A growing interest has been devoted to the contra-rotating propellers （CRPs） due to their high propulsive efficiency, torque balance, low fuel consumption, low cavitations, low noise performance and low hull vibrati...A growing interest has been devoted to the contra-rotating propellers （CRPs） due to their high propulsive efficiency, torque balance, low fuel consumption, low cavitations, low noise performance and low hull vibration. Compared with the single-screw system, it is more difficult for the open water performance prediction because forward and aft propellers interact with each other and generate a more complicated flow field around the CRPs system. The current work focuses on the open water performance prediction of contra-rotating propellers by RANS and sliding mesh method considering the effect of computational time step size and turbulence model. The validation study has been performed on two sets of contra-rotating propellers developed by David W Taylor Naval Ship R ＆ D center. Compared with the experimental data, it shows that RANS with sliding mesh method and SST k-ω turbulence model has a good precision in the open water performance prediction of contra-rotating propellers, and small time step size can improve the level of accuracy for CRPs with the same blade number of forward and aft propellers, while a relatively large time step size is a better choice for CRPs with different blade numbers.展开更多
This paper addresses the open vehicle routing problem with time window(OVRPTW), where each vehicle does not need to return to the depot after completing the delivery task.The optimization objective is to minimize the ...This paper addresses the open vehicle routing problem with time window(OVRPTW), where each vehicle does not need to return to the depot after completing the delivery task.The optimization objective is to minimize the total distance. This problem exists widely in real-life logistics distribution process.We propose a hybrid column generation algorithm(HCGA) for the OVRPTW, embedding both exact algorithm and metaheuristic. In HCGA, a label setting algorithm and an intelligent algorithm are designed to select columns from small and large subproblems, respectively. Moreover, a branch strategy is devised to generate the final feasible solution for the OVRPTW. The computational results show that the proposed algorithm has faster speed and can obtain the approximate optimal solution of the problem with 100 customers in a reasonable time.展开更多
Different cultivars of rice(Oryza sativa)open at different times of the day,and the overlap of anthesis time in rice between the neighbouring cultivars is of crucial importance to the degree of cross pollination in ri...Different cultivars of rice(Oryza sativa)open at different times of the day,and the overlap of anthesis time in rice between the neighbouring cultivars is of crucial importance to the degree of cross pollination in rice.Nevertheless,none of the past experiments with cross pollination between different rice cultivars ever reported the respective flower opening time(FOT)and flower exposure duration(FED)of the parent cultivars,until recently.The authors present here the first record of FOT and FED of 1114 indica rice landraces of South and Southeast Asia,growing during sum-mer and winter seasons in three consecutive years.The authors also present an analysis of the influences of the grow-ing season on the anthesis behaviour,and present the first records of the FOT and FED variability on sunny and cloudy days of a large number of landraces.The data show that rice florets tend to open later in the morning(that is,take longer time to anthesis after sunrise)on sunny days than on cloudy days,and also significantly later during long day seasons(spring and summer)than during short day season(winter);and that FED is inversely related to both FOT and the length of duration from sunrise to first flower opening.The wide ranges of FOT(8:50 a.m.to 12:40 p.m.)and FED(15 to 194 minutes)also suggest the ample time window for receiving pollen from neighbouring cultivars with differ-ent FOT,enhancing the chances of cross pollination between hundreds of rice landraces with FOT and FED overlaps.展开更多
A new approach is presented for deriving the residence time distribution(RTD)in open-type reactors with exclusion of residence in the fore section.Inasmuch as failure to predict the con-version of chemical reactions h...A new approach is presented for deriving the residence time distribution(RTD)in open-type reactors with exclusion of residence in the fore section.Inasmuch as failure to predict the con-version of chemical reactions has been evidenced in many occasions,numerical solution of tracerdispersion in the presence of background concentration gradient of reactant is given to demonstratethe strong effect of background reactant on the true RTD a reactant molecule experiences.Withinthe error of computation,the conversion of a first-order chemical reaction under steady state is shownto be equal in both closed and open reactors,despite difference in relevant展开更多
MUCH has been said about South Africa joining the BRIC.Detractors say that the country is punching way above its weight. One of the biggest critics of the inclusion has been Jim O’Neill,Chairperson of Goldman Sachs A...MUCH has been said about South Africa joining the BRIC.Detractors say that the country is punching way above its weight. One of the biggest critics of the inclusion has been Jim O’Neill,Chairperson of Goldman Sachs Asset Management,who originally coined the term BRIC in 2001. O’Neill is on record as saying that he believes South Africa was invited for political reasons and not economical ones.He says South Africa’s working population is too small,and therefore had plumped for Nigeria to be a better choice to join the BRIC.South Africa’s total population is 50 million with Nigeria triple that at 150 million.展开更多
With the increased number of PMUs in the power grid, effective high speed, realtime methods to ascertain relevant data for situational awareness are needed. Several techniques have used data from PMUs in conjunction w...With the increased number of PMUs in the power grid, effective high speed, realtime methods to ascertain relevant data for situational awareness are needed. Several techniques have used data from PMUs in conjunction with state estimation to assess system stability and event detection. However, these techniques require system topology and a large computational time. This paper presents a novel approach that uses real-time PMU data streams without the need of system connectivity or additional state estimation. The new development is based on the approximation of the eigenvalues related to the decoupled discreet-time power flow Jacobian matrix using direct openPDC data in real-time. Results are compared with other methods, such as Prony’s method, which can be too slow to handle big data. The newly developed Discreet-Time Jacobian Eigenvalue Approximation (DDJEA) method not only proves its accuracy, but also shows its effectiveness with minimal computational time: an essential element when considering situational awareness.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.51079157)
文摘A growing interest has been devoted to the contra-rotating propellers （CRPs） due to their high propulsive efficiency, torque balance, low fuel consumption, low cavitations, low noise performance and low hull vibration. Compared with the single-screw system, it is more difficult for the open water performance prediction because forward and aft propellers interact with each other and generate a more complicated flow field around the CRPs system. The current work focuses on the open water performance prediction of contra-rotating propellers by RANS and sliding mesh method considering the effect of computational time step size and turbulence model. The validation study has been performed on two sets of contra-rotating propellers developed by David W Taylor Naval Ship R ＆ D center. Compared with the experimental data, it shows that RANS with sliding mesh method and SST k-ω turbulence model has a good precision in the open water performance prediction of contra-rotating propellers, and small time step size can improve the level of accuracy for CRPs with the same blade number of forward and aft propellers, while a relatively large time step size is a better choice for CRPs with different blade numbers.
基金supported by the National Natural Science Foundation of China (61963022,51665025,61873328)。
文摘This paper addresses the open vehicle routing problem with time window(OVRPTW), where each vehicle does not need to return to the depot after completing the delivery task.The optimization objective is to minimize the total distance. This problem exists widely in real-life logistics distribution process.We propose a hybrid column generation algorithm(HCGA) for the OVRPTW, embedding both exact algorithm and metaheuristic. In HCGA, a label setting algorithm and an intelligent algorithm are designed to select columns from small and large subproblems, respectively. Moreover, a branch strategy is devised to generate the final feasible solution for the OVRPTW. The computational results show that the proposed algorithm has faster speed and can obtain the approximate optimal solution of the problem with 100 customers in a reasonable time.
文摘Different cultivars of rice(Oryza sativa)open at different times of the day,and the overlap of anthesis time in rice between the neighbouring cultivars is of crucial importance to the degree of cross pollination in rice.Nevertheless,none of the past experiments with cross pollination between different rice cultivars ever reported the respective flower opening time(FOT)and flower exposure duration(FED)of the parent cultivars,until recently.The authors present here the first record of FOT and FED of 1114 indica rice landraces of South and Southeast Asia,growing during sum-mer and winter seasons in three consecutive years.The authors also present an analysis of the influences of the grow-ing season on the anthesis behaviour,and present the first records of the FOT and FED variability on sunny and cloudy days of a large number of landraces.The data show that rice florets tend to open later in the morning(that is,take longer time to anthesis after sunrise)on sunny days than on cloudy days,and also significantly later during long day seasons(spring and summer)than during short day season(winter);and that FED is inversely related to both FOT and the length of duration from sunrise to first flower opening.The wide ranges of FOT(8:50 a.m.to 12:40 p.m.)and FED(15 to 194 minutes)also suggest the ample time window for receiving pollen from neighbouring cultivars with differ-ent FOT,enhancing the chances of cross pollination between hundreds of rice landraces with FOT and FED overlaps.
文摘A new approach is presented for deriving the residence time distribution(RTD)in open-type reactors with exclusion of residence in the fore section.Inasmuch as failure to predict the con-version of chemical reactions has been evidenced in many occasions,numerical solution of tracerdispersion in the presence of background concentration gradient of reactant is given to demonstratethe strong effect of background reactant on the true RTD a reactant molecule experiences.Withinthe error of computation,the conversion of a first-order chemical reaction under steady state is shownto be equal in both closed and open reactors,despite difference in relevant
文摘MUCH has been said about South Africa joining the BRIC.Detractors say that the country is punching way above its weight. One of the biggest critics of the inclusion has been Jim O’Neill,Chairperson of Goldman Sachs Asset Management,who originally coined the term BRIC in 2001. O’Neill is on record as saying that he believes South Africa was invited for political reasons and not economical ones.He says South Africa’s working population is too small,and therefore had plumped for Nigeria to be a better choice to join the BRIC.South Africa’s total population is 50 million with Nigeria triple that at 150 million.
文摘With the increased number of PMUs in the power grid, effective high speed, realtime methods to ascertain relevant data for situational awareness are needed. Several techniques have used data from PMUs in conjunction with state estimation to assess system stability and event detection. However, these techniques require system topology and a large computational time. This paper presents a novel approach that uses real-time PMU data streams without the need of system connectivity or additional state estimation. The new development is based on the approximation of the eigenvalues related to the decoupled discreet-time power flow Jacobian matrix using direct openPDC data in real-time. Results are compared with other methods, such as Prony’s method, which can be too slow to handle big data. The newly developed Discreet-Time Jacobian Eigenvalue Approximation (DDJEA) method not only proves its accuracy, but also shows its effectiveness with minimal computational time: an essential element when considering situational awareness.
