bReeze (version 0.4-4)

turbulence: Calculation of turbulence intensity

Description

Calculates turbulence intensity and mean wind speed for each given direction sector.

Usage

turbulence(mast, turb.set, dir.set, num.sectors=12, 
  bins=c(5, 10, 15, 20), subset, digits=3, print=TRUE)
turb(mast, turb.set, dir.set, num.sectors=12, 
  bins=c(5, 10, 15, 20), subset, digits=3, print=TRUE)

Value

Returns a data frame containing:

wind.speed

Mean wind speed for each direction sector.

total

Total turbulence intensity for each direction sector.

...

Turbulence intensities per direction sector for each given wind speed bin.

Arguments

mast

Met mast object created by mast.

turb.set

Set used for turbulence intensity, specified as set number or set name (optional, if dir.set is given).

dir.set

Set used for wind direction, specified as set number or set name (optional, if turb.set is given).

num.sectors

Number of wind direction sectors as integer value greater 1. Default is 12.

bins

Wind speed bins as numeric vector or NULL if no classification is desired. Default is c(5, 10, 15, 20).

subset

Optional start and end time stamp for a data subset, as string vector c(start, end). The time stamps format shall follow the rules of ISO 8601 international standard, e.g. "2012-08-08 22:55:00".

digits

Number of decimal places to be used for results as numeric value. Default is 3.

print

If TRUE (the default), results are printed directly.

Optional graphical parameters for plotting

The following graphical parameters can optionally be added to customize the plot:

• cex: Numeric value, giving the amount by which text on the plot should be scaled relative to the default (which is 1).

• cex.axis: Amount by which axis annotations should be scaled, as numeric value.

• cex.lab: Amount by which axis labels should be scaled, as numeric value.

• circles: Manual definition of circles to be drawn, as numeric vector of the form c(inner circle, outer circle, interval between the circles).

• col: Colour to be used for the sectors.

• col.axis: Colour to be used for axis annotations -- default is "gray45".

• col.border: Colour to be used for sector borders -- default is NULL (no border is drawn).

• col.circle: Colour to be used for circles -- default is "gray45".

• col.cross: Colour to be used for axis lines -- default is "gray45".

• col.lab: Colour to be used for axis labels -- default is "black".

• fg: If TRUE, sectors are plotted in foreground (on top of axis lines and circles) -- default is FALSE.

• lty.circle: Line type of circles -- default is "dashed". See par for available line types.

• lty.cross: Line type of axis lines -- default is "solid". See par for available line types.

• lwd.border: Line width of the sector borders -- default is 0.5. Only used if col.border is set.

• lwd.circle: Line width of circles, as numeric value -- default is 0.7.

• lwd.cross: Line width of axis lines, as numeric value -- default is 0.7.

• pos.axis: Position of axis labels in degree, as numeric value -- default is 60.

• sec.space: Space between plotted sectors, as numeric value between 0 and 1 -- default is 0.2.

Author

Christian Graul

Details

Turbulence can be perceived as wind speed fluctuations on a relatively short time scale and it strongly depends on surface roughness, terrain features, as well as thermal effects. High turbulence should be avoided, since it is a main driver of fatigue loads and might decrease energy output. A measure of the overall level of turbulence, is the turbulence intensity \(I\), which is defined as: $$I = \frac{\sigma}{\bar v}$$ where \(\sigma\) is the standard deviation of wind speed -- usually measured over a 10-minutes period -- and \(\bar v\) is the mean wind speed over this period.

References

Albers, A. (2010) Turbulence and Shear Normalisation of Wind Turbine Power Curve. Proceedings of the EWEC 2010, Warsaw, Poland

Burton, T., Sharpe, D., Jenkins, N., Bossanyi, E. (2001) Wind Energy Handbook. New York: Wiley

Langreder, W. (2010) Wind Resource and Site Assessment. In: Wei Tong (Ed.), Wind Power Generation and Wind Turbine Design, Chapter 2, p. 49--87, Southampton: WIT Press

See Also

mast

Examples

if (FALSE) {
## load and prepare data
data("winddata", package="bReeze")
set40 <- set(height=40, v.avg=winddata[,2], v.std=winddata[,5],
  dir.avg=winddata[,14])
set30 <- set(height=30, v.avg=winddata[,6], v.std=winddata[,9],
  dir.avg=winddata[,16])
set20 <- set(height=20, v.avg=winddata[,10], v.std=winddata[,13])
ts <- timestamp(timestamp=winddata[,1])
neubuerg <- mast(timestamp=ts, set40, set30, set20)
neubuerg <- clean(mast=neubuerg)


## calculate turbulence intensity
turbulence(mast=neubuerg, turb.set=1)  # default
turbulence(mast=neubuerg, turb.set=1, dir.set=2)  # use different datasets
turbulence(mast=neubuerg, turb.set="set1", dir.set="set2")  # same as above
turbulence(mast=neubuerg, turb.set=1, num.sectors=4)  # change sector number

# calculate turbulence intensity for 1 m/s speed bins and without binning
turbulence(mast=neubuerg, turb.set=1, bins=1:25)
turbulence(mast=neubuerg, turb.set=1, bins=NULL)

# data subset
turbulence(mast=neubuerg, turb.set=1, 
  subset=c(NA, "2010-01-01 00:00:00"))

# change number of digits and hide results
turbulence(mast=neubuerg, turb.set=1, digits=2)
neubuerg.ti <- turbulence(mast=neubuerg, turb.set=1, print=FALSE)
neubuerg.ti


## plot turbulence intensity object
plot(neubuerg.ti)  # default

# change colour, text size etc.
plot(neubuerg.ti, cex.axis=0.7, cex.lab=0.9, circles=c(0.05,0.20,0.05), 
  col="lightgray", col.axis="darkgray", col.border="gray", col.circle="darkgray", 
  col.cross="darkgray", col.lab="darkgray", fg=TRUE, lty.circle="dotdash", 
  lty.cross="longdash", lwd.border=1.2, lwd.circle=1.2, lwd.cross=1.2, 
  pos.axis=135, sec.space=0.6)
}