• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.31 no.2
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• pp.159-164
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• 2013

It is well known that a single moving camera video is capable of extracting the 3-dimensional position of an object. With this in mind, current research performed image-based monitoring to establish a floating structure model using a camcorder system. Following this, the present study extracted frame images from digital camcorder video clips and matched the interest points to obtain relative 3D coordinates for both regular and irregular wave conditions. Then, the researchers evaluated the transformation accuracy of the modified SURF-based matching and image-based displacement estimation of the floating structure model in regular wave condition. For the regular wave condition, the wave generator's setting value was 3.0 sec and the cycle of the image-based displacement result was 2.993 sec. Taking into account mechanical error, these values can be considered as very similar. In terms of visual inspection, the researchers observed the shape of a regular wave in the 3-dimensional and 1-dimensional figures through the projection on X Y Z axis. In conclusion, it was possible to calculate the displacement of a floating structure module in near real-time using an average digital camcorder with 30fps video.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.36 no.2
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• pp.70-79
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• 2024

In this study, we introduce a linear spectral method capable of simulating wave generation and transformation caused by a moving bottom in a 3-dimensional space. The governing equations are linear dynamic free-surface boundary conditions and linear kinematic free-surface boundary conditions, which are solved in Fourier space. Solved velocity potential and free-surface displacement should satisfy continuity equation and kinematic bottom boundary condition. For numerical analysis, a 4th order Runge-Kutta method was utilized to analyze the time integral. The results obtained in Fourier space can be converted into velocity potential and free-surface displacement in a real space using inverse Fourier transform. Regular waves generated by various types of moving bottoms were simulated with the linear spectral method. Additionally, obliquely generated regular waves using specified bottom movements were simulated. The results obtained from the spectral method were compared to analytical solutions, showing good agreement between the two.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.25 no.4
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• pp.244-254
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• 2013

In this study, a method has been developed for estimating the change of nearshore random waves in response to sea-level rise, by extending the method proposed for regular waves by Townend in 1994. The relative changes in wavelength, refraction coefficient, shoaling coefficient, and wave height for random waves are presented as functions of relative change in water depth. The changes in wavelength and refraction coefficient are calculated by using the significant wave period and principal wave direction in the regular-wave formulas. On the other hand, the changes in shoaling coefficient and wave height are calculated by using the formulas proposed for shoaling and transformation of random waves in the nearshore area including surf zone. The results are proposed in the form of both formulas and graphs. In particular, the relative change in wave height is compared with the result for regular waves.

• Journal of the Korean Society of Marine Environment & Safety
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• v.23 no.5
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• pp.558-565
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• 2017

Accurate prediction of wave-structure interactions is important in the safety and design cost effectiveness of fixed and floating offshore structures exposed to extreme environmental conditions. In this study, regular waves and circular column structure interactions for four circular columns in regular waves are analyzed. To simulate 3D two-phase flow, open source computational fluid dynamics libraries, called OpenFOAM, were used. When the four circular columns are arranged in a square array, the interactions according to the incident slopes of the regular waves are analyzed. The wave run-up in the circular column surface was compared according to the slope of the incident wave. It was confirmed that high amplitude waves are generated between the circular columns due to the interaction between the circular column and the incident wave. It is expected that this analytical result will be used as the basic data of the study on the air gap due to the interaction between the structure and incident wave.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.20 no.1
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• pp.49-61
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• 2008

This study investigates the characteristics of stem waves along a vertical wall generated by obliquely incident random waves through laboratory experiments conducted in a wave basin and numerical simulations using REF/DIF S model developed by Kirby and $\ddot{O}zkan$(1994). The investigation is focused on the effect of random waves on the propagation characteristics of stem waves and the difference or similarity between monochromatic and random waves. The results of REF/DIF S model are compared with laboratory measurements and good agreements are obtained. The relative significant wave height along a wall is almost same with monochromatic condition, but the wave pattern along normal to the wall shows a significant difference.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.4 no.2
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• pp.65-75
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• 1984

A comparative study between several methods for the marine drilling riser analysis is carried out. One static analysis method and four dynamic methods are studied. The dynamic analysis methods used are two time domain methods using regular and random waves, and two frequency domain methods using the conventional and an improved linearization techniques. Two different sizes of risers are investigated. The analysis model of the structure is based on the beam-column element with lateral wave/current loads in a vertical plane. The forces on the riser are calculated using a modified farm of the Morison's equation. The finite element method is used to solve the equation for several wave/current conditions.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.11 no.2
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• pp.95-106
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• 1999

A numerical model is represented to calculate the wave fields such as the reflected waves, the transmitted waves and the depth-averaged velocities over submerged breakwaters for the normally incident wave trains of nonlinear mono-chromatic wave and solitary wave. The finite amplitude shallow water equations with the effects of bottom friction are solved numerically in time domain using an explicit dissipative Lax-Wendroff finite difference method. The numerical model is verified by comparisons with the other numerical results and the measured data. It is found that the submerged breakwater may be more useful for protecting the energies of monochromatic waves rather than solitary waves. Finally, the armor stability on submerged breakwater is indirectly analyzed using the hydrodynamic characteristics of flow fields.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2017.11a
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• pp.238-240
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• 2017

파랑 중 선수파의 영향을 줄이기 위해 도입된 Axe Bow선형은 파랑 중 항해 시 선수부에 과도한 Spray현상이 발생한다. 이를 억제하고자 선수 부가물이 도입되었으나, 수치해석적 연구가 필요할 것으로 판단하였다. 선수 부가물은 Spray rail에서 착안하였으며, 구현이 쉽고 설계 파라미터를 제시 할 수 있는 Barge형상으로 적용하였다. 본 연구에서는 선수 부가물의 길이 변화에 따른 Axe Bow 선형의 Spray 억제를 수치해석적으로 고찰하였다.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2018.11a
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• pp.7-8
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• 2018

파 중 선박 조종운동시험을 위하여 선박해양플랜트연구소 공학수조 내 자유항주시험 시스템을 구성하였다. 모형선 내에 제어계측 장비와 PC를 탑재하고 육상 관제 PC에서 원격 통제, 모니터링하며, 레이저 추적 방식으로 모형선 실시간 위치를 계측하였다. 준비된 시스템으로 KVLCC2 1/100 축소모형선의 규칙파 중 선회시험을 수행하였다. 파 중 선회성능은 초반의 전진거리, 전술직경, 정상선회 시의 궤적밀림 거리, 각도 등으로 지수화할 수 있다. 각 지수를 추출하여 분석하였고, 동일한 파장 조건에 대한 궤적밀림 경향은 유사함을 보였다.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.28 no.6
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• pp.332-349
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• 2016

OLAFOAM is the powerful CFD code and is an expanded version of $OpenFOAM^{(R)}$, for wave mechanics simulation. The $OpenFOAM^{(R)}$ does provide many solvers to correspond to each object of the numerical calculation in a variety of fields. OLAFOAM's governing equation bases on VARANS (Volume-Averaged Reynolds-Averaged Navier-Stokes) equation, and the finite volume method is applied to numerical techniques. The program is coded in C++ and run on the Linux operating system. First of all, in this study, OLAFOAM was validated for 1) wave transformation inside porous structure under bore and regular wave conditions, 2) wave transformation by submerged breakwater under regular wave condition, and 3) regular wave transformation and resultant vertical velocity distribution under current by comparison with existing laboratory measurements. Hereafter, this study, which is almost no examination carried out until now, analyzed closely variation characteristics of water surface level, wave height, frequency spectrum, breaking waves, averaged velocity and turbulent kinetic energy around porous submerged breakwater in the wave and current coexisting field for the case of permeable or impermeable rear beach. It was revealed that the wave height fluctuation according to current direction(following or opposing) was closely related to the turbulent kinetic energy, and others.