Development and validation of a universally valid measurement method for the determination of the structural internsity based on 3D laser vibrometry

本研究项目的目标是开发一种普遍有效和易于管理的基于三维激光振动测量的薄壁实际零件和结构的结构强度（STI）测量方法。STI描述了振动结构中结构声的能量流。它提供了能量流动路径的必要信息，这些信息可以可视化，并且可以从这些信息中系统地推导出减少噪声和振动的设计措施。STI通常由机械应力张量和速度矢量的乘积计算，但它也可以由工程力学中已知的内力变量（法向力和剪力，力矩）和速度计算。在文献中，可以找到几种方法来推导壳和梁结构内部的振动量，从它们的外表面测量的量。该项目旨在同时测量由面内振动（法向力）和面外振动（剪力和力矩）引起的STI的各个部分。这样可以验证数值模拟的结果，也可以有效地针对局部结构声传递的优势部分设计有效的降噪减振措施。三维扫描激光测振仪可以同时测量所有振动量（包括面内振动量），也可以同时测量各个空间方向上垂直于表面的振动量，这使得STI测量适用于弯曲梁和壳结构。除了测量STI的计量测定所需的所有相关振动量（应用于几个日益复杂的测试结构）之外，这些振动量的空间导数的计算是另一个重要方面。可以在文献中找到的方法尚未应用于弯曲结构或STI平面内部分的确定。因此，有必要分析这些方法对弯曲结构的适用性，并在必要时加以改进。对于真实的弯曲结构，面外振动的振幅明显高于面内振动。一般来说，它们的比值也取决于振动激励的方向，因此不能先验地知道。当同时测量两种振动时，由于记录电平，可以预期平面内振动的信噪比较低。因此，信号滤波方面，特别是面内振动的信号滤波对于精确的STI分析至关重要。这就是为什么需要开发一种不仅适用于平面外振动，而且适用于平面内振动的滤波方法。

The goal of this research project is the development of a universally valid and manageable measurement method for the structural intensity (STI) of thin-walled real parts and structures based on 3D laser vibrometry. The STI describes the energy flow of structure borne sound within a vibrating structure. It provides the necessary information on the paths of the energy flow, which can be visualized and from which design measures for noise and vibration reduction can be systematically deduced. The STI is generally calculated from the product of the mechanical stress tensor and the velocity vector, but it can also be calculated from the internal force variables known from engineering mechanics (normal and shear forces, moments) and the velocities.In the literature several approaches can be found for the derivation of the vibrational quantities inside shell and beam structures from quantities measured at their outer surface. This project intends to enable a simultaneous measurement of the separate portions of the STI originating from in-plane vibrations (normal forces) and out-of-plane vibrations (shear forces and moments). In this way, results of numerical simulations, which will also be carried out, can be validated, and noise and vibration reduction measures can be designed efficiently and specifically for the dominant portion of the local structure borne sound transfer. 3D scanning laser vibrometers enable the simultaneous measurement of all vibrational quantities (including in-plane quantities) and also the simultaneous measurement of the vibrational quantities normal to the surface in various spatial directions, which makes the STI measurement suitable for curved beam and shell structures.Besides the measurement of all relevant vibrational quantities required for the metrological determination of the STI (applied to several test structures with increasing complexity), the calculation of the spatial derivatives of these vibrational quantities is another important aspect. The approaches that can be found in the literature have not been applied yet to curved structures or for the determination of the in-plane portions of the STI. Thus, it is necessary to analyze these methods with respect to their applicability for curved structures and, if necessary, to enhance them. Out-of-plane vibrations exhibit significantly higher amplitudes for real, curved structures than in-plane vibrations. Generally, their ratio depends on the direction of the vibration excitation as well and, thus, is not known a priori. When both vibrations are measured simultaneously, a lower signal-to-noise ratio can be expected for the in-plane vibrations due to the recording level. Therefore, the aspect of signal filtering particularly for the in-plane vibrations is of utmost importance for a precise STI analysis. This is why a filtering method is to be developed that is not only suitable for the out-of-plane vibrations, but also for the in-plane vibrations.