ANSYS ICEM资料--B3-Prism.ppt

1、Prism Meshing,ICEMCFD/AI*Environment 5.0,7/24/2020,2,Intro to the Prism Process,Process Generates prism (pentahedral/wedge) elements near boundary surfaces Starts from ICEM CFD tetrahedral or tri-surface mesh Batch process Prisms created by extrusion of surface mesh Prisms are made conformal with te

2、trahedral volume mesh if it exists Smoothing yields necessary quality Features Minimal user input required Add prism layers by part Each part can have unique prism properties Prism parameters are filed for later use Can specify specific volume parts for prisms Smoothing in surface normal direction t

3、o handle sharp corners Can specify initial height or use automatic size based on local surface triangle size,7/24/2020,3,Prism Preparation,Preparation Shoot for best possible initial hybrid mesh quality Hybrid mesh is generally difficult to smooth Start with good tetra or tri-surface mesh Choose pri

4、sm options carefully Preparation will save time later Start with a good quality tetra or tri-surface mesh Check aspect ratios Check and fix all diagnostics. Single/multiple edges, Non-manifold vertices, Duplicate elements will crash the prism mesher Visually scan the surface mesh Look for kinks or s

5、harp tent-like structures in the mesh Diagnostics may not reveal all surface discrepancies Make sure part associations are correct Look for a few elements in one part scattered among another part Extruding from a few isolated elements and none of their neighbors will likely crash Modify part assignm

6、ents of offending elements,7/24/2020,4,Prism Features,Prism Features Minimal user input required Number of layers Height ratio Select parts to mesh,7/24/2020,5,Prism - Advanced Options,Prism Advanced Options Specify volume part for prisms Specify brand new part for prisms in void Exponential or line

7、ar Specify 3, Compute params to calculate 4th. Total height should be less than 1/3 the smallest gap for a given part. On changes the direction of prism growth; Off grows prisms in normal direction For one prism layer, more than one step is not needed. If surface mesh has been smoothed with LaPlace,

8、 set surface steps to 0.,7/24/2020,6,Prism - Advanced Options (2),Prism Advanced Options Fewer is better to preserve orthogonality Rather than go below this value, the prisms will stop often leaving pyramidal elements. Use if meshing inside sharp corners. 0.05 is common See later slides,7/24/2020,7,

9、Options Fillet Ratio,Options Fillet Ratio Blends prism grid lines around sharp corners 0 = no fillet 1 = fillet ratio equals prism height If meshing tight spaces with tight curves (less than 60), may not have space for a fillet ratio,Fillet Ratio = 0.0,Fillet Ratio = 0.5,Fillet Ratio = 1.0,7/24/2020

10、,8,Options Max Height Over Base,Options Max height over base Restricts prism aspect ratio Prism layers stop growing in regions where prism aspect ratio would exceed specified value Number of prism layers would not be preserved locally Mesh is made conformal with pyramids at prism boundaries,Max Heig

11、ht Over Base = 1.0,Max Height Over Base not set,7/24/2020,9,Options Max Prism Angle,Options Max prism angle Controls prism layer growth around bends or to adjacent surfaces If prisms stop, edge is made conformal with pyramids Usually set in the 120 to 180 range Experience pays off here. If extruding

12、 from one part and not its neighbor, and the angle between the two surfaces is greater than the specified value, the prisms will detach and be capped with pyramids. This prevents bending the prisms that might create lower-quality internal angles. However, the pyramids can sometimes cause problems, t

13、oo.,Original mesh,Max prism angle = 180 deg.,Max prism angle = 140 deg.,7/24/2020,10,Options Prism Height Limit Factor,Options Prism height limit factor Restricts prism aspect ratio Prism height will not expand once this factor is met Preserves the specified number of prism layers Will fail if sizes

14、 of adjacent elements differ by more than a factor of 2,Limit factor = 0.5,Limit factor not set,7/24/2020,11,Prism Layer Parts,Prism layer parts Check mark indicates prisms will grow from or into that part Select at least one part containing tris Initial Height is first layer thickness Height Ratio

15、is layer-to-layer growth N Layers is number of layers for that part Leave items blank to use the default parameters set in main panel If a surface part for prisms is between two volume parts, specify one or both volume parts for prisms,7/24/2020,12,Smoothing a Tet/Prism Mesh,Smoothing a tet/prism me

16、sh First smooth only the tets and tris Set PENTA_6 to Freeze Dont want to modify the prism layers at this point Once tetra and tri elements are as smooth as possible, smooth all elements Set PENTA_6 to Smooth Decrease the Up to quality value so as not to distort prism elements too much,7/24/2020,13,

17、Splitting Prism Layers,Splitting prism layers If many prism layers are desired, it can be more robust and is always faster to create “fat” layers and then split them with mesh editing Edit Mesh Split Mesh Split Prisms Fix ratio: The first layer is split such that its resulting layers employ the given growth ratio Fix initial height: The first layer is split such that its first sub-layer is of the given height Specify the number of layers to result from each existing layer Can split any or all existing layers,7/24/2020,14,Redistributing Prism Layers,Redistributing prism l