Finite Element Analysis (FEA) is an integral part of structural engineering, and as such, plays a key role in the ship design process. Naval Architect Nikos Papapanagiotou and FEA Engineer Dmitry Volik from C-Job, a Dutch naval engineering company, talk about the relevance of FEA in the field of naval architecture.

'FEA is a computer simulation method of solving complex engineering problems,' said Papapanagiotou, who works at C-Job's head office in the Netherlands. 'It uses a numerical method that simplifies a problem by "chopping" it into smaller pieces.' He uses a curve on an XY axis as an example: 'If we chop this curve into a finite number of smaller elements, and connect each point with straight lines, this gives us a very close result to reality.'

Global, Partial and Local Strength Analyses

For a ship design company like C-Job, FEA can be divided into three areas of detail: global, partial and local strength analyses. Papapanagiotou explains: 'Global FEA concerns the geometry of the whole vessel, and checks mainly behaviour of the ship structure as a whole. This type of analysis is the most important when making the initial decisions of the design process such as principal dimensions (length, breadth) and general arrangement of the vessel.'

As the term suggests, partial analysis is used to analyse a part of the ship. 'This is typically a substantial part of the ship; at least twenty per cent of its total length or three hold lengths. The purpose of this is to investigate in more depth the primary structure of the vessel together with irregularities in the structure such as openings, hatches, doors or ventilation ducts.'


C-Job's FEA Lead Engineer Dmitry Volik (left) and Lead Naval Architect Nikos Papapanagiotou (picture by C-Job).

Additional Forces Call for Local Analysis

C-Job can perform FEA in all of its offices, both in the Netherlands and in Ukraine. The Ukraine office, C-Job Nikolayev, has a team of engineers dedicated to performing FE strength calculations. 'Our work is very similar to what is happening in the Dutch offices and we work very closely with our Dutch colleagues,' said Volik. 'At the moment we mainly work on local strength analysis, but we have the intention to cover global analysis as well, just as our Dutch colleagues do.'

Volik: 'Local FEA can be carried out on any part of the ship, but it is especially useful in areas where more detailed calculations are needed because of additional forces, bending moments, fatigue or vibrations that could affect structural integrity. Therefore, it is generally used to calculate loads on smaller structures such as crane foundations, winches, mooring systems or other mission equipment.'

C-Job performs strength calculations on numerous types of vessels, including heavy lift crane vessels, ferries, yachts, drill ships, barges, dredgers, and cable layers. 'This includes strength and fatigue analysis of ship machinery and offshore and onshore wind equipment and components,' Volik noted. While C-Job uses ANSYS Mechanical and Siemens Femap for FE strength calculations, the team are also able to customise the software. 'This gives us much more flexibility in tasks, creating tools for specific needs, for example.'

Optimising Structure and Dimensions

Papapanagiotou: 'Being able to prove the integrity of a structure is especially important if you are building something for the first time, and for which there are no rules yet.' Yet, FEA can also be utilised during conversion contracts. 'Converting a vessel for a new purpose often involves adding new mission equipment for which it was not originally designed. FEA allows you to check the new loads of the vessel with its new equipment.'

The use of FEA has several advantages. 'The big advantage is that it can be applied at the very early stages of ship design,' explained Papapanagiotou. 'Therefore, it can be done before you make important decisions – it can even help you make them. These decisions relate to optimising the structure and dimensions, which go hand in hand with construction costs. It also allows a deeper insight into material selection and feasibility during the concept stages of design.'

Picture (top): Finite Element mesh of a three-cargo hold model.

Source: C-Job