The global wall shear stress measurement technique using shear-sensitive liquid crystal (SSLC) is extended to wind tunnel measurements. Simple and common everyday equipment is used in the measurement; in particular a ...The global wall shear stress measurement technique using shear-sensitive liquid crystal (SSLC) is extended to wind tunnel measurements. Simple and common everyday equipment is used in the measurement; in particular a tungsten-halogen light bulb provides illumination and a saturation of SSLC coating color change with time is found. Spatial wall shear stress distributions of several typical flows are obtained using this technique, including wall-jet flow, vortex flow generated by a delta wing and junction flow behind a thin cylinder, although the magnitudes are not fully calibrated. The results demonstrate that SSLC technique can be extended to wind tunnel measurements with no complicated facilities used.展开更多
Experiments were conducted in a U-shaped open-channel flume with the intention of investigating the bursting phenomena in the meander channel. The experimental results of the secondary flow fields and the Reynolds she...Experiments were conducted in a U-shaped open-channel flume with the intention of investigating the bursting phenomena in the meander channel. The experimental results of the secondary flow fields and the Reynolds shear stress distributions show that the velocity and velocity fluctuation in the transverse direction are not negligible. Moreover, the bursting process is investigated using the three-dimensional quadrant analysis, which is more accurate than using the traditional two-dimensional quadrant analysis for the meandering channel. It is obtained from the experimental results that the internal group of events occurs more frequently than the external group, particularly the internal ejection and internal sweep events. In addition, the transition probabilities of the movements, which are defined as the changes of events from the current situation to the next situation in a time series, show that the stable organizations of events are the most possible movements, whereas the cross organizations of events have the least possible movements.展开更多
The steady two-dimensional magnetohydrodynamic stagnation flow towards a nonlinear stretching surface is studied. The no-slip condition on the solid boundary is replaced with a partial slip condition. A scaling group ...The steady two-dimensional magnetohydrodynamic stagnation flow towards a nonlinear stretching surface is studied. The no-slip condition on the solid boundary is replaced with a partial slip condition. A scaling group transformation is used to get the invariants. Using the invariants, a third-order ordinary differential equation corresponding to the momentum is obtained. An analytical solution is obtained in a series form using a homotopy analysis method. Reliability and efficiency of series solutions are shown by the good agreement with numerical results presented in the literature. The effects of the slip parameter, the magnetic field parameter, the velocity ratio parameter, the suction velocity parameter, and the power law exponent on the flow are investigated. The results show that the velocity and shear stress profiles are greatly influenced by these parameters.展开更多
For the better use of composites and a deeper insight into the fracture propagation and stress transfer of the interface between fiber and matrix, a theoretical solution of closed form is presented with the assumed bi...For the better use of composites and a deeper insight into the fracture propagation and stress transfer of the interface between fiber and matrix, a theoretical solution of closed form is presented with the assumed bilinear local bond-slip law and a parabolic shear stress distribution along the thickness of the matrix. The load-displacement relationship and interfacial shear stress are obtained for four loading stages. Finally, the effects of Young's modulus of fiber(matrix) and bond length on the performance of the interface are illustrated.展开更多
Residual stresses and deformation of static bonding multi-layer Pyrex7740 glass and aluminum have important effects on performances of bonding parts. The stress and strain finite element analysis of anodic bonding can...Residual stresses and deformation of static bonding multi-layer Pyrex7740 glass and aluminum have important effects on performances of bonding parts. The stress and strain finite element analysis of anodic bonding can optimize the structure and process design, reduce the workload of the experiments, shorten the production cycle, improve the bonding quality, and reduce the process costs. In this paper, residual stresses and deformation in the static bonding two-layer(glass/aluminum), three-layer(glass/aluminum/glass),five-layer(glass/aluminum/glass/aluminum/glass)and seven-layer(glass/aluminum/glass/aluminum/glass/aluminum/glass) samples have been analyzed using nonlinear finite element simulation software MARC. The simulation results show that the shear stress distribution and deformation distribution in different multi-layer glass and aluminum samples are similar. The stress distribution along thickness at different typical positions in all multi-layer samples has characteristics of pulse pattern, which has pulse peak at the position of transition layers and then decreases abruptly to the minimum value at the positions of glass and aluminum. The maximum shear stress is located in the outside surface area in the transition layer between the top unconstrained glass layer and aluminum layer. The displacement distribution along thickness in all multi-layer samples increases gradually from the constrained bottom glass layer to the top unconstrained glass layer with abrupt step increase in the aluminum layers. The maximum deformations occur in aluminum layers. It is found that the minimum deformation distortion and the minimum shear stress occur in the three-layer static bonding sample.展开更多
The numerical simulation of the axial flow impeller blood pump NIVADIII is carried out by using a CFD multiphase flow model. The hydrodynamic performance of the pump and the flow field in the pump are analyzed, and th...The numerical simulation of the axial flow impeller blood pump NIVADIII is carried out by using a CFD multiphase flow model. The hydrodynamic performance of the pump and the flow field in the pump are analyzed, and the shear stress distribution is obtained. A hemolytic prediction model based on the shear stress is built based on the calculation results, and it can be used for quantitative predictions of the hemolytic behavior of a blood pump. Hemolysis tests in vitro were performed 6 times with fresh bovine blood. At each time, the flow of the pump NIVADIII is 5 L/min and the outflow tract pressure is 100 mmHg. According to the tests, the plasma free hemoglobin (FHB) content and the hematocrit (HCT) are measured after 0 s, 0.5 s, 1 s, 1.5 s, …4 s. At the end of each experiment Normal Index of Hemolysis (NIH) of NIVADIII is calculated. The average of NIH is 0.0055 g/100L, almost identical with that obtained from the hemolytic prediction model. This method can be applied in the selection stage of a blood pump.展开更多
It is well known that hemodynamics and wall tension play an important role in the formation,growth and rupture of aneurysms.In the present study,the authors investigated the influence of parent artery segmentation and...It is well known that hemodynamics and wall tension play an important role in the formation,growth and rupture of aneurysms.In the present study,the authors investigated the influence of parent artery segmentation and aneurismal-wall elasticity on patient-specific hemodynamic simulations with two patient-specific cases of cerebral aneurysms.Realistic models of the aneurysms were constructed from 3-D angiography images and blood flow dynamics was studied under physiologically representative waveform of inflow.For each aneurysm three computational models were constructed:Model 1 with more extensive upstream parent artery with the rigid arterial and aneurismal wall,Model 2 with the partial upstream parent artery with the elastic arterial and aneurismal wall,Model 3 with more extensive upstream parent artery with the rigid wall for arterial wall far from the aneurysm and the elastic wall for arterial wall near the aneurysm.The results show that Model 1 could predict complex intra-aneurismal flow patterns and wall shear stress distribution in the aneurysm,but is unable to give aneurismal wall deformation and tension,Model 2 demonstrates aneurismal wall deformation and tension,but fails to properly model inflow pattern contributed by the upstream parent artery,resulting in local misunderstanding Wall Shear Stress (WSS) distribution,Model 3 can overcome limitations of the former two models,and give an overall and accurate analysis on intra-aneurismal flow patterns,wall shear stress distribution,aneurismal-wall deformation and tension.Therefore we suggest that the proper length of extensive upstream parent artery and aneurismal-wall elasticity should be considered carefully in establishing computational model to predict the intra-aneurismal hemodynamic and wall tension.展开更多
The present paper reports the results of a detailed experimental study aimed at investigating the dynamics of a laminar separation bubble, from the origin of separation up to the breakdown to turbulence of the large s...The present paper reports the results of a detailed experimental study aimed at investigating the dynamics of a laminar separation bubble, from the origin of separation up to the breakdown to turbulence of the large scale coherent structures generated as a consequence of the Kelvin-Helmholtz instability process. Measurements have been performed along a flat plate installed within a double contoured test section, designed to produce an adverse pressure gradient typical of Ultra-High-Lift turbine blade profiles, which induces the formation of a laminar separation bubble at low Reynolds number condition. Measurements have been carried out by means of complementary techniques: hot-wire(HW) anemometry, Laser Doppler Velocimetry(LDV) and Particle Image Velocimetry(PIV). The high accuracy 2-dimensional LDV results allow investigating reverse flow magnitude and both Reynolds normal and shear stress distributions along the separated flow region, while the high frequency response of the HW anemometer allows analyzing the amplification process of flow oscillations induced by instability mechanisms. PIV results complement the flow field analysis providing information on the generation and evolution of the large scale coherent structures shed as a consequence of the separated shear layer roll-up, through instantaneous velocity vector maps. The simultaneous analysis of the data obtained by means of the different measuring techniques allows an in depth view of the instability mechanisms involved in the transition/reattachment processes of the separated shear layer.展开更多
基金the Doctorate Creation Foundation of Northwestern Polytechnical University (CX200902)
文摘The global wall shear stress measurement technique using shear-sensitive liquid crystal (SSLC) is extended to wind tunnel measurements. Simple and common everyday equipment is used in the measurement; in particular a tungsten-halogen light bulb provides illumination and a saturation of SSLC coating color change with time is found. Spatial wall shear stress distributions of several typical flows are obtained using this technique, including wall-jet flow, vortex flow generated by a delta wing and junction flow behind a thin cylinder, although the magnitudes are not fully calibrated. The results demonstrate that SSLC technique can be extended to wind tunnel measurements with no complicated facilities used.
基金Supported by National Natural Science Foundation of China(No.50979066 and No.51279124)Foundation for Creative Research Groups of National Natural Science Foundation of China(No.51021004)
文摘Experiments were conducted in a U-shaped open-channel flume with the intention of investigating the bursting phenomena in the meander channel. The experimental results of the secondary flow fields and the Reynolds shear stress distributions show that the velocity and velocity fluctuation in the transverse direction are not negligible. Moreover, the bursting process is investigated using the three-dimensional quadrant analysis, which is more accurate than using the traditional two-dimensional quadrant analysis for the meandering channel. It is obtained from the experimental results that the internal group of events occurs more frequently than the external group, particularly the internal ejection and internal sweep events. In addition, the transition probabilities of the movements, which are defined as the changes of events from the current situation to the next situation in a time series, show that the stable organizations of events are the most possible movements, whereas the cross organizations of events have the least possible movements.
基金Project supported by the National Natural Science Foundation of China (No. 50936003)the Open Project of State Key Laboratory for Advanced Metals and Materials and the Research Foundation of Engineering Research Institute of University of Science and Technology Beijing (No. 2009Z-02)
文摘The steady two-dimensional magnetohydrodynamic stagnation flow towards a nonlinear stretching surface is studied. The no-slip condition on the solid boundary is replaced with a partial slip condition. A scaling group transformation is used to get the invariants. Using the invariants, a third-order ordinary differential equation corresponding to the momentum is obtained. An analytical solution is obtained in a series form using a homotopy analysis method. Reliability and efficiency of series solutions are shown by the good agreement with numerical results presented in the literature. The effects of the slip parameter, the magnetic field parameter, the velocity ratio parameter, the suction velocity parameter, and the power law exponent on the flow are investigated. The results show that the velocity and shear stress profiles are greatly influenced by these parameters.
基金Project supported by the National Natural Science Foundation of China(No.11032005)the Science and Technology Scheme of Guangdong Province(No.2012A030200003)the Science and Technology Scheme of Guangzhou City(No.1563000451)
文摘For the better use of composites and a deeper insight into the fracture propagation and stress transfer of the interface between fiber and matrix, a theoretical solution of closed form is presented with the assumed bilinear local bond-slip law and a parabolic shear stress distribution along the thickness of the matrix. The load-displacement relationship and interfacial shear stress are obtained for four loading stages. Finally, the effects of Young's modulus of fiber(matrix) and bond length on the performance of the interface are illustrated.
基金Supported by the National Natural Science Foundation of China(No.51275332)Shanxi Graduate Outstanding Innovative Projects(No.20123104)
文摘Residual stresses and deformation of static bonding multi-layer Pyrex7740 glass and aluminum have important effects on performances of bonding parts. The stress and strain finite element analysis of anodic bonding can optimize the structure and process design, reduce the workload of the experiments, shorten the production cycle, improve the bonding quality, and reduce the process costs. In this paper, residual stresses and deformation in the static bonding two-layer(glass/aluminum), three-layer(glass/aluminum/glass),five-layer(glass/aluminum/glass/aluminum/glass)and seven-layer(glass/aluminum/glass/aluminum/glass/aluminum/glass) samples have been analyzed using nonlinear finite element simulation software MARC. The simulation results show that the shear stress distribution and deformation distribution in different multi-layer glass and aluminum samples are similar. The stress distribution along thickness at different typical positions in all multi-layer samples has characteristics of pulse pattern, which has pulse peak at the position of transition layers and then decreases abruptly to the minimum value at the positions of glass and aluminum. The maximum shear stress is located in the outside surface area in the transition layer between the top unconstrained glass layer and aluminum layer. The displacement distribution along thickness in all multi-layer samples increases gradually from the constrained bottom glass layer to the top unconstrained glass layer with abrupt step increase in the aluminum layers. The maximum deformations occur in aluminum layers. It is found that the minimum deformation distortion and the minimum shear stress occur in the three-layer static bonding sample.
基金Project supported by the National High Technology Research and Development Program of China (863 Program,Grant No. 2007AA02Z439)The Key Disciplines Group Construction Project of Pudong Health Bureau of Shanghai (Grant No. PKzxkq2010-01)the Outstanding Leaders Training Program of Pudong Health Bureau of Shanghai (Grant No.PKR2011-01)
文摘The numerical simulation of the axial flow impeller blood pump NIVADIII is carried out by using a CFD multiphase flow model. The hydrodynamic performance of the pump and the flow field in the pump are analyzed, and the shear stress distribution is obtained. A hemolytic prediction model based on the shear stress is built based on the calculation results, and it can be used for quantitative predictions of the hemolytic behavior of a blood pump. Hemolysis tests in vitro were performed 6 times with fresh bovine blood. At each time, the flow of the pump NIVADIII is 5 L/min and the outflow tract pressure is 100 mmHg. According to the tests, the plasma free hemoglobin (FHB) content and the hematocrit (HCT) are measured after 0 s, 0.5 s, 1 s, 1.5 s, …4 s. At the end of each experiment Normal Index of Hemolysis (NIH) of NIVADIII is calculated. The average of NIH is 0.0055 g/100L, almost identical with that obtained from the hemolytic prediction model. This method can be applied in the selection stage of a blood pump.
基金supported by the Natioanal Natural Sience Foundation of China (Grant No. 30772234)the Shanghai Leading Academic Discipline Project (Grant No. B112)
文摘It is well known that hemodynamics and wall tension play an important role in the formation,growth and rupture of aneurysms.In the present study,the authors investigated the influence of parent artery segmentation and aneurismal-wall elasticity on patient-specific hemodynamic simulations with two patient-specific cases of cerebral aneurysms.Realistic models of the aneurysms were constructed from 3-D angiography images and blood flow dynamics was studied under physiologically representative waveform of inflow.For each aneurysm three computational models were constructed:Model 1 with more extensive upstream parent artery with the rigid arterial and aneurismal wall,Model 2 with the partial upstream parent artery with the elastic arterial and aneurismal wall,Model 3 with more extensive upstream parent artery with the rigid wall for arterial wall far from the aneurysm and the elastic wall for arterial wall near the aneurysm.The results show that Model 1 could predict complex intra-aneurismal flow patterns and wall shear stress distribution in the aneurysm,but is unable to give aneurismal wall deformation and tension,Model 2 demonstrates aneurismal wall deformation and tension,but fails to properly model inflow pattern contributed by the upstream parent artery,resulting in local misunderstanding Wall Shear Stress (WSS) distribution,Model 3 can overcome limitations of the former two models,and give an overall and accurate analysis on intra-aneurismal flow patterns,wall shear stress distribution,aneurismal-wall deformation and tension.Therefore we suggest that the proper length of extensive upstream parent artery and aneurismal-wall elasticity should be considered carefully in establishing computational model to predict the intra-aneurismal hemodynamic and wall tension.
文摘The present paper reports the results of a detailed experimental study aimed at investigating the dynamics of a laminar separation bubble, from the origin of separation up to the breakdown to turbulence of the large scale coherent structures generated as a consequence of the Kelvin-Helmholtz instability process. Measurements have been performed along a flat plate installed within a double contoured test section, designed to produce an adverse pressure gradient typical of Ultra-High-Lift turbine blade profiles, which induces the formation of a laminar separation bubble at low Reynolds number condition. Measurements have been carried out by means of complementary techniques: hot-wire(HW) anemometry, Laser Doppler Velocimetry(LDV) and Particle Image Velocimetry(PIV). The high accuracy 2-dimensional LDV results allow investigating reverse flow magnitude and both Reynolds normal and shear stress distributions along the separated flow region, while the high frequency response of the HW anemometer allows analyzing the amplification process of flow oscillations induced by instability mechanisms. PIV results complement the flow field analysis providing information on the generation and evolution of the large scale coherent structures shed as a consequence of the separated shear layer roll-up, through instantaneous velocity vector maps. The simultaneous analysis of the data obtained by means of the different measuring techniques allows an in depth view of the instability mechanisms involved in the transition/reattachment processes of the separated shear layer.