• Title/Summary/Keyword: 이중 점근 근사법

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Prediction of the Radiated Noise of a Structure Excited by Harmonic Force Using the Doubly Asymptotic Approximation (이중점근 근사법을 이용한 조화가진 구조물의 방사소음 예측)

  • Han, Seungjin;Jung, Woojin
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.27 no.1
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    • pp.51-56
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    • 2017
  • This paper presents an approach of predicting the radiated noise due to the structural vibration by internal harmonic forces using the doubly asymptotic approximation (DAA). Acoustic transfer vector is derived from the Helmholtz integral equation and the fluid-structure interaction relation of DAA. Numerical results and analytical results of radiated noise for a cylindrical shell were compared and showed that they were consistent in most of frequencies and radiation directions, but showed errors in some radiated directions in the mid-frequency region. Despite these errors, the prediction method will be suitable for practical radiated noise prediction.

A Study on BEM-Based Numerical Simulation Technique for Underwater Explosions (수중 폭발 시뮬레이션을 위한 경계 요소법 기반의 수치 해석 기법 연구)

  • Choung, Joonmo;Lee, Jae-bin
    • Journal of the Society of Naval Architects of Korea
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    • v.57 no.5
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    • pp.271-277
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    • 2020
  • Recoverability and vulnerability of navy ships under underwater explosion are critical verification factors in the acquisition phase of navy ships. This paper aims to establish numerical analysis techniques for the underwater explosion of navy ships. Doubly Asymptotic Approach (DAA) Equation of Motion (EOM) of primary shock wave and secondary bubble pulse proposed by Geers-Hunter was introduced. Assuming a non-compressive fluid, reference solution of the DAA EOM of Geers-Hunter using Runge-Kutta method was derived for the secondary bubble pulse phase with an assumed charge conditions. Convergence analyses to determine fluid element size were performed, suggesting that the minimum fluid element size for underwater explosion analysis was 0.1 m. The spherical and cylindrical fluid domains were found to be appropriate for the underwater explosion analyses from the fluid domain shape study. Because the element size of 0.1 m was too small to be applied to the actual navy ships, a very slender beam with the square solid section was selected for the study of fluid domain existence effect. The two underwater explosion models with/without fluid domain provided very similar results in terms of the displacement and stress processes.