• Title/Summary/Keyword: Hydrodynamic Motion

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Development of Apparatus for Pure Roll-Motion Test of Underwater Vehicles (수중운동체의 순수 횡동요 시험 기구 개발)

  • Kim, Dong-Hwi;Baek, Hyung-Min;Lee, Seung-Keon;Kim, Eun-Soo
    • Journal of Navigation and Port Research
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    • v.45 no.1
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    • pp.16-25
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    • 2021
  • Hydrodynamic coefficients should be accurately estimated to predict the maneuverability of underwater vehicles. Various captive model tests have been performed as part of estimation methods for these coefficients. Estimating hydrodynamic coefficients related to roll motion is important because underwater vehicles are sensitive to changes of roll moment. In this research, a pure roll motion equipment was newly designed to simply estimate hydrodynamic coefficients with respect to roll motion. Roll motion was implemented through a brief mechanical mechanism. The principle of operation, application process, and system identification of the equipment are described. An analysis method of the pure roll test is also suggested. Repeated tests of the newly equipment were carried out to check its reproducibility.

A Motion Analysis of FPSO in Irregular Waves including Swells

  • Kwak Hyun U.;Choi Hang S.;Shin Hyun S.
    • Journal of Ship and Ocean Technology
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    • v.9 no.2
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    • pp.21-28
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    • 2005
  • Recently moored offshore vessels like as FPSO(Floating Production Storage Offloading) are frequently deployed in seas for a long time. For successful operation, the motion behavior of such a vessel in waves must be clarified in advance either theoretically or experimentally. It is of particular interest to examine the behavior, when swells are superposed to seas with different incident angle. Such a situation is actually reported in some offshore oilfield. In this paper, the motion of a FPSO in irregular waves including swells is studied in time domain. Hydrodynamic coefficients and wave forces are calculated in frequency domain using three-dimensional singularity distribution method. Time memory function and added mass at infinite frequency are derived by Fourier transform utilizing hydrodynamic damping coefficients. In the process, the numerical accuracy of added mass at infinite frequency is carefully examined in association with free decay simulations. It is found from numerical simulations that swells significantly affect the vertical motion of FPSO mainly because of their longer period compared to the ordinary sea waves. In particular, the roll motion is largely amplified because the dominant period of swell is closer to the roll natural period than that of seas.

Hydrodynamic Response of Spar with Single and Double Heave Plates in Regular Waves

  • Sudhakar, S.;Nallayarasu, S.
    • International Journal of Ocean System Engineering
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    • v.3 no.4
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    • pp.188-208
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    • 2013
  • The motion response of floating structures should be adequately low to permit the operation of rigid risers along with dry well heads. Though Spar platforms have low heave responses under lower sea state, could become unacceptable in near resonance region of wave periods. Hence the hydrodynamic response, heave in particular, must be examined to ensure that it is minimized. To reduce heave motions, external damping devices are introduced and one such effective damping device is heave plate. Addition of heave plate can provide additional viscous damping and additional added mass in the heave direction which influence the heave motion. The present study focuses on the influence of heave plate on the hydrodynamic responses of Classic Spar in regular waves. The experimental investigation has been carried out on a 1:100 scale model of Spar with single and double heave plates in regular waves. Numerical investigation has been carried out to derive the hydrodynamic responses using ANSYS AQWA. The experimental results were compared with those obtained from numerical simulation and found to be in good agreement. The influence of disk diameter ratio, wave steepness, pretension in the mooring line and relative spacing between the plates on the hydrodynamic responses of Spar are evaluated and presented.

A Study on Hydrodynamic Force Characteristics of Manta-type Unmanned Undersea Vehicle with the Parameter of Appendage Shape (Manta형 무인잠수정의 부가물 형상에 따른 동유체력 특성에 관한 연구)

  • Bae, Jun-Young;Sohn, Kyoung-Ho
    • Journal of Navigation and Port Research
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    • v.33 no.5
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    • pp.309-314
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    • 2009
  • The influence of different appendage shape on the characteristics of hydrodynamic forces on Manta-type Unmanned Undersea Test Vehicle(MUUTV) was discussed experimentally. Fuselage only MUUTV model and two types of MUUTV model with different appendage geometries were considered as the subject of discussion Oblique tow experiment was carried out in circulating water channel with three MUUTV models. A point of difference in hydrodynamic force characteristics among three models was indicated. Furthermore, the linear hydrodynamic derivatives obtained from model experiment were compared with theoretical calculation results from slender body theory, added mass theory and etc. Based on the hydrodynamic force characteristics, motion stability of two types of MUUTV model with different appendage geometries was compared each other. Through the above analysis, the more suitable shape of appendage geometry was made clear.

A Study on Hydrodynamic Force Characteristics of Manta-type Unmanned Undersea Vehicle with the Parameter of Appendage Shape (Manta형 무인잠수정의 부가물 형상에 따른 동유체력 특성에 관한 연구)

  • Bae, Jun-Young;Sohn, Kyoung-Ho
    • Proceedings of the Korean Institute of Navigation and Port Research Conference
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    • 2009.06a
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    • pp.5-6
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    • 2009
  • The influence of different appendage shape on the characteristics of hydrodynamic forces on Manta-Type Unmanned Undersea Test Vehicle(MUUTV) was discussed experimentally. Fuselage only MUUTV model and two types of MUUTV model with different appendage geometries were considered as subject of discussion Oblique tow experiment was carried out in circulating water channel with three MUUTV models. A point of difference in hydrodynamic force characteristics among three models was compared and discussed. Furthermore, the linear hydrodynamic derivatives obtained from model experiment were compared with theoretical calculation results from slender body theory, added mass theory and ete. Based on the hydrodynamic force characteristics, motion stability of two types of MUUTV model with different appendage geometries was discussed and compared each other. Through the above analysis, the more suitable shape of appendage geometry was made clear.

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Estimation of Maneuvering Mathematical Model by System Identification Techniques (시스템 검증에 의한 조종수학 모형의 평가)

  • Lee, Ho-Young;Shin, Hyun-Kyoung
    • Journal of Ocean Engineering and Technology
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    • v.13 no.4 s.35
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    • pp.118-123
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    • 1999
  • The mathematical model used in the simulation of ship's maneuvering contains the hydrodynamic coefficients, which are usually evaluated based on PMM model tests in the towing tank and used to predict ship's maneuvering performance when applied to the proto-type ship. The proper mathematical model has to be developed to predict ship's maneuvering motions with hydrodynamic coefficients very well. The mathematical model for PMM model tests is analyzed with identification program and the hydrodynamic coefficients and maneuvering motions by system identification we compared with those obtained directly from PMM model tests and sea trial. The mathematical model for PMM model tests was established and the magnitudes of ship's maneuvering coefficients were determined. When the identified values of coefficients were used to simulate the maneuvers, a very good agreement was obtained between the numerically simulated motion responses and those obtained from PMM model tests.

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A Study of Hydrodynamic Forces Acting on a Ship Hull Under Lateral Low Speed Motion (저속 횡 이동하는 선박의 선체에 작용하는 유체력에 관한 연구)

  • 이윤석;김순갑
    • Journal of the Korean Institute of Navigation
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    • v.23 no.2
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    • pp.29-42
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    • 1999
  • An accurate method of estimating ship maneuverability needs to be developed to evaluate precisely and improve the maneuverability of ships according to the water depth. In order to estimate maneuverability by a mathematical model. The hydrodynamic forces acting on a ship hull and the flow field around the ship in maneuvering motion need to be estimated. The ship speed new the berth is very low and the fluid flow around a ship hull is unsteady. So, the transient fluid motion should be considered to estimate the drag force acting on the ship hull. In the low speed and short time lateral motion, the vorticity is created by the body and grow up in the acceleration stage and the velocity induced by the vorticity affect to the body in deceleration stage. For this kind of problem, CFD is considered as a goof tool to understand the phenomena. In this paper, the 2D CFD code is used for basic consideration of the phenomena to solve the flow in the cross section of the ship considering the ship is slender and the water depth is large enough. The flow fields Added and hydrodynamic forces for the some prescribed motions are computed and compared with the preliminary experiment results. The comparison of the force with measurement is shown a fairly good agreement in tendency. The 3D Potential Calculation based on the Hess & Smith Theory is employed to predict the surge, sway added mass and yaw added moment of inertia of hydrodynamic coefficients for M/V ESSO OSAKA according to the water depth. The results are also compared with experimental data. Finally, the sway added mass of hydrodynamic coefficients for T/S HANNARA is suggested in each water depth.

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A numerical study on hydrodynamic maneuvering derivatives for heave-pitch coupling motion of a ray-type underwater glider

  • Lee, Sungook;Choi, Hyeung-Sik;Kim, Joon-Young;Paik, Kwang-Jun
    • International Journal of Naval Architecture and Ocean Engineering
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    • v.12 no.1
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    • pp.892-901
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    • 2020
  • We used a numerical method to estimate the hydrodynamic maneuvering derivatives for the heave-pitch coupling motion of an underwater glider. It is very important to assess the hydrodynamic maneuvering characteristics of a specific hull form of an underwater glider in the initial design stages. Although model tests are the best way to obtain the derivatives, numerical methods such as the Reynolds-averaged Navier-Stokes (RANS) method are used to save time and cost. The RANS method is widely used to estimate the maneuvering performance of surface-piercing marine vehicles, such as tankers and container ships. However, it is rarely applied to evaluate the maneuvering performance of underwater vehicles such as gliders. This paper presents numerical studies for typical experiments such as static drift and Planar Motion Mechanism (PMM) to estimate the hydrodynamic maneuvering derivatives for a Ray-type Underwater Glider (RUG). A validation study was first performed on a manta-type Unmanned Undersea Vehicle (UUV), and the Computational Fluid Dynamics (CFD) results were compared with a model test that was conducted at the Circular Water Channel (CWC) in Korea Maritime and Ocean University. Two different RANS solvers were used (Star-CCM+ and OpenFOAM), and the results were compared. The RUG's derivatives with both static drift and dynamic PMM (pure heave and pure pitch) are presented.

Development of 6-DOF Equations of Motion for a Planning Boat Based on the Results of Sea Trial Tests

  • Jeon, Myung-Jun;Lee, Dong-Hyun;Yoon, Hyeon-Kyu
    • Journal of Navigation and Port Research
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    • v.40 no.5
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    • pp.231-239
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    • 2016
  • In general, the attitude of a high-speed planning boat changes following a speed change. Since the hydrodynamic forces acting on a ship differ according to the change of its underwater shape, it is difficult to estimate its hydrodynamic force compared to that of a large commercial ship. In this paper, 6 Degrees Of Freedom (DOF) equations of motion that express the maneuvering motion of a planning boat are modeled by analyzing its motion characteristics based on various sea trial tests. Finally, a maneuvering simulation is carried out and a validation of the equations of motion is confirmed with the results of sea trial tests.

An Experimental Study on Hydrodynamic Forces of Korea Autonomous Surface Ship in Various Loading Conditions

  • Nguyen, Thi Thanh Diep;Mai, Van Thuan;Lee, San;Yoon, Hyeon Kyu
    • Journal of Navigation and Port Research
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    • v.46 no.2
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    • pp.73-81
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    • 2022
  • Currently, shipping by sea is becoming common because of the low price and the safety of goods. The ship is designed as a larger vessel to meet the need of this development. In the design stage, the investigation of hydrodynamic forces acting on the ship hull is very important in predicting the ship's maneuverability. Given that the ship docks at various ports for loading or discharging goods, the ship usually operates in various loading conditions, depending on the site condition and other various factors. Hence, it is necessary to investigate the effect of the loading condition on the hydrodynamic forces acting on the ship, to most accurately determine the maneuverability of the ship. In this study, an experiment of Korea Autonomous Surface Ship (KASS) was conducted at the towing tank of Changwon National University to measure the hydrodynamic forces acting on the KASS. The loading condition considered in this experiment is determined based on the draft, which was decreased by 5% for each loading condition. The smallest draft is 85% of the design draft. The static test as Oblique Towing Test (OTT), Circular Motion Test (CMT), Circular Motion Test with Drift (CMTD) is performed in the various loading conditions. First, the hydrodynamic forces in the Oblique Towing test (OTT) are compared with the result of other institutes. Second, the hydrodynamic forces in various drift angle, yaw rate and loading conditions are measured. Finally, the influence of the loading conditions on the hydrodynamic coefficient is discussed.