If we have catenary of iron chain or seaflex for anchoring the pontoon.
How can we estimate their horizontal stiffness ?

Depending on the mooring you will find some rough estimates of the horizontal stiffness, in the literature. Then you run the program with lower (1/2, 1/4) and higher values (2, 4) times, to see the behavior of the structure.

Which is the range of wave period where the program works properly?

The frequency response, with the wave coherence method, depends very much on the combination of alpha and beta values. The solution some times is unstable in obtaining the matrix aij by eigenvalue solution (see page 37 of the manual, or pg 62 of dr. thesis).

There is an old nice reference of about 40 pages written from Wilson with title “elastic characteristics of moorings”. You can find it in the first volume of the book by Charles Bretschneider Topics in Ocean Engineering, published in 1969 by Gulf Publishing Company, Houston Texas. In this reference there are many tables and graphs to help you pick the characteristics of mooring.

Revised: desember 10, 2015.