Showing 4 results for Wall Shear Stress
Ali Salari, Alireza Sharifi, Hamid Niazmand,
Volume 16, Issue 4 (6-2016)
Abstract
Vertebrobasilar system stenosis is one of the risk factor for deaths caused by stroke, the risk of stenosis in these arteries are highly depend on the people’s age. In the present study, atherosclerosis susceptible sites in vertebrobasilar system at different ages 20, 50 and 70 have been investigated. Numerical method (Fluent software) is employed to solve the equations. Blood flow is simulated in these arteries to investigate probable risky sites (prone to stenosis). To find these locations, critical values of the averaged wall shear stress (AWSS) and oscillatory shear index (OSI) have been studied. By considering the AWSS and OSI criteria in 20 years old person it becomes clear that the risk of stenosis is not considerable at this age, somehow ageing increases OSI figures in the right vertebral artery and in its junction reaching to the critical values, besides at this age, the area of the sites with lower amount of AWSS are stretched significantly. At the age of 70, risky sites are expanded toward right vertebral artery. Furthermore the risk of stenosis in all determined risky sites of age 50 increased at the age of 70.
Hamed Afrasiab, Bahereh Kordrostami,
Volume 16, Issue 5 (7-2016)
Abstract
Stenting is considered to be the favoured tool for therapy of coronary stenosis disease. However, despite the many advantages of this treatment strategy, its outcome may be undermined by the restenosis occurrence in the stent deployment site. Observations have shown that stent deployment in the artery alters the hemodynamic parameters such as wall shear stress and vortices size and prepares the conditions for in-stent restenosis development. Considering this fact, in this paper, the effect of some geometrical parameters such as the shape and the size of the stent strut on the wall shear stress distribution and vortices size is investigated. Furthermore, employment of a stent with partial flexible strut is suggested to decrease the restenosis risk, and the effect of the flexible part stiffness is explored. For this purpose, the interaction between the blood flow and the flexible part is simulated by arbitrary Lagrangian-Eulerian approach in the framework of the finite element method. The results indicate that in stents with circular strut, the partial flexibility of the cross-section can be effective in reducing the restenosis risk by lowering the maximum value of the wall shear stress and considerably decreasing the vortices size. On the other hand, in stents with rectangular struts, it not only does not decrease the shear stress maximum value but also significantly increases the vortices size and may lead to increase of the restenosis risk.
Ghasem Heidarinejad, Mohammad Hosein Roozbahani,
Volume 17, Issue 6 (8-2017)
Abstract
One of the focused problem in airway flow simulation is pulmonary airways modeling. There are two kind of Lung models, one is created anatomically based on bronchial data and second is realistic model which is created based on CT scan images. Unfortunately cause of modeling process or simplification cause of restriction of CPU and time, the result model is different from a really pulmonary airways. Anatomically model are many simplification and realistic model from CT scan have major limitation in CT image resolution and smoothing stage of make out the 3D model. Anyway the lung has many rough and the first thing that is vital on this way is cartilage rings as macro scale roughness. So the presented work, compared the airflow in both simple and modified Horsfield model by cartilage rings in term of time averaged wall shear stress which are important in engineering of Cell-Fluid Interactions (CFI). This is shown that cartilage rings affected the trachea and second generation of brunches so this is not reasonable to neglect the cartilage rings.
F. Niknejad , N. Fatouraee , M. Nabaei ,
Volume 19, Issue 3 (3-2019)
Abstract
Coronary arteries play a vital role in heart nutrition, and if they get stenosis, they will be at risk of developing a heart attack. Coronary artery disease is a progressive disease that is caused by the accumulation of fat particles on the wall of the arteries, leading to thickening of the wall and the formation of layers of plaque on the wall of the arteries and ultimately causing stenosis. In the present study, in order to obtain the effect of percentage and position of stenosis on the pattern of flow and WALL SHEAR STRESS distribution, followed by the progression of atherosclerotic plaques, left coronary artery and its main branches, the anterior and anterior artery, in different conditions according to Medina classification, 50 and 75%, and three different positions of lesion locations based on their distance from carina relative to the center of the branching were modeled. According to the results, WALL SHEAR STRESS and flow ratio and the percentage of inflow into the lateral branch decreased with increasing percentage of stenosis. For example, in Medina type (1.1.1), in 50% diameter stenosis, the flow ratio was 41% of the main branch and it was 37% in 75% diameter stenosis. WALL SHEAR STRESS values are less than 1, even 0.5 Pascal and in critical range in 75% diameter stenosis. Increasing the spacing of the plaque from the center of the branch, the WALL SHEAR STRESS and lateral branch flow ratio increase, and the likelihood of the expansion of the plaque decreases. Based on the development of stenosis severity, modal type (1.0.1) has the highest probability of developing atherosclerotic plaques and total vein occlusion compared to other types of medina.
