1. Performance Prediction and Design Optimization
Midn 1/c Jon P. Silverberg

2. Performance Prediction
The velocity of a ship is inherent to its mission effectiveness
Three methods of determination
Hydrodynamic Tank Testing
Parametric Analysis
Computational Fluid Dynamics

3. Mk II Navy 44 Sail Training Craft
Designer David Pedrick supplied:
Lines Plan
Sail Plan
Parametrically predicted speeds from the IMS Velocity Prediction Program (VPP)
Sailing craft complexities
Six Degrees of Freedom
Propulsion Systems
Lifting Surfaces

4. Performance Prediction Process
Performance predicted for both motoring (upright) and sailing conditions
Three methods of hydrodynamic analysis
Tank Testing
“FKS” Computational Fluid Dynamic (CFD) code
“SPLASH” CFD code
Upright analysis use only hydrodynamic data
Sailing conditions necessitate aerodynamic data and use of a Velocity Prediction Program

5. Initial Parametric Analysis
Needed to determine sailing conditions and sail forces which the IMS VPP did not provide
Predictions were performed with University of Michigan’s “PCSail” developed by David Martin
Derived conditions to test in the tow tank

6. Basic Hydrodynamics Two main components of Resistance
Wavemaking – determined experimentally
Viscous (friction) – calculated
Speed of the model is scaled to reproduce wavemaking characteristics
Turbulence stimulators are added to reproduce viscous flow conditions
Wavemaking results scaled to ship size
Viscous resistance calculated for ship size

7. Tow Tank Testing Tests included Performed more than 570 runs
Data Recorded
Drag
Lift
Yaw Moment
Pitch
Tests included
Upright Conditions
Sailing Conditions
Viscous Corrections
Performed more than 570 runs

8. FKS – CFD Developed by Dr. Noblesse at Carderock NSWC
Calculated the far-field wave spectrum
Far-field waves are the totality of wave interactions
Wavemaking resistance is calculated through the energy required to create the far-field waves
Hull had one degree of freedom (forward)
Lift was not calculated
Simulations were fast
FKS was best suited for upright calculations
Initial investigation made on the Wigley hull

9. Wavemaking Comparison
Spray and pitch
Scale effects in tank testing
Viscous interaction in wavemaking

10. SPLASH – CFD
Development was by Bruce Rosen of South Bay Simulations and Joe Laiosa from Navair at Patuxent River
Calculated inviscid fluid velocities across a discretized hull
Hull had six degrees of freedom
Calculations included upright testing and sailing conditions
SPLASH ran on a high resource system

11. All Upright Data Pitch Effects
Different method of viscous calculations

12. Sailing Hydrodynamic Data
Tank Testing
SPLASH
Utilized MATLAB and MAPLE to interpolate through sailing matrices

13. Mk II Navy 44 VPP Aerodynamics Solution
Analyzed sail forces using basic wing theory
Force coefficients from sails derived from IMS VPP
Solution
Draghydro= Driveaero
Lifthydro= Sideforceaero
RightingMomenthydro = HeelingMomentaero
YawingMomenthydro = YawingMomentaero
Custom VPP had a complex hydrodynamic model and solution but a simplified aerodynamic model

14. Custom VPP written in Excel using Visual Basic
Created three VPPs from Tow Tank data, SPLASH data, and FKS data (which proved unusable)
Predicted speed for any wind condition and angle
Solved by simultaneous equations using finite-difference iteration

15. Performance Predictions
Low wind speeds showed variable results due to simplifications in the aerodynamic model
All other wind speeds showed excellent correlation between all velocity predictions

16. Performance Prediction Conclusions
Tow tank method was limited by scale factors at low model speeds
FKS was limited to upright testing
SPLASH proved a valuable tool when its accuracy was increased with tank data
IMS and PCSail VPP’s provide reliable trends based on extensive hydrodynamic data
Custom VPP provided best results using complex hydrodynamic models
Polars constructed as best fit of all VPP data

17. Rudder Design
Designer David Pedrick provided an unfinished rudder design for the Mk II Navy 44
Three design comparisons
Size (Tow tank and SPLASH)
Planform (SPLASH)
Location and Depth (SPLASH)

18. Size Comparison Comparison of the Pedrick and “Beaver” rudders
Beaver rudder provided better turning ability and upwind ability in high wind speeds
SPLASH and Tank testing results were similar
SPLASH was used for the rest of the testing based on its accuracy and precision

19. Planform Comparison
Picked different shapes to determine the resulting flow patterns
Each shape was analyzed in SPLASH in under two hours
Baseline
Bulge
Elliptical
Tip
Zoid

20. Planform Results
Picked different shapes to determine the resulting flow patterns
Each shape was analyzed in SPLASH in under two hours
Baseline
Bulge
Elliptical
Tip
The Tip rudder was the most efficient rudder
The Tip moved the induced vortex away from the main lifting surface
The Tip rudder showed a drag reduction of 0.8% in turning and 0.2% while sailing upwind

21. Location and Depth Comparison
Forward movement interfered with wake from the keel
Increased depth interfered with keel vortex
No rudder proved better than the baseline
Compared rudders
Moved forward 1.6 ft
Moved forward 3.2 ft
Increased size to maximum draft (85% total draft)
Forward movement thought to reduce drag caused by wavemaking
Size increase thought to increase efficiency by reducing the relative induced drag

22. Rudder Design Conclusions
The Beaver rudder provided better turning and upwind ability, but was slower downwind
Moving the rudder forward or increasing its maximum draft increased drag
By adding a tip onto the Baseline rudder, the overall performance of the Mk II Navy 44 would be improved
CFD was more effective and efficient at redesigning appendages than tow tank testing

23. Future Work Integrate the rudder results into the custom VPP
Larger models should be tested to validate tow tank results
Viscid CFD codes should be used to evaluate the rudder comparisons
An improved Aerodynamic model should be used in the custom VPP
Full-scale testing would validate all of the data once a prototype is built

24. Questions?