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A front-end loader (FEL) mounted on an agricultural tractor is one of the most commonly used implements to mechanize routine agricultural tasks. When the FEL is used with a loaded bucket, careful operation is required to maintain safety and avoid spillage when the tractor passes a bump because a change in the gravity center of the tractor due to varied loadings can affect the stability of the tractor. Use of a boom suspension system consisting of accumulators and orifice dampers can be instrumental in reducing pitching vibrations while increasing the handling performance of the FEL-mounted tractor. The objective of this research was to reduce bump shocks by adding an orifice and a flow control valve to the original hydraulic circuit composed solely of accumulators. A simulation study was performed using the SimulationX program to investigate the effects of an accumulator and an orifice-throttle damper on bump shocks. Results showed that the peak pressure on a boom cylinder and the vertical acceleration of a bucket were significantly affected by use of both an accumulator and an orifice damper. In a field test conducted with a 75-kW tractor, the peak pressure of the boom cylinder, and the root mean square (RMS) vertical acceleration of the bucket and seat were reduced by on average, 23.0, 42.2, and 44.9% respectively, as compared to those measured with the original accumulator system, showing that an improved design for the accumulator hydraulic circuit can reduce bump shocks. Further studies are needed to design a tractor suspension system that includes the effects of cabin suspension and tires as well as dynamic analysis.

This study assessed the performance of a ceramic monolith heat exchanger, estimating heat transfer and pressure drop by numerical computation and the ε-NTU method. A heat exchanger consists of rectangular ducts for exhaust gas, a ceramic core, and rectangular ducts for air and exhaust gases, as well as air in the cross-flow direction. The numerical computations were performed for the whole domain, including the exhaust gas, ceramic core, and air. In addition, the heat exchanger was examined using a conventional ε-NTU method with several Nusselt number correlations from the literature to characterize the flow in the rectangular duct. The results of these numerical computation analyses demonstrated that the effectiveness of the heat exchanger, as demonstrated using the ε-NTU method with Stephan's Nusselt number correlation, came closest to the results of computation with a relative error of 2%. The air-side pressure drops indicated by the results of numerical computation were 13-22% higher than those calculated using the head loss equation with the inclusion of a friction factor that was obtained from previous experiments examining heat transfer conditions.

Turbine power control devices at a nuclear / thermoelectric power plant lead to failure by creating mechanical shocks and strong vibrations that are due to the strong elasticity of a spring and the inertia of the valve face during its rapid movement to block steam. To ensure durability of the turbine power control device, which is the main component in the power plant, it is necessary to develop a device that can prevent such vibrations. In this study, a cushion mechanism is added to the head of the hydraulic servo actuator, which is a turbine power control device. Moreover, the cushion mechanism, which includes various modifies shapes and orifices is investigated dynamically through modeling and simulations.