Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “smoothing”

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 1,243 records · Page 69
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

The calculation of flow over iced airfoils

Progress toward the development of a method for predicting the flowfield of an iced airfoil is described and shown to offer the prospect of a priori calculations of the effects of ice accretion and roughness on airfoil performance. The approach is based on interaction of inviscid flow solutions obtained by a panel method and improved upon by a finite-difference boundary-layer method which, operating in an inverse mode, incorporates viscous effects including those associated with separated flows. Results are presented for smooth, rough and iced airfoils as a function of angle of attack. Those for smooth and rough airfoils confirm the accuracy of the method and its applicability to surfaces with roughness similar to that associated with insect deposition and some forms of ice. Two procedures have been developed to deal with large ice accretion and their performance is examined and shown to be appropriate to the engineering requirements.

Cebeci, Tuncer↗
NASA NTRS1987

10.7-cm solar radio flux and the magnetic complexity of active regions

During sunspot cycles 20 and 21, the maximum in smoothed 10.7-cm solar radio flux occurred about 1.5 yr after the maximum smoothed sunspot number, whereas during cycles 18 and 19 no lag was observed. Thus, although 10.7-cm radio flux and Zurich sunspot number are highly correlated, they are not interchangeable, especially near solar maximum. The 10.7-cm flux more closely follows the number of sunspots visible on the solar disk, while the Zurich sunspot number more closely follows the number of sunspot groups. The number of sunspots in an active region is one measure of the complexity of the magnetic structure of the region, and the coincidence in the maxima of radio flux and number of sunspots apparently reflects higher radio emission from active regions of greater magnetic complexity. The presence of a lag between sunspot-number maximum and radio-flux maximum in some cycles but not in others argues that some aspect of the average magnetic complexity near solar maximum must vary from cycle to cycle. A speculative possibility is that the radio-flux lag discriminates between long-period and short-period cycles, being another indicator that the solar cycle switches between long-period and short-period modes.

Wilson, Robert M.↗
NASA NTRS1988

The expanded Lagrangian system for constrained optimization problems

Smooth penalty functions can be combined with numerical continuation/bifurcation techniques to produce a class of robust and fast algorithms for constrained optimization problems. The key to the development of these algorithms is the Expanded Lagrangian System which is derived and analyzed in this work. This parameterized system of nonlinear equations contains the penalty path as a solution, provides a smooth homotopy into the first-order necessary conditions, and yields a global optimization technique. Furthermore, the inevitable ill-conditioning present in a sequential optimization algorithm is removed for three penalty methods: the quadratic penalty function for equality constraints, and the logarithmic barrier function (an interior method) and the quadratic loss function (an interior method) for inequality constraints. Although these techniques apply to optimization in general and to linear and nonlinear programming, calculus of variations, optimal control and parameter identification in particular, the development is primarily within the context of nonlinear programming.

Poore, A. B.↗
NASA NTRS1988

The geological interpretation of photometric surface roughness

A computer-generated km-scale relief map, whose topographic facets on scales of less than a few m are assumed to have smooth particulate surfaces, is the basis of the present investigation of the relationship between photometrically-derived values of Hapke's (1984) roughness parameter theta and topographic scale. The addition of m-km scale-range relief to the otherwise smooth surface alters integral photometric behavior in a way that is consistent with Hapke's equation; the roughness characterized by theta is an integral property over all scales up to the resolution limit of the photometric data used in its determination. With sufficient phase angle coverage, theta can distinguish terrains with very different integral roughnesses.

Helfenstein, Paul↗
NASA NTRS1988

Using geomagnetic indices to forecast the next sunspot maximum

The Babcock (1961) 'solar dynamo' model and known interactions of the interplanetary magnetic field with the earth's magnetosophere are used to explain the relations found between geomagnetic indices at solar minimum and the sunspot number at the following solar maximum. The work of Kane (1987) is augmented by including recent smoothed aa and Ap indices. A smoothed maximum sunspot number of 163 + or - 40 to peak in October 1990 + or - 9 months for solar cycle 22 is predicted. This value is close to the Schatten and Sofia (1987) value of 170 + or - 25, predicted using more direct solar indicators.

Gonzalez, Guillermo↗
NASA NTRS1988

Interpolation methods for shaped reflector analysis

The diffraction analysis of reflector surfaces which are described only at a discrete set of locations usually leads to the requirement of an interpolation to determine the surface characteristics over a continuum of locations. Two methods of interpolation, the global and the local methods, are presented. The global interpolation representation is a closed-form or series expression valid over the entire surface. The coefficients of a series expression are found by an integration of all of the raw data. Since the number of coefficients used to describe the surface is much smaller than the number of raw data points, the integration effectively provides a smoothing of the raw data. The local interpolation provides a closed-form expression for only a small area of the reflector surface. The subreflector is divided into sectors each of which has constant discretized data. Each area segment is then locally described by a two-dimensional quadratic surface. The second derivative data give the desired smoothed values.

Galindo-Israel, Victor↗
NASA NTRS1988

Structure of rough-wall turbulent boundary layers

Recent experiments have shown that, in rough-wall turbulent boundary layers, drag varies systematically with the spanwise aspect ratio lambda(z) (span/height) of roughness elements. In this paper, the effect of lambda(z) on turbulence structure has been examined. Based on lambda(z), the roughness in a transversely grooved surface with lambda(z) much greater than 1 is the opposite extreme of model plant canopies with lambda(z) much less than 1, studied in wind tunnels, whereas sandgrain is an intermediate type. Second-, third-, and fourth-order turbulence moments have been measured in turbulent boundary layers over transversely grooved and smooth surfaces and compared with available turbulence structure measurements over other types of surfaces. The near-wall turbulence structure is found to vary with lambda(z). The instantaneous motions involved in the flux of shear stress near the wall in smooth and transversely grooved surfaces are opposite in sign to those in three-dimensional roughness. The former is explained in terms of hairpin vortices alone, while the latter group is modeled to have an additional vortex (the so-called necklace vortex which straddles a three-dimensional roughness element near its base).

Bandyopadhyay, Promode R.↗
NASA NTRS1988

Flow Analysis of Space Shuttle Feed Line 17-inch Disconnect Valve

A steady incompressible three-dimensional viscous flow analysis has been conducted for the Space Shuttle External Tank/Orbiter propellant feed line disconnect flapper valves with upstream elbows. The full Navier-Stokes code, INS3D, is modified to handle interior obstacles. Grids are generated by SVTGD3D code. Two dimensional initial grids in the flow cross section with and without the flappers are improved by elliptic smoothing to provide better orthogonality, clustering and smoothness to the three dimensional grid. The flow solver is tested for stability and convergence in the presence of interior flappers. An under-relaxation scheme has been incorporated to improve the solution stability. Important flow characteristics such as secondary flows, recirculation, vortex and wake regions, and separated flows are observed. Computed values for forces, moments, and pressure drop are in satisfactory agreement with water flow test data covering a maximum tube Reynolds number of 3.5 x 10(exp 6). The results will serve as a guide to improved design and enhanced testing of the disconnect.

Kandula, Max↗
NASA NTRS1988

Solution of the Neumann pressure problem in general orthogonal coordinates using the multigrid technique

The multigrid (MG) technique has been advanced for use with Neumann boundary-value problems in clustered curvilinear orthogonal coordinates. This comprises an important step in the analysis of incompressible flow using the velocity-pressure formulation of the Navier-Stokes equations. The finite-difference representation of the problem and the formulation of the restriction and coarse-grid correction operators are examined in detail. Maintaining consistency between these and the integral constraint associated with the Neumann problem is found to be critical for the success of the MG technique. The influence of the smoothing operator is examined by employing Gauss-Seidel, alternating-direction implicit, and strongly implicit techniques. The MG procedure enhances the efficiency of fine-grid solutions of the Neumann problem by a factor of 3 to 14, depending on the type of smoothing operator employed and the values of the problem parameters.

Ghia, U.↗
NASA NTRS1989

Making A Precisely Level Floor

Floor-pouring procedure yields large surface level, smooth, and hard. Floor made of self-leveling, slow-curing epoxy with added black pigment. Epoxy poured to thickness no greater than 0.33 in. (0.84 cm) on concrete base. Base floor seasoned, reasonably smooth and level, and at least 4 in. (10cm) thick. Base rests on thermal barrier of gravel or cinders and contains no steel plates, dividers, or bridges to minimize thermal distortion. Metal retaining wall surrounds base.

Simpson, William G.↗
NASA NTRS1987

Space truss assembly using teleoperated manipulators

Teleoperator experiments were conducted which have demonstrated that a realistic, complex task, typical of those accomplished on-orbit by EVA astronauts, can be done in a smooth, timely manner with manipulators remotely controlled by humans. The real concerns were: (1) do manipulators have sufficient dexterity for these tasks, (2) can sufficient information from the remote site be provided to permit adequate teleoperator control, (3) can reasonable times relative to EVA times be achieved, (4) can the task be completed without frequent and/or damaging impacts among the task components and the manipulators? Positive answers were found to all of these concerns. Tasks times, operator fatigue, and smoothness of operation could be improved by designing the task components and the manipulators for greater compatibility. The data recorded supplements a data base of performance metrics for the same task done in the water immersion training facility as well as space flight and provides management with an objective basis for deciding how and where to apply manipulators in space.

Hankins, Walter W., III↗
NASA NTRS1988

Flight tests of three-dimensional path-redefinition algorithms for transition from Radio Navigation (RNAV) to Microwave Landing System (MLS) navigation when flying an aircraft on autopilot

This report contains results of flight tests for three path update algorithms designed to provide smooth transition for an aircraft guidance system from DME, VORTAC, and barometric navaids to the more precise MLS by modifying the desired 3-D flight path. The first algorithm, called Zero Cross Track, eliminates the discontinuity in cross-track and altitude error at transition by designating the first valid MLS aircraft position as the desired first waypoint, while retaining all subsequent waypoints. The discontinuity in track angle is left unaltered. The second, called Tangent Path, also eliminates the discontinuity in cross-track and altitude errors and chooses a new desired heading to be tangent to the next oncoming circular arc turn. The third, called Continued Track, eliminates the discontinuity in cross-track, altitude, and track angle errors by accepting the current MLS position and track angle as the desired ones and recomputes the location of the next waypoint. The flight tests were conducted on the Transportation Systems Research Vehicle, a small twin-jet transport aircraft modified for research under the Advanced Transport Operating Systems program at Langley Research Center. The flight tests showed that the algorithms provided a smooth transition to MLS.

Hueschen, Richard M.↗
NASA NTRS1988

Measured and predicted pressure distributions on the AFTI/F-111 mission adaptive wing

Flight tests have been conducted using an F-111 aircraft modified with a mission adaptive wing (MAW). The MAW has variable-camber leading and trailing edge surfaces that can change the wing camber in flight, while preserving smooth upper surface contours. This paper contains wing surface pressure measurements obtained during flight tests at Dryden Flight Research Facility of NASA Ames Research Center. Upper and lower surface steady pressure distributions were measured along four streamwise rows of static pressure orifices on the right wing for a leading-edge sweep angle of 26 deg. The airplane, wing, instrumentation, and test conditions are discussed. Steady pressure results are presented for selected wing camber deflections flown at subsonic Mach numbers up to 0.90 and an angle-of-attack range of 5 to 12 deg. The Reynolds number was 26 million, based on the mean aerodynamic chord. The MAW flight data are compared to MAW wind tunnel data, transonic aircraft technology (TACT) flight data, and predicted pressure distributions. The results provide a unique database for a smooth, variable-camber, advanced supercritical wing.

Webb, Lannie D.↗
NASA NTRS1988

Effects of variation in look angle and wavelength in radar images for geologic applications: Implications for SIR-C and Magellan

Implications for SIR-C and Magellan of Seasat, SIR-A/B, and aircraft radar images which show that a variety of geologic targets can have similar backscatter and be indistinguishable under given observing wavelengths and/or look angles are discussed. The SIR-C/X-SAR combination provides three wavelengths, each of which may provide significant information not provided by another, and HH, VV, and one cross polarization each provide different and significant information. For study of unvegetated geological targets in relatively flat terrain, images made at smaller look angles probably provide more information than images from larger look angles. For Magellan, the possible existence of aeolian landforms such as sand dunes or sand sheets on Venus cannot be ruled out simply because they are not seen on radar images. The problem of dissimilar features having identical backscatter must also be considered in the Venusian context, where perhaps lava flows and impact ejecta could have similar high backscatter, or conversely, smooth aeolian materials and smooth volcanic ash (if either exist) could have a similar backscatter.

Blom, R. G.↗
NASA NTRS1989

Multigrid solution of the Navier-Stokes equations on triangular meshes

A Navier-Stokes algorithm for use on unstructured triangular meshes is presented. Spatial discretization of the governing equations is achieved using a finite element Galerkin approximation, which can be shown to be equivalent to a finite volume approximation for regular equilateral triangular meshes. Integration steady-state is performed using a multistage time-stepping scheme, and convergence is accelerated by means of implicit residual smoothing and an unstructured multigrid algorithm. Directional scaling of the artificial dissipation and the implicit residual smoothing operator is achieved for unstructured meshes by considering local mesh stretching vectors at each point. The accuracy of the scheme for highly stretched triangular meshes is validated by comparing computed flat-plate laminar boundary layer results with the well known similarity solution, and by comparing laminar airfoil results with those obtained from various well-established structured quadrilateral-mesh codes. The convergence efficiency of the present method is also shown to be competitive with those demonstrated by structured quadrilateral-mesh algorithms.

Mavriplis, Dimitri J.↗
NASA NTRS1989

Flow boiling with enhancement devices for cold plate coolant channel design

A research program to study the effect of enhancement devices on flow boiling heat transfer in coolant channels, which are heated either from the top side or uniformly, is discussed. Freon 11 is the working fluid involved. The specific objectives are: (1) examine the variations in both the mean and local (axial and circumferential) heat transfer coefficients for a circular coolant channel with either smooth walls or with both a twisted tape and spiral finned walls, (2) examine the effect channel diameter (and the length-to-diameter aspect ratio) variations for the smooth wall channel, and (3) develop an improved data reduction analysis.

Boyd, Ronald D., Sr.↗
NASA NTRS1989

The 3DGRAPE book: Theory, users' manual, examples

A users' manual for a new three-dimensional grid generator called 3DGRAPE is presented. The program, written in FORTRAN, is capable of making zonal (blocked) computational grids in or about almost any shape. Grids are generated by the solution of Poisson's differential equations in three dimensions. The program automatically finds its own values for inhomogeneous terms which give near-orthogonality and controlled grid cell height at boundaries. Grids generated by 3DGRAPE have been applied to both viscous and inviscid aerodynamic problems, and to problems in other fluid-dynamic areas. The smoothness for which elliptic methods are known is seen here, including smoothness across zonal boundaries. An introduction giving the history, motivation, capabilities, and philosophy of 3DGRAPE is presented first. Then follows a chapter on the program itself. The input is then described in detail. A chapter on reading the output and debugging follows. Three examples are then described, including sample input data and plots of output. Last is a chapter on the theoretical development of the method.

Sorenson, Reese L.↗
NASA NTRS1989

Optical properties of sputtered aluminum on graphite/epoxy composite material

Solar absorptance, emittance, and coating thickness were measured for a range of coating thicknesses from about 400 A to 2500 A. The coatings were sputtered from an aluminum target onto 1-inch-diameter substrates of T300/5209 graphite/epoxy composite material with two different surface textures. Solar absorptance and emittance values for the specimens with the smooth surface finish were lower than those for the specimens with the rough surface finish. The ratio of solar absorptance to emittance was higher for the smooth specimens, increasing from 2 to 4 over the coating thickness range, than for the rough ones, which had a constant ratio of about 1. The solar absorptance and emittance values were dependent on the thickness of the sputtered coating.

Witte, William G., Jr.↗