numerical modelling of marine structure behaviours in ... · exp qale-fem 28.5cm below mwl 8.5cm...
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Numerical Modelling of Marine
Structure Behaviours in Steep
Waves
Q.W. Ma and S. Yan
City, University of London
The 136 meter long cargo vessel Mustafa
Kan sank in the Mediterrean Sea. The
Mustafa Kan ….. suffered water ingress in
the engine room from Shipwreck Log. Sept.
2016.
North Sea oil rig battered by waves due to
massive storm swells over the North Sea on
January 10 2015 (BBC News put on YouTube)
One person died and two other were injured
after a large wave hit a semi-submersible
drilling rig operating in the North Sea on 30
Dec 15 from gCaptain
Introduction - Some Recent Marine Incidents
Introduction – question to be asked What went wrong, causing the incidents?
Waves used for design are different from the real waves
Not real spectrum (statistics or not resolved)
Symmetrical design wave
Linear and/or steady survival wave
Current just changing encountered frequency
No effects of wind on waves
Not aware the waves coming in a short time
and so on
Simplification of Wave-Structure interaction
Invariant wetted body surface
Ignoring viscosity and aeration
Rigid body
Forward speed modelled as current in modelling test
and so on
Introduction – how to answer question
Waves:
Modelling real waves in a sea state in a large scale
Modelling full wave-current interaction
Modelling the seabed effects on waves and spectrum
Predicting the large waves coming in a short period
and so on
How to rectify difference and simplification said above?
Wave-Structure interaction
Modelling fully nonlinear wave-structure interaction (WSI)
Modelling Wave breaking effects on WSI
Considering deformable body
and so on
Bottleneck: Inefficiency and incapacity of existing methods
Numerical Modelling Outline
Next Generation
Numerical Modelling Methods
FNPT NS
Hybrid
QALE-FEM ESBI/
Hybrid
ESBI
MLPG_R OpenFOAM
FEM-MLPG
MLPG-SPH
FEM-CIP
FEM-StarCD
FEM-
OpenFOAM
Fully nonlinear
potential theory
Fully nonlinear
viscous theory
(Navier-Stokes
eq.)
IBM
IBM
Solitary wave on a 3D symm. seabed
Individual overturning waves by QALE-FEM
11 11.5 12 12.5 13 13.50.8
1
1.2
1.4
1.6
1.8
z
x-x0
y=0
y=0.5
y=0.8
y=1.1
Profiles at 9.16
Solitary waves over non-symm. Bed
ccb sykhxxZ )(sec)( 20
Seabed geometry may
lead to very different
overturning waves
Yan, S, and Ma, Q.W. (2010) ‘QALE-FEM for modelling 3D overturning waves’, International Journal for Numerical Methods in Fluids, Vol. 63, pp.743 – 768.
Directional and crossing waves by QALE-FEM
Low pass filtered 0.034Hz
Draupner wave (recorded in the
North Sea on 1st, January, 1995)
1200 Crossing-sea
result is closer to the
features of measured
data than the
following-sea result
Adcock, T., Taylor, P., Yan, S., Ma, Q.W., Janssen, P.A.E.M. (2011) ‘Did the Draupner wave occur in a crossing sea?’,
Proceedings of the Royal Society A, Vol. 467, pp. 3004-3021 (doi:10.1098/rspa.2011.0212).
Current effects on waves by QALE-FEM Focusing waves: N=32, xf = 10, τf = 125, ωmin = 0.8683; ωmax = 1.8825; Af
ranging from 0.002 to 0.1488; Current velocity ranges from -0.25cg to 0.25cg
-0.25 -0.2 -0.15 -0.1 -0.05 0 0.05 0.1 0.15 0.2 0.25
1
1.2
1.4
1.6
1.8
Ucx
/cg
* m
ax/A
f
Af=0.1488
Af=0.128
Af=0.1114
Af=0.074
Af=0.037
Af=0.002
Opposite current
effects waves
significantly, but
depends on the
wave magnitude
For small focusing waves, the stronger current makes the wave steeper but
not significant.
For larger focusing waves, the stronger current may make the wave smaller.
Large scale simulation of random waves by
Hybrid ESBI Method A rogue wave of 2𝐻𝑠, (kH)s=0.05,
based on Wallops spectrum ), 16𝑚𝑖𝑛
for the simulation of 1000T0 on a
workstation (3h real time and 20km if
T0 is 10s)
4 rogue waves in random waves
3.2h for simulating 32 x 32 L0
and 100 T0 ( 10X10 km2 and
23m real time if T0 is 14s)
It is possible to simulate the
case up to 1000 T0 using more
powerful workstation available
today overnight.
Wang, JH, Ma, Q.W. and S. Yan (2016), ‘A hybrid model for simulating rogue waves in random seas on a large temporal and spatial scale’, Journal of
Computational Physics 313: 279–309.
Breaking waves by hybrid MLPG_R coupling with potential model -05
Some results
Total (in hrs)
IMLPG_R 8.27
Hybrid 1.44
Focusing waves
Overturning waves
Overtopping
Sriram, Ma and Schlurmann, ‘A Hybrid Method for Modelling Two Dimensional Non-breaking and Breaking Water Waves’, Journal of Computational Physics
272 (2014), 429–454.
FPSO in shallow water by QALE-FEM
15 20 25 30
-0.1
-0.05
0
0.05
0.1
heave f
orc
e/a
recorded heave force 3rd approximation difference
(b)
Comparison of recorded heave force and the
3rd-order approximation for (b) kd=0.94 (ka =
0. 1254, λ =0.833)
Fig.15 Ratio of the second-order
harmonic amplitude of heave force to
that of the first order
0 1 2 3 4 5 6 7 8 9 100
0.05
0.1
0.15
0.2
k/D
b s
pectr
a
bow
stern
Spectra of relative run-up recorded at the
bow and stern of the FPSO (ka = 0.084,
kd=0.63)
Nonlinearity play important role and 2nd components can be significant Yan, S., Ma, Q.W., Lu, Jinshu, Chen, Shuling, 2010 ‘Fully Nonlinear Analysis on Responses of a Moored FPSO to Waves in Shallow Water’, Proceedings
of ISOPE 2010, ISBN 978-1–880653–77-7, Vol. 1., pp. 501-507
Wigley Hull moving in waves by QALE-FEM
Heave R AO (head s ea, F n=0.2)
0
0.5
1
1.5
0 0.5 1 1.5 2 2.5 3
λ/L
He
av
e /
a
E UT(K ashiwagi,2000)
NS M(K ashiwagi,2000)
E xperiment(K ashiwagi,2000)
BE M(Tanizawa,2001)
QALE -F E M
P itc hR AO (head s ea, F n=0.2)
0
0.5
1
1.5
2
0 0.5 1 1.5 2 2.5 3
λ/L
Pit
ch
/ka
E UT(K ashiwagi,2000)
NS M(K ashiwagi,2000)
E xperiment(K ashiwagi,2000)
BE M(Tanizawa,2001)
QALE -F E M
Length (L): 2m; Breadth: 0.3m and Draft: 0.125m; Fn=0.2
Computational results are very similar to the experimental results
Two ways (Frequency by frequency and random waves) of computing
RAOs give similar results what waves are not large
0.8 1 1.2 1.4 1.6 1.8 20
0.5
1
1.5
2
/L
Pitch R
AO
JONSWAP Spectrum(1.8-2.9)
Single frequency (transient test)
Irregular waves modelling
Moving cylinder in focusing waves by QALE-
FEM Focusing waves: fl = 0.34 Hz to fu = 1.02 Hz. Ga = 0.002 for all 32 components; Cylinder moves towards the wave paddle with speed of 0.25m/s
67 67.2 67.4 67.6 67.8 68 68.2 68.4 68.6 68.8 690
5
10
15
20
25
30
35
40
time(s)
pre
ssure
(100P
a)
Exp
QALE-FEM 28.5cm below MWL
8.5cm below MWL
1.5cm above MWL
60 62 64 66 68 70 72 74 76 78 80
-0.1
-0.05
0
0.05
0.1
time(s)
(
m)
(a)WP6 in line with cylinder
Exp
QALE-FEM
Pressure at three positions
Wave elevation at a point in line with cylinder
P2
P3
P4
Acceptable agreement between the QALE-FEM prediction and the experimental data of the pressure recorded on the cylinder surface and of wave elevation
Yan, S., Ma, Q.W., Sriram, V., Qian, L., Ferrer, P.J.M., Schlurmann, T. (2015), ‘Numerical and Experimental Studies of Moving Cylinder in Uni-directional
Focusing Waves’, Proceedings of ISOPE 2015, Vol. 3 (ISBN 978-1-880653-89-0).
2 Wigley Hulls in Oblique Waves by QALE-FEM
Wavemaker: ω√(d/g)=1.7691, a/d=0.03
Numerical Tank: L/d=15; B/d=6
Distance: 1.5
Motion of small body
is affected by the
larger one
Ma, Q.W., and Yan, S. (2009) ‘QALE-FEM for Numerical
Modelling of Nonlinear Interaction between 3D Moored
Floating Bodies and Steep Waves’, International Journal for
Numerical Methods in Engineering, Vol. 78, pp. 713-756
2 structures in oblique waves by QALE-FEM
0 1 2 3 4 5 6 7 80
0.02
0.04
0.06
heave f
orc
e s
pectr
um
/a
a=0.03
a=0.02
a=0.002
0 1 2 3 4 5 6 7 80
0.02
0.04
0.06
sw
ay f
orc
e s
pectr
um
/a
a=0.03
a=0.02
a=0.002
2nd order > 1st order Nonlinear
components
increase
Load on Barge 1 (smaller) in the cases with different wave
amplitudes ( 30o incident angle, Bg=0.15, ω=1.676)
0 1 2 3 4 50
0.1
0.2
roll
spectr
um
/a
with Barge 2
Without Barge 2
Roll spectra of Barge 1 in beam sea (a=0.02, Bg=0.15, Beam Sea, ω=2.167)
Some mode can be enlarged by
other barge
Yan, S. and Ma, Q.W., Cheng, X. (2011) ‘Fully Nonlinear Hydrodynamic Interaction between Two 3D Floating Structures in Close Proximity’,
International Journal of Offshore and Polar Engineering, Vol. 21, No. 2, pp. 1–8.
Violent wave impact on elastic structures by
MLPG_R method Wave impact on a 2D plate
Deflection of plate largely
similar to experimental data
Deflection of plate makes
waves more complicated
Sriram, V and Ma, Q.W. (2012) ‘Improved MLPG_R method for simulating 2D
interaction between violent waves and elastic structures’, Journal of Computational
Physics, 231 (2012), pp. 7650–7670
Overturning Wave impact on a monopole of
OWE by MLPR_R
12 12.5 13 13.5 14 14.50
0.5
1
Pre
ssure
Point 1
Point 2
Second peak at Point 1 is larger
Point 1 and Point 2, on the front side of the cylinder are assigned to record
pressure; they are 0.1 and 0.3 above the mean water level (MWL).
10 10.5 11 11.5 12 12.5 13 13.5 14 14.50
0.5
1
Pre
ssure
Location A
Location B
Location C
wavemaker
er
1:10
MWL
A
B d
5d 1d 0.5d 2.4d
1d
1.1d
C
Pressure history shape
different for different positions
2-phase modelling of ship section impact
Liang Yang, Hao Yang, Shiqiang Yan and Qingwei Ma (2016) "Numerical Investigation of Water Entry Problems Using IBM Method“, IJOPE Paper No. JC-687
0.2 0.21 0.22 0.23 0.24
0
2
4
6
8
10
12
time(s)
Pre
ssure
(kP
a)
(e)P3
0.2 0.21 0.22 0.23 0.24
0
5
10
15
20
25
time(s)
forc
e(N
)(f)F3
IBM
OpenFOAM
Experiment
• IBM results agree well with experimental data
• Entrapped air bubbles are well predicted by the IBM but are not resolved in the OpenFOAM
Exp: t ≈ 0.24s
Exp: t ≈ 0.26s
Dropping height: 300mm
Summary
I. There are still many challenges in marine engineering which affect safe operation and adequate design.
II. We have tried to develop next generation tools/methods for modelling waves and wave-structure interaction to tackle the challenges.
III. The results obtained so far by using fully nonlinear potential methods, full nonlinear viscous methods and hybrid methods show that
– Possible to simulate large waves in large scale
– Possible to simulate interaction between steep/breaking waves and structures
– On the way to desirably tackle the existing challenges but a long way to go
Thank You
Acknowledgement • Supported by
EPSRC projects
(EP/L01467X/1,
EP/N008863/1 and
EP/M022382/1)
• Some results are
produced by Prof.
Sriram V (IIT
Madras, India), Dr.
Jinghua Wang, Dr.
Juntao Zhou, Dr.
Liang Yang in the
same team