Minyee Jiang Naval Surface Warfare Center at Carderock September 1, - - PowerPoint PPT Presentation

Minyee Jiang Naval Surface Warfare Center at Carderock September 1, 2009 STAR Global Forum 2009

STAR-CCM+ in NSWCCD CFD Applications

Hull Resistance prediction CFD Validations Internal flow plus ship-wave interaction Wave slap prediction

Background

 Traditional Submarine Mission: Prior to the end of the Cold

War conflict between two super powers, anti-submarine warfare and the delivery of massive nuclear fire power were the major roles for U.S.

• submarines. The “Silent Service” was the major concern for submarine
• perations. Opportunities for submarine to encounter waves were very

rare .

 New Missions: . Now dealing with multiple small conflicts

through out the world, U.S. submarines are more multi-mission

• riented, including assisting Special Operating Forces. Submarine
• peration is no longer completely silent in deep sea. More often

submarines encounter waves.

 New configurations: Dry Deck Shelter (DDS) and Advanced Seal

Delivery System (ASDS) mounted on host submarines.

ASDS Wave Slap Simulation

 Task Title:

 Initial Investigation of Wave Impact Loading Trends on the ASDS

 Objective:

 Simulate forces on ASDS under various wave height, wavelength, and wave

heading to identify trends where ASDS systems may experience significant forces.

 Results could lead to identification of potential problem areas with high

loading

 Approach:

 Computational Fluid Dynamics approach for pressure loading by

simulation of the interaction of the wave field with the ASDS mated to the host ship

Numerical Tool and Method

STAR-CCM+

A Reynolds Averaged Navier-Stokes (RANS) code, developed by CD- Adapco, was designed to solve wave interaction problems and is applicable to surface ships and submarines.

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.

Volume of Fluid Free Surface Capturing

water air

Geometries for the Numerical Model ASDS on a submarine

The propellers of ASDS and submarine are not included in the numerical model Still water line

ASDS Wave Slap Simulation

Close up View on ASDS

ASDS was raised few inches for grid generation purpose Control surfaces ASDS Hull Pylons and Matting trunk

Computational Domain and Grid

Local Grid Refinement

Cell Zones Region of interest Cells near ASDS Inlet Interest Damping

Grid Topology I

(Single region with stretched wave damping zone)

Velocity Inlet Pressure

• utlet

velocity inlet Velocity inlet

Grid Topology II

(Embedded mesh with stretched wave damping zone)

Velocity Inlet Pressure

• utlet

velocity inlet Interface

Grid Topology III

(Single region without stretched wave damping zone)

Velocity Inlet Pressure outlet Velocity Inlet Velocity inlet

Grid Topology I (Single region)

Because the outlet boundary is located far downstream, free surface is outside the fine grid region even for small pitch angle d =20L

Grid Topology I (Single region)

Free surface enters coarse grid region

Grid Topology II (Embedded Grid)

Interface for grid rotation Free surface stays in fine grid region

Grid Information

 2 - 6 M cells  Evenly distributed cells in the inlet region  Stretched grid size in the damping zone

Wave Conditions

 Averaged Wave Height (H=20 feet)  Averaged Wave Length (λ=262 feet)  Wave Heading: (Beam Sea)  Positions : broach  Forward speeds : 0 knot

Submarine and ASDS at Broach Condition

Free Surface

Wave direction

Sample of the Surface Pressure

Areas with High impact load Pressure Animation

Wave Slap Peak Pressure on ASDS

Large peak pressure with small duration More sustain load

Wave Slap Peak Pressure on ASDS Elements

More vulnerable element

Conclusions

 STAR-CCM+ has been successfully applied to several Navy

vessels for resistance prediction and wave impact analysis.

 More wave slap/slam validations and simulations are in

progress.

 Simulation of LCS-2 requires modeling of interaction of

ship with wave as well as internal flow

 We are gradually increasing our usage at DoD-HPC. We are

expecting to have more allocation available at several computing centers next year.

 Fluid-Structure Interaction (FSI): We are currently waiting

for the release of STAR-CCM+ coupled with ABAQUS for accurately prediction of wave impact load.