Prior to modeling, the most relevant loads and load combinations are to be described carefully. A matter of fact is that results may not be reliable due to a lack of attention for this matter. In many cases the real loads on a ship structure in the live cycle of the vessel are not exactly to describe beforehand and the applied loads on a model have to be a representative approximation depending on the applicable criteria. On the other hand one schould try to find the most critical load condition to avoid calculations of less interest. This job requires experience and deliberation.

The next job prior to modelling is to define the good boundary conditions to avoid too large models. Take into account that larger models are not automatically more reliable. There are many rules to take into account while describing boundary conditions. Furthermore modelling is a matter of experience and knowledge how to describe a structure using abstract element as realistic as possible. It’s much more important than the knowledge about the theory of solving finite element equations! There are thousands of way’s to build a model, however only one might be the good one!

Often annalists are satisfied if there is a suspected relation between deformation and loads and they can represent hotspots at the end of there investigations as shown in a figure of stresses like the figure below.

However the job is not finished when hotspots are found; the real job is still to do:
How to avoid high peak stresses and make the structure detail save without this peak stresses. Peak stresses means an enlarged risk of fatigue failure, even when the maximum value is lesser than the allowable stress. The most efficient way to avoid fatigue failures is to design structure details with care. Everyone should realize that fatigue cracks really occur on many places in the structure and even on small vessels.
Even in superstructures, formerly when made from light alloy, the risk of fatigue often is neglected because nobody suspect fatigue there! Too less attention for how to avoid stress concentrations, for example in faceplates of the primary structure, as well as less attention for quality of workmanship results in many fatigue cracks. These failures may be hidden beyond furniture and makes vibration impediment predictable. One should realize that this inconvenient effect may grow during the lifetime of the structure from zero when the ship is delivered to an unacceptable level.

Especially light alloy structures are very sensitive regarding fatigue! Even on small vessels and yachts an increase of fatigue failures are predictable. We have experience and the knowledge how to handle structure details.

ASC delivers not only the results of the calculations but also advises for alternatives if the structure does not match your expectations. We can offer analysis’s for a fixed price based on a clearly defined plan.