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Hydraulic Loading & Strength
- overview -
Krystian Pilarczyk
www.enwinfo.nl, (english, downloads)
Stability criteria
bop
s
cr
cosF =
DH
k
h1 = K
-0.2
hr
3/2op
s
cr
F =
DH
with maximum 8.0 = DHs
cr
L / H
tan =
opsop
g2u
K
KK 0.035 = D2cr
s
hT
sin
sin - 1 = K
2
s
k
h = K
s
-0.2
h
Current (general) (Pilarczyk)
Waves
Block revetments
b = 0.5 for rip rapb = ½ to 2/3 for blocks and gabions
Breaker index
or
bop
s
cr
cosF =
DH
1.05
Current attack
• Principles
• Velocity distribution
• Turbulence
• Design formulas
• Uncertainties
RSCv
2/13/21SR
nv
Chezy
Manning
C = h1/6/n ;
Strickler: n = ks1/6/25
C= 25(h/ks)1/6
R~h
For granular (non-cohesive) banks, fluvial erosion is modelled as for sediment transport
(with = bank angle):
Fluid Lift (FL)
Fluid Drag (FD)
Friction ()
Particle Weight (W)
Downslope componentof particle weight (Wd)
Normal component of particle weight
(Wn)
Steve Darby
Stability criteria revetments rock - current attack
• (a) K = f G, or
• ½CDρwU²πD²/4=fπD³/6(ρs-ρw)g, providing:
• U²/(2g Δ D) = (2/3)f/CD = φAssuming θ = 42o(for rock), f = tan 42o = 0.90, and CD= 1.0, one obtains: U²/(2g Δ D) = φ = 0.60.
(b) The moment with respect to the turning point S gives the equation: F b = G a, or (½CF ρw U²πD²/4)b=(πD³/6(ρs-ρw)g)a, providing:
U²/(2g Δ D) = (2/3)(a/b)/CF = φAssuming a = b, CF = 1.0, then φ= 0.67. CF is a combination of coefficients for drag and lift forces.
Isbash (1935)
Ub2/(2gD) = φ
Ub = bottom velocityD usually = D50
Dn50 = 0.84 D50
φ = stability factor:φ = 0.7 for exposed stones
and 1.4 for embedded stones
22
tan
tan1cos
sin
sin1
KsSlope factor
Ub2/(2gD Ks) = φ
or
Ub2/(2g φ Ks) =
D
Comparison formulas
Because in Vietnam design codes follow the Chinese codes (which is not correct):
Beginning of movement of granular materials
)()( *
2*
ec
cr
cws
crcr Rf
gD
u
gD
CgUgRIu w //*
)()( *
2*
ec
cr
cws
crcr Rf
gD
u
gD
CgUgRIu w //*
Shields Diagram (D*=d50(g/2)^1/3
us
k
h = K
-0.2
hr
k
h1 = K
-0.2
hr
or
In Pilarczyk formula:
Velocity distribution/profiles
Under ice cover
Comparable with flow in pipes
RSCv Chezy
2/13/21SR
nv Manning
R(hydraulic radius) ~ h (average
depth);
S = energy slope ~ bed slope
C = h1/6/n ;
Strickler: n = ks1/6/25
C= 25(h/ks)1/6
Mean velocity in a stream/rivers (uniform flow):
C = 18 log (12 h/kr)
Inter-relationships:C and n = resistance parameters/functions
Velocity profiles Log law vs. power law. The 1/6 power law is a standard profile, commonly applied to river flow.
Family of curves representing log-law profiles for varying roughnesses. All have the same mean velocity. The red curve uses the roughness parameter z0 = 1/10 of the depth, while the blue line corresponds to z0 = 10-6 times the depth (i.e. a very smooth bottom). The magenta line (z0 = 0.0005 times the depth) corresponds approximately to a 1/6 power law, while the blue line corresponds approximately to a 1/12 power law
A standard USGS practice allows hydrographers to estimate the average flow velocity by either measuring the velocity at 0.6 times the depth or by averaging the velocities measured at 0.2 and 0.8 times the depth.
Standard USGS practice. The red and blue lines give the velocities computed using the 0.6 depth and 0.2/0.8 depth methods, as a fraction of the true mean velocity. The resulting velocity is close to 1.00 over a wide range of bottom roughnesses. The arrows for the 1/6 and 1/12 power laws show the bottom roughness that give log profiles most closely matching these power laws. The 1/6 power law corresponds to typical river flow
and the 1/12 power law might apply in a man-made channel.
Secondary flow. Top: pattern of cross-channel velocity. Bottom: Down-channel velocity contours. The depth of maximum velocity (dashed line) is below the surface, and deepens closer to the side.
How secondary flows change the vertical profile of velocity
http://www.rsnz.org/publish/nzjmfr/1997/15.pdf
Velocity profile
Measurements in UK rivers:
Ub = 0.74 to 0.9 Udepth-average
Ub measured at 10%of the water depth
above the bed
???????
U/Uave=(x+1)(y/h)x ; x = 1/6 developed profile, x = 1/10 non-developed profile
For y =0.4h, U=Uave
y/h = 0.1
x = 1/6, U/Uave= 0.80
x = 1/10, U/Uave= 0.87
U/Usurf=(y/h)x
U/Uave=(x+1)(y/h)x ; x = 1/6 developed profile, x = 1/10 non-developed profile
For y =0.4h, U=Uave
y/h = 0.1
x = 1/6, U/Uave= 1.167 (0.1)0.167 = 1.167 0.681 = 0.80
x = 1/10, U/Uave= 1.1 (0.1)0.1 = 1.1 0.794 = 0.87
y/h = 0.4
x = 1/6, U/Uave= 1.167 (0.4)0.167 = 1.167 0.858= 1
x = 1/10, U/Uave= 1.1 (0.4)0.1 = 1.1 0.912 = 1
0
0,5
1
1,5
2
0 1 2 3 4 5
v(y) [m/s]de
pth
[m]
Velocity Distribution (log)
0
11 ln
yv y V gdS
d
1 lnyd
- =
At what elevation does the velocity equal the average velocity?
For channels wider than 10d
0.4k » Von Kármán constant
V = average velocityd = channel depth
1y de
= 0.368d
0.4d
0.8d
0.2d
V
Designation of Design Flow Velocity Bangladesh
General approach to current attack
- logarithmic velocity profile (Chezy),
sh k
h
gg
C 121log
2
18
22
22
50
6log75.5
12log
18
D
h
k
h
gDg
Ucr
scr
Strickler’s resistance formula for developed velocity profile,
3/13/1
1322
625
ssh k
h
k
h
g
- non-developed profile (Neill, 1967, Pilarczyk, 1995),
2.02.0
13232
ks
h
k
h
sh
StricklerC = 25(h/kr)1/6
C = 18 log (12 h/ks)~ 18 log (1+12h /ks)(for small h/ks)
crhcD
gU
2/2
assuming ks = 2 D50.
crhcD
gU
2/2
- logarithmic velocity profile (Chezy),
sh k
h
gg
C 121log
2
18
22
22
u
g d
C
gd
u
Cc
n
cn
c
c 5050
2
2
dn50 = Dc
Schiereck 2001,
Introduction to Bed, Bank and Shore Protection
C = 18 log (12 h/ks) ~ 18 log (1+12 h/ks)
(for small h/ks)
C K
u* K = Dn
2cs
c
2 2v
50
Often written as
Kv=1 to 1.6; usually 1.2 (turbulence)
Ks = slope factor
crc g
C
D
gU )2
(2/ 22
2.02
5.2)(
h
D
Dg
U c
cws
w
Neill (1967)
Kh = 33/Λh
k
h12log
2 = K
s
2h
crhcD
gU
2/2
- logarithmic velocity profile (Chezy),
sh k
h
gg
C 121log
2
18
22
22
Kh=33/Λh = 33/C2/2g = 33 2g/C2= 33 2g/[18 log (12h/ks)]2
= 2/[log(12h/ks)]2
C = 18 log (12 h/kr)
g2u
K
KK 0.035 = D2cr
s
hT
k
h = K
s
-0.2
h
1k
h12log
2 = K
s
2h
k
h12log
2 = K
s
2h
Kh = 33/Λh
k
h1 = K
s
-0.2
h
Fully-developed profile
Non-developed profile
ks=2D
ks=D
Kh=(h/ks)-1/3
C K
u* K = dn
2cs
c
2 2v
50
g u = d or =
d g
u or d g u2cc
c 27.07.122.1
Isbash, 1930
du
ffdg
u
dgcc
ws
cc
**
2* Re
u
g d
C
gd
u
Cc
n
cn
c
c 5050
2
2
d V Mn 3 3 /
In Schiereck 2001
Shields, 1936
Practical relation;
Including velocity and slope factor
For = 1.33*10-6 m2/s and = 2650 kg/m3, values of the grain size in mm are indicated on the graph.
Shields Diagram (D*=d50(g/2)^1/3
In Schiereck 2001
General Stability Formula for current attack (Pilarczyk)
g2u
K
KK 0.035 = D2cr
s
hT
sin
sin - 1 = K
2
s
k
h = K
s
-0.2
h
k
h1 = K
s
-0.2
hor
• Shields parameter ψ:• riprap, small bags 0.035• placed blocks, large geobags 0.05 • blockmats 0.05 to 0.07
(0.07- if cabled and/or washed-in)
• gabions 0.07 • geomattresses 0.07
Stability parameter Φ: continuous protection edgesRiprap and placed blocks, 1.0 1.5Sand-filled unitsBlock mats, gabions, washed-in blocks, 0.75 1.0 (1.2)Concrete-filled geobags, and geomattresseson proper subgrade (no soil deformation)
Turbulence factor KT:
• Normal turbulence: abutment walls of rivers: KT 1.0
• Increased turbulence:• river bends: KT 1.5• downstream of stilling basins: KT 1.5
• Heavy turbulence• hydraulic jumps: KT 2.0• strong local disturbances: KT 2.0• sharp bends: KT 2.0 (to
2.5)
• Load due to water (screw) jet: KT 3.0 (to 4.0)
(KT = kt2 in Rock Manual ‘07)
(kt U)2
39
Flow attack• pressure fluctuations
/ turbulence• drag forces• lift forces
load
strength
u
gD
Design formula
u
gD
K
K Ks
T h
2
0 035.
Example:• Mattress on a bank of a straight channel, 2 m deep: u
gD3
Rock specifications
Weight gradings and size relations for the standard light and heavy grading classes
1 3
1 0/
,na
WD
g
1 2
1 24/
,sa
WD
g
0 806,n sD D
Ds=equivalent sphere diameter
sD
)
1 3
5050
/
na
WD
g
50
50
0 84,nD
D
Comparison with Maynord USACE:
• Pilarczyk’s formula can be transformed into structure similar to Maynord formula, namely:
5.25.225.1
50 2
035.0
hgK
UhC
hgK
Uh
KD
s
P
scr
Tn
Maynord:
5.2
1
30
hgK
UhCD MD30 = 0.70 D50 (approximately)
CEM2002
Expressed as u =f(d30, h/d30)
CM = Sf Cs Cv CT
(useful for wide grading)
5.2
1
30
hgK
UhCD M
• CM = Sf Cs Cv CT
• Sf = safety factor; 1.1 to 1.5• Cs = 0.3 for angular rock and 0.375 for rounded rock• Cv = velocity distribution coefficient• Cv = 1.0 for straight channels• Cv = 1.25 downstream conrete channels;at the end of
dikes• Cv = 1.283 -0.2log(R/w) for outside bends (1 for R/w > 26)• CT = blanket thickness coef., typically = 1
K1 = side slope correction factor (less conservative than Ks);K1 = -0.672+1.492ctgα-0.449 (ctgα)2+0.045(ctgα)3
sin
sin-1 = K
2
s
Utoe/Uavg= 1.75 – 0.5 log (R/w)Example USACE guide:
hmax/have= 2.07 – 0.19 log (R/w -2)Bend scour/depth
Maynord: For ctgα=3, U=3.5m/s, h=10m, Sf=1.5,Cs=0.3, Cv=1.25, CT=1 and K1=0.97:
• D30 = 0.23 m and D50 = 0.33 m ( Dn50= 0.28m)• Applying Ks = 0.9• D30 = 0.25 m and D50 = 0.36 m ( Dn50= 0.30m)
Pilarczyk:
g2u
K
KK 0.035 = D2cr
s
hT
KT=1.4, Kh =(D/h)0.2= 0.5, Φ=1, Ks=0.9, ψc=0.03 to 0.035:
Dn50= 0.35m for ψc=0.03
Dn50= 0.30m for ψc=0.035
50
50
0 84,nD
D
Escarameia and May
g
UcD b
Tn 2
2
50
ct = 12.3 r – 0.20
riprap (valid for r 0.05):
r = turbulence intensity defined at 10% of the water depth above the bedTypical turbulence levels
SituationTurbulence level
Qualitative Turbulence
intensity (r)
Straight river or channel reaches
normal (low)
0.12
Edges of revetments in straight reaches
normal (high)
0.20
Bridge piers, caissons and spur dikes; transitions
medium to high
0.35 – 0.50
Downstream of hydraulic structures
very high 0.60
0
0,05
0,1
0,15
0,2
0,25
0,3
0 0,2 0,4 0,6 0,8
Ud/(gh)0.5D
n50
/h
Pilarczyk, not fully developed profile
Pilarczyk, fully developed profile
Escarameia and May
Maynord
Figure 2 Increased turbulence (kt = 1.5, r = 0.2 and Cv = 1.25)
Figure 1 Normal turbulence (kt = 1.0, r = 0.12 and Cv = 1.0)
0
0,05
0,1
0,15
0,2
0,25
0,3
0 0,2 0,4 0,6 0,8
Ud/(gh)0.5
Dn5
0/h
Pilarczyk, not fully developed profile
Pilarczyk, fully developed profile
Escarameia and May
Maynord
Figure 1 Normal turbulence (kt = 1.0, r = 0.12 and Cv = 1.0)
Figure 2 Increased turbulence (kt = 1.5, r = 0.2 and Cv = 1.25)
RM 2007
Figrs. 5.93 and 5.94
Hoffmans 2006
• r0 = 0.10 - 0.15 normal turbulence, rivers
• 0.15 - 0.20 non-uniform flow with increased turbulence as below stilling basins, outer bends in rivers
• 0.20 - 0.25 high turbulence as below hydraulic jumps, local disturbances, sharp outer bends
• 0.25 - 0.30 jet impact, hydraulic jump
s
n Kg
UrD
16.0
200
( )gd
Ur
Δ7.0=Ψ
200
gD
Ur
2007.0
s
n Kg
UrD
17.084.0
200
50
50
0 84,nD
D
Uo = depth-average velocity
ro = turbulence related factor
C
gc
U
uc
U
kr
ave0
0
*0
00 ===
where kave is depth-averaged turbulent kinetic energy
C is the Chézy coefficient.with co (≈1.2) a coefficient
For hydraulically smooth conditions, that is for C = 75 m½/s, r0 ≈
0.05 and for hydraulically rough conditions, i.e. C = 25 m½/s, r0 ≈
0.15.
Hoffmans 2006 (cont.)
The depth-averaged relative turbulence intensity (ro)
Soil types
Possible soil gradings and uncertainties
Hydraulic and coastal structures in international perspective; Pilarczyk, K.W.
TPG001.pdf (1016.1 KB) http://repository.tudelft.nl/view/hydro/uuid%3A9c8267d4-cdb6-4c53-8045-15afa6294e04/
http://www.slideshare.net/Pilarczykhttp://www.slideshare.net/Pilarczyk/1-geosyntheticsampgeosystems-pilarczyk-pres-final
; http://www.slideshare.net/Pilarczyk/geosyntheticsampgeosystems-in-coastal-engineering-pilarczyk2009
; http://www.isbnlib.com/author/Krystian_Pilarczyk
www.enwinfo.nl, (english, downloads, design revetments)