| 89 | | |
| 90 | | |
| | 89 | |--- |
| | 90 | {{{#!td style="vertical-align:top" |
| | 91 | [=#create_disturbances '''create_disturbances'''] |
| | 92 | }}} |
| | 93 | {{{#!td style="vertical-align:top" |
| | 94 | L |
| | 95 | }}} |
| | 96 | {{{#!td style="vertical-align:top" |
| | 97 | .T. |
| | 98 | }}} |
| | 99 | {{{#!td |
| | 100 | Switch to impose random perturbations to the horizontal velocity field.\\\\ |
| | 101 | With '''create_disturbances''' = .T., random perturbations can be imposed to the horizontal velocity field at certain times e.g. in order to trigger off the onset of convection, etc..\\\\ |
| | 102 | The temporal interval between these times can be steered with [[dt_disturb]], the vertical range of the perturbations with [[disturbance_level_b]] and [[disturbance_level_t]], and the perturbation amplitude with [[disturbance_amplitude]]. In case of non-cyclic lateral boundary conditions (see [[bc_lr]] and [[bc_ns]]), the horizontal range of the perturbations is determined by [[inflow_disturbance_begin]] and [[inflow_disturbance_end]]. A perturbation is added to each grid point with its individual value determined by multiplying the disturbance amplitude with a uniformly distributed random number. After this, the arrays of u and v are smoothed by applying a Shuman-filter twice and made divergence-free by applying the pressure solver.\\\\ |
| | 103 | The random number generator to be used can be chosen with [[random_generator]].\\\\ |
| | 104 | As soon as the desired flow features have developed (e.g. convection has started), further imposing of perturbations is not necessary and can be omitted (this does not hold for non-cyclic lateral boundaries!). This can be steered by assigning an upper limit value for the perturbation energy (the perturbation energy is defined by the deviation of the velocity from the mean flow) using the parameter [[disturbance_energy_limit]]. As soon as the perturbation energy has exceeded this energy limit, no more random perturbations are assigned.\\\\ |
| | 105 | Timesteps where a random perturbation has been imposed are marked in the local file [[RUN_CONTROL]] by the character "D" appended to the values of the maximum horizontal velocities. |
| | 106 | }}} |
| | 107 | |---- |
