Seakeeping Assessment of Large Seakeeping Assessment of Large Trimaran Trimaran for Naval Aircraft Operations for Naval Aircraft Operations Presented by Mr. Boyden Williams, Mr. Lars Henriksen (Viking Systems), Dr. Igor Mizine (CSC/Advanced Marine Center), and Dr. Nils Salvesen (Viking Systems)
Trimaran Assessment Presentation Topics:. Development of Tool for Motions and Structural Loading Assessment. Design of Hulls by Advanced Fully 3D Hydrodynamic Assessment 3. Application to HALSS Trimaran Concept for Sealift Missions 4. Evaluation to NATO Seakeeping Criteria for Naval Aircraft Operations 5. Evaluation to NATO Seakeeping Criteria for Sealift Transit Operations 6. Presentation of Trimaran Systematic Series Seakeeping Results 7. Interesting Findings, Conclusions, and Future Studies Sponsored by CCDOTT 999-6 High Speed Trimaran Technology Development Program
Background of Selected Vessel - HALSS HALSS helps Early Insertion & Logistic Support: Deploys at High Speed (35 Knots) Operate fixed wing aircraft between advanced base and sea base HALSS helps Force Deployment: Operate fixed wing aircraft for theater operations Arrange and Configure military loads in preparation for early entry to the Theater operations Heavy Air Lift Sea Basing Ship (HALSS) 3
HALSS Principal Characteristics Flight Deck Length Flight Deck Width / Docking Hull Beam Draft Depth Payload: Combat forces sustainment Aircraft Fuel Supply Fixed Wing Aircraft Stowage Factor Main (Flight) Deck II Cargo Deck III (Crossover) & IV Decks HALSS Stowage Factor, FT 74 FT / 8 FT 37.9 FT FT 8,9 ST,65 ST Six C-3J 85,9 SQFT 4, SQFT 5, SQFT 46.7 SQFT/MT Unrefueled Range of Sea Voyage - CONUS to Advanced Base or to JOA, NM at 35 knots >5, NM at 5 knots Followed by days endurance in JOA 4
High Speed Trimaran Seakeeping Study - Objectives Establish Reliable Trimaran Analysis Procedure: Displacement, Velocities, Accelerations; Relative Motions for Slamming and Emergence; Hull Girder Loads and Local Pressures; Interaction between Main and Side Hulls. Determine Criteria for Assessment: Naval Air Operations (NATO STANAG 454, 997) Transit (NATO Generic Frigate) Assess Motion, Slamming, Emergence & Hull Girder Loads: Sea States 4 through 7; Vessel Speeds of 5, 5, 35 knots; Vessel Headings of, 45, 9, 35, 8 degrees; Multiple Hull Configurations 5
Design Variables - Trimaran Synthesis Model a L*sidehull Stagger = MS SH ( LOA LOA ) MH LOA SH SH Y (centerhull) Y* (sidehull) b X* (sidehull) X (Centerhull) MS SH - Distance from AP to Midship of Side Hull LOA SH Overall Length of the Side Hull LOA MH Overall Length of the Main Hull Clearance Separation = Beam MH b Clearance - Distance between the Outside of the Main Hull and the Inside of the Outer Hull at the waterline Beam MH - Maximum Beam of the Main Hull Lcenterhull Stagger of side hulls.,.4,.4 &.8 Separation of side hulls.36,.75,.5 Overall vessel size 5m, m, 5m & 3m 6
Method and Software - Selection Criteria : Ability to Handle Trimaran Type Hull Time-Domain Hydrodynamic Analysis Transformation to Frequency Domain for RAOs / Scaling Non-Linear Capability for Detailed Investigation Ability to Assess NATO Criteria Extendable to FEA Structural Analysis Ability to Rapidly Model Geometric Variations Ability to Work with Existing Software 7
Selection of Hydrodynamic Software Codes Considered LAMP (SAIC) SWAN (MIT) WASIM (DNV implementation of SWAN) WASIM is Chosen as Project Software WASIM is advanced fully 3-D ship motion assessment tool Assessment in Time Domain Capable of Non-Linear Hydrostatics WASIM previously used for trimaran type hull (M/V Triton) Viking Systems has extensive experience with DNV Software WASIM is integrated with SAGA Software 8
Seakeeping Criteria Naval Air Operations NATO STANAG 454 (Edition 3, 997) Single Amplitude RMS Values: Governing Factors Aircraft Handling Sink off bow and OLS limits Ramp Clearance Landing Line-up Performance Limitations Motion Limit Location Roll Period > s, Deg.; Period > s,.5 Deg Pitch Period > s,.5 Deg.; Period > 5s, Deg Vertical Stern Ramp at.8 m Displacement Flight Deck Lateral Stern Ramp at.3 m Displacement Flight Deck Landing Gear Vertical Velocity.7 m/sec Touchdown Point Crosswinds and Landing loads Relative Wind 35 to 4 knots envelope, +/- 5 degrees from the bow 9
Naval Air Operations - Environment Conditions Wind Speed (Kno 6 5 4 3 Wind Speed Over Deck for Flight Operations Wind Speed Minimum Required Speed Over Deck Maximum Required Speed Over Deck Wind - Vessel Wind - Sea State 3 4 5 6 7 Sea State Minimum Vessel Maximum Vessel Wind Speed Sea State Speed Speed (Knots) (Knots) (Knots). 35. 4. 3. 3. 37. 8.5 6.5 3.5 3 3.5.5 6.5 4 9. 6.. 5 4.5.5 5.5 5.5 3. 5.. 6 37.5 -.5.5 7 5.5-6.5 -.5 Head Sea Cases used for Analysis Insufficient Forward Speed to Maintain Maneuverability Using Wind Speed Criteria: The wind associated with a Sea State defines the required vessel speed to maintain 35-4 knot apparent wind speed over flight deck
Seakeeping Criteria - Transit NATO Generic Frigate Criteria (Pattison & Sheridan, 4) Single Amplitude RMS Values: Parameter Roll Angle Pitch Angle Vertical Acceleration Lateral Acceleration Bottom Slamming Index Propeller Emergence Index Comparison to Rule Hull Girder Loads Limit Value 4. deg.5 deg. g. g per hour 9 per hour
Hydrodynamic Analysis Define Vessel and Incoming Waves Panel and Mass Models defined to Represent Vessel Wave Elevation for Time Domain Analysis as Fourier Series of Cosine Waves with Amplitude According to PM Spectrum Recording Output & Results Time Series Recorded for 6 DOF Motions, Velocities & Accelerations Relative Wave Elevations Recorded for Series of 3 Locations Along the Length of Main and Side Hulls Hull Girder Shear Force & Bending Moments Recorded at Stations
Result Processing - Time vs. Frequency Hydrodynamic Analysis is Performed in the Time Domain, Results can be Transformed into Frequency Domain. Result Processing in the Time Domain - Benefits Statistical Analysis of Time Series for Result Variables Ability to Track Occurrence of Individual Phenomenon Unique Analysis Run for Each Sea State, Heading & Speed Result Processing in the Frequency Domain - Benefits Results Transformed into Response Amplitude Operators (RAO) Response to Unit Wave (RAO) Combined with Sea Spectrum Requires Fewer Analysis Runs Saves Computational Time Results can be Scaled for Vessels of Varying Length Reliable and Repeatable Post-Processing of Data is Essential 3
Result Processing Method Validation HALSS is evaluated in both Time and Frequency Domains Roll Motion Results Compared for Sea State 5, 6 & 7 Pitch Motion Results Compared for Sea State 5, 6 & 7 5 Knot Roll Angle 5 Knot Pitch Angle Head Sea Head Sea 3.5 35 8 45 35 45 6.5 4.5 7 9 7 9 5 35 5 35 Following Sea Following Sea Time & Frequency Domain Calculations Provide Nearly Identical Results 4
Result Processing - Time vs. Frequency Frequency Domain Analysis using RAO s possible for Motion, Velocity, Acceleration, Shear and Bending Loads saves calculation time Time Domain Analysis needed for Slamming and Emergence Assessment Head Sea Governs saves calculation time Frequency Domain: Pitch & Roll Motion 3 Wave Spectrum - SS6.5 Pitch RAO - L = 3m.5 Pitch RAO - L = 5m Pitch RAO - L = m Pitch RAO - L = 5m.5..4.6.8..4 Frequency (Rad/s) Heave & Sway Acceleration Vertical Bending Moment Vertical Shear Force Amplitud 5 4.5 4 3.5 3.5.5.5 Time Domain: Slamming Occurrence Center Hull Slamming Occurrence Side Hull Bridge Deck Slamming Occurrence Propeller Emergence Occurrence 5
Results Summary for HALSS HALSS Trimaran Hull Configuration 35 knots in SS7 Head Seas 6
Results Summary for HALSS Comparison of Hydrodynamic Results to NATO Criteria for Naval Air Operations.4 Vertical Displacement at Stern. Pitch Motion. RMS Response Displacement Limit. Vert. Displacement (.8.6.4. 3.5 6.5. 5.5 Pitch Angle (Degree.8.6.4. RMS Response Pitch Limit 3.5 6.5. 5.5. 3 4 5 6 7 Sea State (Vessel Speed Shown in Labels) 3 4 Sea State 5 6 7 (Vessel Speed Shown in Labels).8 Vertical Velocity at Touchdown Point.5 Vertical Acceleration at Bridge Vert. Velocity (m/.7.6.5.4.3.. RMS Response Velocity Limit 3.5 6.5. 5.5. Vert. Acceleration (m/s^.5.5 RMS Response Acceleration Limit 3.5 6.5. 5.5. 3 4 5 6 7 Sea State (Vessel Speed Shown in Labels) 3 4 5 6 7 Sea State (Vessel Speed Shown in Labels) 7
Results Summary for HALSS Comparison of Results to NATO Criteria for Transit Polar Plots to Facilitate Comparisons, 5 m vs. 3 m: 5 m Trimaran Separation =.36 Stagger =.4 Speed =.6 Kts 35 RMS Roll Angle Head Sea 4 9 3 m Trimaran Separation =.36 Stagger =.4 Speed = 5. Kts 45 5 m Trimaran Separation =.36 Stagger =.4 Speed =.6 Kts 35 RMS Pitch Angle Head Sea 4 3.5 3 3 m Trimaran Separation =.36 Stagger =.4 Speed = 5. Kts 45 4.5 9 Roll Criteria.5 SS 5 4 SS 5 SS 5.5 SS 5 7 SS 6 - SS 6 9 7 SS 6 SS 6 9 SS 7 SS 7 SS 7 SS 7 Pitch Criteria 5 35 5 35 Following Sea Follow ing Sea Results for 5 m Vessel Created by Length Scaling RAOs 8
Results Summary for HALSS Comparison of Results to NATO Criteria for Transit Center Hull Propellers Side Hull Propellers Emergences Per Hour 4 35 3 5 5 Center Hull Propeller Emergence - 5 Knot Vessel Speed SS4-5Knots SS5-5Knots SS6-5Knots SS7-5Knots Criteria Emergences Per Hour 7 6 5 4 3 Side Hull Propeller Emergence - 5 Knot Vessel Speed SS4-5Knots SS5-5Knots SS6-5Knots SS7-5Knots Criteria 5 45 9 35 8 Wave Heading 45 9 35 8 Wave Heading Emergences Per Hour Center Hull Propeller Emergence - 35 Knot Vessel Speed 45 SS4-35Knots 4 SS5-35Knots 35 SS6-35Knots SS7-35Knots 3 Criteria 5 5 5 45 9 35 8 Wave Heading Emergences Per Hour Side Hull Propeller Emergence - 35 Knot Vessel Speed 4 SS4-35Knots 35 SS5-35Knots SS6-35Knots 3 SS7-35Knots 5 Criteria 5 5 45 9 35 8 Wave Heading 9
HALSS Transit Slamming and Hull Girder Loads Comparison of Results to NATO Transit Criteria and ABS Rule Loads 3 Center Hull Bottom Slamming 4.5E+7 Vertical Shear Force Envelope - All Directions - 35 Knots Emergences Per Hour 5 5 5 45 9 35 8 Wave Heading No Slamming below Sea State 7 SS7-5Knots SS7-5Knots SS7-35Knots Criteria Head Sea is the worst wave heading for slamming ABS Rule Shear for equivalent monohull = 4.8 x 7 N ABS Rule Bending Moment for equivalent monohull = 4.6 x 9 N-m Bending Moment (N-m) Shear Force (N) 4.E+7 3.5E+7 3.E+7.5E+7.E+7.5E+7.E+7 5.E+6.E+ 5 5 5 3 Longitudinal Location (m) SeaState4 SeaState5 SeaState6 SeaState7 ABS Rule Shear Vertical Bending Moment Envelope - All Directions - 35 Knots 5.E+9 4.5E+9 4.E+9 3.5E+9 3.E+9.5E+9.E+9.5E+9.E+9 5.E+8.E+ 5 5 5 3 Longitudinal Location (m) SeaState4 SeaState5 SeaState6 SeaState7 ABS Rule Bending
HALSS Transit Acceleration Results Comparison of Results to NATO Criteria for Transit 35 Knot Vertical Acceleration 35 Knot Horizontal Acceleration Acceleration at Max Beam 35 Head Sea 6 5 4 3 Acceleration at CL 45 SS7 - Bow SS6 - Bow SS5 - Bow SS4 - Bow Criteria SS7 - MidShips SS7 - Stern SS6 - MidShips SS6 - Stern Acceleration at Max Beam 35 Head Sea.8.6.4 Acceleration at CL 45 SS7 - Bow SS6 - Bow SS5 - Bow SS4 - Bow Criteria SS7 - MidShips SS7 - Stern SS6 - MidShips SS6 - Stern SS5 - MidShips SS5 - Stern. SS5 - MidShips SS5 - Stern 7 9 SS4 - MidShips SS4 - Stern SS7 - Bow 7 9 SS4 - MidShips SS4 - Stern SS7 - Bow 5 Following Sea Vertical Acceleration Criteria 35 SS7 - MidShips SS7 - Stern SS6 - Bow SS6 - MidShips SS6 - Stern SS5 - Bow SS5 - MidShips SS5 - Stern SS4 - Bow SS4 - MidShips SS4 - Stern 5 Following Sea Horizontal Acceleration 35 SS7 - MidShips SS7 - Stern SS6 - Bow SS6 - MidShips SS6 - Stern SS5 - Bow SS5 - MidShips SS5 - Stern SS4 - Bow SS4 - MidShips SS4 - Stern Trimaran meets vertical acceleration criteria up to sea state 6 Trimaran meets horizontal acceleration criteria up to sea state 7
Result Highlights for Other Hull Configurations Result Data Sheet for Each Stagger, Separation, Length, Speed & Sea State
Stagger Influence 5 knots Maximum Response from All Headings.5 Pitch Angle Roll Angle Stagger =. Stagger =.4 Stagger =.4 Stagger =.8 9 8 7 Stagger =. Stagger =.4 Stagger =.4 Stagger =.8.5 6 5 4 3.5 SS4 SS5 SS6 SS7 SS4 SS5 SS6 SS7 Vertical Acceleration at Stern - Centerline 3 Vertical Acceleration at Bow - Centerline.8.6.4. Stagger =. Stagger =.4 Stagger =.4 Stagger =.8.5 Stagger =. Stagger =.4 Stagger =.4 Stagger =.8.5.8.6.4..5 SS4 SS5 SS6 SS7 SS4 SS5 SS6 SS7 3
Separation Influence 5 knots Maximum Response from All Headings.5 Pitch Angle 9 Roll Angle.5 Separation =.36 Separation =.75 Separation =.5 8 7 6 5 Separation =.36 Separation =.75 Separation =.5 4 3.5 SS4 SS5 SS6 SS7 SS4 SS5 SS6 SS7 Vertical Acceleration at Stern - Centerline 3 Vertical Acceleration at Bow - Centerline.8.6.4. Separation =.36 Separation =.75 Separation =.5.5 Separation =.36 Separation =.75 Separation =.5.5.8.6.4..5 SS4 SS5 SS6 SS7 SS4 SS5 SS6 SS7 4
Wave Train Interaction vs. Trimaran Configuration Effect of Stagger along the Center Hull Effect of Separation along the Center Hull The wave train interaction between the hulls increases the amplitude of the standing wave along the length of the center hull for certain hull configurations. This amplification of center hull waves leads to additional bending moment in the hull girder loads and a wave trough in way of the props, which can induce excessive amounts of propeller emergences. Wave Train Interaction can have large impact on trimarans performance Phenomenon can guide the choice of trimaran hull configuration More studies are needed to fully comprehend the impact on design 5
Wave Train Interaction Phenomenon Vessel Configuration with.8 Stagger Ratio /.75 Separation Ratio 35 knots in Sea State 5 6
Structural Design as a Criteria for Seakeeping Assessment The impact of the vessel configurations and hydrodynamic loads on the structural requirements of the vessel are considered in the selection of the optimal design 7
Structural Optimization Ongoing Work The design pressures and accelerations developed with the hydrodynamic analysis can be translated directly to Finite Element Analysis (FEA) models. FEA provides a direct assessment of the variations in motions and loads on the structural requirements of the vessel. Based on present results, a structural optimization routine is being developed 8
Conclusions Systematic Seakeeping Database Established for Trimarans Valuable for synthesis level of design Useful as concept evaluation tools Will be expanded with future work to include structural optimization WASIM / SAGA is a reliable and expandable design tool Strong Wave Train Interaction Phenomenon Identified Early detection allows problem to be addressed at the hull form development stage HALSS Provides Favorable Seakeeping Performance Side hull propeller emergence limiting factor 9