Standards and Practices - Structural Integrity of Offshore Wind Turbines - page 55

cover all aspects of the design and construction of offshore wind
turbines.
3. Nongovernmental organizations and private companies that establish
and maintain technical rules and guidelines for the design, con-
struction, and operation of ships and offshore structures—commonly
known as classification societies—have developed guidelines. The most
comprehensive industry guidelines for offshore wind turbine design,
fabrication, installation, and commissioning have been developed by
classification societies such as DNV, GL, and ABS. These standards are
more comprehensive than are the IEC standards in the sense that they
cover both the load and resistance sides, whereas the IEC standards
cover explicitly only the load side. However, there are still deficiencies
that must be overcome. For instance, the European society guidelines
do not explicitly address environmental site conditions for the United
States (e.g., storms and hurricane conditions for the Gulf of Mexico and
the East Coast). Only the GL rules deal with the design and certification
of wind turbine mechanical and electrical components (e.g., the gear-
box, the generator, and the control systems).
4. Methodologies for strength analysis differ among the various standards
and guidelines and are not always fully delineated. Some standards are
based on strength or limit states design, while others are based on allow-
able stress design. The philosophies underlying these methods are fun-
damentally different, making it difficult to compare such standards
against one another to ensure consistent safety levels, especially when
the standards are applied to novel concepts. There is a need for a clear,
transparent, and auditable set of assumptions for strength analyses.
5. As discussed in Chapter 1, although regulations (MMS 2009) pro-
mulgated by the U.S. Department of Interior's BOEMRE require that
detailed reports for design, construction, and operation of offshore
wind turbines be submitted for BOEMRE approval, they do not spec-
ify standards that an offshore wind turbine must meet. Rather, a third
party (CVA) is charged with reviewing and commenting on the ade-
quacy of design, fabrication, and installation and submitting reports to
BOEMRE indicating the CVA's assessment of adequacy. Moreover,
when a general level of performance such as “safe” is identified, no guid-
ance is provided on how to assess whether this level of performance has