Rotation-free shell formulation is a simple and effective method to model a shell with large deformation. Moreover, it can be compatible with the existing theories of finite element method. However, a rotation-free sh...Rotation-free shell formulation is a simple and effective method to model a shell with large deformation. Moreover, it can be compatible with the existing theories of finite element method. However, a rotation-free shell is seldom employed in multibody systems. Using a derivative of rigid body motion, an efficient nonlinear shell model is proposed based on the rotation-free shell element and corotational frame. The bending and membrane strains of the shell have been simplified by isolating deformational displacements from the detailed description of rigid body motion. The consistent stiffness matrix can be obtained easily in this form of shell model. To model the multibody system consisting of the presented shells, joint kinematic constraints including translational and rotational constraints are deduced in the context of geometric nonlinear rotation-free element. A simple node-to-surface contact discretization and penalty method are adopted for contacts between shells. A series of analyses for multibody system dynamics are presented to validate the proposed formulation. Furthermore,the deployment of a large scaled solar array is presented to verify the comprehensive performance of the nonlinear shell model.展开更多
A new 4-node quadrilateral flat shell element is developed for geometrically nonlinear analyses of thin and moderately thick laminated shell structures. The fiat shell element is constructed by combining a quadrilater...A new 4-node quadrilateral flat shell element is developed for geometrically nonlinear analyses of thin and moderately thick laminated shell structures. The fiat shell element is constructed by combining a quadrilateral area co- ordinate method (QAC) based membrane element AGQ6- II, and a Timoshenko beam function (TBF) method based shear deformable plate bending element ARS-Q12. In order to model folded plates and connect with beam elements, the drilling stiffness is added to the element stiffness matrix based on the mixed variational principle. The transverse shear rigidity matrix, based on the first-order shear deformation theory (FSDT), for the laminated composite plate is evaluated using the transverse equilibrium conditions, while the shear correction factors are not needed. The conventional TBF methods are also modified to efficiently calculate the element stiffness for laminate. The new shell element is extended to large deflection and post-buckling analyses of isotropic and laminated composite shells based on the element independent corotational formulation. Numerical re- sults show that the present shell element has an excellent numerical performance for the test examples, and is applicable to stiffened plates.展开更多
In this paper, the generalized Prandtl-Reuss (P-R) constitutive equations of elastic-plastic material in the presence of finite deformations through a new approach are studied. It analyzes the generalized P-R equation...In this paper, the generalized Prandtl-Reuss (P-R) constitutive equations of elastic-plastic material in the presence of finite deformations through a new approach are studied. It analyzes the generalized P-R equation based on the material corotational rate and clarifies the puzzling problem of the simple shear stress oscillation mentioned in some literature. The paper proposes a modified relative rotational rate with which to constitute the objective rates of stress in the generalized P-R equation and concludes that the decomposition of total deformation rate into elastic and plastic parts is not necessary in developing the generalized P-R equations. Finally, the stresses of simple shear deformation are worked out.展开更多
This paper presents an efficient mesh updating scheme(MUS)for the arbitrary Lagrangian-Eulerian(ALE)formulation of an arbitrarily curved beam based on the corotational method.By discretizing the beam using both Lagran...This paper presents an efficient mesh updating scheme(MUS)for the arbitrary Lagrangian-Eulerian(ALE)formulation of an arbitrarily curved beam based on the corotational method.By discretizing the beam using both Lagrangian elements and ALE elements,the proposed MUS can take full advantage of the simple expression form of the Lagrangian formulation and the accurate moving-load description of the ALE node.The deleting-node and adding-node procedures of the MUS can avoid the negative influence of the variation of the ALE element length on the element accuracy and stiffness matrix singularity.In contrast to the adding-node procedure for Lagrangian elements,interpolation cannot be used directly.Inserting a Lagrangian node in an ALE element is investigated,and the displacement,velocity,and acceleration of the newly added node are evaluated accurately based on the corotational method.Three examples are investigated to verify the validity,computational accuracy and computational efficiency of the proposed MUS by comparing the results of the MUS with those from literature that utilized traditional ALE formulation.These examples show that the proposed MUS has significant advantages in terms of computational time and computer memory.展开更多
In this paper one-point quadrature'assumed strain'mixed element formulation based on the Hu-Washizu variational principle is presented.Special care is taken to avoid hourglass modes and volumetric locking as w...In this paper one-point quadrature'assumed strain'mixed element formulation based on the Hu-Washizu variational principle is presented.Special care is taken to avoid hourglass modes and volumetric locking as well as shear locking.The assumed strain fields are constructed so that those portions of the fields which lead to volumetric and shear locking phenomena are eliminated by projection,while the implementation of the proposed URI scheme is straightforward to suppress hour- glass modes.In order to treat geometric nonlinearities simply and efficiently,a corotational coordinate system is used.Several numerical examples are given to demonstrate the performance of the suggested formulation,including nonlinear static/dynamic mechanical problems.展开更多
Tailward ion outflows in the Martian-induced magnetotail are known to be one of the major channels for Martian atmospheric escape.On the basis of nearly 6.5 years of observations from the Mars Atmosphere and Volatile ...Tailward ion outflows in the Martian-induced magnetotail are known to be one of the major channels for Martian atmospheric escape.On the basis of nearly 6.5 years of observations from the Mars Atmosphere and Volatile EvolutioN(MAVEN)mission,we investigate the statistical distribution of tailward and Marsward fluxes of heavy ions(i.e.,O^(+),and O_(2)^(+))in the near-Mars magnetotail and explore their characteristic responses to the corotating interaction region(CIR),solar wind dynamic pressure,and local magnetic field intensity.Our results show that the tailward fluxes of oxygen ions and molecular oxygen ions in the magnetotail are significantly greater than their Marsward fluxes and that the tailward flux of molecular oxygen ions is generally larger than that of oxygen ions.Furthermore,the tailward ion flux distribution exhibits dependence on the CIR,solar wind dynamic pressure,and local magnetic field strength in a manner stronger than the Marsward ion flux distribution.According to the distribution of tailward ion fluxes,we calculate the corresponding escape rates of heavy ions and show that when the CIR occurs,the total escape rates of oxygen ions and molecular oxygen ions increase by a factor of~2 and~1.2,respectively.We also find that the escape rates of heavy ions increase with the enhancement of solar wind dynamic pressure,whereas the overall effect of the local magnetic field is relatively weak.Our study has important implications for improved understanding of the underlying mechanisms responsible for the Martian atmospheric escape and the evolution of the Martian atmospheric climate.展开更多
Virtual reality-based surgery simulation is becoming popular with the development of minimally invasive abdominal surgery,where deformable soft tissue is modelled and simulated.The mass-spring model(MSM)and finite ele...Virtual reality-based surgery simulation is becoming popular with the development of minimally invasive abdominal surgery,where deformable soft tissue is modelled and simulated.The mass-spring model(MSM)and finite element method(FEM)are common methods used in the simulation of soft tissue deformation.However,MSM has an issue concerning accuracy,while FEM has a problem with efficiency.To achieve higher accuracy and efficiency at the same time,we applied a co-rotational FEM in the simulation of a kidney with a tumour inside,achieving a real-time and accurate deformation simulation.In addition,we set a multi-model representation for mechanical simulation and visual rendering.The implicit Euler method and conjugate gradient method were adopted for setting and solving the linear system.For a realistic simulation of surgery,constraints outside the kidney and between the kidney and tumour were set with two series of mechanical properties for the two models.Experiments were conducted to validate the accuracy and real-time performance.展开更多
Nanotubes form clusters and are found in curved bundles in nano-tube films and nanocomposites.Separation phenomenon is sus-pected to occur in these curved bundles.In this study,the deformation of a single-wall carbon ...Nanotubes form clusters and are found in curved bundles in nano-tube films and nanocomposites.Separation phenomenon is sus-pected to occur in these curved bundles.In this study,the deformation of a single-wall carbon nanotube(SWCNT)interacting with curved bundle nanotubes is analyzed.It is assumed that the bundle is rigid and only van der Waals force acts between the nanotube and the bundle of nanotubes.A new method of model-ing geometric nonlinear behavior of the nanotube due to finite rotation and the corresponding van der Waals force is developed using co-rotational finite element method(CFEM)formulation,combined with small deformation beam theory,with the inclusion of axial force.Current developed CFEM method overcomes the limitation of linear Finite Element Method(FEM)formulation regarding large rotations and deformations of carbon nanotubes.This study provides a numerical tool to identify the critical curvature influence on the interaction of carbon nanotubes due to van der Waals forces and can provide more insight into studying irregula-rities in the electronic transport properties of adsorbed nanotubes in nanocomposites.展开更多
基金supported by the National Natural Science Foundation of China (Grants 11772188, 11132007)
文摘Rotation-free shell formulation is a simple and effective method to model a shell with large deformation. Moreover, it can be compatible with the existing theories of finite element method. However, a rotation-free shell is seldom employed in multibody systems. Using a derivative of rigid body motion, an efficient nonlinear shell model is proposed based on the rotation-free shell element and corotational frame. The bending and membrane strains of the shell have been simplified by isolating deformational displacements from the detailed description of rigid body motion. The consistent stiffness matrix can be obtained easily in this form of shell model. To model the multibody system consisting of the presented shells, joint kinematic constraints including translational and rotational constraints are deduced in the context of geometric nonlinear rotation-free element. A simple node-to-surface contact discretization and penalty method are adopted for contacts between shells. A series of analyses for multibody system dynamics are presented to validate the proposed formulation. Furthermore,the deployment of a large scaled solar array is presented to verify the comprehensive performance of the nonlinear shell model.
文摘A new 4-node quadrilateral flat shell element is developed for geometrically nonlinear analyses of thin and moderately thick laminated shell structures. The fiat shell element is constructed by combining a quadrilateral area co- ordinate method (QAC) based membrane element AGQ6- II, and a Timoshenko beam function (TBF) method based shear deformable plate bending element ARS-Q12. In order to model folded plates and connect with beam elements, the drilling stiffness is added to the element stiffness matrix based on the mixed variational principle. The transverse shear rigidity matrix, based on the first-order shear deformation theory (FSDT), for the laminated composite plate is evaluated using the transverse equilibrium conditions, while the shear correction factors are not needed. The conventional TBF methods are also modified to efficiently calculate the element stiffness for laminate. The new shell element is extended to large deflection and post-buckling analyses of isotropic and laminated composite shells based on the element independent corotational formulation. Numerical re- sults show that the present shell element has an excellent numerical performance for the test examples, and is applicable to stiffened plates.
文摘In this paper, the generalized Prandtl-Reuss (P-R) constitutive equations of elastic-plastic material in the presence of finite deformations through a new approach are studied. It analyzes the generalized P-R equation based on the material corotational rate and clarifies the puzzling problem of the simple shear stress oscillation mentioned in some literature. The paper proposes a modified relative rotational rate with which to constitute the objective rates of stress in the generalized P-R equation and concludes that the decomposition of total deformation rate into elastic and plastic parts is not necessary in developing the generalized P-R equations. Finally, the stresses of simple shear deformation are worked out.
基金supported by the Guangdong Basic and Applied Basic Research Foundation(2022A1515110856)the National Natural Science Foundation of China(Project Nos.62188101 and 12132002)。
文摘This paper presents an efficient mesh updating scheme(MUS)for the arbitrary Lagrangian-Eulerian(ALE)formulation of an arbitrarily curved beam based on the corotational method.By discretizing the beam using both Lagrangian elements and ALE elements,the proposed MUS can take full advantage of the simple expression form of the Lagrangian formulation and the accurate moving-load description of the ALE node.The deleting-node and adding-node procedures of the MUS can avoid the negative influence of the variation of the ALE element length on the element accuracy and stiffness matrix singularity.In contrast to the adding-node procedure for Lagrangian elements,interpolation cannot be used directly.Inserting a Lagrangian node in an ALE element is investigated,and the displacement,velocity,and acceleration of the newly added node are evaluated accurately based on the corotational method.Three examples are investigated to verify the validity,computational accuracy and computational efficiency of the proposed MUS by comparing the results of the MUS with those from literature that utilized traditional ALE formulation.These examples show that the proposed MUS has significant advantages in terms of computational time and computer memory.
文摘In this paper one-point quadrature'assumed strain'mixed element formulation based on the Hu-Washizu variational principle is presented.Special care is taken to avoid hourglass modes and volumetric locking as well as shear locking.The assumed strain fields are constructed so that those portions of the fields which lead to volumetric and shear locking phenomena are eliminated by projection,while the implementation of the proposed URI scheme is straightforward to suppress hour- glass modes.In order to treat geometric nonlinearities simply and efficiently,a corotational coordinate system is used.Several numerical examples are given to demonstrate the performance of the suggested formulation,including nonlinear static/dynamic mechanical problems.
基金supported by the National Natural Science Foundation of China (grants 42025404, 42188101, 41904144, and 41674163)the preresearch projects on Civil Aerospace Technologies (grants D020303, D020104, and D020308)+2 种基金funded by the China National Space Administrationthe B-type Strategic Priority Program of the Chinese Academy of Sciences (grant XDB41000000)the Fundamental Research Funds for the Central Universities (grants 2042021kf1045 and 2042021kf1056)
文摘Tailward ion outflows in the Martian-induced magnetotail are known to be one of the major channels for Martian atmospheric escape.On the basis of nearly 6.5 years of observations from the Mars Atmosphere and Volatile EvolutioN(MAVEN)mission,we investigate the statistical distribution of tailward and Marsward fluxes of heavy ions(i.e.,O^(+),and O_(2)^(+))in the near-Mars magnetotail and explore their characteristic responses to the corotating interaction region(CIR),solar wind dynamic pressure,and local magnetic field intensity.Our results show that the tailward fluxes of oxygen ions and molecular oxygen ions in the magnetotail are significantly greater than their Marsward fluxes and that the tailward flux of molecular oxygen ions is generally larger than that of oxygen ions.Furthermore,the tailward ion flux distribution exhibits dependence on the CIR,solar wind dynamic pressure,and local magnetic field strength in a manner stronger than the Marsward ion flux distribution.According to the distribution of tailward ion fluxes,we calculate the corresponding escape rates of heavy ions and show that when the CIR occurs,the total escape rates of oxygen ions and molecular oxygen ions increase by a factor of~2 and~1.2,respectively.We also find that the escape rates of heavy ions increase with the enhancement of solar wind dynamic pressure,whereas the overall effect of the local magnetic field is relatively weak.Our study has important implications for improved understanding of the underlying mechanisms responsible for the Martian atmospheric escape and the evolution of the Martian atmospheric climate.
基金the National Key Research and Development Program of China(No.2017YFB1302900)the National Natural Science Foundation of China(Nos.81971709,M-0019,and 82011530141)+2 种基金the Foundation of Science and Technology Commission of Shanghai Municipality(Nos.19510712200,and 20490740700)the Shanghai Jiao Tong University Foundation on Medical and Technological Joint Science Research(Nos.ZH2018ZDA15,YG2019ZDA06,and ZH2018QNA23)the 2020 Key Research Project of Xiamen Municipal Government(No.3502Z20201030)。
文摘Virtual reality-based surgery simulation is becoming popular with the development of minimally invasive abdominal surgery,where deformable soft tissue is modelled and simulated.The mass-spring model(MSM)and finite element method(FEM)are common methods used in the simulation of soft tissue deformation.However,MSM has an issue concerning accuracy,while FEM has a problem with efficiency.To achieve higher accuracy and efficiency at the same time,we applied a co-rotational FEM in the simulation of a kidney with a tumour inside,achieving a real-time and accurate deformation simulation.In addition,we set a multi-model representation for mechanical simulation and visual rendering.The implicit Euler method and conjugate gradient method were adopted for setting and solving the linear system.For a realistic simulation of surgery,constraints outside the kidney and between the kidney and tumour were set with two series of mechanical properties for the two models.Experiments were conducted to validate the accuracy and real-time performance.
基金This work was supported by the Texas Institute for the Intelligent Bio-Nano Materials and Structure for Aerospace Vehicles,funded by NASA[NCC-1-02038].
文摘Nanotubes form clusters and are found in curved bundles in nano-tube films and nanocomposites.Separation phenomenon is sus-pected to occur in these curved bundles.In this study,the deformation of a single-wall carbon nanotube(SWCNT)interacting with curved bundle nanotubes is analyzed.It is assumed that the bundle is rigid and only van der Waals force acts between the nanotube and the bundle of nanotubes.A new method of model-ing geometric nonlinear behavior of the nanotube due to finite rotation and the corresponding van der Waals force is developed using co-rotational finite element method(CFEM)formulation,combined with small deformation beam theory,with the inclusion of axial force.Current developed CFEM method overcomes the limitation of linear Finite Element Method(FEM)formulation regarding large rotations and deformations of carbon nanotubes.This study provides a numerical tool to identify the critical curvature influence on the interaction of carbon nanotubes due to van der Waals forces and can provide more insight into studying irregula-rities in the electronic transport properties of adsorbed nanotubes in nanocomposites.