Surface contributions with respect to acoustic energy quantities applied to cavities

通常根据一个或几个现场点的声压，例如驾驶员耳朵处的声压来评估低频车辆腔内的内部噪声问题。然而，这种方法的缺点是，这些点可能没有代表性地被选择，从而导致错误的结果。二十多年来，商业软件一直在提供基于某些点的声压的声学面板贡献分析。这些表面板的贡献是复杂的价值，并在条形图中可视化，每个预定义的板一个值。对于辐射问题，情况不同，在辐射问题中，辐射声功率-能量-占要评估的量。表面对辐射声功率的贡献由声强确定，声强是一个局部量，与表面对声压的(复数值)贡献类似，可以是正的和负的。因此，声学短路可能仍然保留在数据中，从而不清楚地允许识别对辐射声功率有较大贡献的区域。近年来，申请人开发了一种技术，该技术可以可视化没有声短路的表面贡献，并且仅隔离对辐射声功率的非负表面贡献。后来，威廉姆斯将这种结果称为非负强度。该项目的目的是开发一种方法来评估相对于空腔中的声能量的非负表面贡献。这些表面贡献将被可视化和测试。在此基础上，提出了一种用表面积分代替原来用于声能计算的体积积分的有效方法。这将受益于基于边界元方法的分析，尽管这些表面贡献也可以通过应用有限元方法来确定。随后的工作包将通过对声学问题的结构优化所需的有效灵敏度分析来揭示表面贡献的相似性。在此，我们将研究在结构优化或不确定性分析过程中，如果腔体的几何形状保持不变，而自由参数只影响结构设计，如何有效地确定腔体的声能。申请人假设这个问题也与地表贡献密切相关。

Interior noise problems in vehicle cavities at low frequencies are usually assessed based on the sound pressure at one or a few field points, e.g. at the driver's ear. This procedure, however, has the drawback that these points may not be chosen representatively and thus, lead to wrong results. Commercial software has been offering an acoustic panel contribution analysis based on the sound pressure at certain points for more than two decades. These surface panel contributions are complex valued and visualized in a bar chart with one value per predefined panel.The situation is different for radiation problems in which the radiated sound power - an energy quantity - accounts for the quantity to be assessed. The surface contributions to the radiated sound power are determined by the acoustic intensity which is a local quantity and which can be, similar to the (complex valued) surface contributions to the sound pressure, positive and negative. Hence, the acoustic short circuit may still remain in the data and thus, not clearly allowing to identify regions of large contributions to the radiated sound power. In recent years, the applicant has developed a technique which can visualize surface contributions which are free of the acoustic short circuit and just isolate the non-negative surface contributions to the radiated sound power. Later on, Williams has called this resulting quantity as non-negative intensity. It is the aim of the project to develop a method to evaluate non-negative surface contributions with respect to an acoustic energy quantity in cavities. These surface contributions will be be visualized and tested. Then, an efficient method is developed to substitute a surface integral for the volume integral that is originally to be solved for evaluation of the acoustic energy. This will benefit from the analysis based on the boundary element method, even though these surface contributions can also be determined by applying the finite element method. The subsequent working package will reveal similarities of the surface contributions with an efficient sensitivity analysis required in structural optimization for acoustic problems. Here, it will be investigated how to efficiently determining the acoustic energy of a cavity, if, in the process of a structural optimization or an uncertainty analysis, the geometry of the cavity remains constant and the free parameters affect the structural design only. The applicant is assuming that this problem is also closely related to the surface contributions.