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- Type of Document: M.Sc. Thesis
- Language: Farsi
- Document No: 53982 (08)
- University: Sharif University of Technology
- Department: Mechanical Engineering
- Advisor(s): Fallah Rajabzadeh, Famida
- Abstract:
- Blood vessels are subjected to complex mechanical loads, including internal pressure, external pressure, axial stress due to connection to tissues, and the twist caused by movement of the body. The veins and venous valves, which are responsible for returning blood to the heart, become bent and twisted (tortuosity) for various reasons. This venous tortuosity causes valve insufficiency and changes the hemodynamic pattern of blood flow and varicose veins. Studies show that more than a third of old people suffer from varicose veins. These injuries have made it important to study the physical mechanism of venous tortuosity and the function of venous valves.The purpose of this study is to investigate the displacement behavior of veins (tortuosity) and the effects of this tortuosity on the valves of veins under internal pulsatile pressure using the finite element method. In this research, a three-dimensional and ideal model of a vein with a venous valve has been simulated both as a fluid-solid interaction and as a purely solid with the isotropic hyperelastic wall material (Moony-Rivilin model) and anisotropic hyperelastic wall material (Holzapfel model), and the amount of stress and blood flow pattern around the valve as well as the bending of the vein wall in different stretch ratios have been investigated. The results show that by increasing the blood pressure more than the critical pressure, the vein bends, and with increasing pressure, this displacement increases nonlinearly. Also, it is observed that the fluid-solid interaction model predicts less pressure to start the instability of the vein, and in purely solid simulations with the Holzapfel hyperelastic model, the critical pressure is higher. As the stretch ratio decreases, the critical pressure decreases, and at a certain pressure, the vein bends more with a lower stretch ratio. A vein with a stretch ratio of 1.5 has slight bending at normal pressure, but the excessive displacement of the vein at a stretch ratio of 1.1 leads to abnormal opening of the venous valve, a sharp increase in fluid shear stress, and Von-Mises stress of the valve wall and finally causes the blood not to pass correctly through the valve. This means that as the curvature of the vein wall increases, the amount of valve wall Von-Mises stress and the shear stress increases significantly
- Keywords:
- Stability ; Fluid-Solid Interaction ; Varicose ; Critical Pressure ; Vein Valve ; Varicose Veins
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