• 한국해양공학회지
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• 제24권1호
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• pp.20-33
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• 2010

The paper deals with strength design of a riser support installed on floating production storage and offloading (FPSO) vessel under various loading conditions - operation, extreme, damaged, one line failure case (OLFC) and installation. The design problem is formulated such that thickness sizing variables are determined by minimizing the weight of a riser support structure subject to stresses constraints. The initial design model is generated based on an actual FPSO riser support specification. The finite element analysis (FEA) is conducted using MSC/NASTRAN, and optimal solutions are obtained via moving least squares method (MLSM) in the context of response surface based approximate optimization. For the meta-modeling of inequality constraint functions of stresses, a constraint-feasible moving least squares method (CF-MLSM) is used in the present study. The method of CF-MLSM, compared to a conventional MLSM, has been shown to ensure the constraint feasibility in a case where the approximate optimization process is employed. The optimization results present improved design performances under various riser operating conditions.

• ALGAE
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• 제34권4호
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• pp.303-313
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• 2019

Floating seaweed rafts are a surface-pelagic habitat that serve as substrates for benthic flora and fauna. Since 2008, Sargassum horneri clumps have periodically invaded the Korea Strait. In this study, the polymerase chain reaction-free small-organelles enriched metagenomics method was adopted to identify the species of epibiotic eukaryotes present in floating S. horneri fronds. A total of 185 species were identified, of which about 63% were previously undetected or unreported in Korean waters. The rafts harbored a diverse assemblage of eukaryotic species, including 39 Alveolata, 4 Archaeplastida, 95 Opisthokonts, 4 Rhizaria, and 43 Stramenopiles. Of these 185 taxa, 48 species were found at both Sargassum rafts collection stations and included 24 Stramenopiles, 17 Alveolata, and 7 Opisthokonts. Among these, the highest proportion (50%) of species was photo-autotrophic in basic trophic modes, while the proportion of phagotrophic, osmo- or saprotrophic, and parasitic modes were 43.8%, 4.2%, and 2.1%, respectively. This study demonstrates the contribution of floating Sargassum rafts as dispersal vectors that facilitate the spread of alien species.

• International Journal of Fluid Machinery and Systems
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• 제9권3호
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• pp.194-204
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• 2016

Floating ring seals offer an opportunity to reduce leakage flows significantly in rotating machinery. Accordingly, they have been applied successfully to rotating machinery within the last several decades. For rocket turbopump applications, fundamental behavior and design philosophy have been revealed. However, further work is needed to explore the rotordynamic characteristics associated with rotor vibrations. In this study, rotordynamic forces for floating ring seals under rotor's whirling motions are calculated to elucidate rotordynamic characteristics. Comparisons between numerical simulation results and experiments demonstrated in our previous report are carried out. The three-dimensional Reynolds equation is solved by the finite-difference method to calculate hydrodynamic pressure distributions and the leakage flow rate. The entrance loss at the upstream inlet of the seal ring is calculated to estimate the Lomakin effect. The friction force at the secondary seal surface is also considered. Numerical simulation results showed that the rotordynamic forces of this type of floating ring seal are determined mainly by the friction force at the secondary seal surface. The seal ring is positioned almost concentrically relative to the rotor by the Lomakin effect. Numerical simulations agree quite well with the experimental results.

• 대한조선학회논문집
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• 제56권1호
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• pp.11-22
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• 2019

In this paper, a Rankine source method is applied and validated to analyze the hydrodynamic response of a three-dimensional floating structure in the frequency domain. The boundary value problems for radiation and diffraction problem are solved by using a desingularized indirect boundary integral equation method (DIBIEM). The DIBIEM is simpler and faster than conventional methods based on the numerical surface integration of Green's function because the singularities of Green's function are located outside of fluid regions. In case of floating structure with complex geometry, it is difficult to desingularize the singularities of Green's function consistently. Therefore a mixed approach is carried out in this study. The mixed approach is partially desingularized except singularities of the body. Wave drift loads are calculated by the middle-field formulation method that is mathematically simple and has fast convergence. In order to validate the accuracy of the developed program, various numerical simulations are carried out and these results are analyzed and compared with previously published calculations and experiments.

• 대한환경공학회지
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• 제39권5호
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• pp.277-281
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• 2017

최근 강우는 짧은 시간에 많은 비가 오는 특성을 자주 나타낸다. 이런 기상현상 때문에, 초기유출수와 합류식하수관거 월류수의 유입유량과 농도도 변화되고 있다. 이와 같이 유입조건이 변동되는 경우에는, 높은 수면적부하율을 가지는 부상방법이 공공수역의 수질관리에 적합하다. 왜냐하면 부상법은 공공수계의 요구조건을 충족 할 수 있기 때문이다. 현재까지 이러한 부상법의 검증과 진단을 위하여, 공급공기량과 유입SS량의 비율을 반영하여 왔다. 그러나 불행하게도 이러한 방식은 기술진단과 검증을 위한 판단기준으로는 그 한계를 가진다. 왜냐하면 부상속도와 시간요소가 상이한 버블분포에 의해 달라지기 때문이다. 부상속도와 시간은 처리시설의 용량에 영향을 준다. 왜냐하면 시간인자가 시설의 규모를 결정하기 때문이다. 그러므로, 동일한 공급공기량과 유입SS농도간 비율조건에서의 버블분포특성과 부상시간특성을 운영 및 기술진단 및 평가를 위한 판단기준으로 적용하여야만 한다. 따라서 이러한 필요에 따라, 이 논문 내용은 버블분포와 부상시간간 관계의 분석에 대한 실증적 일반화에 관한 연구이다.

• 대한조선학회논문집
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• 제30권2호
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• pp.43-53
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• 1993

부유체 강제동요문제를 수치해석하는 데에는 두가지 어려움이 따른다. 첫째는 교차점주위의 급격한 유동이고 둘째는 무한원방처리이다. 본 논문에서는 무한원방처리에 주안점을 두어, 자유표면의 Taylor 전개 및 F.F.T. 적용으로 계산시간을 단축시켜 수치해석하였다. 즉 Green 정리를 이용하여 해를 표현한 후, 축차방법에 의하여 해를 구한다. 축차단계에서는 계산식을 자유표면 기울기에 대하여 Taylor 전개하여 Convolution 형태로 변형한 후 F.F.T. 를 적용함으로써 계산시간을 O(Nlog N)으로 유지할 수 있었다. 수치검증을 위하여 부유체 선형문제와 압력장의 비선형 문제를 수치해석하여 비교하였고, 이를 확장하여 부유체의 강제동요문제를 수치해석하였는데, 계산시간을 O(Nlog N)으로 유지하면서 수치해석할 수 있었다.

• Journal of Advanced Marine Engineering and Technology
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• 제33권5호
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• pp.705-712
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• 2009

The state changes of ocean covered over 70% of earth surface are one of the greatest factor of weather catastrophe. Recently weather extraordinary events are followed by steep increase of sea water temperature and scientists in various fields are studying and warning the weather changes. In this paper, floating buoy is developed to monitor ocean environments via Orbcomm satellite and a method is proposed to increase measurement accuracy of sea water temperature with common low price temperature sensor. Experimental results are presented to illustrate the usability and effectiveness of the developed system. A web-based real time monitoring system is built to monitor ocean environmental information such as sea and air temperature, salinity according to the position of buoy through the internet for user convenience.

• 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.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1999년도 하계학술대회 논문집 E
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• pp.2287-2289
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• 1999

In this paper, a new method for calculating capacitance in multi-electrode system with arbitrarily shape is presented. This new approach based on divergence theorem and Gauss's law is achieved by Surface-Contacted Element(SCE) for Gaussian surface. To evaluate capacitance in multi-electrode system, two dimensional finite element method using only the elements which is contacted one nod (PE: Point-Element) or two nod (FE: Face-Element) with surface is employed. The proposed SCE method has short computing time to calculate capacitance which is because it uses only SCE elements and needs one calculation loop while exiting FEM method in servral loops. This method is verified by application in calculating capacitance using potential detection device model which is composed with anode, cathode, and floating electrode.

• Journal of Ship and Ocean Technology
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• 제8권3호
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• pp.8-17
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• 2004

A numerical method is developed for computing the free surface flows around a transom stern of a ship at a high Froude number. At high speed, the flow may be detached from the flat transom stern. In the limit of the high Froude number, the problem becomes a planning problem. In the present study, we make the finite-element computations for a transom stern flows around a wedge-shaped floating ship. The numerical method is based on the Hamilton's principle. The problem is formulated as an initial value problem with nonlinear free surface conditions. In the numerical procedures, the domain was discretized into a set of finite elements and the numerical quadrature was used for the functional equation. The time integrations of the nonlinear free surface condition are made iteratively at each time step. A set of large algebraic equations is solved by GMRES(Generalized Minimal RESidual, Saad and Schultz 1986) method which is proven very efficient. The computed results are compared with previous numerical results obtained by others.