Re: [Libmesh-users] Unusual results of transient RB with 7 parameters

[吴家桦Gauvain <cau...@gm...>]

Still a long way to go... Would you please tell me how to view the "truth
solve" solution?

Gauvain

2018-02-27 22:00 GMT+08:00 David Knezevic <dav...@ak...>:

> On Tue, Feb 27, 2018 at 8:55 AM, 吴家桦Gauvain <cau...@gm...>
> wrote:
>
>> Thanks for replying.
>>
>> I did omit the inertia terms in my PDE. Regarding the greedy convergence
>> of 7 parameter transient case, the maximum error bound decreases as usual,
>> from about 40000 to 0.00197 but the result is abnormal like what is
>> described in my first mail. In fact, 3 parameter (thermal conditions)
>> transient case works well and so does 7 parameter steady case. The problem
>> arises when I attempt to combine them together by replacing the assembly
>> function of the stiffness matrix in 3 parameter transient case with that of
>> 7 parameter steady case.
>>
>
> Sounds like you need to do some debugging... e.g. set parameters to have
> min=max and see if it's still abnormal, or view the "truth solve" solution
> or other things like that to try to identify where the problem is.
>
> David
>
>
>
>
>> 2018-02-27 21:21 GMT+08:00 David Knezevic <dav...@ak...>:
>>
>>> On Tue, Feb 27, 2018 at 4:03 AM, 吴家桦Gauvain <cau...@gm...>
>>> wrote:
>>>
>>>> Hi all,
>>>>
>>>> I am trying to make a transient thermoelastic RB model. Both Internal
>>>> heat
>>>> flux and external heat exchange described by Newton's law of
>>>> cooling(Robin
>>>> boundary condition) are considered. It works well when the three thermal
>>>> conditions (heat flux, heat transfer coefficient and ambient
>>>> temperature)
>>>> are chosen as parameters. However, abnormal results are observed when
>>>> the
>>>> material properties (Young's modulus, Poisson's ratio, thermal expansion
>>>> coefficient and heat conductivity) are added as parameters: Three
>>>> displacement components remain 0 and the temperature increases
>>>> drastically
>>>> as the time goes by. What's more, I notice that the difference between
>>>> the
>>>> first and the second POD eigenvalues is extremely large:
>>>>
>>>> POD Eigenvalues:
>>>> eigenvalue 0 = 4.4536e+08
>>>> eigenvalue 1 = 2.45303e-07
>>>> ...
>>>> last eigenvalue = -1.90536e-07
>>>>
>>>> The matrix assembly should not pose problem because it runs well in
>>>> steady
>>>> case and I simply copy the assembly functions without any modification.
>>>> Thus I am really confused and I cannot figure out where the problem is.
>>>> Could you give me some suggestions? Thanks a lot.
>>>>
>>>
>>> Good to hear that it works well in the steady case.
>>>
>>> Regarding the transient case, I have a few comments:
>>>
>>> - The default implementation for transient RB that is used in the
>>> examples is intended for parabolic PDEs, like the heat equation. I guess
>>> your PDE is parabolic since you omit the hyperbolic parts (i.e. the inertia
>>> terms) from the elasticity part of the system?
>>>
>>> - 7 parameters is quite a lot of parameters, so you may just be having
>>> trouble with greedy convergence?
>>>
>>> My main suggestion would be to try to get a simple transient problem
>>> working first, then add more complexity to it until you reach the problem
>>> that you're interested in, e.g. you could start with the heat equation and
>>> then add elasticity terms.
>>>
>>> Regards,
>>> David
>>>
>>>
>>>
>>
>>
>> --
>>
>
>


-- 
*吴家桦 Gauvain*
*Mobile:13316300622*
*Email:g <gau...@fo...>auv...@gm...
<auv...@gm...>*
中山大学中法核工程与技术学院学生
Institut Franco-Chinois de l'Energie
Nucléaire, L'université Sun Yat-sen