# IEC extreme winds

## 1 Test description

In this set of tests we run the different IEC extreme wind models available in Ashes and compare them to the analytical results obtained by computing the equations from IEC-61400-1 (2019). The analytical solution is compared to the Wind speed at hub output of the Rotor sensor. Since we only look at the wind input, the behaviour of the model is not relevant to this set of tests. The model used is the RNA only template with the Loads only option (see Analysis)

The following load cases are tested:
1. Extreme Operating Gust
2. Extreme Operating Gust 25ms
3. Extreme Direction Change
4. Extreme Direction Change 25ms

For this set of tests, the turbine class is I so  the reference wind speed is
$$V_{ref} = 50\text{ m}\cdot \text{s}^{-1}$$
and the reference value for turbulence intensity is
$$I_{ref} = 0.16$$
.

Note that currently all turbines are considered class A when assessing the reference value for turbulence intensity for the IEC extreme wind speeds

The hub height is 102.4 m, which gives a longitudinal turbulence scale parameter
$$\Lambda = 42\text{ m}$$
, and the projected diameter of the rotor is
$$D = 125.9\text{ m}$$
. The Initial wind speed at hub height is
$$V_{hub}=10\text{ m}\cdot\text{s}^{-1}$$
, and the extreme wind is set to start after 5 seconds of simulations.

## 2 Analytical solutions

### 2.1 Extreme Operating Gust

According to the equations defining the Extreme Operating Gust and described in the IEC extreme events section of the user manual, the inputs specified in section 1 give a gust magnitude
$$V_{gust}=5.32\text{ m}\cdot{s}^{-1}$$
. This will produce the output shown in the figure below:

### 2.2

This load case is similar to the previous one but the wind speed at hub height is set to
$$V_{hub} = 25\text{ m}\cdot\text{s}^{-1}$$
. This produces the wind speed at hub height shown in the figure below:

### 2.3  Extreme Direction Change

According to the equations defining the Extreme Direction Change and described in the IEC extreme events section of the user manual, the inputs specified in section 1 give an extreme direction change magnitude
$$\theta_e=36.64\text{ deg}$$
. This will produce the output shown below:

The magnitude of the wind speed does not change

### 2.4 Extreme Direction Change 25ms

This load case is similar to the previous one but the wind speed at hub height is set to
$$V_{hub}=25\text{ m}\cdot{s}^{-1}$$
and the event starts after 10 seconds of simulation. This produces the wind speed at hub height shown in the figure below:

## 3 Results

The report for this test can be found on the following link:

The test is considered passed when all values from the Ashes time series lie within 0.1% of the benchmark time series.