Distance to sea
This test checks the field Distance to sea from the Node sensor.
1 Test description
The model uses the default semisubmersible floater and computes the vertical distance between a given node and the sea surface. 5 nodes across the model are used, and several wave conditions and floater motions are tested.
The load case list below specifies the period, amplitude and heading of the regular waves tested. When pairs of values are given, two wave components are used. For the full spectrum cases, a spectrum with 50 wave components is used.
The cases with the mention - hor motion have the floater moving horizontally along the y direction with an amplitude of 5 m and a period of 12 s.
The cases with the mention - ver motion have the floater moving vertically with an amplitude of 1 m and a period of 2 s.
The tested load cases are
- No waves
- 10s 3m 0deg
- 5s 2m 0deg
- 10s 3m 50deg
- 7s 2m -30deg
- 10s -7s 3m -2m 50deg - -30deg
- full_spectrum
- No waves - hor motion
- 10s 3m 0deg - hor motion
- 5s 2m 0deg - hor motion
- 10s 3m 50deg - hor motion
- 7s 2m -30deg - hor motion
- 10s -7s 3m -2m 50deg - -30deg - hor motion
- full_spectrum - hor motion
- No waves - ver motion
- 10s 3m 0deg - ver motion
- 5s 2m 0deg - ver motion
- 10s 3m 50deg - ver motion
- 7s 2m -30deg - ver motion
- 10s -7s 3m -2m 50deg - -30deg - ver motion
- full_spectrum - ver motion
2 Model description
The model is the default semisubmersible floater, with an initial draft of 19.196 m and a water depth of 200 m.
5 nodes in the model are tested, listed below with their initial coordinates:
- Node Tubular_tower_node, {0, 0, 10.804}
- Node 4, {0, 28.87, 0}
- Node 8, {25, -14.435, 10.804}
- Node 25, {0, 0, -19.196}
- Node 27, {0, 0, 0.804}
The Loads only mode is used for this test, so the floater will not respond to hydrodynamic loads. The only motion of the floater is the imposed sinusoidal motion, either in the horizontal or the vertical direction.
3 Analytical results
For each test, the position of the floater at time t is first computed based on the imposed motion. This position is added to the initial coordinates of the nodes.
The wave elevation at the location of a node of coordinates {x, y, z} is then computed according ot Airy wave theory, as described in the Regular waves document:
$$\zeta(x, y, t) = A\cdot sin(\omega t + k_xx + k_yy)$$
where
$$A$$
is the wave amplitude, $$\omega$$
is the wave circular frequency and $$k_x$$
and $$k_y$$
are the wave numbers in the x- and y-direction.The distance to sea value is then simply the difference between the wave elevation and the z-coordinate of the node.
4 Results
A simulation of 30 seconds is run for each load case. The results are considered passed if the results from Ashes are wothin 0.1% of the analytical solution.
The report for this test can be found on the following link: