Wave response of closed flexible bags

Abstract

Recent environmental considerations, as salmon lice, escape of farmed fish and release of nutrients, have prompted the aquaculture industry to consider the use of closed fish production systems (CFPS). The use of such systems is considered as one potential way of expanding the salmon production in Norway. To better understand the response in waves of such bags, experiments were conducted with a series of 1:30 scaled models of closed flexible bags. The bags and floater were moored in a wave tank and subjected to series of regular waves (wave period between 0.5 and 1.5 s and wave steepness 1/15, 1/30, and 1/60). Three different geometries were investigated; cylindrical, spherical, and elliptical, and the models were both tested deflated (70% filling level) and inflated (100% filling level). Incident waves were measured together with the horizontal and vertical motion of the floater in two points (front and aft). Visual observations of the response were also done using cameras. The main finding from the experiments were that a deflated bag was more wave compliant than an inflated bag, and that the integrity (whether water entered or left the bag over the floater) was challenged for the inflated bags even for smaller waves (identified as wave condition B (1.0 m < H < 1.9 m) in Norwegian Standard NS 9415). A deflated bag is significantly more seaworthy than an inflated bag when it comes to integrity and motion of the floater.