Accepted Manuscripts

Jonathan D Walsh, Quang T. Su and Daniel M. Warren
J. Vib. Acoust   doi: 10.1115/1.4038681
Presented is a test methodology for characterizing the vibration sensitivity of miniature microphones. An ordinary vibration sensitivity experiment becomes difficult because vibrating surfaces are also sources of sound. This sound is picked up by the microphone being tested, changing the result. The sound pressure will be correlated with the vibration signal such that averaging will not serve to increase the accuracy of that result. Previously described techniques reduce the correlated pressure using custom experimental equipment and have geometric limitations. In the improved technique, the microphone is treated like a linear two-input-one-output system. The two input signals (vibration and acoustic pressure) are measured, and the vibration sensitivity is determined using two different spectral analysis techniques. These techniques have good agreement between one another, and measured values fit well into a simple acoustic model of the microphone. A technique for estimating the major source of measurement error indicates that this error is small enough for a reasonable estimate of vibration sensitivity to be made.
TOPICS: Vibration, Microphones, Signals, Errors, Sound pressure, Pressure, Spectroscopy, Acoustics, Emission spectroscopy
Technical Brief  
Hanbo Jiang, Alex Siu Hong Lau and Xun Huang
J. Vib. Acoust   doi: 10.1115/1.4038680
Numerical optimizations are very useful in liner designs for low-noise aeroengines. Although modern computational tools are already very efficient for a single aeroengine noise propagation simulation run, the prohibitively high computational cost of a broadband liner optimization process which requires hundreds of thousands of runs renders these tools unsuitable for such task. To enable rapid optimization using a desktop computer, an efficient analytical solver based on the Wiener-Hopf method is proposed in the current study. Although a Wiener-Hopf-based solver can produce predictions very quickly (order of a second), it usually assumes an idealized straight duct configuration with a uniform background flow that makes it arguable for practical applications. In the current study, we employ the Wiener-Hopf method in our solver to produce an optimized liner design for a semi-infinite annular duct set-up, and compare its noise-reduction effect with an optimized liner designed by the direct application of a numerical finite element solver for a practical aeroengine intake configuration with an inhomogeneous background flow. The near-identical near- and far-field solutions by the Wiener-Hopf-based method and the finite element solvers clearly demonstrate the accuracy and high efficiency of the proposed optimization strategy. Therefore, the current Wiener-Hopf solver is highly effective for liner optimizations with practical set-ups, and is very useful to the preliminary design process of low-noise aeroengines.
TOPICS: Finite element analysis, Optimization, Noise (Sound), Design, Flow (Dynamics), Ducts, Computers, Noise control, Simulation
April Bryan
J. Vib. Acoust   doi: 10.1115/1.4038578
While several numerical approaches exist for the vibration analysis of thin shells, there is a lack of analytical approaches to address this problem. This is due to complications that arise from coupling between the mid-surface and normal coordinates in the transverse differential equation of motion of the shell. In this research, an Uncoupling Theorem for solving the transverse differential equation of motion of doubly curved, thin shells with equivalent radii is introduced. Use of the Uncoupling Theorem leads to the development of an uncoupled transverse differential of motion for the shells under consideration. Solution of the uncoupled spatial equation results in a general expression for the eigenfrequencies of these shells. The theorem is applied to four shell geometries and numerical examples are used to demonstrate the influence of material and geometric parameters on the eigenfrequencies of these shells.
TOPICS: Free vibrations, Thin shells, Shells, Theorems (Mathematics), Differential equations, Vibration analysis, Analytical methods
David Griese, Joshua D. Summers and Lonny Thompson
J. Vib. Acoust   doi: 10.1115/1.4029043
This work defines a finite element model to study the sound transmission properties of aluminium honeycomb sandwich panels. Honeycomb cellular metamaterial structures offer many distinct advantages over homogenous materials because their effective material properties depend on both their constituent material properties and their geometric cell configuration. From this, a wide range of targeted effective material properties can be achieved thus supporting forward design by tailoring the honeycomb cellular materials for specific applications. One area that has not been fully explored is the set of acoustic properties of honeycomb materials and how these can offer increased acoustic design flexibility. Understanding these relations, the designer can effectively tune designs to perform better in specific acoustic applications. One such example is the insulation of target sound frequencies to prevent sound transmission through a panel. This work explores how certain geometric and effective structural properties of in-plane honeycomb cores in sandwich panels affect the sound pressure transmission loss properties of the panel. The two acoustic responses of interest in this work are the general level of sound transmission loss of the panel and the location of the resonance frequencies that exhibit high levels of sound transmission, or low sound pressure transmission loss. Constant mass honeycomb core models are studied with internal cell angles ranging from -45° to +45°. It is shown in this work that models with lower core internal cell angles, under constant mass constraints, have more resonances in the 1-1000 Hz range, but exhibit a higher sound pressure transmission loss between resonant frequencies.
TOPICS: Sound, Honeycomb structures, Geometry, Acoustics, Materials properties, Sound pressure, Resonance, Design, Finite element model, Insulation, Metamaterials, Aluminum, Mechanical properties, Acoustical properties

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