Finite Element Analysis, getting a closer look
Finite Element Analysis (FEA) is an integral part of structural engineering, and as such, plays a key role in the ship design process. In this article, C-Job’s Lead Naval Architect Nikos Papapanagiotou (from the head office in the Netherlands) and FEA Lead Engineer Dmitry Volik (from C-Job’s Ukraine office) talk about the relevance of FEA in the field of naval architecture and C-Job’s own skills and experience in the subject.
“FEA is a computer simulation method of solving complex engineering problems,” opens Nikos. “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.”
Initial decisions
For a ship design company like C-Job, FEA can be divided into three areas of detail: global, partial and local strength analyses. Nikos 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 20 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. Local analysis goes even further into detail, as Dmitry will explain.”
Finite Element discretization of Ordinary WebFrame
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; sharing knowledge is very important,” says Dmitry. “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. “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.” Dmitry goes on to say that the FEA team at C-Job Nikolayev has experience supporting customers with strength calculations on numerous types of vessel. “Heavy lift crane vessels, ferries, yachts, drill ships, barges, dredgers, and cable layers for example,” he notes. “This includes strength and fatigue analysis of ship machinery and offshore and onshore wind equipment and components.” While C-Job uses ANSYS Mechanical (both Classic and Workbench) and Siemens Femap for FE strength calculations, Dmitry points out that the team are also able to customise the software. “This gives us much more flexibility in tasks, creating tools for specific needs, for example.”
Finite Element mesh of a 3-cargo hold model
Optimising structure and dimensions
It is important to note that FEA is not only useful in new build projects, adds Nikos. “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.” Furthermore, FEA can 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.”
Nikos Papapanagiotou, Lead Naval Architect
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