8/13/2019 Mesh Building Tricks and Tips

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Mesh Building Tricks and Tips

A. Suggested Order of Attacka. Generate boundary nodes using the default 1000 m spacing. All

smaller boundary segments ill automatically ha!e nodes placed at

their points of inflection. "Generate"Boundary #odes $ "O%b. Set the inflo and outflo boundaries. &f the boundaries consist ofmore than one segment' use the "Boundary"Set &nflo by Areaor "Boundary"Set &nflo by Area command.

c. Set color display for ma(imum definition )in topographical areayou are orking on. "*isplay"+olours)+ontours"Bed ele!ation"Ma(,min and set range for the portion of the stream bed on hich youare currently focusing.

d. *rag boundary to higher ground if needed. *rag tool o,,-.e. *efine maor' most easily discerned topographical features such as

top of bank' toe of bank' etc. using breaklines.

f. *efine channel features such as thaleg' bars' secondary channelthaleg.g. Triangulate and sa!e your mesh file fre/uently. Sa!e to se/uential

mesh file names. Suggestion sa!e to a ne file after completingeach maor feature.

h. se 2egion 3ills and)or additional breaklines to subdi!ide thechannel such that there are 4 to 10 elements across each channel.This ill re/uire smaller elements in side channels.

i. Subdi!ide the inflo and outflo boundaries into 50 or moreelements using the smooth feature 6see belo7.

. +heck for elements that ha!e a large discrepancy beteen the

ele!ation gi!en in the bed file and the ele!ation calculated from thecomputational mesh. se "*isplay"8arge 9le!ation *ifferenceTriangles to display triangles here the centroid ele!ationdifference e(ceeds the threshold in bright yello. &t is useful to setthe ele!ation difference threshold in "Options"Set 9le!ation*ifference Threshold to a !alue rele!ant to the scale of the studysite. Add nodes to correct this condition.

k. +heck for elements that ha!e poor aspect ratios indicated by a lo/uality inde( 6:&7. The poorest triangle can be found by clicking onthe red triangle icon. &t is often useful to display all triangles belo atarget /uality inde( 60.5 is recommended7. To do so' set the BadTriangle Threshold to 0.5 , "Options"Set Bad Triangle Threshold.Then right click to get the display options menu and select :&!alues. All triangles ):& less than 0.5 ill be displayed.

l. +orrect poor :& triangles by adding or deleting mesh nodes asneeded.

m. ;hen all these acti!ities are completed' sa!e the file as a 2i!er5*input file and supply the upstream ater surface ele!ation 6areasonable estimate ill do7. "3ile"Sa!e as 2i!er5* &nput 3ile

8/13/2019 Mesh Building Tricks and Tips

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B. Mesh Tips and Tricksa. To subdi!ide a breakline segment ithout smoothing place a

floating node on each side of the area you ish to di!ide andtriangulate. Then delete e(traneous nodes and triangulate again.

b. To e(tend an in)outflo boundary hen the bed has beene(tended' delete all floating nodes across the boundary' use theboundary subdi!ider 6hatchet icon7 to place fi(ed nodes on theboundary immediately inside of the e(isting boundary inflectionpoint' drag the inflection points to the desired ne position so theboundary no crosses the channel at the desired e(tendedposition. Add breaklines beteen the ne area and the e(istingmesh nodes to force elements in the e(tended area. Add nodes'triangulate and smooth sufficiently to force 50 nodes on theboundary.

c. To follo e(isting bed breaklines' turn on the Snap to Bed

Breakpoint icon and create breaklines by clicking on the purple bednodes that appear. Take care to click !ery close to the desirednode as the snap feature ill grab the nearest bed breakpoint nodeto the cursor.

d. To continue an e(isting mesh breakline' turn on the Snap to MeshBreakpoint icon and click on the end point of the line you ish tocontinue.

e. Turn off the Snap to Bed Breakpoint and Snap to Mesh Breakpointfeatures hene!er you do not ant to grab an e(isting node. Thismay mean that you ill turn the snap feature on and off se!eraltimes hile building a mesh breakline.

f. The program ill perform calculations much faster if the mesh silace more nodes)elements in areas of significance to the study.This ill allo finer resolution in those areas if needed.