In order to study the vibration mechanism of a marine centrifugal pump unit and explore the contribution of vibration caused by different vibration excitation sources, a marine centrifugal pump with a specific speed of 66.7 was used for research. A numerical calculation model of the flow field and electromagnetic field of the pump unit was established to analyze the frequency spectrum characteristics and contribution of pump unit vibration caused by different excitation sources. Using the modal superposition method, the vibration characteristics of the pump unit caused by fluid excitation and electromagnetic excitation were analyzed. The results show that the main frequency of pump unit vibration caused by fluid excitation was at the 1× blade passing frequency. The main frequency of pump unit vibration caused by electromagnetic excitation was at the 2× utility frequency. The contribution of different excitation sources to the vibration of marine centrifugal pump unit was in the following order: fluid excitation on the inner surface of the pump electromagnetic excitation fluid excitation in the impeller.
Wood grain direction is a three-dimensional quantity that is defined by its angles within and into the plane of the measured surface. These are respectively called the surface and dive angles. An interesting method to measure these angles involves measuring the spatial reflection from the wood surface when illuminated by concentrated light. The cellular shape of the wood microstructure causes the light reflection to be greatest perpendicular to the wood grain. This effect allows the surface and dive angles to be determined by analyzing the spatial variation of the reflected light. The conventional method for doing this involves sampling the reflection intensities around a circle above the wood surface. However, this method is effective only for small dive angles. A new method is described here where light reflection intensity variation is measured along two parallel lines on either side of the illuminated area. It is able to measure the ranges of surface and dive angles of interest in strength grading applications. A laboratory device for making the required spatial reflection measurements is described and experimental results are presented.
The gallop of high voltage transmission line can lead a mass disaster to power facilities but it seems that people are not clear totally about the galloping mechanism. To make sure the safety of power grid, this paper studies deeply on the galloping oscillator model of transmission conductor and given the oscillator model which is globally expressed by dimensionless equation. In addition, it also pointed out that system damping cannot be ignored when a single degree of freedom oscillator model is adopted in analyzing the gallop of transmission lines. For the improved three degree of freedom oscillator model, the numerical solution of conductor galloping response is worked out by using the method of Runge Kutta to solve the differential equations. And the aerodynamic force of the conductors is developed into the third-order by Taylor's formula. The differential equations are simplified and solved by averaging and then the parameters will be analyzed.
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