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
2
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”
3
Definition of nautical bottomMud and ship behaviourPresent proceduresDevelopment of rheological criterionUseful configurations
4
Definition of nautical bottomMud and ship behaviourPresent proceduresDevelopment of rheological criterionUseful configurations
5
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”
6
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:
?
7
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!
8
Definition of nautical bottomMud and ship behaviourPresent proceduresDevelopment of rheological criterionUseful configurations
9
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!
10
-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
-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
12
Onderzoek nautische bodem in WL
13
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!
14
Definition of nautical bottomMud and ship behaviourPresent proceduresDevelopment of rheological criterionUseful configurations
15
Survey methods• Important parameters for ship behaviour:
– Rheologic characteristics– Density
• Required:
unambiguous, simple survey method
16
Survey methods• Echosounding
• Density
• Rheology
17
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
18
Survey methods• Density
– Common practice in most harbours
with muddy bottoms– Relatively simple measurement– Continous or point measurements
19
Survey methods• Density
– Mostly based on correlation with rheology– No universal relationship density – rheology
(mud/sand content, organic fraction, …)– Not always increasing with depth
20
Survey methods• Densiteit
21
Survey methods• Echo sounding
• Density
• Rheology
22
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
23
• rheologie
200 kHz
rheological transition
1987
yield stress
de
pth
200 kHz
1997
rheological transition 1
rheological transition 2
24
Definition of nautical bottomMud and ship behaviourPresent proceduresDevelopment of rheological criterionUseful configurations
25
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
26
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
27
Captive model tests
Mathematical manoeuvring simulation model
• Test variables:
– ship models:
6000 TEU container carrier
bulk carrier
8000 TEU container carrier
• Test variables:
– ship models
– bottom conditions:
layer thickness: 0.5 m - 3.0 m
density: 1100 - 1250 kg/m³
viscosityWATER
MUD
HARD BOTTOM
• 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)
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
Test section (44 m)
mud reservoir
water reservoir
EXPERIMENTAL PROGRAM
33
Mathematical manoeuvring simulation models
Real-time simulations
-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
35
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
36
Definition of nautical bottomMud and ship behaviourPresent proceduresDevelopment of rheological criterionUseful configurations
37
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
38
39
Development of rheological criterion• Controllability requirements (mainly container carriers):
– Controllability of forward speed
– Course stability
– Manoeuvrability at low speed
40
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
41
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
42
Development of rheological criterion• Controllability requirements (mainly container carriers):
– Manoeuvrability at low speed
TUG ASSISTANCE
ARRIVAL/ DEPARTURE BERTH
43
Development of rheological criterion• Controllability requirements (mainly container carriers):
– Manoeuvrability at low speed
TUG ASSISTANCE:BEND AT OLD BREAKWATER
44
Development of rheological criterion• Controllability requirements (mainly container carriers):
– Manoeuvrability at low speed
TUG ASSISTANCE: TURNING MANOEUVRE
45
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
46
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
47
Definition of nautical bottomMud and ship behaviourPresent proceduresDevelopment of rheological criterionUseful configurations
48
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
49
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
50
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
51
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
52
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
53
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
54
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
55
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)
56
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?
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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