Engenharia Naval e Oceânica COPPE/UFRJ & EP/UFRJ 2013 CAE NAVAL & OFFSHORE Windsor Guanabara, Rio de Janeiro/RJ – Brasil 13 de Junho de 2013 SIMULATION OF FLOW AROUND FLOATING STRUCTURES: SHIPS AND PLATFORMS Alexandre T. P. Alho Laboratório de Sistemas de Propulsão DENO/POLI, UFRJ
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Engenharia Naval e Oceânica
COPPE/UFRJ & EP/UFRJ
2013 CAE NAVAL & OFFSHORE
Windsor Guanabara, Rio de Janeiro/RJ – Brasil
13 de Junho de 2013
SIMULATION OF FLOW AROUND FLOATING
STRUCTURES: SHIPS AND PLATFORMS
Alexandre T. P. Alho
Laboratório de Sistemas de Propulsão
DENO/POLI, UFRJ
Engenharia Naval e Oceânica
COPPE/UFRJ & EP/UFRJ 2013 CAE NAVAL & OFFSHORE – Windsor Guanabara, Rio de Janeiro/RJ – Brasil
INTRODUCTION
Preliminary Considerations
▪ Growing demand for high efficiency systems
▪ Demand for accurate predictions in less time and at low costs.
Accurate CFD models: designers can rely on as an effective
design tool.
CFD model must be developed based on a good compromise
between the quality of the numerical result and the computational
effort.
▪ Performance prediction of ships and offshore platforms
Experimental methods are well-established, but are usually
expensive and time-consuming.
Optimization process is virtually impossible based on experimental
methods: very high costs.
Engenharia Naval e Oceânica
COPPE/UFRJ & EP/UFRJ 2013 CAE NAVAL & OFFSHORE – Windsor Guanabara, Rio de Janeiro/RJ – Brasil
INTRODUCTION
Examples of CFD Projects
▪ CFD Predictions of the Hull Resistance and the Wave System of a
Catamaran.
▪ Investigate the performance of passive damping foils on heave
response of a catamaran.
▪ Develop a CFD model to study the effectiveness of passive damping
devices on heave motions of mono-column platforms.
Methodology
▪ The flow around vessel/platform hulls was simulated by means of
commercial CFD code (ANSYS CFX).
▪ Results are validated against experimental data (if available).
Engenharia Naval e Oceânica
COPPE/UFRJ & EP/UFRJ 2013 CAE NAVAL & OFFSHORE – Windsor Guanabara, Rio de Janeiro/RJ – Brasil
CFD PROJECTS – Resistance & Wave Cut
Motivation
▪ Growing demand for high speed multihull vessels.
Catamaran/SWATH concept has been received special attention
good performance in terms of speed and transversal stability.
Objective
▪ Validate a CFD model in terms of its performance on estimating hull
resistance and calculating the wave cuts generated by the hull.
Main Particulars
▪ Length (BP): 27.6 m
▪ Beam (each hull): 2.97 m
▪ Draft (design load): 1.5 m
▪ Block coefficient: 0.653
Engenharia Naval e Oceânica
COPPE/UFRJ & EP/UFRJ 2013 CAE NAVAL & OFFSHORE – Windsor Guanabara, Rio de Janeiro/RJ – Brasil
CFD PROJECTS – Resistance & Wave Cut
Main Particulars
▪ Length (BP): 27.6 m
▪ Beam (each hull): 2.97 m
▪ Draft (design load): 1.5 m
▪ Block coefficient: 0.653
Demihull separation
▪ 2.75 m (22), 5.25 m (42)
and 7.75 m (62):
0.9..2.6 B.
Significant interference effects
-0,15
-0,05
0,05
0,15
0,25
0,35
0,45
0,55
0,1 0,2 0,3 0,4 0,5 0,6
IF
Fn
IF. Sep 22
IF. Sep.42
IF. Sep.62
Engenharia Naval e Oceânica
COPPE/UFRJ & EP/UFRJ 2013 CAE NAVAL & OFFSHORE – Windsor Guanabara, Rio de Janeiro/RJ – Brasil
CFD PROJECTS – Resistance & Wave Cut
Hull Resistance
▪ In most cases, numerical errors are lower than 5.0% (max. 7.2%).
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
0,25 0,3 0,35 0,4 0,45
Re
sis
tan
ce
(g
f)
Fn
Exp.
CFDHump & hollow
behavior well
described.
Unable to resolve
wave-breaking.
Engenharia Naval e Oceânica
COPPE/UFRJ & EP/UFRJ 2013 CAE NAVAL & OFFSHORE – Windsor Guanabara, Rio de Janeiro/RJ – Brasil
CFD PROJECTS – Resistance & Wave Cut
Free surface elevations
Good correlation upstream
and along the hull.
-0,03
-0,02
-0,01
0
0,01
0,02
0,03
-1 -0,5 0 0,5 1 1,5 2 2,5 3 3,5
Wave E
levati
on
x-position
Exp.
CFD
-0,04
-0,03
-0,02
-0,01
0
0,01
0,02
0,03
-1 -0,5 0 0,5 1 1,5 2 2,5 3 3,5
Wave E
levati
on
x-position
Exp.
CFD
-0,04
-0,03
-0,02
-0,01
0
0,01
0,02
0,03
0,04
-1 -0,5 0 0,5 1 1,5 2 2,5 3 3,5
Wave E
levati
on
x-position
Exp.
CFD
FN = 0.389
FN = 0.430
FN = 0.332
Engenharia Naval e Oceânica
COPPE/UFRJ & EP/UFRJ 2013 CAE NAVAL & OFFSHORE – Windsor Guanabara, Rio de Janeiro/RJ – Brasil
CFD PROJECTS – Heave Response
Objective
▪ Investigate the performance of passive damping foils on heave
response of a catamaran viscous damping coefficient.
Main Particulars
▪ Length (BP): 27.6 m
▪ Beam (each hull): 2.97 m
▪ Draft (design load): 1.5 m
▪ Block coefficient: 0.653
Passive damping foil.
Engenharia Naval e Oceânica
COPPE/UFRJ & EP/UFRJ 2013 CAE NAVAL & OFFSHORE – Windsor Guanabara, Rio de Janeiro/RJ – Brasil
CFD PROJECTS – Heave Response
Heave Response
Without Damping Foil With Damping Foil
Engenharia Naval e Oceânica
COPPE/UFRJ & EP/UFRJ 2013 CAE NAVAL & OFFSHORE – Windsor Guanabara, Rio de Janeiro/RJ – Brasil
CFD PROJECTS – Heave Response
Heave Response
Without Damping Foil With Damping Foil
Engenharia Naval e Oceânica
COPPE/UFRJ & EP/UFRJ 2013 CAE NAVAL & OFFSHORE – Windsor Guanabara, Rio de Janeiro/RJ – Brasil
CFD PROJECTS – Heave Response
Objective
▪ Develop a CFD model to study the effectiveness of passive damping
devices on heave motions of mono-column platforms.
Vertical Circular Cylinder
External dia.: 110 m
Moonpool dia.: 50 m
Central Moonpool
Devised to improve response
in waves.
External skirt: damping device
Engenharia Naval e Oceânica
COPPE/UFRJ & EP/UFRJ 2013 CAE NAVAL & OFFSHORE – Windsor Guanabara, Rio de Janeiro/RJ – Brasil
CFD PROJECTS – Heave Response
Free Decay Simulation: Original Skirt
Engenharia Naval e Oceânica
COPPE/UFRJ & EP/UFRJ 2013 CAE NAVAL & OFFSHORE – Windsor Guanabara, Rio de Janeiro/RJ – Brasil
CFD PROJECTS – Heave Response
Validation: Original Skirt
Time [s]
Ve
rtic
al d
isp
lace
me
nt
[Norm
.]
Decay period: good correlation!
Over-estimated amplitude: numerical
simulation did not include the damping
effect of mooring lines, risers, etc.
Numerical (CFD)
Experimental
Engenharia Naval e Oceânica
COPPE/UFRJ & EP/UFRJ 2013 CAE NAVAL & OFFSHORE – Windsor Guanabara, Rio de Janeiro/RJ – Brasil
Free Decay Simulation: Alternative Skirt Geometry
Alternative B
CFD PROJECTS – Heave Response
Engenharia Naval e Oceânica
COPPE/UFRJ & EP/UFRJ 2013 CAE NAVAL & OFFSHORE – Windsor Guanabara, Rio de Janeiro/RJ – Brasil
Objective
▪ Develop a CFD model dedicated to estimate the propulsion factors and
to simulate the self-propulsion test of a hull.
Focus
▪ Design applications.
Main Particulars:
▪ Length (Loa): 73.4 m
▪ Length (Lpp): 70.6 m
▪ Breath (B): 14.8 m
▪ Design draught (T): 2.6 m
▪ Service Speed (VS): 9.5 knt
CFD PROJECTS – Seft-propulsion Test
Engenharia Naval e Oceânica
COPPE/UFRJ & EP/UFRJ 2013 CAE NAVAL & OFFSHORE – Windsor Guanabara, Rio de Janeiro/RJ – Brasil
Hull Performance
▪ Test speed (VS): 9.5 knt
▪ Total resistance (RT): 50.6 kN
▪ Wake coefficient (w): 0.153
CFD PROJECTS – Seft-propulsion Test
Engenharia Naval e Oceânica
COPPE/UFRJ & EP/UFRJ 2013 CAE NAVAL & OFFSHORE – Windsor Guanabara, Rio de Janeiro/RJ – Brasil
Test Results
▪ Propeller revolutions (N): 433 rpm
▪ Propeller thrust (Treq): 65.3 kN
CFD PROJECTS – Seft-propulsion Test
N = 420 rpm
Engenharia Naval e Oceânica
COPPE/UFRJ & EP/UFRJ 2013 CAE NAVAL & OFFSHORE – Windsor Guanabara, Rio de Janeiro/RJ – Brasil
Results Evaluation
▪ Comparison against statistical estimation.
▪ Wake fraction, thrust deduction fraction and relative-rotative efficiency