Iranian Journal of science and Technology (B: Engineering)
Volume:32 Issue: 1, February 2008

The issue of the new elastic terms discovered in the nonlinear dynamic model of an enhanced nonlinear 3D Euler-Bernoulli beam is discussed. While the elastic orientation is negligible, the nonlinear dynamic model governing tension-compression, torsion and two spatial bendings is presented. Considering this model, some new elastic terms can be identified in the variation of elastic potential energy in each bending motion equation, and in each transverse shear force. Due to the new terms, each term of a bending equation and a transverse shear force, finds a counterpart in the other bending equation and transverse shear force, but the equations remain asymmetric. The new terms have arisen, since variation of strains and variation of elastic potential energy are derived from exact strains and exact deformations regarding considerable elastic orientation, then the elastic orientation is neglected. The new terms perish in the nonlinear 3D Euler-Bernoulli beam theory, since elastic orientation is neglected first, then variation of strains and variation of elastic potential energy are derived from the approximated strains.

The rapid growth of space utilization requires construction and maintenance of space structures and satellites in orbit that, in turn, substantiate the application of robotic systems in space. In this paper, a near-minimum-time optimal control law is developed for a rigid space platform with flexible links such as manipulators, solar panels and stabilizing booms during an orientating maneuver with a large angle of rotation. The time optimal control solution for the rigid-body mode is obtained as a bang-bang function and applied to the flexible system after smoothing the control inputs to avoid stimulation of the flexible modes. This will also reflect practical limitations in exerting bang-bang actuator forces/torques, due to delays and non-zero time constants of existing actuation elements. The smoothness of the input command is obtained by reshaping its profile based on consideration of additional derivative constraints. The platform is modeled as a linear undamped elastic system that yields an appropriate model for the analysis of planar rotational maneuvers. The developed control law is applied on a given satellite during a slewing maneuver, and the simulation results show that the modified realistic optimal input compared to the bang-bang solution goes well with the practical limitations and also alleviates the vibrating motion of the flexible appendage, which reveals the merits of the new developed control law.

A modified three-dimensional dispersion model of our previous work5 was modified and used to investigate the effect of droplet size distribution in addition to droplet concentration distribution for the prediction of liquid droplet dispersion and particulate removal efficiency in a venturi type scrubber. For the sake of including droplet size distribution into the model properly, it was assumed that droplet size distribution obeys Rosin-Rammler distribution. The experimental data of Viswanathan et. al. [1] for liquid droplet dispersion and Brink and Contant [2] for particle removal efficiency were used to test the results of this new mathematical model. The results from the model show that by taking droplet size distribution into account the results of the model will be in better agreement with the experimental data.

In this paper the effect of the aspect ratio and filling ratio on the thermal performance of an inclined two-phase closed thermosyphon under normal operating conditions has been investigated experimentally. The experiments were carried out for filling a ratio range of 20%≤F.R≤60% and aspect ratios of 15, 20, and 30 for an inclination angle range of 15°≤Φ≤90°. The thermosyphon was manufactured using a copper tube with an inside and outside diameter of 14 and 16 mm respectively, and a 1000 mm length. Distilled water was used as the working fluid. The heat transfer rate, temperature distribution, and condensation heat transfer coefficient of the inclined two-phase closed thermosyphon were measured. The results showed that the maximum thermal performance of the thermosyphon occurred at 60° for all three aspect ratios and several filling ratios. The thermal performance of the inclined thermosyphon with an inclination angle of 60° was better for a filling ratio of 45%. It was also found that a higher condensation heat transfer coefficient for all three aspect ratios took place between 30 and 45 degrees.

The objective of this research work was to obtain a microorganism capable of decolorizing treated distillery wastewater (TDW). 21 isolated and procured microorganisms were screened for their percentage decolorization. The screening strategy was performed using three different culture media in two main steps. The primary screening was carried out in two stages. In the first stage 10 microorganisms had a lower than 25% decolorization of TDW (with 25% TDW concentration). In the second stage 8 microorganisms had more than a 48% decolorization of TDW. In the secondary screening all 3 different culture media, the effect of TDW concentration, pH and nitrogen source were studied. A fungus identified by morphology examination to be Aspergillus fumigatus U B2, isolated from soil samples taken from the vicinity of the Bidestan Distillery and Food Products, Qazvin, Iran had maximum decolorization of 81%.

This paper presents a failure analysis of journal bearings used in GE-F9 gas turbines. Detailed studies including visual examination, optical microscopy, scanning electron microscopy, XRD and oil analysis were performed to determine the root causes of failure. Based on the results, it was determined that fretting, sulfur attack and fatigue were the main causes of failure.