hydro.h 10.6 KB
Newer Older
1
2
/*******************************************************************************
 * This file is part of SWIFT.
3
 * Copyright (c) 2016 Matthieu Schaller (matthieu.schaller@durham.ac.uk)
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as published
 * by the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program 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 Lesser General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 ******************************************************************************/

20
#include "adiabatic_index.h"
21
#include "dimension.h"
22
#include "equation_of_state.h"
23
24
#include "hydro_properties.h"
#include "kernel_hydro.h"
25
26
27
28
29
30
31
32
33
34
35
36
37
38

/**
 * @brief Returns the internal energy of a particle
 *
 * For implementations where the main thermodynamic variable
 * is not internal energy, this function computes the internal
 * energy from the thermodynamic variable.
 *
 * @param p The particle of interest
 * @param dt Time since the last kick
 */
__attribute__((always_inline)) INLINE static float hydro_get_internal_energy(
    const struct part *restrict p, float dt) {

39
  return p->u + p->u_dt * dt;
40
41
42
43
44
45
46
47
48
49
50
}

/**
 * @brief Returns the pressure of a particle
 *
 * @param p The particle of interest
 * @param dt Time since the last kick
 */
__attribute__((always_inline)) INLINE static float hydro_get_pressure(
    const struct part *restrict p, float dt) {

51
52
53
  const float u = p->u + p->u_dt * dt;

  return gas_pressure_from_internal_energy(p->rho, u);
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
}

/**
 * @brief Returns the entropy of a particle
 *
 * For implementations where the main thermodynamic variable
 * is not entropy, this function computes the entropy from
 * the thermodynamic variable.
 *
 * @param p The particle of interest
 * @param dt Time since the last kick
 */
__attribute__((always_inline)) INLINE static float hydro_get_entropy(
    const struct part *restrict p, float dt) {

69
70
71
  const float u = p->u + p->u_dt * dt;

  return gas_entropy_from_internal_energy(p->rho, u);
72
73
74
75
76
77
78
79
80
81
82
}

/**
 * @brief Returns the sound speed of a particle
 *
 * @param p The particle of interest
 * @param dt Time since the last kick
 */
__attribute__((always_inline)) INLINE static float hydro_get_soundspeed(
    const struct part *restrict p, float dt) {

83
84
85
  const float u = p->u + p->u_dt * dt;

  return gas_soundspeed_from_internal_energy(p->rho, u);
86
}
87

88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
/**
 * @brief Modifies the thermal state of a particle to the imposed internal
 * energy
 *
 * This overrides the current state of the particle but does *not* change its
 * time-derivatives
 *
 * @param p The particle
 * @param u The new internal energy
 */
__attribute__((always_inline)) INLINE static void hydro_set_internal_energy(
    struct part *restrict p, float u) {

  p->u = u;
}

/**
 * @brief Modifies the thermal state of a particle to the imposed entropy
 *
 * This overrides the current state of the particle but does *not* change its
 * time-derivatives
 *
 * @param p The particle
 * @param S The new entropy
 */
__attribute__((always_inline)) INLINE static void hydro_set_entropy(
    struct part *restrict p, float S) {

  p->u = gas_internal_energy_from_entropy(p->rho, S);
}

119
120
121
/**
 * @brief Computes the hydro time-step of a given particle
 *
122
123
124
 * This function returns the time-step of a particle given its hydro-dynamical
 * state. A typical time-step calculation would be the use of the CFL condition.
 *
125
126
 * @param p Pointer to the particle data
 * @param xp Pointer to the extended particle data
127
 * @param hydro_properties The SPH parameters
128
129
130
 *
 */
__attribute__((always_inline)) INLINE static float hydro_compute_timestep(
131
132
    const struct part *restrict p, const struct xpart *restrict xp,
    const struct hydro_props *restrict hydro_properties) {
133
134

  const float CFL_condition = hydro_properties->CFL_condition;
135
136

  /* CFL condition */
137
138
  const float dt_cfl =
      2.f * kernel_gamma * CFL_condition * p->h / p->force.v_sig;
139

140
  return dt_cfl;
141
142
}

143
144
145
146
/**
 * @brief Initialises the particles for the first time
 *
 * This function is called only once just after the ICs have been
147
148
 * read in to do some conversions or assignments between the particle
 * and extended particle fields.
149
150
151
152
 *
 * @param p The particle to act upon
 * @param xp The extended particle data to act upon
 */
153
__attribute__((always_inline)) INLINE static void hydro_first_init_part(
154
    struct part *restrict p, struct xpart *restrict xp) {
155

156
157
158
159
160
  p->ti_begin = 0;
  p->ti_end = 0;
  xp->v_full[0] = p->v[0];
  xp->v_full[1] = p->v[1];
  xp->v_full[2] = p->v[2];
161
162
}

163
164
165
166
/**
 * @brief Prepares a particle for the density calculation.
 *
 * Zeroes all the relevant arrays in preparation for the sums taking place in
167
168
 * the various density loop over neighbours. Typically, all fields of the
 * density sub-structure of a particle get zeroed in here.
169
170
171
 *
 * @param p The particle to act upon
 */
172
__attribute__((always_inline)) INLINE static void hydro_init_part(
173
    struct part *restrict p) {
174

175
176
177
178
179
180
181
182
183
184
185
  p->density.wcount = 0.f;
  p->density.wcount_dh = 0.f;
  p->rho = 0.f;
  p->rho_dh = 0.f;
}

/**
 * @brief Finishes the density calculation.
 *
 * Multiplies the density and number of neighbours by the appropiate constants
 * and add the self-contribution term.
186
187
188
 * Additional quantities such as velocity gradients will also get the final
 *terms
 * added to them here.
189
190
191
192
 *
 * @param p The particle to act upon
 * @param time The current time
 */
193
__attribute__((always_inline)) INLINE static void hydro_end_density(
194
    struct part *restrict p, float time) {
195
196
197

  /* Some smoothing length multiples. */
  const float h = p->h;
198
199
200
  const float h_inv = 1.0f / h;                       /* 1/h */
  const float h_inv_dim = pow_dimension(h_inv);       /* 1/h^d */
  const float h_inv_dim_plus_one = h_inv_dim * h_inv; /* 1/h^(d+1) */
201

202
203
  /* Final operation on the density (add self-contribution). */
  p->rho += p->mass * kernel_root;
204
  p->rho_dh -= hydro_dimension * p->mass * kernel_root;
205
206
207
  p->density.wcount += kernel_root;

  /* Finish the calculation by inserting the missing h-factors */
208
209
  p->rho *= h_inv_dim;
  p->rho_dh *= h_inv_dim_plus_one;
210
  p->density.wcount *= kernel_norm;
211
  p->density.wcount_dh *= h_inv * kernel_gamma * kernel_norm;
212
213
214
215

  const float irho = 1.f / p->rho;

  /* Compute the derivative term */
216
  p->rho_dh = 1.f / (1.f + hydro_dimension_inv * p->h * p->rho_dh * irho);
217
218
219
220
221
}

/**
 * @brief Prepare a particle for the force calculation.
 *
222
223
224
225
226
227
 * This function is called in the ghost task to convert some quantities coming
 * from the density loop over neighbours into quantities ready to be used in the
 * force loop over neighbours. Quantities are typically read from the density
 * sub-structure and written to the force sub-structure.
 * Examples of calculations done here include the calculation of viscosity term
 * constants, thermal conduction terms, hydro conversions, etc.
228
229
230
 *
 * @param p The particle to act upon
 * @param xp The extended particle data to act upon
231
232
 * @param ti_current The current time (on the timeline)
 * @param timeBase The minimal time-step size
233
 */
234
__attribute__((always_inline)) INLINE static void hydro_prepare_force(
235
236
    struct part *restrict p, struct xpart *restrict xp, int ti_current,
    double timeBase) {
237

238
239
240
241
  const float half_dt = (ti_current - (p->ti_begin + p->ti_end) / 2) * timeBase;
  const float pressure = hydro_get_pressure(p, half_dt);

  p->force.pressure = pressure;
242
243
244
245
246
247
}

/**
 * @brief Reset acceleration fields of a particle
 *
 * Resets all hydro acceleration and time derivative fields in preparation
248
 * for the sums taking  place in the various force tasks.
249
250
251
 *
 * @param p The particle to act upon
 */
252
__attribute__((always_inline)) INLINE static void hydro_reset_acceleration(
253
    struct part *restrict p) {
254
255
256
257
258
259
260

  /* Reset the acceleration. */
  p->a_hydro[0] = 0.0f;
  p->a_hydro[1] = 0.0f;
  p->a_hydro[2] = 0.0f;

  /* Reset the time derivatives. */
261
  p->u_dt = 0.0f;
262
  p->force.h_dt = 0.0f;
263
264
265
266
267
268
  p->force.v_sig = 0.0f;
}

/**
 * @brief Predict additional particle fields forward in time when drifting
 *
269
270
271
 * Additional hydrodynamic quantites are drifted forward in time here. These
 * include thermal quantities (thermal energy or total energy or entropy, ...).
 *
272
273
 * @param p The particle
 * @param xp The extended data of the particle
274
275
276
 * @param t0 The time at the start of the drift (on the timeline)
 * @param t1 The time at the end of the drift (on the timeline)
 * @param timeBase The minimal time-step size
277
278
 */
__attribute__((always_inline)) INLINE static void hydro_predict_extra(
279
280
    struct part *restrict p, const struct xpart *restrict xp, int t0, int t1,
    double timeBase) {
281

282
283
284
  /* Drift the pressure */
  const float dt_entr = (t1 - (p->ti_begin + p->ti_end) / 2) * timeBase;
  p->force.pressure = hydro_get_pressure(p, dt_entr);
285
286
287
288
289
}

/**
 * @brief Finishes the force calculation.
 *
290
291
292
 * Multiplies the force and accelerations by the appropiate constants
 * and add the self-contribution term. In most cases, there is nothing
 * to do here.
293
294
295
 *
 * @param p The particle to act upon
 */
296
__attribute__((always_inline)) INLINE static void hydro_end_force(
297
298
    struct part *restrict p) {

299
  p->force.h_dt *= p->h * hydro_dimension_inv;
300
}
301
302
303
304

/**
 * @brief Kick the additional variables
 *
305
306
307
 * Additional hydrodynamic quantites are kicked forward in time here. These
 * include thermal quantities (thermal energy or total energy or entropy, ...).
 *
308
 * @param p The particle to act upon
309
 * @param xp The particle extended data to act upon
310
 * @param dt The time-step for this kick
311
 * @param half_dt The half time-step for this kick
312
 */
313
__attribute__((always_inline)) INLINE static void hydro_kick_extra(
314
315
    struct part *restrict p, struct xpart *restrict xp, float dt,
    float half_dt) {
316

317
318
319
320
321
322
  /* Do not decrease the energy by more than a factor of 2*/
  const float u_change = p->u_dt * dt;
  if (u_change > -0.5f * p->u)
    p->u += u_change;
  else
    p->u *= 0.5f;
323

324
325
  /* Do not 'overcool' when timestep increases */
  if (p->u + p->u_dt * half_dt < 0.5f * p->u) p->u_dt = -0.5f * p->u / half_dt;
326
}
327
328

/**
329
 * @brief Converts hydro quantity of a particle at the start of a run
330
 *
331
332
333
334
 * This function is called once at the end of the engine_init_particle()
 * routine (at the start of a calculation) after the densities of
 * particles have been computed.
 * This can be used to convert internal energy into entropy for instance.
335
336
337
 *
 * @param p The particle to act upon
 */
338
__attribute__((always_inline)) INLINE static void hydro_convert_quantities(
339
    struct part *restrict p) {}