基于流固耦合的复杂血管内血液动力学数值模拟及血管支架有限元分析

为了研究两种复杂形状的血管在不同位置发生病变时,植入支架后,血液的流速变化、管内压力变化,以及二者对于血管支架结构强度的影响,建立不同形状的复杂血管(主动脉血管和动脉分叉血管)模型、血管支架模型、血液模型,在主动脉血管、动脉分叉血管不同病变位置植入血管支架,建立血管-血液-支架的装配模型,导入Fluent进行动力学数值模拟,以血管内压力大小、流速变化为研究对象进行分析。运用流固耦合的技术,将血流对于血管支架作用作为载荷施加到血管支架上,对其进行结构的有限元分析,仿真结果表明在各种情况下,血管支架的强度均校核安全。     

人体两侧椎动脉形态差异及其对血流动力学的影响

目的 分析左右侧椎动脉的几何形态及血流动力学差异,揭示椎动脉狭窄偏侧化现象背后的解剖学和血流动力学机理,为椎动脉狭窄的风险评估及支架治疗优化提供参考。方法 获取15例健康人的头颈部CT血管造影(CT angiography, CTA)图像,构建左右侧椎动脉起始部的三维模型,并测量管径、弯曲度等血管形态特征参数,统计分析了两侧椎动脉的形态差异及影响因素。通过主成分分析筛选出两侧椎动脉的典型模型,并进行血流动力学数值模拟,比较两侧血流流速、壁面剪切应力(Time-Averaged Wall Shear Stress, TAWSS)、振荡剪切因子(Oscillatory Shear Index, OSI)等因素的分布差异。结果 左右侧椎动脉模型形态存在显著性差异,左侧锁骨下动脉的管径及曲率半径更小,左侧椎动脉管径及迂曲度更大,右侧椎动脉起始部分叉处的非平面性更大。典型椎动脉模型的血流动力学对比研究表明,右侧椎动脉内血流流速、流量更小,右侧椎动脉起始部的TAWSS更低,OSI更大,提示右侧椎动脉更易发生狭窄等动脉粥样硬化疾病。结论 本研究阐明了健康人左右侧椎动脉的形态差异,研究了典型椎动脉模型...     

基于电路模型对心脑血管耦合的分析与诊断

研究了脑血管力学参数的改变与血压变化之间的关系,为临床脑中风的诊断和预报提供帮助。将心脑血管作为一个整体,分别对脑循环和体循环建立等效电路模型,并联后作为主动脉输入阻抗。利用心室最小功原理,建立了心脏与脑血管耦合的动力学模型,数值模拟出主动脉根部的阻抗、压力波形以及流速波形,并进一步模拟了常见的心脑血管疾病。研究结果表明,心脏与脑血管之间相互影响,脑血管的阻力以及弹性等力学参数发生变化时,人体的血压也对应着变化,高血压患者是脑中风的高危人群。     

血流脉搏波的特征与生理因素的相关性研究

从动脉血管系统的血管壁、血液以及动脉血管周围组织的生理物性出发,建立了脉搏波波形特征的数学表达式,从物理学以及数学的角度在理论上分析了脉搏波波形的特征随生理参数的变化情况.改变血管的杨氏模量,血液的粘度以及血管半径参数后发现所得的脉搏图与能较好的反映生理信息,本文所得到的结果为脉搏波的波形特征的进一步研究奠定了理论基础,也有助于临床上利用脉搏波的传播特性来分析和诊断相关的疾病.     

热扩散法测量血液流速

介绍了一种利用人体皮肤和接触导体的热传递来无创测量局部皮肤组织中血液流速的方法.使用热量作为指示剂,利用血液是人体内主要热传递媒介的特性,通过测量与人体皮肤接触的金属导体的温度变化,可以得到血液流速.该方法无需加热人体表面组织,结构简单.进行了理论推导、模拟仿真,提出了采用归一化差均值作为表征血液流速的量,并研制了实验系统.利用该实验系统测得的血液流速与用Doppler血流计测得的标准血液流速之间的相关系数达到0.914.     

颈动脉粥样硬化斑块生长部位与血管内膜及血流动力学的相关性分析

目的分析颈动脉粥样硬化斑块生长部位与血管内膜、血流动力学的相关性。方法选取2005年6月-2012年11月期间我院收治1820例颈动脉粥样硬化患者为研究对象,根据其有无斑块和内膜厚度,将研究对象分为6组,比较分析各组之间血流指标变化。分别观察各组血流指标:收缩期峰值血流速度(PSV)舒张末期血流速度(EDV)、血管阻力指数(RI)、血管搏动指数(PI)以及PSV/EDV。结果斑块分布:双侧斑块存在率最高,左侧存在率高于右侧;IMT变厚时双侧受累率最高,且左侧受累率高于右侧。颈总动脉(CCA)有斑块患者的PSV和EDV低于无斑块患者;PI和RI高于无斑块患者,其中双侧斑块者与无斑块患者的血流指标差异最为明显。IMT(内-中膜厚度)增厚患者PSV和EDV低于IMT正常患者,PI和RI高于IMT正常患者。结论颈动脉粥样硬化斑块形成和IMT增厚都表现为双侧受累最多,左侧受累高于右侧,双侧受累对血流动力学影响最显著。     

一种机构动力学的统一方法——键合图法

介绍了基于键合图理论的机构动力学统一方法。给出了一般机构的键合图模型，所推导出的机构动力学统一方程，可分别用于机构动力学正、逆问题，具有规则化的特点，特别适合于计算机自动生成。用实例说明所述方法的有效性。     

软管式波浪能转换装置(续)

正4软管式波浪能量转换装置原理初步分析软管式波浪能转换装置的基本原理源自心血管系统。换言之软管式波浪能转换装置本质上是一种仿生装置,当然人体的心血管系统的血液动力学问题要更为复杂,因为血液是粘性流体,另外血管是软管,血液在血管内的流动不仅仅由心脏泵送压力产生的流动,还由包围血管的肌肉的张弛运动对血管的挤压而对血管内血液流动的辅助作用。简化近似的速度模型,例如斯托克斯流模型、幂律刘模型、泊肃叶流模型、Womersley模型等。可能比     

相似理论和模型试验的结构动响应分析运用

主要讨论了相似理论在结构动力学模型试验中的实际应用问题,目的在于研究如何通过相似理论和缩比模型试验的结果准确预估实际结构的动力学特性。首先,在考虑实际工程试验条件前提下,给定几何参数和物理参数的相似比数,根据相似理论和有限元法推导出非等比缩放的缩比模型和实际模型之间固有振动、频域响应和时域响应之间的相似性关系;然后,通过薄板结构的振动试验来验证这种相似关系的准确性和工程应用价值。通过理论推导和试验证明,根据缩比模型动力学试验结果,运用所推导的动力学相似关系可以准确预估实际结构的动力学特性。     

两自由度小型直升机动力学建模与控制的分析

基于相似性理论设计了具有两自由度的直升机飞行模拟试验平台，以该试验平台为研究对象，利用拉格朗日一欧拉方程与等效力矩相结合的方法推导出系统的动力学模型，预估了试验平台的物理参数；通过试验获得在固定总距角情况下直升机的升力随转速的变化关系。根据动力学方程，设计了具有鲁棒性的PID修正前馈控制算法，运用MATLAB仿真验证了控制器的快速收敛性和有效性。     

A lumped-parameter model to investigate the effect of plantar pressure on arterial blood flow in a diabetic foot

This paper presents a lumped-parameter model for the big-toe region that investigates the effect of plantar pressure on the diameter of the blood vessels, specifically the arteries, in the presence of arterial and/or tissue changes. The model developed in this paper uses a multi-domain energy system approach to develop the lumped-parameter differential equations. Blood flow is modelled as fluidic flow through compliant pipes that have inertia, stiffness, and damping. The tissue material is treated as a soft compliant material that transmits the external force to the blood vessels. Conclusions have been drawn to show the effect of plantar pressure, tissue damage, and their combination on the diameter of the blood vessels. The principles used here can be used to model the entire foot and the model used to investigate the effect of plantar pressure, tissue damage, and arterial changes on different parts of the foot. The work presented here may also have applications in other vascular diseases.     

探讨高血压合并冠心病患者动态血压与心电图的相关性

目的探讨高血压合并冠心病患者的血压波动与ST-T改变及心律失常发生的相关性。方法对88例高血压和/或冠心病患者进行分组研究,其中高血压合并冠心痛组25例,高血压无并发症组28例.冠心病组35例,所有患者均同步监测24h动态血压(ABPM)和动态心电图(DCG),观察不同组血压波动与ST-T改变和心律失常发生的相关性并进行对照分析。结果 ABPM与DCG同步检出高血压合并冠心痛组血压变化与ST-T改变和心律失常发生率为88%,明显高于高血压无并发症组42.9%和冠心病组65.7%,表明高血压合并冠心痛患者血压变化与ST-T改变及心律失常有关联。结论 ABPM与DCG同步检测有助于鉴别血压变化与心脏的关系,对预防心血管事件的发生具有积极的临床意义。     

Influence of different bell-shaped stenoses on the progression of the disease,atherosclerosis

In the present paper, the effect of symmetrical and asymmetrical bell-shaped stenoses on wall pressure drop, streamline contour, and rise in wall shear stress for the progression of the disease, atherosclerosis has been investigated numerically. The governing equations have been solved by finite volume method. Both steady and pulsatile flow at inlet is considered in our study. It is revealed from the study that the impact of wall pressure and peak wall shear stress on progression of disease are always high for asymmetrical shaped stenosis for both steady and pulsatile flow. The impact of asymmetrical shape on plaque deposition zone is less, if the aggravation changes the shape of stenosis due to change in stricture length only keeping percentage of restriction same. Whereas, the impact of asymmetrical shape on plaque deposition zone will be high, if shape of stenosis changes by increasing both stricture length and percentage of restriction for both steady and pulsatile flow. Impact of pulsatile nature of flow on the aggravation of disease is higher at some timesteps in comparison to steady flow.     

基于Fluent的卸压阀内部流场特性数值研究

应用Fluent软件对卸压阀内部流场进行数值仿真分析。以饱和水蒸气为介质,基于壁面函数法和Realizable k-ε湍流模型,分析不同开度、不同进出口压力下阀体内部流速、压力、流量等变化特点。研究表明,随着开度增加,进出口压降呈线性降低,流速变化趋于稳定,出口流量更大。本研究可对卸压阀优化设计提供技术支持。     

高速开关电磁阀力控系统线性增压控制研究

针对防抱死制动系统线性增压需求,建立某高速开关电磁阀阀芯力平衡数学模型,给出阀芯平衡状态附近线性化增量微分表达式,建立液压缸压力变化数学模型,给出液压缸压差的增量表达式,得到高速开关电磁阀力控系统压力和通电电流的传递函数。通过某高速开关电磁阀电磁场和流场的有限元分析,得到阀芯所受电磁力、阀芯所受液压力及流量随阀口开度的变化曲线,研究电磁力、液压力与流量之间的定量关系,阐述高速开关电磁阀力控系统线性增压基本原理,给出力平衡点的稳定条件,提出能够实现线性增压的控制方式;结合流场、电磁场分析结果建立某高速开关阀整体模型,对电磁阀开启过程进行仿真,并进行线性增压试验,验证了该控制方式对于恒流量输出的可行性和仿真计算方法与结果的正确性。     

Design,optimization and numerical simulation of a MicroFlow sensor in the realistic model of human aorta

Among all arterial diseases, aneurysm and atherosclerosis are of great importance. In these diseases the cross-section area of the artery and therefore the blood flow velocity changes. Therefore, it is a good idea to use a micro flow sensor for measuring the blood flow velocity to diagnosing these diseases. In this study, design, geometric optimization and numerical simulation of a hotfilm microsensor in the realistic model of human's aorta are investigated. A normal aorta geometry is extracted from CT Angiography images, and after applying oscillating boundary conditions on the inlet and outlet arteries, blood flow parameters are investigated by computational fluid dynamics (CFD) simulation. After designing the microsensor, the effects of its location in different aorta regions on the blood flow characteristics are numerically investigated. The results show that in the presence of microsensor, streamlines patterns almost remain unchanged while the maximum blood flow velocity in the aorta cross section where the microsensor is located, increases up to 10%. It is also found that the secondary flow weakens when the microsensor enters the artery causing a reduction in velocity measurement error. Furthermore, because of the presence of a catheter, the pressure drop increases up to 768 Pa. Results show that less than 30% of the arterial cross-sectional area where the microsensor is located, senses an increase in temperature.     

Spectral element modeling and analysis of the blood flow through a human blood vessel

As the blood flow characteristics are closely related to various cardiovascular diseases, it is very important to predict them accurate enough in an efficient way. Thus, this paper proposes a one-dimensional spectral element model for human blood vessels with varying cross-sections. The spectral element model is formulated by using the variational approach of finite element formulation. The wave solutions analytically solved in the frequency-domain to satisfy governing equations are used to determine the frequency-dependent interpolation functions. The spectral finite element model is then applied to an example blood vessel to investigate the blood flow rate and blood pressure through the blood vessel.     

Nonlinear model predictive control of a Hammerstein Weiner model based experimental managed pressure drilling setup

Design and implementation of a nonlinear model predictive controller (NMPC) on a pilot scale managed pressure drilling (MPD) setup is demonstrated. The goal of the controller is to maintain constant bottomhole pressure (BHP) and mitigate kick during reservoir influx scenario. Under normal condition, the controller tracks bottomhole pressure to a predefined setpoint. A Hammerstein Weiner nonlinear model has been used for pressure prediction, and genetic optimization algorithm for calculating optimal control input. During reservoir influx the controller switches to flow control mode to balance the pump flow and choke flow. After kick mitigation the controller switches back to pressure regulation mode by revising the setpoint pressure to estimated reservoir pressure. The NMPC controller delivered good performance over PI controller during normal operation, pump failure, and gas kick cases where flow demand changes frequently.     

超声振动辅助电火花铣削间隙流场分析与验证

为研究超声振动对电火花铣削间隙流场的作用,根据流场理论将超声振动辅助电火花铣削间隙流场简化为二维流场,建立间隙流场动力学基本方程并推导出间隙流场在x和y方向的压力变化方程。通过Fluent有限元软件建立二维轴对称旋转仿真模型,验证该方程的正确性。分析了间隙流场交变压力的作用,并进行实验验证。研究结果表明:在超声振动的作用下,加工间隙中电介质沿x和y方向超声频率周期性变化的压力增强了空穴作用,促进了电介质的循环,减少了短路和电弧放电,提高了加工过程的稳定性和加工效率,进而提高工件材料去除率,同时能够减小火花放电凹坑深度,使工件加工表面的熔融金属铺展得更均匀,从而降低工件加工表面粗糙度。