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 1
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 2
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 3
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 4
Numerical Method • STAR-CCM+ (Computational Continuum Mechanics) – Commercial (RANS) solver. – Developed by CD-Adapco STAR Automobile Industry STAR_CCM+ Complex Geometry Easy Model Set Up; Easy Grid Generation Easy in Grid Generation; Pre/Post Processing in One Code COMET Marine Applications: Marine Industry Surface ship Two Phases Flow / Wave Impact Planning Craft Marine Applications: GES Wave Impact GES Wave Impact Drop Test Planning Craft • 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. 5
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. 6
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 one 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 Wavelength Steepness (inches) (HL) 4 in (10.2 cm) 20 ft (6.1 m) 0.034 6 in (15.2 cm) 20 ft (6.1m) 0.050 7
Flat Plate Validation • Sample wave data vs. sinusoidal wave • 5 th order Stokes wave vs. sinusoidal wave 8
Flat Plate Validation Solution and Comparison • Section cut of the CFD Mesh and VOF contours Air Water Hexahedral cells and trimmed mesh 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) 5 th order Stokes wave 9.0 lbf (40.0 N) 5 in (12.7 cm) linear wave 9.5 lbf (42.3 N) Comparison of CFD predicted load with measured load on the half submerged flat plate Comparison of all non-breaking wave forces measured during the experiment 9
General External Structure (GES) Validation Geometry • Geometry – GES with pylons and mating trunk on a host submarine GES, pylons, and mating trunk and patch boundaries defining the areas over which results were reported 10
General External Structure (GES) Validation Mesh • Numerical Mesh: Surface mesh CFD volume mesh on the symmetry plane Interface : Cylindrical interface between the rotational region (free to heave and roll) and the outer (free to heave) region 11
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) Typical wave impact Pressure contours on the GES due to wave impact. Red denotes regions of high pressure and blue regions of low pressure 12
General External Structure (GES) Validation Impact History Time history of normalized impact pressure on the free to heave GES (1DOF and 2DOF) • Time history of normalized impact pressure on the fixed GES (0 DOF). 13
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. 14
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 of 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 5 th 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. 15
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