Cfd&nb mv08122010
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Transcript of Cfd&nb mv08122010
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Navigating through mud:beyond physical modelling
Marc Vantorre Maritime Technology Division, Ghent University
Knowledge Centre ‘Manoeuvring in Shallow and Confined Water (Flanders Hydaulics Reseach, Antwerp)
HSB Workshop, Antwerp, 8 December 2010
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Definitie van de nautische bodem
• PIANC WG30 (1997):the level where physical characteristics of the bottom
reach a critical limit
beyond which contact with a ship’s keel causes
either damage
or unacceptable effects on controllability and manoeuvrability
• Principe: “Blijf van de bodem”
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Definition of nautical bottomMud and ship behaviourPresent proceduresDevelopment of rheological criterionUseful configurations
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Definition of nautical bottomMud and ship behaviourPresent proceduresDevelopment of rheological criterionUseful configurations
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Definition of nautical bottom
• PIANC WG30 (1997):the level where physical characteristics of the bottom
reach a critical limit
beyond which contact with a ship’s keel causes
either damage
or unacceptable effects on controllability and manoeuvrability
• Principle: “Don’t touch the bottom”
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Definition of nautical bottom
• PIANC WG30 (1997):the level where physical characteristics of the bottom
reach a critical limit
beyond which contact with a ship’s keel causes
either damage
or unacceptable effects on controllability and manoeuvrability
• Advantage: generally applicable:
?
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Definition of nautical bottom
• PIANC WG30 (1997):the level where physical characteristics of the bottom
reach a critical limit
beyond which contact with a ship’s keel causes
either damage
or unacceptable effects on controllability and manoeuvrability :
• Difficulty: practical application:– Which physical characteristic?– How to determine critical limit?– Relevance for ship behaviour!
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Definition of nautical bottomMud and ship behaviourPresent proceduresDevelopment of rheological criterionUseful configurations
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Mud and ship behaviour
• Interface water – mud Internal wave generationRelative motion of ship with respect to water and mud layersMainly determined by DENSITY of mud layer Important for navigation above and through mud layers!
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-5
-4.5
-4
-3.5
-3
-2.5
-2
-1.5
-1
-0.5
0
-1 -0.5 0 0.5 1 1.5
inte
rface p
osit
ion
ab
ove s
olid
bo
tto
m (
m)
-12%
-7%+4%
+10%
Layer thickness: 3.0 m
Density: 1100 kg/m³
Ship’s speed: 5 knots
UKC to interface:
Mud and ship behaviour
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-5
-4.5
-4
-3.5
-3
-2.5
-2
-1.5
-1
-0.5
0
-1 -0.5 0 0.5 1 1.5
inte
rface p
osit
ion
ab
ove s
olid
bo
tto
m (
m)
-12%
-7%+4%
+10%
Layer thickness: 3.0 m
Density: 1100 kg/m³
Ship’s speed: 10 knots
UKC to interface:
Mud and ship behaviour
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Onderzoek nautische bodem in WL
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Mud and ship behaviour
• Interface water – mud Internal wave generationRelative motion of ship with respect to water and mud layersMainly determined by DENSITY of mud layer Important for navigation above and through mud layers!
• Rheological characteristics of mud Non-newtonian Thixotropic: relationship shear rate / shear stress depends
on recent history Mainly important for navigation through mud layers!
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Definition of nautical bottomMud and ship behaviourPresent proceduresDevelopment of rheological criterionUseful configurations
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Survey methods• Important parameters for ship behaviour:
– Rheologic characteristics– Density
• Required:
unambiguous, simple survey method
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Survey methods• Echosounding
• Density
• Rheology
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Survey methods• Echo sounding
– High frequency (210 kHz)
“top mud”– Low frequency (33 kHz)
consolidated mud
mostly lower than nautical
bottom
210 kHz
33 kHz
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Survey methods• Density
– Common practice in most harbours
with muddy bottoms– Relatively simple measurement– Continous or point measurements
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Survey methods• Density
– Mostly based on correlation with rheology– No universal relationship density – rheology
(mud/sand content, organic fraction, …)– Not always increasing with depth
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Survey methods• Densiteit
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Survey methods• Echo sounding
• Density
• Rheology
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Survey methods• rheology
– In principal, best suited as criterion for nautical bottom– Practical issues:
• Complex rheology
difficult to characterize by a limited number of parameters (at
least 4)
thixotropy: disturbing mud modifies characteristics
• Dependent on equipment and measuring procedure
– Criterion?• Relative (rheological transition)• Absolute
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• rheologie
200 kHz
rheological transition
1987
yield stress
de
pth
200 kHz
1997
rheological transition 1
rheological transition 2
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Definition of nautical bottomMud and ship behaviourPresent proceduresDevelopment of rheological criterionUseful configurations
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Present procedure in Zeebrugge• Till 2004: density 1150 kg/m³
(cf. rheological transition)
Rheological transition lower than 1.15 t/m³ horizon
Rheological transition higher than 1.15 t/m³ horizon
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Present procedure in Zeebrugge• Since 2004:
– Density 1200 kg/m³– Additional operational parameters:
• Minimum under keel clearance of 10% of draft relative to nautical bottom
• Maximum penetration of keel in upper mud layer of 7% (12%) of draft if sufficient tug assistance is available
– Based on simulations of arriving and departing container carriers by coastal pilots on the ship manoeuvring simulator at Flanders Hydraulics Research, with simulation models based on systematic captive model tests
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Captive model tests
Mathematical manoeuvring simulation model
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• Test variables:
– ship models:
6000 TEU container carrier
bulk carrier
8000 TEU container carrier
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• Test variables:
– ship models
– bottom conditions:
layer thickness: 0.5 m - 3.0 m
density: 1100 - 1250 kg/m³
viscosityWATER
MUD
HARD BOTTOM
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• Mud simulating material = mixture of:
2 chlorinated paraffins
petroleum
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
0.50
1.05 1.1 1.15 1.2 1.25 1.3
density (ton/m³)
dyna
mic
vis
cosi
ty (
Pa
s)
observations CDNBobservations Albert II Dockobservations swinging area IFHR 2004MARIN 1976FHR 1988FHR 1988 (natural)
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3.0 m 1.5 m 0.75 m +10% +15% +26% +32% +10% +15% +26% +32% +10% +15% –12% –7% +4% +10% –1% +4% +15% +21% +4% +9% Mud layer thickness: 3.0 m
+10% +15% +26% +32%
-12% -7% +4% +10% +10% +15% +26% +32%
-1% +4% +15% +21%
Mud layer thickness: 1.5 m
+10% +15%
+4% +9%
Mud layer thickness: 0.75 m
Layer thickness
UKC relative to solid bottom
UKC relative to mud-water interface
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Test section (44 m)
mud reservoir
water reservoir
EXPERIMENTAL PROGRAM
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Mathematical manoeuvring simulation models
Real-time simulations
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-15.0%
-10.0%
-5.0%
0.0%
5.0%
10.0%
15.0%
20.0%
25.0%
30.0%
35.0%
0.95 1 1.05 1.1 1.15 1.2 1.25 1.3
und
er
kee
l cle
ara
nce
to w
ate
r-m
ud
inte
rfa
ce
density (t/m³)
extra tug assistanceOVERALL
Wind E, 6 Bf
-15.0%
-10.0%
-5.0%
0.0%
5.0%
10.0%
15.0%
20.0%
25.0%
30.0%
35.0%
0.95 1 1.05 1.1 1.15 1.2 1.25 1.3
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Present procedure in Zeebrugge+ Survey technique rather simple+ Accounts for behaviour and controllability of ship
- Rather pragmatic- Rheology is only implicitly taken into account, via density- Mathematical models are based on model tests
above/through a homogeneous “mud” layer- Survey with towed density probe not possible
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Definition of nautical bottomMud and ship behaviourPresent proceduresDevelopment of rheological criterionUseful configurations
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Development of rheological criterion• Characteristic of mud layer relevant for effect of contact
between keel and mud due to:– Damage (not probable) or– Uncontrollable behaviour
rheological properties probably dominant• Survey procedure should be based on:
– Mud characteristics with relevant effect on controllability of deep drafted vessels
– Survey methods to measure these characteristics in an unambiguous, simple way
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Development of rheological criterion• Controllability requirements (mainly container carriers):
– Controllability of forward speed
– Course stability
– Manoeuvrability at low speed
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Development of rheological criterion• Controllability requirements (mainly container carriers):
– Controllability of forward speed• Deceleration at arrival
• Acceleration at departure
(cf. cross current)
• Dependent of:
Resistance
Propulsion characteristics
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Development of rheological criterion• Controllability requirements (mainly container carriers):
– Course stability• Entering / leaving breakwaters
• Without tug assistance
• Rectilinear track without excessive use
of rudder
• Lateral force & yawing moment due to
forward speed + sway/yaw motion
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Development of rheological criterion• Controllability requirements (mainly container carriers):
– Manoeuvrability at low speed
TUG ASSISTANCE
ARRIVAL/ DEPARTURE BERTH
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Development of rheological criterion• Controllability requirements (mainly container carriers):
– Manoeuvrability at low speed
TUG ASSISTANCE:BEND AT OLD BREAKWATER
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Development of rheological criterion• Controllability requirements (mainly container carriers):
– Manoeuvrability at low speed
TUG ASSISTANCE: TURNING MANOEUVRE
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Development of rheological criterion• Controllability requirements (mainly container carriers):
– Manoeuvrability at low speed• With own rudder, propeller, bow/stern thrusters
• With tug assistance
• Cf. forces/moments due to pure sway and yaw
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Development of rheological criterion• Additional research
– By means of model tests: not (directly) feasible• Scale effects
• Selection of mud simulation material
– Numerical models• Complete CFD-modelling: very ambitious
• Simplified, relevant configurations
• More insight into relevance of mud characteristics with respect to ship behaviour
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Definition of nautical bottomMud and ship behaviourPresent proceduresDevelopment of rheological criterionUseful configurations
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Useful configurations: overview
• Forces due to direct contact mud – keel
direct effect of mud characteristics
selection of criterion for nautical bottom
• Ship manoeuvres in mud layer with depth dependent characteristics:
which part of mud layer will not be brought into motion?
indirect determination of nautical bottom
more direct link with practice
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Useful configurations: direct contact
• Forces on a flat plate: frictional resistance– Flow parallel to a flat plate with zero thickness, infinite width and
limited length (cf. Froude experiments)– Flow parallel to a flat keel shaped plate with zero thickness from
different inflow angles
in different fluids:– Water (reference)– Homogeneous mud layers with constant rheological
characteristics– Initially homogeneous mud layers with thixotropic characteristics
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Useful configurations: direct contact
• Forces on a keel structure: viscous pressure resistance (form resistance)– Flow along a simplified keel structure from different inflow angles
in different fluids:– Water (reference)– Homogeneous mud layer with constant rheological characteristics– Initially homogeneous mud layers with thixotropic characteristics
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Useful configurations: indirect effect
• Flow as a result of navigating/manoeuvring ship with certain under keel clearance above– Mud with characteristics in the nautical bottom range– Solid bottom
• Simplified configurations:– Complexity– Calculation time– More insight into parameters
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Useful configurations: indirect effect
• Lateral motion of a ship section (2D)– Above solid bottom (reference)– Above/through homogeneous mud layers with constant rheological
characteristics– Above/through mud layers with thixotropic characteristics– Above/through mud layers with depth dependent density and
rheology
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Useful configurations: indirect effect
• Longitudinal motion of a ship– Ship with forward speed above/through mud layer
wave generation in interface:
function of speed, depth to interface, mud density,
under keel clearance, hull form …
simplified calculations
boundary conditions for CFD calculations– Configurations: same as lateral motion
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Further research
• Rudder and propeller behaviour– Essential for manoeuvring and controllability– Essential for determining operational limits– Secundary effect on determination of nautical bottom– Later stage
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Conclusion: Required expertise
A. Rheology of sediments and mud: theoretical base and numerical modelling
B. CFD: Numerical fluid dynamics for non-newtonian fluids with time dependent characteristics (thixotropy)
C. Manoeuvring behaviour: Mathematical modelling and simulation of ship manoeuvres in muddy areas
D. Experimental research and measuring techniques with respect to mud characteristics (lab scale & in situ)
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Conclusion
Model tests: • Wave generation• Overall effect of mud layers on ship behaviour• Operational conditions• Rheology??
Numerical methods:• Account for all characteristics• Micro-scale• Calculation time?• Validation?
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Navigating through mud:beyond physical modelling
Marc Vantorre Maritime Technology Division, Ghent University
Knowledge Centre ‘Manoeuvring in Shallow and Confined Water (Flanders Hydaulics Reseach, Antwerp)
HSB Workshop, Antwerp, 8 December 2010