add example cavity script

Single_phase/example_cavity.py

@@ -0,0 +1,34 @@
+import LBM_3D_SinglePhase_Solver as lb3dsp 
+import time
+
+time_init = time.time()
+time_now = time.time()
+time_pre = time.time()             
+
+
+lb3d = lb3dsp.LB3D_Solver_Single_Phase(50,50,50)
+
+lb3d.init_geo('./geo_cavity.dat')
+lb3d.set_bc_vel_x1([0.0,0.0,0.1])
+lb3d.init_simulation()
+
+for iter in range(50000+1):
+    lb3d.step()
+
+    if (iter%1000==0):
+
+        time_pre = time_now
+        time_now = time.time()
+        diff_time = int(time_now-time_pre)
+        elap_time = int(time_now-time_init)
+        m_diff, s_diff = divmod(diff_time, 60)
+        h_diff, m_diff = divmod(m_diff, 60)
+        m_elap, s_elap = divmod(elap_time, 60)
+        h_elap, m_elap = divmod(m_elap, 60)
+
+        print('----------Time between two outputs is %dh %dm %ds; elapsed time is %dh %dm %ds----------------------' %(h_diff, m_diff, s_diff,h_elap,m_elap,s_elap))
+        print('The %dth iteration, Max Force = %f,  force_scale = %f\n\n ' %(iter, 10.0,  10.0))
+
+        if (iter%10000==0):
+            lb3d.export_VTK(iter)
+