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adhesion.py
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Thu, May 23, 11:44

adhesion.py
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#!/usr/bin/env python
# @file
# @section LICENSE
#
# Copyright (©) 2016-19 EPFL (École Polytechnique Fédérale de Lausanne),
# Laboratory (LSMS - Laboratoire de Simulation en Mécanique des Solides)
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU Affero General Public License as published
# by the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU Affero General Public License for more details.
#
# You should have received a copy of the GNU Affero General Public License
# along with this program. If not, see <https://www.gnu.org/licenses/>.
import sys
import tamaas as tm
import numpy as np
import matplotlib.pyplot as plt
def plotSurface(surface):
fig = plt.figure()
ax = fig.add_subplot(111)
img = ax.imshow(surface)
#fig.colorbar(img)
def constructHertzProfile(size, curvature):
radius = 1. / curvature
x = np.linspace(-0.5, 0.5, size)
y = np.linspace(-0.5, 0.5, size)
x, y = np.meshgrid(x, y)
surface = np.sqrt(radius**2 - x**2 - y**2)
surface -= surface.min()
return surface.copy()
def computeHertzDisplacement(e_star, contact_size, max_pressure, size):
x = np.linspace(-0.5, 0.5, size)
y = np.linspace(-0.5, 0.5, size)
x, y = np.meshgrid(x, y)
disp = np.pi * max_pressure / (4 * contact_size * e_star) * (2 * contact_size**2 - (x**2 + y**2))
return disp.copy()
def main():
grid_size = 128
curvature = 0.5
effective_modulus = 1.
load = 0.1
surface_energy = 0
rho = 2.071e-7
surface = constructHertzProfile(grid_size, curvature)
# SG = tm.SurfaceGeneratorFilterFFT()
# SG.getGridSize().assign(grid_size)
# SG.getHurst().assign(0.8)
# SG.getRMS().assign(0.002);
# SG.getQ0().assign(8);
# SG.getQ1().assign(8);
# SG.getQ2().assign(16);
# SG.getRandomSeed().assign(156);
# SG.Init()
# surface = SG.buildSurface()
print "Max height {}".format(surface.max())
print "Min height {}".format(surface.min())
bem = tm.BemGigi(surface)
bem.setDumpFreq(1)
functional = tm.ExponentialAdhesionFunctional(bem)
functional.setParameter('rho', rho)
functional.setParameter('surface_energy', surface_energy)
bem.setEffectiveModulus(effective_modulus)
bem.addFunctional(functional)
bem.computeEquilibrium(1e-6, load)
tractions = bem.getTractions()
print "Average pressure = {}".format(tractions.mean())
# bem.computeTrueDisplacements()
t_displacements = bem.getTrueDisplacements()
t_gap = bem.getGap()
plotSurface(tractions)
plt.figure()
plt.plot(surface[grid_size/2, :])
plt.title("Surface")
plt.figure()
plt.plot(tractions[grid_size/2, :])
plt.title("Pressure")
plt.figure()
plt.plot(t_gap[grid_size/2, :])
plt.title("Gap")
plt.figure()
plt.plot(t_displacements[grid_size/2, :])
plt.title("Displacement")
plt.figure()
plt.plot(t_displacements[grid_size/2, :] - surface[grid_size/2, :])
plt.title("Disp-surf")
plotSurface(t_displacements)
plt.show()
return 0
# Testing contact area against Hertz solution for solids of revolution
contact_area = tm.SurfaceStatistics.computeContactArea(tractions)
hertz_contact_size = (3 * load / (4 * curvature * effective_modulus))**(1. / 3.)
hertz_area = np.pi * hertz_contact_size**2
area_error = np.abs(hertz_area - contact_area) / hertz_area
print "Area error: {}".format(area_error)
# Testing maximum pressure
max_pressure = tractions.max()
hertz_max_pressure = (6 * load * effective_modulus**2 * curvature ** 2)**(1. / 3.) / np.pi
pressure_error = np.abs(hertz_max_pressure - max_pressure) / hertz_max_pressure
print "Max pressure error: {}".format(pressure_error)
# Testing displacements
hertz_displacements = computeHertzDisplacement(effective_modulus,
hertz_contact_size,
hertz_max_pressure,
grid_size)
# Selecing only the points that are in contact
contact_indexes = [(i, j, tractions[i, j] > 0) for i in range(grid_size) for j in range(grid_size)]
contact_indexes = map(lambda x: x[0:2], filter(lambda x: x[2], contact_indexes))
# Displacements of bem are centered around the mean of the whole surface
# and Hertz displacements are not centered, so we need to compute mean
# on the contact zone for both arrays
bem_mean = 0.
hertz_mean = 0.
for index in contact_indexes:
bem_mean += displacements[index]
hertz_mean += hertz_displacements[index]
bem_mean /= len(contact_indexes)
hertz_mean /= len(contact_indexes)
# Correction applied when computing error
correction = hertz_mean - bem_mean
# Computation of error of displacement in contact zone
error = 0.
hertz_norm = 0.
for index in contact_indexes:
error += (hertz_displacements[index] - displacements[index] - correction)**2
hertz_norm += (hertz_displacements[index] - hertz_mean)**2
displacement_error = np.sqrt(error / hertz_norm)
print "Displacement error (in contact zone): {}".format(displacement_error)
if area_error > 1e-2 or pressure_error > 1e-2 or displacement_error > 1e-4:
return 1
return 0
if __name__ == "__main__":
sys.exit(main())

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