Session: 06-05-01 Marine Hydrodynamics

Submission Number: 154516

Identification of Vertical Centre of Gravity and Ship Mass Using Phase Resolved Wave Prediction Through In-Service Onboard Measurements 

The loading condition of container ships varies with each voyage, significantly impacting their motion behavior. Accurate knowledge of this loading condition is essential to avoid dangerous situations, such as roll resonance which is influenced by the ship's mass and vertical centre of gravity (VCG). The presented method provides real-time VCG and mass estimation in combination with sea state estimation to prevent dangerous motion conditions. Prolate spheroidal wave functions (PSWF) enable the reconstruction of ship motions from measurements and their transformation into the encountered wave profile. The wave angle can be determined by identifying the angular transfer function with the highest correlation. This study investigates three methods to extend the existing procedure in order to estimate ship mass and VCG during the voyage. The first method applies the same principle as used for wave angle estimation, the second method solves the roll differential equation and the third method estimates VCG, ship mass and the wave encounter angle simultaneously. Heave, roll and pitch motions are used to estimate the parameters. Validation with numerically generated data leads to precise parameter reconstruction, while model test validation indicates that nonlinear effects reduce the accuracy. The iterative procedure leads to the smallest deviations from model test and numerical input parameters. Transformation of the heave motion from the center of gravity to the ship ends and sides does not improve the estimates of angle, VCG and mass, but improves the wave profile estimation in long waves when the heave amplitude of the motion point is small. Although higher wave steepness reduces accuracy in wave angle and profile estimation, it does not significantly affect the accuracy of VCG and ship mass estimation. Application to full-scale data shows that using pre-determined mass and VCG for wave angle and profile estimation results in slightly smaller deviations from ERA5 weather data compared to using unknown parameters.

Presenting Author: Malwin Wermbter Hamburg University of Technology

Presenting Author Biography: Malwin Wermbter
Research Assistant at Institute for Fluid Dynamics and Ship Theory
Hamburg University of Technology