Two fundamental approaches can be applied to satellite-formation mission design: active control, where satellites exert forces with their thrusters to maintain a constant or periodic geometry for all or part of each o...
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Two fundamental approaches can be applied to satellite-formation mission design: active control, where satellites exert forces with their thrusters to maintain a constant or periodic geometry for all or part of each orbit, and natural, where satellite orbits are designed to naturally assemble a geometry for all or part of each orbit to within a tolerance defined from scientific requirements. An actively controlled formation can be labeled virtual rigid body (VRB) because geometry is precisely maintained as if the satellites were rigidly connected. This work describes a hierarchical optimization method for minimizing mission design computational complexity and applies this method to the design of VRB, natural-orbit, and multi-impulse solutions for a tetrahedron formation applicable to the proposed magnetospheric multiscale mission. Cost is defined in terms of total fuel per second of observation and tetrahedron geometric quality factor. Although both natural-orbit and active solutions are feasible, the active solutions substantially increase average data quality and observation time per orbit at minimum fuel cost, and the multi-impulse solution does not require thruster use during data collection periods.
optimization algorithm was developed for the simula ti on of ceramic grain growth at atomistic scale. Based on the coordination informa tion of different atoms, a structure of trident tree was applied to save large q ...
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optimization algorithm was developed for the simula ti on of ceramic grain growth at atomistic scale. Based on the coordination informa tion of different atoms, a structure of trident tree was applied to save large q uantities data, so as to solve the problems of large data information and long r unning time. For every atom a binary tree was firstly formed according to the X coordination of atom. If the values of X coordination were the same, the middle sub-tree of first layer formed then a binary tree according to the Y coordinati on of atom. If the values of Y coordination were also the same, the middle sub- tree of second layer formed then a binary tree according to the Z coordination o f atom. In this way the speed of whole program is enhanced obviously. In order t o reduce memory, in this structure only need to store the exterior atoms’ infor mation, an integer is used to store the interior atoms’ information. If other a toms take up an atom’s all adjacent positions, this atom will be deleted in the data structure, for all the adjacent positions’ atoms, the integer’s relative bit will be set 1 to denote that there is an atom in this position but not be s tored in the trident tree. When an outside atom is deleted, for all the bits tha t are set 1,an atom will be added to the trident tree as an outside atom for the relative positions. And for this new added atom, the integer’s relative bi t of all the adjacent position’s atoms should be set 0 to denote that there is no interior atom in this position. In this way, if there are n 3 atoms, onl y need to store 6n 2 quantity’s atoms’ information. Large quantity of mem ory space can then be saved.
A simplified technique for searching for the initial costate values using evolutionary strategies (ES) was presented. A representative low-Earth-orbit (LEO) to geostationary-Earth-orbit (GEO) transfer problem with con...
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A simplified technique for searching for the initial costate values using evolutionary strategies (ES) was presented. A representative low-Earth-orbit (LEO) to geostationary-Earth-orbit (GEO) transfer problem with constant continuous thrust acceleration was examined. The use of ESs for an optimal orbit transfer problem from LEO to GEO was achieved using various searching domain widths. It was concluded that ESs appear to be capable of finding initial sets of adjoint variables, although they do not always find the global solution due to the randomized process in the algorithms.
An understanding of a natural system's information handling can lead to more effective artificial optimization techniques. There are successful optimization algorithms represented in biosystems that have proven us...
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An understanding of a natural system's information handling can lead to more effective artificial optimization techniques. There are successful optimization algorithms represented in biosystems that have proven useful in engineering applications (artificial neural networks, immune system algorithms, etc). The goal of our study is to develop a new biosystem derived an optimization algorithm which is called a DNA algorithm (DNAA) based on optimization procedures in DNA. We have focused on an analogy between optimizing procedures for protein functions using exon shuffling and those for an optimization problem in the engineering field. We used a traveling salesman problem (TSP) for evaluation of the performance of the DNAA. The DNAA could estimate approximately optimal tour routes in the 25-city TSP.
Shape optimization of airfoils involves highly expensive, nonlinear objective(s) and constraint functions often with functional and slope discontinuity that limits the efficient use of gradient-based methods for its s...
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Shape optimization of airfoils involves highly expensive, nonlinear objective(s) and constraint functions often with functional and slope discontinuity that limits the efficient use of gradient-based methods for its solution. Gradient-based methods are not capable of generating a set of pareto solutions as required in multiobjective problems as they work with a single solution and improve it through successive iterations. Population-based, zero-order, stochastic optimization methods are therefore an attractive choice for shape optimization problems as they are easy to implement and effective for highly nonlinear problems. We present a swarm algorithm that is applicable for optimization problems in general, but is here explored for airfoil design optimization studies. The algorithm is based on a sociobehavioral model, and it offers the designer the desired flexibility to solve various unconstrained/constrained, single-/multiobjective forms of the airfoil shape optimization problem. The algorithm handles objectives and constraints separately via pareto ranking and is thus immune to problems of scaling and aggregation that commonly affect penalty-function-based constraint handling schemes. Three different airfoil design optimization problems have been solved to illustrate the algorithm's flexibility and its computational efficiency, which compare favorably with existing stochastic search methods.
We have developed a new optimization paradigm for solving computationally intractable combinatorial optimization and synthesis problems. The technique, named probabilistic constructive, combines the advantages of both...
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We have developed a new optimization paradigm for solving computationally intractable combinatorial optimization and synthesis problems. The technique, named probabilistic constructive, combines the advantages of both constructive and probabilistic optimization mechanisms. Since it is a constructive approach, it has a relatively short runtime and is amenable for the inclusion of insights through heuristic rules. The probabilistic nature facilitates a flexible tradeoff between runtime and the quality of solution, suitability for the superimposition of a variety of control strategies, and simplicity of implementation. After presenting the generic technique, we apply it to a generic NP-complete problem (maximum independent set) and a synthesis and compilation problem (sequential code covering). Extensive experimentation indicates that the new approach provides very attractive tradeoffs between the quality of solution and runtime, often outperforming the best previously published approaches.
A multi-objective, multidisciplinary design optimization methodology for mathematically modeling the distributed satellite system conceptual design problem as an optimization problem has been developed. The tradespace...
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A multi-objective, multidisciplinary design optimization methodology for mathematically modeling the distributed satellite system conceptual design problem as an optimization problem has been developed. The tradespace for distributed satellite systems can be enormous, too large to enumerate, analyze, and compare all possible architectures. The seven-step methodology enables an efficient search of the tradespace for the best families of architectures during the conceptual design phase. Four classes of optimization techniques are investigated, Taguchi, heuristic, gradient, and univariate methods. The heuristic simulated annealing algorithm found the best distributed satellite system architectures with the greatest consistency due to its ability to escape local optima within a nonconvex tradespace. The conceptual design problem scope is then broadened by expanding from single-objective to multiobjective optimization problems, and two variant multi-objective simulated annealing algorithms are developed. Finally, several methods are explored for approximating the true global Pareto boundary with only a limited knowledge of the full design tradespace. In this manner, the methodology serves as a powerful, versatile systems engineering and architecting tool for the conceptual design of distributed satellite systems.
In this work, we present a new image-quality-based optimization process using a USAAF test to estimate the contrast function in the image plane. This strategy permits us to estimate the contrast values with only one i...
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ISBN:
(纸本)0819451339
In this work, we present a new image-quality-based optimization process using a USAAF test to estimate the contrast function in the image plane. This strategy permits us to estimate the contrast values with only one image for the analyzed field, so the computation time of the method is appropriated for an optimization process. This image-quality-based procedure does not present the typical problems in estimating the contrast value in optical systems with odd wave-aberrations because the method uses an image of one extended object. The optimization process is applied to design triplet systems. For a triplet lens system working with an f-number of eight, we obtain a design with a Strehl ratio of 0.91 at full field of view using our optimization process. Finally, we present the optimization process' dependence on the starting systems which is not in correlation with the starting systems' quality.
One of the most significant challenges in conceptual design is managing the tradespace of potential architectures: choosing which design to pursue aggressively, which to keep on the table, and which to leave behind. T...
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One of the most significant challenges in conceptual design is managing the tradespace of potential architectures: choosing which design to pursue aggressively, which to keep on the table, and which to leave behind. The application is presented of a framework for managing a tradespace of architectures not through traditional effectiveness 14 measures such as cost and performance, but instead through a quantitative analysis of the embedded uncertainty in each potential space system architecture. Cost and performance in this approach remain central themes in decision making, but uncertainty serves as the focal lens to identify potentially powerful combinations of architectures to explore concurrently in further design phases.
A method is presented for quantitatively assessing the generalized cost and risk impacts to a space system architecture of a restrictive government launch policy and application is made to the case of the U.S. space t...
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A method is presented for quantitatively assessing the generalized cost and risk impacts to a space system architecture of a restrictive government launch policy and application is made to the case of the U.S. space transportation policy of 1994. For both a restrictive and unrestrictive launch policy scenario, a mixed integer optimization algorithm is used to select the best launch vehicle suite for a given satellite system architecture based on the cost or risk selection rule for a particular type of decision maker. The cost and risk impacts that result in the two scenarios are compared over an extensive matrix of satellite masses, altitudes, inclinations, and constellation arrangements. Generalized launch policy cost impact estimating relationships are derived, and risk impacts are represented by descriptive statistics. The analysis finds that the 1994 U.S. launch policy affects the launch cost and launch risk of many types of satellite system architectures.
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