D3PLOT 22.1

Advanced Options

The Advanced options tab allows users to change the settings that are used for all streamlines. The image (right) shows the default values.

Each streamline is made of small line segments, called "steps". Ideally the steps should be short enough to give accurate results, but long enough to make it quick to compute the streamline. We use an adaptive step-size to get a balance between these.

The streamline can be lengthened (or shortened) by setting the MAX NUMBER OF STEPS to be used in the computation.

SHOW START POINT	Select whether the streamline start points are displayed and set their size.
SHOW EACH STEP	Select whether a point is shown at each step (small segment) of the streamline and set the point size. This can be helpful to check streamline quality.
MAX NUMBER OF STEPS	Change the maximum number of steps that can be used.
STAGNATION SPEED	Streamlines end (stagnate) when they reach an area where the velocity is less than the Stagnation speed .

There are four different STEP-SIZE ADAPTATION schemes available. Each scheme has parameters that can be changed. The relevant parameters are shown at the bottom of the Advanced options menu.

Use HELP in the STEP-SIZE ADAPTATION popup to see the following information about the different schemes.

Name	Description	Parameters	Recommended value (using cell length units)
RK 45 error estimate	This scheme is suitable for most applications. D3Plot increases the number of steps where the estimated error exceeds the Error Tolerance . If the start point is near an area of low velocity, you may need to reduce the Initial Step Length to improve accuracy at the the start.	Initial step length	0.3
RK 45 error estimate		Error tolerance	1e-6
Target stepsize	This scheme gives equally spaced steps. The step length is the Target step length . The scheme becomes unstable if the velocity magnitude gets very small. To avoid this, either find as suitable Stagnation Speed at which to stop the streamline, or use another adaptation scheme.	Target step length	0.3
Angle between steps	This scheme increases the number of steps where the streamline changes direction, and reduces the number of steps where the flow is parallel. Steps cannot be longer than the Max step length . If the streamline misses areas of interest, and to maintain accuracy where the flow is parallel you may need to reduce the Max step length . If the start point is near an area of low velocity, you may need to reduce the Initial Step Length to improve accuracy at the the start. This scheme can be used as a refined version of the Target Stepsize scheme by setting the Max step length to the Target step length.	Initial step length	0.3
Angle between steps		Max step length	3
RK 4 eigenvalue error	This scheme takes the longest time, but can give the most accurate and smooth results. D3Plot estimates a suitable step size such that the error for surrounding eigenvalues does not exceed the Error Tolerance . Steps cannot be longer than the Max step length . To maintain accuracy where the flow is parallel, or very different between adjacent elements you may need to reduce the Max step length . Note: For a 2D analysis this is only implemented where the 2D ICFD Volume is in the x-y plane (z = 0).	Max step length	3
RK 4 eigenvalue error		Error tolerance	1e-5

Step length parameters can be given in different UNITS :

CELL LENGTH	Values are relative to the length of the element the point is in. This allows step length parameters to vary where the model has a finer mesh.
LENGTH	Values are relative to units of length in the model.

For a more detailed description of step-size adaptation schemes see Computational Methods .

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