Stability calculations - wish list#
At the moment the DAVE core offers the following functionality:
carene tables
GM curve including
wind forces
full statics solving such that cranes, attached buoyancy, contact, etc are fully incorporated
Free fluid surfaces are included naturally. This means that there is no “free surface correction” as there is nothing to correct for using work-arounds.
damaged tanks are possible by setting a tank to “free flooding”
free trimming is possible
The stability analysis report section (Vessels module) sets a heel angle, solves statics and then reads the moment required to impose that heel angle. From this the GZ values and wind arm can be derived.
The idea is to develop a automated workflow that applies a number of loadcases, runs them and assembles and reports the relevant results.
Applicable Codes#
IMO
0300/ND –> replaced by DNVGL-ST-N001
DNVGL-ST-N001
DNV-ST-0119 Floating wind turbine structures
Loadcases#
CODES |
||
|---|---|---|
intact |
||
with , without wind |
||
pre-defined range of heel angles, to both sides |
||
damaged single tank |
||
pre-defined range of heel angles, to both sides |
||
with, without wind (different wind speed than for intact) |
||
damaged multiple tanks |
||
0030/ND: Two adjacent compartments on the periphery of the unit shall be considered as one compartment if separated by a horizontal watertight flat within 5 m of the towage waterline |
ND |
User input
wind speed intact
wind speed damaged
free trimming
damaged tanks
(damaged tank pairs)
down-flooding points
a safety factor γstability (default = 1.3) for wind-t
To be calculated and reported#
What |
CODES |
|
|---|---|---|
area under the righting LEVER curve (GZ curve) |
IMO |
|
area under the righting MOMENT curve |
DNVGL |
probably an error in the code as it is compared to the wind arm. |
2nd intercept angle |
||
Area under wind overturning arm |
ND |
|
minimum initial GM value |
IMO, ND |
|
minimum GZ value at 30 degrees |
IMO |
|
angle of heel at which the maximum righting arm is reached |
IMO |
|
Intact range (0 till angle at which the GZ becomes negative) |
ND, DNVGL |
|
Down-flooding angle |
IMO |
Define down-flooding points using Points |
Cargo overhang submergence |
DNVGL |
(do not include, can easily be calculated separately) |
General |
||
Add numerical data of curve in report |
||
Option to calculate GM to both sides |
Wind direction to be changed accordingly |
|
Special cases#
Wind turbines
DNV-ST-0119 Floating wind turbine structures
the operating line on the figure is the wind heeling moment based on the wind speed that produces the largest rotor thrust (section 10.1.4.3 in the 2021 edition), but would be useful to also calculate the same parameter based on the non-operating wind heeling moment so with a parked rotor thrust coefficient. The constrained area between the righting moment curve and the wind heeling curve can then be calculated (total area Ab), then theta max determined using a safety factor γstability (we are using a value of 1.3). Theta max is the heel angle at which the constrained area Aa up to this angle fulfils the equation Ab = Aa γstability.
Wind heeling moment is determined from the wind-force, which is calculated from an
Area
Coeffiecient
Wind speed
Area and coefficient are provided using a “WindArea” node (https://usedave.nl/nodes/wind.html)
Wind speed is an input to the calculation
\(\gamma_{stability}\)
\(\theta_{max}\)
Column stabilized units
Jack-ups
Snips#
DNVGL:
