test reload

python/marblesbag/fluid.py

@@ -15,7 +15,7 @@ class StrongBoundary(Structure):
 
 class fluid_problem :
 
-    def __init__(self, mesh_file_name, g, mu, rho, epsilon, strong_boundaries, notComputeEpsilon):
+    def __init__(self, mesh_file_name, g, mu, rho, epsilon, strong_boundaries):
         nsb = len(strong_boundaries)
         class Bnd :
             def __init__(self, b) :
@@ -31,7 +31,7 @@ class fluid_problem :
         asb = (StrongBoundary*nsb)(*[StrongBoundary(i[0].encode(),i[1],BNDCB(Bnd(i[2]).apply)) for i in strong_boundaries])
         self.asb = asb
         lib.fluid_problem_new.restype = c_void_p
-        self._fp = c_void_p(lib.fluid_problem_new(mesh_file_name.encode(), c_double(g), c_double(mu), c_double(rho), c_double(epsilon), nsb, asb,c_int(notComputeEpsilon)))
+        self._fp = c_void_p(lib.fluid_problem_new(mesh_file_name.encode(), c_double(g), c_double(mu), c_double(rho), c_double(epsilon), nsb, asb))
         if self._fp == None :
             raise NameError("cannot create fluid problem")
 
@@ -39,8 +39,8 @@ class fluid_problem :
         if(self._fp != None) :
             lib.fluid_problem_free(self._fp)
 
-    def adapt_mesh(self, lcmax, lcmin, n_el, alpha, notComputeEpsilon) :
-        lib.fluid_problem_adapt_mesh(self._fp, c_double(lcmax), c_double(lcmin), c_double(n_el), c_double(alpha), c_int(notComputeEpsilon))
+    def adapt_mesh(self, lcmax, lcmin, n_el) :
+        lib.fluid_problem_adapt_mesh(self._fp, c_double(lcmax), c_double(lcmin), c_double(n_el))
 
     def export(self, output_dir, t, it) :
         lib.fluid_problem_export(self._fp, output_dir.encode(), c_double(t), c_int(it))

python/marblesbag/fluid3.py

@@ -16,7 +16,7 @@ class StrongBoundary(Structure):
 
 class fluid_problem :
 
-    def __init__(self, mesh_file_name, g, mu, rho, alpha, strong_boundaries, notComputeEpsilon):
+    def __init__(self, mesh_file_name, g, mu, rho, alpha, strong_boundaries):
         nsb = len(strong_boundaries)
         class Bnd :
             def __init__(self, b) :
@@ -32,7 +32,7 @@ class fluid_problem :
         asb = (StrongBoundary*nsb)(*[StrongBoundary(i[0].encode(),i[1],BNDCB(Bnd(i[2]).apply)) for i in strong_boundaries])
         self.asb = asb
         lib.fluid_problem_new.restype = c_void_p
-        self._fp = c_void_p(lib.fluid_problem_new(mesh_file_name.encode(), c_double(g), c_double(mu), c_double(rho), c_double(alpha), nsb, asb, c_int(notComputeEpsilon)))
+        self._fp = c_void_p(lib.fluid_problem_new(mesh_file_name.encode(), c_double(g), c_double(mu), c_double(rho), c_double(alpha), nsb, asb))
         if self._fp == None :
             raise NameError("cannot create fluid problem")
 
@@ -40,8 +40,8 @@ class fluid_problem :
         if(self._fp != None) :
             lib.fluid_problem_free(self._fp)
 
-    def adapt_mesh(self, lcmax, lcmin, n_el, alpha, notComputeEpsilon) :
-        lib.fluid_problem_adapt_mesh(self._fp, c_double(lcmax), c_double(lcmin), c_double(n_el), c_double(alpha), c_int(notComputeEpsilon))
+    def adapt_mesh(self, lcmax, lcmin, n_el) :
+        lib.fluid_problem_adapt_mesh(self._fp, c_double(lcmax), c_double(lcmin), c_double(n_el))
 
     def export(self, output_dir, t, it) :
         lib.fluid_problem_export(self._fp, output_dir.encode(), c_double(t), c_int(it))

src/fluid_problem.c

@@ -210,7 +210,7 @@ static void fluid_problem_assemble_system(FluidProblem *problem, double *rhs, co
   const double *old_porosity = problem->old_porosity;
   const double mu = problem->mu;
   const double rho = problem->rho;
-  const double *epsilon = problem->epsilon;
+  const double epsilon = problem->epsilon;
   size_t local_size = N_SF*n_fields;
   size_t N_E = mesh->n_elements;
   double *all_local_vector = malloc(N_E*local_size*sizeof(double));
@@ -280,7 +280,7 @@ static void fluid_problem_assemble_system(FluidProblem *problem, double *rhs, co
           dphidp += dphii[k]*dp[k];
           divu += du[k][k];
         }
-        local_vector[iphi+N_SF*DIMENSION] += jw*(epsilon[el[iphi]]*dphidp+phii*(divu+dcdt));
+        local_vector[iphi+N_SF*DIMENSION] += jw*(epsilon*dphidp+phii*(divu+dcdt));
         for (int jphi = 0; jphi < N_SF; ++jphi) {
           double phij = phi[jphi];
           const double *dphij = dphi[jphi];
@@ -312,7 +312,7 @@ static void fluid_problem_assemble_system(FluidProblem *problem, double *rhs, co
             //LOCAL_MATRIX(U,U) += jw*mu*2*0.5*dphiidtau + jw*rho*(phii*phij/dt-phij*dphii[j]*u[j]/c);
             LOCAL_MATRIX(U,U) += jw*mu*2*0.5*dphiidtau + jw*rho*phii*(phij/dt-phij/c*dcdt+udtau/c);
           }
-          LOCAL_MATRIX(P,P) +=  jw*epsilon[el[iphi]]*dphiidphij;
+          LOCAL_MATRIX(P,P) +=  jw*epsilon*dphiidphij;
         }
       }
     }
@@ -453,7 +453,7 @@ static void fluid_problem_compute_porosity(FluidProblem *problem)
   }
 }
 
-FluidProblem *fluid_problem_new(const char *mesh_file_name, double g, double mu, double rho, double alpha, int n_strong_boundaries, StrongBoundary *strong_boundaries, int notComputeEpsilon)
+FluidProblem *fluid_problem_new(const char *mesh_file_name, double g, double mu, double rho, double epsilon, int n_strong_boundaries, StrongBoundary *strong_boundaries)
 {
   static int initialized = 0;
   if (!initialized) {
@@ -473,6 +473,7 @@ FluidProblem *fluid_problem_new(const char *mesh_file_name, double g, double mu,
   problem->mu = mu;
   problem->g = g;
   problem->mesh = mesh;
+  problem->epsilon = epsilon;
   problem->strong_boundaries = malloc(sizeof(StrongBoundary)*n_strong_boundaries);
   problem->n_strong_boundaries = n_strong_boundaries;
   for (int i = 0; i < n_strong_boundaries; ++i) {
@@ -481,7 +482,6 @@ FluidProblem *fluid_problem_new(const char *mesh_file_name, double g, double mu,
     problem->strong_boundaries[i].field = strong_boundaries[i].field;
   }
   problem->porosity = malloc(mesh->n_nodes*sizeof(double));
-  problem->epsilon = malloc(mesh->n_nodes*sizeof(double));
   problem->old_porosity = malloc(mesh->n_nodes*sizeof(double));
   problem->solution = malloc(mesh->n_nodes*n_fields*sizeof(double));
   for (int i = 0; i < problem->mesh->n_nodes; ++i)
@@ -495,20 +495,6 @@ FluidProblem *fluid_problem_new(const char *mesh_file_name, double g, double mu,
   }
   problem->node_volume = malloc(0);
   fluid_problem_compute_node_volume(problem);
-#if DIMENSION == 2
-  for (int i = 0; i < problem->mesh->n_nodes; ++i){
-    problem->epsilon[i] = alpha*sqrt(problem->node_volume[i])*sqrt(problem->node_volume[i])/(problem->mu/problem->rho);
-  }
-#else
-  for (int i = 0; i < problem->mesh->n_nodes; ++i){
-    problem->epsilon[i] = alpha*cbrt(problem->node_volume[i])*cbrt(problem->node_volume[i])/(problem->mu/problem->rho);
-  }
-#endif
-  if(notComputeEpsilon){
-    for (int i = 0; i < problem->mesh->n_nodes; ++i){
-      problem->epsilon[i] = alpha;
-    }
-  }
   // end to remove
   problem->linear_system = NULL;
 #ifdef HXT_HAVE_PETSC
@@ -531,7 +517,6 @@ void fluid_problem_free(FluidProblem *problem)
 {
   free(problem->solution);
   free(problem->porosity);
-  free(problem->epsilon);
   free(problem->old_porosity);
   hxtLinearSystemDelete(&problem->linear_system);
   free(problem->particle_uvw);
@@ -721,7 +706,7 @@ void fluid_problem_adapt_gen_mesh(FluidProblem *problem, double lcmax, double lc
 }
 
 
-void fluid_problem_adapt_mesh(FluidProblem *problem, double lcmax, double lcmin, double n_el, double alpha, int notComputeEpsilon)
+void fluid_problem_adapt_mesh(FluidProblem *problem, double lcmax, double lcmin, double n_el)
 {
   struct timespec tic, toc;
   fluid_problem_adapt_gen_mesh(problem, lcmax, lcmin, n_el);
@@ -767,8 +752,6 @@ void fluid_problem_adapt_mesh(FluidProblem *problem, double lcmax, double lcmin,
   free(newx);
   free(problem->solution);
   problem->solution = new_solution;
-  free(problem->epsilon);
-  problem->epsilon = malloc(new_mesh->n_nodes*sizeof(double));
   free(problem->porosity);
   problem->porosity = malloc(sizeof(double)*new_mesh->n_nodes);
   free(problem->old_porosity);
@@ -786,20 +769,6 @@ void fluid_problem_adapt_mesh(FluidProblem *problem, double lcmax, double lcmin,
     problem->particle_element_id[i] = -1;
   mesh_tree_particle_to_mesh(problem->mesh_tree, problem->n_particles, problem->particle_position, problem->particle_element_id, problem->particle_uvw);
   fluid_problem_compute_node_volume(problem);
-#if DIMENSION == 2
-  for (int i = 0; i < problem->mesh->n_nodes; ++i){
-    problem->epsilon[i] = alpha*sqrt(problem->node_volume[i])*sqrt(problem->node_volume[i])/(problem->mu/problem->rho);
-  }
-#else
-  for (int i = 0; i < problem->mesh->n_nodes; ++i){
-    problem->epsilon[i] = alpha*cbrt(problem->node_volume[i])*cbrt(problem->node_volume[i])/(problem->mu/problem->rho);
-  }
-#endif
-  if(notComputeEpsilon){
-    for (int i = 0; i < problem->mesh->n_nodes; ++i){
-      problem->epsilon[i] = alpha;
-    }
-  }
   fluid_problem_compute_porosity(problem);
   hxtLinearSystemDelete(&problem->linear_system);
   #ifdef HXT_HAVE_PETSC
@@ -809,6 +778,23 @@ void fluid_problem_adapt_mesh(FluidProblem *problem, double lcmax, double lcmin,
   #endif 
 }
 
+void fluid_problem_after_import(FluidProblem *problem)
+{
+  mesh_tree_free(problem->mesh_tree);
+  problem->mesh_tree = mesh_tree_create(problem->mesh);
+  for (int i = 0; i < problem->n_particles; ++i)
+    problem->particle_element_id[i] = -1;
+  mesh_tree_particle_to_mesh(problem->mesh_tree, problem->n_particles, problem->particle_position, problem->particle_element_id, problem->particle_uvw);
+  fluid_problem_compute_node_volume(problem);
+  fluid_problem_compute_porosity(problem);
+  hxtLinearSystemDelete(&problem->linear_system);
+  #ifdef HXT_HAVE_PETSC
+    hxtLinearSystemCreatePETSc(&problem->linear_system,problem->mesh->n_elements,N_N,n_fields,problem->mesh->elements,"fluid");
+  #else
+    hxtLinearSystemCreateLU(&problem->linear_system,new_mesh->n_elements,N_N,n_fields,new_mesh->elements);
+  #endif 
+}
+
 
 void fluid_problem_set_particles(FluidProblem *problem, int n, double *mass, double *volume, double *position, double *velocity, long int *elid)
 {

src/fluid_problem.h

@@ -5,6 +5,12 @@
 #include "mesh_find.h"
 #include "hxt_linear_system.h"
 
+#if DIMENSION==2
+#define N_N 3
+#else
+#define N_N 4
+#endif
+
 typedef struct {
   char *tag;
   int field;
@@ -12,7 +18,7 @@ typedef struct {
 }StrongBoundary;
 
 typedef struct {
-  double *epsilon;
+  double epsilon;
   double rho;
   double mu;
   double alpha;
@@ -46,8 +52,9 @@ void fluid_problem_compute_node_particle_force(FluidProblem *problem, double dt,
 int fluid_problem_implicit_euler(FluidProblem *problem, double dt);
 void fluid_problem_set_particles(FluidProblem *problem, int n, double *mass, double *volume, double *position, double *velocity, long int *elid);
 void fluid_problem_free(FluidProblem *problem);
-FluidProblem *fluid_problem_new(const char *mesh_file_name, double g, double mu, double rho, double alpha, int n_strong_boundaries, StrongBoundary *strong_boundaries, int notComputeEpsilon);
-void fluid_problem_adapt_mesh(FluidProblem *problem, double lcmax, double lcmin, double n_el, double alpha, int notComputeEpsilon);
+FluidProblem *fluid_problem_new(const char *mesh_file_name, double g, double mu, double rho, double epsilon, int n_strong_boundaries, StrongBoundary *strong_boundaries);
+void fluid_problem_adapt_mesh(FluidProblem *problem, double lcmax, double lcmin, double n_el);
 int *fluid_problem_particle_element_id(FluidProblem *problem);
 int fluid_problem_n_particles(FluidProblem *problem);
+void fluid_problem_after_import(FluidProblem *problem);
 #endif

src/fluid_problem_io.c

@@ -143,7 +143,7 @@ int fluid_problem_import_vtk(FluidProblem *problem, const char *filename)
   mb_xml_end_element(r,&gridelement);
   mb_xml_end_element(r,&fileelement);
   mb_xml_reader_destroy(r);
-
+  fluid_problem_after_import(problem);
   return 0;
 }
 

testcases/drop-3d/Metzger/adapt/mesh.geo

+L = 0.05;
+H = 0.6;
+P = 0.02;
+y = 0;
+lc = 0.01;
+
+Point(1) = {-L, H, -P, lc};
+Point(2) = {-L, -H, -P, lc};
+Point(3) = {L, -H, -P, lc};
+Point(4) = {L, H, -P, lc};
+Point(5) = {-L, H, P, lc};
+Point(6) = {-L, -H, P, lc};
+Point(7) = {L, -H, P, lc};
+Point(8) = {L, H, P, lc};
+
+Line(1) = {1, 2};
+Line(2) = {2, 3};
+Line(3) = {3, 4};
+Line(4) = {4, 1};
+Line(5) = {5, 6};
+Line(6) = {6, 7};
+Line(7) = {7, 8};
+Line(8) = {8, 5};
+Line(9) = {5, 1};
+Line(10) = {4, 8};
+Line(11) = {2, 6};
+Line(12) = {3, 7};
+
+Line Loop(1) = {1:4};
+Line Loop(2) = {5:8};
+Line Loop(3) = {9,-4,10,8};
+Line Loop(4) = {2,12,-6,-11};
+Line Loop(5) = {12,7,-10,-3};
+Line Loop(6) = {1,11,-5,9};
+
+Plane Surface(1) = {1};
+Plane Surface(2) = {2};
+Plane Surface(3) = {3};
+Plane Surface(4) = {4};
+Plane Surface(5) = {5};
+Plane Surface(6) = {6};
+Surface Loop(1) = {1,-3,-2,4,1,-5,-2,6};
+Volume(1) = {1};
+Physical Surface("Z") = {1,2};
+Physical Surface("X") = {5,6};
+Physical Surface("Top") = {3};
+Physical Surface("Bottom") = {4};
+Physical Volume("Domain") = {1};
+Physical Point("PtFix") = {1};
+Mesh.Algorithm = 5;
+
+Merge "lc.pos";
+Field[1] = PostView;
+Field[1].IView = 0;
+Background Field = 1;
+
+Mesh.CharacteristicLengthExtendFromBoundary = 0;
+Mesh.CharacteristicLengthFromPoints = 0;

testcases/drop-3d/Metzger/drop.py

+#!/usr/bin/env python
+from marblesbag import fluid3 as fluid
+from marblesbag import scontact3
+
+import numpy as np
+import os
+import time
+import shutil
+import random
+
+def genInitialPosition(filename, r, rout, rhop, compacity) :
+    p = scontact3.ParticleProblem()
+    p.load_msh_boundaries("mesh.msh", ["Top", "Bottom","X","Z"])
+    
+    N = compacity*rout**3/(r**3)
+    e = 2*rout/(6*N/np.pi)**(1./3.)
+    
+    for x in np.arange(rout, -rout, -e):
+        for y in np.arange(rout, -rout, -e):
+            for z in np.arange(rout, -rout, -e):
+                R2 = x**2 + y**2 + z**2
+                if R2<(rout-r)**2:
+                    p.add_particle((x+random.uniform(-e/2+r,e/2-r), y+random.uniform(-e/2+r,e/2-r), z+random.uniform(-e/2+r,e/2-r)), r, 4./3.* r**3 * np.pi * rhop);
+    
+    p.position()[:, 1] += 0.52
+    print(len(p.position()[:, 1] ))
+    p.write_vtk(filename,0,0)
+
+
+outputdir = "MetzgerB1"
+if not os.path.isdir(outputdir) :
+    os.makedirs(outputdir)
+
+t = 0
+ii = 0
+
+initialize = 0
+
+r=154e-6
+R = 3.3e-3
+compacity = .20
+drho = 35.4
+p = scontact3.ParticleProblem()
+#R = np.random.uniform(45e-06, 90e-06, len(x))
+
+#physical parameters
+g =  -9.81
+rhop = 2450
+nu = 1.17/1030.
+rho = 1030#rhop-drho/compacity
+V = 0.5 # todo : estimate V base on limit velocity
+print('V',V)
+tEnd = 1000
+
+#numerical parameters
+lcmin = 0.0004 # approx r*100 but should match the mesh size
+dt = 5e-2
+alpha = 1e-3
+epsilon = alpha*lcmin**2 /nu
+print('epsilon',epsilon)
+
+shutil.copy("mesh.msh", outputdir +"/mesh.msh")
+#scontact2Interface.MeshLoader(p, "funnel.msh", ("Funnel", "Top", "Bottom", "Lateral"))
+
+mu = nu*rho
+
+genInitialPosition(outputdir, r, R, rhop, compacity)
+
+p = scontact3.ParticleProblem()
+p.read_vtk(outputdir,0)
+
+print("r = %g, m = %g\n" %  (p.r()[0], p.mass()[0]))
+print("RHOP = %g" % rhop)
+outf = 10
+outf1 = 100000
+
+
+strong_boundaries = [("Top",1,0.),("Bottom",1,0.),("X",0,.0),("Z",2,0.),("Top",3,0.)]
+fluid = fluid.fluid_problem("mesh.msh",g,nu*rho,rho,epsilon,strong_boundaries)
+
+fluid.set_particles(p.mass(), p.volume(), p.position(), p.velocity())
+
+
+ii = 0
+jj = 0
+tEnd1 = 100
+print(p.velocity()[1,1])
+print(1-compacity)
+
+if initialize:
+    for jj in range(4):
+        dt1 = dt
+        t = 0
+        if jj!=0:
+            fluid.adapt_mesh(5e-3,8e-4,600000)
+        fluid.set_particles(p.mass(), p.volume(), p.position(), p.velocity())
+        
+        while t < tEnd1 : 
+            niter = fluid.implicit_euler(dt1)
+            forces = fluid.compute_node_force(dt1)
+            vn = p.velocity() + forces * dt1 / p.mass()
+            fluid.set_particles(p.mass(), p.volume(), p.position(), p.velocity())
+            if niter < 5 and dt1 < 20:
+                dt1 *= 3
+            elif niter > 5 and dt1 > dt:
+                dt1 /= 3
+            print(dt1)
+            t += dt1
+            ii += 1
+
+ii = 0
+t = 0
+tic = time.clock()
+fluid.export_vtk(outputdir,0,0)
+forces = g*p.mass()
+fluid.set_particles(p.mass(), p.volume(), p.position(), p.velocity())
+while t < tEnd : 
+    if (ii%5==0 and ii != 0):
+       fluid.adapt_mesh(5e-3,8e-4,600000)
+       fluid.set_particles(p.mass(), p.volume(), p.position(), p.velocity())
+    fluid.implicit_euler(dt)
+    forces = fluid.compute_node_force(dt)
+    vn = p.velocity() + forces * dt / p.mass()
+    vmax = np.max(np.hypot(vn[:, 0], vn[:, 1]))
+    nsub = max(1, int(np.ceil((vmax * dt * 4)/min(p.r()))))
+    print("NSUB", nsub,"VMAX",vmax, "VMAX * dt", vmax * dt, "r", min(p.r()))
+    for i in range(nsub) :
+        p.iterate(dt/nsub, forces)  
+    fluid.set_particles(p.mass(), p.volume(), p.position(), p.velocity())
+    t += dt
+    if ii %outf == 0 :
+        ioutput = int(ii/outf) + 1
+        p.write_vtk(outputdir, ioutput, t)
+        fluid.export_vtk(outputdir, t, ioutput)
+    ii += 1
+    print("%i : %.2g/%.2g (cpu %.6g)" % (ii, t, tEnd, time.clock() - tic))

testcases/drop-3d/Metzger/dropReload.py

+#!/usr/bin/env python
+from marblesbag import fluid3 as fluid
+from marblesbag import scontact3
+
+import numpy as np
+import os
+import time
+import shutil
+import random
+
+
+outputdir = "MetzgerB1"
+if not os.path.isdir(outputdir) :
+    os.makedirs(outputdir)
+
+t = 0
+ii = 0
+
+r=154e-6
+R = 3.3e-3
+compacity = .20
+drho = 35.4
+p = scontact3.ParticleProblem()
+#R = np.random.uniform(45e-06, 90e-06, len(x))
+
+#physical parameters
+g =  -9.81
+rhop = 2450
+nu = 1.17/1030.
+rho = 1030#rhop-drho/compacity
+V = 0.5 # todo : estimate V base on limit velocity
+print('V',V)
+tEnd = 1000
+
+#numerical parameters
+lcmin = 0.0004 # approx r*100 but should match the mesh size
+dt = 5e-2
+alpha = 1e-3
+epsilon = alpha*lcmin**2 /nu
+print('epsilon',epsilon)
+
+shutil.copy("mesh.msh", outputdir +"/mesh.msh")
+#scontact2Interface.MeshLoader(p, "funnel.msh", ("Funnel", "Top", "Bottom", "Lateral"))
+
+mu = nu*rho
+
+
+p = scontact3.ParticleProblem()
+p.read_vtk(outputdir,2)
+
+print("r = %g, m = %g\n" %  (p.r()[0], p.mass()[0]))
+print("RHOP = %g" % rhop)
+outf = 10
+outf1 = 100000
+
+#strong_boundaries = [("Top",0,.0),("Top",1,0.),("Top",2,0.),("Box",1,0.),("Box",0,0.),("Box",2,0.),("Top",3,0.)]
+#strong_boundaries = [("Top",0,.0),("Top",1,0.),("Top",2,0.),("Bottom",0,.0),("Bottom",1,0.),("Bottom",2,0.),("X",0,.0),("X",1,0.),("X",2,0.),("Z",0,.0),("Z",1,0.),("Z",2,0.),("Top",3,0.)]
+strong_boundaries = [("Top",1,0.),("Bottom",1,0.),("X",0,.0),("Z",2,0.),("Top",3,0.)]
+fluid = fluid.fluid_problem("mesh.msh",g,nu*rho,rho,epsilon,strong_boundaries)
+print("Import start!!!")
+fluid.import_vtk(outputdir+"/fluid_00002.vtu")
+print("Import done!!!")
+fluid.set_particles(p.mass(), p.volume(), p.position(), p.velocity())
+
+
+
+tEnd1 = 100
+
+ii = 21
+t = 21*5e-5
+tic = time.clock()
+forces = g*p.mass()
+fluid.set_particles(p.mass(), p.volume(), p.position(), p.velocity())
+while t < tEnd : 
+    if (ii%5==0 and ii != 0):
+       fluid.adapt_mesh(5e-3,8e-4,600000)
+       fluid.set_particles(p.mass(), p.volume(), p.position(), p.velocity())
+    fluid.implicit_euler(dt)
+    forces = fluid.compute_node_force(dt)
+    vn = p.velocity() + forces * dt / p.mass()
+    vmax = np.max(np.hypot(vn[:, 0], vn[:, 1]))
+    nsub = max(1, int(np.ceil((vmax * dt * 4)/min(p.r()))))
+    print("NSUB", nsub,"VMAX",vmax, "VMAX * dt", vmax * dt, "r", min(p.r()))
+    for i in range(nsub) :
+        p.iterate(dt/nsub, forces)  
+    fluid.set_particles(p.mass(), p.volume(), p.position(), p.velocity())
+    t += dt
+    if ii %outf == 0 :
+        ioutput = int(ii/outf) + 1
+        p.write_vtk(outputdir, ioutput, t)
+        fluid.export_vtk(outputdir, t, ioutput)
+    ii += 1
+    print("%i : %.2g/%.2g (cpu %.6g)" % (ii, t, tEnd, time.clock() - tic))

testcases/drop-3d/Metzger/mesh.geo

+L = 0.05;
+H = 0.6;
+P = 0.02;
+y = 0;
+lc = 0.01;
+
+Point(1) = {-L, H, -P, lc};
+Point(2) = {-L, -H, -P, lc};
+Point(3) = {L, -H, -P, lc};
+Point(4) = {L, H, -P, lc};
+Point(5) = {-L, H, P, lc};
+Point(6) = {-L, -H, P, lc};
+Point(7) = {L, -H, P, lc};
+Point(8) = {L, H, P, lc};
+Point(9) = {0,H,0,lc};
+Point(10) = {0,-H,0,lc};
+
+Line(1) = {1, 2};
+Line(2) = {2, 3};
+Line(3) = {3, 4};
+Line(4) = {4, 1};
+Line(5) = {5, 6};
+Line(6) = {6, 7};
+Line(7) = {7, 8};
+Line(8) = {8, 5};
+Line(9) = {5, 1};
+Line(10) = {4, 8};
+Line(11) = {2, 6};
+Line(12) = {3, 7};
+
+Line Loop(1) = {1:4};
+Line Loop(2) = {5:8};
+Line Loop(3) = {9,-4,10,8};
+Line Loop(4) = {2,12,-6,-11};
+Line Loop(5) = {12,7,-10,-3};
+Line Loop(6) = {1,11,-5,9};
+
+Plane Surface(1) = {1};
+Plane Surface(2) = {2};
+Plane Surface(3) = {3};
+Plane Surface(4) = {4};
+Plane Surface(5) = {5};
+Plane Surface(6) = {6};
+Surface Loop(1) = {1,-3,-2,4,1,-5,-2,6};
+Volume(1) = {1};
+Physical Surface("Z") = {1,2};
+Physical Surface("X") = {5,6};
+Physical Surface("Top") = {3};
+Physical Surface("Bottom") = {4};
+Physical Volume("Domain") = {1};
+Physical Point("PtFix") = {1};
+
+
+Point(15) = {0,.52,0};
+Field[1] = Attractor;
+Field[1].NodesList = {15};
+
+Field[2] = Threshold;
+Field[2].DistMax = 0.02;
+Field[2].DistMin = 0.01;
+Field[2].LcMax = 0.01;
+Field[2].LcMin = 0.0008;
+Field[2].IField = 1;
+
+Background Field = 2;
+