Research on the rotational inertia of radial piston pump and the optimization method of the pump parameters
This paper aims to propose a method of optimizing the structure of radial piston pump from the aspect of reducing the rotational inertia. A modeling method based on basic dimensions and scale factors is developed. By using this method, three different types of radial piston pumps are studied. And the relative rotational inertia coefficient is adopted to evaluate the difference among them. Further study states that the relative rotational inertia coefficient changes along with the eccentricity ratio and the thickening factor. Finally a criterion is obtained, which could be used to optimize the structure and the dimensions of radial piston pumps.
Study on High Dynamic Variable Speed Hydraulic Control System
A new type of high dynamic variable speed hydraulic control system is developed in this paper. In this system, a fixed displacement hydraulic pump is driven by an electrical motor which is controlled by a frequency inverter, so the discharge of the pump can be modified by changing the speed of the motor. A proportional directional valve is used to acquire higher low-speed control precision and faster dynamic response while the system is decelerating. In order to improve the dynamic response while the system is accelerating, an energy regulation device is employed in the system. The digital simulation results show that this system has higher efficiency than valve control system. Further more it has faster dynamic response and higher low-speed control precision than normal variable speed hydraulic control system.
Cognitive Correlaretes of Physics Achievement of Some Nigeria Senior Secondary Students
Some cognitive correlates of physics achievement of some Nigeria senior secondary students were considered in the study. Specifically, the study examined the relationship between measures of student’s field independency. Cognitive tasks, formal reasoning and their achievement in physics. Purposive and stratified random sampling techniques were employed to obtain a sample of 524 senior secondary two students from six education zones in Kogi State of Nigeria. Three instruments were used. They are science Reasoning Tasks (SRTs). Group Embedded Figures Test (GEFT) and Physics Achievement Test (PAT). Data analysis using multiple regressions reveals that measures of students’ fields’ independency and cognitive tasks predicted student’s achievement in physics generally. However, only measure of field independency predicted students’ achievement in physics in the higher order cognitive demand questions. Measures of formal reasoning had no significant relationship with students’ achievements in physics generally or in higher order cognitive demand questions in physics. However, the overall relationships between measures of field independency, cognitive tasks, formal reasoning and students’ achievement in physics generally and in higher order cognitive demand questions in physics were both significant. Educational implications of these findings were discussed.