• International Journal of Naval Architecture and Ocean Engineering
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• 제5권3호
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• pp.333-347
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• 2013

The present study numerically models the interaction between a regular wave and the roll motion of a rectangular floating structure. In order to simulate two-dimensional incompressible viscous two-phase flow in a numerical wave tank with the rectangular floating structure, the present study used the volume of fluid method based on the finite volume method. The sliding mesh technique is adopted to handle the motion of the rectangular floating structure induced by fluid-structure interaction. The effect of the wave period on the flow, roll motion and forces acting on the structure is examined by considering three different wave periods. The time variations of the wave height and the roll motion of the rectangular structure are in good agreement with experimental results for all wave periods. The present response amplitude operator is in good agreement with experimental results with the linear potential theory. The present numerical results effectively represent the entire process of vortex generation and evolution described by the experimental results. The longer wave period showed a different mechanism of the vortex evolution near each bottom corner of the structure compared to cases of shorter wave periods. In addition, the x-directional and z-directional forces acting on the structure are analyzed.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2004년도 제29회 KOSCI SYMPOSIUM 논문집
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• pp.17-23
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• 2004

In the present work, the numerical model was refined to predict the thermal analysis of energy storage in a fixed beds during (charging ,storing, discharging) mode. The governing energy equations of both fluid and the solid particles along with their initial and boundary conditions are derived using a two-phase, one dimensional model. The refined model is carried out by taking into account change of (air density , air specific heat) with air temperature and also by taking into considerations heat losses from bed to surrounding. Finite difference method was used to obtain solution of two governing energy equations of both fluid and solid particles through a computer program especially constructed for this purpose. The temperature field for the air and the solid are obtained, also efficiency of energy stored inside the bed is computed. Finally using refined model the effect of air flow rate per unit area Ga (0.2, 0.3, and 0.4 kg/$m^2$-s), and inlet air temperature (200, 250, 300 $^{\circ}C$) on energy storage characteristics was studied in three mode ( charging ,storing, discharging). The rock particles of diameter 1 em is used as bed material in this research.

• 한국자동차공학회논문집
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• 제18권5호
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• pp.108-114
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• 2010

The injection nozzle of an electro-hydraulic injector is being opened and closed by movement of a injector's needle which is balanced by pressure at the nozzle seat and at the needle control chamber, at the opposite end of the needle. In this study, the effects of needle movement in a piezo-driven injector on unsteady cavitating flows behavior inside nozzle were investigated by cavitation numerical model based on the Eulerian-Lagrangian approach. Aimed at simulating the 3-D two-phase flow behavior, the three dimensional geometry model along the central cross-section regarding of one injection hole with real design data of a piezo-driven diesel injector has been used to simulate the cavitating flows for injection time by at fully transient simulation with cavitation model. The cavitation model incorporates many of the fundamental physical processes assumed to take place in cavitating flows. The simulations performed were both fully transient and 'pseudo' steady state, even if under steady state boundary conditions. As this research results, we found that it could analyze the effect the pressure drop to the sudden acceleration of fuel, which is due to the fastest response of needle, on the degree of cavitation existed in piezo-driven injector nozzle.

• 한국지구물리탐사학회:학술대회논문집
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• 한국지구물리탐사학회 2003년도 Proceedings of the international symposium on the fusion technology
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• pp.383-389
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• 2003

Clay minerals show a distinct induced-polarization phenomenon, which is one of the most important factors for predicting groundwater flow and contaminant transport. This paper presents a step-by-step process to estimate Cole-Cole parameters from spectral induced-polarization (IP) data measured on the surface of three-dimensional earth. First, the inversion of low-frequency resistivity survey data is made to identify the dc resistivity ${\rho}_dc$ of a volume having IP effects. The other parameters, chargeability m, time constant $\tau$, and frequency dependence c, are sought for the polarizable volume. Next, using multi-frequency data, c can be obtained as high or low asymptotes of the slope of log phase vs. log frequency. Further, for low m, intrinsic $\tau$ is approximated by apparent one, ${\tau}_a$, which is derived from the relation ${{\omega}{\tau}}_a$=1 at an angular frequency $\omega$, where the imaginary component of spectral IP data has an extreme value. Finally, to obtain intrinsic m a two-step linearized procedure has been derived. For a body of given $\tau$ and c, forward modeling with a progression of m values yields a plot of observed vs. intrinsic imaginary components for a frequency. Since this plot is essentially linear, to extract the intrinsic imaginary component is quite simple with an observed value. Using the plot of intrinsic imaginary component vs. m, intrinsic m is determined. We present a synthetic example to illustrate that the Cole-Cole parameters can be recovered from spectral IP data.

• 대한기계학회논문집B
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• 제41권10호
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• pp.685-691
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• 2017

증기 질량 유량의 변화에 따른 증기 터빈 노즐 단의 등엔트로피 노즐 효율을 계산하였다. 증기상태에 관한 압축성 Navier-Stokes 방정식을 기반으로 삼차원 수치해석 모델이 개발되었다. 두 가지의 삼차원 노즐 형상으로 압력, 온도, 속도, 마하수, 그리고 Markov 에너지 손실 계수가 계산되었다. 노즐 블레이드의 두께가 15mm에서 45mm로 증가함에 따라 최대 효율의 질량 유량은 0.9kg/s에서 1.6kg/s로 증가하였으며 최대 등엔트로피 효율은 각각 96.66%, 97.32%로 계산되었다. 질량 유량에 따른 등엔트로피 노즐 효율과 Markov 에너지 손실 계수를 계산하여 Markov 에너지 손실 계수와 등엔트로피 노즐 효율이 선형적 반비례 관계가 있음을 규명하였다.

• 한국추진공학회지
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• 제24권6호
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• pp.28-44
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• 2020

본 연구에서는 무인 항공기용 소형 2행정 엔진의 성능 개선을 위해 다양한 전송 포트 형상의 가스교환 성능을 평가하였다. 성능 평가를 위해 네 가지 전송 포트 형상에 따른 3차원 전산 유체 해석을 진행하였으며, 가스 교환 성능의 정량적 평가를 위해 이상적 소기 모델인 완전 대체 소기 모델과 완전 혼합 소기 모델을 바탕으로 새로운 3단계 소기 모델을 개발하여 해석 결과에 적용하였다. 2행정 엔진의 전송 포트 형상 변경을 통해 흡기의 단락 현상을 효과적으로 줄였으며 가스 교환 과정 동안의 실린더 내 난류 에너지 또한 크게 개선되었다. 또한, 전송 포트 형상 별 3단계 소기 모델의 적용을 통해 가스 교환 성능을 정량적으로 평가할 수 있었으며, 포트 형상 별 소기 양상의 차이를 확인할 수 있었다.

• 한국해안·해양공학회논문집
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• 제23권2호
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• pp.171-181
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• 2011

최근 생산비용을 절감하고 고밀도의 해양에너지발전시스템을 구축하기 위한 다양한 접근이 시도되고 있다. 본 연구에서는 방재와 파랑에너지의 이용이라는 두 목적을 달성하기 위하여 가장 효율적인 에너지의 변환시스템으로 널리 알려져 있는 파력발전장치인 진동수주형(OWC, Oscillating Water Column) 파력발전시스템을 적용한 curtain식 저반사구조물에 대해 단주기파랑의 작용하에서 공기터빈에 직접 작용하는 압축공기의 흐름속도와 구조물에 작용하는 파압에 관한 특성을 3차원수치실험으로부터 검토한다. 해석에서는 기체와 액체의 혼상동적현상을 동일한 지배방정식으로 해석하는 이상류(二相流) 수치모델에 기초한 3차원수치파동수로를 적용하였다. 이로부터 입사파고의 변화와 curtain wall의 침수심에 따른 압축공기의 속도변화 및 작용파압의 특성을 확인하였고, 더불어 반사율이 최소가 되는 주기에서 압축공기의 최대속도가 발생하는 것을 확인하였다.

• Journal of Advanced Research in Ocean Engineering
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• 제1권1호
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• pp.14-24
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• 2015

A three-dimensional multidirectional nonlinear numerical wave tank (NWT) based on the Navier-Stokes equations and the Finite Volume Method (FVM) is developed by using the two-phase hydrodynamic flow solver naoe-FOAM-SJTU based on the open source toolbox OpenFOAM. The free surface is capturing with the Volume Of Fluids (VOF). The directional wave including Stokes wave, solitary wave and nonlinear wave are simulated and verified. The multi-directional waves are also simulated with particular wave spectral such as JONSWAP and wave directional spreading function. The obtained numerical results show the capability of the solver to generate different type of multidirectional nonlinear waves accurately. Meanwhile, it implies that the presented NWT can easily extend to model the wave-structures interactions, which will be great help to the offshore structures design.

• International Journal of Ocean System Engineering
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• 제4권1호
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• pp.49-56
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• 2014

A three-dimensional multidirectional nonlinear numerical wave tank (NWT) based on the Navier-Stokes equations and the Finite Volume Method (FVM) is developed by using the two-phase hydrodynamic flow solver naoe-FOAM-SJTU based on the open source toolbox OpenFOAM. The free surface is capturing with the Volume Of Fluids (VOF). The directional wave including Stokes wave, solitary wave and nonlinear wave are simulated and verified. The multi-directional waves are also simulated with particular wave spectral such as JONSWAP and wave directional spreading function. The obtained numerical results show the capability of the solver to generate different type of multidirectional nonlinear waves accurately. Meanwhile, it implies that the presented NWT can easily extend to model the wave-structures interactions, which will be great help to the offshore structures design.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2011년 춘계학술대회논문집
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• pp.58-64
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• 2011

The objective of this paper is to investigate the gravity effect on the shape characters of natural supercavity. A finite difference solver along with an implicit, dual time, preconditioned, three-dimensional algorithm has been used to solve the two-phase Navier Stokes equations. Numerical solutions were performed for natural supercavitating flow past a disk for different cavitation and Froud numbers. The numerical results were compared with corresponding analytical results in quantitative manner and it was found that the shape of supercavity was reasonably predicted Numerical results indicated that the gravity effect can induce the asymmetry of supercavity. The asymmetry was apparent when the froud number was smaller so that for constant cavitation number when we reduced the froud number the opt of the axis of supercavity increased. Moreover, for specific froud number a decrease in cavitation number resulted in an increase in the offset of the supercavity Numerical results revealed that for froud number greater than 25 the gravity effect is negligible.