Location of Gauss Point in a 4 Node Shell Element

[imurdereri]

Hi All,

I need to know if i can get the locations of the gauss points (gp) of a 4 node shell element (ShellMITC4, ShellDKGQ, ShellNLDKGQ) in a relative or global coordinate system.
For example, if i use the command -xml y get this info for a specific gp and fiber of a layered shell element:

<?xml version="1.0" encoding="UTF-8"?>
<OpenSees
xmlns:xsi = "http://www.w3.org/2001/XMLSchema-instance"
xsi:noNamespaceSchemaLocation = "http://OpenSees.berkeley.edu/xml-schema ... enSees.xsd">
<TimeOutput>
<ResponseType>time</ResponseType>
</TimeOutput>
<ElementOutput eleType="ShellDKGQ" eleTag="1" node1="1" node2="2" node3="7" node4="6">
<GaussPoint number="1" eta="-0.57735" neta="-0.57735">
<SectionOutput secType="LayeredShellFiberSection" secTag="1">
<FiberOutput number="5" zLoc="-0.02408" thickness="0.04816">
<NdMaterialOutput matType="UnknownMovableObject" matTag="4">
<ResponseType>UnknownStrain</ResponseType>
<ResponseType>UnknownStrain</ResponseType>
<ResponseType>UnknownStrain</ResponseType>
<ResponseType>UnknownStrain</ResponseType>
<ResponseType>UnknownStrain</ResponseType>
</NdMaterialOutput>
</FiberOutput>
</SectionOutput>
</GaussPoint>
</ElementOutput>
<Data>

The only thing that ir changes when you look a different gp is mainly this line:

<GaussPoint number="1" eta="-0.57735" neta="-0.57735">

This values are the locations of the gp maybe? and how?

Thanks you very much

[selimgunay]

They are located at 1/sqrt(3) in the four quadrants. Below are the relevant lines from the cpp file

sg[0] = -one_over_root3;
sg[1] = one_over_root3;
sg[2] = one_over_root3;
sg[3] = -one_over_root3;

tg[0] = -one_over_root3;
tg[1] = -one_over_root3;
tg[2] = one_over_root3;
tg[3] = one_over_root3;

[imurdereri]

Thanks for your answer but i still dont get it, sorry

So:

1.- The "eta" and "neta" values equals to 1/sqrt(3) that you say right? <GaussPoint number="1" eta="-0.57735" neta="-0.57735">

And more important:

2.- How can i use that information obtained from the -xml file?

I think i need to understand this last part to know where the gp are located in a global or local coordinate system

[selimgunay]

These values are in the local coordinate system and normalized with respect to the element dimensions

[imurdereri]

Thanks for your answer!

I have a last question to be really sure.
Lets say i have only a shell of dimensions [a x a = 1 x 1] cm and one of the gp's is in the bottom left corner.
The origin of the local coordinate system is located at (X = 0.5 , Y = 0.5) cm in the global coordinate system (right?)

Then, the location in the global system of this gp for this example should be:

xgp = (a/2 - 0.57735*a/2) = 0.211325 cm
ygp = xgp

Can you confirm this please?

Thanks you so much for your help

[selimgunay]

The numbers are correct. It follows a standard FEM formulation

[imurdereri]

Thanks you!

Finally i understand

[dnzbgd]

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