Using the concept of the base forces, a new finite element method （base force element method, BFEM） based on the complementary energy principle is presented for accurate modeling of structures with large displacemen...Using the concept of the base forces, a new finite element method （base force element method, BFEM） based on the complementary energy principle is presented for accurate modeling of structures with large displacements and large rotations. First, the complementary energy of an element is described by taking the base forces as state variables, and is then separated into deformation and rotation parts for the case of large deformation. Second, the control equations of the BFEM based on the complementary energy principle are derived using the Lagrange multiplier method. Nonlinear procedure of the BFEM is then developed. Finally, several examples are analyzed to illustrate the reliability and accuracy of the BFEM.展开更多
A modified energy-balance equation accounting for P-delta effects and hysteretic behavior of reinforced concrete members is derived. Reduced hysteretic properties of structural components due to combined stiffness and...A modified energy-balance equation accounting for P-delta effects and hysteretic behavior of reinforced concrete members is derived. Reduced hysteretic properties of structural components due to combined stiffness and strength degradation and pinching effects, and hysteretic damping are taken into account in a simple manner by utilizing plastic energy and seismic input energy modification factors. Having a pre-selected yield mechanism, energy balance of structure in inelastic range is considered. P-delta effects are included in derived equation by adding the external work of gravity loads to the work of equivalent inertia forces and equating the total external work to the modified plastic energy. Earthquake energy input to multi degree of freedom（MDOF） system is approximated by using the modal energy-decomposition. Energybased base shear coefficients are verified by means of both pushover analysis and nonlinear time history（NLTH） analysis of several RC frames having different number of stories. NLTH analyses of frames are performed by using the time histories of ten scaled ground motions compatible with elastic design acceleration spectrum and fulfilling duration/amplitude related requirements of Turkish Seismic Design Code. The observed correlation between energy-based base shear force coefficients and the average base shear force coefficients of NLTH analyses provides a reasonable confidence in estimation of nonlinear base shear force capacity of frames by using the derived equation.展开更多
The opening of the Panama Canal in 1913 transformed ocean-shipping and the availability of internationally-traded goods, shortened travel time between the Pacific and Atlantic oceans, increased ship tonnage, and spark...The opening of the Panama Canal in 1913 transformed ocean-shipping and the availability of internationally-traded goods, shortened travel time between the Pacific and Atlantic oceans, increased ship tonnage, and sparked the growth of port authorities on both the Atlantic and Pacific coasts of the Panama Canal. Historically, the United States was number one and China was number two in tons of cargo that pass through the canal annually in the high stakes game of import and export markets. Prior to the construction of the Panama Canal, the most efficient way to cross the 82-kilometer isthmus, between the Port of Panama City on the Pacific and the Port of Colon on the Atlantic, was by mule trails through tropical forests and river transportation. Since the construction of the Panama Canal through tropical forests in the 1910s, pesticides have been essential for managing mosquitoes as well as controlling wetland vegetation that blocked lakes, rivers and the canal. The pri<span>mary objective of this research study is to document the long-term environmental impacts of pesticide and herbicide use in the Panama Canal Zone. Many of these chemicals, including 2, 4,-D, 2, 4, 5-T and DDT, have a long half-life under water and some, like arsenic (As), have no half-life. Pesticides </span>and chemicals flowed into Lake Gatun via surface runoff either in solution or attached to the sediment during the rainy season. The by-product 2,3,7,8-tetrachlorodibenzo-<i>p</i>-dioxin (TCDD) is an unanticipated contaminant created during the manufacture of the herbicide 2,4,5-T. TCDD can bio-accumulate in fish and birds and enter into the human food supply. The extent of the current chemical and pesticide contamination on former U.S. military base grounds and in Lake Gatun is unknown. Systematic soil sampling of current and former military bases, chemical disposal sites and Lake Gatun or the Panama Canal sediments is needed to determine if mitigation is necessary.展开更多
Using the concept of base forces as state variables,a new finite element method-the base force element method (BFEM) on complementary energy principle for linear elasticity problems is presented.Firstly,an explicit ex...Using the concept of base forces as state variables,a new finite element method-the base force element method (BFEM) on complementary energy principle for linear elasticity problems is presented.Firstly,an explicit expression of compliance matrix for an element is derived through base forces by dyadic vectors.Then,the explicit control equations of finite element method of complementary energy principle are derived using Lagrange multiplier method.Thereafter,the base forces element procedure for linear elasticity is developed.Finally,several examples are analyzed to illustrate the reliability and accuracy of the formulation and the procedure.展开更多
The transport of the energy and other scalar quantities in turbulence can be controlled by scalar-based volume forces,e.g.,the buoyancy in the turbulent thermal convection or the electric body force in the electrokine...The transport of the energy and other scalar quantities in turbulence can be controlled by scalar-based volume forces,e.g.,the buoyancy in the turbulent thermal convection or the electric body force in the electrokinetic(EK)turbulence,and expressed as∇^(n)A,with A being a control scalar.This paper presents a unified theoretical framework for the transport of the energy and other scalar quantities in the turbulence driven by scalar-based volume forces.Several isolated results that have previously been reported in relation to the turbulent thermal convection(related to n=0)and the EK turbulence(related to n=1)are unified in this theoretical framework.With the theory,the following interesting results are predicted:(1)When n<2/3,the transport of the kinetic energy is dominated by the Kolmogorov scaleηand another small scale l_(A).When n>2/3,the transport of the kinetic energy is controlled by three characteristic small scales:l_(K),l_(ηK) and l_(A).(2)The scaling law range can be divided into an inertial subrange and a volume-force-dominated subrange.(3)In the latter case,the exponents of the power spectra of the velocity and the relevant scalar quantity areη_(u)=(4n-11)/5,η_(A)=-(2n+7)/5,respectively.(4)In the equilibrium state,n cannot exceed 4.(5)The positive exponent of l_(A)∼0.024Ra^(0.107±0.016)_(A.l_(0)) is confirmed in the turbulent thermal convection.展开更多
Influence of the elasticity of the base on vibration isolation performances of single layer, double layer and floating raft vibration isolation systems is investigated systematically. Characteristics of vibration coup...Influence of the elasticity of the base on vibration isolation performances of single layer, double layer and floating raft vibration isolation systems is investigated systematically. Characteristics of vibration coupling between different vibration isolation systems and different elastic bases are analyzed. Moreover the characteristics of vibration acceleration level difference and force transmissibility of different vibration isolation systems are discussed and their simpli- fled expressions are given. In addition the required control forces of active vibration isolation under different installations of actuators for different vibration isolation systems are compared. The results show that for all vibration isolation systems, the addition of the stiffness and damping of the base can enhance their vibration acceleration level difference and force transmissibility. Moreover for floating raft vibration isolation system, the addition of the stiffness and damping of the raft can enhance its vibration isolation performance and reduce the control force required bv active vibration isolation.展开更多
Stable label movement and smooth label trajectory are critical for effective information understanding.Sudden label changes cannot be avoided by whatever forced directed methods due to the unreliability of resultant f...Stable label movement and smooth label trajectory are critical for effective information understanding.Sudden label changes cannot be avoided by whatever forced directed methods due to the unreliability of resultant force or global optimization methods due to the complex trade-off on the different aspects.To solve this problem,we proposed a hybrid optimization method by taking advantages of the merits of both approaches.We first detect the spatial-temporal intersection regions from whole trajectories of the features,and initialize the layout by optimization in decreasing order by the number of the involved features.The label movements between the spatial-temporal intersection regions are determined by force directed methods.To cope with some features with high speed relative to neighbors,we introduced a force from future,called temporal force,so that the labels of related features can elude ahead of time and retain smooth movements.We also proposed a strategy by optimizing the label layout to predict the trajectories of features so that such global optimization method can be applied to streaming data.展开更多
基金supported by the China Postdoctoral Science Foundation Funded Project (20080430038) the Funding Project for Academic Human Resources Development in Institutions of Higher Learning Under the Jurisdiction of Beijing Municipality (05004999200602)
文摘Using the concept of the base forces, a new finite element method （base force element method, BFEM） based on the complementary energy principle is presented for accurate modeling of structures with large displacements and large rotations. First, the complementary energy of an element is described by taking the base forces as state variables, and is then separated into deformation and rotation parts for the case of large deformation. Second, the control equations of the BFEM based on the complementary energy principle are derived using the Lagrange multiplier method. Nonlinear procedure of the BFEM is then developed. Finally, several examples are analyzed to illustrate the reliability and accuracy of the BFEM.
文摘A modified energy-balance equation accounting for P-delta effects and hysteretic behavior of reinforced concrete members is derived. Reduced hysteretic properties of structural components due to combined stiffness and strength degradation and pinching effects, and hysteretic damping are taken into account in a simple manner by utilizing plastic energy and seismic input energy modification factors. Having a pre-selected yield mechanism, energy balance of structure in inelastic range is considered. P-delta effects are included in derived equation by adding the external work of gravity loads to the work of equivalent inertia forces and equating the total external work to the modified plastic energy. Earthquake energy input to multi degree of freedom（MDOF） system is approximated by using the modal energy-decomposition. Energybased base shear coefficients are verified by means of both pushover analysis and nonlinear time history（NLTH） analysis of several RC frames having different number of stories. NLTH analyses of frames are performed by using the time histories of ten scaled ground motions compatible with elastic design acceleration spectrum and fulfilling duration/amplitude related requirements of Turkish Seismic Design Code. The observed correlation between energy-based base shear force coefficients and the average base shear force coefficients of NLTH analyses provides a reasonable confidence in estimation of nonlinear base shear force capacity of frames by using the derived equation.
文摘The opening of the Panama Canal in 1913 transformed ocean-shipping and the availability of internationally-traded goods, shortened travel time between the Pacific and Atlantic oceans, increased ship tonnage, and sparked the growth of port authorities on both the Atlantic and Pacific coasts of the Panama Canal. Historically, the United States was number one and China was number two in tons of cargo that pass through the canal annually in the high stakes game of import and export markets. Prior to the construction of the Panama Canal, the most efficient way to cross the 82-kilometer isthmus, between the Port of Panama City on the Pacific and the Port of Colon on the Atlantic, was by mule trails through tropical forests and river transportation. Since the construction of the Panama Canal through tropical forests in the 1910s, pesticides have been essential for managing mosquitoes as well as controlling wetland vegetation that blocked lakes, rivers and the canal. The pri<span>mary objective of this research study is to document the long-term environmental impacts of pesticide and herbicide use in the Panama Canal Zone. Many of these chemicals, including 2, 4,-D, 2, 4, 5-T and DDT, have a long half-life under water and some, like arsenic (As), have no half-life. Pesticides </span>and chemicals flowed into Lake Gatun via surface runoff either in solution or attached to the sediment during the rainy season. The by-product 2,3,7,8-tetrachlorodibenzo-<i>p</i>-dioxin (TCDD) is an unanticipated contaminant created during the manufacture of the herbicide 2,4,5-T. TCDD can bio-accumulate in fish and birds and enter into the human food supply. The extent of the current chemical and pesticide contamination on former U.S. military base grounds and in Lake Gatun is unknown. Systematic soil sampling of current and former military bases, chemical disposal sites and Lake Gatun or the Panama Canal sediments is needed to determine if mitigation is necessary.
基金supported by the National Natural Science Foundation of China (Grant No. 10972015)
文摘Using the concept of base forces as state variables,a new finite element method-the base force element method (BFEM) on complementary energy principle for linear elasticity problems is presented.Firstly,an explicit expression of compliance matrix for an element is derived through base forces by dyadic vectors.Then,the explicit control equations of finite element method of complementary energy principle are derived using Lagrange multiplier method.Thereafter,the base forces element procedure for linear elasticity is developed.Finally,several examples are analyzed to illustrate the reliability and accuracy of the formulation and the procedure.
基金Projects supported by the National Natural Science Foundation of China(Grant No.11672229).
文摘The transport of the energy and other scalar quantities in turbulence can be controlled by scalar-based volume forces,e.g.,the buoyancy in the turbulent thermal convection or the electric body force in the electrokinetic(EK)turbulence,and expressed as∇^(n)A,with A being a control scalar.This paper presents a unified theoretical framework for the transport of the energy and other scalar quantities in the turbulence driven by scalar-based volume forces.Several isolated results that have previously been reported in relation to the turbulent thermal convection(related to n=0)and the EK turbulence(related to n=1)are unified in this theoretical framework.With the theory,the following interesting results are predicted:(1)When n<2/3,the transport of the kinetic energy is dominated by the Kolmogorov scaleηand another small scale l_(A).When n>2/3,the transport of the kinetic energy is controlled by three characteristic small scales:l_(K),l_(ηK) and l_(A).(2)The scaling law range can be divided into an inertial subrange and a volume-force-dominated subrange.(3)In the latter case,the exponents of the power spectra of the velocity and the relevant scalar quantity areη_(u)=(4n-11)/5,η_(A)=-(2n+7)/5,respectively.(4)In the equilibrium state,n cannot exceed 4.(5)The positive exponent of l_(A)∼0.024Ra^(0.107±0.016)_(A.l_(0)) is confirmed in the turbulent thermal convection.
文摘Influence of the elasticity of the base on vibration isolation performances of single layer, double layer and floating raft vibration isolation systems is investigated systematically. Characteristics of vibration coupling between different vibration isolation systems and different elastic bases are analyzed. Moreover the characteristics of vibration acceleration level difference and force transmissibility of different vibration isolation systems are discussed and their simpli- fled expressions are given. In addition the required control forces of active vibration isolation under different installations of actuators for different vibration isolation systems are compared. The results show that for all vibration isolation systems, the addition of the stiffness and damping of the base can enhance their vibration acceleration level difference and force transmissibility. Moreover for floating raft vibration isolation system, the addition of the stiffness and damping of the raft can enhance its vibration isolation performance and reduce the control force required bv active vibration isolation.
基金supported by the National Key Technology R&D Program(Project No.2017YFB1002604)the National Natural Science Foundation of China(Project Nos.61772298 and 61832016)+1 种基金Research Grant of Beijing Higher Institution Engineering Research CenterTsinghua-Tencent Joint Laboratory for Internet Innovation Technology.
文摘Stable label movement and smooth label trajectory are critical for effective information understanding.Sudden label changes cannot be avoided by whatever forced directed methods due to the unreliability of resultant force or global optimization methods due to the complex trade-off on the different aspects.To solve this problem,we proposed a hybrid optimization method by taking advantages of the merits of both approaches.We first detect the spatial-temporal intersection regions from whole trajectories of the features,and initialize the layout by optimization in decreasing order by the number of the involved features.The label movements between the spatial-temporal intersection regions are determined by force directed methods.To cope with some features with high speed relative to neighbors,we introduced a force from future,called temporal force,so that the labels of related features can elude ahead of time and retain smooth movements.We also proposed a strategy by optimizing the label layout to predict the trajectories of features so that such global optimization method can be applied to streaming data.
