Added Astaroth 2.0

src/standalone/model/host_timestep.cc

@@ -0,0 +1,63 @@
+/*
+    Copyright (C) 2014-2018, Johannes Pekkilae, Miikka Vaeisalae.
+
+    This file is part of Astaroth.
+
+    Astaroth is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    Astaroth 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 General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with Astaroth.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+/**
+ * @file
+ * \brief Brief info.
+ *
+ * Detailed info.
+ *
+ */
+#include "host_timestep.h"
+
+#include "core/math_utils.h"
+
+static AcReal timescale = AcReal(1.0);
+
+AcReal
+host_timestep(const AcReal& umax, const AcMeshInfo& mesh_info)
+{
+    const long double cdt      = mesh_info.real_params[AC_cdt];
+    const long double cdtv     = mesh_info.real_params[AC_cdtv];
+    // const long double cdts     = mesh_info.real_params[AC_cdts];
+    const long double cs2_sound = mesh_info.real_params[AC_cs2_sound];
+    const long double nu_visc  = mesh_info.real_params[AC_nu_visc];
+    const long double eta      = mesh_info.real_params[AC_eta];
+    const long double chi      = 0; // mesh_info.real_params[AC_chi]; // TODO not calculated
+    const long double gamma    = mesh_info.real_params[AC_gamma];
+    const long double dsmin    = mesh_info.real_params[AC_dsmin];
+
+    // Old ones from legacy Astaroth
+    //const long double uu_dt   = cdt * (dsmin / (umax + cs_sound));
+    //const long double visc_dt = cdtv * dsmin * dsmin / nu_visc;
+
+    // New, closer to the actual Courant timestep
+    // See Pencil Code user manual p. 38 (timestep section)
+    const long double uu_dt   = cdt * dsmin / (fabsl(umax) + sqrtl(cs2_sound + 0.0l));
+    const long double visc_dt = cdtv * dsmin * dsmin / max(max(nu_visc, eta), max(gamma, chi)) + 1; // TODO NOTE: comment the +1 out to get scientifically accurate results
+
+    const long double dt = min(uu_dt, visc_dt);
+    return AcReal(timescale) * AcReal(dt);
+}
+
+void
+set_timescale(const AcReal scale)
+{
+    timescale = scale;
+}