Application of STAR-CCM+ in Marine and Off-Shore Engineering:...
Transcript of Application of STAR-CCM+ in Marine and Off-Shore Engineering:...
Application of STAR-CCM+ in Marine and
Off-Shore Engineering: State-of-the-Art
and New Developments
M. Perić, F. Schäfer, E. Schreck, J. Singh
• Main features of STAR-CCM+ relevant for marine and
offshore applications
• Examples of industrial application
• New features under development
Contents
• Easy process automation for maximum productivity
• High-resolution interface-capturing scheme for free surfaces (sharp interfaces, avoiding mixing)
• Different wave models, wave damping
• Cavitation modelling, user calibration
• Dynamic fluid-body interaction (6 DoF body motion), superposition of motions
• Overset grids for maximum flexibility in handling body motion
• Implicit fluid-structure interaction
Important Features of STAR-CCM+
• The scheme combines upwind and downwind discreti-
zation to obtain optimal resolution of free surface
(typically in one cell).
• All fluids involved can be compressible (liquids and
gases).
• Users can modify some parameters for specific control:
– Avoid blending with upwind when marching toward steady-
state solution (raise CFL-limits);
– Activate anti-diffusion to avoid dilution of liquid in gas
through violent sloshing, wave overturning, splashing etc.
(sharpening factor > 0).
High-Resolution Interface-Capturing, I
High-Resolution Interface-Capturing, II
Simulation of sloshing in a tank due to a sinusoidal sway motion: one-cell sharp
interface before wave overturns and smearing after splashing, when the grid is not
fine enough to resolve liquid sheets and droplets . Sharpening prevents dilution
and the interface becomes sharp again…
• STAR-CCM+ offers several wave models (for initialization and boundary conditions; arbitrary direction of propagation):
Linear 1st-order wave theory (for small-amplitude waves);
Non-linear Stokes 5th-order wave theory (after Fenton, 1985);
Pierson-Moskowitz and JONSWAP spectra (long-crested
irregular waves);
Superposition of linear waves with an arbitrary direction of
propagation, amplitude and period (irregular sea states)...
• Accurate wave propagation (with a minimum damping of
amplitude) is achieved by 2nd-order time discretization…
• … which imposes a limit on time-step size (wave propagation
by less than half a cell per time step).
Waves, I
Waves, II
• Any experimental means of wave generation can be easily simulated
in STAR-CCM+, e.g. using an oscillating flap:
• “Beach” is simulated by applying exponentially growing resistance to
vertical fluid motion over a prescribed distance towards boundary.
Waves, III
Wave profile after 100 s of simulation time (> 11 periods).
Note: 1 cell resolution, very small reduction in amplitude…
Scaled 10 times in vertical direction…
• Wave train initialized using Stokes 5th order theory over 1002 m (8 wavelengths); Wave damping applied over the last 300 m; Wave period 8.977 s, wave height 5 m
• 20 cells per wave height, 80 cells per wave length, 2nd-order discretization in time and space (recommended set-up...)
• The homogeneous two-phase model is used, in which
both phases are considered components of a single
effective fluid.
• The equation for volume fraction of vapor has a source
term which describes the growth and collapse of
cavitation bubbles – based on Rayleigh equation:
Cavitation Modeling, I
Bubble radius Saturation pressure
Local pressure
Liquid density
The model has two parameters:
Seed bubbles, uniformly distributed in liquid (n0 bubbles per unit volume
of liquid);
All seed bubbles have the same initial radius.
Volume fraction of vapor in a control volume:
The growth rate of bubble volume:
The source term in equation for vapor volume fraction:
Cavitation Modeling, II
• A multiplier of the source term is provided for user to set up
(default is 1.0):
– Either as a constant or field function;
– May be different for positive (bubble growth) and negative (bubble
collapse) source term.
• This allows implementation of a new (user) cavitation model by
making the multiplier such that the existing source term
cancels out:
Cavitation Modeling, III
→
• Superposition of vessel motion, propeller rotation, and oscillatory
motion of each blade: easy set-up through GUI, no user programming
needed...
Superposition of Motions
Overset Grids, I
Optimization of tidal turbine design using overset grids…
Overset Grids, II
Simulation of lifeboat launching using overset grids…
Patrol Vessel, Validation Study, I
Detailed simulation of flow, resistance, trim and
sinkage were performed at the towing tank facility
“Brodarski Institut” in Zagreb, Croatia…
Patrol Vessel, Validation Study, II
Experiments were performed in
the towing tank of “Brodarski
Institut” in Zagreb, Croatia,
after simulations were finished.
Resistance, trim and sinkage
obtained in experiments
agree well with simulation,
both qualitatively and quanti-
tatively, over the whole range
of Froude numbers.
Examples of Industrial Application, I
Solving a problem with an existing barge, which did not follow the tug…
The barge was deviating
from the course by up to
250 m…
Examples of Industrial Application, II
The barge was deviating
from the course by up to
250 m…
Original aft shape
Modified aft shape
5 modified designs tested in simulation – the best one was implemented…
Course deviation in
simulation reduced to
~1 m – modified vessel
behaved similarly…
Original design
Best modified design
Examples of Industrial Application, III
Examples of Industrial Application, IV
Examples of Industrial Application, V
ORACLE TEAM USA sailing
in San Francisco Bay
(America’s Cup 2013)
ORACLE TEAM USA sailing in a
high-performance computer
cluster (100 million cells, 256
cores; powered by STAR-CCM+,
steered by Mario Caponnetto and
his CFD analysis team)
Examples of Industrial Application, VI
ORACLE TEAM USA: The boat was
designed and optimized solely by
using simulation – no model experi-
ments done… Simulations accompa-
nied the race, guided changes to
vessel (the night before the last race
some modifications to rudder were
done based on simulation results)
and provided performance data to
the crew…
Examples of Industrial Application, VII
• Additional motion models (prescribed in-plane motion +
additional DoF)
• Virtual propeller model (using performance curves, theories or
coupling to external solvers for propeller flow)
• Fluid-Structure-Interaction: Implementing FE-modelling into
STAR-CCM+ (see presentation by Alan Mueller)
• Custom tool for an automatic set-up of standard tests:
resistance, trim+sinkage (in future also PMM, circle, zig-zag…)
• Internal wave generation by mass source terms
• Coupling to potential flow solver for waves and propellers…
• Further developments of overset grids, automatic refinement…
• Hydro-acoustics modelling, etc…
STAR-CCM+: New Developments
New DFBI Motion Types, I
Pure yaw Pure sway
New DFBI body motion options:
- Four-DoF Maneuvering
- Planar Motion Carriage
New DFBI Motion Types, II
Circle test
Virtual Propeller Model, I
Momentum source terms are
added to cells within a speci-
fied disk zone (grid does not
have to be fitted to disk).
SVA Propeller
Virtual Disk
Virtual Propeller Model, II With virtual propeller, free
surface and hull resistance are
well predicted with low cost…
Rotating Propeller
Virtual Propeller
Full-scale hull,
propeller and
rudder,
Free surface
Fixed hull
Froude-number
0.21
Internal Wave Generation
• Waves generated by mass sources/sinks (injection and suction of water)
• Waves reflected off a structure can pass through the internal wave
generator
• Damping applied at all solution domain boundaries, except where
reflection off walls is allowed…
Future Trends
• More powerful and affordable computers = higher demands
from simulation:
More complete system analysis, with all geometrical details;
More transient simulations (URANS, DES and LES),
predicting pressure fluctuation and noise sources (turbulence,
cavitation);
More fluid-structure-interaction (slamming, sloshing) and
other multi-physics (wind, fire, pollution etc.) applications;
Simulation of manoeuvring tests (circle, zig-zag, PMM etc.)
and other experiments in the design phase...
Simulation of interaction (ship + ice, ship + platform, ship +
ship etc.).
More automatic optimization studies...