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Monopropellant hydrazine thruster, depending on their thrust level, specific impulse, and unique functional regime, are widely used in situation control, orbital transmission, and position correction systems of satellites. In these thrusters, hydrazine decomposes by passing through the catalyst bed in a highly exothermic reaction to hot gas products. Hot gases generate thrust force by passing through a convergent-divergent nozzle. Pore scale analysis of catalytic reactions is very common in various industries and is of interest to researchers due to its accuracy. In this paper, the decomposition chamber of a monopropellant hydrazine thruster is numerically simulated with a single-part bed model at the pore-scale. The length of decomposition chamber was 2.48 cm. Then the effects of parameters such as catalyst granule diameter, catalyst bed porosity coefficient and also chamber inlet pressure on the performance of the decomposition chamber and thruster are investigated. Simulations have been performed for catalyst granules with diameters of 0.88, 1.00 and 1.15 mm in three porosity coefficients of 0.4, 0.55 and 0.65. The inlet pressure is also changed from 10 to 25 bar in four different levels. The results showed that the porosity coefficient is the most effective parameter and with its decrease, the specific impulse and temperature rise, while the thrust force and mass flow rate intensify. Also, the size of the catalyst granules affects the performance of the bed and thruster so that by increasing it (at a certain porosity coefficient), a trend similar to the effect of decreasing the porosity coefficient can be seen in the results. On the other hand, with enhancing inlet pressure, the thrust force increases significantly. In this paper, the effect of bed parameters on the thruster performance is discussed in detail, which contains helpful results for researchers that work on improving the decomposition chamber efficiency. [ABSTRACT FROM AUTHOR]

The attempts to identify damping changes in a cracked beam can improve the accuracy of the nonlinear crack identification method. For the purpose of this aim, a parametric nonlinear equation of motion is obtained using the Euler–Bernoulli beam theory and parametric nonlinear breathing crack assumptions. Several experiments were conducted to identify the effect of breathing cracks on changing the damping value in nonlinear vibrations of a cracked beam. Experimental tests have revealed that increasing the crack depth and the level of excitation enlarges the damping coefficient in a vibrating beam. For this reason, the effects of the excitation force and crack depth on the structural damping coefficient are investigated. The obtained results indicated that considering the nonlinear response of a cracked beam and measuring the value of the damping changes can significantly improve the accuracy of the nonlinear crack identification method. [ABSTRACT FROM AUTHOR]