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At least 361 records · Page 20

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NASA NTRS2007

Calculation of Hub Loads at Low Airspeeds with Active Control

The effect of individual blade control (IBC) on the full-scale, low airspeed, level flight UH-60A oscillatory fixed system 4P hub loads and the rotating system blade bending moments is studied. The effect of a single 3P IBC input has been considered in this analytical study. At the low speed under consideration, it has been found that convergence of the comprehensive analysis is important for obtaining good predictions. Good correlation has been obtained with the measured full-scale wind tunnel data for the shapes of the fixed system 4P hub loads variations with the 3P IBC input phase, and also for the "best" phase of the 3P input (for minimum hub loads). The blade bending moment comparison shows mixed results. The 3P lead lag and the 4P flap bending moment trends with the 3P IBC input phase are reasonably predicted, whereas the 5P lead lag bending moment trend is not predicted well. Finally, the prediction of the baseline (no IBC) bending moments needs further study.

Kottapalli, Sesi↗

NASA NTRS1990

A geometric representation scheme suitable for shape optimization

A geometric representation scheme is outlined which utilizes the natural design variable concept. A base configuration with distinct topological features is created. This configuration is then deformed to define components with similar topology but different geometry. The values of the deforming loads are the geometric entities used in the shape representation. The representation can be used for all geometric design studies; it is demonstrated here for structural optimization. This technique can be used in parametric design studies, where the system response is defined as functions of geometric entities. It can also be used in shape optimization, where the geometric entities of an original design are modified to maximize performance and satisfy constraints. Two example problems are provided. A cantilever beam is elongated to meet new design specifications and then optimized to reduce volume and satisfy stress constraints. A similar optimization problem is presented for an automobile crankshaft section. The finite element method is used to perform the analyses.

Tortorelli, Daniel A.↗

NASA NTRS2014

The Development of a Conical Composite Energy Absorber for Use in the Attenuation of Crash/Impact Loads

A design for a novel light-weight conical shaped energy absorbing (EA) composite subfloor structure is proposed. This composite EA is fabricated using repeated alternating patterns of a conical geometry to form long beam structures which can be implemented as aircraft subfloor keel beams or frame sections. The geometrical features of this conical design, along with the hybrid composite materials used in the manufacturing process give a strength tailored to achieve a constant 25-40 g sustained crush load, small peak crush loads and long stroke limits. This report will discuss the geometrical design and fabrication methods, along with results from static and dynamic crush testing of 12-in. long subcomponents.

Littell, Justin D.↗

NASA NTRS1983

Safe structures for future aircraft

The failure mechanisms, design lessons, and test equipment employed by NASA in establishing the airworthiness and crashworthiness of aircraft components for commercial applications are described. The composites test programs have progressed to medium primary structures such as stabilizers and a vertical fin. The failures encountered to date have been due to the nonyielding nature of composites, which do not diffuse loads like metals, and the presence of eccentricities, irregular shapes, stiffness changes, and discontinuities that cause tension and shear. Testing to failure, which always occurred in first tests before the design loads were reached, helped identify design changes and reinforcements that produced successful products. New materials and NDE techniques are identified, together with aircraft structural design changes that offer greater protection to the passengers, fuel antimisting agents, and landing gear systems.

Mccomb, H. G., Jr.↗

NASA NTRS2010

Phalange Tactile Load Cell

A tactile load cell that has particular application for measuring the load on a phalange in a dexterous robot system. The load cell includes a flexible strain element having first and second end portions that can be used to mount the load cell to the phalange and a center portion that can be used to mount a suitable contact surface to the load cell. The strain element also includes a first S-shaped member including at least three sections connected to the first end portion and the center portion and a second S-shaped member including at least three sections coupled to the second end portion and the center portion. The load cell also includes eight strain gauge pairs where each strain gauge pair is mounted to opposing surfaces of one of the sections of the S-shaped members where the strain gauge pairs provide strain measurements in six-degrees of freedom.

Ihrke, Chris A.↗

NASA NTRS1978

On a numerical solution of the plastic buckling problem of structures

An automated digital computer procedure is presented for the accurate and efficient solution of the plastic buckling problem of structures. This is achieved by a Sturm sequence method employing a bisection strategy, which eliminates the need for having to solve the buckling eigenvalue problem at each incremental (decremental) loading stage that is associated with the usual solution techniques. The plastic buckling mode shape is determined by a simple inverse iteration process, once the buckling load has been established. Numerical results are presented for plate problems with various edge conditions. The resulting computer program written in FORTRAN V for the JPL UNIVAC 1108 machine proves to be most economical in comparison with other existing methods of such analysis.

Gupta, K. K.↗

NASA NTRS1982

Superplastic forming/weld-brazing of titanium skin-stiffened compression panels

A study was conducted to exploit the processing advantages of superplastic forming and weld-brazing for the fabrication of titanium skin-stiffened structural components. Small titanium compression panels were fabricated and tested at room temperature. Stiffeners having configurations of a conventional hat shape, beaded shaped web, ribbed shaped web, or stepped shaped web were investigated. The data from the panel tests included load-shortening curves, local buckling strengths, and failure loads. Experimental buckling loads were compared with buckling loads calculated using a finite-element analysis. The superplastic formed/weld-brazed panels having complex shaped stiffeners developed from 20 to 58 percent higher local buckling strengths than panels with conventionally shaped stiffeners.

Royster, D. M.↗

NASA NTRS1977

Load regulating latch

A load regulating mechanical latch is described that has a pivotally mounted latch element having a hook-shaped end with a strike roller-engaging laterally open hook for engaging a stationary strike roller. The latch element or hook is pivotally mounted in a clevis end of an elongated latch stem that is adapted for axial movement through an opening in a support plate or bracket mounted to a structural member. A coil spring is disposed over and around the extending latch stem and the lower end of the coil spring engages the support bracket. A thrust washer is removably attached to the other end of the latch stem and engages the other end of the coil spring and compresses the coil spring thereby preloading the spring and the latch element carried by the latch stem. The hook-shaped latch element has a limited degree of axial travel for loading caused by structural distortion which may change the relative positions of the latch element hook and the strike roller. Means are also provided to permit limited tilt of the latch element due to loading of the hook.

Appleberry, W. T.↗

NASA NTRS1989

The durability of graphite/epoxy laminate subjected to repeated low velocity impact

Low velocity impact has been considered as quasi-static loading, as the dynamic effects are decaying before the pressure reaches its maximum. However, when the impact energy is low enough as not to cause visible damage, the dynamic effect at the beginning of the impact may cause internal damage to the laminate. Laminates were loaded quasi-statically and by impact to the same bending strain and with the same indenter shape several times. The laminates that were subjected to the impact loading failed much more rapidly. Analysis of the problem shows that the stress waves created by the impact at the beginning of contact intensify the damage zone created by the preceding impact until the final failure occurs.

Rotem, A.↗

NASA NTRS2007

Balloon Design Software

PlanetaryBalloon Version 5.0 is a software package for the design of meridionally lobed planetary balloons. It operates in a Windows environment, and programming was done in Visual Basic 6. By including the effects of circular lobes with load tapes, skin mass, hoop and meridional stress, and elasticity in the structural elements, a more accurate balloon shape of practical construction can be determined as well as the room-temperature cut pattern for the gore shapes. The computer algorithm is formulated for sizing meridionally lobed balloons for any generalized atmosphere or planet. This also covers zero-pressure, over-pressure, and super-pressure balloons. Low circumferential loads with meridionally reinforced load tapes will produce shapes close to what are known as the "natural shape." The software allows for the design of constant angle, constant radius, or constant hoop stress balloons. It uses the desired payload capacity for given atmospheric conditions and determines the required volume, allowing users to design exactly to their requirements. The formulations are generalized to use any lift gas (or mixture of gases), any atmosphere, or any planet as described by the local acceleration of gravity. PlanetaryBalloon software has a comprehensive user manual that covers features ranging from, but not limited to, buoyancy and super-pressure, convenient design equations, shape formulation, and orthotropic stress/strain.

Farley, Rodger↗

NASA NTRS1985

Wide-range displacement expressions for standard fracture mechanics specimens

Wide-range algebraic expressions for the displacement of cracked fracture mechanics specimens are developed. For each specimen two equations are given: one for the displacement as a function of crack length, the other for crack length as a function of displacement. All the specimens that appear in ASTM Test for Plane-Strain Fracture Toughness of Metallic Materials (E 399) are represented in addition to the crack mouth displacement for a pure bending specimen. For the compact tension sample and the disk-shaped compact tension sample, the displacement at the crack mouth and at the load line are both considered. Only the crack mouth displacements for the arc-shaped tension samples are presented. The agreement between the displacements or crack lengths predicted by the various equations and the corresponding numerical data from which they were developed are nominally about 3 percent or better. These expressions should be useful in all types of fracture testing including fracture toughness, K-resistance, and fatigue crack growth.

Kapp, J. A.↗

NASA NTRS2003

Passive Ball Capture Joint

A passive ball capture joint has a sleeve with a plurality of bores distributed about a circumference thereof and formed therethrough at an acute angle relative to the sleeve's longitudinal axis. A spring-loaded retainer is slidingly fitted in each bore and is biased such that, if allowed, will extend at least partially into the sleeve to retain a ball therein. A ring, rotatably mounted about the bores, has an interior wall defining a plurality of shaped races that bear against the spring-loaded retainers. A mechanized rotational force producer is coupled to the ring. The ring can be rotated from a first position (that presses the retainers into the sleeve to lock the ball in place) to a second position (that allows the retainers to springback out of the sleeve to release the ball).

Richard A Cloyd↗

NASA NTRS1983

Growth and stability of interacting surface flaws of arbitrary shape

Growth regimes of interacting surface flaws of arbitrary shape are analyzed with the aid of the body force method, and the stability of the process is assessed on the basis of the variation of the load during the growth. It is shown that irregularly shaped flaws are often associated with very high stress intensity factors locally, which tend to change as the flaws grow into more regular shapes. Several examples of various flaw shapes are worked out for illustration, and it is shown that a simple formula seems to provide an accurate estimate of the maximum stress intensity factor for surface flaws of various shapes, which are not very slender. The formula involves the overall maximum tension, as well as the area of the projection of the flaw on the plane normal to the maximum tension.

Murakami, Y.↗

NASA NTRS1959

Hydrodynamic Impact-Load Alleviation with a Penetrating Hydro-Ski

A penetrating hydro-ski was mounted below a model tested previously in the study reported in NACA Technical Note 4401, and a series of impacts were made in the Langley impact basin to determine load alleviation with this type of hydro-ski. The hydro-ski was designed to penetrate through seaway irregularities with a minimum of drag and with small impact loads. The penetrating hydro-ski was small (beam-loading coefficient of 111) and of a streamline shape with the bottom designed for flush retraction into the main model. A series of impacts at fixed trim angles of 8, 16, and 30 deg were made in smooth water and at a fixed trim angle of 8 deg in rough water. The loads and motions of the model were recorded, and photographic observations of the flow and cavities generated in the water by the penetrating hydro-ski were made. The data are presented and the maximum impact loads and maximum drafts of the model with the penetrating hydro-ski are compared with those of the model obtained without the penetrating hydro-ski. Maximum load reductions of 30 to 70 percent in smooth water and of 50 to 80 percent in rough water are indicated. Cavity and flow generation by the penetrating hydro-ski are discussed, and it is indicated that the penetrating hydro-ski moved smoothly through the water and generated deep cavities which are shown by stereophotographs.

Edge, Philip M., Jr.↗

NASA NTRS1989

Absorption and emission line shapes in the O2 atmospheric bands - Theoretical model and limb viewing simulations

A multiple scattering radiative transfer model has been developed to carry out a line-by-line calculation of the absorption and emission limb measurements that will be made by the High Resolution Doppler Imager to be flown on the Upper Atmosphere Research Satellite. The multiple scattering model uses the doubling and adding methods to solve the radiative transfer equation, modified to take into account a spherical inhomogeneous atmosphere. Representative absorption and emission line shapes in the O2 1Sigma(+)g - 3Sigma(-)g atmospheric bands (A,B, and gamma) and their variation with altitude are presented. The effects of solar zenith angle, aerosol loading, surface albedo, and cloud height on the line shapes are also discussed.

Abreu, Vincent J.↗

NASA NTRS1932

Pressure Distribution Over a Thick, Tapered and Twisted Monoplane Wing Model-NACA 81-J

This reports presents the results of pressure distribution tests on a thick, tapered and twisted monoplane wing model. The investigation was conducted for the purpose of obtaining data on the aerodynamic characteristics of the new wing and to provide additional information suitable for use in the design of tapered cantilever wings. The tests included angles of attack up to 90 degrees. The span loading over the wing was approximately of elliptical shape, which gave rise to relatively small bending moments about the root. The angle of zero lift for all sections along the span varied only within plus or minus 0.4 degree of the angle of zero lift for the whole wing, resulting in small leading edge loads for the high-speed condition of flight. The results also add to the available information for the study of large angles of attack.

Wenzinger, Carl J↗

NASA NTRS2017

A Rigid Mid-Lift-to-Drag Ratio Approach to Human Mars Entry, Descent, and Landing

Current NASA Human Mars architectures require delivery of approximately 20 metric tons of cargo to the surface in a single landing. A proposed vehicle type for performing the entry, descent, and landing at Mars associated with this architecture is a rigid, enclosed, elongated lifting body shape that provides a higher lift-to-drag ratio (L/D) than a typical entry capsule, but lower than a typical winged entry vehicle (such as the Space Shuttle Orbiter). A rigid Mid-L/D shape has advantages for large mass Mars EDL, including loads management, range capability during entry, and human spaceflight heritage. Previous large mass Mars studies have focused more on symmetric and/or circular cross-section Mid-L/D shapes such as the ellipsled. More recent work has shown performance advantages for non-circular cross section shapes. This paper will describe efforts to design a rigid Mid-L/D entry vehicle for Mars which shows mass and performance improvements over previous Mid-L/D studies. The proposed concept, work to date and evolution, forward path, and suggested future strategy are described.

Cerimele, Christopher J.↗

NASA NTRS2021

Less Atmospheric Radiative Heating By Dust Due to the Synergy of Coarser Size and Aspherical Shape

Mineral dust aerosols cool and warm the atmosphere by scattering and absorbing solar (shortwave: SW) and thermal (longwave: LW) radiation. However, significant uncertainties remain in dust radiative effects, largely due to differences in the dust size distribution and spectral optical properties simulated in Earth system models. Dust models typically underestimate the coarse dust load (more than 2.5 µm in diameter) and assume a spherical shape, which leads to an overestimate of the fine dust load (less than 2.5 µm) after the dust emissions in the models are scaled to match observed dust aerosol optical depth at 550 nm (DAOD550). Here, we improve the simulated dust properties with data sets that leverage measurements of size-resolved dust concentration, asphericity factor, and refractive index in a coupled global chemical transport model with a radiative transfer module. After the adjustment of size-resolved dust concentration and spectral optical properties, the global and annual average of DAOD550 from the simulation increases from 0.023 to 0.029 and falls within the range of a semi-observationally based estimate (0.030 ± 0.005). The reduction of fine dust load after the adjustment leads to a reduction of the SW cooling at the top of the atmosphere (TOA). To improve agreement against a semi-observationally based estimate of the radiative effect efficiency at TOA, we find that a less absorptive SW dust refractive index is required for coarser aspherical dust. Thus, only a minor difference is estimated for the net global dust radiative effect at TOA (−0.08 vs. −0.00 W m−2 on a global scale). Conversely, our sensitivity simulations reveal that the surface warming is substantially enhanced near the strong dust source regions (less cooling to −0.23 from −0.60 W m−2 on a global scale). Thus, less atmospheric radiative heating is estimated near the major source regions (less heating to 0.15 from 0.59 W m−2 on a global scale), because of enhanced LW warming at the surface by the synergy of coarser size and aspherical shape.

simulated dust properties↗