• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.2
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• pp.79-84
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• 2009

Turbocharger has been widely used in many passenger cars in application with diesel engines because of high power and fuel efficiency. However, flow-induced noise (whoosh or hissing noise) which is generated within a compressor during its operation at marginal surge line can deteriorate noise characteristics. Hissing noise excitation is associated with the generation of turbulence within the turbocharger compressor and radiated through the transmission path in a turbocharger system. In this study, a expansion muffler with lids is devised and installed in the transmission path to reduce the hissing noise. Acoustic and fluid dynamic characteristics for the muffler are investigated which are related to the unsteadiness of turbulence and pressure in the turbocharger system. A transfer matrix method is used to analyze the transmission loss of the muffler. A simple expansion muffler with lids is proposed for the reduction of high frequency component noise. Turbulence simulation is carried out by a standard k - ${\varepsilon}$ model. An optimal design condition of the muffler is obtained by extensive acoustic and fluid dynamic analysis on the engine dynamometer with anechoic chamber. A significant reduction of the hissing noise is achieved at the optimal design of the muffler as compared with the conventional muffler.

• Translational and Clinical Pharmacology
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• v.26 no.4
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• pp.155-159
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• 2018

For regulatory approval of a new drug, the most preferred and reliable source of evidence would be randomized controlled trials (RCT). However, a great number of drugs, being developed as well as already marketed and being used, usually lack proper indications for children. It is imperative to develop properly evaluated drugs for children. And expanding the use of already approved drugs for other indications will benefit patients and the society. Nevertheless, to get an approval for expansion of indications, most often with off-label experiences, for drugs that have been approved or for the development of pediatric indications, either during or after completing the main drug development, conducting RCTs may not be the only, if not right, way to take. Extrapolation strategies and modelling & simulation for pediatric drug development are paving the road to the better approval scheme. Making the use of data sources other than RCT such as EHR and claims data in ways that improve the efficiency and validity of the results (e.g., randomized pragmatic trial and randomized registry trial) has been the topic of great interest all around the world. Regulatory authorities should adopt new methodologies for regulatory approval processes to adapt to the changes brought by increasing availability of big and real world data utilizing new tools of technological advancement.

• Journal of Industrial Technology
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• v.22 no.A
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• pp.19-28
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• 2002

The Nelder-Mead simplex algorithm has been one of the most widely used methods for the nonlinear unconstrained optimization, since 1965. Recently, the new algorithm, (so-called the Fuzzy Simplex Algorithm), with fuzzy logic controllers for the expansion, reflection and contraction process of this algorithm has been proposed. In this paper, this new algorithm is developed. And, the formulation for the optimum design of the power screw's efficiency is made. And then, the developed fuzzy simplex algorithm as well as the original one is applied to this optimum design problem. The Fuzzy simplex algorithm results in a faster convergence in this problem, as reported in other study, too.

• Nuclear Engineering and Technology
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• v.31 no.2
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• pp.172-181
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• 1999

Series expansion methods to compute the exponential of a matrix have been compared by applying them to fuel depletion calculations. Specifically, Taylor, Pade, Chebyshev, and rational Chebyshev approximations have been investigated by approximating the exponentials of bum matrices by truncated series of each method with the scaling and squaring algorithm. The accuracy and efficiency of these methods have been tested by performing various numerical tests using one thermal reactor and two fast reactor depletion problems. The results indicate that all the four series methods are accurate enough to be used for fuel depletion calculations although the rational Chebyshev approximation is relatively less accurate. They also show that the rational approximations are more efficient than the polynomial approximations. Considering the computational accuracy and efficiency, the Pade approximation appears to be better than the other methods. Its accuracy is better than the rational Chebyshev approximation, while being comparable to the polynomial approximations. On the other hand, its efficiency is better than the polynomial approximations and is similar to the rational Chebyshev approximation. In particular, for fast reactor depletion calculations, it is faster than the polynomial approximations by a factor of ∼ 1.7.

• Particle and aerosol research
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• v.10 no.3
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• pp.93-97
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• 2014

Condensation particle counter (CPC) has been one of the most important basic instrument for measuring number concentration of submicron aerosols. The principle of the CPC is to expose aerosols to a supersaturated vapor and cool down which causes adiabatic expansion. The particles grow by heterogenous nucleation to a sufficient size for easy detection by optical method. However, for growth by condensation, CPC essentially needs both saturater and condensor causing a heavy system. Therefore, it is hard to install commercial CPC to tethered balloon package system. In this study, we developed customized CPC for tethered balloon package system called Hy-CPC which is lighter and smaller in structure than commercial CPCs, and evaluated activation efficiency and detection efficiency by Hy-CPC using electrostatic method (electrometer and Faraday cup).

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.17 no.1
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• pp.120-144
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• 2023

With the expansion of digital communication networks, a considerable number of randomization techniques have been invented and implemented to enhance the different data transmission algorithms' levels of security. Steganography is among the data transmissions techniques used to hide secret data. Nowadays, several randomization techniques have been used in steganography to elevate the security of transmitted data. Unfortunately, the majority of these techniques lack some simplicity, efficiency, and flexibility, in addition to other limitations. This research presents a new randomization technique called Rand-Stego. Rand-Stego could be applied/practiced over any steganography technique. It provides simplicity and efficiency and elevates the security level. Examples of implementing the proposed technique on some steganography algorithms will be explored. The proposed and current techniques will be compared. The obtained results show Rand-Stego's superiority in terms of efficiency and flexibility when compared to the current techniques.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.8
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• pp.512-520
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• 2020

This study analyzed the relative operational efficiency and impact factors of regional public hospitals to present benchmarking points for enhancing the efficiency of inefficient regional public hospitals. The survey targets collected and utilized the internal resources and management performance data from 34 regional public hospitals in Korea over the past five years, from 2014 to 2018. The final 33 regional public hospitals were surveyed, excluding Jinan Regional Public Hospital, which opened in 2015, the middle of the survey period. The general characteristics and input/output variables were analyzed by frequency analysis and technical statistics analysis, and Data Envelopment Analysis was performed to measure the operational efficiency index and relative comparison. According to the study, there were 11 efficient hospitals (33.3%) and 22 inefficient hospitals (66.7%). Of the 22 inefficient hospitals, 13 (IRS: Increasing Returns to Scale) required scale expansion, and nine (DRS: Decreasing Returns to Scale) required scale reduction or rebalancing. The significance of this study was that an analysis of the relative efficiency and influencing factors presented specific alternatives or directions that could help enhance the efficiency of the growth of regional public hospitals, sustainable management, and expansion of publicness.

• Journal of Electrical Engineering and Technology
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• v.9 no.5
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• pp.1511-1519
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• 2014

The objective of this paper is to propose a modelling of a small compressed air energy storage system, which drives an induction generator based on a field-oriented control (FOC) principle for a renewable power generation. The proposed system is a hybrid technology of energy storage and electrification, which is developed to use as a small scale of renewable energy power plant. The energy will be transferred from the renewable energy resource to the compressed air energy by reciprocating air compressor to be stored in a pressurized vessel. The energy storage system uses a small compressed air energy storage system, developed as a small unit and installed above ground to avoid site limitation as same as the conventional CAES does. Therefore, it is suitable to be placed at any location. The system is operated in low pressure not more than 15 bar, so, it easy to available component in country and inexpensive. The power generation uses a variable speed induction generator (IG). The relationship of pressure and air flow of the compressed air, which varies continuously during the discharge of compressed air to drive the generator, is considered as a control command. As a result, the generator generates power in wide speed range. Unlike the conventional CAES that used gas turbine, this system does not have any combustion units. Thus, the system does not burn fuel and exhaust pollution. This paper expresses the modelling, thermodynamic analysis simulation and experiment to obtain the characteristic and performance of a new concept of a small compressed air energy storage power plant, which can be helpful in system designing of renewable energy electrification. The system was tested under a range of expansion pressure ratios in order to determine its characteristics and performance. The efficiency of expansion air of 49.34% is calculated, while the efficiency of generator of 60.85% is examined. The overall efficiency of system of approximately 30% is also investigated.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.3282-3287
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• 2007

Lean combustion is one of the most promising method for increasing engine efficiency and reducing the exhaust emission from SI gas engines. Due to the possibility of partial burn and misfire, however, under lean burn operation, stable flame kernel formation and fast burn rate are needed to guarantee a successful subsequent combustion. Experiment data were obtained on a single-cylinder CNG fueled SI engine to investigate the effect of direct injection, spark timing and variation of injection timing. Experimental results show that lean burn limit is ${\lambda}$=1.3 with port injection, and expansion of lean burn limit ${\lambda}$=1.4 with direct injection method, due to increase of turbulence intensity in cylinder and stratified charge. Combustion duration in lean region is improved by using the variation of injection timing.

• Journal of Ocean Engineering and Technology
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• v.17 no.1
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• pp.8-15
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• 2003

본 논문에서는 투과성 유연막이 수면밑 일정한 깊이에 수평으로 잠겨있을 때 투과성 유연막에 의한 파랑제어성능을 살펴보았다. 해석 방법으로는 유체문제는 고유함수전개법 (Eigenfunction expansion method)을 사용하였고, 유연막과 파랑의 상호작용문제는 Newmann 이 제시한 유탄성 이론 (hydro-elastic theory)을 채택하였다. 막의 투과성 효과를 고려하기 위하여 수평막에서의 수직속도는 수평막 상하의 압력차에 선형적으로 비례하며 그들 사이에는 위상차가 없다고 가정한 Darcy 법칙을 사용하였다. 투과성 수평막의 설계변수 (초기장력, 길이, 잠긴 깊이, 공극율)와 입사파의 주파수를 바꿔가면서 반사율과 투과율 그리고 에너지 손실율을 살펴보았다.