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At least 1,135 records · Page 63

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NASA NTRS1983

CLFE2D: A generalized plane strain finite element program laminated composites subject to mechanical and hygrothermal loading

CLFE2D is a two dimensional generalized plane strain finite element code, using a linear, four node, general quadrilateral, isoparametric element. The program is developed to calculate the displacements, strains, stresses, and strain energy densities in a finite width composite laminate. CLFE2D offers any combination of the following load types: nodal displacements, nodal forces, uniform normal strain, or hygrothermal. The program allows the user to input one set of three dimensional orthotropic material properties. The user can then specify the angle of material principal orientation for each element in the mesh. Output includes displacements, stresses, strains and strain densities at points selected by the user. An option is also available to plot the underformed and deformed finite element meshes.

Buczek, M. B.↗

NASA NTRS1984

Centrifugal-reciprocating compressor

A centrifugal compressor is described which includes at least one pair of cylinders arranged in coaxial alignment and supported for angular displacement about a common axis of rotation normally disecting a common longitudinal axis of symmetry for the cylinders. The cylinders are characterized by ported closures located at the mutually remote ends thereof through which the cylinders are charged and discharged, and a pair of piston heads seated within the cylinders and supported for floating displacement in compressive strokes in response to unidirectional angular displacement imparted to the cylinders.

Higa, W. H.↗

NASA NTRS1984

Crustal deformation and earthquakes

The manner in which the Earth's surface deforms during the cycle of stress accumulation and release along major faults is investigated. In an investigation of the crustal deformation associated with a thin channel asthenosphere displacements are reduced from those computed for a half space asthenosphere. A previous finding by other workers that displacements are enhanced when flow is confined to a thin channel is based on several invalid approximations. The major predictions of the finite element model are that the near field postseismic displacements and strain rates are less than those for a half space asthenosphere and that the postseismic strain rates at intermediate distances are greater (in magnitude). The finite width of the asthenosphere ceases to have a significant impact on the crustal deformation pattern when its magnitude exceeds about three lithosphere thicknesses.

Cohen, S. C.↗

NASA NTRS1984

Ion beamlet steering for two-grid electrostatic thrusters

An experimental study of ion beamlet steering in which the direction of beamlets emitted from a two grid aperture system is controlled by relative translation of the grids, is described. The results can be used to design electrostatic accelerating devices for which the direction and focus of emerging beamlets are important. Deflection and divergence angle data are presented for two grid systems as a function of the relative lateral displacement of the holes in these grids. At large displacements, accelerator grid impingements become excessive and this determines the maximum allowable displacement and as a result the useful range of beamlet deflection. Beamlet deflection is shown to vary linearly with grid offset angle over this range. The divergence of the beamlets is found to be unaffected by deflection over the useful range of beamlet deflection. The grids of a typical dished grid ion thruster are examined to determine the effects of thermally induced grid distortion and prescribed offsets of grid hole centerlines on the characteristics of the emerging beamlets. The results are used to determine the region on the grid surface where ion beamlet deflections exceed the useful range. Over this region high accelerator grid impingement currents and rapid grid erosion are predicted.

Homa, J. M.↗

NASA NTRS1984

Dugdale plastic zone size and CTOD equations for the compact specimen

With the aim of applying the Dugdale model to the compact specimen, the equations for stress intensity factor and crack surface displacement are obtained for a pair of pin loads and a uniform stress acting on a segment of the crack surface. The plastic zone size is calculated from the 'finiteness' condition of Dugdale, and the results agree well with collocation results from Terada (1983). The load that causes incipient yielding at the compression point of the compact specimen is calculated from a finite element strip yield analysis for an elastic-perfectly plastic material. The crack tip opening displacement for the compact specimen is calculated by adding the displacement at the tip of the physical crack length due to the pin load and due to the uniform stress. The results are within 1.5 percent of current collocation results.

Newman, J. C., Jr.↗

NASA NTRS1984

A blade loss response spectrum for flexible rotor systems

A shock spectrum procedure is developed to estimate the peak displacement response of linear flexible rotor-bearing systems sugjected to a step change in unbalance (i.e., a blade loss). A progressive and a retrograde response spectrum are established. These blade loss response spectra are expressed in a unique non-dimensional form and are functions of the modal damping ratio and the ratio of rotor spin speed to modal damped whirl speed. Modal decomposition using complex modes is utilized to make use of the unique feature of the spectra for the calculation of the peak blade loss displacement response of the rotor system. The procedure is applied to three example systems using several modal superposition strategies. The results of each are compared to true peak displacement obtained by a separate transient response program.

Nelson, H. D.↗

NASA NTRS1983

A finite element model for sound transmission through panels

A finite element method (FEM) is applied to predicting coupled frequencies and pressures within an acoustic cavity in order to characterize sound transmission through a panel. Structural equations of motion are defined and the FEM model is configured with four-noded plate elements, the lateral displacement and two slopes being the unknowns at every node. Each element then has 12 degrees of freedom (DOF) and the displacement variation is expressed by a 12-term nonconforming polynomial. A consistent mass matrix is used to represent the panel mass matrix and a wave equation governs the acoustic volume. Analysis of pressure and displacement over the panel yields a square coupling matrix, and an eigenanalysis leads to a solution of the forced vibration problem.

Ramakrishnan, J. V.↗

NASA NTRS1985

Reciprocating Magnetic Refrigerator

Unit cools to 4 K by adiabatic demagnetization. Two porous matrices of paramagnetic material gadolinium/gallium/garnet held in long piston called displacer, machined out of Micarta (phenol formaldehyde polymer). Holes in side of displacer allow heat-exchange fluid to flow to and through matrices within. Piston seals on displacer prevent substantial mixing of fluid in two loops. Magnetic refrigerator provides continuous rather than "one-shot" cooling.

Johnson, D. L.↗

NASA NTRS1984

The development of a microprocessor-controlled linearly-actuated valve assembly

The development of a proportional fluid control valve assembly is presented. This electromechanical system is needed for space applications to replace the current proportional flow controllers. The flow is controlled by a microprocessor system that monitors the control parameters of upstream pressure and requested volumetric flow rate. The microprocessor achieves the proper valve stem displacement by means of a digital linear actuator. A linear displacement sensor is used to measure the valve stem position. This displacement is monitored by the microprocessor system as a feedback signal to close the control loop. With an upstream pressure between 15 and 47 psig, the developed system operates between 779 standard CU cm/sec (SCCS) and 1543 SCCS.

Wall, R. H.↗

NASA NTRS1985

Sensitivity derivatives for static test loading boundary conditions

Attention is given to the application of the adjoint variable method under the special combination of displacement and stress boundary conditions which occur when static test conditions are simulated. In the two-step problem-solving method employed, calculation of internal stresses, displacements and total reaction force at the boundary is followed by the calculation of the applied load and the total reaction force due to unit displacements.

Gurdal, Z.↗

NASA NTRS1985

Effects of transverse shearing on cylindrical bending, vibration, and buckling of laminated plates

The displacements for cylindrical bending and stretching of laminated and thick plates are expressed through-the-thickness by a few algebraic terms and a complete set of trigonometric terms. Only a few terms of this series are needed to get sufficiently accurate results for laminated and thick plates. Equations of equilibrium based on a sufficient number of terms of this series for displacements are determined using variational theorems from three-dimensional elasticity. Several examples are worked out. The displacements and stresses are obtained for simply supported isotropic and layered beams with a rectangular cross section and a sinusoidal lateral load distribution. These results are compared to an exact elasticity solution. Results for several approximations are obtained for a simply supported and a clamped beam with a rectangular cross section loaded at the center and results are compared to experimental results. Results are also obtained for isotropic and layered beams with a rectangular cross section for several approximations for the lowest natural frequency and buckling load.

Stein, M.↗

NASA NTRS1985

Axisymmetric solid elements by a rational hybrid stress method

Four-node axisymmetric solid elements are derived by a new version of hybrid method for which the assumed stresses are expressed in complete polynomials in natural coordinates. The stress equilibrium conditions are introduced through the use of additional displacements as Lagrange multipliers. A rational procedure is to choose the displacement terms such that the resulting strains are also of complete polynomials of the same order. Example problems all indicate that elements obtained by this procedure lead to better results in displacements and stresses than that by other finite elements.

Tian, Z.↗

NASA NTRS1985

Observations on the propagation, growth, and predictability of Gulf Stream meanders

During a three-year period, Gulf Stream positions determined by satellite infrared imagery on a grid northeast of Cape Hatteras have been correlated against 'inlet' path parameters (displacement from the mean position, angle, and curvature) monitored by an array of inverted echo sounders. By cross-spectral calculations between these measurements, the downstream coherences, phase speeds, and spatial growth rates were determined. The downstream path predictability from these inlet parameters was tested in a multiple input linear response model. The most energetic meanders, with periods of 33-50 days, remained highly coherent for 300 km downstream, roughly the dominant wavelength, with marginal coherence again at 500-575 km. Phase speeds are frequency dependent and decrease with distance downstream. For the 50- (33) day meanders, phase speeds decreased from 10 (17) km/d at the inlet to 6 (8) km/d at a distance downstream of about 550 km. The average growth rate (spatial e-folding wave number) over the entire region is 1.3 x 10 to the -3rd per km. Within 300 km of the inlet, the multiple coherence accounts for 55-65 percent of the total path-displacement variance, with displacement and angle being the best individual predictors in the first and last halves of this region, respectively.

Vazquez, J.↗

NASA NTRS1984

Initial results of sensitivity tests - Performed on the RE-1000 free-piston Stirling engine

Tests have been performed over several years to investigate the dynamics of a free-piston Stirling engine for the purpose of computer code validation. Tests on the 1 kW (1.33 hp) single cylinder engine have involved the determination of the sensitivity of the engine performance to variations in working space pressure, heater and cooler temperatures, regenerator porosity, power piston mass, and displacer dynamics. Maps of engine performance have been recorded with the use of an 81.2 percent porosity regenerator. Both a high-efficiency displacer and a high-power displacer were tested; efficiencies up to 33 percent were recorded, and power output of approximately 1500 W was obtained. Preliminary results of the sensitivity tests are presented, and descriptions of future tests are given.

Schreiber, J. G.↗

NASA NTRS1985

Vuilleumier cycle cryocooler operating below 8 K

This paper describes the design and development of a Vuilleumier cycle cryocooler (VM cooler) operating below 8 K, for the application of small superconducting devices. Liquid nitrogen has been used as a heat sink of the hot displacer. The annular gap between the phenolic displacer and SUS 304 stainless cylinder has been used as a gap regenerator. In order to obtain the cooling temperature below 3 K, we designed a single stage VM cooler which is precooled to 10 K by another two stage VM cooler. The effect of the mean operating pressure, cycle speed and phase difference between the hot and cold displacer of each VM cooler will be also discussed, including the experimental results.

Matsubara, Y.↗

NASA NTRS1985

Elastic-plastic deformation of a metal-matrix composite coupon with a center slot

A comprehensive experimental analysis of deformations of the surface of a metal-matrix specimen is reported. The specimen is a 6-ply 0 + or - 45 sub s boron-aluminum tensile coupon with a central slot. Moire interferometry is used for high-sensitivity whole-field measurements of in-plane displacements. Normal and shear strains are calculated from displacement gradients. Displacement fields are analyzed at various load levels from 15% to 95% of the failure load. Deformations of the boron fibers could be distinguished from those of the matrix. Highly localized plastic slip zones occur tangent to the ends of the slot. Shear strains and concurrent transverse compressive strains in the slip zones reach approximately 10% and 1%, respectively. Upon unloading, elastic recovery in surrounding regions causes a reverse plastic shear strain in the slip zone of about 4%. Longitudinal normal strains on the unslotted ligament peak at the slot boundary at about 1% strain. The strain concentration factor at the end of the slot decreases with load level and the advance of plasticity.

Post, D.↗

NASA NTRS1985

Dislocation model for aseismic fault slip in the transverse ranges of Southern California

Geodetic data at a plate boundary can reveal the pattern of subsurface displacements that accompany plate motion. These displacements are modelled as the sum of rigid block motion and the elastic effects of frictional interaction between blocks. The frictional interactions are represented by uniform dislocation on each of several rectangular fault patches. The block velocities and fault parameters are then estimated from geodetic data. Bayesian inversion procedure employs prior estimates based on geological and seismological data. The method is applied to the Transverse Ranges, using prior geological and seismological data and geodetic data from the USGS trilateration networks. Geodetic data imply a displacement rate of about 20 mm/yr across the San Andreas Fault, while the geologic estimates exceed 30 mm/yr. The prior model and the final estimates both imply about 10 mm/yr crustal shortening normal to the trend of the San Andreas Fault. Aseismic fault motion is a major contributor to plate motion. The geodetic data can help to identify faults that are suffering rapid stress accumulation; in the Transverse Ranges those faults are the San Andreas and the Santa Susana.

Cheng, A.↗

NASA NTRS1985

Pressure broadening of rotational bands. I - A statistical theory

Absorption of electromagnetic waves by rotational transitions of molecules is formulated for the case in which the wave frequency is displaced from resonance by an amount large compared to the reciprocal duration of a typical binary collision, and also large compared to the differences between frequencies of the strong resonances of the gas. In this far-wing limit, Fano's relaxation operator is reduced to a scalar parameter which depends on the frequency displacement. This relaxation parameter is not symmetric with respect to reflection about resonance, but becomes symmetric when multiplied by the factor exp (h/2pi) (omega sub d)/2kT where omega sub d is the frequency displacement. The theory applies to dipolar molecules of any shape, in collisions with either dipolar or quadrupolar molecules.

Rosenkranz, P. W.↗