Hydraulic butterfly valves have been widely applied in marine engineering because of their large switching torque, low pressure loss and suitability for large and medium diameter pipelines. Due to control problems res...Hydraulic butterfly valves have been widely applied in marine engineering because of their large switching torque, low pressure loss and suitability for large and medium diameter pipelines. Due to control problems resulting from switching angular speeds of the hydraulic butterfly valve, a throttle-governing control mode has been widely adopted, and detailed analysis has been carried out worldwide on the structural principle concerning speed-regulation and the load torque on the shaft while opening or closing a hydraulic butterfly valve. However relevant reports have yet been published on the change law, the error and the influencing factors of the rotational angular velocity of the hydraulic butterfly valve while opening and closing. In this article, research was based on some common specifications of a hydraulic butterfly valve with a symmetrical valve flap existing in a marine environment. The throttle governing system supplied by the accumulator to achieve the switching of the hydraulic control valve was adopted, and the mathematical models of the system were established in the actual conditions while the numerical simulations took place. The simulation results and analysis show that the rotational angular velocity and the error of the hydraulic butterfly valve while switching is influenced greatly by the drainage amount of the accumulator, resulting in pressure loss in the pipeline, the temperature of hydraulic medium and the load of the hydraulic butterfly valve. The simulation results and analysis provide a theoretical basis for the choice of the total capacity of the accumulator and pipeline diameters in a throttle governing system with a hydraulic butterfly valve.It also determines the type and specification of the hydraulic butterfly valve and the design of motion parameters of the transported fluid.展开更多
Detonation of low energy detonating fuse was studied in numerical simulation and experiments in bending conditions using LS_DYNA3D. The results show that pressure of the explosion and detonation velocity decrease in t...Detonation of low energy detonating fuse was studied in numerical simulation and experiments in bending conditions using LS_DYNA3D. The results show that pressure of the explosion and detonation velocity decrease in the same section areas after bending. In bending conditions, detonation wave was similar to small angle comer diffraction. So the detonation velocity was lower than normal velocity.展开更多
The petroleum industry has shown great interest in the study of drilling optimization on pre-salt formations given the low rates of penetration observed so far. Rate of penetration is the key to economically drill the...The petroleum industry has shown great interest in the study of drilling optimization on pre-salt formations given the low rates of penetration observed so far. Rate of penetration is the key to economically drill the pre-salt carbonate rock. This work presents the results of numerical modeling through finite element method and discrete element method for single cutter drilling in carbonate samples. The work is relevant to understand the mechanics of drill bit-rock interaction while drilling deep wells and the results were validated with experimental data raised under simulated downhole conditions. The numerical models were carried out under different geometrical configurations, varying the cutter chamfer size and back-rake angles. The forces generated on the cutter are translated into mechanical specific energy as this parameter is often used to measure drilling efficiency. Results indicate that the chamfer size does not change significantly the mechanical specific energy values, characteristic. Results also show there is a significant increase although the cutter aggressiveness is influenced by this geometrical in drilling resistance for larger values of back-rake angle.展开更多
When applying fiat belts, correct tracking of the belt through the installation has to be assured. Since flat belts are commonly used for conveying and transmission purposes, tracking systems have been well developed,...When applying fiat belts, correct tracking of the belt through the installation has to be assured. Since flat belts are commonly used for conveying and transmission purposes, tracking systems have been well developed, but the ultimate tracking behaviour of the belt can be greatly enhanced by taking special care in the creation of an adequate tracking mechanism. To obtain long-life operation and full value from the equipment, the correct tracking technique plays an important role. This paper deals with two tracking techniques： The skewed and the angled pulley axis. Numerical simulation results are compared with both measurements and an analytical approach. The advantages of numerical simulation compared to experimental tests are ease, convenience and the absence of any safety risk. Compared to analytical approaches the simulation is used for systems for which simple closed form analytic solutions are not possible.展开更多
Yangbajing (YBJ) is located in the Tibetan Plateau, China. The characteristics of solar radiation and its relationship with clouds at YBJ from April 2009 to April 2010 were analyzed in this paper. The annual mean sola...Yangbajing (YBJ) is located in the Tibetan Plateau, China. The characteristics of solar radiation and its relationship with clouds at YBJ from April 2009 to April 2010 were analyzed in this paper. The annual mean solar radiation was 478.4 W m 2 , and the annual mean transmittance was 0.713. The atmospheric mean trans- mittance of clear skies reaches 0.828 when the solar elevation angle (SEA) is greater than 10 degrees. Comparisons with numerical simulations show that the atmosphere of YBJ is clean. Impacts from atmospheric conditions on solar radiation are similar for clear skies during the year because the standard deviation of transmittance in clear skies was less than 0.05 when the SEA was greater than 10 degrees. It is important to understand the impact of clouds on solar radiation without considering other impact factors. In the last part of this article, the authors analyzed and established a statistical quantitative relationship between surface solar radiation and cloud fraction.展开更多
The flow characteristics of the centrifugal fans with different blade outlet angles are basically discussed on steady and unsteady simulations for a rectangular casing fan. The blade outlet angles of the impellers are...The flow characteristics of the centrifugal fans with different blade outlet angles are basically discussed on steady and unsteady simulations for a rectangular casing fan. The blade outlet angles of the impellers are 35° and 25° respectively. The unsteady flow behavior in the passage of the impeller 35° is quite different from that in the steady flow behavior. The large flow separation occurs in the steady flow field and unsteady flow field of the impeller 35°, the flow distribution in the circumferential direction varies remarkably and the flow separation on the blade occurs only at the back region of the fan; but the steady flow behavior in the impeller 25° is almost consistent with the unsteady flow behavior, the flow distribution of the circumferential direction doesn't vary much and the flow separation on the blade hardly occurs. When the circumferential variation of the flow in the impeller is large, the steady flow simulation is not coincident to the unsteady flow simulation.展开更多
A numerical method using AUSMDV scheme and k-ω SST turbulence model with an explicit compressibility correction was developed,and a 3-D numerical simulation of a supersonic flow field with a vertical sonic jet of hyd...A numerical method using AUSMDV scheme and k-ω SST turbulence model with an explicit compressibility correction was developed,and a 3-D numerical simulation of a supersonic flow field with a vertical sonic jet of hydrogen was performed.Good agreement between numerical results and experimental data validated the reliability of the numerical method.Whereafter,two parameters,mass-weighted average total pressure and mixing efficiency,were defined to evaluate the mixing performance of different injection schemes.Based on the numerical method and evaluation criterion,the mixing characteristics of different injection schemes were studied in detail.It was found that for the mixing field of supersonic transverse jet,the near-field mixing is controlled by convection transport while the far-field mixing is controlled by mass diffusion;the circular-hole injection causes a loss of total pressure comparable to the slot injection,but can induce a much higher mixing efficiency because of its 3-D flow characteristic;the variation of injection angle under circular-hole injection mainly affects the near-field mixing degree,and among the five injection angles studied in the present paper,angle 120° is the optimal one;with the increase of the ratio between injector space and diameter,the induced mixing efficiency increases while the caused loss of total pressure can grow greatly;the two-stage injection method designed through reducing the injector area to keep the same hydrogen mass flowrate can induce a much higher mixing efficiency while only a bit larger loss of total pressure when compared to the single-stage injection,and hence the two-stage injection is superior to the single-stage injection.The research results can direct the design of the fuel injection method in the combustor of scramjet engine.展开更多
文摘Hydraulic butterfly valves have been widely applied in marine engineering because of their large switching torque, low pressure loss and suitability for large and medium diameter pipelines. Due to control problems resulting from switching angular speeds of the hydraulic butterfly valve, a throttle-governing control mode has been widely adopted, and detailed analysis has been carried out worldwide on the structural principle concerning speed-regulation and the load torque on the shaft while opening or closing a hydraulic butterfly valve. However relevant reports have yet been published on the change law, the error and the influencing factors of the rotational angular velocity of the hydraulic butterfly valve while opening and closing. In this article, research was based on some common specifications of a hydraulic butterfly valve with a symmetrical valve flap existing in a marine environment. The throttle governing system supplied by the accumulator to achieve the switching of the hydraulic control valve was adopted, and the mathematical models of the system were established in the actual conditions while the numerical simulations took place. The simulation results and analysis show that the rotational angular velocity and the error of the hydraulic butterfly valve while switching is influenced greatly by the drainage amount of the accumulator, resulting in pressure loss in the pipeline, the temperature of hydraulic medium and the load of the hydraulic butterfly valve. The simulation results and analysis provide a theoretical basis for the choice of the total capacity of the accumulator and pipeline diameters in a throttle governing system with a hydraulic butterfly valve.It also determines the type and specification of the hydraulic butterfly valve and the design of motion parameters of the transported fluid.
文摘Detonation of low energy detonating fuse was studied in numerical simulation and experiments in bending conditions using LS_DYNA3D. The results show that pressure of the explosion and detonation velocity decrease in the same section areas after bending. In bending conditions, detonation wave was similar to small angle comer diffraction. So the detonation velocity was lower than normal velocity.
文摘The petroleum industry has shown great interest in the study of drilling optimization on pre-salt formations given the low rates of penetration observed so far. Rate of penetration is the key to economically drill the pre-salt carbonate rock. This work presents the results of numerical modeling through finite element method and discrete element method for single cutter drilling in carbonate samples. The work is relevant to understand the mechanics of drill bit-rock interaction while drilling deep wells and the results were validated with experimental data raised under simulated downhole conditions. The numerical models were carried out under different geometrical configurations, varying the cutter chamfer size and back-rake angles. The forces generated on the cutter are translated into mechanical specific energy as this parameter is often used to measure drilling efficiency. Results indicate that the chamfer size does not change significantly the mechanical specific energy values, characteristic. Results also show there is a significant increase although the cutter aggressiveness is influenced by this geometrical in drilling resistance for larger values of back-rake angle.
文摘When applying fiat belts, correct tracking of the belt through the installation has to be assured. Since flat belts are commonly used for conveying and transmission purposes, tracking systems have been well developed, but the ultimate tracking behaviour of the belt can be greatly enhanced by taking special care in the creation of an adequate tracking mechanism. To obtain long-life operation and full value from the equipment, the correct tracking technique plays an important role. This paper deals with two tracking techniques： The skewed and the angled pulley axis. Numerical simulation results are compared with both measurements and an analytical approach. The advantages of numerical simulation compared to experimental tests are ease, convenience and the absence of any safety risk. Compared to analytical approaches the simulation is used for systems for which simple closed form analytic solutions are not possible.
基金support from the National Special Fund for the Commonweal Industry (Meteorology)of China (Grant No. GYHY200806031)
文摘Yangbajing (YBJ) is located in the Tibetan Plateau, China. The characteristics of solar radiation and its relationship with clouds at YBJ from April 2009 to April 2010 were analyzed in this paper. The annual mean solar radiation was 478.4 W m 2 , and the annual mean transmittance was 0.713. The atmospheric mean trans- mittance of clear skies reaches 0.828 when the solar elevation angle (SEA) is greater than 10 degrees. Comparisons with numerical simulations show that the atmosphere of YBJ is clean. Impacts from atmospheric conditions on solar radiation are similar for clear skies during the year because the standard deviation of transmittance in clear skies was less than 0.05 when the SEA was greater than 10 degrees. It is important to understand the impact of clouds on solar radiation without considering other impact factors. In the last part of this article, the authors analyzed and established a statistical quantitative relationship between surface solar radiation and cloud fraction.
文摘The flow characteristics of the centrifugal fans with different blade outlet angles are basically discussed on steady and unsteady simulations for a rectangular casing fan. The blade outlet angles of the impellers are 35° and 25° respectively. The unsteady flow behavior in the passage of the impeller 35° is quite different from that in the steady flow behavior. The large flow separation occurs in the steady flow field and unsteady flow field of the impeller 35°, the flow distribution in the circumferential direction varies remarkably and the flow separation on the blade occurs only at the back region of the fan; but the steady flow behavior in the impeller 25° is almost consistent with the unsteady flow behavior, the flow distribution of the circumferential direction doesn't vary much and the flow separation on the blade hardly occurs. When the circumferential variation of the flow in the impeller is large, the steady flow simulation is not coincident to the unsteady flow simulation.
文摘A numerical method using AUSMDV scheme and k-ω SST turbulence model with an explicit compressibility correction was developed,and a 3-D numerical simulation of a supersonic flow field with a vertical sonic jet of hydrogen was performed.Good agreement between numerical results and experimental data validated the reliability of the numerical method.Whereafter,two parameters,mass-weighted average total pressure and mixing efficiency,were defined to evaluate the mixing performance of different injection schemes.Based on the numerical method and evaluation criterion,the mixing characteristics of different injection schemes were studied in detail.It was found that for the mixing field of supersonic transverse jet,the near-field mixing is controlled by convection transport while the far-field mixing is controlled by mass diffusion;the circular-hole injection causes a loss of total pressure comparable to the slot injection,but can induce a much higher mixing efficiency because of its 3-D flow characteristic;the variation of injection angle under circular-hole injection mainly affects the near-field mixing degree,and among the five injection angles studied in the present paper,angle 120° is the optimal one;with the increase of the ratio between injector space and diameter,the induced mixing efficiency increases while the caused loss of total pressure can grow greatly;the two-stage injection method designed through reducing the injector area to keep the same hydrogen mass flowrate can induce a much higher mixing efficiency while only a bit larger loss of total pressure when compared to the single-stage injection,and hence the two-stage injection is superior to the single-stage injection.The research results can direct the design of the fuel injection method in the combustor of scramjet engine.
