Mitigation of Fatigue Damage and Vibration Severity of Electric Drivetrains by Systematic Selection of Motion Profiles

The offshore drilling industry is among the most demanding markets for electrical equipment. Heave motion, irregular cyclic loads, harsh weather conditions, and vibrations are causing accelerated deterioration of drilling equipment. One of the most common solutions to these problems is to design actuation systems of such machinery overly conservative to gain additional safety, which results in too high initial investment and maintenance costs. To mitigate the fatigue damage and vibration severity of rotating elements of electric drivetrains operating offshore, this paper presents a comparative analysis of four popular input functions used in motion control of industrial systems. We evaluate them not only by using well-known performance indicators, such as maximum load or velocity, but also by assessing their influence on fatigue life and vibration severity of electric drivetrains. The rainflow counting algorithm is used to assign amplitudes and mean values of distinguished cycles from random loading history. Then, the Palmgren-Miner rule together with S-N curves are applied to determine the total damage for cycles with varying amplitudes. In addition, we quantify the cumulative effect of vibrations and jerk on machine damage by using the metric based on the jerk energy. The importance of this study is illustrated on a full-scale offshore pipe handling machine by benchmarking simulation results with the field data. The outcomes demonstrate not only a serious decrease in damage caused by vibrations for smooth motion profiles, but also provide a basis to formulate rules of thumb for selection of the most suitable motion profile for certain applications.