cfd in subsea lifting analysis.pdf

7/27/2019 CFD in Subsea Lifting Analysis.pdf

1/22

1Page21-Nov-11

CFD in subsea lifting analysis

Subsea Lifting Operations 29-30 November 2011Clarion Hotel Stavanger

Petter Moen


2/22

2Page21-Nov-11

Agenda

Lifting analysis - input

CFD Added mass & damping

Examples on use of CFDBenefits & challenges


3/22

3Page21-Nov-11

Agenda





4/22

4Page21-Nov-11

Workflow for standard lifting analysis through wave zone

Input

Environmental data

Vessel/crane tipmotions

Object mass &volume properties

Hydrodynamicproperties forobject

Couplings data

Analysis

Simplified method

Regular design waveapproach

Time domainanalysis

Output

Design loads

Slack wire?

Weather criteriafor installation


5/22

5Page21-Nov-11

Lifting analysisHydrodynamic coefficients

Traditional approach:

Estimate based on empirical results of simple geometries

- Not always valid for flow regime of interest

- Data only available for limited set of simple geometries

- Interaction effects not captured

Model tests

- Current recognized practice- Expensive

- Time consuming

- Scaling effects?

New approach (acknowledged in DNV-RP-H103):

CFD (Computational Fluid Dynamics) may be used- Alternative to model tests

- Forces, pressures and velocities should be validated with approximatehand-calculations

- Results should be validated with model test results if available


6/22

6Page21-Nov-11

6Page21-Nov-11

Agenda





7/227Page21-Nov-11

CFD Added mass & dampingWhat is CFD?

Colourful Fluid Dynamics? Complicated Fluid Dynamics?

Completely Fictitious Data?

Colours For Directors?

Computational Fluid Dynamics

Calculation of fluid flow and related variables using computers

The fluid (e.g. water) is discretized into small cells forming a mesh

Fluid behaviour needs to be defined at boundaries of problem

(boundary conditions) Conservation equations (mass, momentum, etc.) solved for each cell

in an iterative process (~ impossible to solve analytically)


8/228Page21-Nov-11

CFD Added mass & dampingCalculation of added mass & damping I/II

Forced harmonic oscillations mesh deformation

zzquad

BzAF

or

zlin

BzAF

=

=

0 5 10 15 20 25 30 35 40

-0.2

0

0.2

Time [s]

Motion[m]

0 5 10 15 20 25 30 35 40-100

0

100

Time [s]

Force[kN]

Force-Time series from CFD analysis post processed by leastsquare method in MATLAB

LSMA

Blinor

A

Bquad

(movie)


9/229Page

21-Nov-11

CFD Added mass & dampingCalculation of added mass & damping II/II

Added mass (A) derived directly from least square method

Linear (B1) and quadratic (B2) damping derived from plot oflinearized damping (Blin) as function of oscillation amplitude, z

zzBzBzAF

21=

z

TBzBB

BB

lin

lin

16

3))((

)0(

12

1

=

=

0

510

15

20

25

30

35

40

45

0 1 2 3

B[kN/(m/s)]

Amplitude [m]

Linearized Damping [kN/(m/s)]

Alternative formulation:


10/2210Page

21-Nov-11

10Page21-Nov-11

Agenda





11/2211Page

21-Nov-11

I/IV - MudmatsPerforation ratio of 0, 15 and 25 %


12/2212Page

21-Nov-11

I/IV MudmatsComparison with experiments and CFD

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

0 10 20 30

Ca[-]

Perforation [%]

Mud mat added mass

Subsea7 CFD

BMT CFD

BMT EXP

0.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

0 10 20 30

C

dd[-]

Perforation [%]

Mud mat damping

Subsea 7 CFD

BMT CFD

BMT EXP


13/2213Page

21-Nov-11

II/IV - Suction AnchorAdded mass comparison with experiments

Suction Anchor added mass

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

0 2 4 6 8 10 12

Perforation [%]

Ca[-]

Exp., KC=0.1

Exp., KC=0.6

Exp., KC=1.2

CFD, KC=0.1

CFD, KC=0.6

CFD, KC=1.2

D

A

D

TUKC

=

=

2


14/2214Page

21-Nov-11

10 15 20 25 30 35 40 45 50-500

0

500

Time

Force

Total Hydrodynamic Force

CFD

Experimental

III/IV - Integrated Template Structure (ITS)Comparison with experiments

Max. force with CFD is5% higher than maxin model tests


15/22

15Page21-Nov-11

III/IV - Integrated Template Structure (ITS)Comparison with experiments

0

0.25

0.5

0.75

1

1.25

1.5

1.75

2

0 0.5 1 1.5 2 2.5

Addedma

ss

Amplitude [m]

Normalized added mass

Experimental

CFD

0

1

2

3

4

5

0 0.5 1 1.5 2 2.5

Damping

Amplitude [m]

Normalized damping

Experimental

CFD


16/22

16Page21-Nov-11

IV/IV - Submerged towing of Riser BundleComparison with experiments

Model of riser bundle

Model testing of riser bundle(movie)

CFD analysis of riser bundle(movie)


17/22

17Page21-Nov-11


Forced oscillations only (no current)

Parameter CFD Experiment

Added mass 0.38 0.38

Damping 1.10 0.66

3 4 5 6 7 8 9 10-20

-15

-10

-5

0

5

10

15

20Vertical force on riser bundle

Time

Force

CFD

Exp

Amplitude = 0.017 m

Period = 1 s


18/22

18Page21-Nov-11


Forced oscillations + current

Parameter CFD Experiment

Added mass 0.36 0.34Damping 0.15 0.36

25 26 27 28 29 30 31 32

-60

-40

-20

0

20

40

Vertical force on riser bundle

Time

Force

Exp

CFD

Amplitude = 0.16 m

Period = 1.75 s

Current = 0.75 m/s


19/22

19Page21-Nov-11

19Page21-Nov-11

Agenda





20/22

20Page21-Nov-11

Benefits & challenges of using CFD

+ By using CFD to estimate added mass and damping, the

following effects will be included:+ Effect of Reynolds number (no scale effects)

+ KC-number dependency

+ Shielding/interaction between different parts of structure

+ Other...

+ Less time consuming than model tests

+ Less expensive than model tests

- High user threshold

- More time consuming (and expensive) than simplified

estimate

- Validation required


21/22

21Page21-Nov-11

Questions?


22/22

10 01 11 22Page

seabed-to-surface

www.subsea7.com

cfd in subsea lifting analysis.pdf

Documents