The thrust coefficients and propulsive efficiency of a two-dimensional flexible fin with heaving and pitching motion were computed using FLUENT. The effect of different locations of the pitching axis on propulsive per...The thrust coefficients and propulsive efficiency of a two-dimensional flexible fin with heaving and pitching motion were computed using FLUENT. The effect of different locations of the pitching axis on propulsive performance was examined using three deflexion modes which are respectively, modified Bose mode, cantilever beam with uniformly distributed load and cantilever beam with non-uniformly distributed load. The results show that maximum thrust can be achieved with the pitching axis at the trailing edge, but the highest propulsive efficiency can be achieved with the pitching axis either 1/3 of the chord length from the leading edge in modified Bose mode, or 2/3 of the chord length from the leading edge in cantilever beam mode. At the same time, the effects of the Strouhal number and maximal attack angle on the hydrodynamics performance of the flexible fin were analyzed. Parameter interval of the maximum thrust coefficient and the highest propulsive efficiency were gained. If the Strouhal number is low, high propulsive efficiency can be achieved at low αmax , and vice versa.展开更多
The important parameters that influence the mechanical property of the pavinglayer on an orthotropic steel bridge deck are the paving layer thickness and modulus of the asphaltconcrete surfacing. Three important indic...The important parameters that influence the mechanical property of the pavinglayer on an orthotropic steel bridge deck are the paving layer thickness and modulus of the asphaltconcrete surfacing. Three important indices that control the typical failures of the paving layerare the maximum tensile stress of paving layer, the maximum shear stress between the steel deck andthe paving layer, and the maximum deflection on the paving surface. In this paper, the analyticalmodel of paving systems on orthotropic steel bridge deck is established, and the finite elementmethod is adopted to study the stress and strain of paving system. With the variation of asphaltconcrete modulus in high or low temperature season, the influences of paving layer thickness onthree control indices are researched. The results provide a theoretical basis for the determinationof thickness of the paving layer on the steel bridge deck.展开更多
A novel immune genetic algorithm with the elitist selection and elitist crossover was proposed, which is called the immune genetic algorithm with the elitism （IGAE）. In IGAE, the new methods for computing antibody s...A novel immune genetic algorithm with the elitist selection and elitist crossover was proposed, which is called the immune genetic algorithm with the elitism （IGAE）. In IGAE, the new methods for computing antibody similarity, expected reproduction probability, and clonal selection probability were given. IGAE has three features. The first is that the similarities of two antibodies in structure and quality are all defined in the form of percentage, which helps to describe the similarity of two antibodies more accurately and to reduce the computational burden effectively. The second is that with the elitist selection and elitist crossover strategy IGAE is able to find the globally optimal solution of a given problem. The third is that the formula of expected reproduction probability of antibody can be adjusted through a parameter r, which helps to balance the population diversity and the convergence speed of IGAE so that IGAE can find the globally optimal solution of a given problem more rapidly. Two different complex multi-modal functions were selected to test the validity of IGAE. The experimental results show that IGAE can find the globally maximum/minimum values of the two functions rapidly. The experimental results also confirm that IGAE is of better performance in convergence speed, solution variation behavior, and computational efficiency compared with the canonical genetic algorithm with the elitism and the immune genetic algorithm with the information entropy and elitism.展开更多
Large complex 7A85 aluminum wing-body joint was forged employing isothermal forging process and its mechanical properties were studied.The tensile strength after forging is up to 587.5 MPa in longitudinal direction,15...Large complex 7A85 aluminum wing-body joint was forged employing isothermal forging process and its mechanical properties were studied.The tensile strength after forging is up to 587.5 MPa in longitudinal direction,15% higher than that using free forging.Moreover,the tensile strength of the forging is almost the same in three directions.Isothermal forging also performs well on overall fracture toughness,with a maximum value of 39.8 MPa·m1/2,and that of short transverse direction all reaches 36 MPa·m1/2 and above,with a maximum relative error of only 3.6%.The results indicate that the isothermal forging leads to better performance as well as higher uniformity in mechanical properties.展开更多
A decoding method complemented by Maximum Likelihood (ML) detection for V-BLAST (Verti- cal Bell Labs Layered Space-Time) system is presented. The ranked layers are divided into several groups. ML decoding is performe...A decoding method complemented by Maximum Likelihood (ML) detection for V-BLAST (Verti- cal Bell Labs Layered Space-Time) system is presented. The ranked layers are divided into several groups. ML decoding is performed jointly for the layers within the same group while the Decision Feedback Equalization (DFE) is performed for groups. Based on the assumption of QPSK modulation and the quasi-static flat fading channel, simulations are made to testify the performance of the proposed algorithm. The results show that the algorithm outperforms the original V-BLAST detection dramatically in Symbol Error Probability (SEP) per- formance. Specifically, Signal-to-Noise Ratio (SNR) improvement of 3.4dB is obtained for SEP of 10?2 (4×4 case), with a reasonable complexity maintained.展开更多
Mixed-effects models,also called random-effects models,are a regression type of analysis which enables the analyst to not only describe the trend over time within each subject,but also to describe the variation among ...Mixed-effects models,also called random-effects models,are a regression type of analysis which enables the analyst to not only describe the trend over time within each subject,but also to describe the variation among different subjects.Nonlinear mixed-effects models provide a powerful and flexible tool for handling the unbalanced count data.In this paper,nonlinear mixed-effects models are used to analyze the failure data from a repairable system with multiple copies.By using this type of models,statistical inferences about the population and all copies can be made when accounting for copy-to-copy variance.Results of fitting nonlinear mixed-effects models to nine failure-data sets show that the nonlinear mixed-effects models provide a useful tool for analyzing the failure data from multi-copy repairable systems.展开更多
Tensile properties of as-deformed 2A50 aluminum alloy were investigated in the high temperature solid and semi-solid states. The results show that temperature has almost no effect on the maximum tensile stress between...Tensile properties of as-deformed 2A50 aluminum alloy were investigated in the high temperature solid and semi-solid states. The results show that temperature has almost no effect on the maximum tensile stress between 500 ℃ and 530 ℃, and the maximum tensile stress decreases rapidly when the temperature is above 532 ℃. The ductility decreases with increasing temperature and has an obvious fall when the temperature is above solidus temperature. This alloy almost has no ductility above 537 ℃, and cannot sustain tensile stress above 550℃. A brittle temperature range in which this alloy is prone to form microcracks was derived. The relation between microstructure, fraction solid and tensile properties were also investigated by examining the metallograph and fracture surface morphology of tested specimens, which could provide reference for forecasting the microcracks in this alloy occurring in semi-solid processing.展开更多
基金Supported by the National Natural Science Foundation of China under Grant No.50879031
文摘The thrust coefficients and propulsive efficiency of a two-dimensional flexible fin with heaving and pitching motion were computed using FLUENT. The effect of different locations of the pitching axis on propulsive performance was examined using three deflexion modes which are respectively, modified Bose mode, cantilever beam with uniformly distributed load and cantilever beam with non-uniformly distributed load. The results show that maximum thrust can be achieved with the pitching axis at the trailing edge, but the highest propulsive efficiency can be achieved with the pitching axis either 1/3 of the chord length from the leading edge in modified Bose mode, or 2/3 of the chord length from the leading edge in cantilever beam mode. At the same time, the effects of the Strouhal number and maximal attack angle on the hydrodynamics performance of the flexible fin were analyzed. Parameter interval of the maximum thrust coefficient and the highest propulsive efficiency were gained. If the Strouhal number is low, high propulsive efficiency can be achieved at low αmax , and vice versa.
文摘The important parameters that influence the mechanical property of the pavinglayer on an orthotropic steel bridge deck are the paving layer thickness and modulus of the asphaltconcrete surfacing. Three important indices that control the typical failures of the paving layerare the maximum tensile stress of paving layer, the maximum shear stress between the steel deck andthe paving layer, and the maximum deflection on the paving surface. In this paper, the analyticalmodel of paving systems on orthotropic steel bridge deck is established, and the finite elementmethod is adopted to study the stress and strain of paving system. With the variation of asphaltconcrete modulus in high or low temperature season, the influences of paving layer thickness onthree control indices are researched. The results provide a theoretical basis for the determinationof thickness of the paving layer on the steel bridge deck.
基金Project(50275150) supported by the National Natural Science Foundation of ChinaProjects(20040533035, 20070533131) supported by the National Research Foundation for the Doctoral Program of Higher Education of China
文摘A novel immune genetic algorithm with the elitist selection and elitist crossover was proposed, which is called the immune genetic algorithm with the elitism （IGAE）. In IGAE, the new methods for computing antibody similarity, expected reproduction probability, and clonal selection probability were given. IGAE has three features. The first is that the similarities of two antibodies in structure and quality are all defined in the form of percentage, which helps to describe the similarity of two antibodies more accurately and to reduce the computational burden effectively. The second is that with the elitist selection and elitist crossover strategy IGAE is able to find the globally optimal solution of a given problem. The third is that the formula of expected reproduction probability of antibody can be adjusted through a parameter r, which helps to balance the population diversity and the convergence speed of IGAE so that IGAE can find the globally optimal solution of a given problem more rapidly. Two different complex multi-modal functions were selected to test the validity of IGAE. The experimental results show that IGAE can find the globally maximum/minimum values of the two functions rapidly. The experimental results also confirm that IGAE is of better performance in convergence speed, solution variation behavior, and computational efficiency compared with the canonical genetic algorithm with the elitism and the immune genetic algorithm with the information entropy and elitism.
基金Project(2010CB731701) supported by the National Basic Research Program of ChinaProject(2012ZX04010-081) supported by National Science and Technology Major Program of China
文摘Large complex 7A85 aluminum wing-body joint was forged employing isothermal forging process and its mechanical properties were studied.The tensile strength after forging is up to 587.5 MPa in longitudinal direction,15% higher than that using free forging.Moreover,the tensile strength of the forging is almost the same in three directions.Isothermal forging also performs well on overall fracture toughness,with a maximum value of 39.8 MPa·m1/2,and that of short transverse direction all reaches 36 MPa·m1/2 and above,with a maximum relative error of only 3.6%.The results indicate that the isothermal forging leads to better performance as well as higher uniformity in mechanical properties.
基金Supported by the National Natural Science Foundation of China (No.60172029).
文摘A decoding method complemented by Maximum Likelihood (ML) detection for V-BLAST (Verti- cal Bell Labs Layered Space-Time) system is presented. The ranked layers are divided into several groups. ML decoding is performed jointly for the layers within the same group while the Decision Feedback Equalization (DFE) is performed for groups. Based on the assumption of QPSK modulation and the quasi-static flat fading channel, simulations are made to testify the performance of the proposed algorithm. The results show that the algorithm outperforms the original V-BLAST detection dramatically in Symbol Error Probability (SEP) per- formance. Specifically, Signal-to-Noise Ratio (SNR) improvement of 3.4dB is obtained for SEP of 10?2 (4×4 case), with a reasonable complexity maintained.
文摘Mixed-effects models,also called random-effects models,are a regression type of analysis which enables the analyst to not only describe the trend over time within each subject,but also to describe the variation among different subjects.Nonlinear mixed-effects models provide a powerful and flexible tool for handling the unbalanced count data.In this paper,nonlinear mixed-effects models are used to analyze the failure data from a repairable system with multiple copies.By using this type of models,statistical inferences about the population and all copies can be made when accounting for copy-to-copy variance.Results of fitting nonlinear mixed-effects models to nine failure-data sets show that the nonlinear mixed-effects models provide a useful tool for analyzing the failure data from multi-copy repairable systems.
基金Projects(50774026, 50875059) supported by the National Natural Science Foundation of ChinaProject(20070420023) supported by the China Postdoctoral Science FoundationProject(2008AA03A239) supported by the National High-tech Research and Development Program of China
文摘Tensile properties of as-deformed 2A50 aluminum alloy were investigated in the high temperature solid and semi-solid states. The results show that temperature has almost no effect on the maximum tensile stress between 500 ℃ and 530 ℃, and the maximum tensile stress decreases rapidly when the temperature is above 532 ℃. The ductility decreases with increasing temperature and has an obvious fall when the temperature is above solidus temperature. This alloy almost has no ductility above 537 ℃, and cannot sustain tensile stress above 550℃. A brittle temperature range in which this alloy is prone to form microcracks was derived. The relation between microstructure, fraction solid and tensile properties were also investigated by examining the metallograph and fracture surface morphology of tested specimens, which could provide reference for forecasting the microcracks in this alloy occurring in semi-solid processing.
