Add filter parameters to case options

gravity_current.cpp accepts filter parameters (f_cutoff, f_order,
f_strength) as optional input arguments. Easy adjustment of the
filter is useful when the flow become suddenly becomes too chaotic.

src/cases/gravity_current/gravity_current.cpp

@@ -396,6 +396,11 @@ int main(int argc, char ** argv) {
     option_category("Other options");
     add_option("perturb",&perturb,"Initial perturbation in velocity");
 
+    option_category("Filter options");
+    add_option("f_cutoff",&f_cutoff,0.6,"Filter cut-off frequency");
+    add_option("f_order",&f_order,2.0,"Filter order");
+    add_option("f_strength",&f_strength,20.0,"Filter strength");
+
     // Parse the options from the command line and config file
     options_parse(argc,argv);
 
@@ -459,6 +464,7 @@ int main(int argc, char ** argv) {
         fprintf(stdout,"g = %f, rot_f = %f, rho_0 = %f\n",g,rot_f,rho_0);
         fprintf(stdout,"Time between plots: %g s\n",plot_interval);
         fprintf(stdout,"Initial velocity perturbation: %g\n",perturb);
+        fprintf(stdout,"Filter cutoff = %f, order = %f, strength = %f\n",f_cutoff,f_order,f_strength);
         fprintf(stdout,"Buoyancy frequency squared %g\n",N2_max);
     }
 

src/cases/gravity_current/spins.conf

@@ -36,6 +36,11 @@ plot_interval = 1
 # Perturbation Parameter
 perturb = 1e-3
 
+# Filter Parameters
+f_cutoff = 0.6
+f_order = 2.0
+f_strength = 20.0
+
 # Restart Options
 restart = false
 restart_time = 0.0