Introduction: Venous valves are a type of oneway valves which conduct blood flow toward the heart and prevent its backflow. Any malfunction of these organs may cause serious problems in the circulatory system. Numerical simulation can give us detailed information and point to point data such as velocity, wall shear stress, and von Mises stress from veins with small diameters, as obtaining such data is almost impossible using current medical devices. Having detailed information about fluid flow and valves' function can help the treatment of the related diseases. Methods: In the present work, the blood flow through a venous valve considering the flexibility of the vein wall and valve leaflets is investigated numerically. The governing equations of fluid flow and solid domain are discretized and solved by the Galerkin finite element method. Results: The obtained results showed that the blood velocity increases from inlet to the leaflets and then decreases passing behind the valve. A pair of vortices and the trapped region was observed just behind the valves. These regions have low shear stresses and are capable of sediment formation. Conclusion: The von Mises stress which is a criterion for the breakdown of solid materials was obtained. It was also observed that a maximum value occurred at the bottom of the leaflets.

Excess flow Valves (EFV) for gas-stop systems is generally used in natural gas pipelines to prevent possible damages or destruction due to gas leakage. It can be used in a wide operating range of pressure, but the shut-off flow rate could be in various values at different pressures since natural gas can easily be compressed and can reach higher density. In this study, shut-off and nominal gas flow which effect on a spring force attached to an EFV system simulation by using Fluid Solid Interaction (FSI) strategy was studied. Furthermore, User Define Function (UDF) adapted to simulation to obtain the time-dependent deformation of the spring. The simulations were repeated at five different operating pressures (1-5 bar) with changing flow rates to show if EFV can shut-off the system or not. Results were validated against experimental data of the EFV to show the consistency of the FSI strategy. Moreover, detailed behaviour information of the EFV obtained by means.

Background: The Interaction between the blood and the vessel wall is of great clinical interest in studying cardiovascular diseases, the major causes of death in developed countries.Objective: To understand the effects of incorporating fluid-structure Interaction into the simulation of blood flow through an anatomically realistic model of abdominal aorta and renal arteries reconstructed from CT images.Methods: The fluid is assumed to be incompressible and non-Newtonian and the vessel wall is set to have isotropic elastic properties. The blood flow is assumed to be periodic, therefore, a real pulsatile flow velocity in the entrance of the abdominal aorta of a healthy adult is measured via laser Doppler anemometry and used in this study. The effects of wall flexibility, both rigid and compliant models were also simulated. Results: Comparison of the rigid model with compliant model reveals that velocity and pressure drop in flexible arteries is less than those in rigid arteries. As wall shear stress plays an important role in the function of the cardiovascular system as it has immediate effect on the endothelial histology, the wall shear stress was analyzed, the rigid model wall shear stress magnitude was higher than that in the compliant model. It was also observed that the peak values of wall shear stress in this study were not high enough to be able to damage and strip the endothelial cells. Displacements of vessel walls were also studied, it was found that the wall displacement during the systole was higher than the diastole.Conclusion: Incorporating fluid-structure Interaction and considering vessel wall deformations in studying blood flow through arteries have notable effects on blood flow characteristics.

Thoracic aortic aneurysm (TAA) is a severe cardiovascular disease with a high mortality rate, if left untreated. Clinical observations show that aneurysm growth can be linked to undesirable hemodynamic conditions of the aortic aneurysm. In order to gain more insight on TAA formation, we developed a computational framework in vitro to investigate and compare the flow patterns between pre-aneurismal and post-aneurismal aorta using a deformable wall model. This numerical framework was validated by an in vitro experiment accounting for the patient-specific geometrical features and the physiological conditions. The complex flow behaviors in the pre-aneurismal and post-aneurismal aorta were evaluated experimentally by particle image velocimetry (PIV). Our experimental results demonstrated flow behaviors similar to those observed in the fluid-structure Interaction (FSI) numerical study. We observed a small vortex induced by the non-planarity of pre-aneurismal aorta near the aortic arch in pre-aneurysmal aorta may explain the aneurysm formation at the aortic arch. We found that high endothelial cell action potential (ECAP) correlates with the recirculation regions, which might indicate possible thrombus development. The promising image-based fluid-structure Interaction model, accompanied with an in vitro experimental study, has the potential to be used for performing virtual implantation of newly developed stent graft for treatment of TAA.

Pathological studies have shown that coronary atherosclerotic plaques are more prone to rupture under physical exercise. In this paper, using a fully coupled fluid-structure Interaction (FSI) analysis based on arbitrary Lagrangian- Eulerian (ALE) finite element method, the effect of the coronary blood flow rate increase during physical exercise on the plaque rupture risk is investigated for different plaque types. It is proved that the increase in coronary blood flow rate during physical exercise considerably increases the maximum stress in the plaque fibrous cap which can potentially lead to the plaque rupture. The issue is investigated for different plaque shapes and their vulnerability to exercise condition is compared. It is observed that the diffused plaque type which experiences the maximum stress of 187.9 kPa at rest and 544 kPa at exercise is the most critical plaque type. Because it is subjected to the highest stress in both of these conditions. However, the descending plaque type exhibits the highest susceptibility to physical activity, since its maximum stress increases from 68.9 kPa at rest to 280.5 kPa at exercise which means an increase of about 308%.