1 Scope
This standard specifies additional requirements for assessment of the external conditions at an offshore wind turbine site and it specifies essential design requirements to ensure the engineering integrity of offshore wind turbines. Its purpose is to provide an appropriate level of protection against damage from all hazards during the planned lifetime.
This standard focuses on the engineering integrity of the structural components of an offshore wind turbine but is also concerned with subsystems such as control and protection mechanisms, internal electrical systems and mechanical systems.
A wind turbine shall be considered as an offshore wind turbine if the support structure is subject to hydrodynamic loading. The design requirements specified in this standard are not necessarily sufficient to ensure the engineering integrity of floating offshore wind turbines.
This standard should be used together with the appropriate IEC and ISO standards and the corresponding national standards mentioned in Clause 2. In particular, this standard is fully consistent with the requirements of GB/T 18451.1. The safety level of the offshore wind turbine designed according to this standard shall be at or exceed the level inherent in GB/T 18451.1. In some clauses, where a comprehensive statement of requirements aids clarity, replication of text from GB/T 18451.1 is included.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 18451.1-2012 Wind turbine generator systems - Design requirements (IEC 61400-1:2005, IDT)
GB/T 19001-2008 Quality management systems - Requirements (ISO 9001:2008, IDT)
GB/T 23511-2009 Petroleum and natural gas industries - General requirements for offshore structures (ISO 19900:2002, IDT)
IEC 60721-2-1:2002 Classification of environmental conditions - Part 2-1: Environmental conditions appearing in nature - Temperature and humidity
ISO 2394:1998 General principles on reliability for structures
ISO 2533:1975 Standard atmosphere
ISO 19901-1:2005 Petroleum and natural gas industries - Specific requirements for offshore structures - Part 1: Metocean design and operating conditions
ISO 19901-4:2003 Petroleum and natural gas industries - Specific requirements for offshore structures - Part 4: Geotechnical and foundation design considerations
ISO 19902 Petroleum and natural gas industries - Fixed steel offshore structures
ISO 19903:2006 Petroleum and natural gas industries - Fixed concrete offshore structures
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply in addition to those stated in GB/T 18451.1.
3.1
co-directional (wind and waves)
acting in the same direction
3.2
current
flow of water past a fixed location usually described in terms of a current speed and direction
3.3
design wave
deterministic wave with a defined height, period and direction, used for the design of an offshore structure. A design wave may be accompanied by a requirement for the use of a particular periodic wave theory
3.4
designer
party or parties responsible for the design of an offshore wind turbine
3.5
environmental conditions
characteristics of the environment (wind, waves, sea currents, water level, sea ice, marine growth, scour and overall seabed movement, etc.) which may affect the wind turbine behaviour
3.6
external conditions (wind turbine)
factors affecting operation of an offshore wind turbine, including the environmental conditions, the electrical network conditions, and other climatic factors (temperature, snow, ice, etc.)
3.7
extreme significant wave height
expected value of the highest significant wave height, averaged over 3h, with an annual probability of exceedance of 1/N (“recurrence period”: N years)
3.8
extreme wave height
expected value of the highest individual wave height (generally the zero up-crossing wave height) with an annual probability of exceedance of 1/N (“recurrence period”: N years)
3.9
fast ice cover
rigid continuous cover of ice not in motion
Foreword III
Introduction V
1 Scope
2 Normative references
3 Terms and definitions
4 Symbols and abbreviated terms
4.1 Symbols and units
4.2 Abbreviated terms
5 Principal elements
5.1 General
5.2 Design methods
5.3 Safety classes
5.4 Quality assurance
5.5 Rotor-nacelle assembly markings
6 External conditions
6.1 General
6.2 Wind turbine classes
6.3 Wind conditions
6.4 Marine conditions
6.5 Other environmental conditions
6.6 Electrical power network conditions
7 Structural design
7.1 General
7.2 Design methodology
7.3 Loads
7.4 Design situations and load cases
7.5 Load and load effect calculations
7.6 Ultimate limit state analysis
8 Control and protection system
9 Mechanical systems
10 Electrical system
11 Foundation design
12 Assessment of the external conditions at an offshore wind turbine site
12.1 General
12.2 The metocean database
12.3 Assessment of wind conditions
12.4 Assessment of waves
12.5 Assessment of currents
12.6 Assessment of water level, tides and storm surges
12.7 Assessment of sea ice
12.8 Assessment of marine growth
12.9 Assessment of seabed movement and scour
12.10 Assessment of wake effects from neighbouring wind turbines
12.11 Assessment of other environmental conditions
12.13 Assessment of weather windows and weather downtime
12.14 Assessment of electrical network conditions
12.15 Assessment of soil conditions
13 Assembly, installation and erection
13.1 General
13.2 Planning
13.3 Installation conditions
13.4 Site access
13.5 Environmental conditions
13.6 Documentation
13.7 Receiving, handling and storage
13.8 Foundation/anchor systems
13.9 Assembly of offshore wind turbine
13.10 Erection of offshore wind turbine
13.11 Fasteners and attachments
13.12 Cranes, hoists and lifting equipment
14 Commissioning, operation and maintenance
14.1 General
14.2 Design requirements for safe operation, inspection and maintenance
14.3 Instructions concerning commissioning
14.4 Operator's instruction manual
14.5 Maintenance manual
Annex A (Informative) Key design parameters for an offshore wind turbine
Annex B (Informative) Wave spectrum formulations
Annex C (Informative) Shallow water hydrodynamics and breaking waves
Annex D (Informative) Guidance on calculation of hydrodynamic loads
Annex E (Informative) Recommendations for Design of Offshore Wind Turbine Support Structures with Respect to Ice Loads
Annex F (Informative) Offshore Wind Turbine Foundation Design
Annex G (Informative) Statistical Extrapolation of Operational Metocean Parameters for Ultimate Strength Analysis
Annex H (Informative) Corrosion Protection
Bibliography
