From ee77845bcd2ca66bc6ec0993c07b6747a5d08f05 Mon Sep 17 00:00:00 2001
From: Folkert Nobels <nobels@strw.leidenuniv.nl>
Date: Fri, 24 Jul 2020 13:58:53 +0100
Subject: [PATCH] Add fixed boundary particles to the code (boundary particles
that will never have a velocity)
---
configure.ac | 17 ++++
.../source/GettingStarted/special_modes.rst | 25 ++++++
src/cell.c | 2 +-
src/drift.h | 83 ++++++++++++++++++-
4 files changed, 125 insertions(+), 2 deletions(-)
diff --git a/configure.ac b/configure.ac
index 9a287fdeee..de2cbc2cf7 100644
--- a/configure.ac
+++ b/configure.ac
@@ -409,6 +409,22 @@ elif test "$boundary_particles" != "no"; then
AC_DEFINE_UNQUOTED([SWIFT_BOUNDARY_PARTICLES], [$enableval] ,[Particles with smaller ID than this will be considered as boundaries.])
fi
+# Check if we want to use fixed boundary particles.
+AC_ARG_ENABLE([fixed-boundary-particles],
+ [AS_HELP_STRING([--enable-fixed-boundary-particles],
+ [Set all particles with an ID smaller than @<:@N@:>@ as fixed boundary particles (i.e. receive zero gravity + hydro forces + zero velocity), this mode enables also --enable-boundary-particles and --enable-no-gravity-below-id.]
+ )],
+ [fixed_boundary_particles="$enableval"],
+ [fixed_boundary_particles="no"]
+)
+if test "$fixed_boundary_particles" == "yes"; then
+ AC_MSG_ERROR(Need to specify the ID below which particles get zero forces when using --enable-boundary-particles!)
+elif test "$fixed_boundary_particles" != "no"; then
+ AC_DEFINE_UNQUOTED([SWIFT_NO_GRAVITY_BELOW_ID], [$enableval] ,[Particles with smaller ID than this will have zero gravity forces])
+ AC_DEFINE_UNQUOTED([SWIFT_BOUNDARY_PARTICLES], [$enableval] ,[Particles with smaller ID than this will be considered as boundaries.])
+ AC_DEFINE_UNQUOTED([SWIFT_FIXED_BOUNDARY_PARTICLES], [$enableval] ,[Particles with smaller ID than this will be considered as boundaries.])
+fi
+
# Check whether we have any of the ARM v8.1 tick timers
AX_ASM_ARM_PMCCNTR
AX_ASM_ARM_CNTVCT
@@ -2395,6 +2411,7 @@ AC_MSG_RESULT([
Gravity checks : $gravity_force_checks
Custom icbrtf : $enable_custom_icbrtf
Boundary particles : $boundary_particles
+ Fixed boundary particles : $fixed_boundary_particles
Particle Logger : $with_logger
Python enabled : $have_python
diff --git a/doc/RTD/source/GettingStarted/special_modes.rst b/doc/RTD/source/GettingStarted/special_modes.rst
index ce89d857ab..f9aba5db41 100644
--- a/doc/RTD/source/GettingStarted/special_modes.rst
+++ b/doc/RTD/source/GettingStarted/special_modes.rst
@@ -29,6 +29,31 @@ in the sampling of the halo is reduced.
Note also that this does not affect the hydrodynamic forces. This mode is
purely designed for gravity-only accuracy tests.
+Besides the pure gravity mode, swift also has the boundary particle mode,
+this mode turns off both the gravity forces and hydro forces for all
+particles. Because gas particles only receive hydro this mode only impacts
+gas particles more strictly than other particles. This mode can be
+activated using ``--enable-boundary-particles=N``. This will zero the
+gravitational and hydrodynamic *accelerations* of all particles with ``id``
+(strictly) lower than ``N`` at every time-step. Still if particles have an
+initial velocity they will keep moving at that speed. This compilation
+option also activates ``--enable-no-gravity-below-id=N``.
+
+Typical use cases are hydrodynamical experiments that have boundaries.
+
+Both options discussed above only cancel accelerations and have no impact
+on what can happen in any code module that directly changes the velocity of
+the boundary or no gravity particles. An example of this is momentum
+injection of stellar winds for example. If we additionally want to keep the
+boundary particles fixed at the same position for the whole simulation we can
+use the ``--enable-fixed-boundary-particles=N`` compile option, this option
+explicitly sets the velocity of the boundary particles to zero every time
+step on top of also zeroing the accelerations.
+
+A typical use cases is an idealized setup in which we have a black hole in
+the centre of a galaxy that accretes gas but is not allowed to move from
+the momentum recoil of the gas it swallows.
+
Gravity glasses
~~~~~~~~~~~~~~~
diff --git a/src/cell.c b/src/cell.c
index 784d9e08aa..2d4b863c32 100644
--- a/src/cell.c
+++ b/src/cell.c
@@ -5032,7 +5032,7 @@ void cell_drift_gpart(struct cell *c, const struct engine *e, int force) {
if (gpart_is_inhibited(gp, e)) continue;
/* Drift... */
- drift_gpart(gp, dt_drift, ti_old_gpart, ti_current, grav_props);
+ drift_gpart(gp, dt_drift, ti_old_gpart, ti_current, grav_props, e);
#ifdef SWIFT_DEBUG_CHECKS
/* Make sure the particle does not drift by more than a box length. */
diff --git a/src/drift.h b/src/drift.h
index 6b0a40e877..12bd716ee3 100644
--- a/src/drift.h
+++ b/src/drift.h
@@ -27,6 +27,7 @@
#include "const.h"
#include "debug.h"
#include "dimension.h"
+#include "engine.h"
#include "entropy_floor.h"
#include "hydro.h"
#include "hydro_properties.h"
@@ -42,10 +43,12 @@
* @param ti_old Integer start of time-step (for debugging checks).
* @param ti_current Integer end of time-step (for debugging checks).
* @param grav_props The properties of the gravity scheme.
+ * @param e the #engine
*/
__attribute__((always_inline)) INLINE static void drift_gpart(
struct gpart *restrict gp, double dt_drift, integertime_t ti_old,
- integertime_t ti_current, const struct gravity_props *grav_props) {
+ integertime_t ti_current, const struct gravity_props *grav_props,
+ const struct engine *e) {
#ifdef SWIFT_DEBUG_CHECKS
if (gp->ti_drift != ti_old)
@@ -58,6 +61,29 @@ __attribute__((always_inline)) INLINE static void drift_gpart(
gp->ti_drift = ti_current;
#endif
+#ifdef SWIFT_FIXED_BOUNDARY_PARTICLES
+
+ /* Get the ID of the gpart */
+ long long id = 0;
+ if (gp->type == swift_type_gas)
+ id = e->s->parts[-gp->id_or_neg_offset].id;
+ else if (gp->type == swift_type_stars)
+ id = e->s->sparts[-gp->id_or_neg_offset].id;
+ else if (gp->type == swift_type_black_hole)
+ id = e->s->bparts[-gp->id_or_neg_offset].id;
+ else
+ id = gp->id_or_neg_offset;
+
+ /* Cancel the velocity of the particles */
+ if (id < SWIFT_FIXED_BOUNDARY_PARTICLES) {
+
+ /* Don't move! */
+ gp->v_full[0] = 0.f;
+ gp->v_full[1] = 0.f;
+ gp->v_full[2] = 0.f;
+ }
+#endif
+
/* Drift... */
gp->x[0] += gp->v_full[0] * dt_drift;
gp->x[1] += gp->v_full[1] * dt_drift;
@@ -98,6 +124,21 @@ __attribute__((always_inline)) INLINE static void drift_part(
p->ti_drift = ti_current;
#endif
+#ifdef SWIFT_FIXED_BOUNDARY_PARTICLES
+
+ /* Get the ID of the gpart */
+ const long long id = p->id;
+
+ /* Cancel the velocity of the particles */
+ if (id < SWIFT_FIXED_BOUNDARY_PARTICLES) {
+
+ /* Don't move! */
+ xp->v_full[0] = 0.f;
+ xp->v_full[1] = 0.f;
+ xp->v_full[2] = 0.f;
+ }
+#endif
+
/* Drift... */
p->x[0] += xp->v_full[0] * dt_drift;
p->x[1] += xp->v_full[1] * dt_drift;
@@ -121,6 +162,16 @@ __attribute__((always_inline)) INLINE static void drift_part(
xp->x_diff[k] -= dx;
xp->x_diff_sort[k] -= dx;
}
+
+#ifdef SWIFT_FIXED_BOUNDARY_PARTICLES
+
+ /* Cancel the velocity of the particles */
+ if (id < SWIFT_FIXED_BOUNDARY_PARTICLES) {
+ p->v[0] = 0.f;
+ p->v[1] = 0.f;
+ p->v[2] = 0.f;
+ }
+#endif
}
/**
@@ -146,6 +197,21 @@ __attribute__((always_inline)) INLINE static void drift_spart(
sp->ti_drift = ti_current;
#endif
+#ifdef SWIFT_FIXED_BOUNDARY_PARTICLES
+
+ /* Get the ID of the gpart */
+ const long long id = sp->id;
+
+ /* Cancel the velocity of the particles */
+ if (id < SWIFT_FIXED_BOUNDARY_PARTICLES) {
+
+ /* Don't move! */
+ sp->v[0] = 0.f;
+ sp->v[1] = 0.f;
+ sp->v[2] = 0.f;
+ }
+#endif
+
/* Drift... */
sp->x[0] += sp->v[0] * dt_drift;
sp->x[1] += sp->v[1] * dt_drift;
@@ -185,6 +251,21 @@ __attribute__((always_inline)) INLINE static void drift_bpart(
bp->ti_drift = ti_current;
#endif
+#ifdef SWIFT_FIXED_BOUNDARY_PARTICLES
+
+ /* Get the ID of the gpart */
+ const long long id = bp->id;
+
+ /* Cancel the velocity of the particles */
+ if (id < SWIFT_FIXED_BOUNDARY_PARTICLES) {
+
+ /* Don't move! */
+ bp->v[0] = 0.f;
+ bp->v[1] = 0.f;
+ bp->v[2] = 0.f;
+ }
+#endif
+
/* Drift... */
bp->x[0] += bp->v[0] * dt_drift;
bp->x[1] += bp->v[1] * dt_drift;
--
GitLab