Ni Xianglei, Rizzo Piervincenzo, Daraio Chiara
Department of Civil and Environmental Engineering, University of Pittsburgh, 942 Benedum Hall, 3700 O'Hara Street, Pittsburgh, Pennsylvania 15261, USA.
Rev Sci Instrum. 2011 Mar;82(3):034902. doi: 10.1063/1.3556442.
In this paper we present the design of two actuators for the generation of highly nonlinear solitary waves (HNSWs), which are mechanical waves that can form and travel in highly nonlinear systems. These waves are characterized by a constant spatial wavelength and by a tunable propagation speed, dependent on the wave amplitude. To date, the simplest and widely adopted method to generate HNSWs is by impacting a striker onto a chain of beads of equal size and mass. This operation is conducted manually and it might be impracticable if repetition rates higher than 0.1 Hz are necessary. It is known that the HNSWs' properties, such as amplitude, duration, and speed can be modified by changing the size or the material of the particles, the velocity of the striker, and/or the precompression on the chain. To address the limitations associated with the manual generation of HNSWs we designed, built, and tested two actuators. The first actuator consists of a chain of particles wrapped by an electromagnet that induces static precompression on the chain. This design allows for the generation of solitary waves with controlled properties. The second actuator consists of a chain surmounted by an electromagnet that lifts and releases a striker. This actuator permits the remote and noncontact generation of solitary waves. The performance of both actuators is evaluated by comparing the experimental HNSWs to theoretical predictions, based on the long wavelength approximation.
在本文中，我们展示了两种用于产生高度非线性孤立波（HNSWs）的致动器的设计，高度非线性孤立波是一种能在高度非线性系统中形成并传播的机械波。这些波的特征在于具有恒定的空间波长以及可调的传播速度，传播速度取决于波幅。迄今为止，产生高度非线性孤立波最简单且广泛采用的方法是用撞针撞击一串大小和质量相等的珠子。此操作是手动进行的，如果需要高于0.1赫兹的重复率，可能就不实用了。众所周知，高度非线性孤立波的特性，如振幅、持续时间和速度，可以通过改变粒子的大小或材料、撞针的速度和/或链条上的预压缩来改变。为了解决与手动产生高度非线性孤立波相关的局限性，我们设计、制造并测试了两种致动器。第一种致动器由一串被电磁铁包裹的粒子组成，电磁铁会在链条上产生静态预压缩。这种设计允许产生具有可控特性的孤立波。第二种致动器由一串上方有电磁铁的链条组成，电磁铁会提起并释放撞针。这种致动器允许远程且非接触地产生孤立波。通过将实验得到的高度非线性孤立波与基于长波长近似的理论预测进行比较，来评估这两种致动器的性能。
