Streamline Surface
Use a Streamline Surface plot in 3D () to visualize a vector quantity on surfaces. A streamline is a curve everywhere tangent to an instantaneous vector field. Add Color Expression, Deformation, Export Expressions, Filter, Material Appearance, or Transparency subnodes as needed. Right-click a 3D Plot Group to add these plots from the More Plots submenu.
Go to Common Results Node Settings for links to information about these sections: Data, Expression, Title, Quality, and Inherit Style.
To get the length of the streamlines, use an Export>Plot node. In its Settings window, select the Only export starting points and endpoints check box to include one row with the starting point, the endpoint, and the length of the streamline for each streamline.
Selection
In this section, select the surfaces on which to compute and plot the streamlines (the selected surfaces are not the boundaries where the streamlines should start). The selected surfaces must form a plane. By selecting in the Graphics window and using the tools in the Selection section, select the boundaries (surfaces) on which you want to plot streamlines.
Streamline Positioning
Select one of these options from the Positioning list: Starting-point controlled (the default), Uniform density, or Magnitude controlled. Then follow one of the methods described:
Color and Style
In this section you can control the style and color of the streamlines and add arrows to them, if desired.
Line Style
Under Line style, choose None, Line (the default), or Tube from the Type list to determine the type of streamlines. If you choose None, no streamlines appear, but you can plot arrows that are tangential to the streamlines.
Arrow Style
Under Arrow style, you can add arrows and control their appearance.
From the Type list, choose None (the default) for no arrows, or choose Tangent for arrows that are tangential to the streamlines. If you choose Tangent, these additional settings are available:
From the Arrow distribution list, choose Equal arc length (the default) to distribute the arrows uniformly over the streamlines’ arc length, Equal time to distribute the arrows using the weight function dt/darc, or Equal inverse time to distribute the arrows using the weight function darc/dt.
Select the Number of arrows check box to enter a number for the total number of arrows, on all streamlines, that are plotted. By default, the COMSOL Multiphysics software provides a reasonable number of arrows.
From the Arrow type list, choose Arrowhead (the default), Arrow, or Cone.
From the Arrow length list, choose Normalized (the default), Logarithmic, or Proportional to make the arrows’ sizes depend on the magnitude of the plotted quantity, if desired.
Use the slider, or select the Scale factor check box and enter a scale factor in the associated text field if you want to use another scaling than the one used by default.
From the Color list, choose a color for the streamlines and arrows. Choose Custom to add a custom color using a color palette.
Advanced
Define the following advanced streamline settings as needed.
Advanced Settings for the Streamline Plot
Under Advanced, set these general settings. See also Advanced Section Setting Effects.
The Integration tolerance field default is 0.001. Edit to specify how accurately streamlines are computed.
The Maximum streamline length field makes it possible to control the length of streamlines. Edit the default (Inf) to control the streamlines’ length. Enter the value as a fraction of the mean bounding box’s size. When the Allow backward time integration check box is selected (the default), the maximum length refers to the sum of the lengths of the forward and backward parts.
The Maximum number of integration steps field makes sure that the integration does not continue indefinitely. Edit the default (5000) to control when the computation stops.
The Maximum integration time field sets an upper time limit for the integration. The default is infinity (inf).
The Stationary point stop tolerance can be adjusted to make sure the integration stops near a stationary point in the field. The default is 0.01.
The Loop tolerance field default is 0.01. This is a fraction of the mean of the lengths of the bounding box of the geometry. If a streamline gets closer to its starting point than this distance, the streamline snaps to its starting point and is plotted as a connected loop. See also Method 5: Creating Streamlines with Variable Density and Magnitude Controlled.
Select the Allow backward time integration check box to integrate points from the starting points both in the direction of the vector field and in the opposite direction. This check box is selected by default.
Select the Normalize vector field check box if required. The vector field is normalized pointwise: For each point where the field was evaluated, the vector is replaced by a unit vector in the same direction. If you apply normalization, the speed along the streamline changes. This change means that the other settings in the Advanced section (for example, maximum number of integration steps and maximum integration time) are interpreted differently.
Streamline Positioning Section (Continued)
Method 1: Selecting the Specified Number of Starting Points in the Geometry
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Under Streamline Positioning, from the Positioning list, select Starting-point controlled.
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Enter the number of Points (the default is 20).
Method 2: Creating Streamlines with Uniform Density
The algorithm saturates the entire surface with evenly spaced streamlines.
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Under Streamline Positioning, from the Positioning list, select Uniform density.
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Enter the Separating distance between the streamlines (the default is 0.05).
The value for the separating distance is a fraction of the mean of the lengths of the bounding box of the geometry. In this case, a streamline stops whenever it gets too close to another streamline or itself (or if any of the general termination criteria specified in the Advanced section is fulfilled).
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The Advanced parameters list defaults to Automatic. If required, select Manual to edit these parameters: Boundary element refinement, Fraction of streamlines to ignore, Starting distance factor, or Terminating distance factor.
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Edit the Boundary element refinement if streamlines do not behave as expected near edges on a coarse mesh — try increasing this number. It is a measurement of the density of points on the edges used to set up the structure and is used to measure distances between streamlines. Refining the mesh in the problematic area can also resolve the problem.
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Edit the value in the Fraction of streamlines to ignore field (a fraction 0–1; default value: 0.5) when a streamline is close to itself, typically for spiraling streamlines. This number controls how big part of the streamline, starting from its starting point, that the streamline itself is allowed to get close to, and it might in some cases be useful in order to get a less cluttered streamline plot.
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The Starting distance factor is a factor multiplied with the distance specified in the Separating distance field (as a fraction of the mean of the lengths of the bounding box of the geometry — the default value is 0.05). It sets the minimum distance between streamlines and the starting point for the next streamline.
When the surface is close to be saturated with streamlines, new starting points tend to be positioned where the streamline has nowhere to go before it gets too close other streamlines, resulting in short streamlines. The higher the value of this factor, the more it disqualifies the starting point and thus reduces the number of short streamlines.
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The Terminating distance factor is a factor multiplied with the distance specified in the Separating distance field. It sets the minimum distance between any pair of streamlines. Thus, this distance is the minimal distance under which the integration of a streamline stops.
Method 3: Creating Streamlines with Variable Density and Magnitude Controlled
To create streamlines with a variable density according to the magnitude of the specified vector field:
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Under Streamline Positioning, from the Positioning list, select Magnitude controlled.
The Magnitude controlled setting gives proper streamline plots only for incompressible flow fields. In this case, the algorithm places the streamlines so that the flow between each pair of adjacent streamlines is the same throughout the surface, giving streamlines that are more dense where the magnitude of the field is high.
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Enter a Density (the default is 20). This value is roughly the number of streamlines. Prior to streamline generation, the software computes a rough estimate of the total flow of the flow field in the model, divides this value with the specified Density setting, and uses the resulting value as the flow between each pair of adjacent streamlines.
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If required, from the Advanced parameters list, select Manual to specify the Boundary element refinement as described in Method 2: Creating Streamlines with Uniform Density.
Advanced Section Setting Effects
The Advanced settings have the following effects:
This process stops if:
Finally, the software connects the calculated points for each streamline consecutively with straight lines.