Abstract
The natural frequencies of structures submerged in a fluid are significantly influenced by fluid properties and adjacent structures, which can be expressed by added mass. Some finite element software can effectively determine the added mass matrix of arbitrary structures immersed in viscous fluids, provided the structure lengths are relatively long; however, the added mass specified in a second-order tensor cannot be used as is. Herein, we propose methods to calculate the coupled added mass as a single value for each structure using the MassInFlu code. When the x- and y-directional components of the coupled added mass are unequal, an effective added mass can be determined by rotating the structures or coordinate axes. Various examples considering different scenarios show that the coupled natural frequencies obtained using the coupled or effective added mass coincide with those obtained from fluid-structure interaction analyses.
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Abbreviations
- E :
-
Elastic modulus
- C m :
-
Added mass coefficient
- f :
-
Frequency
- G :
-
Gap between structures
- k :
-
Stiffness of structure
- L :
-
Length of structure
- m :
-
Mass of structure
- M a :
-
Added mass
- m c :
-
Coupled added mass
- m eff :
-
Effective added mass
- R:
-
Radius of structure
- R, r :
-
Rotation matrix
- S :
-
Stokes number
- x :
-
Eigenvector
- ε :
-
Eccentricity
- μ :
-
Dynamic viscosity
- θ :
-
Rotation angle
- ρ :
-
Density
- ω :
-
Angular velocity
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Acknowledgments
This work was supported by the Nuclear Research & Development Program of the National Research Foundation with a grant funded by the Korea Ministry of Science and ICT.
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Jin Haeng Lee received his Ph.D. in Mechanical Engineering, Sogang University, Seoul, Korea. He is currently a Principal Researcher at Korea Atomic Energy Research Institute, Daejeon, Korea. His research interests include mechanical design of reactor and computational solid mechanics.
Jae-Hun Cho received his Master’s degrees in Mechanical Engineering from the Chungnam National University. He is participating in Versatile System Technology Development Div. at Korea Atomic Energy Research Institute. His research interests are mechanical structure design and finite element method.
Sung-Kyun Kim received his Ph.D. in Mechanical Engineering, Chungnam National University, Daejeon, Korea. He is currently in charge of a mechanical design of sodium fast reactor at Korea Atomic Energy Research Institute, Daejeon, Korea. His research interests include dynamics and structural vibrations.
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Lee, J.H., Cho, JH. & Kim, SK. Calculation of coupled added mass of multibody system immersed in fluids. J Mech Sci Technol 35, 3781–3792 (2021). https://doi.org/10.1007/s12206-021-2101-z
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DOI: https://doi.org/10.1007/s12206-021-2101-z