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Formulation and Application of Finite Element techniques for Slender Marine Structures Subjected to Contact Interactions

Longva, Vegard
Doctoral thesis
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URI
http://hdl.handle.net/11250/2358726
Date
2015
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  • Institutt for marin teknikk [3315]
Abstract
The main purpose of this work is to formulate and apply new computational strategies

for two contact-governed problems where existing finite element software suffer from

poor efficiency and lack of robustness. The first problem is concerned with trawl board

pull-over interaction of subsea pipelines while the second deals with reeling analysis of

history-dependent flexible pipes.

Previous numerical models for trawl-pipe interaction based on simplified geometry

modeling has struggled with contact-related convergence problems. A contact element

with a continuous description of the trawl board contact geometry and the pipe geometry

was therefore developed. The assumption of a rigid contact geometry for the trawl board

and the use of line-line and line-point contact kinematics resulted in good numerical efficiency

properties. The ability to predict the pull-over responses depends heavily on the

modeling of the trawl board hydrodynamic loads. A fairly advanced six degree of freedom

load model with precomputed hydrodynamic coefficients was therefore established.

An extensive simulation work was carried out to validate the trawl-pipe computational

strategy and to identify sensitive model parameters. Regarding the former, the proposed

numerical model was demonstrated to predict pull-over load impulses within a 10% margin

of model test measurements and was thus concluded to be capable of describing the

relevant effects of the pull-over. The sensitivity study revealed that the interaction behavior

was greatly influenced by the board-pipe friction coefficient, the tension level in

the wire between board and trawl net, the towing line drag properties and the direction

of over-trawling. Due to the sensitivity of the input parameters, it was concluded that a

proper validation against experimental tests is necessary for future work of similar kind.

Further studies should aim to quantify the degree of non-conservatism present for nonperpendicular

crossings and attempt to improve current design load recommendations by

including more model parameters.

Reeling operations with history-dependent material behavior and extensive contact

interactions along the material transport route are often not feasible to simulate with conventional

finite element software. This relates to contact-related convergence problems

and the need for long meshes with small and equal-sized elements giving poor numerical

efficiency. These issues were successfully solved by developing a Lagrangian-Eulerian

beam formulation that enabled for a virtually fixed mesh in space. The proposed formulation

was subjected to various benchmark tests where it was demonstrated to provide

similar accuracy as the conventional Lagrangian method.

In recent years, subsea contractors have experienced torsional failures in spoolbasevessel

load-out operations of flexible pipes. An idealized finite element model was therefore

established to gain insight into such operations and to identify the mechanisms responsible

for the generated torque. Torsional failures were identified for three different

mechanisms and strategies to avoid them were proposed. A comparison study against a

physical load-out operation should be conducted in future work to quantify the ability to

predict the torque and to reveal possible model deficiencies.
Has parts
Paper 1: Longva, Vegard; Sævik, Svein. A Lagrangian–Eulerian formulation for reeling analysis of history-dependent multilayered beams. Computers & structures 2015 ;Volum 146. s. 44-58 http://dx.doi.org/10.1016/j.compstruc.2014.09.002

Paper 2: Longva, Vegard; Sævik, Svein; Levold, Erik; Ilstad, Håvar. Dynamic simulation of subsea pipeline and trawl board pull-over interaction. Marine Structures 2013 ;Volum 34. s. 156-184 http://dx.doi.org/10.1016/j.marstruc.2013.09.004

Paper 3: Longva, Vegard; Sævik, Svein. A penalty-based contact element for pipe and 3D rigid body interaction. Engineering structures 2013 ;Volum 56. s. 1580-1592 http://dx.doi.org/10.1016/j.engstruct.2013.07.025

Paper 4: Longva and S. Sævik. On prediction of torque in flexible pipe reeling operations using a Lagrangian-Eulerian FE framework. © 2016. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/ published in Marine Structures Volume 46, March 2016, Pages 229–254 http://dx.doi.org/10.1016/j.marstruc.2016.01.004
Publisher
NTNU
Series
Doctoral thesis at NTNU;2015:99

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