Analyzed
the instabilities associated with an isolated blade of a hingeless rotor
helicopter. The research centered around determination of the influence of
geometrical nonlinearities and of key design parameters on the stability of the
system. A patent was granted for identification of significant stabilizing
parameters. (1970 - 1976)
Participated
in official investigation of mast-bumping phenomenon for AH/UH Army
helicopters. (1974)
Developed
an analysis and a successful computer program (FLAIR) used by the major helicopter
manufacturers for predicting aeromechanical stability of bearingless rotor
helicopters. (1977)
Participated
in the NASA Ames UH helicopter accident investigation. (1978)
Developed
an accurate variable order finite element scheme for analyzing vibration and
response of nonuniform rotating beams with discontinuities. (1978)
Member
of the Technical Advisory Group for the Second Generation Comprehensive
Helicopter Analysis System, a computer software system under development by the
U.S. Army. (1979 - 1986)
Developed
a variable-order finite element scheme for aeroelastic stability analysis of
nonuniform rotating blades. This inherently nonlinear problem requires solution
of the equilibrium deformed shape of the blade under the influence of
aerodynamic and inertial loads prior to the actual stability analysis. (1980)
Developed
a new definition of strain in a beam for which strain and rotation are
rigorously uncoupled. The deformation-induced rotations of the beam reference
axis can assume arbitrarily large values, whereas the strain components are
linear in elongations and shears. (1984 - 1986)
Served
as project manager, chief analyst, and co-developer of the General Rotorcraft
Aeromechanical Stability Program (GRASP), a hybrid multi-body/variable-order finite
element program. GRASP has the capability of modeling the complex behavior of
bearingless rotor helicopters. GRASP treats a helicopter as an arbitrary
collection of beam elements and rigid bodies connected together in an arbitrary
fashion, allowing large displacements and rotations, and relative motion
between elements. Rotor aerodynamics for the axial flight and ground contact
conditions, including dynamic inflow, are treated. This powerful program has
over 170,000 lines of FORTRAN 77 code. (1980 - 1986)
Developed
mixed variational formulation for geometrically exact behavior of initially
curved and twisted, anisotropic beams. (1988)
Participated
in developing a mixed finite element method based on geometrically-exact
intrinsic equations for rigid-body dynamics and elastodynamics of beams which
allows for the use of extremely crude shape functions. The method yields very
accurate results for time marching, two-point boundary value problems in space
or time, and space-time behavior of beams. (1989 - 1994)
Participated
in developing a finite element formulation for optimal control problems based
on a weak Hamiltonian form of the necessary conditions, providing a robust,
self-starting method for solving variational optimization problems with
inequality constraints. (1990 - 1996)
Participated
in developing theory and computational algorithms that determine asymptotically
correct elastic constants for anisotropic beams by means of the finite element
method. The computer program VABS contains an implementation of most of these
algorithms. (1990 - present)
Participated
in developing computational algorithms that determine asymptotically correct
elastic constants for anisotropic plates and shells. (1991 - present)
Participated
in developing a dynamics/control formulation for a robust missile guidance
algorithm based on a finite element formulation of weak Hamiltonian (patented).
(1993 - 1995)
Participated
in developing an h-p adaptive finite element scheme for solution of dynamics and
optimal control problems. (1992 - 1998)
Participated
in the development of computational algorithms to transfer data accurately from
meshes for computational fluid dynamics to those for computational structural
dynamics. (1994 - 1996)
Participated
in development of computational algorithms for nonlinear aeroservoelasticity of
high-aspect-ratio-winged HALE aircraft, including flying wing configurations,
and in parametric studies of such aircraft. Participated in development of the
computer program NATASHA - Nonlinear Aeroelastic Trim and Stability of HALE
Aircraft. (1997 - present)
Participated
in development of computational algorithms for nonlinear structural dynamics
and aeroelasticity of wind turbines. (1998 - 2003)
Participated
in development of computational algorithms for nonlinear structural dynamics
and aeroelasticity of missiles. (2000 - 2004)
Developed
geometrically exact, fully intrinsic equations of motion and space-time
compatibility for twisted and curved anisotropic beams. These equations have no
displacement or rotation variables. (2002 – 2003)
Developed
geometrically-exact composite beam element (GCB) for the Rotorcraft
Comprehensive Analysis System (RCAS). (2004)
Participated
in development of geometrically exact, fully intrinsic equations of motion and
space-time compatibility equations for anisotropic plates. These equations have
no displacement or rotation variables. (2006)
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Last Updated 6/6/2008