• Journal of the Korean Society of Safety
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• v.18 no.1
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• pp.19-27
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• 2003

This paper presented an experimental modal analysis of clamped perforated rectangular plates submerged in water. The penetration of holes in the plates had a triangular pattern with P/D (pitch to diameter) 1.750, 2.125, 2.500, 3.000 and 3.750. The natural frequencies of the perforated plates in air were obtained by the Rayleigh-Ritz method and compared with the experimental results. Good agreement was obtained between the analytical solution and experimental result. The experimental results in water showed that the mode shapes are not sensitive to the depth of submergence. The natural frequencies were shown to decrease drastically once the perforated plates come in contact with water. However, the natural frequencies decrease with the depth of submergence until a certain depth is reached, and become the asymptotic values beyond this depth of submergence. The depth of submergence did not affect the damping ratio greatly.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.21 no.10
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• pp.905-915
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• 2011

The free flexural vibration of a hanged clamped-free cylindrical shell partially submerged in water with gap from bottom is investigated. The fluid is assumed to be inviscid and irrotational. The cylindrical shell is modeled by using the Rayleigh-Ritz method based on the Sanders shell theory. The kinetic energy of the fluid is derived by solving the boundary-value problem related to the fluid motion. The natural vibration characteristics of the partially submerged cylindrical shell are discussed with respect to the added virtual mass approach. In this study, experiments were carried out to confirm theoretical results. It was found that theoretical prediction is in good agreement with experimental results.

• Nuclear Engineering and Technology
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• v.51 no.4
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• pp.1008-1016
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• 2019

In the SG (steam generator) of PWR (pressurized water reactor) for a nuclear plant, hundreds of U-shaped tubes are used for the heat exchanger system. They interact with primary pressurized cooling water flow, generating flow-induced vibration in the secondary flow region. A simplified U-tube model is proposed in this study to apply for experiment and its counterpart computation. Using the commercial code, ANSYS-CFX, we first verified the Moody chart, comparing the straight pipe theory with the results derived from CFD (computational fluid dynamics) analysis. Considering the virtual mass of fluid, we computed the major modes with the low natural frequencies through the comparison with impact hammer test, and then investigated the effect of pump flow in the frequency domain using FFT (fast Fourier transform) analysis of the experimental data. Using two-way fluid-structure interaction module in the CFD code, we studied the influence on mean flow rate to generate the displacement data. A feasible CFD method has been setup in this research that could be applied potentially in the field of nuclear thermal-hydraulics.

• Tribology and Lubricants
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• v.40 no.2
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• pp.39-46
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• 2024

The Morton effect (ME) is an instability phenomenon occurring in rotating machineries supported by fluid film bearings and is induced by the thermal deformation of the overhung mass, which is a part of the rotating shaft. Herein, we describe the ME during the high-speed balancing test of a 20 MW class steam turbine. Additionally, to predict the rotating speed at which the ME occurs, we apply the sensitivity vector theory for the steam turbine. During the operation of the steam turbine, we observe a continuous increase in vibration and hysteresis near the rated speed, which is typical of the ME. Increasing the temperature of the lubricating oil supplied to the bearings from 40 to 60℃ suppresses the occurrence of the ME. The rotordynamic analysis for the steam turbine suggests the existence of a mode in which the overhung mass undergoes significant deformation near the rated speed, and we presume that such a mode will increase the occurrence of the ME. The predicted rotating speed of ME occurrence, obtained through the sensitivity vector method, correlates with the test results. Moreover, increasing the temperature of the supplied lubricating oil mitigates the occurrence of ME by reducing the sensitivity between the temperature deviation vector and unbalance mass vector.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.2005-2011
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• 2003

Introducing the interfacial pressure jump terms based on the surface tension into the momentum equations of two-phase two-fluid model, the system of governing equations is turned mathematically into the hyperbolic system. The eigenvalues of the equation system become always real representing the void wave and the pressure wave propagation speeds as shown in the previous manuscript. To solve the interfacial pressure jump terms with void fraction gradients implicitly, the conventional semi-implicit method should be modified as an intermediate iteration method for void fraction at fractional time step. This advanced semi-implicit method (ASIM) then becomes stable without conventional additive terms. As a consequence, including the interfacial pressure jump terms with the advanced semi-implicit method, the numerical solutions of typical two-phase problems can be more stable and sound than those calculated exclusively by using any other terms like virtual mass, or artificial viscosity.

• Journal of computational fluids engineering
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• v.18 no.2
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• pp.99-108
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• 2013

The standard drag force and virtual mass force, which exert to the primary flow direction, are generally considered in two-phase analysis computational codes. In this paper, the lift force, wall lubrication force, and turbulent dispersion force including turbulence models, which are essential for a computational multi-fluid dynamics model and play an important role in motion perpendicular to the primary flow direction, were introduced and verified with conceptual problems.

• 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.

• International Journal of High-Rise Buildings
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• v.1 no.2
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• pp.107-116
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• 2012

The overarching objective of this study is to predict the convective heat transfer around a human body under forced strong airflow conditions assuming a strong wind blowing through high-rise buildings or an air shower system in an enclosed space. In this study, computational fluid dynamics (CFD) analyses of the flow field and temperature distributions around a human body were carried out to estimate the convective heat transfer coefficient for a whole human body assuming adult male geometry under forced convective airflow conditions between 15 m/s and 25 m/s. A total of 45 CFD analyses were analyzed with boundary conditions that included differences in the air velocity, wind direction and turbulence intensity. In the case of approach air velocity $U_{in}=25m/s$ and turbulent intensity TI = 10%, average convective heat transfer coefficient was estimated at approximately $100W/m^2/K$ for the whole body, and strong dependence on air velocity and turbulence intensity was confirmed. Finally, the formula for the mean convective heat transfer coefficient as a function of approaching average velocity and turbulence intensity was approximated by using the concept of equivalent steady wind speed ($U_{eq}$).

• Bulletin of the Society of Naval Architects of Korea
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• v.11 no.1
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• pp.9-16
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• 1974

To contribute towards more accurate estimation of the virtual inertia coefficient for the horizontal vibration of ships, three dimensional correction factor $J_H$ for the added mass of finitely long elliptic prismatic bars in horizontal vibration in a free surface of an ideal fluid are calculated. In the problem formulation Dr. T. Kumai's quasi-finite length concept[1,11,12] is employed. Now that, in Dr. Kumai's work[1] for the horizontal vibration the mathematical model was a circular cylinder, the principal aim of the authors' work is to investigate the influence of the beam-draft ratio B/T on $J_H$. The numerical results of this work are shown in Fig.3 graphically, from which we may recognize that the influence of B/T on $J_H$ is remarkable as much as that of the length-draft ratio L/T(refer to Fig.1 also). In Fig.3 the curves for B/T=2.00 are of those based on Dr. Kumai's result[1]. On the other hand, the experimental data obtained by Burril et al.[9] for the horizontal vibration of finitely long prismatic bars of various cross-section shapes are compared with the theoretical added mass coefficients defined by combination of the authors' $J_H$ from Fig.3 and two dimensional coefficients $C_H$ obtained by Lewis form approximation for the corresponding sections. They are in reasonable correspondence with each other as shown in Fig.2. Finally, considering that the longitudinal profile of full-form ship's hull is well resembled to that of an elliptic cylinder and that the influences of other factors such as the sectional area coefficient and the shape of section contour itself can be well merged in the two dimensional added mass coefficient, the authors recommend that the data given in Fig.3 may be successfully adopted for the three dimensional correction factor the added mass in the horizontal vibration of hull-form ships.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.13 no.1
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• pp.70-78
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• 2003

This paper dealt with an experimental study on the hydroelastic vibration of clamped perforated rectangular plates submerged in water. The penetration of holes in the plates had a triangular pattern with P/D (pitch to diameter) 1.750, 2.125, 2.500, 3.000 and 3.750. The natural frequencies of the perforated plates in air were obtained by the analytical method based on the relation between the reference kinetic and maximum potential energy and compared with the experimental results. Good agreement between the results was found for the natural frequencies of the perforated plates in air. It was empirically found that the natural frequencies of the perforated plate in air increase with an increase of P/D, on the other hand, the natural frequencies of the perforated plate in contact with water decrease with an increase of P/D. Additionally. the effect of the submerged depth on the natural frequency was investigated.