A Detailed Look into the 2017 SNAME OC-8 Comparative Wind Load Study

This paper documents the results from the 2017 Society of Naval Architects and Marine Engineers (SNAME) OC-8 Panel Comparative Wind Load Study. Initial unpublished results were presented at a one-day panel at the 2017 SNAME Maritime Convention; however, the final results are brought together for the first time in this paper. A blind, comparative study was organized through the SNAME OC-8 Panel in 2017 to assess the relative accuracy and repeatability of existing wind load estimation methods. Twenty-five companies and organizations throughout the world participated in this study, which encompassed three available wind load estimation methods: empirical building block procedures, wind tunnel testing, and Computational Fluid Dynamics (CFD). To permit an ‘apples-to-apples’ comparison, the same representative semisubmersible design was used by all participants, including a single physical model shipped consecutively to each of the five wind tunnel facilities participating in the study. The most significant finding from the study is the remarkably low variability in wind tunnel and CFD results relative to the empirical building block method incorporated in the U.S. Code of Federal Regulations (CFR), classification rules, and industry codes for stability calculations. Moreover, only wind tunnel and CFD results were able to accurately quantify the contribution of a lifting force and its effect on the overturning moment. The lessons learned from the comparative study will be incorporated into a long-awaited revision to SNAME's wind tunnel testing guideline, and has inspired the development of a new industry guideline which will broadly address wind load estimation methods in design, including the use of CFD throughout the design spiral.