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5th OpenFOAM UK and Eire User Group Meeting, Dublin, 16-17/Jan/2017
Validation and Verification of theCoupled Solver in FOAM-Extend
Marine Propulsors and Ship Maneouvring
Inno Gatin, Tessa Uroic and Hrvoje Jasak
Faculty of Mechanical Engineering and Naval Architecture, Uni Zagreb, Croatia
Wikki Ltd. United Kingdom
5th OpenFOAM UK and Eire User Group Meeting, Dublin, 16-17 January 2017
Validation and Verification of the Coupled Solver in FOAM-Extend – p. 1
5th OpenFOAM UK and Eire User Group Meeting, Dublin, 16-17/Jan/2017
Outline
Objective
• Announce public release of native Overset Mesh capability
• Present validation and verification results for the coupled pressure-based
incompressible solver
Topics
• Manoeuvring and free sailing simulations: ship under self-propulsion
• Ship propulsor modelling in free sailing simulations
• Validation: Segregated vs Coupled pressure-based solver on propellers
• Pre-announcement of NUMAP Summer 2017 and OFW 12
• Summary
Validation and Verification of the Coupled Solver in FOAM-Extend – p. 2
5th OpenFOAM UK and Eire User Group Meeting, Dublin, 16-17/Jan/2017
Naval Hydro: Manoeuvring Simulations
Basic Manoeuvring and Free Sailing Simulations
• Basic manoeuvring are performed in 2 ways:
1. Prescribed trajectory simulations: using a combination of free 6-DOF
components and prescribed motion in other components. Result of
simulation: force history + motion of free DOFs
2. Free sailing simulations, where forces/moments from the propulsor and
rudder act directly on the hull
◦ Simplified force models for rudder/propulsor at 6-DOF level
◦ CFD modelling of rudders and propulsors
• Mesh motion currently performed as solid body domain motion
• Future plans
◦ Extend the use of hierarchical object structure to facilitate case setup with
rotating propellers and moving rudders
◦ Use a combination of domain motion and algebraic mesh deformation for
hull-rudder-propeller assemble
◦ Use native (fully conservative) Overset Mesh capability for manoeuvring
Validation and Verification of the Coupled Solver in FOAM-Extend – p. 3
5th OpenFOAM UK and Eire User Group Meeting, Dublin, 16-17/Jan/2017
Naval Hydro: Manoeuvring Simulations
Manoeuvring Simulations
• Prescribed trajectory simulations performed routinely: turning circle, zig-zagmanoeuvre
• Free sailing (hull + propulsor) validation under way
◦ Free sailing with prescribed force in 6-DOF system
◦ Turning circle with constant rudder deflection and actuator disk force (better
rudder performance due to propeller jet effects)
◦ “Special manoeuvres”, eg crabbing
• Choice of VOF or level set free surface solver: depending on mesh quality
Validation and Verification of the Coupled Solver in FOAM-Extend – p. 4
5th OpenFOAM UK and Eire User Group Meeting, Dublin, 16-17/Jan/2017
Propulsor Modelling
Modelling of Marine Propulsors: General Grid Interface
• foam-extend is capable of handling turbo-machinery CFD
• General Grid Interface (GGI) and its derived forms
◦ Cyclic GGI
◦ Partial overlap GGI
◦ Mixing plane interface
• capability of cavitation and thrust breakdown: ongoing research
• Harmonic Balance Method: handling period flows in spectral space: typically
approx 80 times faster than conventional transient simulation with spectral
(temporal) accuracy
Validation and Verification of the Coupled Solver in FOAM-Extend – p. 5
5th OpenFOAM UK and Eire User Group Meeting, Dublin, 16-17/Jan/2017
Propulsor Modelling
Actuator Disc Model
• Implementation based on pressure/momentum jump condition on mesh faces
Uc
Un
Ur
C
r
actuator
axis
Uin
• Axial momentum increase in the propeller plane
∆p = L (a0 + a1Un + a2U2
n+ a3U
3
n+ . . .)
• Swirl component of the flow
∆Uc = ω sin(α) (n× r),
• Boundary condition accepts radially non-uniform loading of the pressure jump and
swirl in tabular form: user-defined load (efficiency) profile
Validation and Verification of the Coupled Solver in FOAM-Extend – p. 6
5th OpenFOAM UK and Eire User Group Meeting, Dublin, 16-17/Jan/2017
Propulsor Modelling
Propulsor Modelling: Work-in-Progress
• Simulating ship manoeuvring using rotating propellers is feasible but impractical:
time-step limitation based on propeller rotation
• Proposal: Modelling propellers with actuator disk models: customised disk
performance to match full propeller characterisation
• Rotating propellers; comparison of actuator disks, Multiple Rotating Frames of
Reference (MRF) and rotating propellers for practical thrust simulation
• Currently, practical free sailing simulations are performed with actuator disk
pressure + swirl models to correspond to the propeller performance maps
Validation and Verification of the Coupled Solver in FOAM-Extend – p. 7
5th OpenFOAM UK and Eire User Group Meeting, Dublin, 16-17/Jan/2017
Validation of the Coupled Solver
Validation of the Coupled Solver on Propeller Simulations
• Lloyds Register: A workshop on ship scale hydrodynamic computer
simulation, Southampton, 25 November 2016
• Detailed performance map required for a real (imperfect) full-scale propeller
• . . . to be used in full-scale ship CFD (138 m): free sailing under propulsion
• Experimental data not available for open water propeller test
Validation of the Segregated and Coupled Solver
• Looking to produce identical results independent of choice of solver
• Evaluate performance of the segregated and coupled solver
Turbulence Modelling
• The propeller flow is dominated by the wake flow, which needs to take time to
develop. Therefore, turbulence model convergence is a limiting factor!
Rotating Frames of Reference
• To improve convergence of the segregated solver, using MRF ramping. This is not
required for the coupled solver
Validation and Verification of the Coupled Solver in FOAM-Extend – p. 8
5th OpenFOAM UK and Eire User Group Meeting, Dublin, 16-17/Jan/2017
Validation of the Coupled Solver
Lloyds Register Propeller Simulations: Full Scale DWT General Cargo Vessel REGAL
• Blade diameter: 5.334 meter
• Rotational speed: 71 rpm (7.5 rad/s)
• Advance ratio J = 0.4; inlet velocity 2.4828 m/s
Validation and Verification of the Coupled Solver in FOAM-Extend – p. 9
5th OpenFOAM UK and Eire User Group Meeting, Dublin, 16-17/Jan/2017
Validation of the Coupled Solver
Lloyds Register Propeller: Force and Torque (Segregated left, Coupled right)
0 50 100 150 200 250Iteration
0
100
200
300
400
500
600
Thru
st [
kN
]
0 50 100 150 200 250Iteration
0
100
200
300
400
500
600
700
Thru
st [
kN
]
0 50 100 150 200 250Iteration
-350
-300
-250
-200
-150
-100
Torq
ue
[kN
m]
0 50 100 150 200 250Iteration
-400
-300
-200
-100
0
Torq
ue
[kN
m]
Validation and Verification of the Coupled Solver in FOAM-Extend – p. 10
5th OpenFOAM UK and Eire User Group Meeting, Dublin, 16-17/Jan/2017
Validation of the Coupled Solver
Lloyds Register Propeller: Solver Convergence (Segregated left, Coupled right)
0 100 200 300 400 500Iteration
10-7
10-6
10-5
10-4
10-3
10-2
10-1
100
Res
idu
al
p
Ux Uy
Uz k ω
0 100 200 300Iteration
10-10
10-9
10-8
10-7
10-6
10-5
10-4
10-3
10-2
10-1
100
Res
idual
p
Ux Uy
Uz kω
Convergence and Performance of the Segregated and Coupled Solver
• Both solvers producing identical results with identical discretisation schemes
• Results are consistent with the Lloyds Workshop results
Thrust [kN] Torque [kNm]
Segregated Solver 171.46 106.11
Coupled Solver 171.38 106.03
Lloyds Workshop 168.8, σ 8.9 104.2, σ 6.3
Validation and Verification of the Coupled Solver in FOAM-Extend – p. 11
5th OpenFOAM UK and Eire User Group Meeting, Dublin, 16-17/Jan/2017
Summary and Future Work
Future Work: Propulsor Modelling and Free Sailing Simulations
• Experience shows that K-T/K-Q propeller graphs are unavailable, insufficiently
accurate, or incomplete (radial variation of thrust and torque)
• Creating an automated procedure: evaluating propeller performance suitable for
“smart actuator disk” model
• Examining alternative formulations of actuator disk and harmonic balance to
capture propeller-hull interaction coefficients with more accuracy
• Next step: free sailing, course keeping and manoeuvring in waves
Future Work: Coupled and Segregated Solver (Tessa Uroic, Uni Zagreb)
• Work concentrating on improving performance of the coupled solver
◦ Choice of linear solvers methodology
◦ Advanced options on Algebraic Multigrid coarsening (Ruge-Stuben)
◦ More robust AMG smoother algorithms
◦ Implicit coupled boundary conditions
• Merging the density-based and pressure-based coupled solver methodology
Validation and Verification of the Coupled Solver in FOAM-Extend – p. 12
5th OpenFOAM UK and Eire User Group Meeting, Dublin, 16-17/Jan/2017
Summary
UK and Eire OpenFOAM User Day
• Who’s next for the OpenFOAM UK and Eire User Group Meeting?
12th OpenFOAM Workshop24–27 July 2017 Exeter, UK
German OpenFOAM StammtischUnited 2017, 20-21/Feb/2017, Kassel
NUMAP-FOAM Summer School 2017Zagreb Croatia, 21/Aug–1/Sep/2016
Validation and Verification of the Coupled Solver in FOAM-Extend – p. 13
