This paper addressed cable network configurations to improve surface accuracies for large mesh antennas. In this study, we focused on manufacturing error, assembling error, and sensitivity to displacements of support points. To facilitate accuracy management by the lengths of cables, high stiffness cables were used in surface cable network. Then, low stiffness cables were used in other cables. The effect of the lengths of errors was estimated by analysis and experiments for a test model. Micro-gravity test was also executed to estimate the accuracy of shape adjustment on ground. The sensitivity is calculated under some variations of cable stiffness. From the results, it is clarified that the proposed configuration can reduce the surface distortion and keep high surface accuracy.
This paper first shows the performance limit of gust alleviation controllers without prior gust information. Since control devices, such as elevator, aileron, and thrust, cannot be driven at the same time as their commands are given, the initial acceleration due to wind gust cannot be alleviated with any controllers which do not detect the wind gust a priori. However, if wind gust information is obtained a priori, then the initial acceleration can be suppressed with some controller, which is the second topic of this paper. Designing such controllers is formulated as a design problem of model predictive controllers, which is formulated as a convex Quadratic Programming (QP) problem and is easily solved numerically. Several numerical examples demonstrate the effectiveness of model predictive controllers to suppress the initial acceleration due to wind gust.
The present paper reports the result of a numerical study on efficient solution-adaptive grid refinement algorithms for simulating unsteady flows with discontinuities. We implement a flow feature detection algorithm originally developed for quadrilateral grids by Aftosmis and Kroll (AIAA Paper 91-0124, 1991) to achieve efficient adaptation for triangular grids for simulating strongly unsteady flows with moving discontinuities such as shock waves and contact discontinuities. In their algorithm, the detection of strong shock waves is isolated from that of other smooth flow features, and the threshold for grid refinement is automatically tuned based on the statistics of grids in the smooth flow feature detection step. We illustrate the performance of the algorithm with numerical results for two benchmark problems (shock tube and double Mach reflection problems) of two-dimensional unsteady flows.
L1-SAIF signal is one of the navigation signals of Quasi-Zenith Satellite System, which provides an augmentation function for mobile users in Japan. This paper presents the detail of the tropospheric delay correction in L1-SAIF augmentation. The tropospheric delay correction information is generated at the ground station using the data collected at GEONET (GPS Earth Observation NETwork) stations. The correction message contains the information of the zenith tropospheric delay (ZTD) values at 105 Tropospheric Grid Points (TGP) in the experiment area. From this message a mobile user can acquire the ZTD value at some neighboring TGPs, and estimate the local ZTD value accurately by using a suitable ZTD model function. Only 3 L1-SAIF messages are necessary to provide all of the tropospheric correction information. Several investigations using the actual data observed at many GEONET stations overall Japan have proved that it is possible to achieve the correction accuracy of 13.2mm (rms).
The toy model coaxial helicopter for entertainment has a characteristic that it goes left when the operation for forward motion is made with the controller. The reason for this characteristic was made clear as follows: The phase difference between cyclic pitch and flapping motion is varied with the forward velocity. For this helicopter, the azimuth angles for the cyclic pitch inputs to the lower rotor are determined for a hovering flight. Then, the tip path plane of the lower rotor is inclined to the left and forward, when the operation for forward motion is kept. And the fuselage moves to the left and forward. On the other hand, during the forward motion, the inclination of the tip path plane of the upper rotor is varied by the stabilizer bar, whose motion is mainly determined by the fuselage attitude. Then, there are both moments when the upper rotor suppresses the fuselage motion generated by the lower rotor and when it promotes the fuselage motion.
The effects of antenna shape and magnetic field configuration on thrust performance in a 30W class miniature microwave discharge ion thruster were investigated with the objective of improving its thrust performance. The ion beam currents were measured for three different antenna configurations: disc, star, and cross. The results showed that the optimum antenna shape depends on the desired mass flow level because of the tradeoff between microwave-plasma coupling efficiency and surface area recombination. The ion beam current with various magnitude of magnetic field was measured, since magnetic confinement and microwave-plasma coupling could be affected by the magnetic field configuration. The ion beam current was increased with increasing the number of magnets, though under too much magnitude of magnetic field, the thruster cannot be ignited. So, there is an optimum magnitude of magnetic field. The thrust performance of the miniature microwave discharge ion thruster, i.e., propellant utilization, and ion beam production cost were 0.97 and 600W/A, respectively, at mass flow rate of 0.018mg/s, and incident microwave power of 8W.
In this paper, we propose the method for the measurement of required power and the adjustment of optimum gear ratio in take-off ground running. To get the values of required power and speed, we measured torque of the left side and the right side of pedals, RPM of pedals, and speed of the cockpit frame. In order to improve the take-off speed, some drums were applied, and the optimum gear ratio of the front drum to the rear drum was determined.