• Journal of the Korean Society of Marine Environment & Safety
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• v.25 no.2
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• pp.178-188
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• 2019

When using a distributed system, it is very important to know the intention of a target ship in order to prevent collisions. The action taken by a certain ship for collision avoidance and the action of the target ship it intends to avoid influence each other. However, it is difficult to establish a collision avoidance plan in consideration of multiple-ship situations for this reason. To solve this problem, a Distributed Stochastic Search Algorithm (DSSA) has been proposed. A DSSA searches for a course that can most reduce cost through repeated information exchange with target ships, and then indicates whether the current course should be maintained or a new course should be chosen according to probability and constraints. However, it has not been proven how the parameters used in DSSA affect collision avoidance actions. Therefore, in this paper, I have investigated the effect of the parameters and weight factors of DSSA. Experiments were conducted by combining parameters (time window, safe domain, detection range) and weight factors for encounters of two ships in head-on, crossing, and overtaking situations. A total of 24,000 experiments were conducted: 8,000 iterations for each situation. As a result, no collision occurred in any experiment conducted using DSSA. Costs have been shown to increase if a ship gives a large weight to its destination, i.e., takes selfish behavior. The more lasting the expected position of the target ship, the smaller the sailing distance and the number of message exchanges. The larger the detection range, the safer the interaction.

• Journal of Ocean Engineering and Technology
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• v.23 no.5
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• pp.71-78
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• 2009

In ship design or offshore structure design, the evaluation of buckling strength (or ultimate strength) is critical to the determination of scantling of stiffened plates. For this reason, it is useful to study the effect of applying different formula or the relationship between stiffened plate with buckling utilization factor (UF). It can facilitate a designer to decide how much the scantling should be reinforced or how much can be reduced for an optimal design. This paper conducts a comparative study for three buckling check methods; DNV-Ship-Rule, DNV-RP-C201, DNV-PULS. The capacity curves and 2D contour plot for utilization factors versus bi-axial in-plane stresses are compared. The contour plots of DNV-Ship-Rule and DNV-PULS show smoothly increasing trends of UF as the applied in-plane stresses increase, however that of DNV-RP-C201 shows rapidly increasing trend as the applied stresses go beyond transverse buckling stress. A sensitivity analysis is performed to investigate the influence level of each parameter of a stiffened plate on UF. Resulting from the analysis, plate thickness is identified to be the most affective parameter to UF regardless of the buckling check methods. Based on the addressed study, optimal designs for bottom plate of 165 K tanker corresponding to three formulas are compared with each other. DNV-PULS yields 1 mm and 2 mm less thickness than DNV-Ship-Rule and DNV-RP-C201, respectively.

• Journal of Ocean Engineering and Technology
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• v.33 no.1
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• pp.33-41
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• 2019

Estimating fatigue damage is a very important issue in the design of ships. The springing and whipping response, which is the hydro-elastic response of the ship, can increase the fatigue damage of the ship. So, these phenomena should be considered in the design stage. However, the current studies on the the application of springing and whipping responses at the design stage are not sufficient. So, in this study, a prediction method was developed using fluid-structural interaction analysis to assess of the fatigue damage induced by springing and whipping. The stress transfer function (Stress RAO) was obtained by using the 3D FE model in the frequency domain, and the fatigue damage, including linear springing, was estimated by using the wide band damage model. We also used the 1D beam model to develop a method to estimate the fatigue damage, including nonlinear springing and whipping by the vertical bending moment in the short-term sea state. This method can be applied to structural members where fatigue strength is weak to vertical bending moments, such as longitudinal stiffeners. The methodology we developed was applied to 325K VLOC, and we analyzed the effect of the springing and whipping phenomena on the existing design.

• Journal of computational fluids engineering
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• v.20 no.4
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• pp.93-101
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• 2015

This paper provides numerical results of the simulation for the flow around the hull and the propeller of KCS model ship advancing in shallow water conditions. A finite volume method is used to solve the unsteady Reynolds averaged Navier-Stokes(RANS) equations, where the wave-making problem is solved by using a volume-of-fluid(VOF) method. The wave formed near the hull surface in shallow water conditions shows a deep trough dominant pattern that causes the loss of buoyancy followed by hull squat. The flow past the hull increases as the depth of water decreases. However, the axial flow velocity around the stern shows a reduction in magnitude by the effect of shallow water accompanied by the hull-propeller interaction. As a results, the thrust and torque coefficient increase about 8.3% and 6.2%, respectively for a depth of h/T=3.0 corresponding to a depth Froude number of $F_h=0.693$. The resistance coefficient increases about 11.6% at this Froude number condition.

• Journal of Ship and Ocean Technology
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• v.9 no.1
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• pp.11-26
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• 2005

In this study, the program to investigate the multiple body interaction effects between a floating platform and a shuttle tanker considering the coupled effect of hull (FPSO) with mooring lines and risers was developed. The coupled analysis program, which is called WINPOST-MULT using the hydrodynamic analysis results by WAMIT, was made. For the verification of WINPOST-MULT by means of numerical experiments, two multiple-body models of an FPSO-FPSO and an FPSO-shuttle tanker system are adopted. With the FPSO-FPSO model and a two-mass-spring system to idealize two identical bodies for the 100-year storm wave condition in GOM, the numerical simulations were performed to investigate the interaction effects between two identical bodies. For the more reality, the coupled analysis for the FPSO-shuttle tanker model in the tandem arrangement was carried out in the consideration of the environmental condition of the West Africa Sea as a rather mild condition. Through the case studies with interaction effect and without interaction effect by the iteration method and the combined method, it is verified that the program is a very useful tool for the analysis of the interaction problem of multiple-body system and the coupled problem of the hull/mooring/riser.

• Journal of Navigation and Port Research
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• v.29 no.6 s.102
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• pp.515-522
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• 2005

The ship plating is generally subjected to. combined in-plane load and lateral pressure loads, In-plane loads include axial load and edge shear, which are mainly induced by overall hull girder bending and torsion of the vessel. Lateral pressure is due to. water pressure and cargo. These load components are nat always applied simultaneously, but mare than one can normally exist and interact. Hence, far mare rational and safe design of ship structures, it is af crucial importance to. better understand the interaction relationship af the buckling and ultimate strength far ship plating under combined loads. Actual ship plates are subjected to relatively small water pressure except far the impact load due to. slamming and panting etc. The present paper describes an accurate and fast procedure for analyzing the elastic-plastic large deflection behavior up to. the ultimate limit state of ship plates under combined loads. In this paper, the ultimate strength characteristics of plates under axial compressive loads and lateral pressure loads are investigated through ANSYS elastic-plastic large deflection finite element analysis with varying lateral pressure load level.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• v.29 no.1
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• pp.61-67
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• 2005

The ship plating is generally subjected to combined in-plane load and lateral pressure loads. In-plane loads include axial load and edge shear, which are mainly induced by overall hull ginder bending and torsion of the vessel. Lateral pressure is due to water pressure and cargo. These load components are not always applied simultaneously, but more than one can normally exist and interact. Hence, for more rational and safe design of ship structures, it is of crucial importance to better understand the interaction relationship of the buckling and ultimate strength for ship plating under combined loads. Actual ship plates are subjected to relatively small water pressure except for the impact load due to slamming and panting etc. The present paper describes an accurate and fast procedure for analyzing the elastic-plastic large deflection behavior up to the ultimate limit state of ship plates under combined loads. In this paper, the ultimate strength characteristics of plates under axial compressive loads and lateral pressure loads are inverstigated through ANSYS elastic-plastic large deflection finite element analysis with varying lateral pressure load level.

• Journal of the Society of Naval Architects of Korea
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• v.40 no.4
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• pp.46-52
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• 2003

In ship structures, many parts are in contact with inner or outer fluid as stern, ballast and oil tanks. Fatigue damages can be sometimes observed in these tanks which seem to be caused by resonance. Tank structures in ships are in contact with water and the vibration characteristics are strongly affected by the added mass of containing water. Therefore it is important to predict vibration characteristics of tank structures. In order to estimate the vibration characteristics, the fluid-structure interaction problem has to be solved precisely. In the present paper, we have developed a numerical tool of vibration analysis of 3-dimensional tank structures using finite elements for plates and boundary elements for water region. To verify the present analysis, we have made an experiment for vibration characteristics of a tank with elastic opposite panels. And the added mass effect of containing water and the effect of structural constraint between panels are investigated numerically and discussed.

• Special Issue of the Society of Naval Architects of Korea
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• 2015.09a
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• pp.56-62
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• 2015

In ship structure, many parts are in contact with inner or outer fluid as stern, ballast and oil tanks. Fatigue damages are sometimes observed in these tanks which seem to be caused by resonance with exciting force of engine and propeller. Vibration characteristics of these tanks in contact with fluid are significantly affected by fluid coupling effect. Therefore it is important to exactly predict vibration characteristics of tank structure. In order to estimate the vibration characteristics, the fluid-structure interaction(FSI) problem should be solved precisely. But it is difficult to estimate exactly the magnitude of the fluid coupling effect because it has some problems such as a fluid-structure interaction, influence by the free surface, vibration modes of structural panels and depth of water. In this paper, with fluid coupling effect, the effect of structural constraint between panels on the vibration characteristics are investigated numerically and discussed.

• Journal of Ocean Engineering and Technology
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• v.23 no.6
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• pp.53-60
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• 2009

Recently, since there are several problems in space, the infra-structure and the facilities in the contiguity of the existing harbors due to the trend of enlarging the container capacity of the large container vessel, a special floating platform named as the Mobile Harbor has been proposed conceptually as an effective solution of those problems. Two kinds of hull shapes, a conventional mono-hull type and a catamaran type, are proposed as midway feeders to transfer containers to the harbor on land from a large container ship on near shore. In this study, the motion response and mooring analysis are carried out for comparing the global performance of two types of Mobile Harbor. Robot arm mooring facility specially is devised and newly tried to use for the safe fixation of a large container ship and the Mobile Harbor on near shore. It would be expected for this comparison study to give a guideline to design the efficient hull form for a midway loader.