Plastic strain of steel cylinder

hello

i have modeled a steel cylinder subjected to underwater explosion according to an article model by ABAQUS.

but there is a differece between displacement curve of my model and the article model.

you can see displacement curve of article model is oscillating around 0.8 mm and -0.8 mm but the same curve in my model is oscillating around 0.0 axes.  (Images are attached to this post)

i think its reason is plastic deflection of article model (0.8 mm) .

i should mention that i defined plastic properties of material too.

what is the reason of this difference?

any help is appreciated