• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2002.09a
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• pp.319-322
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• 2002

그라우팅으로 지반 개량된 조간대 퇴적층의 지층구조를 규명하기 위한 방법으로 전기비저항탐사, 굴절법 탄성파탐사, 지하레이더탐사를 실시하였다. 연구대상 지반의 10m 전후 심도에서 해수의 영향을 받는 수평의 저비저항대가 발달하며, 저비저항대는 모래가 우세한 지층에 해당한다. 지반의 탄성파 속도는 1~3km/sec의 범위로 조간대의 미고결 퇴적층과 비교할 때 매우 높은 속도에 보여준다. 지반의 높은 속도는 지반 개량의 효과로 판단된다. 지하레이더탐사에서 퇴적층의 구성 물질에 따라 교반 정도가 달지는데 모래층은 퇴적물과 주입제의 교반이 잘 이루어져 불규칙한 반사면으로 나타나며, 점토층은 교반이 불량하여 개량된 부분은 주상으로 관찰된다. 물리탐사의 결과와 시추조사를 대비할 때 지반 개량은 기반암까지 시행되었으며, 양호한 암반을 지시하는 고비저항대와 고속도층은 내륙으로 갈수록 깊은 심도를 보여준다. 이것은 지반 개량 이전의 기반암 심도와는 상반되는 것으로 지반 개량의 효과는 해안방면의 지층에서 잘 나타난다.

• Journal of Ocean Engineering and Technology
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• v.11 no.3
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• pp.116-123
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• 1997

세계적으로 수요가 증대하고 있는 고속선의 설계시 승선감 또는 내항성은 필수적으로 고려되어야 하는 중요요소이다. 고속선은 필연적으로 과도한 운동을 동반하며 그로 인해 승객들은 극심한 멀미와 구토 등 불쾌한 승선감을 경험하게 된다. 근래에 항공 및 육상 교통수단들의 고급화에 따라 해양 운항선사들도 선박품질의 고급화와 괘적한 승선감 확보에 비상한 관심을 보이며 승객 유치 및 승선률 제고를 도모하고 있다. 본 논문은 고속쌍동선에 대한 내항성능을 추정하고 그 해석결과를 실험과 비교하였다. 상하동요 및 종동요 간의 선형 연성 운동방정식을 사용하였고, 규칙파에 대한 상하동요의 응답특성 곡선을 구하였다. 또한 불규칙파에 대한 운동응답을 추정하기 위하여 ITTC파도 스펙트럼을 적용하였으며, 본 고속쌍동선의 운동성능에 미치는 선수 및 선수각의 영향을 고찰하였다.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.36 no.1
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• pp.33-44
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• 2000

Ships in a seaway will encounter dangerous situation, such as slamming, stranding, and capsizing. The number of capsizing is small, but the loss due to them is very large from the viewpoint of human life, property, and the environmental pollution. The number of capsizing of fishing vessels is about 62% of total number of capsizing, and the half of them is originated from the operational mistake in a seaway. So the dynamics and the capsizing phenomena are to be studied, and the guide for the safe operation of a fishing vessel in a seaway are to be specified. The hydrodynamic forces consist of radiation forces (which are due to the motion of a ship), Froude-Krylov forces (which is due to the incoming waves), and diffraction forces (which is due to the wave and ship interaction). These forces are calculated by well-known strip method. Using the calculated forces, the motion of a ship in a regular sea is obtained. In the real seaway, the waves are very irregular, therefore the statistical analysis is very helpful. In this paper, using the results of the motion in a regular seaway and the wave spectrum, the motion in a irregular seaway are obtained and analyzed.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.20 no.2
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• pp.238-245
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• 2008

To evaluate wave reflection and transmission from buoyant flap-typed storm surge barriers, hydraulic experiments were performed by using regular and irregular wave conditions. Buoyant flap-typed storm surge barriers consist of buoyant main body connected with foundation structure in the seabed by hinge. The characteristics of wave reflection, transmission and dynamic response of the structure were investigated for 36 regular and 4 irregular wave conditions. It was also evaluated the usage of plain plate attached on the buoyant main body as one of alternatives to control wave reflection and transmission. From the hydraulic experiments, it was found that the case of plain plate attached on the offshore side is very effective to improve the wave transmission as well as reflection. But, the effect of the case on the harbor side might be negligible.

• Journal of the Society of Naval Architects of Korea
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• v.42 no.3
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• pp.212-219
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• 2005

Real sea waves in a towing wave basin have been generated using random periodic motion of the segmented wave makers and the wave reflections of sidewalls. Theoretically, the real sea waves can be described by the superposition of many random oblique waves. This paper introduces numerical real sea wave generation in a rectangular wave basin using spectral method that uses a superposition of orthogonal functions which have to satisfy the Laplace equation. Oblique regular waves, long crested irregular waves and real sea waves were simulated and met the requirement of sidewall wave reflection and wave absorption. MLM (Maximum Likelihood Method) and Spatial Fourier Transform were used in order to obtain propagated wave direction characteristics. The estimated results proved the usefulness of the method and the performances showed reasonable directional patterns comparing with generating patterns.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.13 no.4
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• pp.263-272
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• 2001

Recently, some attempts to construct slit caisson-type breakwaters are made in Korea. Since slit caisson-type breakwaters are suitable for relatively deep sea areas, a lot of theoretical and experimental researches have been performed. In this study, the reflection characteristics of vertical slit caisson breakwaters are investigated based on the measured data in two-dimensional hydraulic model tests with irregular waves. The experiments were conducted for various cases; variation of porosity of perforated-wall, width of wave chamber, number of slits for single-and double-chamber, respectively. It is found that in the case when the wave steepness (H/L$_{s}$ ) is small, the reflection coefficients are large. The existing researches have shown that the wave reflection is minimized when the nondimensional width of wave chamber B/L is about 0.2~0.25 for the regular waves. However, for the irregular waves the reflection is lowest when $B/L_2$, is 0.13~0.15. For a same porosity condition, the wave dissipation is stronger as the width of s1it is larger. The double-chamber caisson is superior to single- chamber caisson in the wave dissipating effects.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.6 no.1
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• pp.88-93
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• 1994

This study is concerned with an analytic derivation of the probability density function applicable for wave heights in finite water depth using two different methods. As the first method of the study, a probability density function is developed by applying a series of polynomials which is orthogonal with respect to Rayleigh probability density function. The newly derived probability density function is compared with the histogram constructed from wave data obtained in finite water depth which indicate strong non-Gaussian characteristics. Although the probability density represents the histogram very well. it has negative density at large values. Although the magnitude of the negative density is small. it negates the use of the distribution function fer estimating extreme values. As the second method of the study, a probability density function of wave height is developed by applying the maximum entropy method. The probability density function thusly derived agrees very well with the wave height distribution in shallow water, and appears to be useful in estimating extreme values and statistical properties of wave heights in finite water depth. However, a functional relationship between the probability distribution and the non-Gaussian characteristics of the data cannot be obtained by applying the maximum entropy method.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.3 no.2
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• pp.92-99
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• 1991

A moored body in the sea is subjected to second-order wave forces as well as to linear oscillatory ones. The second-order farces contain slowly-varying components, of which the characteristic frequency can be as low as the natural frequency of horizontal motions of the moored body. As a consequence, the slowly-varying force can excite unexpectedly large horizontal excursion of the body, which may cause a serious damage on the mooring system. In design analysis of Turret-type mooring system which is one of the interesting mooring systems for a floating body. the slowly-varying drift forces and the transient motion of the system during weathervaning are very important. In this paper the slowly-varying drift forces were calculated by using the Quadratic Transfer Function with considering the second order free-wave contributions. Additionaly the transient surge motion of the moored body was simulated with including the roll of the time-memory effect. In this simulation the spring constant of the spread Turret mooring system is updated at every time step for considering the nonlinear effect.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.10 no.3
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• pp.115-126
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• 1990

In the past, seawall and sea dike very higher than sea-water elevation had been constructed mainly to prevent the wave overtopping volume. However, the coastal zone is recently developed for the multipurpose of not only preventing from the coastal disaster but conserving the coastal environment and utilizing the coastal space. In this sense, this paper deals with the artificial reef being able to reduce the overtopping volume. Relations of the overtopping volume to the breaking wave are briefly reviewed theoretically, and fundamental factor affecting it are also obtained experimentally form the artificial reef with the irregular waves, In addition, the numerical simulation is developed to investigate the effects of spectral band width for the overtopping volume. The most effective artificial reef section to reduce the overtopping volume is proposed.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.17 no.3
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• pp.202-212
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• 2005

In the design of an of offshore structure located near an underwater shoal, the same amount of attention given to the wave height may have to be put to the wave induced current as well since some of the wave energy translates to the current. In the present study, two numerical models each based on the nonlinear Boussinesq equation and the linear mild slope equation are applied to calculate the wave deformation and secondly induced current around a shoal. The underwater shoal in Vincent and briggs' experiment (1989) is used here, and all non-breaking wave conditions of the experiment with various monochromatic and unidirectional or multidirectional spectral wave incidences are concerned. Both numerical models clearly showed wave induced currents symmetrically farmed along the centerline over the shoal. The calculated wave heights along a preset line also generally showed very nice agreements with the experimental values.