The flow around manoeuvring ships and hydrodynamic forces are strongly affected by viscous effects, therefore it is anticipated, that application of viscous flow simulation codes will help in providing knowledge about flow features that influence the manoeuvring properties, thus supplementing the traditional experimental methods, and where possible, replacing them. This field is relatively new and there are several steps to be made:
- Substantial improvements in accuracy, efficiency and consistency of computations for simple modes of motion like steady drift, rotation, etc.
- Grid dependency of solutions and recommendations for practical applications
- Adequacy of turbulence models
- The performance of the methods needs to be improved, especially for non-steady simulations
- Studies should be done to determine the dependence of hydrodynamic coefficients on the amplitude of motions
- Propeller and rudder must be incorporated and hull-propeller-rudder interaction during manoeuvres studied
- Evaluation of scale effects
As a more ambitious alternative, direct CFD simulation of a free self-propelled ship or model performing real manoeuvres will be developed. The work package develops in a comprehensive way both methodological and implementation aspects of the methods; extends the applicability of the numerical methods; validates all of the developments against model test results; and renders state-of-the-art methods tools for practical consultancy work.
The overall aim of the Virtual Manoeuvring Basin is to use and further develop advanced CFD tools for predicting the manoeuvring performance of ships. The main approach developed here is based on using series of numerical flow simulations for prescribed simple (uniform or harmonic) modes of motion mirroring captive model tests. This provides hydrodynamic derivatives of forces and moments with respect to the individual degrees of freedom. These derivatives are then used in manoeuvrability simulators to evaluate ship performance in real manoeuvres. In this respect, an important question is to which extent numerical RANSE simulations are better than experimental and potential flow-based techniques and whether a replacement is feasible. In this direction, the following specific objectives are being targeted:
- Development of reliable numerical techniques based on RANSE solutions for the prediction of hydrodynamic derivatives of ship hulls in a variety of flow conditions
- Verification and validation of this approach against model tests
- Assessment of the validity of simplifications used in manoeuvrability predictions regarding the treatment of free surface and seaway, coupling of ship motions and motion amplitude, including quantification of the ensuing effects.
- To establish theoretical and methodological foundations for the application of RANSE-based simulations coupled with ship motions to directly simulate ship manoeuvres in calm water and in waves; validate these methods
Outline Work Plan:
The work package consists of several tasks. The major part are development tasks, concerning
- manoeuvrability in calm water,
- manoeuvrability in waves,
- control surfaces, appendages and propellers and
- direct numerical simulation of ship manoeuvres by RANSE modelling coupled to ship motions,
where RANSE solvers will be tailored to manoeuvrability problems and validated against model tests. On the implementation stage, the generated set of hydrodynamic derivatives made accessible through the integrated VIRTUE software platform will be used to predict ship behaviour in actual manoeuvres by ship motion simulation tools.