Current Issue : July - September Volume : 2012 Issue Number : 3 Articles : 5 Articles
In the secondary chamber of ducted rocket, there exists a relative speed between boron particles and air stream. Hence, the ignition\r\nlaws under static conditions cannot be simply applied to represent the actual ignition process of boron particles, and it is required\r\nto study the effect of forced convective on the ignition of boron particles. Preheating of boron particles in gas generator makes\r\nit possible to utilize the velocity difference between gas and particles in secondary chamber for removal of the liquid oxide layer\r\nwith the aid of Stoke�s forces. An ignition model of boron particles is formulated for the oxide layer removal by considering that it\r\nresults from a boundary layer stripping mechanism. The shearing action exerted by the high-speed flow causes a boundary layer\r\nto be formed in the surface of the liquid oxide layer, and the stripping away of this layer accounts for the accelerated ignition of\r\nboron particles. Compared with the King model, as the ignition model of boron particles is formulated for the oxide layer removal\r\nby considering that it results from a boundary layer stripping mechanism, the oxide layer thickness thins at all times during the\r\nparticle ignition and lower the ignition time....
This paper compares our analog and digital self-powered systems for vibration suppression, and shows experimental results of\r\nmultimodal vibration suppression for both self-powered systems. The experimental results are evaluated in light of the damping\r\nperformance and adaptability under various vibrational conditions.We demonstrate various examples of our innovative vibration\r\nsuppression method, called ââ?¬Å?digital self-powered.ââ?¬Â Proper status switching of an electric circuit made up of an inductor and a\r\nselective switch connected to a piezoelectric transducer attenuates the vibrations. The control logic calculation and the switching\r\nevents are performed with a digital microprocessor that is driven by the electrical energy converted from the mechanical vibration\r\nenergy. Therefore, this vibration suppression system runs without any external power supply. The self-powering feature makes\r\nthis suppression method useful in various applications. To realize an ideal vibration suppression system that is both self-powered\r\nand effective in suppressing multimode vibration, sophisticated control logic is implemented in the digital microprocessor. We\r\ndemonstrate that our digital self-powered system can reduce the vibrational displacements of a randomly excited multimodal\r\nstructure, by as much as 35.5%....
The potential for the ultracompact combustor (UCC) lie in future research to reduced fuel consumption and improved engine\r\nperformance. Velocity measurements performed on the UCC test rig at the Air Force Institute of Technology revealed flow patterns\r\nand time-averaged turbulence statistics for data taken burning hydrogen fuel in a straight and a curved cavity vane configuration.\r\nOver an equivalence ratio from 0.7 to 1.5, the straight vane configuration showed spanwise velocity decreased linearly with distance\r\nfrom the cavity vane over the width of the main channel. Increasing the flow rates and holding the equivalence ratio and ratio of\r\ncavity to main airflow rates constant, flow velocities in the main channel showed an increase with the curved circumferential\r\nconfiguration but a decrease with the straight circumferential configuration. Turbulence intensity is expected to be a major\r\ncontributing factor, specifically since measured at 15% and 21% in the main channel for the straight and curved configurations,\r\nrespectively. The results also show how the radial vane cavity (RVC) created strong vorticity throughout the main flow supporting\r\na recirculation zone for mixing. Peak vorticity occurred farthest from the cavity vane suggesting the angle of the radial vane cavity\r\nis effective in generating increasing flow rotation....
In the present investigation, various factors and trends, related to the usage of two or more sets of inert particles comprised of\r\nthe same material (nominally aluminum) but at different diameters for the suppression of axial shock wave development, are\r\nnumerically predicted for a composite-propellant cylindrical-grain solid rocket motor. The limit pressure wave magnitudes at a\r\nlater reference time in a given pulsed firing simulation run are collected for a series of runs at different particle sizes and loading\r\ndistributions and mapped onto corresponding attenuation trend charts. The inert particles� presence in the central core flow is\r\ndemonstrated to be an effective means of instability symptom suppression, in correlating with past experimental successes in the\r\nusage of particles. However, the predicted results of this study suggest that one needs to be careful when selecting more than one\r\nsize of particle for a given motor application....
This work aims to analyze the stability of the rotational motion of artificial satellites in circular orbit\r\nwith the influence of gravity gradient torque, using the Andoyer variables. The used method in this\r\npaper to analyze stability is the Kovalev-Savchenko theorem. This method requires the reduction\r\nof the Hamiltonian in its normal form up to fourth order by means of canonical transformations\r\naround equilibrium points. The coefficients of the normal Hamiltonian are indispensable in the\r\nstudy of nonlinear stability of its equilibrium points according to the three established conditions\r\nin the theorem. Some physical and orbital data of real satellites were used in the numerical\r\nsimulations. In comparison with previous work, the results show a greater number of equilibrium\r\npoints and an optimization in the algorithm to determine the normal form and stability analysis.\r\nThe results of this paper can directly contribute in maintaining the attitude of artificial satellites....
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