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General Rotorcraft Aeromechanical Stability Program (GRASP): Theory manualThe general rotorcraft aeromechanical stability program (GRASP) was developed to calculate aeroelastic stability for rotorcraft in hovering flight, vertical flight, and ground contact conditions. GRASP is described in terms of its capabilities and its philosophy of modeling. The equations of motion that govern the physical system are described, as well as the analytical approximations used to derive them. The equations include the kinematical equation, the element equations, and the constraint equations. In addition, the solution procedures used by GRASP are described. GRASP is capable of treating the nonlinear static and linearized dynamic behavior of structures represented by arbitrary collections of rigid-body and beam elements. These elements may be connected in an arbitrary fashion, and are permitted to have large relative motions. The main limitation of this analysis is that periodic coefficient effects are not treated, restricting rotorcraft flight conditions to hover, axial flight, and ground contact. Instead of following the methods employed in other rotorcraft programs. GRASP is designed to be a hybrid of the finite-element method and the multibody methods used in spacecraft analysis. GRASP differs from traditional finite-element programs by allowing multiple levels of substructure in which the substructures can move and/or rotate relative to others with no small-angle approximations. This capability facilitates the modeling of rotorcraft structures, including the rotating/nonrotating interface and the details of the blade/root kinematics for various types. GRASP differs from traditional multibody programs by considering aeroelastic effects, including inflow dynamics (simple unsteady aerodynamics) and nonlinear aerodynamic coefficients.
Document ID
19910004449
Acquisition Source
Legacy CDMS
Document Type
Technical Memorandum (TM)
Authors
Hodges, Dewey H.
(NASA Ames Research Center Moffett Field, CA, United States)
Hopkins, A. Stewart
(NASA Ames Research Center Moffett Field, CA, United States)
Kunz, Donald L.
(NASA Ames Research Center Moffett Field, CA, United States)
Hinnant, Howard E.
(NASA Ames Research Center Moffett Field, CA, United States)
Date Acquired
September 6, 2013
Publication Date
October 1, 1990
Subject Category
Structural Mechanics
Report/Patent Number
A-90014
AD-A235144
USAAVSCOM-TM-89-A-003
NAS 1.15:102255
NASA-TM-102255
Accession Number
91N13762
Funding Number(s)
PROJECT: RTOP 992-21-01
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.
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