The interaction between laminar boundary layer reattachment and a rectangular cavity in a hypersonic compression ramp was investigated numerically and experimentally. It was found from the present results that the separation bubble becomes larger than that of the baseline flat ramp case. This is caused by higher adverse pressure gradient due to the cavity end wall. In the flowfield a high temperature separated shear layer collides with the endwall of cavity, where a hot stagnation point is formed. The endwall heat flux becomes about 10 times as large as the maximum heat flux in the baseline flat ramp case.
The authors proposed fiber-optic-based damage monitoring of carbon fiber reinforced plastic (CFRP) bolted joints. Optical fibers were embedded along bolt holes and strain change along the optical fiber induced by internal damage was measured by a Brillouin Optical Correlation Domain Analysis (BOCDA), which is a high spatial resolution distributed strain sensing system. This study began by investigating damage modes of CFRP bolted joints after bearing failure. Effective embedding positions of optical fibers were then proposed and their feasibility was evaluated by finite element analysis simulating the damage propagation in the bolted joint and consequent strain change. Finally, verification tests were conducted using specimens with embedded optical fibers at various positions. It was clearly shown that damage could be detected using residual strain due to fiber-microbuckling (kinking) damage or permanent deformation of neighboring plies. Furthermore, damage size and direction could be estimated from the change in the strain distribution. The system developed is quite useful for a first inspection of large-scale composite structures in aerospace applications.
This paper proposes a feedback control technique for the in-plane motion of a satellite equipped with two thrusters, whose force directions are fixed to the satellite. Such systems have second-order nonholonomic constraints due to the fixed force directions, and moreover their thruster forces are restricted to be unilateral. To control the satellites' global position and orientation, this paper develops a tracking controller to a designed invariant manifold based on the Lyapunov's second method. The developed controller is effective to control the satellite's global motion, even when the model parameters include some range of errors. Simulation results are shown to demonstrate the effectiveness of the developed controller.
The author statistically analyzed on-orbit failure data of recent medium and large satellites based on primary investigations of satellite failures. Random parts failures are only 11% among failures whose causes are identified after investigations. Instead failures caused by design problems (57%) and manufacturing problems (32%) are dominant for on-orbit satellite failures. Propulsion and solar paddle subsystems have a relatively large number of failures caused by manufacturing problems, against which redundant system are partially effective. Mission instruments have a large number of failures caused by design problems. Bus subsystems except for propulsion and solar paddle subsystems have a relatively small number of failures. For these bus subsystems, failures tend to happen deterministically and redundant system may not be effective. Conventional reliability engineering based on the random parts failures seems not to be realistic in our space engineering.