The Stand For Fin Drives Energy Testing

The development of recreational diving and the new biomimetic vehicles for civilian and military purposes indicates that fins drives’ effectiveness should be a standard research procedure. The different sizes, construction and technical solutions of fin thrusters are the reason that no standard has been introduced for evaluating their efficiency. The paper presents an episode of the research carried out as part of a project financed by The National Centre for Research and Development in Poland concerning fin drives development. The first chapter presents a literature analysis of currently used research methods. A different approach to assessing efficiency was indicated, ranging from the study of the diver’s respiratory efficiency to the manipulator measurement methods. The hydrodynamic parameters, which analyzed the propellers, including fins, and the fish swimming motility characteristics, were indicated. The next chapter presents the water tunnel for basic research with measuring equipment and the range of applications. The methodology for assessing the hydrodynamic and energy efficiency of fin’s drives is presented in the third chapter. The fins’ kinematics and dynamics analysis indicated an initial set of geometric, kinematic, and dynamic parameters for energy and functional assessment purposes. The scope of available tests covered issues complex to quantify unambiguously; hence the obtained results were initial. The form made this assessment of successive pool tests, the aim of which was to analyze the kinematics of the fin’s operation. The trials of a representative fins thruster and the comments indicate the test stand’s practical use for testing various propellers.

First report of fish trace fossils (Undichna) from the Middle Devonian Achanarras Limestone, Caithness Flagstone Group

Two newly-discovered specimens of the fish locomotion trace Undichna (U. britannica and Undichna isp.), are described from the Middle Devonian Achanarras Limestone Member (Caithness Flagstone Group, NE Scotland). Fish trace fossils have not previously been reported from the Achanarras Limestone Member, despite decades of study of the unit as a key locality for fish body fossils. The traces comprise discontinuous sinusoidal grooves; one showing multiple parallel incisions, created by the fins of an acanthodian fish swimming close to the substrate. The apparent absence of trace fossils attributable to infaunal or epifaunal benthic organisms suggests that the sediment at the bottom of the lake was relatively inhospitable. The low ichnodiversity of the Achanarras Limestone Member is likely due to low oxygen levels in the depositional environment.Thematic collection: This article is part of the Early Career Research collection available at: https://www.lyellcollection.org/cc/SJG-early-career-research

Flow Field Inside and Around a Square Fish Cage Considering Fish School Swimming Pattern

The interaction between fluid and fish cage with stocked fish is extremely complex, including fluid and structure, as well as fluid and fish swimming behavior. The on-current swimming pattern of fish schools was found toward the incoming flow in the previous laboratory studies, which is different from the circular swimming pattern commonly observed in the farming site. In this study, a pseudo fish school structure model (PFS) was proposed to reproduce the five circular swimming patterns of farmed yellowtail, and to investigate the influence of fish school behaviors on the flow field inside and around a model square fish cage in laboratory experiments. The results showed that the drag force acting on the square fish cage increased with the increase of the current speed for all fish school swimming patterns, but no clear difference was observed between the fish school swimming behavior patterns. Overall, the drag force of the square fish cage considering the farmed fish behavior decreased by 11.8%, compared to the drag force of the fish cage without PFS. The current speeds inside and downstream of the fish cage increased almost linearly with increasing current velocities. Compared with the case of the fish cage without PFS, the current speed inside the cage under motionless closely PFS (C0), revolving closely PFS (CR), motionless loosely PFS (L0) and revolving loosely PFS (LR) conditions changed by 10.8%, 9.4%, 65.8% and 39.7%, respectively. In addition, compared to the case of the fish cage without PFS, the current speeds under C0, CR, L0 and LR conditions decreased by 89.8%, 16.3%, 58.2%, and 31.9%, respectively, at 16.0cm downstream from the fish cage, and decreased by 69.2%, 19.4%, 62.7% and 26.3%, respectively, at 63.6cm downstream from the fish cage. Furthermore, the current speed distribution and relative horizontal turbulence intensity distribution inside and around the fish cage under different fish school swimming pattern was discussed. In the future, we will use live fish to conduct experiments to evaluate fish school models.