Hi Rupak,
The flexible mesh, as the name implies, allows you to have mesh elements of different shapes and sizes. It allows you to use triangular elements, quadrangular elements or both at the same time.
The "standard" mesh only allows for square mesh elements.
The triangular mesh is more appropriate if you expect a two-dimensional flow behavior (such as in flood plains), while the standard and quadrangular meshes are better suited for one-dimensional flow behavior (such as in a river with a well defined flow direction).
Using a flexible mesh allows you to get the best of both worlds by using both triangular and quadrangular mesh simultaneously. On the downside, it is more computationally expensive than a square mesh.
What I said above is more related to MIKE FLOOD applications. If you are thinking about using MIKE 3, I assume it is because you expect a flow with a three-dimensional behavior. In that case, consider whether whether the flood on the horizontal plan is 2D or 1D and the same principles apply.
Best regards,
Ricardo Machado
