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An analysis of the MOD-1 2000 kW horizontal axis wind turbine was given. The MOD-1 design was briefly described, and the analysis used to evaluate the dynamic loads and structural interactions is discussed. The resonant frequency placement, the treatment of unsteady wind loading, and the dynamic load sensitivity to frequency shifts were reviewed for the design.
A very high sensitivity rotating gravity gradiometer onboard the spacecraft is described for measuring the gravitational oblateness of the Sun during a solar probe mission. The proposed instrument would be a self-contained structure in a thermal-vacuum-magnetic shield in the shape of a cross, with a mass of 20 kg and arm length of 1.0 m and thickness of 0.1 m. The sensor inside would have a resonant frequency of 1/30 Hz, a mechanical Q of one million and would use gravitational radiation antenna technology to achieve a sensitivity of 6 x 10 to the minus 8th power Eotvos, which would provide a measurement of the solar oblateness to an accuracy of 1.5 to 6 x 10 to the minus 8th power. The gravity gradiometer will require a spinning spacecraft, so that it will not sense the spacecraft gravity fields, but the gradiometer does not need to be at the spacecraft center of mass, or even on the spacecraft spin axis. Major problem areas to be addressed are demonstration of the instrument sensitivity prior to flight and the measurement and compensation for any residual spacecraft angular rates.
The Riccati transfer matrix method is a new technique for analyzing structural members. This new technique makes use of an existing large catalog of transfer matrices for various structural members such as rotating shafts. The numerical instability encountered when calculating high resonant frequencies, static response of a flexible member on a stiff foundation, or the response of a long member by the transfer matrix method is eliminated by the Riccati transfer matrix method. The computational time and storage requirements of the Riccati transfer matrix method are about half the values for the transfer matrix method. A rotating shaft analysis demonstrates the numerical accuracy of the method.
General background and overview material are presented along with data from studies performed to determine the sensitivity, feasibility, and required performance of systems for a total X-ray telescope assembly. Topics covered include: optical design, mirror support concepts, mirror weight estimates, the effects of l g on mirror elements, mirror assembly resonant frequencies, optical bench considerations, temperature control of the mirror assembly, and the aspect determination system.
A capacitor in which one plate or electrode element is vibratable to achieve a variation in capacitance is described. The capacitor includes two spaced stationary elements. The third element is supported at its center and in the form of a thin diaphragm which is vibrated at its inherent mechanical resonant frequency to achieve a corresponding variation in capacitance between one of the stationary elements and the vibrating diaphragm.
A general overview of piezoelectric resonators is given with emphasis on evolution of the resonator design. Superconducting cavities and crystals at low temperature and the use of resonant frequencies are also discussed.
A mathematical model is presented for the effect of flow on the vibrations of a thin cylindrical shell in a subsonically-flowing acoustic media. The effect of the external acoustic fluid consists of a mass-like term caused by the 'virtual-mass' effect of the fluid and a 'damping-like' term which accounts for the radiation of energy away from the cylinder. For a flowing medium, both of these terms are shown to involve the flow velocity. The effect of flow on the cylinder resonances is examined numerically. While not all modes are affected by the flow, there are some modes which are significantly affected. Usually, the added mass of the fluid increases with flow velocity causing a reduction in the resonant frequency of the shell mode.
Intense electrostatic waves near the upper hybrid resonance frequency (f-UHR) have recently been detected near but beyond the plasmapause between + or -50 deg magnetic latitude at all local times. The paper shows that the electrostatic waves observed with the ISEE 1 plasma wave receiver near f-UHR are in qualitative agreement with linear theory of multicyclotron harmonic emissions. The peak amplitudes and bandwidths observed are similar to those calculated for maximum spatial growth rates. Measurements on Hawkeye of similar waves suggest that the electric field polarization is also consistent with theory. For a wide range of plasma parameters, nonconvective instability or large spatial growth rates occur within the cyclotron band encompassing the cold upper hybrid frequency.
The mechanisms incorporated in the vertical sounding infrared radiometry experiments which were launched on Nimbus 5 in 1972 and on Nimbus 6 in 1975 are discussed. Both use dry lubricants. The Nimbus 5 radiometer includes a rotating chopper driven via a carbon fiber-acetal resin gearwheel. The driving motor runs at 2000 rpm and has completed over 7 x 10 to the 9th power revolutions. Four gear driven filter wheels powered by stepper motors have each completed 2 x 10 to the 8th power changes. The input calibration mirror mechanism and its field of view compensation mechanisms are also described. All 25 ball races used in the experiment are of the film transfer type. The Nimbus 6 radiometer includes two cells. Each contains a piston supported on diaphragm springs and driven electromagnetically. The pistons are 6 cm in diameter with a stroke of 1 cm and are driven at their mechanical resonant frequency of approx. 15 Hz. The calibrating mirrors rotate periodically to view a target. The support pivots are synthetic sapphire ring stones with separate end thrust stones. The problems of mounting these stones to withstand vibration loads is described.
The stratospheric and mesospheric sounder (SAMS) experiment on Nimbus 7 includes a 2 axis scanning mirror and 7 pressure modulator cells. The SAMS experiment is a limb sounding instrument to measure the temperature profile and minor constituents of the atmosphere. The limb scan requires small mirror steps over a 3 deg range, while the scan in azimuth is in larger steps over a 15 deg range. The mirror is plane, 20 cm in diameter, and of zero expansion glass-ceramic. It is supported on two tilt tables, fitted one on the other, with the axes at right angles. The angle of tilt is adjusted by means of recirculating ball screws which are ion plated with lead for lubrication and driven by stepper motors. The seven gas filled cells are each pressure modulated by a 3 cm diameter, 0.3 cm stroke piston which is supported by diaphragm springs and driven electromagnetically at the system's mechanical resonant frequency. The mean pressure of the filling gas, which is the atmospheric constituent being measured, is changed by varying the temperature of a suitable molecular sieve.
A wavelength ID device which consists of an electronic show that the etalon has a finesse F 30 which is maintainable for several days. These tests also demonstrate that the etalon system is capable of resonance frequency stability during similar time periods. With currently available coatings, this level of performance is achievable over an optical bandwidth delta lambda = 3 micrometers centered at lambda = 10 micrometers.
In order to aid in the design of the National Transonic Facility (NTF) control system, test section/plenum response studies were carried out in a 0.186 scale model of the NTF high speed duct. Two types of disturbances, those induced by the model and those induced by the compressor inlet guide vanes were simulated. Some observations with regard to the test section/plenum response tests are summarized as follows. A resonance frequency for the test section/plenum area of the tunnel of approximately 50 Hz was observed for Mach numbers from 0.40 to 0.90. However, since the plenum is 3.1 times (based on volume) too large for the scaled size of the test section, care must be taken in extrapolating these data to NTF conditions. The plenum pressure data indicate the existence of pressure gradients in the plenum. The test results indicate that the difference between test section static pressure and plenum pressure is dependent on test section flow conditions. Plenum response to inlet guide vane type disturbances appears to be slower than plenum response to test section disturbances.
The theory of acoustic plane waves incident on an oblique clamped panel in a rectangular duct was developed from basic theoretical concepts. The coupling theory between the elastic vibrations of the panel (plate) and the oblique incident acoustic plane wave in infinite space was considered in detail, and was used for the oblique clamped panel in the rectangular duct. The partial differential equation which governs the vibrations of the clamped panel (plate) was modified by adding to it stiffness (spring) forces and damping forces. The Transmission Loss coefficient and the Noise Reduction coefficient for oblique incidence were defined and derived in detail. The resonance frequencies excited by the free vibrations of the oblique finite clamped panel (plate) were derived and calculated in detail for the present case.
Significant progress has been made in understanding intense electrostatic waves near the upper hybrid resonance frequency in terms of the theory of multiharmonic cyclotron emission using a classical loss-cone distribution function as a model. Recent observations by Hawkeye 1 and GEOS 1 have verified the existence of loss-cone distributions in association with the intense electrostatic wave events, however, other observations by Hawkeye and ISEE have indicated that loss cones are not always observable during the wave events, and in fact other forms of free energy may also be responsible for the instability. Now, for the first time, a positively sloped feature in the perpendicular distribution function has been uniquely identified with intense electrostatic wave activity. Correspondingly, we suggest that the theory is flexible under substantial modifications of the model distribution function.
The noise reduction characteristics of general-aviation-type, dual-pane windows in various configurations have been experimentally investigated. The effects of inner and outer pane thickness, spacing between the panes, edge conditions, inclination of the inner pane and depressurization of the air in between the panes are presented. The space in between the two window panes is sealed airtight in all cases. Results show that increasing the mass of a 'floating' window pane does not increase the noise reduction below the fundamental resonance frequency. It is concluded that the concept of depressurization of the air between thin (1/8 in) Plexiglas panes and application of multiple-freedom edge conditions for the inner pane are promising to reduce noise levels in general aviation airplanes.
A state-variable feedback approach is utilized for active control of rotorcraft vibration. Fuselage accelerations are passed through undamped second-order filters with resonant frequencies at N/rev. The resulting outputs contain predominantly the N/rev vibration components, phase shifted by 180 deg, and are used to drive the blade pitch to cancel this component of fuselage vibration. The linear-quadratic-gaussian (LQG) method is used to design a feedback control system utilizing these filtered accelerations. The design is based on a nine-degree-of-freedom linear model of the Rotor System Research Aircraft (RSRA) in hover and is evaluated on a nonlinear blade-element simulation of the RSRA for this flight condition. The system is shown to essentially eliminate vibrations at N/rev in all axes. The required blade-pitch amplitude is within the capability of conventional actuators at the N/rev frequency.
Impact-induced strain in piezoelectric ceramic could power a short-range transmitter. Proposed impact-energized radio transmission would eliminate the need for external power sources for batteries, which are often short lived and impractical to replace under operating conditions. Piezoelectric ceramic attached to impact head supplies energy to drive resonant circuit and antenna. Receiver tuned to resonant frequency receives short pulse.
The dielectric properties of polluted waters are measured with a reflection-type resonant cavity at 1.43 GHz. Very small water samples in quartz tubes of known volume are placed in the center of the maximum electric field. Measurement of the resonance-frequency variation and a change of the cavity's quality factor are used to determine the dielectric properties. The microwave emissivity of the polluted water is then calculated via the Fresnel equation and applied to data reductions of microwave radiometer measurements.