Understanding the relationship between normal stiffness and permeability in rock fractures under high and true-triaxial in situ stress conditions is critical to assess hydro-mechanical coupling in the Earth's crus...Understanding the relationship between normal stiffness and permeability in rock fractures under high and true-triaxial in situ stress conditions is critical to assess hydro-mechanical coupling in the Earth's crust.Previous data on stiffness–permeability relations are measured under uniaxial stress states as well as under normal stress.However,many projects involve faulted formations with complex three-dimensional(3D)stress states or significant changes to the original stress state.We rectified this by following the permeability evolution using a true-triaxial stress-permeability apparatus as well as independently applying a spectrum of triaxial stresses from low to high.The relationship between permeability and fracture normal stiffness was quantified using constraints based on the principle of virtual work.The impacts of fracture-lateral and fracture-normal stresses on permeability and normal stiffness evolution were measured.It was found that permeability decreases with increasing fracture-lateral and fracture-normal stresses as a result of Poisson confinement,independent of the orientation of the fracture relative to the stresses.The lateral stresses dominated the evolution of normal stiffness at lower normal stresses(σ_(3)=10 MPa)and played a supplementary role at higher normal stresses(σ_(3)>10 MPa).Moreover,correlations between the evolution of permeability and normal stiffness were extended beyond the low-stiffness,high-permeability region to the high-stiffness,low-permeability region under high fracture-lateral stresses(10–80 MPa)with fracture-normal stress(10–50 MPa)conditions.Again,high lateral stresses further confined the fracture and therefore reduced permeability and increased normal stiffness,which exceeded the previous reported stiffness under no lateral stress conditions.This process enabled us to identify a fundamental change in the flow regime from multi-channel to isolated channelized flow.These results provide important characterizations of fracture permeability in the deep crust,including recovery from deep shale-gas reservoirs.展开更多
New principles of work and energy as well as power and energy rate with cross terms for polar and nonlocal polar continuum field theories were presented and from them all corresponding equations of motion and boundary...New principles of work and energy as well as power and energy rate with cross terms for polar and nonlocal polar continuum field theories were presented and from them all corresponding equations of motion and boundary conditions as well as complete equations of energy and energy rate with the help of generalized Piola's theorems were naturally derived in all and without any additional requirement. Finally, some new balance laws of energy and energy rate for generalized continuum mechanics were established. The new principles of work and energy as well as power and energy rate with cross terms presented in this paper are believed to be new and they have corrected the incompleteness of all existing corresponding principles and laws without cross terms in literatures of generalized continuum field theories.展开更多
This paper presents an energy principle, zero different principle of coupledsystems in photoelasticity, from which the potential energy, the complementary energy,generalized potential energy and generalized complemen...This paper presents an energy principle, zero different principle of coupledsystems in photoelasticity, from which the potential energy, the complementary energy,generalized potential energy and generalized complementary energy variationalprinciples of the coupled systems in photoelasticity are derived What is called the coupled systems means that two deformational bodies, forwhich figures, sizes,loads and boundary conditions are the same and they are all inactual states but they are made of different materials.Prototype body and model body in photoelasticity are essentially the coupledsystems, therefore the above principles become the theoretical basis of defining theinflunce of Poissons ratio v on accuracy of the frozen-stress method.展开更多
According to the basic idea of dual-complementarity,in a simple and unified way proposed by the author,some basic principles in dynamic theory of elastic materials with voids can be established sys- tematically.In thi...According to the basic idea of dual-complementarity,in a simple and unified way proposed by the author,some basic principles in dynamic theory of elastic materials with voids can be established sys- tematically.In this paper, an important integral relation in terms of convolutions is given,which can be con- sidered as the generalized principle of virtual work in mechanics.Based on this relation,it is possible not on- ly to obtain the principle of virtual work and the reciprocal theorem in dynamic theory of elastic materials with voids,but also to derive systematically the complementary functionals for the eight-field,six-field, four-field and two-field simplified Gurtin-type variational principles.Furthermore,with this approach,the in- trinsic relationship among various principles can be explained clearly.展开更多
In recent years, the two-stage control valve has been used more and more in the quantitative loading control system, and its advantages such as fast control response, high quantitative accuracy and low maintenance cos...In recent years, the two-stage control valve has been used more and more in the quantitative loading control system, and its advantages such as fast control response, high quantitative accuracy and low maintenance cost have been widely recognized. Not only can it meet the needs of quantitative loading control, but it can also be used as interlocking cut-off, and its action time and response speed are unmatched by analog control valves. It can still be competent in control scenarios with high response speed requirements.展开更多
Soft grippers are favored for handling delicate objects due to their compliance but often have lower load capacities compared to rigid ones.Variable Stiffness Module(VSM)offer a solution,balancing flexibility and load...Soft grippers are favored for handling delicate objects due to their compliance but often have lower load capacities compared to rigid ones.Variable Stiffness Module(VSM)offer a solution,balancing flexibility and load capacity,for which particle jamming is an effective technology for stiffness-tunable robots requiring safe interaction and load capacity.Specific applica-tions,such as rescue scenarios,require quantitative analysis to optimize VSM design parameters,which previous analytical models cannot effectively handle.To address this,a Grey-box model is proposed to analyze the mechanical response of the particle-jamming-based VSM by combining a White-box approach based on the virtual work principle with a Black-box approach that uses a shallow neural network method.The Grey-box model demonstrates a high level of accuracy in predict-ing the VSM force-height mechanical response curves,with errors below 15%in almost 90%of the cases and a maximum error of less than 25%.The model is used to optimize VSM design parameters,particularly those unexplored combinations.Our results from the load capacity and force distribution comparison tests indicate that the VSM,optimized through our methods,quantitatively meets the practical engineering requirements.展开更多
Due to the complex structures of multi-limbed parallel robots,conventional parallel robots generally have limited workspace,complex kinematics,and complex dynamics,which increases the application difficulty of paralle...Due to the complex structures of multi-limbed parallel robots,conventional parallel robots generally have limited workspace,complex kinematics,and complex dynamics,which increases the application difficulty of parallel robot in industrial engineering.To solve the above problems,this paper proposes a single-loop Sch?nflies motion parallel robot with full cycle rotation,the robot can generate Sch?nflies motion by the most simplified structure.The novel Sch?nflies motion parallel robot is a two-limb parallel mechanism with least links and joints,and each limb is driven by a 2-degree of freedom(DOF)cylindrical driver(C-driver).The full cycle rotation of the output link is achieved by“…R-H…”structure,where the revolute(R)and helical(H)joints are coaxial.Mobility,kinematics,workspace and singularity analysis of the novel Sch?nflies motion parallel robot are analyzed.Then,dynamic model is formulated based on the principle of virtual work.Moreover,a pick-and-place task is implemented by the proposed Sch?nflies motion parallel robot and a serial SCARA robot,respectively.The simulation results verify the correctness of the theoretical model.Furthermore,dynamics performances of the proposed Sch?nflies motion parallel robot and a serial SCARA robot are compared,which reveal the performance merits of the proposed Sch?nflies motion parallel robot.展开更多
A novel design for an electrostriction appliance derived from the theory and application of electromagnetics is presented. The working principle, that is the application of gravitation and elasticity together to reali...A novel design for an electrostriction appliance derived from the theory and application of electromagnetics is presented. The working principle, that is the application of gravitation and elasticity together to realize the ＂shrinking＂ and ＂extending＂ effect from the distortion and transforming power into mechanical energy, is briefly explained. The characteristic parameter relationships are established and the experimental research is performed. Experimental results show that this sort of electrostriction appliance can perform well as regards driving force and beeline displacement, and furthermore, its self-weight is smaller. This makes it suitable for beeline drivers with a high application value, especially for the driver of the bionic appliance. In the application of the electrostriction appliance to a bionics-flapping aircraft, the wings can work with a flapping angle in the range of a certain value by controlling the ＂shrinking＂ and ＂extending＂ of the electrostriction appliance. It can reduce the startup power and the impact load of the driver. The flapping extent of the wings will change when the voltage which is put into the electrostriction appliance varies. This makes it more flexible as the bionics-flapping aircraft realizes different actions of flying.展开更多
Aim To extend several fundamental theorems of conventional elasticity theory to quasicrystalelasticity theory. Methods The basic governing equations of quasicrystal elasticity theory and Gauss's theorem were appli...Aim To extend several fundamental theorems of conventional elasticity theory to quasicrystalelasticity theory. Methods The basic governing equations of quasicrystal elasticity theory and Gauss's theorem were applied in the derivation. Results and Conclusion The principle of virtual work, Betti's reciprocal theorem and the uniqueness theorem of quasicrystal elasticity theory are proud, and some conservative integrals in quasicrystal elasticty theory are obtained.展开更多
Proportional direction valve is one of the most fundamental elements in electronic-hydraulic control technique. Its function is to control the operating speed, direction, position, and strength of output force of the ...Proportional direction valve is one of the most fundamental elements in electronic-hydraulic control technique. Its function is to control the operating speed, direction, position, and strength of output force of the hydraulic actuator continuously. Considering the different application and the cost, the existing technique mainly includes the internal feedback valve used in open loop system, and the electronic closed loop controlled valve used in closed loop system. Because of their different mechanical structure and the gre at different in performance, it brings inconvenience for customer to select, also inconvenience for enterprise to produce. Aiming at this problem, the idea of combining the above two kinds of valves into one body is proposed first, and then the new valve＇s structure to realize this target is designed. The idea intends to apply the displacement pilot flow feedback control principle in present 2-position 2-way valve system to the proportional direction valve of 3-position 4-way system. Newly designed feed forward controller can decouple the interference between the internal feedback and the electronic closed loop. Redundant conversion is designed to electronic switch mode. Experiment on dynamic and static characteristic of new proportional direction valve in internal feedback control mode and electronic closed loop control mode is discussed to prove the new theory is correct. Although the new valve is of excellent dynamic response characteristic, its steady control characteristic in open loop control mode needs to be improved further. The research results prepare one new fundamental element for electronic-hydraulic control technology.展开更多
Plane strain assumption and exponent hardening law are used to investigate the plastic deformation in tube bending. Some theoretical formulae including stress, curvature radius of neutral layer, angle of neutral layer...Plane strain assumption and exponent hardening law are used to investigate the plastic deformation in tube bending. Some theoretical formulae including stress, curvature radius of neutral layer, angle of neutral layer deviation, bending moment, wall thickness variation and crosssection distortion, are developed to explain the phenomena in tube bending and their magnitudes are also determined. During unloading process, the springback angle is deduced using the virtual work principle, and springback radius is also given according to the length of the neutral layer which remains unchanged before and after springback. The theoretical formulae are validated by the experimental results or the validated simulation results in literature, which can be used to auicklv predict the forming aualitv of tube numerical control （NC） bending.展开更多
Pipes inevitably encounter high ambient pressure and bending moment during the deepwater pipe-laying process,which can lead to elliptical buckling and even deterioration failure.For the safety of pipe-laying operation...Pipes inevitably encounter high ambient pressure and bending moment during the deepwater pipe-laying process,which can lead to elliptical buckling and even deterioration failure.For the safety of pipe-laying operation,available formulas for the pipe stability are established on the basis of the assumption of uniform deformation along the tube length and symmetrical buckling.This method can predict the nonlinear response of elliptical collapse of steel circular tubes for different ratios of diameter to thickness（D/t）under pure bending or combined bending and external pressure.In these formulas,the strain-displacement relationship is deduced from the nonlinear ring theory,and the Ramberg-Osgood constitutive model is applied to simulate the inelastic material behavior.Meanwhile,the principle of virtual work is adopted to derive the equilibrium equations.A set of equations is solved by the Newton-Raphson method,and the iterative scheme contains nested iteration for the constitutive relation.In order to check the effectiveness of this theoretical method,illustrative examples are presented in this paper.Besides,the numerical simulation is carried out by use of ANSYS.A comparison of the results shows that the theoretical method can provide reasonable prediction for engineering practice.展开更多
Because the deployable structures are complex multi-loop structures and methods of derivation which lead to simpler kinematic and dynamic equations of motion are the subject of research effort, the kinematics and dyna...Because the deployable structures are complex multi-loop structures and methods of derivation which lead to simpler kinematic and dynamic equations of motion are the subject of research effort, the kinematics and dynamics of deployable structures with scissor-like-elements are presented based on screw theory and the principle of virtual work respectively. According to the geometric characteristic of the deployable structure examined, the basic structural unit is the common scissor-like-element（SLE）. First, a spatial deployable structure, comprised of three SLEs, is defined, and the constraint topology graph is obtained. The equations of motion are then derived based on screw theory and the geometric nature of scissor elements. Second, to develop the dynamics of the whole deployable structure, the local coordinates of the SLEs and the Jacobian matrices of the center of mass of the deployable structure are derived. Then, the equivalent forces are assembled and added in the equations of motion based on the principle of virtual work. Finally, dynamic behavior and unfolded process of the deployable structure are simulated. Its figures of velocity, acceleration and input torque are obtained based on the simulate results. Screw theory not only provides an efficient solution formulation and theory guidance for complex multi-closed loop deployable structures, but also extends the method to solve dynamics of deployable structures. As an efficient mathematical tool, the simper equations of motion are derived based on screw theory.展开更多
The large capacity servo press is traditionally realized by means of redundant actuation, however there exist the over-constraint problem and interference among actuators, which increases the control difficulty and th...The large capacity servo press is traditionally realized by means of redundant actuation, however there exist the over-constraint problem and interference among actuators, which increases the control difficulty and the product cost. A new type of press mechanism with parallel topology is presented to develop the mechanical servo press with high stamping capacity. The dynamic model considering gravity counterbalance is proposed based on the virtual work principle, and then the effect of counterbalance cylinder on the dynamic performance of the servo press is studied. It is found that the motor torque required to operate the press is a lot less than the others when the ratio of the counterbalance force to the gravity of ram is in the vicinity of 1.0. The stamping force of the real press prototype can reach up to 25 MN on the position of 13 mm away from the bottom dead center. The typical deep-drawing process with 1 200 mm stroke at 8 strokes per minute is proposed by means of five order polynomial. On this process condition, the driving torques are calculated based on the above dynamic model and the torque measuring test is also carried out on the prototype. It is shown that the curve trend of calculation torque is consistent to the measured result and that the average error is less than 15%. The parallel mechanism is introduced into the development of large capacity servo press to avoid the over-constraint and interference of traditional redundant actuation, and its dynamic characteristics with gravity counterbalance are presented.展开更多
China's first Mars exploration mission will carry out comprehensive global surveys of the planet from data collected by instruments carried in orbit and roving on the planet itself.Goals of the mission include det...China's first Mars exploration mission will carry out comprehensive global surveys of the planet from data collected by instruments carried in orbit and roving on the planet itself.Goals of the mission include detailed inspections and surveys of key areas on the surface of Mars.One of the main scientific payloads installed on the orbiter is the moderate resolution camera.Its mission is to image the surface of Mars sufficiently to produce a global remote sensing image map of the planet,and to explore and record changes to the topography of Mars,including major geological structures,and to advance research on topography and geomorphology in general.The moderate resolution camera uses a lightweight and compact integrated design;its primary components are an optical module,a focal plane module,a camera control module,a power and interface module,a camera support module,a thermal control module,and a reference module.Radiometric calibration,color calibration,and geometric calibration have been carried out to ensure that the camera can acquire sufficient accurate data to complete mission goals.This paper introduces the camera's detection mission,its system composition,and its working principle;it also describes the camera's ground calibration tests and their results,and provides a reference for processing the camera's scientific data and for future applications.展开更多
Soft robots have unique advantages over traditional rigid robots and have broad application prospects in many fields.To expand their bioinspired applications,we propose a novel Soft Pneumatic Actuator(SPA)associated w...Soft robots have unique advantages over traditional rigid robots and have broad application prospects in many fields.To expand their bioinspired applications,we propose a novel Soft Pneumatic Actuator(SPA)associated with spiral configuration inspired by the structure and unwinding motion of the seahorse tail.Diff erent from bending motion of common soft actuators,the spiral SPA can generate unwinding motion as input air pressure increases.First,to explore the eff ect of diff erent initial spiral types on unwinding performance,three typical spiral SPAs are designed and simulated while keeping the outside arc of actuator body constant.Second,a static model of the spiral SPA is established by combining the hyperelastic material model,geometric relationships,and virtual work principle.To improve model accuracy,two geometric correction parameters are employed and their physical significance is analyzed by finite element simulations.Third,a prototype of the logarithmic spiral SPA(Log_spiral SPA)is fabricated and a Fiber Bragg Grating(FBG)sensor array is designed to detect and reconstruct unwinding shapes of the prototype.Finally,the unwinding performance,static model and output force capability of the prototype are tested and verified.Furthermore,we discuss prospects for this novel spiral SPA and test its practical applications in inchworm-like motion,assisting finger rehabilitation and object capture.展开更多
This paper presents an investigation of temperature, displacement, stress, and induced magnetic field in a half space perfectly-conductive plate. Finite element equations regarding generalized magneto-thermoelasticity...This paper presents an investigation of temperature, displacement, stress, and induced magnetic field in a half space perfectly-conductive plate. Finite element equations regarding generalized magneto-thermoelasticity problems with two relaxation times （i.e., the G-L theory） are derived using the principle of virtual work. For avoiding numerical complication involved in inverse Laplace and Fourier transformation and low precision thereof, the equations are solved directly in time-domain. As a numerical example, the derived equation is used to investigate the generalized magneto-thermoelastic behavior of a semi-infinite plate under magnetic field and subjecting to a thermal shock loading. The results demonstrate that FEM can faithfully predict the deformation of the plate and the induced magnetic field, and most importantly can reveal the sophisticated second sound effect of heat conduction in two-dimensional generalized thermoelastic solids, which is usually difficult to model by routine transformation methods. A peak can be observed in the distribution of stress and induced front and the magnitude of magnetic field at the heat wave the peak decreases with time, which can not be obtained by transformation methods. The new method can also be used to study generalized piezo-thermoelastic problems.展开更多
Based on the nonlinear displacement-strain relationship,the virtual work principle method was used to establish the nonlinear equilibrium equations of steel beams with semi-rigid connections under vertical uniform loa...Based on the nonlinear displacement-strain relationship,the virtual work principle method was used to establish the nonlinear equilibrium equations of steel beams with semi-rigid connections under vertical uniform loads and temperature change.Considering the non-uniform temperature distribution across the thickness of beams,the formulas for stresses and vertical displacements were presented.On the basis of a flowchart for analysis of the numerical example,the effect of temperature change on the elastic behavior of steel beams was investigated.It is found that the maximal stress is mainly influenced by axial temperature change,and the maximal vertical displacement is principally affected by temperature gradients.And the effect of temperature gradients on the maximal vertical displacement decreases with the increase of rotational stiffness of joints.Both the maximal stress and vertical displacement decrease with the increase of rotational stiffness of joints.It can be concluded that the effects of temperature changes and rotational stiffness of joints on the elastic behavior of steel beams are significant.However,the influence of rotational stiffness becomes smaller when the rotational stiffness is larger.展开更多
Electromechanical dynamics analysis and simulation on a rollforming equipment with both sides variable cross-section are discussed in this study.The system includes mechanical parts and electromagnetism parts,and it i...Electromechanical dynamics analysis and simulation on a rollforming equipment with both sides variable cross-section are discussed in this study.The system includes mechanical parts and electromagnetism parts,and it is a strongly coupled electromechanical system.Based on a virtual work principle and given power,generalized forces of this system are obtained.By using Lagrange-Maxwell equations,a model of electromechanical dynamics is established.Differential equations of two-phase winding on d-q axis are obtained by Park transformation,which comes from three-phase winding equations on the A-B-C axis.This system is solved with the 4th order Runge-Kutta's method,and discrete solutions of all variables are obtained.Finally,by using Matlab language,the system is simulated.The results show that the proposed method works very well.展开更多
The micro free-piston swing engine （MFPSE） is a new structure, free-piston internal combustion engine. The dynamic model integrated MFPSE with a power generator and thermodynamic models in compression, power and sca...The micro free-piston swing engine （MFPSE） is a new structure, free-piston internal combustion engine. The dynamic model integrated MFPSE with a power generator and thermodynamic models in compression, power and scavenge processes based on the open thermodynamic systems were presented. A simulation was executed at given geometric parameters and initial conditions. The results manifest that the working principle of MFPSE is feasible.展开更多
基金funded by the joint fund of the National Key Research and Development Program of China(Grant No.2021YFC2902101)National Natural Science Foundation of China(Grant No.52374084)+1 种基金the 111 Project(Grant No.B17009)DE acknowledges support from the G.Albert Shoemaker endowment.
文摘Understanding the relationship between normal stiffness and permeability in rock fractures under high and true-triaxial in situ stress conditions is critical to assess hydro-mechanical coupling in the Earth's crust.Previous data on stiffness–permeability relations are measured under uniaxial stress states as well as under normal stress.However,many projects involve faulted formations with complex three-dimensional(3D)stress states or significant changes to the original stress state.We rectified this by following the permeability evolution using a true-triaxial stress-permeability apparatus as well as independently applying a spectrum of triaxial stresses from low to high.The relationship between permeability and fracture normal stiffness was quantified using constraints based on the principle of virtual work.The impacts of fracture-lateral and fracture-normal stresses on permeability and normal stiffness evolution were measured.It was found that permeability decreases with increasing fracture-lateral and fracture-normal stresses as a result of Poisson confinement,independent of the orientation of the fracture relative to the stresses.The lateral stresses dominated the evolution of normal stiffness at lower normal stresses(σ_(3)=10 MPa)and played a supplementary role at higher normal stresses(σ_(3)>10 MPa).Moreover,correlations between the evolution of permeability and normal stiffness were extended beyond the low-stiffness,high-permeability region to the high-stiffness,low-permeability region under high fracture-lateral stresses(10–80 MPa)with fracture-normal stress(10–50 MPa)conditions.Again,high lateral stresses further confined the fracture and therefore reduced permeability and increased normal stiffness,which exceeded the previous reported stiffness under no lateral stress conditions.This process enabled us to identify a fundamental change in the flow regime from multi-channel to isolated channelized flow.These results provide important characterizations of fracture permeability in the deep crust,including recovery from deep shale-gas reservoirs.
文摘New principles of work and energy as well as power and energy rate with cross terms for polar and nonlocal polar continuum field theories were presented and from them all corresponding equations of motion and boundary conditions as well as complete equations of energy and energy rate with the help of generalized Piola's theorems were naturally derived in all and without any additional requirement. Finally, some new balance laws of energy and energy rate for generalized continuum mechanics were established. The new principles of work and energy as well as power and energy rate with cross terms presented in this paper are believed to be new and they have corrected the incompleteness of all existing corresponding principles and laws without cross terms in literatures of generalized continuum field theories.
文摘This paper presents an energy principle, zero different principle of coupledsystems in photoelasticity, from which the potential energy, the complementary energy,generalized potential energy and generalized complementary energy variationalprinciples of the coupled systems in photoelasticity are derived What is called the coupled systems means that two deformational bodies, forwhich figures, sizes,loads and boundary conditions are the same and they are all inactual states but they are made of different materials.Prototype body and model body in photoelasticity are essentially the coupledsystems, therefore the above principles become the theoretical basis of defining theinflunce of Poissons ratio v on accuracy of the frozen-stress method.
基金The project supported by the Foundation of Zhongshan University Advanced Research Center
文摘According to the basic idea of dual-complementarity,in a simple and unified way proposed by the author,some basic principles in dynamic theory of elastic materials with voids can be established sys- tematically.In this paper, an important integral relation in terms of convolutions is given,which can be con- sidered as the generalized principle of virtual work in mechanics.Based on this relation,it is possible not on- ly to obtain the principle of virtual work and the reciprocal theorem in dynamic theory of elastic materials with voids,but also to derive systematically the complementary functionals for the eight-field,six-field, four-field and two-field simplified Gurtin-type variational principles.Furthermore,with this approach,the in- trinsic relationship among various principles can be explained clearly.
文摘In recent years, the two-stage control valve has been used more and more in the quantitative loading control system, and its advantages such as fast control response, high quantitative accuracy and low maintenance cost have been widely recognized. Not only can it meet the needs of quantitative loading control, but it can also be used as interlocking cut-off, and its action time and response speed are unmatched by analog control valves. It can still be competent in control scenarios with high response speed requirements.
基金supported by the National Key R&D Program of China(Grant No.2019YFB1311200).
文摘Soft grippers are favored for handling delicate objects due to their compliance but often have lower load capacities compared to rigid ones.Variable Stiffness Module(VSM)offer a solution,balancing flexibility and load capacity,for which particle jamming is an effective technology for stiffness-tunable robots requiring safe interaction and load capacity.Specific applica-tions,such as rescue scenarios,require quantitative analysis to optimize VSM design parameters,which previous analytical models cannot effectively handle.To address this,a Grey-box model is proposed to analyze the mechanical response of the particle-jamming-based VSM by combining a White-box approach based on the virtual work principle with a Black-box approach that uses a shallow neural network method.The Grey-box model demonstrates a high level of accuracy in predict-ing the VSM force-height mechanical response curves,with errors below 15%in almost 90%of the cases and a maximum error of less than 25%.The model is used to optimize VSM design parameters,particularly those unexplored combinations.Our results from the load capacity and force distribution comparison tests indicate that the VSM,optimized through our methods,quantitatively meets the practical engineering requirements.
基金Supported by China Postdoctoral Science Foundation(Grant No.2023M740663)National Natural Science Foundation of China(Grant No.51975039)。
文摘Due to the complex structures of multi-limbed parallel robots,conventional parallel robots generally have limited workspace,complex kinematics,and complex dynamics,which increases the application difficulty of parallel robot in industrial engineering.To solve the above problems,this paper proposes a single-loop Sch?nflies motion parallel robot with full cycle rotation,the robot can generate Sch?nflies motion by the most simplified structure.The novel Sch?nflies motion parallel robot is a two-limb parallel mechanism with least links and joints,and each limb is driven by a 2-degree of freedom(DOF)cylindrical driver(C-driver).The full cycle rotation of the output link is achieved by“…R-H…”structure,where the revolute(R)and helical(H)joints are coaxial.Mobility,kinematics,workspace and singularity analysis of the novel Sch?nflies motion parallel robot are analyzed.Then,dynamic model is formulated based on the principle of virtual work.Moreover,a pick-and-place task is implemented by the proposed Sch?nflies motion parallel robot and a serial SCARA robot,respectively.The simulation results verify the correctness of the theoretical model.Furthermore,dynamics performances of the proposed Sch?nflies motion parallel robot and a serial SCARA robot are compared,which reveal the performance merits of the proposed Sch?nflies motion parallel robot.
文摘A novel design for an electrostriction appliance derived from the theory and application of electromagnetics is presented. The working principle, that is the application of gravitation and elasticity together to realize the ＂shrinking＂ and ＂extending＂ effect from the distortion and transforming power into mechanical energy, is briefly explained. The characteristic parameter relationships are established and the experimental research is performed. Experimental results show that this sort of electrostriction appliance can perform well as regards driving force and beeline displacement, and furthermore, its self-weight is smaller. This makes it suitable for beeline drivers with a high application value, especially for the driver of the bionic appliance. In the application of the electrostriction appliance to a bionics-flapping aircraft, the wings can work with a flapping angle in the range of a certain value by controlling the ＂shrinking＂ and ＂extending＂ of the electrostriction appliance. It can reduce the startup power and the impact load of the driver. The flapping extent of the wings will change when the voltage which is put into the electrostriction appliance varies. This makes it more flexible as the bionics-flapping aircraft realizes different actions of flying.
文摘Aim To extend several fundamental theorems of conventional elasticity theory to quasicrystalelasticity theory. Methods The basic governing equations of quasicrystal elasticity theory and Gauss's theorem were applied in the derivation. Results and Conclusion The principle of virtual work, Betti's reciprocal theorem and the uniqueness theorem of quasicrystal elasticity theory are proud, and some conservative integrals in quasicrystal elasticty theory are obtained.
基金supported by National Natural Science Foundation of China (Grant No. 50575156)Shanxi Provincial Natural Science Foundation of China (Grant No. 2008011053)
文摘Proportional direction valve is one of the most fundamental elements in electronic-hydraulic control technique. Its function is to control the operating speed, direction, position, and strength of output force of the hydraulic actuator continuously. Considering the different application and the cost, the existing technique mainly includes the internal feedback valve used in open loop system, and the electronic closed loop controlled valve used in closed loop system. Because of their different mechanical structure and the gre at different in performance, it brings inconvenience for customer to select, also inconvenience for enterprise to produce. Aiming at this problem, the idea of combining the above two kinds of valves into one body is proposed first, and then the new valve＇s structure to realize this target is designed. The idea intends to apply the displacement pilot flow feedback control principle in present 2-position 2-way valve system to the proportional direction valve of 3-position 4-way system. Newly designed feed forward controller can decouple the interference between the internal feedback and the electronic closed loop. Redundant conversion is designed to electronic switch mode. Experiment on dynamic and static characteristic of new proportional direction valve in internal feedback control mode and electronic closed loop control mode is discussed to prove the new theory is correct. Although the new valve is of excellent dynamic response characteristic, its steady control characteristic in open loop control mode needs to be improved further. The research results prepare one new fundamental element for electronic-hydraulic control technology.
基金the National Natural Science Foundation of China (No.51164030)National Defense Key Disciplines Laboratory of Light Alloy Processing Science and Technology, Nanchang Hangkong University (No.gf201501001) for the support on this research
文摘Plane strain assumption and exponent hardening law are used to investigate the plastic deformation in tube bending. Some theoretical formulae including stress, curvature radius of neutral layer, angle of neutral layer deviation, bending moment, wall thickness variation and crosssection distortion, are developed to explain the phenomena in tube bending and their magnitudes are also determined. During unloading process, the springback angle is deduced using the virtual work principle, and springback radius is also given according to the length of the neutral layer which remains unchanged before and after springback. The theoretical formulae are validated by the experimental results or the validated simulation results in literature, which can be used to auicklv predict the forming aualitv of tube numerical control （NC） bending.
基金supported by the National High Technology Research and Development Programof China(863 Program,Grant No.2006AA09A105)
文摘Pipes inevitably encounter high ambient pressure and bending moment during the deepwater pipe-laying process,which can lead to elliptical buckling and even deterioration failure.For the safety of pipe-laying operation,available formulas for the pipe stability are established on the basis of the assumption of uniform deformation along the tube length and symmetrical buckling.This method can predict the nonlinear response of elliptical collapse of steel circular tubes for different ratios of diameter to thickness（D/t）under pure bending or combined bending and external pressure.In these formulas,the strain-displacement relationship is deduced from the nonlinear ring theory,and the Ramberg-Osgood constitutive model is applied to simulate the inelastic material behavior.Meanwhile,the principle of virtual work is adopted to derive the equilibrium equations.A set of equations is solved by the Newton-Raphson method,and the iterative scheme contains nested iteration for the constitutive relation.In order to check the effectiveness of this theoretical method,illustrative examples are presented in this paper.Besides,the numerical simulation is carried out by use of ANSYS.A comparison of the results shows that the theoretical method can provide reasonable prediction for engineering practice.
基金Supported by National Natural Science Foundation of China(Grant No.51175422)
文摘Because the deployable structures are complex multi-loop structures and methods of derivation which lead to simpler kinematic and dynamic equations of motion are the subject of research effort, the kinematics and dynamics of deployable structures with scissor-like-elements are presented based on screw theory and the principle of virtual work respectively. According to the geometric characteristic of the deployable structure examined, the basic structural unit is the common scissor-like-element（SLE）. First, a spatial deployable structure, comprised of three SLEs, is defined, and the constraint topology graph is obtained. The equations of motion are then derived based on screw theory and the geometric nature of scissor elements. Second, to develop the dynamics of the whole deployable structure, the local coordinates of the SLEs and the Jacobian matrices of the center of mass of the deployable structure are derived. Then, the equivalent forces are assembled and added in the equations of motion based on the principle of virtual work. Finally, dynamic behavior and unfolded process of the deployable structure are simulated. Its figures of velocity, acceleration and input torque are obtained based on the simulate results. Screw theory not only provides an efficient solution formulation and theory guidance for complex multi-closed loop deployable structures, but also extends the method to solve dynamics of deployable structures. As an efficient mathematical tool, the simper equations of motion are derived based on screw theory.
基金supported by National Science and Technology Major Project of China(Grant Nos.2010ZX04017-013,2010ZX04004-112)National Natural Science Foundation of China(Grant No.51205248)+1 种基金Shanghai Municipal Natural Science Foundation of China(Grant No.12ZR1445200)Doctoral Programs Foundation of Ministry of Education of China(Grant No.20120073120060)
文摘The large capacity servo press is traditionally realized by means of redundant actuation, however there exist the over-constraint problem and interference among actuators, which increases the control difficulty and the product cost. A new type of press mechanism with parallel topology is presented to develop the mechanical servo press with high stamping capacity. The dynamic model considering gravity counterbalance is proposed based on the virtual work principle, and then the effect of counterbalance cylinder on the dynamic performance of the servo press is studied. It is found that the motor torque required to operate the press is a lot less than the others when the ratio of the counterbalance force to the gravity of ram is in the vicinity of 1.0. The stamping force of the real press prototype can reach up to 25 MN on the position of 13 mm away from the bottom dead center. The typical deep-drawing process with 1 200 mm stroke at 8 strokes per minute is proposed by means of five order polynomial. On this process condition, the driving torques are calculated based on the above dynamic model and the torque measuring test is also carried out on the prototype. It is shown that the curve trend of calculation torque is consistent to the measured result and that the average error is less than 15%. The parallel mechanism is introduced into the development of large capacity servo press to avoid the over-constraint and interference of traditional redundant actuation, and its dynamic characteristics with gravity counterbalance are presented.
文摘China's first Mars exploration mission will carry out comprehensive global surveys of the planet from data collected by instruments carried in orbit and roving on the planet itself.Goals of the mission include detailed inspections and surveys of key areas on the surface of Mars.One of the main scientific payloads installed on the orbiter is the moderate resolution camera.Its mission is to image the surface of Mars sufficiently to produce a global remote sensing image map of the planet,and to explore and record changes to the topography of Mars,including major geological structures,and to advance research on topography and geomorphology in general.The moderate resolution camera uses a lightweight and compact integrated design;its primary components are an optical module,a focal plane module,a camera control module,a power and interface module,a camera support module,a thermal control module,and a reference module.Radiometric calibration,color calibration,and geometric calibration have been carried out to ensure that the camera can acquire sufficient accurate data to complete mission goals.This paper introduces the camera's detection mission,its system composition,and its working principle;it also describes the camera's ground calibration tests and their results,and provides a reference for processing the camera's scientific data and for future applications.
基金mainly supported by the National Natural Science Foundation,China(No.U1813216 and No.61903215)The Guangdong Natural Science Foundation,China(No.2018A030310679)+1 种基金The Basic Research Program of Shenzhen,China(No.JCYJ20180306174321766)The Open Project of Shenzhen Institute of Artificial Intelligence and Robotics for Society,China(No.ACO1202005004)。
文摘Soft robots have unique advantages over traditional rigid robots and have broad application prospects in many fields.To expand their bioinspired applications,we propose a novel Soft Pneumatic Actuator(SPA)associated with spiral configuration inspired by the structure and unwinding motion of the seahorse tail.Diff erent from bending motion of common soft actuators,the spiral SPA can generate unwinding motion as input air pressure increases.First,to explore the eff ect of diff erent initial spiral types on unwinding performance,three typical spiral SPAs are designed and simulated while keeping the outside arc of actuator body constant.Second,a static model of the spiral SPA is established by combining the hyperelastic material model,geometric relationships,and virtual work principle.To improve model accuracy,two geometric correction parameters are employed and their physical significance is analyzed by finite element simulations.Third,a prototype of the logarithmic spiral SPA(Log_spiral SPA)is fabricated and a Fiber Bragg Grating(FBG)sensor array is designed to detect and reconstruct unwinding shapes of the prototype.Finally,the unwinding performance,static model and output force capability of the prototype are tested and verified.Furthermore,we discuss prospects for this novel spiral SPA and test its practical applications in inchworm-like motion,assisting finger rehabilitation and object capture.
基金The project supported by the National Natural Science Foundation of China(10132010 and 10472089)
文摘This paper presents an investigation of temperature, displacement, stress, and induced magnetic field in a half space perfectly-conductive plate. Finite element equations regarding generalized magneto-thermoelasticity problems with two relaxation times （i.e., the G-L theory） are derived using the principle of virtual work. For avoiding numerical complication involved in inverse Laplace and Fourier transformation and low precision thereof, the equations are solved directly in time-domain. As a numerical example, the derived equation is used to investigate the generalized magneto-thermoelastic behavior of a semi-infinite plate under magnetic field and subjecting to a thermal shock loading. The results demonstrate that FEM can faithfully predict the deformation of the plate and the induced magnetic field, and most importantly can reveal the sophisticated second sound effect of heat conduction in two-dimensional generalized thermoelastic solids, which is usually difficult to model by routine transformation methods. A peak can be observed in the distribution of stress and induced front and the magnitude of magnetic field at the heat wave the peak decreases with time, which can not be obtained by transformation methods. The new method can also be used to study generalized piezo-thermoelastic problems.
基金Project(50478075) supported by the National Natural Science Foundation of ChinaProject(YBJJ0817) supported by Scientific Research Foundation of Graduate School of Southeast University
文摘Based on the nonlinear displacement-strain relationship,the virtual work principle method was used to establish the nonlinear equilibrium equations of steel beams with semi-rigid connections under vertical uniform loads and temperature change.Considering the non-uniform temperature distribution across the thickness of beams,the formulas for stresses and vertical displacements were presented.On the basis of a flowchart for analysis of the numerical example,the effect of temperature change on the elastic behavior of steel beams was investigated.It is found that the maximal stress is mainly influenced by axial temperature change,and the maximal vertical displacement is principally affected by temperature gradients.And the effect of temperature gradients on the maximal vertical displacement decreases with the increase of rotational stiffness of joints.Both the maximal stress and vertical displacement decrease with the increase of rotational stiffness of joints.It can be concluded that the effects of temperature changes and rotational stiffness of joints on the elastic behavior of steel beams are significant.However,the influence of rotational stiffness becomes smaller when the rotational stiffness is larger.
基金Supported by the National Science and Technology Support Program(No.2011BAG03B03)Inner Mongolia University of Technology Science and Research Projects of China(No.X201338)
文摘Electromechanical dynamics analysis and simulation on a rollforming equipment with both sides variable cross-section are discussed in this study.The system includes mechanical parts and electromagnetism parts,and it is a strongly coupled electromechanical system.Based on a virtual work principle and given power,generalized forces of this system are obtained.By using Lagrange-Maxwell equations,a model of electromechanical dynamics is established.Differential equations of two-phase winding on d-q axis are obtained by Park transformation,which comes from three-phase winding equations on the A-B-C axis.This system is solved with the 4th order Runge-Kutta's method,and discrete solutions of all variables are obtained.Finally,by using Matlab language,the system is simulated.The results show that the proposed method works very well.
基金National Natural Science Foundation(50375078)Key Discipline Construction Program of Beijing.
文摘The micro free-piston swing engine （MFPSE） is a new structure, free-piston internal combustion engine. The dynamic model integrated MFPSE with a power generator and thermodynamic models in compression, power and scavenge processes based on the open thermodynamic systems were presented. A simulation was executed at given geometric parameters and initial conditions. The results manifest that the working principle of MFPSE is feasible.
