the-Art and New Developments S. Enger, M. Peri , F. Schfer, E. - - PowerPoint PPT Presentation

Application of STAR-CCM+ in Marine and Off-Shore Engineering: State-of- the-Art and New Developments

• S. Enger, M. Perić, F. Schäfer, E. Schreck, J.

Singh

• 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

• f 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

• btained in experiments

agree well with simulation, both qualitatively and quanti- tatively, over the whole range

• f 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 Propell ller Virtu tual l 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

• ther 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...