DiscretizeMember function, which dates back many years, was recently superseded by the line mesh command, written by Minjie. In addition to creating boundaries for solid meshes, as shown in this post, you can use line meshes to discretize a frame member (2D or 3D) into beam-column elements–just pass the optional element type and arguments to the mesh command.
Below is example code for a portal frame model. First, define nodes for the joints.
import openseespy.opensees as ops H = 360 L = 144 ops.wipe() ops.model('basic','-ndm',2,'-ndf',3) ops.node(1,0,0); ops.fix(1,1,1,1) ops.node(2,0,L) ops.node(3,H,L) ops.node(4,H,0); ops.fix(4,1,1,1)
Next, define line meshes with the element type and arguments that would come after the nodes in the regular element command–in this case, the transformation tag and beam integration tag for a
dispBeamColumn element. The mesh type is 0 (not an FSI analysis) and there are 3 DOFs per node.
E = 29000 # W14x90 A = 26.5 Ic = 999 ops.section('Elastic',1,E,A,Ic) ops.beamIntegration('Legendre',1,1,2) # W18x76 A = 22.3 Ig = 1330 ops.section('Elastic',2,E,A,Ig) ops.beamIntegration('Legendre',2,2,2) # Corotational transformation ops.geomTransf('Corotational',1) # Number of elements/member Nele = 8 # Columns c = L/Nele # tag Npts nodes type dofs size eleType transfTag beamIntTag ops.mesh('line',1,2,*[1,2],0,3,c,'dispBeamColumn',1,1) ops.mesh('line',2,2,*[3,4],0,3,c,'dispBeamColumn',1,1) # Beam c = H/Nele # tag Npts nodes type dofs size eleType transfTag beamIntTag ops.mesh('line',3,2,*[2,3],0,3,c,'dispBeamColumn',1,2)
And that’s pretty much it.
DiscretizeMember, the line mesh is easier because it doesn’t require you to keep track of node and element tags to pass into the function–the numbering of nodes and elements is handled internally.
The meshes shown in this post were plotted using the
opsvis package developed by Seweryn Kokot.
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