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second derivation of temperature

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Old   June 12, 2014, 23:11
Default second derivation of temperature
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Hi,everyone!
I want to define a source term including the second derivation of temperature. I use the macros DEFINE_SOURCE and DEFINF_ADJUST. Here is the code:
DEFINE_ADJUST(my_adjust,d)
{
Thread *t;
cell_t c;
if (! Data_Valid_P())
return;

thread_loop_c(t,d)
{
begin_c_loop(c,t)
{
C_UDSI(c,t,1)=C_T_G(c,t)[0];
C_UDSI(c,t,2)=C_T_G(c,t)[1];
C_UDSI(c,t,3)=C_T_G(c,t)[2];
}
end_c_loop(c,t)
}
}

DEFINE_SOURCE(uds_source, c, t, dS, eqn)
{
real source;
source=-0.000143472*(C_UDSI_G(c,t,1)[0]+C_UDSI_G(c,t,2)[1]+C_UDSI_G(c,t,3)[2]);
dS[eqn]=0;
return source;
}
I use an interpreted udf. I've tried solve/set/expert temporary solver memory [yes], and iterated some steps before hooking DEFINE_ADJUST. After I hook DEFINE_ADJUST, it can calculate without any problems. But once I include the source term, I meet the error access_violation.
Can you help me with some advice on my problem. I am looking forward to your reply. Thank you in advance.
sunjian
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Old   June 13, 2014, 03:43
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Do you get the same error if you replace the line
Code:
source=-0.000143472*(C_UDSI_G(c,t,1)[0]+C_UDSI_G(c,t,2)[1]+C_UDSI_G(c,t,3)[2]);
by the following line?
Code:
source=-0.000143472*(C_UDSI(c,t,1)[0]+C_UDSI(c,t,2)[1]+C_UDSI(c,t,3)[2]);
If you get the same problems without the gradient, the problem is that the UDS is not defined; if you do not get the same problems, the problem is related to the gradient.
Having this information might bring you one small step closer to the solution...
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Old   June 13, 2014, 08:27
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Hi, pakk. Thank you for your reply. I replace the line
CODE: source=-0.000143472*(C_UDSI_G(c,t,1)[0]+C_UDSI_G(c,t,2)[1]+C_UDSI_G(c,t,3)[2]);
with the following line
CODE: source=-0.000143472*(C_UDSI(c,t,1)+C_UDSI(c,t,2)+C_UDSI(c, t,3));

Then I get the same error. You said maybe the uds is not defined. But what can I do to solve this problem? Is there something wrong in DEFINE_ADJUST?
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Old   June 13, 2014, 09:52
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Try to plot the UDS. Is it zero on some parts of your domain? Then something is wrong in the adjust-part, maybe it did not hook to all cell zones.
Otherwise, I would have to think really hard.
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Old   June 15, 2014, 05:23
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Hi, pakk. It's very nice of you to reply. Thank you again.
I tried to iterated with hooking the adjust-part and without including UDS transport equation 0 (I need to obtain User Scalar 0 in this equation) because as long as I include UDS transport equation 0, I will get the error access_violation. And I found that User Scalar 1, User Scalar 2 and User Scalar 3 were mostly not zero, though in some parts they might be zero (most of the values were near zero). On this occasion, is something wrong in the adjust-part?
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Old   June 18, 2014, 02:50
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Hi,pakk.
I read a UDF showgrad.c in section Gradient(G) and Reconstruction Gradient(RG) Vector Macros in UDF Manual. I include the code below in my code.
CODE:
DEFINE_ON_DEMAND(showgrad)
{
Domain *domain;
Thread *t;
domain=Get_Domain(1);
if (! Data_Valid_P())
return;
Message0(" >>> entering show-grad: \n ");
thread_loop_c(t, domain)
{
Message0("::::\n ");
Message0(":::: Gradients :::: \n ");
Message0("::::\n ");
if (NNULLP(THREAD_STORAGE(t, SV_T_G)))
{
Message0("Gradient of T is available \n ");
}
if (NNULLP(T_STORAGE_R_NV(t,SV_UDSI_G(1))))
{
Message0("Gradient of UDSI(1) is available \n ");
}
if (NNULLP(T_STORAGE_R_NV(t,SV_UDSI_G(2))))
{
Message0("Gradient of UDSI(2) is available \n ");
}
if (NNULLP(T_STORAGE_R_NV(t,SV_UDSI_G(3))))
{
Message0("Gradient of UDSI(3) is available \n ");
}
}
}
After the calculation with attaching the adjust-part and without attaching UDS transport equation 0, showgrad is executed and shows gradient of T, UDSI(1), UDSI(2) and UDSI(3) are available. So I think maybe the error happens in the source in UDS transport equation 0. Am I right?
The source term is Laplacian of temperature as follows:
source=a*(d2T/dX2+d2T/dY2+d2T/dZ2)
My code is:
DEFINE_SOURCE(uds_source, c, t, dS, eqn)
{
real source;
source=-0.000143472*(C_UDSI_G(c,t,1)[0]+C_UDSI_G(c,t,2)[1]+C_UDSI_G(c,t,3)[2]);
dS[eqn]=0;
return source;
}
But I can't find any problem here. Can you give some suggestions?
I'm looking forward to you reply. Thank you.
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Old   June 18, 2014, 03:16
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Simplify your uds_source until it works. In that way you might identify in which step the problem occurs.

Some suggestions:

Code:
DEFINE_SOURCE(uds_source, c, t, dS, eqn)
{
real source;
source=-0.000143472*(C_UDSI_G(c,t,1)[0]);
dS[eqn]=0;
return source;
}
Code:
DEFINE_SOURCE(uds_source, c, t, dS, eqn)
{
real source;
source=-0.000143472*(C_UDSI(c,t,1)[0]);
dS[eqn]=0;
return source;
}
Code:
DEFINE_SOURCE(uds_source, c, t, dS, eqn)
{
real source;
source=-0.000143472;
dS[eqn]=0;
return source;
}
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Old   June 19, 2014, 04:06
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Hi, pakk. Thank you for your help!
I've found where the error happens. In my UDF, I also define a UDS flux for UDS transport equation 0. I want to obtain the flux that equals the negative product of density and velocity. I use the code below firstly:
DEFINE_UDS_FLUX(A_flux, f, t, i)
{
real NV_VEC(vec), NV_VEC(A),dens,flux;
F_AREA(A, f, t);
dens=F_R(f,t);
NV_DS(vec,=,F_U(f,t),F_V(f,t),F_W(f,t),*,dens);
flux=NV_DOT(vec,A);
return - flux;
}
The error access_violation always occurs. Then I try the code below:
DEFINE_UDS_FLUX(A_flux, f, t, i)
{
return - F_FLUX(f,t);
}
It can iterate now. Both of the codes can be compiled without any error. Do you know what the mistake is in the first code?
Best regards.
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Old   June 19, 2014, 05:04
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You should look at the example in the manual for DEFINE_UDS_FLUX. It has a comment about the density not being available for all BCs, and how to solve it. I don't know if this is causing the problem, but you could try it.
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Old   June 23, 2014, 05:32
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Hi, pakk. I have another question about the outlet boundary condition. I simulate the heat transfer in duct. For the inlet, I set the velocity-inlet condition and the user scalar 0 is set constant value 0. Here's no question. But for the fully-developed flow, I set the outflow condition and the BC should be (A*\nabla T)inlet = (A*\nabla T)outlet, where A is user scalar 0. For BC like this, how can I define it? I couldn't find a similar example in UDF manual. Could you help me with some clue? Thank you very much.
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Old   June 23, 2014, 05:55
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Quote:
Originally Posted by sunjian View Post
Hi, pakk. I have another question about the outlet boundary condition. I simulate the heat transfer in duct. For the inlet, I set the velocity-inlet condition and the user scalar 0 is set constant value 0. Here's no question. But for the fully-developed flow, I set the outflow condition and the BC should be (A*\nabla T)inlet = (A*\nabla T)outlet, where A is user scalar 0. For BC like this, how can I define it? I couldn't find a similar example in UDF manual. Could you help me with some clue? Thank you very much.
If A at the inlet is set at the constant value 0, then (A*\nabla T)inlet=0, isn't it?
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Old   June 23, 2014, 10:25
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Yes, you are right. So I just need to define (A*\nabla T)outlet = 0. Is it right? I'll have a try and see what I will get. Thank you very much.
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Old   July 18, 2014, 08:53
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Hi everyone!!
I have a similar problem. I'm trying to calculate the laplacian of temperature field in order to introduce it into the source terme of energy equation. Here there is a simplification of my C code.

DEFINE_ADJUST(adjust_gradient, domain)
{
Thread *t;
cell_t c;

if (! Data_Valid_P())
return;

thread_loop_c (t,domain)
{
begin_c_loop (c,t)
{
C_UDSI(c,t,0)=C_T_RG(c,t)[0];
C_UDSI(c,t,1)=C_T_RG(c,t)[1];
C_UDSI(c,t,2)=C_T_RG(c,t)[2];
}
end_c_loop (c,t)
}

}

DEFINE_SOURCE(energy_source,c,t,ds,eqn)
{

real source;

source=20*C_UDSI(c,t,0);

C_UDMI(c,t,0)=C_UDSI(c,t,0);
C_UDMI(c,t,1)=source;
C_UDMI(c,t,2)=C_UDSI_G(c,t,0)[0]; /*some calculus for testing the data*/
C_UDMI(c,t,3)=1/C_UDSI_G(c,t,0)[0];
C_UDMI(c,t,4)=100*C_UDSI_G(c,t,0)[0];

ds[eqn]=0;
return source;

}

The operations I make are:
  • Add User Scalars and memory
  • Inactivate UDS equations
  • Tape solver/set/expert---> yes for "keep temporary solver memory ...."
  • Launch the computation

SO I have 2 principal problems:
  1. Sometimes, I receive a "segmentation fault" error message: this is due to the lines
    C_UDSI(c,t,0)=C_T_G(c,t)[0];
    C_UDSI(c,t,1)=C_T_G(c,t)[1];
    C_UDSI(c,t,2)=C_T_G(c,t)[2];

    If I use C_T(c,t), there's no more problems...whyyy??;
  2. In this case, if I plot "Reconstruction dT/dx", Scalar 0 and Memory 0, they should coincide but there some little differences.

Is there someone who can help me, pleeease???

Thank you guys!!!
Stefano
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