Ames Research Center
The Ames Research Center—with research responsibilities within aerodynamics, aeronautical and space vehicle studies, reentry and thermal protection systems, simulation, biomedical research, human factors, nanotechnology, and information technology—is one of the world’s premier aerospace research establishments. It was the second NACA laboratory, established in 1939 as war loomed in Europe. The Center was built initially to provide for expansion of wind tunnel facilities beyond the space and power generation capacity available at Langley. Accordingly, in the computer age, Ames became a major center for computational fluid dynamics methods development. Ames also developed a large and active structures effort, with approximately 50 to 100 researchers involved in the structural disciplines at any given time. Areas of research include structural dynamics, hypersonic flight and r-entry, rotorcraft, and multidisciplinary design/analysis/optimization. These last two are discussed briefly below.
In the early 1970s, a joint NASA-U. S. Army rotorcraft program led to a significant amount of rotorcraft flight research at Ames. "The flight research activity initially concentrated on control and handling issues. . . . Later on, rotor aerodynamics, acoustics, vibration, loads, advanced concepts, and human factors research would be included as important elements in the joint program activity.” As is typically the case, this effort impacted the direction of analytical work as well in rotor aeroelastics, aeroservoelastics, acoustics, rotor-body coupling, rotor air loads prediction, etc. For example, a "comprehensive analytical model” completed in 1980 combined structural, inertial, and aerodynamic models to calculate rotor performance, loads, noise, vibration, gust response, flight dynamics, handling qualities, and aeroelastic stability of rotorcraft. Other efforts were less comprehensive and produced specialized methods for treating various aspects of the rotorcraft problem, such as blade aeroelasticity. The GeneralRotorcraft Aeromechanical Stability Program (GRASP) combined finite elements with concepts used in spacecraft multibody dynamics problems, treating the helicopter as a structure with flexible, rotating substructures.
Rotorcraft analysis has to be multidisciplinary, because of the many types of coupling that are active. Fixed wing aircraft have not always been treated with a multidisciplinary perspective, but the multi-disciplinary analysis and optimization of aircraft is a growing field and one in which Ames has made many valuable contributions. The Advanced Concepts Branch, not directly associated with Structures & Loads but responsible for multidisciplinary vehicle design and optimization studies, has performed and/or sponsored much of this work.
A general-purpose optimization program, CONMIN, was developed jointly by Ames and by the U. S. Army Air Mobility Research &
Development Laboratory in 1973 and had been used extensively by NASA Centers and contractors through the 1990s. Garret Vanderplaats was the principal developer. Because it is a generic mathematical function minimization program, it can in principle drive any design/analysis process toward an optimum. CONMIN has been coupled with many different types of analysis programs, including NASTRAN.
Aircraft Synthesis (ACSYNT) was an early example of a multidisciplinary aircraft sizing and conceptual design code. Like many early (and some current) total-vehicle sizing and synthesis tools, ACSYNT did not actually perform structural analysis but instead used empirically based equations to estimate the weight of airframe structure. ACSYNT was initially released in the 1970s and has been widely used in the aircraft industry and at universities. Collaboration between Ames and the Virginia Polytechnic Institute’s CAD Laboratory, to develop a computer – aided design (CAD) interface for ACSYNT, eventually led to the commercialization of ACSYNT and the creation of Phoenix Integration, Inc., in 1995. Phoenix Integration is currently a major supplier of analysis integration and multidisciplinary optimization software.
Tools such as ACSYNT are very practical, but it has also been a goal at Ames to couple the prediction of aerodynamic forces and loads to more rigorous structural design and analysis, which would give more insight into the effects of new materials or novel vehicle configurations. To this end, a code called ENSAERO was developed, combining finite element structural analysis capability with high-fidelity Euler (inviscid) and Navier-Stokes (viscous) aerodynamics solutions. "The code is capable of computing unsteady flows on flexible wings with vortical flows,” and provisions were made to include control or thermal effects as well. ENSAERO was introduced in 1990 and developed and used throughout the 1990s.
In a cooperative project with Virginia Tech and McDonnell-Douglas Aerospace, ENSAERO was eventually coupled with NASTRAN to provide higher structural fidelity than the relatively limited structural capability intrinsic to ENSAERO. Guru Guruswamy was the principal developer.
In the late 1990s, Juan Alonso, James Reuther, and Joaquim Martins, with other researchers at Ames, applied the adjoint method to the problem of combined aerostructural design optimization. The adjoint method, first applied to purely aerodynamic shape optimization in the late 1980s by Dr. Antony Jameson, is an approach to optimization that provides revolutionary gains in efficiency relative to traditional methods, especially when there are a large number of design variables. It is not an exaggeration to say that adjoint methods have revolutionized the art of aerodynamic optimization. Technical conferences often contain whole sessions on applications of adjoint methods, and several aircraft companies have made practical applications of the technique to the aerodynamic design of aircraft that are now in production. Bringing this approach to aerostructural optimization is extremely significant.