Spacecraft structures are subject to a series of load environments during their service life, with the most severe of these occurring during the spacecraft's launch and ascension through the atmosphere. In particular, acoustic loads imposed on stowed satellites within the launch vehicle fairing can result in high mechanical loads on sensitive spacecraft hardware. These acoustic loads have the potential to damage important components and as such it is necessary to accurately characterize and predict the acoustic launch environment for a given mission. This research investigates the Sound Pressure Level (SPL) that can be measured in and around spacecraft cavities resulting from a known excitation and the resultant structural responses. Linear finite element analysis (FEA) is coupled with the Boundary Element method (BEM) to analyze spacecraft acoustic environments and corresponding structural responses at low frequencies on the order of the structural modes.
Analytical capability for predicting acoustic environments inside the launch vehicle has improved significantly in recent years; however, while it is easy to perform an analysis and obtain results, the modeling effort can become unnecessarily complicated and analytical data can be hard to interpret. This work seeks to alleviate unnecessary complexity in the low-frequency regime of acoustic modeling by examining the fundamentals of coupled BEM-FEM analysis and applying simplification to a spacecraft model where possible to achieve results verified against direct field acoustic testing (DFAT) methods. / Master of Science / The modern spacecraft is a complicated assembly inclusive of panels, sophisticated instruments, harnesses, actuators, tanks, reflectors, and connecting hardware. Throughout its service life, it will be subjected to a series of dynamic load environments that have the potential to cause damage or compromise the intended mission. These environments are anticipated and simulated both analytically and experimentally to qualify the spacecraft within some confidence level.
One of the most severe dynamic environments that a spacecraft faces is the acoustic loading created by noise from the rocket engines at launch and aerodynamic turbulence on the launch vehicle during ascension. These noise levels, well above the threshold of human pain, cause the structure to vibrate at a variety of frequencies with significant force. Anticipated acoustic environments are simulated for spacecraft assemblies in testing using advanced audio equipment in efforts to produce equivalent measureable structural responses. In recent years, commercial software has been developed to create computer models of spacecraft that can be studied to predict these intense vibrations and where they will happen, which serves as an important consideration in the design process. Efforts are underway to improve the fidelity of these analytical models and correlate them with measured test data.
This work uses analytical models for the acoustic test environment at low frequencies to predict field levels between closely-spaced structural panels and the associated structural vibrations produced. Results are compared with test data and a trade study is conducted to assess modeling techniques and assumptions.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/83460 |
| Date | 05 June 2018 |
| Creators | Marshall, Peter Johannes |
| Contributors | Aerospace and Ocean Engineering, Kapania, Rakesh K., McQuigg, Thomas Dale, Philen, Michael K. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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