This paper proposes a semi-empirical model to predict a ship’s speed loss at arbitrary wave heading.In the model,the formulas that estimate a ship’s added resistance due to waves attacking from different heading ang...This paper proposes a semi-empirical model to predict a ship’s speed loss at arbitrary wave heading.In the model,the formulas that estimate a ship’s added resistance due to waves attacking from different heading angles have been further developed.A correction factor is proposed to consider the nonlinear effect due to large waves in power estimation.The formulas are developed and verified by model tests of 5 ships in regular waves with various heading angles.The full-scale measurements from three different types of ships,i.e.,a PCTC,a container ship,and a chemical tanker,are used to validate the proposed model for speed loss prediction in irregular waves.The effect of the improved model for speed loss prediction on a ship’s voyage optimization is also investigated.The results indicate that a ship’s voyage optimization solutions can be significantly affected by the prediction accuracy of speed loss caused by waves.展开更多
This paper presents an analysis based on analytical method for solid rotor motors for determining the rotor eddy current losses due to the current harmonics of the stator winding. The accuracy of the analytical result...This paper presents an analysis based on analytical method for solid rotor motors for determining the rotor eddy current losses due to the current harmonics of the stator winding. The accuracy of the analytical results is verified by experiments.展开更多
The mass loss and nose blunting of a projectile during high-speed deep penetration into concrete target may cause structural destruction and ballistic trajectory instability of the penetrator,obviously reducing the pe...The mass loss and nose blunting of a projectile during high-speed deep penetration into concrete target may cause structural destruction and ballistic trajectory instability of the penetrator,obviously reducing the penetration efficiency of penetrator.Provided that the work of friction between projectile and target is totally transformed into the heat to melt penetrator material at its nose surface,an engineering model is established for the mass loss and nose-blunting of the ogive-nosed projectile.A dimensionless formula for the relative mass loss of projectile is obtained by introducing the dimensionless impact function I and geometry function N of the projectile.The critical value V c0of the initial striking velocity is formulated,and the mass loss of projectile tends to increase weakly nonlinearly with I/N when V0〉V c0,whilst the mass loss is proportional to the initial kinetic energy of projectile when V0展开更多
High speed and high efficiency synchronized electric motors are favored in the automotive industry and turbo machinery industry worldwide because of the demands placed on efficiency. Herein an electric motor thermal c...High speed and high efficiency synchronized electric motors are favored in the automotive industry and turbo machinery industry worldwide because of the demands placed on efficiency. Herein an electric motor thermal control system using cooling air which enters from the drive end of the motor and exits from the non-drive end of the motor as the rotor experiences dissipates heat is addressed using CFD. Analyses using CFD can help to find the appropriate mass flow rate and windage losses while satisfying temperature requirements on the motor. Here, the air flow through a small annular gap is fed at 620 L/min (0.011 kg/sec) as the rotor spins at 100,000 rpm (10,472 rad/sec) and the rotor dissipates 200 W. The CFD results are compared with experimental results. Based upon the CFD findings, a novel heat transfer correlation suitable for large axial Reynolds number, large Taylor number, small annular gap Taylor-Couette flows subject to axial cross-flow is proposed herein.展开更多
In order to obtain accurate characteristics of wireless channels in the viaduct area of China, a channel meas- urement was taken in a railway viaduct scenario of the Zhengzhou-Xi＇an passenger dedicated line with a ba...In order to obtain accurate characteristics of wireless channels in the viaduct area of China, a channel meas- urement was taken in a railway viaduct scenario of the Zhengzhou-Xi＇an passenger dedicated line with a bandwidth of 50 MHz at 2.35 GHz. The single-slope log-distance model is used to analyze the path-loss （PL）, and the distribution of shadow fading （SF） is obtained by statistical methods, which shows that the normal distribution fits the samples well. Ricean K-factor is analyzed by the method of moments, and the variation of K-factor is given along the measured route. Small scale such as delay spread and Doppler behavior are parameterized. Based on empirical channel measurement, this paper provides parameters for the evaluation and simulation work on viaduct scenarios of high-speed railway.展开更多
为在保证货主满意度的同时尽可能地控制航运成本,在考虑北极东北航线气象条件和自愿速度损失的基础上,建立北极东北航线航速优化模型,通过带精英策略的非支配排序遗传算法(elitist non-dominated sorting genetic algorithm,NSGA-Ⅱ)和...为在保证货主满意度的同时尽可能地控制航运成本,在考虑北极东北航线气象条件和自愿速度损失的基础上,建立北极东北航线航速优化模型,通过带精英策略的非支配排序遗传算法(elitist non-dominated sorting genetic algorithm,NSGA-Ⅱ)和逼近理想解排序法(technique for order preference by similarity to ideal solution,TOPSIS)筛选出最佳折中解。选取北极东北航线沿线重要港口进行案例分析,结果表明:当航运成本降低时,货主总体满意度会下降,船公司可以根据各货主的重要性调整航速,以平衡航运成本和货主满意度;对比考虑自愿速度损失与无自愿速度损失的北极东北航线航速优化模型发现,两者的优化结果存在显著差异,自愿速度损失直接影响航速优化模型的准确性;航速优化对时间窗较为敏感,较大的时间窗可以为减速和提高船舶能效提供更大的机会空间。展开更多
基金Open access funding provided by Chalmers University of Technology.The authors acknowledge the financial support from the European Commission(Horizon 2020)project EcoSail(Grant Number 820593)We are also grateful to the support from the Swedish Foundation for International Cooperation in Research and Higher Education(CH2016-6673)+1 种基金National Natural Science Foundation of China(NSFC-51779202)The second author thanks the funding from the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie(Grant Number 754412)and VGR MoRE2020.
文摘This paper proposes a semi-empirical model to predict a ship’s speed loss at arbitrary wave heading.In the model,the formulas that estimate a ship’s added resistance due to waves attacking from different heading angles have been further developed.A correction factor is proposed to consider the nonlinear effect due to large waves in power estimation.The formulas are developed and verified by model tests of 5 ships in regular waves with various heading angles.The full-scale measurements from three different types of ships,i.e.,a PCTC,a container ship,and a chemical tanker,are used to validate the proposed model for speed loss prediction in irregular waves.The effect of the improved model for speed loss prediction on a ship’s voyage optimization is also investigated.The results indicate that a ship’s voyage optimization solutions can be significantly affected by the prediction accuracy of speed loss caused by waves.
文摘This paper presents an analysis based on analytical method for solid rotor motors for determining the rotor eddy current losses due to the current harmonics of the stator winding. The accuracy of the analytical results is verified by experiments.
基金supported by the National Outstanding Young Scientists Foundation of China(11225213)the Funds for Creative Research Groups of China(51321064)the National Natural Science Foundation of China(11172282 and 51378015)
文摘The mass loss and nose blunting of a projectile during high-speed deep penetration into concrete target may cause structural destruction and ballistic trajectory instability of the penetrator,obviously reducing the penetration efficiency of penetrator.Provided that the work of friction between projectile and target is totally transformed into the heat to melt penetrator material at its nose surface,an engineering model is established for the mass loss and nose-blunting of the ogive-nosed projectile.A dimensionless formula for the relative mass loss of projectile is obtained by introducing the dimensionless impact function I and geometry function N of the projectile.The critical value V c0of the initial striking velocity is formulated,and the mass loss of projectile tends to increase weakly nonlinearly with I/N when V0〉V c0,whilst the mass loss is proportional to the initial kinetic energy of projectile when V0
文摘High speed and high efficiency synchronized electric motors are favored in the automotive industry and turbo machinery industry worldwide because of the demands placed on efficiency. Herein an electric motor thermal control system using cooling air which enters from the drive end of the motor and exits from the non-drive end of the motor as the rotor experiences dissipates heat is addressed using CFD. Analyses using CFD can help to find the appropriate mass flow rate and windage losses while satisfying temperature requirements on the motor. Here, the air flow through a small annular gap is fed at 620 L/min (0.011 kg/sec) as the rotor spins at 100,000 rpm (10,472 rad/sec) and the rotor dissipates 200 W. The CFD results are compared with experimental results. Based upon the CFD findings, a novel heat transfer correlation suitable for large axial Reynolds number, large Taylor number, small annular gap Taylor-Couette flows subject to axial cross-flow is proposed herein.
基金supported by the National Science & Technology Pillar Program(No.2012BAF14B01)the National Natural Science Foundation of China(No.61171105)China Mobile Research Institute
文摘In order to obtain accurate characteristics of wireless channels in the viaduct area of China, a channel meas- urement was taken in a railway viaduct scenario of the Zhengzhou-Xi＇an passenger dedicated line with a bandwidth of 50 MHz at 2.35 GHz. The single-slope log-distance model is used to analyze the path-loss （PL）, and the distribution of shadow fading （SF） is obtained by statistical methods, which shows that the normal distribution fits the samples well. Ricean K-factor is analyzed by the method of moments, and the variation of K-factor is given along the measured route. Small scale such as delay spread and Doppler behavior are parameterized. Based on empirical channel measurement, this paper provides parameters for the evaluation and simulation work on viaduct scenarios of high-speed railway.
文摘为在保证货主满意度的同时尽可能地控制航运成本,在考虑北极东北航线气象条件和自愿速度损失的基础上,建立北极东北航线航速优化模型,通过带精英策略的非支配排序遗传算法(elitist non-dominated sorting genetic algorithm,NSGA-Ⅱ)和逼近理想解排序法(technique for order preference by similarity to ideal solution,TOPSIS)筛选出最佳折中解。选取北极东北航线沿线重要港口进行案例分析,结果表明:当航运成本降低时,货主总体满意度会下降,船公司可以根据各货主的重要性调整航速,以平衡航运成本和货主满意度;对比考虑自愿速度损失与无自愿速度损失的北极东北航线航速优化模型发现,两者的优化结果存在显著差异,自愿速度损失直接影响航速优化模型的准确性;航速优化对时间窗较为敏感,较大的时间窗可以为减速和提高船舶能效提供更大的机会空间。
