The Experts below are selected from a list of 234 Experts worldwide ranked by ideXlab platform

S Z Feng - One of the best experts on this subject based on the ideXlab platform.

  • steady and transient heat transfer analysis using a stable node based smoothed finite Element method
    International Journal of Thermal Sciences, 2016
    Co-Authors: Z C Li, S Z Feng
    Abstract:

    Abstract In order to cure the instability of NS-FEM and further improve the accuracy, a stable node-based smoothed finite Element method (SNS-FEM) is formulated for steady and transient heat transfer problems using linear triangular and Tetrahedron Element. In present method, both smoothed temperature gradient and variance of temperature gradient in smoothing domains are considered. The accuracy, computational efficiency and stability of SNS-FEM are examined through several numerical examples with different kinds of boundary conditions. It is found that present method is more accurate and efficient than traditional finite Element method (FEM) and NS-FEM. Most importantly, compared with NS-FEM, present SNS-FEM can be very stable when dealing with transient heat transfer problems.

  • A temporal stable node-based smoothed finite Element method for three-dimensional elasticity problems
    Computational Mechanics, 2013
    Co-Authors: H Feng, X.y. Cui, S Z Feng
    Abstract:

    A stabilized node-based smoothed finite Element method (sNS-FEM) is formulated for three-dimensional (3-D) elastic-static analysis and free vibration analysis. In this method, shape functions are generated using finite Element method by adopting four-node Tetrahedron Element. The smoothed Galerkin weak form is employed to create discretized system equations, and the node-based smoothing domains are used to perform the smoothing operation and the numerical integration. The stabilization term for 3-D problems is worked out, and then propose a strain energy based empirical rule to confirm the stabilization parameter in the formula. The accuracy and stability of the sNS-FEM solution are studied through detailed analyses of benchmark cases and actual elastic problems. In elastic-static analysis, it is found that sNS-FEM can provide higher accuracy in displacement and reach smoother stress results than the reference approaches do. And in free vibration analysis, the spurious non-zero energy modes can be eliminated effectively owing to the fact that sNS-FEM solution strengths the original relatively soft node-based smoothed finite Element method (NS-FEM), and the natural frequency values provided by sNS-FEM are confirmed to be far more accurate than results given by traditional methods. Thus, the feasibility, accuracy and stability of sNS-FEM applied on 3-D solid are well represented and clarified.

H Feng - One of the best experts on this subject based on the ideXlab platform.

  • a stable nodal integration method with strain gradient for static and dynamic analysis of solid mechanics
    Engineering Analysis With Boundary Elements, 2016
    Co-Authors: H Feng, Xiangyang Cui
    Abstract:

    Abstract A stable nodal integration method with strain gradient (SNIM-SG) for curing the temporal instability of node-based smoothed finite Element method (NS-FEM) is proposed for dynamic problems using linear triangular and Tetrahedron Element. In each smoothing domain, except for considering the smoothed strain into the calculation of potential energy functional as NS-FEM, a term related to strain gradient is taken into account as a stabilization term. The proposed SNIM-SG can achieve appropriate system stiffness in strain energy between FEM and NS-FEM solutions and obtains quite favorable results in elastic and dynamic analysis. The accuracy and stability of SNIM-SG solution are studied through detailed analyzes of benchmark cases and practical engineering problems. In elastic-static analysis, it is found that SNIM-SG can provide higher accuracy in displacement field than the reference approaches do. In free vibration analysis, the spurious non-zero energy modes can be eliminated effectively owing to the fact that SNIM-SG solution strengths the original relatively soft NS-FEM, and SNIM-SG is confirmed to obtain fairly accurate natural frequency values in various examples. All in all, SNIM-SG cures the flaws of NS-FEM and enhances the dominant of nodal integration. Thus, the efficacy of the presented formulation in solving solid mechanics problems is well represented and clarified.

  • A temporal stable node-based smoothed finite Element method for three-dimensional elasticity problems
    Computational Mechanics, 2013
    Co-Authors: H Feng, X.y. Cui, S Z Feng
    Abstract:

    A stabilized node-based smoothed finite Element method (sNS-FEM) is formulated for three-dimensional (3-D) elastic-static analysis and free vibration analysis. In this method, shape functions are generated using finite Element method by adopting four-node Tetrahedron Element. The smoothed Galerkin weak form is employed to create discretized system equations, and the node-based smoothing domains are used to perform the smoothing operation and the numerical integration. The stabilization term for 3-D problems is worked out, and then propose a strain energy based empirical rule to confirm the stabilization parameter in the formula. The accuracy and stability of the sNS-FEM solution are studied through detailed analyses of benchmark cases and actual elastic problems. In elastic-static analysis, it is found that sNS-FEM can provide higher accuracy in displacement and reach smoother stress results than the reference approaches do. And in free vibration analysis, the spurious non-zero energy modes can be eliminated effectively owing to the fact that sNS-FEM solution strengths the original relatively soft node-based smoothed finite Element method (NS-FEM), and the natural frequency values provided by sNS-FEM are confirmed to be far more accurate than results given by traditional methods. Thus, the feasibility, accuracy and stability of sNS-FEM applied on 3-D solid are well represented and clarified.

S. M. Yunus - One of the best experts on this subject based on the ideXlab platform.

Nicholas Ayache - One of the best experts on this subject based on the ideXlab platform.

  • Soft Tissue Modeling for Surgery Simulation
    Handbook of Numerical Analysis, 2004
    Co-Authors: Hervé Delingette, Nicholas Ayache
    Abstract:

    This chapter presents different algorithms for modeling soft tissue deformation in the context of surgery simulation. These algorithms make radical simplifications about tissue material property, tissue visco-elasticity and tissue anatomy. The chapter describes the principles and the components of a surgical simulator. It also presents the process of building a patient-specific hepatic surgery simulator from a set of medical images. The different stages of computation leading to the creation of a volumetric tetrahedral mesh from a medical image are especially emphasized. Later, it describes the five main hypotheses that are made in the proposed soft tissue models. Moreover, the main equations of isotropic and transversally anisotropic linear elasticity in continuum mechanics are also presented. The discretization of these equations is presented that are based on finite Element modeling. The simple linear Tetrahedron Element is presented that provide closed form expressions of local and global stiffness matrices. After describing the types of boundary conditions existing in surgery simulation, the static and dynamic equilibrium equations in their matrix form are derived. The chapter introduces a first model of soft tissue; it is based on the off-line inversion of the stiffness matrix and can be computed very efficiently as long as no topology change is required. A second soft tissue model allows to perform cutting and tearing but with less efficiency as the previous model. A combination of the two previous models, called “hybrid model” is also presented in the chapter. It also introduces an extension of the second soft tissue model that implements large displacement elasticity.

  • Soft Tissue Modeling for Surgery Simulation
    Handbook of Numerical Analysis, 2004
    Co-Authors: Hervé Delingette, Nicholas Ayache
    Abstract:

    Publisher Summary This chapter presents different algorithms for modeling soft tissue deformation in the context of surgery simulation. These algorithms make radical simplifications about tissue material property, tissue visco-elasticity and tissue anatomy. The chapter describes the principles and the components of a surgical simulator. It also presents the process of building a patient-specific hepatic surgery simulator from a set of medical images. The different stages of computation leading to the creation of a volumetric tetrahedral mesh from a medical image are especially emphasized. Later, it describes the five main hypotheses that are made in the proposed soft tissue models. Moreover, the main equations of isotropic and transversally anisotropic linear elasticity in continuum mechanics are also presented. The discretization of these equations is presented that are based on finite Element modeling. The simple linear Tetrahedron Element is presented that provide closed form expressions of local and global stiffness matrices. After describing the types of boundary conditions existing in surgery simulation, the static and dynamic equilibrium equations in their matrix form are derived. The chapter introduces a first model of soft tissue; it is based on the off-line inversion of the stiffness matrix and can be computed very efficiently as long as no topology change is required. A second soft tissue model allows to perform cutting and tearing but with less efficiency as the previous model. A combination of the two previous models, called “hybrid model” is also presented in the chapter. It also introduces an extension of the second soft tissue model that implements large displacement elasticity.

Yvan Chastel - One of the best experts on this subject based on the ideXlab platform.

  • Estimation of constitutive parameters using an inverse method coupled to a 3D finite Element software
    Journal of Materials Processing Technology, 2002
    Co-Authors: Romain Forestier, Elisabeth Massoni, Yvan Chastel
    Abstract:

    Forming process simulations require a precise knowledge of the input material parameters. These parameters are usually estimated from mechanical tests. The classical analysis of these tests are usually based on a few assumptions: material flow homogeneity, isothermal conditions, etc. But in some cases with strain localisation or self-heating, these assumptions overestimate material strength. Analysis techniques using inverse methods are then good alternatives. This paper deals with the estimation of mechanical parameters using an inverse method. The direct model is a 3D forming process simulation software (FORGE3®). The numerical formulation is based on a mixed finite Element method using two unknowns, the velocity and the pressure. The Tetrahedron Element is linear in velocity and pressure and the thermal problem is solved using a linear Element. The inverse problem associated with the estimation of mechanical parameters is expressed as a least square problem. The aim is to obtain output of the direct model which fits experimental data measured during the mechanical test. The optimisation problem is solved using a Gauss-Newton algorithm. At the end of the optimisation, an estimation of confidence intervals is done. A Gauss-Newton algorithm requires the computation of the derivatives of the output with respect to the parameters to be identified. In this work, a semi-analytical differentiation is performed. The proposed method is first validated on artificial experimental data obtained from direct simulations of hot uniaxial compressions for a viscoplastic cylinder. The confidence interval is provided by the algorithm for different configurations with additional random noise. Finally a real steel compression test is analysed to provide parameters for the Norton-Hoff viscoplastic law

  • Estimation of constitutive parameters using an inverse method coupled to a 3D finite Element software
    Journal of Materials Processing Technology, 2002
    Co-Authors: Romain Forestier, Elisabeth Massoni, Yvan Chastel
    Abstract:

    International audienceForming process simulations require a precise knowledge of the input material parameters. These parameters are usually estimated from mechanical tests. The classical analysis of these tests are usually based on a few assumptions: material flow homogeneity, isothermal conditions, etc. But in some cases with strain localisation or self-heating, these assumptions overestimate material strength. Analysis techniques using inverse methods are then good alternatives. This paper deals with the estimation of mechanical parameters using an inverse method. The direct model is a 3D forming process simulation software (FORGE3®). The numerical formulation is based on a mixed finite Element method using two unknowns, the velocity and the pressure. The Tetrahedron Element is linear in velocity and pressure and the thermal problem is solved using a linear Element. The inverse problem associated with the estimation of mechanical parameters is expressed as a least square problem. The aim is to obtain output of the direct model which fits experimental data measured during the mechanical test. The optimisation problem is solved using a Gauss-Newton algorithm. At the end of the optimisation, an estimation of confidence intervals is done. A Gauss-Newton algorithm requires the computation of the derivatives of the output with respect to the parameters to be identified. In this work, a semi-analytical differentiation is performed. The proposed method is first validated on artificial experimental data obtained from direct simulations of hot uniaxial compressions for a viscoplastic cylinder. The confidence interval is provided by the algorithm for different configurations with additional random noise. Finally a real steel compression test is analysed to provide parameters for the Norton-Hoff viscoplastic la