the generation principle of adaptive mesh is to map a simpler region on a parameter plane onto the calculation domain on physical plane through coordinate transformation
so that it is a one -to -one mapping between the boundaries of rectangular and calculation domain and between the inner parts of the domain
thus the finite difference method can be applied directly on the parameter plane and need not consider the shape of physical boundary
even if the boundary of calculation boundary is unsteady
the use of such a coordinate system makes the calculation still run on a fixed equidistant uniformly rectangular grid system yet its boundary is coincident with that of physical domain all the time
so it greatly simplifies the calculation and the values on boundary can be used directly to grid points without any interpolation
so that the boundary conditions can be expressed exactly and the boundary errors caused by regular mesh can be overcome efficiently