The Response of a Weathervaning Vessel in Cyclonic Conditions: A New Tool

Response-based analysis (RBA) is widely regarded as the most accurate method for predicting long-term non-linear responses of weathervaning offshore installations under extreme metocean conditions, such as tropical cyclones. This approach performs statistical analysis directly on vessel responses, rather than on metocean parameters, and thus requires a comprehensive response time-history database for accurate probabilistic calculations. Recent advances in synthetic and hindcast metocean data over the past decade have enabled the generation of response databases through numerical simulations, allowing reliable estimates of 100- and 10,000-year return period responses for weathervaning vessels. However, most simulations rely on software packages designed for single-case analysis, which are not well-suited to handle the millions of sea states required for long-term response calculations in RBA. This paper introduces a newly developed computational tool at the University of Western Australia, namely HART (Heading and Response Tool), specifically tailored to calculate weathervaning vessel responses under extreme metocean conditions, with focus on tropical cyclones, incorporating optimized capabilities for efficiently managing large metocean datasets. HART uses frequency domain analysis and response transfer functions to calculate vessel responses for evolving metocean conditions during the passage of a tropical cyclone. These time histories can be sourced from a synthetic metocean database or field measurements. Each cyclonic sea state can be represented by either a discretized or parametric directional wave spectrum. For each combination of wind, current, and sea state, HART performs a heading analysis, and spectral response analysis, estimating stochastic responses at key locations on the vessel. Finally, the application of HART is demonstrated through response calculations on a generic turret-moored Floating Production Storage and Offloading (FPSO) facility exposed to tropical cyclones on Australia’s North West Shelf. Comparative analysis shows that HART produces results consistent with those of traditional commercial software while significantly reducing computation time, underscoring its potential for integration into statistical post-processing and response-based analysis workflows.