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.

Along with resistance and stability considerations resulting from wind loads, the focus of aerodynamic investigations of the hull above water is also on the problems of exhaust and intake from ventilation and air conditioning systems and the analysis of exhaust gas concentrations. The latter applies primarily to yachts and passenger ships, where comfort aspects are an important design criterion.

Due to the complex geometry of superstructures or masts, turbulence and recirculation zones can arise which can be examined in terms of gas distribution. To process such inquiries, numerical methods can offer possible solutions in order to verify structural aspects and to carry out calculations on variants.

Through simulation the following aspects may be considered:

• Calculation of wind, exhaust gas, intake and exhaust flow, and detection of mutual interactions
• Detailed visualisation of the flow and fluid concentrations, i.e. the exhaust gas
• Calculation of the flow around the whole ship (not linked to specific measurement positions)
• Temperature distribution for the detection of “hotspots”
• Accounting for the wind profile
• Calculation for full-scale version

The wake fields between model and full-scale show differences because of the underlying physics. In model-scale the boundary layer is thicker relative to full-scale and the bilge vortex more pronounced. This results in differences in the inflow to the propeller between model and ship, which should be considered when designing the propeller. Through the use of numerical methods, the wake field can be calculated for both the model and the ship. Thus it is possible, already while designing the ship lines, to evaluate the wake field and the influence of geometry modifications or appendages. Further, the wake field can be made available for propeller design.

The numerical simulations offer the following advantages:

• Calculation of the wake field in the preliminary design stage
• Calculation of the wake field for the Reynolds number of the vessel
• Evaluation of the velocity components of the wake for any radius and angular increments
• Visualising the inflow and presentation of the causes (for example, separations) for potential irregularities