Boundary forces

Boundary forces

This is an example of cs_user_extra_operations which computes boundary forces

Example 1: compute total forces on a boundary zone (subset of boundary faces).

  {
    cs_field_t *b_forces = cs_field_by_name_try("boundary_stress");
 
    if (b_forces != nullptr) {
      cs_real_3_t total_b_forces = {0., 0., 0.};
      const cs_real_t *b_face_surf = domain->mesh_quantities->b_face_surf;
      const cs_real_3_t *bpro_forces = (cs_real_3_t *)b_forces->val;
 
      /* get zone from its name, here "selected_wall" */
      const cs_zone_t *zn = cs_boundary_zone_by_name("selected_wall");
 
      for (cs_lnum_t e_id = 0; e_id < zn->n_elts; e_id++) {
        cs_lnum_t face_id = zn->elt_ids[e_id];
        for (cs_lnum_t i = 0; i < 3; i++)
          total_b_forces[i] += bpro_forces[face_id][i] * b_face_surf[face_id];
      }
 
      /* parallel sum */
      cs_parall_sum(3, CS_REAL_TYPE, total_b_forces);
    }
  }

Example 2: compute pressure forces on a boundary zone (subset of boundary faces).

  {
    const cs_real_3_t *b_f_face_normal
      = (cs_real_3_t *)domain->mesh_quantities->b_face_normal;
 
    cs_real_3_t total_b_p_forces = {0., 0., 0.};
 
    /* get zone from its name, here "selected_wall" */
    const cs_zone_t *zn = cs_boundary_zone_by_name("selected_wall");
 
    /* compute static pressure on selected boundary faces */
    cs_real_t *p_b_val;
    CS_MALLOC(p_b_val, zn->n_elts, cs_real_t);
    cs_post_b_pressure(zn->n_elts, zn->elt_ids, p_b_val);
 
    for (cs_lnum_t e_id = 0; e_id < zn->n_elts; e_id++) {
      cs_lnum_t face_id = zn->elt_ids[e_id];
      for (cs_lnum_t i = 0; i < 3; i++)
        total_b_p_forces[i] += p_b_val[e_id]*b_f_face_normal[face_id][i];
    }
 
    CS_FREE(p_b_val);
 
    /* parallel sum */
    cs_parall_sum(3, CS_REAL_TYPE, total_b_p_forces);
  }