The following Python code helps you to extract the external elements or the external edge of any 2D orphan mesh (triangular elements).

Let me know if you are having any problem with the code. Contact me here or: mario_giorgi@hotmail.com

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#Create 3 lists and get the number of elements within the part

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face1Elements=list()

face2Elements=list()

face3Elements=list()

q=len(mdb.models['MODEL_NAME'].parts['PART_NAME'].elements)

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#The code extracts the feature's edge from the orphan mesh and creates a set called "SET_EDGES" 

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for i in range (0,q):

c=mdb.models['MODEL_NAME'].parts['PART_NAME'].elements[i].getAdjacentElements()

if len(c)<3:

w=mdb.models['MODEL_NAME'].parts['PART_NAME'].elements[i].getElemEdges()

for ii in range (0,3):

if len(w[ii].getElements())<2:

if ii==0:

face1Elements.append(w[ii].getElements()[0].label)

if ii==1:

face2Elements.append(w[ii].getElements()[0].label)

if ii==2:

face3Elements.append(w[ii].getElements()[0].label)

mdb.models['Model-1'].parts['PART_NAME'].Surface(name='SET_EDGES',face1Elements=mdb.models['Model-1'].parts['PART_NAME'].elements.sequenceFromLabels(face1Elements),face2Elements=mdb.models['Model-1'].parts['PART_NAME'].elements.sequenceFromLabels(face2Elements),face3Elements=mdb.models['Model-1'].parts['PART_NAME'].elements.sequenceFromLabels(face3Elements), )

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