[Nek5000-users] Volume of an element

[nek5000-users at lists.mcs.anl.gov]

Thanks Paul for your Kind replay. You were right. I want to get the volume associated with each grid point. And I tried the code below, but at each time when I run I get different answers for volume so I think my ocde is not rubust. Could you please verify my code below. 


nxyz = nx1*ny1*nz1 
n = nx1*ny1*nz1*nelv 

vol = vlsum(bm1(1,1,1,1),nxyz) 
a=glmax(vol,1) 
b=glmin(vol,1) 

do e=1,n 
volume = vlsum(bm1(e,1,1,1),nxyz) 
open (unit=10,file="hcoeff.dat") 
write (10,7020) a,b,volume 
7020 format(7f20.14) 
enddo 



Regards 

Sijo GEORGE 


De: "nek5000-users" <nek5000-users at lists.mcs.anl.gov> 
À: "nek5000-users" <nek5000-users at lists.mcs.anl.gov> 
Envoyé: Lundi 26 Février 2018 21:46:02 
Objet: Re: [Nek5000-users] Volume of an element 






Dear Sijo, 




We typically refer to elements as the structures that have (N+1)^3 

points. (Here, N+1 = lx1.) 




They are enumerated in nek5000 by the element number, e: 




integer e 




nxyz = nx1*ny1*nz1 

do e=1,nelt 

volume = volel(e) 

volume = vlsum(bm1(1,1,1,e),nxyz) 

enddo 




would both yield the same value for the volume of element e. 




It appears to me that you are after something different, however. 

It seems like you want to associate a volume with each grid point. 

If that is the case, then the entries of the diagonal mass matrix, bm1, 

are indeed the quantities that you want. 




Each entry of bm1(i,1,1,1) for i=1 to n:=nxyz*nelt, corresponds to the 

integral of the underlying basis function. 




That is, if we think about a function phi_i(x) such that 




u(x) = sum_i=1^n u(i,1,1,1)*phi_i(x) 




then 




bm1(i,1,1,1) = \int phi_i(x) dx 




where the integral (\int) is taken over the entire computational domain. 




[ Note that we really don't have such a global phi_i(x) ... I use it simply 

for illustration, here.] 




hth 




Paul 






From: Nek5000-users <nek5000-users-bounces at lists.mcs.anl.gov> on behalf of nek5000-users at lists.mcs.anl.gov <nek5000-users at lists.mcs.anl.gov> 
Sent: Monday, February 26, 2018 11:59:19 AM 
To: nek5000-users 
Subject: [Nek5000-users] Volume of an element 
Hi Neks, 

How to calculate volume of an element in a 3D mesh? If i write 

n = nx1*ny1*nz1*nelv 
do i=1,n 
v(i) = volume(1,1,1,i) 
enddo 


Can i store the volume of each element into a varibale called v? 


What happens if i use bm1(1,1,1,i)? Instead of volume(1,1,1,i) 


Thanks 
Sijo 



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