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

[吴家桦Gauvain <cau...@gm...>]

I solve with truth_solve and find the result is also bizarre, which is the
same as the previous ones. I may have to check the matrix assembly. Thank
you so much for your help.

Gauvain

2018-02-28 0:44 GMT+08:00 David Knezevic <dav...@ak...>:

> On Tue, Feb 27, 2018 at 9:48 AM, 吴家桦Gauvain <cau...@gm...>
> wrote:
>
>> Still a long way to go... Would you please tell me how to view the "truth
>> solve" solution?
>>
>
> RBConstruction::truth_solve take an int argument. If that's negative then
> it doesn't plot. If it's positive then it plots the "truth solution" in the
> steady-state case. In the transient case, if you set the int to be 10, for
> example, then it will plot every 10th time step.
>
> I suggest you do some solves with truth_solve directly and look at the
> solution since that will allow you to set up specific parameters and do a
> solve and check that it looks right. Note that train_reduced_basis also
> calls truth_solve and it has the int argument set to -1 so that it doesn't
> plot anything.
>
> David
>
> P.S. As usual, make sure you're using a direct solver (e.g. MUMPS) during
> debugging to eliminate incomplete solver convergence as one possible source
> of problems.
>
>
> 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 <(331)%20630-0622>*
>> *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
>>
>
>


-- 
*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