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Foundation ::
Engineering Applications ::
FREDOM
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FREDOM
Frequency Domain Propagation Model
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SOURCE CODE AVAILABLE
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In the past, no systematic procedure was available to rocket engine designers to account for fluid borne acoustic loadings on engine components. As a result, a number of engine problems and failures related to internal fluid loading have occurred over the years. Many internal fluid loading problems occur in ducts or internal component passages connecting various engine components. This loading is due to propagation of noise from sources such as pumps, combustion, and duct bends. Also, acoustic resonances of these ducts could amplify the fluid loading affects to a large extent.
FREDOM is designed to solve fluid loading problems. It is a 1-D frequency domain propagation code that can handle various boundary conditions and inputs. It determines the frequency response of a system to a certain input (forcing function). The propagation modeling is done using planar 1-D wave equations. FREDOM sees a fluid flow system as a series of elements and nodes. An element is a continuous section of the system for which the cross-sectional area, density of the fluid, thermodynamic sound speed, duct's elastic modulus, and wall thickness parameters do not change.
FREDOM uses the matrix solver from a previously existing program called FREQPL, however, FREDOM provides additional features. It automates the entire theoretical process by writing, internally, the equations for the system. The user only needs to set up four input files for the system and does not have to have a highly technical background in acoustics. Automation further reduces the risk of mathematical errors and the time it takes to solve a problem. FREDOM accounts for boundary conditions of the system automatically. A coefficient matrix is created so that a solution for any variable is possible. FREDOM works in the frequency domain, thus, it requires less time to solve a problem than codes that work in the time domain. Finally, FREDOM allows for small area changes in the duct due to the distensibility of the material.
FREDOM carries the NASA case number MFS-29971. It was originally released as part of the COSMIC collection.
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