Numerical simulation of a self-propelled fish-like swimmer with rigid and flexible caudal fins

Aim: In this paper, numerical simulations were conducted to investigate the swimming performances, hydrodynamics performances and wake structures of a self-propelled swimmer with rigid and flexible caudal fins.Methodology: The kinematics model of the swimmer was constructed using thunniform swimming. Using computational fluid dynamics (CFD) method, the systematic study of swimmer with rigid and flexible caudal fins was carried out. Results: The results showed that the caudal fin flexibility is beneficial to the fast-start of fish but not conducive to the fast cruising of fish. The fish with rigid caudal fin has larger cruising velocity inquasi-steady swimming and smaller forward acceleration in fast-start stage. In addition, the caudal fin flexibility is also beneficial to the heading stability of fish’s self-propelled swimming. The pressure distribution on the fish surface indicates that most of the thrust is generated by the leading-edge region of the caudal fin. The visualization of wake structures showed the existence of the attached leading-edge vortex (LEV) in thunniform swimming. Interpretation: Based on the present simulations, the hydrodynamic performance of tuna during self-propelled swimming was analyzed in detail. Researchers can use these findings to design bionic robot fish with rigid and flexible tails.

Compatibility between Oncomelania hupensis and different isolates of Schistosoma japonicum in China.

Oncomelania hupensis from six localities were used for infection with different isolates of Schistosoma japonicum in the mainland of China, ie Anhui in the east, Hubei in the center, Guangxi in the south, Sichuan in the West, Yunnan in the southwest and Fujian in the southeast. Snails from Anhui and Hubei were readily infected with the local isolate of S. japonicum and cross infection also took place readily between the snails and the schistosomes from these two places. Snails from Sichuan and Yunnan were refractory to infection with schistosome isolates from Hubei and Anhui, but the isolates from Sichuan and Yunnan were able to develop in snails from Hubei and Anhui. Though the Guangxi isolate developed readily in both Anhui and Guangxi snails, the average precercarial period in the former was significantly longer than in the latter. None of the other snails from Sichuan, Yunnan and Fujian became infected. On the other hand, snails from Guangxi infected with Anhui parasites also had a longer precercarial period than that in Anhui snails. Snails from Fujian were readily infected with the isolates from Anhui and Yunnan. The present results suggest that there might be different geographic strains of S. japonicum and their Oncomelania snail hosts in the mainland of China.