The gas-liquid-solid three-phase mixed flow is the most general in multiphase mixed transportation. It is significant to exactly solve the coupling hydraulic transient problems of this type of multiphase mixed flow in...The gas-liquid-solid three-phase mixed flow is the most general in multiphase mixed transportation. It is significant to exactly solve the coupling hydraulic transient problems of this type of multiphase mixed flow in pipelines. Presently, the method of characteristics is widely used to solve classical hydraulic transient problems. However, when it is used to solve coupling hydraulic transient problems, excessive interpolation errors may be introduced into the results due to unavoidable multiwave interpolated calculations. To deal with the problem, a finite difference scheme based on the Steger- Warming flux vector splitting is proposed. A flux vector splitting scheme is established for the coupling hydraulic transient model of gas-liquid-solid three-phase mixed flow in the pipelines. The flux subvectors are then discretized by the Lax-Wendroff central difference scheme and the Warming-Beam upwind difference scheme with second-order precision in both time and space. Under the Rankine-Hugoniot conditions and the corresponding boundary conditions, an effective solution to those points located at the boundaries is developed, which can avoid the problem beyond the calculation region directly induced by the second-order discrete technique. Numerical and experimental verifications indicate that the proposed scheme has several desirable advantages including high calculation precision, excellent shock wave capture capability without false numerical oscillation, low sensitivity to the Courant number, and good stability.展开更多
The present paper summarizes the results of previous studies, including the structure and principle of the rotary ring flume for researching the fine sediment movement, the mechanism of the flume, method of eliminatin...The present paper summarizes the results of previous studies, including the structure and principle of the rotary ring flume for researching the fine sediment movement, the mechanism of the flume, method of eliminating the influence of the centrifugal force and sediment movement experiments with periodic alternating current. Also included are the experiment-based relationship among sediment concentration, bed shear stress and silt carrying capacity, a proposed erosion-deposition function and bed erosion-deposition calculation together with the results of verification.展开更多
The plume interaction above an alternating diffuser in stagnant water is studied with 3D Reynolds-averaged NavierStokes equations （RANS） combined with a buoyancy-extended κ-ε model. The steady three-dimensional tu...The plume interaction above an alternating diffuser in stagnant water is studied with 3D Reynolds-averaged NavierStokes equations （RANS） combined with a buoyancy-extended κ-ε model. The steady three-dimensional turbulent flow and temperature fields are computed by use of the finite volume method on a non-uniform high resolution orthogonal grid. The numerical predictions demonstrate a generic flow pattern for different turbulent heated jet discharges： the buoyant jets on each side of the diffuser first merge to form an essentially two-dimensional plume which bends back toward the diffuser centerline due to a low pressure cavity. In general, an under-pressure exists in the cavity until the plumes merge; the pressure increases to slightly positive afterwards. Two-dimensionality of the scalar and flow field is attained much later than the point of zero pressure. The position of merging point is governed by mainly four parameters - the discharge densimetfic Froude number, the port diameter and space, and the horizontal distance between alternating jet nozzles. A formula from numerical simulations is obtained through regression analysis and it is used to predict the position of plume merging point. The predicted temperature fields are comparable to previous experiments.展开更多
Due to the decrease in the number of switches for the four-switch three-phase alternating current-direct current(FSTP AC-DC)converter,it can easily lead to DC-link capacitor voltage imbalance and the system stability ...Due to the decrease in the number of switches for the four-switch three-phase alternating current-direct current(FSTP AC-DC)converter,it can easily lead to DC-link capacitor voltage imbalance and the system stability reduction.In order to solve these problems,a finite control set model predictive control(FCS-MPC)for FSTP AC-DC converters with DC-link capacitor voltage balancing is proposed.In this strategy,in order to facilitate calculation,theαβcoordinate system model is established and all voltage vectors are evaluated by establishing a cost function.During the whole process,phase locked loop(PLL)and complex modulation strategy are not required.In the new established cost function,the additional objective term of suppressing capacitor voltage fluctuation is to eliminate effectively the capacitor voltages oscillations and deviations and improve the system reliability.The simulation results show that the proposed strategy can keep the capacitor voltage balancing and has good dynamic and static performance.展开更多
基金supported by the Natural Science Foundation Project of CQ CSTC (No. 2010BB7421)
文摘The gas-liquid-solid three-phase mixed flow is the most general in multiphase mixed transportation. It is significant to exactly solve the coupling hydraulic transient problems of this type of multiphase mixed flow in pipelines. Presently, the method of characteristics is widely used to solve classical hydraulic transient problems. However, when it is used to solve coupling hydraulic transient problems, excessive interpolation errors may be introduced into the results due to unavoidable multiwave interpolated calculations. To deal with the problem, a finite difference scheme based on the Steger- Warming flux vector splitting is proposed. A flux vector splitting scheme is established for the coupling hydraulic transient model of gas-liquid-solid three-phase mixed flow in the pipelines. The flux subvectors are then discretized by the Lax-Wendroff central difference scheme and the Warming-Beam upwind difference scheme with second-order precision in both time and space. Under the Rankine-Hugoniot conditions and the corresponding boundary conditions, an effective solution to those points located at the boundaries is developed, which can avoid the problem beyond the calculation region directly induced by the second-order discrete technique. Numerical and experimental verifications indicate that the proposed scheme has several desirable advantages including high calculation precision, excellent shock wave capture capability without false numerical oscillation, low sensitivity to the Courant number, and good stability.
文摘The present paper summarizes the results of previous studies, including the structure and principle of the rotary ring flume for researching the fine sediment movement, the mechanism of the flume, method of eliminating the influence of the centrifugal force and sediment movement experiments with periodic alternating current. Also included are the experiment-based relationship among sediment concentration, bed shear stress and silt carrying capacity, a proposed erosion-deposition function and bed erosion-deposition calculation together with the results of verification.
文摘The plume interaction above an alternating diffuser in stagnant water is studied with 3D Reynolds-averaged NavierStokes equations （RANS） combined with a buoyancy-extended κ-ε model. The steady three-dimensional turbulent flow and temperature fields are computed by use of the finite volume method on a non-uniform high resolution orthogonal grid. The numerical predictions demonstrate a generic flow pattern for different turbulent heated jet discharges： the buoyant jets on each side of the diffuser first merge to form an essentially two-dimensional plume which bends back toward the diffuser centerline due to a low pressure cavity. In general, an under-pressure exists in the cavity until the plumes merge; the pressure increases to slightly positive afterwards. Two-dimensionality of the scalar and flow field is attained much later than the point of zero pressure. The position of merging point is governed by mainly four parameters - the discharge densimetfic Froude number, the port diameter and space, and the horizontal distance between alternating jet nozzles. A formula from numerical simulations is obtained through regression analysis and it is used to predict the position of plume merging point. The predicted temperature fields are comparable to previous experiments.
基金National Natural Science Foundation of China(No.61741508)
文摘Due to the decrease in the number of switches for the four-switch three-phase alternating current-direct current(FSTP AC-DC)converter,it can easily lead to DC-link capacitor voltage imbalance and the system stability reduction.In order to solve these problems,a finite control set model predictive control(FCS-MPC)for FSTP AC-DC converters with DC-link capacitor voltage balancing is proposed.In this strategy,in order to facilitate calculation,theαβcoordinate system model is established and all voltage vectors are evaluated by establishing a cost function.During the whole process,phase locked loop(PLL)and complex modulation strategy are not required.In the new established cost function,the additional objective term of suppressing capacitor voltage fluctuation is to eliminate effectively the capacitor voltages oscillations and deviations and improve the system reliability.The simulation results show that the proposed strategy can keep the capacitor voltage balancing and has good dynamic and static performance.
