• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.6
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• pp.17-24
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• 2020

In this study, series of nonlinear seismic analysis were performed on a reinforced concrete intake tower surrounded by water. To consider the fluid effect around the structure, analysis models were composed using an added mass and CEL approach. At this time, the implicit method was used for the added mass model, and the explicit method was used for the fluid structure interaction model. The input motions were scaled to correspond to 500, 1000, and 2400 years return period of the same artificial earthquake. To estimate the counteractivity of the fluid coupled model, models without fluid effect were constructed and used as a reference. The material models of concrete and reinforcement were selected to consider the nonlinear behavior after yielding, and analysis were performed by ABAQUS. As results, in the acceleration response spectrum of the structure, it was found that the influence of the surrounding fluid reducing the peak frequency and magnitude corresponding to the fundamental frequency of the structure. However, the added mass model did not affect the peak value corresponding to the higher mode. The sectional moments were increased significantly in the case of the added mass model than those of the reference model. Especially, this amplification occurred largely for a small-sized earthquake response in which linear behavior is dominant. In the fluid structure interaction model, the sectional moment with a low frequency component amplifies compared to that of the reference model, but the sectional moment with a high requency component was not amplified. Based in these results, it was evaluated that the counteractivity of the additive mass model was greater than that of the fluid structure interaction model.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2000.10a
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• pp.377-386
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• 2000

Hybrid mass dampers consist of passive tuned mass dampers and active mass dampers. They have the advantage that passive tuned mass dampers are still operated even when active mass dampers are stopped by excessive disturbances or power failure. This paper begins first with the comparative analysis of tuned mass dampers, hybrid mass dampers, and active mass dampers. Next more detailed study is carried out on the hybrid mass dampers: cascade hybrid mass dampers (CHMD) and active tuned mass dampers (ATMD). CHMD is regarded as more reasonable device because of its lighter active mass than ATMD's. However CHMD can not neglect stroke saturation problem caused by the length limitation of active damper mass. We compensate the saturation problem with nonlinear restoring force. The restoring force is calculated based on the states and phases of active mass dampers and added to the control force. It is shown that the presented compensation method prevents CHMD from saturation behavior without apparent changes of control force and responses compared to those in case of not considering the saturation problem.

• Proceedings of the KSME Conference
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• 2001.11a
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• pp.465-470
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• 2001

In this study, the seismic analysis of rack structure with fluid-structure interaction is performed through use of the Finite Element Method(FEM) code ANSYS. Fluid-structure interaction can specify in terms of an hydrodynamic effect which is defined as the added mass per unit length divided by the area of the cross section. Using the Floor Response Spectrum(FRS) obtained through the time-history analysis, modal analysis and seismic analysis under Operating Basis Earthquake(OBE) and Safe Shutdown Earthquake(SSE) condition is carried out. The fluid-structure interaction effects on the rack structure are investigated.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2004.05a
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• pp.167-171
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• 2004

The Spar platform with deep draft is characterized as effective structure in extreme wave condition, which has larger natural period than that of waves in sea. In this paper, the time simulation of motion responses of Spar with catenary mooring line is presented in irregular waves. The memory effect is modeled by added mass at infinite frequency and convolution integrals in terms of wave damping coefficients. The added mass, wave damping coefficients and wave exciting forces are obtained from three-dimensional panel method in the frequency domain. The motion equations are consisted of forces for inetia, memory effect, hydrostatic restoring, wave exciting and mooring line. The forces of mooring line are modeled as quasi-static catenary cable.

• Journal of Ocean Engineering and Technology
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• v.23 no.3
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• pp.6-13
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• 2009

Based on the boundary element method, the motion responses and transmission coefficients of a moored floating breakwater were investigated in oblique waves. To satisfy the outgoing radiation condition in the far field, the fluid domain was divided into inner and outer regions. The complete solution could be obtained by applying the matching conditions between the eigenfunction-based outer solution and BEM-based inner solution. Using the developed predictive tools, the wave exciting forces, added mass, damping coefficients, motion responses, and transmission coefficients were assessed for various combinations of breakwater configuration, wave heading, mooring cables properties, and wave characteristics. It was found that the transmission coefficient for a moored floating breakwater was closely dependent on the motion responses, which were greatly amplified at the resonant frequencies.

• Journal of Advanced Research in Ocean Engineering
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• v.2 no.1
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• pp.12-21
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• 2016

In this paper, the $2^{nd}$ order hydrodynamic force effect of heaving submerged circular cylinder is considered, with the linear potential theory. Boundary value problem (BVP) is expanded up to the $2^{nd}$ order by using of the perturbation method and the $2^{nd}$ order velocity potential is calculated by means of integral equation technique using the classical Green's function expressed in cylindrical coordinates. The method of solving BVP is based on eigenfunction expansions. With different cylinder heights and heaving frequencies, graphical results are presented. As a result of the study, the cause of oscillatory force pattern is analyzed with the occurrence of negative added mass when a top of the cylinder gets closer to the free surface.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2005.11b
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• pp.65-68
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• 2005

In this paper, a theoretical study is carried out on the hydroelastic vibration of a rectangular tank wall. It is assumed that the tank wall is clamped along the plate edges. The fluid velocity potential is used for the simulation of fluid domain and to obtain the added mass due to wall vibration. In addition, the vibration characteristics of stiffened wall of the rectangular tank are investigated. Assumed mode method is utilized to the stiffened plate model and hydrodynamic force is obtained by the proposed approach. The coupled natural frequencies are obtained from the relationship between kinetic energies of a wall including fluid and the potential energy of the wall. The theoretical result is compared with the three-dimensional finite element method and then added mass effect is discussed due to tank length and potential mode.

• Journal of the Society of Naval Architects of Korea
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• v.41 no.5
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• pp.1-7
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• 2004

The Spar platform with deep draft is characterized as effective structure in extreme wave condition, which has larger natural period than that of waves in sea. In this paper, the time domain simulation of motion responses of Spar with catenary mooring line is presented in irregular waves. The memory effect is modeled by added mass at infinite frequency and convolution integrals in terms of wave damping coefficients. The added mass, wave damping coefficients and wave exciting forces are obtained from three-dimensional panel method in the frequency domain. The motion equations are consisted of forces for inertia, memory effect, hydrostatic restoring, wave exciting and mooring line. The forces of mooring line are modeled as quasi-static catenary cable.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 1999.10a
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• pp.83-90
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• 1999

This paper presents a method of seismic analysis for a cylindrical liquid storage structure on horizontally layered half-space considering the effects of the interior fluid and exterior soil medium in the frequency domain. the horizontal and rocking motions of the structures are included in this study. The fluid motion is expressed in terms of analytical velocity potential function which can be obtained by solving the boundary value problem including the sloshing behavior of the fluid as well as deformed configuration of the structure. The effect of the fluid is included in the equation of motion as the impulsive added mass and a frequency-dependent convective added mass along the nodes on the wetted boundary with structure. The soil medium is presented using the 3-D axisymmetric finite elements and dynamic infinite elements. The present method can be applied to the structures embedded in ground as well as on ground since it models the soil medium directly as well as the structure. For the purpose of vertification dynamci characteristics of a tank on homogeneous half-space is analyzed. Comparison of the present results with those by others shows good agreement.

• Bulletin of the Society of Naval Architects of Korea
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• v.17 no.2
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• pp.11-16
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• 1980

For vibration analysis of stiffened plates the orthotropic plate analogy is commonly accepted. As to stiffened plates in contact with water, however, there is still much uncertainty in estimation of the added mass because of the lack of direct methods. The authors, considering that for added mass of plates there are many reliable data derived theoretically or experimentally available, suggest a method to estimate the added mass of a stiffened plate by combining the mass increase factor, $\beta$, of an equivalent orthotropic plate and the correction factor, $\kappa$, for the effects of stiffeners. The latter is to be derived from systematic experimental investigations. Then, the natural frequency in water, f', can be calculated from that in air, f, by the equation $f'=f/\sqrt{1+\kappa\beta}$. To investigate practical applicability of this method, a systematic experiment was carried out with five uniaxially stiffened plates. Each of them had a plate of same size, $600mm{\times}600mm{\times}3.2mm$, but stiffeners of different size in the web-depth, 41.6mm, 51.2mm or 66.8mm and of different spacing 75mm, 100mm, or 150mm. Natural frequencies were measured under simply supported-edge conditions in both air and water, and corresponding $\kappa$ values derived. In spite of wide variations of web-depth and spcae of stiffeners, the experimental results show that the diversity of $\kappa$ values is not remarkable; mean values of $\kappa$ are 1.31 with standard deviation of 0.025 for the first modes and 1.27 with that 0.077 for the second modes. Hence, the authors concluded that the above $\kappa$ values can be used generally for the cases of uniaxially stiffened plates both sides of which contact with water, and that $\kappa$ values of general use for the cases of cross-stiffened plates may also be obtainable from similar experiments.