Study Of Active Vibration Control For Marine Reciprocating Machinery

The marine reciprocating machinery mentioned in this thesis includes diesel engine andair compressor mainly. Such machines always cause vibration which has the line spectrumcharacteristic. The line spectrum contains a fundamental frequency and its harmonics that arerelated to the rotational speed. It is hardly to guarantee the good effect at the low frequencyband through passive vibration control for the machines. So this kind of vibration often bringslarge problems in practical application. In this thesis, an active vibration control method isexplored to solve this vibration matters.Firstly the vibration characteristic of the reciprocating machinery is analyzed. And thetest result on a diesel engine is exhibited to explain the vibration spectrum whose high linesmainly locate in the low frequency band. A adaptive LMS algorithm is derived for thisvibration characteristic in next chapter. And the z-domain transfer function of the new systemcomposed of the adaptive filter and the original system is deduced as well. The results showthat when the reference signal is sinusoidal, the sinusoidal frequency will be the same as thezero point of the transfer function between the desired signal and the error signal. So thedesired effect of the algorithm is proved in a more distinct way.Finally, a better application of the algorithm for the active vibration control of thereciprocating machinery is explored through a series of experiments. In order to study thestructural characteristics and to provide relevant data for the subsequent experiments andsimulations some are performed. The preparative experiments contain the modal testing, thetransfer function testing and offline identification of the secondary paths. After that the centralactive vibration control experiments that based on the traditional filtering xLMS algorithm(taking into account the coupling between channels and do not consider coupling), the combfiltering algorithm and the improved filtering xLMS algorithm are performed. A faster andmore stable DSP controller is used in the experiments on which the c programs of the abovealgorithms are run successfully. The elaborate design of the c programs refer to the algorithmprinciple, the frequency measurement, the reference signal generator, the digital filters designand the Simulink simulation. Double DSP’s cooperative work is achieved that overcomes theproblem may coming with the large amount of computation. Among these experiments, theinnovative experiment with the improved filtering xLMS algorithm got the best effect. So a better active vibration control method for reciprocating machinery is found.