The internal variability of a ten-member ensemble of the regional climate model REMO over Europe is investigated. It is shown that the annual cycle of internal variability behaves differently compared to earlier studi...The internal variability of a ten-member ensemble of the regional climate model REMO over Europe is investigated. It is shown that the annual cycle of internal variability behaves differently compared to earlier studies that focused on other regions. To gain better insight into the dependence of the internal variability on the boundary forcing variability, a circulation type classification is performed on the forcing data. It can be shown that especially in the winter season internal variability is dependent on the circulation type included in the boundary forcing, whereas in the summer season the level and pattern of internal variability is rather independent from the circulation type of the driving field. It is concluded that for Europe the internal variability of REMO in winter is governed by circulation patterns related to the North-Atlantic Oscillation, whereas in summer local processes play a bigger role.展开更多
A nonlinear critical layer and a Kelvin cat's eye excited thereupon are simulated through four schemes in the context of a nonlinear quasi-geostrophic barotropic vorticity equation model with forced stationary wav...A nonlinear critical layer and a Kelvin cat's eye excited thereupon are simulated through four schemes in the context of a nonlinear quasi-geostrophic barotropic vorticity equation model with forced stationary wave acting along the southern boundary to investigate effects of tropical steady forcing on the genesis,maintenance and oscillation of a subtropical high(STH).Evidence suggests that the southern forcing is responsible for the planetary quasi-steady anticyclonic Kelvin cat's eye- form flow field inside the nonlinear critical layer,with the eye shifting,vigor and shape changing quite similar to the behaviors of a summer STH,in striking contrast to the northern stationary forcing.As such,the southern boundary-caused cat's eye is likely to be an even more important mechanism for STH genesis and evolution.In addition,a physical mechanism is introduced for quasi-steady planetary wave moving through the critical layer at subtropical latitudes.展开更多
Down-hole tubular string buckling is the most classic and complex part of tubular string mechanics in well engineering. Studies of down-hole tubular string buckling not only have theoretical significance in revealing ...Down-hole tubular string buckling is the most classic and complex part of tubular string mechanics in well engineering. Studies of down-hole tubular string buckling not only have theoretical significance in revealing the buckling mechanism but also have prominent practical value in design and control of tubular strings. In this review, the basic principles and applicable scope of three classic research methods （the beam-column model, buck- ling differential equation, and energy method） are intro- duced. The critical buckling loads and the post-buckling behavior under different buckling modes in vertical, inclined, horizontal, and curved wellbores from different researchers are presented and compared. The current understanding of the effects of torque, boundary condi- tions, friction force, and connectors on down-hole tubular string buckling is illustrated. Meanwhile, some unsolved problems and controversial conclusions are discussed. Future research should be focused on sophisticated description of buckling behavior and the coupling effect of multiple factors. In addition, active control of down-hole tubular string buckling behavior needs some attention urgently.展开更多
The lattice Boltzmann method （LBM） is a useful technique for simulating multiphase flows and modeling complex physics. Specifically, we use LBM combined with a direct-forcing （DF） immersed boundary （IB） method t...The lattice Boltzmann method （LBM） is a useful technique for simulating multiphase flows and modeling complex physics. Specifically, we use LBM combined with a direct-forcing （DF） immersed boundary （IB） method to simulate fluid-particle interactions in two-phase particulate flows. Two grids are used in the simulation： a fixed uniform Eulerian grid for the fluid phase and a Lagrangian grid that is attached to and moves with the immersed particles. Forces are calculated at each Lagrangian point. To exchange numerical information between the two grids, discrete delta functions are used. The resulting DF IB-LBM approach is then successfully applied to a variety of reference flows, namely the sedimentation of one and two circular particles in a vertical channel, the sedimentation of one or two spheres in an enclosure, and a neutrally buoyant prolate spheroid in a Couette flow. This last application proves that the developed approach can be used also for non-spherical particles. The three forcing schemes and the different factors affecting the simulation （added mass effect, corrected radius） are also discussed.展开更多
A Constrained Interpolation Profile （CIP）-based model is developed to predict the mooring force of a two-dimensional floating oil storage tank under wave conditions, which is validated against to a newly performed e...A Constrained Interpolation Profile （CIP）-based model is developed to predict the mooring force of a two-dimensional floating oil storage tank under wave conditions, which is validated against to a newly performed experiment. In the experiment, a box-shaped floating oil storage apparatus is used. Computations are performed by an improved CIP-based Cartesian grid model, in which the THINC/SW scheme （THINC： tangent of hyperbola for interface capturing; SW： Slope Weighting）, is used for interface capturing. A multiphase flow solver is adopted to treat the water-air-body interactions. The Immersed Boundary Method （IBM） is implemented to treat the body surface. Main attention is paid to the sum force of mooring line and velocity field around the body. It is found that the sum force of the mooring line increases with increasing wave amplitude. The body suffers from water wave impact and large body motions occur near the free surface. The vortex occurs near the sharp edge, i.e., the sharp bottom comers of the float- ing oil storage tank and the vortex shedding can be captured by the present numerical model. The present model could be further improved by including turbulence model which is currently under development. Comparison between the computational mooring forces and the measured mooring forces is presented with a reasonable agreement. The developed numerical model can predict the mooring line forces very well.展开更多
In this article, the circulation of the South China Sea （SCS）, which is idealized as the rectangular basin with constant depth, is studied under Kuroshio boundary forces. Starting from the linearly quasi-geostrophic...In this article, the circulation of the South China Sea （SCS）, which is idealized as the rectangular basin with constant depth, is studied under Kuroshio boundary forces. Starting from the linearly quasi-geostrophic vorticity equation, the solution of the SCS circulation is given in the form of corrected Fourier series under proper boundary conditions. The results show that the intruded current flows westward and separates into the northward branch and the southward branch before arriving at the western boundary. The southward branch flows out of the SCS through the southwestern passage, at the same time, the induced cyclonic （anti-clockwise） ring almost occupies the middle and southern parts, and concomitant anti-cyclonic （clockwise） vortex appears between the cyclone and the western boundary. While the northward branch outflows through the northeastern passage, the anti-cyclonic （clockwise） ring is triggered at the northern part of the SCS. The above two vortexes are both intensified if the south-entering and the north-leaving current loop intrusion are superposed. The outer flow of the northern vortex flows westward, then northward, and then eastward, and it is very similar to the configuration of the SCS Warm Current （SCSWC） at the northern part of the SCS, thus, a kind of generating mechanism of the SCSWC is presented.展开更多
文摘The internal variability of a ten-member ensemble of the regional climate model REMO over Europe is investigated. It is shown that the annual cycle of internal variability behaves differently compared to earlier studies that focused on other regions. To gain better insight into the dependence of the internal variability on the boundary forcing variability, a circulation type classification is performed on the forcing data. It can be shown that especially in the winter season internal variability is dependent on the circulation type included in the boundary forcing, whereas in the summer season the level and pattern of internal variability is rather independent from the circulation type of the driving field. It is concluded that for Europe the internal variability of REMO in winter is governed by circulation patterns related to the North-Atlantic Oscillation, whereas in summer local processes play a bigger role.
基金This work is supported jointly by the Foundation of Meteorological Sciences of China Meteorological Administration the National Natural Science Foundation of China.
文摘A nonlinear critical layer and a Kelvin cat's eye excited thereupon are simulated through four schemes in the context of a nonlinear quasi-geostrophic barotropic vorticity equation model with forced stationary wave acting along the southern boundary to investigate effects of tropical steady forcing on the genesis,maintenance and oscillation of a subtropical high(STH).Evidence suggests that the southern forcing is responsible for the planetary quasi-steady anticyclonic Kelvin cat's eye- form flow field inside the nonlinear critical layer,with the eye shifting,vigor and shape changing quite similar to the behaviors of a summer STH,in striking contrast to the northern stationary forcing.As such,the southern boundary-caused cat's eye is likely to be an even more important mechanism for STH genesis and evolution.In addition,a physical mechanism is introduced for quasi-steady planetary wave moving through the critical layer at subtropical latitudes.
基金the financial support from the Natural Science Foundation of China (NSFC,51221003,U1262201)the Science Foundation of China University of Petroleum,Beijing (No.00000)supported by other projects (Grant Numbers:2014A-4214,2013AA064803,2011ZX05009-005)
文摘Down-hole tubular string buckling is the most classic and complex part of tubular string mechanics in well engineering. Studies of down-hole tubular string buckling not only have theoretical significance in revealing the buckling mechanism but also have prominent practical value in design and control of tubular strings. In this review, the basic principles and applicable scope of three classic research methods （the beam-column model, buck- ling differential equation, and energy method） are intro- duced. The critical buckling loads and the post-buckling behavior under different buckling modes in vertical, inclined, horizontal, and curved wellbores from different researchers are presented and compared. The current understanding of the effects of torque, boundary condi- tions, friction force, and connectors on down-hole tubular string buckling is illustrated. Meanwhile, some unsolved problems and controversial conclusions are discussed. Future research should be focused on sophisticated description of buckling behavior and the coupling effect of multiple factors. In addition, active control of down-hole tubular string buckling behavior needs some attention urgently.
文摘The lattice Boltzmann method （LBM） is a useful technique for simulating multiphase flows and modeling complex physics. Specifically, we use LBM combined with a direct-forcing （DF） immersed boundary （IB） method to simulate fluid-particle interactions in two-phase particulate flows. Two grids are used in the simulation： a fixed uniform Eulerian grid for the fluid phase and a Lagrangian grid that is attached to and moves with the immersed particles. Forces are calculated at each Lagrangian point. To exchange numerical information between the two grids, discrete delta functions are used. The resulting DF IB-LBM approach is then successfully applied to a variety of reference flows, namely the sedimentation of one and two circular particles in a vertical channel, the sedimentation of one or two spheres in an enclosure, and a neutrally buoyant prolate spheroid in a Couette flow. This last application proves that the developed approach can be used also for non-spherical particles. The three forcing schemes and the different factors affecting the simulation （added mass effect, corrected radius） are also discussed.
基金supported by the National Natural Science Foundation of China (51209184,51279186,51479175)
文摘A Constrained Interpolation Profile （CIP）-based model is developed to predict the mooring force of a two-dimensional floating oil storage tank under wave conditions, which is validated against to a newly performed experiment. In the experiment, a box-shaped floating oil storage apparatus is used. Computations are performed by an improved CIP-based Cartesian grid model, in which the THINC/SW scheme （THINC： tangent of hyperbola for interface capturing; SW： Slope Weighting）, is used for interface capturing. A multiphase flow solver is adopted to treat the water-air-body interactions. The Immersed Boundary Method （IBM） is implemented to treat the body surface. Main attention is paid to the sum force of mooring line and velocity field around the body. It is found that the sum force of the mooring line increases with increasing wave amplitude. The body suffers from water wave impact and large body motions occur near the free surface. The vortex occurs near the sharp edge, i.e., the sharp bottom comers of the float- ing oil storage tank and the vortex shedding can be captured by the present numerical model. The present model could be further improved by including turbulence model which is currently under development. Comparison between the computational mooring forces and the measured mooring forces is presented with a reasonable agreement. The developed numerical model can predict the mooring line forces very well.
基金Project supported by the National Natural Science Foundation of China (Grant Nos: 40176008, 40576020) and the Major State Basic Research Development Program of China (Grant No: G1999043800)
文摘In this article, the circulation of the South China Sea （SCS）, which is idealized as the rectangular basin with constant depth, is studied under Kuroshio boundary forces. Starting from the linearly quasi-geostrophic vorticity equation, the solution of the SCS circulation is given in the form of corrected Fourier series under proper boundary conditions. The results show that the intruded current flows westward and separates into the northward branch and the southward branch before arriving at the western boundary. The southward branch flows out of the SCS through the southwestern passage, at the same time, the induced cyclonic （anti-clockwise） ring almost occupies the middle and southern parts, and concomitant anti-cyclonic （clockwise） vortex appears between the cyclone and the western boundary. While the northward branch outflows through the northeastern passage, the anti-cyclonic （clockwise） ring is triggered at the northern part of the SCS. The above two vortexes are both intensified if the south-entering and the north-leaving current loop intrusion are superposed. The outer flow of the northern vortex flows westward, then northward, and then eastward, and it is very similar to the configuration of the SCS Warm Current （SCSWC） at the northern part of the SCS, thus, a kind of generating mechanism of the SCSWC is presented.
