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.
Universal acoustic modelling framework for electrical drives
The interdisciplinary task of assessing the acoustic characteristics of electrical drive-systems gains importance in traction, industrial and consumer applications. This study presents a universal acoustic modelling framework for efficient, high-quality acoustic modelling of electrical drives. The objective is to make drive acoustic modelling and assessment of an integral part of drive-system design. The approach integrates directly into the general drive-system design process and can be applied to all types of machines (synchronous, induction, switched reluctance and direct current). Inverter-operation-related switching frequencies and spatial machine harmonics are routinely taken into account. The process is applicable to machines with rotor or stator skew as well as to outer-rotor and transversal-flux machines. It combines the two fast and user-interactive steps system simulation and vibration synthesis. The underlying model parameters are obtained via automated offline finite-element simulations based on generic input parameters. This allows using complex electromagnetic and structural models without computation time becoming prohibitive. Application examples are given for permanent magnet synchronous machine traction drives for (hybrid) electric vehicles as well as a for a switched-reluctance auxiliary drive. Simulated run-up spectrograms for structure-borne sound are validated against measurements and operational deflections are presented.
5.63 and 5.80 MeV levels of Ne20; de-excitation branching
Abstract The ratio Г γ /Г for the 5.63 and 5.80 MeV levels of Ne 20 has been determined to be 0.077 (±0.008) and −4 , respectively, by using the C 12 (C 12 , α)Ne 20 reaction and determining the fraction of the events in which the alpha-particle and the Ne 20 recoil are present in coincidence at the kinematically correct angles. In both cases these results in themselves are shown to imply radiative E1 transition (5.63→1.63 and 5.80→0, respectively) probabilities ⪡5 × 10 −5 Weisskopf units. When taken together with the life-time for the 5.63 MeV level measured by Evans et al . values of Г( E1 ) ≲ 5 × 10 −6 and Г α ≈ 6% of the particle estimate are obtained for this state.