• Nuclear Engineering and Technology
• /
• v.35 no.1
• /
• pp.1-13
• /
• 2003

In this study, an effective method to estimate the fundamental frequencies of co-axial cylinders immersed in fluid is proposed. The proposed method makes use of the equivalent mass or density that is derived from the added mass matrix caused by the fluid-structure interaction (FSI) phenomenon. The equivalent mass is defined from the added mass matrix based on a 2-D potential flow theory. The theory on two co-axial cylinders extended to the case of three cylinders. To prove the validity of the proposed method, the eigenvalue analyses upon coaxial cylinders coupled with fluid gaps are peformed using the equivalent mass. The analyses results upon various fluid gap is conditions reveal that the present method could provide accurate frequencies and be suitable for expecting the fundamental frequencies of fluid coupled cylinders in beam mode vibration.

• Journal of Mechanical Science and Technology
• /
• v.18 no.12
• /
• pp.2125-2136
• /
• 2004

In this paper, a numerical application algorithm for applying the CFAM (Consistent Fluid Added Mass) matrix for a core seismic analysis is developed and applied to the 7-ducts core system to investigate the fluid effects on the dynamic characteristics and the seismic time history responses. To this end, three cases such as the in-air condition, the in-water condition without the fluid coupling terms, and the in-water condition with the fluid coupling terms are considered in this paper. From modal analysis, the core duct assemblies revealed strongly coupled out-of-phase vibration modes unlike the other cases with the fluid coupling terms considered. From the results of the seismic time history analysis, it was also verified that the fluid coupling terms in the CFAM matrix can significantly affect the impact responses and the seismic displacement responses of the ducts.

• Structural Engineering and Mechanics
• /
• v.54 no.4
• /
• pp.711-723
• /
• 2015

This study investigates the identification of added mass and its location in the glass fiber reinforced polymer (GFRP) beam structures. The main emphasis of this paper is to ascertain the importance of inclusion of rotational degrees of freedom (dofs) in the introduction of added mass or damage identification. Two identification indices that include the rotational dofs have been introduced in this paper: the modal force index (MFI) and the modal rotational curvature index (MRCI). The MFI amplifies damage signature using undamaged numerical stiffness matrix which is related to changes in the altered mode shapes from the original mode shapes. The MRCI is obtained by using a higher derivative of rotational mode shapes. Experimental and numerical results are compared with the existing methods leading to a conclusion that the contributions of the rotational modes play a key role in the identification of added mass. The authors believe that the similar results are likely in the case of damage identification also.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.4 no.3
• /
• pp.83-98
• /
• 2000

유연한 액체 저장탱크 내 유체의 부가질량 및 슬러싱 강성행렬을 도출하는 새로운 방법을 제시하였다. 비점성, 비압축성 이상유체를 표면 출렁임을 고려하여 경계요소법에 의하여 모델링하였다. 유체의 표면과 저장탱크 벽체의 접촉면과 같은 불연속 경계를 다루기 위해 특별한 과정을 도입하였다. 원통형 액체저장탱크의 지진응답해석에 적용하여 우수한 결과를 얻을 수 있음을 확인하였다.

• Journal of KSNVE
• /
• v.9 no.5
• /
• pp.928-935
• /
• 1999

Vertical pumps are widely used owing to the fact that they occupy small floor space. In this type of pumps, however, the vibrational problems are very important, since, in many cases, they have less stiffness in comparison with lateral pumps. This study presents a simple solution method for calculating the natural frequencies and modes of vertical pumps. In this study, a mode of a vertical pump was developed and the nondimensional parameters for the vibrational characteristics of it were determined. Added mass was calculated for the effects of water and the transfer matrix method was used.

• Journal of the Earthquake Engineering Society of Korea
• /
• v.5 no.5
• /
• pp.25-33
• /
• 2001

For the seismic design and analysis of LMR(liquid metal reactor) being developed in Korea, it is necessary to develop the simple seismic analysis model including the fluid-structure interaction effects. In this paper, the theoretical backgrounds for the fluid added mass of the immersed concentric cylinders are investigated and the seismic analysis code using the Runge-Kutta algorithm, which can consider the fluid added mass matrix in system matrix, are developed to perform the time history seismic analysis. Form the coupled modal analysis and the seismic analysis for the simple immersed concentric cylinders, it is verified that the fluid added mass significantly affect the vibration characteristics and the seismic responses. Therefore the fluid coupled effects should be carefully considered in seismic response analysis of the immersed concentric cylinders.

• Proceedings of the Korean Nuclear Society Conference
• /
• 2003.10a
• /
• pp.476.1-476.1
• /
• 2003

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2012.10a
• /
• pp.229-230
• /
• 2012

The free flexural vibration of a cantilever plate partially submerged in a fluid is investigated. The fluid is assumed to be inviscid and irrotational. The virtual mass matrix is derived by solving the boundary-value problem related to the fluid motion using elliptical coordinates. The introduction of the elliptical coordinates naturally leads to the use of the Mathieu function. Hence, the virtual mass matrix which reflects the effect of the fluid on the natural vibration characteristics is expressed in analytical form in terms of the Mathieu functions. The virtual mass matrix is then combined with the dynamic model of a thin rectangular plate obtained by using the Rayleigh-Ritz method. This combination is used to analyze the natural vibration characteristics of a partially submerged cantilever plate qualitatively. Also, the non-dimensionalized added virtual mass incremental factors for a partially submerged cantilever plate are presented to facilitate the easy estimation of natural frequencies of a partially submerged cantilever plate. The numerical results validate the proposed approach.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.15 no.2
• /
• pp.488-496
• /
• 1991

Dynamic chanracterisitcs and control of a submerged working robot manipulator have been investigated for articulated type robot manipulator with three revoluted joints. A dynamic equation of the manipulator has been derived. The dynamic equation includes not only mass matrix, centrifugal and Coriolis terms and gravity terms but also added mass, buoyant force and drag force terms, which are important terms for underwater motion description. A series of simulations using computed torque method have been performed for the cases of straight and circular trajectory motion controls. The results of this study show that the dynamic characteristics of the submerged working robot manipulator are very different from that of the manipulator which works in air. The influences of added mass, buoyant force and drag force terms to the total required torques have been discussed as distribution ratios to the total required torques.

• 한국태양에너지학회:학술대회논문집
• /
• 2008.04a
• /
• pp.348-358
• /
• 2008

Unlike structures in the air, the vibration analysis of a submerged or floating structure such as offshore structures is possibly only when the fluid-structures is understood, as the whole or part of the structure is in contact with water. Through the comparision between the experimental result and the finite element analysis result for a simple cylindrical model, it was verified that an added mass effects on the cylindrical structure. Using the commercial FEA program ANSYS(v.11.0), underwater added mass was superposed on the mass matrix of the structure. A frequency response analysis of forced vibration in the frequency considered the dynamic load was also performed. It was proposed to find the several important modes of resonance peak for these fixed cylindrical type structures. Furthermore, it is expected that the analysis method and the data in this study can be applied to a dynamic structural design and dynamic performance evaluation for the ground and marine purpose of power generator by wind.