Samtech有限元仿真解决方案 Back Share LMS Engineering Services performed a modal test campaign on Goodrich landing gear for the Airbus A380 Safeguarding 1,300,000 pounds during takeoff and landing aircraft landing gear modal test A380 1.gifIn the Super Rig at Goodrich Corporation’s landing gear facility in Oakville, Ontario (Canada), LMS engineering consultants subjected a body landing gear prototype assembly for the Airbus A380 to Experimental Modal Analysis (EMA). After suspending the 12,000 pound body gear 12 feet high above concrete, they applied burst-random and stepped-sine excitation up to 1,000 Newton force levels. The major landing gear mode shapes extracted from the test data, both in static and fully extended stroke, supported structural studies at Airbus and helped engineers verify finite element (FE) models generated by Goodrich’s Landing Gear division. The world’s largest landing systems supplier Goodrich landing gear has a distinguished history that dates back to 1926, when Cleveland Pneumatic Company, now part of Goodrich, introduced the industry’s first air-oil landing gear strut. Goodrich merged with Menasco in 1999 to become the world’s largest supplier of landing systems. Today, Goodrich delivers landing systems to major aircraft companies, including Agusta, Airbus, Boeing, Bombardier, Gulfstream and Lockheed Martin. The success of Goodrich’s Landing Gear division is measured with each take-off and landing that is executed with its equipment. Since the Airbus A380 weighs approximately 1,300,000 pounds when fully loaded with passengers, luggage and fuel, this double-deck jetliner sets rigorous requirements on landing gear design and development. To assure safe and comfortable takeoff, landing and taxiing of this super-size aircraft, Airbus selected Goodrich for the development and production of the A380 landing gear systems. Building on LMS’s expert modal testing skills To support the structural testing campaign to be performed on the right-hand body landing gear system, Goodrich contracted the US-based team of LMS Engineering Services. “The LMS assignment involved EMA on a landing gear system, which allowed Goodrich to validate FE models of this rather complex mechanical assembly,” said Alvin Fong, Manager of Landing Gear Performance at Goodrich’s Oakville landing gear facility. “The six-wheel aircraft landing gear modal test A380 2.giflanding gear system weighs approximately 12,000 pounds, and its size exceeds 25 feet when fully extended. In landing gear system development, it is our task to meet the required modal stability and structural performance to ensure that the gear will safely react to all loads and circumstances it will encounter throughout its service life.” The structural test campaign for the A380 landing gear was performed at the Goodrich Landing Gear test facility in Oakville. The central feature of this facility is the Super Rig, an extremely large steel structure that encompasses nine test bays, each capable of handling an A380 body or wing gear. The entire Super Rig structure sits in a three-foot deep pit approximately the size of two football fields. The body landing gear prototype to be subjected to the modal test campaign filled bay #2 to the limit. The steel rig structure allowed the large body landing gear to be suspended in free conditions. The test set-up also required LMS to fabricate two solid stands, each filled with 5,000 pounds of concrete. To avoid free-play in landing gear joints as much as possible, LMS consultants pre-loaded the body landing gear unit with static forces they applied vertically through soft bungee straps. The measurement equipment consisted of latest-generation SCADAS 316 hardware as well as LMS Test.Lab software including the LMS PolyMAX modal parameter estimator. The equipment also controlled the excitation management of shaker systems. Verifying the validity of the modal test set-up To be able to provide sufficient energy while performing modal tests on a specimen of this size and weight, LMS engineering consultants installed multiple shakers. Two electro-dynamic shakers – capable of generating 1,000 Newton peak forces – were conditioned to provide either burst-random or stepped-sine system excitation. Initial modal tests showed that the test rig itself exhibits dominant fore-aft motion around and 8 Hertz. As these dominant frequencies fall within the 0 to 10 Hertz frequency and of interest for landing gear modal testing, significant dynamic coupling between ear modes and test rig modes was observed. To keep a close eye on this rig-gear interference throughout the test campaign, LMS engineers added a number of rig measurement points to the modal test geometry of the landing gear unit. To verify the quality of the modal test set-up, LMS consultants evaluated autopower spectra as well as Frequency Response Function (FRF) coherence and reciprocity. These checks indicate whether all input energy aircraft landing gear modal test A380 3.gifis present at the output side, and whether excitation and measurement points are located favorably. Autopower spectra related to front and rear shaker excitation showed that both shakers inputs were of the same force level and excited all frequencies equally across the frequency range of interest. “When evaluating structural FRF coherence and reciprocity, the two burst-random shaker inputs created only limited non-linear landing gear behavior in static stroke and extended positions, at specified force levels between 5 and 15 Newton,” Paul Weal, Business Development Manager of LMS Engineering Services, explained. “However, when increasing force levels firmly using stepped-sine excitation – 200 up to 1,000 Newton – we identified stronger non-linear behavior, mainly as a result of slight backlash that was present in the huge landing gear joint connections. When testing at highest force levels, the resulting bending and torsion modes became truly visible, as we witnessed displacements of about 1 inch. With the help of driving point FRF functions, we quantified the evolution of growing non-linearity that is exhibited in response to increasing force levels.” Selecting the modes of the landing gear The actual modal analysis test campaign started with the selection of the landing gear modes. LMS consultants quickly obtained insight into modal resonance through the sum blocks function of LMS Test.Lab, which emphasizes modal resonance by displaying the summation of all measured FRFs. Based on the acquired data, the individual modal parameters were extracted using the innovative LMS PolyMAX curve fitter. The modal parameters then served as a basis to synthesize FRFs through calculation. aircraft landing gear modal test A380 4.gifThe high level of correlation between measured and synthesized FRFs showed that the modal analysis was successful in accurately reproducing the measured FRFs. Fong said, “The most significant modes retrieved for the landing gear static stroke configuration were fore-aft, lateral and torsion resonance below 15 Hertz. For extended stroke, the identified fore-aft, lateral and torsion modes were lower than static stroke. In general, the measured mode frequencies turned out to be lower that their predicted counterparts. The project confirms the modal characteristics of the right-hand body landing gear system Goodrich developed for the new Airbus A380 airliner. The major mode shapes extracted from the test data were used to verify FE landing gear models here at Goodrich, and supported structural investigations at Airbus.” Supporting landing gear and full-aircraft simulations aircraft landing gear modal test A380 5.gifThe survey also explored potential dynamic influences of the Super Rig on the mode shapes of the actual landing gear, and validated the need for further testing to characterize the attachment points of the landing gear to the Super Rig. The modal analysis showed strong coupling of the landing gear and test rig dynamics, particularly in the 5 and 8 Hertz regions. For example, considerable rig fore-aft motion in combination with slight gear fore-aft motion was observed between 5.1 and 5.2 Hertz. In reviewing and discussing the test data, Fong’s experience in the design of airframe engine mounts as well as LMS engineering consultants’ modal testing expertise was most helpful in delivering better insight into landing gear performance. “The experimental modal analysis test campaign helped further enhance virtual models of the body landing gear, supporting both stability studies and structural investigations,” Fong conclu
Posted on: Tue, 20 Aug 2013 08:20:57 +0000
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