in this paper comparison is made on the basis of soil strata. Various responses are taken for the comparison. STAAD PRO software is used for analysis. PEB structure is used for analysis in staad pro software. Prof. G. S. Patil | Dr. Prof. M. B. Choug
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Dryer Design
FOREBAY
DESIGN OF FOREBAY
PROJECT
ABC PROJECT
RIVER
ABC RIVER
REGION
PAKISTAN
DESIGN ENGINEER
M. ASIF
INPUT 3
Q H Q P
=
1.20
=
3.00
L H D H d H A H
=
5000.0 2.50
m m m
= = =
1.18 2.94 0.41 14710
=
12258
= = =
500.0 1.00 0.79
= = =
3.82 393 131
=
0.1
hrs
Non-peaking time
T PK T N-P
=
23.9
hrs
Volume of water required for peaking
V PK
=
1080
m
Width of forebay (at start) Width of forebay (at end) Length of forebay Depth of forebay (including freeboard)
W Fs W FE
= = = =
20.0 12.6 23.1 8.0
m m m m
Minimum diverted water - Headrace Design discharge - Penstock
m /s 3 m /s
( = Peak discharge)
Length of headrace Diameter/Bed width of headrace Depth of flow in headrace X-sectional X-sectional area of flow Velocity in headrace Volume of headrace Time of travel (upto forebay)
v H V H t H
2
m m/s 3
m sec
Length of penstock Diameter of penstock X-sectional X-sectional area of flow Velocity in penstock Volume of penstock Time of travel (upto turbines)
L P D P A P v P V P t P
m m 2
m m/s 3
m sec
Peaking time
3
-
L F d F
Page 1 of 14
FOREBAY
Freeboard in forebay
F.B
=
1.5
m
Slope for vertical transition Length of vertical transition
z L VT
Δx of vertical transition
Δx VT
= = =
1.0 7.5 5.3
1v : zh m m
w t w b
=
0.5
m
=
0.8
m
w s t sE t sC l b
= =
0.8 1.0
m m
= =
0.5 10.0
m m
D H
= =
2.5 15
m degree
SIDE WALLS GEOMETRY
Width of side walls at top Width of side walls at bottom Extension of bottom slab at each end Thickness of bottom slab at each end Thickness of bottom slab in center Length of thicker bottom slab
should be < 10
TRANSITION LENGTH (PLAN VIEW)
Diameter/Bed width of headrace Transition angle
β
LT
Transition length
Transition length - horizontal (required) L HT L HT Transition length (provided)
TOTAL HEADLOSS IN FOREBAY (Entrance + Friction + Gate Slot)
Total headloss in Forebay
h LT
=
Headrace invert / BL at end Water level at end of headrace
B.L hr
= =
0.002
m
-
W HR
1457.62 m asl 1458.80 m asl
Page 3 of 14
FOREBAY
(Wall top level will be constant throughout the entire length of forebay including u/s transition) EL WT Wall top level = 1460.29 m asl B.L s Bed level of forebay at start = 1452.29 m asl Longitudinal slope of forebay
S
=
Bed level of forebay at end
B.L e
=
1451.79 m asl
Maximum water level in forebay (end)
W max
=
1458.79 m asl
Allowable fluctuation in water level
σ allow
=
Minimum water level in f orebay Minimum water level in f orebay
W min
= =
W min
1.0
1.4
%
m
1457.39 m asl 1456.24 m asl
(provided) (required)
Longitudinal Section
1462.0
) l s 1460.0 a m1458.0 ( n1456.0 o i t 1454.0 a v e 1452.0 l E 1450.0 0.0
5.0
10.0
15.0
20.0
Distance (m)
25.0
30.0
Useful capacity of forebay (designed) Flow available from headrace
Normally a volume of Q P x 120 m (or two minutes at maximum plant flow) will be satisfactory for mechanical governors. For digital governors the control volume can be further reduced Check
VF ≥ VF-R
Water level in forebay Useful volume in forebay Total volume in forebay
=
O.K.
۩
= = =
1452
1456
1457
1458
1459
0
671
1065
1458
1851
0
1828
2222
2615
3009
Time
Forebay inflow
Initial forebay volume
Forebay outflow
Final forebay volume
Spill
(hrs)
(m /s)
3
(m )
(m /s)
3
(m )
(m /s)
0
648
0
648
0
masl 3
m 3 m
freeboard 0
3
3
3
Page 4 of 14
FOREBAY
1
6:PM
1.2
648
3
0
0.00
2
7:PM
1.2
648
3
0
0.00
3
8:PM
1.2
648
3
0
0.00
4
9:PM
1.2
648
3
0
0.00
5
10:PM
1.2
648
1.2
648
0.00
6
11:PM
1.2
648
1.2
648
0.00
7
12:PM
1.2
648
1.2
648
0.00
8
1:AM
1.2
648
1.2
648
0.00
9
2:AM
1.2
648
1.2
648
0.00
10
3:AM
1.2
648
1.2
648
0.00
11
4:AM
1.2
648
1.2
648
0.00
12
5:AM
1.2
648
1.2
648
0.00
13
6:AM
1.2
648
1.2
648
0.00
14
7:AM
1.2
648
1.2
648
0.00
15
8:AM
1.2
648
1.2
648
0.00
16
9:AM
1.2
648
1.2
648
0.00
17
10:AM
1.2
648
1.2
648
0.00
18
11:AM
1.2
648
1.2
648
0.00
19
12:AM
1.2
648
1.2
648
0.00
20
1:PM
1.2
648
1.2
648
0.00
21
2:PM
1.2
648
1.2
648
0.00
22
3:PM
1.2
648
1.2
648
0.00
23
4:PM
1.2
648
1.2
648
0.00
24
5:PM
1.2
648
1.2
648
0.00
Rack Cleaning Machine
RCM
=
no
Width of trashrach
bra nt bch
Peak storage Min. operating WL: penstock
#NAME? Lower W.L. 1456.24 masl
-
Number of rack bars
n
bch b
(yes or no - in small letters) Ref: GTZ Publication "High head Hydropower"
1
Width of rack bars Clearance between rack bars Angle of bars with horizontal
t b α
= = =
12.0 150.0 76.0
mm mm degrees
Width of Trashrack Channel width / diameter Number of rack bars
b ra b ch
= =
2000.0 1863.0
mm mm
n n
=
11.4
no.
"
"
"
Page 5 of 14
FOREBAY
Effective head from center of penstock h e D bm Diameter of bellmouth for penstock
=
6.8
m
=
1.5
m
v bm
=
1.70
m/s
Entrance velocity in bellmouth Average flow velocity between bars
v bars v e
Average flow velocity between bars
v bars
Ref: Mosonyi "Vol-I: page # 537"
b
=
0.81
m/s
1 t
Q 1 t b ve sin
Arack
Minimum trashrack area (r equired)
A rack
=
0.38
m
Trashrack area provided
A rack
=
4.00
m
=
O.K.
Arack-provided ≥ Arack-min
(calculated)
t b
Minimum trashrack area (r equired)
Check
Dbm 1.5 D
Ref: ESHA Guide
=
0.80
2
2
۩
Provide Spilling Arrangement Crest level of spill section
YES
Width of spill section (crest length) Allowable surcharge over crest
"
"
"
Check
H
=
1458.79 m asl
= =
Q CL S H
Discharge over ogee crest "
EL C L S
Q
Q ≥ 2.0QP
10.0 0.75
m m
3 / 2
Ref: C.V. Davis 3
=
14.17
=
O.K.
= = =
156.0 1.62 1.26
m m m
Ref: C.V. Davis
=
0.50
m
fbs 0.4 yc
=
15.0
degree
=
16.0
m
m /s
۩
Length of spill channel ( Δx)
L S
Bed width of spill channel Depth of water in spill channel
w S d S f.b. S
Free board in spill channel Transition angle Transition length (horizontal)
β L T
Page 6 of 14
FOREBAY
Bed elevation of channel at forebay Bed elevation of channel at end Slope of spill channel Friction Coefficient (concrete)
1460.0 ) l s a 1459.8 m1459.6 ( n1459.4 o i t 1459.2 a v e 1459.0 l E r 1458.8 e t 1458.6 a W1458.4 0.00
Qs
m
Rating Curve (Spill Channel Option)
1460.2
qs
3
m /s/m
10.00
Elevation
Flow
1458.29
0.00
1458.47
0.37
1458.64
1.06
1458.82
1.89
1459.00
2.81
1459.17
3.79
1459.35
4.81
1459.52
5.85
1459.70
6.92
1459.88
8.00
1460.05
9.10
Page 7 of 14
FOREBAY
CONCERETE VOLUME FOR SPILL CHANNEL OPTION
t t w t
Thickness of top slab Width of side walls at top Width of side walls at bottom Thickness of bottom slab Extension of bottom slab at each end Total depth of headrace channel
w b t s w s h c
= = = =
0.20 0.30 0.40 0.30
m m m m
= =
0.30 1.77
m m
PCC blinding layer (0.1m thick) Top slab
YES NO
X-sectional area of channel (RCC area) A xc
=
2.15
2
m
C B b 2wb 2ws t s L C B
Concrete quantity in bottom slab
=
141.34
C S wt hc C S
Concrete quantity in side walls
1
hc wb wt 2 L
2 193.28
=
3
m
3
m
C ts b 2wt t t L 3
Concrete quantity in top slab
C ts
=
0.00
m
Total concrete quantity (RCC)
C Rcc
=
334.62
m
PCC quantity in blinding layer
C Pcc
=
47.11
m
3
3
1460.5 1460 1459.5 1459 1458.5 1458
0.0 1458.0
2.3
1458.3
0.0 1458.3
2.3
1460.1
0.3 1458.3
2.6
1460.1
0.4 1460.1
2.7
1458.3
0.7 1460.1
3.0
1458.3
0.7 1458.3
3.0
1458.0
2.3 1458.3
0.0
1458.0
2.0
2.5
1457.5 0.0
0.5
1.0
1.5
3.0
3.5
Diameter of spill pipe Depth of flow Length of spill channel ( Δx)
D S
Mannings friction factor (steel)
y s L S
= = =
2.00 1.50 156.0
n
=
0.0130
m m m
Page 8 of 14
FOREBAY
Flow area
A
=
2.527
Wetted perimeter Hydraulic radius Top width Hydraulic depth
P R T D
= = = =
4.189 0.603 1.732 1.459
2
Ref: C.V. Davis
m m m m m
Ref: C. Nalluri 2.00
f z a
= =
0.87 4.189
h
= =
-0.500 θ 240.00
2θ
1
y
Mannings equation
V
Flow velocity
V
"
"
=
3.88
m/s
Q S Q Sma
= =
9.82
11.58
m /s 3 m /s
=
O.K.
=
0.0
"
"
"
Discharge capacity Maximum discharge capacity QS ≥ 1.5QP
Check
Rating curve at given distance
x
n
S 1 / 2 R 2 / 3
3
(at y = 93.8% of d i)
۩ m (from start)
Rating Curve (Spill Pipe Option)
1460.5
) l s a 1460.0 m ( n 1459.5 o i t a v e 1459.0 l E r e t 1458.5 a W 1458.0 0.00
2.00
4.00
6.00
8.00
10.00
12.00
14.00
Flow (cumecs)
Elevation
Flow
1458.3
0.00
1458.5
0.22
1458.7
0.94
1458.9
2.11
1459.1
3.63
1459.3
5.38
1459.5
7.23
1459.7
9.01
1459.9
10.52
1460.1
11.47
1460.2
11.58
STEEL QUANTITY FOR SPILL PIPE OPTION
Thickness of steel sheet (provided) Density of steel
t s ρ s
= =
8.0
mm
7850.0
kg/m
3
Ref: Flowadvisor
Page 9 of 14
FOREBAY
t min
Minimum thickness of steel sheet
D K
(K = 500 & D in mm)
400
Ref: Warnick
Minimum thickness of steel sheet Corrosion allowance
t min c a
= =
6.25 1.00
mm mm
Effective thickness of penstock
t e
=
7.00
mm
=
O.K.
Check
te ≥ tmin
۩ 2
t d i 2 s d 2 1000 As i 4
4
2
X-sectional area of steel
A s
=
0.050
m
Volume of steel Weight of steel Weight of steel (5% increse for joints)
V s W s W s
= = =
7.87 61.8 64.9
m tons tons
Width of steel sheet Length of steel sheet No. of steel sheets
w l n
= = =
6.33 6.0 26
m m no.
Froude Number
F
3
Ref: Mosonyi
R
V
Ref: C.V. Davis
gD
(Where V & D are velocity and depth of flow entering the jump) Froude Number - before the jump
F R1
=
0.84
dimensionless
(Recommended Froude Number 4.5 ≤ F R1 ≤ 9, for stable & steady hydraulic jump) Ratio of conjugate depths
D2 D1
0.5 1 8F R21 1
Depth before the jump Depth after the jump
D 1 D 2
= =
1.26 0.99
Length of stilling basin " " " " Alternatively Length of stilling basin
L B L B
= =
α (D2 - D1)
"
L B
"
"
"
L B 4.5 =
-1.4
Ref: L.W. Mays
m m
m
D2 F R0.38 4.77
m Ref: L.W. Mays
Height of walls of basin " " " "
H B H B
= =
D2 + 0.1 * (D1 + V1) 1.4
m
Page 10 of 14
FOREBAY
2.5 * D 1
Height of baffle blocks " " " "
h B H B
= =
Number of baffle blocks
n w B
=
2
=
0.41
Width of baffle blocks
3.2
m
SCOUR DEPTH BELOW WATER SURFACE
Scour depth of rivers subject to fluctuating flood throughout the year
Q R 0 . 78 C r
Scour depth below water surface
3 / 10
(in British unit system) Cr =
Scour depth below water surface
R
=
0.88
m
Flushing discharge Diameter of flushing pipe
Q f D f L f
= =
0.60 0.80
m /s m
8.5 0.0130
m
n
= =
h e h emin
= =
6.1 3.6
m m
2.00
-
Length of flushing pipe Mannings friction factor (steel) Effective head from center of pipe Minimum effective head
Thickness of steel sheet (provided) Density of steel
t s
Minimum thickness of steel sheet
t min
ρ s
D K
3
(K = 500 & D in mm)
400
Ref: Warnick
Minimum thickness of steel sheet Corrosion allowance
t min c a
= =
3.25 1.00
mm mm
Effective thickness of penstock
t e
=
5.00
mm
=
O.K.
Check
te ≥ tmin
Ref: Flowadvisor
۩ 2
t d i 2 s d i2 1000
Page 11 of 14
FOREBAY
s
4
4 2
X-sectional area of steel
A s
=
0.015
m
Volume of steel Weight of steel
= =
0.13 1.01
m tons
Weight of steel (5% increse for joints)
V s W s W s
=
1.06
tons
Width of steel sheet
w
=
2.53
m
Length of steel sheet No. of steel sheets
l n
= =
6.0 2
m no.
3
Ref: Mosonyi
This is an impact-type energy dissipator equipped with a hanging-type, L-shaped baffle, contained in a relatively small boxlike structure, which requires no tail water for successful performance. The use of the impact-type stilling basin is limited to installation where the velocity at the entrance to the stilling basin does not greatly exceed 30 ft/s (9.1 m/s). For discharges 3
exceeding 10 m /s, it may be more economical to consider multiple units side by side.
Page 12 of 14
FOREBAY
Diameter of flushing pipe Flushing discharge Flow velocity (orifice flow) Froude Number
D f Q f
=
2.62
ft
0.80 3
m 3
V F R1
= = =
88.89 16.43 1.79
2.52 ft /s ft/s 5.0 dimensionless
W / D ratio (from DOSD graph) Where:
W / D
=
4.70
dimensionless
Depth of flow entering the basin
D
=
2.33
ft
=
0.71
m
W
=
10.93
ft
=
3.33
m
Alternatively: Inside width of stilling basin (from graph) W E L /E 1 Loss in energy (from graph)
= =
6.00 53
ft %
=
1.83
m
Select the larger value of width i.e. Inside width of stilling basin
=
10.93
ft
=
3.33
m
m /s m/s
(D = square root of flow area)
Inside width of stilling basin
W
The dimensions of various components as shown in the above figure, are given below; Total depth of basin at start (H = 3/4 W) Total length of basin (L = 4/3 W) Distance of baffle from inlet (a = 1/2 W) Height of baffle (b = 3/8 W)
H
=
8.20
ft
=
2.50
m
L a b
= = =
14.58 5.47 4.10
ft ft ft
= = =
4.44 1.67 1.25
m m m
Depth of basin at end (c = 1/2 W) Length of baffle top (d = 1/8 W)
c d
= =
5.47 1.37
ft ft
= =
1.67 0.42
m m
Page 13 of 14
FOREBAY
e = 1/12 W
e
=
0.91
ft
=
0.28
m
Thickness of baffle (t = 1/12 W) Riprap stone size (drock = 1/20 W) Length of riprap (Lrr = W)
