• The Korean Journal of Rheology
• /
• v.11 no.2
• /
• pp.112-121
• /
• 1999

An MR(Magneto-Rheological) fluids damper is designed and applied to vibration suppression of a 1/4 car model. The damping constant of MR damper changes according to input current which is controlled in a semi-active way. Several control algorithms are compared in simulations and experiments. The advantage of the proposed Frequency shaped LQ control is that passenger comfort is emphasized in the range of 4~8Hz and driving safety is emphasized around the resonance frequency of unsprung mass.

• Journal of KIISE:Computer Systems and Theory
• /
• v.37 no.2
• /
• pp.90-102
• /
• 2010

Flash memory has been widely used as an important storage device for consumer electronics. For the flash memory-based storage systems, FTL (Flash Translation Layer) is used to handle the mapping between a logical page address and a physical page address. Especially, log buffer-based FTLs provide a good performance with small-sized mapping information. In designing the log buffer-based FTL, one important factor is to determine the mapping structure between data blocks and log blocks, called associativity. While previous works use static associativity fixed at the design time, we propose a new log block mapping scheme which adjusts associativity based on the run-time workload. Our proposed scheme improves the I/O performance about 5~16% compared to the static scheme by adjusting the associativity to provide the best performance.

• KDI Journal of Economic Policy
• /
• v.19 no.1
• /
• pp.3-50
• /
• 1997

경제자유화(經濟自由化)와 규제완화(規制緩和)라는 세계적인 흐름과 함께 우리나라도 1992년 이후 자본시장(資本市場)을 점진적으로 개방(開放)하고 있다. 본 연구에서는 우선 몇몇 핵심 거시경제변수(巨視經濟變數)들의 상관관계(相關關係)가 자본거래의 자유화와 더불어 어떻게 변화할 것인가에 대한 이론적(理論的)인 배경(背景)을 설명하고 있다. 여기에서는 무엇보다도 자본자유화(資本自由化)와 더불어 나타나게 되는 실질환율체상(實質換率切上)및 경상수지적자(經常收支赤字)의 의미를 합리적인 경제주체들이 자원(資源)을 보다 효율적(效率的)으로 배분(配分)하고자 하는 노력의 결과로 나타나는 현상으로 파악하고 있다. 즉 자본시장의 개방은 상대적으로 높은 국내의 자본생산성 및 실질이자율을 향한 해외자본의 유입(자본수지(資本收支)의 흑자(黑字))을 초래하며, 대외부문의 항등식을 고려하는 한 이는 경상수지(經常收支)의 적자(赤字)로 연결된다. 또한 본 연구에서는 신고전파적(新古典派的) 장기모형(長期模型)과 케인즈적(的) 단기모형(短期模型)에 기초한 거시경제 모형을 구성하고 자본자유화(資本自由化)의 속도(速度), 환율(換率)및 통화정책(通貨政策)의 변화에 따른 거시경제의 동태적(動態的) 시간경로(時間經路)를 계량화하고자 노력하였다. 예를 들어 경상수지적자(經常收支赤字)의 폭은 자본자유화의 추진속도 및 거시정책에 의존할 것이나, 예상하지 못한 큰 충격이 도래하지 않는 경우 향후 2~3년간 GDP 대비 3% 내외에 이를 것으로 추정되며, 그 이후에는 실질이자율의 하락과 함께 적자폭도 축소될 것으로 나타나고 있다. 그리고 실질환율(實質換率)의 시간경로는 자본유입과 함께 지속적으로 절상될 수는 없으며 개방초기의 절상에 이어 점차 절하되는 추세에 놓이게 될 것이다. 자본시장의 개방에 따른 경상수지의 적자는 국내의 (실물)자본축적을 보다 용이하게 함으로써 실질이자율(實質利子率)을 하락(下落)시킬 것으로 기대되나 그 효과는 연 0.2%포인트 이내에 머무를 것으로 추정되었다. 아울러 자본자유화의 초기단계에 발생할 환율절상은 수출의 가격경쟁력을 약화시켜 단기적(短期的)으로 경기침체(景氣沈滯)를 유발할 수 있으나 중장기적(中長期的)으로 성장잠재력(成長潛在力)을 확충시킨다.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.3 no.4
• /
• pp.47-57
• /
• 1983

The parameter of impulse response of groundwater proposed by Kraijenhoff, that is, the reservoir coefficient j is determined on the basis of the least squares criteria. The degree (${\alpha}$) which expresses how much each sequential storm contributes to groundwater flow through the saturated soil is obtained by the optimization techniques which minimize deviations between observed and derived runoff hydrograph, and the convolution summation for the linear theory is used. A numerical example for this study is carried out for a storm event of Goose Creek basin near Leesburg, Virginia. As the results, the groundwater unit hydrograph and baseflow were able to be obtained. The used optimization technique is suited to the purpose of this study in case of the constraints. It is judged that the results allow the determination of baseflow.

• The KIPS Transactions:PartB
• /
• v.13B no.4 s.107
• /
• pp.369-376
• /
• 2006

The degradation and its inverse modeling can achieve restoration of corrupted image, caused by scaled digitization and electronic transmission. De-speckle process on the noisy document(or SAR) images is one of the basic examples. Non-linearity of the speckle noise model may hinder the inverse process. In this paper, our study is focused on investigation of the restoration methods for bi-level document image degraded by the impulse noise model. Our study shows that, on bi-level document images, the weighted-median filter and the Lee filter methods are very effective among other spatial filtering methods, but wavelet filter method is ineffective in aspect of processing speed: approximately 100 times slower. Optimal values of the weight to be used in the weighted median filter are investigated and presented in this paper.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.17 no.3
• /
• pp.231-240
• /
• 2016

Recently, fake test data of power cables in nuclear power plants was a terrible shock to the citizens. Some cable companies manipulated the test data to make unfair profits. In addition, fake test data cases were found in military supplies. The fake test data cases focused on parts of army's tank, armored car. This paper propose a new method that can detect fake test data using known statistical methods. In addition, the method was implemented in Microsoft Excel to allow easy use. Lastly, a check sheet was proposed to check the validity of the test system of military suppliers. By detecting and checking the fake test data, it is expected that our new method will play an important role in quality assurance of military supplies.

• Composites Research
• /
• v.12 no.4
• /
• pp.42-54
• /
• 1999

FMLC(Fiber-Metal Laminate Composites) is a new structural material combining thin metal laminate with adhesive fiber prepreg, it nearly include all the advantage of metallic materials, for example: good plasticity, impact resistance, processibility, light weight and excellent fatigue properties. This research studied the optimum design of the FMLC subject to various loading conditions using genetic algorithm. The finite element method based on the shear deformation theory was used for the analysis of FMLC. Tasi-Hill failure criterion and Miser yield criterion were taken as fitness functions of the fiber prepreg and the metal laminate, respectively. The design variables were fiber orientation angles. In genetic algorithm, the tournament selection and the uniform crossover method were used. The elitist model was also used to be effective evolution strategy and the creeping random search method was adopted in order to approach a solution with high accuracy. Optimization results were given for various loading conditions and compared with CFRP(Carbon Fiber Reinforced Plastic). The results show that the FMLC is more excellent than the CFRP in point and uniform loading conditions and it is more stable to unexpected loading because the deviation of failure index is smaller than that of CFRP.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.41 no.7
• /
• pp.489-495
• /
• 2017

An experimental study on supersonic jets produced by supersonic nozzles at low operating pressure ratio is conducted. In the present experiments, particle image velocimetry (PIV) was employed to quantitatively specify the jet flowfield, and a color Schlieren optical method was applied to observe the same jets qualitatively. Convergent-divergent nozzles were used to generate the jet flow with design Mach numbers of 1.5 and 1.8. Nozzle pressure ratios (NPRs) were varied from 4 to 7. A good comparison of the jet size from the Schlieren images with the theoretical values is obtained. The obtained images clearly showed the major features of the under-expanded jet and over-expanded jet.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.3 no.4
• /
• pp.58-66
• /
• 1999

The flow characteristics of supersonic ejectors is often subject to compressibility, unsteadiness and shock wave systems. The numerical works carried out thus far have been of one-dimensional analyses or some Computational Fluid Dynamics(CFD) which has been applied to only a very simplified configuration. For the design of effective ejector-pump systems the effects of secondary mass flow on the supersonic ejector flow should be fully understood. In the present work the supersonic ejector-pump flows with a secondary mass flow were simulated using CFD. A fully implicit finite volume scheme was applied to axisymmetric compressible Navier-Stokes equations. The standard two-equation turbulence model was employed to predict turbulent stresses. The results obtained showed that the flow characteristics of constant area mixing tube types were nearly independent of the secondary flow rate, but the flow fields of ejector system with the second-throat were strongly dependent on the secondary flow rate due to the effect of the back pressure near the primary nozzle exit.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.30 no.3
• /
• pp.191-198
• /
• 2017

To study the behavior of structures subject to blast loads it is important to calculate the loads due to the explosives accurately, especially in the case of interior explosions. It is known that numerical method based on computational fluid dynamics can estimate relatively accurate blast load due to the interior explosion including reflection effect. However, the numerical method has disadvantages that it is difficult to model the analysis and it takes much time to analyze it. Therefore, in this study, the analytical method which can include the reflection effect of the interior explosion was studied. The target structures were set as the slabs of residential buildings subject to interior explosion that could lead to massive casualties and progressive collapses. First, the numerical method is used to investigate the interior explosion effect and the maximum deflection of the slab which was assumed to be elastic, and compared with the analytical method proposed in this study. In the proposed analytical method, we determine the weighting factor of the reflection effect using the beam theory so that the explosion load calculation method becomes more accurate.