• International Journal of Ocean System Engineering
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• v.3 no.4
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• pp.175-187
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• 2013

Moonpools are vertical wells in a floating body used onboard many types of vessels like Exploration and drilling vessels, Production barges, Cable-laying vessels, Rock dumping vessels, Research and offshore support vessels. Moonpool gives passage to underwater activities for different types of ships as per their mission requirements. It is observed that inside a moonpool considerable relative motions may occur, depending on shape, depth of the moonpool and on the frequency range of the waves to which the ship is exposed. The vessel responses are entirely different in zero and non-zero Froude number. Former situation is paid attention in this study as the mission requirement of the platform is to be in the particular location for long period of operation. It is well known that there are two modes of responses depending on the shape of the moonpool viz., piston mode for square shape and sloshing mode for rectangular shapes with different aspect ratios of opening like 1:1.5 and 1:2 ratios. Circular shaped moonpool is also tested for measuring the responses. The vessel moored using heavy lines are modelled and tested in the wave basin. The pretensions of the lines are varied by altering the touchdown points and the dynamic tensions on the lines are measured. The different modes of oscillations of water column are measured using wave gauge and the vessel response at a particular situation is determined. RAOs calculated for various situations provide better insight to the designer.

• Journal of Ocean Engineering and Technology
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• v.26 no.1
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• pp.70-77
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• 2012

In this study, a numerical analysis of offshore installation using a floating crane with heave compensator is carried out in time domain. The motion analysis of crane vessels is based on floating body dynamics using convolution integral and the crane wire is treated as simple spring. The lifted structure is assumed as a rigid body with 3 degree-of-freedom translational motion. The heave compensator is numerically modelled by the generalized spring-damper system. Firstly, forced motion simulations of crane wire system are carried out to figure out the basic principle of heave compensator. The transfer function of crane wire system is obtained and effective wave period of heave compensator are found. Then, coupled analysis of crane vessel, crane wire, and lifted structure are performed in regular and irregular sea conditions. Two different crane vessels and two lifted structures (suction pile and manifold) are considered in this study. Through a series of numerical calculations, the effective zone of heave compensator is investigated with respect to wave period and crane wire length.

• Special Issue of the Society of Naval Architects of Korea
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• 2011.09a
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• pp.112-116
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• 2011

The noise analysis is usually carried out in the early structure design stage for the main areas in a vessel such as an accommodation, an engine room, HVAC System and etc. If the analysis results are higher than the noise limits based on guideline, appropriate countermeasures are established to reduce noise levels and applied to the vessel. But excessive noise induced the main or auxiliary equipment and high pressure steam system is very difficult to check in the initial design stage, and local noise problems frequently appear in actual vessels. This paper deals with excessive noise of the engine control room on LNG carrier. It includes the cause analysis of excessive noise, the countermeasure, and verification. Also, it proves suitability of the countermeasure through the on-board test.

• International Journal of Naval Architecture and Ocean Engineering
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• v.13 no.1
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• pp.208-222
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• 2021

Managing with the presence of sea ice is the primary challenge in the operation of floating platforms in the Arctic region. It is widely accepted that offshore structures operating in Arctic conditions need station-keeping methods as well as ice management by icebreakers. Dynamic Positioning (DP) is one of the station-keeping methods that can provide mobility and flexibility in marine operations. The presence of sea ice generates complex external forces and moments acting on the vessel, which need to be counteracted by the DP system. In this paper, an icevaning control algorithm is proposed that enables Arctic offshore vessels to perform DP operations. The proposed icevaning control enables each vessel to be oriented toward the direction of the mean environmental force induced by ice drifting so as to improve the operational safety and reduce the overall thruster power consumption by having minimum external disturbances naturally. A mathematical model of an Arctic offshore vessel is summarized for the development of the new icevaning control algorithm. To determine the icevaning action of the Arctic offshore vessel without any measurements and estimation of ice conditions including ice drift, task and null space are defined in the vessel model, and the control law is formulated in the task space. A backstepping technique is utilized to handle the nonlinearity of the Arctic offshore vessel's dynamic model, and the Lyapunov stability theory is applied to guarantee the stability of the proposed icevaning control algorithm. Experiments are conducted in the ice tank of the Korea Research Institute of Ships and Ocean Engineering to demonstrate the feasibility of the proposed approach.

• The Journal of Fisheries Business Administration
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• v.38 no.1 s.73
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• pp.71-96
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• 2007

This study is aimed to investigate how the structure of Korean and Chinese fisheries has been changed since the Fisheries Agreement between Korea and China came into effect. This investigation was accomplished from a comparative point of view by using statistic data in the literatures published by both Korea and China. Results of this study are summarized as follows; First, it was revealed that the decreasing rate of fish production of marine capture fisheries in Korea was lowered more by 5.1%, while it was decreased by only 0.1% in China. Second, comparative results on changes in production of offshore fisheries showed that the production of Korean offshore fisheries in 2003 was reduced by 26% compared to that in 1999, while the production of China offshore fisheries was decreased by 22%. In addition, although the production of marine capture fisheries in the East region of China was reduced by 10%, on the contrary, the production of marine capture fisheries in Liaoning, Hebei, Tianjin, Jiangsu, Zhejiang, and Fujian that have mostly impacted by the Korea-China Fisheries Agreement was increased by 7%. Third, results on fishing capacity of marine fisheries indicated that the number of vessels and total horse power in Korea were increased by 1.2% and 44.9%, respectively, while total tonnage was reduced by 23.9%, For China, the number of vessels and total horse power were increased by 0.5% and 12.6%, respectively. Total tonnage was also increased by 11.7%. Finally, the production per Korean vessel was decreased by 17.8% in 2003 compared to that in 1999. On the contrary, the production per Chinese vessel was increased by 8.1% in 2003. The production per tonnage was increased by 3.2% in Korea, while it was reduced by 2.7% in China. In conclusion, it could be said that the Korea-China Fisheries Agreement has had a positive impact on the fisheries production of China, while it has had a negative impacts on that of Korea, relatively.

• Journal of the Korea Society of Computer and Information
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• v.26 no.12
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• pp.255-264
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• 2021

In this paper, we propose operations and maintenance (O&M) planning approach for floating offshore wind farm using the mathematical optimization. To be specific, we present a MILP (Mixed Integer Linear Programming that suggests the composition of vessels, technicians, and maintenance works on a weekly basis. We reflect accessibility to wind turbines based on weather data and loss of power generation using the Jensen wake model to identify downtime cost that vary from time to time. This paper also includes a description of two-stage approach for maintenance planning & detailed scheduling and numeric analysis of the number of vessels and technicians on the O&M cost. Finally, the MILP model could be utilized in order to establish the suitable and effective maintenance planning reflecting domestic situation.

• Journal of the Korea Society of Computer and Information
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• v.28 no.9
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• pp.149-158
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• 2023

With the global paradigm shift towards climate change, the shipbuilding industry is also considering propulsion systems that utilize eco-friendly fuels various propulsion systems are gaining attention as a result. In conventional propulsion systems, typically consisting of propellers and rudders, have evolved into a diverse range of systems due to the development of a special propulsion system known as the azimuth thruster. While azimuth thrusters were previously commonly installed on tugboats, they are now extensively used on offshore plant operation ships equipped with dynamic positioning systems. However, these azimuth thrusters require different steering methods compared to conventional propulsion systems, leading to a significant learning curve for the crew members boarding such vessels. Furthermore the availability of education related to these special propulsion systems is limited. This study aims to analyze accidents caused by inadequate control of vessels equipped with azimuth thrusters using the STAMP technique. And it proposes the necessity of standard steering commands for the safe operation of vessels equipped with special propellers.

• Ocean and Polar Research
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• v.28 no.4
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• pp.439-449
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• 2006

This study was aimed at measuring the fishing capacity of Powered Anchovy Drag Net Fisheries (PADNF) in Korea using Peak-to-Peak(PTP) and Data Envelopment Analysis(DEA) methods recommended by FAO. In the analysis, both fishing capacities of total PADNF and individual PADNF vessels were measured with time series data and cross sectional data, respectively. In addition, the results of the DEA measurement were analyzed in order to determine reduction levels of fishing capacity. In case of total PADNF, the results by rn and DEA methods showed a similar rate of capacity utilization (79%), indicating the capacity was not utilized enough. In addition, the sensitivity analysis suggested that the number of vessels should be reduced by 20%, and the gross tonnage and the horse power should be reduced by 20% and 21%, respectively if the current catch is to stay at the 2004 level. The DEA results on individual PADNF vessels indicated the capacity utilization was 75% on average, showing some differences in capacity utilization among vessels (31%-100%). The results of the study would be useful for measuring production efficiency in PADNF. They would also provide good policy information for efficient use of resources and capacity reduction levels, which are useful far vessel buyback programs of coastal and offshore fisheries.

• Journal of Navigation and Port Research
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• v.41 no.5
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• pp.287-296
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• 2017

The Formal Safety Assessment (FSA) is a structured and systematic methodology developed by the IMO, aimed at assessing the risk of vessels and recommending the method to control intolerable risks, thereby enhancing maritime safety, including protection of life, health, the marine environment and property, by using risk analysis and cost-benefit assessment. While the FSA has mostly been applied to merchant vessels, it has rarely been applied to a DP vessel, which is one of the special purpose vessels in the offshore industry. Furthermore, most of the FSA has been conducted so far by using the Fault Tree Analysis tool, even though there are many other risk analysis tools. This study carried out the FSA for safe operation of DP vessels by using the Bayesian network, under which conditional probability was examined. This study determined the frequency and severity of DP LOP incidents reported to the IMCA from 2001 to 2010, and obtained the Risk Index by applying the Bayesian network. Then, the Risk Control Options (RCOs) were identified through an expert brainstorming and DP vessel simulations. This study recommends duplication of PRS, regardless of the DP class and PRS type and DP system specific training. Finally, this study verified that the Bayesian network and DP simulator can also serve as an effective tool for FSA implementation.

• Journal of the Korean Society of Marine Environment & Safety
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• v.28 no.6
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• pp.973-991
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• 2022

Globally, several countries with sea are using eco-friendly energy resources through offshore wind power development by overcoming the weak point of the existing power generation method. The sea has the advantage of being able to develop large scale wind farms in wide waters, but the installation of marine structures threatens the safe operation of vessels. Accordingly, a standard guideline for safe navigation by analyzing the mutual effects between ship routes and offshore wind site was presented by the PIANC. Nonetheless, the standard guideline calculated the same safe distance in all situations. Therefore, this study developed a calculation model for an optimal safe distance between ship routes and offshore wind sites by reflecting the ship's maneuvering, encounter situations, environmental force, traffic density, offshore wind power generators, and channel types. As a result of the validation simulation, the developed model showed that the optimal safe distance was secured.