Considering the velocity anisotropy of the solid/fluid relative motion and employment of the BISQ theory based on the one-dimensional porous isotropic case, we establish a two-phase anisotropic elastic wave equation t...Considering the velocity anisotropy of the solid/fluid relative motion and employment of the BISQ theory based on the one-dimensional porous isotropic case, we establish a two-phase anisotropic elastic wave equation to simultaneously include the Biot and the squirt mechanisms in terms of both the basic principles of the fluid’s mass conservation and the elastic-wave dynamical equations in the two-phase anisotropic rock. Numerical results, while the Biot-flow and the squirt-flow effects are simultaneously considered in the transversely isotropic (Tl) poroelastic medium, show that the attenuation of the quasi P-wave and the quasi SV-wave strongly depend on the permeability anisotropy, and the attenuation behavior at low and high frequencies is contrary. Meanwhile, the attenuation and dispersion of the quasi P-wave are also affected seriously by the anisotropic solid/fluid coupling additional density.展开更多
In this paper, the convection structure in a rectangular channel with a horizontal flow was studied for the aspect ratio ГA=12 and the separation ratio ψ=-0.11. Our simulations were preformed by solving the hydrodyn...In this paper, the convection structure in a rectangular channel with a horizontal flow was studied for the aspect ratio ГA=12 and the separation ratio ψ=-0.11. Our simulations were preformed by solving the hydrodynamic equations using the SIMPLE method. In the system of binary fluid convection with a horizontal flow, a Periodically Localized Traveling Wave （PLTW） state was found. It has similar behavior to classical Rayleigh-Benard convection in a binary fluid mixture, but the region and wave number of convection change periodically with time. The instability of PLTW depends on the Rayleigh number r and the intensity of horizontal flows Re for given ψ. Thus, the PLTW convection results from the competition between the horizontal flow and the counter-propagating wave near the onset of convection.展开更多
Viscous fluid model and potential flow model with and without artificial damping force(f=-μV,μ the damping coefficient and V the local averaging flow velocity) are employed in this work to investigate the phenomenon...Viscous fluid model and potential flow model with and without artificial damping force(f=-μV,μ the damping coefficient and V the local averaging flow velocity) are employed in this work to investigate the phenomenon of fluid resonance in narrow gaps between multi-bodies in close proximity under water waves.The numerical results are compared with experimental data available in the literature.The comparison demonstrates that both the viscous fluid model and the potential flow model are able to predict the resonant frequency reasonably well.However the conventional potential flow model(without artificial damping term) significantly over-predicts the wave height in narrow gaps around the resonant frequency.In order to calibrate the appropriate damping coefficient used for the potential model and make it work as well as the viscous fluid model in predicting the resonant wave height in narrow gaps but with little computational efforts,the dependence of damping coefficient μ on the body geometric dimensions is examined considering the parameters of gap width Bg,body draft D,body breadth ratio Br and body number n(n = 2,3),where Br = BB/BA for the case of two bodies(Body A and Body B) with different breadths of BA and BB,respectively.It was confirmed that the damping coefficient used for the potential flow model is not sensitive to the geometric dimensions and spatial arrangement.It was found that μ∈ [0.4,0.5] may guarantee the variation of Hg/H0 with kh to be generally in good agreement with the experimental data and the results of viscous fluid model,where Hg is the excited wave height in narrow gaps under various dimensionless incident wave frequencies kh,H0 is the incident wave height,k = 2π/L is the wave number and h is the water depth.展开更多
The convection structure in a rectangular channel with a horizontal flow forΓ = 12 was studied. The simulations were preformed by solving the hydrodynamic equations using theSIMPLE method. The convective behavior in ...The convection structure in a rectangular channel with a horizontal flow forΓ = 12 was studied. The simulations were preformed by solving the hydrodynamic equations using theSIMPLE method. The convective behavior in an absolutely and convectively unstable regime wasstudied. The results show that the two types of convection patterns in this system appear dependingon the convection intensity and horizontal flow. A periodically localized traveling wave state wasfound in this system.展开更多
An experimental research was carried out to study the fluid mechanics of underwater supersonic gas jets. High pressure air was injected into a water tank through converging-diverging nozzles (Laval nozzles). The jets ...An experimental research was carried out to study the fluid mechanics of underwater supersonic gas jets. High pressure air was injected into a water tank through converging-diverging nozzles (Laval nozzles). The jets were operated at different conditions of over-, full- and under-expansions. The jet sequences were visualized using a CCD camera. It was found that the injection of supersonic air jets into water is always accompanied by strong flow oscillation, which is related to the phenomenon of shock waves feedback in the gas phase. The shock wave feedback is different from the acoustic feedback when a supersonic gas jet discharges into open air, which causes screech tone. It is a process that the shock waves enclosed in the gas pocket induce a periodic pressure with large amplitude variation in the gas jet. Consequently, the periodic pressure causes the jet oscillation including the large amplitude expansion. Detailed pressure measurements were also conducted to verify the shock wave feedback phenomenon. Three kinds of measuring methods were used, i.e., pressure probe submerged in water, pressure measurements from the side and front walls of the nozzle devices respectively. The results measured by these methods are in a good agreement. They show that every oscillation of the jets causes a sudden increase of pressure and the average frequency of the shock wave feedback is about 5–10 Hz.展开更多
Over the past 10 years, the number of broadband seismic stations in China has increased significantly. The broadband seismic records contain information about shear-wave splitting which plays an important role in reve...Over the past 10 years, the number of broadband seismic stations in China has increased significantly. The broadband seismic records contain information about shear-wave splitting which plays an important role in revealing the upper mantle anisotropy in the Chinese mainland. Based on teleseismic SKS and SKKS phases recorded in the seismic stations, we used the analytical method of minimum transverse energy to determine the fast wave polarization direction and delay time of shear-wave splitting. We also collected results of shear-wave splitting in China and the surrounding regions from previously published papers. From the combined dataset we formed a shear-wave splitting dataset containing 1020 parameter pairs. These splitting parameters re- veal the complexity of the upper mantle anisotropy image. Our statistical analysis indicates stronger upper mantle anisotropy in the Chinese mainland, with an average shear-wave time delay of 0,95 s; the anisotropy in the western region is slightly larger （1.01 s） than in the eastern region （0.92 s）. On a larger scale, the SKS splitting and surface deformation data in the Tibetan Plateau and the Tianshan region jointly support the lithospheric deformation mode, i.e. the crust-lithospheric mantle coherent deformation. In eastern China, the average fast-wave direction is approximately parallel to the direction of the absolute plate motion; thus, the upper mantle anisotropy can be attributed to the asthenospheric flow. The area from the Ordos block to the Sichuan Basin in central China is the transition zone of deformation modes between the east and the west regions, where the anisotropy images are more complicated, exhibiting ＂fossil＂ anisotropy and/or two-layer anis^3trc^py. The c^llisi（3n between the Indian Plate and the Eurasian Plate is the main factor of upper mantle anisotropy in the western region of the Chinese mainland, while the upper mantle anisotropy in the eastern region is related to the subduction of the Pacific Plate and the Philippine Sea Plate be展开更多
为研究漂浮式风力机驳船式平台的动态响应,建立基于ITI Energy Barge平台的NREL 5MW漂浮式风力机模型。通过辐射/衍射理论并结合有限元方法,调用水动力学软件AQWA,考虑风、浪、流环境的联合作用,对平台的动态响应进行数值模拟分析,得到...为研究漂浮式风力机驳船式平台的动态响应,建立基于ITI Energy Barge平台的NREL 5MW漂浮式风力机模型。通过辐射/衍射理论并结合有限元方法,调用水动力学软件AQWA,考虑风、浪、流环境的联合作用,对平台的动态响应进行数值模拟分析,得到了各波浪力随波浪频率的变化及平台在纵荡、垂荡和纵摇方向上的动态响应。结果表明:平台在低频波浪时容易出现较大响应;随着海洋环境恶劣程度的增加,平台的动态响应增大;平台在垂荡方向RAOs要大于纵荡方向。展开更多
This article is devoted to experimental study on the control of the oblique shock wave around the ramp in a low-temperature supersonic flow by means of the magnetohydrodynamic （MHD） flow control technique. The purpo...This article is devoted to experimental study on the control of the oblique shock wave around the ramp in a low-temperature supersonic flow by means of the magnetohydrodynamic （MHD） flow control technique. The purpose of the experiments is to take advantage of MHD interaction to weaken the oblique shock wave strength by changing the boundary flow characteristics around the ramp. Plasma columns are generated by pulsed direct current （ DC ） discharge, the magnetic fields are generated by Nd-Fe-B rare-earth permanent magnets and the oblique shock waves in supersonic flow are generated by the ramp. The Lorentz body force effect of MHD interaction on the plasma-induced airflow velocity is verified through particle image velocimetry（PIV）measurements. The experimental results from the supersonic wind tunnel indicate that the MHD flow control can drastically change the flow characteristics of the airflow around the ramp and decrease the ratio of the Pitot pressure after shock wave to that before it by up to 19.66% ,which leads to the decline in oblique shock wave strength. The oblique shock waves in front of the ramp move upstream by the action of the Lorentz body force. The discharge characteristics are analyzed and the MHD interaction time and consumed energy are determined with the help of the pulsed DC discharge images. The interaction parameter corresponding to the boundary layer velocity can reach 1.3 from the momentum conservation equation. The velocity of the plasma column in the magnetic field is much faster than that in the absence of magnetic field force. The plasma can strike the neutral gas molecules to transfer momentum and accelerate the flow around the ramp.展开更多
文摘Considering the velocity anisotropy of the solid/fluid relative motion and employment of the BISQ theory based on the one-dimensional porous isotropic case, we establish a two-phase anisotropic elastic wave equation to simultaneously include the Biot and the squirt mechanisms in terms of both the basic principles of the fluid’s mass conservation and the elastic-wave dynamical equations in the two-phase anisotropic rock. Numerical results, while the Biot-flow and the squirt-flow effects are simultaneously considered in the transversely isotropic (Tl) poroelastic medium, show that the attenuation of the quasi P-wave and the quasi SV-wave strongly depend on the permeability anisotropy, and the attenuation behavior at low and high frequencies is contrary. Meanwhile, the attenuation and dispersion of the quasi P-wave are also affected seriously by the anisotropic solid/fluid coupling additional density.
基金Project supported by SRF for ROCS, SEM(Grant No:220542), the Specific Fund of Higher Educational Doctoral Programme of Xi’an University of Technology (Grant No:220327) and the Key Project of Shaanxi Education Committee(Grant No:05JK271).
文摘In this paper, the convection structure in a rectangular channel with a horizontal flow was studied for the aspect ratio ГA=12 and the separation ratio ψ=-0.11. Our simulations were preformed by solving the hydrodynamic equations using the SIMPLE method. In the system of binary fluid convection with a horizontal flow, a Periodically Localized Traveling Wave （PLTW） state was found. It has similar behavior to classical Rayleigh-Benard convection in a binary fluid mixture, but the region and wave number of convection change periodically with time. The instability of PLTW depends on the Rayleigh number r and the intensity of horizontal flows Re for given ψ. Thus, the PLTW convection results from the competition between the horizontal flow and the counter-propagating wave near the onset of convection.
基金supports from the Natural National Science Foundation of China (Grant Nos.50909016,50921001 and 10802014)support of ARC Discovery Project Program (Grant No. DP0557060)supported by the Open Fund from the State Key Laboratory of Structural Analysis for Industrial Equipment (Grant No. GZ0909)
文摘Viscous fluid model and potential flow model with and without artificial damping force(f=-μV,μ the damping coefficient and V the local averaging flow velocity) are employed in this work to investigate the phenomenon of fluid resonance in narrow gaps between multi-bodies in close proximity under water waves.The numerical results are compared with experimental data available in the literature.The comparison demonstrates that both the viscous fluid model and the potential flow model are able to predict the resonant frequency reasonably well.However the conventional potential flow model(without artificial damping term) significantly over-predicts the wave height in narrow gaps around the resonant frequency.In order to calibrate the appropriate damping coefficient used for the potential model and make it work as well as the viscous fluid model in predicting the resonant wave height in narrow gaps but with little computational efforts,the dependence of damping coefficient μ on the body geometric dimensions is examined considering the parameters of gap width Bg,body draft D,body breadth ratio Br and body number n(n = 2,3),where Br = BB/BA for the case of two bodies(Body A and Body B) with different breadths of BA and BB,respectively.It was confirmed that the damping coefficient used for the potential flow model is not sensitive to the geometric dimensions and spatial arrangement.It was found that μ∈ [0.4,0.5] may guarantee the variation of Hg/H0 with kh to be generally in good agreement with the experimental data and the results of viscous fluid model,where Hg is the excited wave height in narrow gaps under various dimensionless incident wave frequencies kh,H0 is the incident wave height,k = 2π/L is the wave number and h is the water depth.
文摘The convection structure in a rectangular channel with a horizontal flow forΓ = 12 was studied. The simulations were preformed by solving the hydrodynamic equations using theSIMPLE method. The convective behavior in an absolutely and convectively unstable regime wasstudied. The results show that the two types of convection patterns in this system appear dependingon the convection intensity and horizontal flow. A periodically localized traveling wave state wasfound in this system.
基金supported by the National Natural Science Foundation of China (Grant No. 10672144)the Natural Science Foundation of Zhejiang Province of China (Grant No. Y107073.)
文摘An experimental research was carried out to study the fluid mechanics of underwater supersonic gas jets. High pressure air was injected into a water tank through converging-diverging nozzles (Laval nozzles). The jets were operated at different conditions of over-, full- and under-expansions. The jet sequences were visualized using a CCD camera. It was found that the injection of supersonic air jets into water is always accompanied by strong flow oscillation, which is related to the phenomenon of shock waves feedback in the gas phase. The shock wave feedback is different from the acoustic feedback when a supersonic gas jet discharges into open air, which causes screech tone. It is a process that the shock waves enclosed in the gas pocket induce a periodic pressure with large amplitude variation in the gas jet. Consequently, the periodic pressure causes the jet oscillation including the large amplitude expansion. Detailed pressure measurements were also conducted to verify the shock wave feedback phenomenon. Three kinds of measuring methods were used, i.e., pressure probe submerged in water, pressure measurements from the side and front walls of the nozzle devices respectively. The results measured by these methods are in a good agreement. They show that every oscillation of the jets causes a sudden increase of pressure and the average frequency of the shock wave feedback is about 5–10 Hz.
基金supported by the National Natural Science Foundation of China(Grants Nos.90914005,91014006,41174070)the Basic Pro-ject in the Ministry of Science and Technology(Grants No.2006FY1101100)
文摘Over the past 10 years, the number of broadband seismic stations in China has increased significantly. The broadband seismic records contain information about shear-wave splitting which plays an important role in revealing the upper mantle anisotropy in the Chinese mainland. Based on teleseismic SKS and SKKS phases recorded in the seismic stations, we used the analytical method of minimum transverse energy to determine the fast wave polarization direction and delay time of shear-wave splitting. We also collected results of shear-wave splitting in China and the surrounding regions from previously published papers. From the combined dataset we formed a shear-wave splitting dataset containing 1020 parameter pairs. These splitting parameters re- veal the complexity of the upper mantle anisotropy image. Our statistical analysis indicates stronger upper mantle anisotropy in the Chinese mainland, with an average shear-wave time delay of 0,95 s; the anisotropy in the western region is slightly larger （1.01 s） than in the eastern region （0.92 s）. On a larger scale, the SKS splitting and surface deformation data in the Tibetan Plateau and the Tianshan region jointly support the lithospheric deformation mode, i.e. the crust-lithospheric mantle coherent deformation. In eastern China, the average fast-wave direction is approximately parallel to the direction of the absolute plate motion; thus, the upper mantle anisotropy can be attributed to the asthenospheric flow. The area from the Ordos block to the Sichuan Basin in central China is the transition zone of deformation modes between the east and the west regions, where the anisotropy images are more complicated, exhibiting ＂fossil＂ anisotropy and/or two-layer anis^3trc^py. The c^llisi（3n between the Indian Plate and the Eurasian Plate is the main factor of upper mantle anisotropy in the western region of the Chinese mainland, while the upper mantle anisotropy in the eastern region is related to the subduction of the Pacific Plate and the Philippine Sea Plate be
文摘为研究漂浮式风力机驳船式平台的动态响应,建立基于ITI Energy Barge平台的NREL 5MW漂浮式风力机模型。通过辐射/衍射理论并结合有限元方法,调用水动力学软件AQWA,考虑风、浪、流环境的联合作用,对平台的动态响应进行数值模拟分析,得到了各波浪力随波浪频率的变化及平台在纵荡、垂荡和纵摇方向上的动态响应。结果表明:平台在低频波浪时容易出现较大响应;随着海洋环境恶劣程度的增加,平台的动态响应增大;平台在垂荡方向RAOs要大于纵荡方向。
基金National Natural Science Foundation of China(50776100)
文摘This article is devoted to experimental study on the control of the oblique shock wave around the ramp in a low-temperature supersonic flow by means of the magnetohydrodynamic （MHD） flow control technique. The purpose of the experiments is to take advantage of MHD interaction to weaken the oblique shock wave strength by changing the boundary flow characteristics around the ramp. Plasma columns are generated by pulsed direct current （ DC ） discharge, the magnetic fields are generated by Nd-Fe-B rare-earth permanent magnets and the oblique shock waves in supersonic flow are generated by the ramp. The Lorentz body force effect of MHD interaction on the plasma-induced airflow velocity is verified through particle image velocimetry（PIV）measurements. The experimental results from the supersonic wind tunnel indicate that the MHD flow control can drastically change the flow characteristics of the airflow around the ramp and decrease the ratio of the Pitot pressure after shock wave to that before it by up to 19.66% ,which leads to the decline in oblique shock wave strength. The oblique shock waves in front of the ramp move upstream by the action of the Lorentz body force. The discharge characteristics are analyzed and the MHD interaction time and consumed energy are determined with the help of the pulsed DC discharge images. The interaction parameter corresponding to the boundary layer velocity can reach 1.3 from the momentum conservation equation. The velocity of the plasma column in the magnetic field is much faster than that in the absence of magnetic field force. The plasma can strike the neutral gas molecules to transfer momentum and accelerate the flow around the ramp.
