• 한국항해학회지
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• 제10권2호
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• pp.139-155
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• 1986

In this paper the dynamic effects due to the free water motions in tanks upon the lateral motion of a floating body in regular waves are calculated, in order to obtain the relationship between a motion of a floating body and that of the free water in tanks. Under the assumption that the fluid is ideal and motion amplitudes are small, velocity potential of the fluid in tanks is calculated by the source distribution method and the hydrodynamic forces and moments are calculated by the integration of fluid pressures over the tank surface. Hydrodynamic effects of the fluid on the floating body are expressed in terms of added mass and coupling coefficient obtained from the integration. Computations are carried out for ship with seven wide center tanks and comparisons between the liquid cargo loading case and the rigid cargo loading case are shown.

• International Journal of Naval Architecture and Ocean Engineering
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• 제7권2호
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• pp.409-425
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• 2015

In this paper, we employ a dynamics modeling method for investigating a multi-body dynamics system of semi-submersible autonomous underwater vehicles consisting of a towing vehicle operated near the water surface, a tow cable, and a towfish. The towfish, which is towed by a marine cable for the purposes of exploration or mine hunting, is modeled with a Six-Degree-of-Freedom (6-DOF) equation of motion that reflects its hydrodynamics characteristics. The towing cable, which can experience large displacements and deformations, is modeled using an absolute nodal coordinate formulation. To reflect the hydrodynamic characteristics of the cable during motion, the hydrodynamic force due to added mass and the drag force are imposed. To verify the completeness of the modeling, a few simple numerical simulations were conducted, and the results confirm the physical plausibility of the model.

• 천문학회보
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• 제43권2호
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• pp.54.1-54.1
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• 2018

Recent observational studies suggest that the environmental effects can shape the evolution of galaxies in clusters. In an attempt to better understand this process, we perform idealized radiation-hydrodynamic simulations of RAM pressure stripping on star-forming galaxies using RAMSES-RT. We find that extended HI disks are easily stripped by moderate ICM winds, while there is no significant decrease in the total mass of molecular gas. RAM pressure tends to compress the molecular gas, leading to enhanced star formation especially when the gaseous disk is hit by edge-on winds. On the other hand, strong ICM winds that are expected to operate at the centre of clusters strip both HI and molecular gas from the galaxy. Interestingly, we find that the strong ICM winds can induce the formation of relatively dense (~1H/cc) HI gas clouds at a distance from the disk.

• Wind and Structures
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• 제32권4호
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• pp.341-354
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• 2021

Articulated towers are one of the class of compliant offshore structures that freely oscillates with wind and waves, as they are designed to have low natural frequency than ocean waves. The present study deals with the dynamic response of a double-pendulum articulated tower under hydrodynamic and aerodynamic loads. The wind field is simulated by two approaches, namely, single-point and multiple-point. Nonlinearities such as instantaneous tower orientation, variable added mass, fluctuating buoyancy, and geometrical nonlinearities are duly considered in the analysis. Hamilton's principle is used to derive the nonlinear equations of motion (EOM). The EOM is solved in the time domain by using the Wilson-θ method. The maximum, minimum, mean, and standard deviation and salient power spectral density functions (PSDF) of deck displacement, bending moment, and central hinge shear are drawn for high and moderate sea states. The outcome of the analyses shows that tower response under multiple-point wind-field simulation results in lower responses when compared to that of single-point simulation.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1993년도 봄 학술발표회논문집
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• pp.165-172
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• 1993

A non-linear mathematical model has been developed for the dynamic analysis of the reactor internals. The model includes a lumped mass and stiffness with non-linear members such as gap-spring. As hydrodynamic couplings have also been considered in the model, the effect of fluid/structure interaction between internals components due to their immersion in a confining fluid can be studied for the dynamic response analysis. The reactor internals responses for seismic and pipe break excitations have been calculated for the case of with-and without-hydrodynamic couplings.

• 소음진동
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• 제7권4호
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• pp.655-661
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• 1997

건물내 동적계가 수중에 있고 유체동적효과가 클 경우, 건물을 지진절연하면 일반적인 경향과는 달리 계의 지진응답이 오히려 증가될 수 있다. 본 논문에서는 건물내 수조에 잠긴 계에 대하여 단순화된 복합모델의 동적해석을 통하여 건물의 지진절연이 건물내 수중계의 지진응답에 어떻게 그리고, 최대로 얼마나 영향을 주는지를 보인다. 이 때 응답을 줄이기 위한 내진설계방안으로서 유체질량효과를 조절하는 유체간극의 최적화를 수행하여 그 효과를 살펴보았고, 간극조절이 곤란한 경우의 대안으로서 지진절연된 건물내 수중계를 다시 지진절연하는 방안을 제안하였으며 적절한 이중절연방식의 조합에 대한 효율을 비교하였다.

• 천문학회보
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• 제44권2호
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• pp.55.3-55.3
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• 2019

We present a pipeline to estimate baryonic properties of a galaxy inside a dark matter (DM) halo in DM-only simulations using a machine trained on high-resolution hydrodynamic simulations. As an example, we use the IllustrisTNG hydrodynamic simulation of a (75 h^-1 Mpc)³ volume to train our machine to predict e.g., stellar mass and star formation rate in a galaxy-sized halo based purely on its DM content. An extremely randomized tree (ERT) algorithm is used together with multiple novel improvements we introduce here such as a refined error function in machine training and two-stage learning. Aided by these improvements, our model demonstrates a significantly increased accuracy in predicting baryonic properties compared to prior attempts --- in other words, the machine better mimics IllustrisTNG's galaxy-halo correlation. By applying our machine to the MultiDark-Planck DM-only simulation of a large (1 h^-1 Gpc)³ volume, we then validate the pipeline that rapidly generates a galaxy catalogue from a DM halo catalogue using the correlations the machine found in IllustrisTNG. We also compare our galaxy catalogue with the ones produced by popular semi-analytic models (SAMs). Our so-called machine-assisted semi-simulation model (MSSM) is shown to be largely compatible with SAMs, and may become a promising method to transplant the baryon physics of galaxy-scale hydrodynamic calculations onto a larger-volume DM-only run. We discuss the benefits that machine-based approaches like this entail, as well as suggestions to raise the scientific potential of such approaches.

• 해양환경안전학회:학술대회논문집
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• 해양환경안전학회 2004년도 춘계학술발표회
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• pp.107-112
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• 2004

선박의 대형화 추세에 따른 항만 운영의 효율성 및 대형 선박의 접안 안전성을 향상시키기 위해서는 먼저 선체에 작용하는 접안에너지를 합리적으로 산출하여야 한다. 선박의 접안에너지는 방충재와 같은 항만시설물의 설계에 대한 허용 기준을 결정하는 변수임과 동시에 도선사 및 선박의 조선자에게는 예인선의 필요 마력이나 접안속도 둥을 결정하는데 있어 중요한 판단 요소로 활용된다. 본 연구에서는 현재 사용되고 있는 운동역학적인 방법을 토대로 한 접안에너지 산출 방법에 대해 유체역학적인 측면에서 문제를 제기하고, 부두 전면의 수심과 선박의 형상에 따라 변화하는 천수역 선체부가질량을 고려한 접안에너지의 산출 방법을 제안한다. 또한 천수역에서 선체에 작용하는 부가질량을 고려한 접안에너지 산출 방법을 사용하여 1600TEU급에서 12000TEU급까지의 컨테이너 선박을 대상으로 계통적으로 각각의 접안에너지를 계산하고, 현행의 접안에너지 산출방법과 비교 검토를 실시한다.

• 한국항공우주학회지
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• 제39권3호
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• pp.232-241
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• 2011

하이브리드 로켓은 난류 산화제 유동과 고체 추진제의 기화로 인한 분사 유동 사이의 상호 작용에 의해 복잡한 형태의 혼합 전단층이 존재한다는 특별한 성질을 가지고 있다. 본 논문에서는 유동 간섭에 의해 표면에서 발생하는 진동 유동의 물리적 특성을 연구하기 위하여 압축성 효과를 고려한 질량분사가 있는 덕트 유동의 LES(Large Eddy Simulation) 해석을 수행하였다. 계산 결과에 따르면, 기화 질량이 분출됨에 따라 주유동방향 와류의 특성이 강해지고 국부적으로 발생하는 역류 현상을 근거로 벽면 근방에서 원주방향 와류가 생성됨을 확인하였다. 그리고 시간 특성을 갖고 나타나는 와류 흘림 현상은 혼합 전단층에 기인한 유동 불안정성에 의해 촉진되었으며, 분출유동에 의해 발달한 고유 진동 유동을 의미하는 압력 섭동의 특정 진동수가 $\omega$=8.8에서 검출됨을 확인하였다.

• 천문학회보
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• 제41권1호
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• pp.39.4-40
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• 2016

We aim to investigate formation of satellite sub-galactic structures around isolated dwarf galaxies using cosmological hydrodynamic zoom simulations. For this, we modify a cosmological hydrodynamic code, GADGET-3, in a way that includes gas cooling down to T~10K, gas heating by universal reionization when z < 8.9, UV shielding for high density regions of $n_{shield}$ > $0.014cm^{-3}$, star formation in the dense regions ($n_H$ > $100cm^{-3}$), and supernova feedback. To get good statistics, we perform three different simulations for different target galaxies of the same mass of ${\sim}10^{10}M_{sun}$. Each simulation starts in a cubic box of a side length of 1Mpc/h with 17 million particles from z = 49. The mass of dark matter (DM) and gas particle is $M_{DM}=4.1{\times}10^3M_{sun}$ and $M_{gas}=7.9{\times}10^2M_{sun}$, respectively, thus each satellite sub-galactic structure can be resolved with more than hundreds or thousands particles. We analyze total 90 sub-galactic structures that have formed outside of the main halos but infall the main halos. We found that 1) mini halos that interact more with the other mini halos tend to accrete the more mass, 2) mini halos that interact more before the reionization tend to form more stars, 3) mini halos with the more interaction tend to approach closer to the galactic center and have the lower orbital circularity, 4) survivals even in the strong tidal fields evolve baryon dominated system, such as globular clusters.