This paper presents a multibody formulation for helicopter nonlinear dynamic analysis. Cartesian coordinates are used to represent the eanfiwration of each body. This approach involves more unknown coordinates than ~ ~ arcstrictly necessary todefine theeonfigurationof thesystem; henee,eonstraint cqustionslinking the redundant coordinates are an integral part of the formulation. In classienl rotorcraft methodologies, elsstic bodies are revrescnted in a local. rotaline frame of reference which amounts to sevarntine rieid body and elastic motions... ..'The appn,ach f#,II~,vcd in this "ark dupurli radieilll) tnom lhis rlu~sirul appn,:teh: tltr tulsl ,owtian c,tall elaclir bndie\ i, tlirectl) rcfcrrcrl 11, a single inrrlill frsmf.'l,hi~ xl,proarh readily ulla,vs 1 1~~ dr$plc,pm~nt of rennl,ulrr models to deal wilh arbitrarily complex multibody eonfig&ations. In this~work, finite rotati& are represented using the components of the conformal rotation vectnr, and the constraint equations are enforced via an augmented Lagrangian formulation. Simple numerical examples are presented to validate the formulation, and the ela~sical ground resonance problem is treated here as a multihody prohlem. Good correlation is found between analytical solutions and multibody formulations. 0. A. BAUCHAU JOURNAL OF THE AMERICAN HELICOPTER SOCIETY
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