The management of severe tricuspid regurgitation(TR)in elderly patients has been transformed by transcatheter edge-to-edge repair(TEER),now a cornerstone for those at prohibitive surgical risk.[1]However,with increasi...The management of severe tricuspid regurgitation(TR)in elderly patients has been transformed by transcatheter edge-to-edge repair(TEER),now a cornerstone for those at prohibitive surgical risk.[1]However,with increasing procedural volumes,recurrent TR after TEER is emerging as a relevant clinical challenge.[2]Although three-dimensional(3D)echocardiography provides superior characterization of complex post-procedural orifices,its role in guiding the difficult decision between redo intervention and conservative management in octogenarians remains insufficiently defined.[3,4]展开更多
Mixing processes of hot and cold fluids in a tee with and without sin- tered copper spheres are simulated by FLUENT using the large-eddy simulation (LES) turbulent flow model and the sub-grid scale (SGS) Smagorins...Mixing processes of hot and cold fluids in a tee with and without sin- tered copper spheres are simulated by FLUENT using the large-eddy simulation (LES) turbulent flow model and the sub-grid scale (SGS) Smagorinsky-Lilly (SL) model with buoyancy. Comparisons of numerical results of the two cases with and without sintered copper spheres show that the porous medium significantly reduces velocity and temper- ature fluctuations because the porous medium can effectively restrict the fluid flow and enhance heat transfer. The porous medium obviously increases the pressure drop in the main duct. The porous medium reduces the power spectrum density (PSD) of tempera- ture fluctuations in the frequency range from 1 Hz to 10 Hz.展开更多
The temperature fluctuation caused by thermal striping phenomena of hot and cold fluids mixing results in cyclical thermal stress fatigue failure of the pipe wall. Mean temperature difference between hot and cold flui...The temperature fluctuation caused by thermal striping phenomena of hot and cold fluids mixing results in cyclical thermal stress fatigue failure of the pipe wall. Mean temperature difference between hot and cold fluids was often used as thermal load in previous analysis of thermal fatigue failure, thereby the influences of the amplitude and frequency of temperature fluctuation on thermal fatigue failure were neglected. Based on the mechanism of flow and heat transfer which induces thermal fatigue, the turbulent mixing of hot and cold water in a tee junction is simulated with FLUENT platform by using the Large-eddy simulation(LES) turbulent flow model with the sub-grid scale(SGS) model of Smagorinsky-Lilly(SL) to capture the amplitude and frequency of temperature fluctuation. In a simulation case, hot water with temperature of 343.48 K and velocity of 0.15 m/s enters the horizontal main duct with the side length of 100 mm, while cold water with temperature of 296.78 K and velocity of 0.3 m/s enters the vertical branch duct with the side length of 50 mm. The numerical results show that the mean and fluctuating temperatures are in good agreement with the previous experimental data, which describes numerical simulation with high reliability and accuracy; the power spectrum density(PSD) on top wall is higher than that on bottom wall(as the frequency less than 1 Hz), while the PSD on bottom wall is relatively higher than that on top wall (as the frequency of 1-10Hz). The temperature fluctuations in full mixing region of the tee junction can be accurately captured by LES and can provide the theoretical basis for the thermal stress and thermal fatigue analyses.展开更多
This paper deals with static pull and push bending tests on two-dimensional (2D) orthogonal EW220/5284 twill weave fabric (TWF) composite tee-joints processed with the resin transfer moulding (RTM) technique. St...This paper deals with static pull and push bending tests on two-dimensional (2D) orthogonal EW220/5284 twill weave fabric (TWF) composite tee-joints processed with the resin transfer moulding (RTM) technique. Static pull and push bending properties are determined and failure initiation mechanism is deduced from experimental observations. The experiments show that the failure initiation load, on average, is greater for push bending than for pull bending, whereas the scatter is smaller for push bending than for pull bending. The failure mode of RTM-made tee-joints in pull bending tests can be reckoned to be characteristic of debonding of resin matrix at the interface between the triangular resin-rich zone and the curved web of tee-joint until complete separation of the curved web from the bottom plate. In contrast, as distinct from the products subject to pull bending loading, the RTM tee-joints in push bending tests experience matrix cracking and fibre fracture from outer layers to inner layers of the bottom plate until catastrophic collapse resulting from the bending. Three-dimensional finite element (FE) models are presented to simulate the load transfer path and failure initiation mechanism of RTM-made TWF composite tee-joint based on the maximum stress criterion. Good correlation between experimental and numerical results is achieved.展开更多
摘要The management of severe tricuspid regurgitation(TR)in elderly patients has been transformed by transcatheter edge-to-edge repair(TEER),now a cornerstone for those at prohibitive surgical risk.[1]However,with increasing procedural volumes,recurrent TR after TEER is emerging as a relevant clinical challenge.[2]Although three-dimensional(3D)echocardiography provides superior characterization of complex post-procedural orifices,its role in guiding the difficult decision between redo intervention and conservative management in octogenarians remains insufficiently defined.[3,4]
基金supported by the National Natural Science Foundation of China (No. 50906002)the National Basic Research Program of China (No. 2011CB706900)+1 种基金the Research Fund for the Doctoral Program of Higher Education of China (No. 20090010110006)the Beijing Novel Program of China (No. 2008B16)
摘要Mixing processes of hot and cold fluids in a tee with and without sin- tered copper spheres are simulated by FLUENT using the large-eddy simulation (LES) turbulent flow model and the sub-grid scale (SGS) Smagorinsky-Lilly (SL) model with buoyancy. Comparisons of numerical results of the two cases with and without sintered copper spheres show that the porous medium significantly reduces velocity and temper- ature fluctuations because the porous medium can effectively restrict the fluid flow and enhance heat transfer. The porous medium obviously increases the pressure drop in the main duct. The porous medium reduces the power spectrum density (PSD) of tempera- ture fluctuations in the frequency range from 1 Hz to 10 Hz.
基金supported by National Natural Science Foundation of China(Grant No. 50906002)National Basic Research Program of China(973 Program, Grant No. 2011CB706900)Beijing Novel Program of China(Grant No. 2008B16)
摘要The temperature fluctuation caused by thermal striping phenomena of hot and cold fluids mixing results in cyclical thermal stress fatigue failure of the pipe wall. Mean temperature difference between hot and cold fluids was often used as thermal load in previous analysis of thermal fatigue failure, thereby the influences of the amplitude and frequency of temperature fluctuation on thermal fatigue failure were neglected. Based on the mechanism of flow and heat transfer which induces thermal fatigue, the turbulent mixing of hot and cold water in a tee junction is simulated with FLUENT platform by using the Large-eddy simulation(LES) turbulent flow model with the sub-grid scale(SGS) model of Smagorinsky-Lilly(SL) to capture the amplitude and frequency of temperature fluctuation. In a simulation case, hot water with temperature of 343.48 K and velocity of 0.15 m/s enters the horizontal main duct with the side length of 100 mm, while cold water with temperature of 296.78 K and velocity of 0.3 m/s enters the vertical branch duct with the side length of 50 mm. The numerical results show that the mean and fluctuating temperatures are in good agreement with the previous experimental data, which describes numerical simulation with high reliability and accuracy; the power spectrum density(PSD) on top wall is higher than that on bottom wall(as the frequency less than 1 Hz), while the PSD on bottom wall is relatively higher than that on top wall (as the frequency of 1-10Hz). The temperature fluctuations in full mixing region of the tee junction can be accurately captured by LES and can provide the theoretical basis for the thermal stress and thermal fatigue analyses.
基金National Natural Science Foundation of China (E050603)Aeronautical Science Foundation of China (20095251024)
摘要This paper deals with static pull and push bending tests on two-dimensional (2D) orthogonal EW220/5284 twill weave fabric (TWF) composite tee-joints processed with the resin transfer moulding (RTM) technique. Static pull and push bending properties are determined and failure initiation mechanism is deduced from experimental observations. The experiments show that the failure initiation load, on average, is greater for push bending than for pull bending, whereas the scatter is smaller for push bending than for pull bending. The failure mode of RTM-made tee-joints in pull bending tests can be reckoned to be characteristic of debonding of resin matrix at the interface between the triangular resin-rich zone and the curved web of tee-joint until complete separation of the curved web from the bottom plate. In contrast, as distinct from the products subject to pull bending loading, the RTM tee-joints in push bending tests experience matrix cracking and fibre fracture from outer layers to inner layers of the bottom plate until catastrophic collapse resulting from the bending. Three-dimensional finite element (FE) models are presented to simulate the load transfer path and failure initiation mechanism of RTM-made TWF composite tee-joint based on the maximum stress criterion. Good correlation between experimental and numerical results is achieved.