The Experts below are selected from a list of 24918 Experts worldwide ranked by ideXlab platform

P Wang - One of the best experts on this subject based on the ideXlab platform.

  • interactive re analysis in mechanical Design evolution part ii rapid evaluation of boundary element integrals
    Computers & Structures, 2001
    Co-Authors: J Trevelyan, P Wang
    Abstract:

    Abstract A boundary element method elasticity model of a Design can evolve simultaneously with the geometry. Re-analysis following a Design Perturbation requires rapid response in updating stress contours in order to guide the Design effectively. This paper describes some integration schemes which enhance the response in comparison with current methods. It is found that the use of look up tables containing integral solutions offers acceptable accuracy in stress solutions, and that this accuracy can be achieved in a reduced time in comparison with conventional re-useable intrinsic sampling point (RISP) Gauss Legendre integration. The RAM requirements are considered in association with the benefits to be gained, and suggested look-up table refinements proposed.

J Trevelyan - One of the best experts on this subject based on the ideXlab platform.

  • interactive re analysis in mechanical Design evolution part ii rapid evaluation of boundary element integrals
    Computers & Structures, 2001
    Co-Authors: J Trevelyan, P Wang
    Abstract:

    Abstract A boundary element method elasticity model of a Design can evolve simultaneously with the geometry. Re-analysis following a Design Perturbation requires rapid response in updating stress contours in order to guide the Design effectively. This paper describes some integration schemes which enhance the response in comparison with current methods. It is found that the use of look up tables containing integral solutions offers acceptable accuracy in stress solutions, and that this accuracy can be achieved in a reduced time in comparison with conventional re-useable intrinsic sampling point (RISP) Gauss Legendre integration. The RAM requirements are considered in association with the benefits to be gained, and suggested look-up table refinements proposed.

Timothy Tzen Vun Yap - One of the best experts on this subject based on the ideXlab platform.

  • Signal Design for the identification of multivariable ill-conditioned systems using virtual transfer function between inputs
    IET Control Theory & Applications, 2012
    Co-Authors: Ai Hui Tan, Timothy Tzen Vun Yap
    Abstract:

    A novel method to Design Perturbation signals for the identification of multivariable ill-conditioned systems is presented. The method uses multisine signals to simultaneously perturb all input–output channels of the system. The correlated harmonic component is set according to a virtual transfer function between inputs, which is defined based on the case where equal Perturbation is achieved in all directions of the output state-space. This ensures that all singular values of the system, as well as the relative gain array at steady-state, are identified with a sufficiently high accuracy – a criterion important for model-based control. A case study based on a simulated multizone furnace is used to illustrate the superiority of the proposed technique over a competing Design.

Ai Hui Tan - One of the best experts on this subject based on the ideXlab platform.

  • Signal Design for the identification of multivariable ill-conditioned systems using virtual transfer function between inputs
    IET Control Theory & Applications, 2012
    Co-Authors: Ai Hui Tan, Timothy Tzen Vun Yap
    Abstract:

    A novel method to Design Perturbation signals for the identification of multivariable ill-conditioned systems is presented. The method uses multisine signals to simultaneously perturb all input–output channels of the system. The correlated harmonic component is set according to a virtual transfer function between inputs, which is defined based on the case where equal Perturbation is achieved in all directions of the output state-space. This ensures that all singular values of the system, as well as the relative gain array at steady-state, are identified with a sufficiently high accuracy – a criterion important for model-based control. A case study based on a simulated multizone furnace is used to illustrate the superiority of the proposed technique over a competing Design.

Raeisi Najafi Ahmad - One of the best experts on this subject based on the ideXlab platform.

  • Multiscale Design of nonlinear materials using a shape optimization scheme based on an interface-enriched GFEM
    2016
    Co-Authors: Raeisi Najafi Ahmad
    Abstract:

    Motivated by key advances in manufacturing techniques, the tailoring of materials with specific macroscopic properties has been the focus of active research in mechanical engineering and materials science over the past decade. The key challenge in this line of work is how to optimize the material microstructure to achieve a desired macroscopic constitutive response. The overwhelming majority of this type of inverse Design work relies on topology optimization based, primarily, on linear theory. In this work, we develop and implement a method to Design particulate composites at the mesoscale using a shape optimization scheme to minimize or maximize a nonlinear cost function at the macroscale while satisfying a set of constraints associated, for example, with the volume fraction of inclusions or with the manufacturing technique. The optimization method relies on three key ‘modules’: multiscale modeling, sensitivity analysis, and optimization. The multiscale modeling is based on a nonlinear finite element solver, which combines a classical homogenization scheme with a NURBS-based Interface-enriched Generalized Finite Element Method (NIGFEM) used to capture accurately and efficiently the displacement field in a heterogeneous material with a finite element discretization that does not conform to the material interfaces. Damage evolution is captured using a three-parameter isotropic damage model able to simulate a wide range of failure responses. The proposed gradient-based shape optimization scheme relies on the stationary nature of the non-conforming meshes used to discretize the periodic unit cell, thereby avoiding mesh distortion issues that plague conventional finite-element-based shape optimization studies. In the current approach, the finite element approximation space used in the NIGFEM is augmented with NURBS to allow for the accurate capture of the weak discontinuity present along complex, curvilinear material interfaces. NURBS are also used to parameterize the Design geometry precisely and compactly by a small number of Design variables. To compute the derivatives of the cost and constraint functions with respect to the Design variables, we also formulate an analytic nonlinear sensitivity, which is simplified by the fact that only the enrichment control points on material interfaces move, appear or disappear during the shape optimization process. The derivations uncover subtle but important new terms involved in the sensitivity of shape functions and their spatial derivatives. Our analytic nonlinear shape sensitivity avoids the technical difficulties encountered in the finite difference or semi-analytical schemes when the boundary intersects an element very close to a node in a non-conforming mesh. In these situations, the boundary may move to another element during the Design Perturbation step, resulting in changes of the mesh topology, making the differentiation of the stiffness matrix and load vector problematic. We apply the NIGFEM shape optimization scheme to several 2D and 3D structural problems including some benchmark and application examples to demonstrate the performance and accuracy of the method. Based on the multiscale approach, we also Design the microstructure of a periodic particulate composite to optimize the volume fraction and distribution of the inclusions for a desired macroscopic nonlinear stress-strain curve