• Journal of the Computational Structural Engineering Institute of Korea
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• v.33 no.1
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• pp.45-53
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• 2020

Analytical and experimental studies show that the dynamic behavior of liquid storage tanks is significantly influenced by the fluid-structure interaction (FSI). The effects of FSI must be rigorously considered for accurate earthquake analysis and seismic design of liquid storage tanks. In this study, a dynamic analysis of a rectangular liquid storage tank subjected to bi-directional earthquake ground motions is performed and its dynamic characteristics are examined, with the effects of FSI rigorously considered. Hydrodynamic pressure is evaluated using the finite-element approach with acoustic elements and applied to the structure. The responses of the rectangular tank subjected to bi-directional earthquake ground motions are thus obtained. It can be observed that the incident angle of bi-directional horizontal ground motions has significant effects on the dynamic responses of the considered system. Therefore, the characteristics of the system must be considered in its seismic design and performance evaluation.

• International Journal of Naval Architecture and Ocean Engineering
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• v.8 no.5
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• pp.487-495
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• 2016

In the offshore project such as semi-submersible FPU and FPSO, the free fall type life boat called TEMPSC (Totally Enclosed Motor Propelled Survival Craft) has been installed for the use of an emergency evacuation of POB (People on Board) from the topside platform. For the design of life boat arrangement for semi-submersible FPU in the initial design stage, the drop height and launch angle are required fulfill with the limitation of classification society rule and Company requirement, including type of approval as applicable when intact and damage condition of the platform. In this paper, we have been performed the numerical studies to find proper arrangement for the life boats consider drop height in various environmental conditions such as wave, wind and current. In the calculations, the contributions from static and low frequency (LF) motions are considered from the hydrodynamic and mooring analysis as well as damage angle from the intact and damage stability analysis. Also, Air-gap calculation at the life boat positions has been carried out to check the effect on the life boat arrangement. The air-gap assessment is based on the extreme air-gap method includes the effect of 1st order wave frequency (WF) motions, 2nd order low frequency roll/pitch motion, static trim/heel and set down.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.4
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• pp.501-509
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• 2010

A floating crane is a crane-mounted ship and is used to assemble or to transport heavy blocks in shipyards. In this paper, the static and dynamic response of a floating crane and a heavy block that are connected using elastic booms and wire ropes are described. The static and dynamic equations of surge, pitch, and heave for the system are derived on the basis of flexible multibody system dynamics. The equations of motion are fully coupled and highly nonlinear since they involve nonlinear mass matrices, elastic stiffness matrices, quadratic velocity vectors, and generalized external forces. A floating frame of reference and nodal coordinates are employed to model the boom as a flexible body. The nonlinear hydrostatic force, linear hydrodynamic force, wire-rope force, and mooring force are considered as the external forces. For numerical analysis, the Hilber-Hughes-Taylor method for implicit integration is used. The dynamic responses of the cargo are analyzed with respect to the results obtained by static and numerical analyses.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.12
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• pp.1489-1495
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• 2012

In this study, we perform the structural analysis of a floating offshore wind turbine tower by considering the dynamic response of the floating platform. A multibody system consisting of three blades, a hub, a nacelle, the platform, and the tower is used to model the floating wind turbine. The blades and the tower are modeled as flexible bodies using three-dimensional beam elements. The aerodynamic force on the blades is calculated by the Blade Element Momentum (BEM) theory with hub rotation. The hydrostatic, hydrodynamic, and mooring forces are considered for the platform. The structural dynamic responses of the tower are simulated by numerically solving the equations of motion. From the simulation results, the time history of the internal forces at the nodes, such as the bending moment and stress, are obtained. In conclusion, the internal forces are compared with those obtained from static analysis to assess the effects of wave loads on the structural stability of the tower.

• Journal of the Society of Naval Architects of Korea
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• v.30 no.1
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• pp.45-64
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• 1993

This paper dealt with the application of a numerical method developed by the authors using the matching method proposed in the previous paper on "The Nonlinear motions of cylinders(I)[16]", and Cauchy's theorem to the problems associated with hydrodynamic forces acting on a heaving cylinders translating in a calm water and also motions of cylinders in waves. In spectral method. body boundary condition in submerged case is satisfied exactly but one in floating case is not satisfied exactly. In the numerical code developed here, the boundary condition at the free-surface and body surface is satisfied exactly at its instaneous position. It is of interest to note that the present scheme could be applied to a free-surface-piercing body without experiencing a difficulty in the numerical convergence. The computed results are compared with other results([6], [12]).

• Journal of the Society of Naval Architects of Korea
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• v.52 no.1
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• pp.25-33
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• 2015

Following the previous works on the natural frequency of heaving circular cylinder, i.e. Lee and Lee (2013) and Kim and Lee (2013), an investigation of the same spirit on the 2-dimensional cylinder of Lewis form has been conducted. As before, the natural frequency is defined as that corresponding to the local maximum of the MCFR (Modulus of Complex Frequency Response), which is given by the equation of motion in the frequency domain analysis. Hydrodynamic coefficients were found by using the Ursell-Tasai method, and numerical results for them were obtained up to much higher frequencies than before, for which the method was known as numerically unstable in the past. For a wide range of H, the beam-draft ratio, and ${\sigma}$, the sectional area coefficient, including their practical ranges for a ship, results for the natural frequency were computed and presented in this work. Two approximate values for the natural frequency, one proposed by Lee (2008) and another one by the damped harmonic oscillator, were also compared with the current results, and for most cases it was observed that the current result is between the two values. Our numerical results showed that the values of the local maximum of MCFR as well as the natural frequencye increase as ${\sigma}$ increases while H decreases. At present, extension of the present finding to the 3-dimensional ship via the approximate theory like the strip method looks promising.

• Journal of the Society of Naval Architects of Korea
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• v.38 no.4
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• pp.30-38
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• 2001

The current is considered in the conventional manoeuvering equation. This equation is represented as the nonlinear state and measurement equations in which external forces and the direction and the velocity of current are augmented as that variables. The external forces are modeled as the third-order Gauss-Markov processes and the direction and the velocity of current are assumed to be constant. The augmented state variables are estimated with extended Kalman-Bucy filter and the fixed-interval smoother. While Hwang estimated motion state variables, hydrodynamic coefficients and the current variables simultaneously by using extended Kalman filter, external forces of surge, sway and yaw and the direction and the velocity of current are the only parameters to be estimated in the estimation-before-modeling method. The current variables are satisfactorily estimated in simulation process where the measurement noise is present.

• Journal of the Society of Naval Architects of Korea
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• v.39 no.3
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• pp.64-74
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• 2002

A special purposed program for ship hull strength analysis considering whipping phenomena is developed. In this program, the non-linear hydrodynamic impact force is considered using the momentum slamming theory and the hull girder is modeled as elastic body on the base of Timoshenko's beam theory. The numerical verifications are conducted in the view points that the effect of slamming impact force, the effect of hydro-elastic formulation, and the effect of various design parameters such as ship speed, wave amplitude, wave length and others. By the application of a real ship design process, the availability of the program is proved. This program has a GUI function for many I/O data process as well as the function to show the 2-D ship motion in the graphic window, and has other available functions for the whipping analysis.

• Journal of the Earthquake Engineering Society of Korea
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• v.9 no.2 s.42
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• pp.47-58
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• 2005

Dynamic response analysis in time dimain is conducted for floating bridges with discrete pontoons subject to spatial variation of ground motions. The Spatial variation of ground motions is considered with the coherency function model which represents wave passage, incoherence and local site effects. The superstructure of the bridge is represented by space frame and elastic catenary cable elements, the abutment us modelde with the spring element of FHWA guideline for considering soil structure interaction and the concept of retardation function is utilized to consider the frequency dependency of the hydrodynamic coefficients which are obtainde by boundary element method. multiple support excitations considering the spatial variation. The noticeable amplification of the response can be shown when the spatial variation of ground motions is incorporated in the anallysis of floating bridges.

• Journal of the Korean Institute of Navigation
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• v.10 no.2
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• pp.97-114
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• 1986

Ship's maneuverability is very important factor in safe ship handling and economical ship operation. Steering characteristics are consisted of course stability and maneuverability. Today in many advanced ship-building countries, they study ship's course stability, using model ship tests, such as straight line tests, rotating arm tests and Planar Motion Mechanism (PMM) etc., in tow in tanks. It is the purpose of this paper to provide ship's handlers with better understanding of steering characteristics and to help them in safe controlling and manevering . In this paper, the author simulated response of various vessels, running straight course with constant speed, and they are disturbed by small external disturbance of one degree yaw angle with no angular velocity . The author used the hydrodynamic derivtives resulted at tests of Davidson's laboratory in Stevens Institute of Technology, New Jersey, U.S.A. Course stability was evaluated and analyzed in various respects, such as block coefficient, ratio of ship's length to beam, draft and rudder area ratio etc. The obtained results are as follows : (1) The ship's course stability is affected by magnitude of block coefficient greatly. In case that the block coefficient is more than 0.7, the deviation varies at nearly same rate but the requistite time to reach the steady course is different. (2) The ship's course stability is affected by magnitude of L/B. When the dimensionless time reaches about 3, the deviation and requisite time to reach the steady course are influenced nearly same. After the dimensionless time is about 3, they change on invariable ratio. (3) The effect to course stability by L/T and RA' can be neglected. (4) The reason why thy VLCC and container feeder vessel are unstable on their course is that their block coefficient is generally more than 0.8 and the ratio of ship's length to beam is about 6.0.