Use the Release node to release particles into the model from a selected set of domains. The release times, initial position, and initial value of any auxiliary dependent variables can be specified. The sections available are based on the Formulation in the physics interface Particle Release and Propagation section. If Newtonian, Newtonian, first order, Lagrangian, or Hamiltonian are selected, also enter an initial velocity.

Select a Distribution function: List of values (default), Uniform, Normal., or Lognormal.

Enter Release times (SI unit: s) or click the Range button () to select and define a range of specific times. At each release time, particles are released with initial position and velocity as defined in the following sections.

Enter the Number of values, along with the First time value (SI unit: s) and the Last time value (SI unit: s). In addition, select whether the Sampling from distribution should be Deterministic or Random. When Deterministic is selected, an array of length Number of values of uniformly spaced release times is generated. This array starts with the First time value and ends with the Last time value exactly. The release times are reproducible each time the solution is computed.

When Random is selected, an array of random numbers of length Number of values, with a minimum lower limit of the First time value and maximum upper limit of the Last time value is generated. In this case, a release time of exactly the first and last time values is extremely unlikely.

Enter the Number of values along with the Mean (SI unit: s) and the Standard deviation (SI unit: s). In addition, select whether the Sampling from distribution should be Deterministic or Random. When Deterministic is selected, an ordered array of length Number of values of normally distributed release times is generated. The release times are more closely spaced around the value entered for the Mean and the spacing of the release time drops off according to the value of the Standard deviation. The release times are reproducible each time the solution is computed.

When Random is selected, the normal or lognormal distribution is generated by pseudorandom sampling, so there may be some statistical error.

Select an Initial position: Mesh based (the default), Density, or Random.

For Mesh based the particles are released from a set of positions determined by a selection of geometric entities (of arbitrary dimension) in the mesh.

Select a Refinement factor between 1 and 5 (the default is 1), where the centers of the refined mesh elements are used. Thus, the number of positions per mesh element is refine^dim, except for pyramids, where it is (4*refine2-1)*refine/3.

For Density the particles are positioned in the selected domains by sampling from a user-defined spatial distribution. Enter a value for the Number of particles per release N (dimensionless). The default is 1. Enter a value or expression for the Density proportional to ρ (dimensionless). The default is 1.

The field Density proportional to is an expression; the resulting particle distribution approximately has a density that is proportional to this expression. The resulting distribution looks a bit random, and it depends on the underlying mesh.

Select a Release distribution accuracy order between 1 and 5 (the default is 5), which determines the integration order that is used when computing the number of particles to release within each mesh element. The higher the accuracy order, the more accurately particles will be distributed among the mesh elements.

The Position refinement factor (default 0) must be a nonnegative integer. When the refinement factor is 0, each particle is always assigned a unique position, but the density is taken as a uniform value over each mesh element. If the refinement factor is a positive integer, the distribution of particles within each mesh element is weighted according to the density, but it is possible for some particles to occupy the same initial position. Further increasing the Position refinement factor increases the number of evaluation points within each mesh element to reduce the probability of multiple particles occupying the same initial position.

For Random the particles are released at random positions within the selected entities. If particles are released at multiple release times, the initial positions are uniquely generated for each release time. By contrast, for Density the particle positions are the same at each release time.

The Number of particles per release is the number before velocity, release time and auxiliary dependent variable multiplication, so the actual number of model particles generated by the Release feature may be significantly larger.

For The Mathematical Particle Tracing Interface this section is shown when Newtonian, Newtonian, first order, Lagrangian, or Hamiltonian is selected as the Formulation.

Select an option from the Initial velocity list: Expression (the default), Kinetic energy and direction, Constant speed, spherical, Constant speed, hemispherical, Constant speed, cone, Constant speed, Lambertian (3D only), or Maxwellian.

For Constant speed, spherical, Constant speed, hemispherical, Constant speed, cone, Constant speed, Lambertian, and Maxwellian, select an option from the Sampling from distribution list: Deterministic (the default) or Random. If Deterministic is selected, the initial velocity is computed by sampling from the velocity distribution in a deterministic and reproducible manner. If Random is selected, the particle velocity is sampled from the distribution using pseudorandom numbers and may not always generate the same results.

For Constant speed, spherical, Constant speed, hemispherical, Constant speed, cone, and Constant speed, Lambertian, select the Allow nonuniform speeds in distribution check box to allow particles from the same release point to have different initial speeds. This check box has no effect on the initial velocity directions of the released particles, only their velocity magnitudes. If this check box is selected, expressions for the initial speed in terms of the particle index can return a unique value for each particle in the distribution.

Select an option from the Released particle properties list. At least one instance of the Particle Properties node is always available, because it is a default feature. If other instances of the Particle Properties feature have been added to the model, then they can be selected from the list. Use this input to specify which type of particle is released when modeling multiple particle species.

This section is only available for The Particle Tracing for Fluid Flow Interface and is only shown when the Compute particle temperature check box is selected in the physics interface Additional Variables section. Enter a value or expression for the Initial particle temperature Tp,0 (SI unit: K). The default value is 293.15 K.

This section is only available for The Particle Tracing for Fluid Flow Interface and is only shown when Specify particle mass is selected from the Particle size distribution list in the physics interface Additional Variables section.

The initial particle mass can be a single value or can be sampled from a distribution. Select an option from the Distribution function list: None (the default), Normal, Lognormal, Uniform, or List of values.

When None is selected, enter an initial value mp,0. The default value is 10-9 kg.

Select Normal to create a normal distribution function, Lognormal to create a log-normal distribution function, or Uniform to create a uniform distribution function. For any of these distributions, select an option from the Sampling from distribution check box: Deterministic (the default) or Random. For Random sampling the mean and standard deviation may not be exactly equal to the specified values but will statistically converge as the number of particles is increased.

The Number of values N (default 1) sets the number of values that are sampled from the distribution function at each release point.

For the Normal or Lognormal distribution enter the Mean particle mass (default 10-9 kg) and Particle mass standard deviation (default 10-10 kg). For the Uniform distribution enter the Minimum particle mass mp,min (default 10-9 kg) and the Maximum particle mass mp,max (default 2 × 10-9 kg). Select List of values to enter a list of numerical values for the initial particle mass directly.

This section is only available for The Particle Tracing for Fluid Flow Interface and is only shown when Specify particle diameter is selected from the Particle size distribution list in the physics interface Additional Variables section. The options in this section allow you to release many particles from each release point with different initial diameters.

The initial particle diameter can be a single value or can be sampled from a distribution. Select an option from the Distribution function list: None (the default), Normal, Lognormal, Uniform, or List of values.

When None is selected, enter an initial value dp,0. The default value is 1 μm.

Select Normal to create a normal distribution function, or Uniform to create a uniform distribution function. The Number of values N (default 1) sets the number of points in the distribution function. For the Normal distribution enter the Mean particle diameter (default 1 μm) and Particle diameter standard deviation (default 0.1 μm). For the Uniform distribution enter the Minimum particle diameter dp,min (default 1 μm) and the Maximum particle diameter dp,max (default 2 μm).

Select Lognormal to create a log-normal distribution function. Then select one of the following options from the Specify list:

For a Normal, Lognormal, or Uniform distribution, select an option from the Sampling from distribution check box: Deterministic (the default) or Random. For Random sampling the mean and standard deviation may not be exactly equal to the specified values but will statistically converge as the number of particles is increased.

Alternatively, select List of values to enter a list of numerical values for the initial particle diameter directly.

This section is only available for The Particle Tracing for Fluid Flow Interface and is only shown when the Enable macroparticles check box is selected in the physics interface Additional Variables section. Enter a value or expression for the Initial multiplication factor nn,0 (dimensionless). The default value is 1.

This section is available if an Auxiliary Dependent Variable has been added to the model.

For each of the Auxiliary Dependent Variables added to the model, choose a Distribution function for the initial value of the auxiliary dependent variables and whether the initial value of the auxiliary dependent variables should be a scalar value or a distribution function.

The number of particles simulated can increase substantially and the following options are available for each of the Auxiliary Dependent Variables added to the model.

For Normal, Lognormal, or Uniform, select an option from the Sampling from distribution list: Deterministic (the default) or Random. For Random the mean and standard deviation will statistically converge to the specified values as the Number of values is increased.

The Number of values sets the number of values that are sampled from the distribution function at each release point. So, if particles are released at 100 points, and the Number of values is 100, a total of 10,000 particles will be released. If a number of velocity values are also sampled at each release point, this number might be substantially higher.

By default auxiliary dependent variables are initialized after all other degrees of freedom. Select the Initialize before particle momentum check box to compute the initial value of the auxiliary dependent variable immediately after computing the initial particle position. By selecting this check box it is possible to define the initial particle velocity as a function of the auxiliary dependent variables. The order of initialization for the auxiliary dependent variables is described in more detail in Initialization of Auxiliary Dependent Variables in the Particle Tracing Modeling chapter.

This section is shown if Newtonian or Newtonian, first order is selected from the Formulation list in the physics interface Particle Release and Propagation section.

By default the Subtract moving frame velocity from initial particle velocity check box is cleared. Select this check box to offset the initial velocity of released particles if the frame is moving. If the check box is selected, choose an option from the Background velocity check box: From rotating frame (the default) or User defined. If From rotating frame is selected then there should be an active instance of the Rotating Frame feature in the model. If User defined is selected, enter values or expressions for the components of the background velocity vb (SI unit: m/s) directly. Thus, if this check box is cleared, particle velocity is always initialized with respect to the moving frame, which may be noninertial. If the check box is selected, the velocity is initialized with respect to the laboratory frame (that is, a fixed noninertial frame).