Adhesion between two clean surfaces was investigated using a surface-activated bonding method in an ultrahigh vacuum (UHV) at room temperature. Adhesion was observed in all combinations of SUS440C/Ti-6Al-4V, INCONEL718/Ti-6Al-4V, A7075/SUS440C, SUS304/Al and INCONEL718/SUS440C. To understand the basic problems of UHV bonding, the influence of the surface roughness on bonding strength and interface structure has been studied. The surface roughness at the nanometer scale strongly influenced the bonding strength. In the case of SUS304 and Al, surfaces with less than l nm (RMS) had a high bonding strength of over 80 MPa. The interface does not have a thick reaction layer, only an amorphous layer on the order of several nanometers. Separation of the SUS304/Al interface by heat treatment has been also studied. A specimen heated at 823 K for 2 hr in a vacuum separated spontaneously without any external mechanical force. Separation occurred at the interface between the Al and the layer of the reaction products. This separation occurred only if the specimen was heated in a vacuum or argon atmosphere. The specimen did not separate when it was heated in air, nitrogen or oxygen atmospheres. The separated SUS304 could be re-bonded to Al at room temperature.
This novel control logic for a shock absorber using particle-dispersion Electro-Rheological (ER) fluid is a powerful means of shock attenuation for satellite instruments that are subjected to lift-off shock or pyrodevice ignition shock. Satellite instruments may be damaged when the acceleration generated by the input shock exceeds their critical acceleration value. The proposed method attenuates the shock so that the instrument’s acceleration does not exceed the critical value, even when the shock is too large to be accepted. In contrast to conventional linear shock controls, the proposed shock control does not attempt to attenuate a small shock in order to prepare for attenuating a coming large shock. This innovative nonlinear control enables the absorber to effectively attenuate a powerful shock. Numerical simulations show that the new shock absorber system attenuates shocks better than a passive system or a conventional linear control system.
Numerical analyses were performed to clarify the power conversion mechanisms in a 1 kW-class continuous-wave laser thruster. Laser plasma heating and radiation emission from the plasma, which dominate in the power conversion balance, were the focus of this analysis. The calculation results show that low laser power absorption and large radiation loss from the plasma result in low thruster performance. The results also show that optimization of the nozzle shape and use of regenerative-cooling can substantially improve thruster performance.
Conventional optimization methods are based on a deterministic approach since their purpose is to find out an exact solution. However, such methods have initial condition dependence and the risk of falling into local solution. In this paper, we propose a new optimization method based on the concept of path integrals used in quantum mechanics. The method obtains a solution as an expected value (stochastic average) using a stochastic process. The advantages of this method are that it is not affected by initial conditions and does not require techniques based on experiences. We applied the new optimization method to a hang glider design. In this problem, both the hang glider design and its flight trajectory were optimized. The numerical calculation results prove that performance of the method is sufficient for practical use.
The vibrational relaxation of oxygen by O2–O collision is studied using physical kinetics and molecular collision dynamics in the temperature range from 2,000 K to 7,000 K. This study shows that all the potential energy surfaces appearing in the collision must be taken into account to correctly calculate the rate constant, and that the Bethe-Teller theory is inadequate to describe vibrational relaxation in a strong non-equilibrium state. This study also validates existing experimental models widely used to describe vibrational relaxation.
Most severe pilot-induced oscillations (PIOs) are characterized as the presence of actuator rate limiting. Rate limiting causes phase lag and magnitude reduction between the limiter input and output when the input signal rate exceeds the rate limitation. This is the main cause of PIOs. Herein, two controllers, in which actuator rate limiting is redefined as input constraints, are designed based on the model predictive control (MPC) strategy and applied to the pilot-aircraft loop in both parallel and serial manners. In the parallel implementation, the MPC controller can suppress rate-limiter-based PIOs. In the serial implementation, the MPC controller can compensate the phase lag due to rate limiting, and hence, help the pilot prevent PIOs from occurring in advance.
A sidewall-compression-type scramjet engine was tested under Mach 4 flight conditions. The tested engine had an inlet, a constant cross-sectional area isolator, a constant cross-sectional area combustor, a diverging combustor, and an internal nozzle. In a previous study under the same flight conditions, the maximum thrust increment using fuel injection within the constant-area combustor was 1,380 N at an equivalence ratio of 0.31, and further fuel injection resulted in combustor-inlet interaction (designated as CII). To suppress the CII in the present study, we attempted (1) two-stage fuel injection within the constant-area combustor and the diverging combustor and (2) a boundary layer bleed on the top wall. The former was to suppress heat release around the first-stage fuel injectors in the constant-area combustor, and the latter was to decrease interaction length by decreasing the boundary layer thickness on the top wall. In the case of two-stage fuel injection, the maximum thrust increment was 2,230 N at an equivalence ratio of 0.63. In the case of the boundary layer bleed, on the other hand, the maximum thrust increment was 2,300 N at an equivalence ratio of 0.66. Thus, two-stage fuel injection and boundary layer bleed led to 62% and 67% higher maximum thrust increments than that obtained in the previous study, respectively. Finally, both the two-stage fuel injection and boundary layer bleed were applied simultaneously to obtain the best thrust performance, and the maximum thrust increment was 2,560 N at an equivalence ratio of 0.95. As a result, we obtained an 86% higher maximum thrust increment than that in the previous study. The thrust achievement factor, which was defined as the ratio of the maximum thrusts obtained from experiment and theoretical prediction, under this condition was estimated as 70%.