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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.

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At least 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

New optimality criteria methods - Forcing uniqueness of the adjoint strains by corner-rounding at constraint intersections

In new, iterative continuum-based optimality criteria (COC) methods, the strain in the adjoint structure becomes non-unique if the number of active local constraints is greater than the number of design variables for an element. This brief note discusses the use of smooth envelope functions (SEFs) in overcoming economically computational problems caused by the above non-uniqueness.

Rozvany, G. I. N.↗
NASA NTRS1992

Membrane triangles with corner drilling freedoms. I - The EFF element

The formulation of 3-node 9-DOF membrane elements with normal-to-element-plane rotations (drilling freedoms) is examined in the context of parametrized variational principles. In particular, attention is given to the application of the extended free formulation (EFF) to the construction of a triangular membrane element with drilling freedoms that initially has complete quadratic polynomial expansions in each displacement component. The main advantage of the EFF over the free formulation triangle is that an explicit form is obtained for the higher-order stiffness.

Alvin, Ken↗
NASA NTRS1994

The gravitational potential of a homogeneous polyhedron or don't cut corners

A polyhedron can model irregularly shaped objects such as asteroids, comet nuclei, and small planetary satellites. With minor effort, such a model can incorporate important surface features such as large craters. Here we develop closed-form expressions for the exterior gravitational potential and acceleration components due to a constant-density polyhedron. An equipotential surface of Phobos is illustrated.

Werner, Robert A.↗
NASA NTRS1998

Dynamics of Liquids in Edges and Corners (DYLCO): IML-2 Experiment for the BDPU

Knowledge of the behavior of fluids possessing free surfaces is important to many fluid systems, particularly in space, where the normally subtle effects of surface wettability play a more dramatic and often surprising role. DYLCO for the IML-2 mission was proposed as a simple experiment to probe the particular behavior of capillary surfaces in containers of irregular cross section. Temperature control was utilized to vary the fluid-solid contact angle, a questionable thermodynamic parameter of the system, small changes in which can dramatically influence the configuration, stability, and flow of a capillary surface. Container shapes, test fluid, and temperature ranges were selected for observing both local changes in interface curvature as well as a global change in fluid orientation due to a critical wetting phenomenon. The experiment hardware performed beyond what was expected and fluid interfaces could be readily digitized post flight to show the dependence of the interface curvature on temperature. For each of the containers tested surfaces were observed which did not satisfy the classic equations for the prediction of interface shape with constant contact angle boundary condition. This is explained by the presence of contact angle hysteresis arising from expansion and contraction of the liquid during the heating and cooling steps of the test procedure. More importantly, surfaces exceeding the critical surface curvature required for critical wetting were measured, yet no wetting was observed. These findings are indeed curious and pose key questions concerning the role of hysteresis for this critical wetting phenomena. The stability of such surfaces was determined numerically and it is shown that stability is enhance (reduced) when a surface is in its 'advancing' ('receding') state, The analysis shows complete instability as the critical wetting condition is reached. The case of ideal dynamic wetting is addressed analytically in detail with results of significant flow characteristics presented in closed form. The solutions indicate a square root of T dependence of the capillary 'rise' rate which is corroborated by drop tower tests. The analysis clearly shows that infinite time is necessary for surfaces to reorient at the critical wetting transition.

Langbein, D.↗
NASA NTRS2001

Corner Wrinkling at a Square Membrane Due to Symmetric Mechanical Loads

Thin-film membrane structures are under consideration for use in many future gossamer spacecraft systems. Examples include sunshields for large aperture telescopes, solar sails, and membrane optics. The development of capabilities for testing and analyzing pre-tensioned, thin film membrane structures is an important and challenging aspect of gossamer spacecraft technology development. This paper presents results from experimental and computational studies performed to characterize the wrinkling behavior of thin-fi[m membranes under mechanical loading. The test article is a 500 mm square membrane subjected to symmetric comer loads. Data is presented for loads ranging from 0.49 N to 4.91 N. The experimental results show that as the load increases the number of wrinkles increases, while the wrinkle amplitude decreases. The computational model uses a finite element implementation of Stein-Hedgepeth membrane wrinkling theory to predict the behavior of the membrane. Comparisons were made with experimental results for the wrinkle angle and wrinkled region. There was reasonably good agreement between the measured wrinkle angle and the predicted directions of the major principle stresses. The shape of the wrinkle region predicted by the finite element model matches that observed in the experiments; however, the size of the predicted region is smaller than that determined in the experiments.

Blandino, Joseph R.↗
NASA NTRS2005

Gold coatings for cube-corner retro-reflectors

We report on a comparative study of optical performance of gold films deposited by resistive and e-beam evaporation, including measurements of the scattering from the coated surfaces. The effects of oxygen bombardment and titanium under-layer on optical properties and adhesion were evaluated. The influence of surface preparation on the optical properties was examined also.

reflectors↗
NASA NTRS2008

Thermal Cycle Reliability and Failure Mechanisms of CCGA and PBGA Assemblies with and without Corner Staking

Area array packages (AAPs) with 1.27 mm pitch have been the packages of choice for commercial applications; they are now starting to be implemented for use in military and aerospace applications. Thermal cycling characteristics of plastic ball grid array (PBGA) and chip scale package assemblies, because of their wide usage for commercial applications, have been extensively reported on in literature. Thermal cycling represents the on-off environmental condition for most electronic products and therefore is a key factor that defines reliability.However, very limited data is available for thermal cycling behavior of ceramic packages commonly used for the aerospace applications. For high reliability applications, numerous AAPs are available with an identical design pattern both in ceramic and plastic packages. This paper compares assembly reliability of ceramic and plastic packages with the identical inputs/outputs(I/Os) and pattern. The ceramic package was in the form of ceramic column grid array (CCGA) with 560 I/Os peripheral array with the identical pad design as its plastic counterpart.

plastic ball grid array (PBGA)↗
NASA NTRS2012

Ion source with corner cathode

An ion source may include first, second, and third electrodes. The first electrode may be a repeller having a V-shaped groove. The second electrode may be an electron emitter filament disposed adjacent the base of the V-shaped groove. The third electrode may be an anode that defines an enclosed volume with an aperture formed therein adjacent the electron emitter filament. A potential of the first electrode may be less than a potential of the second electrode, and the potential of the second electrode may be less than a potential of the third electrode. A fourth electrode that is disposed between the electron emitter filament and the anode may be used to produce a more collimated electron beam.

Herrero, Federico A.↗
NASA NTRS2013

Multi-Step Ka/Ka Dichroic Plate with Rounded Corners for NASA's 34m Beam Waveguide Antenna

A multi-step Ka/Ka dichroic plate Frequency Selective Surface (FSS structure) is designed, manufactured and tested for use in NASA's Deep Space Network (DSN) 34m Beam Waveguide (BWG) antennas. The proposed design allows ease of manufacturing and ability to handle the increased transmit power (reflected off the FSS) of the DSN BWG antennas from 20kW to 100 kW. The dichroic is designed using HFSS and results agree well with measured data considering the manufacturing tolerances that could be achieved on the dichroic.

antenna↗