Recent advances in vibroacoustics
Numerous vibroacoustics advances and problems in the aerospace industry have occurred over the last 15 years. This article addresses some of these that developed from engineering programmatic task-work at the NASA Glenn Research Center at Lewis Field.
Coupling Analysis for the Thermo-Acoustic-Vibration Response of a Thin-Walled Box
Monitor and control unit is essential to almost all of the modern aircrafts or spacecrafts, which always places in a relatively closed space and requires a compatible mechanical environment to ensure its normal function. The acoustic, vibration and thermal loads developed in the operation of the aircraft determine a complex environment for its monitor and control unit. In particular, there should be couple effect among the thermal, vibration and acoustic responses. This article presents numerical simulation studies on a thermo-acoustic-vibration response of a typical thin-walled box, to reveal the multi-physics environment of the monitor and control unit. The thermo-structural equations were proposed and solved numerically, following that the vibro-acoustic analysis was implemented. The coupled algorithm was developed to simulate the structure response and sound distribution, and predict the acoustic loss during transmitting through the box shell. The validation cases of the vibration and acoustic response of a plate were performed at first. The outcome provides the multi-physics environment prediction method for designing and optimizing the monitor and control unit.
Numerical analysis of surface crack propagation in flexible pavements using XFEM and cohesive zone model
Surface initiated (top-down) cracking in the longitudinal direction of pavements has become a predominant mode of failure in thick asphalt pavements. Most previous researchers studied crack propagation using the traditional Linear Elastic Fracture Mechanics (LEFM) method by calculating the stress intensity factor around the crack tip. In this paper, Extended Finite Element Method (XFEM) was used to study the key factors causing surface initiated crack propagation under surface tension and/or shear. A two-dimensional (2-D) finite element (FE) model for a two-lane flexible pavement was built to predict pavement responses and crack propagation potential under various scenarios. It was found that surface tension is the major driving force for crack propagation when the crack is at some distance away from tire loading. The results show that the distance from the location of crack to tire loading, the depth and direction of the crack, and the modulus ratio between the hot-mix asphalt (HMA) layer and the base layer have significant influences on crack propagation under surface tension. On the other hand, this study shows that shear stress can induce surface initiated crack propagation near the loading area as the shear resistance of material becomes low at the high temperature.