Hello Haydar!

The following suggestions may be valuable for you about your problem:

Advice 1. Problem may be related to initial values. I advise you to do what Dimitrios K. Fytanidis told you;

Advice 2. Problem may be related to discretization scheme. If the problem is not solved using advice in 1, you should change the discretization scheme to low-order discretization scheme. For example, the spatial discretization is first-order-upwind, the transient formulation is first order implicit; The first order scheme is the most steady scheme;

Advice 3. Problem may be related to mesh. The mesh you used may be too rough.  The ideal mesh is hexahedron (3D) or quadrangle (2D). If your mesh includes too much unstructured grids, even includes high skew cells, it is easy to diverge during calculation. Therefore, if the plobelm is not solved by advice 1 and advice 2, i think you should improve your mesh;

Advice 4. Problem may be related to source item in momentum equation. if the above suggestion still not resolve your problem, I advise you unload all source items firstly, then calculate some iterations, then load your UDF again;

Advice 5. Problem may be related to the formulation of source item. if using above advices, the problem still be not resolved, I advice you to check your formulation of source item, whether there is wrong format or unreasonable formulation. You can change the source items into other any simple format, to check whether the divergence is related to formulation of source item; After that, if the calculation succeed, then the problem result from the wrong or unreasonable source item.

At last, by the above steps, I think your question may be solved.

My e-mail  is [email protected]

Wish you good luck! 

Hello Haydar!

Could you please try the following:

1.unload the UDF and Run 1-2 iterations using a constant Temperature (without the UDF profile)

2. stop the simulation

3. load the UDF

4. restart the simulation without initialization

This way we can see whether the problem is related to the initial Temperature values or not.

Please, let me know if the problem is still there.

Kind regards,

Dimitrios

Hello Haydar!

The following suggestions may be valuable for you about your problem:

Advice 1. Problem may be related to initial values. I advise you to do what Dimitrios K. Fytanidis told you;

Advice 2. Problem may be related to discretization scheme. If the problem is not solved using advice in 1, you should change the discretization scheme to low-order discretization scheme. For example, the spatial discretization is first-order-upwind, the transient formulation is first order implicit; The first order scheme is the most steady scheme;

Advice 3. Problem may be related to mesh. The mesh you used may be too rough.  The ideal mesh is hexahedron (3D) or quadrangle (2D). If your mesh includes too much unstructured grids, even includes high skew cells, it is easy to diverge during calculation. Therefore, if the plobelm is not solved by advice 1 and advice 2, i think you should improve your mesh;

Advice 4. Problem may be related to source item in momentum equation. if the above suggestion still not resolve your problem, I advise you unload all source items firstly, then calculate some iterations, then load your UDF again;

Advice 5. Problem may be related to the formulation of source item. if using above advices, the problem still be not resolved, I advice you to check your formulation of source item, whether there is wrong format or unreasonable formulation. You can change the source items into other any simple format, to check whether the divergence is related to formulation of source item; After that, if the calculation succeed, then the problem result from the wrong or unreasonable source item.

At last, by the above steps, I think your question may be solved.

My e-mail  is [email protected]

Wish you good luck! 

Hello Dimitrios and Maoming

Thanks to you guys.

The problem was mesh and initial values. I improved the mesh, and checked the initial temperature values because I use a temperature profile varying from 300 K upto 450 K.

I made a mistake when entering the surface body (wall) temperature which should be 0.

Kind regards

Haydar

Hi Maoming,

Could you helps for this please,

I got identical problem as below after 3370 iterations in my 3D bluff body cantilevered using UDF

# Divergence detected in AMG solver: x-momentum -> Increasing relaxation sweeps!

# You may try the enhanced divergence recovery with (rpsetvar 'amg/protective-enhanced? #t)

reversed flow in 7250 faces on outflow 6.

Divergence detected in AMG solver: x-momentum

Divergence detected in AMG solver: y-momentum

Divergence detected in AMG solver: z-momentum

Divergence detected in AMG solver: pressure correction

Divergence detected in AMG solver: pressure correction

Error at Node 0: floating point exception

Error at Node 1: floating point exception

I just modify length bluff body from all case including UDF which original case it is running well. In addition, the case without UDF is run well.

If you do not mind I sent you original UDF and my modified UDF. I am totally a new comer in UDF

Thanks a lot in advance

regards

Barata