Modified Optimality Criteria Research Articles

주어진 고유주파수를 갖는 구조물의 위상최적설계

Topology optimization is applied to determine the layout of a structural component with a specified frequency by minimizing the difference between the specified structural frequency and a given frequency. The homogenization design method is employed and the topology design problem is solved by the optimality criteria method. The value of a weighting factor in the optimality criteria plays an important role in this topology design problem. The modified optimality criteria method approximated by using the binomial expansion is suggested to determine the suitable value of the weighting factor, which makes convergence stable. If a given frequency is set as an excited frequency, it is possible to avoid resonance by moving away the specified structural frequency from the given frequency. The results of several test problems are compared with previous works and show the validity of the proposed algorithm.

Unified topology design of static and vibrating structures using multiobjective optimization

Since structural design is usually required to perform in more than one environment, the ability to consider multiple objectives has to be included within the framework of topology optimization. A unified topology design methodology is proposed to generate structures satisfying both static and vibration performance measures using the multiobjective optimization approach. The weighted sum of conflicting objectives resulting from the norm method is used to generate the optimal compromise solutions, and the decision function is set to select the preferred solution. The objective function is defined by the mean compliance and mean eigenvalue to design a flexible structure which meets both the static and vibration requirements. The optimality conditions of the bicriteria problem are derived based on the modified optimality criteria method. To substantiate this approach, illustrated examples are presented both for verification and application.

A Regularized LMS Algorithm for Narrowband Interference Rejection in Direct Sequence Spread Spectrum Communications

A regularized LMS technique is presented that uses a modified optimality criterion which enhances the detection capabilities of direct sequence spread spectrum systems. The rejection filter is updated based upon an additional regularization input which limits the self-noise of the filter, especially at moderate signal-to-interference power ratios. The regularization is controlled by a single scalar parameter, that can be varied to produce the optimal Wiener filter weights or the decision-feedback filter weights. An advantage of the regularized filter is that the weight error surface is quadratic, leading to well behaved convergence properties for adaptive implementations. Simulation results are presented which compare the regularized filter to the optimal Wiener filter and the decision-feedback filter.

A NEW METHOD OF SEQUENTIAL APPROXIMATE OPTIMIZATION FOR STRUCTURAL OPTIMIZATION PROBLEMS

Abstract In this paper a new method of sequential approximate optimization is introduced to solve some structural optimization problems. This new method employs a new intermediate variable which has two variable parameters to linearize the objective and constraint functions in terms of the intermediate variable. The approximated optimization problem obtained by using this method is separable, and it can always be convex if the parameters are properly chosen. The approximated optimization problem is then simply solved by using the dual method. The new method can be considered as a generalization of the current sequential approximate optimization methods such as CONLIN, MMA and DSQP, and it can also be reduced to a modified optimality criteria method. Several guidelines and calculation methods for determining the parameters in the intermediate variable are discussed in this paper. It is shown that the new method can greatly accelerate the convergence of the optimization process compared with previous methods, and is more general and flexible to deal with various optimization problems.

Linearly constrained direct-sequence spread-spectrum interference rejection

A constrained least-squares technique is presented that utilizes a modified optimality criterion which enhances the detection capabilities of direct sequence spread spectrum systems. The standard least-squares rejection filter adds distortion to the decision variable at the output of the despreading operation. Constraints are introduced into the least-squares solution of the rejection filter which reduce the self-noise of the filter while simultaneously retaining its interference rejection properties. Two types of constraint conditions are considered. The first is a correlation matching property for the rejection filter output. This constraint induces the filter to pass the chip sequence undistorted. The second type of constraint is energy reduction, which induces the filter to achieve minimal energy. Both constraint types are successful at increasing the output signal-to-noise ratio (SNR). Simulation results are presented which demonstrate the output SNR improvement by using the constrained rejection filter.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Comparing the stratigraphic record to estimates of phylogeny

The age of first occurrence of taxa remains an underutilized source of information in phylogenetic analysis. In this paper I develop a method whereby one can measure the fit of the stratigraphic record to an estimated phylogenetic tree. The method works as follows: (1) each of the internal nodes excluding the root node of a phylogenetic tree is visited, (2) the oldest age of first occurrence for the taxa above the node is compared to the oldest age of first occurrence for the sister node, and (3) if the age above the node is the same age or younger than the age below the node, then the node is stratigraphically consistent. A measure of the total fit of the stratigraphic record to the tree is the proportion of nodes that are stratigraphically consistent (expressed as the stratigraphic consistency index, SCI). This measure of stratigraphic fit is sensitive to errors in phylogenetic estimation as well as to missing lineages (or parts of lineages). The significance of the fit of the stratigraphic record to the tree can be determined through a permutation approach that generates the null distribution for SCI under the hypothesis that the stratigraphic fit is no better than would be expected at random. The method is applied to several studies taken from the literature. Almost all published trees had significant SCI values, meaning the trees fit the stratigraphic record quite well. Applications of stratigraphic consistency for determining the confidence that should be placed in a phylogenetic estimate, for determining the root of a tree, and as a modified optimality criterion for estimating phylogenetic trees are discussed.

Optimal Layout Theory: Allowance for selfweight

Structural layout theory is based on two underlying concepts, i.e., the Prager-Shield theory of plastic design and the notion of structural universe. In this paper, optimal layout theory is extended to allow for the effect of selfweight (dead load). The proposed extension is of practical importance because in the design of long-span structures selfweight is a significant load component and the total weight is strongly dependent on the choice of layout. The application of the modified optimality criteria is illustrated with examples of minimum weight grillages (truss grids) as well as plane frames. The degree of economy achieved is then demonstrated through comparisons with nonoptimal solutions. It is also shown that in the preceding examples both primal and dual formulations give the same minimum weight. This comparison is a convenient check on the optimality of the proposed solutions.