Search

Thrombosis is a complex biological process which involves many biochemical reactions and is influenced by blood flow. Various computational models have been developed to simulate natural thrombosis in diseases such as aortic dissection (AD), and device-induced thrombosis in blood-contacting biomedical devices. While most hemodynamics-based models consider the role of low shear stress in the initiation and growth of thrombus, they often ignore the effect of thrombus breakdown induced by elevated shear stress. In this study, a new shear stress-induced thrombus breakdown function is proposed and implemented in our previously published thrombosis model. The performance of the refined model is assessed by quantitative comparison with experimental data on thrombus formation in a backward-facing step geometry, and qualitative comparison with in vivo data obtained from an AD patient. Our results show that incorporating thrombus breakdown improves accuracy in predicted thrombus volume and captures the same pattern of thrombus evolution as measured experimentally and in vivo. In the backward-facing step geometry, thrombus breakdown impedes growth over the step and downstream, allowing a stable thrombus to be reached more quickly. Moreover, the predicted thrombus volume, height and length are in better agreement with the experimental measurements compared to the original model which does not consider thrombus breakdown. In the patient-specific AD, the refined model outperforms the original model in predicting the extent and location of thrombosis. In conclusion, the effect of thrombus breakdown is not negligible and should be included in computational models of thrombosis. [ABSTRACT FROM AUTHOR]

Stent graft-induced new entry tear (SINE) is a serious complication in aortic dissection patients caused by the stent-graft itself after thoracic endovascular aortic repair (TEVAR). The stability of SINE is a key indicator for the need and timing of reinterventions. This study aimed to understand the role of hemodynamics in SINE stability by means of computational fluid dynamics (CFD) analysis based on patient-specific anatomical information. Four patients treated with TEVAR who developed a distal SINE (dSINE) were included; two patients had a stable dSINE and two patients experienced expansion of the dSINE upon follow-up examinations. CFD simulations were performed on geometries reconstructed from computed tomography scans acquired upon early detection of dSINE in these patients. Computational results showed that stable dSINEs presented larger regions with low time-averaged wall shear stress (TAWSS) and high relative residence time (RRT), and partial thrombosis was observed at subsequent follow-ups. Furthermore, significant systolic antegrade flow was observed in the unstable dSINE which also had a larger retrograde flow fraction (RFF) on the SINE plane. In conclusion, this pilot study suggested that high RRT and low TAWSS may indicate stable dSINE by promoting thrombosis, whereas larger RFF and antegrade flows inside dSINE might be associated with its expansion. [ABSTRACT FROM AUTHOR]

Nowadays X70 steel has been used as a core material for the construction of high-pressure, large-diameter and high-strength steel pipelines. The wall of piplines of an operating pipline system will deform in various degrees. Severe deformation will lead to microcracks or even a fracture. The ultrasonic flaw detection method is designed for the detection and evaluation of microcracks and defects caused by the deformation of X70 steel. However, an effective method to measure the stress level of X70 steel accurately is still lacking since the deformation of X70 steel often occurs within the elastic stage or plastic stage. Through conducting an experiment to study the tensile test of X70 steel specimens under a constant temperature, and measuring the propagation time and amplitude of ultrasonic LCR wave simultaneously to conclude the law of the propagation of ultrasonic LCR wave in elastic-plastic deformation of X70 steel, and determine the relationship between the propagation time and the amplitude of ultrasonic LCR wave and the deformation degree of X70 steel. According to the study, the deformation degree of X70 steel could be determined by the propagation time of ultrasonic LCR wave and the amplitude of the first wave: the level of stress could be calculated within the elastic stage and the deformation degree could be calculated within the plastic stage. The study results provide an effective support for the stress measurement of X70 steel by ultrasonic LCR wave. [ABSTRACT FROM AUTHOR]

Air curtain is an effective means to stop the propagation of smoke in buildings to provide smoke-free area for safe egress of occupants in case of fires. To understand its effectiveness of smoke confinement in tunnel fires, full-scale tests were conducted in a tunnel of 140 m long and with varying heights of 5.0 m to 5.9 m and varying widths of 5.8 m to 10.8 m. A 20 cm-wide air curtain spanning entire lateral section was installed underneath the tunnel ceiling. The experiment showed that air curtain at exit velocities of 12 m/s and 16 m/s can stop the propagation of smoke produced by 1 MW fire and 2 MW fire respectively. Numerical simulation using ANSYS FLUENT was then conducted and the numerical results were basically consistent with those of experiment. To explore how the design parameters of air curtain, i.e., the width, the exit velocity and its angle, affect its effectiveness of smoke confinement at varying heat release rates, a number of numerical simulations were further conducted. The relationship of design parameters of air curtain with heat release rates was proposed and it can be used in the design of air curtain in tunnel fires. [ABSTRACT FROM AUTHOR]