CFD Modeling of a Submersible in a Realistic Surfaced Sea State - - PowerPoint PPT Presentation

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CFD Modeling of a Submersible in a Realistic Surfaced Sea State Condition for Predictions of Hydrodynamic Wave Impact Loading

Minyee Jiang, David Drazen (NSWCCD) and Jack Lee (NAVSEA)

STAR 2011 June 28 - June 29, 2011, Chicago, USA

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Agenda

• Background and Introduction
• Numerical Method
• Flat Plate Validation
• Geometry
• Mesh
• Solution and Comparison
• General External Structure (GES) Validation
• Geometry
• Mesh
• Solution and Comparison
• Conclusion

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Background

• Conventional surface ship wave impact damage

– Designed to sustain strong wave impacts – Damage from unforeseen sea condition

• 17 December 1944 task 38 of the sixth fleet encountered a small but

violent typhoon which caused sever damage to the fleet

• Traditional submarine role

– Quiet – Stealth – Hydrodynamiclyclean shape

• Unconventional submarine special missions

– Deep Submergence Rescue Vehicle (DSRV) – Special force operation DDS ...

• Wave slap while emerging

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Wave Impact Load Design

• Experiment: Instrumented model-scale experiments in a wave tank

– Expensive and time consuming – Model construction and collection of sufficient data

• Numerous computational studies on

– Surface ships – Circular cylinder – Offshore structures – Submarine related configurations

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Numerical Method

• STAR-CCM+ (Computational Continuum Mechanics)

– Commercial (RANS) solver. – Developed by CD-Adapco

• Version 4.02 and 5.04 were used for these studies
• The free surface and wave interaction modeling making STAR-CCM+

the best choice for these applications.

STAR

Automobile Industry Complex Geometry Easy Grid Generation

COMET

Marine Industry Two Phases Flow / Wave Impact Marine Applications: GES Wave Impact Drop Test Planning Craft

STAR_CCM+

Easy Model Set Up; Easy in Grid Generation; Pre/Post Processing in One Code Marine Applications: Surface ship Planning Craft GES Wave Impact

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VOF

VOF Volume of fluid (VOF) is one of the approaches for accurately computing free surface flows and breaking waves. Grid cells near the free surface are filled partially with air and water and computed appropriately based on VOF.

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Flat Plate Validation

• An experiment was conducted at the Naval Surface Warfare Center,

Carderock Division (NSWCCD) in 2005 (Anne Fullerton, Tom Fu)

• Measured the hydrodynamic loads of regular, non-breaking waves on a
• ne foot (0.305 m) square plate
• Three different levels of plate

submergence (full, half and none)

• Three different plate angles

(0°,+45°, -45°)

Wave amplitude (inches) Wavelength Steepness (HL) 4 in (10.2 cm) 20 ft (6.1 m) 0.034 6 in (15.2 cm) 20 ft (6.1m) 0.050

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Flat Plate Validation

• Sample wave data vs. sinusoidal wave
• 5th order Stokes wave vs. sinusoidal wave

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Flat Plate Validation Solution and Comparison

• Section cut of the CFD Mesh and VOF

contours

Wave Amplitude Impact force Measured (4 in, 10.2 cm) 9.0-11.0 lbf (40.0 – 48.9 N) 4 in (10.2 cm) linear wave 7.5 lbf (33.4 N) 5th order Stokes wave 9.0 lbf (40.0 N) 5 in (12.7 cm) linear wave 9.5 lbf (42.3 N)

Comparison of all non-breaking wave forces measured during the experiment Comparison of CFD predicted load with measured load on the half submerged flat plate

Air Water

Hexahedral cells and trimmed mesh

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General External Structure (GES) Validation Geometry

• Geometry –

GES, pylons, and mating trunk and patch boundaries defining the areas

• ver which results were reported

GES with pylons and mating trunk on a host submarine

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General External Structure (GES) Validation Mesh

• Numerical Mesh:

Interface: Cylindrical interface between the rotational region (free to heave and roll) and the outer (free to heave) region

Surface mesh CFD volume mesh on the symmetry plane

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General External Structure (GES) Validation Solution

• Typical wave impacts on a GES.

Input wave:

• H=20 ft (6.1 m)
• λ=262 ft (79.9 m)

Pressure contours on the GES due to wave impact. Red denotes regions of high pressure and blue regions of low pressure Typical wave impact

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General External Structure (GES) Validation Impact History

• Time history of normalized impact

pressure on the fixed GES (0 DOF).

Time history of normalized impact pressure on the free to heave GES (1DOF and 2DOF)

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General External Structure (GES) Validation Comparison

Normalized measured loads on GES body in ±y direction. Data has been binned in 1 ft (0.3 m) wave height bins. Symbols represent the mean and the error bars denote the standard deviation of the data within the bin.

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Conclusions

• The two validations cases considered in this study clearly show the

capability of a CFD tool, STAR-CCM+, to reasonably predict the wave impact load for both simple and complex geometries.

• The meshing tool in STAR-CCM+ is sophisticated enough to model details
• f the complex geometry including the small parts and gaps between
• elements. The wave impact load on these discrete elements or regions of

the body can then be examined in detail.

• Both linear waves and 5th order Stokes waves have been used and show

good agreement with measured data. STAR-CCM+ is currently working on extending the wave feature to allow irregular waves as an input.

• Future work will also focus on the inclusion of additional degrees of

freedom to better simulate the motion of the model in complex seaways.