Hydrodynamical effect of parallelly swimming fish using computational fluid dynamics method

Abstract

Fish form schools because of many possible reasons. However, the hydrodynamic mechanism whereby the energy efficiency of fish schools is improved still remains unclear. There are limited examples of fish models based on actual swimming movements using simulation, and the movements in existing models are simple. Therefore, in this study, we analyzed the swimming behavior of Biwa salmon (Oncorhynchus sp., a salmonid fish) using image analyses and formulated its swimming motion. Moreover, computational fluid dynamics analysis was carried out using the formulated swimming motion to determine the fluid force acting on the fish body model with real fish swimming motion. The swimming efficiency of the fish model under parallel swimming was obtained from the calculated surrounding fluid force and compared for different neighboring distances. The flow field around the fish model was also examined. The swimming efficiency of two fish models swimming parallelly was improved by approximately 10% when they were separated by a distance of 0.4L, where L is the total length of the model. In addition, the flow field behind the fish body was examined under both inphase and antiphase conditions and at inter-individual distances of 0.8L and 1.2L. The apparent flow speed in the distance range of 0.5–2.0L from the midpoint of the snouts of the two individuals was lower than the swimming speed. The pressure distribution on the fish model showed an elevated pressure at the caudal fin. Interestingly, we obtained an isopleth map similar to that of a caudal peduncle. To avoid a negative thrust, the aft part of the body must be thin, as shown in the isopleth map obtained in this study.

Designs, motion mechanism, motion coordination, and communication of bionic robot fishes: a survey

“…The results show that, in the absence of any control by the two fish, the vortex generated by the leading fish deflected the path of the following fish. Khalid et al found that the undulating frequency of the following fish does not affect the vortex and time-averaged drag of the leading fish at a certain Strouhal number [48] . Furthermore, it appeared to be more favorable for the leading fish when both fish kept swimming in tandem formation.…”

“…• There is a lack of sufficient research on motion coordination and communication of multiple robot fishes. Multiple robot fishes in an appropriate formation have been shown to reduce energy consumption [47][48][49][50][51][52][53] . In nature, the number of fish in a school is usually greater than three, and the school is in a three-dimensional formation.…”

“…The most basic form of this is two fish swimming in parallel formation. The efficiency of two fish when swimming in parallel was analyzed by Doi et al [49].…”