The use of numerical calculation methods offers many possibilities to investigate ship manoeuvres. In general, numerical calculations analogous to PMM-experiments (Planar Motion Mechanism) are carried out in which static and dynamic simulations are performed to determine the forces and moments as a function of a specific movement of the ship. From this, the hydrodynamic coefficients can be derived and fed into a mathematical model. With the calculation of a complete set of hydrodynamic coefficients, any manoeuvre can be simulated. To verify the quality of the numerical calculations, the calculation results are continually validated with the corresponding measured values.

Numerical simulations allow to:

• Simulate manoeuvring behaviour in model and full-scale
• Simulation of static and dynamic tests
• Visualisation of flow, detection of separating flow
• Design of control elements such as rudders, thrusters, etc.

The rudder is by far the most frequently used control element; it operates in the wash of the propeller. Below, the pressure distribution on the rudder for a rudder angle of δ_R = 20° with a rotating propeller is shown.

The use of numerical methods offers many opportunities to examine ships at sea. The SVA can use the program system UTHLANDE or RANSE Method depending on the application. UTHLANDE provides the ability to perform seaway calculations based on linear and non-linear strip method. Using this method, monohulls and catamarans can be studied over a wide range of applications and short- and long-term statistics can be calculated. For special cases or the simulation of non-linear applications, RANSE Method (ANSYS Fluent) is used.

With numerical calculations, issues can be examined in terms of added resistance or the acceleration and motion behavior of ships. Added resistance at sea is an essential aspect in order to determine power requirements and operating costs of vessels correctly. The motion behaviour at sea, however, is an essential aspect of comfort and determines the operating limits of ships.

The numerical seaway simulations with RANSE procedures include the following applications:

• Seaway from any direction, stationary and in motion
• Calculation of regular and irregular sea states, with the focus on the calculation of regular seaway
• Determination of the added resistance
• Determination of accelerations

An initial ship design is rarely optimal in terms of its hydrodynamic efficiency. Often, a new design is derived from geometries of existing ships and “manually” adjusted for the new mission profile. To maximise the economic, environmental, and in particular, fuel efficient operation, the vessel geometry can be optimised without effecting other design criteria such as displacement distribution, load capacity, speed, stability, wake distribution, etc. This optimisation is performed with the use of CFD methods, either by means of a mathematically based, automatic optimisation, or knowledge based on the groundwork of decades of experience of engineers.
For this optimisation, among other things, various parametric models of the “CAESES” software are used. The optimisation is done on the basis of viscous CFD calculations, since these are considerably more reliable in optimising than the potential theory method. The savings benefits are generally considerable and give, over the life of the vessel, a significant increase of the “return on investment”. Classical optimisation tasks are the optimisation of bows, bulbous bows, and sterns. While on new designs an optimal concept is at once available, in the area of retrofitting, especially a bulbous bow, optimisation makes sense. Generally, this is done for the customer’s predefined mission profile fully parametrically. The example shows the development of the drag resistance of a ship geometry depending on the variation of the bulbous bow.
As a secondary condition of minimum resistance or propeller thrust, optimisation of the flow into a propeller (homogeneity of the wake) can be considered.

Propeller struts, stabiliser fins and other appendages can make a significant contribution to the ship’s resistance. Through the optimised shape and alignment of the appendages, the resistance and the loading of the attachments are minimised. Accordingly the propeller wash becomes homogeneous, improving the quality and efficiency of propulsion and contributing to the reduction of vibration and noise.