Presel efficiently assembles the superelements created by the Sesam preprocessors to form a complete model of a structure.

Utilise the superelement technique
The superelement technique involves creating first level superelements of parts of the structure. Using the Sesam modelling programs Patran-Pre and/or GeniE. Using Presel these part models are assembled through two or more levels to form the complete model.

When going on to perform structural analysis in Sesam’s general purpose FE program, Sestra, the equation systems for each first and higher level superelement are formed, and reduced, successively until the whole system has been solved. Results for the complete model, or for selected superelements only, may be taken into a Sesam program module for results evaluation or further processing.

Sesam offers the most advanced use of the superelement (sub-structuring) technique available in the market: There are no restriction on the total number of superelements, the number of superelement repetitions, the number of superelement levels and the number of loads. Moreover, the superelement technique is integrated in all parts of Sesam from preprocessor to postprocessor.

The reduction methods available in Sestra for dynamic analysis profit by splitting the model into part models. So even though the superelement technique mathematically is limited to static analysis the same methodology applies to dynamic analysis. In fact, a superelement model initially established for static analysis may with few or no modifications be used in a subsequent dynamic analysis.

Benefits
Split models into super-elements and save modelling and analysis time

• Dividing a model into separate superelements allows for concurrent modelling and results evaluation, with different engineers working on the different parts in parallel. This leads to an overall reduction in both project man-hours and duration.
• Identical parts of the model need only be modelled once, and the superelement reused when assembling the complete structure in Presel.
• Working with smaller parts ( i.e. superelements) increases realiability of data and reduces probability of modelling errors
• If part of the structure needs to be re-designed, only those superelements covering the areas containing the changes need to be re-modelled and re-computed.

References
The use of Presel, and superelements in particular, has enabled users to analyse and verify the structural design of complete platforms, such as TLPs, spars, sem-submersibles and FPSOs using Sesam. Recent examples include the design of the Matterhorn and Typhoon TLPs by Atlantia Offshore of Houston, Texas.