Multibody dynamics in arterial system

There are many things in common between hemodynamics in arterial systems and multibody dynamics in mechanical systems Hemodynamics is concerned with the forces generated by the heart and the resulting motion of blood through the multi-branched vascular system The conventional hemodynamics model has been intended to show the general behavior of the body arterial system with the frequency domain based linear model The need for detailed models to analyze the local part like coronary arterial tree and cerebral arterial tree has been required recently Non-linear analysis techniques are well-developed in multibody dynamics In this paper, the studies of hemodynamics are summarized from the view of multibody dynamics Computational algorithms of arterial tree analysis is derived, and proved by experiments on animals The flow and pressure of each branch are calculated from the measured flow data at the ascending aorta The simulated results of the carotid artery and the ihac artery show in good accordance with the measured results     

On the effect of shear-thinning rheology on hemodynamic characteristics in basilar tip aneurysms with implication of two distinct flow patterns

Intra-aneurysmal hemodynamics such as wall shear stress and complex flow structures have been implicated as one of the important factors on the growth and risk of rupture of an aneurysm. In this study, the sensitivity of intra-aneurysmal blood flow dynamics to the shear-thinning rheological model is investigated by using the idealized geometries of a basilar tip aneurysm with two representative anterior-posterior (AP) tilting angles (2° and 30°). By choice of different rheological models, time-averaged hemodynamic factors such as wall shear stress, oscillatory shear index and relative residence time exhibited only minor effects. However, highly unstable flow present in idealized aneurysm model with 2° AP tilting angle facilitated an evident change in the instantaneous local flow dynamics with a considerable increase in effective viscosity. Nevertheless, the distinct hemodynamic phenotype, which characterizes the gross intraaneurysmal flow pattern, was independent of the choice of rheological model. This result suggests that the shear thinning viscous effect is of secondary importance in the gross hemodynamics in a basilar tip aneurysm but is appreciably enhanced on the instantaneous hemodynamics with unstable complex flow structures.     

The effects of the tilt angle of a bileaflet mechanical heart valve on blood flow and leaflet motion

Diseased heart valves can be replaced with bileaflet mechanical heart valves (BMHVs), which may be affected by complications such as hemolysis, platelet activation and device failure. These complications are closely related to the characteristics of blood flow through mechanical valves and leaflet dynamics, and can become worse with tilted implantation of BMHVs. This study simulated the interactions of blood flow and leaflet motion for BMHVs implanted at different tilt angles. A fluid-structure interaction (FSI) method was employed to solve the problems of blood flow and leaflet motion interactively. A validation of the present numerical methods was performed against data produced in a previous work, indicating that the method presented in this study is reliable. Our results reveal detailed blood flow and leaflet motion in an aorta caused by the systole and diastole of the ventricle. As the tilt angle increased, the degree of asymmetry of blood flow and the time delay in the motions of the two different leaflets also increased, which may cause worsening of complications.     

Finite element simulation of blood flow in a flexible carotid artery bifurcation

Numerical simulations for the blood flow are carried out to investigate the effect of the flexible artery wall on the flow field and to determine the wall shear stresses in the carotid artery wall. To solve the equation of motion for the structure in typical fluid-structure interaction (FSI) problems, it is necessary to calculate the fluid force on the surface of the structure explicitly. To avoid complexity due to the necessity of additional mechanical constraints, we use the combined formulation including both the fluid and structure equations of motion into a single coupled variational equation. The Navier-Stokes equations for fluid flow are solved using a P2P1 Galerkin finite element method (FEM) and mesh movement is achieved using arbitrary Lagrangian-Eulerian (ALE) formulation. The Newmark method is employed to solve the dynamic equilibrium equations for linear elastic solid mechanics. The time-dependent, three-dimensional, incompressible flows of Newtonian fluids constrained in the flexible wall are analyzed. The study shows strongly skewed axial velocity and flow separation in the internal carotid artery (ICA). Flow separation results in locally low wall shear stress. Further, strong secondary motion in the ICA is observed.     

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.     

Numerical simulation of the wall shear stress distribution in a carotid artery bifurcation

Journal of Mechanical Science and Technology - The effect of stenosis for a carotid artery bifurcation with elastic and rigid walls is investigated numerically. In the present study, the blood flow...     

Influence of strut cross-section of stents on local hemodynamics in stented arteries

Stenting is a very effective treatment for stenotic vascular diseases, but vascular geometries altered by stent implantation may lead to flow disturbances which play an important role in the initiation and progression of restenosis, especially in the near wall in stented arterial regions. So stent designs have become one of the indispensable factors needed to be considered for reducing the flow disturbances. In this paper, the structural designs of strut cross-section are considered as an aspect of stent designs to be studied in details. Six virtual stents with different strut cross-section are designed for deployments in the same ideal arterial model. Computational fluid dynamics(CFD) methods are performed to study how the shape and the aspect ratio(AR) of strut cross-section modified the local hemodynamics in the stented segments. The results indicate that stents with different strut cross-sections have different influence on the hemodynamics. Stents with streamlined cross-sectional struts for circular arc or elliptical arc can significantly enhance wall shear stress(WSS) in the stented segments, and reduce the flow disturbances around stent struts. The performances of stents with streamlined cross-sectional struts are better than that of stents with non-streamlined cross-sectional struts for rectangle. The results also show that stents with a larger AR cross-section are more conductive to improve the blood flow. The present study provides an understanding of the flow physics in the vicinity of stent struts and indicates that the shape and AR of strut cross-section ought to be considered as important factors to minimize flow disturbance in stent designs.     

减振器节流阀非线性特性的有限元模拟分析

探讨汽车筒式液阻减振器节流阀非线性动态特性的有限元分析方法。利用ADINA有限元分析软件分别建立板阀型节流阀的结构动力学模型和流体动力学模型,并利用其液一固耦合分析模块,对此耦合模型进行瞬态响应分析,得到阀的非线性节流特性、阀板的动态运动响应以及节流阀内流场特性。模拟计算结果与实验结果具有较好的一致性,节流阀在工作时开度很小,液体压力场具有强不均匀性,液体对阀板的作用力也具有不均匀性,板阀型预载阀的节流特性接近于线性,节流通道在大流量下对节流阀的特性有较大影响,     

Dynamic behavior of valve system in linear compressor based on fluid-structure interaction

In refrigerator designs, the linear compressor is preferable to the recipro-type compressor, due to its higher energy efficiency. The linear compressor’s valve system, however, causes significant noise, not only in the steady state but also in the transient state. To accurately predict the behavior of the suction and discharge valve system in both states, the interaction between the fluid flowing through the valves and the structural deformation of the valves needs to be understood. In the present study, the steady-state behaviors of the valve system were numerically analyzed using ADINA software, which takes fluid-structure interaction (FSI) into account. This computational analysis thereafter was experimentally validated. The effects of a pre-load of the conical compression spring on the dynamic characteristics of the valve system also were analyzed.     

Computational study on the hemodynamics of the bypass shunt directly connecting the left ventricle to a coronary artery

A shunt from the left ventricle to the left anterior descending artery is being developed for coronary artery occlusive disease, in which the shunt or conduit connects the the left ventricle (LV) with the diseased artery directly at a point distal to the obstruction. To aid in assessing and optimizing its benefit, a computational model of the cardiovascular system was developed and used to explore various design conditions. Computational fluid dynamic analysis for the shunt hemodynamics was also done using a commercial finite element package. Simulation results indicate that in complete left anterior descending artery (LAD) occlusion, flow can be returned to approximately 65% of normal, if the conduit resistance is equal for forward and reverse flow. The net coronary flow can increase to 80% when the backflow resistance is infinite. The increases in flow rate produced by asymmetric flow resistance are enhanced considerably for a partial LAD obstruction, since the primary effect of resistance asymmetry is to prevent leakage back into the ventricle during diastole. Increased arterial compliance has little effect on net flow with a symmetric shunt, but considerably augments it when the resistance is asymmetric. The computational results suggest that an LV-LAD conduit will be beneficial when the resistance due to artery stenosis exceeds 27 PRU. if the resistance is symmetric. Fluid dynamic simulations for the shunt flow show that a recirculating region generated near the junction of the coronary artery with the bypass shunt. The secondary flow is induced at the cutting plane perpendicular to the axis direction and it is in the attenuated of coronary artery.     

脑梗死患者颈动脉病变超声表现特点及超声的诊断价值

目的:探讨脑梗死患者颈动脉病变超声表现特点,分析彩色多普勒超声诊断脑梗死的价值。方法:选择2017年2月至2019年6月我院收治的102例脑梗死患者(脑梗死组)和同期门诊和住院部接诊的93例非心脑血管疾病患者(对照组),均进行颈动脉二维灰阶和彩色多普勒超声检查,比较两组颈动脉斑块检出、分布、斑块性质、颈动脉狭窄率以及颈动脉血流参数[动脉收缩期峰值流速(PSV)、舒张期血流速度(EDV)和平均血流速度(Vean)]差异。受试者工作特征曲线(ROC)分析彩色超声多普勒血流参数诊断脑梗死的价值。结果:脑梗死组共检出颈动脉斑块175块,对照组31块,观察组平均每人检出斑块数块高于对照组[(1.21±0.33)VS(0.30±0.09)块,P<0.05],两组斑块分布均以颈动脉分叉处居多(50.68%、65.52%),差异无统计学差异(P>0.05)。脑梗死组颈动脉内-中膜厚度(IMT)分布以有斑块形成和可造成颈动脉狭窄为主(73.53%),对照组以IMT正常和单纯内膜增厚为主(69.90%),两组IMT分布差异显著(P<0.05)。脑梗死组颈动脉斑块以易损斑块为主(60.57%),对照组颈动脉斑块以稳定性斑块为主(93.55%),两组斑块性质差异显著(P<0.05),脑梗死组颈动脉狭窄率高于对照组[(42.12±6.35)%VS(12.01±3.14)%,P<0.05]。脑梗死组颈PSV、EDV、Vean均小于对照组(P<0.05),PI、RI大于对照组(P<0.05)。ROC分析结果显示PSV、EDV、Vean、PI、RI诊断脑梗死的曲线下面积(AUC)分别为0.826、0.659、0.662、0.852、0.612,灵敏度分别为70.59%、59.80%、61.76%、73.53%、58.82%,特异度分别为80.65%、73.11%、70.97%、82.80%、67.74%。结论:脑梗死患者存在明显的颈动脉粥样硬化斑块形成和血流动力学改变,彩色多普勒超声血流参数对脑梗死的诊断具有较高应用价值。     

Numerical Investigation on Fluid Structure Interaction Considering Rotor Deformation for a Centrifugal Pump

The existing research for unsteady flow field and the corresponding flow induced vibration analysis of centrifugal pump are mainly carried out respectively without considering the interaction between fluid and structure. The ignorance of fluid structure interaction (FSI) means that the energy transfer between fluid and structure is neglected. To some extent, the accuracy and reliability of unsteady flow and rotor deflection analysis should be affected by this interaction mechanism. In this paper, a combined...     

Mechanical behavior of arteries under inflation and extension

In order to understand the blood vessel of artery responding to medical treatments, there is a need to quantify the biomechanical behavior of the vessel. Using video dimension analyser, mechanical pressure-diameter relationships of passive carotid artery with and without balloon inflated at various axial loads were measured. Inversion test was also analytically modeled to address the heterogeneity of artery due to constituents. The pressure-diameter curves and stress distribution across the arterial wall were calculated. The simulation showed that the inversion tests, in comparison to other mechanical tests, provided additional information to develop the strain energy function describing arterial behavior     

Significance of hemodynamic effects on the generation of atherosclerosis

Atherosclerosis, which is a degenerative vascular disease, is believed to occur in the blood vessels due to deposition of cholesterol or low density hpoprotein (LDL) Atherosclerotic lumen narrowing causes reduction of blood flow due to hemodynamic features Several hypothetical theories related to the hemodynamic effects have been reported. high shear stress theory, low shear stress theory, high shear stress gradient theory, flow separation and turbulence theory, and high pressure theory However, no one theory clearly explains the causes of atherosclerosis The objective of the present study was to investigate the mechanism of the generation of atherosclerosis In the study, the database of Korean carotid and coronary arteries for geometrical and hemodynamic clinical data was established The atherosclerotic sites were predicted by the computer simulations. The results of the computer simulation were compared with the in vivo experimental results, and then the pathogenesis of atherosclerosis by using the clinical data and several hypothetical theories were investigated From the investigation, it was concluded carefully that the mechanism of the generation of atherosclerosis was related to the hemodynamic effects such as flow separation and oscillatory wall shear stress on the vessel walls     

A structural analysis on the leaflet motion induced by the blood flow for design of a bileaflet mechanical heart valve prosthesis

This paper presents a structural analysis on the rigid and deformed motion of the leaflet induced by the blood flow required in the design of a bileaflet mechanical heart valve (MHV) prosthesis. In the study on the design and the mechanical characteristics of a bileaflet mechanical heart valve, the fluid mechanics analysis on the blood flow passing through leaflets, the kinetodynamics analysis on the rigid body motion of the leaflet induced by the pulsatile blood flow, and the structural mechanics analysis on the deformed motion of the leaflet are required sequentially and simultaneously. Fluid forces computed in the previous hemodynamics analysis on the blood flow are used in the kinetodynamics analysis on the rigid body motion of the leaflet. Thereafter, the structural mechanics analysis on the deformed motion of the leaflet follows to predict the structural strength variation of the leaflet as the leaflet thickness changes. Analysis results show that structural deformations and stresses increase as the fluid pressure increases and the leaflet thickness decreases. Analysis results also show that the leaflet becomes structurally weaker and weaker as the leaflet thickness becomes smaller than 0.6 mm.     

冲击气流作用下放空管道流固耦合动力学分析

为了解决某装气站放空管线排气放空时引起的管路振动问题,建立流固耦合三维动力有限元模型,采用瞬态时间历程分析方法对放空管道进行冲击气流下管道动力响应仿真分析。其中管道内流体分别选择氮气和液化气,建立现有管道流固耦合三维动力有限元模型;进行2种流体介质下管道结构动力响应对比。通过研究管道在冲击气流作用下的振动机理和振动特性,从管道结构入手提出了该放空管道振动控制的措施,给出了减振方案。建立减振方案中管道的流固耦合动力有限元模型,进行仿真分析并与原方案计算结果进行了对比,发现管道系统的振动得到大幅度的降低,验证了所提出的减振方案可以对管道振动进行合理有效的控制,确保了管道振动幅度在安全裕度内。     

A venous pulse Doppler catheter-tip flowmeter for measuring arterial blood velocity, flow, and diameter in deep arteries.

Numerous schemes have been used for measuring hemodynamic properties of deeply lying arteries; however, all have their limitations. This paper describes a new relatively nontraumatic intravenous approach that uses a catheter in connection with a pulsed ultrasonic Doppler velocity meter (PUDVM) and an echo track. The catheter was initially tested in a hydraulic model system for calibration of velocity and flow parameters. Lately, the catheter has permittted measurements of local instantaneous blood velocity, flow, and wall motion characteristics in adult Beagle dogs in the abdominal aorta and iliac artery. Evaluation studies have been conducted to compare the catheter-tip recordings with an independent method for measuring blood flow and wall motion. Coupling of this catheter-tip device with the PUDVM and echo track provides chronic measurements of hemodynamic parameters in these deep vessels which were virtually impossible to obtain previously. This technique may prove useful in monitoring vessel pathology longitudinally as well as in basic experimental situations requiring flow and arterial wall mechanical properties.     

Elastohydrodynamic Analysis of a Rotary Lip Seal Using Flow Factors

An elastohydrodynamic analysis of a rotary lip seal is performed numerically, incorporating both the fluid mechanics of the lubricating film and the elastic deformation of the lip. Asperities on the lip surface dominate the behavior of the flow field in the lubricating film and are taken into account through the use of flow factors. Because previous analyses treated those asperities deterministically, they required very large computation times. The present approach is much less computationally intensive because the asperities are treated statistically. Because cavitation and asperity orientation play important roles, these are taken into account in the computation of the flow factors. An asperity distortion analysis is introduced to model the complex variations in the asperity distribution on the surface of the lip. Results of the analysis show how the operating parameters of the seal and the characteristics of the asperities affect such seal characteristics as the thickness of the lubricating film, reverse pumping rate, power dissipation, and liftoff speed.     

SCR系统隔膜泵瞬态流量特性分析

隔膜泵是Urea-SCR系统中使用最广泛使用的动力单元,其流量稳定性对系统计量精度有较大影响。受隔膜易变形及配流阀参数的影响,隔膜泵瞬时流量易出现较大波动。要避免或减小这种瞬时流量波动现象,必须进行隔膜泵动态特性分析。鉴于隔膜泵结构及材料特点,提出了一种双向FSI模型,经试验验证,该模型可有效预测隔膜泵动态特性。分析结果显示,减小压出阀弹簧刚度、压出阀阀芯质量及压出阀开启压力均可在一定程度上减小隔膜泵瞬时流量波动现象。所采用方法及所得结果可为相近产品的分析提供理论参考。     

Fluid-structure coupling effects on periodically transient flow of a single-blade sewage centrifugal pump

A partitioned fluid-structure interaction (FSI) solving strategy that depends on problem characteristics is applied to quantitatively obtain the coupling effects of a fluid-structure system in a single-blade centrifugal pump on the unsteady flow. A two-way coupling method is employed to realize strong FSI effects in the calculation procedure. The successful impeller oscillation measurement using two proximity sensors validated the FSI simulation accuracy in a complicated and practical fluid-structure system having a rotating component. The results show that the hydrodynamic force deviation can be observed in the results for the coupled versus uncoupled cases. Additionally, the coupled unsteady pressure is larger than the uncoupled value for every monitoring point at every impeller rotation position. Comparison results for different monitoring points under an overload condition and partial-load condition display the same regularities. To some extent, this interaction mechanism would affect the accuracy and reliability of the unsteady flow and rotor deflection analysis.