• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.2
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• pp.521-527
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• 2020

In offshore structures, the mean viscous drift force due to drag is considered to be a design part that has not been considered until recently. In particular, it is most important to calculate the drift force acting on a vertical cylinder considering both waves and currents in the low frequency region. This paper presents a process for deriving analytical solutions for the drift forces acting on a fixed vertical cylinder considering waves and currents. The area of the cylinder was considered by dividing it into a splash zone above the free surface and a submerged zone below the free surface. The presence of waves is considered only in the Splash Zone, and in the case of waves and currents, the equations were obtained for both the splash and submerged zones. The results show that drift forces occur due to the significant viscous effects in both the splash zone and the submerged zone. Therefore, the analytical solutions derived in this study can be used to calculate the drift force using the given design variables and form a theoretical basis for judging whether the magnitude of the drift force in each case has a dominant influence within a specific physical range.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.3
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• pp.503-509
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• 2020

In offshore floating structures, the viscous mean drift force due to drag is considered a design part that has not been considered until recently. In this paper, an analytical solution for the viscous mean drift forces on a floating vertical cylinder considering the waves and currents was obtained. The area was considered by dividing it into a splash zone above the free surface and a submerged zone below the free surface. In the case of waves, only the splash zone was considered; in the case of waves and currents, equations were obtained in both the splash zone and the submerged zone. The RAO results of previous studies were used to compare the calculated results with the drift forces acting on the fixed cylinder. Except for the case in only waves in the splash zone, the viscous mean drift force acting on the floating cylinder was larger than the drift force acting on the relatively fixed cylinder in most frequencies. In particular, the increase was greater when the currents were considered to be more important. Therefore, these results provide the inference for the viscous drift force due to drag in the design of floating offshore structures.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.33 no.5
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• pp.287-296
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• 2020

The wave-impact load on offshore structures can be divided into green-water and wave-slamming impact loads. These wave impact loads are known to have strong nonlinear characteristics. Although the wave impact loads are dealt with in the current classification rules in the shipping industry, their strong nonlinear characteristics are not considered in detail. Therefore, to investigate these characteristics, wave-impact loads induced by a breaking wave on a circular cylinder were analyzed. A model test was carried out to measure the wave-impact loads due to breaking waves in a two-dimensional (2D) wave tank. To generate a breaking wave, the focusing wave method was applied. A series of 2D tank tests under a horizontal wave impact was carried out to investigate the structural responses of the cylindrical structure, which were obtained from the measured model test data. According to the results, we proposed a structural damage-estimation procedure of an offshore tubular member due to a wave impact load. Furthermore, a recommended wave-impact load is suggested that considers the minimum required thickness of each member. From the experimental results, we found that the required minimum thickness is dependent on the impact pressure located in a three-dimensional space on the surface of a tubular member.

• Journal of the Korea Concrete Institute
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• v.25 no.4
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• pp.401-409
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• 2013

In the present study, numerical analysis was performed for hydrodynamic motion and structural performance on four different concrete floating structures, which have same cross-section but different length. The hydrodynamic analysis of floating structures is carried out using ANSYS AQWA with the different 34 wave load on regular wave period from three seconds to ten seconds in 35 m water depth. In order to evaluate structural performance of floating structures under the critical wave load which obtained from hydrodynamic analysis. The integrated analysis is also carried out through the mapping method, which can directly connect the wave-induced hydraulic pressure obtained form ANSYS AQWA to Finite Element Model in ANSYS Mechanical. As a results of this study, the hydrodynamic motion of floating structures is decreased as the length of structure increased. It means that the effect of wave-structure interaction is strongly dependent on the relationship between a wave period and a length of structure. Moreover, it is found that tension stress on bottom slab of floating structure is occurred by the critical wave load, the sectional force is not influenced by length of a structure.

• Journal of the Society of Naval Architects of Korea
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• v.30 no.4
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• pp.153-168
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• 1993

The ship sailing among waves suffers from the various wave loads that comes from its motion throughout its life. In the rationally-based design, the dynamic structural analysis is carried out using dynamic wave loads provided from the results of the ship motion calculation as the rigid body. This method is based on the linear theory assumed low wave height and small amplitude of motion. But at the rough sea condition, relatively high wave compared to the height ship's depth is induced the large ship motion, so configuration of the ship section below waterline changes rapidly at each time. This re-sults in a non-linear problem. Considering above situation we have already introduced the non-linear dynamic strength analysis method for the hull girder(refer vol. 29. No.4 November, 1992, Journal of SNAK). In this paper, estimation of the hull girder strength for various ship types such as tankers, containers and log carriers is carried out based on the introduced non-linear method. We expect that the results will be used as useful basic data for the es-timation of dynamic strength of ships in the rough sea.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.13 no.3
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• pp.195-201
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• 2001

The time simulation of slow drift motions of moored FPSO in waves is presented. The equation of motion based on Cummin's theory of impulse responses are employed, and are consisted of horizontal plane motions such as surge, sway and yaw. The added mass, wave damping coefficients, first order wave exciting forces and the second order wave drift forces involved in the equations are obtained from three-dimensional panel method in the frequency domain. The mooring lines are modeled as quasi-static catenary cable. As a numerical example, time domain analyses are carried out for a box-type FPSO in long crest irregular wave condition.

• Bulletin of the Society of Naval Architects of Korea
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• v.32 no.1
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• pp.36-39
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• 1995

본고에서는 고속선의 항행 안전성과 관련된 공통의 문제로서 파랑중 조종성능에 관해서 언급하 고자 한다. 파랑중 조종성능이 문제시되는 것은 선박이 추파(following seas) 또는 추사 파(quartering seas)를 받으면서 고속으로 항해할 때이다. 보통의 속도 범위에서 운항되는 일반 선박중에서도 컨테이너선, 어선 등과 같이 비교적 속력이 빠른 선박은 추사파중에서 선수 동 요가 크게 일어나며, 보침을 위한 조타량이 커짐과 동시에 힁동요가 심하게 일어나는 것으로 알려져 있다. 이러한 불안정 현상은 정도의 차이는 있을지언정 고속선에서도 마찬가지 경향을 보이고 있다. 파랑중 조종성능을 요약하면 추파 또는 추사파중에서의 복원성과 보침성 문제에 귀착된다, 추사파중에서의 복원성 문제는 선체 중심이 파정에 위치할 때 복원력 저하로써 설명될 수 있으며, 이러한 현상은 파장과 선체 길이가 거의 같고 선속이 파속과 거의 같은 조건하에서 일어난다고 알려져 있다. 이러한 조건을 만족하는 선속은 Froude수 0.4 정도로서 고속선의 운항 범위에 미달되는 속도이다. 추사파중에서의 보침성 문제는 브로칭(broaching-to) 현상으로써 설명될 수 있으며, 브로칭 현상은 파장이 선체 길이의 2배 정도이고, 선속과 파속이 거의 같은 조건하에서 일어난다고 알려져 있다. 이러한 조건을 만족하는 선속은 Froude수 0.56 정도로서 고속선의 운항 범위와 일치하는 속도이다. 따라서 본고에서는 고속선을 대상으로 하기 때문에 복원성 문제는 다루지 아니하고 브로칭 현상에 관해서만 간략히 기술하기로 한다.

• Journal of Navigation and Port Research
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• v.31 no.1 s.117
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• pp.21-27
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• 2007

The wave load and its influence on the response of offshore structure have been well investigated through the statistical approach based on the linear theory. The linear approach has a limitation to apply the extreme condition such as extreme wave, which corresponds to extreme value of wave spectrum. The main topic of present study is to develop an efficient numerical method to predict wave load induced by extreme wave. As a numerical method, finite element method based on variational principle is adopted. The frequency-focusing method is applied to generate the extreme wave in the numerical wave tank. The wave load on the bottom mounted vertical cylinder is investigated. The hydroelastic response of the vertical cylinder is also investigated so as to compare the wave loads with the rigid body case in the extreme wave condition.

• 한국기계연구소 소보
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• v.4 no.1
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• pp.71-76
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• 1981

• Journal of the Korean Society for Marine Environment & Energy
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• v.1 no.1
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• pp.102-111
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• 1998

Ocean monitoring facilities are divided into two types, fixed type and floating type. This paper deals with wane load calculation and mooring system for a floating monitoring facility. Wave load and drift forces are calculated for an example case of floating monitoring buoy To enlarge holding power of anchor, circular pile model test was performed. A program for horizontal force of circular pile in sand was made and the calculated result showed fairy good agreement with the result of model test. It is expected that this method will provide good estimation for the holding power of the prototype of circular pile anchor which is relied upon SCUBA activity for installation.