Deliverable D4.3 presents the basic design and hydrodynamic optimization of the AUTOFLEX vessel, building on the concept from Task 4.2 to create “Oskar 2.0” – a refined, energy-efficient design validated through numerical simulations and physical model testing.
Design Development and Optimization Methodology
The design evolved through a multi-stage optimization process:
- Hull Form Optimization involved two rounds using CAESES parametric modeling, evaluating 1,254 hull variants through XPAN (a potential flow tool) before CFD validation of the best candidates.
- CFD Simulations used STAR-CCM+ with RANS and IDDES turbulence models, validated against DST model test data for resistance, wake fields, and propulsor performance in deep and shallow water.
- Model Testing was conducted at DST’s shallow water basin with a 1:7.75 scale model, testing three loading conditions, three water depths (hw/d ratios from 1.24 to 6.1), and speeds from 5-14 km/h.
- Propulsion Design combined potential flow methods (AKPA suite) with CFD to optimize ducted azimuth thrusters with controllable pitch propellers.
Key Technical Achievements
- Optimized Hull Form (#98) – 55m length with 2m bow extension achieving lower resistance while maintaining cargo capacity and providing space for autonomous systems.
- High-Efficiency Propulsion featuring twin 0.85m diameter ducted azimuth thrusters with CPP (design P/D = 1.2), 4-blade configuration, and 0.65 blade area ratio for operation across varying conditions.
- Validated Performance shows power demand significantly below initial estimates in most scenarios, with propulsive efficiency ηD = 0.56 at design conditions.
- Shallow Water Capability maintains adequate under-keel clearance and avoids propeller ventilation even at reduced draughts, with controlled dynamic trim across all tested conditions.
- Cargo Flexibility accommodates 24 TEU in containers, with capability for diverse bulk and break-bulk cargoes while maintaining stability margins.
Design Challenges and Solutions
- Hull optimization balanced competing objectives including resistance reduction, dynamic trim control, cargo capacity, and regulatory compliance across varying conditions.
- Propeller cavitation was addressed through increased blade area ratio (0.65), controllable pitch capability, and careful blade loading distribution and submergence.
- Stability requirements posed challenges for containerized cargo, requiring careful mass distribution with heavy containers in lower tiers or ballasting for operational flexibility.
- Integration of swappable battery systems within regulatory constraints affected cargo arrangement and vessel center of gravity, highlighting areas for potential regulatory evolution.
- Headbox design needs further optimization – the cylindrical shapes show flow separation that could be reduced through streamlined fairing development.
Validation and Performance Verification
- CFD Validation Studies showed excellent agreement with model test data for resistance (within measurement accuracy), dynamic sinkage and trim, and wake field characteristics across depth ratios.
- Model-to-Full-Scale Extrapolation used depth-dependent form factor corrections to account for shallow water effects on viscous resistance, validated against full-scale CFD simulations.
- Propulsor Performance Verification showed strong correlation between open water CFD predictions and measurements for thrust, torque, and efficiency across pitch settings from P/D = 0.2 to 1.4.
- Self-Propulsion Analysis confirmed design estimates with computed shaft power (14.665 kW at 10 km/h, deep water, LC1) within 0.6% of initial predictions.
Impact and Future Development
- The AUTOFLEX “Oskar 2.0” design demonstrates that systematic hydrodynamic optimization using CFD and model testing can achieve substantial performance improvements for inland vessels in shallow water environments.
- Power demand reductions of 15-20% compared to the initial concept enable extended range on battery power and improved total cost of ownership through reduced energy consumption.
- The design methodology combining parametric hull modeling, multi-fidelity optimization, and experimental verification provides a foundation for future autonomous inland vessel development.
- Further optimization is possible in stern shape refinement, headbox fairing design, and hull-propulsor interaction for additional performance gains.
Outlook: Foundation for Advanced Development
The basic design serves as the foundation for upcoming work in Task 4.4 (Maneuvering model development) and integration with other work packages:
- Validated hull geometry and propulsion characteristics for maneuverability simulation
- Established power demand profiles across operational envelope for energy system sizing
- Confirmed stability and loading characteristics for operational planning
- Physical model and numerical setups prepared for advanced maneuvering studies
Partner Contributions
This basic design resulted from contributions across the AUTOFLEX consortium:
DST – Hull form development, hydrostatics and intact stability analysis, model testing, and CFD validation
SO – Propulsor design, CFD simulations, and hydrodynamic optimization
ISE – Supporting analyses and design integration
These efforts produced a technically mature, experimentally validated vessel design ready for the next phase of autonomous system integration and operational assessment.
Download D4.3
Main Particulars: AUTOFLEX “Oskar 2.0”
- Length overall: 55 m
- Beam overall: 6.6 m
- Draught: 1.93 m
- Depth: 2.6 m
- Displacement: 651.7 t
- Cargo capacity: 24 TEU
- Deadweight: 532.6 t
- Lightship weight: 119.1 t
- Block coefficient: 0.901
- Propulsion: Fully electric, 2 × ducted azimuth thrusters (CPP, D = 0.85 m)it amet, consectetur adipiscing elit. Ut elit tellus, luctus nec ullamcorper mattis, pulvinar dapibus leo.