Showing papers on "Minimum weight published in 1998"

Genetic algorithms in optimal detailed design of reinforced concrete members

Abstract: Genetic algorithms emulate biologic evolutionary concepts to solve search and optimization problems. In this work, they are employed to perform the optimal detailed design of reinforced concrete members of multistory buildings. The objective is to convert the required reinforcement in square centimeters, given at a number of cross sections, into a set of reinforcing bars of specific diameter and length located at specific places along the member taking into account different criteria and rules of design practice. The anchorage lengths are taken into account, and the bars are cut at appropriate locations. For such problems, enumeration methods lead to expensive solutions, whereas genetic algorithms tend to provide near-optimal solutions in reasonable computing time. The genetic algorithms used in this work are based on a roulette wheel reproduction scheme; single, multiple-point, and uniform crossover; and constant or variable mutation schemes. A constant or variable elitist strategy is also used that passes the best designs of a generation to the next generation. The method decides the detailed design on the basis of a multicriterion objective that represents a compromise between a minimum weight design, a maximum uniformity, and the minimum number of bars for a group of members. By varying the weighting factors, designs with different characteristics result. Various parameters of the genetic algorithm are considered, and the corresponding results are presented.

Inverse maximum capacity problems

Abstract: LetE be a finite set, ℱ be a family of subsets ofE and¯C be a capacity vector for all elements ofE. For eachF∈ℱ, define thecapacity ofF as the minimum capacity occurring inF. The problem which we discuss in this paper is how to change the vector¯C as little as possible so that a givenF 0∈8o has the maximum capacity. This model contains inverse maximum capacity spanning tree problem, inverse maximum capacity path problem and etc. as its special cases. We transform the problem into the minimum weight cut set problem and show that this problem can be solved efficiently if an efficient algorithm for finding minimum weight cut set of ℱ is available.

Subsea control cable

Abstract: A subsea control cable includes an outer sheath and cables, conduits etc. arranged inside the sheath, and also at least one weight element. The weight element includes at least one strength member extending continuously along the entire length of the control cable, to which strength member there is attached a weight element or elements. The weight of the weight element in relation to the diameter of the control cable varies along the length of the control cable, e.g., from a predetermined minimum weight/diameter ratio, where the weight element consists only of the strength element, to a predetermined maximum weight/diameter ratio, where the cross-section of the control cable is filled to the maximum with the weight member.

Optimal Layout of Bridge Trusses by Genetic Algorithms

Abstract: In this paper we present an approach to the layout and shape-optimization problem of bridge truss structures using genetic algorithms. The objective is to find an optimal layout design that will have minimum weight or material volume, subject to performance constraints related to member stresses, joint displacements, and member buckling. An automated two-stage optimization search process, which integrates structural analysis by finite-element method, genetic algorithms, and cognitive topology patterns (domain knowledge), is developed to solve the optimal problem. Two examples concerning bridge truss structure are investigated to demonstrate the effectiveness of the proposed method in solving these layout-optimization problems.

Structural design optimization with reliability constraints using tabu search

Abstract: Tabu search is a discrete-variable optimization algorithm with the ability to avoid entrapment by local optima and hence continue searching for global optima, in this paper tabu search is applied to optimal structural design, in terms of weight minimization, of a space truss. The design variables are the cross-sectional areas of members, which take discrete values. An implementation of tabu search in a structural design context is presented which features λ-depth neighbourhoods and a search backtrack facility. Furthermore, through the use of reliability constraints, the presented formulation shows how the effects of variations in material strength (in tension and compression) and applied loading may be analysed. Numerical investigations show that tabu search may readily cope with problems that include stochastic variables and, additionally, reveal the effects of displacement constraints and (Euler) buckling on minimum weight designs.

Weight of faces in plane maps

Abstract: Precise upper bounds are obtained for the minimum weight of minor faces in normal plane maps and 3-polytopes with specified maximum vertex degree.

Antichain codes

Abstract: We show that almost all codes satisfy an antichain condition. This states that the minimum length of a two dimensional subcode of C increases if the subcode is constrained to contain a minimum weight codeword. In particular, almost no code satisfies the chain condition.

Optimal truss-structure design using real-coded genetic algorithms

Abstract: Optimization of truss-structures for finding optimal cross-sectional size, topology, and configuration of 2-D and 3-D trusses to achieve minimum weight is carried out using real-coded genetic algorithms (GAs). All the above three optimization techniques have been made possible by using a novel representation scheme. Although the proposed GA uses a fixed-length vector of design variables representing member areas and change in nodal coordinates, a simple member exclusion principle is introduced to obtain differing topologies. Moreover, practical considerations, such as inclusion of important nodes in the optimized structure is taken care of by using a concept of basic and non-basic nodes. Stress, deflection, and kinematic stability considerations are also handled using constraints. In a number of 2-D and 3-D trusses, the proposed technique finds intuitively optimal or near-optimal trusses, which are also found to have smaller weight than those that are reported in the literature.

Distributed Matroid Basis Completion via Elimination Upcast and Distributed Correction of Minimum-Weight Spanning Trees

Abstract: This paper proposes a time-efficient distributed solution for the matroid basis completion problem. The solution is based on a technique called climination upcast, enabling us to reduce the amount of work necessary for the upcast by relying on the special properties of matroids. As an application, it is shown that the algorithm can be used for correcting a minimum weight spanning tree computed for a D-diameter network, after k edges have changed their weight, in time O(k+D).

Displacement based multilevel structural optimization: beams, trusses, and frames

Abstract: When attempting to perform true multidisciplinary design optimization (MDO) in a realistic and complex environment, economy of time and effort are two of the most desirable attributes of any approach, in the overall optimization and in the sub-disciplines. A new and efficient methodology for the MDO subset of structural optimization was recently developed and applied to the minimum weight optimization of small two- and three-dimensional statically indeterminate truss structures under size, strength, and displacement constraints. In this paper, the approach is extended to large three-dimensional trusses, to one- and two-dimensional beams, and to two-dimensional frames. Specifically, finite element based multilevel optimization is performed on these structures. In the system level optimization, the load unbalance resulting from the substitution of approximate displacements into the stiffness equations is minimized. These approximate displacements are obtained from assumed polynomially based global displacement functions whose coefficients are the design variables. In the subsystem level optimizations, the weight of each element is minimized under the action of nonlinear stress constraints. Here, the cross sectional dimensions of the individual elements are the design variables. The approach is quite effective since the optimization task is distributed and broken down into a number of small and efficient subtasks, each with a rather limited number of variables, making it amenable to distributed and parallel computing.

Motion control and shape optimization of a suitlike flexible arm

Abstract: A method of motion control as well as shape optimization is proposed for the preliminary design of a suitlike flexible arm, which is composed of some variable-length and fixed-length beams. The large deformation, variable geometry and motion of the flexible structure are calculated by dynamic finite element analysis (FEA) using the step by step time integration method. A neural-networks-inverse-model, which learns nonlinear behaviour of the flexible structure, has been applied for the motion control as an inverse model of the flexible arm. For this geometrically nonlinear structure and time response problem, the optimum shape of the cross-section has been calculated under constraints of stress, stiffness and minimum weight with FEA and sensitivity analysis combined with fuzzy rules. This method has been applied for the design of a flexible arm, which simulates a process of lifting a human body and moving it. The calculated optimum shape has a much higher stiffness with decrease in weight in comparison with the initial shape. Moreover, the calculated motion agrees well with the one aimed for and the flexible arm reduces the impact force.

Weight and counting efficiency optimization in a moderated neutron detection system

Abstract: This paper describes a technique in which a polyethylene moderated neutron detector was designed in order to have the optimum combination of maximum counting efficiency and minimum weight. Such a detector would be of use in arms control, counter proliferation or treaty verification applications, in which measurement time and system portability are important considerations. In such applications, the neutron source may be a spontaneous fissioning isotope such as Pu 240 . After consideration of many different neutron detection schemes, the paper concludes that the best detection scheme for this problem would be a system which utilizes He 3 gas filled detectors surrounded by a moderator material. The “moderator weight efficiency” concept was developed as the basis for comparisons of different moderators and geometries. The MCNP neutron transport code was then used to evaluate moderator efficiencies for these different systems. The moderators considered by the paper included light water, heavy water, graphite, and polyethylene. The moderator geometries considered were a variety of shapes between (and including) planar and cylindrical. The paper describes an optimized system, which was found to have a combination of maximum performance and minimum moderator and system weight. The optimized detector was then fabricated and experimentally tested against another system, one which is currently employed in the INF treaty between Russia and the United States. Results are presented which show that the “optimized” system has higher counts per unit moderator (and system) weight than the INF comparison system.

Algorithms for Measuring Perturbability in Matroid Optimization

Abstract: of a matroid measures the maximum increase in the weight of its minimum weight bases that can be produced by increases of a given total cost on the weights of its elements. We present an algorithm for computing this function that runs in strongly polynomial time for matroids in which independence can be tested in strongly polynomial time. Furthermore, for the case of transversal matroids we are able to take advantage of their special structure to design a faster algorithm for computing the perturbability function.

A Linear-Time Approximation Scheme for Minimum Weight Triangulation of Convex Polygons

Abstract: A linear-time heuristic for minimum weight triangulation of convex polygons is presented. This heuristic produces a triangulation of length within a factor 1 + e from the optimum, where e is an arbitrarily small positive constant. This is the first subcubic algorithm that guarantees such an approximation factor, and it has interesting applications.

Optimisation of the fast craft deck structure by the genetic algorithms

Abstract: The genetic algorithm (GA) was applied to study the minimum weight problem of the fast craft hull structure with several design variables. A computer code was built for optimization of the fast craft hull structure. The crossover strategy with random number of cutting points was proposed. The fitness function was based on loads and strength criteria suggested by the classification rules. Some results of calculations are presented in the paper. In conclusion the GA is recommended for practical application in design of ship hull structures.

Probabilistic thin shell structural design

Abstract: This paper proposes an integrated design process for design and analysis of thin shell structures that are often used in spacecraft. The proposed integrated design process is able to: (1) identify the optimal structural design with minimum weight; (2) calculate the reliability of the identified optimal structural design; and (3) calculate the probability density functions of identified optimal structural design's weight and manufacturing cost. A FEBREL Preliminary Design (FEBREL/PD) code has been developed to simulate the integrated design process. Several design options including skinstringer-frame, waffle, and isogrid cylinders are available within FEBREL/PD. A thin shell cylinder with a skin-stringer- frame design is used to demonstrate the usefulness of this integrated design process.

Minimum weight shape and size optimization of truss structures made of uncertain materials

Abstract: Truss structures are optimized with respect to minimum weight with constraints on the value of some displacement and on the member stresses. The truss is considered made of an uncertain material, i.e. the value of the material constants are not known in a deterministic way, and each member may then exhibit a different value of stiffness, within a limited range of variation. The optimization must be done so that optimal solutions remain feasible for each value that the material constants may take for the considered uncertainty. In the present work a nonprobabilistic approach to uncertainty is used, and a variation of the material moduli with a, probabilistically speaking, uniform distribution over a convex and linearly bounded domain is considered. The two-step method is used to include the uncertainty within the optimization, where a diagonal quadratic approximation is used for the Objective function and the constraints. Solutions for some of the most classical truss examples are found and compared with those obtained using nominal values of material constants.

The Application of Sequential Convex Programming to Large-Scale Structural Optimization Problems

Abstract: : Structural design problems are often modeled using finite element methods. Such models are often characterized by constraint functions that are not explicitly defined in terms of the design variables. These functions are typically evaluated through numerical finite element analysis (FEA). Optimizing large-scale structural design models requires computationally expensive FEAs to obtain function and gradient values. An optimization approach which uses the SCP sequential convex programming algorithm of Zillober, integrated as the optimizer in the Automated Structural Optimization System (ASTROS), is tested. The traditional approach forms an explicitly defined approximate subproblem at each design iteration that is solved using the method of modified feasible directions. In an alternative approach, the SCP subroutine is called to formulate and solve the approximate subproblem. The SCP method is an implementation of the Method of Moving Asymptotes algorithm with five different asymptote determination strategies. This study investigates the effect of different asymptote determination strategies and constraint retention strategies on computational efficiency. The approach is tested on three large-scale structural design models, including one with constraints from multiple disciplines. Results and comparisons to the traditional approach are given. The largest of the three models, which had 1527 design variables and 6124 constraints, was solved to optimality with ASTROS for the first time using a mathematical programming method. The structural weight of the resulting design is 9% lower than the previously recorded minimum weight.

Minimum Weight Triangulations

Abstract: A triangulation of a given set S of n points in the plane is a maximal set of non-crossing line segments (called edges) which have both endpoints in S. A triangulation partitions the interior of the convex hull of the given point set into triangles. It is used in many areas of engineering and scientific applications such as finite element methods, approximation theory, numerical computation, computer-aided geometric design, and etc.

The Optimum Structural Design of the High-speed Surface Effect Ship using Composite Materials - Minimum Weight Design

Abstract: Recently, many researches are carried for high-speed and light craft. In this study, the optimum structural design procedure and the computer program are developed to minimize the hull weight of SES(Surface Effect Ship) built of composite materials. Three types of composite materials-Sandwich, Single Skin and Hybrid type- are considered and the efficiency of each type is investigated. In design process, the optimum design of main members is performed at first considering longitudinal strength. And then, the transverse member design is performed considering torsional strength SSDP(Structural Synthesis Design program) of U.S. Navy is adopted for design algorithm and DnV classification nile for design loads and strength criteria. For optimum structural design, ES 1+1 optimization technique is used.

A method to find cosets of the first-order Reed-Muller code with a high minimum weight

Abstract: weight Abstract - A new method to find balanced Boolean functions with a high nonlinearity is presented.