Final report for WP4.3: Enhancement of design methods ... - Upwind
Final report for WP4.3: Enhancement of design methods ... - Upwind
Final report for WP4.3: Enhancement of design methods ... - Upwind
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UPWIND WP4: Offshore Support Structures and Foundations<br />
13. Longer simulation requirements and how this relates to wind/wave stationarity has to be discussed.<br />
Wind and sea spectra shall be extended to cover the requirements <strong>of</strong> simulations with proper time<br />
length. It is proposed to extend the minimum simulation time <strong>of</strong> every single time series from 10 to 20<br />
minutes to capture slow drift motions. The total required simulation time at every wind speed bin, <strong>for</strong><br />
e.g. DLC 1.1 to reach statistical convergence should not be less than 3 hours.<br />
14. Importance <strong>of</strong> radiation and diffraction effects as well as wind/wave misalignment is to be considered<br />
on the hydrodynamic model. For some types <strong>of</strong> structures the radiation and diffraction <strong>for</strong>ces have the<br />
same order <strong>of</strong> magnitude. As a result the Morison’s equation neglecting the diffraction components is<br />
not applicable anymore. Enhanced panel <strong>methods</strong> may be applied. Hybrid <strong>for</strong>mulations applying the<br />
drag <strong>for</strong>ces according to the Morison’s equation but including diffraction and radiation terms as analysed<br />
by classic <strong>methods</strong> may be a convenient solution <strong>for</strong> part <strong>of</strong> the hydrodynamic analysis.<br />
15. Mooring and riser systems shall be considered as a new component with associated failure modes in<br />
the wave turbine concept <strong>design</strong>. Failure modes shall be considered in the turbine safety system with a<br />
following safety chain release (safety system activation) if threshold values are reached:<br />
a. e.g. extreme heel angle during operation<br />
b. vertical motion<br />
c. extreme yaw <strong>of</strong> the floater<br />
d. station keeping (deviation from reference point)<br />
16. Condition monitoring systems may have to be extended to cover mooring specific issues (e.g. pretension<br />
control <strong>for</strong> taut moorings).<br />
17. Ice loads can be important <strong>for</strong> the mooring systems and shall be further analyzed.<br />
The presence <strong>of</strong> ice will change the dynamics <strong>of</strong> a floating wind turbine considerably, as the significant<br />
horizontal displacement experienced by the structure under normal conditions will be impeded. This effect<br />
shall be considered <strong>for</strong> the <strong>design</strong> <strong>of</strong> floating wind turbines to be installed at sites where sea ice is<br />
expected to occur. This shall include guidance on modelling ice loads <strong>for</strong> floating turbines and possible<br />
extension <strong>of</strong> the ice <strong>design</strong> load cases.<br />
18. Inclining, stability and watertight integrity requirements shall be considered according to the IMO intact<br />
stability code IS-Code 2008, unless other national regulations are mandatory on where the device will<br />
be installed. The unmanned plat<strong>for</strong>m should be treated as a pontoon. Damage instability is to be considered<br />
according to Offshore Rules and approved by National Authorities.<br />
19. For transport ships that brings personnel to the site, the SPS-Code is to be applied, if no national regulations<br />
are mandatory. The IS-and the SPS-codes refer to the SOLAS document (definitions, etc...).<br />
a. IS-Code 2008 International Code on Intact Stability, Res. MSC.267(85) adopted 2008<br />
b. SPS-Code Code - Code <strong>of</strong> Safety <strong>for</strong> Special Purpose Ships, Res. MSC.266(84) adopted 2008<br />
c. SOLAS Consolidated Edition, 2010 Consolidated text <strong>of</strong> the International Convention <strong>for</strong> the<br />
Safety <strong>of</strong> Life at Sea, 1974, and its Protocol <strong>of</strong> 1988: articles, annexes and certificates<br />
20. Safety system, sensors <strong>for</strong> water in tanks, draft control, deck clearance shall be included. Alarm operator<br />
or activation <strong>of</strong> the safety system if threshold values are reached should be specified.<br />
21. Safety factors (including non-redundant mooring systems) shall be considered <strong>for</strong> moorings. Guidance<br />
is given in ISO 19901-7.<br />
22. For station keeping systems where no redundancy is available higher safety factors should be applied<br />
and need further consideration.<br />
23. Assessment <strong>of</strong> seismicity may be <strong>of</strong> significant importance <strong>for</strong> <strong>design</strong> <strong>of</strong> tension leg plat<strong>for</strong>ms.<br />
24. Ship impact loads due to normal operations should be revised, since more severe consequences are<br />
expected as <strong>for</strong> fixed <strong>of</strong>fshore structures and due to the fact that two bodies are moving. Another issue<br />
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