IEA 15-MW monopile weight

1 Test description

This test compares the weight of the monopile for the IEA 15-MW model as specified in Gaertner et al. (2020) to the weight of the model implemented in Ashes. Therefore, the tower and the RNA are not included in this test. The figure below illustrates the model.

Note that the onshore template is used for this test. Therefore, buoyancy loads are not included in this test.

2 Analytical solution

The mass of the monopile reported in Table 1-1 of Gaertner et al. (2020) is 1 318 t. Note that the transition piece is modeled as a point mass at the top of the monopile, and its mass is included in the mass of the monopile. With an acceleration due to gravity 
$$g = 9.80665\text{m}\cdot{s}^{-2}$$
, the weight the monopile will be
$$W = g\cdot1318=12.925\text{ MN}$$

For this test, we use the output Reaction force (magnitude) of the Support sensor. This output omits the bottom half of the lowest element of the monopile. 
This element has a radius
$$r = 5\text{ m}$$
, a thickness
$$t = 0.0553\text{ m}$$
and a length 
$$l = 5\text{ m}$$
. According to Table 4-1 in Gaertner et al. (2020), the density of the material used for the monopile is 
$$d = 8400\text{ kg}\cdot{m}^{-3}$$
 (this includes mass for outfitting).
The weight the lowest element is thus
$$W_{el}=\left(\pi r^2-\pi(r-t)^2\right)\cdot l\cdot d\cdot g=712\text{ kN}$$

The magnitude of the reaction force will thus be
$$F = W-W_{el}/2=12.569\text{ MN}$$

3 Results

The test is considered passed if the results from Ashes are within 0.01% of the results from the specification document.

The report for this test can be found on the following link: monopile weight.pdf