Two stroke slow speed diesel engines are mainly used in deep sea going vessels such as container ships, bulk carriers, and tankers. In this article, a numerical model is developed and solved to relate impact occurrence and magnitude on engine structure to rigid body tribodynamics of the crosshead guide system for a two‐stroke marine engine. To achieve this, the reciprocating piston group is coupled to the crosshead guide shoes through the crosshead guide pin. The resulting second order nonlinear differential equations are solved for displacements, velocities, and friction characteristics of the system. The rigid body motions are important in identifying occurrences and the intensities of transient impacts between contacting surfaces. These impacts influence noise and vibration characteristics of the engine. A study of the coupled system at different engine running speeds as well as varying crosshead guide system clearances is performed. It is observed that secondary displacements, velocities, and friction characteristics increase with increase in speed and clearance on the crosshead guide system. Consequently, the impact on the engine structure increase with increase in these tribodynamic characteristics of the system. This impact is transferred to the engine surface as vibration and noise responses.
In this article, an underwater hull cleaning robot model based on propeller thrust adsorption is established for near-wall conditions. By using a computational fluid dynamics method, which is proven feasible by comparing a calm water resistance simulation with its experimental data, the influence of floating body shape and wall distance on its hydrodynamic characteristics is studied. Then, the body force propeller model is used to analyze the interaction between the propeller flow field and the flow field around the underwater cleaning robot. Compared with the cuboid floating body, the results show that the streamlined appearance can greatly reduce front high-pressure area, the pressure drag between the front and rear ends, and the viscous resistance. Its drag coefficient is reduced by 11.5%. The presence of the hull will increase the pressure drag and viscous resistance of the underwater hull cleaning robot, which is similar to the "shallow water blockage effect" of a ship. For this model, the decrease in the wall distance results in a progressive increase in resistance and drag coefficient. As the wall distance is .15 m, the drag coefficient of the underwater hull cleaning robot increases by 4.55%, compared with the limitless water field. For the body force propeller model, the study indicates that when the flow velocity is constant, both the resistance in the forward direction and the adsorption force of the underwater hull cleaning robot increase with the increase in rotation speed of the propeller. The thrust propeller generates a higher increase in resistance and a lower increase in adsorption force compared with the adsorption of the propeller. When the rotation speed is constant, the resistance of the underwater hull cleaning robot increases, with the increase in the flow velocity, and the adsorption force of the underwater hull cleaning robot first decreases and then increases. Therefore, it must be fully considered that the significant influence of the hull and the propeller on the underwater hull cleaning robot can provide theoretical guidance for future related design and research.
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