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
A statistical damage detection and condition assessment scheme for existing structures is developed. First a virtual work error estimator is defined to express the discrepancy between a real structure and its analytic...A statistical damage detection and condition assessment scheme for existing structures is developed. First a virtual work error estimator is defined to express the discrepancy between a real structure and its analytical model, with which a system identification algorithm is derived by using the improved Newton method. In order to investigate its properties in the face of measurement errors, the Monte Carlo method is introduced to simulate the measured data. Based on the identified results, their statistical distributions can be assumed, the status of an existing structure can be statistically evaluated by hypothesis tests. A 5-story, two-bay steel frame is used to carry out numerical simulation studies in detail, and the proposed scheme is proved to be effective.展开更多
A systematic methodology for solving the inverse dynamics of the Delta robot is presented.First,the inverse kinematics is solved based on the vector method.A new form of the Jacobi matrix formulized by the vectors is ...A systematic methodology for solving the inverse dynamics of the Delta robot is presented.First,the inverse kinematics is solved based on the vector method.A new form of the Jacobi matrix formulized by the vectors is obtained so the three types kinematics singularities namely inverse, direct and combined types, can be identified with the physical meaning.Then based on the principle of virtual work, a methodology for driving the dynamical equations of motion is developed.Meanwhile the whole actuating torques, the torques caused by the gravity, the velocity and the acceleration are computed respectively in the numerical example. Results show that torque caused by the acceleration term is much bigger than the other two terms.This approach leads to efficient algorithms since the constraint forces and moments of the robot system have been eliminated from the equations of motion and there is no differential equation for the whole procedure when the principle of virtual work is applied to solving the inverse dynamical problem.展开更多
Energy methods and the principle of virtual work are commonly used for obtaining solutions of boundary value problems (BVPs) and initial value problems (IVPs) associated with homogeneous, isotropic and non-homogeneous...Energy methods and the principle of virtual work are commonly used for obtaining solutions of boundary value problems (BVPs) and initial value problems (IVPs) associated with homogeneous, isotropic and non-homogeneous, non-isotropic matter without using (or in the absence of) the mathematical models of the BVPs and the IVPs. These methods are also used for deriving mathematical models for BVPs and IVPs associated with isotropic, homogeneous as well as non-homogeneous, non-isotropic continuous matter. In energy methods when applied to IVPs, one constructs energy functional (<i>I</i>) consisting of kinetic energy, strain energy and the potential energy of loads. The first variation of this energy functional (<em>δI</em>) set to zero is a necessary condition for an extremum of <i>I</i>. In this approach one could use <i>δI</i> = 0 directly in constructing computational processes such as the finite element method or could derive Euler’s equations (differential or partial differential equations) from <i>δI</i> = 0, which is also satisfied by a solution obtained from <i>δI</i> = 0. The Euler’s equations obtained from <i>δI</i> = 0 indeed are the mathematical model associated with the energy functional <i>I</i>. In case of BVPs we follow the same approach except in this case, the energy functional <i>I</i> consists of strain energy and the potential energy of loads. In using the principle of virtual work for BVPs and the IVPs, we can also accomplish the same as described above using energy methods. In this paper we investigate consistency and validity of the mathematical models for isotropic, homogeneous and non-isotropic, non-homogeneous continuous matter for BVPs that are derived using energy functional consisting of strain energy and the potential energy of loads. Similar investigation is also presented for IVPs using energy functional consisting of kinetic energy, strain energy and the potential energy of loads. The computational approaches for BVPs and the IVPs designed using energy functional and principle of virtual work, their consistency and validity are also investigated. Classical continuum mechanics (CCM) principles <i>i.e.</i> conservation and balance laws of CCM with consistent constitutive theories and the elements of calculus of variations are employed in the investigations presented in this paper.展开更多
By expanding the yielding function according toTaylor series and neglecting the high order terms, the elastoplastic constitutive equation is written in a linear complementary form. Based on this linear complementary f...By expanding the yielding function according toTaylor series and neglecting the high order terms, the elastoplastic constitutive equation is written in a linear complementary form. Based on this linear complementary form and the principle of virtual work, a finite element-complementary method is derived for elastoplastic problem. This method is available for materials which satisfy either associated or nonassociated flow rule. In addition, the existence and uniqueness oj solution for the method are also discussed and some useful conclusions are given.展开更多
The virtual displacement principle of elasto-plastic damage mechanics is presented. A linear complementary method for elasto-plastic damage problem is proposed by using FEM technique. This method is applicable to solv...The virtual displacement principle of elasto-plastic damage mechanics is presented. A linear complementary method for elasto-plastic damage problem is proposed by using FEM technique. This method is applicable to solving the damage structure analysis of hardened and softened nonlinear material.展开更多
The stiffness reduction is studied in detail of compact W-Shapes （wide-flange steel shapes） that results from yielding of the cross-section due to uniaxial bending and axial compression. Three-dimensional m-p-τ su...The stiffness reduction is studied in detail of compact W-Shapes （wide-flange steel shapes） that results from yielding of the cross-section due to uniaxial bending and axial compression. Three-dimensional m-p-τ surface plots developed from detailed fiber element models of a W8x31 are used to develop a generalized material model for direct implementation in the virtual work method. A portal steel frame is used to illustrate the virtual work method with the nonlinear material model in a first-order, inelastic analysis implementation and in a second-order, inelastic analysis condition. The nonlinear modeling capabilities of MASTAN2 are used to verify the accuracy of the virtual work results and are found to be in very close agreement.展开更多
The principle of virtual displacements(PVDs)extended to elasto-thermo-electric problems includes virtual internal elastic,thermal and electric works.The governing equations have displacement vector,temperature and ele...The principle of virtual displacements(PVDs)extended to elasto-thermo-electric problems includes virtual internal elastic,thermal and electric works.The governing equations have displacement vector,temperature and electric potential as primary variables of the problem,and the elasto-thermal,elasto-electric and pure elastic problems are obtained as particular cases by deleting the appropriate contributions in the general elasto-thermo-electric variational statement.The most sensitive issue is given by thermal coupling because the thermo-elastic and thermo-electric effects change depending on the type of load and analysis considered(mechanical load,temperature or electric potential imposed and free vibration analysis).This feature means that the form of the virtual internal thermal work in such variational statements changes depending on the analysis performed and the load applied.Results about multilayered plates and shells suggest the appropriate extension of the variational statement for each analysis,and they give an exhaustive explanation for several forms of the PVD proposed.展开更多
To measure the working band of a digital attenuator automatically,a program based on virtual instrument was carried out,using Agilent E8362B network analyzer as its measuring tool.In the program,the attenuation values...To measure the working band of a digital attenuator automatically,a program based on virtual instrument was carried out,using Agilent E8362B network analyzer as its measuring tool.In the program,the attenuation values can be automatically written into Excel table to form the frequency-attenuation curve.Finally,through analyzing the attenuation in different frequency,the best working band of the digital attenuator can be determined easily,and the whole process is automated.Compared with the traditional way of changing the measured parameters manually and recording the measured data one by one,the developed method in the paper can avoid the cumbersome manual operation and its possible errors to improve the measurement accuracy and efficiency.展开更多
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
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The National Natural Science Foundation of China(No50538020)
文摘A statistical damage detection and condition assessment scheme for existing structures is developed. First a virtual work error estimator is defined to express the discrepancy between a real structure and its analytical model, with which a system identification algorithm is derived by using the improved Newton method. In order to investigate its properties in the face of measurement errors, the Monte Carlo method is introduced to simulate the measured data. Based on the identified results, their statistical distributions can be assumed, the status of an existing structure can be statistically evaluated by hypothesis tests. A 5-story, two-bay steel frame is used to carry out numerical simulation studies in detail, and the proposed scheme is proved to be effective.
基金Supported by National Natural Science Foundation of China (No. 50375106) andKey Laboratory of Intelligent Manufacturing at Shantou University Grant (No. Imstu-2002-11).
文摘A systematic methodology for solving the inverse dynamics of the Delta robot is presented.First,the inverse kinematics is solved based on the vector method.A new form of the Jacobi matrix formulized by the vectors is obtained so the three types kinematics singularities namely inverse, direct and combined types, can be identified with the physical meaning.Then based on the principle of virtual work, a methodology for driving the dynamical equations of motion is developed.Meanwhile the whole actuating torques, the torques caused by the gravity, the velocity and the acceleration are computed respectively in the numerical example. Results show that torque caused by the acceleration term is much bigger than the other two terms.This approach leads to efficient algorithms since the constraint forces and moments of the robot system have been eliminated from the equations of motion and there is no differential equation for the whole procedure when the principle of virtual work is applied to solving the inverse dynamical problem.
文摘Energy methods and the principle of virtual work are commonly used for obtaining solutions of boundary value problems (BVPs) and initial value problems (IVPs) associated with homogeneous, isotropic and non-homogeneous, non-isotropic matter without using (or in the absence of) the mathematical models of the BVPs and the IVPs. These methods are also used for deriving mathematical models for BVPs and IVPs associated with isotropic, homogeneous as well as non-homogeneous, non-isotropic continuous matter. In energy methods when applied to IVPs, one constructs energy functional (<i>I</i>) consisting of kinetic energy, strain energy and the potential energy of loads. The first variation of this energy functional (<em>δI</em>) set to zero is a necessary condition for an extremum of <i>I</i>. In this approach one could use <i>δI</i> = 0 directly in constructing computational processes such as the finite element method or could derive Euler’s equations (differential or partial differential equations) from <i>δI</i> = 0, which is also satisfied by a solution obtained from <i>δI</i> = 0. The Euler’s equations obtained from <i>δI</i> = 0 indeed are the mathematical model associated with the energy functional <i>I</i>. In case of BVPs we follow the same approach except in this case, the energy functional <i>I</i> consists of strain energy and the potential energy of loads. In using the principle of virtual work for BVPs and the IVPs, we can also accomplish the same as described above using energy methods. In this paper we investigate consistency and validity of the mathematical models for isotropic, homogeneous and non-isotropic, non-homogeneous continuous matter for BVPs that are derived using energy functional consisting of strain energy and the potential energy of loads. Similar investigation is also presented for IVPs using energy functional consisting of kinetic energy, strain energy and the potential energy of loads. The computational approaches for BVPs and the IVPs designed using energy functional and principle of virtual work, their consistency and validity are also investigated. Classical continuum mechanics (CCM) principles <i>i.e.</i> conservation and balance laws of CCM with consistent constitutive theories and the elements of calculus of variations are employed in the investigations presented in this paper.
文摘By expanding the yielding function according toTaylor series and neglecting the high order terms, the elastoplastic constitutive equation is written in a linear complementary form. Based on this linear complementary form and the principle of virtual work, a finite element-complementary method is derived for elastoplastic problem. This method is available for materials which satisfy either associated or nonassociated flow rule. In addition, the existence and uniqueness oj solution for the method are also discussed and some useful conclusions are given.
文摘The virtual displacement principle of elasto-plastic damage mechanics is presented. A linear complementary method for elasto-plastic damage problem is proposed by using FEM technique. This method is applicable to solving the damage structure analysis of hardened and softened nonlinear material.
文摘The stiffness reduction is studied in detail of compact W-Shapes （wide-flange steel shapes） that results from yielding of the cross-section due to uniaxial bending and axial compression. Three-dimensional m-p-τ surface plots developed from detailed fiber element models of a W8x31 are used to develop a generalized material model for direct implementation in the virtual work method. A portal steel frame is used to illustrate the virtual work method with the nonlinear material model in a first-order, inelastic analysis implementation and in a second-order, inelastic analysis condition. The nonlinear modeling capabilities of MASTAN2 are used to verify the accuracy of the virtual work results and are found to be in very close agreement.
文摘The principle of virtual displacements(PVDs)extended to elasto-thermo-electric problems includes virtual internal elastic,thermal and electric works.The governing equations have displacement vector,temperature and electric potential as primary variables of the problem,and the elasto-thermal,elasto-electric and pure elastic problems are obtained as particular cases by deleting the appropriate contributions in the general elasto-thermo-electric variational statement.The most sensitive issue is given by thermal coupling because the thermo-elastic and thermo-electric effects change depending on the type of load and analysis considered(mechanical load,temperature or electric potential imposed and free vibration analysis).This feature means that the form of the virtual internal thermal work in such variational statements changes depending on the analysis performed and the load applied.Results about multilayered plates and shells suggest the appropriate extension of the variational statement for each analysis,and they give an exhaustive explanation for several forms of the PVD proposed.
基金Fujian Province Key Technology Projects Fund(No.2006H0092)
文摘To measure the working band of a digital attenuator automatically,a program based on virtual instrument was carried out,using Agilent E8362B network analyzer as its measuring tool.In the program,the attenuation values can be automatically written into Excel table to form the frequency-attenuation curve.Finally,through analyzing the attenuation in different frequency,the best working band of the digital attenuator can be determined easily,and the whole process is automated.Compared with the traditional way of changing the measured parameters manually and recording the measured data one by one,the developed method in the paper can avoid the cumbersome manual operation and its possible errors to improve the measurement accuracy and efficiency.
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.
