It’s been noted for some time that in the combination of very high speeds and watercraft, there is a high degree of uncertainty and difficulty in predicting performance and behavior. Most manufacturers use their experience gained from more of a trial and error approach as the key to the performance they have derived. In aerospace for example, there is far more computational analysis carried out on every detail of the design, before committing to manufacture.
Structural analysis (FEA) has been increasingly used to optimize metallic & composite structures, but the inherent problem is always which load cases are applied, and the difficulties in measuring accurately the surface pressures and forces that hulls encounter in seas at higher speeds. Traditional studies on test hulls using pressure gauges have been carried out, but the conclusion has mostly been that the pressure variation is so highly concentrated and distributed, that a true insight into what is really going on is difficult to gleam.
When it comes to analyzing a hull, it is extremely difficult to know what pressure distribution to apply in simulations to properly analyze hull slamming (typically the peak loadcase on a high speed boat).
Current industry practice
The current CFD tools available are very focused in what can be simulated, especially when looking at more than one aspect at the same time. This is satisfactory for looking at the aerodynamics on its own or for running a hydrodynamic analysis, but it is fraught with danger and erratic results especially at high speed. Running an accurate multiphase fluid analysis has been the holy grail for designers in order to properly simulate, understand and optimize a hull.
However, the limitations of existing software and CFD codes, the finding of people able to conduct this analysis, as well as the computing requirements needed to deliver decent resolution have been a barrier to using these tools for the general marine industry, and especially the high speed sector.
CMN NAVAL approach
The Group has materialized a series of programs with a number of CFD companies (both consultants and software companies), to try and get to the root of this problem. However, none could provide a suitable answer and so the only option was to use the tools on single phase flow in isolation, optimizing from there, and combining the results manually into the calculations.
Around spring last year, CMN NAVAL contacted an aerodynamics team grouped in academia (fresh off the back of designing of a high profile land speed record project). In addition to this team, the Group recruited Formula 1 aerodynamics experts to consult on a number of projects, in order to bring in a type of thinking not usually met in the marine industry.
Results
The results of the collaboration (which is on-going), are two-fold:
Bespoke CFD software has been created specifically and exclusively to resolve the problems outlined above. Furthermore, the inclusion of some state of the art AI (Artificial Intelligence) features, more commonly found in automotive and aerospace industries, has been successfully completed.
A high speed vessel is being designed using all these techniques and methods, combining all the experience of the design team and consultants.
At present, it was possible to optimize the hull and deck geometries to generate 60% more lift and with less drag than the conventional high performance baseline design and significant further gains are still being found.