Design Considerations for Offshore Wind Turbines in US Waters - The American Way

Abstract

This paper addresses unique design considerations for the support structure of an offshore wind turbine in US waters and how the Working Stress Design (WSD) approach can be applied. The Load and Resistance Factor Design (LRFD) criteria specified in IEC 61400-3 are primarily developed based on the experience from offshore wind turbines installed in European coastal areas. Due to the higher variability of the wind and wave climate in hurricane-prone areas, offshore wind turbines in US waters would not achieve the same level of safety as those in European waters if the existing IEC design criteria were applied. To address this, a set of acceptance criteria, accounting for the unique design consideration related to tropical storms, has been developed and are published in the ABS Guide for Building and Classing Offshore Wind Turbine Installations. Extensive calibrations have been carried out to verify the adequacy of design load conditions and structural design requirements of the ABS WSD-based design criteria. Metocean conditions in the US Gulf of Mexico (GoM) and East Coast were used in the calibrations to calculate the aerodynamic and hydrodynamic loads as well as the structural responses of the typical designs of offshore wind turbines.

Quantifying the Hurricane Catastrophe Risk to Offshore Wind Power

“…To mitigate the risks of hurricanes, offshore wind turbines can be designed for higher maximum wind speeds, designed to track the wind direction (yaw) quickly enough to match wind changes in a hurricane even if grid power is cut off, or placed in areas with lower hurricane risk, as discussed by Rose et al . Efforts are underway to determine design standards for offshore wind turbines in hurricane‐prone areas . Battery backup is a low‐cost way to maintain yawing capability when grid power is interrupted .…”

Reliability Analysis of Offshore Wind Structures Considering the Korean Met-Ocean Conditions

“…where, F.S., γm, and γf denote a factor of safety, partial material factor, and partial load factor, respectively. Table 1 represents factors of safety, partial material factor, and partial load factor (ABS, 2010;IEC, 2009;ISO, 2007;Yu, Samuelsson, and Tan, 2011).…”

Design Load Cases Required for Offshore Wind Turbines in Hurricane-Prone Regions

“…The comparison results essentially imply that the "normal" and "abnormal" conditions defined in IEC 61400-3 might be considered equivalent to the "operating" and "extreme" conditions defined in API RP 2A-WSD. Yu et al (2011b) presented the technical background of the design criteria recently published in the ABS Guide for Building and Classing Offshore Wind Turbine Installations, where the design requirement for offshore wind turbine support structures in hurricane-prone regions was specifically defined. The paper discussed unique design considerations for the support structure of an offshore wind turbine in US waters and how the Working Stress Design (WSD) approach would be applied.…”

“…As indicated inYu et al (2011b), the return period of the design environmental conditions should be determined from the perspective of an overall design approach (i.e., "a design recipe"). The present parametric comparisons are intended to provide a means of evaluating the effect of the return period of design environmental conditions in combination with other design parameters on structural responses and the safety margin of an offshore wind turbine support structure.…”