Minyee Jiang Naval Surface Warfare Center at Carderock

September 1, 2009STAR 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 operations. 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 oriented, including assisting Special Operating Forces. Submarine operation 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 MethodSTAR-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.

VOFVolume 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 ModelASDS 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 surfacesASDS Hull

Pylons and Matting trunk

Computational Domain and GridLocal Grid RefinementCell Zones

Region of interest

Cells near ASDSInlet

Interest

Damping

Grid Topology I (Single region with stretched wave damping zone)

Velocity Inlet

Pressure outlet

velocity inlet

Velocity inlet

Grid Topology II (Embedded mesh with stretched wave damping zone)

Velocity Inlet

Pressure outlet

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 ConditionFree 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.