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  • Other Sources  (541)
  • AERODYNAMICS  (366)
  • STRUCTURAL MECHANICS  (175)
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  • 1980-1984  (541)
  • 1925-1929
  • 1981  (541)
  • 1
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    Curved-flow, rolling-flow, and oscillatory pure-yawing wind-tunnel test methods for determination of dynamic stability derivatives (1981)
    In:  CASI
    Details
    Publication Date: 2011-10-14
    Description: The test capabilities of the Stability Wind Tunnel of the Virginia Polytechnic Institute and State University are described, and calibrations for curved and rolling flow techniques are given. Oscillatory snaking tests to determine pure yawing derivatives are considered. Representative aerodynamic data obtained for a current fighter configuration using the curved and rolling flow techniques are presented. The application of dynamic derivatives obtained in such tests to the analysis of airplane motions in general, and to high angle of attack flight conditions in particular, is discussed.
    Keywords: AERODYNAMICS
    Type: AGARD Dyn. Stability Parameters; 13 p
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  • 2
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    An analytic solution to the classical two-body problem with drag (1981)
    In:  CASI
    Details
    Publication Date: 2006-02-14
    Description: The two body problem was analyzed with a specific drag model. The model treats drag as a force proportional to the vector velocity and inversely proportional to the distance to the center of attraction. The solution is expressed in terms of known functions and is of a simple and compact form. The time of flight is expressed as a quadrature in the true anomaly. The results are: (1) development of a vector differential equation which allows analysis of an infinite number of gravitational and drag models; and (2) obtaining the solution of a linear differential equation using the inverse method of laplace transforms.
    Keywords: AERODYNAMICS
    Type: Houston Univ. The 1981 NASA ASEE Summer Fac. Fellowship Program, Vol. 2; 22 p
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  • 3
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    Langley high-lift research on a high-aspect-ratio supercritical wing configuration (1981)
    In:  CASI
    Details
    Publication Date: 2006-02-14
    Description: To determine the low speed performance characteristics of a representative high aspect ratio supercritical wing, two low speed jet transport models were fabricated. A 12-ft. span model was used for low Reynolds number tests in the Langley 4- by 7-Meter Tunnel and the second, a 7.5-ft. span model, was used for high Reynolds number tests in the Ames 12-foot Pressure Tunnel. A brief summary of the results of the tests of these two models is presented and comparisons are made between the data obtained on these two models and other similar models. Follow-on two and three dimensional research efforts related to the EET high-lift configurations are also presented and discussed.
    Keywords: AERODYNAMICS
    Type: Advan. Aerodyn.: Selected NASA Res.; p 55-77
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  • 4
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    Measured transonic unsteady pressures on an energy efficient transport wing with oscillating control surfaces (1981)
    In:  CASI
    Details
    Publication Date: 2006-02-14
    Description: Highlight results are presented from subsonic and transonic pressure measurement studies conducted in the Langley Transonic Dynamics Tunnel on a supercritical wing model representative of an energy efficient transport design. Steady- and unsteady-pressure data were acquired on the upper and lower wing surface at an off-design Mach number of 0.60 and at the design Mach number of 0.78, for a Reynolds number of 2.2 x 10(6) (based on the wing average chord). The model configuration consisted of a sidewall-Mounted half-body fuselage and a semi-span wing with an aspect ratio of 10.76, a leading-edge sweepback angle of 28.8 degrees, and supercritical airfoil sections. The wing is instrumented with 252 static pressure orifices and 164 dynamic pressure gages. Model test variables included wing angle of attack, control-surface mean deflection angle, control-surface oscillating deflection angle and frequency, and phasing between oscillating leading-edge and trailing-edge controls when used together.
    Keywords: AERODYNAMICS
    Type: Advan. Aerodyn.: Selected NASA Res.; p 21-36
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  • 5
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    Vortex-flow aerodynamics - An emerging design capability (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Promising current theoretical and simulational developments in the field of leading edge vortex-generating delta, arrow ogival wings are reported, along with the history of theory and experiment leading to them. The effects of wing slenderness, leading edge nose radius, Mach number and incidence variations, and planform on the onset of vortex generation and redistribution of aerodynamic loads are considered. The range of design possibilities in this field are consequential for the future development of strategic aircraft, supersonic transports and commercial cargo aircraft which will possess low-speed, high-lift capability by virtue of leading edge vortex generation and control without recourse to heavy and expensive leading edge high-lift devices and compound airfoils. Attention is given to interactive graphics simulation devices recently developed.
    Keywords: AERODYNAMICS
    Type: Astronautics and Aeronautics; 19; May 1981
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  • 6
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    Practical implementation of the double linear damage rule and damage curve approach for treating cumulative fatigue damage (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Simple procedures are given for treating cumulative fatigue damage under complex loading history using either the damage curve concept or the double linear damage rule. A single equation is given for use with the damage curve approach; each loading event providing a fraction of damage until failure is presumed to occur when the damage sum becomes unity. For the double linear damage rule, analytical expressions are given for determining the two phases of life. The procedure comprises two steps, each similar to the conventional application of the commonly used linear damage rule. Once the sum of cycle ratios based on Phase I lives reaches unity, Phase I is presumed complete, and further loadings are summed as cycle ratios based on Phase II lives. When the Phase II sum attains unity, failure is presumed to occur. It is noted that no physical properties or material constants other than those normally used in a conventional linear damage rule analysis are required for application of either of the two cumulative damage methods described. Illustrations and comparisons are discussed for both methods.
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal of Fracture; 17; Apr. 198
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  • 7
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    Surface phenomena in elasticity (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Problems of elasticity associated with the behavior of free surfaces of elastic bodies are reviewed with particular reference to the propagation of characteristic waves and the criteria of wrinkling of free surfaces. All transformations are given for the case when a free surface of an elastic body is streamlined by the flow of inviscid fluid. The wrinkling phenomenon is illustrated by example.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Elasticity; 11; Apr. 198
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  • 8
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    Longitudinal grooves for bluff body drag reduction (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Wind tunnel test results are presented for four axisymmetric bluff body configurations in order to determine their effect on form and pressure drag. It was found that drag reductions on the order of 40% are obtainable with an afterbody incorporating four longitudinal 'V' grooves. Although this effect may be due to the functioning of the grooves as longitudinal, continuous vortex generators, it is concluded that further research is needed to elucidate the physical basis of the test results. Optimization of the effect will be useful in base drag reduction for such vehicles as automobiles and cargo aircraft with sharply upswept afterbodies.
    Keywords: AERODYNAMICS
    Type: AIAA Journal; 19; Apr. 198
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  • 9
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    Vectored injection into compressible laminar and turbulent boundary layers (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: A fundamental analysis of two-dimensional supersonic boundary layer flow, both laminar and turbulent, is presented for a wide range of normal and nonnormal mass-transfer velocities. The analysis is based on the numerical solution of the Navier-Stokes equations, and results are compared with available theoretical and experimental data. Certain cases of practical importance, for which results are not presently available, are referred to.
    Keywords: AERODYNAMICS
    Type: Computer Methods in Applied Mechanics and Engineering; 25; Jan. 198
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  • 10
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    Report of the panel on theoretical aerodynamics (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Interactions between theoretical aerodynamics and the NTF are discussed. The development and validation of computational fluid dynamics computer codes, the determination of Reynolds number scaling laws, and extension of the data bases of entrainment type turbulence models to include high Reynolds number data are recommended areas of study. The major benefit theoretical aerodynamics could have on the NTF is in the quantitative description of wind tunnel wall interference effects.
    Keywords: AERODYNAMICS
    Type: High Reynolds Number Res. - 1980; p 277-286
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  • 11
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    High Reynolds number research requirements for space vehicle design (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Requirements of entry vehicle design requiring high Reynolds number wind tunnel testing are discussed. The space shuttle orbiter, development of future space transportation systems, and planetary entry data analysis are considered.
    Keywords: AERODYNAMICS
    Type: High Reynolds Number Res. - 1980; p 265-274
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  • 12
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    Report of the panel on aeroelasticity and unsteady aerodynamics (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The status of recommended areas of study for the NTF are reviewed. Transonic and control surface unsteady aerodynamics, and buffet onset and loads are considered. Testing of dynamically scaled flutter models is discussed.
    Keywords: AERODYNAMICS
    Type: High Reynolds Number Res. - 1980; p 237-246
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  • 13
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    Model experience in the Langley 0.3-m transonic cryogenic tunnel (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The model building, development, and testing experience gained during 8 years of operation of the 0.3-m Transonic Cryogenic Tunnel (TCT) is summarized. The summary is divided into four portions: (1) models tested in the 0.3-m TCT's original octagonal test section; (2) models tested in the present two dimensional test section; (3) models tested as a part of tunnel calibration and the development of advanced technology airfoils; and (4) development of a new way to construct two dimensional airfoil models. Design requirements imposed on the models by high Reynolds number testing at cryogenic temperatures are reviewed.
    Keywords: AERODYNAMICS
    Type: High Reynolds Number Res. - 1980; p 53-73
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  • 14
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    Reliability-based optimization under random vibration environment (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: A methodology of formulating the optimum design problem for structural systems with random parameters and subjected to random vibration as a mathematical programming problem is presented. The proposed method is applied to the optimum design of a cantilever beam with a tip mass and a truss structure supporting a water tank. The excitations are assumed to be Gaussian processes and the geometric and material properties are taken to be normally distributed random variables. The probabilistic constraints are specified for individual failure modes since it is easier to specify the reliability level for each failure mode keeping in view the consequences of failure in that particular mode. The time parameter appearing in the random vibration based constraints is eliminated by replacing the probabilities of failure by suitable upper bounds. The numerical results demonstrate the feasibility and effectiveness of applying the reliability-based design concepts to structures with random parameters and operating in random vibration environment.
    Keywords: STRUCTURAL MECHANICS
    Type: Computers and Structures; 14; 5-6,; 1981
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  • 15
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    SPAR analysis of LDEF vibration characteristics (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: This paper presents a structural dynamic modeling of the Long Duration Exposure Facility (LDEF), which is a Space Shuttle payload of passive scientific experiments contained in trays mounted on a large cylindrically shaped structure. Special detailed finite element modeling, using the SPAR system of computer programs was required to obtain good agreement between analytical and test vibrations modes. Experimental trays contributed significantly to overall LDEF stiffnesses, and these contributions were realistically represented for each tray by the stiffness matrix of an equivalent orthotropic panel in the overall LDEF SPAR model. Orthotropic stiffnesses for this panel were obtained from finely detailed statically loaded tray SPAR models in which stiffness coupling was accounted for along with partial relative sliding allowed by the tray clamping attachments. Joint boundary conditions were also significant in the structural dynamic modeling of LDEF, and static data proved valuable in assessing modeling of local end fittings.
    Keywords: STRUCTURAL MECHANICS
    Type: Computers and Structures; 13; Aug. 198
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  • 16
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    Effectiveness of leading-edge vortex flaps on 60 and 75 degree delta wings (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: A series of wind tunnel tests were run on 60 and 75 deg sweep delta wings to examine the effectiveness of leading-edge vortex flaps. Tests results showed that leading-edge vortex flaps are effective in giving large increases in lift-to-drag ratio and decreases in drag over a wide range of angle of attack. Tests on inverted flaps on the 60 deg delta wing showed substantial increases in lift and drag and may indicate a possibility of using inverted flaps on delta wings in the landing portion of flight. The 60 deg data were compared with that for a 75 deg sweep delta wing confirming that leading-edge vortex flap effectiveness is stronger as sweep is increased. Pitching moment effects due to vortex flaps use were also examined.
    Keywords: AERODYNAMICS
    Type: Journal of Aircraft; 18; Apr. 198
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  • 17
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    Partially confined multiple jet mixing (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Results of hot-wire measurements in an incompressible partially confined jet issuing from an array of rectangular nozzles, equally spaced with their small dimensions aligned are presented. The quantities measured include mean velocity and the Reynolds stress in the two central planes of the jet at stations covering up to 115 widths (small dimension of a nozzle) downstream of the nozzle exit. For downstream distances greater than 60 widths, the flowfield is observed to be nearly homogenous and the turbulence appears to be quite similar to that of a grid generated turbulence.
    Keywords: AERODYNAMICS
    Type: AIAA Journal; 19; Mar. 198
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  • 18
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    Unsteady Newton-Busemann flow theory. I - Airfoils (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Newtonian flow theory for unsteady flow at very high Mach numbers is completed by the addition of a centrifugal force correction to the impact pressures. The correction term is the unsteady counterpart of Busemann's centrifugal force correction to impact pressures in steady flow. For airfoils of arbitary shape, exact formulas for the unsteady pressure and stiffness and damping-in-pitch derivatives are obtained in closed form, which require only numerical quadratures of terms involving the airfoil shape. They are applicable to airfoils of arbitrary thickness having sharp or blunt leading edges. For wedges and thin airfoils these formulas are greatly simplified, and it is proved that the pitching motions of thin airfoils of convex shape and of wedges of arbitrary thickness are always dynamically stable according to Newton-Busemann theory. Leading-edge bluntness is shown to have a favorable effect on the dynamic stability; on the other hand, airfoils of concave shape tend toward dynamic instability over a range of axis positions if the surface curvature exceeds a certain limit. As a byproduct, it is also shown that a pressure formula recently given by Barron and Mandl for unsteady Newtonian flow over a pitching power-law shaped airfoil is erroneous and that their conclusion regarding the effect of pivot position on the dynamic stability is misleading.
    Keywords: AERODYNAMICS
    Type: AIAA Journal; 19; Mar. 198
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  • 19
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    Evidence of imbedded vortices in a three-dimensional shear flow (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Vortex phenomena encountered in an investigation of the streamwise development of the three-dimensional wake region behind the tip of a three-dimensional wedge model are reported. Pressure profiles were measured by pitot probes downstream of a tip with a nearly constant surface pressure level and a nearly continuous surface curvature in a blowdown air tunnel operating at Mach 6. Rather than the simple three-dimensional quasi-parallel shear flow expected, the measurements indicated the presence of a flow with large deficits in longitudinal pitot pressure, which are usually associated with the core region of quasi-steady longitudinal vortices. Vapor screen flow visualizations also support the presence of longitudinal vortices located primarily in the tip region and evidently forming in the vicinity of the wake neck. An increase in overall wake thickness by 100% is also observed. The origin of the vortices as quasi-steady Taylor-Gortler vortices generated in the concavely curved shear layer near the wake neck is considered. It is pointed out that the existence of longitudinal vortexes suggests that three-dimensional turbulence modeling may be much more difficult than previously supposed.
    Keywords: AERODYNAMICS
    Type: AIAA Journal; 19; Mar. 198
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  • 20
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    Existence of axisymmetric modes of thin cylindrical shells with axial displacement restraint (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: A necessary and sufficient condition is derived for the existence of the axisymmetric mode of cylindrical shells with a radial displacement having one half wave along the axis and axial displacement restrained at both ends. The condition is purely geometric and consists of an upper bound on the mean radius of thickness ratio for a given fixed value of the length to mean radius ratio, above which the mode with one half wave in radial displacement along the axis ceases to exist. The proof is based on enforcing two basic lemmas concerned with the simplicity of the eigenvalues of the shell and the uniform ordering of these eigenvalues with the number of nodes of their corresponding radial displacement eigenfunctions.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Sound and Vibration; 74; Feb. 8
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  • 21
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    Proposed aeroelastic and flutter tests for the National Transonic Facility (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Tests that can exploit the capability of the NTF and the transonic cryogenic tunnel, or lead to improvements that could enhance testing in the NTF are discussed. Shock induced oscillation, supersonic single degree control surface flutter, and transonic flutter speed as a function of the Reynolds number are considered. Honeycombs versus screens to smooth the tunnel flow and a rapid tunnel dynamic pressure reducer are recommended to improve tunnel performance.
    Keywords: AERODYNAMICS
    Type: NASA. Langley Research Center High Reynolds Number Res. - 1980; p 153-161
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  • 22
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    Report of the wind tunnel/flight correlation panel (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Basic calibration of the tunnel prior to conducting any tests, the areas requiring wind tunnel/flight test correlation for validating the NTF, and recommendations for achieving validation of the NTF are discussed.
    Keywords: AERODYNAMICS
    Type: NASA. Langley Research Center High Reynolds Number Res. - 1980; p 249-262
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  • 23
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    High lift technology (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The NASA Langley high lift technology program is reviewed and elements of the program which are considered Reynolds number sensitive are discussed. The Energy Efficient Transport (EET) and Supersonic Cruise Research (SCR) models proposed for high lift studies in the National Transonic Facility (NTF) are described. Recommendations regarding the NTF facility and test techniques are presented.
    Keywords: AERODYNAMICS
    Type: High Reynolds Number Res. - 1980; p 197-213
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  • 24
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    Wall interference effects: Status review (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The interference technology incorporated into the NTF design (hardware) and the emerging transonic wall interference assessment correction procedures (software) to be employed when the NTF becomes operational was reviewed. It is anticipated that the early experiments will provide data relevant to wall interference effects.
    Keywords: AERODYNAMICS
    Type: High Reynolds Number Res. - 1980; p 123-241
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  • 25
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    Configuration aerodynamics (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Static aerodynamic research related to aircraft configurations in their cruise or combat modes is discussed. Subsonic transport aircraft, transonic tactical aircraft, and slender wing aircraft are considered. The status and plans of Langley's NTF configuration research program are reviewed. Recommendations for near term configuration research are made.
    Keywords: AERODYNAMICS
    Type: High Reynolds Number Res. - 1980; p 217-234
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  • 26
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    Comments on Reynolds number effects and the role of NTF in the development of air vehicles (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: The National Transonic Facility (NTF) capability to match the full scale Reynolds numbers of all but the largest airplanes is discussed. Conversion factors to enable calculation of Sl-unit equivalents for all U.S. units are listed. Using data from several facilities, analytic methods, and flight test data, a competetive aircraft in the relatively low Reynolds number was developed. The NTF offers the capability to obtain data at full scale Reynolds numbers in the cruise condition for most of the products, and will be much closer than previous tunnels to full scale Reynolds number for the operating envelopes. It is primarily on the operating envelope that Reynolds number effects are most important and least predictable.
    Keywords: AERODYNAMICS
    Type: NASA. Langley Research Center High Reynolds Number Res. - 1980; p 143-148
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  • 27
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    Effect of elastic end rings on the eigenfrequencies of thin cylinders (1981)
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    Publication Date: 2011-08-18
    Description: The effect of elastic end rings on the eigenfrequencies of thin cylindrical shells is studied by using an exact solution of the linear eigenvalue problem. The out-of-plane and torsional rigidities of the rings are responsible for the overall shell stiffness. Considerable mode interaction exists for modes with low circumferential wave numbers when the mass of the ring is comparable with that of the shell. The hypothetical simply supported and clamped boundary conditions are practically impossible to realize with a finite-mass ring for relatively short and thin shells.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Sound and Vibration; 74; Jan. 8
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  • 28
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    Solution of the transonic full potential equation in conservative form using an implicit algorithm (1981)
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    Publication Date: 2011-08-18
    Description: The paper presents numerical solutions of the full potential equation in conservative form. The iteration scheme used is a fully implicit approximate factorization technique and provides a significant improvement in convergence speed relative to standard successive line overrelaxation algorithms. The spatial differencing algorithm is centrally differenced in both subsonic and supersonic regions to maintain stability. This effectively approximates rotated differencing, thereby greatly improving the reliability of the algorithm.
    Keywords: AERODYNAMICS
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  • 29
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    Computation of airfoil buffet boundaries (1981)
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    Publication Date: 2011-08-18
    Description: The ILLIAC IV computer has been programmed with an implicit, finite-difference code for solving the thin layer compressible Navier-Stokes equation. Results presented for the case of the buffet boundaries of a conventional and a supercritical airfoil section at high Reynolds numbers are found to be in agreement with experimentally determined buffet boundaries, especially at the higher freestream Mach numbers and lower lift coefficients where the onset of unsteady flows is associated with shock wave-induced boundary layer separation.
    Keywords: AERODYNAMICS
    Type: AIAA Journal; 19; Nov. 198
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  • 30
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    Stress-intensity factors and crack-opening displacements for round compact specimens (1981)
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    Publication Date: 2011-08-18
    Description: An improved method of boundary collocation based on the complex variable analysis of Muskhelishvili (1953) is applied to the two-dimensional stress analysis of round compact specimens with pin-loaded holes. Stress intensity factors and crack opening displacements are calculated for various round compact specimens as a function of crack-length-to-specimen-width ratios. A wide-range equation for the stress intensity factors and equations for crack-surface displacements and load-point displacements are developed.
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal of Fracture; 17; Dec. 198
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  • 31
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    Multi-parameter yield zone model for predicting spectrum crack growth (1981)
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    Publication Date: 2011-08-18
    Description: A phenomenological load interaction model referred to as the Multi-Parameter Yield Zone model is presented which accounts for crack growth retardation caused by previous overloads, acceleration due to current overloads, and underload effects. In the present model, load interaction effects are calculated utilizing a residual stress intensity concept. Crack growth retardation and acceleration are accounted for by decreasing or increasing, respectively, the effective stress ratio used in a modified Forman's (1967) crack growth equation. Results of spectrum crack growth predictions for 2219-T851 aluminum are presented.
    Keywords: STRUCTURAL MECHANICS
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  • 32
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    A crack-closure model for predicting fatigue crack growth under aircraft spectrum loading (1981)
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    Publication Date: 2011-08-18
    Description: The present paper is concerned with the development and application of an analytical model of cyclic crack growth that includes the effects of crack closure. The model was based on a concept like the Dugdale model, but was modified to leave plastically deformed material in the wake of the advancing crack tip. The model was used to correlate crack growth rates under constant-amplitude loading and to predict crack growth under aircraft spectrum loading on 2219-T851 aluminum alloy plate material. The predicted crack growth lives agreed well with experimental data. The ratio of predicted-to-experimental lives ranged from 0.66 to 1.48.
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  • 33
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    A root-mean-square approach for predicting fatigue crack growth under random loading (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: A method for predicting fatigue crack growth under random loading which employs the concept of Barsom (1976) is presented. In accordance with this method, the loading history for each specimen is analyzed to determine the root-mean-square maximum and minimum stresses, and the predictions are made by assuming the tests have been conducted under constant-amplitude loading at the root-mean-square maximum and minimum levels. The procedure requires a simple computer program and a desk-top computer. For the eleven predictions made, the ratios of the predicted lives to the test lives ranged from 2.13 to 0.82, which is a good result, considering that the normal scatter in the fatigue-crack-growth rates may range from a factor of two to four under identical loading conditions.
    Keywords: STRUCTURAL MECHANICS
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    Some approximations in the linear dynamic equations of thin cylinders (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Theoretical analysis is performed on the linear dynamic equations of thin cylindrical shells to find the error committed by making the Donnell assumption and the neglect of in-plane inertia. At first, the effect of these approximations is studied on a shell with classical simply supported boundary condition. The same approximations are then investigated for other boundary conditions from a consistent approximate solution of the eigenvalue problem. The Donnell assumption is valid at frequencies high compared with the ring frequencies, for finite length thin shells. The error in the eigenfrequencies from omitting tangential inertia is appreciable for modes with large circumferential and axial wavelengths, independent of shell thickness and boundary conditions.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Sound and Vibration; 76; June 22
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    Application of unsteady airfoil theory to rotary wings (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: A clarification is presented on recent work concerning the application of unsteady airfoil theory to rotary wings. The application of this theory may be seen as consisting of four steps: (1) the selection of an appropriate unsteady airfoil theory; (2) the resolution of that velocity which is the resultant of aerodynamic and dynamic velocities at a point on the elastic axis into radial, tangential and perpendicular components, and the angular velocity of a blade section about the deformed axis; (3) the expression of lift and pitching moments in terms of the three components; and (4) the derivation of explicit expressions for the components in terms of flight velocity, induced flow, rotor rotational speed, blade motion variables, etc.
    Keywords: AERODYNAMICS
    Type: Journal of Aircraft; 18; July 198
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  • 36
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    Cyclic plasticity models and application in fatigue analysis (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: An analytical procedure for prediction of the cyclic plasticity effects on both the structural fatigue life to crack initiation and the rate of crack growth is presented. The crack initiation criterion is based on the Coffin-Manson formulae extended for multiaxial stress state and for inclusion of the mean stress effect. This criterion is also applied for the accumulated damage ahead of the existing crack tip which is assumed to be related to the crack growth rate. Three cyclic plasticity models, based on the concept of combination of several yield surfaces, are employed for computing the crack growth rate of a crack plane stress panel under several cyclic loading conditions.
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    The coupling between flow instabilities and incident disturbances at a leading edge (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: It is now generally agreed that an external disturbance field, such as an incident acoustic wave, can effectively couple to instabilities of a flow past a trailing edge. One purpose of the present paper is to show that there are situations where a similar coupling can occur at a leading edge. The process is analyzed and the effects of experimentally controllable parameters are assessed. It is important to account for such phenomena when evaluating the effect of external disturbances on transition.
    Keywords: AERODYNAMICS
    Type: Journal of Fluid Mechanics; 104; Mar. 198
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  • 38
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    A discrete vortex method for the non-steady separated flow over an airfoil (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: A discrete vortex method was used to analyze the separated non-steady flow about a cambered airfoil. The foil flow modelling is based on the thin lifting-surface approach, where the chordwise location of the separation point is assumed to be known from experiments or flow-visualization data. Calculated results provided good agreement when compared with the post-stall aerodynamic data of two airfoils. Those airfoil sections differed in the extent of travel of the separation point with increasing angle of attack. Furthermore, the periodic wake shedding was analyzed and its time-dependent influence on the airfoil was investigated.
    Keywords: AERODYNAMICS
    Type: Journal of Fluid Mechanics; 102; Jan. 198
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  • 39
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    Pathfinder model program for the National Transonic Facility (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: An overview of the Pathfinder Models Program is presented. The Pathfinder program is a major research and development activity in support of the National Transonic Facility Activation Plan. The program scope, models design approach, and Pathfinder model configurations are presented along with a discussion of major supportive program activities. The anticipated design criteria for NTF models are presented.
    Keywords: AERODYNAMICS
    Type: High Reynolds Number Res. - 1980; p 37-52
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  • 40
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    Wind loads for bar-truss structures (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: An analysis method developed to calculate the wind loads on the nodes or joints of the truss type support structure of the 64 meter antenna is described. The method uses the CBAR element and GRID coordinate cards of the NASTRAN or IDEAS structural analysis programs as inputs to the computer model of the structure. Cross flow principles and vector analysis are also used in the analysis. The algorithms used are described and probable accuracy of the solution is discussed.
    Keywords: STRUCTURAL MECHANICS
    Type: The Telecommun. and Data Acquisition; p 149-153
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  • 41
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    Temperature-dependent creep buckling of plates (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Time-dependent lateral deflection of flat rectangular plates is predicted by the Norton-Bailey (Norton 1929, Bailey 1935) power law for material creep. The plates have a through-thickness steady-state temperature distribution, and the effects are considered by using Maxwell's law to modify the power creep law. Equations are derived for creep exponents of 3 and 5, using the sandwich plate element to predict creep buckling of plates. Predictions of creep buckling with a temperature variation between the inner and outer plate surfaces are found to be somewhat dependent on the creep buckling relationship assumed. When significant scatter justifies a variation in the creep constants up to an order of magnitude, discrepancies in predictions using the two exponents are reasonable, and for one engineering material, the predictions have the same degree of agreement with experimental data as have the respective creep laws.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Thermal Stresses; 4; Apr. 198
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  • 42
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    Trailing edge noise prediction using Amiet's method (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Amiet's (1976, 1978) solution to the problem of airfoil trailing edge noise prediction is discussed in light of the results of evanescent wave theory's application to the measured surface pressure behavior near the trailing edge of an airfoil with a turbulent boundary layer. The method employed by Amiet has the advantage of incorporating the effect of finite chord in its solution. The assumed form of the pressure distribution is examined as well as the constant turbulent boundary layer convection assumption, which is found to be unnecessarily restrictive.
    Keywords: AERODYNAMICS
    Type: Journal of Sound and Vibration; 77; Aug. 8
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  • 43
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    Forebody drag reduction (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: It is shown that the mechanisms of forebody drag reduction by means of either a spike or a forward-facing jet are similar, with the maximum achievable drag reduction being of the same order. Because the jet may be a relatively cool gas, however, the forward facing jet has the additional capability of reducing the aerodynamic heating that is so severe at high Mach numbers. By means of the correlation presented, jet ejection parameters may be chosen to achieve maximum permissible forebody drag reduction. The correlation method uses a momentum coefficient that characterizes jet efflux and freestream conditions.
    Keywords: AERODYNAMICS
    Type: AIAA Journal; 19; Oct. 198
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  • 44
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    Unsteady Newton-Busemann flow theory. II - Bodies of revolution (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: A complete Newtonian flow theory is presented for unsteady flow past oscillating bodies of revolution of general shape at very high Mach numbers, consideration being given to a centrifugal force correction to the impact pressures. Expressions are obtained for the unsteady pressure and the stability derivatives are presented in closed form. It is stressed that the correction for the centrifugal force, which arises because of the curved trajectories that fluid particles follow along the surface subsequent to their impact, must not be neglected. If the correction is included, the theory is shown to be in excellent agreement with experimental results for relatively sharp cones. Theoretical results are in poor agreement with experimental results in air for bodies having moderate or large-nose bluntness.
    Keywords: AERODYNAMICS
    Type: AIAA Journal; 19; Oct. 198
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  • 45
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    Vibrations of three-dimensional pipe systems with acoustic coupling (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: A general algorithm is developed to calculate the beam-type dynamic response of three dimensional multiplane finite length pipe systems, consisting of elbow and straight ducts with continuous interfaces. Emphasis is on secondary acoustic wave effects giving rise to coupling mechanisms; and the simulation accounts for one-dimensional elastoacoustic coupling from a plane acoustic wave and secondary loads resulting from wave asymmetries. The transfer matrix approach is adopted in modeling the elastodynamics of each duct, with allowance for distribution loads. Secondary loads from plane wave distortion are considered with a solution of the Helmholtz equation in an equivalent rigid waveguide, and effects of path imperfection are introduced as a perturbation from the hypothetical perfectly straight pipe. Computations indicate that the one-dimensional acoustic assumption is valid for frequencies below one-half the first cut-off frequency, and the three-dimensional acoustic effects produce an increase in response levels near and above cut-off.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Sound and Vibration; 78; Sept. 8
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  • 46
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    Structural synthesis - Its genesis and development (1981)
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    Publication Date: 2011-08-18
    Description: An historical account is given of the development, from its conception in 1960, of the structural synthesis method. While synthesis techniques lag behind analytical ones in both sophistication and application, the structural design procedures created by combining finite element analysis and mathematical programming algorithms have progressed to the point of maturity. As in the case of finite element analysis, use and acceptance of structural synthesis methodology depends on the development and distribution of easily used and well-documented, production-quality computer programs. Attention is given such elementary applications of synthesis methods as the three-bar truss, an integrally stiffened waffle plate, a stiffened cylindrical shell, aircraft fuselage window panels, the structural efficiency of graphite-epoxy hat-stiffened panels, and an idealized delta wing.
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA Journal; 19; Oct. 198
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  • 47
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    Green's function for cracks of equal length from a circular hole in an infinite sheet (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: Stress-intensity factors are obtained for twin collinear cracks emanating from a hole in an infinite plate. Point forces that tend to make the crack surfaces separate and slide are applied to one of the cracks. A conformal mapping and the Muskelishvili formulation involving series representation of the Kolosov stress functions are used to derive the solutions. The variation of stress-intensity factor with crack length and with point of application of the loads is presented for both crack tips.
    Keywords: STRUCTURAL MECHANICS
    Type: Res Mechanica Letters; 1; Dec. 198
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  • 48
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    An empirical stress-intensity factor equation for the surface crack (1981)
    In:  Other Sources
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    Publication Date: 2011-08-18
    Description: This paper presents an empirical stress-intensity factor equation for a surface crack as a function of parametric angle, crack depth, crack length, plate thickness and plate width for tension and bending loads. The stress-intensity factors used to develop the equation were obtained from a previous three-dimensional, finite-element analysis of semielliptical surface cracks in finite elastic plates subjected to tension or bending loads. A wide range of configuration parameters was included in the equation. The ratios of crack length to plate thickness and the ratios of crack depth to crack length ranged from 0 to 1.0. The effects of plate width on stress-intensity variations along the crack front were also included. The equation was used to predict patterns of surface-crack growth under tension or bending fatigue loads. The equation was also used to correlate surface-crack fracture data for a brittle epoxy material within + or - 10 percent for a wide range of crack shapes and crack sizes.
    Keywords: STRUCTURAL MECHANICS
    Type: Engineering Fracture Mechanics; 15; 1-2,; 1981
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  • 49
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    Top-mounted inlet system feasibility for transonic-subsonic fighter aircraft applications (1981)
    In:  CASI
    Details
    Publication Date: 2017-10-02
    Description: To inlet flow field and engine inlet performance data for an advanced fighter aircraft configuration were obtained over the Mach 0.6 to 2.0 range. The studies not only provided extensive data for the baseline arrangement, but also evaluated the effects of key aircraft configuration variables (inlet location, canopy-dorsal integration, wing leading-edge extension planform area, and variable incidence canards) on top inlet performance. In order to set these data in the context of practical aircraft systems top inlet performance is compared with that of more conventional inlet/airframe integrations. The results of these evaluations show that, for the top inlet configuration tested, relatively good inlet performance and compatibility characteristics are maintained during subsonic and transonic maneuver. However, at supersonic speeds, flow expansion over the forebody and wings causes an increase in local inlet Mach number subsequently reduces inlet performance levels. These characteristics infer that although top inlets many not pose a viable design option for aircraft requiring a high degree of supersonic maneuverability, they have distinct promise for vehicles with subsonic and transonic maneuver capabilities.
    Keywords: AERODYNAMICS
    Type: AGARD Aerodyn. of Power Plant Installation; 17 p
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  • 50
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    Impact of high-alpha aerodynamics on dynamic stability parameters of aircraft and missiles (1981)
    In:  CASI
    Details
    Publication Date: 2017-10-02
    Description: The aerodynamic phenomena associated with high angles of attack and their effects on the dynamic stability characteristics of airplane and missile configurations are examined. Information on dynamic effects is limited. Steady flow phenomena and their effects on the forces and moments are reviewed. The effects of asymmetric vortices and of vortex bursting on the dynamic response of flight vehicles are reviewed with respect to their influence on: (1) nonlinearity of aerodynamic coefficients with attitude, rates, and accelerations; (2) cross coupling between longitudinal and lateral directional models of motion; (3) time dependence and hysteresis effects; (4) configuration dependencey; and (5) mathematical modeling of the aerodynamics.
    Keywords: AERODYNAMICS
    Type: AGARD Dyn. Stability Parameters; 18 p
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    An assessment of theoretical models for viscous and transonic flow (1981)
    In:  CASI
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    Publication Date: 2017-10-02
    Description: Topics discussed include shear flow models, simplified models for treating separation, classical linear theory, a local linearization theory, a transonic linear theory, a transonic nonlinear theory, the experiment of Davis, and the experiment of Tijdeman. It is concluded that shear flow models, which have proven very accurate in taking into account boundary layer effects for panel flutter, are likely to be less so for lifting surface flutter. For many applications in transonic flow, transonic linear theory will be adequate.
    Keywords: AERODYNAMICS
    Type: AGARD Boundary Layer Effects on Unsteady Airloads; 28 p
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  • 52
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    Experimental studies of scale effects on oscillating airfoils at transonic speeds (1981)
    In:  CASI
    Details
    Publication Date: 2017-10-02
    Description: Scale effects are discussed with reference to a conventional airfoil (NACA 64A010) and a supercritical airfoil (NLR 7301) at mean flow conditions that support both weak and strong shock waves. During the experiment the Reynolds number was varied from 3 x 10 to the sixth power at time history data are presented over the range of reduced frequencies that are important in aeroelastic applications. The experimental data show that viscous effects are important in the case of the supercritical airfoil at all flow conditions and in the case of the conventional airfoil under strong shock wave conditions. Some frequency dependent viscous effects were also observed.
    Keywords: AERODYNAMICS
    Type: AGARD Boundary Layer Effects on Unsteady Airfoils; 13 p
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    Computational methods in nonlinear structural and solid mechanics; Proceedings of the Symposium, Washington, D.C., October 6-8, 1980. Symposium sponsored by the George Washington University and NASA (1981)
    In:  Other Sources
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    Publication Date: 2016-03-09
    Description: Topics discussed include computational strategies for nonlinear problems in structural mechanics, time integration techniques and the numerical solution of nonlinear algebraic equations, material characterization and nonlinear fracture mechanics, nonlinear interaction problems, and seismic response and the nonlinear analysis of concrete structures. Also considered are nonlinear problems for nuclear reactors, crash dynamics and impact problems, nonlinear problems of fibrous composites and advanced nonlinear applications, and computerized symbolic manipulation and nonlinear analysis software systems.
    Keywords: STRUCTURAL MECHANICS
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  • 54
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    Natural laminar flow data from full-scale flight and wind-tunnel experiments (1981)
    In:  Other Sources
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    Publication Date: 2018-12-01
    Description: Experimental results obtained at NASA Langley during studies of natural laminar flow (NLF) over commercially produced aircraft surfaces are reported. The general aviation aircraft examined were light aircraft, yet displayed NLF extents close to the maximum available and equivalent to high performance business aircraft flying envelopes. Sublimating chemicals and acoustic detection techniques were employed to measure the boundary layer transition. Theoretical predictions of boundary layer stability were found to match well with the experimental data, with consideration given to both swept wings and the amplitudes of allowable waves on the airfoil surfaces. The presence of the NLF on the airfoil surfaces confirmed the benefits available from use of composite materials for airfoil surfaces.
    Keywords: AERODYNAMICS
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    Methods and models for predicting fatigue crack growth under random loading (1981)
    In:  Other Sources
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    Publication Date: 2016-03-09
    Description: Papers are presented in the volume summarizing the baseline data, methodology, procedures, and results of a round-robin analysis which was conducted to predict the fatigue crack growth in 2219-T851 aluminum center-cracked specimens subjected to flight loading in random cycle-by-cycle format. The objective of the analysis was to assess whether data from constant-amplitude fatigue crack growth tests on center-cracked specimens can be used to predict fatigue crack growth lives under random loading. The following approaches are discussed in detail: a root-mean-square approach, a crack-closure model, a multi-parameter yield zone model, and a load-interaction model.
    Keywords: STRUCTURAL MECHANICS
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    Natural Laminar Flow Flight Experiment (1981)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: A supercritical airfoil section was designed with favorable pressure gradients on both the upper and lower surfaces. Wind tunnel tests were conducted in the Langley 8 Foot Transonic Pressure Tunnel. The outer wing panels of the F-111 TACT airplane were modified to incorporate partial span test gloves having the natural laminar, flow profile. Instrumentation was installed to provide surface pressure data as well as to determine transition location and boundary layer characteristics. The flight experiment encompassed 19 flights conducted with and without transition fixed at several locations for wing leading edge sweep angles which varied from 10 to 26 at Mach numbers from 0.80 to 0.85 and altitudes of 7620 meters and 9144 meters. Preliminary results indicate that a large portion of the test chord experienced laminar flow.
    Keywords: AERODYNAMICS
    Type: NASA. Langley Research Center Advan. Aerodyn. and Active Controls; p 135-144
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    Aerodynamic drag reduction tests on a box-shaped vehicle (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The intent of the present experiment is to define a near optimum value of drag coefficient for a high volume type of vehicle through the use of a boattail, on a vehicle already having rounded front corners and an underbody seal, or fairing. The results of these tests will constitute a baseline for later follow-on studies to evaluate candidate methods of obtaining afterbody drag coefficients approaching the boattail values, but without resorting to such impractical afterbody extensions. The current modifications to the box-shaped vehicle consisted of a full and truncated boattail in conjunction with the faired and sealed underbody. Drag results from these configurations are compared with corresponding wind tunnel results of a 1/10 scale model. Test velocities ranged up to 96.6 km/h (60 mph) and the corresponding Reynolds numbers ranged up to 1.3 x 10 to the 7th power based on the vehicles length which includes the boattail. A simple coast-down technique was used to define drag.
    Keywords: AERODYNAMICS
    Type: NASA-CR-176982 , NAS 1.26:176982
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    Why use case studies rather than simulation-gaming techniques or library research? (1981)
    In:  Other Sources
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    Publication Date: 2016-06-07
    Description: Method which present a student with a more challenging and true to life situation of needing to conduct research in a problem solving context--and not thinking about organization of format until research and thinking are complete are investigated. Simulation-gaming techniques which attempt to teach initiative and creativity that library research are used for this purpose. However, it is shown case studies provide the greatest opportunities to engage the students in problem solving situations in which they develop skills as researchers and writers.
    Keywords: AERODYNAMICS
    Type: NASA. Langley Research Center Tech. Commun., Pt. 1; p 99-103
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    The phenomenon of dynamic stall (1981)
    In:  Other Sources
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    Publication Date: 2019-01-25
    Description: Dynamic stall and its consequences which are important to aircraft design and operation are discussed. A certain degree of unsteadyness always accompanies the flow over streamlined bodies at high angle of attack, however, the stall of lifting surface undergoing unsteady motion is more complex than static stall. Dynamic stall remains a major unsolved problem with a variety of applications in aeronautics, hydrodynamics and wind engineering.
    Keywords: AERODYNAMICS
    Type: Von Karman Inst. for Fluid Dynamics Unsteady Airloads and Aeroelastic Probl. in Separated and Transonic Flow; 28 p
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    Prediction of blade vortex interaction noise from measured blade pressure (1981)
    In:  Other Sources
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    Publication Date: 2019-01-25
    Description: The impulsive nature of noise due to the interaction of a rotor blade with a tip vortex is studied. The time signature of this noise is calculated theoretically based on the measured blade surface pressure fluctuation of an operational load survey rotor in slow descending flight and is compared with the simultaneous microphone measurement. Particularly, the physical understanding of the characteristic features of a waveform is extensively studied in order to understand the generating mechanism and to identify the important parameters. The interaction trajectory of a tip vortex on an acoustic planform is shown to be a very important parameter for the impulsive shape of the noise. The unsteady nature of the pressure distribution at the very leading edge is also important to the pulse shape. The theoretical model using noncompact linear acoustics predicts the general shape of interaction impulse pretty well except for peak amplitude which requires more continuous pressure information along the span at the leading edge.
    Keywords: AERODYNAMICS
    Type: DGLR Seventh European Rotorcraft and Powered Lift Aircraft Forum; 20 p
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    On Hybrid and mixed finite element methods (1981)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: Three versions of the assumed stress hybrid model in finite element methods and the corresponding variational principles for the formulation are presented. Examples of rank deficiency for stiffness matrices by the hybrid stress model are given and their corresponding kinematic deformation modes are identified. A discussion of the derivation of general semi-Loof elements for plates and shells by the hybrid stress method is given. It is shown that the equilibrium model by Fraeijs de Veubeke can be derived by the approach of the hybrid stress model as a special case of semi-Loof elements.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-175551 , NAS 1.26:175551
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    Two-dimensional aerodynamic characteristics of an airfoil designed for two (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: An airfoil designed for helicopter rotor application is investigated. The airfoil is designed to increase maximum normal force coefficient while maintaining favorable drag divergence and pitching moment characteristics. Two modifications are also tested. Maximum normal force coefficient varies from 1.14 to 0.90 at Mach numbers from about 0.35 to 0.65. Both modifications decreased drag coefficient at zero normal force coefficient for Mach numbers near drag divergence, but were less beneficial at a normal force coefficient of -0.2.
    Keywords: AERODYNAMICS
    Type: NASA-TP-1965 , L-14825 , NAS 1.60:1965 , AVRADCOM-TR-81-B-6
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    Selected advanced aerodynamic and active control concepts development (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A task for the Energy Efficient Transport program conducted: (1) The design and wind tunnel development of high-aspect-ratio supercritical wings, investigating the cruise speed regime and also high-lift. (2) The preliminary design and evaluation of an aircraft combining a high-aspect-ratio supercritical wing with a winglet. (3) Active Controls: The determination of criteria, configuration, and flying qualities associated with augmented longitudinal stability of a level likely to be acceptable for the next generation transport; and the design of a practical augmentation system. The baseline against which the work was performed and evaluated was the Douglas DC-X-200 twin engine derivative of the DC-10 transport. The supercritical wing development showed that the cruise and buffet requirements could be achieved and that the wing could be designed to realize a sizable advantage over today's technology. Important advances in high lift performance were shown. The design study of an aircraft with supercritical wing and winglet suggested advantages in weight and fuel economy could be realized. The study of augmented stability, conducted with the aid of a motion base simulator, concluded that a negative static margin was acceptable for the baseline unaugmented aircraft.
    Keywords: AERODYNAMICS
    Type: NASA-CR-3469 , NAS 1.26:3469
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    Finite element forced vibration analysis of rotating cyclic structures (1981)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: A capability was added to the general purpose finite element program NASTRAN Level 17.7 to conduct forced vibration analysis of tuned cyclic structures rotating about their axes of symmetry. The effects of Coriolis and centripetal accelerations together with those due to linear acceleration of the axis of rotation were included. The theoretical development of this capability is presented.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-165430 , NAS 1.26:165430 , D2536-941008
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    Forced vibration analysis of rotating cyclic structures in NASTRAN (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A new capability was added to the general purpose finite element program NASTRAN Level 17.7 to conduct forced vibration analysis of tuned cyclic structures rotating about their axis of symmetry. The effects of Coriolis and centripetal accelerations together with those due to linear acceleration of the axis of rotation were included. The theoretical, user's, programmer's and demonstration manuals for this new capability are presented.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-165429 , NAS 1.26:165429 , D2536-941007
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  • 66
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    Subsonic and transonic pressure measurements on a high-aspect-ratio supercritical-wing model with oscillating control surfaces (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A high aspect ratio supercritical wing with oscillating control surfaces is described. The semispan wing model was instrumented with 252 static orifices and 164 in situ dynamic pressure gases for studying the effects of control surface position and sinusoidal motion on steady and unsteady pressures. Data from the present test (this is the second in a series of tests on this model) were obtained in the Langley Transonic Dynamics Tunnel at Mach numbers of 0.60 and 0.78 and are presented in tabular form.
    Keywords: AERODYNAMICS
    Type: NASA-TM-83201 , L-14831 , NAS 1.15:83201
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    Line-spring model for surface cracks in a Reissner plate (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: In this paper the line-spring model developed by Rice and Levy for a surface crack in elastic plates is reconsidered. The problem is formulated by using Reissner's plate bending theory. For the plane strain problem of a strip containing an edge crack and subjected to tension and bending new expressions for stress intensity factors are used which are valid up to a depth-to-thickness ratio of 0.8. The stress intensity factors for a semi-elliptic and a rectangular crack are calculated. Considering the simplicity of the technique and the severity of the underlying assumptions, the results compare rather well with the existing finite element solutions.
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal of Engineering Science; 19; 10, 1; 1981
    Format: text
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  • 68
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    On numerical nonlinear analysis of highly flexible spinning cantilevers (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The general nonlinear discretized equations of motion of spinning elastic solids and structures are derived as a set of nonlinear ordinary differential equations for the case when the strain-displacement and velocity-displacement relations are nonlinear up to the second order. It is shown that the cost of generation of such equations is proportional to the fourth power of the number of degrees of freedom. A computer program is written to automatically generate the equations for the case of spinning cantilevers with initial imperfections. The types and the number of the coordinate functions used in the trial solution are parameters of the program.
    Keywords: STRUCTURAL MECHANICS
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  • 69
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    Mixed models and reduced/selective integration displacement models for nonlinear analysis of curved beams (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Simple mixed models are developed for use in the geometrically nonlinear analysis of deep arches. A total Lagrangian description of the arch deformation is used, the analytical formulation being based on a form of the nonlinear deep arch theory with the effects of transverse shear deformation included. The fundamental unknowns comprise the six internal forces and generalized displacements of the arch, and the element characteristic arrays are obtained by using Hellinger-Reissner mixed variational principle. The polynomial interpolation functions employed in approximating the forces are one degree lower than those used in approximating the displacements, and the forces are discontinuous at the interelement boundaries. Attention is given to the equivalence between the mixed models developed herein and displacement models based on reduced integration of both the transverse shear and extensional energy terms. The advantages of mixed models over equivalent displacement models are summarized. Numerical results are presented to demonstrate the high accuracy and effectiveness of the mixed models developed and to permit a comparison of their performance with that of other mixed models reported in the literature.
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal for Numerical Methods in Engineering; 17; Apr. 198
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  • 70
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    A Galerkin type finite element method for rotary-wing aeroelasticity in hover and forward flight (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: A Galerkin finite element method for the spatial discretization of the nonlinear, nonselfadjoint, partial differential equations governing rotary-wing aeroelasticity is presented. This method reduces algebraic manipulative labor significantly when compared to the global Galerkin method based on assumed modes. Furthermore, the Galerkin finite element method is ideally suited to treat rotor blades with discontinuous mass and stiffness distribution and structurally redundant configurations as they appear in bearingless rotors. Implementation of the method is illustrated for the coupled flap-lag aeroelastic problem of hingeless rotor blades in hover and forward flight. Numerical results for stability and response illustrate the numerical properties and convergence behavior of the method. It is concluded that the Galerkin finite element method is a practical tool for solving rotary-wing aeroelastic stability and response problems.
    Keywords: STRUCTURAL MECHANICS
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    Optimum structural design with plate bending elements - A survey (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: A survey is presented of recently published papers in the field of optimum structural design of plates, largely with respect to the minimum-weight design of plates subject to such constraints as fundamental frequency maximization. It is shown that, due to the availability of powerful computers, the trend in optimum plate design is away from methods tailored to specific geometry and loads and toward methods that can be easily programmed for any kind of plate, such as finite element methods. A corresponding shift is seen in optimization from variational techniques to numerical optimization algorithms. Among the topics covered are fully stressed design and optimality criteria, mathematical programming, smooth and ribbed designs, design against plastic collapse, buckling constraints, and vibration constraints.
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA Journal; 19; Apr. 198
    Format: text
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  • 72
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    Vibration and local instability of thermally stressed plates (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The vibration and buckling of a double wedge square cantilever plate has been investigated. It is shown that the free vibration modes, which occur at Delta T ref = 0, transition into the buckled modes which occur at Delta T ref = Delta T ref-cr for the respective mode. Delta T ref-cr for a particular mode is defined as the magnitude of thermal load at which the frequency of the particular mode vanishes. The analysis yields the same number of buckling eigenvalues and buckling modes as there are vibration eigenvalues and vibration modes. Gradual application of the load in the analysis permits the change in each vibration frequency of interest and its associated mode to be followed up to the load at which the frequency of the mode becomes zero. This constitutes the limit of linear theory. As the load is increased, the thin edges of the plate begin to deform during vibration. This local deformation, which begins in the vibration mode, is shown to transition into the phenomena of local edge buckling at Delta T ref-cr for the mode.
    Keywords: STRUCTURAL MECHANICS
    Type: Computer Methods in Applied Mechanics and Engineering; 25; Mar. 198
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    Unpowered Aerodynamic Characteristics of a 15-Percent Scale Model of a Twin-Engine Commuter Aircraft (1981)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: An experimental investigation was conducted in the Ames 12-Foot Pressure Wind Tunnel to determine the unpowered aerodynamic characteristics of a 15-percent-scale model of a twin-engine commuter aircraft. Model longitudinal aerodynamic characteristics were examined at discrete flap deflections for various angle-of-attack and wind-tunnel-velocity ranges with the empennage on and off. Data are presented for the basic model configuration consisting of the fuselage, wing, basic wing leading edge, double slotted flaps, midengine nacelles, and empennage. Other configurations tested include a particle-span drooped leading edge (dropped outboard of the engine nacelles), a full-span drooped leading edge, low- and high-mounted engine nacelles, and a single-slotted flap. An evaluation was made of the model mounting system by comparing data obtained with the model mounted conventionally on the wind-tunnel model-support struts and the model inverted.
    Keywords: AERODYNAMICS
    Type: NASA-TM-81284 , A-8552
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  • 74
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    The influence of unsteady aerodynamics on hingeless rotor ground resonance (1981)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: Calculations of the model frequency and damping for a hingeless rotor on a gimballed support in hover are compared with measured results for two configurations (differing in blade flap stiffness). Good correlation is obtaned when an inflow dynamics model is used to account for the influence of the unsteady aerodynamics. The effect of the unsteady aerodynamics is significant for this rotor system. The inflow dynamics model introduces additional states corresponding to perturbations of the wake-induced velocity at the rotor disk. The calculations confirm the experimental observation that the inflow mode introduced by these additional states is measurable for one configuration but not for the other.
    Keywords: AERODYNAMICS
    Type: NASA-TM-81302 , A-8635 , USAAVRADCOM-TR-81-B-16
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  • 75
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    Cold-air performance of compressor-drive turbine of Department of Energy upgraded automobile gas turbine engine. 1: Volute-manifold and stator performance (1981)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: The aerodynamic performance of the inlet manifold and stator assembly of the compressor drive turbine was experimentally determined with cold air as the working fluid. The investigation included measurements of mass flow and stator-exit fluid torque as well as radial surveys of total pressure and flow angle at the stator inlet and annulus surveys of total pressure and flow angle at the stator exit. The stator-exit aftermixed flow conditions and overall stator efficiency were obtained and compared with their design values and the experimental results from three other stators. In addition, an analysis was made to determine the constituent aerodynamic losses that made up the stator kinetic energy loss.
    Keywords: AERODYNAMICS
    Type: NASA-TM-82682 , DOE/NASA/1011-34 , E-572 , AVRADCOM-TR-80-C-20
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    Design considerations for composite fuselage structure of commercial transport aircraft (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The structural, manufacturing, and service and environmental considerations that could impact the design of composite fuselage structure for commercial transport aircraft application were explored. The severity of these considerations was assessed and the principal design drivers delineated. Technical issues and potential problem areas which must be resolved before sufficient confidence is established to commit to composite materials were defined. The key issues considered are: definition of composite fuselage design specifications, damage tolerance, and crashworthiness.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-159296 , LR-29540
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  • 77
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    An experimental investigation of the aerodynamics and cooling of a horizontally-opposed air-cooled aircraft engine installation (1981)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: A flight-test based research program was performed to investigate the aerodynamics and cooling of a horizontally-opposed engine installation. Specific areas investigated were the internal aerodynamics and cooling mechanics of the installation, inlet aerodynamics, and exit aerodynamics. The applicable theory and current state of the art are discussed for each area. Flight-test and ground-test techniques for the development of the cooling installation and the solution of cooling problems are presented. The results show that much of the internal aerodynamics and cooling technology developed for radial engines are applicable to horizontally opposed engines. Correlation is established between engine manufacturer's cooling design data and flight measurements of the particular installation. Also, a flight-test method for the development of cooling requirements in terms of easily measurable parameters is presented. The impact of inlet and exit design on cooling and cooling drag is shown to be of major significance.
    Keywords: AERODYNAMICS
    Type: NASA-CR-3405
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    An experimental and analytical investigation of the aerodynamics of a hypersonic vehicle at free stream Mach 6 (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The goal of this research is the assessment of the validity of existing three dimensional numerical programs in the prediction of the flow fields about general three dimensional hypersonic bodies. A detailed experimental research program was performed in which surface and flow field pressures were mapped. The results of the experimental work were compared with existing inviscid programs. Improvements were made on the existing numerical methods to include angle of attack. A summary of this work is presented.
    Keywords: AERODYNAMICS
    Type: NASA-CR-164133
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    Aerodynamic preliminary analysis system 2. Part 2: User's manuals (1981)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: An aerodynamic analysis system based on potential theory at subsonic/supersonic speeds and impact type finite element solutions at hypersonic conditions is described. Three dimensional configurations having multiple nonplanar surfaces of arbitrary planform and bodies of noncircular contour may be analyzed. Static, rotary, and control longitudinal and lateral directional chracteristics may be generated. The analysis has been implemented on a time sharing system in conjunction with an input tablet digitizer and an interactive graphics input/output display and editing terminal to maximize its responsiveness to the preliminary analysis problem. Typical simulation indicates that program provides an efficient analysis for systematically performing various aerodynamic configuration tradeoff and evaluation studies.
    Keywords: AERODYNAMICS
    Type: NASA-CR-165628 , NA-80-374-PT-2
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  • 80
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    Aerodynamic prediction techniques for hypersonic configuration design (1981)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: An investigation of approximate theoretical techniques for predicting aerodynamic characteristics and surface pressures for relatively slender vehicles at moderate hypersonic speeds was performed. Emphasis was placed on approaches that would be responsive to preliminary configuration design level of effort. Potential theory was examined in detail to meet this objective. Numerical pilot codes were developed for relatively simple three dimensional geometries to evaluate the capability of the approximate equations of motion considered. Results from the computations indicate good agreement with higher order solutions and experimental results for a variety of wing, body, and wing-body shapes for values of the hypersonic similarity parameter M delta approaching one.
    Keywords: AERODYNAMICS
    Type: NASA-CR-165651 , NA-80-611
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  • 81
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    Application of the line-spring model to a cylindrical shell containing a circumferential or axial part-through crack (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: An approximate solution was obtained for a cylindrical shell containing a part-through surface crack. It was assumed that the shell contains a circumferential or axial semi-elliptic internal or external surface crack and was subjected to a uniform membrane loading or a uniform bending moment away from the crack region. A Reissner type theory was used to account for the effects of the transverse shear deformations. The stress intensity factor at the deepest penetration point of the crack was tabulated for bending and membrane loading by varying three dimensionless length parameters of the problem formed from the shell radius, the shell thickness, the crack length, and the crack depth. The upper bounds of the stress intensity factors are provided by the results of the elasticity solution obtained from the axisymmetric crack problem for the circumferential crack, and that found from the plane strain problem for a circular ring having a radial crack for the axial crack. The line-spring model gives the expected results in comparison with the elasticity solutions. Results also compare well with the existing finite element solution of the pressurized cylinder containing an internal semi-elliptic surface crack.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-164058
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  • 82
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    The phenomenon of dynamic stall (1981)
    In:  CASI
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    Publication Date: 2019-06-28
    Description: The general features of dynamic stall on oscillating airfoils are explained in terms of the vortex shedding phenomenon, and the important differences between static stall, light dynamic stall, and deep stall are described. An overview of experimentation and prediction techniques is given.
    Keywords: AERODYNAMICS
    Type: NASA-TM-81264 , A-8464
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  • 83
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    Design and fabrication of a stringer stiffened discrete-tube actively cooled panel for a hypersonic aircraft (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A 0.61 x 1.22 m (2 x 4 ft) test panel was fabricated and delivered to the Langley Research Center for assessment of the thermal and structural features of the optimized panel design. The panel concept incorporated an aluminum alloy surface panel actively cooled by a network of discrete, parallel, redundant, counterflow passage interconnected with appropriate manifolding, and assembled by adhesive bonding. The cooled skin was stiffened with a mechanically fastened conventional substructure of stringers and frames. A 40 water/60 glycol solution was the coolant. Low pressure leak testing, radiography, holography and infrared scanning were applied at various stages of fabrication to assess integrity and uniformity. By nondestructively inspecting selected specimens which were subsequently tested to destruction, it was possible to refine inspection standards as applied to this cooled panel design.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-3403 , REPT-7430-927001
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  • 84
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    Aeropropulsive characteristics of twin nonaxisymmetric vectoring nozzles installed with forward-swept and aft-swept wings (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: An investigation was conducted in the Langley 16 Foot Transonic Tunnel to determine the aeropropulsive characteristics of a single expansion ramp nozzle (SERN) and a two dimensional convergent divergent nozzle (2-D C-D) installed with both an aft swept and a forward swept wing. The SERN was tested in both an upright and an inverted position. The effects of thrust vectoring at nozzle vector angles from -5 deg to 20 deg were studied. This investigation was conducted at Mach numbers from 0.40 to 1.20 and angles of attack from -2.0 deg to 16 deg. Nozzle pressure ratio was varied from 1.0 (jet off) to about 9.0. Reynolds number based on the wing mean geometric chord varied from about 3 million to 4.8 million, depending upon free stream number.
    Keywords: AERODYNAMICS
    Type: NASA-TP-1778 , L-13902
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  • 85
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    Experimental investigation of vortices shed by various wing fin configurations (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Forty-six different fins, which were members of twelve plan-form families, were tested. A two dimensional Boeing single element airfoil at an angle of attack of eight degrees and a sweepback angle of thirty-two was used to simulate a portion of the wing of a generator aircraft. Various free stream velocities were used to test any individual fin at its particular angle of attack. While the fin itself was mounted on the upper surface of the generator model, the angle of attack of each fin was varied until stall was reached and/or passed. The relative fin vortex strengths were measured in two ways. First, the maximum angular velocity of a four blade rotor placed in the fin vortex center was measured with the use of a stroboscope. Second, the maximum rolling moment on a following wing model placed in the fin vortex center was measured by a force balance.
    Keywords: AERODYNAMICS
    Type: NASA-CR-163874 , ISU-ERI-AMES-81112
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    Design data for brazed Rene 41 honeycomb sandwich (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Strength data, creep data and residual strength data after cyclic thermal exposure were obtained at temperatures from 78 K to 1144 K (-320 F to 1600 F). The influences of face thickness, core depth, core gage, cell size and thermal/stress exposure conditions on the mechanical design properties were investigated. A braze alloy and process was developed that is adequate to fully develop the strength of the honeycomb core while simultaneously solution treating and aging the Rene 41 fact sheets. New test procedures and test specimen configurations were developed to avoid excessive thermal stresses during cyclic thermal exposure.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-3382 , D180-26187-1
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  • 87
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    Steady and nonsteady supersonic turbulent afterbody flow (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The effect of the specific heat ratio gamma of the incoming ideal gas on the flow properties, especially on pressure distributions along the base and sting surfaces and on reattachment distance, was investigated. The specific heat ratios considered were gamma = 1.2, 1.4, and 1.667. Also, effects of other major parameters, such as eddy-viscosity coefficient (or effective Reynolds number) and Mach number, on the afterbody pressure and reattachment distance were studied and are discussed. Evolution of shock induced flow and stabilization time were examined and are discussed for a transient problem. The important influence of the flow-field geometry, pressure distributions, and reattachment distance on the aerodynamics radiative heat transfer for an atmosphere entry probe in high speed flight are briefly described.
    Keywords: AERODYNAMICS
    Type: NASA-TP-1769 , A-8271
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  • 88
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    Prediction of laminar and turbulent primary and secondary flows in strongly curved ducts (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The analysis is based on a primary secondary velocity decomposition in a given coordinate system, and leads to approximate governing equations which correct an a priori inviscid solution for viscous effects, secondary flows, total pressure distortion, heat transfer, and internal flow blockage and losses. Solution of the correction equations is accomplished as an initial value problem in space using an implicit forward marching technique. The overall solution procedure requires significantly less computational effort than Navier-Stokes algorithms. The solution procedure is effective even with the extreme local mesh resolution which is necessary to solve near wall sublayer regions in turbulent flow calculations. Computed solutions for both laminar and turbulent flow compared very favorably with available analytical and experimental results. The overall method appears very promising as an economical procedure for making detailed predictions of viscous primary and secondary flows in highly curved passages.
    Keywords: AERODYNAMICS
    Type: NASA-CR-3388 , R80-900007-12
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  • 89
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    A new solution-adaptive grid generation method for transonic airfoil flow calculations (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The clustering algorithm is controlled by a second-order, ordinary differential equation which uses the airfoil surface density gradient as a forcing function. The solution to this differential equation produces a surface grid distribution which is automatically clustered in regions with large gradients. The interior grid points are established from this surface distribution by using an interpolation scheme which is fast and retains the desirable properties of the original grid generated from the standard elliptic equation approach.
    Keywords: AERODYNAMICS
    Type: NASA-TM-81330 , A-8733
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  • 90
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    Equivalence of macroscopic and microscopic Griffith conditions for subcritical crack growth (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Exact relations are derived for a simple bond-snapping model of fracture and numerical results from a previous work are presented. A lattice model with a nonlinear cohesive force law is then considered. In both cases, the results confirm the equivalence of the microscopic and macroscopic Griffith conditions. The Griffith stress intensity is to be identified with the quiescent stress intensity.
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal of Fracture; 17; June 198
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  • 91
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    Structural analysis of general shells. Volume 2: User instructions for STAGSC-1 (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-CR-165671 , LMSC-D633873
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  • 92
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    Effect of leading-edge vortex flaps on aerodynamic performance of delta wings (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The effect of leading-edge vortex flaps on the aerodynamic characteristics of highly swept-back wings is analytically investigated, using the free vortex sheet method. The method, based on a three-dimensional inviscid flow model, is an advanced panel type employing quadratic doublet distributions to represent the wing surface, rolled-up vortex sheet and wake and is capable of computing forces, moments and surface pressures.
    Keywords: AERODYNAMICS
    Type: Journal of Aircraft; 18; Sept
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  • 93
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    Instability and transition in rotating disk flow (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The stability of three-dimensional rotating disk flow is investigated, including the effects of Coriolis forces and streamline curvature. The numerical results show that the critical Reynolds number for establishment of stationary vortex flow is 287. These vortices spiral outward at an angle of about 11.2 deg, and transition to turbulence occurs when their total amplification is about e to the 11th. New experimental results are also reported on the spatial growth rates of the stationary vortices. It is shown that the analysis gives growth rates that compare much better with the experimental results than do results obtained using the Orr-Sommerfeld equation. The experimental results tend to support the numerical prediction that the number of stationary vortices varies directly with the Reynolds number. The calculations also indicate the existence of weakly unstable propagating (type II) modes at low Reynolds numbers (Critical Reynolds Number being approximately equal to 49).
    Keywords: AERODYNAMICS
    Type: AIAA Journal; 19; Sept
    Format: text
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  • 94
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    Stresses in adhesively bonded joints - A closed-form solution (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The general plane strain problem of adhesively bonded structures consisting of two different, orthotropic adherends is considered, under the assumption that adherend thicknesses are constant and small in relation to the lateral dimensions of the bonded region, so that they may be treated as plates. The problem is reduced to a system of differential equations for the adhesive stresses which is solved in closed form, with a single lap joint and a stiffened plate under various loading conditions being considered as examples. It is found that the plate theory used in the analysis not only predicts the correct trend for adhesive stresses but gives surprisingly accurate results, the solution being obtained by assuming linear stress-strain relations for the adhesive.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Composite Materials; 15; May 1981
    Format: text
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  • 95
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    Effect of sweep angles on aerodynamic performance of double arrow wing - An analytical study (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Hybrid wing planforms are studied for adoption on supersonic transport and fighter aircraft. The free vortex sheet method is used to determine effects of the leading-edge sweep angles on the aerodynamic performance of a double arrow wing with a strake. Results show lift and drag increase with the increase of the inboard and outboard leading-edge sweep angles. However, the lift-to-drag ratio is little influenced by the changes in these sweep angles. Spanwise surface pressure distributions on the aft region are influenced by the inboard sweep angle while the outboard sweep angle has no effect on these pressures. Finally, the experimental data and predicted results are compared to show good agreement.
    Keywords: AERODYNAMICS
    Type: Journal of Aircraft; 18; Aug. 198
    Format: text
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  • 96
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    One dimensional modelling of failure in laminated plates by delamination buckling (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: When low speed objects impact composite laminated plates delamination may result. Under inplane compression such delaminations may buckle and tend to enlarge the delaminated area which can lead to loss of global plate stability. This process is modelled here in a first attempt by a delaminating beam-column wherein the local delamination growth, stability and arrest are governed by a fracture mechanics-based energy release rate criterion.
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal of Solids and Structures; 17; 11, 1; 1981
    Format: text
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  • 97
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    Magnetically induced cylindrical stress waves in a thermoelastic conductor (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The problem of stress wave generation in a linear thermoelastic solid by a pulsed magnetic field is investigated both analytically and experimentally for a cylindrically symmetric conducting solid. A dynamic response analysis is developed to correlate magnetic, thermal, and stress fields in the solid with the time history of the electric current. In the experiment, a transient magnetic field was applied normal to a large conducting plate with a circular hole. Initially the field was confined to the interior of the circular hole. The field was generated by discharging a large capacitor bank through a solenoidal coil. The plane-stress cylindrical stress waves are 1-D in nature. The relative effects of the magnetic body force and thermoelastic stresses, both generated by the electromagnetic field, are assessed.
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal of Solids and Structures; 17; 11, 1; 1981
    Format: text
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  • 98
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    Recent advances in reduction methods for nonlinear problems (1981)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: Status and some recent developments in the application of reduction methods to nonlinear structural mechanics problems are summarized. The aspects of reduction methods discussed herein include: (1) selection of basis vectors in nonlinear static and dynamic problems, (2) application of reduction methods in nonlinear static analysis of structures subjected to prescribed edge displacements, and (3) use of reduction methods in conjunction with mixed finite element models. Numerical examples are presented to demonstrate the effectiveness of reduction methods in nonlinear problems. Also, a number of research areas which have high potential for application of reduction methods are identified.
    Keywords: STRUCTURAL MECHANICS
    Format: text
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  • 99
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    Stability and control characteristics of a three-surface advanced fighter configuration at angles of attack up to 45 deg (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The tests were conducted at Mach numbers from 0.40 to 0.90, at angles of attack up to 45 deg for the lower Mach numbers, and at angles of sideslip up to 15 deg. The model variations under study included adding a canard surface and deflecting horizontal tails, ailerons, and rudders.
    Keywords: AERODYNAMICS
    Type: NASA-TM-83171 , L-14433
    Format: application/pdf
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  • 100
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    Development of an unsteady aerodynamic analysis for finite-deflection subsonic cascades (1981)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: An unsteady potential flow analysis, which accounts for the effects of blade geometry and steady turning, was developed to predict aerodynamic forces and moments associated with free vibration or flutter phenomena in the fan, compressor, or turbine stages of modern jet engines. Based on the assumption of small amplitude blade motions, the unsteady flow is governed by linear equations with variable coefficients which depend on the underlying steady low. These equations were approximated using difference expressions determined from an implicit least squares development and applicable on arbitrary grids. The resulting linear system of algebraic equations is block tridiagonal, which permits an efficient, direct (i.e., noniterative) solution. The solution procedure was extended to treat blades with rounded or blunt edges at incidence relative to the inlet flow.
    Keywords: AERODYNAMICS
    Type: NASA-CR-3455 , R81-914777-7
    Format: application/pdf
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