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The prediction of pogo contains a major source of uncertainty in the difficulty of defining the dynamic characteristics of certain components. An overview of the space shuttle technology with respect to each the following pogo problem areas is presented: structure, tank-liquid interaction, feedline, engine (pump), pogo-loop/control-loop interaction, and stability analysis.
This computer program manual describes in two parts the automated combustor design optimization code AUTOCOM. The program code is written in the FORTRAN 4 language. The input data setup and the program outputs are described, and a sample engine case is discussed. The program structure and programming techniques are also described, along with AUTOCOM program analysis.
The results obtained in an exploratory evaluation of ceramics for automobile thermal reactors are summarized. Candidate ceramic materials were evaluated in several reactor designs by using both engine-dynamometer and vehicle road tests. Silicon carbide contained in a corrugated-metal support structure exhibited the best performance, lasting 1100 hr in engine-dynamometer tests and more than 38,600 km (24000 miles) in vehicle road tests. Although reactors containing glass-ceramic components did not perform as well as those containing silicon carbide, the glass-ceramics still offer good potential for reactor use with improved reactor designs.
A torsional stress analysis of hollow fans blades by the finite element method is presented. The fans are considered to be double circular arc blades, hollowed 30 percent, and twisted by a component of the centrifugal force by the rated revolution. The effects of blade hollowing on strength and rigidity are discussed. The effects of reinforcing webs, placed in the hollowed section in varying numbers and locations, on torsional rigidity and the convergence of stresses, are reported. A forecast of the 30 percent hollowing against torsional loadings is discussed.
An efficient computer aided design and analysis capability applicable to large space structures was developed to relieve the engineer of much of the effort required in the past. The automated capabilities can be used to rapidly synthesize, evaluate, and determine performance characteristics and costs for future large spacecraft concepts. The interactive design and evaluation of advanced spacecraft program (IDEAS) is used to illustrate the power, efficiency, and versatility of the approach. The coupling of space environment modeling algorithms with simplified analysis and design modules in the IDEAS program permits rapid evaluation of completing spacecraft and mission designs. The approach is particularly useful in the conceptual design phase of advanced space missions when a multiplicity of concepts must be considered before a limited set can be selected or more detailed analysis. Integrated spacecraft systems level data and data files are generated or subsystems and mission reexamination and/or refinement and for more rigorous analyses.
A survey of some trends in aircraft design was made in an effort to determine the relation between research, development, test, and evaluation (RDT and E) and aircraft mission capability, requirements, and objectives. Driving forces in the history of aircraft include the quest for speed which involved design concepts incorporating jet propulsion systems and low drag features. The study of high speed design concepts promoted new experimental and analytical research techniques. These research techniques, in turn, have lead to concepts offering new performance potential. Design trends were directed toward increased speed, efficiency, productivity, and safety. Generally speaking, the research and development effort has been evolutionary in nature and, with the exception of the transition to supersonic flight, little has occurred since the origin of flight that has drastically changed the basic design fundamentals of aircraft. However, this does not preclude the possibility of dramatic changes in the future since the products of research are frequently unpredictable. Advances should be expected and sought in improved aerodynamics (reduced drag, enhanced lift, flow field exploitation); propulsion (improved engine cycles, multimode engines, alternate fuels, alternate power sources); structures (new materials, manufacturing techniques); all with a view toward increased efficiency and utility.
The results of a space station conceptual design and evaluation study are summarized. The study represented a temporary focusing. Three space station configurations are characterized for user and crew requirements, operation and safety accommodations, engineering considerations including assembly and growth, structural dynamics, communications, thermal control and power systems, as well as system cost.
Unified constitutive material models were developed for structural analyses of aircraft gas turbine engine components with particular application to isotropic materials used for high-pressure stage turbine blades and vanes. Forms or combinations of models independently proposed by Bodner and Walker were considered. These theories combine time-dependent and time-independent aspects of inelasticity into a continuous spectrum of behavior. This is in sharp contrast to previous classical approaches that partition inelastic strain into uncoupled plastic and creep components. Predicted stress-strain responses from these models were evaluated against monotonic and cyclic test results for uniaxial specimens of two cast nickel-base alloys, B1900+Hf and Rene' 80. Previously obtained tension-torsion test results for Hastelloy X alloy were used to evaluate multiaxial stress-strain cycle predictions. The unified models, as well as appropriate algorithms for integrating the constitutive equations, were implemented in finite-element computer codes.
Unified constitutive material models were developed for structural analyses of aircraft gas turbine engine components with particular application to isotropic materials used for high-pressure stage turbine blades and vanes. Forms or combinations of models independently proposed by Bodner and Walker were considered. These theories combine time-dependent and time-independent aspects of inelasticity into a continuous spectrum of behavior. This is in sharp contrast to previous classical approaches that partition inelastic strain into uncoupled plastic and creep components. Predicted stress-strain responses from these models were evaluated against monotonic and cyclic test results for uniaxial specimens of two cast nickel-base alloys, B1900+Hf and Rene 80. Previously obtained tension-torsion test results for Hastelloy X alloy were used to evaluate multiaxial stress-strain cycle predictions. The unified models, as well as appropriate algorithms for integrating the constitutive equations, were implemented in finite-element computer codes.
The crucial importance of a thorough understanding of the psychological and interpersonal dimensions of Mars flights is indicated. This is necessary both to reduce the chances that psychological problems or interpersonal frictions will threaten the success of Mars missions and to enhance the quality of life of the people involved. Adaptation to interplanetary flight will depend on an interplay of the psychological stresses imposed by the missions and the psychological strengths and vulnerabilities of the crewmembers involved. Stresses may be reduced through environmental engineering, manipulating crew composition, and the structuring of situations and tasks. Vulnerabilities may be reduced through improving personnel selection procedures, training personnel in psychological and group dynamics, and providing mechanisms for emotional support. It is essential to supplement anecdotal evidence regarding the human side of space travel with the results of carefully conducted scientific research.
The introduction of the supercomputer and recent advances in both Reynolds averaged, and large eddy simulation fluid flow approximation techniques to the Navier-Stokes equations, have created a robust environment for the exploration of problems of interest to the Navy in general, and the Naval Underwater Systems Center in particular. The nature of problems that are of interest, and the type of resources needed for their solution are addressed. The goal is to achieve a good engineering solution to the fluid-structure interaction problem. It is appropriate to indicate that a paper by D. Champman played a major role in developing the interest in the approach discussed.
The theoretical development of the forced steady state analysis of the structural dynamic response of a turbine engine having nonlinear connecting elements is discussed. Based on modal synthesis, and the principle of harmonic balance, the governing relations are the compatibility of displacements at the nonlinear connecting elements. There are four displacement compatibility equations at each nonlinear connection, which are solved by iteration for the principle harmonic of the excitation frequency. The resulting computer program, TETRA 2, combines the original TETRA transient analysis (with flexible bladed disk) with the steady state capability. A more versatile nonlinear rub or bearing element which contains a hardening (or softening) spring, with or without deadband, is also incorporated.
Silicon carbide is of great interest for structural use in aircraft and automobile engines. This ceramic combines high thermal conductivity and low coefficient of thermal expansion, and consequently has good thermal shock resistance. However, like other ceramics, silicon carbide shows strength variability due to processing flaws such as large voids, shrinkage cracks, and inclusions. Agglomerates in the starting powder seem to be the predominant cause of such defects. Improved processing techniques such as slurry pressing and hot isostatic pressing (HIP) were employed to minimize these defects and to improve strength and reliability in the fabricated material. For this purpose 2-inch diameter disks were fabricated by various consolidation techniques. These include: dry pressing and sintering, slurry pressing and sintering, and slurry pressing and HIPing. The results are discussed.
The failure information propagation model (FIPM) data base was developed to store and manipulate the large amount of information anticipated for the various Space Shuttle Main Engine (SSME) FIPMs. The organization and structure of the FIPM data base is described, including a summary of the data fields and key attributes associated with each FIPM data file. The menu-driven software developed to facilitate and control the entry, modification, and listing of data base records is also discussed. The transfer of the FIPM data base and software to the NASA Marshall Space Flight Center is described. Complete listings of all of the data base definition commands and software procedures are included in the appendixes.
This paper presents the effects of downstream film cooling, with and without leading edge showerhead film cooling, on turbine-vane external heat transfer. Steady-state experimental measurements were made in a three-vane linear two-dimensional cascade. The principal independent parameters were maintained over ranges consistent with actual engine conditions. The test matrix was structured to provide an assessment of the independent influence of parameters of interest, namely, exit Mach number, exit Reynolds number, coolant-to-gas temperature ratio, and coolant-to-gas pressure ratio. The data obtained indicate that considerable cooling benefits can be achieved by utilizing downstream film cooling. The downstream film cooling process was shown to be a complex interaction of two competing mechanisms. The thermal dilution effect, associated with the injection of relatively cold fluid, results in a decrease in the heat transfer to the airfoil. Conversely, the turbulence augmentation, produced by the injection process, results in increased heat transfer to the airfoil.
The modeling and simulation of hypersonic vehicles which involve the interaction of a number of major technical disciplines including aerodynamics, structures, heat transfer, propulsion, and control engineering are described. Finite element numerical formulations of individual disciplines including their appropriate integration for multidisciplinary simulation are presented. An efficient unstructured grid generation strategy, evolved by modifying an existing code, is developed.
A numerical study is reported of the three-dimensional nonreacting supersonic flow field produced by three parallel fuel injection schemes. Such injections are being considered as a means of enhancing fuel mixing in future Scramjet engine designs. The strength of vortex structures produced by ramp injectors and by rocket/jet interactions are quantified and their relative effectiveness in enhancing the fuel mixing process is addressed. An experimental setup for validation of the above numerical results has been constructed and preliminary results are presented. For the flow field parameters chosen, the ramp generated vorticity is found to be considerably larger than that generated by the shock. The unsteady recirculating flow field in the wake of the injector appears also to give rise to important additional vorticity and mixing.
This study gives an overview of the future technologies in aeronautics. This collaborative effort relies upon the input of numerous experts from around the country. Specific issues covered include subsonic transport aircraft, high-speed civil transport aircraft short-haul aircraft, environmental issues, operational issues, aerodynamics, propulsion, materials and structures, avionics and control, and cognitive engineering. The appendices include bibliography, abbreviations and acronyms, and NASA fiscal year 1992 aeronautics funding (table) and participants. The forward states that over the last decade, foreign aircraft manufacturers have made significant inroads into the global aircraft market, to the detriment of U.S. interests. Recommendations are made to counter that trend.