Numerical Simulation and Testing Analysis of Adaptive Heave Motion Measurements

Accurate heave measurements are important in the application of marine field to actively compensate for wave motion of a ship. An MTi unit is used to measure the heave motion of the ship in this paper. The primary error of heave measurements come from white noise and constant or slowly varying bias. The process of time integral of acceleration eliminates the white noise and a highpass filter is used to remove the bias. Then the first time integral of acceleration get the heave speed. The bilinear transformation is used to design IIR digital filter based on the conversion of analog prototype filter. Numerical simulation gets a conclusion that the mean absolute errors of heave speed measurements have relation to the cutoff frequencies of the filter. The cutoff frequency which depends proportionally to heave motion frequencies calls suboptimal cutoff frequency. The numerical simulation proves that the adaptive highpass filter with suboptimal cutoff frequency improves the precision of heave measurements. The test of heave motion measurements certifies the usefulness and correctness of the heave motion measurements with MTi unit and adaptive filter.