• 한국전산유체공학회:학술대회논문집
• /
• 한국전산유체공학회 2008년도 춘계학술대회논문집
• /
• pp.675-678
• /
• 2008

The effect of wave and current interactions on jet-like current flowing against waves was investigated based on numerical simulations. The numerical simulations are conducted by a combined model system of REF/DIF(a wave model) plus SHORECIRC(a current model) and a Boussinesq equation model, FUNWAVE. In the simulations, regular and irregular waves refracted due to the jet-like opposing current were focused along the core region of current, and the jet-like current was earlier spreaded when the waves had larger wave heights. The numerical results show that the rapid change of wave height distribution in transverse direction near current inlet plays a significant role to spread the jet-like current. In other words, the gradients of radiation stress forcing in transverse direction have a more significant effect on the jet-like current than its relatively small gradients forcing in flowing direction, which tend to accelerate the current, do. In conclusion, it is indispensible to take into account the interaction effect of wave transformation and current characteristics when waves meet the opposing jet-like current such as river mouth.

• 대한토목학회논문집
• /
• 제12권2호
• /
• pp.265-274
• /
• 1992

하천에 사고로 대량으로 유입된 유독성 유기오염물인 anthracene의 농도를 예측하기 위한 수학적 모형이 제안되었다. 이 수학적 모형은 물리적, 화학적 및 생물학적 반응을 고려한 6개의 미분방정식으로 구성되어 있으며, 5개의 입력변수와 9개의 반응계수를 포함하고 있다. 주어진 조건하에 제안된 수학적 모형을 대상으로 dynamic simulations와 민감도 분석을 수행한 결과 유입된 이 오염물의 농도를 검출한계내로 예측이 가능하였고, 용존 빛 부유고형물에 흡착된 이 오염물의 농도변화에 가장 큰 영향을 주어 가장 정확히 추정하여야할 주요 반응계수는 확산계수와 이동계수 및 흡착계수이었다. 이 연구에서 제안된 수학적 모형은 anthracene 뿐만아니라 이와 유사한 화학적 특성의 유기오염물의 경우에도 활용이 가능할 것으로 기대된다.

• ETRI Journal
• /
• 제41권6호
• /
• pp.838-849
• /
• 2019

We present a permanent magnet-based spherical wheel motor that can be used in omnidirectional mobility applications. The proposed motor consists of a ball-shaped rotor with a magnetic dipole and a hemispherical shell with circumferential air-core coils attached to the outer surface acting as a stator. Based on the rotational symmetry of the rotor poles and stator coils, we are able to model the rotor poles and stator coils as dipoles. A simple physical model constructed based on a torque model enables fast numerical simulations of motor dynamics. Based on these numerical simulations, we test various control schemes that enable constant-speed rotation along arbitrary axes with small rotational attitude error. Torque analysis reveals that the back electromotive force induced in the coils can be used to construct a control scheme that achieves the desired results. Numerical simulations of trajectories confirm that even without explicit methods for correcting the rotational attitude error, it is possible to drive the motor with a low attitude error (<5°) using the proposed control scheme.

• 천문학회지
• /
• 제41권1호
• /
• pp.7-15
• /
• 2008

We carried out a set of simulations to reproduce the performance of wide-field NEO surveys based on the revised population model of Near Earth Objects (NEOs) constructed by Morbidelli (2006). This is the first time where the new model is carefully compared with discovery statistics, and with the exception of population model, the simulation is identical to the procedure described in Moon et al. (2008). Our simulations show rather large discrepancy between the number of NEO discoveries made by the actual and the simulated surveys. First of all, unlike Bottke et al. (2002)'s, Morbidelli (2006)'s population model overestimates the number of NEOs. However, the latter reproduces orbit distributions of the actual population better. Our analysis suggests that both models significantly underestimate Amors, while overestimating the number of Apollos. Our simulation result implies that substantial modifications of both models are needed for more accurate reproduction of survey observations. We also identify Hungaria region (HU) to be one of the most convincing candidates that supply a large fraction of asteroids to the inner Solar System.

• 대한조선학회논문집
• /
• 제45권2호
• /
• pp.124-131
• /
• 2008

This paper presents the analysis of resistance performance and bow waves for the resistance-minimized hull form of small fishing boat by using numerical simulations and model tests. The resistance-minimized hull form is developed from an original hull form which is selected from existing small fisher boats in our country. In order to estimate the resistance performance for the original and the developed hull form, several numerical simulations and model tests are carried out. Marker and Cell(MAC) method and Marker-Density method are adopted to simulate the free-surface bow waves around advancing hull surface. The results of numerical simulations are compared with the model tests in towing tank. The results show that the resistance performance of the resistance-minimized hull form is improved than that of the original hull form. The results of this study will be a good guide to the hull form development of small fishing boats in future.

• 한국군사과학기술학회지
• /
• 제19권3호
• /
• pp.330-338
• /
• 2016

Impregnation of shear-thickening fluid(STF) into high-strength fabrics makes a considerable improvement on the ballistic performance of fabric armors. Understanding dissipation augmentation due to shear thickening effects on yarn-yarn and yarn-projectile friction is of great importance in liquid armor research. This paper takes a shearthickening effect into account in numerical simulations by using a velocity-dependent friction model. Impact simulations were performed to validate the friction model as well as to evaluate the ballistic performance of STF-fabrics. Impact simulations on neat fabrics were also conducted to provide baseline results for comparison.

• Wind and Structures
• /
• 제10권2호
• /
• pp.99-119
• /
• 2007

Estimations of wind flow over terrain are often needed for applications such as pollutant dispersion, transport safety or wind farm location. Whilst field studies offer very detailed information regarding the wind potential over a small region, the cost of instrumenting a natural fetch alone is prohibitive. Wind tunnels offer one alternative although wind tunnel simulations can suffer from scale effects and high costs as well. Computational Fluid Dynamics (CFD) offers a second alternative which is increasingly seen as a viable one by wind engineers. There are two issues associated with CFD however, that of accuracy of the predictions and set-up and simulation times. This paper aims to address the two issues by demonstrating, by way of an investigation of wind potential for the Askervein Hill, that a good level of accuracy can be obtained with CFD (10% for the speed up ratio) and that it is possible to automate the simulations in order to compute a full wind rose efficiently. The paper shows how a combination of script and session files can be written to drive and automate CFD simulations based on commercial software. It proposes a general methodology for the automation of CFD applied to the computation of wind flow over a region of interest.

• 한국지반환경공학회 논문집
• /
• 제20권9호
• /
• pp.5-11
• /
• 2019

최근 국내 도심지 지반침하 및 함몰이 빈번히 발생함에 따라 지반침하에 대한 불안감 또한 증가하고 있다. 그로 인해 GPR를 통한 지하 공동 탐지 지반함몰 모사실험 지반의 거동을 확인하기 위한 수치해석 등의 연구가 진행되고 있다. 국내의 경우 공동위험도 평가를 최근에 마련하였으나 현재의 지반상태 파악에 초점을 두었기 때문에 향후 발생할 수 있는 지반침하 및 함몰에 대한 예측을 정량적으로 하기 힘들다. 따라서 본 연구에서는 지반침하/함몰의 기하학적 변수인 공동크기와 토피두께를 변화시키며 총 30개의 case에 대한 수치해석을 수행하였다. 이 결과를 바탕으로 현재의 상태 뿐 아니라 향후 발생할 시기를 정량적으로 예측할 수 있는 방법을 제시하였다.

• International Journal of Naval Architecture and Ocean Engineering
• /
• 제12권1호
• /
• pp.843-855
• /
• 2020

X-plane submarines show better maneuverability as they have much longer span of control plane than that of cross plane submarines. In this study, captive model tests were conducted to evaluate the maneuverability of an X-plane submarine using Computational Fluid Dynamics (CFD) and a mathematical maneuvering model. For CFD analysis, SNUFOAM, CFD software specialized in naval hydrodynamics based on the open-source toolkit, OpenFOAM, was applied. A generic submarine Joubert BB2 was selected as a test model, which was modified by Maritime Research Institute Netherlands (MARIN). Captive model tests including propeller open water, resistance, self-propulsion, static drift, horizontal planar motion mechanism and vertical planar motion mechanism tests were carried out to obtain maneuvering coefficients of the submarine. Maneuvering simulations for turning circle tests were performed using the maneuvering coefficients obtained from the captive model tests. The simulated trajectory showed good agreement with that of free running model tests. From the results, it was proved that CFD simulations can be applicable to obtain reliable maneuvering coefficients for X-plane submarines.

• Nuclear Engineering and Technology
• /
• 제55권11호
• /
• pp.4048-4056
• /
• 2023

The feasibility of using the Monte Carlo code MCS to generate multigroup cross sections for nodal diffusion simulations RAST-F of liquid metal fast reactors is investigated in this paper. The performance of the MCS/RAST-F code system is assessed using steady-state simulations of the ANTS-100e core. The results show good agreement between MCS/RAST-F and MCS reference solutions, with a keff difference of less than 77 pcm and root-mean-square differences in radial and axial power of less than 0.5% and 0.25%, respectively. Furthermore, the MCS/RAST-F reactivity feedback coefficients are within three standard deviations of the MCS coefficients. To validate the internal thermal-hydraulic (TH) feedback capability in RAST-F code, the coupled neutronic/TH1D simulation of ANTS-100e is performed using the case matrix obtained from MCS branch calculations. The results are compared to those obtained using the MARS-LBE system code and show good agreement with relative temperature differences in fuel and coolant of less than 0.8%. This study demonstrates that the MCS/RAST-F code system can produce accurate results for core steady-state neutronic calculations and for coupled neutronic/TH simulations.