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Kim, Hyoung-Chul,Kim, Kyong-Hwan,Kim, Moo-Hyun,Hong, Keyyong International Society of Offshore and Polar Engine 2017 International journal of offshore and polar engine Vol.27 No.1
<P>The global performance of the KRISO square-type semisubmersible multiunit floating offshore wind turbine ( MUFOWT) in irregular waves is numerically simulated by using a multiturbine floater-mooring coupled dynamic analysis program. The developed time-domain numerical-simulation tool is extended from the FAST-CHARM3D coupled dynamics program for a single turbine on a single floater. FAST has been developed by the National Renewable Energy Laboratory for years for the single unit. Recently, KRISO has designed and studied a square-type semisubmersible MUFOWT in which four 3 MW wind turbines are installed at each corner of a single floater. Additionally, 24 point-power-absorber-type linear-generator-based wave energy converters are set up, with six wave energy converters at each side of the platform. For verification, KRISO performed a series of model tests for this MUFOWT with 1: 50 Froude scale. In this paper, the MUFOWT simulation program is used to reproduce KRISO's model test results. In the fully-coupled multiturbine/hull/mooring dynamic simulations, the complete second-order difference-frequency wave forces are also included. The analysis results are systematically compared with the model test results, which shows reasonable correlation between them.</P>
Yield Strength Prediction of UOE Pipes: From Forming to Flattening
Yi, Jiwoon,Kang, Soo-Chang,Koh, Hyun-Moo,Choo, Jinkyo F International Society of Offshore and Polar Engine 2018 International journal of offshore and polar engine Vol.28 No.2
<P>With the advent of higher steel grades for offshore pipelines and the reliance of the UOE forming process on trial and error, knowing the final yield strength of the pipe beforehand would be beneficial in terms of time and cost. However, predicting the yield strength of the UOE pipe constitutes a difficult task because of the alteration of the material properties throughout the forming process. Moreover, the yield strength is measured by tensile test executed on specimens obtained by flattening samples cut from the formed pipe, but this flattening process also alters the properties of the material. Accordingly, this study presents a 2-D finite element method (FEM) program considering both forming and flattening processes to predict the yield strength of the UOE pipe measured by tensile test. The results show that the simulation predicts the yield strength with good accuracy.</P>
A Model Test for Deepwater Lifting and Lowering Operations of a Subsea Manifold
Nam, Bo-Woo,Kim, Nam-Woo,Choi, Young-Myung,Hong, Sa Young,Kim, Jong-Wook International Society of Offshore and Polar Engine 2016 International journal of offshore and polar engine Vol.26 No.3
<P>This paper presents an experimental study of the deepwater lifting and lowering operations of a subsea manifold. A series of model tests with an installation vessel, a crane system, and a manifold were performed at the Ocean Engineering Basin of the Korea Research Institute of Ships and Ocean Engineering (KRISO). The lifting and lowering operations during the crane installation of the subsea equipment were tested under both regular and irregular wave conditions. White noise and regular wave tests were first carried out to investigate the vessel motion and wire tension responses during the deepwater lifting operation. The effect of the equipment weight and water depth was also studied. To overcome the limitation of the water depth in the basin, a new experimental technique using a truncated hoisting system was introduced. The effect of the passive heave compensator on the hoisting wire tension was discussed.</P>
Zhao, Luman,Roh, Myung-Il,Ham, Seung-Ho International Society of Offshore and Polar Engine 2018 International journal of offshore and polar engine Vol.28 No.2
<P>Ship-mounted cranes are used widely in the transportation and installation of heavy loads at sea. To minimize the sway motion induced by the harsh environment, the cranes are equipped with antisway-compensation equipment. To effectively test the feasibility of the antisway algorithms at the early design stage, the hardware-in-the-loop simulation (HILS) technique can efficiently be used for the proposed technique of this study. In this study, it is applied to the example of the antisway control of a crane on an offshore support vessel during the installation operation of subsea equipment using the HILS.</P>
Comparative Study of Water-Impact Problem for Ship Section and Wedge Drops
Hong, Sa Young,Kim, Kyong-Hwan,Hwang, Sung Chul International Society of Offshore and Polar Engine 2017 International journal of offshore and polar engine Vol.27 No.2
<P>A comparative study of a water-entry problem was conducted as a focused session of ISOPE-2016, Rhodes by the International Hydrodynamic Committee (IHC) of ISOPE. Thirteen institutions participated, and twenty different numerical results were investigated and compared with one another and with model test data. Some promising results were obtained even though there is still a long way to go to draw general conclusions. Four numerical cases were investigated, and several measures of comparison have been discussed.</P>
Control Strategy for a Ventilated Supercavitating Vehicle in Initial Phase
Kim, Seonhong,Kim, Nakwan International Society of Offshore and Polar Engine 2016 International journal of offshore and polar engine Vol.26 No.2
<P>Supercavitation reduces the resistance of an underwater vehicle by enveloping it in a bubble. When the velocity of the vehicle is low and the depth is significant, natural supercavitation is inhibited. Consequently, an artificial cavity to which gas is supplied, called a ventilated cavity, is used to maintain the supercavitating condition. This study models ventilated supercavity according to the cavity closure type and the design depth and proposes a ventilation control strategy that swiftly changes the closure type from the toroidal vortex regime to the twin vortex regime in the initial phase of flight. Numerical simulations verify the efficacy of the proposed strategy.</P>