Study on Unsteady Hydrodynamic Performance of Propeller in Waves

The speed of a ship sailing in waves always slows down due to the decrease in efficiency of the propeller. So it is necessary and essential to analyze the unsteady hydrodynamic performance of propeller in waves. This paper is based on the numerical simulation and experimental research of hydrodynamics performance when the propeller is under wave conditions. Open-water propeller performance in calm water is calculated by commercial codes and the results are compared to experimental values to evaluate the accuracy of the numerical simulation method. The first-order Volume of Fluid(VOF) wave method in STAR CCM+ is utilized to simulate the three-dimensional numerical wave. According to the above prerequisite, the numerical calculation of hydrodynamic performance of the propeller under wave conditions is conducted, and the results reveal that both thrust and torque of the propeller under wave conditions reveal intense unsteady behavior. With the periodic variation of waves, ventilation, and even an effluent phenomenon appears on the propeller. Calculation results indicate, when ventilation or effluent appears, the numerical calculation model can capture the dynamic characteristics of the propeller accurately, thus providing a significant theory foundation forfurther studying the hydrodynamic performance of a propeller in waves.

Research on the mechanical properties and electrical conductivity of cement mortar based on recycled nano-iron boride

Traditional cement-based materials are being gradually replaced by nanomodified cement-based materials because the traditional materials cannot meet the production needs of modern society.Nano-iron boride(nano-FeB)is a high-performance nanomaterial prepared from waste iron powder during construction.Its one-dimensional structure is similar to that of carbon nanotubes,which makes it a potential candidate for nano-reinforcement materials.In this paper,the effects of different contents of recycled nano-FeB(0%,0.05%,0.075%,and 0.1 wt.%,based on cement weight)on the mechanical properties and electrical conductivity of cement mortar were studied.The results showed that the mechanical properties of the composite cement mortar were improved with the addition of nano-FeB.When the content of nano-FeB was 0.075%,the 28 d compressive strength and flexural strength of the composite cement mortar increased by 60.2%and 42.1%,respectively.In addition,a 0.075%nano-FeB content favorably improved the conductivity of cement mortar.Compared with that of the control group,the volume resistivity of the composite cement mortar decreased by one order of magnitude.