fem simulations of non-linear interactions of waves and ... · triangular 6-node prism element 6 5...
TRANSCRIPT
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1
FEM Simulations of Non-linear Interactions of Waves and Floating Structures
by
Professor Guo Xiong Wu
The LRET Research CollegiumSouthampton, 11 July – 2 September 2011
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Professor G. X. Wu Department of Mechanical Engineering
University College [email protected]
FEM simulation of nonlinear interactions of waves and floating structures in the context of carbon capture and transportation into ocean spaces
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Governing Equations and Boundary Conditions
The fluid is assumed to be incompressibleand inviscid,and the flow is irrotational.
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On the free surface:
On the body surface:
nU
n
,xDt
Dx
,yDt
Dy
,zDt
Dz
221 gz
DtD
Pressure p=0Governing equation: 02
Fully nonlinear solution
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Mesh Generation
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Element types
8-node quadrilateral element
(-1,0)
(-1,1)(0,1)
(1,1)
(1,0)
(-1,1)(0,-1)
(-1,-1)
7
68
4 3
251
o
20-node brick element
16 15
1413
2019
1817
8 7
65
12
11
10
4 3
9 21
(-1,0,-1)
(-1,0,1)
(1,1,-1)
(1,-1,-1)
(1,1,-1)
(1,1,1)
Triangular 6-node prism element
6
5
4
3
2
1
3-node triangular element
3
21
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The fluid domain is subdivided into many simplezones, in which mesh may be generated moreeasily. A multi-block mesh is then generated byunifying all grids in the simple zones together;
The numbers of nodes on the boundary of eachzone should be provided.
Multi-block structured meshes
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Multi-block structured meshes…
Mesh 5
Mesh 1
Mesh 2
Mesh 3
Mesh 4
A multi-block mesh for a circular cylinder formed by combining five simple meshes together
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Multi-block structured meshes…
Mesh for two circular cylinders (8-node quadrilateral element)
Mesh for four circular cylinders (8-node quadrilateral element)
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Multi-block structured meshes…
Mesh for five floating semicircular cylinders (8-node quadrilateral element)
Mesh for eight floating rectangular cylinders (8-node quadrilateral element)
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Multi-block Structured Meshes…
3D mesh for a twin Wigley ship (20-node brick element)
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Delaunay and tri-tree methods: only requiresboundary information including nodes andelement numbers.
Unstructured meshes
2D unstructured meshes
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a) To improve the numerical stability;
b) To use 2-D smoothing techniques.
•Using hybrid mesh:
Unstructured meshes…
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Unstructured Meshes…(a)
(b)
(a) Unstructured mesh without smoothing; (b) Hybrid mesh with smoothing applied within structured mesh (Wu, Ma & Eatcok Taylor 1996, 21st ONR, Trondheim)
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Unstructured meshes…
Seven truncated cylinders (6-node prism element)(Wang & Wu, J.Fluids & Strus 2006)
Seven bottom-mounted cylinders (6-node prism element)
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Finite Element Method
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p
SJJ
JJpIS
nI
SJJ
JJI SIdNfNdSfNdNN
pn
p
J
JJ zyxN ,,
Velocity potential is written in terms of the shape functions:
02 dNI
The Galerkin method:
Discretised equation after using the Green’s identity:
Discretisation of equation
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BA
pI SI 321 ,,
ppJIIJ SJSIdNNA
and
p
SJJ
JJpIS
nII SIdNfNdSfNB
pn
Matrix form of the equation
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Direct method: the Gaussian elimination orCholesky method is employed to solve thelinear (sparse and) symmetric system andCuthill-McKee method to optimize bandwidth;
Iterative method: the conjugate gradientmethod with a symmetric successive overrelaxation (SSOR) preconditioner is used andonly nonzero elements in the stiffness matrixare stored.
Solve the linear system
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Calculate first-order (velocity) and second- order derivatives
Method by differentiating the shape function;
Difference method;
Galerkin method (Global projection method).
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n
i
ii
n
i
ii
n
i
ij z
Nzy
Nyx
Nx 111
, ,
i
i
i
i
i
i
N
N
N
zyx
zyx
zyx
zNy
Nx
N 1
where
Method by differentiating the shape functions
(Wang, Wu & Drake, 2007, Ocean Eng.)
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Employ a cubic polynomial to express the velocitypotential along the vertical direction :(Ma, Wu &Eatock Taylor 2001, Int.J. Nume. Meth. in Fluids)
32 dzczbza 232 dzczb
zw
mzim
myi
mxi
kzik
kyi
kxi
lwl
lvlu
lwl
lvlu
On the free surface:
)(),,(z
,y
,x
wvuu
. and + nodesby formed vector a ),1,2,=( of components the
are & , and
ikikl
lllll
k
kz
ky
kxk
ikik
Differential method
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Galerkin method(Wu & Eatock Taylor, App. Ocean Res 1994)
0)( dNu i
}]{[}]{[ BuA
dNNBdNNA jiijjiij
,
.
In matrix form:
where
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Equation to Calculate the Force
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dsngzFbS
t
2
21
0 1 2 3 4 5Time
19
19.25
19.5
19.75
20
20.25
20.5
20.75
21
Forc
e
The Force acting on the body
dsnbS
t
Problems with evaluation of : instability andsawteeth behaviour
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Evaluation of :(Wu, J. Fluids & Strucs. 1998)
t
In the fluid domain : 02 t
On the free surface: gzt 21
On the moving boundary:
)]([.).(
Ur
nnUnrU
nt
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To employ high order shape functions to calculatethe second order derivatives directly.
To introduce auxiliary functions to avoidcalculating the second order derivatives.
Methods to handle the second order derivatives such as in the moving boundary conditionn /
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02 i
ii n
n
0i
0
ni
)6,,2,1( ii
in the fluid domain:
on the body surface:
on the free surface:
on other boundaries:
Introduce auxiliary functions
(Wu & Eatock Taylor 2003, Ocean Eng)
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,6)1,2,( )21(
})()](][)[({
6
1
iACdsn
gz
dsnVrVnrVF
jjij
SS
i
Siii
bf
b
For multiple structures, the force on i-th body:
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Numerical Examples
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Comparison with experiment
2-D floating bodies in forced motions ;
2-D resonance problems (second order & fully nonlinear);
2-D solitary wave problems;
3-D sloshing problems .
Using structured mesh
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The history of irregular wave at x=3.436 for α=0.612 (Solid line: shorter tank L=14.64; Dash line: longer tank L=44.64; +: experimental data from Nestegard, 1999)
The history of irregular wave at x=3.436 for α=0.749 (Solid line: shorter tank L=14.64; Dash line: longer tank L=44.64; +: experimental data from Nestegard, 1999)
Using structured mesh…
The history of irregular wave at x=3.436 for α=0.612 (Solid line: shorter tank L=14.64; Dash line: longer tank L=44.64; +: experimental data from Nestegard, 1999)
The history of irregular wave at x=3.436 for α=0.749 (Solid line: shorter tank L=14.64; Dash line: longer tank L=44.64; +: experimental data from Nestegard, 1999)
Using structured mesh…
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Using structured mesh…
Wave profile at time 0.4s (a) Fully nonlinear result; (b) Experimental result (Retzler et al, 2000); (c) Linear result
Using structured mesh…
Wave profile at time 0.4s (a) Fully nonlinear result; (b) Experimental result (Retzler et al, 2000); (c) Linear result
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Using structured mesh
tAX sin2-D floating bodies in vertical motions
Dimension of trapezoid-shape body
d
b
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Using structured mesh…
t=7T (A=0.4d,Ka=2) t=7.2T (A=0.4d,Ka=2)
t=7.4T (A=0.4d,Ka=2) t=7.6T (A=0.4d,Ka=2)
t=7.8T (A=0.4d,Ka=2) t=8T (A=0.4d,Ka=2)
snapshots of meshes for single cylinder at different time steps (α=75o)
2-D floating bodies in forced motions tAX sin
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Using structured mesh…
2-D floating bodies in forced motions tAX sin
0 2 4 6 8 10-2
-1
0
1
2 (b)
t/T
t/T
/A
Fig. Wave histories at (a) x=-2d and (b) x=-3d (Ka=2.0 and A/d=0.4) FEM; BEM
0 2 4 6 8 10-2
-1
0
1
2 (a)
/A
0 2 4 6 8 10-4
-2
0
2
4 FEM BEM
F/g
Ad
Comparison of vertical forces between the FEM and the BEM at Ka=2.0 and A=0.4d
Comparisons of waves and forces between FEM and BEM
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2-D second-order analysis in time domain: two rectangular cylinders in heave (Wang & Wu, 2008, Ocean Eng.)
Using structured mesh…
tAX sin
Comparison of waves at the right side of cylinder one at the first orderresonant frequency (a) A=0.0125d (b) A=0.025d (c) A=0.05d
0 10 20 30 40-30-20-10
0102030 (c)
t/T
t/T
/A
0 10 20 30 40-30-20-10
0102030 (b)
/A
0 10 20 30 40-30-20-10
0102030
fully nonlinear; linear; linear+second order
(a)
/A
t/T
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Using structured mesh…
Linear free surface profiles at the first order resonant frequency
-5 -4 -3 -2 -1 0 1 2 3 4 5-30
-20
-10
0
10
20 t/T=39.0 t/T=39.2 t/T=39.4 t/T=39.6 t/T=39.8 t/T=30.0
/A
x/
2-D second-order analysis in time domain: two rectangular cylinders in heave (Wang & Wu, 2008, Ocean Eng.)tAX sin
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0 10 20 30 40-3
-2
-1
0
1
2
3 Fully nonlinear Linear Linear plus second order
Comparison of waves at the right side of cylinder one =0.54' and A=0.05d
/A
t/T
(at the second order resonant frequency )
Using structured mesh… 2-D second-order analysis in time domain: two rectangular cylinders
in heave (Wang & Wu, 2008, Ocean Eng.)tAX sin
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Using structured mesh… 2-D fully nonlinear analysis : two rectangular
cylinders in heave (A=0.0125d ) tAX sin
0 50 100 150 200-100
-50
0
50
100
150
Comparion of waves at the right side of cylinder one at the first order resonant frequency
Fully nonlinear Linear Linear+second order
/A
t/T
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Using structured mesh…
Wave profiles at A=0.05d (at the first order resonant frequency)
2-D fully nonlinear analysis : two rectangular cylinders in heave tAX sin
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Using structured mesh…
Waves and forces at the second order resonant frequency
160 180 200-4
-2
0
2
4
F y/gd
A
t/T
t/T160 180 200
-4
-2
0
2
4
F x/gd
A t/T160 180 200
-4
-2
0
2
4
/A
2-D fully nonlinear analysis : two rectangular cylinders in heave (A=0.2d)tAX sin
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Using structured mesh… 2-D fully nonlinear analysis : nine wedge-shaped
cylinders in heave tAX sin
0 10 20 30 40 190 192 194 196 198 200-30
-20
-10
0
10
20
30
40
Histories of hydrodynamic forces at first order resnonat frequency and A=0.005d
F y/gd
A
Cylinder 1 Cylinder 2 Cylinder 3 Cylinder 4 Cylinder 5
t/T
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Using structured mesh… 2-D fully nonlinear analysis : nine wedge-shaped
cylinders in heave tAX sin
0 10 20 30 40 190 192 194 196 198 200-40
-30
-20
-10
0
10
20
30
40
50/
A
Histories of waves at the midpoint of two neighboring cylindersat first order resnonat frequency and A=0.005d
cylinders 1 and 2 cylinders 2 and 3 cylinders 3 and 4 cylinders 4 and 5
t/T
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Using structured mesh… 2-D fully nonlinear analysis : nine wedge-shaped
cylinders in heave tAX sin
Wave profiles at t/T=45, 45.04, 45.08,…,47.32 atA=0.04d.
(at the first order resonant frequency )
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Using structured mesh… 2-D solitary wave problems
Finite element mesh for two solitary waves colliding with each other (8-node quadrilateral element)
![Page 47: FEM Simulations of Non-linear Interactions of Waves and ... · Triangular 6-node prism element 6 5 4 3 2 1 3-node triangular element 3 1 2 The fluid domain is subdivided into many](https://reader036.vdocuments.mx/reader036/viewer/2022062607/604cbd788c46ff603c418010/html5/thumbnails/47.jpg)
Using structured mesh…
2-D solitary wave problems
Wave profiles for two waves colliding with each other(L=10Leff, H1=0.6h, xp1=3Leff, H2=0.2h, xp2=7Leff ,where Leff is the efficient wave length )
![Page 48: FEM Simulations of Non-linear Interactions of Waves and ... · Triangular 6-node prism element 6 5 4 3 2 1 3-node triangular element 3 1 2 The fluid domain is subdivided into many](https://reader036.vdocuments.mx/reader036/viewer/2022062607/604cbd788c46ff603c418010/html5/thumbnails/48.jpg)
Using structured mesh…
2-D solitary wave problems
Wave profiles for one wave overtaking another(L=25Leff, H1=0.6h, xp1=3Leff, H2=0.2h xp2=5Leff )
![Page 49: FEM Simulations of Non-linear Interactions of Waves and ... · Triangular 6-node prism element 6 5 4 3 2 1 3-node triangular element 3 1 2 The fluid domain is subdivided into many](https://reader036.vdocuments.mx/reader036/viewer/2022062607/604cbd788c46ff603c418010/html5/thumbnails/49.jpg)
Using structured mesh…
2-D solitary wave problems
Wave profiles for a solitary wave propagates over a step(a) without step (b) with step
![Page 50: FEM Simulations of Non-linear Interactions of Waves and ... · Triangular 6-node prism element 6 5 4 3 2 1 3-node triangular element 3 1 2 The fluid domain is subdivided into many](https://reader036.vdocuments.mx/reader036/viewer/2022062607/604cbd788c46ff603c418010/html5/thumbnails/50.jpg)
Using structured mesh…
2-D solitary wave problems
35 40 45 50 55 60 65 70 75-0.5
0.0
0.5
1.0
1.5
2.0
/H
Fully nonlinear Computaiton by Seabra-Santos et al (1987) Experiment by Seabra-Santos et al (1987)
Comparison of histories of waves at x=21m(a solitary wave propagates over a step)
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Using structured mesh…
2-D solitary wave problems
0 20 40 60 80-0.2
0.0
0.2
0.4
0.6 0 20 40 60 80-0.2
0.0
0.2
0.4
0.6
(b)
/H
/H
Histories of waves at the (a) left side and (b) right side of the cylinder
H/h=0.1 H/h=0.2 H/h=0.3
(a)
(Interactions of solitary waves with a floating rectangular cylinder)
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Using structured mesh…
2-D solitary wave problems
0 20 40 60 80-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0 0 20 40 60 80-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
F y/gd
HF x/
gdH
H/h=0.1 H/h=0.2 H/h=0.3
Histories of hydrodynamic forces on the cylinder
(Interactions of solitary waves with a floating rectangular cylinder)
![Page 53: FEM Simulations of Non-linear Interactions of Waves and ... · Triangular 6-node prism element 6 5 4 3 2 1 3-node triangular element 3 1 2 The fluid domain is subdivided into many](https://reader036.vdocuments.mx/reader036/viewer/2022062607/604cbd788c46ff603c418010/html5/thumbnails/53.jpg)
Using structured mesh… 3-D sloshing problems (Wu, Ma Eatock Taylor 1998,
Applied Ocean Res)
![Page 54: FEM Simulations of Non-linear Interactions of Waves and ... · Triangular 6-node prism element 6 5 4 3 2 1 3-node triangular element 3 1 2 The fluid domain is subdivided into many](https://reader036.vdocuments.mx/reader036/viewer/2022062607/604cbd788c46ff603c418010/html5/thumbnails/54.jpg)
Using structured mesh…
Snapshots of free surface in some cases
3-D sloshing problems (Wu, Ma Eatock Taylor 1998, Applied Ocean Res)
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2-D wave-making problem;
2-D wave radiation by floating wedged-shape bodies;
2-D solit
3-D large amplitude motions of vertical cylinders and motions of a floating FPSO;
3-D wave-making problem for non-wall-sided cylinders;
3-D second-order diffraction by multiple cylinders in the time domain;
3-D wave-making problem for multiple cylinders;
3-D wave radiation by multiple cylinders.;
Using unstructured mesh
![Page 56: FEM Simulations of Non-linear Interactions of Waves and ... · Triangular 6-node prism element 6 5 4 3 2 1 3-node triangular element 3 1 2 The fluid domain is subdivided into many](https://reader036.vdocuments.mx/reader036/viewer/2022062607/604cbd788c46ff603c418010/html5/thumbnails/56.jpg)
o
y
x
h
L
Sketch of a tank
Wave maker
Using unstructured mesh…
)/,/5539.1 ,sin( ghthgtAX
2-D wave-making problems (Wang & Wu 2006, J. Fluids & Strucs.)
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0 5 10 15 20 25-0.10
-0.05
0.00
0.05
0.10
0.15 Fully nonlinear Linear Linear plus second order
Comparison of wave histories at x=1.167h (A/h=0.05)
/h
Using unstructured mesh…
2-D wave-making problems (Wang & Wu, 2006)
Wave profile in the tank at =24.26 (A/h=0.1)
![Page 58: FEM Simulations of Non-linear Interactions of Waves and ... · Triangular 6-node prism element 6 5 4 3 2 1 3-node triangular element 3 1 2 The fluid domain is subdivided into many](https://reader036.vdocuments.mx/reader036/viewer/2022062607/604cbd788c46ff603c418010/html5/thumbnails/58.jpg)
Using unstructured mesh…
Wave profile at τ=58.63 (a wedged-shape body in the tank)
2-D wave-making problems (Wang & Wu, J. Fluids & Struc. 2006)
![Page 59: FEM Simulations of Non-linear Interactions of Waves and ... · Triangular 6-node prism element 6 5 4 3 2 1 3-node triangular element 3 1 2 The fluid domain is subdivided into many](https://reader036.vdocuments.mx/reader036/viewer/2022062607/604cbd788c46ff603c418010/html5/thumbnails/59.jpg)
Using unstructured mesh…
2-D wave radiation by floating wedged-shape bodies (Wang & Wu 2006, J. Fluids & Strus.)
a
Sketch of a floating wedge
d
)/ ,sin,2( hgtAYdh
![Page 60: FEM Simulations of Non-linear Interactions of Waves and ... · Triangular 6-node prism element 6 5 4 3 2 1 3-node triangular element 3 1 2 The fluid domain is subdivided into many](https://reader036.vdocuments.mx/reader036/viewer/2022062607/604cbd788c46ff603c418010/html5/thumbnails/60.jpg)
Using unstructured mesh…
Single wedge )75,4.0,2( odA
2-D wave radiation by floating wedged-shape bodies (Wang & Wu 2006, J. Fluids & Strucs.)
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Twin wedges )75,1.0,2( odA
2-D wave radiation by floating wedged-shape bodies (Wang & Wu 2006, J. Fluids & Strucs.)
Using unstructured mesh…
![Page 62: FEM Simulations of Non-linear Interactions of Waves and ... · Triangular 6-node prism element 6 5 4 3 2 1 3-node triangular element 3 1 2 The fluid domain is subdivided into many](https://reader036.vdocuments.mx/reader036/viewer/2022062607/604cbd788c46ff603c418010/html5/thumbnails/62.jpg)
3-D large motions of vertical cylinders (Wu & Hu, 2004,Proc. Roy. Soc. London)
Wave profiles by two cylinders undergoing periodic oscillation at t=T, 2T, …, 6T
Using unstructured mesh…
![Page 63: FEM Simulations of Non-linear Interactions of Waves and ... · Triangular 6-node prism element 6 5 4 3 2 1 3-node triangular element 3 1 2 The fluid domain is subdivided into many](https://reader036.vdocuments.mx/reader036/viewer/2022062607/604cbd788c46ff603c418010/html5/thumbnails/63.jpg)
0 10 20 30 40 50 600
5
10
15x/a
t
Time history of the displacement of the FPSO at A =0.01h
Wave profile around a FPSO
Motions of a FPSO in a tank (Wu & Hu 2004, Proc. Roy. Soc. London)
Using unstructured mesh…
![Page 64: FEM Simulations of Non-linear Interactions of Waves and ... · Triangular 6-node prism element 6 5 4 3 2 1 3-node triangular element 3 1 2 The fluid domain is subdivided into many](https://reader036.vdocuments.mx/reader036/viewer/2022062607/604cbd788c46ff603c418010/html5/thumbnails/64.jpg)
0.25hcylinder
Dimension of truncated cylinder with flare
still water surface
a
0.25h
3-D wave-making problem for non-wall-sided cylinders (Wang, Wu & Drake, Ocean Eng. 2007)
Using unstructured mesh…
![Page 65: FEM Simulations of Non-linear Interactions of Waves and ... · Triangular 6-node prism element 6 5 4 3 2 1 3-node triangular element 3 1 2 The fluid domain is subdivided into many](https://reader036.vdocuments.mx/reader036/viewer/2022062607/604cbd788c46ff603c418010/html5/thumbnails/65.jpg)
Using unstructured mesh…
Sketch of a 3-D tank)sin,1416.0,7,72.0,12( tAXhrhLhBhL wc
3-D wave-making problem for non-wall-sided cylinders (Wang, Wu & Drake, Ocean Eng. 2007)
![Page 66: FEM Simulations of Non-linear Interactions of Waves and ... · Triangular 6-node prism element 6 5 4 3 2 1 3-node triangular element 3 1 2 The fluid domain is subdivided into many](https://reader036.vdocuments.mx/reader036/viewer/2022062607/604cbd788c46ff603c418010/html5/thumbnails/66.jpg)
Using unstructured mesh…
0 10 20 30 40 50 60-2
-1
0
1
2
=80o
=75o
Comparison of wave histories for two bottom mounted cylinders at A/h=0.04(=2,x=Lwc-2r)
/A
3-D wave-making problem for non-wall-sided cylinders (Wang, Wu & Drake, Ocean Eng. 2007)
![Page 67: FEM Simulations of Non-linear Interactions of Waves and ... · Triangular 6-node prism element 6 5 4 3 2 1 3-node triangular element 3 1 2 The fluid domain is subdivided into many](https://reader036.vdocuments.mx/reader036/viewer/2022062607/604cbd788c46ff603c418010/html5/thumbnails/67.jpg)
Using unstructured mesh…
Free surface around the cylinder (α=75o)
3-D wave-making problem for non-wall-sided cylinders (Wang, Wu & Drake, Ocean Eng. 2007)
![Page 68: FEM Simulations of Non-linear Interactions of Waves and ... · Triangular 6-node prism element 6 5 4 3 2 1 3-node triangular element 3 1 2 The fluid domain is subdivided into many](https://reader036.vdocuments.mx/reader036/viewer/2022062607/604cbd788c46ff603c418010/html5/thumbnails/68.jpg)
Using unstructured mesh…
1
2
3
y
xo
aLcy
4
Incident waves
Four-cylinder cases
A1 B1
A2
B2
A3B3
A4
B4
Four-cylinder cases at the second order trapped mode frequency (Wang & Wu 2006, J. Fluids & Strucs.)
![Page 69: FEM Simulations of Non-linear Interactions of Waves and ... · Triangular 6-node prism element 6 5 4 3 2 1 3-node triangular element 3 1 2 The fluid domain is subdivided into many](https://reader036.vdocuments.mx/reader036/viewer/2022062607/604cbd788c46ff603c418010/html5/thumbnails/69.jpg)
Using unstructured mesh…
Four-cylinder cases at the second order trapped mode frequency (Wang & Wu 2006, J. Fluids & Strucs.)
10 15 20-4
-2
0
2
4(a)
/A
t/T10 15 20
-4
-2
0
2
4
t/T
/A
(b)
10 15 20-4
-2
0
2
4
t/T
/A
(e)
(d)(c)
10 15 20-4
-2
0
2
4
t/T
/A
10 15 20-4
-2
0
2
4
t/T
/A
10 15 20-4
-2
0
2
4
Wave histories for cylinders one, two and three at k0a=0.468(a) A1; (b) B1; (c) A2; (d) B2; (e) B3; (f) A3
linear; second order; linear plus second order
t/T
/A
(f)
![Page 70: FEM Simulations of Non-linear Interactions of Waves and ... · Triangular 6-node prism element 6 5 4 3 2 1 3-node triangular element 3 1 2 The fluid domain is subdivided into many](https://reader036.vdocuments.mx/reader036/viewer/2022062607/604cbd788c46ff603c418010/html5/thumbnails/70.jpg)
Using unstructured mesh…
Four-cylinder cases at the second order trapped mode frequency(Wang & Wu 2006, J. Fluids & Strucs.)
10 15 20-10-505
10
Histories of force and moment on cylinder two at k0a=0.468 linear; linear plus second order
t/T
Mx/
ga3 A
10 15 20-4-2024
t/T
F y/ga
2 A
10 15 20-15-10-505
1015
t/T
My/
ga3 A
10 15 20-10-505
10
t/T
F x/ga
2 A
![Page 71: FEM Simulations of Non-linear Interactions of Waves and ... · Triangular 6-node prism element 6 5 4 3 2 1 3-node triangular element 3 1 2 The fluid domain is subdivided into many](https://reader036.vdocuments.mx/reader036/viewer/2022062607/604cbd788c46ff603c418010/html5/thumbnails/71.jpg)
Using unstructured mesh…
Four-cylinder cases at the second order trapped mode frequency (Wang & Wu 2006, J. Fluids & Strucs.)
Wave profiles at t=16T(a) linear; (b) linear plus second order
(a) (b)
![Page 72: FEM Simulations of Non-linear Interactions of Waves and ... · Triangular 6-node prism element 6 5 4 3 2 1 3-node triangular element 3 1 2 The fluid domain is subdivided into many](https://reader036.vdocuments.mx/reader036/viewer/2022062607/604cbd788c46ff603c418010/html5/thumbnails/72.jpg)
Using unstructured mesh…
3-D wave-making problem for multiple cylinders (Wang & Wu 2010, Ocean Eng)
Sketch of the 3-D tank
![Page 73: FEM Simulations of Non-linear Interactions of Waves and ... · Triangular 6-node prism element 6 5 4 3 2 1 3-node triangular element 3 1 2 The fluid domain is subdivided into many](https://reader036.vdocuments.mx/reader036/viewer/2022062607/604cbd788c46ff603c418010/html5/thumbnails/73.jpg)
Using unstructured mesh…
3-D wave-making problem for multiple cylinders.
Wave profile at τ=127.8 and A=0.02h
(Seven cylinder cases , r=0.1416, B=20r, h=1.0, L=18)
![Page 74: FEM Simulations of Non-linear Interactions of Waves and ... · Triangular 6-node prism element 6 5 4 3 2 1 3-node triangular element 3 1 2 The fluid domain is subdivided into many](https://reader036.vdocuments.mx/reader036/viewer/2022062607/604cbd788c46ff603c418010/html5/thumbnails/74.jpg)
Using unstructured mesh… 3-D wave-making problem for multiple cylinders
is close to the trapped mode frequency15.2(Seven cylinder cases, r=0.1416,B=20r, h=1.0,L=18)
![Page 75: FEM Simulations of Non-linear Interactions of Waves and ... · Triangular 6-node prism element 6 5 4 3 2 1 3-node triangular element 3 1 2 The fluid domain is subdivided into many](https://reader036.vdocuments.mx/reader036/viewer/2022062607/604cbd788c46ff603c418010/html5/thumbnails/75.jpg)
Using unstructured mesh… 3-D wave-making problem for multiple cylinders
(Seven cylinder cases, r=0.1416,B=20r, h=1.0,L=18)
![Page 76: FEM Simulations of Non-linear Interactions of Waves and ... · Triangular 6-node prism element 6 5 4 3 2 1 3-node triangular element 3 1 2 The fluid domain is subdivided into many](https://reader036.vdocuments.mx/reader036/viewer/2022062607/604cbd788c46ff603c418010/html5/thumbnails/76.jpg)
Using unstructured mesh… 3-D wave-making problem for multiple cylinders
(Seven cylinder cases, r=0.1416,B=20r, h=1.0,L=18)
![Page 77: FEM Simulations of Non-linear Interactions of Waves and ... · Triangular 6-node prism element 6 5 4 3 2 1 3-node triangular element 3 1 2 The fluid domain is subdivided into many](https://reader036.vdocuments.mx/reader036/viewer/2022062607/604cbd788c46ff603c418010/html5/thumbnails/77.jpg)
Using unstructured mesh… 3-D wave-making problem for multiple cylinders
The maximum force is on the middle cylinder (cylinder 4)
(Seven cylinder cases, r=0.1416,B=20r, h=1.0,L=18)
![Page 78: FEM Simulations of Non-linear Interactions of Waves and ... · Triangular 6-node prism element 6 5 4 3 2 1 3-node triangular element 3 1 2 The fluid domain is subdivided into many](https://reader036.vdocuments.mx/reader036/viewer/2022062607/604cbd788c46ff603c418010/html5/thumbnails/78.jpg)
Using unstructured mesh…
3-D wave-making problem for multiple cylinders
(Seven cylinder cases, r=0.1416, B=20r, h=1.0, L=18)
![Page 79: FEM Simulations of Non-linear Interactions of Waves and ... · Triangular 6-node prism element 6 5 4 3 2 1 3-node triangular element 3 1 2 The fluid domain is subdivided into many](https://reader036.vdocuments.mx/reader036/viewer/2022062607/604cbd788c46ff603c418010/html5/thumbnails/79.jpg)
Using unstructured mesh…
3-D wave-making problem for multiple cylinders (Wang & Wu 2010, Ocean Eng)
Wave profile at τ=137.63 and A=0.02h ( )
is the trapped mode frequency1057.2
1057.2
(Eighteen cylinder cases, r=0.1416,B=20r)
![Page 80: FEM Simulations of Non-linear Interactions of Waves and ... · Triangular 6-node prism element 6 5 4 3 2 1 3-node triangular element 3 1 2 The fluid domain is subdivided into many](https://reader036.vdocuments.mx/reader036/viewer/2022062607/604cbd788c46ff603c418010/html5/thumbnails/80.jpg)
Using unstructured mesh…
3-D wave-making problem for multiple cylinders (Wang & Wu 2010, Ocean Eng)
(Eighteen cylinder cases, r=0.1416,B=20r)
![Page 81: FEM Simulations of Non-linear Interactions of Waves and ... · Triangular 6-node prism element 6 5 4 3 2 1 3-node triangular element 3 1 2 The fluid domain is subdivided into many](https://reader036.vdocuments.mx/reader036/viewer/2022062607/604cbd788c46ff603c418010/html5/thumbnails/81.jpg)
Using unstructured mesh…
3-D wave-making problem for multiple cylinders (Wang & Wu 2010, Ocean Eng)
(Eighteen cylinder cases, r=0.1416,B=20r)
![Page 82: FEM Simulations of Non-linear Interactions of Waves and ... · Triangular 6-node prism element 6 5 4 3 2 1 3-node triangular element 3 1 2 The fluid domain is subdivided into many](https://reader036.vdocuments.mx/reader036/viewer/2022062607/604cbd788c46ff603c418010/html5/thumbnails/82.jpg)
12121 ,sin (b) and sin )( XXtAXtAXXa
)0.1,4,06.0,5.1,3( kaaLaAadah cy
Using unstructured mesh…
3-D wave radiation by multiple cylinders: two-cylinder cases in horizontal motions
![Page 83: FEM Simulations of Non-linear Interactions of Waves and ... · Triangular 6-node prism element 6 5 4 3 2 1 3-node triangular element 3 1 2 The fluid domain is subdivided into many](https://reader036.vdocuments.mx/reader036/viewer/2022062607/604cbd788c46ff603c418010/html5/thumbnails/83.jpg)
Meshes around cylinders at t=8T, 8.2T, 8.4T, 8.6T, 8.8T, 9T
tAX sin
)0.1,4,6.0,5.1,3( kaaLaAadah cy
Using unstructured mesh…
3-D wave radiation by multiple cylinders: four-cylinder cases in vertical motions
![Page 84: FEM Simulations of Non-linear Interactions of Waves and ... · Triangular 6-node prism element 6 5 4 3 2 1 3-node triangular element 3 1 2 The fluid domain is subdivided into many](https://reader036.vdocuments.mx/reader036/viewer/2022062607/604cbd788c46ff603c418010/html5/thumbnails/84.jpg)
The finite element method is efficient in simulations ofnonlinear wave-structure interactions;
Both structured and unstructured meshes can be used inthe simulations. The former is more stable in thesimulation and the and the latter is more suitable forcomplex domains;
Enhanced interactions between multiple structures arestrong at the resonant or the nearly trapped modefrequency.
The waves and forces have strong nonlinear features atthe first and second order resonant or the nearly trappedmode frequency.;
Methods to calculate the velocity still need further study inboth 2-D and 3-D cases when using unstructured meshes.
It is still a big challenge to use fully 3-D unstructuredmeshes in fully nonlinear wave simulations.
Summary
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References• Wu, G.X. and Eatock Taylor, R. (1994) "Finite element analysis of two-dimensional
non-linear transient water waves" Appl. Ocean Res.,. Vol.16, pp.363-372• Wu, G.X. and Eatock Taylor, R. (1995) "Time stepping solutions of the two
dimensional non-linear wave radiation problem" Ocean Engineering, Vo.22, pp785-798
• Wu, G.X. (1998) "Hydrodynamic force on a rigid body during impact with liquid", J. Fluids and Structures, Vol.12, pp.549-559
• Wu, G.X., Ma, Q.W and Eatock Taylor, R. (1998) "Numerical simulation of sloshing waves in a 3D tank based on a finite element method", Appl. Ocean Res., Vol.20, pp.337-355
• Ma, Q.W., Wu, G.X. and Eatock Taylor, R. (2001a) "Finite element simulation of fully nonlinear interaction between vertical cylinders and steep waves- part 1: methodology and numerical procedure", Int. J. Nume. Meth. in Fluids, Vol.36, pp265-285
• Ma, Q.W., Wu, G.X. and Eatock Taylor, R. (2001b) "Finite element simulation of fully nonlinear interaction between vertical cylinders and steep waves- part 2: numerical results and validation", Int. J. Nume. Meth. in Fluids, Vol.36, 287-308
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References• Hu, P., Wu, G.X. and Ma. Q.W. (2002) “Numerical simulation of nonlinear wave
radiation by a moving vertical cylinder” Ocean Eng., Vol.29, pp.1733-1750 • Wu, G.X. and Eatock Taylor, R. (2003) “The coupled finite element and boundary
element analysis of nonlinear interactions between waves and bodies” Ocean Eng. , Vol.30, pp. 387-400
• Wu, G.X. and Hu, Z.Z, (2004) “Simulation of nonlinear wave interactions between waves and floating bodies through a finite element based numerical tank” Proc. Roy. Soc. London , Vol.A460, pp.2979-2817
• Wang, C.Z. and Wu, G.X. (2006) “An unstructured mesh based finite element simulation of wave interactions with non-wall-sided bodies”, J. Fluids & Structures, Vol.22, pp.441-461
• Wang, C.Z. and Wu, G.X. (2007) “Time domain analysis of second order wave diffraction by an array of vertical cylinders”, J. Fluids & Structures, Vol23, pp.605-631
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References• Wang, C.Z., Wu, G.X. and Drake, K. (2007) “Interactions between nonlinear water
waves and non-wall-sided 3D structures”, Ocean Engineering, Vol.34, pp.1182-1196
• Wu, G.X (2007) “Second order resonance of sloshing in a tank”, Ocean Engineering Vol.34, pp.2345-2349
• Wang, C.Z. and Wu, G.X. (2008) “Analysis of second order resonance in wave interactions with floating bodies through a finite element method” Ocean Engineering, Vol.35, 717-726
• Eatock Taylor, R., Wu, G.X., Bai, W and Hu, Z.Z. (2008) “Numerical wave tanks based on finite element and boundary element modelling”, J. of Offshore Mechanics and Arctic Engineering, ASME Vol.130, 03001(1)-03001(8)
• Wang, C.Z. and Wu, G.X., 2010,Interactions between fully nonlinear water waves and an array of cylinders in a wave tank, Ocean Engineering, Vol. 37, pp. 400-417
• Wang, C.Z., Wu, G.X. and B.C. Khoo. (2011).” Fully nonlinear simulation of resonant motion of liquid confined between floating structures”, Computers and Fluids,Vol.44, pp89-101
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References• Wang, C.Z., Wu, G.X. (2011).”A brief summary of finite element method
applications to nonlinear wave-structure interactions”, Journal of Marine Science and applications, Vol.10, pp127-138
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Thank you!
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