Showing papers on "Minimum weight published in 2012"

Topology optimization for minimum weight with compliance and stress constraints

Abstract: The paper deals with a formulation for the topology optimization of elastic structures that aims at minimizing the structural weight subject to compliance and local stress constraints. The global constraint provides the expected stiffness to the optimal design while a selected set of local enforcements require feasibility with respect to the assigned strength of material. The Drucker–Prager failure criterion is implemented to handle materials with either equal or unequal behavior in tension and compression. A suitable relaxation of the equivalent stress measure is implemented to overcome the difficulties related to the singularity problem. Numerical examples are presented to discuss the features of the achieved optimal designs along with performances of the adopted procedure. Comparisons with pure compliance–based or pure stress–based strategies are also provided to point out differences arising in the optimal design with respect to conventional approaches, depending on the assumed material behavior.

Design of a minimum weight dual active bridge converter for an Airborne Wind Turbine system

Abstract: The design procedure for a bidirectional DAB dc-dc converter, which provides a high dc voltage of 8kV to the tether of a 100 kW Airborne Wind Turbine (AWT) system, is presented. The maximum allowed weight of the dc-dc converter is 25 kg and, thus, the main challenge is the realization of a light-weight DAB converter. The investigated dc-dc converter is split up into 16 single DAB modules with a rated power of 6.25 kW and a dc port voltage of 2kV. Thus, a weight of less than 25 kg/16 = 1.56 kg needs to be achieved for a single DAB module. The design method used to obtain the minimum weight DAB converter, based on the evaluation of a power-to-weight ratio versus efficiency Pareto Front γ-η-Pareto Front) is presented in this paper. For this purpose the transient voltages and currents of the employed SiC JFETs during switching are discussed in detail, since the respective measurement results allow for a prediction of the switching losses. Moreover, the calculated transformer is realized and experimental results are used to verify the weight, the losses, and the cooling system performance of the transformer. For a single DAB module a weight of m = 1.43 kg, an efficiency of η = 97%, and a power-to-weight ratio of γ = 4.4kW/kg results.

Weighted geometric set cover problems revisited

Abstract: We study several set cover problems in low dimensional geometric settings. Specifically, we describe a PTAS for the problem of computing a minimum cover of given points by a set of weighted fat objects. Here, we allow the objects to expand by some prespecified δ-fraction of their diameter. Next, we show that the problem of computing a minimum weight cover of points by weighted halfplanes (without expansion) can be solved exactly in the plane. We also study the problem of covering ℝ d by weighted halfspaces, and provide approximation algorithms and hardness results. We also investigate the dual settings of computing minimum weight simplex that covers a given target point. Finally, we provide a near linear time algorithm for the problem of solving a LP minimizing the total weight of violated constraints needed to be removed to make it feasible.

Exact Algorithms for Edge Domination

Abstract: An edge dominating set in a graph G=(V,E) is a subset of the edges D⊆E such that every edge in E is adjacent or equal to some edge in D. The problem of finding an edge dominating set of minimum cardinality is NP-hard. We present a faster exact exponential time algorithm for this problem. Our algorithm uses O(1.3226n) time and polynomial space. The algorithm combines an enumeration approach of minimal vertex covers in the input graph with the branch and reduce paradigm. Its time bound is obtained using the measure and conquer technique. The algorithm is obtained by starting with a slower algorithm which is refined stepwisely. In each of these refinement steps, the worst cases in the measure and conquer analysis of the current algorithm are reconsidered and a new branching strategy is proposed on one of these worst cases. In this way a series of algorithms appears, each one slightly faster than the previous one, ending in the O(1.3226n) time algorithm. For each algorithm in the series, we also give a lower bound on its running time. We also show that the related problems: minimum weight edge dominating set, minimum maximal matching and minimum weight maximal matching can be solved in O(1.3226n) time and polynomial space using modifications of the algorithm for edge dominating set. In addition, we consider the matrix dominating set problem which we solve in O(1.3226n+m) time and polynomial space for n×m matrices, and the parametrised minimum weight maximal matching problem for which we obtain an Oź(2.4179k) time and space algorithm.

Optimum topology design of various geometrically nonlinear latticed domes using improved harmony search method

Abstract: Domes are elegant and economical structures used in covering large areas. They are built in various forms. According to their form, they are given special names such as lamella, network, and geodesic domes. In this paper, optimum topological design algorithm is presented that determines the optimum number of rings, the optimum height of crown and tubular section designations for the member groups of these domes. The design algorithm developed has a routine that generates the data required for the geometry of these domes automatically. The minimum weight of each dome is taken as the objective function. The design constraints are implemented according to the provision of LRFD-AISC (Load and Resistance Factor Design---American Institute of Steel Constitution). The optimum topological design problem that considers these constraints turns out to be discrete programming problem. Improved harmony search algorithm is suggested to determine its optimum solution. The design algorithm also considers the geometric nonlinearity of these dome structures. Design examples are presented to demonstrate the effectiveness and robustness of the design optimization algorithm developed.

A hybridized tabu search approach for the minimum weight vertex cover problem

Abstract: The minimum weight vertex cover problem is a basic combinatorial optimization problem defined as follows. Given an undirected graph and positive weights for all vertices the objective is to determine a subset of the vertices which covers all edges such that the sum of the related cost values is minimized. In this paper we apply a modified reactive tabu search approach for solving the problem. While the initial concept of reactive tabu search involves a random walk we propose to replace this random walk by a controlled simulated annealing. Numerical results are presented outperforming previous metaheuristic approaches in most cases.

Minimum-weight sandwich structure optimum design subjected to torsional loading

Abstract: As one of the most valued structural engineering innovations developed by the composites industry, sandwich structures are now used extensively in automotive, aerospace and civil infrastructure due to the main advantage of lightweight. This paper develops a minimum weight optimization method for sandwich structure subjected to torsion load. The design process are identified for a sandwich structure required to meet the design constraint of torsion stiffness. The optimum solutions show that at optimum design the core weight accounts for 66.7% of the whole sandwich structure. To illustrate the newly developed optimum design solutions, numerical examples are presented for sandwich structures made of either isotropic face skins or orthotropic composite face skins. Agreement between the theoretical analysis and the examples results is good.

Using genetic algorithm for the optimization of seismic behavior of steel planar frames with semi-rigid connections

Abstract: Beam-column connections have a significant role in the results of the analysis and the design of steel frames. In this paper, a genetic algorithm has been used for the non-linear analysis and design of steel frames. For minimizing the weight of frames, while satisfying the applied constraints and restraints such as the limits of normal and combined stresses, criteria such as target displacement(s) and the number and locations of plastic hinges were used. To analyze and design the frame elements, I and box-shaped standard sections were used for beams and columns, respectively. Finally, some clues for finding optimizing semi-rigid connection stiffness values for beam-to-column connections have been obtained. The degrees of these rigidities are obtained by a genetic algorithm during the procedure of optimization in order to reach a frame with the minimum weight. SAP2000 structural analysis program was used to perform modal analysis and linear and non-linear static solutions as well as the design of the elements. A MATLAB program was written for the process of optimization. The procedure of optimization was based on a weight minimization carried out for 9 steel frames. Thus, the optimum connection stiffness could be obtained for minimizing the weight of the structure. The results show that the non-linear analysis gives less weight for short period frames with semi-rigid connections compared to those of linear ones. However, by increasing the periods of frames, much less weights are obtained in the case of non-linear analysis with semi-rigid connections.

Population diversity based inertia weight adaptation in Particle Swarm Optimization

Abstract: In this paper, we propose two new inertia weight adaptation strategies in Particle Swarm Optimization (PSO). The two inertia weight adaptation strategies are based on population diversity. In the search process of an optimization algorithm, there must be a balance between exploration and exploitation. Exploration means to explore different areas of the search space in order to have high probability to find good promising solutions. Exploitation means to concentrate the search around a promising region in order to refine a candidate solution. The exploration and exploitation are two conflicted objectives of an optimization algorithm. A good optimization algorithm should optimally balance the two conflicted objectives. With the first strategy, the algorithm focus on the exploration at the beginning of the search, and focus on exploitation at the end of search. Particles' inertia weights are randomly initialized within the range [0.4,0.9], the minimum weight gets increased at the beginning of search to enhance the exploration ability, and the maximum weight gets decreased at the end of search to enhance the exploitation ability. With the second strategy, particles' inertia weights are set at the same value, and this value is adaptively changed according to the distance between the gbest and the centre of swarm. The porposed PSOs are compared with the standard PSO. Experimental results show that a PSO with adaptive inertia weight could obtain performance as good as the standard PSO, and even better on some multimodal problems.

Minimum weight dynamo and fast opinion spreading

Abstract: We consider the following multi---level opinion spreading model on networks. Initially, each node gets a weight from the set {0,…,k−1}, where such a weight stands for the individuals conviction of a new idea or product. Then, by proceeding to rounds, each node updates its weight according to the weights of its neighbors. We are interested in the initial assignments of weights leading each node to get the value k−1 ---e.g. unanimous maximum level acceptance--- within a given number of rounds. We determine lower bounds on the sum of the initial weights of the nodes under the irreversible simple majority rules, where a node increases its weight if and only if the majority of its neighbors have a weight that is higher than its own one. Moreover, we provide constructive tight upper bounds for some class of regular topologies: rings, tori, and cliques.

Application of multi-layer graphs in the design of MPLS networks

Abstract: It is suggested to use multi-layer graphs as a mathematical model in the design of MPLS networks. The application of this model makes it possible to design multi-service telecommunication systems simultaneously at several levels and to reduce the problem to the search of the minimum weight graph.

Minimum Weight Dynamo and Fast Opinion Spreading

Abstract: We consider the following multi--level opinion spreading model on networks. Initially, each node gets a weight from the set [0..k-1], where such a weight stands for the individuals conviction of a new idea or product. Then, by proceeding to rounds, each node updates its weight according to the weights of its neighbors. We are interested in the initial assignments of weights leading each node to get the value k-1 --e.g. unanimous maximum level acceptance-- within a given number of rounds. We determine lower bounds on the sum of the initial weights of the nodes under the irreversible simple majority rules, where a node increases its weight if and only if the majority of its neighbors have a weight that is higher than its own one. Moreover, we provide constructive tight upper bounds for some class of regular topologies: rings, tori, and cliques.

Design of Composite Risers for Minimum Weight

Abstract: The use of composite materials in offshore engineering for deep sea oil production riser systems has drawn considerable interest due to the potential weight savings and improvement in durability. The design of composite risers consists of two stages: (1) local design based on critical local load cases, and (2) global analysis of the full length composite riser under global loads and assessment of critical locations. In the first stage, eight different material combinations were selected and their laminate configurations optimised under local load considerations. Stage two includes a final local stress analysis of the critical sections of the riser under the combined loads determined in the global analysis. This paper describes two design methodologies of the composite riser to provide minimum structural weight and shows that the use of off angle fibre orientations in addition to axial and hoop reinforcements offer substantial weight savings and ensure the structural capacity. Keywords—Composite Riser; Composite Tubular; Finite Element Modelling; Global Design; Local Design; Offshore Engineering.

Discrete Optimum Design of Sinusoidal Corrugated Web Girder

Abstract: The use of sinusoidal corrugated web girder for the box-type girders and gable steel main frames has recently been increasing very much. The reasons are that the thin web of the girder affords a significant weight reduction compared with rolled beam and welded built-up girder, and that corrugation prevents the buckling failure of the web. Improvements of the automatic fabrication process makes mass production of the corrugated web and unit possible, and applications of this girder have been extended considerably. Thus, the research for the optimum design processer considering the production data is needed practically. For doing this research, we develope the discrete optimum structural design program in consideration of production list data for the research, and the program apply to the single girder under the uniform load and the concentrated load as numerical example. We consider objective function as minimum weight of the girder, and use slenderness ratio, stress of flanges and corrugated web, and the girder deflection as the constraint functions. And also the Genetic Algorithms is adopted to search the global minimum point by using the production list as a discrete design variable. Finally, to verify the optimality of the design, we conduct a comparison of the results of the discrete optimum design with those of the continuous one, and also analyze the characteristics of the optimum cross-section.

Approximations on Minimum Weight Triangulations and Minimum Weight Pseudo-Triangulations Using Ant Colony Optimization Metaheuristic

Abstract: Globally optimal triangulations and pseudo-triangulations are difficult to be found by deterministic methods as, for most type of criteria, no polynomial algorithm is known. In this work, we consider the Minimum Weight Triangulation (MWT) and Minimum Weight Pseudo-Triangulation (MWPT) problems of a given set of n points in the plane. This paper shows how the Ant Colony Optimization (ACO) metaheuristic can be used to find high quality triangulations and pseudo-triangulations of minimum weight. For the experimental study presented here we have created a set of instances for MWT and MWPT problems since no reference to benchmarks for these problems were found in the literature. Through the experimental evaluation, we assess the applicability of the ACO metaheuristic for MWT and MWPT problems considering greedy and Simulated Annealing algorithms.

Apparatus and method for setting an optical path in an optical network

Abstract: An auxiliary graph representing connection relations between nodes on a plurality of lightpaths in an optical network is created using a plurality of edges each connecting a pair of nodes. The plurality of lightpaths includes first lightpaths existing in the optical network and the second lightpaths to be set to accommodate traffic that is newly generated for the optical network. Each of the plurality of edges is assigned a weight value indicating a magnitude of increase in power consumption of network devices allocated to the each edge. For start and end nodes, a minimum weight path that has a path weight value minimum among paths each being a continuous sequence of edges that starts from the start node and reaches the end node is obtained, where the path weight value is a total sum of weight values assigned to the continuous sequence of edges.

An efficient info-gain algorithm for finding frequent sequential traversal patterns from web logs based on dynamic weight constraint

Abstract: Many frequent sequential traversal pattern mining algorithms have been developed which mine the set of frequent subsequences traversal pattern satisfying a minimum support constraint in a session database. However, previous frequent sequential traversal pattern mining algorithms give equal weightage to sequential traversal patterns while the pages in sequential traversal patterns have different importance and have different weightage. Another main problem in most of the frequent sequential traversal pattern mining algorithms is that they produce a large number of sequential traversal patterns when a minimum support is lowered and they do not provide alternative ways to adjust the number of sequential traversal patterns other than increasing the minimum support. In this paper, we propose a frequent sequential traversal pattern mining algorithm with dynamic weight constraint. Our main approach is to add the weight constraints into the sequential traversal pattern while maintaining the downward closure property. A weight range is defined to maintain the downward closure property and pages are given different weights and traversal sequences assign a minimum and maximum weight. In scanning a session database, a maximum and minimum weight in the session database is used to prune infrequent sequential traversal subsequence by doing downward closure property can be maintained. Our method produces a few but important sequential traversal patterns in session databases with a low minimum support, by adjusting a weight range of pages and sequence. The support and confidence are the most popular measures for sequential patterns. The support evaluates frequencies of the patterns and the confidence evaluates frequencies of patterns in the case that sub-patterns are given. These parameters are meaningful and important for some applications. The information gain metric which is widely used in the information theory field, may be useful to evaluate the degree of surprise of the pattern. Target is finding set of patterns that have information gain higher than minimum information gain threshold.

Effect of ribs and stringer spacings on the weight of aircraft structure for aluminum material

Abstract: Low cost and less weight are the two primary objectives of any aircraft structure. Efficient design of aircraft components is therefore, required to reduce cost and weight of the aircraft structure. For components with compressive loadng, Ribs and stringer spacings and stringer cross-section play a major role in achieving less weight. The main objective of the present study was aimed at establishing optimum stringer and ribs spacings and stringer cross-section for minimum weight of buckling design driven components using FEM packages. The analysis of effect of plate with ribs and stringer spacing was modeled in FEM to study the effect of these on the weight of aircraft structure using aluminum as material. The analysis was carried out through linear buckling analysis of the model. The software tools used were HyperMesh as a pre and post processor and Radioss as a solver.

On the equivalence of minimum compliance and stress-constrained minimum weight design of trusses under multiple loading conditions

Abstract: This article is devoted to topology optimization of trusses under multiple loading conditions. Compliance minimization with material volume constraint and stress-constrained minimum weight problem are considered. In the case of a single loading condition, it has been shown that the two problems have the same optimal topology. The possibility of extending this result for problems involving multiple loading conditions is examined in the present work. First, the compliance minimization problem is formulated as a multicriterion optimization problem, where the conflicting criteria are the compliances of the different loading conditions. Then, the optimal topologies of the stress-constrained minimum weight problem and the multicriterion compliance minimization problem for a simple test example are compared. The results verify that when multiple loading conditions are involved, the stress-constrained minimum weight topology cannot be obtained in general by solving the compliance minimization problem.

Note on the Minimum Weight States in the su(2)-Algebraic Many-Fermion Model —Extension of the Role of the Auxiliary su(2)-Algebra—

Abstract: The role of the auxiliary su(2)-algebra proposed by the present authors in the latest paper is extended. Its aim is to determine the minimum weight states completely. With the aid of scalar operators for the auxiliary algebra, new aspects are added to the minimum weight states in the aligned scheme discussed in the latest paper. Some simple examples are shown.

Approximating infeasible 2VPI-systems

Abstract: It is a folklore result that testing whether a given system of equations with two variables per inequality (a 2VPI system) of the form xi−xj=cij is solvable, can be done efficiently not only by Gaussian elimination but also by shortest-path computation on an associated constraint graph. However, when the system is infeasible and one wishes to delete a minimum weight set of inequalities to obtain feasibility (MinFs2=), this task becomes NP-complete. Our main result is a 2-approximation for the problem MinFs2= for the case when the constraint graph is planar using a primal-dual approach. We also give an α-approximation for the related maximization problem MaxFs2= where the goal is to maximize the weight of feasible inequalities. Here, α denotes the arboricity of the constraint graph. Our results extend to obtain constant factor approximations for the case when the domains of the variables are further restricted.

Full and maximal squashed flat antichains of minimum weight.

Abstract: any n;k and positive real numbers ; , we determine all SFFA and all SMFA of minimum weight jAj + jBj . Based on this, asymptotic results on SMFA with minimum size and minimum BLYM value, respectively, are derived.

Minimum Weight Euclidean t-spanner is NP-Hard

Abstract: Given a set P of points in the plane, an Euclidean t-spanner for P is a geometric graph that preserves the Euclidean distances between every pair of points in P up to a constant factor t. The weight of a geometric graph refers to the total length of its edges. In this paper we show that the problem of deciding whether there exists an Euclidean t-spanner, for a given set of points in the plane, of weight at most w is NP-hard for every real constant t > 1, both whether planarity of the t-spanner is required or not.

A Reliable Connected Dominating Set Algorithm in Wireless Sensor Networks

Abstract: The connected dominating set (CDS) has been proposed as a virtual backbone or routing to alleviate the broadcasting storm problem in wireless sensor networks. Since the nodes in CDS need to carry other node’s trac, it is desirable that the CDS is reliable. In this paper, we dene the concepts of area-faultrate as a weight to select dominator. Then it is proved that the reliability optimization for CDS is a minimum weight connected dominating set (MWCDS) problem. Therefore, an algorithm of MWCDS called RCDS is proposed. The results show that (1) the RCDS has guaranteed quality by proving that its total weight is within a small constant factor of the optimum networks; (2) the RCDS network has a smaller backbone, a smaller total weight, as well as a longer lifetime.