Structural damping in contacts and joints subjected to simultaneous action of normal and tangential vibrations (Relaxation damping)

本项目致力于结构阻尼的主动控制，这是一个在许多工程领域都很重要但尚未得到令人满意的解决的问题。例如，一些参与国际空间站设计的工程师报告说，由于国际空间站的结构阻尼较弱，宇航员在永久的、严重的噪音污染下工作和生活。由于国际空间站的金属结构和没有减震材料，即使是微小的噪声源也往往成为一个大问题，例如小型空间站的噪音在地球上几乎不会被察觉。这个问题仍然没有解决，因为重量限制排除了重型阻尼器的使用。在这种情况下，依靠结构减振是有用的，例如通过利用接触摩擦。在本项目中，我们将尝试通过摩擦接触来控制结构的阻尼--要么使用结构中已有的接头，要么使用为控制阻尼的特定目的而引入的接触。虽然微滑移节点对实际结构的减振有重要贡献，但仍不可能对其进行精确建模和控制。从我们的角度来看，这有两个原因：一方面，有摩擦的切向接触问题在数学上特别困难--由于接触中出现的各种非线性和边界条件的复杂性，这些条件是先验未知的，必须在求解过程中迭代确定。另一个原因是，到目前为止，摩擦接触中似乎忽略了一个重要的耗散机制。这种耗散机制是我们最近提出的，我们称之为“松弛阻尼”。根据载荷类型的不同，它可能对总耗散的贡献很大，甚至成为主要的耗散机制。尤其重要的是，这种衰减可以以一种简单的方式进行控制。该项目的主要目的是对切向振动和法向振动同时作用下摩擦接触的松弛阻尼进行全面的实验和理论研究。首先将从实验上验证现有的松弛阻尼理论，然后进一步的实验研究将提供松弛阻尼相对于经典的“Mindlin阻尼”和材料内部损失的相对贡献信息。在此基础上，提出并实现了基于摩擦接触的结构阻尼力主动控制方法。实验研究将通过实验仪器进行，该实验仪器应作为项目的一部分进行设计和建造。根据所获得的结果，将制定有效和低磨损的结构减振策略，并以实例系统实施。

The present project is dedicated to the active control of structural damping, a problem that is both important and not yet satisfactorily solved in many areas of engineering. For example, some engineers involved in the design of the International Space Station report that, due to the weak structural damping of the ISS, astronauts work and live under permanent, heavy noise pollution. Due to the metal structure of the ISS and the absence of damping material, even small sources of noise tend to become a big problem, e.g. the noise of a small that would be barely noticeable on Earth. This problem remains unsolved since weight constraints preclude the use of heavy dampers. In such cases it can be useful to rely on structural damping, e.g. by taking advantage of contact friction. In this project we will attempt to control structural damping through frictional contacts - either using joints already present in the structure or contacts introduced for the specific purpose of damping control. Although joints with micro sliding make an important contribution to the damping of real structures, it is still not possible to accurately model and therefore control them. From our perspective, there are two reasons for this: On the one hand, problems of tangential contact with friction are particularly difficult mathematically - due to various non-linearities occurring in the contact and the complexity of the boundary conditions, which are unknown a priori and must be determined iteratively during the solution process. The other reason is that an important dissipation mechanism seems to have been overlooked in frictional contacts so far. This dissipation mechanism was recently proposed by us and is called "relaxation damping". Depending on the type of loading it may contribute significantly to the total dissipation, or even become the main dissipation mechanism. Of particular importance is that this damping can be controlled in a simple manner. The main objective of the project is a comprehensive experimental and theoretical study of relaxation damping in frictional contacts under simultaneous action of tangential and normal vibration. First the existing theory of relaxation damping will be verified experimentally, then further experimental studies will provide information about the relative contribution of relaxation damping compared to classic "Mindlin damping" and to internal losses in the material. Based on that, methods for the active control of structural damping through frictional contact will be developed and implemented. Experimental studies will be carried out by means of an experimental apparatus, which shall be designed and constructed as part of the project. From the obtained results, strategies for effective and low-wear structural damping will be developed and implemented for an example system.