• Title, Summary, Keyword: Hydrodynamic Motion

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Study on Coning Motion Test for Submerged Body (몰수체의 원추형시험에 관한 연구)

  • Park, Jong-Yong;Kim, Nakwan;Rhee, Key-Pyo;Yoon, Hyeon Kyu;Kim, Chanki;Jung, Chulmin;Ahn, Kyoungsoo;Lee, Sungkyun
    • Journal of Ocean Engineering and Technology
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    • v.29 no.6
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    • pp.436-444
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    • 2015
  • A submerged body is sensitive to changes in the roll moment because of the small restoring moment and moment of inertia. Thus, a method for predicting the roll-related hydrodynamic coefficients is important. This paper describes a deduction method for the hydrodynamic coefficients based on the results of a coning motion test. A resistance test, static drift test, and coning motion test were performed to obtain the coefficients in the towing tank of Seoul National University. The sum of the hydrodynamic force, inertial force, gravity, and buoyancy was measured in the coning motion test. The hydrodynamic force was deduced by subtracting the inertial force, gravity, and buoyancy from the measured force. The hydrodynamic coefficients were deduced using the regression method.

Hydrodynamic Forces Acting on Porpoising Craft at High-Speed

  • Katayama, Toru;Ikeda, Yoshiho
    • Journal of Ship and Ocean Technology
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    • v.3 no.2
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    • pp.17-26
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    • 1999
  • An experimental investigation on hydrodynamic forces acting on a porpoising craft at high advanced speeds up to Froude numbers Fn=6.0(Fn=U\ulcorner:Lo\ulcorner denote overall length of ship) in calm water is performed. Captive model tests and forced motion tests are carried out to measure the hydrodynamic forces. The results show that significant nonlinear effects for motion amplitudes appear in the restoring, the added mass and the damping coefficients. The experimental results are compared with the results of a prediction method of the hydrodynamic forces include the nonlinear effects, and show a good agreement with them. A simulation using the predicted hydrodynamic forces in a nonlinear motion equation is carried out to obtain the porpoising motion of a craft in calm water. The calculated results are in fairly good agreement with experimental ones.

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Proportional and Derivative Control of Hydrodynamic Journal Bearings (동압 베어링의 비례 및 미분 제어)

  • 노병후;김경웅
    • Tribology and Lubricants
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    • v.17 no.4
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    • pp.283-289
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    • 2001
  • The paper presents the stability characteristics of a rotor-bearing system supported by actively controlled hydrodynamic journal bearing. The proportional and derivative controls including coupled motion are adopted for the control algorithm to control the hydrodynamic journal bearing with a circumferentially groove. Also, the cavitation algorithm implementing the Jakobsson-Floberg-Olsson boundary condition is adopted to predict cavitation regions in the fluid film more accurately than a conventional analysis which uses the Reynolds condition. The stability characteristics of a rotor-bearing system supported by actively controlled hydrodynamic journal bearing are investigated for various control gains with the Routh-Hurwitz criteria using the linear dynamic coefficients which are obtained from the perturbation method. It is found that the speed at onset of the instability is increased for both proportional and derivative control of the bearing. It is also found that the proportional and derivative control of the coupled motion is more effective than that of the uncoupled motion.

The Hydrodynamic Interaction Effects between Two Barges on the Motion Responses (상호작용을 고려한 두 바아지의 운동응답)

  • S.P.,Ann;K.P.,Rhee
    • Bulletin of the Society of Naval Architects of Korea
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    • v.24 no.1
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    • pp.29-34
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    • 1987
  • In this paper, a three dimensional singularity distribution method is applied to investigate the hydrodynamic interactions between two barges floating on a free surface of a deep water. The results show that the hydrodynamic interaction forces are important in the calculation responses of two barges floating in each other's vicinity. Furthermore the trends of hydrodynamic forces due to the motion of body itself are different from those of a single barged, and the motions of the seaward barge can sometimes exceed those of the seaward barged.

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A Study on Proportional and Derivative Control of Fluid Film Journal Bearings (유체 윤활 베어링의 비례 및 미분 제어에 관한 연구)

  • 노병후;김경웅
    • Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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    • pp.212-217
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    • 2001
  • This paper presents the stability characteristics of a rotor-bearing system supported by actively controlled hydrodynamic journal bearing. The proportional and derivative controls including coupled motion are adopted for the control algorithm to control the hydrodynamic journal bearing with a circumferentially groove. Also, the cavitation algorithm implementing the Jakobsson-Floberg-Olsson boundary condition is adopted to predict cavitation regions in the fluid film more accurately than conventional analysis which uses the Reynolds condition. The stability characteristics are investigated with the Routh-Hurwitz criteria using the linear dynamic coefficients which are obtained from the perturbation method. The stability characteristics of the rotor-bearing system supported by active controlled hydrodynamic journal bearing are investigated for various control gain. It is found that the speed at onset of instability is increased for both proportional and derivative control of the bearing, and the proportional and derivative control of coupled motion is more effective than proportional and derivative control of uncoupled motion.

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Hydrodynamic Behavior Analysis of Vertical-Cylindrical Liquid-Storge Tanks by Mathematically Analytic Method (수학적 해석 방법에 의한 액체저장탱크의 액동압 거동 해석)

  • Park, Jong-Ryul;Oh, Taek-Yul
    • Proceedings of the KSME Conference
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    • pp.628-635
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    • 2001
  • Hydrodynamic behavior and response of vertical-cylindrical liquid-storage tank is considered. The equation of the liquid motion is shown by Laplace's differential equation with the fluid velocity potential. The solution of the Laplace's differential equation of the liquid motion is expressed with the modified Bessel functions. Only rigid tank is studied. The effective masses and heights for the tank contents are presented for engineering design model.

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Estimation of Hydrodynamic Derivatives of Full-Scale Submarine using RANS Solver

  • Nguyen, Tien Thua;Yoon, Hyeon Kyu;Park, Youngbum;Park, Chanju
    • Journal of Ocean Engineering and Technology
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    • v.32 no.5
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    • pp.386-392
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    • 2018
  • It is necessary to predict hydrodynamic derivatives when assessing the maneuverability of a submarine. The force and moment acting on the vehicle may affect its motion in various modes. Conventionally, the derivatives are determined by performing captive model tests in a towing tank or applying a system identification method to the free running model test. However, a computational fluid dynamics (CFD) method has also become a possible tool to predict the hydrodynamics. In this study, virtual captive model tests for a full-scale submarine were conducted by utilizing a Reynolds-averaged Navier-Stokes solver in ANSYS FLUENT version 18.2. The simulations were carried out at design speed for various modes of motion such as straight forward, drift, angle of attack, deflection of the rudder, circular, and combined motion. The hydrodynamic force and moment acting on the submarine appended rudders and stern stabilizers were then obtained. Finally, hydrodynamic derivatives were determined, and these could be used for evaluating the maneuvering characteristics of the submarine in a further study.

Estimation of Hydrodynamic Derivatives of Submarine Model by Using VPMM Test (VPMM 시험을 이용한 잠수함 모형의 유체력 미계수 추정)

  • Jung, Jin-Woo;Jeong, Jae-Hun;Kim, In-Gyu;Lee, Seung-Keon
    • Journal of Navigation and Port Research
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    • v.38 no.2
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    • pp.97-103
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    • 2014
  • In these days, the world has been increasing navy forces such as aircraft carriers and high-tech destroyers etc. and the importance of submarines is being emphasized. Therefore, accurate values of the derivatives in equations of motion are required to control motion of the submarines. Hydrodynamic derivatives were measured by the vertical planar motion mechanism(VPMM) model test. VPMM equipment gave pure heave and pitch motion respectively to the submarine model and the forces and moments were acquired by load cells. As a result, the hydrodynamic derivatives of the submarine are provided through the Fourier analysis of the forces and moments in this paper.

The Prediction of Hydrodynamic Forces Acting on Ship Hull in Laterally Berthing Maneuver Using CFD

  • Lee, Yun-Sok
    • Journal of Navigation and Port Research
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    • v.27 no.3
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    • pp.253-258
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    • 2003
  • To evaluate the unsteady motion in laterally berthing maneuver, it is necessary to grasp very clearly the magnitude and properties of the hydrodynamic forces acting on ship hull in shallow water. In this study, numerical calculation was made to investigate quantitatively the hydrodynamic force according to the water depth for Wigley model using the CFD (Computational Fluid Dynamics) technique. Comparing the computational results to the experimental ones, the validity of the CFD method was verified. The numerical solutions evaluated the hydrodynamic force with good accuracy, and then captured the features of the flow field around the ship in detail. The transitional lateral force in a state ranging from rest to uniform motion is modeled by using the concept of the circulation.

Circular Motion Test Simulation of KVLCC1 Using CFD (CFD를 이용한 KVLCC1의 Circular Motion Test 시뮬레이션)

  • Shin, Hyun-Kyoung;Jung, Jae-Hwan
    • Journal of the Society of Naval Architects of Korea
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    • v.47 no.3
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    • pp.377-387
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    • 2010
  • In this study, the turbulent free surface around KVLCC1 employed in the circular motion test simulation is numerically calculated using a commercial CFD(Computational Fluid Dynamics) code, FLUENT. Also, hydrodynamic forces and yaw moments around a ship model are calculated during the steady turning. Numerical simulations of the turbulent flows with free surface around KVLCC1 have been carried out by use of RANS equation based on calculation of hydrodynamic forces and yaw moments exerted upon the ship hull. Wave elevation is simulated by using the VOF method. VOF method is known as one of the most effective numerical techniques handling two-fluid domains of different density simultaneously. Boundary layer thickness and wake field are changed various yaw velocities of ship model during the steady turning. The calculated hydrodynamic forces are compared with those obtained by model tests.