The symmetries of the （2＋1）-dimensional nonlinear incompressible non-hydrostatic Boussinesq （INHB） equations, which describe the atmospheric gravity waves （GWs）, are researched in this paper. The Lie symmetries...The symmetries of the （2＋1）-dimensional nonlinear incompressible non-hydrostatic Boussinesq （INHB） equations, which describe the atmospheric gravity waves （GWs）, are researched in this paper. The Lie symmetries and the corresponding reductions are obtained by means of classical Lie group approach. Calculation shows the INHB equations are invariant under some Galilean transformations, scaling transformations, and space-time translations. The symmetry reduction equations and similar solutions of the INHB equations are proposed.展开更多
Previous studies show that temporal irreversibility(TI),as an important indicator of the nonlinearity of time series,is almost uniformly overestimated in the daily air temperature anomaly series over China in NCEP rea...Previous studies show that temporal irreversibility(TI),as an important indicator of the nonlinearity of time series,is almost uniformly overestimated in the daily air temperature anomaly series over China in NCEP reanalysis data,as compared with station observations.Apart from this highly overestimated TI in the NCEP reanalysis,some other important atmospheric metrics,such as predictability and extreme events,might also be overestimated since there are close relations between nonlinearity and predictability/extreme events.In this study,these issues are fully addressed,i.e.,intrinsic predictability,prediction skill,and the number of extreme events.The results show that intrinsic predictability,prediction skill,and the occurrence number of extreme events are also almost uniformly overestimated in the NCEP reanalysis daily minimum and maximum air temperature anomaly series over China.Furthermore,these overestimations of intrinsic predictability,prediction skill,and the number of extreme events are only weakly correlated with the overestimated TI,which indicates that the quality of the NCEP reanalysis should be carefully considered when conclusions on both predictability and extreme events are derived.展开更多
The cost and safety of geotechnical engineering are highly depending on the accuracy of soil shear strength parameters.There are three methods often used to estimate soil shear strength parameters,i.e.,moment method,3...The cost and safety of geotechnical engineering are highly depending on the accuracy of soil shear strength parameters.There are three methods often used to estimate soil shear strength parameters,i.e.,moment method,3-sigma rule and linear regression method.In this study,the accuracy of these three methods is compared.Traditional linear regression method(LRM)can only offer the mean of shear strength parameters.Some engineers misuse the standard error of shear strength indexes as the standard deviations.Such misuse may highly underestimate the uncertainty and induce high risk to the geotechnical design.A modified LRM is proposed to determine both the mean and variance of shear strength parameters.The moment method,three-sigma rule and LRM are used to analyze the tri-axial test data in Xiaolangdi Hydraulic Project and three numerical shear strength tests.The results demonstrate that:1)The modified LRM can offer the most accurate estimation to shear strength parameters;2)A dimensionless formula is much preferred in LRM rather than a dimensional formula.The stress ratio formula is much better than stress relation in the shear strength parameter analysis.The proposed method is applicable to shear strength parameter analysis for tri-axial test data,direct shear test and the un-drained shear strength test of stratified clay.展开更多
Vortex methods have been alternative tools of finite element and finite difference methods for several decades. This paper presents a brief review of vortex method development in the last decades and introduces effici...Vortex methods have been alternative tools of finite element and finite difference methods for several decades. This paper presents a brief review of vortex method development in the last decades and introduces efficient vortex methods developed for high Reynolds number bluff body flows and suitable for running on parallel computer architectures. Included in this study are particle strength exchange methods, core-spreading method, deterministic particle method and hybrid vortex methods. Combined with conservative methods, vortex methods can comprise the most available tools for simulations of three-dimensional complex bluff body flows at high Reynolds numbers.展开更多
A thermodynamic model was developed to analyze the performance of cogeneration plant based on irreversible recuperative Brayton cycle. A parameter, dimensionless total useful energy rate (DTUER), was used as the crite...A thermodynamic model was developed to analyze the performance of cogeneration plant based on irreversible recuperative Brayton cycle. A parameter, dimensionless total useful energy rate (DTUER), was used as the criterion for performance optimization of cogeneration plant. The effects of cycle parameters, internal irreversibilities, and recuperator efficiency on maximum DTUER and on the efficiency at maximum DTUER were numerically investigated. The relation between DTUER and cogeneration efficiency was also analyzed. The results show that there exists an optimal compressor pressure ratio which maximizes the DTUER. It is also found that there exists an optimal power-to-heat ratio which results in a dual-maximum DTUER.展开更多
In order to improve the security and reliability for autonomous underwater vehicle （AUV） navigation, an H∞ robust fault-tolerant controller was designed after analyzing variations in state-feedback gain Operating c...In order to improve the security and reliability for autonomous underwater vehicle （AUV） navigation, an H∞ robust fault-tolerant controller was designed after analyzing variations in state-feedback gain Operating conditions and the design method were then analyzed so that the control problem could be expressed as a mathematical optimization problem. This permitted the use of linear matrix inequalities （LMI） to solve for the Hv controller for the system. When considering different actuator failures, these conditions were then also mathematically expressed, allowing the H∞ robust controller to solve for these events and thus be fault-tolerant. Finally, simulation results showed that the H∞ robust fault-tolerant controller could provide precise AUV navigation control with strong robustness.展开更多
Remotely sensed spectral data and images are acquired under significant additional effects accompanying their major formation process, which greatly determine measurement accuracy. In order to be used in subsequent qu...Remotely sensed spectral data and images are acquired under significant additional effects accompanying their major formation process, which greatly determine measurement accuracy. In order to be used in subsequent quantitative analysis and assessment, this data should be subject to preliminary processing aiming to improve its accuracy and credibility. The paper considers some major problems related with preliminary processing of remotely sensed spectral data and images. The major factors are analyzed, which affect the occurrence of data noise or uncertainties and the methods for reduction or removal thereof. Assessment is made of the extent to which available equipment and technologies may help reduce measurement errors.展开更多
There are a lot of uncertainties in the mining engineering, and they make a notable impact on the engineering. The uncertainties of the physical and mechanical properties of geotectonic mass, the surrounding rock stab...There are a lot of uncertainties in the mining engineering, and they make a notable impact on the engineering. The uncertainties of the physical and mechanical properties of geotectonic mass, the surrounding rock stability, the nature condition, the equipment operation, the personnel and the external environment are proposed and described. The stochastic analysis should be widely used for considering the impacts of the uncertainty on the mining engineering. The economical risk analysis and the stochastic index system should also be set up in the mining engineering.展开更多
Traditional reliability analysis requires probability distributions of all the uncertain parameters.However,in many practical applications,the variation bounds can be only determined for the parameters with limited in...Traditional reliability analysis requires probability distributions of all the uncertain parameters.However,in many practical applications,the variation bounds can be only determined for the parameters with limited information.A complex hybrid reliability problem then will be caused when the random and interval variables coexist in a same structure.In this paper,by introducing the response surface technique,we develop a new hybrid reliability method to efficiently compute the interval of the failure probability of the structure due to the probability-interval hybrid uncertainty.The present method consists of a sequence of iterations.At each step,a response surface model is constructed for the limit-state function by using a quadratic polynomial and a modified axial experimental design method.An approximate hybrid reliability problem is created based on the response surface model,which is subsequently solved by an efficient decoupling approach.An updating strategy is suggested to improve the quality of the response surface and whereby ensure the reliability analysis precision.A computational procedure is then summarized for the whole iterations.Four numerical examples and also a practical application are provided to demonstrate the effectiveness of the present method.展开更多
Absolute integrability and its absolute value inequality for fuzzy-number-valued func- tions are worth to be considered.In this paper,absolute integrability and its absolute value inequality for fuzzy-number-valued fu...Absolute integrability and its absolute value inequality for fuzzy-number-valued func- tions are worth to be considered.In this paper,absolute integrability and its absolute value inequality for fuzzy-number-valued functions are discussed by means of the characteristic the- orems of nonabsolute fuzzy integrals and the embedding theorem,i.e.,the fuzzy number space can be embedded into a concrete Banach space.Several necessary and sufficient conditions and examples are given.展开更多
The crossflow instability of a three-dimensional (3-D) boundary layer is an important factor which affects the transition over a swept-wing.In this report,the primary instability of the incompressible flow over a swep...The crossflow instability of a three-dimensional (3-D) boundary layer is an important factor which affects the transition over a swept-wing.In this report,the primary instability of the incompressible flow over a swept wing is investigated by solving nonlinear parabolized stability equations (NPSE).The Floquet theory is applied to study the dependence of the secondary and high-frequency instabilities on curvature,Reynolds number and angle of swept (AOS).The computational results show that the curvature in the present case has no significant effect on the secondary instabilities.It is generally believed that the secondary instability growth rate increases with the magnitude of the nonlinear mode of crossflow vortex.But,at a certain state,when the Reynolds number is 3.2 million,we find that the secondary instability growth rate becomes smaller even when the magnitude of the nonlinear mode of the crossflow vortex is larger.The effect of the angle of swept at 35,45 and 55 degrees,respectively,is also studied in the framework of the secondary linear stability theory.Larger angles of swept tend to decrease the spanwise spacing of the crossflow vortices,which correspondingly helps the stimulation of 'z' mode.展开更多
This article reports the homotopy solution for stagnation point flow of a non-Newtonian fluid. An incompressible second grade fluid impinges on the wall either orthogonally or obliquely. The resulting nonlinear proble...This article reports the homotopy solution for stagnation point flow of a non-Newtonian fluid. An incompressible second grade fluid impinges on the wall either orthogonally or obliquely. The resulting nonlinear problems have been solved by a homotopy analysis method （HAM）. Convergence of the series solutions is checked. Such solutions are compared with the numerical solutions presented in a study lint. J. Non-Linear Mech. 43 （2008） 941]. Excellent agreement is noted between the numerical and series solutions.展开更多
基金Supported by the Scientific Research Foundation for the Doctors of University of Electronic Science and Technology of China Zhongshan Institute under Grant No. 408YKQ09the National Natural Science Foundation of China under Grant No. 10735030
文摘The symmetries of the （2＋1）-dimensional nonlinear incompressible non-hydrostatic Boussinesq （INHB） equations, which describe the atmospheric gravity waves （GWs）, are researched in this paper. The Lie symmetries and the corresponding reductions are obtained by means of classical Lie group approach. Calculation shows the INHB equations are invariant under some Galilean transformations, scaling transformations, and space-time translations. The symmetry reduction equations and similar solutions of the INHB equations are proposed.
基金funded by the National Natural Science Foundation of China[grant numbers 41475048,41675049,41705041]。
文摘Previous studies show that temporal irreversibility(TI),as an important indicator of the nonlinearity of time series,is almost uniformly overestimated in the daily air temperature anomaly series over China in NCEP reanalysis data,as compared with station observations.Apart from this highly overestimated TI in the NCEP reanalysis,some other important atmospheric metrics,such as predictability and extreme events,might also be overestimated since there are close relations between nonlinearity and predictability/extreme events.In this study,these issues are fully addressed,i.e.,intrinsic predictability,prediction skill,and the number of extreme events.The results show that intrinsic predictability,prediction skill,and the occurrence number of extreme events are also almost uniformly overestimated in the NCEP reanalysis daily minimum and maximum air temperature anomaly series over China.Furthermore,these overestimations of intrinsic predictability,prediction skill,and the number of extreme events are only weakly correlated with the overestimated TI,which indicates that the quality of the NCEP reanalysis should be carefully considered when conclusions on both predictability and extreme events are derived.
基金Project(2017YFC0404803) supported by the National Key Research and Development Program of ChinaProject(51678040) supported by the National Natural Science Foundation of ChinaProject(8192034) supported by the Beijing Municipal Natural Science Foundation,China
文摘The cost and safety of geotechnical engineering are highly depending on the accuracy of soil shear strength parameters.There are three methods often used to estimate soil shear strength parameters,i.e.,moment method,3-sigma rule and linear regression method.In this study,the accuracy of these three methods is compared.Traditional linear regression method(LRM)can only offer the mean of shear strength parameters.Some engineers misuse the standard error of shear strength indexes as the standard deviations.Such misuse may highly underestimate the uncertainty and induce high risk to the geotechnical design.A modified LRM is proposed to determine both the mean and variance of shear strength parameters.The moment method,three-sigma rule and LRM are used to analyze the tri-axial test data in Xiaolangdi Hydraulic Project and three numerical shear strength tests.The results demonstrate that:1)The modified LRM can offer the most accurate estimation to shear strength parameters;2)A dimensionless formula is much preferred in LRM rather than a dimensional formula.The stress ratio formula is much better than stress relation in the shear strength parameter analysis.The proposed method is applicable to shear strength parameter analysis for tri-axial test data,direct shear test and the un-drained shear strength test of stratified clay.
基金Project (No. 50236030) supported by the National Natural Science Foundation of China
文摘Vortex methods have been alternative tools of finite element and finite difference methods for several decades. This paper presents a brief review of vortex method development in the last decades and introduces efficient vortex methods developed for high Reynolds number bluff body flows and suitable for running on parallel computer architectures. Included in this study are particle strength exchange methods, core-spreading method, deterministic particle method and hybrid vortex methods. Combined with conservative methods, vortex methods can comprise the most available tools for simulations of three-dimensional complex bluff body flows at high Reynolds numbers.
基金Project(2011FJ1007-1) supported by the Funds of Key Science and Technology of Hunan Province, ChinaProject(YB2010B027)supported by the Funds for the Author of Provincial Excellent Doctoral Dissertation of Hunan Province, ChinaProject(KF200903)supported by the Opening Funds of Hunan Provincial Key Laboratory of Safe Mining Techniques of Coal Mines, China
文摘A thermodynamic model was developed to analyze the performance of cogeneration plant based on irreversible recuperative Brayton cycle. A parameter, dimensionless total useful energy rate (DTUER), was used as the criterion for performance optimization of cogeneration plant. The effects of cycle parameters, internal irreversibilities, and recuperator efficiency on maximum DTUER and on the efficiency at maximum DTUER were numerically investigated. The relation between DTUER and cogeneration efficiency was also analyzed. The results show that there exists an optimal compressor pressure ratio which maximizes the DTUER. It is also found that there exists an optimal power-to-heat ratio which results in a dual-maximum DTUER.
基金Supported by the Heilongjiang Postdoctoral Foundation under Grant No. LH-04010
文摘In order to improve the security and reliability for autonomous underwater vehicle （AUV） navigation, an H∞ robust fault-tolerant controller was designed after analyzing variations in state-feedback gain Operating conditions and the design method were then analyzed so that the control problem could be expressed as a mathematical optimization problem. This permitted the use of linear matrix inequalities （LMI） to solve for the Hv controller for the system. When considering different actuator failures, these conditions were then also mathematically expressed, allowing the H∞ robust controller to solve for these events and thus be fault-tolerant. Finally, simulation results showed that the H∞ robust fault-tolerant controller could provide precise AUV navigation control with strong robustness.
文摘Remotely sensed spectral data and images are acquired under significant additional effects accompanying their major formation process, which greatly determine measurement accuracy. In order to be used in subsequent quantitative analysis and assessment, this data should be subject to preliminary processing aiming to improve its accuracy and credibility. The paper considers some major problems related with preliminary processing of remotely sensed spectral data and images. The major factors are analyzed, which affect the occurrence of data noise or uncertainties and the methods for reduction or removal thereof. Assessment is made of the extent to which available equipment and technologies may help reduce measurement errors.
文摘There are a lot of uncertainties in the mining engineering, and they make a notable impact on the engineering. The uncertainties of the physical and mechanical properties of geotectonic mass, the surrounding rock stability, the nature condition, the equipment operation, the personnel and the external environment are proposed and described. The stochastic analysis should be widely used for considering the impacts of the uncertainty on the mining engineering. The economical risk analysis and the stochastic index system should also be set up in the mining engineering.
基金supported by the National Science Foundation for Excellent Young Scholars(Grant No.51222502)the Key Project of Chinese National Programs for Fundamental Research and Development(Grant No.2010CB832700)+1 种基金the National Natural Science Foundation of China(Grant No.11172096)the Key Program of the National Natural Science Foundation of China(Grant No.11232004)
文摘Traditional reliability analysis requires probability distributions of all the uncertain parameters.However,in many practical applications,the variation bounds can be only determined for the parameters with limited information.A complex hybrid reliability problem then will be caused when the random and interval variables coexist in a same structure.In this paper,by introducing the response surface technique,we develop a new hybrid reliability method to efficiently compute the interval of the failure probability of the structure due to the probability-interval hybrid uncertainty.The present method consists of a sequence of iterations.At each step,a response surface model is constructed for the limit-state function by using a quadratic polynomial and a modified axial experimental design method.An approximate hybrid reliability problem is created based on the response surface model,which is subsequently solved by an efficient decoupling approach.An updating strategy is suggested to improve the quality of the response surface and whereby ensure the reliability analysis precision.A computational procedure is then summarized for the whole iterations.Four numerical examples and also a practical application are provided to demonstrate the effectiveness of the present method.
基金the National Natural Science Foundation of China （No. 10771171） the Scientific Research Item of Gansu Education Department （No. 0601-20）.
文摘Absolute integrability and its absolute value inequality for fuzzy-number-valued func- tions are worth to be considered.In this paper,absolute integrability and its absolute value inequality for fuzzy-number-valued functions are discussed by means of the characteristic the- orems of nonabsolute fuzzy integrals and the embedding theorem,i.e.,the fuzzy number space can be embedded into a concrete Banach space.Several necessary and sufficient conditions and examples are given.
基金supported by the National Natural Science Foundation of China(Grant Nos. 90505005 and 10932005)
文摘The crossflow instability of a three-dimensional (3-D) boundary layer is an important factor which affects the transition over a swept-wing.In this report,the primary instability of the incompressible flow over a swept wing is investigated by solving nonlinear parabolized stability equations (NPSE).The Floquet theory is applied to study the dependence of the secondary and high-frequency instabilities on curvature,Reynolds number and angle of swept (AOS).The computational results show that the curvature in the present case has no significant effect on the secondary instabilities.It is generally believed that the secondary instability growth rate increases with the magnitude of the nonlinear mode of crossflow vortex.But,at a certain state,when the Reynolds number is 3.2 million,we find that the secondary instability growth rate becomes smaller even when the magnitude of the nonlinear mode of the crossflow vortex is larger.The effect of the angle of swept at 35,45 and 55 degrees,respectively,is also studied in the framework of the secondary linear stability theory.Larger angles of swept tend to decrease the spanwise spacing of the crossflow vortices,which correspondingly helps the stimulation of 'z' mode.
文摘This article reports the homotopy solution for stagnation point flow of a non-Newtonian fluid. An incompressible second grade fluid impinges on the wall either orthogonally or obliquely. The resulting nonlinear problems have been solved by a homotopy analysis method （HAM）. Convergence of the series solutions is checked. Such solutions are compared with the numerical solutions presented in a study lint. J. Non-Linear Mech. 43 （2008） 941]. Excellent agreement is noted between the numerical and series solutions.
