Monopropellant propulsion systems are widely used especially for low cost attitude control or orbit correction (orbit maintenance). To optimize the total propulsion system, subsystems should be optimized. Chemical decomposition, aerothermodynamics, and structure disciplines demand different optimum condition such as tank pressure, catalyst bed length and diameter, catalyst bed pressure, and nozzle geometry. Subsystem conflicts can be solved by multidisciplinary design optimization (MDO) technique with simultaneous optimization of all subsystems with respect to any criteria and limitations. In this paper, monopropellant propulsion system design algorithm is presented and the results of the proposed algorithm are validated. Then, multidisciplinary design optimization of hydrazine propulsion system is proposed. The goal of optimization can be selected as minimizing the total mass (including propellant), minimizing the propellant mass (maximizing the Isp), or minimizing the dry mass. Minimum total mass, minimum propellant mass, and minimum dry mass are derived using MDO technique. It is shown that minimum total mass, minimum dry mass, and minimum propellant mass take place in different conditions. The optimum parameters include bed-loading, inlet pressure, mass flow, nozzle geometry, catalyst bed length and diameter, propellant tank mass, specific impulse (Isp), and feeding mass which are derived using genetic algorithm (GA).
The main protection equipment in radial distribution networks are non-directional overcurrent relays (NDOCR) and fuses which are coordinated using the conventional protection coordination method. By installing distributed generations (DGs) in the network, reverse short-circuit currents (SCC), injected from DGs, can lead to false tripping of NDOCRs and false melting of fuses. In the previous studies, some methods have been proposed to overcome these issues using directional overcurrent relays, fault current limiter, and adaptive methods that relay on communication. The present paper proposes a new coordination method to prevent these issues without the need for installing a new equipment, by proposing a new set of selectivity constraints. Here, selectivity between equipment is established, and false tripping and false melting issues are mitigated. The coordination of protection equipment according to the proposed method requires the use of optimization algorithms, and therefore, the proposed method is formulated as a mixed-integer linear programming method to take advantage of mathematical optimization algorithms. The proposed coordination method is applied to a real distribution network and the results indicate the high efficiency of the proposed method in dealing with false relay tripping and fuse melting issues.
Applying flat systems technique in attitude fault tolerant control of an under-actuated satellite has been investigated in this article. The main purpose of this study is development and implementation of a new idea in order to recovery of satellite stability and its acceptable performance in actuator fault scenarios. Solving the attitude fault tolerant control problem is based on consideration a realistic assumption which can show the ability of FTC system in managing the fault scenarios. Lose of effectiveness of actuators which could be caused in many of fault scenarios, modeled and simulated by multiplicative model. Thanks to provided new idea in this study it will be proven that, a wide range of actuator fault scenarios with different intense of faults could be managed without need to reconfiguring the main controller. Usage of this idea affects in reducing the volume of main controller computations and provides an appropriate base for its robust designing in other to dealing with systematically fault scenarios. Furthermore, the provided active fault tolerant attitude control scheme uses analytical redundancy system which could be considered as analytical observer. The suggested analytical observer by this technique, which belongs to nonlinear observer category, can observe all of the dynamic variables in allowable range of error. Practical implications of this study belong in this fact which analytical redundancy based on new idea in order to maintaining stability could be a perfect option in different fault scenarios such as systematically uncertainties and sensor faults. Hence this idea could be implemented without need to any physical instrument.
General TermsFault tolerant, flatness based control.
Introduction:The aim of this study was to investigate the work related stress among Iranian nurses with/without needlestick injuries (NIs) as an exposure factor to blood-borne pathogens.
Materials and Method:This study was conducted on 1070 nurses in Iranian public hospitals. The data were collected using a NIs questionnaire and the HSE Management Standards Indicator Tool and then, analyzed through independent ttest and logistic regression.
Results:The mean work related stress scores among the groups of nurses with/without NIs were 114.49 and 110.37, respectively. Moreover, the mean for five out of the seven stress component including control, managerial support, peer support, role clarity, and change were lower in the group of nurses with NIs, as compared to the other group, resulting in a significant difference between the two groups regarding the five stress component and work related stress (p<0.05).Further, the results showed that work related stress was significantly correlated with the variables of age, work experience, BMI, work shift the NIslast occurred, the way the NIs last occurred and received/unreceived Hepatitis B vaccine(p<0.05).
Conclusion:The NIs incidence was observed to cause increased levels of work related stress and its associated stressors among nurses. Accordingly, the work related stress level increased after the NI incidence and over time, the work related stress severity declined among nurses. Post-Nıs work related stress is considered as a mild PTSD with less severe effects. Therefore, it is essential to take control measures to reduce the work related stress and its negative effects.
Satellites constantly face the turbulences and external torques and so they may exhibit chaotic behavior and what is expected will not happen. On the other hand, it is so difficult or impossible to do some missions by only one satellite. These missions include the Earth observation for different purposes, observation of objects in space, etc. that can become more accurate by several synchronized satellites and also the costs of setting up and control with establishment of small satellites will be much cheaper. In this article, neural network controllers are used for synchronization of two chaotic satellites (which called master and slave satellites). Neural network controllers such as NARMA-L2 and Predictive controllers have been applied very successfully in the identification and control of dynamic systems. Both of the neural controllers have very good performance in the synchronization of two chaotic satellites, but each one has its advantages and disadvantages which in this article they will be described. Finally, results of the simulation have shown the very good performance of these neural controllers in the ideal synchronization of the salve chaotic satellite with the master chaotic satellite.
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