The limit equilibrium method （LEM） is widely used for sliding stability evaluation of concrete gravitydams. Failure is then commonly assumed to occur along the entire sliding surface simultaneously.However, the brit...The limit equilibrium method （LEM） is widely used for sliding stability evaluation of concrete gravitydams. Failure is then commonly assumed to occur along the entire sliding surface simultaneously.However, the brittle behaviour of bonded concrete-rock contacts, in combination with the varying stressover the interface, implies that the failure of bonded dam-foundation interfaces occurs progressively. Inaddition, the spatial variation in cohesion may introduce weak spots where failure can be initiated.Nonetheless, the combined effect of brittle failure and spatial variation in cohesion on the overall shearstrength of the interface has not been studied previously. In this paper, numerical analyses are used toinvestigate the effect of brittle failure in combination with spatial variation in cohesion that is taken intoaccount by random fields with different correlation lengths. The study concludes that a possible existenceof weak spots along the interface has to be considered since it significantly reduces the overallshear strength of the interface, and implications for doing so are discussed.展开更多
This paper introduces the mathematical model of ammonia and urea reactors and suggested three methods for designing a special purpose controller. The first proposed method is Adaptive model predictive controller, the ...This paper introduces the mathematical model of ammonia and urea reactors and suggested three methods for designing a special purpose controller. The first proposed method is Adaptive model predictive controller, the second is Adaptive Neural Network Model Predictive Control, and the third is Adaptive neuro-fuzzy sliding mode controller. These methods are applied to a multivariable nonlinear system as an ammonia–urea reactor system. The main target of these controllers is to achieve stabilization of the outlet concentration of ammonia and urea, a stable reaction rate, an increase in the conversion of carbon monoxide(CO) into carbon dioxide(CO_2) to reduce the pollution effect, and an increase in the ammonia and urea productions, keeping the NH_3/CO_2 ratio equal to 3 to reduce the unreacted CO_2 and NH_3, and the two reactors' temperature in the suitable operating ranges due to the change in reactor parameters or external disturbance. Simulation results of the three controllers are compared. Comparative analysis proves the effectiveness of the suggested Adaptive neurofuzzy sliding mode controller than the two other controllers according to external disturbance and the change of parameters. Moreover, the suggested methods when compared with other controllers in the literature show great success in overcoming the external disturbance and the change of parameters.展开更多
A hybrid method of limit equilibrium and finite element internal force for analysis of arch dam stability against sliding is presented.The finite element internal force method(FEIFM) is used to provide more accurate t...A hybrid method of limit equilibrium and finite element internal force for analysis of arch dam stability against sliding is presented.The finite element internal force method(FEIFM) is used to provide more accurate thrust forces acting on the faces of a slip body,and the limit equilibrium method(LEM) is employed to evaluate the factor of safety of the slip body.The method presented can deal with a slip body with large amount of geometrically complex slip faces.In addition,compared with the traditional LEM,it can meet the balance condition of the forces in the slip faces.An example shows that the factor of safety obtained by the method presented agrees well with the theoretical solution.A practical example is also presented to demonstrate the application of the method in the stability analysis of an arch dam project.The results from the examples show that the method is promising in analysis of arch dam stability against sliding.展开更多
The Three Gorges Project is one of the essential key projects for flood controlling and water resources regulation in the Yangtze River. The project includes a river-crossing dam, underground powerhouses, and navigati...The Three Gorges Project is one of the essential key projects for flood controlling and water resources regulation in the Yangtze River. The project includes a river-crossing dam, underground powerhouses, and navigation structures. Because of the huge size and complicated construction technologies, the project faced a series of challenging engineering issues. In terms of rock mechanics, there are many key technical issues, including the sliding resistance and stability of the dam section along the foundations of powerhouses No.l-5, the ,,;lope stability of the double-line five-stage shiplock, excavation of large-scale underground powerhouses, and curtain grouting under the dam. With decades of scientific research and 16 years of practical construction experiences and reservoir operations, these key technical issues in construction of the Three Gorges Project are successfully resolved, which will attribute to the development of hydropower technology. On the basis of the monitoring data during construction and normal operation periods of the Three Gorges Project, this paper presents a systematic analysis of these key rock mechanical issues in terms of behaviors, solutions, dynamic controlling, monitoring arrangement and integrated assessment.展开更多
The objective of this research was to assess the characteristics of seismic induced damage and the deformation patterns of pre-stressed cement-grouted cables that are used for rock slope stabilization projects subject...The objective of this research was to assess the characteristics of seismic induced damage and the deformation patterns of pre-stressed cement-grouted cables that are used for rock slope stabilization projects subjected to quasi-static cyclic loading.The experimental configuration includes the installation of 15 pre-stressed cables in a slope model made of concrete blocks(theoretically rigid rock mass) on top of a pre-existing sliding surface.The study showed that:(i) The pre-stressed cables exhibited great seismic performance.Rapid displacement of the model blocks was observed after the complete loss of the initial pre-stress load under continued applied cyclic loads and exceedance of the state of equilibrium,which implies the higher the initial pre-stress load,the better the seismic performance of the rock anchor;(ii) The failure of the pre-stressed cables was due to fracture at the connection of the tendons and cable heads under cyclic loading.The sequence of failure had a distinct pattern.Failure was first observed at the upper row of cables,which experienced the most severe damage,including the ejection of cable heads.No evidence of de-bonding was observed during the cyclic loading;(iii) The stress distribution of the bond length for pre-stressed cables was highly non-uniform.High stress concentrations were observed at both the fixed end and the free end of the bond length both before and immediately after the state of equilibrium is exceeded.The results obtained can be used to evaluate the overall performance of pre-stressed rock anchors subject to seismic loading and their potential as rockfall prevention and stabilization measures.展开更多
Stabilizing pile is a kind of earth shoring structure frequently used in slope engineering. When the piles have cantilever segments above the ground,laggings are usually installed to avoid collapse of soil between pil...Stabilizing pile is a kind of earth shoring structure frequently used in slope engineering. When the piles have cantilever segments above the ground,laggings are usually installed to avoid collapse of soil between piles. Evaluating the earth pressure acting on laggings is of great importance in design process.Since laggings are usually less stiff than piles,the lateral pressure on lagging is much closer to active earth pressure. In order to estimate the lateral earth pressure on lagging more accurately,first,a model test of cantilever stabilizing pile and lagging systems was carried out. Then,basing the experimental results a three-dimensional sliding wedge model was established. Last,the calculation process of the total active force on lagging is presented based on the kinematic approach of limit analysis. A comparison is made between the total active force on lagging calculated by the formula presented in this study and the force on a same-size rigid retaining wall obtained from Rankine's theory. It is found that the proposed method fits well with the experimental results.Parametric studies show that the total active force on lagging increases with the growth of the lagging height and the lagging clear span; while decreases asthe soil internal friction angle and soil cohesion increase.展开更多
An autonomous approach and landing（A＆L） guidance law is presented in this paper for landing an unpowered reusable launch vehicle（RLV） at the designated runway touchdown. Considering the full nonlinear point-mass ...An autonomous approach and landing（A＆L） guidance law is presented in this paper for landing an unpowered reusable launch vehicle（RLV） at the designated runway touchdown. Considering the full nonlinear point-mass dynamics, a guidance scheme is developed in threedimensional space. In order to guarantee a successful A＆L movement, the multiple sliding surfaces guidance（MSSG） technique is applied to derive the closed-loop guidance law, which stems from higher order sliding mode control theory and has advantage in the finite time reaching property.The global stability of the proposed guidance approach is proved by the Lyapunov-based method.The designed guidance law can generate new trajectories on-line without any specific requirement on off-line analysis except for the information on the boundary conditions of the A＆L phase and instantaneous states of the RLV. Therefore, the designed guidance law is flexible enough to target different touchdown points on the runway and is capable of dealing with large initial condition errors resulted from the previous flight phase. Finally, simulation results show the effectiveness of the proposed guidance law in different scenarios.展开更多
The stability of a gravity dam against sliding along deep-seated weak planes is a universal and important problem encountered in the construction of dams.There is no recommended method for stability analysis of the da...The stability of a gravity dam against sliding along deep-seated weak planes is a universal and important problem encountered in the construction of dams.There is no recommended method for stability analysis of the dam on deep-seated weak planes under earthquake condition in Chinese design codes.Taking Tingzikou dam as an example,the research in this paper is focused on searching a proper way to evaluate the seismic safety of the dam against sliding along deep-seated weak planes and the probable failure modes of dam on deep-seated weak planes during earthquake.It is concluded that there are two probable failure modes of the dam along the main weak geological planes in the foundation.In the first mode,the concrete tooth under the dam will be cut and then the dam together with part foundation will slide along the muddy layer;in the second mode,the dam together with part foundation will glide along the path consist of the weak rock layer under the tooth and the muddy layer downstream the tooth.While there is no geological structure planes to form the second slip surface,the intersection of the main and the second slip surface is 40 to 80 m downstream from dam toe,and the angle between the second slip surface and the horizontal plane probably be 25 to 45 degrees.展开更多
This paper presents control strategies for finite-time stabilization of a class of nonholonomic dynamic systems with unknown virtual control coefficients and system parameters. The minimal dilation degree technique an...This paper presents control strategies for finite-time stabilization of a class of nonholonomic dynamic systems with unknown virtual control coefficients and system parameters. The minimal dilation degree technique and the terminal sliding mode control scheme with finite-time convergence are used to design the controllers. The systematic control strategy development involves the introduction of state transformations and the application of recursive terminal sliding mode structure. Depending on whether the system in question can be converted into a time-invariant linear system or not, two control schemes are proposed respectively guaranteeing that system states converge to zero in finite time. The effectiveness and the robust feature of the developed control approaches are testified by two practical examples： the simplified underactuated hovercraft system and the parking problem for a mobile robot of the unicycle type.展开更多
文摘The limit equilibrium method （LEM） is widely used for sliding stability evaluation of concrete gravitydams. Failure is then commonly assumed to occur along the entire sliding surface simultaneously.However, the brittle behaviour of bonded concrete-rock contacts, in combination with the varying stressover the interface, implies that the failure of bonded dam-foundation interfaces occurs progressively. Inaddition, the spatial variation in cohesion may introduce weak spots where failure can be initiated.Nonetheless, the combined effect of brittle failure and spatial variation in cohesion on the overall shearstrength of the interface has not been studied previously. In this paper, numerical analyses are used toinvestigate the effect of brittle failure in combination with spatial variation in cohesion that is taken intoaccount by random fields with different correlation lengths. The study concludes that a possible existenceof weak spots along the interface has to be considered since it significantly reduces the overallshear strength of the interface, and implications for doing so are discussed.
文摘This paper introduces the mathematical model of ammonia and urea reactors and suggested three methods for designing a special purpose controller. The first proposed method is Adaptive model predictive controller, the second is Adaptive Neural Network Model Predictive Control, and the third is Adaptive neuro-fuzzy sliding mode controller. These methods are applied to a multivariable nonlinear system as an ammonia–urea reactor system. The main target of these controllers is to achieve stabilization of the outlet concentration of ammonia and urea, a stable reaction rate, an increase in the conversion of carbon monoxide(CO) into carbon dioxide(CO_2) to reduce the pollution effect, and an increase in the ammonia and urea productions, keeping the NH_3/CO_2 ratio equal to 3 to reduce the unreacted CO_2 and NH_3, and the two reactors' temperature in the suitable operating ranges due to the change in reactor parameters or external disturbance. Simulation results of the three controllers are compared. Comparative analysis proves the effectiveness of the suggested Adaptive neurofuzzy sliding mode controller than the two other controllers according to external disturbance and the change of parameters. Moreover, the suggested methods when compared with other controllers in the literature show great success in overcoming the external disturbance and the change of parameters.
基金supported by the National Natural Science Foundation of China (Grant Nos. 51079046, 50909041, 50809025, and 50879024)the National Science and Technology Support Plan (Grant Nos. 2008BAB29B03 and 2008BAB29B06)+5 种基金the Special Fund of State Key Laboratory of China (Grant Nos. 2009586012, 2009586912, and 2010585212)the Fundamental Research Funds for the Central Universities (Grant Nos. 2009B08514, 2010B20414, 2010B01414, and 2010B14114)the China Hydropower Engineering Consulting Group Co. Science and Technology Support Project (Grant No. CHC-KJ-2007-02)the Jiangsu Province "333 High-Level Personnel Training Project" (Grant No. 2017-B08037)the Graduate Innovation Program of Universities in Jiangsu Province (Grant No. CX09B_163Z)the Science Foundation for the Excellent Youth Scholars of Ministry of Education of China (Grant No. 20070294023)
文摘A hybrid method of limit equilibrium and finite element internal force for analysis of arch dam stability against sliding is presented.The finite element internal force method(FEIFM) is used to provide more accurate thrust forces acting on the faces of a slip body,and the limit equilibrium method(LEM) is employed to evaluate the factor of safety of the slip body.The method presented can deal with a slip body with large amount of geometrically complex slip faces.In addition,compared with the traditional LEM,it can meet the balance condition of the forces in the slip faces.An example shows that the factor of safety obtained by the method presented agrees well with the theoretical solution.A practical example is also presented to demonstrate the application of the method in the stability analysis of an arch dam project.The results from the examples show that the method is promising in analysis of arch dam stability against sliding.
文摘The Three Gorges Project is one of the essential key projects for flood controlling and water resources regulation in the Yangtze River. The project includes a river-crossing dam, underground powerhouses, and navigation structures. Because of the huge size and complicated construction technologies, the project faced a series of challenging engineering issues. In terms of rock mechanics, there are many key technical issues, including the sliding resistance and stability of the dam section along the foundations of powerhouses No.l-5, the ,,;lope stability of the double-line five-stage shiplock, excavation of large-scale underground powerhouses, and curtain grouting under the dam. With decades of scientific research and 16 years of practical construction experiences and reservoir operations, these key technical issues in construction of the Three Gorges Project are successfully resolved, which will attribute to the development of hydropower technology. On the basis of the monitoring data during construction and normal operation periods of the Three Gorges Project, this paper presents a systematic analysis of these key rock mechanical issues in terms of behaviors, solutions, dynamic controlling, monitoring arrangement and integrated assessment.
基金financially supported by the National Basic Research Program of China (973 Program) (Grant No.2013CB733202)the National Natural Science Foundation of China (Grant No.41102191)+1 种基金the State Key Laboratory of Geohazard Prevention and Geoenvironment Protection (Chengdu University of Technology) (Grant No.SKLGP2011Z019)the National Natural Science Foundation of China (Grant No.11670589)
文摘The objective of this research was to assess the characteristics of seismic induced damage and the deformation patterns of pre-stressed cement-grouted cables that are used for rock slope stabilization projects subjected to quasi-static cyclic loading.The experimental configuration includes the installation of 15 pre-stressed cables in a slope model made of concrete blocks(theoretically rigid rock mass) on top of a pre-existing sliding surface.The study showed that:(i) The pre-stressed cables exhibited great seismic performance.Rapid displacement of the model blocks was observed after the complete loss of the initial pre-stress load under continued applied cyclic loads and exceedance of the state of equilibrium,which implies the higher the initial pre-stress load,the better the seismic performance of the rock anchor;(ii) The failure of the pre-stressed cables was due to fracture at the connection of the tendons and cable heads under cyclic loading.The sequence of failure had a distinct pattern.Failure was first observed at the upper row of cables,which experienced the most severe damage,including the ejection of cable heads.No evidence of de-bonding was observed during the cyclic loading;(iii) The stress distribution of the bond length for pre-stressed cables was highly non-uniform.High stress concentrations were observed at both the fixed end and the free end of the bond length both before and immediately after the state of equilibrium is exceeded.The results obtained can be used to evaluate the overall performance of pre-stressed rock anchors subject to seismic loading and their potential as rockfall prevention and stabilization measures.
基金financially supported by the National Key Technology Research and Development Program of the Ministry of Science and Technology of China under Grant No. 2012BAJ22B06
文摘Stabilizing pile is a kind of earth shoring structure frequently used in slope engineering. When the piles have cantilever segments above the ground,laggings are usually installed to avoid collapse of soil between piles. Evaluating the earth pressure acting on laggings is of great importance in design process.Since laggings are usually less stiff than piles,the lateral pressure on lagging is much closer to active earth pressure. In order to estimate the lateral earth pressure on lagging more accurately,first,a model test of cantilever stabilizing pile and lagging systems was carried out. Then,basing the experimental results a three-dimensional sliding wedge model was established. Last,the calculation process of the total active force on lagging is presented based on the kinematic approach of limit analysis. A comparison is made between the total active force on lagging calculated by the formula presented in this study and the force on a same-size rigid retaining wall obtained from Rankine's theory. It is found that the proposed method fits well with the experimental results.Parametric studies show that the total active force on lagging increases with the growth of the lagging height and the lagging clear span; while decreases asthe soil internal friction angle and soil cohesion increase.
基金co-supported by the National Natural Science Foundation of China (Nos. 51407011, 11372034, 11572035)
文摘An autonomous approach and landing（A＆L） guidance law is presented in this paper for landing an unpowered reusable launch vehicle（RLV） at the designated runway touchdown. Considering the full nonlinear point-mass dynamics, a guidance scheme is developed in threedimensional space. In order to guarantee a successful A＆L movement, the multiple sliding surfaces guidance（MSSG） technique is applied to derive the closed-loop guidance law, which stems from higher order sliding mode control theory and has advantage in the finite time reaching property.The global stability of the proposed guidance approach is proved by the Lyapunov-based method.The designed guidance law can generate new trajectories on-line without any specific requirement on off-line analysis except for the information on the boundary conditions of the A＆L phase and instantaneous states of the RLV. Therefore, the designed guidance law is flexible enough to target different touchdown points on the runway and is capable of dealing with large initial condition errors resulted from the previous flight phase. Finally, simulation results show the effectiveness of the proposed guidance law in different scenarios.
文摘The stability of a gravity dam against sliding along deep-seated weak planes is a universal and important problem encountered in the construction of dams.There is no recommended method for stability analysis of the dam on deep-seated weak planes under earthquake condition in Chinese design codes.Taking Tingzikou dam as an example,the research in this paper is focused on searching a proper way to evaluate the seismic safety of the dam against sliding along deep-seated weak planes and the probable failure modes of dam on deep-seated weak planes during earthquake.It is concluded that there are two probable failure modes of the dam along the main weak geological planes in the foundation.In the first mode,the concrete tooth under the dam will be cut and then the dam together with part foundation will slide along the muddy layer;in the second mode,the dam together with part foundation will glide along the path consist of the weak rock layer under the tooth and the muddy layer downstream the tooth.While there is no geological structure planes to form the second slip surface,the intersection of the main and the second slip surface is 40 to 80 m downstream from dam toe,and the angle between the second slip surface and the horizontal plane probably be 25 to 45 degrees.
基金supported by National Natural Science Foundation of China(No.61273091)Project of Taishan Scholar of Shandong Province of China,and the Ph.D.Programs Foundation of Ministry of Education of China
文摘This paper presents control strategies for finite-time stabilization of a class of nonholonomic dynamic systems with unknown virtual control coefficients and system parameters. The minimal dilation degree technique and the terminal sliding mode control scheme with finite-time convergence are used to design the controllers. The systematic control strategy development involves the introduction of state transformations and the application of recursive terminal sliding mode structure. Depending on whether the system in question can be converted into a time-invariant linear system or not, two control schemes are proposed respectively guaranteeing that system states converge to zero in finite time. The effectiveness and the robust feature of the developed control approaches are testified by two practical examples： the simplified underactuated hovercraft system and the parking problem for a mobile robot of the unicycle type.
