Inducing rostrum interfacial waves by fluid-solid coupling in a Chinese river dolphin(Lipotesvexillifer)

Abstract

Through numerically solving the appropriate wave equations, propagation of biosonar signals in a Chinese river dolphin (baiji) was studied. The interfacial waves along the rostrum-tissue interfaces, including both compressional (longitudinal) and shear (transverse) waves in the solid rostrum through fluid-solid coupling were examined. The baiji's rostrum was found to effect acoustic beam formation not only as an interfacial wave generator but also as a sound reflector. The wave propagation patterns in the solid rostrum were found to significantly change the wave movement through the bone. Vibrations in the rostrum, expressed in solid displacement, initially increased but eventually decreased from posterior to anterior sides, indicating a complex physical process. Furthermore, the comparisons among seven cases, including the combination of (1) the rostrum, melon, and air sacs; (2) rostrum-air sacs; (3) rostrum-melon; (4) only rostrum; (5) air sacs-melon; (6) only air sacs; and (7) only melon revealed that the cases including the rostrum were better able to approach the complete system by inducing rostrum-tissue interfacial waves and reducing the differences in main beam angle and -3 dB beam width. The interfacial waves in the rostrum were considered complementary with reflection to determine the obbligato role of the rostrum in the baiji's biosonar emission. The far-field beams formed from complete fluid-solid models and non-fluid-solid models were compared to reveal the effects brought by the consideration of shear waves of the solid structures of the baiji. The results may provide useful information for further understanding the role of the rostrum in this odontocete species.

Biosonar signal propagation in the harbor porpoise's (Phocoena phocoena) head: The role of various structures in the formation of the vertical beam

“…Previous studies have used numerical models and experimental measurements to display that the internal structures in the dolphin's head such as the air sacs, melon and skull contribute to the formation of biosonar beam (Aroyan et al, 1992;Houser et al, 2004;Au et al, 2010;Cranford et al, 2014;Finneran et al, 2014;Wei et al, 2014;Song et al, 2016;Wei et al, 2016). Aroyan et al (1992) suggested that the air sacs and skull were the dominant factors in shaping the beam and the melon might be capable of mild focusing in the formation of the short-beaked common dolphin's biosonar beam.…”

“…where q 0 denotes the equilibrium density (kg/m 3 ), c s is the speed of sound (m/s), while q d and Q m are dipole and monopole sources, respectively Song et al, 2016). The density q 0 and the speed of sound c s can both be non-constant in space.…”

The influence of air-filled structures on wave propagation and beam formation of a pygmy sperm whale (Kogia breviceps) in horizontal and vertical planes

“…1,2 Beam studies conducted on many species either from simulations or experiments revealed important information. [14][15][16][17][18][19][20][21] However, few were conducted on the pygmy sperm whale, mainly from morphology perspectives. [22][23][24][25][26][27] The pygmy sperm whale (Kogia breviceps), has a larger head than those of bottlenose dolphins (Tursiops truncatus) and the Indo-Pacific humpback dolphin (Sousa chinensis), and K. breviceps was reported to produce narrowband and high frequency clicks, with peak frequencies ranging from 60 to 160 kHz.…”

Finite element simulation of broadband biosonar signal propagation in the near- and far-field of an echolocating Atlantic bottlenose dolphin (Tursiops truncatus)

“…There is a general consensus on the roles of the skull and air sacs from the results of prior numerical simulation research and experimental measurements (Aroyan et al, 1992;Houser et al, 2004;Au et al, 2010;Finneran et al, 2014;Cranford et al, 2014;Wei et al, 2014;Song et al, 2016;Wei et al, 2016;Wei et al, 2017;Wei et al, 2018). Although there are differences in the geometry of the air sacs and rostrum across species, these structures act as acoustic reflectors because of impedance mismatch between them and the surrounding soft tissues directing the waves forward to form a radiating beam.…”

“…In order to investigate the specific details of how these structures function and further increase our understanding of the mechanics of biosonar sound production and propagation, numerical modeling techniques have been applied to simulate the biosonar systems of odontocetes (Aroyan et al, 1992;Aroyan et al, 2001;Krysl et al, 2006;Cranford et al, 2014;Wei et al, 2014;Wei et al, 2016;Song et al, 2016;Wei et al, 2017;Wei et al, 2018). There is a general consensus on the roles of the skull and air sacs from the results of prior numerical simulation research and experimental measurements (Aroyan et al, 1992;Houser et al, 2004;Au et al, 2010;Finneran et al, 2014;Cranford et al, 2014;Wei et al, 2014;Song et al, 2016;Wei et al, 2016;Wei et al, 2017;Wei et al, 2018).…”