Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “BENDING”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,369 records · Page 76
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

Vibration characteristics of hexagonal radial rib and hoop platforms

Experiment and analysis have been used to characterize the modes of vibration of planar radial rib and hoop hexagonal platforms. Finite element analysis correlated very well with experimental results. The sensitivity of mode shapes and frequencies to cable stiffness and initial tension is presented. Threshold values have been identified, above which changes in cable stiffness do not affect the first few platform vibration modes. Primary vibration modes of the radial rib platform involve beam bending. Vibration modes of the hoop platform exhibit both beam bending and frame bending and torsion. Results indicate for low order polygonal structures, the radial rib concept produced a higher fundamental frequency. For high order polygonal structures, the hoop concept has the potential to achieve a higher fundamental frequency than the radial rib concept.

Belvin, W. K.↗
NASA NTRS1984

Measurement of thigmomorphogenesis and gravitropism by non-intrusive computerized video image processing

A video image processing instrument, DARWIN (Digital Analyser of Resolvable Whole-pictures by Image Numeration), was developed. It was programmed to measure stem or root growth and bending, and coupled to a specially mounted video camera to be able to automatically generate growth and bending curves during gravitropism. The growth of the plant is recorded on a video casette recorder with a specially modified time lapse function. At the end of the experiment, DARWIN analyses the growth or movement and prints out bending and growth curves. This system was used to measure thigmomorphagenesis in light grown corn plants. If the plant is rubbed with an applied force load of 0.38 N., it grows faster than the unrubbed control, whereas 1.14 N. retards its growth. Image analysis shows that most of the change in the rate of growth is caused in the first hour after rubbing. When DARWIN was used to measure gravitropism in dark grown oat seedlings, it was found that the top side of the shoot contracts during the first hour of gravitational stimulus, whereas the bottom side begins to elongate after 10 to 15 minutes.

Jaffe, M. J.↗
NASA NTRS1984

Comparison of experimental and computational compressible flow in a S-duct

This paper describes experimental measurements of secondary flow in a constant area, circular cross-section 30-30 deg S-duct, and compares the results obtained with the computations performed using the PEPSIG code, a parabolized Navier-Stokes code. The flow entering the duct was turbulent, with entrance Mach number of 0.6, and the boundary layer thickness at the duct entrance was 10 percent of the duct diameter. The duct mean radius of curvature to the duct diameter was 5.077. Flow parameters were measured at six stations along the length of the duct. These measurements were made using a five-port cone probe. At least ten radial traverses were made at each station on both sides of the symmetry plane. Wall static pressures along three azimuth angles of zero, 90, and 180 deg along the duct were measured. Plots presenting the secondary velocity field as well as contour plots of the total and static-pressure fields have been obtained. Strong secondary flows were observed in the first bend, and these continued into the second bend with the formation of new vorticity in the opposite sense in the second bend. The flow exiting the duct contained two pairs of counter-rotating vortices. The computational results are in general agreement with the experiments. However, it appears that the computations underestimate the extent of the pressure distortion, due to simplifications made in the pressure field calculations.

Vakili, A.↗
NASA NTRS1985

A 4-node Bilinear Isoparametric Element in Rockwell NASTRAN

The development and evaluation of the Rockwell NASTRAN four node quadrilateral (QUAD4) element is presented. The element derivation utilizes bilinear isoparametric techniques both for membrane and bending characteristics. The QUAD4 element coordinate system, membrane properties, lumped mass matrix, and treatment of warping are based upon the COSMIC/NASTRAN QDMEMI element while the bending characteristics are based on a paper by T. J. R. Hughes. The effects of warping on the bending stiffness, consistent mass, and geometric stiffness are based upon a paper by R. H. MacNeal. Numerical integration is accomplished by Gaussian quadrature on a 2 x 2 grid. Practical user support features include variable element thickness, thermal analysis and layered composite material definitions.

Liao, C.↗
NASA NTRS1986

Effects of Gear-Cutter Geometry on Performance

Bending stress reduced by improving tooth-fillet design. Using optimized gear-cutter design technology, gear designer reduces bending stresses by up to 20 percent. Reduction in bending stress is result of improved geometry of tooth fillet, which, in turn, results in significant improvement in horsepower-per-pound ratio. Gears run quieter and smoother than spur-gear system.

Folenta, D.↗
NASA NTRS1985

Minimum pressure for a zero-prebreathe pressure suit

There are two current approaches to reducing the risk of decompression sickness during repeated extravehicular activity (EVA) without prebreathing 100 percent oxygen. One approach suggests the use of different pressures in the transfer vehicle, the station, and the suit. The other would use advanced pressure-suit technology to build a suit that will make different pressures unnecessary provided the bends-free suit pressure is reasonable and can be readily determined. Research at the USAF School of Aerospace Medicine since November 1982 has been directed at determining this suit pressure using human subjects at simulated altitudes of 16,500 to 10,000 feet (7.8 to 10 psia). An earlier report of this ongoing research showed that bends is not totally eliminated at 7.8 psia. The present study is a continuation of this effort to define a 'bends-free' suit pressure with the initial results suggesting that this pressure begins at around 9.5 psia (from a 14.7 psia station).

Krutz, R. W., Jr.↗
NASA NTRS1985

Electrical, structural and chemical characterization of Si sheet material

Web Dendritic Si ribbons are deformed under a well-defined four point bending stress. Since the mechanical properties of Si are known to depend on the 0 content of the material, 0 measurements using Fourier Transform Infrared Spectroscopy were done to determine a proper control sample of non-defected single crystal Si. Four point bending revealed a unique two step bending behavior for the Web Si ribbons. An initial theory for this behavior involves the interaction of the dislocations generated by the deformation with the central twin planes of the ribbons. Measurements showed a uniformly high 0 content for the Web Si ribbons, approximately 10 to the 18th power atoms/cu.cm. The Web samples had a much broader absorption peak at 9 microns than is usually seen for well-annealed single crystal Si. This broadening is thought to be related to stress in the Web Si ribbons. Two samples containing a known amount of residual stress support this hypothesis. Also, a shoulder on the infrared absorption peak associated with interstitial 0 in Si appears in the transmission vs. wavenumber plots for some of the Web samples. This shoulder has been associated with 0-vacancy complexes or with 0 at dislocations. The O content and configuration do not seem to correlate with the growth configuration of the Web Si ribbon.

Ast, D. G.↗
NASA NTRS1987

Reducing shuttle-payload dynamic interaction with notch filters

The use of notch filters centered on the estimated bending frequencies to reduce the effect of low-frequency Shuttle-payload dynamic interaction is investigated. The Shuttle-payload dynamics that are studied are with payloads attached to the Shuttle Remote Manipulator System (RMS). Other payload-orbiter connection such as payloads pivoted out of the cargo bay on a tilt table can lead to low-frequency bending modes. Payloads attached to the RMS will, however, present greater problems in that the bending modes will be hard to predict and will tend to vary with time as the RMS changes in orientation.

Appleby, Brent D.↗
NASA NTRS1987

Duct flows with swirl

The physics of the flow interaction between swirl and secondary flow was studied in duct bends relevant to the design of advanced aircraft nozzle systems. Both laminar and turbulent subsonic flows were investigated in generic duct bends for different amounts of swirl. The flow calculations are based on an economical three-dimensional spatial marching method employed in an existing computer code (PEPSIG). The computational method and code were extended to allow azimuthal periodicity and solutions in which the polar coordinate singularity occurs in the interior of the flow field. These extensions are needed to address swirling flow and twisted centerlines arising in out-of-plane bends. It was found that appropriate amounts of swirl can reduce total pressure loss relative to nonswirling cases. This conclusion was found to be insensitive to computational mesh.

Tsai, Tommy M.↗
NASA NTRS1986

Prediction of blade stresses due to gust loading

An analysis is developed for investigating the response of a rotor-fuselage system in a three-dimensional gust field wherein the gust velocity conponents can have arbitrary variation in space and time. Each rotor blade undergoes flap bending, lag bending and torsional deflections. The blades are divided into beam elements and each element consists of fifteen nodal degrees of freedom. Quasi-steady strip theory is used to obtain the aerodynamic loads. Unsteady aerodynamic effects are introduced through dynamic inflow modeling. Dynamic stall and reverse flow effects are also included. The fuselage is allowed five degrees of freedom: vertical, longitudinal, lateral, pitch and roll motions. The gust response equations are linearized about the vehicle trim state and the blade steady-state deflected position, and then solved by time integration. The blade bending moments, which determine blade stresses, are evaluated using the force summation technique. Systematic studies are made to identify the importance of several parameters including dynamic stall, forward speed, lag stiffness, gust profile, gust penetration rate and gust velocity direction.

Bir, Gunjit↗
NASA NTRS1987

Fracture study of windshield glass panes

The major stresses which cause crack propagation in windshield glass panes are induced by bending moments which result from the pressure differentials across the panes. Hence the stress intensity factors for the finite plate with the semi-elliptical surface flaw and edge crack under the bending moments are examined. The results show that the crack growth will be upperbound if it is computed by using the stress intensity factor for the finite plate with the edge crack subjected to pure bending moments. Furthermore, if the ratio of crack depth to plate thickness, a/t, is within 0.3, the stress intensity factor can be conservatively assumed to be constant at the value of a/t equal to zero. A simplified equation to predict the structural life of glass panes is derived based on constant stress intensity factor. The accuracy of structural life is mainly dependent on how close the empirical parameter, m, can be estimated.

Yeh, H. Y.↗
NASA NTRS1988

Mach number effects on transonic aeroelastic forces and flutter characteristics

Transonic aeroelastic stability analysis and flutter calculations are presented for a generic transport-type wing based on the use of the CAP-TSD (Computational Aeroelasticity Program - Transonic Small Disturbance) finite-difference code. The CAP-TSD code was recently developed for transonic unsteady aerodynamic and aeroelastic analysis of complete aircraft configurations. A binary aeroelastic system consisting of simple bending and torsion modes was used to study aeroelastic behavior at transonic speeds. Generalized aerodynamic forces are presented for a wide range of Mach number and reduced frequency. Aeroelastic characteristics are presented for variations in freestream Mach number, mass ratio, and bending-torsion frequency ratio. Flutter boundaries are presented which have two transonic dips in flutter speed. The first dip is the usual transonic dip involving a bending-dominated flutter mode. The second dip is characterized by a single degree-of-freedom torsion oscillation. These aeroelastic results are physically interpreted and shown to be related to the steady state shock location and changes in generalized aerodynamic forces due to freestream Mach number.

Mohr, Ross W.↗
NASA NTRS1986

An experiment for determining the Euler load by direct computation

A direct algorithm is presented for computing the Euler load of a column from experimental data. The method is based on exact inextensional theory for imperfect columns, which predicts two distinct deflected shapes at loads near the Euler load. The bending stiffness of the column appears in the expression for the Euler load along with the column length, therefore the experimental data allows a direct computation of bending stiffness. Experiments on graphite-epoxy columns of rectangular cross-section are reported in the paper. The bending stiffness of each composite column computed from experiment is compared with predictions from laminated plate theory.

Thurston, Gaylen A.↗
NASA NTRS1988

Mach number effects on transonic aeroelastic forces and flutter characteristics

Transonic aeroelastic stability analysis and flutter calculations are presented for a generic transport-type wing based on the use of the CAP-TSD (Computational Aeroelasticity Program - Transonic Small Disturbance) finite-difference code. The CAP-TSD code was recently developed for transonic unsteady aerodynamic and aeroelastic analysis of complete aircraft configurations. A binary aeroelastic system consisting of simple bending and torsion modes was used to study aeroelastic behavior at transonic speeds. Generalized aerodynamic forces are presented for a wide range of Mach number and reduced frequency. Aeroelastic characteristics are presented for variations in freestream Mach number, mass ratio, and bending-torsion frequency ratio. Flutter boundaries are presented which have two transonic dips in flutter speed. The first dip is the usual transonic dip involving a bending-dominated flutter mode. The second dip is characterized by a single degree-of-freedom torsion oscillation. These aeroelastic results are physically interpreted and shown to be related to the steady state shock location and changes in generalized aerodynamic forces due to freestream Mach number.

Mohr, Ross W.↗
NASA NTRS1988

Surface and through crack problems in orthotropic plates

The present treatment of the general mode I crack problem in bending- and membrane-loaded orthotropic plates proceeds by formulating the bending problem for a series of planar and through-cracks; by independently varying the six independent constants, the effect of material orthotropy on the stress intensity factor is determined. The surface-crack problem is then formulated by means of the line-spring model, using a transverse-shear theory of plate bending. Attention is given to composite laminates with through-cracks or semielliptic surface cracks. A significant effect is noted for material orthotropy.

Erdogan, F.↗
NASA NTRS1989

Aircraft modal supression system: Existing design approach and its shortcomings

The bending of flexible body aircraft may degrade the ride coMfort of passengers. This is especially noticeable towards the aft end of the aircraft (due to the relatively large tail surfaces) which may easily be excited when flying through turbulence. In addition, some aircraft may experience a front body bending mode which can be annoying to the cabin crew and first class passengers. Normally, this dominant body bending mode falls between 1 to 5 Hz. This range is easily perceived by the human body. Also, in some situations, the rigid body control law may be out of phase with the mode and aggravate the vibration. Hence, an active modal suppression system is desirable for improving the ride quality of the airplane. The size of the mathematical model, which has both the airplane rigid body and flexible characteristics, could easily exceed 100 states. The computational burden and fidelity of this large structural model is addressed.

Ho, J. K.↗
NASA NTRS1990

Direct formulation of a 4-node hybrid shell element with rotational degrees of freedom

A simple 4-node assumed-stress hybrid quadrilateral shell element with rotational or drilling degrees of freedom is formulated. The element formulation is based directly on a 4-node element. This direct formulation requires fewer computations than a similar element that is derived from an internal 8-node isoparametric element in which the midside degrees of freedom are eliminated in favor of rotational degree of freedom at the corner nodes. The formulation is based on the principle of minimum complementary energy. The membrane part of the element has 12 degrees of freedom including rotational degrees of freedom. The bending part of the element also has 12 degrees of freedom. The bending part of the quadratic variations for both in-plane and out-of-plane displacement fields and linear variations for both in-plane and out-of-plane rotation fields are assumed along the edges of the element. The element Cartesian-coordinate system is chosen such as to make the stress field invariant with respect to node numbering. The membrane part of the stress field is based on a 9-parameter equilibrating stress field, while the bending part is based on a 13-parameter equilibrating stress field. The element passes the patch test, is nearly insensitive to mesh distortion, does not lock, possesses the desirable invariance properties, has no spurious modes, and produces accurate and reliable results.

Aminpour, Mohammad A.↗