## General Mechanical

#### Solution not convergin

• mekafime
Subscriber

Hi, I try to modelate this kind of connection , but I have a critical error:

The solver engine was unable to converge on a solution for the nonlinear problem as constrained.  Please see the Troubleshooting section of the Help System for more information.

How I can to know which is the error?

Thanks

• peteroznewman
Subscriber

Look at your Newton-Raphson Force Residual plots to see where the solver is having trouble converging. Make smaller/better shaped elements near the area of maximum N-R Force Residual.

Regards,

Peter

• Sandeep Medikonda
Ansys Employee

Yes, also please see these suggestions from the help section:

When Advanced Contact is NOT Present in the Model ...

Check for sufficient supports to prevent rigid body motion (structural) or check for thermal material curves or convection curves which rise and/or fall sharply over the temperature range (thermal).

If you encounter a convergence error during a thermal analysis that is using contact, consider modifying the Thermal Conductance property.

When Advanced Contact IS Present in the Model ...

Check for sufficient supports to prevent rigid body motion or that contact with other parts will prevent rigid motion.

Check that the loading is of a reasonable nature. Unlike linear problems whose results will scale linearly with the loading, advanced contact is nonlinear and convergence problems may arise if the loading is too big or small in a real world setting.

If the contact type is frictionless, try setting the type to rough. This may help some problems to converge if any possible sliding is not constrained.

Check that the mesh is sufficiently fine on faces that may be in contact. Too coarse a mesh may cause inaccurate answers and convergence difficulties.

Consider softening the normal contact stiffness KN to a value of .1. The default value is 1 and may be changed by setting the Normal Stiffness. Smaller KN multipliers will allow more contact penetration which may cause inaccuracies but may allow problems to converge that would not otherwise.

If symmetric contact is being used (by default the contact is symmetric), consider using asymmetric contact pairs. This may help problems that experience oscillating convergence patterns due to contact chattering. The program can be directed to automatically use asymmetric contact in the Details view of the Contact Folder.

Regards,

Sandeep

Best Practices to post on the Student Community

• mekafime
Subscriber

Hi,

I used Newton-Raphson Residual Force and in the 3 cases, el error is in the diagonal of the connection, but has not another element around.

• Sandeep Medikonda
Ansys Employee

Can you explain, what kind of analysis you are performing and provide details/snapshots of any contacts, analysis settings etc?

Regards,

Sandeep

• mekafime
Subscriber

Attached

• Sandeep Medikonda
Ansys Employee

I am unable to look at the file, maybe someone else on the community can take a look at it.

Regards,

Sandeep

• mekafime
Subscriber

Hi

Analysis no lineal of a connection K-gap rhs and chs.

Contacts between diagonals and chord is fricctionless and weld with diagonals and chord is bonded.

Axials forces in each diagonal tension and compression.

• Sandeep Medikonda
Ansys Employee

I vaguely remember seeing this model before. Did Peter help you with this before?

Coming to your model, can you show the details/snapshots of the contact and the material you are using? Also, what mesh do you have? Can you try a run dropping the mid-size nodes?

Regards,

Sandeep

• mekafime
Subscriber

Hi,

No, this is new.

Frictionless between diagonal and chord.

Weld between diagonal, bonded.

Weld between chord, bonded.

Mesh

About: "Can you try a run dropping the mid-size nodes?"  How can I do that?

• Sandeep Medikonda
Ansys Employee

Just change Element Order under Details of "Mesh" to Linear and run a case?

Also, I was referring to the Details of the Contacts?

• mekafime
Subscriber

Hi

I have the same error, I already changed to linear.

this details?

• mekafime
Subscriber

Hi,

I tried run the analysis using Element order; inear , but .. I have this: "Lower order pyramid elements are present in the analysis.  Having a large number of pyramids may cause the model to become too stiff.  Check results carefully."

• Sandeep Medikonda
Ansys Employee

But why are you changing the element type/mesh? Just change from quadratic to linear hex.

Can you try adding some stabilization and try as well?

Also, what materials are you working with?

Regards,

Sandeep

• mekafime
Subscriber