(scour-protection-design-methods)=
# Scour Protection Design Methodology

For details of the code implementation, please see the
[Scour Protection Design API documentation](#scour-protection-design-api).

## Scour Protection Design

This module calculates the required scour protection material for a fixed
substructure to avoid seabed erosion around the installation. It is based on
a [DNV GL standard](https://rules.dnvgl.com/docs/pdf/DNV/codes/docs/2014-05/Os-J101.pdf)
{cite:p}`dnv2014osw` and geometric calculations {cite:p}`boem2018vineyard`.

The potential depth of the a free forming scour pit is calculated using a
simplified version of the relationship presented in the DNV GL report (equation
J.5):

$\frac{S}{D} = 1.3$

where $S$ is the calculated depth of the scour pit and $D$ is the
overall diameter of the substructure. The default value (1.3) is a conservative
assumption and may be overridden by the user as follows:

```python
config = {
    ...

    "scour_protection_design": {
        "scour_depth_equilibrium": 1.2
    }

    ...
}
```

The radius of the scour pit is then calculated using the soil friction
angle ($\phi$) and a simple geometric relationship:

$r = \frac{D}{2} + \frac{S}{tan(\phi)}$

The default value for $\phi$ is 33.5deg, representing the soil
friction angle for medium density sand. The total volume of scour
protection material is then calculated as follows,

$V = \pi * t * r^2$

where $t$ represents the depth of the scour protection material. This
value defaults to 1m in the code, which represents an appropriate initial
assumption and not a complete design. For sites that exhibit greater seafloor
currents, the scour protection layer may be as thick as 2m, whereas calmer
sites may only need 0.3-0.5m of material. In the absence of a geotechnical
study, this value is difficult to calculate and is instead presented to user as
a configurable input so the cost impacts of different thicknesses can be
investigated.

Terms:
: - $S =$ Scour depth
  - $D =$ Monopile diameter
  - $r =$ Radius of scour protection from the center of the monopile
  - $\phi =$ Soil friction angle

Default Assumptions:
: - $\frac{S}{D} = 1.3$
  - $\phi = 33.5$
    \* Angle for medium density sand

## References

```{bibliography}
:style: unsrtalpha
:filter: docname in docnames
```