NASA Scientific and Technical Aerospace Reports

20040111380 Computer Sciences Corp., Hampton, VA, USA
A Grid Generation System for Multi-Disciplinary Design Optimization
Jones, William T.; Samareh-Abolhassani, Jamshid; [1995]; 9 pp.; In English; Copyright; Avail: CASI; A02, Hardcopy
A general multi-block three-dimensional volume grid generator is presented which is suitable for Multi-Disciplinary
Design Optimization. The code is fast, robust, highly automated, and written in ANSI C for platform independence. Algebraic
techniques are used to generate and/or modify block face and volume grids to reflect geometric changes resulting from design
optimization. Volume grids are generated/modified in a batch environment and controlled via an ASCII user input deck. This
allows the code to be incorporated directly into the design loop. Generated volume grids are presented for a High Speed Civil
Transport (HSCT) Wing/Body geometry as well a complex HSCT configuration including horizontal and vertical tails, engine
nacelles and pylons, and canard surfaces.
Author
Computational Grids; Design Optimization; Grid Generation (Mathematics); Multidisciplinary Design Optimization; Aircraft
Design; Three Dimensional Models; Multigrid Methods
20040111381 NASA Langley Research Center, Hampton, VA, USA
Effects of Sonic Line Transition on Aerothermodynamics of the Mars Pathfinder Probe
Gnoffo, Peter A.; Weilmuenster, K. James; Braun, Robert D.; Cruz, Christopher I.; [1995]; 14 pp.; In English
Report No.(s): AIAA Paper 95-1825; No Copyright; Avail: CASI; A03, Hardcopy
Flow field solutions over the Mars Pathfinder Probe spanning the trajectory through the Martian atmosphere at angles of
attack from 0 to 11 degrees are obtained. Aerodynamic coefficients derived from these solutions reveal two regions where the
derivative of pitching moment with respect to angle of attack is positive at small angles of attack. The behavior is associated
with the transition of the sonic line location between the blunted nose and the windside shoulder of the 70 degree half-angle
cone in a gas with a low effective ratio of specific heats. The transition first occurs as the shock layer gas chemistry evolves
from highly nonequilibrium to near equilibrium, above approximately 6.5 km/s and 40 km altitude, causing the effective
specific heat ratio to decrease. The transition next occurs in an equilibrium flow regime as velocities decrease through 3.5 km/s
and the specific heat ratio increases again with decreasing enthalpy. The effects of the expansion over the shoulder into the
wake are more strongly felt on the fustrum when the sonic line sits on the shoulder. The transition also produces a
counter-intuitive trend in which windside heating levels decrease with increasing angle of attack resulting from an increase
in the effective radius of curvature. Six-degree-of-freedom trajectory analyses utilizing the computed aerodynamic coefficients
predict a moderate, 3 to 4 degree increase in total angle of attack as the probe, spinning at approximately 2 revolutions per
minute, passes through these regions.
Author
Aerodynamic Coeffıcients; Aerothermodynamics; Angle of Attack; Flow Distribution; Mars Atmosphere; Mars Pathfinder;
Trajectories; Trajectory Analysis; Enthalpy
20040111508 Maryland Univ., College Park, MD
Control of Systems With Periodic Coefficients, With Application To Active Rotor Control
Celi, Roberto; Lovera, Marco; Colaneri, Patrizio; Jun. 30, 2004; 174 pp.; In English; Original contains color illustrations
Contract(s)/Grant(s): DAAD19-01-1-0415
Report No.(s): AD-A425484; ARO-41569.2-EG; No Copyright; Avail: CASI; A08, Hardcopy
The project focused on the analysis and synthesis of active rotor controls. The rotor was modeled as a periodic system.
The key accomplishments are: (i) First systematic study of the effect of zeros in rotorcraft aeromechanics. The ‘zeros’ play
a key role in the closed-loop behavior of the system. As rotor active controls become feasible, the calculation of zeros needs
to become a routine design step. (ii) First study of the effects of closed-loop HHC/IBC on the aeroelastic stability of a
helicopter rotor including, for example, the in-plane damping. This is especially important for configurations with inherently
low in-plane damping such as bearingless rotors. (iii) Presentation to the rotorcraft community of techniques for the analysis
of periodic systems developed in other areas of engineering, e.g., in the signal processing and control engineering
communities. (iv) First study of the effects of closed-loop HHC/IBC on the aeroelastic stability of a helicopter, including the
effects of the discrete elements, and of different sampling and update rates in the system. In all cases, a realistic mathematical
model was used, with typically more than 35 degrees of freedom, including blade flexibility and nonlinear rigid body
dynamics.
DTIC
Active Control; Aeroelasticity; Coeffıcients; Periodic Functions; Rotary Wings
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