finitestrain.pyΒΆ

In this script we solve the nonlinear Saint Venant-Kichhoff problem on a unit square domain (optionally with a circular cutout), clamped at both the left and right boundary in such a way that an arc is formed over a specified angle. The configuration is constructed such that a symmetric solution is expected.

 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
from nutils import mesh, function, solver, export, cli, testing
import numpy

def main(nelems:int, etype:str, btype:str, degree:int, poisson:float, angle:float, restol:float, trim:bool):
  '''
  Deformed hyperelastic plate.

  .. arguments::

     nelems [10]
       Number of elements along edge.
     etype [square]
       Type of elements (square/triangle/mixed).
     btype [std]
       Type of basis function (std/spline).
     degree [1]
       Polynomial degree.
     poisson [.25]
       Poisson's ratio, nonnegative and stricly smaller than 1/2.
     angle [20]
       Rotation angle for right clamp (degrees).
     restol [1e-10]
       Newton tolerance.
     trim [no]
       Create circular-shaped hole.
  '''

  domain, geom = mesh.unitsquare(nelems, etype)
  if trim:
    domain = domain.trim(function.norm2(geom-.5)-.2, maxrefine=2)
  bezier = domain.sample('bezier', 5)

  ns = function.Namespace()
  ns.x = geom
  ns.angle = angle * numpy.pi / 180
  ns.lmbda = 2 * poisson
  ns.mu = 1 - 2 * poisson
  ns.ubasis = domain.basis(btype, degree=degree).vector(2)
  ns.u_i = 'ubasis_ki ?lhs_k'
  ns.X_i = 'x_i + u_i'
  ns.strain_ij = '.5 (u_i,j + u_j,i)'
  ns.energy = 'lmbda strain_ii strain_jj + 2 mu strain_ij strain_ij'

  sqr = domain.boundary['left'].integral('u_k u_k d:x' @ ns, degree=degree*2)
  sqr += domain.boundary['right'].integral('((u_0 - x_1 sin(2 angle) - cos(angle) + 1)^2 + (u_1 - x_1 (cos(2 angle) - 1) + sin(angle))^2) d:x' @ ns, degree=degree*2)
  cons = solver.optimize('lhs', sqr, droptol=1e-15)

  energy = domain.integral('energy d:x' @ ns, degree=degree*2)
  lhs0 = solver.optimize('lhs', energy, constrain=cons)
  X, energy = bezier.eval(['X_i', 'energy'] @ ns, lhs=lhs0)
  export.triplot('linear.png', X, energy, tri=bezier.tri, hull=bezier.hull)

  ns.strain_ij = '.5 (u_i,j + u_j,i + u_k,i u_k,j)'
  ns.energy = 'lmbda strain_ii strain_jj + 2 mu strain_ij strain_ij'

  energy = domain.integral('energy d:x' @ ns, degree=degree*2)
  lhs1 = solver.minimize('lhs', energy, lhs0=lhs0, constrain=cons).solve(restol)
  X, energy = bezier.eval(['X_i', 'energy'] @ ns, lhs=lhs1)
  export.triplot('nonlinear.png', X, energy, tri=bezier.tri, hull=bezier.hull)

  return lhs0, lhs1

If the script is executed (as opposed to imported), nutils.cli.run() calls the main function with arguments provided from the command line. For example, to keep with the default arguments simply run python3 finitestrain.py (view log). To select quadratic splines and a cutout add python3 finitestrain.py btype=spline degree=2 trim=yes (view log).

77
78
if __name__ == '__main__':
  cli.run(main)

Once a simulation is developed and tested, it is good practice to save a few strategic return values for regression testing. The nutils.testing module, which builds on the standard unittest framework, facilitates this by providing nutils.testing.TestCase.assertAlmostEqual64() for the embedding of desired results as compressed base64 data.

 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
class test(testing.TestCase):

  @testing.requires('matplotlib')
  def test_default(self):
    lhs0, lhs1 = main(nelems=4, etype='square', btype='std', degree=1, poisson=.25, angle=10, restol=1e-10, trim=False)
    with self.subTest('linear'): self.assertAlmostEqual64(lhs0, '''
      eNpjYICB8ku8+icMthvOM+K42G1ga6Rv/Mh42YVcQwnj/8bzTW5fUDbaaNxtomwK18CQfCnxkuPFL+f7
      zt06d/Rc1rnbZ73Pyp4VPvvwzOwz7mckz3w4ffL0stMtpwGSOirA''')
    with self.subTest('non-linear'): self.assertAlmostEqual64(lhs1, '''
      eNpjYICBMu1b+jKGFw2bjdy1LICkk/Fx4+bLjwxdjAVM2k1uX1A22mjcbaJsCtfAoHz53sXiC27nGc6p
      nD94Tutc5dlLZyLOSpw9fab4DOsZyTMfTp88vex0y2kA6e4nVQ==''')

  @testing.requires('matplotlib')
  def test_mixed(self):
    lhs0, lhs1 = main(nelems=4, etype='mixed', btype='std', degree=1, poisson=.25, angle=10, restol=1e-10, trim=False)
    with self.subTest('linear'): self.assertAlmostEqual64(lhs0, '''
      eNoBZACb/wAAAADV0WwvAAChMAAAtjEAAKgyXjBl0UUyMjPeMyXQjzESM/ozqDQjMtvQsTOLNCM1AAAA
      AIfS7NEAAM/RAADQzwAAmc7czsvOU871zUrNMs0NzenMk8xQzPDLGczJy6bLhMsZ2Sx5''')
    with self.subTest('non-linear'): self.assertAlmostEqual64(lhs1, '''
      eNoBZACb/wAAAAAr3xowAAD9MAAA1DEAAI8yHzGKLIEySDPKM6fS9TFCMwM0mzQjMtvQsTOLNCM1AAAA
      AD/TYNEAAN7QAAA3zwAACc7SzgnPEc6TzdjMZ80TzdHMa8wXzPDLGczJy6bLhMthnih2''')

  @testing.requires('matplotlib')
  def test_spline(self):
    lhs0, lhs1 = main(nelems=4, etype='square', btype='spline', degree=2, poisson=.25, angle=10, restol=1e-10, trim=False)
    with self.subTest('linear'): self.assertAlmostEqual64(lhs0, '''
      eNpjYECAa1e+aE3Qu6Nfa9BlmHoxU/eHgbIRs3Gs8bwLr/S4jayNfxn7mGy/sEz/qNFz4wUmL0xuX/Az
      EDDWMrlromyKZAxDlg6bbppOw1WXi2nnqy8svSBxwf980Ln3Z9+ffXP2+Nm8s6xnT59pOdNzJveM3Rnm
      M/dOS55hOXPn9PbTU0+3nAYAZeQ9sA==''')
    with self.subTest('non-linear'): self.assertAlmostEqual64(lhs1, '''
      eNpjYEAAZ21dXWF9WYNug3RDPu1i/RzDYKNfRi7Gn5V9DVKNkoy/G+uaiF/qM/hi9NN4pckZk9sX/AwE
      jLVM7poomyIZw3BIp0/H/a7qpf4LD85tvTD1wtrz+87tPRt8Vvuc0Lm1Z43PLjmTfGbXmQVn0s/onHl7
      euNpyTMsZ+6c3n566umW0wB4sDra''')