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1

Study on the effects of preheated wall/plates in microthruster systems

Lekzian E., Parhizkar H., Ebrahimi A.

Journal of Theoretical and Applied Mechanics

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2018

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Vol. 56 nr 3

713--725

EN

In the present paper, eﬀects of pre-heated walls/plates on microthrusters performance are studied using a DSMC/NS solver. Three microthruster conﬁguration types are studied. Type 1 is a cold gas microthrster. Microthruster type 2 has pre-heated walls. Pre-heated plates are inserted inside the chamber of microthruster type 3. It is observed that in microthruster type 2 the ﬂow is accelerated and the speciﬁc impulse is elevated. However, by insertion of the pre-heated plates in microthruster type 3, viscous eﬀects have stronger negative inﬂuence and the thrust is decreased. By implementing temperature gradients on walls in type 2 and on plates in type 3, it is observed that a higher temperature gradient enhances performance parameters of microthruters. Among all types of microthrusters, microthruster type 2 with pre-heated walls has the highest thrust and speciﬁc impulse. Microthruster type 3 with a temperature gradient of 300-500K has the minimum thrust due to a considerable decrease in the mass ﬂow rate.

2

Continuous model for flexural vibration analysis of a Timoshenko cracked beam

Heydari M., Ebrahimi A., Behzad M.

Archives of Mechanics

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2013

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Vol. 65, nr 4

265–-288

EN

In this paper, a continuous model for vibration analysis of a beam with an open edge crack including the effects of shear deformation and rotary inertia is presented. A displacement field is suggested for the beam and the strain, and stress fields are calculated. The governing equation of motion for the beam has been obtained using Hamilton’s principle. The equation of motion is solved with a modified Galerkin method and the natural frequencies and mode shapes are obtained. A good agreement has been observed between the results of this research and the results of previous work done in this fiels. The results are also compared to results of a similar model with Euler-Bernoulli assumptions to confirm the advantages of the proposed model in the case of short beams.

3

A new continuous model for flexural vibration analysis of a cracked beam

Behzad M., Ebrahimi A., Meghdari A.

Polish Maritime Research

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2008

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nr 2

32-39

EN

In this paper a new continuous model for vibration analysis of a beam with an open edge crack is presented. A quasi-linear displacement filed is suggested for the beam and the strain and stress fields are calculated. The equation of motion of the beam is calculated using the Hamilton principle. The calculated equation of motion is solved with a modified weighted residual method and the natural frequencies and mode shapes are obtained. The results are compared with those obtained by finite element method and an excellent agreement has been observed. The presented model is a simple and accurate method for analysis of the cracked beam behavior near or far from the crack tip.