Electric vehicles generally have a better noise, vibration, and harshness quality than traditional vehicles due to the relatively quiet electric motors. By contrast, the noise, vibration, and harshness issues of the driveline system become more outstanding and significant in the absence of the “masking effect” by the engine. The electrification of the powertrain has also brought many changes in the sources or transmission of vibration, which has led to some new noise, vibration, and harshness issues. Specifically, the intense vibration of the prototype bus appears when driving in third gear, which makes the passengers uncomfortable. This paper presents an efficient analytical strategy for identifying the resonance sources and vibration transmission for a pure electric bus. The strategy incorporates order analysis, operating deflection shape, and transfer path analysis. Order analysis shows that the resonance is primarily caused by the second-order excitation associated with the driveline, and the vibration sources are further identified using operating deflection shape analysis. Moreover, the vibration transfer paths from the driveline to the bus floor are quantitatively determined by the transfer path analysis method. The results show that the coupling vibration of the powertrain and the rear drive axle, which amplifies the resonance of the whole driveline, is transmitted to the bus floor primarily through powertrain mounts and V rods. Based on the results, the design and structure modifications of the driveline and transfer paths are recommended to handle this issue. The proposed identification strategy would be beneficial for accurate and efficient engineering troubleshooting on the vibration issues.

Acoustic/elastic metasurfaces as a kind of two-dimensional metamaterials are of subwavelength thickness and show remarkable ability of acoustic/elastic wave manipulation. They have potential applications in various fields such as acoustic imaging, communications, cloaking, camouflage, vibration/noise control, energy harvesting, nondestructive testing, etc. In this review, we mainly summarize recent developments in acoustic/elastic phase gradient metasurfaces, including design principles, design of functional elements, wave field manipulation with applications, design of tunable metasurfaces, as well as the emerging digital coding metasurfaces. At last, we outline the future research directions in this field.

No abstract

In this paper, a tunable arc-shaped acoustic metasurface (AAM) carpet cloak has been proposed and systematically investigated. The AAM carpet cloak consists of covers, rotors, bolts and nuts. The rotors can be rotated continuously within the covers to form a reconfigurable hook channel mechanism. By setting various rotational angles, we construct two-dimensional (2D) tunable AAM carpet cloaks to achieve excellent stealth performances under different operating conditions. Numerical simulations and experimental results for the 2D carpet cloaks show good agreements. Furthermore, simulated results for three-dimensional (3D) carpet cloaks have demonstrated that tapered objects are successfully escaping from being detected. The tunable hook channel mechanism can be flexibly applied to arbitrarily curved metasurface carpet cloaks, making them closer to practical invisibility acoustic devices.

No abstract