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The first method is usually deemed to give more precise results than the second. It is the default method in AVL, xflr5 and flow5.
This error message occurs in triangular linear analyses, if one of the triangular panels has an invalid geometry, i.e. has a null area. This occurs when the three vertices are aligned within the working precision, or when at least two of the vertices are coincident, again within the working precision.
The goal is to have the automatic mesher detect and discard these triangles, but some may still remain if generated by early versions of the application, or due to the manual translation of nodes to remove free edges.
Remesh the fuselage, if necessary with a slightly different mesh size.
Set a size for the fuselage mesh elements close to the size of the wing elements.
Clean the fuselage geometry by removing all the small faces before meshing it.
This error occurs in triangular uniform analysis, if a triangle is not connected to any neighbour triangle.
In such a case, the algorithm cannot calculate a local doublet gradient and outputs the error message. As a consequence, the local pressure coefficients are invalid. However, this will most likely make little difference to the overall lift, drag, and moments.
Results will be generated despite the error message.
Remove the free edges.