A Method for Fatigue Analyses of Electro-Mechanical Submarine Cables

A method of conducting fatigue analyses of sub marine electro-mechanical cables is developed. The procedure is divided into three parts. The first portion of the analysis consists of predicting the tension history of the cable configuration under consideration. A frequency domain cable dynamics program is used to predict the cable´s response in each sea state. These are combined using the probability of occurrence for each sea state to produce a yearly tension history of the cable. The second portion of the procedure is an analysis of internal cable stresses. A cable stress analysis program based on strain energy methods is used to predict the loads in each component of a multi component cable for a given set of load conditions. Load transfer between cable components, tension torque relationships, and the axial, torsional, radial compressive and principal stresses in each component are predicted. A parametric analysis of the cable is conducted for a range of tensions derived by the earlier dynamic analyses. This parametric analysis yields a stress history for each component of the cable. The third portion of the procedure is to use the predicted stress histories for each cable component is a fatigue analysis. Several approaches to calculating fatigue can be used, among these are Miner´s Rule and Manson´s approach (5). The results of this method allow the cable designer to evaluate a particular cable design for a specific application. Catastrophic failures from cable breakage or yielding of one or more cable components, such as the conductor or hermetic sheath, are examined. Additionally, the cable´s fatigue life can be estimated. The cable designer can use this method to conduct a parametric analysis to determine what design modifications are necessary to meet a given set of operating conditions.