• Journal of the Society of Naval Architects of Korea
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• v.48 no.4
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• pp.368-374
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• 2011

Recently, the ship vibration analysis technique has been well set up by using FEM. The methods considering the hydrodynamic added mass and damping of the fluid surrounding a floating ship have been well developed, so that they can be calculated by using the commercial package FEM programs such as MSC/NASTRAN, ADINA and ANSYS. Especially, MSC/NASTRAN has the functions to consider the fluid in tanks(MFLUID) and to solve the Fluid-Structure Interaction(FSI) problem(DMAP). In this study, the global ship vibration with considering the added mass distributed at the grid points on the wetted shell surface is introduced to. In the new method, the velocity potentials of the fluid surrounding a floating ship are calculated by solving the Lapalce equation using the Boundary Element Method(BEM), and the point mass is obtained by integrating the potentials at the points. Then, the global vibration analyses of the ship structure with distributed added mass on the wetted surface are carried out for an oil/chemical tanker. During the future sea trial, the results will be confirmed by measurement.

• 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.

• Journal of Ocean Engineering and Technology
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• v.11 no.2
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• pp.91-99
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• 1997

This paper presents theoretical formulations and numerical computations for predicting first-and second-order hydrodynamic force on a ship advvancing in waves. The theoretical formulation leads to linearized radiation and diffration problems solving the three-dimensional Green function integral equations over the mean wetted body surface. Green function representing a translating and pulsating source potantial for infinite water depth is used. In order to solve integral equations for three dimentional flows using Green function efficiently, the Hoff's method is adopted for numerical calculation of the Green function. Based on the first-order solution, the mean seconder-order forces and moments are obtained by directly integrating second-order pressure over the mean wetted body surface. The calculated items are carried out for analyzing the seakeeping characteristics of Series 60. The calculated items are hydrodynamic coefficients, wave exciting forces, frequency response functions and addd resistance in waves.

• Journal of Navigation and Port Research
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• v.44 no.2
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• pp.53-64
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• 2020

This paper discusses the hydrodynamic characteristics of a catamaran at low speed. In this study, the Delft 372 catamaran model was selected as the target hull to analyze the hydrodynamic characteristics by using the RANS (Reynold-Averaged Navier-Stokes) numerical method. First, the turbulence study and mesh independent study were conducted to select the appropriate method for numerical calculation. The numerical method for the CFD (Computational Fluid Dynamic) calculation was verified by comparing the hydrodynamic force with that obtained experimentally at high speed condition and it rendered a good agreement. Second, the virtual captive model test for a catamaran at low speed was conducted using the verified method. The drift test with drift angle 0-180 degrees was performed and the resulting hydrodynamic forces were compared with the trends of other ship types. Also, the pure rotating test and yaw rotating test proposed by Takashina, (1986) were conducted. The Fourier coefficients obtained from the measured hydrodynamic force were compared with those of other ship types. Conversely, pure sway test and pure yaw test also were simulated to obtain added mass coefficients. By analyzing these results, the hydrodynamic coefficients of the catamaran at low speed were estimated. Finally, the maneuvering simulation in low speed conditions was performed by using the estimated hydrodynamic coefficients.

• Bulletin of the Society of Naval Architects of Korea
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• v.23 no.2
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• pp.21-26
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• 1986

An analysis is made of hydrodynamic forces acting horizontally on a two-dimensional cylinder, when it is exposed to incident waves and consequently undergoes a swaying motion in shallow water. Applying the method of matched asymptotic expansions the added mass, wave damping and the wave exciting force are obtained in terms of the difference in potential across the cylinder in a simple manner. The potential jump is related to the so-called blockage coefficient which is determined purely from geometry. It is found that the wave damping coefficient can not exceed the blockage coefficient.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2002.09a
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• pp.147-154
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• 2002

Dynamic response analysis are conducted for a floating bridge subjected to multiple support earthquake excitation. The floating bridge used in this study is supported by discrete floating pontoons and horizontal pretension cables supported at both ends of the bridge. The bridge is modeled with finite elements and the hydrodynamic added mass and added damping due to the surrounding fluid around pontoons are obtained using boundary elements. Multiple support excitation is introduced at both ends of the bridge and the time history response is compared to that of a simultaneous excitation. The results shows that the differences between two results are not so large except for cable tension for which the multiple support excitation yields larger values. During the analysis the concept of retardation function is utilized to consider the frequency dependency of the hydrodynamic coefficients.

• 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.

• 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.

• Bulletin of the Society of Naval Architects of Korea
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• v.24 no.2
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• pp.47-54
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• 1987

Linear and nonlinear hydrodynamic force, which acts on submerged circular and eilliptic cylinders in oscillations as well as in advancing motion, are investigated as an initial-boundary value problem using a numerical method, which makes use of the source distribution on the body surface and the spectral method for treating the free surface waves. In the numerical code developed here, the boundary condition at the body surface is linearized. Using the numerical code so attained, nonlinear effects for different forward speeds and of the large-amplitude motion are computed. One of the major findings is that, when the forward speed is large, the added mass has its minimum and the damping force change rapidly around the frequency corresponding to the speed-frequency parameter, $\tau$=0.25, Compared to the result of Grue's [10], who used linear theory to get abrupt changes in values of the added mass and the damping force at the frequency corresponding to $\tau$=0.25, the present study, which takes nonlinear effects into account, shows much smoother variations near the frequency.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.45.1-45.1
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• 2014

structure of matters of Lambda cold dark matter (CDM) cosmology on detailed numerical simulations. To accomplish our research goal, we have added the following baryonic physics on the existing cosmological hydrodynamic code, Gadget-2: 1) radiative heating and cooling, 2) reionization of the Universe and UV shielding, 3) star formation, 4) energy and metallicity feedback by supernova. In addition, we included cluster formation to distinguish clustered star formation inside the very high density gas clumps from the field star formation. Our simulations cover a cubic box of a side length 4Mpc/h with 130 million particles. The mass of each particles is $3.4{\times}104Msun$, thus the GCs can be resolved with more than hundreds particles. We discuss various properties of the GCs such as mass function, specific frequency, baryon-to-dark matter ratio, metallicity, spatial distribution, and orbit eccentricity distribution as functions of redshift. We also discuss how the formation and evolution of the GCs are affected by UV shielding.