Mobility Analysis of Structure-borne Noise Paths in a Simplified Rotorcraft Gearbox System
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The Ohio State University / OhioLINK
2010
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ndltd-OhioLink-oai-etd.ohiolink.edu-osu12768849442021-08-03T06:00:01Z Mobility Analysis of Structure-borne Noise Paths in a Simplified Rotorcraft Gearbox System Srinivasan, Vijay Mechanical Engineering vibration noise sound radiation gear gear noise gearbox airframe rotorcraft strut mobility mobility synthesis isolation friction static transmission error finite element analysis linear time invariant <p>This thesis presents a mobility analysis of a simplified helicopter gearbox system focusing on structure-borne noise, based on linear time-invariant system theory. The internal gear dynamic system, with a unity spur gear pair, shafts and bearings, is modeled as an 8 degree of freedom linear time-invariant system with static transmission error and sliding friction as the primary excitations with assumed magnitudes that are uniform throughout the entire frequency range (5-20000 Hz). Natural frequencies are obtained and eigenvalue derivatives are used to identify variations in each natural frequency with respect to small changes in each system parameter using a Taylor's series approximation. Analytical expressions are derived through the mobility synthesis technique for the linear and rotational motions of the gear and pinion, dynamic transmission error and dynamic bearing and mesh forces in terms of the effective shaft/bearing stiffnesses, mesh stiffness, masses and inertias of the gears and shafts. These results are compared with the direct matrix inversion methods. The asymptotic trends in the frequency responses are compared with static forces. The gear motions predicted by this model are used to predict sound radiation from the casing by means of experimental pressure/acceleration transfer functions. Measured individually for line of action and off-line of action paths, these transfer functions are considered to be made up of separate transfer functions corresponding to the gear system response, bearing transmissibility, casing transmissibility and sound radiation efficiency. The variation of the overall transfer function for changes in internal sub-system parameters (mesh stiffness, bearing/shaft stiffness) is formulated assuming that the bearing and casing characteristics remain unaffected. These modified transfer functions are then employed to predict the effect of assumed variation in the internal parameters and source excitations on the radiated sound.</p><p>Further, finite element models of the external system, including gearbox casing, struts and airframe, are developed to examine the path and receiver issues. The casing is modeled based on drawings of the NASA Glenn Research Center's gear noise test rig. The modeling of the struts and airframe are based on assumed dimensions and configurations. Natural frequencies, mode shapes and harmonic responses are obtained for each structural component with assumed boundary conditions for a frequency range of 50 - 5000 Hz. A simplified lumped parameter system is developed where the gearbox casing and airframe are represented by lumped masses and the struts are represented by longitudinal and flexural springs. Isolation effectiveness of the struts is calculated based on the individual driving point mobilities using the finite element results as well as the lumped parameter approximation. It is shown through both calculations that the struts provide better isolation along their transverse direction along which they are more compliant, than along their longitudinal direction. The presence of a mobility mismatch between contiguous components is discussed. A higher mismatch in the mobilities at the interfaces provides a more effective vibration isolation while poor mismatch leads to poor isolation at specific frequency ranges.</p> 2010-09-27 English text The Ohio State University / OhioLINK http://rave.ohiolink.edu/etdc/view?acc_num=osu1276884944 http://rave.ohiolink.edu/etdc/view?acc_num=osu1276884944 unrestricted This thesis or dissertation is protected by copyright: all rights reserved. It may not be copied or redistributed beyond the terms of applicable copyright laws. |
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NDLTD |
| language |
English |
| sources |
NDLTD |
| topic |
Mechanical Engineering vibration noise sound radiation gear gear noise gearbox airframe rotorcraft strut mobility mobility synthesis isolation friction static transmission error finite element analysis linear time invariant |
| spellingShingle |
Mechanical Engineering vibration noise sound radiation gear gear noise gearbox airframe rotorcraft strut mobility mobility synthesis isolation friction static transmission error finite element analysis linear time invariant Srinivasan, Vijay Mobility Analysis of Structure-borne Noise Paths in a Simplified Rotorcraft Gearbox System |
| author |
Srinivasan, Vijay |
| author_facet |
Srinivasan, Vijay |
| author_sort |
Srinivasan, Vijay |
| title |
Mobility Analysis of Structure-borne Noise Paths in a Simplified Rotorcraft Gearbox System |
| title_short |
Mobility Analysis of Structure-borne Noise Paths in a Simplified Rotorcraft Gearbox System |
| title_full |
Mobility Analysis of Structure-borne Noise Paths in a Simplified Rotorcraft Gearbox System |
| title_fullStr |
Mobility Analysis of Structure-borne Noise Paths in a Simplified Rotorcraft Gearbox System |
| title_full_unstemmed |
Mobility Analysis of Structure-borne Noise Paths in a Simplified Rotorcraft Gearbox System |
| title_sort |
mobility analysis of structure-borne noise paths in a simplified rotorcraft gearbox system |
| publisher |
The Ohio State University / OhioLINK |
| publishDate |
2010 |
| url |
http://rave.ohiolink.edu/etdc/view?acc_num=osu1276884944 |
| work_keys_str_mv |
AT srinivasanvijay mobilityanalysisofstructurebornenoisepathsinasimplifiedrotorcraftgearboxsystem |
| _version_ |
1719429173493104640 |