• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.4
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• pp.65-75
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• 1993

Presented is a method for nonstationary response analysis of an offshore guyed tower subjected to strong earthquake motions under moderate random waves and current loadings. By taking the time varying envelope function and the auto-correlation function of the ground acceleration in terms of complex exponential functions, an analytical procedure is developed for computing time varying variances of the tower response. The stationary responses due to small random waves are obtained by using frequency domain method, and the results are combined with the nonstationary results due to earthquakes. Finally, the expected maximum responses are estimated. Through the example analyses, the nonstationary method developed in this study is verified, and the contributions of the earthquake, wave and current loadings to the total maximum response are investigated.

• Journal of the Society of Naval Architects of Korea
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• v.51 no.5
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• pp.369-379
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• 2014

Planing hull forms have significant influences on those hydrodynamic performances in calm water and in waves. Therefore, the hydrodynamic performance of a planing vessel should be predicted by model tests or theoretical calculations, and be confirmed whether it shows the performance requirements at the design stage. In this study, four planing hull forms are designed with the goal of the improvement of resistance and seakeeping performance, and 1/6.5 scale model tests are carried out in Seoul National University towing tank. The effects of design parameters such as length-to-beam ratio, deadrise angle and forebody shape on the hydrodynamic performance are investigated, based on model test results. Running attitude and resistance of model ships in calm water are also estimated by empirical formulae proposed by Savitsky (1964; 2007; 2012), and compared with the model test results. It is shown that calm water performance of non-prismatic planing hulls can be predicted well by Savitsky (2012)'s formula which improves the original Savitsky(1964/2007)'s formula by taking into account the variations of deadrise angles, and the actual angles between the hull bottom and the free surface.

• Journal of the Society of Naval Architects of Korea
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• v.43 no.5 s.149
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• pp.529-537
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• 2006

International Maritime Organization (IMO) is planning to include the Alternative Assessment of the Weather Criterion in the new Intact Stability (IS) Code to be revised. In this study, the procedure of the model test in the Interim Guidelines was reviewed by carrying out the model test and analyzing the test results. For this purpose, RO/RO passenger ship whose ratios of breadth to draft and the height of weight to draft were above 3.5 and above 0.6 respectively was selected as a test ship. Drifting test and motion test in regular waves were performed to estimate the hydrodynamic heeling lever and roll-back angle. Motion tests in waves were carried out in the three wave steepness conditions to measure roll-back angle and examine the feasibility of so called, the Three-step method. Using the test data, satisfaction of the Weather Criterion was assessed for the test ship by using the alternative method and compared with the current method.

• Journal of Korea Water Resources Association
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• v.42 no.4
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• pp.297-307
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• 2009

For reliable water quality simulation by semi distributed model, accurate daily runoff simulation should have preceded. In this study, newly developed channel routing method which is nonlinear storage method is combination of Muskingum routing method and variable storage routing method and temporally weighted average curve number method were applied for effect analysis of water quality simulation. Developed modules, which are added in SWAT models and simulation, were conducted for the Chungju dam watershed. The simulation result by each module applied effect. As a result of analysis contribute water quality modeling, nonlinear storage method is more effective than temporally weighted average curve number method. Nutrient loading discharge was affected by development of runoff delaying from improvement of channel routing, because of characteristics of nonpoint source pollution.

• Proceedings of the Korea Water Resources Association Conference
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• 2021.06a
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• pp.336-336
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• 2021

기후변화와 도시화로 인한 집중 호우와 불투수층 증가로 도시 홍수의 발생 빈도와 규모가 증가하고 있다. 인적, 물적 자원이 집중되어 있는 도시유역의 특성상 침수가 발생하면 이로 인한 직접적 피해 뿐만 아니라 사회경제적 2차 피해를 발생한다. 도시 홍수로 인한 피해를 줄이고 도시의 재해에 대한 회복력을 키우기 위해서는 관측과 더불어 정확한 모의 기술이 중요하다. 한편, 격자 기반 도시 홍수 모의는 집중 호우에 따른 침수의 시공간적 발생 양상을 물리적으로 해석하는 방법으로, 지표수-우수관거 이중배제 통합 모의, 수치기법, 병렬컴퓨팅, 수질 연계 모의 등의 측면에서 지금까지 많은 발전이 이루어져 왔다. 최근들어 원격탐사 기술의 발달로 공간해상도 1미터 수준 혹은 그 이상의 초고해상도 지형자료가 많은 지역에서 대해 가용해지고 있으며, 도시 홍수 해석에 이와 같은 초고해상도 자료를 적용하기 위한 연구가 활발히 진행되고 있다. 본 연구에서는 초고해상도 지형 및 토지 피복 자료의 공간해상도가 침수해석에 미치는 영향을 분석한다. 도시침수의 두가지 주요 요인인 내수침수와 외수범람 중에서 극한 강우에 의한 내수침수해석 사례만을 주요 연구 범위로 한다. 초고해상도 입력자료의 격자기반 도수 해석 모형으로는 운동파 기반의 2차원 지표 흐름 해석 모형을 적용하고, 초고해상도 모의의 효율적 계산을 위해 하이브리드 병렬 컴퓨팅 기술을 이용한다. 초고해상도 입력자료 적용 사례 대비, 공간해상도 저하에 따라 침수 면적이나 깊이 등에서 어떤 변화가 있는지 정량적으로 검토한다. 또한, 강우의 강도 및 공간분포가 초고해상도 도시 홍수 해석에 미치는 영향에 대해서 분석한다. 모의 결과로부터 도시 홍수 해석시 거리 단위(street-level) 정확도의 재현을 위해 적정한 공간해상도를 분석하고, 초고해상도 도시 홍수 모의를 이용한 기후변화에 따른 극한 홍수의 도시지역 영향 분석 및 회복력 개선 관련 연구의 가능성에 대해 논의한다.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.20 no.2
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• pp.157-167
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• 2008

The aeration of an overtopping wave on a vertical structure generated by a plunging wave was investigated through laboratory measurements of void fraction. The overtopping wave occurring after wave breaking becomes multi-phased and turbulent with significant aeration, so that the void fraction of the flow is of importance. In this study, fiber optic reflectometer and bubble image velocimetry were employed to measure the void fraction, velocity, and layer thickness of the overtopping flow. Mean properties were obtained by ensembleand time-averaging the repeated instantaneous void fractions and velocities. The mean void fractions show that the overtopping wave is very high-aerated near the overtopping wave front and relatively low-aerated near the deck surface and rear free surface of the wave. The flow rate and momentum of the overtopping flow estimated using the measured data show that the void ratio is an important parameter to consider in the multiphase flow. From the similarity profiles of the depth-averaged void fraction, velocity, and layer thickness, one-dimensional empirical equations were obtained and used to estimate the flow rate and momentum of the overtopping flow.

• Journal of the Korean Society of Marine Environment & Safety
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• v.29 no.2
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• pp.248-253
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• 2023

Most offshore platforms utilize chain mooring systems for position keeping. However, information regarding related design modification processes is scarce in literature. This study focuses on the floating liquefied natural gas (LNG) bunkering terminal (FLBT) as the target of shore platform and analyzes the corresponding initial mooring design and model tests via numerical simulations. Subsequently, based on the modified design conditions, a new mooring system design is proposed. Adjusting the main direction of the mooring line bundle according to the dominant environmental direction is found to significantly reduce the mooring design load. Even turret-moored offshore platforms are exposed to beam sea conditions, leading to high mooring tension due to motions in beam sea conditions. Collinear environmental conditions cannot be considered as design conditions. Mooring design loads occur under complex conditions of wind, waves, and currents in different environmental directions. Therefore, it is essential appropriately assign the roll damping coefficients during mooring analysis because the roll has a significant effect on mooring tension.

• Journal of the Society of Naval Architects of Korea
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• v.29 no.1
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• pp.71-80
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• 1992

The Seakeeping committee of Korea Towing Tank Conference executed the cooperative experimental study on deck wetting phenomena using S-175 contatiner model ships. Two members, Korea Research Institute of Ships and Ocean Engineering(KRISO) and Hyundai Maritime Research Institute(HMRI) participated in the study. This study was initiated by the ITTC(International Towing Tank Conference) Seakeeping Committee as the cooperative study of the 19th ITTC aiming at the establishement of the model test procedure on the deck wetting phenomena. Special emphasis was made on the determination of reliable record length for experimental measurement on rarely occurring events(such as deck wetness, slamming etc). Comparisons were made on both the test results and the test procedrues in this research. The measured frequencies of deck wetting show remarkable deviations between the runs. This fart implies that sufficiently long record length is required in the deck wetness measurement compared to the conventional ship motion tests. Careful considerations were made on the physical interpretation of the deck wetting phenomena, the correlation between the measured relative motion at stemhead and the measured deck wetness, and the estimation of deck wetting frequencies by Poisson process.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.8 no.4
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• pp.23-32
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• 1988

The rates of infiltration contributed to the flow fo water in an unconfined aquifer under the partially penetrated stream at an ungaged station and the corresponding base flow in channel are coupled by using the hydraulic and/or hydrologic characteristics obtained from the geomorphologic and soil maps. For the determination of groundwater flow, the linearized model which is originally Boussinesq's nonlinear equation is applied in this study. Also, a stream flow routing model for base flow in channel is based on a simplification of the Saint-venant. The distributed runoff model with piecewise spatial uniformity is presented for obtaining its solution based on a finite difference technique of the kinematic wave equations. The method developed in this study was tested to the Bocheong watershed(area : $475.5km^2$) of the natural stream basin which is one of tributaries in Geum River basin in Korea. As a result, it is suggested that the rationality of hydro-graph separation according to a wide variability in hydrogeologic properties be worked out as developing the physically based subsurface model. The results of the present model are shown to be possible to simulate a base flow due to an arbitrary rate of infiltration for ungaged basins.

• Journal of Korea Water Resources Association
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• v.38 no.3 s.152
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• pp.213-222
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• 2005

This study is a sensitivity analysis of the parameters which affect the simulation results under various design rainfall conditions, using the SWMM model, for three selected basins in urban areas. The sensitivity of the peak flow rate is defined by $S_Q$ (=1.0 - (min. ratio of peak flow rate/max. ratio of peak flow rate)), and the rainfall conditions are classified in terms of design rainfall frequency, duration, and distribution. The simulation results show that in most conditions the parameters - the impermeable area ratio, the sewer slope, and the initial infiltration capacity - have more significant effects on the results than other parameters. As the design rainfall frequency increases, the sensitivity of the sewer slope and sewer roughness increases, while the parameters related with the surface runoff decrease. When the rainfall duration increases, the sensitivities of most parameters of surface runoff and sewer flow decrease. Also, at the 1st quarterly Huff rainfall distribution condition, the impermeable area ratio has high sensitivity, but at the 4th quarterly condition the parameters related with sewer flow show higher sensitivities. These tendencies can be explained by considering the procedure for computing the effective rainfall and kinematic wave on the surface and sewer flow.