Application:

The following two main aspects are addressed:

1. The time domain simulation of pre-defined manoeuvres, which are zigzag manoeuvres, turning circles and Williamson turns (M.O.B.), each starting from a specific initial condition. Environmental conditions like wind, sea waves and current can be additionally considered.
2. Station keeping and crabbing calculations can be performed for a range of wind angles under the optional influence of sea waves and current. With the wind speed set to a specific maximum, the results from the computation are the power distribution and the total required power, optimized for minimum total power consumption, for each wind direction. If the total installed power is not sufficient to keep the position, the maximum attainable wind speed is calculated.

Currently MANOEUV works with the following propulsion and manoeuvring devices, which can be positioned freely: convetional propulsion setup with rudders and propellers, flap-type rudders, azimuth drives and tunnel thrusters.

From the geometry input to the actual manoeuvre definition, several features help with the necessary input data. Results from precomputational steps (e.g. hull force distribution) can be viewed using an internal viewer. This provides essential information on the correct tuning of the physical representation of the numerical method. 

The integrated analysis of the results shows the simulation results as diagrams and tables. The output data are stored in human-readable XML-files. 

The pre-computational step to determine independent force components equilibrium is divided into the calculation of 

• added masses
• rudder forces in the propeller slipstream
• hull rudder/pod interaction
• lateral propeller forces
• thrust deduction
• pod: strut and gondola forces

Fig. 1: Hull panel grid (top) and detail (bottom) of rudder and propeller in Paraview 

Theoretical Background:

The MANOEUV module is based on works by Söding, Krüger and Schumann. The primary principle is that all forces and moments on the ship’s body can be divided into separate components. Most of these force and moment components are resultants of calculations based on the potential flow theory.

Because the potential theory is based on ideal assumptions, several corrections and additional calculations are then affected to account for real conditions. The MANOEUV module has been validated by full-scale RANSE (Reynolds-averaged Navier Stokes Equations) calculations and a multitude of model test results. Simulation results agree well with full-scale trials and model test results. For manoeuvers, it is presumed that the ship is in forward motion and that the propeller provides thrust in this direction. The manoeuvering is calculated in three degrees of freedom: surge, sway, and yaw. The roll motion is taken into account in a static manner. The ship’s movements are calculated in a body-fixed coordinate system and then transferred to the earth-fixed coordinate system. Thrust provided by tunnel thrusters is taken into consideration at full stop and at speed with the corresponding loss of effectiveness.

The hull is idealized as a slender body. The linear components of the overall hull force are calculated based on the slender body theory. The quadratic components of the overall hull force are determined by using cross-flow coefficients defined along the length of the hull. Added masses for transient forces are calculated by a panel method. The thrust delivered by the propeller is calculated based on the open water curve of the propeller. The lateral force, yaw and roll moments of the propeller are calculated by a vortex lattice method as are the forces from the rudder, but under consideration of an empirically-based thickness correction. The interaction forces between rudder and propeller are modelled based on a mean surrounding flow acting in conjunction with the propeller slip stream on the rudder surface. Rudder-hull interaction is calculated by a vortex lattice method as well as the wake of the ship’s hull. The effects of wind forces are considered based on the work by Blendermann. Environmental wind at constant speed can be considered along with the fair wind. Current and mean wave forces can be taken into account. Multiple propellers, rudders, azimuth and tunnel thrusters can be modelled.

Fig. 1 show the hull panel grid with rudder and propeller arrangement. The three dimensional representation is displayed with Paraview so that the user can ensure the correct placement of devices.

Depending on the processing power and discretisation this pre-computational step takes approximately less than an hour. Subsequent numerical simulations of individual manoeuvres, as well as station-keeping calculations, are then performed within a matter of seconds. This is what makes the MANOEUV very suitable for initial design investigations.

Fig. 2: Example - Turning circle with (red) and without (black) current

Fig. 2 shows a track plot of two turning circle manoeuvres with same helm angle and approach speed, but one under the influence of current (red) and the other without (black).

References:

[1] Blendermann, W.: Wind Forces on Ships (in German); report no. 467, report, Institute for Ship Building, University of Hamburg, 1986

[2] Krüger, S.: A Panel Method for Predicting Ship-Propeller Interaction in Potential Flow; Ship Technology Research, Vol. 45:134-140, 1998

[3] Krüger S., Abels W., Greitsch L.: SESIS - Development of an Integrated Design and Simulation Tool for Ships, Integration into Full-Mission Simulator (in German), report, TUHH, May 2009

[4] Schumann, C.: MANOEUV Version 1.0 – A Program for Computing Manoeuvring and Station-keeping of Ships (in German), SchiffsRat, interal report, May 2016

[5] Söding, H.: Prediction of Ship Steering Capabilities; Ship Technology Research, Vol. 29:3-29, 1982