No abstract

No abstract

In this paper, a two-dimensional fluid model was developed to study the radio frequency (RF) hollow cathode discharge (HCD) in argon at 1 Torr. The evolutions of the particle density distribution and the ionization rate distribution in RF HCD at 13.56 MHz indicate that the discharge mainly occurs inside the hollow cathode. The spatio-temporal distributions of the ionization rate and the power deposition within the hollow cathode imply that sheath oscillation heating is the primary mechanism to sustain the RF HCD, whereas secondary electron emission plays a negligible role. However, as driving frequency decreases, secondary electron heating becomes a dominant mechanism to sustain the discharge in RF hollow cathode.

Viscoelastic dampers are one of the most popular earthquake mitigation devices for building structures with a large number of applications in civil engineering. The seismic performance of viscoelastic dampers is greatly affected by viscoelastic materials. The present paper addresses the theoretical and experimental studies of the viscoelastic damper. The regular polyhedron chain network models for viscoelastic materials are proposed based on the molecular chain network microstructures and the temperature–frequency equivalent principle. Several dynamic property tests for the viscoelastic damper at different temperatures, frequencies, and displacements are carried out, and the proposed models are verified by comparing the numerical and experimental results. The comparisons show that the viscoelastic damper has perfect energy dissipation capacity, and the regular polyhedron chain network models can well describe the mechanical properties of the viscoelastic damper at different environmental temperatures and excitation frequencies.

A new viscoelastic micro-vibration isolation and mitigation platform is proposed to reduce disturbances generated by flywheels on board spacecraft. Firstly, property tests on the high-damping viscoelastic material used in the micro-vibration isolation and mitigation element are conducted. Experimental results show that the developed viscoelastic material has better energy dissipation capability under micro-vibration conditions. A mathematic model is employed to describe the dynamic properties of the high-damping viscoelastic material and is used to model the isolation and mitigation element. Secondly, a viscoelastic micro-vibration isolation and mitigation platform, which consists of four elements, is proposed and the analytical model of the coupled system that consists of the platform with flywheel is established. Finally, the isolation and mitigation performances of this micro-vibration isolation and mitigation platform are analyzed and discussed. The results show that the isolation and mitigation platform can effectively reduce the micro-vibration disturbances induced by the flywheel.