From the viewpoint of the utilization of space environment technology, much more enlargements of space structures, such as a space antenna or a solar cell of satellites, have been expected to improve the performance of these structures. In addition, space environments under high vacuum and micro gravity without man spatial restrictions make us construct the large-scale space structures more easily. Recent examples of these structures are International Space Station and Engineering Test Satellite VIII "KIKU No. 8" (ETS-VIII) of Japan Aerospace Exploration Agency (JAXA).
However, these space structures are required to be lightweight due to the weight limitation during rocket launching. To satisfy this requirement, lightweight materials, such as aluminum or carbon fiber reinforced plastics (CFRP), have been widely adopted. However, using these materials leads to the highly flexible space structures which are weak from the aspect of vibrations. Structural vibrations in space tend to take place easily induced by external forces due to thermal shock, attitude control, or so on. Additionally, these vibrations are low frequency ones due to the state of space environment.
Moreover, higher-order vibration should be concerned for space structures. Acoustic loading caused during rocket launching process, whose frequency bandwidth is up to several thousands Hertz, may trigger higher-order vibrations for the space structures in a payload fairing structure. Also, not only space structures, but also turbine blades used in aircraft engines or gas turbines have the higher-order vibration issues. High frequency vibrations of turbine blades arise from fast rotation, which are crucial from the viewpoint of high cycle fatigue (HCF) failure.
To consider the above mentioned backgrounds, many studies on the vibration measurement and control using sensors and actuators have been carried out. However, it is one of the important issues to construct a mechanically simple, small and light vibration control system in the design of space structures. The main reason is that designing of space structures has many restrictions for fulfilling various requirements, such as weight, power supply or reliability.
In this thesis, structural vibration control for a specific lower-order or higher-order single mode using the modal sensor and the modal actuator is presented. A modal sensor system for identifying the specific vibration mode, which is mechanically simple, is developed by one accelerometer and one band-pass filter so as to be easily equipped to the structures. Moreover, a modal actuator system to generate a modal control force for controlling the specific vibration mode is also developed by one piezoelectric patch. It is shown that the proposed vibration control system is effective for suppression of single modal vibration regardless of a lower-order or higher-order modal vibration through the numerical and experimental verifications.
edited by Yoshio WADA