In order to realize a high accuracy space structure system, shape and vibration controls using smart structures are studied. Two prototypes of smart reflectors were developed and investigated. One was a long smart beam system equipped with Macro Fiber Composites (MFCs) and the other was a smart reconfigurable reflector equipped with smart actuators. The smart actuator was designed for the smart reconfigurable reflector and it consisted of a piezoelectric stack actuator and a displacement magnification mechanism. Experiments of the shape and vibration controls of the long smart beam were carried out and their performance were investigated. The performance of the smart actuator was also investigated through numerical simulations and experiments. The results are reported in this paper.
The characteristics of a CFRP deformable reflector system were investigated through experiments and numerical simulations. The CFRP reflector was mounted on an actuation system and deformed by three actuators, which were placed one each on three concentric lines that were 120° away from each other. In the experiments, three types of reflector deformation were achieved by operating each actuator individually, and the deformations were measured by a photogrammetric measurement system. The deformations were analyzed and compared using Zernike polynomials. The apparent anisotropic deformations of the quasi-isotropic CFRP shell were observed, and the tilt and astigmatism modes were determined to be outstanding. In order to investigate the effects of actuator stiffness, a few numerical simulations with higher stiffness of the actuators were performed. The results reveal that with the increased actuator stiffness, deformations became larger, while the outstanding modes did not vary.
This study investigates a large reconfigurable antenna system consisting of cable networks. The beam shapes of reconfigurable antennas can be modified by changing the shape of the antenna reflectors. Two types of control actuation—one using tie cables and the other using boundary cables—are considered. For each type, two control methods are applied; they are cable tension control and cable initial length control. Numerical simulations are carried out to investigate characteristics such as robustness against disturbances and natural frequencies. The results of these simulations are compared to determine the appropriate control system of the antenna. It is shown that the tie cable control by the initial length control is preferable. In the case where the operation modes are predetermined, the boundary cable controls are also applicable.
Hot-film-anemometer measurements were carried out in a shear flow between a flat plate and a moving plate fitted with an array of tall fences. The effect of spatial restriction by the fences on the inner-layer structure of the boundary layer developing on the flat-plate side was investigated. It was revealed that the inner-layer structure was maintained even when the tips of the fences were passing at a distance y + = 45 from the flat plate; the flow did not become laminar-like until the tips reached y + = 25. These results suggested the physical view that the inner layer of wall turbulence has a tough, self-sustaining structure, which is uniquely determined under a given mean wall shear stress and is hardly influenced by outer-layer disturbances provided that its own spatial extent of about 45 ν/ u * from the wall is maintained.
The objective of this study was to develop a mechanical model for cohesive, plastic behavior of soil by the Distinct Element Method (DEM). The DEM has been applied to solve problems of soil-tool interaction. There is still a need for improving the representation of complicated soil behavior and reaction forces on the machine parts. This study focused on the improvement of mechanical relationships between elements and the procedure to determine the DEM parameters. One of the improvements was the representation of plastic behavior of soil in compression. By assigning different values to the spring constant for loading and unloading/reloading, soil plastic deformation was well represented. In order to model the cohesive soil, tensile force between contacting elements was considered. Although the tensile force between elements have been employed and called as adhesion or bonding in some research papers, the method to determine the related parameters have not been established yet. In this study, the concept of intrinsic stress was used and its value was determined by the cohesion and internal friction angle that were obtained from soil shear test. The laboratory tests were carried out for verification of the developed soil model. We conducted wedge penetration tests using 30 and 90 degree wedges. One of the wedge penetration tests was used to obtain DEM parameters. The other wedge penetration test was used to establish the validity of parameters.
