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首页> 外文期刊>Acta acustica united with acustica >Experimental and Numerical Investigation of a Complex Submerged Structure. Part II: Sound Radiation
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Experimental and Numerical Investigation of a Complex Submerged Structure. Part II: Sound Radiation

机译：复杂水下结构的实验和数值研究。第二部分：声辐射

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The intention of the paper is to demonstrate the abilities and limitations of commercial Finite Element (FEM) and Boundary Element (BEM) packages, concerning the low frequency sound radiation of a complex submerged structure under free field conditions. Low frequency in this context means, that the considered frequencies are well below the coincidence frequency with Helmholtz numbers ka ≤ 1. The investigated object consists of two cylindrical shells with different radii, connected by a conical section and covered with hemispherical end caps. It contains ring stiffeners, flanges and rectangular frames. Part I of the paper covered the experimental and numerical modal analysis of the structure. The determined eigenmodes, achieved with a coupled FEM-BEM approach, served as velocity boundary conditions for the calculation of the sound radiation. A direct collocational boundary element scheme was used to compute two and three dimensional directivity diagrams of the particular eigenmodes of the investigated structure. The experiments were carried out on the research vessel PLANET in a Norwegian fjord with a water depth of more than 250 m. The submerged object was excited by an internal self mounted shaker at previously determined discrete eigenfrequencies of the structure below 300 Hz. Two dimensional directivity diagrams were measured by turning the object perpendicular to its axis of symmetry, while registrating the radiated sound by means of a vertical linear array at a distance of about 60 m. Thus, surface and bottom reflections of the radiated sound could be excluded. Experimental and numerical directivity diagrams will be shown for two particular frequencies.
机译：本文的目的是证明商业有限元（FEM）和边界元（BEM）软件包的功能和局限性，涉及自由场条件下复杂淹没结构的低频声辐射。在此情况下，低频意味着所考虑的频率远低于亥姆霍兹数ka≤1的重合频率。被研究物体由两个半径不同的圆柱壳组成，它们通过圆锥形截面连接并覆盖有半球形端盖。它包含环形加劲肋，法兰和矩形框架。本文的第一部分介绍了结构的实验和数值模态分析。通过耦合的FEM-BEM方法获得的确定的本征模式用作计算声辐射的速度边界条件。使用直接配置边界元方案来计算所研究结构的特定本征模的二维和三维方向图。实验是在水深超过250 m的挪威峡湾的PLANET研究船上进行的。水下物体由内部自安装式振动器以预先确定的低于300 Hz的结构离散本征频率激发。通过将物体垂直于其对称轴旋转，同时借助垂直线性阵列在约60 m的距离处记录辐射声，来测量二维方向图。因此，可以排除辐射声的表面和底部反射。将针对两个特定频率显示实验和数值方向图。

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