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Problem in Sparse linear solvers

Posted Jul 22, 2012, 10:09 a.m. EDT Structural Mechanics Version 4.1 2 Replies

Pavan Kumar Penumakala

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Dear Mr.Ivar and COMSOL users

I am modeling thermal stresses during solidification.

first i did heat transfer with solidification(by increasing cp of the steel ). then I used solid mechanics.
all works fine ..
when i use Yong modulus as constant 70e9 model works fine..
but when i use temperature dependant Young modulus the error comes..

when Temp=20C ,E=200GPa
Temp=1440C ,E=0 GPa
in the liquid state to eliminate stresses Yongmodulus value is used as 0 GPa
similarly posiions ratio is 0.49 in liquid and 0.3 for solid steel..
this way of modeling is followed by many users but i read that , it cuases ILL CONDITIONING OF GLOBAL MATRICES which might be a problem for sparse liner solvers.

so i tried different solvers but i am unsuccessful ..

when E=constant ..model works
when E= temperature dependent value model gives the error

'''Inverted mesh element near coordinates (0.564742, 0.443981)'''

i tried to use the damping factor as
initial damping factor 0.01
recovery damping factor 0.01

i tried many ways .but got the same error
can you please put me out of this problem

i am attching my model here

Attachments:

uncoupled3.mph

2 Replies Last Post Jul 24, 2012, 4:51 a.m. EDT

Nagi Elabbasi Facebook Reality Labs

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Posted: 1 decade ago

When Young’s Modulus drops to zero the structural mechanics problem is no longer well posed. The nodes can move around easily and lead to the inverted mesh error that you’re getting. Also depending on how you define the temperature dependence the modulus may become negative if the temperature exceeds 1440oC which is unphysical.

Nagi Elabbasi
Veryst Engineering

Pavan Kumar Penumakala

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Posted: 1 decade ago

Dear Nagi Elabbasi

i completely agree with you..
i am solving a solidification problem ..

liquid slowly turns to solid..

in one computational cell there is comibaniation liquid and solid (caleed mushy)

how to elimnate stresses in liquid part of the computational cell
any suggestions regarding this

and can you provide some useful solver settings in structural mechanics problems particulary when we use rate dependent creep or visco plastic laws..
the comsol documentation provides some tips but when i solve my own problem

because if its difficulty i am spending much time on solver settings..

if you can provide some more tips about this i will be greatly thankful to you..

thanks
pavan

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Problem in Sparse linear solvers

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