A 2-step reaction model is used to analyze the interaction between (i) a fuel-air multi-stratified vortical mixing layer and (ii) strong pressure waves caused by rapid combustion of the mixed region. During the 1st-stage induction period where no heat release occurs, a large-scale vortical structure evolves, generating a wide contact surface and extended mixing between fuel and air. During the ensuing 2nd-stage exothermic reaction, the locally premixed fuel-air rapidly burns and produces strong pressure waves, where three different Da numbers are parametrically tested to evaluate the amplitude of generated pressure waves and to find out the possibility to trigger a detonation wave. The results show that (1) the 2nd-stage exothermic reaction starts at the core of each vortex where “Reaction Rate (YCH4)(YO2)2exp(-Ze/T*)” is high, (2) then the generated strong pressure waves promote the reaction at the outermost stratified region of each vortex, and (3) spot-like flames formed in the premixed region propagate toward the surrounding unburned region, due to conventional defraglation mechanism. (4) On the other hand, delayed combustion starts in the braid region where mixing is highly inactive. (5) Finally, after the consumption of premixed reactants, a diffusion flame with a low mass consumption rate prevails. The highest Da number simulation naturally has generated the strongest pressure waves, indicating the possibility of shock wave occurrence and transition to detonation.
A series of hypervelocity impact tests has been conducted to investigate the shield design concept of JEM pressure module, i. e., bumper and isogrid pressure wall, against orbital debris impact. A two-stage light-gas gun has been newly developed for the purpose of improving test capability and the tests were carried out under the impact velocity of up to 6.8km/s with sphere aluminum projectiles of 3-9mm diameters. Main purposes of the tests are to examine (1) penetration hole diameters, (2) unzipping failure (uncontrolled mode of crack propagation) of pressure wall, (3) failure tolerant performance of isogrid pressure wall, and (4) impact damage to pressure wall by inserting MLI. More than 120 impact tests were successfully performed and significant test results were obtained. Summaries of the test results are followings: (1) penetration hole diameters are almost same size as ‘Goodwin;’ prediction, (2) critical crack length, which initiates unzipping failure of pressure wall, is much larger than that predicted by the Newman's static equation, (3) crack propagation is slightly contained by the isogrid rib of pressure wall, and (4) penetration hole becomes smaller, while crack length becomes larger by installing MLI between bumper and pressure wall.
This paper describes an approach to control the vibration of flexible structures based on the power flow concept. The μ-synthesis is used to design the controller that optimizes the power flow and retains the robustness for the unmodeled dynamics. The power flow control is based on SEA (Statistical Energy Analysis), and it is able to augment the vibration damping by controlling the power flow that flows into the plant from the outside. The plant model for controller synthesis is found using the identification method called transfer function curve fitting. For identified model, the controller that achieves both performance and robustness is designed using μ-synthesis. Designed controller is evaluated by numerical analysis and experiments. As the results, it is shown that the proposed approach can design the controller with good performance and robustness.
Measurements of combustion response function of a non-metalized composite solid propellant have been carried out using two different type transient L* burners at comparatively low pressure condition. A rubber ball has been utilized to change the nozzle throat area abruptly in a pulse-like manner or in a step-like manner. Experimental data on induced transient pressure have been processed to obtain the combustion response function by either the direct Fourier transform method or curve fitting method based on quasi-steady combustion model. The transient L* burner results agree rather well with those obtained by the modulated L* burner tests in the low frequency range below 100Hz. Furthermore if standard three parameter expression of response function is adopted, the curve fitting method works well in broader frequency range.
A shock tube theory is developed by considering the energy loss at the diaphragm section. By using the theory, a shock tube flow with a finite diaphragm opening time can be obtained. From the calculated results, it is found that a transitional and complex flow exists behind the leading shock wave. After that, the maximum shock Mach number is attained. The maximum shock Mach number calculated by the theory is larger than that by simple theory when the diaphragm pressure ratio is high enough. However, the maximum shock Mach number which can be obtained in experiments is limited by the diaphragm opening time and the tube length of the lower pressure side. The theory is validated in comparison with the experimental data from reference.
This paper presents a simple numerical procedure for determining the true anomaly as a function of time in elliptical orbital motions. Applying Kepler's second law to a number of satellite-position samples over one revolution yields directly the solution, where solving Kepler's equation is not required. The procedure can be coded in a few instruction lines. True anomaly errors as depending on the eccentricity are evaluated.