Al-Khwarizmi Engineering Journal

This paper compares the accuracy of the HF propagation’s prediction programs for HF circuit links between Iraq and different points world wide during August 2018 when solar cycle 24 (start 2009 end 2020) was at minimal activity and also finds out the best communication mode used. Prediction programs like the Voice of America Coverage Analysis Program and the International Telecommunication Union Recommendation RS 533 had been used to generate high frequency circuit link parameters such as the Maximum Usable Frequency and Frequency of Transsmision. Depending on the predicted parameters (data), real radio contacts had been done using a radio transceiver from Icom model IC 7100 with 100W radiated power, tuner box and a homemade dipole antenna 10 meters in length and 8 meters in height above the ground. From the correlation between the predicted data and the observed data, the result was inaccurate.

This valve is intended for use in valves for steering movement, using the qualities of the Magneto-rheological (MR) fluid to regulate the fluid, direct contact without the utilization of moving parts like a spool, a connection between electric flux, and fluid power was made, The simulation was done to employ the\" finite element method of magnetism (FEMM)\" to arrive at the best design. This software is used for magnetic resonance valve finite element analysis. The valve\'s best performance was obtained by using a closed directional control valve in the normal state normally closed (NC) MR valve, with simulation results revealing the optimum magnetic flux density in the absence of a current and the shedding condition, as well as the optimum pressure. Finally, the MR valve proved successful in proportionally dominant in the direction and the quickness of the hydraulic actuators, and the new model allows hydraulic valves to be replaced with smaller valves while also lowering complexity.(Some of the figures in this article are only available in color in the online edition.)

The maintenance of the diesel engine parts in any electric power station contains many problems that lead to stopping. Several reasons lead to such problems; these reasons should be analyzed and evaluated in order to eliminate their effects. This paper is based on evaluation of the main causes that lead to diesel engine injector failure as a main part of electric power stations, using fault tree analysis (FTA). The FTA is the most broadly utilized strategies in the industrial area to perform reliability analysis of complex designing frameworks. A fault tree is a logical representation of the relationship of basic events that lead to a given unwanted event (i.e., top event).Starting with introducing the FTA and how it could be utilized in analyzing the reasons of main issues that lead to that the injector stops working, in which the probability of occurrence of each issue is calculated. The application of the root cause analysis principle of diesel engine injector failure in diesels Haditha station is chosen as a case under study. According to the probabilities’ evaluation by using the FTA based on of the causes under the top event its value was (0.80). It is concluded from the analysis that the three largest values of the occurrence of a problem with the diesel engine injector are 0.50 for fuel problems, 0.20 for overloads, and 0.18 for nozzle head corrosion. Plant management can define a specific plan with taking into consideration the calculated value of each cause in order to reduce their impacts and to avoid long downtime hours compared to operating hours. Finally, recommandations are suggested to overcome these causes.

Lower extremity exoskeletons can assist with performing particular functions such as gait assistance, and physical therapy support for subjects who have lost the ability to walk. This paper presents the analysis and evaluation of lightweight and adjustable two degrees of freedom, quasi-passive lower limb device to improve gait rehabilitation. The exoskeleton consists of a high torque DC motor mounted on a metal plate above the hip joint, and a link that transmits assistance torque from the motor to the thigh. The knee joint is passively actuated by spring installed parallel with the joint. The action of the passive component (spring) is combined with mechanical output of the motor to provide a good control on the designed exoskeleton while walking. The results show that muscles\' efforts on both the front and the back sides of the user\'s leg were decreased when walking using the exoskeleton with the motor and spring.