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Conference programme 

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Poster session

Lead Session Chair:
Stephan Barth, Managing Director, ForWind - Center for Wind Energy Research, Germany
Manuel Beauvais STX France Solutions, France
Co-authors:

(1) STX France Solutions, Saint-Nazaire, France (2) Bureau Veritas, Nantes, France (3) ICAM Nantes, Nantes, France

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Poster
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Presenter's biography

Biographies are supplied directly by presenters at OFFSHORE 2015 and are published here unedited

R&D project engineer at STX France Solutions, Manuel beauvais is graduated from UTT (Technology University of Troyes) as mechanical engineer.

Working for three years in its company, Manuel Beauvais has acquired major skills in offshore wind turbine loads prediction, structural calculations and optimisation and soil behaviour.

Abstract

Collision troubles : towards a new and powerful analysis method for an accurate design with less important risks.

Introduction

With the growth of offshore wind energy sector and associated size of wind farms, installation, exploitation and marine traffic becomes important around and inside the dedicated maritime areas. As a consequence, collision risk between vessels but also from a vessel into a structure is rising. Already seen as a major concern to guarantee the safety and operational durability of offshore structures in the oil & gas sector, risk is nowadays multiplied and object of dedicated studies.

For this reason, continuous research is being carried out in this field to characterize collision and failure procedure of offshore structures and the impacting vessels.

Approach

Lot of numerical simulations and various models have been developed to model the crushing process and to assess the damage of offshore platforms when they are impacted by a vessel.

As an example, Biehl used the non-linear finite element code LS-DYNA to study different offshore wind turbine support structures (monopile, jacket and tripod) impacted by single and double hull tankers and cargo ships with implicit and explicit resolution schemes. However, LS-DYNA models are really CPU and engineering time consuming, limiting the number of cases covered by designers and then the facility of respect of design rules.

Main body of abstract

In the framework of the research project called CHARGEOL, ICAM, Bureau Veritas and STX France are validating an industrial procedure and numerical software using a new approach methodology. This tool gives the opportunity to reduce CPU time by over than 1000 times and increase the number of collision cases and impact on structure design possibilities.For remind and according to certification rules, total structure behaviour object to collision case need to be calculated and structural impact can be evaluated through design code checks. Considering LS-DYNA simulations, preliminary studies covering the following point of interest have been carried out:

- Analysis of the contribution of the non-impacted braces and legs regarding the overall energy dissipation when a vessel comes in collision with structure
- Sensitivity analysis to several parameter like gravity, wind induced force, soil stiffness, etc...
- Analysis of the force transfer from the impacted leg section to the non-impacted braces with the objective to quantify the loads which cause serious stamping and plastic deformation of the non-impacted legs

Based on these results, a software has been developed using dedicated analytical formulations that account for energy dissipation procedure and behaviour of truss structures when a collision occurs. Moreover, taking into account soil stiffness but also wind turbine characteristics, etc… model used through the software is really accurate.


Conclusion

As mentioned above, ICAM, Bureau Veritas and STX France are currently validating this innovative and industrial tool in order to use it in early design stage. For validation, LS-DYNA simulations are performed and compared with tool results. Comparisons with laboratory tests are also performed.

Thanks to this new software and associated understanding of collision risk analysis, STX France and its partners are able to implement analysis in a really early design stage, reducing risk of problems during design phases, improving capability of design and associated knowledge and giving obviously more guarantee regarding safety and operational durability of the structures.


Learning objectives
- numerical simulations have been developed to model the crushing process and to assess damage on wind turbine supporting structures

- STX France and partners are validating an industrial procedure and numerical software using a super element based methodology in order to handle collision cases

- reduce CPU time by over than 1000 times but doesn't forget to take into account soil stiffness but also wind turbine characteristics,... for good accuracy of the model.