Generate Structure
The Generate Structure app uses stochastic geometric modeling on a grain-based distance field to generate a 3D structure model. The app uses the same structure generation algorithm as the Generate Digital Twin From 2D and the Generate Digital Twin From 3D apps. It can therefore be used to
- find an initial guess for the optimization run in one of the other apps, or
- generate digital twins with the parameters found in one of the other apps.
This generation is done in three steps:
- A package of grains is generated by GrainGeo - Create Grains and removing overlap up to a certain degree. The grain generator uses spheres, ellipsoids or convex polyhedrons with enclosing ellipsoids, depending on the settings.
- Based on this grain package, a Euclidean distance field is generated.
- Using GrainGeo - Stochastic Field Thresholding, an isotropic Gaussian Random Field is generated, overlaid with the Euclidean distance field and thresholded to reach the targeted porosity.
The figure below illustrates an example of different overlay strengths for a target with 30% solid volume percentage. After generation, the structure is cleansed to remove artifacts.
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Modules needed to run this GeoApp:
GrainGeo
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Clicking Edit... opens the Generate Structure dialog. At the top, define a Result File Name for the result file and the result folder containing the generated structure.
Overlay Grains and Gauss Field Settings
The Overlay Strength is the field overlay strength in percentage. At 100% overlay strength the result will only show the grain package, while at 0% overlay strength the result will show only the Gaussian random field. If no Random Field is used, this value is automatically set to 100%. If no Grain Generator is used, this value is automatically set to 0%.
Check Invert Grains for Overlay to switch pore and solid material. In this case, the grain generator creates the pore space, and the background becomes the solid material.
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Grain Generator
Select the basic shape used to generate the 3D structure. Select None as Grain Generator to use only the Gaussian random field for the structure generation. The app uses the GrainGeo - Create Grains command to create the grain structure. Be aware that all lengths are given in the unit voxel.
For the Sphere shape, the diameters are Gaussian distributed. Select the mean diameter and the standard deviation.
For the Ellipsoid shape, the first diameter is Gaussian distributed. Select the mean diameter and the standard deviation. For the other two diameters, fixed aspect ratios are used.
For the Convex Polyhedron shape, an ellipsoid is used as enclosing object. Select the mean diameter and the standard deviation. For the other two diameters, fixed aspect ratios are used.
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Random Field
Domain Size: NX, NY, NZ and Voxel Length
Define the domain size and resolution of the created 3D structure model. When changing the Voxel Length, be aware that the parameters of the Random Field and the Grain Generator are given in units of the voxel length.
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Solid Volume Percentage, Pore and Solid Materials
The Solid Volume Percentage defines the percentage of grid cells filled with the Solid Material.
You can select one material for the solid part and one fluid material to fill the pores.
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Random Seed
The random seed is used for the grain structure generation with GrainGeo - Create and to create the Gaussian random field.
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Results
The default settings create a sphere packing overlaid with a random field of short correlation length.
