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)