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Performance Prediction and Design Optimization
Performance Prediction and Design Optimization
Midn 1/c Jon P. SilverbergMidn 1/c Jon P. Silverberg
Performance PredictionPerformance Prediction
• The velocity of a ship is inherent to its mission effectiveness
• Three methods of determination– Hydrodynamic Tank Testing– Parametric Analysis– Computational Fluid Dynamics
• The velocity of a ship is inherent to its mission effectiveness
• Three methods of determination– Hydrodynamic Tank Testing– Parametric Analysis– Computational Fluid Dynamics
Mk II Navy 44 Sail Training CraftMk II Navy 44 Sail Training Craft
• Designer David Pedrick supplied:– Lines Plan– Sail Plan– Parametrically predicted speeds from the
IMS Velocity Prediction Program (VPP)
• 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
• Sailing craft complexities– Six Degrees of Freedom– Propulsion Systems– Lifting Surfaces
Performance Prediction Process
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
• 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
Initial Parametric AnalysisInitial Parametric Analysis
• Needed to determine sailing conditions and sail forces which the IMS VPP did not provide
• 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
• Predictions were performed with University of Michigan’s “PCSail” developed by David Martin
• Derived conditions to test in the tow tank
Basic HydrodynamicsBasic 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
• 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
Tow Tank Testing
Tow Tank Testing
• Data Recorded– Drag– Lift– Yaw Moment– Pitch
• Data Recorded– Drag– Lift– Yaw Moment– Pitch
• Tests included• Upright Conditions• Sailing Conditions• Viscous Corrections
• Performed more than 570 runs
• Tests included• Upright Conditions• Sailing Conditions• Viscous Corrections
• Performed more than 570 runs
FKS – CFDFKS – 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
• 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
• 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
Wavemaking ComparisonWavemaking Comparison
Scale effects in tank testingScale effects in tank testing
Spray and pitchSpray and pitch
Viscous interaction in wavemaking
Viscous interaction in wavemaking
SPLASH – CFDSPLASH – CFD
• 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
• 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
Development was by Bruce Rosen of South Bay Simulations and Joe Laiosa from Navair at Patuxent River
Development was by Bruce Rosen of South Bay Simulations and Joe Laiosa from Navair at Patuxent River
All Upright DataAll Upright Data
0
500
1,000
1,500
2,000
2,500
3,000
3,500
4,000
4,500
5,000
0 2 4 6 8 10 12
Velocity [knots]
Res
ista
nce
[lb
s]
Tank
FKS
SPLASH
0
500
1,000
1,500
2,000
2,500
3,000
3,500
4,000
4,500
5,000
0 2 4 6 8 10 12
Velocity [knots]
Res
ista
nce
[lb
s]
Tank
FKS
SPLASH
Different method of viscous calculations
Different method of viscous calculations
Pitch EffectsPitch Effects
Sailing Hydrodynamic
Data
Sailing Hydrodynamic
Data
SPLASHSPLASH
Tank Testing
Tank Testing
Utilized MATLAB and MAPLE to interpolate through sailing matrices
Utilized MATLAB and MAPLE to interpolate through sailing matrices
Mk II Navy 44 VPPMk II Navy 44 VPP• Aerodynamics
– Analyzed sail forces using basic wing theory– Force coefficients from sails derived from IMS VPP
• Aerodynamics– Analyzed sail forces using basic wing theory– Force coefficients from sails derived from IMS VPP
• Solution– Draghydro= Driveaero
– Lifthydro= Sideforceaero
– RightingMomenthydro = HeelingMomentaero
– YawingMomenthydro = YawingMomentaero
• Solution– Draghydro= Driveaero
– Lifthydro= Sideforceaero
– RightingMomenthydro = HeelingMomentaero
– YawingMomenthydro = YawingMomentaero
Custom VPP had a complex hydrodynamic model and solution but a simplified aerodynamic model
Custom VPP had a complex hydrodynamic model and solution but a simplified aerodynamic model
• 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
• 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
Solved by simultaneous equations using finite-difference iteration
Performance PredictionsPerformance Predictions
Low wind speeds showed variable results due to simplifications in the aerodynamic model
Low wind speeds showed variable results due to simplifications in the aerodynamic model
All other wind speeds showed excellent correlation between all velocity predictions
All other wind speeds showed excellent correlation between all velocity predictions
Performance Prediction ConclusionsPerformance 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
• 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
Rudder DesignRudder 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)
• 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)
Size ComparisonSize Comparison • Comparison of the Pedrick and “Beaver” rudders
• Beaver rudder provided better turning ability and upwind ability in high wind speeds
• 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
• SPLASH and Tank testing results were similar• SPLASH was used for the rest of the testing
based on its accuracy and precision
Planform ComparisonPlanform Comparison
• Picked different shapes to determine the resulting flow patterns
• Each shape was analyzed in SPLASH in under two hours
• Picked different shapes to determine the resulting flow patterns
• Each shape was analyzed in SPLASH in under two hours
BaselineBaseline BulgeBulge EllipticalElliptical TipTip ZoidZoid
Planform ResultsPlanform Results
• Picked different shapes to determine the resulting flow patterns
• Each shape was analyzed in SPLASH in under two hours
• Picked different shapes to determine the resulting flow patterns
• Each shape was analyzed in SPLASH in under two hours
BaselineBaseline BulgeBulge EllipticalElliptical TipTip • The Tip rudder was the most efficient rudder
• The Tip moved the induced vortex away from the main lifting surface
• 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
The Tip rudder showed a drag reduction of 0.8% in turning and 0.2% while sailing upwind
Location and Depth ComparisonLocation and Depth Comparison
• Compared rudders– Moved forward 1.6 ft– Moved forward 3.2 ft– Increased size to
maximum draft (85% total draft)
• 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
• Forward movement thought to reduce drag caused by wavemaking
• Size increase thought to increase efficiency by reducing the relative induced drag
• Forward movement interfered with wake from the keel
• Increased depth interfered with keel vortex
• No rudder proved better than the baseline
• Forward movement interfered with wake from the keel
• Increased depth interfered with keel vortex
• No rudder proved better than the baseline
Rudder Design ConclusionsRudder 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
• 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
Future WorkFuture 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
• 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