A New Approach to Vibration Mitigation of Moving-load Problems

与传统的静止(但动态)载荷相比，移动载荷的动态问题在分析和实验上更难解决。然而，它们非常常见，出现在桥梁、道路和铁轨上的交通流量、输送液体的管道、离合器、刹车和滑块等机械部件、涉及金属去除的机械加工作业、木锯和起重机中。人们认为，移动负载问题在许多现代机器应用中可能是非常重要的，特别是在需要小质量和非常高速度的操作时，例如计算机磁盘驱动器和高速加工。人行天桥(例如千禧大桥)和轻质大跨度地板特别容易受到行走(以及为后者跳舞或跳跃)的人的激励，现在已成为土木工程和结构工程师特别关注的问题。近年来高速列车的发展也带来了严重的新的技术挑战。由移动载荷引起的典型问题包括产生不需要的噪声、颤振、非线性和自激振动，从而导致不稳定和/或大幅值极限环。必须认识到，移动载荷激发振动是不可避免的。因此，研究的中心问题不是完全抑制移动荷载引起的振动，因为这是不可能实现的，而是要减轻由此引起的振动。移动荷载激励的振动一般不是平稳的，具有频率范围宽、幅值大的特点，很难抑制和控制。这一新建议的目的是系统地研究移动荷载动力问题的减振问题。移动荷载问题的非平稳性质造成了双重困难：(1)当移动结构穿过空间域时，时变频率形成频带；(2)频率也随移动结构的速度而变化。因此，以前建立的方法，如将频率分配给固定值和瞬时最优控制，将不会很好地发挥作用，或者可能根本不起作用。结构振动控制可以基于几种策略：(1)经典线性最优控制，(2)极点和零点配置，(3)瞬时最优控制，(4)独立模态空间控制，(5)有界状态控制。虽然结构振动控制的许多工作都是基于一阶状态空间方程，但直接处理二阶运动方程是振动工程师的自然框架。此外，Ram和Mottershead于2007年首次针对对称系统提出了基于容纳器的逆方法，然后在2009年由本申请人将其推广到非对称系统，这种方法具有特别的吸引力，因为容纳器很容易测量，并且只需要少量自由度；不需要知道质量、刚度或阻尼阵，从而可以避免数值建模错误(尽管有限元模型很有用，但不需要)。主动振动控制一直是一个重要的研究课题，近年来在解决实际工程应用中显示出了相当大的前景，但除了相对很少的例外情况外，移动荷载问题的主动解还很少被研究。大量用于非移动荷载问题的主动控制方法和理论在很大程度上被移动荷载问题所忽略。这种明显的缺席提供了一个不容错过的机会，可以创造一个新的知识体系，并将其应用于新的应用。申请者的目标是为解决长期存在但不断扩大的移动载荷动力学问题领域带来新的想法，并利用主动和被动控制实现移动载荷动力学中的振动缓解。

Dynamic problems with moving loads are analytically and experimentally more difficult to solve than problems with conventional stationary (but dynamic) loads. They are however very commonplace, occurring in traffic flows on bridges, roads and rail tracks, pipelines carrying fluids, machine parts such as clutches, brakes and sliders, machining operations involving metal removal, wood saws and cranes. It is believed that moving-load problems are likely to be extremely important in many modern machine applications, especially where low mass and very high speeds of operation are required, such as computer disk drives and high speed machining. Foot bridges (for example, the Millennium Bridge) and light-weight long-span floors are particularly susceptible to excitation by people walking (and also dancing or jumping for the latter) and have now become of particular concern to civil and structural engineers. The development of high speed trains in recent years has also posed serious and new technological challenges. Typical problems caused by moving loads include generation of unwanted noise, chatter, nonlinear and self-excited vibrations leading to instability and/or large-amplitude limit cycles. It must be recognised that it is inevitable that moving loads excite vibration. So the central research issue is not to completely suppress vibration excited by moving loads, because that is impossible to achieve, but rather to mitigate vibration thus caused. Vibrations excited by moving loads are not stationary in general and are characterised by a wide frequency range and high-amplitude, hence it is very difficult to reduce and control. The purpose of this new proposal is to study vibration mitigation of moving-load dynamic problems in a systematic way.The non-stationary nature of moving-load problems creates a two-fold difficulty: (1) time-varying frequencies form bands as the moving structure traverses the spatial domain and (2) the frequencies also vary with the speed of the moving structure. Therefore previously established methodologies, such as assigning frequencies to fixed values and instantaneous optimal control, would not work well or possibly not at all. New control concepts have to be explored, which is the major motivation of this new project.Structural vibration control may be based on several strategies: (1) classical linear optimal control, (2) pole and zero assignment, (3) instantaneous optimal control, (4) independent modal space control, and (5) bounded state control. While many works on structural vibration control are based on the first-order state-space formulation, direct treatment of the second-order equation of motion is the natural framework to vibration engineers. In addition, receptance-based inverse methods, first put forward for symmetric systems by Ram and Mottershead in 2007 and then extended to asymmetric systems by this applicant in 2009, have a particular appeal in that receptances are easy to measure and are required at only a small number of degrees-of-freedom; there is no need to know mass, stiffness or damping matrices so that numerical modelling errors can be avoided (a finite element model, though useful, is not required). Active vibration control has been a major research topic and has shown considerable promise in solving practical engineering applications in recent years, but with a relatively very small number of exceptions, active solutions of moving-load problems have rarely been studied. The abundant wealth of active control methods and theories used in non-moving-load problems have largely been left out of moving-load problems. This glaring absence presents a not-to-be-missed opportunity to create a new body of knowledge and apply it to novel applications. The applicant aims to bring fresh ideas into solving the long-standing but continuously expanding field of moving-load dynamic problems and achieve vibration mitigation in moving-load dynamics using active and passive control.