Measurements of the complex dynamic shear compliance and loss tangent of pilot whale blubber and the role of blubber in flow-noise reduction

Abstract

The complex dynamic shear compliances and loss tangents of pilot whale blubber (BLB), pork-belly fat (PBF), and beef-belly fat (BBF) have been measured over a frequency range of ≃ 45 to 4500 Hz, using the Fitzgerald apparatus [E. R. Fitzgerald and J. D. Ferry, J. Colloid Sci. 8, 1–34 (1953)]. Representative values at 100 Hz for J* and tan ζ PBF, J* = 3 × 10−9 cm2/dyn, tan ζ = 0.5; BLB, J* = 2 × 10−6 cm2/dyn, tan ζ = 0.7; BBF, J* = 2 × 10−8 cm2/dyn, tan ζ = 0.1. Thus beef-belly fat is ≃ 100 times stiffer (less compliant) and pork-belly fat is ≃ 15 times less stiff (more compliant) than whale blubber. The general shape of the compliance curves are similar except for a frequency shift in the peak values. The broad peak in J* and tan ζ implies a relaxation mechanism in all three fats. The high loss tangent in blubber and its intermediate value of compliance suggests that it plays a role in reducing flow noise by acting as a “matched load” to the boundary layer “turbulence generator.” A polyvinyl gel, with dynamic shear properties closely matched to those of blubber, is proposed as a “synthetic blubber: for studies of turbulent flow over compliant surfaces.” [Work had fragmentary support from NUSC/NLON.]