The helicopter-ship dynamic interface software Ondeck was initially developed by the Australian Defence Science and Technology Orgainsation (DSTO) in 1988.
Since then it has been extensively modified to improve fidelity and permit the analysis of a wide range of helicopters and ships. AVT has been primarily responsible for Improving the code since 1997.
The current capability is detailed below.
Performance
- 14-16 times real time on a 1.3Ghz Pentium machine
Helicopter Models Developed*
- S70B-2 Seahawk
- MH60 Seahawk
- S70A Black Hawk
- SK 50/50A Sea King
- MRH90
- ARH Tiger
- Squirrel (ADF)
- Lynx Mk90b
- SH-2G Seasprite
- CH-47 Chinook
- S92
- Bell 222 (Generic)
* use subject to conditions. Manufacturing data must be supplied for lashed or restrained system analysis or high fidelity modelling.
Helicopter Modeling
- 6 DOF fuselage rigid body with integrated multi-degree of freedom undercarriage models including drag links and multi-stage oleos
- Non-linear oleo and tyre stiffness and damping models
- Additional coupled systems such as handling systems can be readily integrated.
Additional Software Used
- Standalone Matlab dynamics program for undercarriage component optimisation and qualification
Ship Motion Data Input
- Tilt table
- Sinusoidal 6 degree of freedom input
- SHIPMO7 frequency domain data
- FREDYN Time domain ship motion data
- Experimental data
- IMU Real time ship motion data (MHA System)
Tyre Contact Modeling
- Dynamic contact patch elements employed to enable both tyre adhesion and full sliding
- Accurate contact modeling based on tyre sectional properties enabling up to 85 deg combined lateral and longitudinal contact between the tyre and contact surface
- Multi surface tyre interaction enabling tyre interaction with ramps and other obstacles to be accurately modeled.
Friction Model
- Modified friction ellipse concept with tunable longitudinal and lateral friction coefficients for brakes on/off conditions, wet/dry deck conditions and static and dynamic motion.
Restraint System Models
- DeckLock / Harpoon with actuation model and limit load ann gimble limit criteria
- RAST / RSD model with limit load criteria. RSD can be traversed from flight deck to hangar.
- MacTaggart Scott TRIGON system. Standby mode functional. Traverse / Render modes almost complete.
Wind Loads Model
- Lateral wind fuselage model only at this stage
- 2D drag drag model is under development
Rotor Loads Model
- A flapping blade element rotor loads model has recently been implemented.
- This provides improved dynamic response characteristics as well as improved aerodynamic modelling.
- Matlab testing and further Ondeck verification is underway.
Lashing Models
- Non-linear models for chains, nylons and mitigators
- Moving axle and drag link lashings modeled
Limit Conditions
- Wheel sliding. Defined by elliptical envelope patch initialised about tyre contact point
- Wheel lift off
- Lashing loads
- Airframe tie down point loads
- Ship tie down point loads
- Undercarriage component loads
- Airframe / undercarriage clearance
- RAST Loads / Decklock loads and gimble limits / TRIGON
- Relative motion position and attitude limits
Analysis
- Real-time limit analysis using the Maritime Helicopter Aid (MHA)
- Assessment of helicopter - ship combination sea state capability
- Ship motion unrestrained and restrained limit analysis for FOCFT.
- Batch procedures for rapid limit determination using sinusoidal input, irregular SHIPMO7 data or irregular FREDYN data
- Landing loads assessment for combined vertical decent rate, drift rate and relative helicopter-ship attitudes
- Lashing scheme optimisation and sensitivity analysis
- Airframe and undercarriage clearance studies
- Fatigue analysis
- Assessment of ship suitability for helicopter operations
