designing dredging equipment
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112 September 200612 September 2006
Designing Dredging EquipmentOE4671/WB3408
Prof.ir. W.J.Vlasblm
Section Dredging engineering
September 12, 2006 2
Purpose of the lecture
• To design a particular type of dredger on basis of (simple) dredging processes.
• Such a method can be used for many design problems!
September 12, 2006 3
Course development
• Introduction lecture in the 5th quarter
• Assignment for one or two persons can be done the whole year around.
• Total 4 credits (ECT)
September 12, 2006 4
Assignments for hydraulic dredgers
• Trailing Suction Hopper Dredger (TSHD) for large reclamation works
• Multi Purpose TSHD for maintenance and beach nourishments
• Gravel Trailing Suction Hopper Dredgers• Cutter Suction Dredger• Environmental Dredger• Plain Suction Dredger• Dustpan Dredger
September 12, 2006 5
Assignments for mechanical dredgers
• The backhoe dredger• The grab dredger• Bucket ladder dredger
September 12, 2006 6
Trailing Suction Hopper Dredger
September 12, 2006 7
Cutter Dredger
September 12, 2006 8
Plain Suction Dredger
September 12, 2006 9
Plain Suction Dredger
September 12, 2006 10
Dustpan Dredger
September 12, 2006 11
The Environmental Dredger
September 12, 2006 12
The Backhoe Dredger
September 12, 2006 13
The Grab orClamshell Dredger
September 12, 2006 14
Bucket Ladder Dredger
September 12, 2006 15
Work Load
The assignment for• the TSHD, CSD are for 2 students• The other ones are for 1 student
September 12, 2006 16
Designing DredgingEquipment
Dredging installation
Propulsion (optional)
General layout
Productions
Prime movers (main engines)
September 12, 2006 17
Design productions
Working hours
Delays
Effficeincy
Yearly production
Excavating production
Soil type
Losses
Transport production
Losses
Deposing
Situ production
September 12, 2006 18
Design basis = yearly output in m3
(production)
• To be translated to the significant design parameters. • Depends on the scale (or cycle) of the process.• Large scales
• Hopper dredger ⇒ volume and load per trip• Barge unloader dredger ⇒ Barge volume• Backhoe dredger ⇒ the volume per cycle
• Continuous operating dredgers or equipment m3/week or m3/month
September 12, 2006 19
Design Basis (2)
• Small scale:• “Wall” speed of a breach mm/s• Pump output in m3/s• Cutter head Excavated output in
m3/s• Bucket ladder dredger Buckets/min• Backhoe dredger Bucket volume/cycle• Grab dredger Grab volume/cycle
September 12, 2006 20
Problems during translation
• Change of volumes • In many cases the contractor is paid in volumes
removed, but many processes are based on mass.• Working hours per week (168 or 84 or 40)• Down time• Overhaul & Maintenance • Bunkering, crew changes, etc• Delays due to weather conditions
September 12, 2006 21
Concentration (1/3)
• By volume
• By weight
• Delivered
sv
m
UVolume sandCMixture volume U
= =
s s sw v
m m m
USand massC CMixture mass U
ρ ρρ ρ
= = =
//
s svd
m m
U time QCU time Q
= =
September 12, 2006 22
Concentrations (2/3)
• Ratio between Cvd & Cv follows from:
• Ratio between Cw & Cv
s s v vd svd
m m v m
Q v AC C vCQ v A C v
= = ⇒ =
s w sw v
m v m
CC CC
ρ ρρ ρ
= ⇒ =
September 12, 2006 23
Concentrations (2/3)
•In horizontal transport vs < vm → slip•In vertical transport vs ≈ vm the difference is the settling velocity
vd s
v m
C vC v
=
September 12, 2006 24
Mixture Volumetric Densities Concentration
• Massmixture=massliquid+masssolids
(1 )
"Note U is volume"
sm m f f s s v
m
m f v s v
m fv
s f
UU U U with CU
C C
C
ρ ρ ρ
ρ ρ ρ
ρ ρρ ρ
= + =
= − +
−=
−
⇔
September 12, 2006 25
Volume changes
• When removing soil the insitu density will change; mostly from a dense to a loose state⇒Increase in porosity; f.I. From 40 to 50%⇒Porosity n is ratio pore volume over total volume⇒Condition: V1(1-n1)=V2(1-n2)
Examples:⇒Sand; n1=0.4 and n2=.5 gives V2/ V1=0.6/0.5=1.2⇒Rock; n1=0 and n2=.4 gives V2/ V1=1/0.6=1.7
September 12, 2006 26
Losses
Every dredging process can have losses, called spillage• More excavated than picked up by the flow or bucket• Non removed loads in TSHD’s, particular when the
loads is pumped ashore or rainbowed.• Unstable slopes after dredging (plain suction dredgers)• In accurate placing of material• Losses due to current and waves
September 12, 2006 27
Excavating production
Mechanically Hydraulically
September 12, 2006 28
Mechanical excavation Specific Energy Concept (SPE)
Energy required to excavated 1m3 of soilDimension is Joule/m3
or per unit of time J/s/m3/s=W/m3/s,
That equals a power over production
powerSPE power SPE productionproduction
= ⇒ = ×
September 12, 2006 29
Mechanical Excavating
September 12, 2006 30
Mechanical Excavating
September 12, 2006 31
Mechanical Excavating
September 12, 2006 32
Hydraulic excavationMomentum of flow
A reasonable assumption is that the jet- production is linear with the total momentum flux of the jet system independent of the trail speed.
M I Qu Q p P
psand w ww
wpower
pressure
= ⋅ = ⋅ = ⋅ =α αρ αρρ
α ρ2 2
( )( )
1
1sand dredged
sand sand sand dredged sand
Q n Q
M Q n Qρ ρ
= −
= = −
September 12, 2006 33
Excavation by dragheads is hydraulically
September 12, 2006 34
Water injection dredger
September 12, 2006 35
Transport production
Mechanicallyship/barge conveyor
Hydraulicallypipeline
September 12, 2006 36
Mechanical transport
• Trailing suction hopper dredger• Barges
• Be aware of the effective load, because the unloading is not always 100%
September 12, 2006 37
Transport by barges
September 12, 2006 38
By Trailing Suction Hopper Dredgers
September 12, 2006 39
Hydraulic transportPump-pipeline system
mixture
water
mixture
water
1
2
3
4
Flow [m3/s]
Pressure [kPa]
September 12, 2006 40
Hydraulic transport
September 12, 2006 41
Methods of deposing (1/2)
September 12, 2006 42
Methods of deposing (2/2)
September 12, 2006 43
disposing
September 12, 2006 44
Rainbowing
September 12, 2006 45
Mechanical Assistance
September 12, 2006 46
Design examples
September 12, 2006 47
TSHD
September 12, 2006 48
Example 1
Design a Trailing Suction Hopper Dredger that can dredge yearly 5 Mm3 coarse sand & gravel at 75 nautical miles from a port.
The dredger works 5 days at 24 hoursBunkers will be taken in the weekendOverhaul 2 weeksWeather delays 3 weeksWorkability 95%Christmas 1 week
September 12, 2006 49
Designing TSHD
Main dimensions
Dredging installation
Propulsion
General layout
September 12, 2006 50
Main dimensions
Working hours
Delays
Effficeincy
Yearly production
Hopper capacity and Payload
Soil type
Dead weight
Displacement
Main dimensions ship LxBxT
Bock coefficient
Overflow losses
September 12, 2006 51
Cycle time
First estimate of dredge cycle:Sailing to the dredging area: 75/15=3.0 hrLoading =1.5Sailing to the unloading area: =3.0Unloading =1.5Total =9.0 hr
September 12, 2006 52
Required load/trip
Available hours: (52-6)x5x24=5520Effective hours: 0.95x 5520=5244Number of trips per year: 5244/9= 582Required volume per trip: 5,000,000/582=8591 m3
In coarse sand & gravel max.filling hopper is 90%Required hopper volume: 8591/.9=9546 10000 m3
Density of sand & gravel in hopper 2000 kg/m3
PayLoad is: 8600x2=17200 tonHopper density: load/volume=1.72 t/m3.
⇒
September 12, 2006 53
Deadweight & lightweight
Crew and their possessions, consumer goods, spare parts, and ballast water and payload.
Deadweight=1.05 x payload Light weight as function of deadweight
y = -3E-06x2 + 0.5586xR2 = 0.9607
0
5,000
10,000
15,000
20,000
25,000
0 10,000 20,000 30,000 40,000 50,000 60,000 70,000
Deadweight [t[
Ligh
t wei
ght [
t]
September 12, 2006 54
Displacement
y = 0.6827xR2 = 0.9929
y = 0.3173xR2 = 0.9622
0
10,000
20,000
30,000
40,000
50,000
60,000
70,000
0 20,000 40,000 60,000 80,000 100,000
Displacement [t]
Wei
ght [
t]
G Light weightDead weight
September 12, 2006 55
Block coefficient
CLBTb =∇
T
BL
Cb =
September 12, 2006 56
Ship Numbers
Ships Numbers
012345678
1965 1970 1975 1980 1985 1990 1995 2000
Year of Construction
L/B
, B/H
, B/T
L/BB/HB/T
September 12, 2006 57
Dredging installation
Cvd
Required pump capacity
Overflow losses
Overflowlosses equal as assumed?
Yes
Main DimensionsNo
Pumps and pipelines
September 12, 2006 58
Pump capacities
• 10000 m3 in 90 min=1.85 m3/s including pores or 1.85x0.6=1.11 m3/s excluding pores
• Assume Cvd=0.2 → capacity Q=1.11/0.25=5.55 m3/s or per suction tube 2.8 m3/s
• Critical velocity for course sand is 5 m/s, so pipe diameter is 0.85 m → 0.85 m
• In coarse sand and gravel there are no overflow losses to account for.
September 12, 2006 59
Excavation process
September 12, 2006 60
Calculated the required jet pressure
•Sand mass follows from production
•Momentum follows from:With α=0.1
2 2 powerw jet w w
w pressure
PpI Q u Qp
α αρ αρ α ρρ
⋅ = ⋅ = ⋅ =
( )( )
1
1sand dredged
sand sand sand dredged sand
Q n Q
M Q n Qρ ρ
= −
= = −
sandM Iα= ⋅
September 12, 2006 61
Relation between Qmix, Qjet and Qerosion
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Qjet / Qmixture
Cvd/(1-n)=0Cvd/(1-n)=0.2Cvd/(1-n)=0.4Cvd/(1-n)=0.6Cvd/(1-n)=0.8
September 12, 2006 62
Pumps and pipelines
Submerged pump required?
Yes
No
Depth of submerged pump
Determine headlossesand power(s)
Choose pump(s)
Determine jet capacityand pressure
September 12, 2006 63
k
hs
Hρwater
ρmixture
Non cohesive material
Submerged pump required?
( )ρ ρ ξ ρ ρ ξ ρwater mixture z mixture mixture mixturegH Vac gh v g H k v+ = + = − +12
12
2 2
September 12, 2006 64
Hydraulic transport
• From seabed into the hopper• From hopper to the shore
• Mostly empirical relations (Matousek)
• For gravel dredgers this is mostly be mechanically
September 12, 2006 65
Pump characteristics
September 12, 2006 66
Propulsion
For dredging & sailing
Bow trust power
Total Installed
Power balance
General layout
September 12, 2006 67
Propulsion power
y = 0.4641x - 510.11R2 = 0.8741
0
5000
10000
15000
20000
25000
0 10000 20000 30000 40000 50000
Displacement [t]
Pp [k
W]
September 12, 2006 68
Bow trust power
Bow trust power
y = 0.1758x - 19.495R2 = 0.8036
0500
1,0001,5002,0002,5003,0003,500
0 2,000 4,000 6,000 8,000 10,000 12,000 14,000 16,000
Propulsion power during trailing [kW]
Bow
trus
t pow
er [k
September 12, 2006 69
General Arrangement
September 12, 2006 70
General Arrangement of gravel dredger
September 12, 2006 71
Simple general arrangment
Lhopper = 62 mLship= 165 m
Bship= 33
Bhopper= 25 m
Tship= 13,2
Hhopper= 13
Hship= 14,7
G H ICA KFB ED MJ L N
See figureB7.1
September 12, 2006 72
The Cutter Suction Dredger
September 12, 2006 73
Example 2
Design a cutter dredger that can dredge dredge yearly 5 Mm3 rock with a unconfined compressive strength of 5 MPa. The tensile strength is 1 Mpa
The dredgers have to work 168 hrs a week.Yearly overhaul 4 weeksChristmas leave 1 weekGeneral delays 10%Dredging delays 20SPE~qu
September 12, 2006 74
Required cut production
Available hours (52-5)x168=7896Non dredging hours:0.3x7896=2369Dredging hours 7896-2369=5527Estimated spillage 25%Required hourly output: 1.25x5000000/5527=±1130 m3.Qdredged=1130/3600=0.314 m3/sTime losses due to stepping, spud changes 15%Qcut=0.31/0.85=0.37 m3/sSPE=5MJ/m3. Required mean cutter power 0.37x5=1.85 MW
September 12, 2006 75
Cutter head productions c.q. Spillage
•The rotational speed of the cutter head causes spillage.
•The productivity c.q. spillage depends on the ratio:
•For sand the productivity is:
•For rock the productivity is much lower
32.5 pumpr
cutter
QP
Rω≈
September 12, 2006 76
Cutter head productions c.q. Spillage
RELATIVE PRODUCTION
01020304050607080
0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80
Flow number [-]
Pr [%
]
Gravel 10 mm Gravel 15 mm Ladder 25 deg. Sand
September 12, 2006 77
Cutter head production processin rock or gravel
September 12, 2006 78
Cutter head dimensions for rock with 25 % spillage
0
20
40
60
80
100
120
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0Cutter diameter [m]
Cut
ter
head
spe
ed [r
pm]
0
2
4
6
8
10
12
Pum
p ca
paci
ty [m
3/s]
Vm=2.67 m/s Vm=3.5 m/s Vm=5 m/s
Capacities
cutter head speeds
September 12, 2006 79
Pump capacity and concentrations
Qdredged=0.314 m3/sQmixture=3.5 m3/s
( )1dredgedsandvd
mixture mixture
Q nQCQ Q
−= =
September 12, 2006 80
Pumping distances and installed pump power
• Knowledge of hydraulic losses can be found in the lecture notes of Matousek c.q. Talmon
• Knowledge of dredge pump can be found on our website and is downloadable.
September 12, 2006 81
Lightweight of pontoon
y = 0.3485xR2 = 0.925
0
2,000
4,000
6,000
8,000
10,000
0 5,000 10,000 15,000 20,000 25,000
Total installed power [kW]
Lig
ht w
eigh
t [t]
September 12, 2006 82
Pontoon dimensions (1/2)
0.00
2.00
4.00
6.00
8.00
10.00
12.00
0 1000 2000 3000 4000 5000 6000 7000 8000 9000
Light weight [t]
L/B
& B
/T
L/B B/T
September 12, 2006 83
Pontoon dimensions (2/2)
y = 0.4664xR2 = 0.9597
01,000
2,0003,000
4,0005,000
6,0007,000
8,0009,000
10,000
0 5,000 10,000 15,000 20,000 25,000
BLD [m3]
Lig
ht w
eigh
t [t]
September 12, 2006 84
Simple Plan
September 12, 2006 85
Backhoe dredger
September 12, 2006 86
Example 3
• A backhoe dredger have to dredge 500 m3/in fine sand with a SPE of .7MJ/m3.
• Calculated the Bucket size and cylinder forces
September 12, 2006 87
Fill Degree & Bulk factor
Soil type Filling degree Bulking factor Soft clay 1.5 1.1 Hard clay 1.1 1.3 Sand & Gravel 1 1.05 Rock; well blasted 0.7 1.5 Rock, unblasted 0.5 1.7
September 12, 2006 88
Dredge Cycle
• Cycle times of the bucket depends on the dredging depth and soil type, but are in the order between 20 and 40 seconds.
• The cycle consists of:• • Digging• • Lifting and swinging• • Dumping• • Swinging and lowering• • Positioning.
September 12, 2006 89
Crane weight versus bucket size for soft soil
y = -7E-06x2 + 0.0494x + 1.5486R2 = 0.9778
0
5
10
15
20
25
30
0 100 200 300 400 500 600
Crane weight [ton]
Buc
ket s
ize
[m3]
bucket2
September 12, 2006 90
Required power
Liebherr Excavators
y = 4.4679xR2 = 0.9936
0
500
1000
1500
2000
2500
0 100 200 300 400 500 600
Crane weight [tons]
Pow
er [k
W]
September 12, 2006 91
Relation for existing dredgers
0.00
200.00
400.00
600.00
800.00
1000.00
1200.00
0.00 5.00 10.00 15.00 20.00
Bucket size [m3]
Inst
alle
d po
wer
[kW
]
Rock buckets
September 12, 2006 92
Light weight pontoon
0
200
400
600
800
1000
1200
1400
1600
1800
0 250 500 750 1,000 1,250
Total installed power [kW]
Lig
ht w
eigh
t [t]
September 12, 2006 93
Pontoon volume
y = 0.4713xR2 = 0.6122
0200
400600
8001000
12001400
16001800
0 500 1000 1500 2000 2500 3000
LBD [m3]
Lig
ht w
eigh
t [t]
September 12, 2006 94
Ships numbers for BHD
0.001.002.003.004.005.006.007.008.009.00
0 200 400 600 800 1,000 1,200 1,400 1,600 1,800
Light weight [t]
L/B
& B
/t
L/B B/T
September 12, 2006 95
Simple Plan
September 12, 2006 96
Newer ideas can be discussed
September 12, 2006 97
The shallow draught TSHD
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