7. Mechanical Sciences
The Army's reliance on mobile systems to perform its mission requires a major research effort in the mechanical sciences to provide the technology base that will enable the development of vehicles and their armaments with significantly advanced capabilities to meet the requirements of the future battlefield. The Army Mechanics Coordinating Group (MECOG), with representatives from all participating RDECs, ARL Directorates, and the Corps of Engineers' Waterways Experiment Station, developed a strategy for focusing the Army's future research programs in the mechanical sciences on the most opportune and important areas.
b. Major Research Areas
The MECOG developed the appropriate research thrusts and assigned priorities, while continually coordinating in-house and extramural research efforts in the four major fields of mechanical sciences that are critical to Army interests:
(1) Structures and dynamics
(2) Solid mechanics
(3) Fluid dynamics
(4) Combustion and propulsion.
Structures and Dynamics In the area of structures and dynamics the research topic areas are structural dynamics and simulation and air vehicle dynamics. The higher priority research thrusts in structural dynamics and simulation are ground vehicle and multi-body dynamics, structural damping, and smart structures and active controls. For example, the innovative use of smart structures, combined with other approaches, offers a promising avenue to the desired goal of significant vibration reduction in Army vehicles, particularly helicopters, by the next decade, as shown in Figure V14.
Figure V-14. As smart materials and structures are introduced into helicopters, vibrations and accompanying structural fatigue will be greatly reduced.
Such reductions offer the possibility of an order of magnitude increase in weapon platform stability, with resulting improvements in the reliability of onboard equipment, the lethality of weapon systems, and greatly reduced pilot fatigue, equipment maintenance, and repairs. Smart structure applications to Army aviation and ground vehicles show significant promise in interior and exterior noise control, adaptive structural control, and enhanced vehicle performance. For air vehicle dynamics, the higher priority research thrusts are integrated aeromechanics analysis, rotorcraft numerical analysis, helicopter blade loads and dynamics, and projectile aeroelasticity.
Solid Mechanics In the area of solid mechanics, the research topic areas are the mechanical behavior of materials, the integrity and reliability of structures, and tribology. The classes of materials of interest are functional gradient materials and heterogeneous materials. In mechanical behavior, the higher priority research thrusts are material response in the state of non-equilibrium or transient state including penetration mechanics and damage initiation and propagation. In addition, the mechanical response under coupled effects of electric, magnetic, and thermal fields is of great interest. The research in the area of integrity and reliability of structures focuses on damage tolerance, damage control, and life prediction. In the area of tribology, dynamic friction, lubrication, and surface topology in low heat rejection environments are emphasized.
Fluid Dynamics For fluid dynamics the research topic areas are unsteady aerodynamics, aeroacoustics, and vortex dominated flows. The higher priority research thrusts in unsteady aerodynamics are dynamic stall/unsteady separation, maneuvering missiles/projectiles, and rotating stall and surge in turbo machinery. In aeroacoustics it is helicopter blade noise generation, propagation, and control; and in vortex dominated flows they are rotorcraft wakes and interactional aerodynamics.
Combustion and Propulsion For combustion and propulsion, the research topic areas are small gas turbine engine propulsion technology, reciprocating engine technology, solid gun propulsion, liquid gun propulsion, and novel gun propulsion. The higher priority research thrusts in small gas turbine engine propulsion are in critical combustion processes, enhanced optimization, and integration of miniature sensors and active controls. For reciprocating engine technology the higher priority research thrusts are in ultra-low heat rejection environments, enhanced air utilization, and cold start phenomena. For solid gun propulsion the major thrusts are in ignition and combustion dynamics and high performance solid propellant charge concepts. For liquid gun propulsion they are in atomization and spray combustion, ignition, and combustion mechanisms and instability, hazards, and vulnerability. The higher priority thrusts in novel gun propulsion are electrothermal-chemical (ETC) propulsion, active control mechanisms, and novel ignition mechanisms.
c. Other Research Areas
In the research area addressing maneuvering projectiles, supercomputing has provided significant advances in predictive capabilities, and massively parallel supercomputing promises to couple computational fluid dynamics (CFD) with computational efforts in other disciplines. Current computational systems allow for the static CFD of complex shapes or propulsion systems. Future advances will lead toward multidisciplinary computations of maneuvering smart munitions, integrated propulsion systems, flight dynamics, guidance and control, structural dynamics, and divert technology. Algorithms are being researched to allow a smart munition to be flown through the computer, allowing the design evaluation of complex trajectory maneuvers. Concurrent with these efforts, complementary research is being pursued in CFD of multi-body aerodynamics to predict and define submunition dispense systems (see Figure V15). Future multidisciplinary computations in this research area will lead to coupled dynamics and aerodynamics in hyper-velocity launch technology and low speed military delivery systems.
Figure V-15. As computational capabilities (memory and speed) increase, more complex simulations of rotorcraft configurations become possible.
d. Benefits of Research
The development of high performance small gas turbines will continue to be advanced by anticipated progress in the prediction of rotating stall and surge in turbo machinery as well as the understanding of impeller/diffuser coupling and interactions through advances in 3D computational fluid dynamic simulation of these flow fields. For example, 3D computational fluid dynamic simulations of turbo machinery flows resulted in highly loaded, yet efficient turbo machinery components such as the advanced two-stage compressor configuration shown in Figure V16. Future applications of this advancing capability to other gas turbine engine components will make possible the attainment of the ambitious Integrated High Performance Turbine Engine Technology (IHPTET) goal of an increase of 120 percent in the turbo shaft power-to-weight ratio by the year 2005, also shown in the figure. Mechanical sciences have a significant impact on five Technology Areas (Chapter IV): Aerospace Propulsion and Power, Air and Space Vehicles, Individual Survivability and Sustainability, Conventional Weapons, and Ground Vehicles.
Figure V-16. Advances in 3-D computational fluid dynamics have produced a more compact, lighter weight, 2-stage compressor, resulting in improvements in turboshaft power-to-weight ratios.
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