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Virtual Vibration Testing Of External Stores
Navy SBIR 2010.1 - Topic N101-015 NAVAIR - Mrs. Janet McGovern - [email protected] Opens: December 10, 2009 - Closes: January 13, 2010 N101-015 TITLE: Virtual Vibration Testing Of External Stores TECHNOLOGY AREAS: Air Platform, Battlespace, Weapons ACQUISITION PROGRAM: Joint Strike Fight; PMA-259, Air-to-Air Missile Systems OBJECTIVE: Develop a structural dynamics modeling tool which will provide an accurate physics-based solution for predicting non-linear vibration response, and employ the modeling tool for conducting "virtual" vibration testing. DESCRIPTION: Because of the complexity and extreme cost associated with "high fidelity simulation" of vibration loads in a laboratory environment, the current practice and goal of the laboratory vibration test is to recreate the effects of the service use vibration environment using electrodynamic shaker systems. Electrodynamic shakers provide input excitation for matching store vibration response measured during captive carriage flight testing. Vibration excitation resulting from platform captive carriage is transmitted to the weapon through multiple paths and sources; whereas, in a laboratory vibration test, loads are typically induced through a single shaker input. Likewise, the laboratory test boundary conditions and resulting load interface impedances can be significantly different than the "real world" or service use environment. As a result of the differences in load path, boundary conditions, and impedances between flight and the laboratory, input forces generated during test can be much different than those experienced during flight causing unrepresentative failures. Examples where laboratory vibration test loads created unrepresentative failures during all-up-round (AUR) testing include complete failure of forward and aft components and bomb racks for various AUR bomb vibration tests, and lug, hanger, component joint, and launcher failure during HARM, Sparrow, Sidewinder, and JSOW testing. Failures due to insufficient testing have significant impact on design cost and schedule which result in critical delivery impact to the warfighter. An alternate approach would use a highly accurate dynamic modeling tool to analyze the laboratory test configuration for comparison with the "real world" store / aircraft interface, and allow for "tuning" of the laboratory test configuration to achieve test loads that more accurately represent the service use environment. Tuning of the laboratory test would include test fixture design that more accurately represents the service use store/aircraft interface along with accurate estimates for optimum location of the shaker input forces. Upon completion of the modeling, a "virtual" laboratory vibration test could be conducted which would assess the test configuration and resulting failure modes prior to conducting the actual test. Eventual validation of the virtual test model could then be used to forgo future laboratory vibration testing to qualify airframe or other system modifications which may occur as the weapon system matures. The current practice of using finite element analysis (FEA) for modeling and predicting vibration response of complex, non-linear structural systems does not provide the necessary accuracy at frequencies much beyond the first few structural modes of the weapon system. Because commercially available FEA tools utilize linear elastic theory only, FEA can not accurately predict vibration response due to inherent nonlinearities associated with either the aircraft/store interface or the laboratory shaker system interface. In order to exercise the linear-elastic FEA models to output results for use with non-linear vibration problems, the FEA model is typically adjusted by a process which introduces non-realistic structural properties to achieve dynamic response equivalent to output derived experimentally for a unique set of boundary conditions only. Thus, the development of a dynamic modeling tool which combines the ability of linear elastic theory and non-linear problem solving algorithms would provide a robust physics-based solution to process virtual vibration test models, rather than the "trial-and-error" methodology currently in practice which relies entirely on experimental data for each unique structural non-linearity and associated dynamic environment. PHASE I: Develop a concept for an accurate non-linear structural dynamics model for a simple non-linear store / aircraft configurations e.g., store hanger and rail. PHASE II: Develop and demonstrate an accurate non-linear structural dynamics model for a typical store/platform configuration and apply the information to design an accurate non-linear structural dynamics model for a typical store/shaker interface configuration. Verify results output by the non-linear store/shaker interface structural dynamics model by conducting vibration testing on representative store/platform configuration hardware using various random vibration input levels and spectra. PHASE III: Produce a validated virtual vibration test system based on the non-linear structural dynamics modeling tool developed in Phases I and II. PRIVATE SECTOR COMMERCIAL POTENTIAL: The structural dynamics design industry e.g., those involved in manufacture of automobiles, heavy equipment, buildings, bridges, space vehicles, weapons, recreational vehicles and accessories, etc. will benefit through extension of their technology base. REFERENCES: 2. MIL-STD-810G, "Environmental Engineering Considerations and Laboratory Tests", 31 October 2008 KEYWORDS: vibration; structural dynamics; modeling; non-linear; virtual testing; electrodynamic shaker
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