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Abstract Abstract：Based on the structural features, boundary conditions and fluid flow velocity of the narrow gap coaxial equipment supporting cylinders in the reactor vessel, the structure is simplified to a coaxial cylindrical shell with one fixed end and free end, and the fluid inside and outside the cylindrical shell is simplified to irrotational, non-viscous, incompressible fluid. Under seismic conditions, the coaxial cylindrical shell is coupled through the fluid pressure field, and its radial displacement mode determines the pressure field in the narrow gap fluid domain. Therefore, the radial orthogonal displacement modes of the cylindrical shell in the form of series are constructed to satisfy the boundary condition with one fixed end and the other free end, and the pressure field basis function of the wave equation is satisfied. From this basis functions, the additional mass theoretical formula of the shell-typevibration modes of a coaxial cylindrical shell with a fixed end and a free end is derived considering fluid-solid interraction. With the increase of the basis function series terms, the additional mass results calculated by this formula converge quickly. When the number of basis function terms is greater than 50, the additional mass calculation accuracy meets the requirements. When n=1 in this formula, namely, only the beam mode of the coaxial cylindrical shell is considered, the formula deduced in this paper degenerates to the beam-type vibration mode additional mass formula of the coaxial cylindrical shell deduced by Au-Yang M K [3]. In order to facilitate engineering applications, the additional mass coefficient is defined with reference to the Russian standard "Nuclear Power Plant Equipments and Pipes Strength Calculation Specification", and the additional mass results of the coaxial cylindrical shell derived in this paper are given in the form of a design curve. In order to verify the above theoretical formulas, this paper establishes a finite element model of coaxial cylinders containing narrow gap fluid domains with different height-to-diameter ratios, different gaps and different wall thicknesses, and the comparable calculation results are obtained with the theoretical results. The modal results of the finite element model show that when the height-to-diameter ratio of the cylindrical shell is less than or equal to 2.0, the frequency error of the main vibration mode is within 5%; at the same time, the author designed a modal experiment of a double-layer coaxial cylinder taking fluid-structure interraction into account. The frequency and vibration mode results of the modal test further verify the correctness of the additional mass theoretical formula derived in this paper.
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Received: 23 June 2021
Published: 15 February 2022
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2022, Vol. 43 
