• The KSFM Journal of Fluid Machinery
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• v.17 no.4
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• pp.19-29
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• 2014

In addition to the development of micro hydro turbine, the challenge in micro hydro turbine design as sustainable hydro devices is focused on the optimization of turbine runner blade which have decisive effect on the turbine performance to reach higher efficiency. A multi-objective optimization method to optimize the performance of runner blade of propeller turbine for micro turbine has been studied. For the initial design of planar blade cascade, singularity distribution method and the combination of the Bezier curve parametric technology is used. A non-dominated sorting genetic algorithm II(NSGA II) is developed based on the multi-objective optimization design method. The comparision with model test show that the blade charachteristics is optimized by NSGA-II has a good efficiency and load distribution. From model test and scale up calculation, the maximum prototype efficiency of the runner blade reaches as high as 90.87%.

• International Journal of Fluid Machinery and Systems
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• v.2 no.2
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• pp.102-109
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• 2009

A design optimization system for Francis turbine was developed. The system consists of design program and CFD solver. Flow passage shapes are optimized automatically by using the system with Multi-Objective Genetic Algorithm (MOGA). In this study, the system was applied to a high specific speed Francis turbine (nSP = 250m-kW). The runner profile and the draft tube shape were optimized to decrease hydraulic losses. As the results, it was shown that the turbine efficiency was improved in wide operating range, furthermore, the height of draft tube was reduced with the hydraulic performance kept.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.05a
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• pp.611-616
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• 2003

The headphone is regarded as the most effective means for reproducing 3-dimentional virtual sound due to its channel separation property. However, there still exist several serious problems in headphone reproduction, such as, 'front-back confusion' and in-head localization'. These well-known problems are in general assessed by the subjective test that is based on human judgment. In this paper, an objective test is conducted in parallel with the subject test in order to validate the objective reproduction performance. Such a combined approach may be a more scientific and systematic approach to the reproduction performance.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.6 no.7
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• pp.1802-1814
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• 2012

In order to guide users to select the most optimal access network in heterogeneous wireless networks, a network selection algorithm is proposed which is designed based on multi-objective discrete particle swarm optimization (Multi-Objective Discrete Particle Swarm Optimization, MODPSO). The proposed algorithm keeps fast convergence speed and strong adaptability features of the particle swarm optimization. In addition, it updates an elite set to achieve multi-objective decision-making. Meanwhile, a mutation operator is adopted to make the algorithm converge to the global optimal. Simulation results show that compared to the single-objective algorithm, the proposed algorithm can obtain the optimal combination performance and take into account both the network state and the user preferences.

• Korean Journal of Optics and Photonics
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• v.34 no.6
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• pp.248-260
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• 2023

A 0.5-numerical-aperture (NA) refractive-reflective objective, composed of a low-NA refractive and a reflective focal reducer, is designed. A 0.25-NA Lister objective is used for the refractive. A two-spherical-mirror system, corrected for spherical aberration, coma, and astigmatism is used for the reflective focal reducer. In spite of high NA, the refractive-reflective objective has an 18-mm working distance and improved imaging performance, compared to the 0.25-NA Lister objective.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.5
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• pp.535-543
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• 2014

In the robust optimization field, the robustness of the objective function emphasizes an insensitive design. In general, the robustness of the objective function can be achieved by reducing the change of the objective function with respect to the variation of the design variables and parameters. However, in conventional methods, when an insensitive design is emphasized, the performance of the objective function can be deteriorated. Besides, if the numbers of the design variables are increased, the numerical cost is quite high in robust optimization for nonlinear programming problems. In this research, the robustness index for the objective function and a process of robust optimization are proposed. Moreover, a method using the supremum of linearized functions is also proposed to reduce the computational cost. Mathematical examples are solved for the verification of the proposed method and the results are compared with those from the conventional methods. The proposed approach improves the performance of the objective function and its efficiency.

• Journal of Korean Institute of Industrial Engineers
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• v.22 no.2
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• pp.277-302
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• 1996

The overall performance of BISDN depends significantly on the interconnection network or the switch fabric. Hence, it is extremely important to evaluate the performance of the network or the fabric. The well developed performance models also provide insight into the factors that determine design tradeoffs as well as quantitative estimates of their importance. The objective of this paper is to investigate and critically compare all the developed performance analysis models of FPS according to internal switch fabric structure, traffic assumptions, performance measures, methodologies, etc. FPSs are described according to their internal fabric structure. Brief history of FPS performance analysis is mentioned and performance analysis modeling is discussed.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.16 no.6
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• pp.509-516
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• 1991

In this paper, we propose on objective evaluation model of telephone transmission qulity in order to estimate a satisfaction score regarding speech quality in a relephone network. As the degradantion factors of telephone transmission quality, this model takes into account transmission loss, noise, distortion, talker echo and sidetone. A performance index[PI] is introduced for five psychological factors affecting telephone speech qualty, and a Mean Opinion Score(MOS) is estimated from the sum of all Pis. The simulation results indicate theat the MOS obtained from the objective evaluation model is in good agreement with that of subjective evaluation.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.17 no.9
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• pp.2191-2198
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• 2013

This paper proposes a RFID cell planning scheme for indoor location-awareness. We theoretically develop four objective functions that yield objective goals significant to the optimal design of a RFID cell topology and simulation is conducted to evaluate the performance of the proposed RFID cell planning scheme. We also evaluate the performance of the proposed technique after practically installing RFID readers in an indoor space to configure a RFID cell topology. Performance evaluations are conducted in terms of the following objective goals: minimal number of RFID readers for configuring a RFID cell topology, maximal RFID cell coverage areas for indoor location-awareness, minimal overlapping cells, and maximal indoor location-awareness accuracy.

• 한국신재생에너지학회:학술대회논문집
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• 2006.11a
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• pp.97-100
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• 2006

Accelerating ability is one of the most important performance of the vehicle. Unlike conventional internal combustion vehicles and power-assist hybrid vehicles, the maximized acceleration of dual mode hybrid vehicles is not simply. achieved by maximizing engine or motor torque Because of the dynamic stability of planetary gear, speeds and torques control of engine, motor 1 and motor 2 is essential and according to control value, acceleration performance is changed There are two control values which are velocity and torque for each component totalling six. These six values can be variables for an objective function. However, because three velocity variables can be regarded as only one variable speed ratio and the remaining three torque variables can be solved analytically, without complicated numerical algorithm the solution for the objective function can be obtained. This optimized solution shows the best performance possible to the specified dual mode system.