A two-dimensional(2D)computational model for simulation of incipient sediment motion for noncohesive uniform and non-uniform particles on a horizontal bed was developed using the Discrete Element Method(DEM).The model...A two-dimensional(2D)computational model for simulation of incipient sediment motion for noncohesive uniform and non-uniform particles on a horizontal bed was developed using the Discrete Element Method(DEM).The model was calibrated and verified using various experimental data reported in the literature and compared with different theories of incipient particle motion.Sensitivity analysis was done and the effects of relevant parameters were determined.In addition to hydrodynamic forces such as drag,shear lift and Magnus force,the particle-particle interaction effects were included in the model.The asymptotic critical mobility number was evaluated for various critical particle Reynolds numbers(R*)in the range of very small and very large R*.The obtained curve is classified into four regions.It was found that in the linear region,the drag force has the principal role on the initiation of motion.Moreover,the critical mobility number is independent of particle diameter.A procedure for estimating the critical shear velocity directly from the information on particle diameter and roughness height was developed.Finally,the mechanism of incipient motion for the different regions was studied and the effect of different forces on the incipient particle motion was obtained.It was found that the maximum effects of lift and Magnus forces were,respectively,less than ten and twenty percent of the total force.The drag force,however,was typically the dominant force accounting for majority of the net hydrodynamic force acting on sediment particles at the onset of incipient motion.展开更多
In this paper, a new numerical scheme for solving first-order hyperbolic partial differential equations is proposed and is implemented in the simulation study of macroscopic traffic flow model with constant velocity a...In this paper, a new numerical scheme for solving first-order hyperbolic partial differential equations is proposed and is implemented in the simulation study of macroscopic traffic flow model with constant velocity and linear velocity-density relationship. Macroscopic traffic flow model is first developed by Lighthill Whitham and Richards (LWR) and used to study traffic flow by collective variables such as flow rate, velocity and density. The LWR model is treated as an initial value problem and its numerical simulations are presented using numerical schemes. A variety of numerical schemes are available in literature to solve first order hyperbolic equations. Of these the well-known ones include one-dimensional explicit: Upwind, Downwind, FTCS, and Lax-Friedrichs schemes. Having been studied carefully the space and time mesh sizes, and the patterns of all these schemes, a new scheme has been developed and named as one-dimensional explicit Tolesa numerical scheme. Tolesa numerical scheme is one of the conditionally stable and highest rates of convergence schemes. All the said numerical schemes are applied to solve advection equation pertaining traffic flows. Also the one-dimensional explicit Tolesa numerical scheme is another alternative numerical scheme to solve advection equation and apply to traffic flows model like other well-known one-dimensional explicit schemes. The effect of density of cars on the overall interactions of the vehicles along a given length of the highway and time are investigated. Graphical representations of density profile, velocity profile, flux profile, and in general the fundamental diagrams of vehicles on the highway with different time levels are illustrated. These concepts and results have been arranged systematically in this paper.展开更多
Oilfield A is a fractured buried hill reservoir in Bohai bay of China. In order to solve the difficult problem of water flooding timing and method in oilfield. Considering the characteristics of the buried hill fractu...Oilfield A is a fractured buried hill reservoir in Bohai bay of China. In order to solve the difficult problem of water flooding timing and method in oilfield. Considering the characteristics of the buried hill fractures with stress sensitivity and strong heterogeneity, the ECLIPSE software was used in the research, and a three-dimensional injection-production numerical model for horizontal wells in buried hill reservoirs is established. According to the main research factors in water flooding, a series of water flooding schemes are designed, and the optimization of water flooding timing, oil recovery rate and water flooding mode in buried hill reservoirs were carried out. The results show that the optimum pressure level of fractured reservoir is about 70% of the original reservoir pressure. The optimal water flooding method is the conventional water flooding in the initial stage, when the water cut reaches 80%, it is converted into periodic water flooding. The oil recovery is the highest when the water injection period is 4 months. Field tests show that conventional water flooding is carried out in the initial stage of the oilfield A when the pressure is reduced to 70% of the original. Periodic water flooding is carried out when water cut is 80%. Good development results had been achieved in the 10 years since oilfield A was put into production. The average productivity of single well reached 300 m3/d in the initial stage, at present, the water cut is 60%, and the recovery degree is 18.5%, which is better than that of similar oilfields. This technology improves the water flooding effect of blocky bottom water fractured dual media reservoirs in metamorphic buried hills, and provides a reference for the development of similar reservoirs.展开更多
The filter paper and activated carbon which filled inside the gas filter have porous media characteristics. In order to study the flow field structure in the filter layer and the activated carbon layer, Computational ...The filter paper and activated carbon which filled inside the gas filter have porous media characteristics. In order to study the flow field structure in the filter layer and the activated carbon layer, Computational Fluid Dynamics method is used to simulate the aerodynamic characteristics of a simplified gas filter. The inertial and viscosity parameters of porous media are solved by Forchheimer equation. The three-dimensional N-S equation and the modified low Reynolds number k-ε turbulence model are adopted to analyze the influence of the explosion-proof plate on the gas filter’s aerodynamic characteristics. The results showed that the air age in the upstream of the activated carbon plates was small, which easily caused the rapid penetration of the Poisonous gas. And in the downstream and around of the activated carbon plates, the air age is larger, formed dead zone, the utilization rate of activated carbon is lower. The explosion-proof plate increases the pressure drop of the gas filter, the air age distribution in the filter layer is more uniform and the utilization rate of filter paper is improved. However, the explosion-proof plate has little influence on the flow field structure of the activated carbon layer.展开更多
We investigate under what conditions transient simulation could be used to integrate backward in time so that the initial field could be recovered from later histories. In this paper we use realistic examples and find...We investigate under what conditions transient simulation could be used to integrate backward in time so that the initial field could be recovered from later histories. In this paper we use realistic examples and find that, in long histories, traces of the initial field would be present only in the exact analytical solutions. We conclude that the recovery of initial field is possible only if the equations could be solved analytically or only short time periods are involved. In practice, it is not possible to detect those traces by measurements or observations. If numerical procedures are used, truncation and discretization errors are always present. Fine-tuning of system parameters used or transforming time into another pseudo time frame may allow numerical integration to be carried out backward in time. But numerical instability is still a problem. Large spurious increases found by numerical procedures are most likely due to numerical inaccuracy and instability.展开更多
The demand for natural gas in the world is increasing day by day. The efficient and flexible LNG becomes the preferred method for natural gas storage and transportation and has gradually entered people’s daily life. ...The demand for natural gas in the world is increasing day by day. The efficient and flexible LNG becomes the preferred method for natural gas storage and transportation and has gradually entered people’s daily life. The enclosure system is the key core of LNG transport and storage vessels for storage of LNG at -163°C for isolation and thermal insulation. A new type of flat half-film prismatic LNG enclosure system has been developed for the shortcomings of the existing LNG cargo enclosure system. Through the breakthrough and mastery of key core technologies such as the overall layout and integration of the system, anti-leakage technology, liquid tank fixing technology, and large-scale friction stir welding (P-FSW) flat-line pipeline development technology, we’ll strive to fill the gap in the intelligent construction technology of large aluminum alloy tanks in China. The tank was subjected to water vapor test and numerical simulation. The results show that the structural strength of the FSP-LNG tank meets the strength check standard of IGC Code.展开更多
In this study, flow structures and mixing performance in a blade-free planetary mixer, which combines rotation and revolution motions inside a cylindrical vessel, are numerically investigated. Flow fields in the mixer...In this study, flow structures and mixing performance in a blade-free planetary mixer, which combines rotation and revolution motions inside a cylindrical vessel, are numerically investigated. Flow fields in the mixer vessel are simulated in a single rotating reference frame with various revolution speeds and a fixed rotation speed. The mixing process is investigated by a Lagrangian particle tracking method and the mixing performance is evaluated based on particle concentration. The results of the numerical simulations show that a vortical flow with an axis inclined with respect to the rotation axis of the vessel is generated by the combined influence of the rotation and revolution motions. The flow structure and vortical flow intensity vary as a function of the precession rate, which is the ratio of the revolution speed to rotation speed. The mixing performance of the blade-free planetary mixer is found to be maximum at aspecific precession rate.展开更多
After long-term waterflooding in unconsolidated sandstone reservoir, the high-permeability channels are easy to evolve, which leads to a significant reduction in water flooding efficiency and a poor oilfield developme...After long-term waterflooding in unconsolidated sandstone reservoir, the high-permeability channels are easy to evolve, which leads to a significant reduction in water flooding efficiency and a poor oilfield development effect. The current researches on the formation parameters variation are mainly based on the experiment analysis or field statistics, while lacking quantitative research of combining microcosmic and macroscopic mechanism. A network model was built after taking the detachment and entrapment mechanisms of particles in unconsolidated sandstone reservoir into consideration. Then a coupled mathematical model for the formation parameters variation was established based on the network modeling and the model of fluids flowing in porous media. The model was solved by a finite-difference method and the Gauss-Seidel iterative technique. A novel field-scale reservoir numerical simulator was written in Fortran 90 and it can be used to predict 1) the evolvement of high-permeability channels caused by particles release and migration in the long-term water flooding process, and 2) well production performances and remaining oil distribution. In addition, a series of oil field examples with inverted nine-spot pattern was made on the new numerical simulator. The results show that the high-permeability channels are more likely to develop along the main streamlines between the injection and production wells, and the formation parameters variation has an obvious influence on the remaining oil distribution.展开更多
Abutment pressure distribution is different when a longwall panel is passing through the abandoned gate roads in a damaged coal seam. According to the geological condition of panel E13103 in Cuijiazhai Coal Mine in Ch...Abutment pressure distribution is different when a longwall panel is passing through the abandoned gate roads in a damaged coal seam. According to the geological condition of panel E13103 in Cuijiazhai Coal Mine in China, theoretical analysis and finite element numerical simulation were used to determine the front pressure distribution characteristics when the longwall face is 70, 50, 30, 20, 10, and 5 m from the abandoned roadways. The research results show that the influence range of abutment pressure is 40 to 45 m outby the face, and the peak value of front abutment pressure is related to the distance between the face and abandoned roadways. When the distance between the longwall face and abandoned roadways is reduced from 50 to 10 m, the front abutment pressure peak value kept increasing. When the distance is 10 m, it has reached the maximum. The peak value is located in 5 to 6 m outby the faceline. When the distance between the longwall face and abandoned roadways is reduced from 10 to 5 m, the front abutment pressure sharply decreases, the intact coal yields and is even in plastic state. The peak value transfers to the other side of the abandoned roadways. The research results provide a theoretical basis for determining the advance support distance of two roadways in the panel and the reinforcement for face stability when the longwall face is passing through the abandoned roadways.展开更多
A review of simulation results, devoted to time-dependent modeling of the initial stage of the formation of large-scale vortices in the troposphere in the vicinity of the intertropical convergence zone, is presented. ...A review of simulation results, devoted to time-dependent modeling of the initial stage of the formation of large-scale vortices in the troposphere in the vicinity of the intertropical convergence zone, is presented. The simulation results were obtained not long ago with the help of the mathematical model of the neutral wind system of the lower atmosphere, developed earlier in the Polar Geophysical Institute. The utilized mathematical model produces three-dimensional distributions of the atmospheric parameters in the height range from 0 to 15 km over a limited region of the Earth’s surface. Simulation results were obtained for the case when the limited three-dimensional simulation domain, situated at low latitudes, is intersected by an intertropical convergence zone in the west-east direction. The reviewed simulation results were obtained for various initial configurations of the intertropical convergence zone. Results of numerical modeling have indicated that the origin of convexities in the form of the intertropical convergence zone can lead to the formation of different large-scale vortices in the lower atmosphere, in particular, a tropical cyclone, pair of cyclonic vortices, pair of cyclonic-anticyclonic vortexes, and triplet of cyclonic vortices. The simulation results, obtained earlier and presented individually in various editions, are reviewed and summarized in the present paper. A physical mechanism, responsible for the formation of the simulated large-scale vortices in the vicinity of the intertropical convergence zone, is discussed.展开更多
In the design of rock sheds for the mitigation of risk due to rapid and long landslides, a crucial role is played by the evaluation of the impact force exerted by the flowing mass on the rock sheds. This paper is focu...In the design of rock sheds for the mitigation of risk due to rapid and long landslides, a crucial role is played by the evaluation of the impact force exerted by the flowing mass on the rock sheds. This paper is focused on the influencing factors of the impact force of dry granular flow onto rock shed and in particular on the evaluation of the maximum impact force. The coupled DEM-FEM model calibrated with small-scale physical experiment is used to simulate the movement of dry granular flow coupled with impact forces on the rock-shed. Based on the numerical results, three key stages were identified of impact process, namely startup streams slippery, impact and pile-up. The maximum impact force increases linearly with bulk density, and the maximum impact force exhibits a power law dependence on the impact height and slop angle respectively. The sensitivities of bulk density, impact height, and slope angle on the maximum impact force are: 1.0, 0.496, and 2.32 respectively in the benchmark model. The parameters with high sensitivity should be given priority in the design of the rock shed. The results obtained from this study are useful for facilitating design of shed against dry granular flow.展开更多
In order to explore the internal wind field flow characteristics of T4-72 type centrifugal fan, the three-dimensional model was established based on PRO/E software. Combined with computational fluid Dynamics Software ...In order to explore the internal wind field flow characteristics of T4-72 type centrifugal fan, the three-dimensional model was established based on PRO/E software. Combined with computational fluid Dynamics Software Fluent 6.3, the standard model and SIMPLEC algorithm were used to simulate the wind field inside the fan. Analysis of the flow characteristics, velocity distributed and pressure distributed of the internal fluid model of the T4-72 centrifugal fan, combined with the theoretical formula to obtain the full pressure, power and efficiency performance parameters of the fan. The centrifugal fan performance curve is drawn. While compared with the experimental data, it is found that the internal flow disturbance is strong when the fan is running under low load condition and high load condition, which affects the performance of the fan and reduces the life of the fan. The numerical simulation results are consistent with the experimental results. The overall performance parameters of the fan are in good agreement, verifying the reliability of the simulation results;when the fan works between 1 - 1.4 times the rated flow rate, it can obtain a more stable flow field while maintaining higher efficiency, which provides a new idea for the optimization of the subsequent fan.展开更多
The fluid identification of carbonate reservoir is a key factor to hydrocarbon exploration and reservoir development. In order to simulate the seismic response characteristics of the cave in the carbonate reservoir, t...The fluid identification of carbonate reservoir is a key factor to hydrocarbon exploration and reservoir development. In order to simulate the seismic response characteristics of the cave in the carbonate reservoir, three sets of models were designed, including the caves varied in width, the caves filled with different solids, and the oil-gas-water model. The numerical simulation technique was used to carry out the forward modeling and the AVO (Amplitude varies with offset) response characteristics of the three groups of models were analyzed. The results show that the AVO characteristics can be observed when the cave reaches a certain extent in the horizontal direction. When the surrounding rock is constant, the absolute value of the intercept of the AVO curve increases with the Vp/Vs decrease. The AVO technology can effectively identify the gas cave. The effect is not obvious to water or oil cave.展开更多
文摘A two-dimensional(2D)computational model for simulation of incipient sediment motion for noncohesive uniform and non-uniform particles on a horizontal bed was developed using the Discrete Element Method(DEM).The model was calibrated and verified using various experimental data reported in the literature and compared with different theories of incipient particle motion.Sensitivity analysis was done and the effects of relevant parameters were determined.In addition to hydrodynamic forces such as drag,shear lift and Magnus force,the particle-particle interaction effects were included in the model.The asymptotic critical mobility number was evaluated for various critical particle Reynolds numbers(R*)in the range of very small and very large R*.The obtained curve is classified into four regions.It was found that in the linear region,the drag force has the principal role on the initiation of motion.Moreover,the critical mobility number is independent of particle diameter.A procedure for estimating the critical shear velocity directly from the information on particle diameter and roughness height was developed.Finally,the mechanism of incipient motion for the different regions was studied and the effect of different forces on the incipient particle motion was obtained.It was found that the maximum effects of lift and Magnus forces were,respectively,less than ten and twenty percent of the total force.The drag force,however,was typically the dominant force accounting for majority of the net hydrodynamic force acting on sediment particles at the onset of incipient motion.
文摘In this paper, a new numerical scheme for solving first-order hyperbolic partial differential equations is proposed and is implemented in the simulation study of macroscopic traffic flow model with constant velocity and linear velocity-density relationship. Macroscopic traffic flow model is first developed by Lighthill Whitham and Richards (LWR) and used to study traffic flow by collective variables such as flow rate, velocity and density. The LWR model is treated as an initial value problem and its numerical simulations are presented using numerical schemes. A variety of numerical schemes are available in literature to solve first order hyperbolic equations. Of these the well-known ones include one-dimensional explicit: Upwind, Downwind, FTCS, and Lax-Friedrichs schemes. Having been studied carefully the space and time mesh sizes, and the patterns of all these schemes, a new scheme has been developed and named as one-dimensional explicit Tolesa numerical scheme. Tolesa numerical scheme is one of the conditionally stable and highest rates of convergence schemes. All the said numerical schemes are applied to solve advection equation pertaining traffic flows. Also the one-dimensional explicit Tolesa numerical scheme is another alternative numerical scheme to solve advection equation and apply to traffic flows model like other well-known one-dimensional explicit schemes. The effect of density of cars on the overall interactions of the vehicles along a given length of the highway and time are investigated. Graphical representations of density profile, velocity profile, flux profile, and in general the fundamental diagrams of vehicles on the highway with different time levels are illustrated. These concepts and results have been arranged systematically in this paper.
文摘Oilfield A is a fractured buried hill reservoir in Bohai bay of China. In order to solve the difficult problem of water flooding timing and method in oilfield. Considering the characteristics of the buried hill fractures with stress sensitivity and strong heterogeneity, the ECLIPSE software was used in the research, and a three-dimensional injection-production numerical model for horizontal wells in buried hill reservoirs is established. According to the main research factors in water flooding, a series of water flooding schemes are designed, and the optimization of water flooding timing, oil recovery rate and water flooding mode in buried hill reservoirs were carried out. The results show that the optimum pressure level of fractured reservoir is about 70% of the original reservoir pressure. The optimal water flooding method is the conventional water flooding in the initial stage, when the water cut reaches 80%, it is converted into periodic water flooding. The oil recovery is the highest when the water injection period is 4 months. Field tests show that conventional water flooding is carried out in the initial stage of the oilfield A when the pressure is reduced to 70% of the original. Periodic water flooding is carried out when water cut is 80%. Good development results had been achieved in the 10 years since oilfield A was put into production. The average productivity of single well reached 300 m3/d in the initial stage, at present, the water cut is 60%, and the recovery degree is 18.5%, which is better than that of similar oilfields. This technology improves the water flooding effect of blocky bottom water fractured dual media reservoirs in metamorphic buried hills, and provides a reference for the development of similar reservoirs.
文摘The filter paper and activated carbon which filled inside the gas filter have porous media characteristics. In order to study the flow field structure in the filter layer and the activated carbon layer, Computational Fluid Dynamics method is used to simulate the aerodynamic characteristics of a simplified gas filter. The inertial and viscosity parameters of porous media are solved by Forchheimer equation. The three-dimensional N-S equation and the modified low Reynolds number k-ε turbulence model are adopted to analyze the influence of the explosion-proof plate on the gas filter’s aerodynamic characteristics. The results showed that the air age in the upstream of the activated carbon plates was small, which easily caused the rapid penetration of the Poisonous gas. And in the downstream and around of the activated carbon plates, the air age is larger, formed dead zone, the utilization rate of activated carbon is lower. The explosion-proof plate increases the pressure drop of the gas filter, the air age distribution in the filter layer is more uniform and the utilization rate of filter paper is improved. However, the explosion-proof plate has little influence on the flow field structure of the activated carbon layer.
文摘We investigate under what conditions transient simulation could be used to integrate backward in time so that the initial field could be recovered from later histories. In this paper we use realistic examples and find that, in long histories, traces of the initial field would be present only in the exact analytical solutions. We conclude that the recovery of initial field is possible only if the equations could be solved analytically or only short time periods are involved. In practice, it is not possible to detect those traces by measurements or observations. If numerical procedures are used, truncation and discretization errors are always present. Fine-tuning of system parameters used or transforming time into another pseudo time frame may allow numerical integration to be carried out backward in time. But numerical instability is still a problem. Large spurious increases found by numerical procedures are most likely due to numerical inaccuracy and instability.
文摘The demand for natural gas in the world is increasing day by day. The efficient and flexible LNG becomes the preferred method for natural gas storage and transportation and has gradually entered people’s daily life. The enclosure system is the key core of LNG transport and storage vessels for storage of LNG at -163°C for isolation and thermal insulation. A new type of flat half-film prismatic LNG enclosure system has been developed for the shortcomings of the existing LNG cargo enclosure system. Through the breakthrough and mastery of key core technologies such as the overall layout and integration of the system, anti-leakage technology, liquid tank fixing technology, and large-scale friction stir welding (P-FSW) flat-line pipeline development technology, we’ll strive to fill the gap in the intelligent construction technology of large aluminum alloy tanks in China. The tank was subjected to water vapor test and numerical simulation. The results show that the structural strength of the FSP-LNG tank meets the strength check standard of IGC Code.
文摘In this study, flow structures and mixing performance in a blade-free planetary mixer, which combines rotation and revolution motions inside a cylindrical vessel, are numerically investigated. Flow fields in the mixer vessel are simulated in a single rotating reference frame with various revolution speeds and a fixed rotation speed. The mixing process is investigated by a Lagrangian particle tracking method and the mixing performance is evaluated based on particle concentration. The results of the numerical simulations show that a vortical flow with an axis inclined with respect to the rotation axis of the vessel is generated by the combined influence of the rotation and revolution motions. The flow structure and vortical flow intensity vary as a function of the precession rate, which is the ratio of the revolution speed to rotation speed. The mixing performance of the blade-free planetary mixer is found to be maximum at aspecific precession rate.
文摘After long-term waterflooding in unconsolidated sandstone reservoir, the high-permeability channels are easy to evolve, which leads to a significant reduction in water flooding efficiency and a poor oilfield development effect. The current researches on the formation parameters variation are mainly based on the experiment analysis or field statistics, while lacking quantitative research of combining microcosmic and macroscopic mechanism. A network model was built after taking the detachment and entrapment mechanisms of particles in unconsolidated sandstone reservoir into consideration. Then a coupled mathematical model for the formation parameters variation was established based on the network modeling and the model of fluids flowing in porous media. The model was solved by a finite-difference method and the Gauss-Seidel iterative technique. A novel field-scale reservoir numerical simulator was written in Fortran 90 and it can be used to predict 1) the evolvement of high-permeability channels caused by particles release and migration in the long-term water flooding process, and 2) well production performances and remaining oil distribution. In addition, a series of oil field examples with inverted nine-spot pattern was made on the new numerical simulator. The results show that the high-permeability channels are more likely to develop along the main streamlines between the injection and production wells, and the formation parameters variation has an obvious influence on the remaining oil distribution.
基金National Key R&D Program of China (No.2017YFC060300204)Yue Qi Young Scholar Project,CUMTB and Yue Qi Distinguished Scholar Project (No.800015Z1138)China University of Mining & Technology,Beijing.
文摘Abutment pressure distribution is different when a longwall panel is passing through the abandoned gate roads in a damaged coal seam. According to the geological condition of panel E13103 in Cuijiazhai Coal Mine in China, theoretical analysis and finite element numerical simulation were used to determine the front pressure distribution characteristics when the longwall face is 70, 50, 30, 20, 10, and 5 m from the abandoned roadways. The research results show that the influence range of abutment pressure is 40 to 45 m outby the face, and the peak value of front abutment pressure is related to the distance between the face and abandoned roadways. When the distance between the longwall face and abandoned roadways is reduced from 50 to 10 m, the front abutment pressure peak value kept increasing. When the distance is 10 m, it has reached the maximum. The peak value is located in 5 to 6 m outby the faceline. When the distance between the longwall face and abandoned roadways is reduced from 10 to 5 m, the front abutment pressure sharply decreases, the intact coal yields and is even in plastic state. The peak value transfers to the other side of the abandoned roadways. The research results provide a theoretical basis for determining the advance support distance of two roadways in the panel and the reinforcement for face stability when the longwall face is passing through the abandoned roadways.
文摘A review of simulation results, devoted to time-dependent modeling of the initial stage of the formation of large-scale vortices in the troposphere in the vicinity of the intertropical convergence zone, is presented. The simulation results were obtained not long ago with the help of the mathematical model of the neutral wind system of the lower atmosphere, developed earlier in the Polar Geophysical Institute. The utilized mathematical model produces three-dimensional distributions of the atmospheric parameters in the height range from 0 to 15 km over a limited region of the Earth’s surface. Simulation results were obtained for the case when the limited three-dimensional simulation domain, situated at low latitudes, is intersected by an intertropical convergence zone in the west-east direction. The reviewed simulation results were obtained for various initial configurations of the intertropical convergence zone. Results of numerical modeling have indicated that the origin of convexities in the form of the intertropical convergence zone can lead to the formation of different large-scale vortices in the lower atmosphere, in particular, a tropical cyclone, pair of cyclonic vortices, pair of cyclonic-anticyclonic vortexes, and triplet of cyclonic vortices. The simulation results, obtained earlier and presented individually in various editions, are reviewed and summarized in the present paper. A physical mechanism, responsible for the formation of the simulated large-scale vortices in the vicinity of the intertropical convergence zone, is discussed.
文摘In the design of rock sheds for the mitigation of risk due to rapid and long landslides, a crucial role is played by the evaluation of the impact force exerted by the flowing mass on the rock sheds. This paper is focused on the influencing factors of the impact force of dry granular flow onto rock shed and in particular on the evaluation of the maximum impact force. The coupled DEM-FEM model calibrated with small-scale physical experiment is used to simulate the movement of dry granular flow coupled with impact forces on the rock-shed. Based on the numerical results, three key stages were identified of impact process, namely startup streams slippery, impact and pile-up. The maximum impact force increases linearly with bulk density, and the maximum impact force exhibits a power law dependence on the impact height and slop angle respectively. The sensitivities of bulk density, impact height, and slope angle on the maximum impact force are: 1.0, 0.496, and 2.32 respectively in the benchmark model. The parameters with high sensitivity should be given priority in the design of the rock shed. The results obtained from this study are useful for facilitating design of shed against dry granular flow.
文摘In order to explore the internal wind field flow characteristics of T4-72 type centrifugal fan, the three-dimensional model was established based on PRO/E software. Combined with computational fluid Dynamics Software Fluent 6.3, the standard model and SIMPLEC algorithm were used to simulate the wind field inside the fan. Analysis of the flow characteristics, velocity distributed and pressure distributed of the internal fluid model of the T4-72 centrifugal fan, combined with the theoretical formula to obtain the full pressure, power and efficiency performance parameters of the fan. The centrifugal fan performance curve is drawn. While compared with the experimental data, it is found that the internal flow disturbance is strong when the fan is running under low load condition and high load condition, which affects the performance of the fan and reduces the life of the fan. The numerical simulation results are consistent with the experimental results. The overall performance parameters of the fan are in good agreement, verifying the reliability of the simulation results;when the fan works between 1 - 1.4 times the rated flow rate, it can obtain a more stable flow field while maintaining higher efficiency, which provides a new idea for the optimization of the subsequent fan.
文摘The fluid identification of carbonate reservoir is a key factor to hydrocarbon exploration and reservoir development. In order to simulate the seismic response characteristics of the cave in the carbonate reservoir, three sets of models were designed, including the caves varied in width, the caves filled with different solids, and the oil-gas-water model. The numerical simulation technique was used to carry out the forward modeling and the AVO (Amplitude varies with offset) response characteristics of the three groups of models were analyzed. The results show that the AVO characteristics can be observed when the cave reaches a certain extent in the horizontal direction. When the surrounding rock is constant, the absolute value of the intercept of the AVO curve increases with the Vp/Vs decrease. The AVO technology can effectively identify the gas cave. The effect is not obvious to water or oil cave.