Help with Error: Input elems are in mixed order

Do you have first order or second order (mid nodes) elements in your model?

Second order

I was able to get past the problem, however the mesh quality is poor. Because of the complexity of the geometry, I am getting some small elements next to much larger ones..for instance in places where two of the fractures intersect.

Is there a way to control the relative size of neighboring elements?  I would like to achieve a better quality of the 2D mesh of the fractures.

What is the parameter in HM that allows me to control this aspect of the mesh?

Based on defined element size Hm will generate mesh.What element quality checks you are applying in your model?

I was having some problems with numerical stability because the elements become very skewed in the complex parts of the model. I would like to have the mesh generated such that the elements are not very skewed. I am not sure exactly how to control this with HM.

The attached picture shows the complex fracture geometry that I am trying to mesh. I would like to minimize the amount of distortion of the mesh elements. Is there an approach that you can suggest to achieve this?  For instance, an element should not be more that 2 times larger than any neighbouring element

<?xml version="1.0" encoding="UTF-8"?>

Would the right approach be to set the min elem size and max deviation values?

Should I use first order elements?

Try with first order elements.one cannot connect first order element directly with second order element.

Should I use first order elements?

That depend to your solver, to your objective.

For example, with FE solver, 1st order TET elements are not good (too stiff) for Static analysis. 2nd order TET elements are better.

However, with Explicite solver (like LS-Dyna, MSC/Dytran,...) you can not use high-order elements.