| Extreme Wind Window | |
The Extreme Wind window calculates the 50-year extreme wind speed using several methods. You can access this window by choosing from the menu.
Tip: You can use the Extreme Wind window only if you have the Professional or higher edition of Windographer. Please visit www.windographer.com for information on the pricing and capability of each edition.
Use the Speed sensor drop-down box at the top left of the window to choose the wind speed data column for which you want to calculate the 50-year extreme wind speed. If you intend to estimate the 50-year extreme wind speed at hub height and your dataset does not include measured wind speed data at hub height, before you use the Extreme Wind window you will have to use the Vertical Extrapolation window to create a synthetic wind speed data column at hub height.
If the wind speed sensor that you have selected has an associated maximum data column, you can use this window to calculate the 50-year extreme gust by choosing the Gusts mode. If the gust option is disabled, that means the wind speed sensor does not have an associated maximum data column, so you must return to the Configure Dataset window and associate a max column with that wind speed data column. Note that the EWTSII calculation cannot calculate the 50-year extreme gust.
The filter settings controls allow you to focus on a specific subset of data. For details, please see the article on filtering data.
Once you have selected a wind speed and set any filters, the Wind speed characteristics section shows the mean wind speed and Weibull k of the filtered data.
Right-click any graph to change its properties, copy the image to the clipboard, or export it to a file. Right-click on any table to export it to a file, or copy it. See the article on exporting graphs or exporting tables for more information.
Windographer calculates the 50-year extreme wind speed using multiple algorithms, and shows the results of each so that you can see how they compare:
| Algorithm | Description |
|---|---|
| Periodic Maxima | Fits a Gumbel distribution to the peak wind speeds measured in each fixed time period |
| Method of Independent Storms | Fits a Gumbel distribution to the peak wind speed occurring in each independent storm event |
| EWTS II | Uses a function that predicts the extreme to average wind speed ratio from the Weibull k value |
Windographer displays a table of the resulting 50 year maximum mean wind speeds (or gusts, depending on your setting) for each method on the left side of the window. The table updates whenever you change any of the algorithm settings on any of the three tabs.
Windographer also provides on each tab a detailed breakdown that explains how it calculated the results. The EWTS II results consist simply of the standardized EWTS II curves with a line indicating the Weibull k value used to calculate the expected 50 year wind speeds. The results for Periodic Maxima method and Method of Independent Storms are somewhat more complicated. On these tabs Windographer shows the peak wind speeds for each period or storm (respectively), the PDF, CDF, and linearized CDF graphs of the peak wind speeds, a probability of exceedence graph, and a graph of expected extreme wind speed versus return period. Each graph has a corresponding tabular view.
The time series graph shows the discovered peak wind speeds for each time period (on the Periodic Maxima tab) or each independent storm (on the Method of Independent Storms tab). The table also shows the peak wind speeds, with some added information. For example, the Periodic Maxima tab shows the data recovery rate of each period, and the Method of Independent Storms tab shows the start and end time of each storm, as well as the center of the time step in which the storm maximum occurred.
The PDF graph shows both a PDF of the actual data (the peak wind speeds) and a fitted Gumbel distribution. The table shows the distribution of probability over each of the bins. Note that these are "annualized" PDFs, meaning that these probabilities represent the probability of experiencing an wind speed in a certain range over one year, not over one time period or one storm. Windographer calculates these PDFs by first calculating the annualized CDFs (real and fitted) and then differentiating them.
The CDF graph shows an annualized CDF of the peak wind speeds and a fitted Gumbel CDF. Again, "annualized" refers to the fact that the probabilities on the graph represent the probability of seeing an annual extreme wind speed below a certain value. The graph can also optionally display the "adjusted plotting positions", which are the points actually used to perform the Gumbel curve fit. To understand how Windographer calculates the adjusted plotting positions and why they are used for the curve fit, see the articles on the Harris 1996 algorithm and the Harris 1999 algorithm.
The tabular view includes the data that appears on the graph, plus some additional detail. This table is the same for both the CDF and Linearized CDF options, and therefore includes data from both graphs. The table lists:
The linearized CDF graph shows the same curves and data points as the CDF graph, except that the data is linearized by taking the negative logarithm of the negative logarithm of each y value. This makes it easier to see the quality of the Gumbel curve fit, because data points that fit the Gumbel distribution perfectly would appear in a straight line in this graph.
The tabular view here is same as the tabular view for the CDF option, as mentioned above.
The probability of exceedence graph shows the probability of the peak wind speed for a given year exceeding a certain value. The POE for both the actual data (transformed from POE for the original time period into annual probabilities) and the curve fit are both shown.
The tabular view shows all the same data as the graphical view, except that the original single storm / period probabilities of exceedence are given alongside the annualized probabilities.
The return period graph shows the expected amount of time required to experience an given peak wind speed during that period, according to the Gumbel curve fit. The tabular view shows this same data for a fixed set of peak wind speeds.
See also
Gumbel Distribution definition
Cumulative Distribution Function definition