Triantafyllou Michael S.

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Triantafyllou
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Michael S.
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  • Technical Report
    WHOI cable : time domain numerical simulation of moored and towed oceanographic systems
    (Woods Hole Oceanographic Institution, 1997-11) Gobat, Jason I. ; Grosenbaugh, Mark A. ; Triantafyllou, Michael S.
    This report presents a numerical framework for analyzing the statics and dynamics of cable strctures commonly encountered in oceanographic engineering practice. The numerical program, WHOI Cable, features a nonlinear solver that includes the effects of geometric and material nonlinearties, bending stiffness for seamless modeling of slack cables, and a model for the interaction of cable segments with the seafoor. The program solves both surface and subsurface single-point mooring problems, systems with both ends anchored on the bottom, and towing and drifter problems. Forcing includes waves, current, ship speed, and pay-out of cable. The programs that make-up WHOI Cable run under Unix, DOS, and Windows. There is a familiar Windows-style interface available for Windows 95 and Windows NT platforms. In the report, the mathematical and numerical framework for WHOI Cable is described, followed by detailed instructions for formulating problem input files and running the codes. Examples are included in an appendix to highlight the range of problems that WHOI Cable can solve.
  • Article
    Swimming kinematics and efficiency of entangled North Atlantic right whales
    (Inter-Research, 2017-01-12) van der Hoop, Julie ; Nowacek, Douglas P. ; Moore, Michael J. ; Triantafyllou, Michael S.
    Marine mammals are streamlined for efficient movement in their relatively viscous fluid environment and are able to alter their kinematics (i.e. fluke stroke frequency, amplitude, or both) in response to changes in force balance. Entanglement in fishing gear adds significant drag and buoyant forces that can impact swimming behaviors across a range of timescales. We deployed biologging tags during the disentanglement of 2 North Atlantic right whales Eubalaena glacialis to (1) examine how their kinematics changed in response to drag and buoyancy from entanglement in fishing gear, and (2) calculate resultant changes in swimming efficiency for one individual. We observed variable responses in dive behavior, but neither whale appeared to exploit added buoyancy to reduce energy expenditure. While some of the observed changes in behavior were individually specific, some swimming kinematics were consistently modulated in response to high drag and buoyancy associated with entangling gear, affecting thrust production. In high drag and buoyancy conditions, fluke strokes were significantly shorter and more variable in shape, and gliding was less frequent. Thrust and efficiency significantly differed among dive phases. Disentanglement reduced thrust coefficients ~4-fold, leading to 1.2 to 1.8-fold lower power (W). Ideal propulsive efficiency was significantly lower when entangled, though we detected no difference in observed propulsive efficiency between the conditions. Similar to carrying heavy objects or changing shoes, we present another condition where animals perceive unique movement constraints over seconds to minutes and develop compensatory strategies, altering their movement accordingly.
  • Preprint
    Wake-induced `slaloming' response explains exquisite sensitivity of seal whisker-like sensors
    ( 2015-08) Beem, Heather R. ; Triantafyllou, Michael S.
    Blindfolded harbour seals are able to use their uniquely shaped whiskers to track vortex wakes left by moving animals and identify objects that passed by 30 s earlier, an impressive feat, as the flow features have velocities as low as 1 mm s−1. The seals sense while swimming, hence their whiskers are sensitive enough to detect small-scale changes in the flow, while rejecting self-generated flow noise. Here we identify and illustrate a novel flow mechanism, causing a large-amplitude ‘slaloming’ whisker response, which allows artificial whiskers with the identical unique undulatory geometry as those of the harbour seal to detect the features of minute flow fluctuations when placed within wakes. Whereas in open water the whisker responds with very low-amplitude vibration, once within a wake, it oscillates with large amplitude and, importantly, its response frequency coincides with the Strouhal frequency of the upstream cylinder, making the detection of an upstream wake and an estimation of the size and shape of the wake-generating body possible. This mechanism has some similarities with the flow mechanisms observed in actively controlled propulsive foils within upstream wakes and trout swimming behind bluff cylinders in a stream, but there are also differences caused by the unique whisker morphology, which enables it to respond passively and within a much wider parametric range.