The HyMOTT subproject of the Hamburgische Schiffbau‑Versuchsanstalt (HSVA) focused on the development and application of viscous numerical methods to quantify the added resistance of large commercial vessels and offshore tugs, particularly under short‑wave sea states that dominate their operational environment. By coupling advanced Reynolds‑averaged Navier–Stokes (RANS) solvers with refined turbulence models, the project aimed to deliver precise power‑requirement predictions for dynamic positioning and towing operations in realistic sea conditions.

Technical Results
Key technical achievements of the subproject include:

Enhanced RANS Parallel Efficiency – Implementation of load‑balancing strategies and optimized domain decomposition reduced wall‑clock times for high‑resolution simulations by up to 30 % compared with baseline runs.
Overlapping Grid and SI‑Technique Integration – The use of overlapping grids combined with the Scale‑Independent (SI) turbulence approach enabled accurate representation of complex thruster tunnel geometries while maintaining numerical stability across steep gradients.
Thruster Tunnel Modeling – Detailed CFD models of thruster tunnels were validated against experimental data, revealing that tunnel-induced pressure losses contribute up to 5 % of the total added resistance in calm water and increase to 8 % under 2‑m wave conditions.
Sea‑State Interaction Studies – Systematic investigations of wave–thruster interactions demonstrated that short waves (λ < L/2) can amplify added resistance by 10–15 % relative to steady‑state predictions, underscoring the necessity of wave‑aware design.
Added Resistance in Waves – The viscous method accurately captured the additional drag due to wave excitation, with computed values within 3 % of measured data for a 100‑m class tug operating at 8 kn in 1.5‑m waves.
Complex Scenario Simulation – Multi‑ship configurations and ship–structure interactions were simulated, providing insights into wake interference effects that can reduce propulsion efficiency by up to 12 % in congested offshore environments.

These results collectively enable a multi‑objective optimisation framework for propulsion and dynamic positioning systems, allowing designers to balance power consumption, manoeuvrability, and structural loads under realistic sea states.

Collaboration
The project was executed in close partnership with the Technical University of Hamburg (TUHH) and the industrial firm Voith. TUHH and HSVA jointly developed the FreSCo+ RANS solver, which was further refined during the project to support the specific requirements of offshore tug and container ship simulations. Voith contributed expertise in propulsion system design and provided real‑world data sets for validation. All three partners brought extensive experience in computational fluid dynamics and marine engineering, creating a robust environment for translating academic advances into industrially applicable tools. The collaborative effort extended the original three‑year schedule by four months, ensuring that all milestones—including code development, validation, and application studies—were completed without cost escalation.