**3.2.1 Time series of cable tensions**

As a typical case, Fig. 9 shows the time series of the cable tensions in the wave conditions *Hs*=4.0cm, *Tp*=1.1s and *d*=30cm within the time 160s. In the figure, *C*11 represents the front cable at the onshore side, *C*12 the back cable at the onshore side, *C*21 the front cable at the offshore side and *C*22 the back cable at the offshore side. It can be seen that the time series of tensions of the cables *C*11 and *C*12 at the onshore side are very similar, as well similar are those of the cables *C*21 and *C*22 at the offshore side. It shows that under the normal incident irregular wave actions the tunnel element does only two-dimensional motions. This can also be observed in the experiment from the movement of the tunnel element.
