• Journal of Korean Society of Coastal and Ocean Engineers
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• v.32 no.1
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• pp.1-10
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• 2020

The application of multiphase flows is increasingly being applied to analyze phenomena such as single phase flows where the fluid boundary changes continuously over time or the problem of mixing a liquid phase and a gas phase. In particular, multiphase flow models that take into account incompressible Newtonian fluids for liquid and gas are often applied to solve the problems of the free water surface such as wave fields. In general, multi-phase flow models require time-based the surface tracking of each fluid's phase boundary, which determines the accuracy of the final calculation of the model. This study evaluates the advection performance of representative VOF-type boundary tracking techniques applied to various CFD numerical codes. The effectiveness of the FCT method to control the numerical flux to minimize the numerical diffusion in the conventional VOF-type boundary tracking method and advection calculation was mainly evaluated. In addition, the possibility of tracking performance of free surface using CIP method (Yabe and Aoki, 1991) was also investigated. Numerical results show that the FCT-VOF method introducing an anti-diffusive flux to precent excessive diffusion is superior to other methods under the confined conditions in this study. The results from this study are expected to be used as an important basic data in selecting free surface tracking techniques applied to various numerical codes.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.31 no.3
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• pp.141-145
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• 2018

The paper presents a new dynamic displacement measurement system. The developed displacement measurement system consists of a sensor module, a base module and a computation module. The sensor module, which contains a force-balanced accelerometer and low-price RTK-GNSS, measures the high-precision acceleration with sampling frequency of 100Hz, the low-precision displacement and velocity with sampling frequency of 10Hz. The measured data is transferred to the computation module through LAN cable, and precise displacement is estimated in real-time with 100Hz sampling frequency through a two stage Kalman filter. The field test was conducted at San Francisco-Oaklmand Bay bridge, CA, USA to verify the precision of the developed system, and it showed the RMSE was 1.68mm.

• The Korean Journal of Financial Management
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• v.12 no.1
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• pp.129-143
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• 1995

우리 나라의 금융기관들은 금융환경(金融環境)의 급격한 변화 속에서 일대 전환기를 맞고 있다. 대내적으로는 금리자유화를 비롯한 금융자율화(金融自律化)의 추진, 금융산업의 개편 등의 금융구조 조정이 진행되고 있고, 대외적으로는 국내금융시장에 대한 개방압력(開放壓力)이 가중되고 있다. 본 연구의 목적(目的)은 이상의 다양한 금융환경의 변화 중에서 1991년과 1993년에 실시된 1,2단계 금리자유화조치가 은행의 경영위험에 어떠한 영향을 미쳤는지를 증권시장(證券市場)의 반응을 통하여 규명하고자 한다. 구체적으로 일반적인 예상과 같이 금리자유화로 인하여 은행의 위험이 증가하였는지 아니면 금리자유화가 은행의 자금조달과 운용에 있어서 자율성과 유연성을 확보해 주어서 오히려 은행위험을 감소시켰는지를 실증적으로 검증한다. 주가자료를 이용하는 증권시장의 반응을 통한 은행위험의 분석은 은행에 관련된 재무정보를 신속하고 충분히 반영하는 효율적 시장이며 회계자료를 이용하여 은행위험을 추정하는 방법이 부적절하다는 가정하에서 합리화된다. 은행 위험은 은행감독 당국의 관심대상인 총위험과 은행주식 투자자의 관심대상인 체계적 위험의 두요소를 대상으로 한다. 본 연구의 증권시장반응을 통한 실증분석결과에 의하면 금리자유화조치 이후 은행의 위험은 예상과는 달리 증가하지 않은 것으로 나타났다. 은행총위험은 증가하지 않았으며 체계적 위험은 오히려 2차 금리자유화 이후 하락하는 결과를 보여준다. 이는 금리자유화 조치가 은행의 자금조달과 운영에 있어서 운신의 폭을 넓혀줌으로써 금리 변동폭 증대로 인한 위험증가를 상쇄함을 의미한다. 이러한 결과는 미국의 금리자유화조치에 관련된 대부분의 연구결과와 일치한다. 또한 위험은 개별은행의 재무특성에 따라서 상이한 변화를 보여주었다. 특히 자산규모가 작은 후발은행의 경우 자금조달과 운영의 측면에서의 제한이 완화됨으로써 위험이 감소함을 보여준다. 따라서 정부당국자는 금리자유화의 긍정적 효과를 극대화하는 방향으로 적극적으로 금리자유화를 추진하는 것이 바람직하다.

• Journal of Korean Tunnelling and Underground Space Association
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• v.13 no.5
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• pp.413-430
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• 2011

Consideration on the explosion resistant design of infrastructure has increased in the recent years. The explosion load is caused by gas explosion or bomb blast. In this study an analytical model is developed, whereby the tunnel structure is divided in several elements that are schematized as single degree of freedom mass-spring-dashpot systems on gas explosion. Using this simple model a sensitivity analysis has been carried out on tunnel structure design parameters such as explosive peak pressure, duration of the load, thickness of structure, burial depth. Finite element method was used to investigate the dynamic response and plastic zone of a tunnel under gas explosion. And it was found from the comparison of the analysis results that there are slight differences in the response of the intermediate wall between the single degree of freedom mass-spring-dashpot model and FEM.

• Korean Journal of Agricultural and Forest Meteorology
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• v.7 no.1
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• pp.91-97
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• 2005

Class A evaporation pan has been used throughout the world to measure free water evaporation mainly by manual observation once a day. In this study, a new automatic water level measurement method is used for understanding of free water evaporation and numerical analysis. This new technique measures the weight of buoyancy bar in water, and does not need calibration because it is not affected by water density change with water temperature. Field observations of evaporation were made near Haenam Meteorological Station over paddy field located in southwestern Korea from 20 April to 30 May 2004 and the data from ten clear days (16 - 25 May) were used for this analysis. The observed total evaporation was about 50.7mm during this period whereas the estimated from an empirical equation was 50.4mm. As expected, the pan evaporation is well correlated with wind speed and the vapor pressure deficit between the water surface and the air.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.2
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• pp.41-50
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• 2003

In this paper, nonlinear parallel structural analyses are introduced by using the parallel multifrontal solver and damage localization for 2D and 3D crack models is presented as the application of nonlinear parallel computation. The parallel algorithms related with nonliear reduce the amount of memory used is carried out because many variables should be utilized for this highly nonlinear damage analysis. Also, Riks' continuation method is parallelized to search the solution when strain softening occurs due to damage evolution. For damage localization problem, several computational models having up to around 1-million degree of freedoms are used. The parallel performance in this nonlinear parallel algorithm is shown through these examples and the local variation of damage at crack tip is compared among the models with different degree of freedoms.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39A no.3
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• pp.161-163
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• 2014

We consider the device-to-device (D2D) communication underlaying multi-cell interference system, in which the cellular downlink (DL) resource is reused by K cells and two D2D transmission links within each cell. In this paper, it has been shown that the downlink intra-cell and inter-cell interference can be effectively handled by interference alignment (IA) technique, as long as the simultaneous D2D links are properly selected or power-controlled so that they may not incur interference to the base stations in the same and neighbor cells. In particular, we provides the IA technique that can achieve the theoretically maximum possible degree of freedom (DOF), demonstrating that a total of (K+1)M degrees of freedom (DOFs) can be achieved for K-cell interference system with two underlaying D2D links, where base stations, cellular UE's, and D2D UE's all have M transmit and receive antennas.

• Journal of the Society of Naval Architects of Korea
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• v.39 no.1
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• pp.16-27
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• 2002

A level-set method is used for analyzing the behaviors of gas bubbles in two fluids incompressible viscous flow domain. The governing equations are solved by using a finite volume method. The numerical results are verified by comparing with the experimental and other computational results. Computations for the deformations and motions of one or multi-bubbles in the flow domain with the initial undisturbed free interface are conducted. It can be seen that numerical results for different surface tension and density ratio arise very different behaviors of bubbles. When bubbles rise near the free interface, the free interface gives some great influence on the behaviors of bubbles. The present results computed by a level-set method give useful information about the properties of bubble motions and deformations.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.1
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• pp.90-100
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• 1993

A finite element formulation of vibration control of a laminated plate with piezoelectric sensor/ actuators is presented. Classical lamination theory with the induced strain actuation and Hamilton's principle are used to formulate the equations of motion of the system. The total charge developed on the sensor layer is calculated from the direct piezoelectric equation. The equations of motion and the total charge are discretized with 4 node, 12 degrees of freedom quadrilateral plate bending elements with one electrical degree of freedom. The mass and stiffness of the piezoelectric layer are introduced by treating them as another layer in laminated plate. Piezoelectric sensor/actuators are distributed, but discrete due to the geometry of electrodes. By defining an i.d. number of electrode for each element, modelling of electrodes with variable geometry can be achieved. The static response of a piezoelectric bimorph beam to electrical loading and sensor voltage to given displacement are calculated. For a laminated plate under the negative velocity feedback control, the direct time response by the Newmark-.betha. method and damped frequencies and modal damping ratios by modal state space analysis are derived.

• Elastomers and Composites
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• v.35 no.2
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• pp.98-105
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• 2000

Using FT-IR and contact angle measurements it is observed that the chemical surface treatments on virgin carbon blacks lead to a change of the surface properties, including surface functionality and surface free energy It is found that the developments of surface functional groups on acidically and basically treated (ACB and BCB in this study, respectively) carbon blacks are largely correlated with the specific component of surface free energy of the carbon blacks. However, a significant advantage of compounding composites is gained by BCB or NCB (nonpolar chemical treatment) specimens, resulting in improving the hardness, elongation at break, and tensile strength. Particularly, it is seen that the tensile strength of the composites are greatly depended on the London dispersive component of surface free energy determined from the contact angle measurements. It is then concluded that the London dispersion component of carbon blacks plays an important role in an organic rubbers-based compounding composite system.