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Results for “Structural constraints”

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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Structural optimization with flutter speed constraints using maximized step size

A procedure is presented for the minimization of structural mass while satisfying flutter speed constraints. The procedure differs from other optimization methods in that the flutter speed is exactly satisfied at each resizing step, and the step size is determined by a direct minimization of the objective function (mass) for each set of flutter derivatives calculated. In conjunction with this method, a new move vector is suggested which results in a very efficient resizing procedure.

Oconnell, R. F.↗
NASA NTRS1990

Stacking optimization of compressor blades of gas turbine engines

A procedure is presented to obtain optimal designs of axial compressor blades with structural design constraints. Coefficients of the polynomials defining the circumferential tilting angles and the axial leaning distances of the airfoil cross sections from the initial design geometry are used as design variables. The compressor blades are modeled by 20-node solid elements. An efficient finite element method is developed for modal analysis and sensitivity analysis with respect to the design variables. Based on this information, a sequential linear programming method is applied to calculate the required change of geometry for the desired structural design constraints.

Cheu, Tsu-Chien↗
NASA NTRS1974

Automated structural design with aeroelastic constraints - A review and assessment of the state of the art

A review and assessment of the state of the art in automated aeroelastic design is presented. Most of the aeroelastic design studies appearing in the literature deal with flutter, and, therefore, this paper also concentrates on flutter. The flutter design problem is divided into three cases: as isolated flutter mode, neighboring flutter modes, and a hump mode which can rise and cause a sudden, discontinuous change in the flutter velocity. Synthesis procedures are presented in terms of techniques that are appropriate for problems of various levels of difficulty. Current trends, which should result in more efficient, powerful and versatile design codes, are discussed. Approximate analysis procedures and the need for simultaneous consideration of multiple design requirements are emphasized.

Stroud, W. J.↗
NASA NTRS1982

Correction of lunar seismograms for instrumental and near-surface effects and constraints on the velocity structure of the lunar interior

Long-period lunar seismograms were studied with the aim of identifying consistent sets of direct shear and secondary wave arrivals, thus constraining the velocities in the lunar mantle and the depths of the velocity discontinuities. Two velocity models were used to locate the natural impacts and the shallow moonquakes and to obtain the travel time residuals. Seismic sections were made of the radial, transverse, and vertical components of ground motion for impacts, shallow, and deep moonquakes in order to search for consistent sets of secondary wave arrivals. No conclusive set of secondary arrivals could be recognized on the seismic sections and thus the velocities and depths of the velocity discontinuities cannot be severely constrained by secondary arrivals. It is likely that the crust is thinner than 50 km and that a first-order discontinuity separates the upper and lower crust at a depth of between 20 and 30 km.

Horvath, P.↗
NASA NTRS1985

Application of singular value decomposition to structural dynamics systems with constraints

Singular value decomposition is used to construct a coordinate transformation for a linear dynamic system subject to linear, homogeneous constraint equations. The method is compared with two commonly used methods, namely classical Gaussian elimination and Walton-Steeves approach. Although the classical method requires fewer numerical operations, the singular value decomposition method is more accurate and convenient in eliminating the dependent coordinates. Numerical examples are presented to demonstrate the application of the method.

Juang, J.-N.↗
NASA NTRS1985

Constraints on the rheological structure of the mantle

Rheological models of the mantle are at present limited to radial symmetry, usually with homogeneous linearly viscous or viscoelastic incompressible layers. While such models are probably overly simple, they readily allow calculation of geophysical effects, such as post glacial rebound and related changes in the Earth's shape. They are also directly applicable to problems of global mantle flow and plate motions.

Oconnell, R. J.↗
NASA NTRS1987

Constraints on the lithospheric structure of Venus from mechanical models and tectonic surface features

The evidence for the extensional or compressional origins of some prominent Venusian surface features disclosed by radar images is discussed. Using simple models, the hypothesis that the observed length scales (10-20 km and 100-300 km) of deformations are controlled by dominant wavelengths arising from unstable compression or extension of the Venus lithosphere is tested. The results show that the existence of tectonic features that exhibit both length scales can be explained if, at the time of deformation, the lithosphere consisted of a crust that was relatively strong near the surface and weak at its base, and an upper mantle that was stronger than or nearly comparable in strength to the upper crust.

Zuber, Maria T.↗
NASA NTRS1989

Constraints on the deep structure and dynamic processes beneath the Alps and adjacent regions from an analysis of gravity anomalies

Gravity anomalies over the Alps and the Molasse Basin are examined, focusing on the relationship between the anomalies and the tectonic processes beneath the region. Bouguer gravity anomalies measured in France, Germany, Italy, and Switzerland are analyzed. No large isostatic anomalies are observed over the Alps and an elastic model is unable to account for gravity anomalies over the Molasse Basin. These results suggest that the dynamic processes that flexed the European plate down, forming the Molasse Basin and building the Alpine chain, have waned. It is proposed that the late Cenozoic uplift of the region may be due to a diminution or termination of downwelling of mantle material.

Lyon-Caen, Helene↗
NASA NTRS1990

Constraints on the subsurface structure of Europa

The wedge-shaped bands appearing near the anti-Jovian point on Europa are tension cracks which, after formation on an intact lithosphere, have facilitated the rotation of ice-lithosphere sections decoupled from the silicate interior. Such factors as fluid pressure, surface temperature, silicate impurities in the ice, and strain rates, would have affected the processes in question. A minimum degree of differentiation is required for Europa to mechanically decouple the rotated ice lithosphere from the underlying, predominantly silicate mantle.

Golombek, M. P.↗
NASA NTRS1993

Constraints on lithospheric thermal structure for the Indian Ocean from depth and heat flow data

Models for the thermal evolution of oceanic lithosphere are primarily constrained by variations in seafloor depth and heat flow with age. These models have been largely based on data from the Pacific and Atlantic Ocean basins. We construct seafloor age relations for the Indian Ocean which we combine with bathymetric, sediment isopach and heat flow data to derive curves for depth and heat flow versus age. Comparison of these curves with predictions from three thermal models shows that they are better fit by the shallower depths and higher heat flow for the GDH1 model, which is characterized by a thinner and hotter lithosphere than previous models.

Shoberg, Tom↗
NASA NTRS1996

Gravitational Constraints on the Internal Structure of Ganymede

Before the arrival of the Galileo spacecraft in the jovian system, there was little information on the interior structure of jupiter's largest moon, Ganymede. Its mean density (1,940 kg/cu m), determined by the Pioneer and Voyager spacecraft, implies a composition that is roughly 60% rock and 40% ice, which could be uniformly mixed or differentiated into a rocky core and icy mantle. Here we report measurements by the Galileo spacecraft of Ganymede's overall density and the spherical harmonics, J(sub 2) and C(sub 22) of its gravitational field. These data show clearly that Ganymede has differentiated into a core and mantle. Combined with the recent discovery of an intrinsic magnetic field, our gravity results suggest that Ganymede has a metallic core of radius 400-1,300 km surrounded by a silicate mantle, which is in turn enclosed by an ice she approx.800 km thick. Depending on whether the core is pure iron or an alloy of iron and iron sulphide, it could account for as little as 1.4% or as much as one-third of the total mass. If the ice were stripped away, Ganymede could look much like lo' in terms of its size and internal mass distribution.

Anderson, J. D.↗
NASA NTRSDate not supplied

Comparison of Acoustic Models and Trajectory Generation Methods for an Acoustically-Aware Aircraft

Motivation - Noise management is one of the major barriers to Urban Air Mobility - Approaches to noise mitigation (non-exhaustive) - Vehicle configuration - Directivity control via propeller phase synchronization - Trajectory optimization Objective - Create framework for trajectory generation integrating location-based acoustic metrics and vehicle performance limitations - Multiple trajectory optimization methods and acoustic noise models - Mission-relevant constraints - Mission duration, airspace restrictions, ... - Vehicle dynamic constraints - Aircraft structural limitations, min/max airspeed, ... - Vehicle separation/obstacle avoidance - Acoustic constraints at a number of discrete observer locations

Kasey A. Ackerman↗