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The rotor speed control of windmills plays an essential roll in their practical use. Rotor speed control technology is indispensable not only in attainning a high level of energy conversion efficiency but also in avoiding damage to the windmill rotor system under very strong wind conditions. The present study was conducted as a part of the component technology research and development program for the 20kw horizontal axis windmill system development project sponsored by the Science and Technology Agency of the Japanese government. A hydraulic pitch control system for a 1kw class windmill (a pioneering sub-scale model for the 20kw windmill) was developed and improved through repeated tests in the NAL low speed wind tunnel and through outdoor tests. Our original application of the electromagnetic proportional hydro-relief valve to the hydraulic pitch control system of windmills brought an outstanding reduction of the variation in windmill rotational speed. The test results confirm the excellent characteristics of the windmill rotor speed control. The practicality of the hydraulic pitch control system has been proving itself in the 20kw windmill operation since December 1985., 資料番号: NALTR0931000, レポート番号: NAL TR-931

A high-speed digital controller for aeroelastic controls was designed and made. The purpose was to minimize adverse phase lag which is inevitably produced by the CPU time of digital processing. The delay deteriorates control performances on rather rapid phenomena like aircraft flutter. With fix-point operation the controller realized 417 microseconds of throughput time including the A/D and D/A conversion. This corresponds to a high sampling rate of 2.4kHz. The controller furnishes two channels, each of which can be implemented with up to the eighth order control laws allowing the coupling terms. Control laws can be loaded by changing coefficients for multiplication in its expansion form. These coefficients are calculated and transferred by a peripheral computer through the GP-IB busline. At the stage of D/A conversion, the number of bit-shifts associated with a scaling is made programmable to avoid overflow and to lessen inaccuracy due to the truncation error. A sample period is also selectable through the GP-IB busline. This period ranges from 1 ms to 500μs. In the appendix, a program is presented for converting from the continuous transfer function in the Laplace domain to a discrete transfer function in the z-domain with the aid of Tustin’s approximation., 資料番号: NALTR1014000, レポート番号: NAL TR-1014

A simple method was developed to determine the focal point of the Laser 2 Focus velocimeter. The method requires only a conventional hot-wire anemometer, which is traversed across the dual beams at diverse beam-axis locations. The squared hot-wire bridge output indicates the mean value of the beam intensity exposed on the hot-wire element. Eventually, the maximal bridge output along the beam axis is referred to as the focal point. Furthermore, the method can be extended to measure laser-beam properties such as beam separation, beam diameter, relative beam intensity on the dual beams, beam divergence and cross-sectional beam-intensity distribution. Measurement error in determining the beam diameter is estimated by using a simple beam model., 資料番号: NALTR1043000, レポート番号: NAL TR-1043

A gust generating system was constructed for the test of a gust alleviation device conducted in the NAL′s 6.5m×5.5m low speed wind tennel. This system makes use of tip vortices shedding from a pair of cantileved, oscillating wings. The Dryden model of atmospheric turbulence was successfully simulated with this system; and wind tunnel tests for developing a gust load alleviation technique for an energy efficient type of future transport with a high aspect ratio wing were conducted with good results., 資料番号: NALTR0929000, レポート番号: NAL TR-929