Abstract
At present, the technology of measuring the net volume of a net cage in the real sea is still rare and limited. This study proposes an alternative way of accessing the remaining volume of an aquaculture net cage in both model and full scales. This new approach is called the alternative reduction coefficient (ARC), which is the ratio of the deformed height between a floating collar and a tube sinker to its original height. Its counterpart is the volume reduction coefficient (VRC), which is the ratio of deformed volume to undeformed volume. In the comparison against the existing experimental studies in the model scale, the maximum error of the current-only case is about 11.6%, and that of the wave-current case is about 23%. For the full-scale fish cage subjected to regular waves and current, the simulated results show that the maximum gap of the remaining volume between ARC and VRC is about 13.6% and 15.3% for current-only and wave-current conditions respectively. The results also show that the greater the wave steepness, the larger the error. Finally, in the simulation of the full-scale net cage subjected to irregular waves and current, the results show that the probabilities of the two methods are both a normal distribution and they are very similar, and the Pearson correlation coefficient of the two methods is about 0.937, the bias of the minimum value is only about 0.73%, that of the maximum value is about 7.18%, and that of the standard deviation is about 5.43%. Therefore, we concluded that ARC is an acceptable method of evaluating the remaining volume of fish cages in the real sea.
