Added an option to disable particle movement in GIZMO_SPH.

src/const.h

@@ -55,6 +55,10 @@
 #define SLOPE_LIMITER_PER_FACE
 #define SLOPE_LIMITER_CELL_WIDE
 
+/* Options to control the movement of particles for GIZMO_SPH. */
+/* This option disables particle movement */
+#define GIZMO_FIX_PARTICLES
+
 /* Source terms */
 #define SOURCETERMS_NONE
 //#define SOURCETERMS_SN_FEEDBACK

src/hydro/Gizmo/hydro.h

@@ -79,13 +79,19 @@ __attribute__((always_inline)) INLINE static void hydro_timestep_extra(
 __attribute__((always_inline)) INLINE static void hydro_first_init_part(
     struct part* p, struct xpart* xp) {
 
-  xp->v_full[0] = p->v[0];
-  xp->v_full[1] = p->v[1];
-  xp->v_full[2] = p->v[2];
-
   p->primitives.v[0] = p->v[0];
   p->primitives.v[1] = p->v[1];
   p->primitives.v[2] = p->v[2];
+
+#if defined(GIZMO_FIX_PARTICLES)
+  p->v[0] = 0.;
+  p->v[1] = 0.;
+  p->v[2] = 0.;
+#else
+  xp->v_full[0] = p->v[0];
+  xp->v_full[1] = p->v[1];
+  xp->v_full[2] = p->v[2];
+#endif
 }
 
 /**
@@ -357,6 +363,13 @@ __attribute__((always_inline)) INLINE static void hydro_end_force(
   /* Add normalization to h_dt. */
   p->force.h_dt *= p->h * hydro_dimension_inv;
 
+#if defined(GIZMO_FIX_PARTICLES)
+  p->a_hydro[0] = 0.0f;
+  p->a_hydro[1] = 0.0f;
+  p->a_hydro[2] = 0.0f;
+
+  p->du_dt = 0.0f;
+#else
   /* Set the hydro acceleration, based on the new momentum and mass */
   /* NOTE: the momentum and mass are only correct for active particles, since
            only active particles have received flux contributions from all their
@@ -383,6 +396,7 @@ __attribute__((always_inline)) INLINE static void hydro_end_force(
 
     p->du_dt = 0.0f;
   }
+#endif
 }
 
 /**

src/hydro/Gizmo/hydro_io.h

@@ -23,6 +23,13 @@
 #include "io_properties.h"
 #include "riemann.h"
 
+/* Set the description of the particle movement. */
+#if defined(GIZMO_FIX_PARTICLES)
+#define GIZMO_PARTICLE_MOVEMENT "Fixed particles."
+#else
+#define GIZMO_PARTICLE_MOVEMENT "Particles move with flow velocity."
+#endif
+
 /**
  * @brief Specifies which particle fields to read from a dataset
  *
@@ -155,6 +162,9 @@ void writeSPHflavour(hid_t h_grpsph) {
   /* Riemann solver information */
   io_write_attribute_s(h_grpsph, "Riemann solver type",
                        RIEMANN_SOLVER_IMPLEMENTATION);
+
+  /* Particle movement information */
+  io_write_attribute_s(h_grpsph, "Particle movement", GIZMO_PARTICLE_MOVEMENT);
 }
 
 /**