The unsteady performance of drag and double reverse propeller podded propulsors in open water was numerically simulated using a computational fluid dynamics （CFD） method. A moving mesh method was used to more realis...The unsteady performance of drag and double reverse propeller podded propulsors in open water was numerically simulated using a computational fluid dynamics （CFD） method. A moving mesh method was used to more realistically simulate propulsor working conditions, and the thrust, torque, and lateral force coefficients of both propulsors were compared and analyzed. Forces acting on different parts of the propulsors along with the flow field distribution of steady and unsteady results at different advance coefficients were compared. Moreover, the change of the lateral force and the difference between the abovementioned two methods were mainly analyzed. It was shown that the thrust and torque results of both methods were similar, with the lateral force results having the highest deviation展开更多
One of the key challenges in largescale network simulation is the huge computation demand in fine-grained traffic simulation.Apart from using high-performance computing facilities and parallelism techniques,an alterna...One of the key challenges in largescale network simulation is the huge computation demand in fine-grained traffic simulation.Apart from using high-performance computing facilities and parallelism techniques,an alternative is to replace the background traffic by simplified abstract models such as fluid flows.This paper suggests a hybrid modeling approach for background traffic,which combines ON/OFF model with TCP activities.The ON/OFF model is to characterize the application activities,and the ordinary differential equations(ODEs) based on fluid flows is to describe the TCP congestion avoidance functionality.The apparent merits of this approach are(1) to accurately capture the traffic self-similarity at source level,(2) properly reflect the network dynamics,and(3) efficiently decrease the computational complexity.The experimental results show that the approach perfectly makes a proper trade-off between accuracy and complexity in background traffic simulation.展开更多
Based on an exact CAD model of hydro-mechanical continuously variable transmission （HMCVT） gearbox which can transmit 180 horsepower, virtual prototype of the HMCVT was built. Revolution speed of shafts, gears and c...Based on an exact CAD model of hydro-mechanical continuously variable transmission （HMCVT） gearbox which can transmit 180 horsepower, virtual prototype of the HMCVT was built. Revolution speed of shafts, gears and clutches of the HMCVT were calibrated by using results obtained by theoretical calculation and test methods. The needed power and torques of both mechanical power input shaft and hydropower input shaft were calculated by simulation. Hydraulic power distributing ratio and power flow of the system was also studied. The analysis results showed that cycle power was produced inevitably when the output shaft speed of HMCVT change smoothly during mechanical and hydraulic working state HM1 to HM4, and the instantaneous maximum cycle power was 39.5%. Then the overall transmission efficiency of HMCVT was studied, and the maximum overall efficiency of the system was about 87%. The results of the studies gave references to select suited engine and variable displacement pump for the HMCVT, and to develop rational speed control strategies for the HMCVT by changing displacement ratio of variable displacement pump.展开更多
Interaction between rotor and struts has great effect on the performance of small axial fan systems. The small axial fan systems are selected as the studied objects in this paper, and four square struts are downstream...Interaction between rotor and struts has great effect on the performance of small axial fan systems. The small axial fan systems are selected as the studied objects in this paper, and four square struts are downstream of the rotor. The cross section of the struts is changed to the cylindrical shapes for the investigation： one is in the same hy- draulic diameter as the square struts and another one is in the same cross section as the square struts. Influence of the shape of the struts on the static pressure characteristics, the internal flow and the sound emission of the small axial fans are studied. Standard K-s turbulence model and SIMPLE algorithm are applied in the calculation of the steady fluid field, and the curves of the pressure rising against the flow rate are obtained, which demonstrates that the simulation results are in nice consistence with the experimental data. The steady calculation results are set as the initial field in the unsteady calculation. Large eddy simulation and PISO algorithm are used in the transient calculation, and the Ffowcs Williams-Hawkings model is introduced to predict the sound level at the eight monitoring points. The research results show that： the static pressure coefficients of the fan with cylindrical struts increase by about 25% compared to the fan with square strum, and the efficiencies increase by about 28.6%. The research provides a theoretical guide for shape optimization and noise reduction of small axial fan with struts.展开更多
基金Supported by National Natural Science Foundation of China （41176074, 51209048,51379043,51409063） High tech ship research project of Ministry of industry and technology （G014613002） The support plan for youth backbone teachers of Harbin Engineering University （HEUCFQ1408）
文摘The unsteady performance of drag and double reverse propeller podded propulsors in open water was numerically simulated using a computational fluid dynamics （CFD） method. A moving mesh method was used to more realistically simulate propulsor working conditions, and the thrust, torque, and lateral force coefficients of both propulsors were compared and analyzed. Forces acting on different parts of the propulsors along with the flow field distribution of steady and unsteady results at different advance coefficients were compared. Moreover, the change of the lateral force and the difference between the abovementioned two methods were mainly analyzed. It was shown that the thrust and torque results of both methods were similar, with the lateral force results having the highest deviation
基金supported by the Science and Technology Project of Zhejiang Province(No. 2014C01051)the National High Technology Development 863 Program of China( No.2015AA011901)
文摘One of the key challenges in largescale network simulation is the huge computation demand in fine-grained traffic simulation.Apart from using high-performance computing facilities and parallelism techniques,an alternative is to replace the background traffic by simplified abstract models such as fluid flows.This paper suggests a hybrid modeling approach for background traffic,which combines ON/OFF model with TCP activities.The ON/OFF model is to characterize the application activities,and the ordinary differential equations(ODEs) based on fluid flows is to describe the TCP congestion avoidance functionality.The apparent merits of this approach are(1) to accurately capture the traffic self-similarity at source level,(2) properly reflect the network dynamics,and(3) efficiently decrease the computational complexity.The experimental results show that the approach perfectly makes a proper trade-off between accuracy and complexity in background traffic simulation.
基金The authors acknowledge the support of Project supported by recommend international advanced agricultural science and technology plan of Ministry of Agriculture of China （Grant No. 2010-Z18）, and the National Natural Science Foundation of China （Grant No. 51275249）.
文摘Based on an exact CAD model of hydro-mechanical continuously variable transmission （HMCVT） gearbox which can transmit 180 horsepower, virtual prototype of the HMCVT was built. Revolution speed of shafts, gears and clutches of the HMCVT were calibrated by using results obtained by theoretical calculation and test methods. The needed power and torques of both mechanical power input shaft and hydropower input shaft were calculated by simulation. Hydraulic power distributing ratio and power flow of the system was also studied. The analysis results showed that cycle power was produced inevitably when the output shaft speed of HMCVT change smoothly during mechanical and hydraulic working state HM1 to HM4, and the instantaneous maximum cycle power was 39.5%. Then the overall transmission efficiency of HMCVT was studied, and the maximum overall efficiency of the system was about 87%. The results of the studies gave references to select suited engine and variable displacement pump for the HMCVT, and to develop rational speed control strategies for the HMCVT by changing displacement ratio of variable displacement pump.
基金supported by National Natural Science Foundation of China(No.51276172)National Science and Technology Support Project(No.2013BAF05B01)etc
文摘Interaction between rotor and struts has great effect on the performance of small axial fan systems. The small axial fan systems are selected as the studied objects in this paper, and four square struts are downstream of the rotor. The cross section of the struts is changed to the cylindrical shapes for the investigation： one is in the same hy- draulic diameter as the square struts and another one is in the same cross section as the square struts. Influence of the shape of the struts on the static pressure characteristics, the internal flow and the sound emission of the small axial fans are studied. Standard K-s turbulence model and SIMPLE algorithm are applied in the calculation of the steady fluid field, and the curves of the pressure rising against the flow rate are obtained, which demonstrates that the simulation results are in nice consistence with the experimental data. The steady calculation results are set as the initial field in the unsteady calculation. Large eddy simulation and PISO algorithm are used in the transient calculation, and the Ffowcs Williams-Hawkings model is introduced to predict the sound level at the eight monitoring points. The research results show that： the static pressure coefficients of the fan with cylindrical struts increase by about 25% compared to the fan with square strum, and the efficiencies increase by about 28.6%. The research provides a theoretical guide for shape optimization and noise reduction of small axial fan with struts.
