Finite Element Modeling of the NASA Langley Aluminum Testbed Cylinder

Branch,Membercodes, modeling techniques and optimization methodsused in the prediction of aircraft interior noise. Thepurpose of the current program is to develop highfidelity, manageable ATC numerical models based onaccurate geometric, structural and material t)rot)ertiesof the participating components. The componentstructures, up to complete _selage configurations,require experimental validation performed on thephysical model. Recent numerical modeling and vibro-acoustic modal testing pursued at the NASA Langley islisted in References l-8. This report discusses thefinite element model development and validation ofthree isolated components and six assembledconfigurations through comparison with modalfrequencies fi_om experimental modal surveys. Updatedand refined finite element models that exhibit increasedcorrelation with the measured modal data arediscussed.Aluminum Testbed CylinderThe Aluminum Testbed Cylinder (ATC), shown inFigure 1, was designed as a simplified model of anaircraft fixselage structure. Six configurations ofcomponent assemblies were considered (Tablel). Thebare frame substructure of Configuration I includeslongitudinal stringers, ring frames and end rings. Thecylindrical section of the testbed with the longitudinalstringers is 144 inches long with a diameter of 48inches. Nine aluminum ring frames are evenly spacedover the length of the cylinder and twenty-fourstringers are equally distributed around thecircumtbrence. The aluminum end rings have a 2-inchby 1.5-inch cross-section. Configuration II adds a plateto each end of the bare frame cylinder section C'able 1).Each end plate consists of a two-inch-thickparticleboard with a half inch-thick piece of plywoodattached. Configuration III in 'Fable 1 constitutes thebare ficame, without the end plates, but covered with a0.040-inch thick alum\nun1 skin. The skin isassembled from four 144-inch-long overlappingaluminum sheets. Configuration IV includes the bareframe, the skin and the end plates. One-quarter inchthick fiberglass-reinlbrced epoxy composite domes,featuring pressure release devices and access plates, are1American Institute of Aeronamics and Astronautics