10.flow over weir
TRANSCRIPT
UNIVERSITI MALAYSIA PAHANG
FACULTY OF CIVIL ENGINEERING AND ENVIRONMENTAL
HYDRAULIC & HYDROLOGY LABORATORYFLOW OVER WEIR
SUBJECT CODE DAA 3911EXPERIMENT TITLE FLOW OVER WEIRDATE OF EXPERIMENT 10/01/2011GROUP NUMBER & SECTION GROUP 11 SECTION 25 & 26GROUP MEMBER NAME & ID NUMBER
1. AHMAD MUSTAQIM BIN MOHAMED RADZI AA09194
2. RAZIN BARWIN BINTI ABDUL SAMAD AA09195
3. MOHD.AIZAD BIN JOHARI AA09197
4. AMIRUDDIN BIN ROZLAN AA09198
5. MOHD ZAHARIN BIN TARUDIN AA10183
6. YANG WENBIAO AA09202
LECTURER/PERSON IN CHARGEMARKS
REMARKS
ENDORESMENT
TABLE OF CONTENT
Title Page
1. Introduction 2
2. Principle 2-3
3. Objective 3
4. Apparatus 3
5. Procedure 4
6. Result 5-7
7. Discussion/Analysis 8
8. Conclusion 9-10
9. References & Appendices 11
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INTRODUCTION
As the depth of flow above the base of a notch is related to the volume flow rate through
it, the notch forms a useful flow measurement device. The classical results for flow over
notches are obtained by application of the Bernoulli equation, from a point well up-
stream to a point just above the notch.
PRINCIPLE
This approach requires a number of very substantial assumptions and it yields the
following results:
For rectangular notch
Q = 2/3 Cd b√2g h⅔
Where:
Cd = unloading coefficient
b = width of the neckline or the width of the wier
h = height of the load or the height of the water on the crest or wier threshold
For the V-shape weir
Q = 8/15 Cd √2g tan θ/2 h5/2
Where:
Cd = unloading coefficient
θ/2 = the vertex semi-angle or the neckline
h = the load height
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The coefficient Cd is required to accommodate the effects of the simplified assumptions
in the theory. These can be rearranged to give:
For rectangular notch:
Cd = 3Q
2b √2g H3/2
For Vee notch:
Cd = 3Q
8 tan θ/2√2g H5/2
OBJECTIVE
i) To determine the characteristics of open-channel flow over, a rectangular
notch and then a triangular (Vee) notch
ii) To determine the values of the discharge coefficient, Cd for both notches
APPARATUS
i) Set of flow over weir apparatus
ii) Hydraulic Bench
iii) Stop watch
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PROCEDURE
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Set and immobilize the nonius of the caliber to zero
Then, flow the water to the channel until it unloads through the
weir
Adjust the flow of the water and stabilize it. Next, point the hook until the edge of its touch the water surface and take a reading of the nonius
Let the water flow and measure the value of the load height using the scale in the volumetric tank and the chronometer
Repeat above procedure but with different height of water
Put the weir into the Hydraulic Bench, and then adjust the hook right to the bottom of the weir.
The same procedure are done to rectangular and vee weir
RESULT
Rectangular Weir
Volume
m3
Time
s
Flow
m3/s(Q)
Height
m
Log
Q
Log
h
Cd Q
theoretical
0.005 5.8 0.000862 0.056 -3.0645 -1.2518 0.0302 0.001162
0.005 6.1 0.000820 0.051 -3.0862 -1.2924 0.0287 0.001105
0.005 9.2 0.000543 0.043 -3.2652 -1.3665 0.0190 0.000732
0.005 10.1 0.000495 0.038 -3.3054 -1.4202 0.0173 0.000666
0.005 21.1 0.000237 0.029 -3.6253 -1.5376 0.0083 0.000319
Vee Weir
Volume
m3
Time
s
Flow
m3/s(Q)
Height
m
Log
Q
Log
h
Cd Q
theoretical
0.005 16.9 0.0002959 0.035 -3.5289 -1.4559 0.001400 0.0000592
0.005 14.8 0.0003378 0.033 -3.4713 -1.4814 0.001599 0.0000676
0.005 16.5 0.0003030 0.031 -3.5186 -1.5086 0.001434 0.0000606
0.005 22.7 0.0002203 0.025 -3.6570 -1.6021 0.001043 0.0000441
0.005 52.2 0.0000958 0.020 -4.0186 -1.6990 0.000453 0.0000191
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CALCULATION
Q = AV
For rectangular weir: For vee weir:
A = bh A = (½) bh X 2
b = 0.03m b = 0.08m
h = 0.082m h = 0.04m
= 0.00246m3 = 0.0032 m3
Example:
For rectangular notch:
Cd = 3Q .
2b √2g H3/2
= 3(0.000862)
2(0.03) (√2 x 9.81) (0.082) 3/2
= 0.0302
For Vee notch:
Cd = 3Q
8 tan θ/2√2g H5/2
= 3(0.0002959)
8 tan 90/2√2 x 9.81 x (0.04) 5/2
= 0.001400
For rectangular notch:
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Q = 2/3 Cd b √ 2 g h 2/3
= 2/3 (0.0302) (0.03) √ 2 (9.81) (0.082) 2/3
= 0.001162 m3/s
For Vee notch:
Q = 8/15 Cd√ 2 g tan ǿ/2 h 5/2
= 8/15 (0.001400) √ 2 (9.81) tan 90/2 (0.04)5/2
= 0.0000592 m3/s
DISCUSSION/ANALYSIS
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The experiment objective is to establish the relationship between head over the
weir and discharge for a sharp crested weir. In this experiment, we can prove the
objective. The head over weir directly relation with the discharge of water. If the head
over the weir is high, the discharges of water also increase.
If the specific energy increases, the discharge also increases. It’s maybe because
when the discharge of water is high, the water friction at the sharp crested weir is high
and that why the head of over weir is also high. A uniform flow may theoretically be
steady or unsteady, depending on whether or not the depth changes with time.
An open channel is conduit in which water flows with a free surface. The
classification of open channel flow is made according to the change in flow respect to
time and space. Open channel flow is uniform if the depth of flow is the same at every
section of the channel.
A uniform flow may theoretically be steady or unsteady, depending on whether or not the
depth changes with time. The establishment of unsteady uniform flow requires that the
water surface fluctuate with time while remaining parallel to the channel bottom. Since it
is impossible for this condition to occur within a channel, steady uniform flows are the
fundamental type of flow treated in open channel hydraulics.
CONCLUSION
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For the overall experiment we do this experiment well and most achieve the
objective this experiment. From our results, the value of the theoretical and experiment is
have a different. Form overall results we get, the value of theory is more than experiment
value. But we feel so good cause achieve the objective this test (determine the value of
the discharge coefficient and determine the characteristic of open-channel flow over)
well. This experiment is very important to know the direction and also the flow rate of
the water. This experiment also to known the head of the pressure at the high of head
(always use in construction dam). This test also important to known the area around the
damn can happen the flooding in several years.
1)90 ° V-Notch Weir - The 90 ° V-notch weir, in figure, is most accurate when
measuring discharges of less than 500 gpm. The maximum discharge that can be
accurately measured is approximately 5,000 gpm. The sides of the notch are inclined
outwardly at 45 ° from the vertical.
2) Rectangular-Notch Weir - The rectangular-notch weir is illustrated in figure. This is
the oldest type of weir now in use. Its simple construction makes it the most popular. The
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discharge equation for the rectangular-notch weir is gives discharge values for
rectangular-weir notch lengths of up to 4 feet and depths of flow or head of up to 1.5 feet.
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REFERENCES & APPENDICES
http://www.aquatext.com/calcs/weir%20flow.htmhttp://www.buffer.forestry.iastate.edu/Virtual_Risdal_Tour/Site_12/stop_12.htmhttp://www.cee.mtu.edu/~dwatkins/ce3600_labs/weir.pdfhttp://chl.erdc.usace.army.mil/chl.aspx?p=s&a=PUBLICATIONS!419 From books:
Engineering Laboratory Manual: Hydraulic& Hydrology Laboratory: Flow Over Weir
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