Bollard Force Study Based on Vibration Frequency Method

Abstract

Existing bollard force measurement methods have not yet been able to realise simple, accurate, and efficient measurements of the bollard force of a single ship’s cable. In this paper, an experimental study on the measurement of ship bollard force is carried out with reference to the calculation method of measuring the cable force of a diagonal cable. Based on the fundamental frequency method and the frequency difference method, a new comprehensive method is proposed to detect the fundamental frequency of cable vibration. A study on the identification of the cable condition based on the measured vibration data is also carried out. Experimental studies on the error rate of different data acquisition positions, excitation methods, excitation positions, wetted cables, different temperatures, and other influencing factors were conducted, and a new excitation method based on environmental excitation and artificial excitation was proposed. By analysing the calculated values of the vibration frequency method and the tensile values of the prototype test platform, it is concluded that the data acquisition position, excitation position, and excitation method have a small influence on the measured value of the ship’s bollard force, and the range of the error rate increases by about 1.5% under the wetting of the cable and ±2% under the low temperature (2 °C), with the integrated error range of −5% to 4%, and the error rate can satisfy the normal distribution well, and the measurement accuracy is corrected by correcting the length of the cable. The measurement accuracy is corrected by correcting the cable length. It is proved that the method has strong feasibility and applicability, and can effectively realise simple, accurate, and efficient measurement of ship bollard force.

Keywords

• frequency method
• cable force
• measurement accuracy
• error analysis