• 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. The computer program VAPAS contains an implementation of most of these algorithms. (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)