The present paper treats the flutter suppression of composite plate wings with segmented piezoelectric sensors and actuators. In the first report of this paper, fundamental mechanism of flutter suppression based on the measurement and control of specific vibration modes is examined for composite plate wings. Aeroelastic analysis of composite plates is based on the finite element method and the subsonic unsteady lifting surface theory. The minimum state method is applied to approximate the unsteady aerodynamic forces as the transfer functions of the Laplace variable. PVDF sensors are used as a modal sensor for measurement of specific modal displacements, and PZT actuators are used as actuators of flutter suppression, which generate the modal forces for specific modes. The importance of the measurement and control of the first torsional vibration mode for the flutter suppression is clarified through the numerical examples.
The present paper treats the flutter suppression of composite plate wings with segmented piezoelectric sensors and actuators. In the second report of this paper, validity of the flutter suppression based on the optimal placement of sensors and actuators is examined for composite plate wings. Modal sensor for measurement of the modal displacement of the first torsional vibration mode is designed by the optimal placement of PVDF sensors based on the minimization criterion of observation spillover. Actuation system to generate the modal force for the first torsional vibration mode is designed by the optimal placement of PZT actuators based on the minimization criterion of control spillover. Aeroelastic analysis of composite plates is based on the finite element method and the subsonic unsteady lifting surface theory. The minimum state method is applied to approximate the unsteady aerodynamic forces as the transfer functions of the Laplace variables. The effectiveness of optimal placement of sensors and actuators in the flutter suppression is clarified through the numerical examples.
In inter-satellite links with many Low Earth Orbit (LEO) satellites, each satellite will communicate with one or more satellites. In such cases, a satellite needs multiple, small, and light optical antennas. A communication link between satellites is not sustained at high latitudes because antenna drive angles are large due to high relative angular rates. To reduce such link lost time, a wide drive range with high speed is required for optical antennas. To meet these requirements, we propose a coude path type optical antenna. Furthermore, optical fiber application will be required to achieve optical communication of the next generation of gigabit class. Therefore, it is necessary to develop the technology which introduces the laser received with the optical antenna to an optical fiber. The optical antenna’s experimental model is equipped with optical fiber. This paper describes the mechanism, control system and experimental results of the optical antenna we have developed. The principle and performance of the coude path type optical antenna with optical fiber was verified by using an experimental model of the optical antenna.
The low-speed flow for a 45deg-swept delta wing is numerically simulated to examine the effects of a hybrid method consisting of leading edge rotation and trailing edge jet on aerodynamic forces. Computation has been performed at an angle of attack of 20deg and a Reynolds number of 2.0×104 based on the wing root chord. Under these conditions, the flow is fully separated from the wing surface, so that no suction peaks due to leading edge vortices are observed over the upper surface of the wing. By using the hybrid method, lift coefficient can become 85% higher than that of the baseline delta wing without any high lift device.
In this study, a numerical calculation was performed for an electrothermal pulsed plasma thruster (PPT) using solid propellants of poly-tetrafluoroethylene (PTFE). The calculation simultaneously simulates unsteady phenomena of discharge, heat transfer into/inside the PTFE, ablation of PTFE and plasma flow. A calculated result showed the existence of considerable amount of ablation delaying to the discharge. However, it was also suggested that the ablation should not be regarded as late time ablation (LTA) which is generally thought as a factor of low performance. The calculated performances roughly agreed with experimental results obtained with a PPT in our laboratory. Furthermore, calculated results predicted that the performance would improve by reducing the cavity cross-sectional area to 1/4 (1.6mm2) and the cavity length to 1/2 or less (≤6mm) with a constant stored energy of 14.6J.
A new cooling structure of C/C composites was made to use in high temperature environment over 2000K. A stainless steel tube was used as a cooling channel. The stainless steel tube was fixed to the C/C composites by the elastic force of each material. The performance of the cooling structure was evaluated by heating tests and numerical analysis. In the result of the numerical analysis, it was shown that the surface can be cooled below 2000K under the condition of surface heat flux of 10MW/m2. However, it was shown experimentally that the cooling performance gets extremely worse due to the plastic deformation of the tube when the temperature of the tube rises more than 600K.