Hi, everyone hope you are well.
Recently, I am studying on my thesis. It is under corrosion model. But for this I need to know derivation or mathematical calculation for
Shape function for ellipsoidal pits

I just found this function from this book.

Advances in Marine Structures edited by Carlos Guedes Soares, Wolfgang Fricke (google book 152 page)

But I need to know how this function came from? In this book it said about this function but did not said how it came from? (Any derivation or mathematical calculation)

What is the meaning of W0 , (X-X0) and other symbol? Is there any derivation or mathematical calculation on this function. I search whole internet but find nothing. If anyone can help me ..