In flexible long arm operation, residual vibration due to excitation degrades working efficiency. Input Shaping method decreases residual vibration in flexible systems by filtering the reference command with sequence of impulses known as input shaper. The principle of Input Shaping is very simple, but it is necessary to consider implementation hardware, especially in the space system. In this paper, ground experimental setup of an 8m long space robotic arm is constructed, and the effect on vibration suppression using Input Shaping is considered. The results of the ground experiment are discussed.
For astronomical observing missions by formation flying satellites in LEO, satellites require control force to keep the relative position, against Keplerian orbit in an inertia coordinate frame. Since satellites require propulsion systems, i.e. thrusters, but the use of thrusters limits the mission lifetime associated with the finite fuel supply. Thus the authors propose the formation flight using electromagnetic force. In this method, the electromagnetic force between super-conducting magnets are used for the relative position control. This method has the obvious advantage of no-fuel to acquire control force. Since such large magnetic moment in earth magnetism generates large disturbance torque, the magnetic moments should be sinusoidal with shorter period than that of the orbit period. Therefore, this paper proposes the relative position control by changing the phase difference between sinusoidal magnetic moments. The proposed method was evaluated with numerical simulations and the results shows the feasibility of the proposed formation flight.
Combined Laser Induced Ignition and Plasma Spectroscopy has a potential to give in situ measurement of fuel equivalence ratio in the laser ignition event at an exact time and location of plasma initiation. This method is an extension of a non-intuitive gaseous-composite measurement technique, i.e. Laser Induced Plasma Spectroscopy, to simultaneous ignition utilizing the same plasma source both for gaseous composite measurements and ignition. Calibration methods so far are not sufficient in terms of accuracy. The present study utilizes a new calibration technology without energy measurement under the ignition case. The example dealt in this study is a single injector combustor which provides a time-varying non-uniform fuel equivalence ratio under fuel lean cases. The result showed that the present calibration method is valid for the present measurement of the fuel equivalence ratio, and that the data is very useful to understand the ignition process of the configuration given.
In this paper, to understand the mechanism of delamination propagation in low-velocity impact problems, a weight-drop test is performed for quasi-isotropic composite plates of 32 plies. Due to the high computational cost, up to date, there have been almost no computational effects for simulating the damage propagations in quasi-isotropic composite laminates of 32 plies. This low-velocity impact problem is further numerically modeled and the damage propagation is simulated. A stress-based criterion is adopted for modeling various in-plane damages, such as transverse matrix cracking. A bi-linear cohesive interface model is employed for interface damages, such as delaminations. Moreover, to remove the numerical instability in simulations when using the traditional cohesive model, we propose a new technique, i.e., adaptive cohesive model. The effectiveness of this cohesive model is investigated using a DCB example. Then, it is applied to the low-velocity impact problem of quasi-isotropic composite laminates of 32 plies. The validity of the proposed numerical methodology is verified by comparing the numerical results with the experimental results.
In our microgravity experiments for a near-critical mixing surface liquid jet it is observed that the liquid column is disintegrated with a certain, short wavelength at a relatively short distance from the nozzle exit. In the present paper, the underlying physics of this peculiar behavior are explored on the basis of a theoretical model, because the phenomena may be a candidate mechanism for the breakup of liquid ligament involved in turbulent atomization. It is found that the short-wavelength breakup is caused by the presence of the jet tip which contracts by the action of surface tension. The presence of the nozzle exit does not play any essential role on this disintegration, but at low pressure it leads to the excitation of long-wavelength breakup due to the Rayleigh type of instability wave which is generated from the capillary wave reaching the nozzle exit and reflecting.
In this paper, we address simultaneous structure/controller design of flexible space structures. In particular, we consider optimal placement of sensors and actuators together with control design. Even though the original problem is non-convex, we transform it into a convex one via a novel approach. In particular, nonlinear parameter relationship is described as a bound of a convex region in a parameter space. Bounding the region by a set of tangential lines, we seek optimal solutions that approach the bound of the region.
The paper reports several steps taken to reduce vibration responses of a 50kg-class micro-satellite structure, which is subjected to severe mechanical/vibratory environment during launching. In order to satisfy the required mechanical interface conditions, anti-vibration design of satellite structure was modified to enhance damping capacity of the structure by applying adherent aisogrid-panel, honeycomb panel, polyimid-tape-inserted connections, and damping pads. Considerable reduction of vibration responses was confirmed by vibration test of structural-thermal model.