The fascinating mechanical inventions aiming at the welfare of the human kind started from ancient Egyptians and continued development through different eras. In the medieval centuries, the Islamic civilization paid wonderful attention to mechanical engineering. Banu Mosa invented 100 ingenious devices including automatic fountains and automatic feedback level control systems. Al-Jazari invented 50 mechanical devices including automatic fountains, clocks, positive displacement pumps and robotics. Taqi Al-Din invented a 6-cylinder positive displacement pump. Those great inventers used clean-energy prime movers in the form of windmills, overshot water wheels and undershot water wheels (turbines). This paper focuses only on windmills, water wheels and automatic fountains.

The objective of this paper is to investigate the dynamics of the barrel assembly-recoil mechanism of military cannons when using air springs and a constant damping coefficient hydraulic damper in their recoil mechanisms. The elastic characteristics of the air spring is nonlinear and the recoil mechanism orientation introduces extra nonlinearity to the dynamic model of the system. An extremely nonlinear model of the barrel assembly is derived and solved using Runge-Kutta 4 method to provide the dynamic response of the barrel assembly upon firing. The simulation results using the data of a Howitzer M114 cannon are presented for recoil mechanism orientation ? 50 degrees. The performance of the recoil mechanism is evaluated through the minimum and maximum displacements of the barrel assembly and the settling time of its response upon firing. The effect of the number of air springs on the performance of recoil mechanism is investigated. The analysis shows that it is possible with air springs to obtain barrel assembly response similar to that of a critically damped second-order system. It is possible with proper selection of the recoil assembly parameters to decrease the maximum barrel displacement to 54 mm and the settling time to less than 2 seconds.

Door closing mechanisms are used in all building venues using air conditioning systems to reduce thermal losses. One of the closing mechanisms is the torsional type. The visco-elastic characteristics of the closing mechanism may exhibit certain sort of nonlinearities from its linear characteristics. The dynamics of the door with nonlinear characteristic with positive and negative deviation from the linear characteristics of the door closing mechanism are studied. The system dynamics are defined by a nonlinear ordinary second-order differential equation which is solved using Runge-Kutta 4 technique through the MATLAB environment. Two types of nonlinearity are considered depending on the deviation from the linear characteristics of the closing mechanism. One type reveals dynamic behaviour similar to that of overdamped linear dynamic system while the other type reveals dynamic behaviour similar to that of underdamped linear dynamic system. The second type has large effect on the door dynamics where the maximum deviation in the door dynamic response may exceed 700 % from the linear characteristics of the door.

Robustness is one of the requirements used in controllers and compensators design. This paper examines the robustness of a Notch and a Sallen-Key compensator when used to control a highly oscillating second-order process.
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