FIRST- AND SECOND-ORDER WAVE-INDUCED DYNAMIC RESPONSE OF SUBMERGED FLOATING TUNNELS

Submerged floating tunnel concepts have been developed for the purpose of crossing wide straits with a span length of many kilometers. The frequencies of the first dynamic modes of these structures may typically be of the order of one minute or more. This implies that amplified dynamic response effects need to be assessed both for the wave-frequency and the low frequency regimes. The first order (i.e. wave frequency) dynamic response has been found to depend strongly on wave direction and wave spreading. This is also be expected to apply for the second-order response. Furthermore, the small inherent damping levels for the low-frequency response will imply that high dynamic amplification may occur. These issues are addressed by the present paper. Computational methods for evaluation of the hydrodynamic loading and the associated dynamic response are addressed. Both simplified assessment as well as more refined calculation procedures are considered. A specific case study is considered for the purpose of illustrating the relative effects of the various response components. The example structure is a tunnel with a double cross-section which was developed for crossing of the Sognefjord located at the West Coast of Norway. The same type of floating tunnel is also relevant for crossing of other fjord spans.