• Journal of Ocean Engineering and Technology
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• v.19 no.6 s.67
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• pp.58-63
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• 2005

The estimation of springing responses for recent ships is carried out, and application to a ship design is described. To this aim, springing effects on hull girder were re-evaluated, including non-linear wave excitations and torsional vibrations of the hull. The Timoshenko beam model was used to calculate stress distribution on the hull girder, using the superposition method. The quadratic strip method was employed to calculate the hydrodynamic forces and moments on the hull. In order to remove the irregular frequencies, we adopted 'rigid lid' on the hull free surface level, and addedasymptotic interpolation along the high frequency range. Several applications were carried out on the following existing ships: The Bishop and Price's container ship, S-175 container ship, large container, VLCC, and ore carrier. One of them is compared with the ship measurement result, while another with that of the model test. The comparison between the analytical solution and the numerical solution for a homogeneous beam-type artificial ship shows good agreement. It is found that Most springing energy comesfrom high frequency waves for the ships having low natural frequency and North Atlantic route etc. Therefore, the high frequency tail of the wave spectrum should be increased by $\omega$$\^{-3}$ instead of $\omega$$\^{-4}$ or $\omega$$\^{-5}$ for the springing calculation.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2006.11a
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• pp.426-426
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• 2006

선박이 천 흘수 및 수로를 운항하는 경우 바닥과 벽면의 영향으로 인해 선체침하 및 비대칭적인 힘이 선체 주위에 발생하여 바닥이나 다른 선박 혹은 수로의 벽에 충돌하는 현상이 발생한다. 특히, 수로가 많은 유럽이나 북미를 운항하는 해운회사와 항해사들은 선박의 충돌을 방지하기 위해서 중요한 문제로 다루고 있다. 따라서, 본 연구에서는 선박의 안전한 항해를 위해 수치해석을 이용하여 선박과 벽면 사이에 발생하는 유체역학적 힘, 즉 Sway force와 Yaw Moment를 정성적으로 추정하고자 하였다. 천 흘수 유동 해석용 프로그램을 작성하였으며, 검증을 위해서 Wigley 선형에 적용하여 h/T별로 계산을 수행하여 시험결과와 비교하였다. 그리고, 벽면효과를 해석 할 수 있는 프로그램을 작성하여 실적선인 원유운반선 2척에 대하여 3가지 파라메터, 즉 선속, 수심 그리고 선박과 벽면 사이 거리의 변화에 따른 다양한 계산을 수행하였다. 계산된 결과는 시험결과 및 기 발표된 수치해석 결과와 비교하였다. 기 발표된 논문에서는 시험결과와 계산결과가 상이한 결론을 보여 주었는데, 그 이유는 수치해석에 있어서 자유표면 문제를 선형화된 자유표면 조건식을 사용한 부분을 가장 큰 이유로 언급하였다. 하지만, 본 연구의 결과는 Sway force와 Yaw Moment가 기 발표된 논문의 시험결과와 정성적으로 일치함을 보여 주었다. 본 연구를 통해 수치해석 방법으로 선박에 작용하는 비대칭 유동에 대한 유체역학적인 힘을 정성적으로 추정할 수 있었고, 제한된 수로에서 선박의 조종성 예측 및 수로 설계시 유용한 정보를 제공할 수 있을 것이라고 판단되어 진다.

• Journal of Ocean Engineering and Technology
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• v.23 no.1
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• pp.16-23
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• 2009

The three-dimensional ship motion with forward speed was solved by a finite element method in the time domain. A boundary value problem was described in the frame of a fixed-body reference, and the problem was formulated according to Double-Body and Neumann-Kelvin linearizations. Laplace's equation with boundary conditions was solved by a classical finite element method based on the weak formulation. Chebyshev filtering was used to get rid of an unwanted saw-tooth wave and a wave damping zone was adopted to impose a numerical radiation condition. The time marching of the free surface was performed by the 4th order Adams-Bashforth-Moulton method. Wigley I and Wigely III models were considered for numerical validation. The hydrodynamic coefficients and wave exciting forces were validated by a comparison with experimental data and the numerical results of the Wigley I. The effects of the linearization are also discussed. The motion RAO was also checked with a Wigley III model through mono-chromatic and multi-chromatic regular waves.

• Journal of Institute of Control, Robotics and Systems
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• v.20 no.4
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• pp.402-407
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• 2014

In this paper, residual sway control of objects that are moved underwater is investigated. The fuel transfer system in a nuclear power plant transfers the nuclear fuel rods underwater. The research on the dynamics of the loads transferred in different mediums (water and air) and their control methods have not been fully developed yet. The attenuation characteristics of the fuel transfer system have been studied to minimize its residual vibration by considering the effects of hydrodynamic forces acting on the fuel rod. First, a mathematical model is derived for the underwater fuel transfer system, and then experiments have been conducted to study the dynamic behavior of the rod while it travels underwater. Lastly, the residual vibration at the end point is minimized using the input shaping technique.

• Journal of the Society of Naval Architects of Korea
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• v.53 no.1
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• pp.10-17
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• 2016

When a planing hull straightly runs and turns, its floating position and pitch angle are changed depending on its speed, and large transient motion happens. In this paper, six degrees of freedom(6 DOF) equations of motion, which could simulate the motion of a planing hull, are established. Static and dynamic forces in vertical plane are modeled using pre-calculated displacements and metacentric heights depending on various draft, lift under bottom, and vertical damping coefficients which are used to tune the final motion. Hydrodynamic coefficients in horizontal plane at various equilibrium state are calculated by using Lewandowski's empirical formula and the speed-dependent equilibrium state are calculated beforehand by Savitsky's formula. The speed effects are considered by curve-fitting the coefficients at various speed to the polynomials. Accelerating, decelerating and backing, turning, and zig-zag are simulated and compared with the sea trial results, and it is confirmed that the speed reduction, roll, and pitch during such maneuvers of sea trial and simulation are well consistent.

• KSTLE International Journal
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• v.4 no.1
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• pp.18-26
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• 2003

Recently, fluid dynamic bearings (EDBs) have important applications in miniature rotating machines such as those found in the computer information storage industry, due to their outstanding low acoustic noise and NRRO (Non-Repeatable Run Out) characteristics. This research investigates the dynamic behavior of fluid dynamic bearings composed of hydrodynamic herringbone groove journal and spiral groove thrust bearing. The five degrees of freedom of FDB are considered to describe the real motion of a general rotor bearing system. The Reynolds equation and five nonlinear equations of motion for the dynamic behavior are solved simultaneously, The incompressible Reynolds equation is solved by using the finite element method (FEM) in order to calculate the pressure distribution in a fluid film and the five equations of motion by using the Runge-Kutta method. The reaction forces and moments are obtained by integrating the pressure along the fluid film. Numerical results are validated by comparing with the previously published experimental and numerical results. As a result the dynamic behavior of FDB spindle such as orbit, floating height, and angular orbit is investigated by considering the conical motion under the static and dynamic load conditions.

• Journal of the Korean Society of Marine Environment & Safety
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• v.24 no.5
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• pp.537-544
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• 2018

In this study, a simple, efficient, user-based program called SCAR was developed for evaluating the sliding and collapse of artificial reefs due to hydrodynamic forces in ocean environments. SCAR was developed by applying Delphi code and a Graphical User Interface (GUI) based on the Morison formula for evaluating and analyzing the stability of artificial reefs. SCAR can be applied widely for design and stability evaluation of fishery structures (such as artificial reefs or other underwater structures) in undergraduate and graduate courses and by experts in the field.

• Journal of the Society of Naval Architects of Korea
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• v.33 no.4
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• pp.162-174
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• 1996

Longline type aquaculture facilities in the open sea are based on the cable-buoy-weight mooring system. For their optimal design it is necessary to estimate tensions along the mooring lines including the attachment points of buoys and weights. However, the dynamic analysis is very complicated due to the nonlinear behaviors of the mooring lines and the effects of wave and current. In this paper, parametric studies for various buoy-weight cases are shown. Finite difference scheme is employed in obtaining eigenfrequencies in the frequency domain. Nonlinear hydrodynamic drag forces are equivalently linearized.

• Bulletin of the Society of Naval Architects of Korea
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• v.38 no.3
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• pp.88-92
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• 2001

H. Kim, B.K. Lee and C.K. Rheem have been experimentally studied to clarified the mechanism of thrust force generated by sculling motion for the propulsion of Korean small boats. The experimental investigations have been conducted under the bollard condition by installing a scull at the end of a trimming tank of towing tank. The sculling motion produced by the skilful fisherman and the resultant venerated forces have been measured in respect to the Cartesian coordinate fitted to the pivot point of the scull. ("An Experimental Study on the Propulsive Characteristics of Sculls". J. of the Soc. of Naval Arch. of Korea, Vol. 26, No. 3, 1989, pp.13-24) Through these experiments the trajectory of the blade tip and the angular displacement of the blade section have been measured as shown in Fig. 1 and 2 of this paper. And at the same time the resultant hydrodynamic force components are expressed in Fig. 3 and 4. These three dimensional data of sculling motion and generated real time force components are the unique experimental information which could clarify the thrust force generating mechanism of sculling motion. The experimental results have been reanalyzed by focusing the relation between instantaneous attack angle of blade section and the resultants real time force components. Through these investigation it is found out that the conventional imagination that the 7cull motion should be effective in generating lift force must be reconsidered because the attack angle of scull blade are too great to free from stall phenomena during the sculling operation.

• International Journal of Naval Architecture and Ocean Engineering
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• v.5 no.2
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• pp.287-301
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• 2013

The present paper deals with the problems of yaw angle effects on podded propulsor performance. The study aims at providing insights on characteristics of podded propulsors in azimuthing condition. In this regard, a wide numerical simulation that concerned yaw angle effect measurement on podded propeller performance was performed. The Reynolds-Averaged Navier Stokes (RANS) based solver is used in order to study the variations of hydrodynamic characteristics of podded propulsor at various angles. At first, the propeller is analyzed in open water condition in absence of pod and strut. Next flow around pod and strut are simulated without effect of propellers. Finally, the whole unit is studied in zero yaw angle and azimuthing condition. Structured and unstructured mesh techniques are used for single propeller and podded propulsor. The performance curves of the propeller obtained by numerical method are compared and verified by the experimental results. The characteristic parameters including the torque and thrust of the propeller, the axial force and side force of unit are presented as function of velocity advance ratio and yaw angle. The results shows that the propeller thrust, torque and podded unit forces in azimuthing condition depend on velocity advance ratio and yaw angle.