From the graph, it is found that the frequency is independent of the structural damping, which was observed from the top of each line at the same frequency.
From the graph, it was found that the frequency value does not depend on the Structural damping, which have from the amount of each line are at the same frequency positions.
The graph will be found that the value of the frequency, it would be up to Structural damping which observation. From the top of the line, but it is the location of the frequency.