Modal quantities and their usage for evaluation of radiated sound power

振动结构会辐射声音。辐射声功率是量化这种声音的量度。它是一个全局量，这使得评估成本高昂，特别是在需要在某个频率范围内求解的情况下。这是由于在大多数外部声学问题的公式中系统矩阵隐含地依赖于频率这一事实的结果。因此，在这些情况下几乎不使用类似于解决内部声学问题的模态方法。外部声学有两种模式。这些是依赖于频率的辐射模式和与频率无关的简正模式。它们都非常适合作为辐射声功率重建的基函数。然而，这些模式的相似点和差异很少被研究，因此几乎不为人所知。很明显，如果控制结构参数且流体几何形状保持不变，两者都非常适合用于频率范围内的分析以及结构声学优化中的应用。该项目将从一个工作包开始，提供用于评估频率相关辐射模式和频率无关正常模式的工具。第二步包括对正常模式进行更详细的研究，了解其物理性质。预计第二步的结果可以帮助理解两种模式的相似点和差异。该项目的关键部分在于找到标准，将频率无关的简正模态分类为与辐射声功率评估相关或不相关的模态。有关与辐射声功率相关的模态的知识对于频率范围内的模态叠加和结构声学优化非常有价值。

Vibrating structures radiate sound. The radiated sound power is a measure to quantify this sound. It is a global quantity, which makes evaluation costly in particular in cases requiring solution over a frequency range. This is a consequence of the fact that system matrices depend implicitly upon frequency in most formulations for the exterior acoustic problem. Therefore, modal methods similar to solution of the interior acoustic problem are hardly used in these cases. There are two types of modes in external acoustics. These are the frequency depending radiation modes and frequency independent normal modes. Both of them are well suited as basis functions for reconstruction of the radiated sound power. However, similarities and differences of these modes are barely studied and, thus, hardly known. It is just clear that both are well suited to be used for analysis over frequency ranges and for application in structural-acoustic optimization if structural parameters are controlled and the fluid geometry remains unchanged. The project will start with a working package to provide tools for evaluation of frequency depending radiation modes and frequency independent normal modes. The second step includes a more detailed investigation of normal modes understand their nature with respect to physics. It is expected that the results of the second step allow to understand similarities and differences of both types of modes. Crucial part of the project consists in finding criteria to categorize frequency independent normal modes into modes to be relevant or not relevant for evaluation of the radiated sound power. Knowledge about the modes being relevant for the radiated sound power can be valuable for modal superposition over a frequency range and in structural-acoustic optimization.