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  • Other Sources  (529)
  • STRUCTURAL MECHANICS  (277)
  • COMMUNICATIONS AND RADAR  (252)
  • 1980-1984  (529)
  • 1950-1954
  • 1983  (529)
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  • 1
    Publication Date: 2011-08-19
    Description: A constitutive theory is presented for representing the anisotropic viscoplastic behavior of high-temperature alloys that possess directional properties resulting from controlled grain growth or solidification. The theory is an extension of a viscoplastic model that has been applied in structural analyses involving isotropic metals. Anisotropy is introduced through the definition of a vector field that identifies a preferential (solidification) direction at each material point. Following the development of a full multiaxial theory, application is made to homogeneously stressed elements in pure shear and to a uniaxially stressed rectangular block in plane stress with the stress direction oriented at an arbitrary angle with the material direction. It is shown that an additional material parameter introduced to characterize the degree of anisotropy can be determined on the basis of simple creep tests.
    Keywords: STRUCTURAL MECHANICS
    Type: Nuclear Engineering and Design (ISSN 0029-5493); 83; 389-396
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  • 2
    Publication Date: 2011-08-18
    Description: Link margin estimates are calculated for 30/20 GHz satellite communication systems employing closely-spaced (4 to 100 km) 'dual diversity' switched ground sites. The link margin estimates are based on a new analysis in which the bivariate rain attenuation density function for two correlated ground sites is modelled by an exponential density function. The results of the exponential density function analysis enable derivation of a direct relation between rain margin estimates and probability of exceedance (link availability). Margins typically in the range 2 to 12 dB are calculated for various ground site separations and summarized for seven city locations and five satellite orbit positions over the U.S. The results can be easily extended to other EHF satellite frequencies and other locations.
    Keywords: COMMUNICATIONS AND RADAR
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  • 3
    Publication Date: 2011-08-18
    Description: It is shown that, for convolutionally coded transmission over bandwidth-constrained channels, a mere reversal of the switching direction at the encoder output produces a change in the system bit error probability performance. This change is significant when the Viterbi demodulator/decoder is matched to the total channel memory and is more significant for linear channels than for nonlinear ones. The reversal of switching direction is a simple demonstration of the fact that the well-known optimum codes for the linear AGWN channel are no longer necessarily optimum for a bandwidth-constrained channel with or without the addition of channel nonlinearity. It is concluded that potentially significant performance improvement can be obtained by matching the encoder (through the appropriate choice of tap weights and modulo-2 summers) to the channel in addition to matching the demodulator/decoder to the channel for a given encoder.
    Keywords: COMMUNICATIONS AND RADAR
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  • 4
    Publication Date: 2011-08-18
    Description: The force input mobility of an infinite elastic circular cylindrical shell filled with fluid is derived by using the spectral equations of motion. Mobilities are evaluated and their physical interpretations are discussed for a steel shell of thickness h/a = 0.05 filled with water and vibrating in the n = 0, 1 and 2 circumferential modes. The results are subsequently used to analyze the related situations of wave transmission through a radial ring constraint and the far field vibrational energy distributions between the contained fluid and the shell wall for line and point driving forces.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Sound and Vibration (ISSN 0022-460X); 87; 409-427
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  • 5
    Publication Date: 2011-08-18
    Description: The boundary collocation method was used to generate Mode 1 stress intensity and crack mouth opening displacement coefficients for externally radially cracked ring segments subjected to three point radial loading. Numerical results were obtained for ring segment outer-to-inner radius ratios (R sub o/R sub i) ranging from 1.10 to 2.50 and crack length to segment width ratios (a/W) ranging from 0.1 to 0.8. Stress intensity and crack mouth displacement coefficients were found to depend on the ratios R sub o/R sub i and a/W as well as the included angle between the directions of the reaction forces. Previously announced in STAR as N83-35413
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Testing and Evaluation (ISSN 0090-3973); 11; 357-359
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  • 6
    Publication Date: 2011-08-18
    Description: The error probability performance of differential detection of narrow-band FM is determined and compared with the analogous results for limiter-discriminator detection of the same modulation. It is shown that over a large class of benign and hostile environments, e.g., Gaussian IF filter, AWGN, partial-band noise jamming, the differential detector offers no theoretical performance advantage over the limiter-discriminator receiver with integrate-and-dump postdetection filtering.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Communications (ISSN 0090-6778); COM-31; 1227-123
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  • 7
    Publication Date: 2011-08-18
    Description: Two methods for identifying the mass, damping and stiffness matrices of a linear vibrating system are presented. Both methods require the measurement of acceleration, velocity and displacement at various locations of the system. In the first method, the response of the system subjected to known forces is used while the second method employs the free vibration data. The unknown parameters are recovered through the standard least squares procedure. Numerical results are presented for several examples.
    Keywords: STRUCTURAL MECHANICS
    Type: JPL Proc. of the Workshop on Appl. of Distributed System Theory to the Control of Large Space Struct.; p 511-520
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  • 8
    Publication Date: 2011-08-18
    Description: A general approach to the optimal control of large space antennas based on their RF/structural characteristics is described. The approach consists of defining a cost functional based on the degradation of the RF performance of the antenna and using the structural model as the dynamic system. The method is applied to the design of an optimal controller for a 55-m, wrap-rib offset-fed antenna. The controller's goal is to minimize the variations of the peak electric field of the antenna due to feed displacements.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Proc. of the Workshop on Appl. of Distributed System Theory to the Control of Large Space Struct.; p 181-194
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  • 9
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    Publication Date: 2011-08-18
    Description: The problem of potential instability caused by actuator dynamics is examined. Two ways of overcoming it are discussed: rate feedback with compensation and position feedback with tuning filters.
    Keywords: STRUCTURAL MECHANICS
    Type: JPL Proc. of the Workshop on Appl. of Distributed System Theory to the Control of Large Space Struct.; p 119-142
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  • 10
    Publication Date: 2011-08-18
    Description: (Previously announced in STAR as N82-24501)
    Keywords: STRUCTURAL MECHANICS
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  • 11
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    Publication Date: 2011-08-18
    Description: A functional description of the GCF and its relationships with other elements of the DSN and NASCOM is presented together with development objectives and goals and comments on implementation activites in support of flight projects.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommun. and Data Acquisition Rept.; p 200-209
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  • 12
    Publication Date: 2011-08-18
    Description: The operational mobile VLBI data acquisition system (MV-3) requires that a voice link be established between the mobile data system and a fixed site. A communications subsystem was incorporated in the MV-3 design which consists of HF radio, VHF mobile radio telephone and conventional land line telephone. The HF antenna design was optimized for short and long range transmission using both inverted V and yagi antennas mounted on a self-supporting telescoping mast.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommun. and Data Acquisition Rept.; p 210-219
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  • 13
    Publication Date: 2011-08-18
    Description: Measurements of the S-band performance of the DSS 13 26-meter antenna, equipped with the second generation S-X common aperture feed, are reported. Aperture efficiency and overall antenna gain results are compared with predicted values. The elevation dependence of the aperture efficiency is reported.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommun. and Data Acquisition Rept.; p 89-94
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  • 14
    Publication Date: 2011-08-18
    Description: Antenna arraying is a crucial Deep Space Network technique in maximizing the science return of planetary and comet encounters. The equations which describe the total figure of merit for a multiple system of arrayed antennas are developed. An example is given for three Canberra DSN antennas and the Parkes 64-m antenna to be arrayed for the Voyager 2 Uranus flyby.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommun. and Data Acquisition Rept.; p 83-88
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  • 15
    Publication Date: 2011-08-18
    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: The Telecommun. and Data Acquisition Rept.; p 20-29
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  • 16
    Publication Date: 2011-08-18
    Description: A class of receivers called conditionally nulling receivers is defined for quantum noise limited optical communications. These receivers have the ability to decide at each moment in time whether or not to coherently combine a predetermined local oscillator field with the received optical field, prior to performing an energy measurement (photodetection) on the combined field. Conditionally nulling receivers are applicable to pulse position modulation and related modulation schemes, which have the property that, at each moment in time, the transmitted signal is in one of only two states, on or off. The local oscillator field which may or may not be added by the receiver is an exact replica of the negative of the received on field; hence, the receiver can exactly null the on signal if the on signal is present and the receiver chooses to use the local field. An ideal conditionally nulling receiver achieves very nearly the same error probability (within a multiplicative factor varying froom 1 to 2.15) as the optimum quantum measurement for quantum noise limited detection of M-ary PPM signals. In contrast, other known receiving methods, such as direct, heterodyne, and homodyne detection, are exponentially suboptimum.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommun. and Data Acquisition Rept.; p 30-42
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  • 17
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    Publication Date: 2011-08-18
    Description: Problems encountered by aerospace designers in attempting to optimize whole aircraft are discussed, along with possible solutions. Large scale optimization, as opposed to component-by-component optimization, is hindered by computational costs, software inflexibility, concentration on a single, rather than trade-off, design methodology and the incompatibility of large-scale optimization with single program, single computer methods. The software problem can be approached by placing the full analysis outside of the optimization loop. Full analysis is then performed only periodically. Problem-dependent software can be removed from the generic code using a systems programming technique, and then embody the definitions of design variables, objective function and design constraints. Trade-off algorithms can be used at the design points to obtain quantitative answers. Finally, decomposing the large-scale problem into independent subproblems allows systematic optimization of the problems by an organization of people and machines.
    Keywords: STRUCTURAL MECHANICS
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  • 18
    Publication Date: 2011-08-18
    Description: A set of standard formatting rules for the data sets, and a standard computer-readable language with which to describe the data, are two tools which are used to create the Standard Format Data Unit (SFDU). The NASA/JPL proposal for creation and utilization of SFDUs is presented, and its relationship to recommendations from the Consultative Committee for Space Data Systems (CCSDS) is discussed. Several current and planned implementations of the SFDU concept among major space flight projects are identified. The purpose of creating the concept of an SFDU is to allow members of the science community to share national and global resource data independently of project or program. The feedback from SFDU implementation efforts is considered an essential part of the CCSDS activity. Even though the CCSDS specifically deals with space data systems, the SFDU concept can be applied to practically every data system on an open network. The SFDU is in the early phase of CCSDS standard definition work, and must go through several other phases before being formally recommended as an international standard.
    Keywords: COMMUNICATIONS AND RADAR
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  • 19
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    Publication Date: 2011-08-18
    Description: A simplified buckling analysis is presented for a family of periodic lattice structures such as those proposed for large space structures. A transcendental 6 x 6 matrix of eigenvalues is shown to be sufficient for modeling buckling behavior because member stiffnesses are based on an exact solution of the beam-column equation. Exact stiffnesses are derived for a curved member, thus allowing modeling of imperfect lattice structures. Comparisons of predictions of the lattice model with those available from shell and beam theory underscore the inaccuracies introduced by treating the lattice structure as a continuum. Sample calculations are provided for an isogrid cylinder and a three element double-laced truss.
    Keywords: STRUCTURAL MECHANICS
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  • 20
    Publication Date: 2011-08-18
    Description: Truss beams with members having viscous damping are modeled with a Timoshenko beam. Procedures for deriving the equivalent bending rigidity, transverse shear rigidity, and damping are presented. Explicit expressions for these equivalent beam properties are obtained for a specific truss beam. The beam model thus established is then used to investigate the effect of damping in free vibration. Finally, the beam is employed in the estimation of structural parameters in a simply-supported truss beam using a random search algorithm.
    Keywords: STRUCTURAL MECHANICS
    Type: JPL Proc. of the Workshop on Appl. of Distributed System Theory to the Control of Large Space Struct.; p 531-545
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  • 21
    Publication Date: 2011-08-18
    Description: Simple, practical methods for damping reflector vibrations and designing antenna-feed attitude control systems in large deployable spaceborne antennas are proposed. The former involves a movable damper which is positioned so that the rate-of-change of total vibrational energy is minimized. The latter introduces a mechanical decoupler between the flexible boom and the antenna-feed, whereby the feed-attitude control system can be designed independent of boom dynamics. The validity of these approaches are substantiated by analytical studies, computer simulation, and experimental studies.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Proc. of the Workshop on Appl. of Distributed System Theory to the Control of Large Space Struct.; p 143-161
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  • 22
    Publication Date: 2011-08-18
    Description: A general approach for distributed parameter modeling of complex dynamical systems is described. The method consists of dividing the system in parts which can be modeled by simple partial differential equations and coupling the equations thus obtained by applying Hamilton's variational formalism to the entire system. The modeling of a large, offset-fed, wrap-rib antenna is presented to illustrate the approach. Although such models are perhaps not as precise as finite element models, they can be useful for initial physical insight and parametric design.
    Keywords: STRUCTURAL MECHANICS
    Type: Proc. of the Workshop on Appl. of Distributed System Theory to the Control of Large Space Struct.; p 89-102
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  • 23
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    Publication Date: 2011-08-18
    Description: The hybrid experimental-numerical stress-analysis technique, which saw limited applications during the 1950's, has been resurrected with the vastly improved numerical techniques of the 1970's. By inputing the experimental results as initial and boundary conditions, modern computer codes are executed in its generation and application modes to yield results which are unobtainable when only one of the two techniques is used. The hybrid technique thus exemplifies the complementary role of the experimental and numerical techniques.
    Keywords: STRUCTURAL MECHANICS
    Type: (ISSN 0014-4851)
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  • 24
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    Publication Date: 2011-08-18
    Description: Technology features of a beam forming network (BFN) employing ferrite devices to provide multiple beam antenna pattern control for satellites used in telecommunications are described. The BFN produces the phase and amplitude distribution for each horn in an antenna array, with the number of horns in the array being equal to the number of outputs in the BFN. One configuration involves microwave switches and permits illumination of a single feed horn at a time using ferrite latching circulators that function by reversing the circulation direction. A more flexible version, yielding a variable amplitude distribution across the feed horn array to accommodate changing traffic patterns or serving a TDMA system, includes the capability of forming nulls in the system with a variable phase shifter in the input ports. The antenna scan angles in phased arrays can be limited to 8 deg from center. Acceptable insertion losses have been demonstrated in BFN with hundreds of ports and switching rates as high as 10 kHz.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Microwave Journal (ISSN 0026-2897); 26; Aug. 198
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  • 25
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    Publication Date: 2011-08-18
    Description: Fourier transforms and the Wiener-Hopf technique are used in conjunction with plane elastostatics to examine the singular crack tip stress field in the double cantilever beam (DCB) specimen. In place of the Dirac delta function, a family of functions which duplicates the important features of the concentrated forces without introducing unmanageable mathematical complexities is used as a loading function. With terms of order h-squared/a-squared retained in the series expansion, the dimensionless stress intensity factor is found to be K (h to the 1/2)/P = 12 to the 1/2 (a/h + 0.6728 + 0.0377 h-squared/a-squared), in which P is the magnitude of the concentrated forces per unit thickness, a is the distance from the crack tip to the points of load application, and h is the height of each cantilever beam. The result is similar to that obtained by Gross and Srawley by fitting a line to discrete results from their boundary collocation analysis.
    Keywords: STRUCTURAL MECHANICS
    Type: International Journal of Fracture (ISSN 0376-9429); 22; June 198
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  • 26
    Publication Date: 2011-08-18
    Description: A fracture mechanics approach to the well-known delamination problem in composite materials is presented. Based on the theory of anisotropic laminate elasticity and interlaminar fracture mechanics concepts, the composite delamination problem is formulated and solved. The exact order of the delamination crack-tip stress singularity is determined. Asymptotic stress and displacement fields for an interlaminar crack are obtained. Fracture mechanics parameters such as mixed-mode stress intensity factors, KI, KII, KIII, and the energy release rate, G, for composite delamination problems are defined. To illustrate the fundamental nature of the delamination crack behavior, solutions for edge-delaminated graphite-epoxy composites under uniform axial extension are presented. Effects of fiber orientation, ply thickness, and delamination length on the interlaminar fracture are examined.
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Composite Materials (ISSN 0021-9983); 17; May 1983
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  • 27
    Publication Date: 2011-08-18
    Description: Previously cited in issue 13, p. 2112, Accession no. A82-30182
    Keywords: STRUCTURAL MECHANICS
    Type: (ISSN 0001-1452)
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  • 28
    Publication Date: 2011-08-18
    Description: Stress-intensity factors are obtained for point loaded equal length cracks emanating from a circular hole in an infinite plate. A series approach and the Muskhelishvili formulation in the two-dimensional theory of elasticity are used to derive the solution. The applicability of the solution is demonstrated by using it as a Green's function to obtain stress-intensity factors in the case of (1) biaxial tension and pure shear of an infinite plate and (2) tension and pin loading of a plate with cracks emanating from one hole in a row of holes.
    Keywords: STRUCTURAL MECHANICS
    Type: Res Mechanica (ISSN 0143-0084); 9; 2, 19; 1983
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  • 29
    Publication Date: 2011-08-18
    Description: Previously cited in issue 13, p. 2111, Accession no. A82-30171
    Keywords: STRUCTURAL MECHANICS
    Type: (ISSN 0021-8669)
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  • 30
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    Publication Date: 2011-08-18
    Description: Previously cited in issue 13, p. 2110, Accession no. A82-30166
    Keywords: STRUCTURAL MECHANICS
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  • 31
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    Publication Date: 2016-06-07
    Description: The Anthropometric Measurements Laboratory has accumulated a large body of data from a number of previous experiments. The data is very noisy, therefore it requires the application of some signal processing schemes. Moreover, it was not regarded as time series measurements but as positional information; hence, the data is stored as coordinate points as defined by the motion of the human body. The accumulated data defines two groups or classes. Some of the data was collected from an experiment designed to measure the flexibility of the limbs, referred to as radial movement. The remaining data was collected from experiments designed to determine the surface of the reach envelope. An interactive signal processing package was designed and implemented. Since the data does not include time this package does not include a time series element. Presently the results is restricted to processing data obtained from those experiments designed to measure flexibility.
    Keywords: COMMUNICATIONS AND RADAR
    Type: NASA. Johnson (Lyndon B.) Space Center The 1983 NASA/ASEE Summer Faculty Fellowship Research Program Research Reports; NASA. Johnson (Lynd
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  • 32
    Publication Date: 2016-06-07
    Description: The objectives of the hot section technology (HOST) burner liner cyclic rig test program are basically threefold: (1) to assist in developing predictive tools needed to improve design analyses and procedures for the efficient and accurate prediction of burner liner structural response; (2) to calibrate, evaluate and validate these predictive tools by comparing the predicted results with the experimental data generated in the tests; and (3) to evaluate existing as well as advanced temperature and strain measurement instrumentation, both contact and noncontact, in a simulated engine cycle environment. The data generated will include measurements of the thermal environment (metal surface temperatures) as well as structural (strain) and life (fatigue) responses of simulated burner liners and specimens under controlled boundary and operating conditions. These data will be used to calibrate, compare and validate analytical theories, methodologies and design procedures, as well as improvements in them, for predicting liner temperatures, stress-strain responses and cycles to failure. Comparison of predicted results with experimental data will be used to show where the predictive theories, etc. need improvements. In addition, as the predictive tools, as well as the tests, test methods, and data acquisition and reduction techniques, are developed and validated, a proven, integrated analysis/experiment method will be developed to determine the cyclic life of a simulated burner liner.
    Keywords: STRUCTURAL MECHANICS
    Type: Turbine Eng. Hot Sect. Technol. (HOST); p 181-193
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  • 33
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    Publication Date: 2016-06-07
    Description: The HOST Liner Cyclic Program is utilizing two types of test apparatus, rectangular box rigs and a full annular rig. To date two quartz lamp cyclic box rigs have been tested and a third is to begin testing in late October 1983. The box rigs are used to evaluate 5x8 inch rectangular linear samples. A 21 inch diameter outer liner simulator is also being built up for testing beginning in April 1984. All rigs are atmospheric rigs. The first box rig, a three 6-kVA lamp installation, was operated under adverse conditions to determine feasibility of using quartz lamps for cyclic testing. This work was done in December 1981 and looked promising. The second box rig, again using three 6-kVA lamps, was operated to obtain instrumentation durability information and initial data input to a Finite Element Model. This limited test program was conducted in August 1983. Five test plates were run. Instrumentation consisted of strain gages, thermocouples and thermal paint. The strain gages were found to fail at 1200 F as expected though plates were heated to 1700 F. The third box rig, containing four 6-kVA lamps, is in build up for testing to begin in late October 1983. In addition to 33 percent greater power input, this rig has provision for 400 F backside line cooling air and a viewing port suitable for IR camera viewing. The casing is also water cooled for extended durability.
    Keywords: STRUCTURAL MECHANICS
    Type: Turbine Eng. Hot Sect. Technol. (HOST); p 195-204
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  • 34
    Publication Date: 2016-06-07
    Description: The objective of this program is to produce a series of new computer codes that permit more accurate and efficient three dimensional inelastic analysis of selected hot section components - combustor liners, turbine blades and turbine vanes. The computer codes embody a progression of mathematical models and are streamlined to take advantage of geometrical features, loading conditions, and forms of material response that distinguish each group of selected components.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Lewis Research Center Turbine Eng. Hot Sect. Technol. (HOST); p 179-180
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  • 35
    Publication Date: 2016-06-07
    Description: The objective of this research is to develop an analytical tool capable of economically evaluating the cyclic time dependent plasticity which occurs in hot section engine components in areas of strain concentration resulting from the combination of both mechanical and thermal stresses. The techniques developed must be capable of accommodating large excursions in temperatures with the associated variations in material properties including plasticity and creep. The overall objective of this proposed program is to develop advanced 3-D inelastic structural/stress analysis methods and solution strategies for more accurate and yet more cost effective analysis of combustors, turbine blades, and vanes. The approach will be to develop four different theories, one linear and three higher order with increasing complexities including embedded singularities.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA. Lewis Research Center Turbine Eng. Hot Sect. Technol. (HOST); p 175-177
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  • 36
    Publication Date: 2016-06-07
    Description: A major unresolved question in the field of atmospheric research using VHF radar techniques is the relative merit of the two most widely used systems. These systems are the Doppler method and the spaced antenna method. It has been suggested that one radar of each type be operated side by side for a direct comparison of the two techniques. This duplication of effort is not cost effective. The major components of both systems are identical, and one radar could be operated in both modes by proper design of a suitable antenna system and by proper data analysis. The Chung-Li radar will be able to switch between modes on a time scale of seconds and is the first VHF radar to be able to directly compare the Doppler data with spaced antenna data. The system will have performance comparable with the present SOUSY spaced antenna system and will provide mesospheric data in addition to stratospheric and tropospheric data. The major specifications of the Chung-Li radar are given.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Intern. Council Sci. Unions Middle Atmosphere Program, Vol. 9; p 383-386
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  • 37
    Publication Date: 2016-06-07
    Description: The Wave Propagation Laboratory is developing a ground-based remote sensing system called PROFILER to measure troposphere parameters currently measured in operational meteorology by radiosondes. The prototype PROFILER uses two radars for wind sounding: a 6-m radar located at Platteville, Colorado, and a 33-cm radar located at Denver's Stapleton International Airport. In addition, a network of three 6-m wind-profiling radars is being installed in Colorado, and a fourth site is planned. The location of the five radars, their characteristics, and their limitations are described.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Intern. Council Sci. Unions Middle Atmosphere Program, Vol. 9; p 325-329
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  • 38
    Publication Date: 2016-06-07
    Description: The European Incoherent Scatter Radar Facility also has facilities which can be used for coherent scatter research of the middle atmosphere. The observatory consists of two independent systems which allow observations of the upper, middle, and lower atmosphere: a tristatic UHF radar capable of vector drift measurements, and a monostatic VHF system. The characteristics of the components are are described including inter-site communication, on-line displays, and the real-time operating system. Analysis of about 60 hours of middle atmosphere observations in 1982 indicate that EISCAT's capabilities to measure mesospheric parameters should improve during moderately or strongly disturbed conditions, enabling measurement of profiles of wind velocity, electron density, and temperature/collision frequency, and in some instances, ion masses. Because of not yet optimized transmit-receive switching, some limitations exist in the monostatic mode when observing coherent scattering in the stratosphere at short ranges.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Intern. Council Sci. Unions Middle Atmosphere Program, Vol. 9; p 305-314
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  • 39
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    In:  CASI
    Publication Date: 2016-06-07
    Description: The spaced antenna drift method is a simple and relatively inexpensive method for determination of atmospheric wind velocities using radars. The technique has been extensively tested in the mesosphere at high and medium frequencies, and found to give reliable results. Recently, the method has also been applied to VHF observations of the troposphere and stratosphere, and results appear to be reliable. This paper discusses briefly the principle of the method, and investigates both its strengths and weaknesses. Some discussions concerning criticisms of the technique are also given, and it is concluded that while these criticisms may be of some concern at times, appropriate care can ensure that the method is at least as viable as any other method of remote wind measurement. At times, the technique has definite advantages.
    Keywords: COMMUNICATIONS AND RADAR
    Type: International Council of Scientific Unions Middle Atmosphere Program, Vol. 9; p 171-186
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  • 40
    Publication Date: 2016-06-07
    Description: Spectrum analysis and correlation methods used to measure the horizontal and vertical velocities of radar echo signals are examined mathematically. Topics include scattering/reflection geometry, monostatic versus bistatic operation, spaced antenna measurements, radar interferometry and the Doppler method. Vertical velocity determination, optimum pointing angles, and time resolution for periodic variations are also investigated.
    Keywords: COMMUNICATIONS AND RADAR
    Type: International Council of Scientific Unions Middle Atmosphere Program, Vol. 9; p 150-163
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  • 41
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    In:  CASI
    Publication Date: 2016-06-07
    Description: Doppler spectra of VHF radar returns typically indicate a Gaussian back-ground shape with superimposed spikes. An average of 10 Doppler spectra are shown which are calculated from a time series of seven min of complex data. A proper Gaussian fit to the background distribution is possible by neglecting the strong amplitude spikes. If this background distribution is due to beam width broadening, either diffuse reflection or rather isotropic scattering is required. If beam width broadening is neglected, the width of the distribution is given by turbulent velocity fluctuations. The reflected component is about 1/3 of the scattered component. It is assumed that the amplitude spikes due to diffuse reflection indicate a Gaussian frequency distribution such as for the amplitudes due to scattering.
    Keywords: COMMUNICATIONS AND RADAR
    Type: International Council of Scientific Unions Middle Atmosphere Program, Vol. 9; p 112-113
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  • 42
    Publication Date: 2016-06-07
    Description: The effects on the signal detectability of varying the pulse repetition rate (PRF), peak pulse power (p(pk)) and pulse width (tau(p)) (tp) are examined. Both coded and uncoded pulses are considered. The following quantities are assumed to be constant; (1) antenna area, (z)echo reflectivity, (3) Doppler shift, (4) spectral width, (5) spectral resolution, (6) effective sampling rate, and (7) total incoherent spectral averagaing time. The detectability is computed for two types of targets.
    Keywords: COMMUNICATIONS AND RADAR
    Type: International Council of Scientific Unions Middle Atmosphere Program, Vol. 9; p 100-104
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  • 43
    Publication Date: 2016-06-07
    Description: VHF radar echoes are greatly enhanced near the zenith relative to other directions. This enhancement must be due to reflection from horizontally stratified laminate of refractive index. The refractivity laminate are due to the displacements of low frequency buoyancy (internal gravity) waves acting on the background vertical gradient of refractivity. VANZANDT (1982) has shown that the observed spectra of mesoscale wind fluctuations in the troposphere and lower stratosphere are modeled by a universal spectrum of buoyancy (internal gravity) waves. Since the observed frequency spectrum is red, the buoyancy wave model of the vertical displacement spectrum is strongly enhanced near the zenith. In other terms, the resulting refractivity irregularities are strongly stratified.
    Keywords: COMMUNICATIONS AND RADAR
    Type: International Council of Scientific Unions Middle Atmosphere Program, Vol. 9; p 78-80
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  • 44
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    In:  CASI
    Publication Date: 2016-06-07
    Description: Following reception and analog to digital conversion (A/D) conversion, atmospheric radar backscatter echoes need to be processed so as to obtain desired information about atmospheric processes and to eliminate or minimize contaminating contributions from other sources. Various signal processing techniques have been implemented at mesosphere-stratosphere-troposphere (MST) radar facilities to estimate parameters of interest from received spectra. Such estimation techniques need to be both accurate and sufficiently efficient to be within the capabilities of the particular data-processing system. The various techniques used to parameterize the spectra of received signals are reviewed herein. Noise estimation, electromagnetic interference, data smoothing, correlation, and the Doppler effect are among the specific points addressed.
    Keywords: COMMUNICATIONS AND RADAR
    Type: International Council of Scientific Unions Middle Atmosphere Program, Vol. 9; p 535-542
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  • 45
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    In:  CASI
    Publication Date: 2016-06-07
    Description: Many radars used for wind sounding generate Doppler power spectra as output. For compact data archiving purposes, as well as for data analysis, several parameters were produced to characterize each spectrum. The parameters chosen were noise level, echo signal strength, velocity, and width. Because the derived parameters may be the only quantities available for future analysis, it was important that they did not contain biases imposed by the derivation techniques. This consideration led to a processing scheme in which the parameters were derived independently for each spectrum.
    Keywords: COMMUNICATIONS AND RADAR
    Type: International Council of Scientific Unions Middle Atmosphere Program, Vol. 9; p 546-547
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  • 46
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    In:  CASI
    Publication Date: 2016-06-07
    Description: The individual steps in the data processing scheme applied to most radars used for wind sounding are analyzed. This processing method uses spectral analysis and assumes a pulse Doppler radar. Improvement in the signal to noise ratio of some radars is discussed.
    Keywords: COMMUNICATIONS AND RADAR
    Type: International Council of Scientific Unions Middle Atmosphere Program, Vol. 9; p 528-531
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  • 47
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    In:  CASI
    Publication Date: 2016-06-07
    Description: The range of phenomena of the MST radar technique to divide the steerability versus nonsteerability problem into two broad with a third subset that lies between these two limits are studied. Processes that vary on a horizontal scale which are comparable to the area of the probing radar beam can best be fully steerable beams. The use of fixed beam systems would be a long term study of the mean wind field. Orographic effects due to mountain ridges and/or land-sea interfaces demand steerable beams, particularly if the effects are three dimensional in character. In view of their lack of moving parts fixed beam systems are more reliable. It is assumed that the reliability of a system is inversely proportioned to the number of moving parts. This is not a problem for fixed beam systems.
    Keywords: COMMUNICATIONS AND RADAR
    Type: International Council of Scientific Unions Middle Atmosphere Program, Vol. 9; p 463-464
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  • 48
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    In:  CASI
    Publication Date: 2016-06-07
    Description: The optimum design choice for the MST radar antenna was considered. The following factors are required: directivity and gain; beam width and its symmetry; sidelobe levels, near and wide angle; impedance matching; feeder network losses; polarization diversity; steerability; cost effectiveness; and maintainability. The directivity and related beam forming aspects of various antenna elements and directivity aspects when such elements are formed into an array are discussed. Array performance for important variables, in particular, the spacing of the elements is considered.
    Keywords: COMMUNICATIONS AND RADAR
    Type: International Council of Scientific Unions Middle Atmosphere Program, Vol. 9; p 456-462
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  • 49
    Publication Date: 2016-06-07
    Description: The transceiver (TR) switch developed at NOAA's Aeronomy Laboratory for use in their 50 kW peak power, 50 MHz transmitter is described. The switch mounts inside the transmitter chassis and was designed to be compact while retaining the ability to handle well over 50 kW peak power at average power levels up to 2 kW. The TR switch is a conventional TR/ATR design with equivalent /4 transmission line sections constructed of lumped constant coils and transmitting capacitors in ''Tee' sections. Two TR sections are placed in series to achieve adequate receiver protection. The switch is set into the ''transmit' mode by forward biasing the 3 pin diodes to about 1.2 amperes each. The receive mode is achieved by back biasing the diodes to -15 volts. A directional coupler is also incorporated into the TR switch box to provide a convenient monitor point for forward and reflected transmitter power.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Intern. Council Sci. Unions Middle Atmosphere Program, Vol. 9; p 431-432
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  • 50
    Publication Date: 2016-06-07
    Description: The transceiver (TR) module of a middle and upper atmospheric radar is described. The TR module used in the radar is mainly composed of two units: a mixer (MIX unit) and a power amplifier (PA unit). The former generates the RF wave for transmission and converts the received echo to the IF signal. A 41.5-MHz local signal fed to mixers passes through a digitally controlled 8-bit phase shifter which can change its value up to 1,000 times in a second, so that the MU radar has the ability to steer its antenna direction quickly and flexibly. The MIX unit also contains a buffer amplifier and a gate for the transmitting signal and preamplifier for the received one whose noise figure is less than 5 dB. The PA unit amplifies the RF signal supplied from the MIX unit up to 63.7 dBm (2350 W), and feeds it to the crossed Yagi antenna.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Intern. Council Sci. Unions Middle Atmosphere Program, Vol. 9; p 421-423
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  • 51
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    Publication Date: 2016-06-07
    Description: Decoding techniques and equipment used by MST radars are described and some recommendations for new systems are presented. Decoding can be done either by software in special-purpose (array processors, etc.) or general-purpose computers or in specially designed digital decoders. Both software and hardware decoders are discussed and the special case of decoding for bistatic radars is examined.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Intern. Council Sci. Unions Middle Atmosphere Program, Vol. 9; p 416-420
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  • 52
    Publication Date: 2016-06-07
    Description: The 41-MHz coherent-scatter radar located northeast of the University of Illinois at Urbana is being used for studies of the troposphere, stratosphere and mesosphere regions. The antenna consists of 1008 halfwave dipoles with a physical aperture of 11000 sq m. Transmitted peak power is about 750 kW. Clear-air returns may be received from 6 km to 90 km altitude. Autocorrelation functions of the scattered signal are calculated on-line. From the autocorrelation functions the scattered power, line-of-sight velocity and signal correlation time are calculated. Some aspects of the troposphere/stratosphere and the mesosphere observations are discussed. Capabilities and limitations of the Urbana MST radar are pointed out, and recent and planned improvements to the radar are described.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Intern. Council Sci. Unions Middle Atmosphere Program, Vol. 9; p 346-356
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  • 53
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    In:  Other Sources
    Publication Date: 2016-06-07
    Description: All Mesosphere, Stratosphere, Troposphere (MST) radars now in operation or under construction use the monostatic mode, that is to say, the same antenna for both transmitting and receiving. Consequently, it is never possible to determine more than one component of the atmospheric velocity at one point in space. Two important properties of gravity waves which are difficult if not impossible to determine by the monostatic method are discussed. The first of these is the polarization of the gravity waves; that is, the complex ratio of the wave functions of vertical and horizontal motion. A second quantity of importance is the horizontal wavelength of gravity waves. Both of these problems could be overcome by use of a bistatic system. Such a system has the additional advantage of making it possible to measure at very low altitudes, and to look away from the transmitter (for example to make a horizontal section through a thunderstorm). However, bistatic operation, in the practical sense, requires not only an additional highly directive antenna, but also that both the transmitting and receiving antennas should be fully steerable.
    Keywords: COMMUNICATIONS AND RADAR
    Type: International Council of Scientific Unions Middle Atmosphere Program, Vol. 9; p 170
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  • 54
    Publication Date: 2016-06-07
    Description: Three techniques of direct measurement are presented from which velocities may be obtained: (1) Doppler frequency shift, (2) spaced antenna drift, (3) spatially modulated transverse beam measurements. Emphasis is placed on the Doppler frequency measurement approach. It will compare bistatic with monostatic configurations as regards received power (or sensitivity), spatial resolution, Doppler shift and avoidance of ground clutter.
    Keywords: COMMUNICATIONS AND RADAR
    Type: International Council of Scientific Unions Middle Atmosphere Program, Vol. 9; p 164-169
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  • 55
    Publication Date: 2014-09-10
    Description: The theoretical and experimental study of a 1.5-meter offset dual shaped reflector at 31.4 GHz is detailed. An efficiency of 84.5 percent, a likely new record for reflector antennas, was ascertained through careful measurements. For larger low noise reflector systems, a 2- to 3-dB improvement in G/T performance over the state of the art ultra low noise ground stations and 90 percent or better aperture efficiency now appear feasible.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommun. and Data Acquisition Rept.; p 1-14
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  • 56
    Publication Date: 2014-09-12
    Description: The Search for Extraterrestrial Intelligence (SETI) requires low noise broadband total power radiometers of high gain stability. Preliminary results of SETI field tests for a variety of receiver configurations at Deep Space Station 13 are discussed. The power spectra of Deep Space Network low noise receiving systems exhibit I/F noise whose spectral index is significantly smaller than unity. The gain stability of the S-band systems tested is almost 0.0001. An appendix presents a derivation of the power spectrum of the output of a square law detector.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommun. and Data Acquisition Rept.; p 159-168
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  • 57
    Publication Date: 2014-09-12
    Description: The application of modern planetary radar techniques to a comet passing in close proximity to Earth is discussed. These techniques have the potential to determine the nature of cometary origins, structure, and internal dynamics. Moreover, the understanding gained could very likely negate or corroborate one of the prevailing hypotheses regarding the origin of the solar system: that comets are the remainder of the primordial out of which the planets coalesced approximately 4.5 billion years ago. In 1983, two unique opportunities were presented to observe a comet very near to Earth. The last such encounter was several centuries ago.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommun. and Data Acquisition Rept.; p 114-115
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  • 58
    Publication Date: 2014-09-11
    Description: The dynamic characteristics of the Solar Array Flight Experiment (SAFE) structure during deployment and retraction are investigated. The SAFE structure consists of a deployable mast with an attached solar blanket designed with accordion type folds to permit packaging in a small volume. The planar form of the blanket geometry during deployment is maintained by a blanket tension/guidewire system. Structurally, the mast is modeled as an Euler beam column with inplane and out of plane bending and finite torsional stiffness. For out of plane motion, the blanket is modeled as a distributed mass uniformly supported by the three guidewires. For inplane motion the blanket displacements are assumed to vary linearly from the mast base to the mast tip. The mathematical model uses a virtual work formulation, required because the axial loading on the mast is nonconservative, combined with assumed beam modes to derive the differential equations of motion. Consideration of the time dependent boundary conditions results in an infinite set of ODE with time dependent coefficients. Finally, correlation of mast tip accelerations to mast base bending moments for specified modal motions are indicated.
    Keywords: STRUCTURAL MECHANICS
    Type: Res. Rept.: 1983 NASA(ASEE Summer Faculty Fellowship Program; 24 p
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  • 59
    Publication Date: 2014-09-11
    Description: Traditional composite lamination theory was used to predict composite graphite-epoxy laminate stiffnesses for comparison to quasi-experimental stiffnesses developed from cylindrical bottle pressure testing. Stiffness sensitivities were examined for variations in constituent materials and geometric properties. The material component interactions examined were the fiber longitudinal and transverse Young's modulus, the fiber shear modulus and primary Poisson's ratio, the resin Young's modulus, shear modulus, and Poisson's ratio. The geometric variation of the helical winding angle was also examined. Two computer programs were written to generate the data used to demonstrate the stiffness variations.
    Keywords: STRUCTURAL MECHANICS
    Type: Alabama Univ. Res. Rept.: 1983 NASA(ASEE Summer Faculty Fellowship Program; 34 p
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  • 60
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    Publication Date: 2014-09-11
    Description: The Earth's atmosphere consists mostly of the dry components oxygen (about 21% by volume), nitrogen (about 78% by volume) argon (about 1% by volume), and wet components (water vapor, clouds and rain). Water vapor at 100% relative humidity is approximately 1.7% by volume assuming the U.S. Standard Atmosphere, 15 C, at sea level. A communications link through the atmosphere suffers attenuation from both the dry and wet components. This results in a decreased signal to noise ratio (SNR) of the communications link due to both the signal attenuation and the increased noise temperature resulting from thermal emission.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Deep Space Network: A Radio Commun. Instr. for Deep Space Exploration; 18 p
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  • 61
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    Publication Date: 2014-09-11
    Description: Analysis of spacecraft to ground communications link performance and a description of the Deep Space Network system is provided. Due to the tremendous distances involved in communicating between the spacecraft at the edge of our solar system and Earth, communications link performance is stretched to the limit of theoretical predictions. This is required in order to return the maximum amount of data possible during critical events such as planetary flybys. The link analysis provides a basis for the initial link design before spacecraft launch and performance prediction and monitoring during spacecraft flight. Additionally, it indicates what performance upgrades are required for mission extensions and new missions. Performance is improved through the use of a larger antenna collecting area, greater transmitter power, lower receiving system noise temperature and more sophisticated data coding schemes. The performance of the Deep Space Station configuration which serves as the ground portion of the communications link is assessed.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Deep Space Network: A Radio Commun. Instr. for Deep Space Exploration; 25 p
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  • 62
    Publication Date: 2014-09-10
    Description: The major objective of the Deep Space Network in the period 1983-2000 is the fulfillment of the extremely diverse telecommunications requirements of the known and anticipated users. Deep space exploration projects will continue to occupy a dominant role, although in the mid-1980s, with the completion of the Networks Consolidation Program, high Earth orbiter projects will become substantial users of the Network. Also playing an increasingly important role in the Network of the next decade will be non-flight projects, such as Geodynamics, Radio Astronomy, Radar Astronomy, and the Search for Extraterrestrial Intelligence (SETI). The major challenge in meeting the primary Network objective of the next decade will be that of providing increased performance as required by users at costs which can be borne by NASA in an environment of limited resources. Emphasis will be on increased commonality, flexibility, and automation to reduce maintenance and operations costs, and lower mission costs.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Deep Space Network: A Radio Commun. Instr. for Deep Space Exploration; 21 p
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  • 63
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    Publication Date: 2014-09-10
    Description: The Command System provides the means by which a project controls the activities of its spacecraft from the Earth. An overview of the Multimission Command (MMC) System is presented. The major components within the MMC System are discussed, with emphasis on the telecommunications related implementations. Two versions of the spacecraft command detection system the Viking Heritage command detector and the NASA standard command detector are summarized. The former prevails in the existing flight projects and the latter will likely be adopted by the missions of the near future. The preparation of Design Control Tables for the control of command link performance between Deep Space Stations and the spacecraft is also discussed.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Deep Space Network: A Radio Commun. Instr. for Deep Space Exploration; 24 p
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  • 64
    Publication Date: 2014-09-10
    Description: The advantage of 32-GHz links, the estimated link performance, and developments in the fields of antennas, low noise preamplifiers, radiometry, and propagation studies are discussed. A description of ways to demonstrate 32-GHz link capability concludes the discussion.
    Keywords: COMMUNICATIONS AND RADAR
    Type: The Telecommun. and Data Acquisition Rept.; p 165-175
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  • 65
    Publication Date: 2014-09-10
    Description: An experiment to measure the elastic deflection of the DSS 14 concrete pedestal under the weight of the antenna was conducted in February 1983 and is compared to a similiar experiment made in 1968. Comparison of the results confirms the decrease in elastic modulus measured on core samples recently taken from the pedestal.
    Keywords: STRUCTURAL MECHANICS
    Type: The Telecommun. and Data Acquisition Rept.; p 89-91
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  • 66
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    Publication Date: 2011-08-18
    Description: The exciting discoveries of the Shuttle Imaging Radar-A (SIR-A) experiment prompted a refly of the instrument to be designated the Shuttle Imaging Radar-B. The SIR-B instrument will reuse the hardware flown for the SIR-A mission and add some interesting refinements. The two radar sensors are described in detail. The SIR-A and SIR-B instruments are both tailored for use on the Space Shuttle. They are physically configured to fit in the Shuttle's payload bay, are powered and cooled by shuttle systems, are controlled by the crew or from the ground, and record data on board or beam it to the ground using the orbiter's data links. The radars are designed to accommodate a range of orbiter altitudes and have built in operating modes to cover a wide variety of mission objectives. The flexibility and utility of these radars make them ideal, cost effective instruments for research in the Space Shuttle environment.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Spaceborne Imaging Radar Symp.; p 26-31
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  • 67
    Publication Date: 2011-08-18
    Description: The uniform geometrical theory of diffraction (GTD) is employed for calculating the edge diffracted fields from the finite ground plane of a microstrip antenna. The source field from the radiating patch is calculated by two different methods: the slot theory and the modal expansion theory. Many numerical and measured results are presented to demonstrate the accuracy of the calculations and the finite ground plane edge effect.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Antennas and Propagation (ISSN 0018-926X); AP-31; July 198
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  • 68
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    Publication Date: 2011-08-18
    Description: A numerical technique is presented to optimize the performance of arbitrary antenna arrays under realistic conditions. An experimental-computational algorithm is formulated in which n-dimensional minimization methods are applied to measured data obtained from the antenna array. A numerical update formula is used to induce partial derivative information without requiring special perturbations of the array parameters. The algorithm provides a new design for the antenna array, and the method proceeds in an iterative fashion. Test case results are presented showing the effectiveness of the algorithm.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Antennas and Propagation (ISSN 0018-926X); AP-31; July 198
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  • 69
    Publication Date: 2011-08-18
    Description: An unconditionally stable implicit-explicit method is proposed for the analysis of transient coupled thermal stress waves, and the computer-implementation aspects of the method are discussed. In the method proposed here, the mechanical displacement and temperature are used as independent variables. The resulting coupled finite element matrix equations are symmetric.
    Keywords: STRUCTURAL MECHANICS
    Type: Computers and Structures (ISSN 0045-7949); 17; 3, 19; 1983
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  • 70
    Publication Date: 2011-08-18
    Description: It is shown that even though the capacity per photon can be made to increase without bound, the capacity per channel use (for best power efficiency) is always less than 2 nats per symbol. Furthermore, it approaches 2 nats per symbol as the bandwidth expansion factor goes to infinity. Previously announced in STAR as N82-20121
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Communications (ISSN 0090-6778); COM-31; April 19
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  • 71
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    Publication Date: 2011-08-18
    Description: Previously cited in issue 13, p. 2112, Accession no. A82-30186
    Keywords: STRUCTURAL MECHANICS
    Type: (ISSN 0001-1452)
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  • 72
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    Publication Date: 2011-08-18
    Description: Previously cited in issue 13, p. 2108, Accession no. A82-30124
    Keywords: STRUCTURAL MECHANICS
    Type: AIAA Journal (ISSN 0001-1452); 21; 1729-173
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  • 73
    Publication Date: 2011-08-18
    Description: Internal waves which are among the most commonly observed oceanic phenomena in the SEASAT SAR imagery are discussed. These waves are associated with the vertical displacements of constant water density surfaces in the ocean. Their amplitudes are maximum at depths where the water density changes most rapidly usually at depths from 50 to 100 m, whereas the horizontal currents associated with these waves are maximum at the sea surface where the resulting oscillatory currents modulate the sea surface roughness and produce the signatures detected by SAR.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Spaceborne Imaging Radar Symp.; p 118-120
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  • 74
    Publication Date: 2011-08-18
    Description: The performance of the Interim Digital SAR Processor (IDP) was evaluated. The IDP processor was originally developed for experimental processing of digital SEASAT SAR data. One phase of the system upgrade which features parallel processing in three peripheral array processors, automated estimation for Doppler parameters, and unsupervised image pixel location determination and registration was executed. The method to compensate for the target range curvature effect was improved. A four point interpolation scheme is implemented to replace the nearest neighbor scheme used in the original IDP. The processor still maintains its fast throughput speed. The current performance and capability of the processing modes now available on the IDP system are updated.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Spaceborne Imaging Radar Symp.; p 93-95
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  • 75
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    Publication Date: 2011-08-18
    Description: Digital processors for spaceborne imaging radars and application of the technology developed for airborne SAR systems are considered. Transferring algorithms and implementation techniques from airborne to spaceborne SAR processors offers obvious advantages. The following topics are discussed: (1) a quantification of the differences in processing algorithms for airborne and spaceborne SARs; and (2) an overview of three processors for airborne SAR systems.
    Keywords: COMMUNICATIONS AND RADAR
    Type: JPL Spaceborne Imaging Radar Symp.; p 89-92
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  • 76
    Publication Date: 2011-08-18
    Description: Starting with mission definitions and constraints for the NASA proposed Shuttle Active Microwave Experiments (SAMEX) and Free Flying Imaging Radar Experiment (FIREX), Hughes Aircraft Company has compiled and studied the technology available for slotted waveguide planar array antennas suitable for spaceborne SAR application. Antenna performance is derived, and fabrication techniques are discussed. Mission requirements will always lead to an aperture subdivided into waveguide modules, thereby validating a module definition for other mission building blocks. Finally, a specific design is proposed for a SAMEX mission using the modules as RF aperture building blocks, resulting in a (nominal) 15.1 meter by 5.5 meter extensile dual polarized L-, C-, and X-band planar array with an associated extensile graphite/epoxy support structure. Antenna development begin with a fabrication method development study involving a representative portion of an antenna module.
    Keywords: COMMUNICATIONS AND RADAR
    Type: JPL Spaceborne Imaging Radar Symp.; p 35-40
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  • 77
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    In:  Other Sources
    Publication Date: 2011-08-18
    Description: Geologic applications of spaceborne radar images, specifically SEASAT in southern California and SIR-A in Indonesia are illustrated.
    Keywords: COMMUNICATIONS AND RADAR
    Type: JPL Spaceborne Imaging Radar Symp.; p 5-9
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  • 78
    Publication Date: 2011-08-18
    Description: The development of novel electro-optic spatial light modulators (both one and two dimensional) which allows real-time coherent optical SAR processors to be implemented is outlined. It is suggested that the availability of such processors may initiate new mission applications not presently envisioned due to current digital processor limitations.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Spaceborne Imaging Radar Symp.; p 107-109
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  • 79
    Publication Date: 2011-08-18
    Description: Aerospace research and the respective applications microwave tasks with respect to remote sensing, position finding and communication are discussed. The radar activities are directed at point targets, area targets and volume targets; they center around signature research for earth and ocean remote sensing, target recognition, reconnaissance and camouflage and imaging and area observation radar techniques (SAR and SLAR). The radar activities cover a frequency range from 1 GHz up to 94 GHz. The radar program is oriented to four possible application levels: ground, air, shuttle orbits and satellite orbits. Ground based studies and measurements, airborne scatterometers and imaging radars, a space shuttle radar, the MRSE, and follow on experiments are considered.
    Keywords: COMMUNICATIONS AND RADAR
    Type: JPL Spaceborne Imaging Radar Symp.; p 136-139
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  • 80
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    In:  Other Sources
    Publication Date: 2011-08-18
    Description: The SEASAT SAR and Shuttle Imaging Radar SIR-A experiments demonstrated that spaceborne synthetic aperture radars provide synoptic images of land and ocean features. Radar images clearly show geologic structures, morphologic features, clear cutting, subsurface features (in very arid regions), agricultural and urban land use, ocean surface waves, current boundaries, internal waves, ice floes and numerous other ocean features which affect the surface roughness.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Spaceborne Imaging Radar Symp.; p 131-135
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  • 81
    Publication Date: 2011-08-18
    Description: The geophysical science problems in the sea ice area which at present concern understanding the ice budget, where ice is formed, how thick it grows and where it melts, and the processes which control the interaction of air-sea and ice at the ice margins is discussed. The science problems relate to basic questions of sea ice: how much is there, thickness, drift rate, production rate, determination of the morphology of the ice margin, storms feeling for the ice, storms and influence at the margin to alter the pack, and ocean response to a storm at the margin. Some of these questions are descriptive and some require complex modeling of interactions between the ice, the ocean, the atmosphere and the radiation fields. All involve measurements of the character of the ice pack, and SAR plays a significant role in the measurements.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Spaceborne Imaging Radar Symp.; p 116-117
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  • 82
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    In:  Other Sources
    Publication Date: 2011-08-18
    Description: Stereo viewing is a valuable tool in photointerpretation and is used for the quantitative reconstruction of the three dimensional shape of a topographical surface. Stereo viewing refers to a visual perception of space by presenting an overlapping image pair to an observer so that a three dimensional model is formed in the brain. Some of the observer's function is performed by machine correlation of the overlapping images - so called automated stereo correlation. The direct perception of space with two eyes is often called natural binocular vision; techniques of generating three dimensional models of the surface from two sets of monocular image measurements is the topic of stereology.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Spaceborne Imaging Radar Symp.; p 53-55
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  • 83
    Publication Date: 2011-08-18
    Description: The Shuttle Imaging Radar (SIR-A) obtained images over the southern portion of the San Rafael Swell in eastern Utah. SEASAT SAR and LANDSAT MSS images and thermal inertia data from the Heat Capacity Mapping Mission (HCMM) were correlated with the SIR-A data. Radar images obtained with different incidence angles and different illumination directions were compared with images obtained in other portions of the spectrum for geologic remote sensing.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Spaceborne Imaging Radar Symp.; p 13-16
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  • 84
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    In:  Other Sources
    Publication Date: 2011-08-18
    Description: The objectives selected for ERS-1 which are primarily intended to facilitate the exploitation of coastal oceans, including ice infested waters, and to facilitate the development of improved global weather information through the provision of information on the weather conditions over the oceans of the word are outlined. Additionally, land objectives will be addressed using the synthetic aperture radar incorporated in the payload.
    Keywords: COMMUNICATIONS AND RADAR
    Type: JPL Spaceborne Imaging Radar Symp.; p 140-142
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  • 85
    Publication Date: 2011-08-18
    Description: Understanding the SAR response to surface wave is a central issue in the analysis of SAR ocean images. The imaging mechanism for gravity waves and the practical question of just which characteristics of the ocean wave field can be measured remotely using SAR were examined. Assessments of wave imaging theory are based primarily on comparisons of the directional wave height variance spectrum psi (K) measured by in situ buoys with estimates from SAR images. Other criteria are also recommended, e.g., the effects of focus adjustments. It is assumed that fluctuations in SAR image intensity are proportional to fluctuations in ocean surface height. If this were true, the Fourier power spectrum of a SAR image and corresponding surface measurements of psi would coincide. Differences between SAR estimates based on this hypothesis and buoy measurements of psi are then used to begin the assessment of rival wave imaging theories.
    Keywords: COMMUNICATIONS AND RADAR
    Type: JPL Spaceborne Imaging Radar Symp.; p 124-127
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  • 86
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    In:  Other Sources
    Publication Date: 2011-08-18
    Description: Current and future microstrip antenna technology development for Spaceborne Synthetic Aperture Radars (SAR) are summarized. Some of the electrical and mechanical characteristics of previously and presently developed microstrip SAR antennas are shown. The SEASAT, the SIR-A and presently the SIR-B antennas are all designed for operation at L-band with approximately 22 MHz of bandwidth. The antennas have linear polarization with minimum of 20 dB of polarization purity. Both the SEASAT and SIR-A antennas were designed for a fixed pointing angle of 20.5 deg and 47 deg, respectively. However, the SIR-B has the added feature of mechanical beam steering in elevation (range). With the exception of different mechanical characteristics, it is concluded that present spaceborne SAR antennas have only single frequency and single polarization performance. The lack of large spaceborne antennas operating at the higher degree of fabrication tolerance required for a given performance; and larger feed and radiating element losses.
    Keywords: COMMUNICATIONS AND RADAR
    Type: JPL Spaceborne Imaging Radar Symp.; p 32-34
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  • 87
    Publication Date: 2011-08-18
    Description: The launch of spaceborne SARs during the 1980's is discussed. The satellite SARs require high quality and high throughput ground processors. Compression ratios in range and azimuth of greater than 500 and 150 respectively lead to frequency domain processing and data computation rates in excess of 2000 million real operations per second for C-band SARs under consideration. Various hardware architectures are examined and two promising candidates and proceeds to recommend a fast, programmable hardware architecture for spaceborne SAR processing are selected. Modularity and programmability are introduced as desirable attributes for the purpose of HTSP hardware selection.
    Keywords: COMMUNICATIONS AND RADAR
    Type: JPL Spaceborne Imaging Radar Symp.; p 99-104
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  • 88
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    In:  Other Sources
    Publication Date: 2011-08-18
    Description: A number of remote sensing systems deployed in satellites to view the Earth which are successful in gathering data on the behavior of the world's snow and ice covers are described. Considering sea ice which covers over 10% of the world ocean, systems that have proven capable to collect useful data include those operating in the visible, near-infrared, infrared, and microwave frequency ranges. The microwave systems have the essential advantage in observing the ice under all weather and lighting conditions. Without this capability data are lost during the long polar night and during times of storm passage, periods when ice activity can be intense. The margins of the ice pack, a region of particular interest, is shrouded in cloud between 80 and 90% of the time.
    Keywords: COMMUNICATIONS AND RADAR
    Type: JPL Spaceborne Imaging Radar Symp.; p 113-115
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  • 89
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    In:  Other Sources
    Publication Date: 2011-08-18
    Description: Current SAR data processing techniques for spaceborne SAR systems utilize commercial equipment to carry the computation load. For a data set such as SEASAT, the resulting throughput rate is two to three orders of magnitude slower than real time. Such rates impede the progress of scientific investigations and preclude the potential for any practical operational SAR mission. It is suggested that a set of special-purpose hardware could be designed for efficient SAR data processing so that real time rates are both practical and affordable.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Spaceborne Imaging Radar Symp.; p 96-98
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  • 90
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    Publication Date: 2011-08-18
    Description: The SEASAT-A synthetic aperture radar, the first spaceborne SAR, utilized an all solid state RF signal synthesizer and L-band transmitter to drive a corporately fed flat plate array. The RF signal synthesizer generated a linear FM ""CHIRP'' waveform and provided stable CW reference signals used to upconvert the received signal to a unified S-band downlink channel, and to synchronize satellite control logic. The transmitter generated 1200 watts peak RF power (66 watts average) at a center frequency of 1.275 GHz from 354 watts of DC prime power. Linear FM CHIRP swept symmetrically around the center frequency with a bandwidth of 19.05 MHz and a pulse duration of 33.8 sec. Pulse repetition rate was variable from 1647 to 1944 pps. These transmitter signal parameters combined with the flat plate 34 x 7.5 ft aperture at an orbital altitude of 498 miles and a look angle 20 deg off nadir gave the SAR an 85 foot resolution over a 15.5 mile wide swath.
    Keywords: COMMUNICATIONS AND RADAR
    Type: JPL Spaceborne Imaging Radar Symp.; p 41-47
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  • 91
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    In:  Other Sources
    Publication Date: 2011-08-18
    Description: Spaceborne imaging radars for the decade of the '90s will be called upon to provide increased illumination parameter flexibility, polar orbital coverage, and to operate from the same platform with other advanced sensors such as multilinear arrays. The potential information content in accurately merged microwave infrared, or microwave visible images is enormous by comparison to either radar images alone or visible/infrared images alone, since microwave images are principally responsive to surface geometry whereas visible/infrared images are highly sensitive to surface chemistry. A strawman system concept in which a SAR and multilinear array (MLA) are flown on a polar orbiting free flyer at 800 km altitude is discussed. Data would be relayed to ground via the TDRSS (or equivalent).
    Keywords: COMMUNICATIONS AND RADAR
    Type: JPL Spaceborne Imaging Radar Symp.; p 19-25
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  • 92
    Publication Date: 2011-08-18
    Description: A correlation of known archaeologic sites with the mapped locations of the streamcourses is expected and may lead to new interpretations of early human history in the Sahara. The valley networks, faults, and other subjacent bedrock features mapped on the SIR-A images are promising areas for ground water and mineral exploration. Additionally, the analogies between the interplay of wind and running water in the geologic history of the Sahara and of Mars are strengthened by the SIR-A discoveries of relict drainage systems beneath the eolian veneer of Egypt and Sudan.
    Keywords: COMMUNICATIONS AND RADAR
    Type: Spaceborne Imaging Radar Symp.; p 10-12
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  • 93
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    Publication Date: 2011-08-18
    Description: Previously cited in issue 01, p. 60, Accession no. A83-10900
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Aircraft (ISSN 0021-8669); 20; 907-912
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  • 94
    Publication Date: 2011-08-18
    Description: Previously cited in issue 13, p. 2109, Accession no. A82-30152
    Keywords: STRUCTURAL MECHANICS
    Type: Journal of Aircraft (ISSN 0021-8669); 20; 899-906
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  • 95
    Publication Date: 2011-08-18
    Description: An examination of the impact of mismatch on the performance of convolutionally encoded/Viterbi decoded narrow-band FM with limiter/discriminator detection is presented. Attention was given to the potential gain available by the combination of this type of system in terms of hard and soft decision decoding. Soft decision decoding was demonstrated to offer only approximately 0.3 dB better performance than hard decision coding. It was also shown, through a technique involving the number of clicks occurring in each detection interval, that both soft and hard decision decoding bit error probability performance could be improved. It is concluded that the mismatch between the coding channel and the decoding metric of the Viterbi algorithm is responsible for reducing the difference between hard and soft decoding metrics.
    Keywords: COMMUNICATIONS AND RADAR
    Type: IEEE Transactions on Communications; COM-31; Jan. 198
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  • 96
    Publication Date: 2011-08-18
    Description: A fracture mechanics analysis has been developed that describes the progress of delamination damage in composite plates struck by a hard spherical object. The analysis is based on large deflection plate mechanics for circular isotropic plates wherein multiple axisymmetric delaminations grow. Test data show that the analysis predicts the influence of plate thickness, support conditions, and matrix toughness on the onset and propagation of delamination.
    Keywords: STRUCTURAL MECHANICS
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  • 97
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    Publication Date: 2011-08-18
    Description: A three-dimensional element based on the total Lagrangian description of large deformations of a layered anisotropic composite medium is developed, validated, and used to analyze layered composite shells. The element contains the following features: geometric nonlinearity, dynamic (transient) behavior, and arbitrary lamination scheme and lamina properties. Numerical results of nonlinear bending, natural vibration, and transient response are presented to illustrate the capabilities of the element.
    Keywords: STRUCTURAL MECHANICS
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  • 98
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    In:  CASI
    Publication Date: 2016-06-07
    Description: One of the primary drivers that prompted the initiation of the hot section technology (HOST) program was the recognized need for improved cyclic durability of costly hot section components. All too frequently, fatigue in one form or another was directly responsible for the less than desired durability, and prospects for the future weren't going to improve unless a significant effort was mounted to increase our knowledge and understanding of the elements governing cyclic crack initiation and propagation lifetime. Certainly one of the important factors is the ability to perform accurate structural stress-strain analyses on a routine basis to determine the magnitudes of the localized stresses and strains since it is these localized conditions that govern the initiation and crack growth processes. Developing the ability to more accurately predict crack initiation lifetimes and cyclic crack growth rates for the complex loading conditions found in turbine engine hot sections is of course the ultimate goal of the life prediction research efforts. It has been found convenient to divide the research efforts into those dealing with nominally isotropic and anisotropic alloys; the latter for application to directionally solidified and single crystal turbine blades.
    Keywords: STRUCTURAL MECHANICS
    Type: Turbine Eng. Hot Sect. Technol. (HOST); p 205-207
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  • 99
    Publication Date: 2016-06-07
    Description: The Hot Section Technology (HOST) Project is a NASA-sponsored endeavor to improve the durability of advanced gas turbine engines for commercial and military aircraft. Through improvements in the analytical models and life prediction systems, designs for future hot section components , the combustor and turbine, will be more accurately analyzed and will incorporate features required for longer life in the more hostile operating environment of high performance engines.
    Keywords: STRUCTURAL MECHANICS
    Type: Turbine Eng. Hot Sect. Technol. (HOST); p 1-6
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  • 100
    Publication Date: 2016-06-07
    Description: The building of operational clear air radar wind profilers is discussed. The choice of operating frequency and antenna configuration for these profilers is examined. The cost and performance of a (10 lambda) 2 antenna array versus operating frequency over the range 30 to 400 MHz is compared. To simplify the comparison the array beam will be fixed and the array will be uniformly fed. Yagi and coaxial collinear (COCO) cable antennas are compared, although other configurations may be competitive. It is assumed that the array is driven by a typical 50 kW peak power, 1 kW average, power transmitter located at the array edge when calculating feedline power handling requirements and when system performance is compared. For this comparison an array aperture of (10 lambda) 2 was chosen since a one way beam width of 5 deg or less is desirable to limit beam spreading effects.
    Keywords: COMMUNICATIONS AND RADAR
    Type: International Council of Scientific Unions Middle Atmosphere Program, Vol. 9; p 470-476
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