Abstract: : Three-dimensional trusses are designed for minimum weight, subject to constraints on: member stresses, Euler buckling, joint displacements and system natural frequencies. Multiple static load conditions are considered. The finite element displacement method of analysis is used and eigenvalues are calculated using the subspace iteration technique. All gradient information is calculated analytically. The design problem is cast as a multi-level numerical optimization problem. The joint coordinates are treated as system variables. For each proposed configuration, the member sizes are updated as a sub-optimization problem. This sub-problem is efficiently solved using approximation concepts in the reciprocal variable space. The multi-level approach is shown to be an effective technique which conveniently takes advantage of the most efficient methods available for the member sizing problem. Examples are presented to demonstrate the method. The optimum configuration is shown to be strongly dependent on the constraints which are imposed on the design. (Author)

Abstract: : The problem of shape optimization to minimize stress concentration factors is presented. Design variables are chosen such that optimal configurations can be produced for a cylindrical pressure vessel with an end closure and nozzle intersection. A system model is formed in which the stress gradients are calculated numerically using the finite elements method and optimization is performed by the penalty function technique. Various examples of the design algorithm are presented showing optimal geometries together with plots of boundary stress concentrations for the sequence of designs generated. (Author)

Abstract: In the past, much of the work done in structural optimization consisted of resizing the members of fixed configuration models. There is, however, a broad class of plate and shell problems in which an additional 'reduction in mass can be attained by including in the design process the capability for varying the shape of boundaries and the shape and location of cutouts. This additional capability has made it necessary to address other problems such as how to maintain an adequate finite element model, how to define perfectly general shapes which satisfy a number of criteria, and how to impose the proper constraints so that a realistic design results. The shape design capability is demonstrated on practical problems which result in as much as 35% weight savings over a uniform thickness design with fixed boundaries.

Abstract: The study of shape optimization for skeletal structures is extended to a simple case of the finite element method using plane stress, constant strain triangular elements. Following earlier work, the method developed neglects the constitutive equations and is formulated using only node equilibrium and a stress-type objective function from plasticity theory. A form of constitutive equation subsequently appears through the Kuhn-Tucker conditions. As a result, the optimization algorithm used takes on the appearance of an analysis-redesign procedure. Two plane stress, beam-type examples are included.

Abstract: This thesis describes the development of a fuel depletion strategy that maximizes cycle length in boiling water reactor (BWR) cores. The cycle length maximization problem was formulated in terms of a core reactivity maximization scheme which provided solution to a terminal state optimization problem as well as to the optimal depletion strategy search. The nonlinear optimization problem was solved through an iterative application of linear programming involving linearization of the objective function and constraint equations. The nuclear-thermal-hydraulic model representing BWR cores was solved in a fully coupled, nonlinear form outside of the linear programming algorithm. For our numerical study, a large BWR core was modeled through a finite-difference form of the axial one-dimensional, two group neutron diffusion equation with control rods and thermal-hydraulic feedback represented. The optimal terminal state that results in maximum cycle length at the end-of-cycle for a given fuel loading is obtained through two phases, involving burnup shape optimization and cycle length extension, respectively. The optimal fuel depletion strategy is obtained through optimization of control rod pattern such that the loss in core reactivity over each depletion interval is minimized subject to power distribution constraints. The maximum cycle length obtained in our one dimensional axial depletion calculation indicates an increase of 7.4% over the corresponding Haling result, suggesting potential improvement in fuel utilization through proper control poison management. We also conclude that both the optimal terminal state and the optimal depletion strategy strongly depend upon the power distribution constraints. The fuel cycle is extended at the expense of power peaking margin. The optimal terminal state results in a bimodal bottom-peaked burnup shape and a top-peaked power distribution with the power peaking factor at the design limit. The optimal depletion calculation shows that the optimal power distribution is bimodal and time dependent with, the peaking factor at the design limit. The optimal power distribution is more skewed than the traditional Haling shape and bottom-peaked for most of the fuel cycle. For a short time interval around a coreaverage burnup of 3 GWD/T the power distribution is toppeaked reflecting the high depletion rate of the distributed burnable poison.

Abstract: : A theoretical and experimental study was undertaken into the crushing behavior of axially compressed short thin-walled open-section columns The effect of initial geometry of panels as well as distribution and magnitude of shape imperfections on the efficiency of energy absorption was examined Results of model test on 01mm thick aluminum foil specimens have shown that the panels collapsing in the symmetric and asymmetric deformation mode provide respectively, upper and lower bound for the energy absorbed in any other buckling mode In both of the extreme cases, the crush response of the panel was predicted theoretically with a reasonable accuracy It is shown that an optimum design of columns against crush can be achieved by introducing a beneficial geometric imperfections of a specified magnitude shape so that the structure will be forced to collapse in the most energy efficient deformation mode

Abstract: : A technique to determine effectively an uniformly stressed shape of two-dimensional design bodies under body force, which has been suggested already by the authors and is so-called Pattern Transformation method, will be explained plainly. This technique is one of the stress-ratio methods and based on an iterative method consisting of the following steps. In the first step, the deviation of a given shape from the design object is judged by the comparison with the stress at each point on the boundary and the design objective stress. In the next step, the given shape is modified to approach that to an optimum shape by the proportional transformation of the finite elements constituting the boundary. By applying this technique the optimum strength shapes of the rotating disks with some spokes such as the flywheel, the belt wheel and the gear of large diameter are obtained. Furthermore the validity of the obtained shape is examined experimentally by the spinning fracture test. (Author)

Abstract: A method for analyzing the stresses in toroidal shells of revolution, acted upon by arbitrary force fields, is described The equations of Reisnner for orthotropic, axisymmetric shells of revolution are derived and solved for finite-thickness toroidal shells As a design tool for the shape optimization of fusion magnets, such as the in-plane load support systems of toakamaks or bumpy tori, the analytical technique is a major extension of the work of WH Gray et al, which solved the stress equation for bending free toroidal shell shapes, subjected to a Lorentz force The work described below is simultaneously an extension of the theory of shells and an alteration of the perceived 'optimal' shape for tokamak toroidal field magnets