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Part B - Verifications and approval requirements 
4.3 Design phase 
4.3.1 Preliminary remarks 
In the following considerations, the assumption is made that the wind turbine type has already 
been selected at the point of reviewing the design and that a valid offshore type certification 
for this turbine type is available. In the case of a pilot installation or a new development for 
which, due to time restrictions, a type certification cannot or cannot yet be issued, it may, in 
individual cases, be permissible to present another suitable verification for obtaining approval 
for the RNA, where this has already been accordingly clarified. 
Once all the verification reports pertaining to the site conditions, loading assumptions and 
support structure have been presented, a certificate of conformity for the rotor/nacelle assem 
bly is generally issued by the appointed inspector. The design review phase is concluded 
through the issue of the certificate of conformity. 
The preconditions for issuing the certificate of conformity are that there have been no changes 
to the RNA (technical management and safety system, engine, rotors, electrical systems) with 
respect to the offshore wind turbine type certification, that the site-specific loads on the RNA 
do not exceed the permissible loads specified in the type certification and that the influence 
of the local marine environment has been accordingly taken into account through the imple 
mentation of a climate control system, corrosion protection and similar in the respective type 
certification. 
4.3.2 Requirements and required verifications 
Based on the site conditions and the design basis, as well as the technical management and 
safety concept of the offshore wind turbine, the site-specific loading conditions relevant to the 
design shall be accordingly defined. The scope of the loading condition definitions shall be 
assessed by the appointed inspector. It is recommended for the loading conditions to be 
evaluated by the appointed inspector before the simulation and calculation of the loading as 
sumptions starts, in order to avoid duplicate simulations. All loading conditions shall be con 
sidered that are necessary in order to demonstrate the structural integrity of the offshore wind 
turbines. 
A basic differentiation is drawn between operational stability loads for demonstrating opera 
tional stability and extreme loads for demonstrating general stability against collapse (strength, 
stability, external stability against collapse). The operational stability loads shall represent op 
eration of the offshore wind turbines over a service life of at least 20 years. Should the desig 
nated service life be less than the 25-year approval period, appropriate verification shall be 
submitted in good time prior to the end of the designated service life with a view to continuing 
operations (e. g. based on the “DNV GL Guideline for the Continued Operation of Wind Tur 
bines”). The extreme loads shall include all events that can lead to the greatest possible loads, 
whereby consideration shall be given to the probability of their simultaneous occurrence (e. g. 
“50-year gust”, “50-year wave”, extreme angle of approach of the rotor, collision with a serv 
ice ship, ice pressure). 
The combination of external conditions and installation statuses shall be represented and jus 
tified for the corresponding project and the site according to (or if necessary based on) the 
applicable guidelines and standards. The partial safety factors of the effects of the codes of 
practice used shall be taken into account. The calculation methods, e. g. simulation proc 
esses, number of implementations and combination of wind and wave loads, shall be de 
scribed and any simplifying assumptions shall be justified.