-
To measure Vertical Wind Shear Ex-
ponent, Wind power density from a
given data set & to prepare Wind
speed frequency Histogram, Wind rose
With Comment on the Site
1. Introduction:
1.1 Vertical Wind Shear Exponent: Wind Shear is defined as the
change in horizontal wind speed with a change in height
measured
in the vertical direction. The wind shear exponent () should be
determined for each site, because its magnitude is influenced by
site-specific characteristics.Mathmetically from definition
Vertical
Wind Shear Exponent isi1
The wind speed profile or the change in wind speed with height
is found to be given by the power law
In the equations-
i. V1 is the Speed measured at hight z1 ii. V2 is the Speed
measured at hight z2
iii. z1 is height corresponding to the measured velocity V1 iv.
z1 height corresponding to the measured velocity V1 v. z2 is the
height where velocity v2 has to be measured
1.2 Wind Power Density:
-
Wind power density (WPD) is a truer indication of a sites wind
energy potential than wind speed alone. Its value combines the
effect of a sites wind speed distribution and its dependence on air
density and wind speed. WPD is defined as the wind power available
per unit area swept by the
turbine blades. Mathmetically from definition Wind power density
(WPD) i2
In the equations-
i. is the density of the air measured in unit
ii. V=Vi is the wind Speed measured in unit
1.3 Wind Rose: wind rose is a graphic tool used by
meteorologists to give a succinct view of how wind speed and
direction are typically distributed at a particular location.
Historically, wind roses were predeces-
sors of the compass rose (found on maps), as there was no
differentiation between a cardinal di-
rection and the wind which blew from such a direction. using a
polar coordinate system of grid-
ding, the frequency of winds over a long time period are plotted
by wind direction, with color
bands showing wind ranges. The directions of the rose with the
longest spoke show the wind di-
rection with the greatest frequency. Presented in a circular
format, the modern wind rose shows
the frequency of winds blowing from particular directions over a
thirty-year period. The length
of each "spoke" around the circle is related to the frequency
that the wind blows from a particular
direction per unit time. Each concentric circle represents a
different frequency, emanating from
zero at the center to increasing frequencies at the outer
circles. A wind rose plot may contain ad-
ditional information, in that each spoke is broken down into
color-coded bands that show wind
speed ranges. Wind roses typically use 16 cardinal directions,
such as North (N), NNE, NE, etc.,
although they may be subdivided into as many as 32 directions.
in terms of angle measurement
in degrees, north corresponds to 0/360, east to 90, south to 180
and west to 270.compiling a
wind rose is one of the preliminary steps taken in constructing
airport runways, as aircraft per-
form their best take-offs and landings pointing into the
wind.i3
2.Introduction With The Instruments Used By Stations For the
Measuemnt Purpose:
As data was provided by the Government of the peoples Republic
of Banglades, Bangladesh Meteorological Department, Climate
Division, Agargaon, Dhaka-1207,so we werent acquineted with any of
the measurements.The stations use instruments both electrical
&
nonelectrical,mechanical,electromecinal etc in nature which are
operated in both automatically &
manually.An overview of the most commonly used instruments for
the observation of the wind
resources is outlined.
2.1Wind speed and Direction The wind can vary in a number of
ways both in terms of its speed and also its direction. As a
result, different pieces of equipment are needed to measure these
different characteristics
i7.
-
2.2Weather Vanes Weather vanes are one of the oldest of all
weather instruments, working by swinging around in
the wind to show which direction it is blowing from. The head of
the cockerel would point into
the wind, indicating the direction the wind was blowing
fromi7
.
2.3Wind Socks Another device used to measure the wind is a
windsock. This instrument is found mainly at air-
ports, seaports and other open areas such as mountain roads
where a visual indication of the wind
is needed. Windsocks actually show both the direction and speed
of the wind. The direction is
shown when the wind blows into the open end and the sock points
the way the wind is blowing.
The shape and movement of the windsock give an indication of
wind strength. If it is flapping
about gently, the wind is only light, whereas if it sticks out
in a straight line the wind is much
stronger. This information is very useful to people on both
ships and planes, and sometimes to
car drivers tooi7
.
2.4Anemometer The main instrument used to measure the speed of
the wind is an anemometer. The little cups on
this device catch the wind and spin round at different speeds
according to the strength of the
wind. A recording device is used to count how many times they
spin round in a given time. If
you have ever seen an anemometer, you will have noticed that the
cups spin round very fast in a
strong breezei7
.
2.5Beaufort Scale It is also possible to measure the speed of
the wind by looking at its effects on the local environ-
ment. In 1805, Admiral Francis Beaufort invented a scale of this
type for measuring winds at sea
by describing their effect on ships and waves. His scale was
later adapted for use on land, and
the same system is still used by many weather stations
todayi7
.
2.6wind Speed Classes Distribution Electricity production
obtained from a given wind speed and wind turbine type, varies a
lot with
the wind speed distribution around the mean value. It is
essential to know the distribution of wind speeds on the project
site. Wind distribution is expressed in
% of occurrence for each class of 1m/s (0 to 1m/s, 1 to 2m/s,
etc)i7.
3.Calculation of Wind sheer Exponent for Chandpur(at 50m):
Wind sheer betweeni5 Based on annual wind speedi6
1(between 20 & 10m) 0.407
-
2(between 30 & 20m) 0.169
3(between 30 & 10m) 0.319
0.3
5(between 50 & 10m)
4.Wind Power Deinsity(WPD) Calculation:
600 UTC 900 UTC 1200 UTC 1500 UTC 1800 UTC 2100 UTC Avgerage
speed at 10mAverage speed at 50m WPD at 10m WPD at 50m
----- ---- ----- ---- ----- ---- ------ --- ----- ---- -----
---- ------- ---
Speed Dir Speed Dir Speed Dir Speed Dir Speed Dir Speed Dir
2 180 2 180 2 180 2 180 2 180 2 180 2 11.00145445 4.92 0
2 180 3 180 5 180 5 130 3 130 2 160 2.8 415.125 13.50048
43995857
3 230 2 130 3 180 2 130 2 160 3 160 3 6.708203932 16.605
185.649544
5 230 6 200 4 200 1 290 2 200 2 200 3.5 7.826237921 26.368125
294.8046
6 180 5 180 4 130 5 130 5 130 3 130 4 8.94427191 39.36
440.058178
2 130 2 180 2 180 0 0 2 130 2 130 1.8 4.024922359 3.58668
40.1003015
5 230 4 180 5 130 2 130 2 130 2 130 3.3 7.379024326 22.101255
247.099543
2 130 2 130 2 130 2 130 2 130 0 0 1.8 4.024922359 3.58668
40.1003015
0 0 2 130 0 0 0 0 0 0 2 130 0.6 1.341640786 0.13284
1.48519635
2 130 3 130 1 130 2 180 0 0 0 0 1.5 3.354101966 2.075625
23.206193
4 130 4 130 3 130 2 130 1 130 1 130 2.8 6.260990337 13.50048
150.939955
5 130 5 230 4 230 2 230 1 130 0 0 3 6.708203932 16.605
185.649544
2 230 2 230 2 130 2 130 0 0 2 130 1.5 3.354101966 2.075625
23.206193
3 230 4 230 4 180 3 180 3 180 2 180 2.9 6.484597135 14.999235
167.696545
4 230 2 230 2 230 0 0 0 0 0 0 1.3 2.906888371 1.351155
15.1063721
4 180 0 0 0 0 0 0 0 0 9 20 2.1 4.695742753 5.695515
63.6777935
4 90 2 180 2 90 0 0 0 0 2 90 1.8 4.024922359 3.58668
40.1003015
2 90 4 130 4 130 3 130 3 130 2 130 2.8 6.260990337 13.50048
150.939955
4 130 6 160 5 130 4 130 3 130 3 130 3.6 8.049844719 28.69344
320.802412
5 230 5 230 5 130 6 180 4 130 3 130 4 8.94427191 39.36
440.058178
4 180 6 180 3 110 2 180 2 180 2 180 3.1 6.93181073 18.321465
204.840206
6 200 5 200 3 200 4 160 3 200 3 200 3.6 8.049844719 28.69344
320.802412
3 230 3 230 3 160 1 130 1 130 2 130 2.9 6.484597135 14.999235
167.696545
3 110 3 130 2 130 2 230 2 230 0 0 2 4.472135955 4.92
55.0072722
2 160 2 160 2 230 2 160 0 0 7 90 1.9 4.248529157 4.218285
47.16186
10 90 8 90 10 90 10 90 10 90 10 160 8.8 19.6773982 419.10528
4685.73948
7 160 7 160 4 90 4 90 4 90 4 130 6.6 14.75804865 176.81004
1976.79634
4 160 5 130 4 180 2 160 4 130 0 0 3.1 6.93181073 18.321465
204.840206
2 180 2 180 2 230 1 230 0 0 1 230 1.3 2.906888371 1.351155
15.1063721
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
2 360 2 360 2 130 0 0 0 0 2 130 1.5 3.354101966 2.075625
23.206193
------- ---- ------- ----- ------ ----- ------- ---- ------ ----
------- ------ ------- ---
Average 3.5 3.5 3 2.3 2 2.4 2.7 5.Wind Speed Frequency Histogram
& Wind Rose Plots:
5.1Wind Speed Frequency Histogram Plots:
-
5.1.1wind Speed Frequency Histogram At 10m:
Fig 1:Wind Speed Frequency Histogarm at 10m height
5.1.2wind Speed Frequency Histogram At 50m:
-
Fig 2:Wind Speed Frequency Histogarm at 50m height
5.1.3Wind Speed Frequency Histogram At 10m Vs Wind Speed
Frequency Histogram At 50m:
-
Fig 3:Wind Speed Frequency Histogarm at 10m height Vs. Wind
Speed Frequency Histogarm at 50m height
5.2Wind Rose plot of July 1992: The wind data provided by the
Government of the people's Republic of Banglades, Bangladesh
Meteorological Department, Climate Division, Agargaon,
Dhaka-1207 contains wind data from
the year 1990 to 2000.For the experiment the data of july 1992
was taken into consideration. The
data was from the Cahndpur station.
-
Fig 4:OriginLab Origin Pro9 cell configuration for plotting
WindRose of July,1992
-
Fig 5 :Wind Rose plot at 10m height
6.Wagon Wheel (Wheel Chart) Plot Of WPD (Wind Power Density) In
360 Direction:
-
Fig 6:OriginLab Origin Pro9 cell configuration for plotting WPD
of July,1992
Fig 7:Wheel Chart plot of WPD of July,1992
-
7.Method Of Plotting of Windrose & WPD Wheel Chart Using
Originlab Origin Pro9: A. Categorize the velocities corresponding
to the direction in groups. The Grouping is
based on two factors. One of them is Direction & other one
is the magnitude of veloci-
ty in a given range.
B.Then input the A(X), B(Y) till G(Y),
-
C.Click plot ->specialized ->theta(X)r(Y)
-
click add,ok.
D.Theta & r are ticked as follow
-
the windrose is then generated.
E.CLick set my angular range to change the increment to
22.5,ok.Right click on the de-gree of angle ->Tick Labels.
Change type to Tick-indexed datas,choose [Book1]Sheet1!B
for dataset,ok
(***[Book1]Sheet1!B represents column B(Y)***)
F.At the bottom right of the window,select stack column.
G.The windrose will then converted into this form.
-
8.Discussion & Comment on the site:
From the wind rose plot the most wind are found to be
distributed in the E-W direction (i.e.: be-
tween 90-270 range) with a little existence (0-16.43 w/m2)
between the 270-300 & 67.5-22.5 ranges. So almost no wind speed
thus the wind power exist in the W-WNW-NW-NNW-N-NNE-NE-ENE-E
(270-90) direction. So in case of establishment of wind turbines on
our ana-lyzing site for the power generation purpose, turbines with
the capability of rotating in between
90-270 directions will be more effective and efficient(as
utilization of most of the wind power is ensured)rather than
capable of rotating in the whole 360 direction. Comparison between
the wind speed frequency histogram at 10m & at 50m suggests
that the least available speed in the
10m & 50m are 2m/s & 4.48m/s respectively. The turbine
operating at 10m wind speed will be-
come larger with the long blades if the power has to be
generated at that height. Another problem
associated with this turbine is difficulties of maintenance. As
these types of turbines, response at
a low speed wind flow the turbine has to be sensible enough to
response at least at this speed
with the capability of surviving in high windy & aberrant
situations keeping it in mind while de-
signing. On the other hand, wind turbines operating at 50m
height will be able to generate more
power than a turbine operating at 10m height. The efficiency
& the performance of such turbine
exceeds turbine operating at 10m height in a more acceptable
& efficient way. With the little
maintenance, these turbines operate smoothly & continuously
for long time. The problem of
large turbine with long blades & the ability of surviving a
high wind gust & windstorm can easi-
ly be overcame by utilizing these types of turbines. The
designers are advised to design turbines
operating at 50m height wind speed with an allowance of rotation
in the W-WNW-NW-NNW-
N-NNE-NE-ENE-E (270-90) as these are found to be the most
important design criteria for our discussed site.
Discussion
1.Wind rose plot at 10m, Wind rose plot at 50m, Wheel chat of
power density at 10m & Wheel chat of power density at 50m are
found to be identical. As all the plots are polar plots so
all of them shoulde & are in circular in shape. However Wind
power density (WPD) is much
larger than wind speed but is mathematically proportional to the
speed at 10m (V3)
& wind speed
at
-
50m(at height h2) is also proportional to the wind speed at
10m(at height h1).So,mathmetically
i. WPD=1/2V3 V3 [As & are constants & always gives the
same value]
ii. V2=V1(Z2/Z1) V1(Z2/Z1)
[As (Z2/Z1)
is a constant & always gives the same val-
ue]
In the graphical plots they maintain the same relationship &
shapes also but the range & value
changes with their dependence with each other showing on the
equation.
2.In case of wind speed frequency histogram the relationship
stays the same,resulting a simi-larity in the shape between the
plot at 10m & plot at 50m.Though wind speed frequency
histo-
gram is a bar diagram plot of wind speed Vs. time & as both
the speed are represented in the
same time scale here with velocity at 50m keeping a mathematical
relationship with the wind
speed at 50m,thus their shape resembles each other with the same
kind of ups & downs which
varies in the same pattern while values are different at each
point.
3.A perfect valued wind shear exponent () wasnt able to be
calculated as wind shear exponent () at 50m wasnt found in any of
the data provided & also in the web, so the founded values of
the wind shear exponent () were averaged but as it was measured in
the 30m height so the rule of arithmetic(value of wind shear
exponent, at 30m height/3050)is applied to calculate the wind shear
exponent () at 50m which may be quite different form the actual
value of wind shear exponent () exists in the 50m.Thus the other
factors dependent upon the wind shear exponent () will also be
affected resulting a deviation in the whole calculation. The
purpose of the exper-iment was to have a solid understanding of the
analyzed wind resource measurement technique,
which was successfully achieved through working practically,
researching on the relevant field
& by brainstorming. A clear outline, not any faded, shady
out-sketch are achieved about the
whole wind resource assessment. So checking any sites acceptance
for the wind power estab-lishment can be done with ease with the
acquired knowledge. So, the main purpose of the whole
experiment (the solid understanding & learning of the whole
assessment process) was gained
which overcomes the issue associated with wind shear exponent ()
related errors in measure-ments.
9.Conclusion: The provided data was in the text format it was
imported to the excel spreadsheet using the data
import option which allows importation of data from other valid
sources. The equations were set
up after calculating the value of wind shear exponent () in two
different cells, which provides the wind power density &
average speed at 50m relating on the equation.The wind speed
fre-
quency histogram plot were performed using the excel column
plot.As radar plot dosent give the perfect wind rose plot shapes so
for a perfect wind rose plotting OriginLab Origin Pro9 software
was used.
-
i i,2 Chapter-9,page:7-9,Wind Resource Assesment Handbook
3 Page:83-84,Wind Energy explained:Theory,Design and
Application, Wind rose - Wikipedia, the free
encyclopedia(www.wikipedia.com/Windrose)
5,6 EFFECT OF WIND SHEAR COEFFICIENT ON WIND VELOCITY AT COASTAL
SITES OF BANGLADESH
by A. K. Azad, M. M. Alam and Manabendra Saha(Proceedings of the
International Conference on Mechani-
cal Engineering 2011 (ICME2011) 18-20 December 2011, Dhaka,
Bangladesh, ICME11-RE-012)
7 lecture 3,Climetology.IRE,DU(1
st semester)