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The structural performance of 17 meter diameter wind turbine rotors is discussed. Test results for typical steady and vibratory stress measurements are summarized along with predicted values of stress based on a quasi-static finite element model.
Based on the belief that actual flight hardware development of large space systems will necessitate a formalized method of integrating the various engineering discipline analyses, an efficient highly user oriented software system capable of performing interdisciplinary design analyses with tolerable solution turnaround time is planned Specific analysis capability goals were set forth with initial emphasis given to sequential and quasi-static thermal/structural analysis and fully coupled structural/control system analysis. Subsequently, the IAC would be expanded to include a fully coupled thermal/structural/control system, electromagnetic radiation, and optical performance analyses.
A wind tunnel investigation of the acoustic and aerodynamic characteristics of two hybrid inlets installed on a JT15D-1 turbofan engine was performed. The hybrid inlets combined moderate throat Mach number and wall acoustic treatment to suppress the fan inlet noise. Acoustic and aerodynamic data were recorded over a range of flight and engine operating conditions. In a simulated flight environment, the hybrid inlets provided significant levels of suppression at both design and off-design throat Mach numbers with good aerodynamic performance. A comparison of inlet noise at quasi-static and forward-speed conditions in the wind tunnel showed a reduction in the fan tones, demonstrating the flight cleanup effect. High angles of attack produced slight increases in fan noise at the high acoustic directivity angles.
In this paper, plasma injection is defined as an increase of particle flux in a detector of finite bandwidth. Injection can result from dynamic processes or from spacecraft penetration of a quasi-static spatial structure produced by a steady magnetospheric convection pattern. ATS-5 particle spectrograms are found to provide examples of plasma injection events of both sorts. Dynamic injection occurs both with and without local magnetic signatures. For events not associated with clear local magnetic signatures, convection theory with a steady or a time-varying uniform electric field can account for the energy dispersion of injected particles with energy less than 50 keV. The paper concludes with a discussion of the way in which the convection boundaries are related to the substorm injection boundary of Mauk and McIlwain. Several alternative expressions for the local time and K(p) dependence of the injection boundary are given.
Electric field oscillations at frequencies centered below 10 Hz were measured by a payload equipped with double-probe electric field detectors which was launched into the dayside auroral oval during the Greenland rocket campaign on January 11, 1975. These oscillations exceeded an amplitude of 3 mV/m broadband and occurred over a period of about 90 s. These oscillations occurred during a proton injection event when the quasi-static electric field was less than 20 mV/m on the average. However, during a brief 2-s interval the electric field exceeded 50 mV/m. Analysis of the amplitude as a function of the spin frequency showed that the electric field was confined to a plane perpendicular to the magnetic field. The power spectrum was of the form f to the -6.5 + or - 1.5 power, where f is the frequency over the range from 8 to 18 Hz. The existence of a large electric field fluctuation in a spatially or temporally confined region of low-amplitude turbulence suggests that this may be an observation of the low-altitude projection of a turbulent region associated with electrostatic shocks which have recently been observed at higher altitudes.
Refined quasi-static and conductance methods, based on effectively thin composite insulating layers, low-carrier-concentration bulk semiconductors, and low-level illumination, have been applied to an improved characterization of the (100) Si-SiO2 interface. Accurate measurement of both the total density of interface states and its major components as a function of energy in the forbidden gap have been made over four decades (10-billion to 100-trillion states/eV sq cm) on a single sample. The normal U-shaped density of states is resolved into separate valence- and conduction-band-derived contributions as well as impurity-derived contributions corresponding to concentrations on the order of 20 ppm at the interface.
The paper considers whether a neighboring magnetostatic equilibrium exists to allow a magnetic field initially in a force-free configuration to accommodate any imposed weak pressure. The following problem is treated. The foot points of the field are fixed and the plasma is frozen into the field lines under the approximation of infinite electrical conductivity. A weak pressure is introduced. It is determined infinitesimal plasma displacements exist to adjust the field lines to a new equilibrium without changing the field line connectivity. The analysis is carried out for the bipolar force-free fields forming one of two evolutionary sequences modeling the development of the preflare stage. It was found that for the force-free field corresponding to the quasi-static stage of evolution, the neighboring magnetostatic equilibrium always exists and the imposed gas pressure can be accommodated with a slight departure of the field from being exactly force free.
A comprehensive theoretical model was formulated to study the development of convective burning in a solid propellant crack which continually deforms due to burning and pressure loading. In the theoretical model, the effect of interrelated structural deformation and combustion processes was taken into account by considering (1) transient, one dimensional mass, momentum, and energy conservation equations in the gas phase; (2) a transient, one dimensional heat conduction equation in the solid phase; and (3) quasi-static deformation of the two dimensional, linear viscoelastic propellant crack caused by pressure loading. Partial closures may generate substantial local pressure peaks along the crack, implying a strong coupling between chamber pressurization, crack combustion, and propellant deformation, especially when the cracks are narrow and the chamber pressurization rates high. The maximum pressure in the crack cavity is generally higher than that in the chamber. The initial flame-spreading process is not affected by propellant deformation.
Observations suggesting the sequential expansion and compression of the Jovian plasma sheet are reported. Plasma flow in the vicinity of Jupiter was monitored by the four modulated-grid Faraday cups on board each of the Voyager spacecraft at times of closest Jupiter approach. Sensor measurements reveal the flow of magnetospheric plasma to be directed away from the equatorial current sheet near local noon and to be directed towards the sheet in the dusk to midnight sector. The observed flow patterns are interpreted in terms of short-time-scale perturbations of magnetic flux tubes due to the compression of the dayside magnetosphere by the solar wind. It is noted that such a dynamic motion is quite different from what would be expected of slower, quasi-static equilibrium plasma sheet expansion and contraction.
Small redshifts and weakenings of high n lines in members of the Si series observed over a sunspot are interpreted as due to the Stark effect. Other origins, including Doppler motions, appear to be excluded. The spectra were obtained with high spatial resolution using the NRL high-resolution telescope and spectrograph. The origin of the Stark effect is not yet certain. An interpretation in terms of a quasi-static quadratic effect would require rather high perturber densities. An alternative interpretation would be a motional Stark effect, arising perhaps through the presence of magnetohydrodynamic waves.
A 'material modeling' methodology for predicting the creep rupture behavior of unidirectional advanced composites is proposed. In this approach the parameters (obtained from short-term tests) required to make the predictions are the three principal creep compliance master curves and their corresponding quasi-static strengths tested at room temperature (22 C). Using these parameters in conjunction with a failure criterion, creep rupture envelopes can be generated for any combination of in-plane loading conditions and ambient temperature. The analysis was validated experimentally for one composite system, the T300/934 graphite-epoxy system. This was done by performing short-term creep tests (to generate the principal creep compliance master curves with the time-temperature superposition principle) and relatively long-term creep rupture tensile tests of off-axis specimens at 180 C. Good to reasonable agreement between experimental and analytical results is observed.
An instrumentation system in flight tests for noise research is described which utilizes miniature transducers to measure low-amplitude, high-frequency fluctuating pressures in a jet engine mounted under the wing of a turboprop aircraft. The system employs a rotor-mounted FM telemeter to acquire data from eight fan-blade-mounted transducers which are subjected to up to 75,000 g's of loading. Data is transmitted from the rotor to an antenna mounted in the inlet-duct wall using a low-power, close-coupled RF link. The blade pressures and other inlet and stator-vane fluctuating pressures are recorded on airborne, magnetic-tape recorders. The flight instrumentation described also includes PCM techniques to encode and record a variety of quasi-static measurements to provide engine and aircraft performance data. The instrumentation and experimental measurements are of value to an improved understanding of noise sources in jet engines and for the advancement of jet-engine ground noise testing techniques.
It is shown that the effects of constraint on the response of composite materials can be classified as (1) in-plane effects, and (2) through-the-thickness effects; with in-plane constraint being the principal contributor to notched strength and changes in notched strength under quasi-static loading. It is also determined that the constraint situations that produce the greatest static strength do not minimize the extent of damage that develops under either static or cyclic loading, and that through-the-thickness constraint controls the pattern and spacing of transverse cracks in the characteristic damage state that determines those of strength and stress in unnotched laminates. It is concluded that the mode and the extent of damage in notched and unnotched constrained plies is governed by the stress state in those plies, as determined by the constraining ones, and the relationship of stress and strength states.
The ISEE-1 satellite frequently passes through electrostatic shocks and the low altitude auroral particle acceleration region at geocentric radial distances less than approximately 7 earth radii and as low as greater than or equal to 2 earth radii. A sampling of data from the quasi-static electric field experiment during 22 such passes revealed events (defined as regions of low frequency turbulence) containing electrostatic shocks (defined as an electric field greater than or equal to 100 mV/m) during eight of the passes, which is an occurrence frequency comparable to that obtained near apogee on the S3-3 satellite. Examination of three such electrostatic shocks shows that typical potentials of a few kV and latitudinal scale widths mapped to the ionosphere of a few km are encountered. From the latitudinal widths of the shocks and from the magnitudes of their observed electric fields, it is argued that the parallel electric field and auroral particle acceleration region may be confined to geocentric distances less than a few earth radii.
This paper presents an introduction to a global campaign of simultaneous quasi-static electric field measurements from radars, balloons, and satellites at various places within the earth's environment for April 8-14, 1978. The 7-day time period encompassed both extended magnetically quiet times as well as two magnetic storms. These storms were related to SSCs that followed solar flares, one of which included a day-long solar proton event. The wide variety of instrumentation and associated operating modes involved in this campaign is described. Sample conjunctions between satellites and ionospheric measurements are shown that demonstrate that field line mapping is valid under certain circumstances. Some of the largest ionospheric electric fields ever reported with greater than 100-km scale size occurred on April 11, and these events are discussed in detail.
Systems such as the Maypole deployable reflector have a distributed parameter nature. The flexible column and hoop structure and the circular antenna of 30-100 meter diameter which it supports are described by partial, rather than ordinary, differential equations. Progress completed in reduced order modelling andd controller design and digital parameter estimation and control is summarized. Topics covered include depolyment and on-orbit operation; quasi-static (steady state) operation; dynamic distributed parameter system; autoregressive moving average identification; frequency domain procedures; direct or implicit active control; adaptive observers; parameter estimation using a linear reinforcement learning factor; feedback control; and reduced order modeling for nonlinear systems.
It was the objective of the work reported here, and in the companion paper 1 . A broader examination of wind turbine dynamic response to turbulence, and attempts to ascertain the features of turbulence that wind turbines are most sensitive to were made. A statistical description of the wind input including all three wind components and allowing linear wind gradients across the rotor disk, was used together with quasi-static aerodynamic theory and an elementary structural model involving only a few degrees of freedom. The idea was to keep the turbine model simple and show the benefits of this type of statistical wind representation before attempting to use a more complex turbine model. As far as possible, the analysis was kept in the simplest form, while still preserving key physical responses.
Two fundamental concepts of fracture mechanics are used to develop a theory of the earthquake mechanism which specifically predicts observed time-dependent rupture phenomena such as slow earthquakes, postseismic rupture growth and afterslip, multiple events, foreshocks, and aftershocks. The theory also predicts that there must be a nucleation stage prior to an earthquake, and suggests a physical mechanism by which one earthquake may trigger another. Investigations show that all earthquakes must be preceded by a quasi-static slip over a portion of the rupture surfaces, although it may be difficult to detect in practice, and a study of delayed multiple events characterizes the strength of some barriers in the earth as having a stress corrosion index of about 24.