Showing papers on "Minimum weight published in 2003"

Modelling topology optimization problems as linear mixed 0–1 programs

Abstract: This paper deals with topology optimization of discretized continuum structures. It is shown that a large class of non-linear 0-1 topology optimization problems, including stress- and displacement-constrained minimum weight problems, can equivalently be modelled as linear mixed 0-1 programs. The modelling approach is applied to some test problems which are solved to global optimality.

Challenges in Comparing Numerical Solutions for Optimum Weights of Stiffened Shells

Abstract: Optimizations of stiffened shells with different stiffener shapes performed to rank and identify the optimum designs during the preliminary design trade studies require a large number of analyses and hence rely on the useof efficient but approximate analysis methods. In the design of shells, the treatment of imperfections on buckling loads and stresses is of paramount importance. It is demonstrated how conservativeness of the approximate analyses used in buckling load calculation, the number of variables optimized (design freedom), and nonstructural constraints influence the weight of optimum designs. This demonstration is based on the results of a trade study performed to compare minimum weight designs of stiffened shells optimized under stress and buckling constraints for a reusable launch vehicle tank. PANDA2 was selected for the present study because it uses approximate analysis procedures that permit the many thousands of structural analyses needed for global optimization and it also has sophisticated machinery for generating imperfections and accounting for their effects. Optimum weights were influenced not only by material choice, number of optimization variables, and manufacturing constraints, but also by the analysis model conservativeness. Optimization of shells with effect of initial imperfections exhibited substantial weight differences between different stiffened-shell concepts, partly because of conservativeness in the analysis.

Design optimization of mechanical systems using genetic algorithms

Abstract: This papei- prcsents an algorithni foi· the design of minimum weight of speed reducer., gear train, subject to a specificd set of constraints. The study is p rimari1y aimed to expose the potential of genetic algorithms, to discuss their application capabilities, and to show the concept of these algorithms as optiinization techniques an d their scope of application by implementing them to the speed reducer. Results obtained for the minimum \Veight of speed reducer are prescnted to provide insight into the capabilities of these tecbniques. Genetic algorithms are efficient search techniqucs which are inspircd froni natural genetics selection process to cxplore a given search space.

Geometric Codes over Fields of Odd Prime Power Order

Abstract: We obtain improved bounds for the minimum weight of the dual codes associated with the codes from finite geometries in the case of odd order, and some results that apply also to the dual codes of non-desarguesian planes of odd order.

Kitchen safety device and method for controlling operation of a heating appliance

Abstract: A kitchen safety device automatically deactivates a heating appliance. The safety device includes an operator control panel which communicates with the appliance. The control panel includes input buttons for entering minimum weight and minimum time criteria for items placed on a cooking surface of the appliance. A weight sensor is operatively connected to the cooking surface of the appliance and communicates with the control panel. Upon activation of the appliance, the sensor operates to detect a positive application of the minimum weight onto the cooking surface within the prescribed minimum time. In the absence of a positive application within the prescribed minimum time, the sensor signals the control panel to deactivate the appliance.

Stochastic search methods

Abstract: Sophisticated search techniques form the backbone of modern machine learning and data analysis. Computer systems that are able to extract information from huge data sets (data mining), to recognize patterns, to do classification, or to suggest diagnoses, in short, systems that are adaptive and — to some extent — able to learn, fundamentally rely on effective and efficient search techniques. The ability of organisms to learn and adapt to signals from their environment is one of the core features of life. Technically, any adaptive system needs some kind of search operator in order to explore a feature space which describes all possible configurations of the system. Usually, one is interested in “optimal” or at least close to “optimal” configurations defined with respect to a specific application domain: the weight settings of a neural network for correct classification of some data, parameters that describe the body shape of an airplane with minimum drag, a sequence of jobs assigned to a flexible production line in a factory resulting in minimum idle time for the machine park, the configuration for a stable bridge with minimum weight or minimum cost to build and maintain, or a set of computer programs that implement a robot control task with a minimum number of commands.

Probabilistic design of aerospace vehciles: coupling global and local requirements

Abstract: This paper presents a probabilistic optimization methodology for conceptual design of aerospace vehicles that takes into account linkages between global and local design requirements. Multiple disciplinary analyses such as geometry, weights, structures, aerodynamics, trajectory, propulsion, thermal protection, operations and maintainability etc. are involved in the overall conceptual design. The global design considered in this paper optimizes the geometry for minimum weight while satisfying aerodynamic constraints. The local design illustrated here relates to structural sizing of vehicle components, e.g., liquid hydrogen tank. The optimization formulation includes probabilistic constraints, which are evaluated using the limit state-based reliability analysis methodology. The global and local designs are linked through probabilistic data flow relating to vehicle geometry and component weight, and the optimization at both levels is achieved through an iterative process.

On dual based lower bounds for the sequential ordering problem with precedences and due dates

Abstract: The Sequential Ordering Problem (herewith, SOP) with precedence relationships was introduced in Escudero (1988), and extended to cover release and due dates in Escudero and Sciomachen (1993). It has a broad range of applications, mainly in production planning for manufacturing systems. The problem consists of finding a minimum weight Hamiltonian path on a directed graph with weights on the nodes and the arcs, satisfying precedence relationships among the nodes and given lower and upper bounds on the weights of the Hamiltonian subpaths. In this paper we present a model for the constrained minimum weight Hamiltonian path problem with precedences and due dates forcing constraints, and introduce related valid cuts that can be used in a separation framework for the dual (Lagrangian based) relaxation of the problem. We also provide an heuristic separation procedure to obtain those cuts, so-called the Lagrangian Relax-and-Cut (LRC) scheme. Computational experience is given for variations of some SOP cases already reported in the literature.

Automatic food production method in which sliced food is automatically produced in weighed portions that have a minimum weight, whereby an extra slice is cut with each portion and added to it, if it falls below a minimum weight

Abstract: Method for automatically correcting the weight of sliced food portions whereby: a slicer cuts a first portion of n slices and a second portion of at most n minus 1 slices, but preferably with one slice. The second portion is stored in a buffer while the first portion is weighed and compared with a set weight value. If the first portion is underweight, the second portion is automatically added to it.

Minimum Weight With Stress Constraints Topology Optimization

Abstract: Sizing and shape structural optimization problems are normally stated in terms of a minimum weight approach with constraints that limit the maximum allowable stresses and displacements. However, topology structural optimization problems have been traditionally stated in terms of a maximum stiffness (minimum compliance) approach. In this kind of formulations, the aim is to distribute a given amount of material in a certain domain, so that the stiffness of the resulting structure is maximized (the compliance, or energy of deformation, is minimized) for a given load case. Thus, the material mass is restricted to a predefined percentage of the maximum possible mass, while no stress or displacement constraints are taken into account. In this paper we analyze and compare both approaches, and we present a FEM minimum weight with stress constraints (MWSC) formulation for topology structural optimization problems. This approach does not require any stabilization technique to produce acceptable optimized results, while no truss-like final solutions are necessarily obtained. Several 2D examples are presented. The optimized solutions seem to be correct from the engineering point of view, and their appearence could be considered closer to the engineering intuition than the traditional trusslike results obtained by means of the widespread maximum stiffness (minimum compliance) approaches.

Optimum Structural Design of High-Speed Surface Effect Ships Built of Composite Materials

Abstract: A surface effect ship is known to be comparable to a high-speed ship For the structural design of surface effect ships, advanced design methods are needed which can reflect the various loading conditions different from those of conventional ships Also, minimum weight design is essential because hull weight significantly affects the lift, thrust powering and high-speed performance This paper presents the procedure of optimum structural design and a computer program to minimize the hull weight of surface effect ships built of composite materials By using the developed computer program, the optimum structural designs for three types of surface effect ships-built of sandwich plate only, stiffened single skin plate only, and both plates-are carried out and the efficiency of each type is investigated in terms of weight The computer program, developed herein, successfully reduced the hull weight of surface effect ships by 15-30% compared with the original design Numerical results of optimum structural designs are presented and discussed

An upper bound for the minimum weight of dual codes of Figueroa planes

Abstract: In this note we give an explicit construction for words of weight 2q 3 - q 2 - q in the dual p-ary code of the Figueroa plane of order q 3, where q > 2 is any power of the prime p. When p is odd this then allows us, for the Figueroa planes, to improve on the previously known upper bound of 2q 3 for the minimum weight of the dual p-ary code of any plane of order q 3. The construction is the same as one that applies to desarguesian planes of order q 3 as described in [3].

An Approximation Algorithm for the Minimum Weight Vertex-Connectivity Problem in Complete Graphs with Sharpened Triangle Inequality

Abstract: Consider a complete graph G with the edge weights satisfying the β-sharpened triangle inequality: weight(u,v) ≤ β (weight(u,x) + weight(x,v) ), for 1/2 ≤ β < 1. We study the NP-hard problem of finding a minimum weight spanning subgraph of G which is k-vertex-connected, k≥ 2, and give a detailed analysis of an approximation quadratic-time algorithm whose performance ratio is \(\frac{\beta}{1 - \beta}\).

Weight Optimization of an Aerobrake Structural Concept for a Lunar Transfer Vehicle

Abstract: An aerobrake structural concept for a lunar transfer vehicle was weight optimized through the use of the Taguchi design method, finite element analyses, and element sizing routines Six design parameters were chosen to represent the aerobrake structural configuration The design parameters included honeycomb core thickness, diameter-depth ratio, shape, material, number of concentric ring frames, and number of radial frames Each parameter was assigned three levels The aerobrake structural configuration with the minimum weight was 44 percent less than the average weight of all the remaining satisfactory experimental configurations In addition, the results of this study have served to bolster the advocacy of the Taguchi method for aerospace vehicle design Both reduced analysis time and an optimized design demonstrated the applicability of the Taguchi method to aerospace vehicle design

Optimal design for thin-walled box beam based on material strength reliability

Abstract: According to the reliability of material strength, the optimal design for the cross sectional size of thin-walled box beam was studied. Firstly the cross sectional size as design random variable was determined, then its stochastic nature was researched, with which the objective function is to seek the maximum reliability of the beam under given constraint conditions. This way is not the same as the conventional optimal design for the minimum weight of the material. With establishing the optimal objective, the reliability of the material under conditions of static and fatigue was considered. The corresponding calculated expression are given. Normally the cross section sizes are fitted to the normal distribution, for the simplification of the design variable, the variation of the section size is assumed as a dependent variable proportional to the mean of the size. The way is different not only with the conventional optimal design but also with the common reliability design. The maximum reliability of material is obtained, meanwhile the are of the cross section is reduced, i. e., the weight of the material is decreased.

Manufacturing tolerances and multiple loading conditions in structural configuration optimization

Abstract: Most structures, during their service life, are subjected to several loading conditions; moreover, during their assembly, some or all of the assumed design variables are varied due to manufacturing imperfections. In the case of an optimum structure this can be especially dangerous. The problem of imperfections is a random one and its possible solution is not easily applicable due to its complexity. There is thus a need to give designers a tool that will enable them to incorporate the manufacturing tolerances in a relatively simple way. The proposed approach is deterministic, giving approximate minimum weight design with a safety margin. This is because limits of constraints are reduced by products of sensitivities multiplied by given tolerances. This paper is illustrated with two minimum weight designs of truss configurations, under three loading conditions each. Copyright © 2003 John Wiley & Sons, Ltd.

Weight optimization of a very large dewar for flight applications

Abstract: The design optimization of a dewar with a very large cold stage, for flight applications, is described. The optimization was achieved with the aid of Cosmos/m Finite Elements software, in order to arrive at a dewar of minimum weight. The design concept incorporate a symmetrical base, which includes cavities and ribs. The number and dimensions of the frame ribs were varied in order to arrive at weight optimization consistent with maintaining the cold stage natural frequency and deflections within the required limits. The final result of this weight optimization process was a dewar with a 25% weight reduction as compared with a more conventional dewar wiht a solid base. The weight of the new dewar, the natural frequencies and center of mass location were 522gm, 1095Hz, 1435Hz, 2022Hz, 3239Hz 0, 17.4mm, 0, respectively. The weight of the traditional dewar, the natural frequencies and center of mass location were 709gm, 1080Hz, 1411Hz, 2111Hz, 3230Hz, 0,15.0mm, 0, repsectively.

Minimum weight design of non‐linear elastic structures with multimodal buckling constraints

Abstract: It well known that multimodal instability is an event particularly relevant in structural optimization. Here, in the context of non-linear stability theory, an exact method is developed for minimum weight design of elastic structures with multimodal buckling constraints. Given an initial design, the method generates a sequence of improved designs by determining a sequence of critical equilibrium points related to decreasing values of the structural weight. Multimodal buckling constraints are imposed without repeatedly solving an eigenvalue problem, and the difficulties related to the non-differentiability in the common sense of state variables in multimodal critical states, are overcome by means of the Lagrange multiplier method. Further constraints impose that only the first critical equilibrium states (local maxima or bifurcation points) on the initial equilibrium path of the actual designs are taken into account. Copyright © 2002 John Wiley & Sons, Ltd.

Optimal Design for Thin-Walled Box Beam Based on Material Strength Reliability

Abstract: According to the reliability of material strength,the optimal design for the cross sectional size of thin-walled box beam was studied.Firstly the cross sectional size as design random variable was determined,then its stochastic nature was researched,with which the objective function is to seek the maximum reliability of the beam under given constraint conditions.This way is not the same as the conventional optimal design for the minimum weight of the material.With establishing the optimal objective,the reliability of the material under conditions of static and fatigue was considered.The corresponding calculated expressions are given.Normally the cross section sizes are fitted to the normal distribution,for the simplification of the design variable,the variation of the section size is assumed as a dependent variable proportional to the mean of the size.The way is different not only with the conventional optimal design but also with the common reliability design.The maximum reliability of material is obtained,meanwhile the area of the cross section is reduced,i.e.,the weight of the material is decreased.

Optimisation of structures by the optimality criteria method

Abstract: A robust computer procedure for weight minimisation of a high–rise and portal frames under the deflection constraint at various locations is presented. It replaces the conventional tedious and unreliable manual assessment for minimum weight design. Several practical considerations such as the Invariance or lower limit of wall thickness for fire resistance or building services requirements are Included in the optimisation procedure. The method is readily used in practical optimisation design of steel and reinforced concrete structures against the deflection limit.

Optimum design of prestressed concrete beams by a modified grid search method

Abstract: A computer program has been developed for the optimum design of prestressed concrete beams under flexure. Optimum values of prestressing force, tendon configuration, and cross-sectional dimensions are determined subject to constraints on the design variables and stresses. 28 constraints have been used including flexural stresses, cover requirement, the aspect ratios for top and bottom flanges and web part of a beam and ultimate moment. The objective function contains cost of concrete, prestressing force and formwork. Using this function, it is possible to obtain minimum cost design, minimum weight or cross-sectional area of concrete design and minimum prestressing force design. Besides the idealized I-shaped cross-section, which is widely used in literature, a general I-shaped cross-section with eight geometrical design variables are used here. Four examples, one of which is available in the literature and the others are modified form of it, have been solved for minimum cost and minimum cross-sectional area designs and the results are compared. The computer program, which employs modified grid search optimization method, can assist a designer in producing efficient designs rapidly and easily. Considerable savings in computational work are thus made possible.