A new family of modal methods for the calculation of eigenvector derivatives in non-self-adjoint systems with a singular coefficient matrix is developed. The family contains the modal and modified modal methods as a subset. In the family, the component of the mth eigenvector in the expansion of the derivative of the jth eigenvector is multiplied by various powers of the eigenvalue ratio lambda(i)/lambda(m), thereby accelerating convergence. The family of methods is applied to a self-adjoint example problem, namely, a cantilever beam whose root depth Is used as the design variable to which the sensitivity of the first four mode shapes is sought. Two different numbers of elements are used to model the beam in two cases in an effort to investigate the effect of the system size on the performance of the new methods. Central processor time and number of modes needed for convergence are determined. For a given problem, one of the methods in the family takes the smallest number of modes and shortest time to converge. The method is applied to a non-self-adjoint system with zero eigenvalues as well. The family is compared with Nelson's method and the modified Rudisill and Chu method on the basis of operation counts and is expected to perform better than the two when more than one eigenvector derivative is of interest.


A new steering law for redundant control moment gyroscope clusters
Tekinalp, Ozan (Elsevier BV, 2005-10-01)
A new inverse kinematics algorithm is developed that may provide singularity avoidance or may be used for quick transition through a singularity with small torque errors. To avoid singularities, angular momentum trajectory of the control moment gyro cluster during the maneuver is to be simulated in advance for the calculation of singularity free gimbal histories. The steering law proposed accurately generates the required torques making it suitable to be used in a feedback system. The desired gimbal traject...
Nonlinear flutter calculations using finite elements in a direct Eulerian-Lagrangian formulation
Seber, Guclu; Bendiksen, Oddvar O. (American Institute of Aeronautics and Astronautics (AIAA), 2008-06-01)
A fully nonlinear aeroelastic formulation of the direct Eulerian-Lagrangian computational scheme is presented in which both structural and aerodynamic nonlinearities are treated without approximations. The method is direct in the sense that the calculations are done at the finite element level, both in the fluid and structural domains, and the fluid-structure system is time-marched as a single dynamic system using a multistage Runge-Kutta scheme. The exact nonlinear boundary condition at the fluid-structure...
Two-dimensional unsteady Navier-Stokes solution method with moving overset grids
Tuncer, İsmail Hakkı (American Institute of Aeronautics and Astronautics (AIAA), 1997-03-01)
A simple numerical algorithm to localize intergrid boundary points and to interpolate unsteady solution variables across two-dimensional, structured overset grids is presented. Overset grids are allowed to move in time relative to each other. Intergrid boundary points are localized in a triangular stencil on the donor grid by a directional search algorithm. The final parameters of the search algorithm give the interpolation weights at the intergrid boundary point. Numerical results are presented for steady ...
Time-domain calculation of sound propagation in lined ducts with sheared flows
Özyörük, Yusuf (American Institute of Aeronautics and Astronautics (AIAA), 2000-05-01)
A recent application of the time-domain equivalent of the classical acoustic impedance condition, i.e., the particle displacement continuity equation, to numerical simulations of a Bow-impedance tube in the time domain yielded reasonably good results with uniform mean flows. The present paper extends this application to include sheared mean-flow effects on sound propagation over acoustically treated walls. To assess the prediction improvements with sheared flows, especially at relatively high Mach numbers, ...
Computational study of subsonic flow over a delta canard-wing-body configuration
Tuncer, İsmail Hakkı (American Institute of Aeronautics and Astronautics (AIAA), 1998-07-01)
Subsonic flowfields over a close-coupled, delta canard-wing-body configuration at angles of attack of 20, 24,2, and 30 deg are computed using the OVERFLOW Navier-Stokes solver Computed flowfields are presented in terms of particle traces, surface streamlines, and leeward-side surface pressure distributions for the canard-on and -off configurations. The interaction between the canard and the wing vortices, wing vortex breakdown, and the influence of the canard on vortex breakdown are identified, The comparis...
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