• Advances in Computational Design
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• v.1 no.2
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• pp.175-194
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• 2016

Nature has provided inspiration for most of the man-made technologies. Scientists believe that dolphins are the second to humans in smartness and intelligence. Echolocation is the biological sonar used by dolphins for navigation and hunting in various environments. This ability of dolphins is mimicked in this paper to develop a new optimization method. Dolphin Echolocation Optimization (DEO) is an optimization method based on dolphin's approach for hunting food and exploration of environment. DEO has already been developed for discrete optimization search space and here it is extended to continuous search space. DEO has simple rules and is adjustable for predetermined computational cost. DEO provides the optimum results and leads to alternative optimality curves suitable for the problem. This algorithm has a few parameters and it is applicable to a wide range of problems like other metaheuristic algorithms. In the present work, the efficiency of this approach is demonstrated using standard benchmark problems.

• Nuclear Engineering and Technology
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• v.55 no.6
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• pp.2315-2324
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• 2023

Space nuclear reactors are becoming popular in deep space exploration owing to their advantages of high-power density and stability. Following the fourth-generation nuclear reactor technology, a conceptual design of the dual drum-controlled space molten salt reactor (D²-SMSR) is proposed. The reactor concept uses molten salt as fuel and heat pipes for cooling. A new reactivity control strategy that combines control drums and safety drums was adopted. Critical physical characteristics such as neutron energy spectrum, neutron flux distribution, power distribution and burnup depth were calculated. Flow and heat transfer characteristics such as natural convection, velocity and temperature distribution of the D²-SMSR under low gravity conditions were analyzed. The reactivity control effect of the dual-drums strategy was evaluated. Results showed that the D²-SMSR with a fast spectrum could operate for 10 years at the full power of 40 kWth. The D²-SMSR has a high heat transfer coefficient between molten salt and heat pipe, which means that the core has a good heat-exchange performance. The new reactivity control strategy can achieve shutdown with one safety drum or three control drums, ensuring high-security standards. The present study can provide a theoretical reference for the design of space nuclear reactors.

• Journal of the Korean Society of Propulsion Engineers
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• v.24 no.1
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• pp.17-23
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• 2020

Upper stage of launch vehicle mainly injects a lunar explorer from low earth orbit to the moon at a distance of 380,000 km. In foreign lunar explorer, the upper stage is separated from the explorer after the explorer is injected into the earth-moon transfer trajectory, and the lunar explorer then uses on-board propellant to carry out mid-course correction maneuvers and lunar orbit insertion maneuvers. This study describes a newly presented small liquid upper stage. Using a small liquid upper stage with a wet mass of 2.9 tonnes, the lunar explorer not only can be injected earth-moon transfer trajectory but also can be performed lunar orbit insertion. This study provides acceptable mass range of the lunar explorer and the scope of acceptable mission range also describes based on the launch from Naro Space Center.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.38 no.4
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• pp.277-284
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• 2001

Viterbi algorithm is widely used in digital communication system for FEC(forward error correction). Each communication systems based on the Viterbi algorithm use specific Viterbi decoder which has different code parameter values. Even if Viterbi decoder has the same code parameters, it can be varied by the design architecture adopted. We propose the parameterized VHDL model generator for the efficiency of the design. It makes it possible to achieve shorter design time and lower design cost. The model generator searches the design space available and finds out the optimal design point to generate a decoder model.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.41 no.12
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• pp.950-958
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• 2013

The Lunar orbiter is expected to be inserted into a ~300km low Earth orbit using Korea Space Launch Vehicle-II(KSLV-II). After the states are successfully determined with obtained tracking data, the Trans Lunar Injection(TLI) burn has to be done at appropriate epoch to send the lunar orbiter to the Moon. In this study, we describe in detail the mission scenario of the Korean lunar orbiter from the launch at NARO Space Center to lunar orbit insertion(LOI) stage following direct transfer trajectory. We investigate the launch window including launch azimuth, delta-V profile according to TLI and LOI burn positions. We also depict the visibility conditions of ground stations and solar eclipse duration to understand the characteristics of the direct transfer trajectory. This paper can be also helpful not only for overall understanding of ${\Delta}V$ trend by changing TOF and coasting time but for selecting launch epoch and control parameters to decrease fuel consumption.

• International Journal of Aeronautical and Space Sciences
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• v.14 no.4
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• pp.341-349
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• 2013

This paper considers the optimum design of flexbeam cross-sections for a full-scale bearingless helicopter rotor, using an efficient hybrid optimization algorithm based on particle swarm optimization, and an improved genetic algorithm, with an effective constraint handling scheme for constrained nonlinear optimization. The basic operators of the genetic algorithm, of crossover and mutation, are revisited, and a new rank-based multi-parent crossover operator is utilized. The rank-based crossover operator simultaneously enhances both the local, and the global exploration. The benchmark results demonstrate remarkable improvements, in terms of efficiency and robustness, as compared to other state-of-the-art algorithms. The developed algorithm is adopted for two baseline flexbeam section designs, and optimum cross-section configurations are obtained with less function evaluations, and less computation time.

• JSTS:Journal of Semiconductor Technology and Science
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• v.4 no.4
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• pp.286-292
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• 2004

In this paper we present a static performance estimation technique of on-chip bus architectures. The proposed technique requires the static scheduling of function blocks of a task to analyze bus conflicts caused by simultaneous accesses from processing elements to which function blocks are mapped. To apply it to multitask applications, the concurrent execution of the function blocks of different tasks also should be considered. Since tasks are scheduled independently, considering all cases of concurrency in each processing element is impractical. Therefore we make an average estimate on the effects of other tasks with respect to bus request rate and bus access time. The proposed technique was incorporated with our exploration framework for on-chip bus architectures, Its viability and efficiency are validated by a preliminary example.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2000.10a
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• pp.141-148
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• 2000

In system design, it is not always possible that all decision makers can cooperate fully and thus avoid conflict. They each control a specified subset of design variables and seek to minimize their own cost functions subject to their individual constraints. However, a system management team makes every effort to coordinate multiple disciplines and overcome such noncooperative environment. Although full cooperation is difficult to achieve, noncooperation also should be avoided as possible. Our approach is to predict the results of their cooperation and generate approximate Pareto set for their multiple objectives. The Pareto set can be obtained according to the degree of one's conceding coupling variables in the other's favor. We employ approximation concept for modelling this coordination and the mutiobjective genetic algorithm for exploring the coupling variable space for obtaining an approximate Pareto set. The approximation management concept is also used for improving the accuracy of the Pareto set. The exploration for the coupling variable space is more efficient because of its smaller dimension than the design variable space. Also, our approach doesn't force the disciplines to change their own way of running analysis and synthesis tools. Since the decision making process is not sequential, the required time can be reduced comparing to the existing multidisciplinary optimization techniques. This approach is applied to some mathematical examples and structural optimization problems.

• International Journal of Quality Innovation
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• v.7 no.1
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• pp.98-111
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• 2006

The paper presents the design of an optical profilometer, a device used for the reconstruction of the micro-geometry of mechanical parts in applications where high precision is needed. The design is based on Robust Design, a major' methodology for quality improvement of engineering systems. Several design solutions, namely different hardware and software setups of the device, are compared in order to select a configuration realising a desired trade-off between performance and cost. The peculiarity of the design strategy is the use of a computer model of the measurement process where the physical part of the process is simulated. This allows for an extensive exploration of the design space, thus opening the way to product innovation.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.1B
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• pp.71-79
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• 2011

This paper proposes a compiled-code simulator generation system based-on machine description language for efficient design space exploration in designing an embedded system optimized for a specific application. The proposed system generates a compiled-code simulator which maintains the functional accuracy of an event-driven simulator by determining instruction fetch and decoding processes statically. Generated simulator takes instruction-level and cycle-level simulation for estimating performances in embedded core. To show the efficiency of the constructed compiled-code simulator generator, architecture exploration had been performed for the JPEG encoder application. Starting with MIPS R3000 processor for one embedded core, the proposed system can produce the core showing optimized execution time for the application programming. In this process, a huge amount of simulation time has been used. Cycle-level compiled-code simulator has the functional accuracy and shows performance improvement by 21.7% in terms of simulation speed on the average when compared with an event-driven simulator.