Ship Vibration Data Acquisition System And Data Analysis

Ship vibration is one of the main factors affecting the habitability of merchant ships degrading the durability of the ships’ structure and stealth performance as well. Severe vibration even affects the normal operation of ship. Estimating the vibration of ships is important for both vibration isolated designing and evaluating whether the magnitude of vibration meets the criterion. So far ship vibration acquisition and analysis are mainly done by vibration analyzer, which is not able to measure long term vibration when the ship is performing long term task.This research developed a FPGA based ship vibration data acquisition system which includes three axis ICP acceleration sensor and its constant current power source, data storage module, data transmission module and calendar module. Three channel signal can be sampled synchronously at the rate of 10 KSPS. Data collecting program is designed and vibration data can be collected for up to three month in the 8GB Flash memory, and can be uploaded via USB or WIFI. Code is designed with VHDL.Octave frequency spectrum analysis method is a commonly used in vibration analysis. The thesis introduces the traditional octave analysis methods, and applies multirate signal processing principle to octave analysis which improves frequency resolution from high to low frequency progressively. Principle of multirate octave analysis is introduced in detail. Resolution, computational complexity and memory space are compared via simulation and the key part of the algorithm is implemented in FPGA.The collected vibration data is analyzed and the results demonstrate that the main excitation of poop deck is propeller vane frequency excitation, and rudder engine room has a high frequency modal response excited by hydraulic pressure pulse. Correlation between each measurement point is not obvious.