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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 793 records · Page 44

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NASA NTRS1983

The influence of gyroscopic forces on the dynamic behavior and flutter of rotating blades

The structural dynamics of a cantilever turbomachine blade mounted on a spinning and precessing rotor are investigated. Both stability and forced vibration are considered with a blade model that increases in complexity (and verisimilitude) from a spring-restrained point mass, to a uniform cantilever, to a twisted uniform cantilever turbomachine blade mounted on a spinning and precessing rotor are investigated. Both stability and forced vibration are considered with a blade model that increases in complexity (and verisimilitude) from a spring-restrained point mass, to a uniform cantilever, to a twisted uniform cantilever, to a tapered twisted cantilever of arbitrary cross-section. In every instance the formulation is from first principles using a finite element based on beam theory. Both ramp-type and periodic-type precessional angular displacements are considered. In concluding, forced vibrating and flutter are studied using the final and most sophisticated structural model. The analysis of stability is presented and a number of numerical examples are worked out.

Sisto, F.↗

NASA NTRS1983

Flutter and forced response of mistuned rotors using standing wave analysis

A standing wave approach is applied to the analysis of the flutter and forced response of tuned and mistuned rotors. The traditional traveling wave cascade airforces are recast into standing wave arbitrary motion form using Pade approximants, and the resulting equations of motion are written in the matrix form. Applications for vibration modes, flutter, and forced response are discussed. It is noted that the standing wave methods may prove to be more versatile for dealing with certain applications, such as coupling flutter with forced response and dynamic shaft problems, transient impulses on the rotor, low-order engine excitation, bearing motion, and mistuning effects in rotors.

Bundas, D. J.↗

NASA NTRS1984

On the dynamics of equatorial forcing of climate teleconnections

A number of observational, theoretical, and modeling studies have been conducted on the remote influence of the tropics on the midlatitudes. Teleconnection in the geopotential height field between the tropics and the extratropics associated with the Southern Oscillation in the so-called Pacific-North America (PNA) pattern, has often been cited as an example of such remote influence. Simmons et al. (1983) have shown that teleconnections such as PNA may arise both from barotropic instability of the extratropical zonal flow and from tropical forcing. The present investigation is only concerned with the dynamics of the part of the atmospheric teleconnection which arises from tropical forcing. Some fundamentals of Rossby wave theory in unsheared flow are discussed along with the linear response to equatorial forcing for horizontally, sheared zonal mean flow. A global shallow-water spectral model is employed in conjunction with a theoretical analysis to show the teleconnection patterns which develop under different large-scale mean circulation conditions.

Lau, K.-M.↗

NASA NTRS1984

The acoustic radiation force on a heated (or cooled) rigid sphere - Theory

A finite amplitude sound wave can exert a radiation force on an object due to second-order effect of the wave field. The radiation force on a rigid small sphere (i.e., in the long wavelength limit), which has a temperature different from that of the environment, is presently studied. This investigation assumes no thermally induced convection and is relevant to material processing in the absence of gravity. Both isotropic and nonisotropic temperature profiles are considered. In this calculation, the acoustic effect and heat transfer process are essentially decoupled because of the long wavelength limit. The heat transfer information required for determining the force is contained in the parameters, which are integrals over the temperature distribution.

Lee, C. P.↗

NASA NTRS1984

A finite element method for nonlinear forced vibrations of rectangular plates

The finite element method has been extended to determine the response of large amplitude forced vibrations of thin plates. A harmonic force matrix of a rectangular element under uniform harmonic excitation is developed for nonlinear forced vibration analysis. Inplane deformation and inertia are both considered in the formulation. Results obtained are compared with simple elliptic response, perturbation and other approximation solutions.

Mei, C.↗

NASA NTRS1984

The preliminary checkout, evaluation and calibration of a 3-component force measurement system for calibrating propulsion simulators for wind tunnel models

The propulsion simulator calibration laboratory (PSCL) in which calibrations can be performed to determine the gross thrust and airflow of propulsion simulators installed in wind tunnel models is described. The preliminary checkout, evaluation and calibration of the PSCL's 3 component force measurement system is reported. Methods and equipment were developed for the alignment and calibration of the force measurement system. The initial alignment of the system demonstrated the need for more efficient means of aligning system's components. The use of precision alignment jigs increases both the speed and accuracy with which the system is aligned. The calibration of the force measurement system shows that the methods and equipment for this procedure can be successful.

Scott, W. A.↗

NASA NTRS1984

Lateral fluid forces acting on a whirling centrifugal impeller in vaneless and vaned diffuser

Fluid forces on a rotating centrifugal impeller in whirling motion were studied. A two dimensional impeller installed in a parallel-walled vaneless and vaned diffuser whirled on a circular orbit with various positive and negative angular velocities. It is shown that the fluid forces exert a damping effect on the rotor in most operating conditions, but become excitatory when the impeller operates at very low partial discharge while rotating far faster than the whirl speed. The fluid forces were expressed in terms of mass, damping and stiffness matrices. Impellers with the same geometry and whirl condition are calculated. Quantitative agreement is obtained especially in positive whirl.

Ohashi, H.↗

NASA NTRS1985

Turbine blade-tip clearance excitation forces

The results of an effort to assess the existing knowledge and plan the required experimentation in the area of turbine blade tip excitation forces is summarized. The work was carried out in three phases. The first was a literature search and evaluation, which served to highlight the state of the art and to expose the need for an articulated theoretical experimental effort to provide not only design data, but also a rational framework for their extrapolation to new configurations and regimes. The second phase was a start in this direction, in which several of the explicit or implicit assumptions contained in the usual formulations of the Alford force effect were removed and a rigorous linearized flow analysis of the behavior of a nonsymmetric actuator disc was carried out. In the third phase a preliminary design of a turbine test facility that would be used to measure both the excitation forces themselves and the flow patterns responsible for them were conducted and do so over a realistic range of dimensionless parameters.

Martinez-Sanchez, M.↗

NASA NTRS1984

Evolution of oceanic lithosphere - A driving force study of the Nazca plate

The role of the evolution of oceanic lithosphere in driving oceanic plates is tested with elastic and viscous finite element modelling of the Nazca plate. The results indicate that ridge-push forces, when distributed over that portion of the oceanic lithosphere giving rise to the force, predict a stress state that varies more spatially than does previous modelling with ridge forces concentrated at the ridge crest. In particular, the component of stress normal to the ridge vanishes near the ridge for the new modelling. Stress states have also been calculated for a variety of slab-pull models, which include possible dependence on age, rate, and angle of subduction. The predicted stresses vary substantially near the trench among the models with less variation farther from the trench.

Richardson, R. M.↗

NASA NTRS1985

Hydromagnetic buoyancy force in the solar atmosphere

A quantitative definition of the hydromagnetic buoyancy force in the solar atmosphere is presented, on the basis of a numerical analysis of the hydromagnetic characteristics of a circular flux tube. It is shown that the peripheral inhomogeneity of ambient hydromagnetic pressure in the solar atmosphere can lead to hydromagnetic buoyancy in the presence of an extraneous body. The results of the flux tube analyses showed that the strength of the force is often equal to or greater than the gravitational force of the solar atmosphere, and may be responsible for the stationary equilibria of quiescent solar prominences, as well as the outward motions of coronal transients. A diagram is presented in order to describe the field lines in the large-scale solar magnetic field in the presence of hydromagnetic buoyancy.

Yeh, T.↗

NASA NTRS1985

Finite element method for nonlinear forced vibrations of circular plates

Geometric nonlinearities for large amplitude free and forced vibrations of circular plates are investigated. Inplane displacement and inertia are included in the formulation. Finite element method is used. Harmonic force matrix for nonlinear forced vibration analysis is introduced and derived. Various out-of-plane and inplane boundary conditions are considered. The relations of amplitude - frequency ratio for different boundary conditions and various loads conditions are presented.

Decha-Umphai, K.↗

NASA NTRS1985

Forced response analysis of an aerodynamically detuned supersonic turbomachine rotor

High performance aircraft-engine fan and compressor blades are vulnerable to aerodynamically forced vibrations generated by inlet flow distortions due to wakes from upstream blade and vane rows, atmospheric gusts, and maldistributions in inlet ducts. In this report, an analysis is developed to predict the flow-induced forced response of an aerodynamically detuned rotor operating in a supersonic flow with a subsonic axial component. The aerodynamic detuning is achieved by alternating the circumferential spacing of adjacent rotor blades. The total unsteady aerodynamic loading acting on the blading, as a result of the convection of the transverse gust past the airfoil cascade and the resulting motion of the cascade, is developed in terms of influence coefficients. This analysis is used to investigate the effect of aerodynamic detuning on the forced response of a 12-blade rotor, with Verdon's Cascade B flow geometry as a uniformly spaced baseline configuration. The results of this study indicate that, for forward traveling wave gust excitations, aerodynamic detuning is very beneficial, resulting in significantly decreased maximum-amplitude blade responses for many interblade phase angles.

Hoyniak, D.↗

NASA NTRS1984

Design and implementation of a compliant robot with force feedback and strategy planning software

Force-feedback robotics techniques are being developed for automated precision assembly and servicing of NASA space flight equipment. Design and implementation of a prototype robot which provides compliance and monitors forces is in progress. Computer software to specify assembly steps and makes force feedback adjustments during assembly are coded and tested for three generically different precision mating problems. A model program demonstrates that a suitably autonomous robot can plan its own strategy.

Premack, T.↗

NASA NTRS1986

Analysis of the physical atomic forces between noble gas atoms, alkali ions and halogen ions

The physical forces between atoms and molecules are important in a number of processes of practical importance, including line broadening in radiative processes, gas and crystal properties, adhesion, and thin films. The components of the physical forces between noble gas atoms, alkali ions, and halogen ions are analyzed and a data base for the dispersion forces is developed from the literature based on evaluations with the harmonic oscillator dispersion model for higher order coefficients. The Zener model of the repulsive core is used in the context of the recent asymptotic wave functions of Handler and Smith; and an effective ionization potential within the Handler and Smith wave functions is defined to analyze the two body potential data of Waldman and Gordon, the alkali-halide molecular data, and the noble gas crystal and salt crystal data. A satisfactory global fit to this molecular and crystal data is then reproduced by the model to within several percent. Surface potentials are evaluated for noble gas atoms on noble gas and salt crystal surfaces with surface tension neglected. Within this context, the noble gas surface potentials on noble gas and salt crystals are considered to be accurate to within several percent.

Wilson, J. W.↗

NASA NTRS1985

Analytical prediction of labyrinth-seal-flow-induced arotor excitation forces

An analytical method to calculate the rotor excitation forces arising from labyrinth seals is presented. The objective is to model the gas flow through the seal clearance passages and cavities when the rotor is positioned eccentricly relative to the stator center. The seal flow model used in the analysis yields solutions which validate the experimentally observed influence of seal parameters on seal forces reported in the literature. The analytically predicted seal pressure distributions and forces were compared with published experimental results.

Rajakumar, C.↗

NASA NTRS1987

High-Pressure Valve With Controlled Seating Force

Poppet and seat less likely to be damaged by faulty operation. Improvements in widely-used high-pressure valve increase accuracy of preloading of poppet. Redesigned valve prevents metal shavings and other debris from developing during operation, installation, or removal. New features include secondary seal in cap. Belleville washers create precise value of seating force. If installer attempts to exceed force, torque limiter gives tactile and aural warning and makes further force increases difficult.

Bradley, R. H.↗

NASA NTRS1987

Device for quick changeover between wind tunnel force and pressure testing

This device allows for expeditious and repeated changeovers between pressure and force testing and which uses a minimum internal volume of a wind tunnel test structure. A matrix configuration of holes is located on the outer surface of the structure. Pressure tubes lead through the internal cavity of the structure from test sites to this outer surface matrix configuration. A pressure tube connector with a corresponding matrix of holes is connected to the surface of the structure. Pressure tubes leading from remotely located transducers are joined to the connector, thus forming pressure passageways from the test sites to the transducers to allow for pressure testing. When force testing is required, the pressure tube connector is disconnected and a cover plate is connected. The cover plate seals the exposed internal pressure tubes. Also, the outer surface of the cover plate conforms to the exterior of the structure, providing the necessary smooth surface for force testing. If further pressure testing is required, the cover plate can be disconnected and the pressure tube connector reconnected.

Wood, Richard M.↗

NASA NTRS1986

Force-free magnetic fields - The magneto-frictional method

The problem under discussion is that of calculating magnetic field configurations in which the Lorentz force j x B is everywhere zero, subject to specified boundary conditions. We choose to represent the magnetic field in terms of Clebsch variables in the form B = grad alpha x grad beta. These variables are constant on any field line so that each field line is labeled by the corresponding values of alpha and beta. When the field is described in this way, the most appropriate choice of boundary conditions is to specify the values of alpha and beta on the bounding surface. We show that such field configurations may be calculated by a magneto-frictional method. We imagine that the field lines move through a stationary medium, and that each element of magnetic field is subject to a frictional force parallel to and opposing the velocity of the field line. This concept leads to an iteration procedure for modifying the variables alpha and beta, that tends asymptotically towards the force-free state. We apply the method first to a simple problem in two rectangular dimensions, and then to a problem of cylindrical symmetry that was previously discussed by Barnes and Sturrock (1972). In one important respect, our new results differ from the earlier results of Barnes and Sturrock, and we conclude that the earlier article was in error.

Yang, W. H.↗