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Seonho Cho - One of the best experts on this subject based on the ideXlab platform.

  • Isogeometric configuration Design sensitivity analysis of finite deformation curved beam structures using Jaumann strain formulation
    Computer Methods in Applied Mechanics and Engineering, 2016
    Co-Authors: Myung-jin Choi, Minho Yoon, Seonho Cho
    Abstract:

    Abstract Using an isogeometric approach, a continuum-based configuration Design sensitivity analysis (DSA) method is developed for curved Kirchhoff beams with multi-patch junctions. Under the total Lagrangian formulation, large deformations considering the initial curvature of curved beams are described by geometrically exact beam theory (GEBT) and Jaumann strain formulation. In the isogeometric approach, the higher order continuity and the exact description of initial geometry are naturally embedded using NURBS basis functions. In multi-patch models, C 0 -continuity of physical displacement or C 1 -continuity of displacement component at junction is weakly imposed using the Lagrange multiplier method. The superior accuracy of isogeometric analysis (IGA) is verified through the comparison with the results of finite element analysis (FEA) using cubic Hermite interpolation. In the DSA, a material derivative is utilized and the kinematical description of GEBT is consistently employed to express orientation Design variations. Contrary to the IGA-based DSA, the Hermite basis function explicitly depends on Design in the FEA-based DSA due to its element length parameter. Moreover, since the Design Velocity field is approximated using the nodal Velocity imposed at nodal tangential vector, the amount of Design perturbations should be very small to obtain precise Design sensitivity.

  • Shape Design optimization of SPH fluid---structure interactions considering geometrically exact interfaces
    Structural and Multidisciplinary Optimization, 2011
    Co-Authors: Min-geun Kim, Hyun-seok Kim, Seonho Cho
    Abstract:

    Fluid---structure interaction problems are solved by applying a smoothed particle hydrodynamics method to a weakly compressible Navier---Stokes equation as well as an equilibrium equation for geometrically nonlinear structures in updated Lagrangian formulation. The geometrically exact interface, consisting of B-spline basis functions and the corresponding control points, includes the high order geometric information such as tangent, normal, and curvature. The exactness of interface is kept by updating the control points according to the kinematics obtained from response analysis. Under the scheme of explicit time integration and updated Lagrangian formulation, the required shape Design Velocity should be updated at every single step. The update scheme of Design Velocity is developed using the sensitivity of physical Velocity. The developed sensitivity analysis method is further utilized in gradient-based shape optimization problems and turns out to be very efficient since the interaction pairs of particles determined in the response analysis can be directly utilized.

  • Efficient Design sensitivity analysis of incompressible fluids using SPH projection method
    Structural and Multidisciplinary Optimization, 2009
    Co-Authors: Seonho Cho
    Abstract:

    Using the direct differentiation method, a Design sensitivity analysis method for time-dependent incompressible fluids is developed. The fluid behavior is described as the motion of particles involved by the SPH method. In the SPH projection method, instead of changing the fluid density, incompressibility is enforced by the pressure Poisson equation derived from pressure projection, which enable to use larger time steps. In spite of the additional pressure Poisson equation, the computational cost for the Design sensitivity is not expensive since the factorized system matrix of pressure Poisson equation can be utilized. Aforementioned computational efficiency is very beneficial for the Design sensitivity computation required for every time step in explicit time integration and updated Lagrangian schemes, for which an update scheme of Design Velocity field is developed using the Velocity sensitivity. Through demonstrative numerical examples, the developed DSA method turns out to be efficient and shows excellent agreement with finite differencing.

  • Configuration Design sensitivity analyss of nonlinear transient dynamics
    International Journal of Vehicle Design, 2002
    Co-Authors: Seonho Cho, Kyu Yeul Lee
    Abstract:

    A continuum-based configuration Design sensitivity analysis (DSA) method is developed for the transient dynamic response of nonlinear structural systems. The first-order variations of energy forms, load form, and kinematic and structural responses with respect to the configuration Design variables are derived. For the configuration Design, both shape and orientation variations contribute to the first-order variation of the governing equation. A material derivative approach is employed to represent the shape variation. The shape and orientation Design variations usually defined in element local coordinates are expressed in terms of global coordinates in this paper. A direct differentiation method is used since it is more appropriate for both path independent and path dependent problems than the adjoint variable method. For the structural domain, updated Lagrangian formulation is used so that the Design Velocity field that defines the mapping between initial and perturbed Design Velocity field that defines the mapping between initial and perturbed Designs is updated at each updated configuration. The Hughes-Liu truss/beam element based on the degeneration of an 8-node isoparametric solid is selected to discretise the struuctural domain. The objective stress and strain measures and Jaumann rate-based incrementally objective stress integration scheme are employed to handle large rotation effects. In temporal domain, an explicitly central difference method is used for time integration. For accurate numerical implementation, a fixed time step, sufficiently smaller than the critical time step that is determined by element geometry and material properties, is selected to remove the effect of time step sensitivity on the sensitivity of the performance measures. The developed DSA method is implemented to validate the accuracy and efficiency of the proposed method, which yields very good agreement with the central finite difference results.

  • Design sensitivity analysis and optimization of non‐linear transient dynamics. Part II—configuration Design
    International Journal for Numerical Methods in Engineering, 2000
    Co-Authors: Seonho Cho, K.k. Choi
    Abstract:

    For con"guration Design of non-linear dynamic structures, such as crashworthiness Design, a continuumbased con"guration Design sensitivity analysis (DSA) and optimization methods are developed. The same transient dynamic analysis method used in Part I of this paper is employed here. The elastic}plastic material and "nite strain and rotation e!ect are considered. The "rst-order variations of the energy forms, load form and kinematic and structural responses with respect to con"guration Design variables are derived. For the con"guration Design, both the shape and orientation variations contribute to the "rst-order variation of the equations of motion. The angular Design Velocity "eld associated with Euler angles is used to represent the orientation variation to obtain accurate Design sensitivity results. Like Part I of the paper, the updated Lagrangian formulation and direct di!erentiation method are used for DSA for the path-dependent problem. For the updated Lagrangian formulation, the Design Velocity "eld that de"nes the mapping between the initial and perturbed Designs should also be updated at each con"guration. Numerical implementation of con"guration DSA and optimization is carried out for "xed time steps using DYNA3D and the modi"ed feasible direction (MFD) method. It is observed that the proposed DSA method yields better sensitivity results than the "nite di!erence method for the highly non-linear problem. Design optimization is carried out using the Design sensitivity information.Copyright ( 2000 John Wiley & Sons, Ltd.

Kuang-hua Chang - One of the best experts on this subject based on the ideXlab platform.

  • Continuum shape sensitivity analysis and what-if study for two-dimensional multi-scale crack propagation problems using bridging scale decomposition
    Structural and Multidisciplinary Optimization, 2015
    Co-Authors: Yunxiang Wang, Kuang-hua Chang
    Abstract:

    This paper presents a shape sensitivity analysis and what-if study for two-dimensional multi-scale crack propagation problems using bridging scale decomposition. The sensitivity equations are derived in a continuum setting using direct differentiation method based on a continuum variational formulation of the bridging scale. Due to the fact that the crack propagation speed in an atomistic simulation is discrete in Design, and cannot be formulated as a continuous function of shape Design variables, we propose a hybrid method that combines analytical sensitivity analysis with finite difference approach. The finite difference part of the sensitivity analysis is only intended for calculating the sensitivity of crack growth speed based on the analytically obtained sensitivity coefficients of structural responses. The theoretical development on sensitivity formulation in this paper extends the application of the method to irregular-shaped finite elements and general Design Velocity fields. Furthermore, we evaluate and compare several performance measures that quantify crack propagation speed based on crack tip locations for sensitivity analysis and ultimately for structural optimization. A two-dimensional beam example is used to verify the accuracy of the proposed sensitivity approach. It is also demonstrated through a what-if study that with an adequate performance measure, the impact of macroscopic shape changes on microscopic crack propagation speed can be accurately predicted.

  • Integration of topology and shape optimization for Design of structural components
    Structural and Multidisciplinary Optimization, 2001
    Co-Authors: Poh-soong Tang, Kuang-hua Chang
    Abstract:

    This paper presents an integrated approach that supports the topology optimization and CAD-based shape optimization. The main contribution of the paper is using the geometric reconstruction technique that is mathematically sound and error bounded for creating solid models of the topologically optimized structures with smooth geometric boundary. This geometric reconstruction method extends the integration to 3-D applications. In addition, commercial Computer-Aided Design (CAD), finite element analysis (FEA), optimization, and application software tools are incorporated to support the integrated optimization process. The integration is carried out by first converting the geometry of the topologically optimized structure into smooth and parametric B-spline curves and surfaces. The B-spline curves and surfaces are then imported into a parametric CAD environment to build solid models of the structure. The control point movements of the B-spline curves or surfaces are defined as Design variables for shape optimization, in which CAD-based Design Velocity field computations, Design sensitivity analysis (DSA), and nonlinear programming are performed. Both 2-D plane stress and 3-D solid examples are presented to demonstrate the proposed approach.

  • a cad based Design parameterization for shape optimization of elastic solids
    Advances in Engineering Software, 1999
    Co-Authors: Edwin Hardee, Kuang-hua Chang, K.k. Choi, Jian Tu, Iulian Grindeanu, Xiaoming Yu
    Abstract:

    Abstract In this paper a CAD-based Design sensitivity analysis (DSA) and optimization method using Pro/ENGINEER for shape Design of structural components is presented. The CAD-based Design model is critically important for multidisciplinary shape Design optimization. Only when each discipline can compute the Design sensitivity coefficients of the CAD-based Design model, can a true multidisciplinary what-if study, trade-off analysis, and Design optimization be carried out. The proposed method will allow the Design engineer to compute Design sensitivity coefficients of structural performance measures such. as stress and displacement, evaluated using existing finite element analysis (FEA) tools, both h- and p-versions, with respect to Design variables defined in the parameterized CAD model. The proposed method consists of (i) a CAD-based Design parameterization technique that ties the structural DSA and optimization to a CAD tool; (ii) a Design Velocity field computation that defines material point movement due to Design change in CAD geometry, satisfies linearity and regularity requirements, and supports both hand p-version FEA meshed using existing mesh generators; and (iii) a Design optimization method that supports structural geometric and finite element model updates in Pro/ENGINEER during the optimization process.

  • A study of Design Velocity field computation for shape optimal Design
    Finite Elements in Analysis and Design, 1994
    Co-Authors: Kuang-hua Chang
    Abstract:

    Abstract Design Velocity field computation is an important step in computing shape Design sensitivity coefficients and updating a finite element mesh in the shape Design optimization process. Applying an inappropriate Design Velocity field for shape Design sensitivity analysis and optimization will yield inaccurate sensitivity results or a distorted finite element mesh, and thus fail in achieving an optimal solution. In this paper, theoretical regularity and practical requirements of the Design Velocity field are discussed. The crucial step of using the Design Velocity field to update the finite element mesh in the Design optimization process is emphasized. Available Design Velocity field computation methods in the literature are summarized and their applicability for shape Design sensitivity analysis and optimization is discussed. Five examples are employed to discuss applicability of these methods. It was found that a combination of isoparametric mapping and boundary displacement methods is ideal for the Design Velocity field computation.

K.k. Choi - One of the best experts on this subject based on the ideXlab platform.

  • A material derivative approach in Design sensitivity analysis of three-dimensional contact problems
    International Journal of Solids and Structures, 2002
    Co-Authors: Kiyoung Yi, K.k. Choi
    Abstract:

    A shape Design sensitivity analysis (DSA) and the optimization of a three-dimensional (3-D) contact problem is proposed using a material derivative approach. A penalty-regularized contact variational equation is differentiated with respect to the shape Design parameter. A die shape DSA is also carried out by defining a Design Velocity field at rigidbody geometry. The material derivative that is consistent with the frictional return-mapping scheme is derived by using nonassociative plasticity. A linearized Design sensitivity equation is solved without iteration by using a meshfree method at each converged load step. In order to improve the convergence behavior of the contact problem, a C 2 -continuous contact surface is constructed from the scattered set of particles. The accuracy and efficiency of the proposed method is shown using two-dimensional and 3-D Design examples of the DSA and optimization process. 2002 Elsevier Science Ltd. All rights reserved.

  • Design Sensitivity Analysis for the Meshfree Shell Structure
    Volume 2A: 27th Design Automation Conference, 2001
    Co-Authors: K.k. Choi, Nam H. Kim, Mark E. Botkin
    Abstract:

    Abstract A unified Design sensitivity analysis method for a meshfree shell structure with respect to sizing, shape, and configuration Design variables is presented in this paper. A shear deformable shell formulation is characterized by a CAD connection, thickness degeneration, meshfree discretization, and nodal integration. The Design variable is selected from the CAD parameters, and a consistent Design Velocity field is then computed by perturbing the surface geometric matrix. The material derivative concept is used to obtain a Design sensitivity equation in the parametric domain. Numerical examples show the accuracy and efficiency of the proposed Design sensitivity analysis method compared to the analytical solution and the finite difference solution.

  • Design sensitivity analysis and shape optimization of structural components with hyperelastic material
    Computer Methods in Applied Mechanics and Engineering, 2000
    Co-Authors: K.k. Choi, W. Duan
    Abstract:

    Abstract A continuum-based Design sensitivity analysis (DSA) method is developed for structural components with hyperelastic (incompressible) material. A mixed variational principle (MVP) and the total Lagrangian formulation are used for nonlinear analysis. Effects of large displacements, large strains, and material nonlinearities are included in the analysis model, using appropriate kinematics and constitutive relations. The material property and shape DSA using both the direct differentiation method (DDM) and the adjoint variable method (AVM) are discussed. For shape DSA, the material derivative concept is used to compute effects of the shape variation. The boundary displacement and isoparametric mapping methods are employed to compute the Design Velocity field. Both hydrostatic pressure and structural stiffness are considered as constraints for Design optimization, which is carried out by integrating shape Design parameterization, Design Velocity computation, DSA, nonlinear analysis, and the optimization method. Examples such as, an engine mount and a bushing demonstrate the feasibility of the proposed optimization method for Designing structural components using hyperelastic material.

  • Design sensitivity analysis and optimization of non‐linear transient dynamics. Part II—configuration Design
    International Journal for Numerical Methods in Engineering, 2000
    Co-Authors: Seonho Cho, K.k. Choi
    Abstract:

    For con"guration Design of non-linear dynamic structures, such as crashworthiness Design, a continuumbased con"guration Design sensitivity analysis (DSA) and optimization methods are developed. The same transient dynamic analysis method used in Part I of this paper is employed here. The elastic}plastic material and "nite strain and rotation e!ect are considered. The "rst-order variations of the energy forms, load form and kinematic and structural responses with respect to con"guration Design variables are derived. For the con"guration Design, both the shape and orientation variations contribute to the "rst-order variation of the equations of motion. The angular Design Velocity "eld associated with Euler angles is used to represent the orientation variation to obtain accurate Design sensitivity results. Like Part I of the paper, the updated Lagrangian formulation and direct di!erentiation method are used for DSA for the path-dependent problem. For the updated Lagrangian formulation, the Design Velocity "eld that de"nes the mapping between the initial and perturbed Designs should also be updated at each con"guration. Numerical implementation of con"guration DSA and optimization is carried out for "xed time steps using DYNA3D and the modi"ed feasible direction (MFD) method. It is observed that the proposed DSA method yields better sensitivity results than the "nite di!erence method for the highly non-linear problem. Design optimization is carried out using the Design sensitivity information.Copyright ( 2000 John Wiley & Sons, Ltd.

  • a cad based Design parameterization for shape optimization of elastic solids
    Advances in Engineering Software, 1999
    Co-Authors: Edwin Hardee, Kuang-hua Chang, K.k. Choi, Jian Tu, Iulian Grindeanu, Xiaoming Yu
    Abstract:

    Abstract In this paper a CAD-based Design sensitivity analysis (DSA) and optimization method using Pro/ENGINEER for shape Design of structural components is presented. The CAD-based Design model is critically important for multidisciplinary shape Design optimization. Only when each discipline can compute the Design sensitivity coefficients of the CAD-based Design model, can a true multidisciplinary what-if study, trade-off analysis, and Design optimization be carried out. The proposed method will allow the Design engineer to compute Design sensitivity coefficients of structural performance measures such. as stress and displacement, evaluated using existing finite element analysis (FEA) tools, both h- and p-versions, with respect to Design variables defined in the parameterized CAD model. The proposed method consists of (i) a CAD-based Design parameterization technique that ties the structural DSA and optimization to a CAD tool; (ii) a Design Velocity field computation that defines material point movement due to Design change in CAD geometry, satisfies linearity and regularity requirements, and supports both hand p-version FEA meshed using existing mesh generators; and (iii) a Design optimization method that supports structural geometric and finite element model updates in Pro/ENGINEER during the optimization process.

Byung Man Kwak - One of the best experts on this subject based on the ideXlab platform.

  • Optimization of finite element grids using shape sensitivity analysis in terms of nodal positions
    Finite Elements in Analysis and Design, 1997
    Co-Authors: Koo Tae Kang, Byung Man Kwak
    Abstract:

    Abstract An approach of finite element grid optimization is proposed as an application of the shape Design sensitivity analysis. Change of the mesh is described by Design Velocity fields that can be simply obtained by a piecewise linear interpolation from the nodal positions. For a given topology of finite elements mesh, the strain energy is maximized for static problems and the eigenvalues are minimized for eigenvalue problems with respect to the nodal positions. Numerical examples for the Timoshenko beams and the Mindlin plates are obtained and the proposed approach is shown to be a feasible method that can be used for shape or configuration Designs where large distortion of meshes is often involved.

  • Optimal Chip Layout on a Printed Circuit Board Using Design Sensitivity Analysis of Subdomain Configuration
    Journal of Electronic Packaging, 1995
    Co-Authors: Seo Jin Joo, Byung Man Kwak
    Abstract:

    A chip layout problem is formulated as a new class of shape optimal Design called a subdomain optimization, where the chips correspond to subdomains whose configuration and location are to be decided. Shape Design sensitivity analysis for a perturbed subdomain is made based on the concept of material derivative and adjoint system. Introducing a suitable category of Design Velocity fields, the change of the configuration is adequately describable. Sensitivities and optimal positions of chips on a printed circuit board are obtained and their accuracy discussed.

  • Sensitivity Analysis and Optimization of Chip Layout on Printed Circuit Board
    Elsevier Studies in Applied Electromagnetics in Materials, 1995
    Co-Authors: Byung Man Kwak
    Abstract:

    A chip layout optimal Design is considered, where chip position with respect to the printed circuit board is the Design to be determined. The concept of material derivative and adjoint system has been used for expressing the layout Design sensitivity. Introducing a suitable category of Design Velocity fields, the change of the layout is adequately describable. Sensitivities and optimal positions of chips are obtained and discussed.

  • Optimization of Boundary Conditions for Maximum Fundamental Frequency of Vibrating Structures
    AIAA Journal, 1993
    Co-Authors: Jae Hong Son, Byung Man Kwak
    Abstract:

    A sensitivity formula of eigenvalues with respect to the change of boundary conditions is derived using the material derivative concept based on a variational formulation. The change of boundary conditions is described with the introduction of the tangential component of the Design Velocity field used in shape Design. Simply supported and partially welded plates are taken as numerical examples to check the accuracy of the sensitivity formula. The sensitivites of the distinct and multiple eigenvalues calculated by the formulas are compared with those calculated by finite differences. Optimal support locations are then determined by use of a gradient-based optimization method. It is shown that a crossing of eigenvalues can occur in the solution process.

Essam A. Gooda - One of the best experts on this subject based on the ideXlab platform.

  • Economical Velocity through pipeline networks “Case Studies of Several Different Markets”
    alexandria engineering journal, 2018
    Co-Authors: Mohamad R. Sakr, Essam A. Gooda
    Abstract:

    Abstract In this research, a new concept for the economic pipeline Design was presented. The new concept is called economic Design Velocity. Considering a simple pipeline, a mathematical model was presented to relate different types of annual costs to the Design Velocity of pipeline. At least annual cost, the Design Velocity is called the economic Velocity. Relationships between Design Velocity and different parameters related to the pipeline were presented to show the effect of pipeline length, static head, capital recovery factor, flow discharge, pipeline accessories, as well as excavation and backfill on the economic Design Velocity. Three different markets were considered to estimate the annual cost of different components of pipeline. These markets are: Lebanese, United States, and Indian. Two different types of pipe materials were considered: ductile iron and high density polyethylene pipes. The economical velocities for ductile iron were 1.00 m/s, 1.70 m/s, and 0.90 m/s for Lebanon, United States of America, and India, respectively. The economical velocities for high density polyethylene were 1.75 m/s, 1.00 m/s, and 1.95 m/s for Lebanon, United States of America, and India, respectively. The Economical velocities of Indian and Lebanese markets were very similar to each other. The economical Velocity for India and Lebanon is low while that for United States of America is high for ductile iron; whereas the economical Velocity for India and Lebanon is high while that for United States of America is low for high density polyethylene.

  • Economical Velocity through pipeline networks “Case Studies of Several Different Markets”
    Elsevier, 2018
    Co-Authors: Mohamad R. Sakr, Essam A. Gooda
    Abstract:

    In this research, a new concept for the economic pipeline Design was presented. The new concept is called economic Design Velocity. Considering a simple pipeline, a mathematical model was presented to relate different types of annual costs to the Design Velocity of pipeline. At least annual cost, the Design Velocity is called the economic Velocity. Relationships between Design Velocity and different parameters related to the pipeline were presented to show the effect of pipeline length, static head, capital recovery factor, flow discharge, pipeline accessories, as well as excavation and backfill on the economic Design Velocity. Three different markets were considered to estimate the annual cost of different components of pipeline. These markets are: Lebanese, United States, and Indian. Two different types of pipe materials were considered: ductile iron and high density polyethylene pipes. The economical velocities for ductile iron were 1.00 m/s, 1.70 m/s, and 0.90 m/s for Lebanon, United States of America, and India, respectively. The economical velocities for high density polyethylene were 1.75 m/s, 1.00 m/s, and 1.95 m/s for Lebanon, United States of America, and India, respectively. The Economical velocities of Indian and Lebanese markets were very similar to each other. The economical Velocity for India and Lebanon is low while that for United States of America is high for ductile iron; whereas the economical Velocity for India and Lebanon is high while that for United States of America is low for high density polyethylene. Keywords: Annual cost, Economic Velocity, Mathematical mode