Finite Element Analysis of Rack-Pinion System of a Jack-up Rig
In offshore mobile jack-up rig, platforms are generally supported by movable jacking system where strength of rack and pinion are very crucial in determining the design life of the superstructure. In this study, a number of finite element models have been developed for noble 7 teeth-pinions to investigate the strength of this jacking system. Since rack-pinion contact patterns change with the rotation of the shaft, models are developed for every 10 degree rotation starting from 0 to 50 degree where elasto-plastic properties of both rack and pinion is considered. Therefore, it is expected that each pinion tooth experiences different stress and displacement as it contacts with rack at different orientation. Elasto-plastic finite element analyses are conducted for worst possible load cases of the gear including self-weight of the platform, wind load, hydrodynamics force as per American Bureau of Shipping (ABS) guideline. The stress distribution of the pinion shows that maximum stress occurs at the root of the tooth, mainly due to bending effect. The analysis reveals that maximum stress in rack and pinion are found to be 1103 MPa and 682 MPa, respectively which is very close to the corresponding material capacity. The outcome of this study will certainly contribute in designing future rack-pinion system for offshore jack-up rigs and similar other structures.
Keywords - Rack-pinion, Finite element, Geometric Analysis, Stress Analysis.