Simplify water freezing regression test (#73)

* Simplify water freezing regression test

* Link build status badge to Travis page

README.md

@@ -5,7 +5,7 @@ is an engine for constructing PDE-based simulations
 discretized in space with mixed finite elements
 and in time with finite differences.
 
-![](https://travis-ci.org/geo-fluid-dynamics/sapphire.svg?branch=master)
+[![Build Status](https://travis-ci.org/geo-fluid-dynamics/sapphire.svg?branch=master)](https://travis-ci.org/geo-fluid-dynamics/sapphire)
 [![DOI](https://zenodo.org/badge/157389237.svg)](https://zenodo.org/badge/latestdoi/157389237)
 
 

tests/model_validation/test__convection_coupled_phasechange.py

@@ -75,24 +75,6 @@ def test__validate__melt_octadecane__regression():
 
 def freeze_water(endtime, s, tau, rx, nx, rt, nt, q, outdir = ""):
 
-    mu_l__SI = 8.90e-4  # [Pa s]
-
-    rho_l__SI = 999.84  # [kg / m^3]
-
-    nu_l__SI = mu_l__SI/rho_l__SI  # [m^2 / s]
-
-    t_f__SI = endtime  # [s]
-
-    L__SI = 0.038  # [m]
-
-    Tau = pow(L__SI, 2)/nu_l__SI
-
-    t_f = t_f__SI/Tau
-
-    """ For Kowalewski's water freezing experiment,
-    at t_f__SI 2340 s, t_f = 1.44.
-    """
-
     sim = sapphire.benchmarks.freeze_water_in_cavity.Simulation(
         quadrature_degree = q,
         element_degree = rx - 1,
@@ -104,15 +86,15 @@ def freeze_water(endtime, s, tau, rx, nx, rt, nt, q, outdir = ""):
             + "rx{0}_nx{1}_rt{2}_nt{3}/".format(rx, nx, rt, nt)
             + "q{0}/".format(q))))
 
-    sim.timestep_size = sim.timestep_size.assign(t_f/float(nt))
+    sim.timestep_size = sim.timestep_size.assign(endtime/float(nt))
 
     sim.solid_velocity_relaxation_factor = \
         sim.solid_velocity_relaxation_factor.assign(tau)
 
     sim.smoothing = sim.smoothing.assign(s)
 
 
-    sim.solutions, _, = sim.run(endtime = t_f)
+    sim.solutions, _, = sim.run(endtime = endtime)
 
 
     print("Liquid area = {0}".format(sim.liquid_area))
@@ -124,7 +106,7 @@ def test__validate__freeze_water__regression(datadir):
 
     sim = freeze_water(
         outdir = datadir,
-        endtime = 2340.,
+        endtime = 1.44,
         s = 1./200.,
         tau = 1.e-12,
         rx = 2,