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满意解决的问题。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，宇航员在长期的、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缺乏阻尼材料，即使是很小的噪声源也会成为一个大问题，例如，在地球上几乎察觉不到的小型空间站的噪音。这个问题仍然没有解决，因为重量限制排除了使用重型阻尼器。在这种情况下，依靠结构阻尼是有用的，例如通过利用接触摩擦。在这个项目中，我们将尝试通过摩擦接触来控制结构阻尼——要么使用结构中已经存在的关节，要么使用为阻尼控制的特定目的而引入的接触。虽然具有微滑动的关节对实际结构的阻尼有重要的贡献，但仍然不可能精确地建模并控制它们。从我们的角度来看，这有两个原因：一方面，由于接触中出现的各种非线性和边界条件的复杂性，切向接触与摩擦的问题在数学上特别困难，这些条件是先验未知的，必须在求解过程中迭代确定。另一个原因是迄今为止在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，称为“松弛阻尼”。根据荷载类型的不同，它可能对总耗散起重要作用，甚至成为主要的耗散机制。特别重要的是，这种阻尼可以用一种简单的方式来控制。该项目的主要目的是对切向和法向振动同时作用下摩擦接触中的松弛阻尼进行全面的实验和理论研究。首先，现有的弛豫阻尼理论将得到实验验证，然后进一步的实验研究将提供关于弛豫阻尼与经典的“Mindlin阻尼”和材料内部损失的相对贡献的信息。在此基础上，将开发并实现通过摩擦接触主动控制结构阻尼的方法。实验研究将通过实验装置进行，该实验装置应作为项目的一部分进行设计和建造。根据所获得的结果，将为实例系统开发和实施有效和低磨损的结构阻尼策略。

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.