Broken armour wire
Tension is applied to a short segment of flexible pipe. Then a wire is broken and the tension is further increased.
Model description
Flexible pipe
Two different models are provided:
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A model applying 16 wires in each layer, where each represents an equal share of wires in the layer
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A model applying 8 representative wires in the outer layer, while the inner layer has 8 single wires and 7 scaled wires representing the remaining armour wires
Boundary conditions and loads
Global
One end of the pipe is fixed in all degrees of freedom:
# Type NodId DOF # end 1 BONCON GLOBAL 1 1 BONCON GLOBAL 1 2 BONCON GLOBAL 1 3 BONCON GLOBAL 1 4 BONCON GLOBAL 1 5 BONCON GLOBAL 1 6
and loaded by internal pressure and tension in the other end:
# Hist Dir NODE Load CLOAD 100 1 41 0.25 # # Hist Elnr1 P1 Elnr2 P2 PILOAD 200 3001 2 3040 2 #
Armour wire boundary conditions
The armour wires are fixed in all translatory degrees of freedom (1,2,3) an in torsion (4) at both ends. These boundary conditions are in the helix system and represent no axial sliding (dof 1), no transvers sliding (dof 2), no radial contraction (dof 3) and no twisting about the armour wire axis (dof 4)
BONCON GLOBAL 10001 1 repeat 16 41 BONCON GLOBAL 10001 2 repeat 16 41 BONCON GLOBAL 10001 3 repeat 16 41 BONCON GLOBAL 10001 4 repeat 16 41 # BONCON GLOBAL 10041 1 repeat 16 41 BONCON GLOBAL 10041 2 repeat 16 41 BONCON GLOBAL 10041 3 repeat 16 41 BONCON GLOBAL 10041 4 repeat 16 41 # BONCON GLOBAL 20001 1 repeat 16 41 BONCON GLOBAL 20001 2 repeat 16 41 BONCON GLOBAL 20001 3 repeat 16 41 BONCON GLOBAL 20001 4 repeat 16 41 # BONCON GLOBAL 20041 1 repeat 16 41 BONCON GLOBAL 20041 2 repeat 16 41 BONCON GLOBAL 20041 3 repeat 16 41 BONCON GLOBAL 20041 4 repeat 16 41
Scaling of wires
When a wire is used to repreent more than one wire, scaling of the wire properties must be given by a factor:
ELPROP tenslayer1 shearhelix rectangle 5e-3 2e-3 0.0785e-6 0.0 3.81 300 300 -10 ELPROP tenslayer2 shearhelix rectangle 5e-3 2e-3 0.0785e-6 0.0 4.06 300 300 -10
The corresponding contact must be scaled with the same factor:
# EleGroupName EleType Gap0 TuneTime AUTOMNPC AutoSearch Scalefact ELPROP contlayer1 layercontact D D D D 3.81 ELPROP contlayer2 layercontact D D D D 3.81 ELPROP contlayer3 layercontact D D D D 4.06 ELPROP contlayer4 layercontact D D D D 4.06
Wire break
The process of breaking the wire(s) is modelled by use of the ELHIST approach. This allows for the stiffness of an element to be scaled with a time history THIST. If the scaling is negative, the stiffnesses are set to zero. In this model, the stiffness is hence reduced from full level to zero during the time span 4 to 5 s into the analysis.
# elstart elend hist
ELHIST 10321 10321 500
#
THIST 500 0.0 1.0
4.0 1.0
6.0 -1.0
10.0 -1.0
Mixing single and representative wires in one layer
To obtain a combination of single and representative wires in the same layer, two separate element groups are applied. The nodes for each group must be positioned according to the circumferential fraction the group should fill, and with proper angular spacing.
This also requires two separate set of contact groups to be defined towards the inside layer and the outside layer.
Results
The images below shows the axial stresse in the inner layer after wires have been broken. For the 16 wires model, one wire represents 3.81 single wires.
| When stresses are displayed, the broken elements will display a dummy (high) value. |
Relevant files
| You will have to extend the simulation time to 10 s. |
Go to bflex2010 file - Model with 16 representative wires in each layer
Go to bflex2010 file - MOdel with 8 representative wires in the outer layer, 8 single + 7 representative wires in the inner layer
User manual for reference
Processing of files from command line
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bflex2010 -n bflex2010_01
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bflex2010 -n bflex2010_02