Redesign of plates by large admissible perturbations

Structural and Multidisciplinary Optimization

2000

A methodology for topology redesign of complex structures by LargE Admissible Perturbations (LEAP) is developed. LEAP theory is extended to solve topology redesign problems using 8-node solid elements. The corresponding solution algorithm is developed as well. The redesign problem is defined as a two-state problem. State S1 has undesirable characteristics and/or performance not satisfying certain designer specifications. The unknown State S2 has the desired structural response and locally optimum topology. First, the general nonlinear perturbation equations relating specific response of States S1 and S2 are derived. Next, a LEAP algorithm is developed which solves successfully two-state problems for large structural changes (on the order of 100%-300%) of State S2, without repetitive finite element analyses, based on the initial State S1 and the specifications for State S2. The solution algorithm is based on an incremental predictor-corrector method. The optimization problems formulated in both the predictor and corrector phases are solved using commercial nonlinear optimization solvers. Minimum change is used as the optimality criterion. The designer specifications are imposed as constraints on modal dynamic and/or static displacement. The static displacement general perturbation equation is improved by static mode compensation thus reducing errors significantly. The moduli of elasticity of solid elements are used as redesign variables. The LEAP and optimization solvers are implemented in code RESTRUCT (REdesign of STRUCTures) which postprocesses finite element analyses results of MSC-NASTRAN. Several topology redesign problems are solved successfully by code RESTRUCT to illustrate the methodology and study its accuracy. Performance changes on the order of 3300% with high accuracy are achieved with only 3-5 intermediate finite element analyses (iterations) to arrest

Section: Structural Perturbation Equationsmentioning

confidence: 94%

Section: Literature Reviewmentioning

confidence: 99%

Section: Literature Reviewmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Topology and performance redesign of complex structures by large admissible perturbations

Suryatama

Structural and Multidisciplinary Optimization

2000

“…Bernitsas and Tawekal (1991) solved the problem of model calibration by LEAP in a cognate space. Stiffened plate and shell elements were added by Bernitsas and Rim (1994). Bernitsas and Suryatama (1999) improved the static deflection redesign algorithm by introducing static mode compensation.…”

mentioning

confidence: 99%

Topology redesign for performance by large admissible perturbations

Miao

2006

Struct Multidisc Optim

A methodology is developed for optimal structural topology design subject to several performance constraints. Eight-node solid elements are used to model the initial structure, which is a uniform solid block satisfying the boundary conditions and subjected to external loading. The Young modulus of each solid element or group of elements is used as redesign variable. A minimum change function is used as an optimality criterion. Performance constraints include static displacements, natural frequencies, forced response amplitudes, and static stresses. These constraints are treated by the large admissible perturbation methodology which makes it possible to achieve the performance objectives incrementally without trial and error or repetitive finite element analyses for changes in the order of 100-300%. Thus, the optimal topology is reached in about four to five iterations, where each iteration includes one finite element analysis and setting of an upper limit for the value of the modulus of elasticity to produce a manufacturable structure. Several numerical applications are presented using three different benchmark structures to demonstrate the methodology and the impact of performance constraints on the generated topology. Keywords Topology • Performance • Optimization • Structural redesign • Large admissible perturbations 1 Background The goal of structure optimization is to improve the performance of any given objective set in a structural environment

Integrated Redesign of Large-Scale Structures by Large Admissible Perturbations

Blouin

Journal of Offshore Mechanics and Arctic Engineering

Morrison

2003

In structural redesign (inverse design), selection of the number and type of performance constraints is a major challenge. This issue is directly related to the computational effort and, most importantly, to the success of the optimization solver in finding a solution. These issues are the focus of this paper, which provides and discusses techniques that can help designers formulate a well-posed integrated complex redesign problem. LargE Admissible Perturbations (LEAP) is a general methodology, which solves redesign problems of complex structures with, among others, free vibration, static deformation, and forced response amplitude constraints. The existing algorithm, referred to as the Incremental Method is improved in this paper for problems with static and forced response amplitude constraints. This new algorithm, referred to as the Direct Method, offers comparable level of accuracy for less computational time and provides robustness in solving large-scale redesign problems in the presence of damping, nonstructural mass, and fluid-structure interaction effects. Common redesign problems include several natural frequency constraints and forced response amplitude constraints at various frequencies of excitation. Several locations on the structure and degrees of freedom can be constrained simultaneously. The designer must exercise judgment and physical intuition to limit the number of constraints and consequently the computational time. Strategies and guidelines are discussed. Such techniques are presented and applied to a 2,694 degree of freedom offshore tower.