• Journal of the Korean Society of Propulsion Engineers
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• v.16 no.3
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• pp.41-48
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• 2012

A study to determine the optimal jet conditions for maximizing altitude of the sounding rocket is conducted. The behavior of a simplified one-dimensional momentum equation including aerodynamic drag is investigated. The case where an analytic solution exists and the case where the mass flow rate is constant are calculated. The solutions are compared with numerical solutions. It is shown that there are the optimal jet conditions for maximizing altitude of a sounding rocket and the optimal condition is a function of the rocket mass ratio.

• Journal of the korean Society of Automotive Engineers
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• v.15 no.3
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• pp.36-46
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• 1993

In CVT vehicle, the engine speed is completely decoupled from the vehicle speed within the range from maximum transmission ratio to minimum transmission ratio. This allows the engine to operate in optimal state(e.g. best fuel economy or maximum power mode.) In this study, the CVT control algorithm for optimal operation of engine is suggested. In order to implement the real time digital control of electro-hydraulic CVT system, a software called CVTCON has been developed. CVTCON also includes the CVT operation module, (2) system test module, (3) system control module and (4) data management module. By using the CVTCON and the electro-hydraulic CVT system, two modes of experiments were carried out: constant throttle opening mode and acceleration mode. From the experimental result, it was found that the algorithm suggested in this study showed optimal operation of the CVT system.

• The Korean Journal of Applied Statistics
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• v.13 no.2
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• pp.207-224
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• 2000

Generally cluster size is predetermined when we use the stratified two-stage cluster sampling But in case that the sizes of clusters vary greatly one may want to make the sizes to be about equal. In this paper we study the optimal cluster size in stratified twostage cluster sampling. Also we find the optimal primary sampling unit sizes and optimal secondary sampling unit sizes under the given cost restriction.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.20 no.10
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• pp.702-709
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• 2008

In this paper, the optimal thermal storage time of an air-conditioning system with slab thermal storage in office building was analyzed on the basis of the gradient method algorithm. The sum of room temperature deviation and heat extraction rate was set to the criterion function. It was calculated that four hours is the optimal thermal storage time under the standard evaluation criterion. Furthermore, some case studies were executed by controlling ratio of weight functions of room temperature deviation and heat extraction rate in criterion function. It is possible to design many kinds of optimal operation of an air-conditioning system with slab thermal storage by controlling ratio of the weight functions in criterion function.

• Journal of the Semiconductor & Display Technology
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• v.21 no.4
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• pp.163-167
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• 2022

In this paper, an optimization design method of a diffuser using Bernoulli's theorem was reviewed. The aspect ratio of the cylindrical diffuser chamber and the diameter ratio of the air inlet and outlet were used as design parameters. For the optimal design of the cylindrical diffuser chamber, the air flow inside the chamber was simulated using ANSYS while changing the aspect ratio of the chamber. In order to confirm the simulation results, the diffuser manufactured using the laser processing machine was measured. Through ANSYS simulation and measurement, it was found that the optimal design condition was when the aspect ratio (chamber height/radius) of the diffuser chamber was 1/2 and the diameter ratio of the air inlet and outlet was also 1/2.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.20 no.4
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• pp.31-38
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• 2021

In this paper, we proposed an optimal design for determining the shape of a lifting lug freely by applying a multivariate function to the D-type lug, which is commonly used in shipyards. We derived the optimal aspect ratio of the lug through structural analysis and analyzed the safety and behavior of the lug aspect ratio. As a result, two types of final candidates, both lighter than the existing lug weight, were suitable for the ratio. They were found to have the greatest force at an angle of 45 degrees when a load of 100 tons was imposed. When the horizontal and vertical feature ratio of the lug was 1:3, it showed excellent results in terms of safety rates while maintaining weight reduction and functional aspects.

• Journal of the Korea institute for structural maintenance and inspection
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• v.11 no.4
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• pp.152-158
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• 2007

This is a fundamental research to utilize alkali activated cement(AAC) in concrete. The compressive strength of AAC concrete were measured for the various mixing ratios of activator/fly ash, and the mixing ratios of water glass, NaOH, and water among the activators. The mixing ratio of fine and coarse aggregates was maintained constantly. The relationships between the compressive strength and mixing ratios were analyzed to find the optimal mixing ratio of AAC concrete. As the results, the optimal mixing ratio of activator/fly ash in AAC concrete was 0.7, and that of water glass, NaOH, water among the activator was 4.0:1.0:2.5 for the maximum compressive strength.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38B no.6
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• pp.446-453
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• 2013

Clustering schemes have been adopted as an efficient solution to prolong network lifetime and improve network scalability. In such clustering schemes cluster ratio is represented by the rate of the number of cluster heads and the number of total nodes, and affects the performance of clustering schemes. In this paper, we mathematically analyze an optimal clustering ratio in wireless sensor networks. We consider a multi-hop to one-hop transmission case and aim to provide the optimal cluster ratio to minimize the system hop-count and maximize packet reception ratio between nodes. We examine its performance through a set of simulations. The simulation results show that the proposed optimal cluster ratio effectively reduce transmission count and enhance energy efficiency in wireless sensor networks.

• The KSFM Journal of Fluid Machinery
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• v.15 no.3
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• pp.32-38
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• 2012

This paper is aimed to propose the design database(DB) of the inline micro-turbine for 5kW class. CFD analysis is performed to investigate the effect of a turbine on each parameter. This study showed that RadhaKrishna's data is different from the 5kW class in the low-head and the micro-turbine. Therefore, new DB for the design of inline micro-turbine for 5kW class could be needed. This study configured new design DB for the design of inline micro-turbine for 5kW class. The DB of this study showed that the optimal hub ratio(Dp/DR), the optimal body ratio(Db/DR) and the optimal range of body length ratio(Lh/DR) is 50%, 1.1 and 2.3 to 2.9, respectively.

• Proceedings of the KIPE Conference
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• 2016.07a
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• pp.231-232
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• 2016

This paper investigates the design of multi-winding coupled inductor for minimum inductor current ripple. Based on the general circuit model of coupled inductor together with the operating principles of dc-dc converter, the relationship between the ripple size of inductor current and the coupling factor is derived under the different duty ratio. The optimal coupling factor of n-phase multi-winding coupled inductor which corresponds to a minimum inductor ripple current becomes -(1/n-1), i.e. a complete inverse coupling without leakage inductance, as the duty ratio of steady-state operating point approaches 1/n, 2/n, ${\cdots}$ or (n-1)/n. In an opposite manner, the optimal coupling factor value of zero, i.e. zero mutual inductance, is required when the duty ratio of steady-state operating point approaches either zero or one. Therefore, coupled inductors having optimal coupling factor can minimize the ripple current of inductor and inductor size.