from __future__ import absolute_import
import numpy as np
from .imperfection import Imperfection
[docs]class Dimple(Imperfection):
"""Dimple imperfection
References
----------
Wullschleger, L. and Meyer-Piening, H.-R.. Buckling of geometrically
imperfect cylindrical shells - definition of a buckling load.
International Journal of Non-Linear Mechanics 37 (2002) 645-657.
"""
def __init__(self, thetadeg, pt, a, b, wb):
super(Dimple, self).__init__()
self.thetadeg = thetadeg
self.pt = pt
self.a = a
self.b = b
self.wb = wb
# plotting options
self.xaxis = 'wb'
self.xaxis_label = 'Imperfection amplitude, mm'
def rebuild(self):
cc = self.impconf.conecyl
pt = self.pt
r, z = cc.r_z_from_pt(pt)
self.x, self.y, self.z = self.get_xyz()
cl = np.rad2deg(self.a/2./r)
self.r, z = cc.r_z_from_pt(self.pt)
cl_side = np.sin(np.deg2rad(cl))*self.r
self.zlow = self.z - cl_side
self.rlow, z = cc.r_z_from_pt(self.zlow/cc.H)
self.zup = self.z + cl_side
self.rup, z = cc.r_z_from_pt(self.zup/cc.H)
self.thetadeg1 = self.thetadeg - cl
self.thetadeg2 = self.thetadeg + cl
self.thetadeg = self.thetadeg % 360.
self.thetadeg1 = self.thetadeg1 % 360.
self.thetadeg2 = self.thetadeg2 % 360.
self.thetadegs = [self.thetadeg1, self.thetadeg, self.thetadeg2]
self.pts = [self.zlow/cc.H, self.z/cc.H, self.zup/cc.H]
self.name = ('dimple_pt_%03d_theta_%03d'
% (int(self.pt*100), int(self.thetadeg)))
def calc_amplitude(self):
return self.wb
[docs] def create(self):
"""Realizes the dimple imperfection in the finite element model
The nodes corresponding to this imperfection are translated.
.. note:: Must be called from Abaqus.
"""
from __main__ import mdb
cc = self.impconf.conecyl
mod = mdb.models[cc.model_name]
part_shell = mod.parts['Shell']
a = self.a
b = self.b
wb = self.wb
dim = 1.5*max(self.a, self.b)
xMin = self.x - dim
xMax = self.x + dim
yMin = self.y - dim
yMax = self.y + dim
zMin = self.z - dim
zMax = self.z + dim
box_nodes = part_shell.nodes.getByBoundingBox(xMin,yMin,zMin,
xMax,yMax,zMax)
box_nodes = np.array(box_nodes, dtype=object)
def calc_dr_dz(x, y, z):
zeta = (z-self.z) + b/2.
dist = np.sqrt((x-self.x)**2 + (y-self.y)**2)
pt = z / cc.H
r,z = cc.r_z_from_pt(pt)
alpha = 2*np.arcsin(dist / (2.*r))
arc = alpha*r
drR = -wb/2.*np.cos(np.pi*arc/a)*(1-np.cos(2*np.pi*zeta/b))
dr = drR*np.cos(cc.alpharad)
dz = drR*np.sin(cc.alpharad)
check = (zeta < 0.) | (zeta > b)
dr[check] = 0
dz[check] = 0
check = (arc < 0.) | (arc > a/2.)
dr[check] = 0
dz[check] = 0
return dr, dz
local_csys = part_shell.features['part_cyl_csys']
local_csys = part_shell.datums[local_csys.id]
xs, ys, zs = np.array([node.coordinates for node in box_nodes]).T
drs, dzs = calc_dr_dz(x=xs, y=ys, z=zs)
check = drs!=0
box_nodes = box_nodes[check]
drs = drs[check]
dzs = dzs[check]
for node, dr, dz in zip(box_nodes, drs, dzs):
part_shell.editNode(localCsys = local_csys,
nodes = (node,),
offset1 = dr,
offset3 = dz)
# Reference:
# Wullschleger, L. and Meyer-Piening, H.-R.. Buckling of geometrically
# imperfect cylindrical shells - definition of a buckling load. International
# Journal of Non-Linear Mechanics 37 (2002) 645-657.
