不同工况,采用基于TruVOF方法跟踪自由液面、Favor技术实现网格优化的湍流数学模型,对U形渠道机翼形量水槽水跃问题进行三维数值模拟,分析了水跃的时均流场、共轭水深、发生位置、跃长、断面流速分布以及水跃段能量损失等相关水力特性。采用与原型1∶1比尺的水工模型试验资料对模拟结果进行验证,结果表明,二者吻合较好。通过对实测与数值仿真的共轭水深数据进行统计分析,得到了适用于U形渠道机翼形量水槽水跃共轭水深的近似计算公式。研究结果对机翼形量水槽在平原缓坡灌区末级渠系的应用研究提供了一定的参考和建议。

网式过滤器的计算模型选择及内部流场分析

为了解网式过滤器内部流场特性,分别采用Fluent软件提供的Standard k-ε、RNGk-ε及Realizable k-ε模型同多孔介质阶跃模型耦合计算,通过物理试验与计算结果对比,确定了Realizable k-ε模型与多孔介质阶跃模型能更好地模拟网式过滤器中的流场。在此基础上,分析了该过滤器的内部流场,指出排污口固体边界和出水口边界条件对该过滤器的速度流场和压强场分布规律影响很大;滤网内、外侧的水流流速沿X轴分布不均匀,从而影响了网式过滤器的过滤效率及使用寿命,其结构有待进一步研究。

挡烟垂壁作用下狭长通道内烟气输运特征研究

为揭示挡烟垂壁对狭长通道火灾烟气特征及温度分布的影响,运用火灾动力学软件FDS,研究了狭长通道内不同高度挡烟垂壁下火灾烟流运动行为,重点探讨了密度跳跃过程及近火源区烟气特征参数变化。结果表明:挡烟垂壁增加了密度跳跃中翻滚区的长度,缩小了卷吸空气范围,造成烟气质量流率相应减少;挡烟垂壁对烟气垂直速度分布的影响主要作用在挡烟区,且与垂壁高度有关;垂高大于0.3 m,受挡烟垂壁高度影响,在垂直高度1.5~2 m位置出现一定速度的烟气逆流,速度分布曲线呈现与无挡烟垂壁不同的凹陷区,非挡烟区烟气垂直速度服从高斯分布;与无挡烟垂壁相比,挡烟垂壁上游顶棚附近温度普遍增高,下游温度衰减速率随挡烟垂壁高度的增加而加快。

上下游水位对平底板水闸闸堰出流淹没界限的影响

本文对平底板水闸闸堰出流界限及淹没界限进行了探讨，认为闸孔出流及堰流的界限不仅与闸门的相对开度有关，而且还受水闸上下游水位的影响，并给出了闸堰出流淹没界限的判别指标和波状水跃状况下的淹没界限．

青草沙水库下游水闸水力特性试验分析研究

青草沙水库是建于潮汐河口江心的大型水库。水库水闸运行水头低,水头相对变幅大,具有双向引排水功能,水流条件复杂。为此通过模型试验,研究了水闸引排水运行水流流态、低Fr数水跃消能等关键水力特性,为水闸的设计评估和安全运行调度提供技术支撑,也为沿海类似水闸提供设计和运行管理经验。