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  • Other Sources  (568)
  • STRUCTURAL MECHANICS  (355)
  • COMMUNICATIONS AND RADAR  (213)
  • 1985-1989  (568)
  • 1955-1959
  • 1985  (568)
  • 1
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    DSN frequency and timing system, Mark 4-85 (1985)
    In:  CASI
    Details
    Publication Date: 2006-02-14
    Description: As part of the Deep Space Network (DSN) Mark IVA implementation program, the DSN frequency and timing system is currently undergoing changes. With the implementation of signal processing centers (SPC) at each deep space communications complex (DSCC), major changes to the frequency and timing distribution equipment were necessary. A functional description of the Mark IVA frequency and timing system (FTS) as it exists today and planned capabilities through 1988 is given.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommun. and Data Acquisition Progr. Rept.; p 113-119
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  • 2
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    Use of ground radar to detect reentering debris (1985)
    In:  CASI
    Details
    Publication Date: 2006-02-14
    Description: The velocity of the particles is required to identify the type of particles producing the ionization trails. A method of approximating the velocity of a meteor from radar data was developed. The method requires the time between the spacings of the Fresnel interference fringes, the range to the ionization trail, and the wavelength of the radar system. The orbital mechanics of the problem are evaluated, if the particles originate with the shuttle, the orbital mechanics will substantiate the relative position of the particles with the position of the shuttle. A program to determine spacecraft orbital decay due to perturbations is utilized for a preliminary evaluation of the orbital mechanics of the problem. Many assumptions concerning the size, shape, density, etc. of the particles are necessary for the preliminary evaluation. The results do not negate the possibility that the events observed by the radar are reentering particles originating from the shuttle.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Orbital Debris; p 164-169
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  • 3
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    CV-990 L-band SAR: A calibration experiment (1985)
    In:  CASI
    Details
    Publication Date: 2006-02-14
    Description: Calibrated image data is required by most users of synthetic aperture radar (SAR) data particularly those attempting to classify targets based upon their radar backscatter signature as a function of frequency polarization or incidence angle. In this experiment, the backscatter derived by calibrating the NASA/JPL CV-990 L-band SAR, and the backscatter reported from a pass of the NASA/JSC C-130 scatterometer as the two instruments flew over the same site at different times are compared.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA(JPL Aircraft SAR Workshop Proc.; p 17-20
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  • 4
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    Radar system description (1985)
    In:  CASI
    Details
    Publication Date: 2006-02-14
    Description: A brief overview is given of the hardware and software utilized to generate the CV-990 synthetic aperture radar's image products. The on-board hardware is described, then the operational processing software, and finally the image products that are routinely available.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA(JPL Aircraft SAR Workshop Proc.; p 5-12
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  • 5
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    Improved mapping of radio sources from VLBI data by least-square fit (1985)
    In:  CASI
    Details
    Publication Date: 2006-02-14
    Description: A method is described for producing improved mapping of radio sources from Very Long Base Interferometry (VLBI) data. The method described is more direct than existing Fourier methods, is often more accurate, and runs at least as fast. The visibility data is modeled here, as in existing methods, as a function of the unknown brightness distribution and the unknown antenna gains and phases. These unknowns are chosen so that the resulting function values are as near as possible to the observed values. If researchers use the radio mapping source deviation to measure the closeness of this fit to the observed values, they are led to the problem of minimizing a certain function of all the unknown parameters. This minimization problem cannot be solved directly, but it can be attacked by iterative methods which we show converge automatically to the minimum with no user intervention. The resulting brightness distribution will furnish the best fit to the data among all brightness distributions of given resolution.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommun. and Data Acquisition Progr. Rept.; p 199-210
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  • 6
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    Comparison of the calibration of ionospheric delay in VLBI data by the methods of dual frequency and Faraday rotation (1985)
    In:  CASI
    Details
    Publication Date: 2006-02-14
    Description: When both S-band and X-band data are recorded for a signal which has passed through the ionosphere, it is possible to calculate the ionospheric contribution to signal delay. In Very Long Baseline Interferometry (VLBI) this method is used to calibrate the ionosphere. In the absence of dual frequency data, the ionospheric content measured by Faraday rotation, using a signal from a geostationary satellite, is mapped to the VLBI observing direction. The purpose here is to compare the ionospheric delay obtained by these two methods. The principal conclusions are: (1) the correlation between delays obtained by these two methods is weak; (2) in mapping Faraday rotation measurements to the VLBI observing direction, a simple mapping algorithm which accounts only for changes in hour angle and elevation angle is better than a more elaborate algorithm which includes solar and geomagnetic effects; (3) fluctuations in the difference in total electron content as seen by two antennas defining a baseline limit the application of Faraday rotation data to VLBI.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommun. and Data Acquisition Progr. Rept.; p 11-23
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  • 7
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    SETI radio spectrum surveillance system (1985)
    In:  CASI
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    Publication Date: 2006-02-14
    Description: The SETI Radio Spectrum Surveillance System (SRSSS) will provide a data base for assessing the radio frequency interference (RFI) environment for SETI and minimizing RFI disruptions during the search. The system's hardware and software are described and the sensitivity of the system is discussed.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommun. and Data Acquisition Progr. Rept.; p 173-184
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  • 8
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    Propagation and radiation characteristics of a multimode corrugated waveguide feedhorn (1985)
    In:  CASI
    Details
    Publication Date: 2006-02-14
    Description: A prototype of the multimode corrugated feedhorn which will be used in the 400 kW CW Ka-band radar system is described. A rough design is done using coupled mode theory and standard corrugated waveguide modes. A more exact analysis using mode matching techniques is then used which takes into account the effect of a finite number of corrugations per wavelength and determines the modes which are reflected from the device. A prototype feedhorn has been constructed and measured. These experimental results are then compared to the theoretical predictions which agree satisfactorily closely.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommun. and Data Acquisition Progr. Rept.; p 57-67
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  • 9
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    A VLBI survey at 2.29 GHz (1985)
    In:  CASI
    Details
    Publication Date: 2006-02-14
    Description: The Deep Space Network (DSN) is establishing a high-accuracy VLBI celestial reference frame. The results of a search for suitable radio sources to be used in constructing this frame are given. The VLBI observations using DSN baselines at 2.29 GHz with fringe spacings of about 3 milliarcseconds have been performed on 1398 radio sources spread over the entire sky. Of those, 917 sources were detected including 93% of the identifed BL Lacertae objects, 86% of Quasars and 36% of galaxies. The resulting catalog of compact radio sources is also useful for various astrophysical studies and in the formation of VLBI celestial reference frames.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommun. and Data Acquisition Progr. Rept.; p 1-10
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  • 10
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    A new 70-meter antenna quadripod with reduced RF blockage (1985)
    In:  CASI
    Details
    Publication Date: 2006-02-14
    Description: The new subreflector mount (quadripod) for the 64-meter to 70-meter antenna extension project was the result of many trial designs aimed at reducing radio frequency spherical and plane wave blockage and minimizing structural weight while satisfying strength and natural frequency requirements. An optimum design emerged which has a gain improvement of 0.32 dB over the present 64-meter design. Some of the trial designs made and the final optimum configuration selected are described.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommun. and Data Acquisition Progr. Rept.; p 24-30
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  • 11
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    16-QAM and trellis-coded 16-QAM on nonlinear channels (1985)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The use of 16-QAM on bandlimited nonlinear satellite channels, in uncoded and trellis-coded form, for bandwidth efficient modulation (ideally 4 bps/Hz) is discussed. To avoid severe degradation due to AM/AM and AM/PM distortion, or to avoid the need for large back-off, predistorting the 16-QAM constellation at the modulator is considered. Performance for varying back-off settings for uncoded and coded 16-QAM is simulated, and it is found that the four-state trellis code has a coding gain of about 8 dB, larger than expected based on linear channel analysis, while the 16-state code gains only marginally beyond this.
    Keywords: COMMUNICATIONS AND RADAR
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  • 12
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    2400 bit/s DMSK modem for mobile satellite service (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The letter describes the implementation of a differentially coherent receiver suitable for bursty signal transmission over fading channels. To meet the severe system phase response requirement, this implementation is conducted at baseband. Means of frequency correction (AFC) is also shown. This receiver is simple and can easily be fabricated using VLSI technology.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Electronics Letters (ISSN 0013-5194); 21; 965
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  • 13
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    An optimized bandwidth efficient demand assigned protocol for integrated Mobile Satellite Services (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: This paper describes the design of a demand assigned protocol based on bandwidth efficiency for integrated services of a Mobile Satellite System (MSS). An MSS provides data (closed-ended) and voice (open-ended) communications services for a large number of mobile users dispersed over a wide geographical area. Each mobile requests its desired service through a designated set of channels to a network management center. Either pure or slotted ALOHA random access scheme can be used to make connection requests, while data and voice communications are demand assigned. All channels have equal bandwidth and can be adaptively used for reservation requests, data connections or voice connections to maximize the bandwidth utilization. In this paper, perfect communications channels are assumed. It has been shown that, for the case considered, using the slotted ALOHA scheme for making connection requests can save about 30 percent on the total number of channels over using the pure ALHOA scheme.
    Keywords: COMMUNICATIONS AND RADAR
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  • 14
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    Test and analysis correlation for structural dynamic systems (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: In this paper the authors summarize the activities at the Jet Propulsion Laboratory (JPL) in modifying the structural mathematical model to correlate with its modal test results. In addition to the results from the Viking and Galileo spacecrafts, developments in the parameter estimation of structural mathematical models of large flexible structures using Multiple Boundary Condition Tests (MBCT) are presented.
    Keywords: STRUCTURAL MECHANICS
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  • 15
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    Analytical results for post-buckling behaviour of plates in compression and in shear (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The postbuckling behavior of long rectangular isotropic and orthotropic plates is determined. By assuming trigonometric functions in one direction, the nonlinear partial differential equations of von Karman large deflection plate theory are converted into nonlinear ordinary differential equations. The ordinary differential equations are solved numerically using an available boundary value problem solver which makes use of Newton's method. Results for longitudinal compression show different postbuckling behavior between isotropic and orthotropic plates. Results for shear show that change in inplane edge constraints can cause large change in postbuckling stiffness.
    Keywords: STRUCTURAL MECHANICS
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  • 16
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    Buckling of simply supported plate assemblies subject to shear loading (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: An analysis is presented of the shear buckling load of an arbitrary simply-supported prismatic plate assembly or stiffened panel configuration. The method utilizes stiffness matrices developed by Wittrick (1968). For the restraint of simple support along edges perpendicular to the longitudinal direction, various wavelengths of response are combined using an energy method that involves only a boundary integral. Numerical results for plate and panel configurations show the accuracy and convergence of the method.
    Keywords: STRUCTURAL MECHANICS
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  • 17
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    Nonlinear finite element models of laminated plates and shells (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: In this expository paper a first-order shear deformation laminate theory that accounts for the von Karman strains is described and its finite element model is developed. The element also accounts for Hill's elastic-perfectly plastic material model. Sample applications of the present element to linear and nonlinear bending of laminated plates and shells are presented. Numerical results showing the effects of boundary conditions, lamination scheme, and loading on the deflections and stresses are also presented. It is found that the effect of shear deformation and boundary conditions on deflections are significant.
    Keywords: STRUCTURAL MECHANICS
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  • 18
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    The combined effects of stress and moisture on the structural integrity of composites (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A variational approach is used to model the moisture content and distribution profiles which cause swelling in polymers and composites which are used as aircraft structural components. The moisture intrusion stems from humidity, which makes the problem one of diffusion of mass from the environment into a semiinfinite plate with a given diffusion coefficient and thickness. Lagrangian, ordinary differential equations are defined for the mass diffusion, including driving force, mass potential and volume dissipation expressions. Account is taken of the effects of stress on diffusivity, including the dilatational stress caused by inhomogeneous swelling of the material. It is noted that material near the top and bottom of a part undergoes the most swelling, and the evolution of moisture diffusion in the materials is traced. Finally, experimental data are used to define differential equations for predicting the final moisture distribution within the material.
    Keywords: STRUCTURAL MECHANICS
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  • 19
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    Further results on rate 1/N convolutional code constructions with minimum required SNR criterion (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: New good (K, 1/N) convolutional codes for 8 or = to K or = to 13 and 2 or = to N or = to 8 were found and tabulated which require minimum signal-to-noise ratio (SNR) for given desired bit error rates (BER) with Viterbi decoding. The transfer function bound was used for the BER evaluations. These low-rate codes are expected to have a number of applications, especially for systems having large bandwidth-bit time products such as deep space and spread spectrum communication systems.
    Keywords: COMMUNICATIONS AND RADAR
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  • 20
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    Land vehicle antennas for satellite mobile communications (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Antenna designs applicable to future satellite mobile vehicle communications are examined. Microstrip disk, quadrifilar helix, cylindrical microstrip, and inverted V and U crossed-dipole low gain antennas (3-5 dBic) that provide omnidirectional coverage are described. Diagrams of medium gain antenna (9-12 dBic) concepts are presented; the antennas are classified into three types: (1) electronically steered with digital phase shifters; (2) electronically switched with switchable power divider/combiner; and (3) mechanically steered with motor. The operating characteristics of a conformal antenna with electronic beam steering and a nonconformal design with mechanical steering are evaluated with respect to isolation levels in a multiple satellite system. Vehicle antenna pointing systems and antenna system costs are investigated.
    Keywords: COMMUNICATIONS AND RADAR
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  • 21
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    Modeling the filament winding process (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A model is presented which can be used to determine the appropriate values of the process variables for filament winding a cylinder. The model provides the cylinder temperature, viscosity, degree of cure, fiber position and fiber tension as functions of position and time during the filament winding and subsequent cure, and the residual stresses and strains within the cylinder during and after the cure. A computer code was developed to obtain quantitative results. Sample results are given which illustrate the information that can be generated with this code.
    Keywords: STRUCTURAL MECHANICS
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  • 22
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    Vibration and buckling of rotating, pretwisted, preconed beams including Coriolis effects (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The effects of pretwist, precone, setting angle and Coriolis forces on the vibration and buckling behavior of rotating, torsionally rigid, cantilevered beams were studied. The beam is considered to be clamped on the axis of rotation in one case, and off the axis of rotation in the other. Two methods are employed for the solution of the vibration problem: (1) one based upon a finite-difference approach using second order central differences for solution of the equations of motion, and (2) based upon the minimum of the total potential energy functional with a Ritz type of solution procedure making use of complex forms of shape functions for the dependent variables. The individual and collective effects of pretwist, precone, setting angle, thickness ratio and Coriolis forces on the natural frequencies and the buckling boundaries are presented. It is shown that the inclusion of Coriolis effects is necessary for blades of moderate to large thickness ratios while these effects are not so important for small thickness ratio blades. The possibility of buckling due to centrifugal softening terms for large values of precone and rotation is shown.
    Keywords: STRUCTURAL MECHANICS
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  • 23
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    FH/MFSK performance in multitone jamming (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The performance of frequency-hopped (FH) M-ary frequency-shift keyed (MFSK) signals in partial-band noise as analyzed in the open literature. The previous research is extended to the usually more effective class of multitone jamming. Some objectives researched are: (1) To categorize several different multitone jamming strategies; (2) To analyze the performance of FH/MSFK signaling, both uncoded with diversity, assuming a noncoherent energy detection metric with linear combining and perfect jamming state side information, in the presence of worst case interference for each of these multitone categories; and (3) To compare the effectiveness of the various multitone jamming techniques, and contrast the results with the partial band noise jamming case.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Journal on Selected Areas in Communications (ISSN 0733-8716); SAC-3; 627-643
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  • 24
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    Erasure information for a Reed-Solomon decoder (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Many Reed-Solomon decoders, including the one decoding the outer code for Voyager data from Uranus, assume that all symbols have the same chance of being correct or incorrect. Insome cases, like in a burst of incorrect symbols, this is not the case, and a Reed-Solomon decoder could make use of this. The use of information about bit quality sent to the Reed-Solomon from an (inner) Viterbi decoder is examined, as well as information about the error status of adjacent symbols in decoding interleaved Reed-Solomon encoded symbols. It is discovered that, in a region of interest, only about 0.04 dB can gained.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommunications and Data Acquisition Report; p 39-44
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  • 25
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    Decoding convolutionally encoded images (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: Maximum Likelihood Convolutional Decoding, which is used by the Deep Space Network for short constraint-length convolutional codes, assumes that all strings of information bits are equally likely. In some cases, like image data, this is not the case. The use of information about an adjacent pixel in decoding convolutionally encoded Voyager images is examined. It is discovered that, in a region of interest, as much as 2 dB may be gained.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommunications and Data Acquisition Report; p 34-38
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  • 26
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    In search of a 2-dB coding gain (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A recent code search found a (15,1/5), a (14,1/6), and a (15,1/6) convolutional code which, when concatenated with a 10-bit (1023,959) Reed-Solomon (RS) code, achieves a bit-error rate (BER) of 0.000001 at a bit signal-to-noise ratio (SNR) of 0.50 dB, 0.47 dB and 0.42 B, respectively. All of these three codes outperform the Voyager communication system, our baseline, which achieves a BER of 10.000001 at bit SNR of 2.53 db, by more than 2 dB. The 2 dB coding improvement goal was exceeded.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommunications and Data Acquisition Report; p 26-33
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  • 27
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    Application of Ritz vectors for dynamic analysis of large structures (1985)
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    Publication Date: 2011-08-19
    Description: The use of an orthogonal set of specially selected Ritz vectors is shown to be very effective in reducing the cost of dynamic analysis by modal superposition. Several mechanical structures are examined, and the Ritz vector approach is compared to the classical eigenvector approach on the basis of cost, accuracy and elapsed analysis (throughput) time. Mathematical proof of the completeness of orthogonal Ritz vectors is provided for the case of a positive definite mass matrix and a symmetric stiffness matrix.
    Keywords: STRUCTURAL MECHANICS
    Type: Computers and Structures (ISSN 0045-7949); 21; 3, 19
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  • 28
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    Hybrid analytical technique for nonlinear analysis of structures (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA Journal (ISSN 0001-1452); 23; 938-946
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  • 29
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    Buckling of a sublaminate in a quasi-isotropic composite laminate (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The buckling of an elliptic delamination embedded near the surface of a thick quasi-isotropic laminate was predicted. The thickness of the delaminated ply group (the sublaminate) was assumed to be small compared to the total laminate thickness. Finite-element and Rayleigh-Ritz methods were used for the analyses. The Rayleigh-Ritz method was found to be simple, inexpensive, and accurate, except for highly anisotropic delaminated regions. Effects of delamination shape and orientation, material anisotropy, and layup on buckling strains were examined. Results show that: (1) the stress state around the delaminated region is biaxial, which may lead to buckling when the laminate is loaded in tension; (2) buckling strains for multi-directional fiber sublaminates generally are bounded by those for the 0 deg and 90 deg unidirectional sublaminates; and (3) the direction of elongation of the sublaminate that has the lowest buckling strain correlates with the delamination growth direction.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Composite Materials (ISSN 0021-9983); 19; 2-18
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  • 30
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    The Spectrum Orbit Utilization Program (SOUP) used for DBS plan analysis at RARC '83 (1985)
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    Publication Date: 2011-08-19
    Description: This paper describes the history, functions, and usage of the program that was used to analyze the plans for direct broadcast satellite service developed in the course of the 1983 Regional Administrative Radio Conference for ITU Region 2. Given the requirements for direct broadcast service by the administrations, the conference delegates (1) developed the appropriate technical parameters; (2) made tentative assignments to the orbit locations, frequencies, and polarizations of space stations, (3) calculated the interferences and margins of such assignments through the use of the Spectrum Orbit Utilization Program (SOUP); and (4) iterated this procedure until an acceptable plan was found.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Journal on Selected Areas in Communications (ISSN 0733-8716); SAC-3; 44-49
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  • 31
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    Experimental results supporting the determination of service quality objectives for DBS systems (1985)
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    Publication Date: 2011-08-19
    Description: A summary of the results of a joint United States and Canadian program on subjective measurements of the picture degradation caused by noise and interference on an NTSC encoded color television signal is given in this paper. The effects of system noise, cochannel and adjacent channel interference, and both single entry and aggregate as well as a combination of these types of interference were subjectively evaluated by expert and nonexpert viewers under reference conditions. These results were used to develop the rationale used at RARC '83 to establish the service quality objective for planning the DBS service for the American continents.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Journal on Selected Areas in Communications (ISSN 0733-8716); SAC-3; 87-99
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  • 32
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    Birds and insects as radar targets - A review (1985)
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    Publication Date: 2011-08-19
    Description: A review of radar cross-section measurements of birds and insects is presented. A brief discussion of some possible theoretical models is also given and comparisons made with the measurements. The comparisons suggest that most targets are, at present, better modeled by a prolate spheroid having a length-to-width ratio between 3 and 10 than by the often used equivalent weight water sphere. In addition, many targets observed with linear horizontal polarization have maximum cross sections much better estimated by a resonant half-wave dipole than by a water sphere. Also considered are birds and insects in the aggregate as a local radar 'clutter' source. Order-of-magnitude estimates are given for many reasonable target number densities. These estimates are then used to predict X-band volume reflectivities. Other topics that are of interest to the radar engineer are discussed, including the doppler bandwidth due to the internal motions of a single bird, the radar cross-section probability densities of single birds and insects, the variability of the functional form of the probability density functions, and the Fourier spectra of single birds and insects.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE, Proceedings (ISSN 0018-9219); 73; 205-227
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    Convolutional coding combined with continuous phase modulation (1985)
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    Publication Date: 2011-08-19
    Description: Background theory and specific coding designs for combined coding/modulation schemes utilizing convolutional codes and continuous-phase modulation (CPM) are presented. In this paper the case of r = 1/2 coding onto a 4-ary CPM is emphasized, with short-constraint length codes presented for continuous-phase FSK, double-raised-cosine, and triple-raised-cosine modulation. Coding buys several decibels of coding gain over the Gaussian channel, with an attendant increase of bandwidth. Performance comparisons in the power-bandwidth tradeoff with other approaches are made.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Communications (ISSN 0090-6778); COM-33; 20-29
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    Spread spectrum communications. Volume 1, 2 & 3 (1985)
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    Publication Date: 2011-08-19
    Description: The design and operation of spread-spectrum (SS) communication systems are examined in an introductory text intended for graduate engineering students and practicing engineers. Chapters are devoted to an overview of SS systems, the historical origins of SS, basic concepts and system models, antijam communication systems, pseudonoise generators, coherent direct-sequence systems, noncoherent frequency-hopped systems, coherent and differentially coherent modulation techniques, pseudonoise acquisition and tracking in direct-sequence receivers, time and frequency synchronization of frequency-hopped receivers, low-probability-of-intercept communication, and multiple-access communication. Graphs, diagrams, and photographs are provided.
    Keywords: COMMUNICATIONS AND RADAR
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    Verification of large space structures using scale modelling laws (1985)
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    Publication Date: 2011-08-19
    Description: The feasibility of testing large space structures in 1-g environment for the purpose of verifying its performance requirement is considered. Because of the difference in test objectives as compared to the conventional structural systems, the scale modelling laws are examined. The investigation is performed on a generic structural element, a space beam. A preliminary conclusion is obtained based on the results.
    Keywords: STRUCTURAL MECHANICS
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    A retransmission protocol for the message service of a land mobile satellite experiment (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The objectives of NASA's land mobile satellite experiments are discussed. The assigned multiple access protocol combined with a retransmission scheme is to provide reliable transmission of data messages from mobiles to base stations (BSs). The sequences for communication between mobiles and BSs, mobiles and the network management center (NMC), and BSs and NMC are examined, and an example of mobiles/BSs communication is provided. The performance of the retransmission protocol and data message reservation and message channels delays are analyzed. A bit error rate of 0.001 is observed for satellite channels in a mobile environment and the message error probability is between 0-0.1.
    Keywords: COMMUNICATIONS AND RADAR
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    Generation, modulation and reception of orthogonally polarized signals (1985)
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    Publication Date: 2011-08-19
    Description: The radiating electromagnetic field of a dipole antenna is considered. By allowing the dipole to rotate about its midpoint, one can construct an entire set of signal polarizations wherein distinct members of the set are mutually orthogonal. It is shown how these signals can be modulated and demodulated to convey information. These ideas are then generalized, and both balanced, as well as unbalanced quadrapole modulations are defined. Methods of receiver synchronization to such signals are described, as well as their potential application to multiple access and anti-jam communications.
    Keywords: COMMUNICATIONS AND RADAR
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  • 38
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    Mixed models and reduction method for dynamic analysis of anisotropic shells (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A time-domain computational procedure is presented for predicting the dynamic response of laminated anisotropic shells. The two key elements of the procedure are: (1) use of mixed finite element models having independent interpolation (shape) functions for stress resultants and generalized displacements for the spatial discretization of the shell, with the stress resultants allowed to be discontinuous at interelement boundaries; and (2) use of a dynamic reduction method, with the global approximation vectors consisting of the static solution and an orthogonal set of Lanczos vectors. The dynamic reduction is accomplished by means of successive application of the finite element method and the classical Rayleigh-Ritz technique. The finite element method is first used to generate the global approximation vectors. Then the Rayleigh-Ritz technique is used to generate a reduced system of ordinary differential equations in the amplitudes of these modes. The temporal integration of the reduced differential equations is performed by using an explicit half-station central difference scheme (Leap-frog method). The effectiveness of the proposed procedure is demonstrated by means of a numerical example and its advantages over reduction methods used with the displacement formulation are discussed.
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    Prediction of stable crack growth and instability using the V sub R-curve method (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: A methodology is presented for predicting stable crack growth and instability of cracked structural components from results of laboratory tests on metallic materials under plane-stress conditions. The methodology is based on the displacement V sub R at the tip of a stably tearing crack. Basically, the V sub R-curve method is a resistance curve approach, such as K sub R and J sub R, except that the 'crack drive' is written in terms of crack-tip displacement instead of K or J. The relationship between crack-tip-opening displacement, crack length, specimen type, and tensile properties is derived from the Dugdale model for the cracked structure of interest. This report describes the laboratory test procedure and calculations used to obtain the V sub R resistance curve from fracture tests of compact or of middle-crack tension (formally center-crack) specimens. The analysis procedure used to predict stable crack growth and instability of any through-the-thickness crack configuration made of the same material and thickness, and tested under the same environmental conditions, is presented. The various limitations of the present V sub R curve method are given. Four example calculations and predictions are shown.
    Keywords: STRUCTURAL MECHANICS
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    An evaluation of fracture analysis methods (1985)
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    Publication Date: 2011-08-19
    Description: The results of an experimental and predictive round robin on the applications of fracture analysis methods are presented. The objective of the round robin was to verify whether fracture analysis methods currently in use can or cannot predict failure loads on complex structural components containing cracks. Fracture results from tests on a number of compact specimens were used to make the predictions. The accuracy of the prediction methods was evaluated in terms of the variation in the ratio of predicted to experimental failure loads, and the predictions methods are ranked in order of minimum standard error. A range of applicability of the different methods was also considered in assessing their usefulness. For 7075-T651 aluminum alloy, the best methods were: the effective K sub R curve; the critical crack-tip opening displacement (CTOD) criterion using a finite element analysis; and the K sub R curve with the Dugdale model. For the 2024-T351 aluminum alloy, the best methods included: the two-parameter fracture criterion (TPFC); the CTOD parameter using finite element analysis; the K-curve with the Dugdale model; the deformation plasticity failure assessment diagram (DPFAD); and the effective K sub R curve with a limit load condition. For 304 stainless steel, the best methods were the limit load analysis; the CTOD criterion using finite-element analysis TPFC and DPFAD. Some sample experimental results are given in an appendix.
    Keywords: STRUCTURAL MECHANICS
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    An adaptive quantization method for burst mode synthetic aperture radar data (1985)
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    Publication Date: 2011-08-19
    Description: Synthetic aperture radar (SAR) has high data rate because it collects and processes the data coherently. The data rate limitation of the system has to be satisfied while maintaining good image quality. Thus, a quantizer with minimum data rate and high SNR should be employed. An adaptive quantization method is proposed for the burst mode SAR. This adaptive quantizer uses uniformly quantized data to select a subset of bits which is equivalent to changing the step size of the uniform quantizer. A simple implementation which uses the previous burst data to compute the local statistics for the bit selection is presented. The use of previous burst simplifies the implementation because it does not require storage or delay; however, an abrupt change in the terrain could result in incorrect bit selection. An error analysis of this implementation and comparison of two burst mode SAR images formed using the uniformly quantized and adaptively quantized data is presented.
    Keywords: COMMUNICATIONS AND RADAR
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  • 42
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    Efficient calculation of optimum design sensitivity (1985)
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    Publication Date: 2011-08-19
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA Journal (ISSN 0001-1452); 23; 1798-180
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  • 43
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    Analysis of elliptical and circular microstrip antennas using moment method (1985)
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    Publication Date: 2011-08-19
    Description: A method of calculating the input impedance of either a circular or a slightly elliptical microstrip antenna excited by a coaxial probe is presented. Using the reaction integral equation and the exact dyadic Green's function, the finite substrate thickness is taken into account in the formulation. Good agreement with experimental results for an elliptical patch is obtained and a design procedure for a circularly polarized antenna is presented.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Antennas and Propagation (ISSN 0018-926X); AP-33; 954-959
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  • 44
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    On the probability density function of the squared envelope of a sum of random phase vectors (1985)
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    Publication Date: 2011-08-19
    Description: Weber et al. (1980) have found that a generic problem arises in the study of multiuser FHMA/MFSK systems. According to this problem, the presence of the other channel users acts as interference to reception of the desired user's transmission. The present investigation is concerned with a recursive solution in which the recursion parameter is the number of vectors in the sum. A mathematical characterization of such a solution is presented, taking into account the simple two-vector case in which a well-known closed form result is possible. Some numerical results are also discussed. It is pointed out that the considered recursive solution provides a break in the bottleneck associated with the exact computation of the error probability performance of multiuser FHMA/MFSK systems and single access MFSK systems corrupted by multitone jamming.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Communications (ISSN 0090-6778); COM-33; 993-996
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  • 45
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    Vibrations of twisted cantilever plates - A comparison of theoretical results (1985)
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    Publication Date: 2011-08-19
    Description: As a result of significant differences in the published results for various methods of analysis involving the use of finite element techniques, there are now some questions regarding the adequacy of these methods to predict accurately the vibratory characteristics of highly twisted cantilever plates. In an attempt to help in a resolution of the arising problems, a joint government/industry/university research effort was initiated. The primary objective of the present paper is to summarize the theoretical methods used in the study and show samples of the obtained results. The study provided 19 sets of theoretical results which are derived from beam theory, shell theory, and finite element methods.
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal for Numerical Methods in Engineering (ISSN 0029-5981); 21; 1365-138
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  • 46
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    Dynamics of flexible bodies in tree topology - A computer-oriented approach (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Guidance, Control, and Dynamics (ISSN 0731-5090); 8; 584-590
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  • 47
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    Probabilistic combination of vehicle dynamic vibration and acoustically induced random accelerations (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Aircraft (ISSN 0021-8669); 22; 825
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  • 48
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    Comments on 'A technique for improving the efficiency of M-ary signaling' (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Communications (ISSN 0090-6778); COM-33; 877
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  • 49
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    Performance of a normalized energy metric without jammer state information for an FH/MFSK system in worst case partial band jamming (1985)
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    Publication Date: 2011-08-19
    Description: For a frequency-hopped noncoherent MFSK communication system without jammer state information (JSI) in a worst case partial band jamming environment, it is well known that the use of a conventional unquantized metric results in very poor performance. In this paper, a 'normalized' unquantized energy metric is suggested for such a system. It is shown that with this metric, one can save 2-3 dB in required signal energy over the system with hard decision metric without JSI for the same desired performance. When this very robust metric is compared to the conventional unquantized energy metric with JSI, the loss in required signal energy is shown to be small. Thus, the use of this normalized metric provides performance comparable to systems for which JSI is known. Cutoff rate and bit error rate with dual-k coding are used for the performance measures.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Communications (ISSN 0090-6778); COM-33; 869-877
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    Thermal-structural analysis of large space structures - An assessment of recent advances (1985)
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    Publication Date: 2011-08-19
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Spacecraft and Rockets (ISSN 0022-4650); 22; 385-393
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  • 51
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    Postbuckling of long orthotropic plates under combined loading (1985)
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    Publication Date: 2011-08-19
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA Journal (ISSN 0001-1452); 23; 1267-127
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    Generative engineering databases - Toward expert systems (1985)
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    Publication Date: 2011-08-19
    Description: Engineering data management, incorporating concepts of optimization with data representation, is receiving increasing attention as the amount and complexity of information necessary for performing engineering operations increases and the need to coordinate its representation and use increases. Research in this area promises advantages for a wide variety of engineering applications, particularly those which seek to use data in innovative ways in the engineering process. This paper presents a framework for a comprehensive, relational database management system that combines a knowledge base of design constraints with a database of engineering data items in order to achieve a 'generative database' - one which automatically generates new engineering design data according to the design constraints stored in the knowledge base. The representation requires a database that is able to store all of the data normally associated with engineering design and to accurately represent the interactions between constraints and the stored data while guaranteeing its integrity. The representation also requires a knowledge base that is able to store all the constraints imposed upon the engineering design process.
    Keywords: STRUCTURAL MECHANICS
    Type: Computers and Structures (ISSN 0045-7949); 20; 1-3,
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  • 53
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    Double symbol error rates for differential detection of narrow-band FM (1985)
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    Publication Date: 2011-08-19
    Description: This paper evaluates the double symbol error rate (average probability of two consecutive symbol errors) in differentially detected narrow-band FM. Numerical results are presented for the special case of MSK with a Gaussian IF receive filter. It is shown that, not unlike similar results previously obtained for the single error probability of such systems, large inaccuracies in predicted performance can occur when intersymbol interference is ignored.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Communications (ISSN 0090-6778); COM-33; 394-398
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    Postbuckling of long orthotropic plates in combined shear and compression (1985)
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    Publication Date: 2011-08-19
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA Journal (ISSN 0001-1452); 23; 788-794
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    Dual-band reactively loaded microstrip antenna (1985)
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    Publication Date: 2011-08-19
    Description: A previously derived theory is applied to a microstrip antenna with a reactive load to produce a dual-band radiator. A model consisting of a rectangular patch radiator loaded with a variable length short-circuited coaxial stub was investigated experimentally. Comparisons of theoretical predictions and experimental data are made for the impedance and resonant frequencies as a function of the position of the load, the length of the stub, and the characteristic impedance of the stub.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Antennas and Propagation (ISSN 0018-926X); AP-33; 556-561
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    VLBI collimation-tower technique for time-delay studies of a large ground-station communications antenna (1985)
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    Publication Date: 2011-08-19
    Description: A need for an accurate but inexpensive method for measuring and evaluating time delays of large ground antennas for VLBI applications motivated the development of the collimation tower technique. Supporting analytical work which was performed primarily to verify time delay measurement results obtained for a large antenna when the transmitter was at a collimation distance of 1/25 of the usual far field criterion is discussed. Comparisons of theoretical and experimental results are also given.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Antennas and Propagation (ISSN 0018-926X); AP-33; 549-556
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    Development and use of the computer software package for planning the 12 GHz broadcasting-satellite service at RARC '83 (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The 1983 Regional Administrative Radio Conference (RARC '83) had mainly the objective to draw up a plan of detailed frequency assignments and orbital positions for the 12 GHz broadcasting-satellite service (BSS) in ITU Region 2 (the Western Hemisphere) and associated feeder links (earth-to-space) in the 17 GHz band. It was found that for RARC '83 new planning methods and procedures would be needed. The new requirements made it necessary to develop a new generation of planning software. Attention is given to the development of the computer programs to be used at the conference, the package of computer programs, and the use of the computer programs.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Journal on Selected Areas in Communications (ISSN 0733-8716); SAC-3; 36-43
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    Coupled transient response of tiles bonded elastically to a finite flexible plate (1985)
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    Publication Date: 2011-08-19
    Description: Presented are several methods to study a system of tiles bonded elastically to a finite flexible plate responding to an impulse. First, a one-dimensional (1-D) approximation to the system is constructed using Timoshenko beam theory and transfer matrices. This simulates a strip one tile wide. Modal analysis determines the transient response to an impulse of short duration. Also presented are parametric studies of the effect of bond stiffness and the effect of stiffening from inplane stresses produced by large out-of-plane deflections. A two-dimensional (2-D) model is constructed from the eigenfunctions of the 1-D model in a Galerkin method using pairwise products of the 1-D modes as trial functions. Comparison of the two models establishes a factor applied to peak impulse pressure for results to agree.
    Keywords: STRUCTURAL MECHANICS
    Type: Acoustical Society of America, Journal (ISSN 0001-4966); 77; 1027-103
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    Nonlinear analysis of laminated shells including transverse shear strains (1985)
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    Publication Date: 2011-08-19
    Description: Numerical results obtained using a doubly curved, shear deformable shell element are presented for geometrically nonlinear analysis of laminated composite shells. The element is based on an extension of Sanders' shell theory and accounts for the von Karman strains and transverse shear strains. The sample numerical results presented here for the geometrically nonlinear analysis of laminated composite shells should serve as references for future investigations.
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA Journal (ISSN 0001-1452); 23; 440
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    New short constraint length, rate 1/N convolutional codes which minimize the required SNR for given desired bit error rates (1985)
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    Publication Date: 2011-08-19
    Description: It is pointed out that for a convolutional coding system, the Bit Error Rate (BER) at the Viterbi decoder output is upper-bounded by the transfer function bound. A large number of rate 1/N convolutional codes have been reported. The criteria used for determining the quality of a code in code search procedures, however, may not be very suited for cases in which the required BER is in the moderate range. For this reason, it may be best to select the code with the aim to minimize the required SNR for a given disired BER. Partial code searching techniques are presented, and a table listing the code search results is provided.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Communications (ISSN 0090-6778); COM-33; 171-177
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    Vector diffraction analysis of reflector antennas with mesh surfaces (1985)
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    Publication Date: 2011-08-19
    Description: Reflector antennas with mesh surfaces are used extensively in many satellite and ground antenna systems. A strip-aperture modeling of commonly used mesh surfaces is presented which provides considerable versatility in characterizing the mesh cells. The mesh transmission coefficients are constructed using a Floquet-modal expansion in conjuction with two dominant aperture modes. To account for the mesh local coordinates, the Eulerian angle transformation is invoked to obtain the total induced current on the curved reflector surface. General formulas are presented to show how the solid surface induced current is modified due to the transmission through the mesh. The effects of a variety of mesh configurations on both the co-polar and cross-polar patterns of reflector antennas are studied by numerically evaluating the vector diffraction integral using the Jacobi-Bessel expansion. For some special cases, a comparison is made with the results of the commonly used wire-grid formulation. Many of the numerical data are tailored to the dimensions of a conceptually designed mesh deployable offset reflector of the land mobile satellite system (LMSS).
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Antennas and Propagation (ISSN 0018-926X); AP-33; 76-90
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    Lewis' enhanced laboratory for research into the fatigue and constitutive behavior of high temperature materials (1985)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Lewis Research Center's high temperature fatigue laboratory has undergone significant changes resulting in the addition of several new experimental capabilities. New materials testing systems have been installed enabling research to be conducted in multiaxial fatigue and deformation at high temperature, as well as cumulative creep-fatigue damage wherein the relative failure-life levels are widely separated. A key component of the new high-temperature fatigue and structures laboratory is a local, distributed computer system whose hardware and software architecture emphasizes a high degree of configurability, which in turn, enables the researcher to tailor a solution to the problem at hand.
    Keywords: STRUCTURAL MECHANICS
    Type: Turbine Engine Hot Section Technology, 1985; p 361-371
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    Creep-fatigue behavior of NiCoCrAlY coated PWA 1480 (1985)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: This study of high-temperature fatigue and creep-fatigue behavior is part of a program to identify the basic features of the effects of temperature, creep, fatigue, and environment on the behavior of a single crystal superalloy, a bulk coating alloy, and a coated alloy system. A system was selected which has had considerable production experience: the Ni-base superalloy, PWA 1480, and the NiCoCrAlY coating, PWA 276. Isothermal behavior was studied first. A series of fatigue and creep fatigue tests of the types commonly designated as pp, cp, pc and cc were conducted. These tests were conducted at various constant total strain ranges. The creep-fatigue cycles employed constant stress dwells at the maximum and/or minimum load. Test results are given.
    Keywords: STRUCTURAL MECHANICS
    Type: Turbine Engine Hot Section Technology, 1985; p 351-360
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    High temperature stress-strain analysis (1985)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: The objectives of the high temperature structures program are threefold: to assist in the development of analytical tools needed to improve design analysis and procedures for the efficient and accurate prediction of the nonlinear structural response of hot-section components; to aid in the calibration, validation, and evaluation of the analytical tools by comparing predictions with experimental data; and to evaluate existing as well as advanced temperature and strain measurement instrumentation.
    Keywords: STRUCTURAL MECHANICS
    Type: Turbine Engine Hot Section Technology, 1985; p 287-301
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    Planning, creating and documenting a NASTRAN finite element model of a modern helicopter (1985)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Mathematical models based on the finite element method of structural analysis as embodied in the NASTRAN computer code are widely used by the helicopter industry to calculate static internal loads and vibration of airframe structure. The internal loads are routinely used for sizing structural members. The vibration predictions are not yet relied on during design. NASA's Langley Research Center sponsored a program to conduct an application of the finite element method with emphasis on predicting structural vibration. The Army/Boeing CH-47D helicopter was used as the modeling subject. The objective was to engender the needed trust in vibration predictions using these models and establish a body of modeling guides which would enable confident future prediction of airframe vibration as part of the regular design process.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Ames Research Center Rotorcraft Dynamics 1984; p 307-324
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    Nonlinear analysis of an axisymmetric structure subjected to non-axisymmetric loading (1985)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The development of the SHELPC finite element computer program is detailed. This program is specialized to simulate the nonlinear material behavior which results from combustor liner hot streaks. This problem produces a nonlinear Fourier Series type loading on an axisymmetric structure. Example cases are presented.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Lewis Research Center Nonlinear Constitutive Relations for High Temp. Appl., 1984; p 311-327
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    Effects of bearing deadbands on bearing loads and rotor stability (1985)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The Jeffcott model of a turbopump which was modified by adding deadband (clearance) effects along with fluid seal forces are currently understood. Equations of motion for the model were written in polar coordinates, and a constant side force was added to the model to account for the likely misalignment between bearings and seals. The force models and system equations of motion are described as well as limit cycle, and stability analyses. Studies of systems with rotor imbalance and with or without side effects were studied for three types of motion. Results show that: (1) deadband does not affect stability-in-the-large; (2) stability-in-the small is enhanced by deadband and side force; (3) bearings loads are highest for motion with synchronous or nonsynchronous periodic enclosing origin; (4) side force acting in concert with deadband effects may either increase or decrease bearing loads; and (5) bearing loads in a stable pump are determined primarily by rotor imbalance and side forces.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Marshall Space Flight Center Advan. High Pressure O2(H2 Technol.; p 345-365
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    Technical overview structural dynamics (1985)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Structural dynamics technology development in support of SSME was initiated in November 1980. The objective identified was to develop improved understanding of the operating dynamic characteristics of high-performance liquid rocket systems in order to: increase lifetime and performance; decrease weight; identify incipient failures; meet deflection requirements; decrease costs; predict effect of imposed changes; and determine changes to meet specified requirements. A series of tasks was identified and work was started on the most urgent tasks. In 1983, the program was made into a joint program with NASA-Lewis Research Center.
    Keywords: STRUCTURAL MECHANICS
    Type: Advan. High Pressure O2(H2 Technol.; p 261
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    Nastran's Application in Agricultural Engineering (1985)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Finite element analysis has been recognized as a valuable solution method by agricultural engineers. NASTRAN has been obtained by the Agricultural Engineering Department at the University of Georgia. The NASTRAN Thermal Analyzer has been used in the teaching program for an undergraduate course in heat transfer and will be used for a new graduate course in finite element analysis. The NASTRAN Thermal Analyzer has also been applied to several research problems in the Agricultural Engineering Department.
    Keywords: STRUCTURAL MECHANICS
    Type: COSMIC 13th NASTRAN (R) Users' Colloq.; p 273-288
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    An Elastic Analysis of a Plated Bone to Determine Fracture Gap Motion (1985)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: An elastic analysis to determine fracture gap motions occurring in the osteotomized and plated canine femur was performed using the finite element program NASTRAN. The femur was idealized as a hollow right cylinder, and transverse anisotropy was assumed for the elastic properties of the bone. A 3-D 360 degree model consisting of 224 isoparametric quadrilateral hexahedral and 11 beam elements was created. A range of plate stiffnesses was tested by varying the modulus of elasticity of the plate from 207 GPa to 1 GPA. Moments were applied in the plane of the plate, about the axis of the plate, and in the plane of the screws. Results showed that, for plates of typical geometry and elastic modulus under 10 GPa, the contribution to fracture gap motion occurring due to deformation in the bone was negligible compared to that contribution from deformation in the plate.
    Keywords: STRUCTURAL MECHANICS
    Type: COSMIC 13th NASTRAN (R) Users' Colloq.; p 308-319
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    Direct Transient Analysis of a Fuze Assembly by Axisymmetric Solid Elements (1985)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: A fuze assembly, which consists of three major parts, nose, collar and sleeve, was designed to survive severe transverse impact giving a maximum base acceleration of 20.000 G. It is shown that hoop failure occurred in the collar after the impact. They also showed that by bonding the collar to the nose, the collar was able to survive the same impact. To find out the effectiveness of the bonding quantitatively, axisymmetric solid elements TRAPAX and TRIAAX were used in modelling the fuze and direct transient analysis was performed. The dynamic stresses in selected elements on the bonded and unbonded collars were compared. The peak hoop stresses in the unbonded collar were found to be up to three times higher than those in the bonded collar. The NASTRAN results explained the observed hoop failure in the unbonded collar. In addition, static and eigenvalue runs were performed as checks on the models prior to the transient runs. The use of the MPCAX cards and the existence and contributors of the calculated first several nearly identical natural frequencies are addressed.
    Keywords: STRUCTURAL MECHANICS
    Type: COSMIC 13th NASTRAN (R) Users' Colloq.; p 431-452
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    Experience with Free Bodies (1985)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Some of the problems that confront an analyst in free body modeling, to satisfy rigid body conditions are discussed and with some remedies for these problems are presented. The problems of detecting these culprits at various levels within the analysis are examined. A new method within NASTRAN for checking the model for defects very early in the analysis without requiring the analyst to bear the expense of an eigenvalue analysis before discovering these defects is outlined.
    Keywords: STRUCTURAL MECHANICS
    Type: COSMIC 13th NASTRAN (R) Users' Colloq.; p 378-388
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  • 73
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    Nondestructive ultrasonic measurement of bolt preload using the pulsed-phase locked-loop interferometer (1985)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Achieving accurate preload in threaded fasteners is an important and often critical problem which is encountered in nearly all sectors of government and industry. Conventional tensioning methods which rely on torque carry with them the disadvantage of requiring constant friction in the fastener in order to accurately correlate torque to preload. Since most of the applied torque typically overcomes friction rather than tensioning the fastener, small variations in friction can cause large variations in preload. An instrument called a pulsed phase locked loop interferometer, which was recently developed at NASA Langley, has found widespread use for measurement of stress as well as material properties. When used to measure bolt preload, this system detects changes in the fastener length and sound velocity which are independent of friction. The system is therefore capable of accurately establishing the correct change in bolt tension. This high resolution instrument has been used for precision measurement of preload in critical fasteners for numerous applications such as the space shuttle landing gear and helicopter main rotors.
    Keywords: STRUCTURAL MECHANICS
    Type: Welding, Bonding and Fastening, 1984; p 197-209
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    The design and development of a spacecraft appendage tie down mechanism (1985)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The design and evolution is described of a spacecraft Appendage Tie Down Mechanism (ATDM). Particular emphasis is paid to the mechanical aspects of using dry lubricants to increase the efficiency of acme threads and worm gearing. The ATDM consists of five major components. These are a dc torque motor, a worm gear speed reducer, the tension bolt (or T-bolt), nut capture and centering jaws and the capture nut. In addition, there are several minor components such as limit switch assemblies and an antibackdrive mechanism which couples the drive motor to the worm shaft. A development model of the ATDM in various configurations was under test for some time. In its latest version, it has successfully completed thermal vacuum testing, vibration testing, and extended life testing.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Ames Research Center 19th Aerospace Mech. Symp.; p 167-177
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    The properties of thin-section, four-point-contact ball bearings in space (1985)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Thin section, four-point-contact ball bearings are increasinly employed in spacecraft mechanisms because of the potential advantages they offer. However, litte was previously known of their torque, thermal conductance and stiffness properties at conditions anticipated for their use in space. An investigation of these properties are described. It was found that frictional (Coulomb) torque, thermal conductance and stiffness all show marked dependence on the bearing preload, the housing design, the bearing external fit (i.e., free fit or interference) and on the thermal gradient across the races. Optimum bearing performance is achieved only if these properties are well understood. The necessary data to understand these properties are provided.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Ames Research Center 19th Aerospace Mech. Symp.; p 141-166
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    Application of traction drives as servo mechanisms (1985)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The suitability of traction drives for a wide class of aerospace control mechanisms is examined. Potential applications include antenna or solar array drive positioners, robotic joints, control moment gyro (CMG) actuators and propeller pitch change mechanisms. In these and similar applications the zero backlash, high torsional stiffness, low hysteresis and torque ripple characteristics of traction drives are of particular interest, as is the ability to run without liquid lubrication in certain cases. Wear and fatigue considerations for wet and dry operation are examined along with the tribological performance of several promising self lubricating polymers for traction contracts. The speed regulation capabilities of variable ratio traction drives are reviewed. A torsional stiffness analysis described suggests that traction contacts are relatively stiff compared to gears and are significantly stiffer than the other structural elements in the prototype CMG traction drive analyzed. Discussion is also given of an advanced turboprop propeller pitch change mechanism that incorporates a traction drive.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Ames Research Center 19th Aerospace Mech. Symp.; p 119-139
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    The design and development of a constant-speed solar array drive (1985)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The design and development of a constant-speed solar array drive system for use in high power communications satellites is described. The relationship between continuity of motion in the solar array drive and spacecraft attitude disturbance is investigated. The selection of the system design based on the design requirements including spacecraft disturbance is discussed. The system comprises two main parts: the drive mechanism including small angle stepper motor and reduction gearing and the control electronics including ministepping drive circuits, such that a very small output step size is achieved. Factors contributing to discontinuities in motion are identified and discussed. Test methods for measurement of very small amplitudes of discontinuity at low rotational rates are described to assist in the testing of similar mechanisms.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Ames Research Center 19th Aerospace Mech. Symp.; p 103-118
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    Design and development of a linear thermal actuator (1985)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The design and development of a linear thermal actuator (LTA) for space applications is described. The actuator is driven by thermal energy and utilizes the property of thermal expansion to do work. Equations to predict performance are developed and used to optimize the design of the development model LTA. Design details and test results are presented and discussed.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Ames Research Center 19th Aerospace Mech. Symp.; p 87-102
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    Drag-compensated, precision-powered hinge system (1985)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The design of a high precision powered hinge is complicated by the unavoidable presence of parasitic drag torque resulting mainly from friction and transfer of power, signals, and fluids across the hinge. Regardless of the type of drive system selected, it is impossible to completely eliminate all parasitic drag. However, the mechanism described here comes very close to providing a drag free system. All sources of parasitic drag torque are collected on a shaft which is powered by an electric motor independent of the main hinge drive. Under control of a sensor, the electric motor applies a compensating torque equal to that of the parasitic drag torque, allowing the main hinge drive to operate in a practically drag free environment with very high positioning precision.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Ames Research Center 19th Aerospace Mech. Symp.; p 75-86
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    A modular docking mechanism for in-orbit assembly and spacecraft servicing (1985)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: A Docking Mechanism concept is described which is suitable for use with autonomous docking systems. The central feature of using simple cylindrical handles on one side and a type of prism seating on the other is offered as a practical method of achieving a standardized structural interface without freezing continued development of the latches, either technically or commercially. The main emphasis in docking mechanism concepts is in two directions: (1) a very simple docking mechanism, involving mainly the latch mechanism to achieve a structural link; and (2) a sophisticated Docking Mechanism, where the latch mechanism is designed for nonrigid spacecraft and the achievement of very low dynamic interactions between spacecraft during the docking process.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Ames Research Center 19th Aerospace Mech. Symp.; p 59-74
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    Development of an energy-absorbing passenger seat for a transport aircraft (1985)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Commercial air transport passenger safety and survivability, in the event of an impact-survivable crash, are subjects receiving increased technical focus/study by the aviation community. A B-720 aircraft, highly instrumented, and remotely controlled from the ground by a pilot in a simulated cockpit, was crashed on a specially prepared gravel covered impact site. The aircraft was impacted under controlled conditions in an air-to-ground gear-up mode, at a nominal speed of 150 knots and 4-1/2 deg glide slope. Data from a number of on board, crash worthiness experiments provided valuable information related to structural loads/failure modes, antimisting kerosene fuel, passenger and attendant restraint systems and energy absorbing seats. The development of an energy absorbing (EA) seat accomplished through innovative modification of a typical modern standard commercial aviation transport, three passenger seat is described.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Ames Research Center 19th Aerospace Mech. Symp.; p 39-58
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    The Galeleo spacecraft magnetometer boom (1985)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The Galileo spacecraft utilizes a deployable lattice boom to position three science instruments at remote distances from the spacecraft body. An improved structure and mechanism to precisely control deployment of the boom, and the unique deployment of an outer protective cover are described.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Ames Research Center 19th Aerospace Mech. Symp.; p 1-22
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    Hoop/column antenna deployment mechanism overview (1985)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The hoop/column antenna program is directed toward the development of a cost effective, large area, self deploying reflector antenna system. Large surface area antenna systems are required in future space missions involving improved land communications, Earth resources observation, and the study of intergalactic energy sources. The hoop/column antenna is a concept where a large antenna system can be packaged within the Space Transportation System (Shuttle) payload bay, launched into Earth orbit where it is released either for deployment as an Earth observation or communications antenna, or boosted into deep space as an intergalactic energy probe. Various mechanisms and support structures are described that are required to deploy the hoop, which is used to support the antenna reflective surface, and the column that is used to position the antenna feeds and the reflector. It also describes a proof-of-concept model (15 meters in diameter) that is currently being ground tested to determine the adequacy of the deployment mechanisms.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Ames Research Center 19th Aerospace Mech. Symp.; p 23-37
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    New Enhancements in April 85 NASTRAN Release (1985)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Several features were added to COSMIC NASTRAN, along with some enhancements to improve or update existing capabilities. Most of these additions and enhancements were provided by industry users to be incorporated into NASTRAN for wider use. DIAG 48 provides a synopsis of significant developments in past NASTRAN releases (1983-1985) and indexes all diagnostic output messages and operation requests (DOMOR). Other features include: volume and surface computation of the 2-D and 3-D elements, NOLIN5 input and; NASTRAN PLOTOPT-N (where N = 2, 3, 4, or 5); shrink element plots; and output scan. A nonprint option on stress and force output request cards was added. Automated find and nofind options on the plot card, fully stressed design, high level plate elements, eigenvalue messages, and upgrading of all FORTRAN source code to the ANSI standard are enhancements made.
    Keywords: STRUCTURAL MECHANICS
    Type: COSMIC 13th NASTRAN (R) Users' Colloq.; p 1-30
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    Discharge pulse phenomenology (1985)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: A model was developed which places radiation induced discharge pulse results into a unified conceptual framework. Only two phenomena are required to interpret all space and laboratory results: (1) radiation produces large electrostatic fields inside insulators via the trapping of a net space charge density; and (2) the electrostatic fields initiate discharge streamer plasmas similar to those investigated in high voltage electrical insulation materials; these streamer plasmas generate the pulsing phenomena. The apparent variability and diversity of results seen is an inherent feature of the plasma streamer mechanism acting in the electric fields which is created by irradiation of the dielectrics. The implications of the model are extensive and lead to constraints over what can be done about spacecraft pulsing.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA. Lewis Research Center Spacecraft Environ. Interactions Technol., 1983; p 483-509
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    Characteristics of EMI generated by negative metal-positive dielectric voltage stresses due to spacecraft charging (1985)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Charging of spacecraft surfaces by the environmental plasma can result in differential potentials between metallic structure and adjacent dielectric surfaces in which the relative polarity of the voltage stress is either negative dielectric/positive metal or negative metal/positive dielectric. Negative metal/positive dielectric is a stress condition that may arise if relatively large areas of spacecraft surface metals are shadowed from solar UV and/or if the UV intensity is reduced as in the situation in which the spacecraft is entering into or leaving eclipse. The results of experimental studies of negative metal/positive dielectric systems are given. Information is given on: enhanced electron emission I-V curves; e(3) corona noise vs e(3) steady-state current; the localized nature of e(3) and negative metal arc discharge currents; negative metal arc discharges at stress thresholds below 1 kilovolt; negative metal arc discharge characteristics; dependence of blowoff arc discharge current on spacecraft capacitance to space (linear dimension); and damage to second surface mirrors due to negative metal arcs.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA. Lewis Research Center Spacecraft Environ. Interactions Technol., 1983; p 437-452
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    Reliability of structural brittle materials (1985)
    In:  Other Sources
    Details
    Publication Date: 2016-06-07
    Description: Traditionally, the use of brittle materials has been avoided in demanding structural applications because of their unreliability. They have been used however, due to other desirable properties, in nonstructural applications or where the mechanical load is minimal. The most common method utilized today for the design approach of brittle materials is the probabilistic, which takes into consideration the flaw and stress distribution within the brittle material. It does not take into consideration the fracture mechanics effect of strength degradation while aging under a mechanical load. This project will combine the two methods, probabilistic and fracture mechanics, into a more reliable design method for brittle materials.
    Keywords: STRUCTURAL MECHANICS
    Type: Alabama Univ. Res. Rept.: 1984 NASA/ASEE Summer Faculty Fellowship Program (NASA-CR; 18p
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    Novel applications of the NASA/GSFC Viterbi decoder hardware simulator (1985)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The NASA/GSFC developed an all digital, real time, programmable Viterbi decoder simulator operating at rates up to 6 Msps. With this simulator, the bit error rate (BER) performance of convolutionally encoded/Viterbi decoded Shuttle-TDRSS return link channels under pulsed radio frequency interference (RFI) conditions has been predicted. The principles of the simulator are described with special emphasis on the channel simulator and the essential interaction between CLASS software and the simulator. The sensitivity of coded BER as function of several illustrative RFI parameters is discussed for two typical Shuttle-TDRSS return link configurations.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA. Johnson Space Center Space Shuttle Tech. Conf., Pt. 2; p 821-830
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  • 89
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    Electronics systems test laboratory testing of shuttle communications systems (1985)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Shuttle communications and tracking systems space to space and space to ground compatibility and performance evaluations are conducted in the NASA Johnson Space Center Electronics Systems Test Laboratory (ESTL). This evaluation is accomplished through systems verification/certification tests using orbiter communications hardware in conjunction with other shuttle communications and tracking external elements to evaluate end to end system compatibility and to verify/certify that overall system performance meets program requirements before manned flight usage. In this role, the ESTL serves as a multielement major ground test facility. The ESTL capability and program concept are discussed. The system test philosophy for the complex communications channels is described in terms of the major phases. Results of space to space and space to ground systems tests are presented. Several examples of the ESTL's unique capabilities to locate and help resolve potential problems are discussed in detail.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Space Shuttle Tech. Conf., Pt. 2; p 831-849
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  • 90
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    The Communications link analysis and simulation system (CLASS) (1985)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The Communications Link Analysis and Simulation System (CLASS) is a comprehensive, computerized communications and tracking system analysis tool under development by the Networks Directorate of the NASA/GSFC. The primary use of this system is to provide the capability to predict the performance of the Tracking and Data Relay Satellite system (TDRSS) User Communications and Tracking links through the TDRSS. The general capabilities and operational philosophy of the current and final versions of the CLASS are described along with some examples of analyses which have been performed utilizing the capabilities of this system.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA. Johnson Space Center Space Shuttle Tech. Conf., Pt. 2; p 787-797
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  • 91
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    Shuttle payload S-band communications system (1985)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The Shuttle payload S-band communications system design, operational capabilities, and performance are described in detail. System design requirements, overall system and configuration and operation, and laboratory/flight test results are presented. Payload communications requirements development is discussed in terms of evolvement of requirements as well as the resulting technical challenges encountered in meeting the initial requirements. Initial design approaches are described along with cost-saving initiatives that subsequently had to be made. The resulting system implementation that was finally adopted is presented along with a functional description of the system operation. A description of system test results, problems encountered, how the problems were solved, and the system flight experience to date is presented. Finally, a summary of the advancements made and the lessons learned is discussed.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Space Shuttle Tech. Conf., Pt. 2; p 767-776
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  • 92
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    TDRSS S-shuttle unique receiver equipment (1985)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Beginning with STS-9, the Tracking and Date Relay Satellite system (TDRSS) will start providing S- and Ku-band communications and tracking support to the Space Shuttle and its payloads. The most significant element of this support takes place at the TDRSS White Sands Ground Terminal, which processes the Shuttle return link S- and Ku-band signals. While Ku-band hardware available to other TDRSS users is also applied to Ku-Shuttle, stringent S-Shuttle link margins have precluded the application of the standard TDRSS S-band processing equipment to S-Shuttle. It was therfore found necessary to develop a unique S-Shuttle Receiver that embodies state-of-the-art digital technology and processing techniques. This receiver, developed by Motorola, Inc., enhances link margins by 1.5 dB relative to the standard S-band equipment and its bit error rate performance is within a few tenths of a dB of theory. An overview description of the Space Shuttle Receiver Equipment (SSRE) is presented which includes the presentation of block diagrams and salient design features. Selected, measured performance results are also presented.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA. Johnson Space Center Space Shuttle Tech. Conf., Pt. 2; p 777-786
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    Shuttle ku-band communications/radar technical concepts (1985)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Technical data on the Shuttle Orbiter K sub u-band communications/radar system are presented. The more challenging aspects of the system design and development are emphasized. The technical problems encountered and the advancements made in solving them are discussed. The radar functions are presented first. Requirements and design/implementation approaches are discussed. Advanced features are explained, including Doppler measurement, frequency diversity, multiple pulse repetition frequencies and pulse widths, and multiple modes. The communications functions that are presented include advances made because of the requirements for multiple communications modes. Spread spectrum, quadrature phase shift keying (QPSK), variable bit rates, and other advanced techniques are discussed. Performance results and conclusions reached are outlined.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Space Shuttle Tech. Conf., Pt. 2; p 757-766
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    Shuttle S-band communications technical concepts (1985)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Using the S-band communications system, shuttle orbiter can communicate directly with the Earth via the Ground Spaceflight Tracking and Data Network (GSTDN) or via the Tracking and Data Relay Satellite System (TDRSS). The S-band frequencies provide the primary links for direct Earth and TDRSS communications during all launch and entry/landing phases of shuttle missions. On orbit, S-band links are used when TDRSS Ku-band is not available, when conditions require orbiter attitudes unfavorable to Ku-band communications, or when the payload bay doors are closed. the S-band communications functional requirements, the orbiter hardware configuration, and the NASA S-band communications network are described. The requirements and implementation concepts which resulted in techniques for shuttle S-band hardware development discussed include: (1) digital voice delta modulation; (2) convolutional coding/Viterbi decoding; (3) critical modulation index for phase modulation using a Costas loop (phase-shift keying) receiver; (4) optimum digital data modulation parameters for continuous-wave frequency modulation; (5) intermodulation effects of subcarrier ranging and time-division multiplexing data channels; (6) radiofrequency coverage; and (7) despreading techniques under poor signal-to-noise conditions. Channel performance is reviewed.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Space Shuttle Tech. Conf., Pt. 2; p 720-756
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    On numerical integration and computer implementation of viscoplastic models (1985)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Due to the stringent design requirement for aerospace or nuclear structural components, considerable research interests have been generated on the development of constitutive models for representing the inelastic behavior of metals at elevated temperatures. In particular, a class of unified theories (or viscoplastic constitutive models) have been proposed to simulate material responses such as cyclic plasticity, rate sensitivity, creep deformations, strain hardening or softening, etc. This approach differs from the conventional creep and plasticity theory in that both the creep and plastic deformations are treated as unified time-dependent quantities. Although most of viscoplastic models give better material behavior representation, the associated constitutive differential equations have stiff regimes which present numerical difficulties in time-dependent analysis. In this connection, appropriate solution algorithm must be developed for viscoplastic analysis via finite element method.
    Keywords: STRUCTURAL MECHANICS
    Type: Nonlinear Constitutive Relations for High Temp. Appl., 1984; p 187-200
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    A comparison of two contemporary creep-fatigue life prediction methods (1985)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: A comparison of two contemporary approaches to creep fatigue life prediction, the Continuous Damage Mechanics as developed at ONERA, and Strain Range Partitioning, is presented. The general framework of each of these approaches, both being crack initiation life prediction tools, are examined. The basis for, and implications of each predictive method are discussed, relative to the material class(es) for which each was developed, as well as to their general applicability. Evident is a need for critical experiments capable of discriminating among the models; to this end, the question of choice of experiment and material is addressed.
    Keywords: STRUCTURAL MECHANICS
    Type: Nonlinear Constitutive Relations for High Temp. Appl., 1984; p 125
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    Finite element modeling of cracked bodies using the Bodner-Partom flow law (1985)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: The Bodner-Partom flow law which models viscoplastic material behavior has been used to represent two nickel-base superalloys, Gatorized IN100 and Inconel 718 at elevated temperature. Procedures for the determination of the material parameters are presented along with a discussion of the physical significance of each parameter. The material model is then used in finite element computations to evaluate the response of cracked bodies to monotonic, sustained, or cyclic loading. Geometries investigated include the center cracked panel, the compact tension specimen, and the single cracked ring under tension. A Hybrid Experimental Numerical (HEN) procedure has been used to deduce crack growth rates from experimental displacement measurements which are input into finite element computations. The results of several studies conducted over the last several years are summarized.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Lewis Research Center Nonlinear Constitutive Relations for High Temp. Appl., 1984; p 283-296
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  • 98
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    Multiaxial fatigue low cycle fatigue testing (1985)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: Multiaxial testing methods are reviewed. Advantages and disadvantages of each type test is discussed. Significant multiaxial data available in the literature is analyzed. The yield theories are compared for multiaxial fatigue analysis.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Lewis Research Center Nonlinear Constitutive Relations for High Temp. Appl., 1984; p 221-236
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  • 99
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    Thermomechanically induced pre- and postbuckling of general structure (1985)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: An algorithmic solution strategy which enables handling the positive/indefinite stiffness characteristics associated with the pre and postbuckling of structures subject to complex thermomechanical loading fields was developed. The flexibility of the procedure is such that it can be applied to both finite difference and element type simulations. Due to the generality of the algorithmic approach developed, both kinematic and thermal/mechanical type material nonlinearity including inelastic effects can be treated. This includes the possibility of handling completely general thermomechanical boundary conditions. To demonstrate the scheme, the results of several benchmark problems are presented.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Lewis Research Center Nonlinear Constitutive Relations for High Temp. Appl., 1984; p 153-167
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    Symmetric Composite Laminate Stress Analysis (1985)
    In:  CASI
    Details
    Publication Date: 2016-06-07
    Description: It is demonstrated that COSMIC/NASTRAN may be used to analyze plate and shell structures made of symmetric composite laminates. Although general composite laminates cannot be analyzed using NASTRAN, the theoretical development presented herein indicates that the integrated constitutive laws of a symmetric composite laminate resemble those of a homogeneous anisotropic plate, which can be analyzed using NASTRAN. A detailed analysis procedure is presented, as well as an illustrative example.
    Keywords: STRUCTURAL MECHANICS
    Type: COSMIC 13th NASTRAN (R) Users' Colloq.; p 234-244
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