Flow fields in the constant-area mixing tubes of ejector jets were investigated under the starting-limit conditions of an aerodynamic choking mode by performing numerical simulations and cold flow experiments. Pressure recovery was almost completed in the shock-train region. The length of the shock-train region (Lst) was measured under various conditions. Lst was proportional to the mass flow rate ratio of the secondary flow to the primary flow when this ratio was less than 0.15. On the other hand, Lst became almost constant when the mass flow rate ratio exceeded 0.15. Numerical studies showed that this change was caused by the difference in the mechanism of the flow fields. In the cases with low air mass flow rates, the primary and secondary flows almost mixed in a region between the inlets of the mixing tubes and the choking points. The pressure was recovered by a pseudo-shock-wave generated downstream of the choking point. On the other hand, when the mass flow rate ratio was higher than 0.15, the primary and secondary flows were clearly separated at the choking point. The pressure recovery was achieved by the mixing between the primary and secondary flows downstream of the choking point.
This paper summarizes tests to investigate the outcome of low-velocity and hypervelocity impacts on two identical target micro-satellites. The targets were 15cm × 15cm × 15cm in size and 740g in mass. One test was performed using a 39-g aluminum alloy sphere at a speed of 1.45km/s while the other was performed using a 4-g aluminum alloy sphere at a speed of 4.44km/s. The targets were completely fragmented after both tests. This paper also proposes a new approach to improve the calculation of cross-sectional area of fragments and a new technique for modeling the area-to-mass ratio distribution of fragments. It can be concluded that the area-to-mass ratio distribution model resulting from the proposed methods fits very well to the fragments observed with the micro-satellite impact tests.
Present paper is an analytical work on a patch repair problem. An exact solution is obtained for double lap patch-repaired circular plates with debondings between the two patches and the base plate subjected to a uniform axisymmetric radial displacement, where no bending deformation is considered. The explicit solution based on a simplified plate model excellently agreed with a finite element solution. Through a parametrical study on the strain distribution and the energy release rates for the debondings based on the analytical solution, various general rules on the design of the patch repairs are elaborated.
Attenuation of sound by water droplets in air is analytically investigated. This is one of the mechanisms of the noise reduction in actual rocket launch where water is injected to jet plume. The scattering and absorption by the droplets are considered as the attenuation mechanisms. It is found that the absorption is superior to the scattering for fine droplets, such as fog or mist. Then we estimate the attenuation of sound for the experiment using subscale solid rocket motors. The result agrees well with the experimental data within the frequency range where the assumptions of this study are valid.
The present paper treats a structural vibration control for a specific lower-order or higher-order single mode using the modal sensor and the modal actuator. In this paper, we examine the validity of modal sensor in the vibration measurement and control of CFRP cantilevered plates. 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. Here, the location of accelerometer is optimized based on the minimization criterion of observation spillover. Moreover, a modal actuator system to generate a modal control force for controlling the specific vibration mode is also developed by one piezoelectric patch. The location of PZT piezoelectric patch is also optimized and the independent modal space control based on the LQR control theory is applied in this research. The numerical and experimental results show that the proposed vibration control system is effective for suppression of single modal vibration regardless of a lower-order or higher-order modal vibration.