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.
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For models using The Charged Particle Tracing Interface the Release Current Magnitude section is available instead of Release Times when the Particle release specification is set to Specify current. Enter a value for the Release current magnitude I (SI unit: A). The default is 1 nA. For models using The Particle Tracing for Fluid Flow Interface the Mass Flow Rate section is available instead of Release Times when the Particle release specification is set to Specify mass flow rate. Enter a value for the Mass flow rate (SI unit kg/s). The default is 1dn either case, all particles are released at time t = 0. The expression for the Release current magnitude or Mass flow rate should only depend on parameters and global variables, not on particle variables such as the particle mass.
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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.
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If the model includes a Particle-Particle Interaction then there is a risk that the force may become infinite if the initial particle positions are not unique. When modeling particle-particle interactions the Position refinement factor should be 0 to ensure that initial positions are unique. However, it may then be necessary to refine the mesh to get an accurate initial distribution of particle positions if the density is not uniform.
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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.
For The Charged Particle Tracing Interface and
The Particle Tracing for Fluid Flow Interface this section is shown when
Newtonian or
Newtonian, first order 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.
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For Expression enter coordinates for the Initial particle velocity v0 (SI unit: m/s) based on space dimension. The defaults are 0 m/s.
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For Kinetic energy and direction enter the Initial kinetic energy E0 (SI unit: J). The default is 1 keV. Then enter coordinates for the Initial particle direction L0 (dimensionless) based on space dimension. The expression for the initial direction is automatically normalized to unity.
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For Constant speed, spherical a total of Nvel particles are released in a circle or sphere at each release point, each with the same speed. Enter the following:
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Speed v (SI unit: m/s). The default is 1 m/s.
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For Constant speed, hemispherical a total of Nvel particles are released in a hemisphere or half circle at each release point, each with the same speed. Enter the:
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Speed v (SI unit: m/s). The default is 1 m/s.
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A direction vector for the Hemisphere axis r (dimensionless). This sets the direction of the north pole of the hemisphere or half circle.
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For Constant speed, cone a total of Nvel particles are released at each release point, each with the same speed. The velocity distribution is a cone of angle α for 3D components and an arc of half-angle α for 2D. Enter the:
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Speed v (SI unit: m/s). The default is 1 m/s.
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A direction vector for the Cone axis r (dimensionless). This sets the direction of the cone axis for 3D components or the centerline of the arc for 2D.
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A Cone angle α (SI unit: rad).
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The Constant speed, Lambertian option is only available in 3D. It generates Nvel particles for each release point, each with the same speed. The velocity distribution is a hemisphere in which the angle distribution follows the cosine law. Enter the:
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Speed v (SI unit: m/s). The default is 1 m/s.
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For Maxwellian enter the:
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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.
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For example, if Constant speed, hemispherical is selected from the Initial velocity list, the Allow nonuniform speeds in distribution check box is selected, and the expression for the initial speed is 2[m/s]*(random(pt.pidx)+0.5), then particles will be released with directions sampled from an isotropic hemisphere and with speeds sampled pseudorandomly between 0 and 2 m/s.
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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.
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.
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:
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For Mean and standard deviation (the default), enter the following:
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For Count median diameter and geometric standard deviation, enter the following:
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For Sauter mean diameter and geometric standard deviation, enter the following:
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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.
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.
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When None is selected, enter an initial value (rp0).
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For Normal, the initial values are sampled from a normal or Gaussian distribution. Enter the Number of values (default 1), Mean (default 0), and Standard deviation (default 1).
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For Lognormal, the initial values are sampled so that their logarithms follow a normal distribution. Enter the Number of values (default 1), Mean (default 0), and Standard deviation (default 1). An advantage of the Lognormal distribution over the Normal distribution is that, if the Mean is positive, all the sampled values will be positive.
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For Uniform, enter the Number of values (default 1), Minimum (default 0), and Maximum (default 1).
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Select List of values to enter a set of numerical values directly.
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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).