This paper complements an earlier paper by the same author titled “Joint Seakeeping Response Processes for Determining Structural Loads,” presented at the 2002 SNAME Annual Meeting. That paper put forward a variety of methods appropriate to the characterization of joint processes, including phase co-factors, cross co-spectral moments, and joint normal techniques. The present paper exploits cross co-spectral moments to determine principal axes for joint seakeeping processes and explores their behavior and properties in appropriate parameter spaces. The convergence of time domain realizations of these joint processes on the principal axes is also demonstrated through Fourier-Stiljes simulations and conditional probabilities. One example application is to determine the orientation in space of principal axes for vector processes such as translational accelerations in vessel coordinates. As shown by a referenced paper cited in the conclusions, the method can be extended to Von Mises stress and rainflow fatigue.
Authors: Bruce L. Hutchison, PE; Benjamin B. Ackers, PE; Timothy S. Leach, PE