For the Initial Particle Parameters, the user can choose to Create Particles according to the options set afterwards or to Load Particles from File. For the second option, the user browses, selects, and opens an existing *.gpp (GeoDict particle parameters) file. This file may origin from a previous AddiDict simulation or may be generated using the GeoDict’s Python API, see the Automation user guide.
When the user selects Create Particles, the parameters for the particles can be set.
The position of the particles at the beginning of the injection, are chosen from the Particle Start Position pull-down menu:
Inflow Plane assigns all particles to start from the inflow plane of the fluid.
With Box all particles are positioned in a rectangle whose size can be defined by setting valid ranges for each spatial direction.
With Sphere a spherical injection volume for the particles is defined by entering center and radius of the sphere.
The unit used to define the lower and upper corner of the box for each coordinate direction, or the center and radius of the sphere, can be defined at the right top of the AddiDict Options dialog.
With Chosen Material IDs, the material(s) where the particles start can be selected. Each pore and porous material are possible as particle start position.
With Everywhere selected, the particles can start in each pore and porous material available in the structure in memory.
The Particle Positioning Weights allow to define the distribution of the particle start positions to the possible positions, defined under Particle Start Position.
With Uniform, all possible start positions have the same probability that particles start there.
For Velocity, the probability of particles starting at a possible position, depends on the fluid velocity. The higher the velocity, the higher the probability that a particle will start at a specific position. This will lead to uniform particle concentration in the flow.
With Distance, the probability depends on the distance from solid voxels. Choosing this option leads to more particles in the core flow and less particles near surfaces of solid voxels.
Choose GivenField, to define the starting probability dependent on a predefined field. This field is defined as a GeoDict volume file (*.guf, *.vol, etc.). If this file is loaded, the Volume Field that should be used for the particle positioning can be selected.
Particles to be transported are placed randomly in the Particle Start Position volume and may move randomly due to Brownian motion. The Random Seed sets the seed of the underlying random number generator. The same random seed produces identical results, whereas results with different random seeds are similar but not identical.
The Particle Start Velocity determines the initial particle velocities at the starting positions. If Fluid Velocity is chosen, every particle starts with the local velocity of the fluid flow. If Given Velocity is chosen, every particle starts with the entered velocity. The given velocity can be applied in all three directions or only in Z-direction.
The Particle Start Time defines when the particles are released to the flow. Through the Edit button, the particle start time can be set to be Constant, or to follow a distribution: Uniformly in interval, Gaussian, or an arbitrary Probability Distribution.
A Constant particle start time releases all particles at the same time, defined under Value.
Particles can be released Uniformly in interval by specifying the beginning and ending of the time interval.
For particles to be released following a Gaussian distribution, the Mean Value, the Standard Deviation, and the Distribution Width of the distribution need to be defined. The particle release times are centered on the Mean Value and vary according to the Standard Deviation.
The value in Distribution Width corresponds to the range on both sides of the mean value limiting the particle release time value that is accepted. A Distribution Width of 1 means that release time values may deviate only from -1 s to +1 s from the given Mean Value.
The parameters must be set so that no negative values are possible. For example, a release time mean value of 1 s and a distribution width of 2 s would lead to an error message appearing, as the time could reach a value less than zero.
Checking Cut-Off Distribution restricts the start times selected by the random number generator to the interval defined by the distribution bounds. Otherwise, random numbers outside of this interval are set to the distribution bounds.
With Probability Distribution, a discrete distribution for the particle release time can be defined. The table describes the probability (Count Probability) of a release time taking a certain Value.
The sum of all Count Probabilities defined in the table needs to sum up to one. Especially for large tables, the Normalize button for this Probability Sum can be helpful, that scales the count probabilities to sum up to one. The Number of Rows can be increased or decreased to enter the desired number of release time Values and their Count Probability, between 0 and 1. The buttons Load and Save allow loading a previously defined probability distribution and saving the current one for later use.
The Number of Particles determines the number of particles inserted into the geometry over the entire simulation period.
Particle End Position
Three options are available for the Particle End Position:
Particles always leave the simulation when they leave the computational domain at a defined outflow plane.
Optionally, particles can also leave the simulation when they hit a voxel with one of the defined material IDs, i.e., they are not considered anymore in the computation.
Additionally, particles can stop moving and leave the simulation if the particle displacement is larger than a predefined maximum value. This option can be used to, e.g., simulate a long channel (like in a catalytic converter) that is much longer in flow direction compared to the other two directions. By defining a maximum displacement, the simulation can be run on a much shorter channel in flow direction but with periodic boundary conditions.
