IB 362Lecture 5 – Life in a fluid medium

Marine Biology: Function, Biodiversity, Ecology, 3/e

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FIG. 8.3 Top: the location of the cuttlebone of a cuttlefish. Bottom: cross section showing chambers, which may be filled with water or gas.

Marine Biology: Function, Biodiversity, Ecology, 3/e

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FIG. 5.1 Two different situations in which one can find the size l and velocity V, parameters necessary to determine the Reynolds number. (a) An object (a sea squirt) is stationary in moving water. (b) An object (a fish) is moving through the water.

Marine Biology: Function, Biodiversity, Ecology, 3/e

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FIG. 5.2 Water flow can be visualized as streamlines, which indicate the path that individual particles would take. Particles move along streamlines, not across them. In this illustration, water is flowing around a fixed cylinder, which is viewed in cross section.

Marine Biology: Function, Biodiversity, Ecology, 3/e

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FIG. 5.4 Flow over the bottom at slow velocity. Water velocity maintains an average mainstream laminar velocity well above the bottom, but velocity decreases to zero at the bottom surface. Near the bottom is a thin boundary layer, where velocity decreases linearly down to the bottom surface. (Not to scale: boundary layer is often less than 1 cm thick.)

Marine Biology: Function, Biodiversity, Ecology, 3/e

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FIG. 5.5 Flow velocity through a pipe and the principle of continuity. The product of cross-sectional area and velocity is constant. Therefore, if cross-sectional area x decreases by half, the velocity doubles.

Marine Biology: Function, Biodiversity, Ecology, 3/e

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FIG. 5.3 Laminar and turbulent flow. Blue lines represent paths of flow. (After Vogel, 1994.)

Marine Biology: Function, Biodiversity, Ecology, 3/e

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FIG. 5.8 Flow patterns around a cylinder (view is down the axis of the cylinder, looking at the cross section). Note the irregular flow in the wake of the cylinder.

Marine Biology: Function, Biodiversity, Ecology, 3/e

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FIG. 5.11 Different types of wake downcurrent of a cylinder, at different Reynolds numbers. (After Vogel, 1994.)

Marine Biology: Function, Biodiversity, Ecology, 3/e

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FIG. 5.9 Changes (left to right) of the sea anemone Metridium senile as the water velocity increases. Withdrawal of the tentacle crown reduces drag.

Marine Biology: Function, Biodiversity, Ecology, 3/e

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FIG. 5.6 How a sponge generates a relatively high exit velocity through its excurrent channels. (a) The low velocity of the water from flagellated cells in flagellated chambers is compensated by the far greater total cross-sectional area of the flagellated chambers relative to the excurrent opening of the sponge. (b) Diagram of flagellated sponge cells. (After Vogel, 1994.)

(movie of sponge flow/feeding)

Marine Biology: Function, Biodiversity, Ecology, 3/e

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FIG. 5.7 Bernoulli’s principle. (a) Differences in pressure above and below a moving flatfish create lift. (After Vogel, 1994.) (b) A raised mound on one end of a buried U-shaped tube places it in a slightly higher current velocity relative to the other opening, which is flush with the sediment. Water moving past the two holes creates a pressure difference, with lower pressure on the raised area, and this drives water through the tube. Length of arrows is proportional to water velocity.

(Movie of jellyfish swimming/feeding)

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FIG. 8.6 Swimming in fishes. Components of force generated by undulation are shown.

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FIG. 8.7 Undulations of fish range from those that are nearly equally distributed throughout the length of the body, such as in a fast-swimming eel (at left), to undulations that are focused in the tail region, such as in a tuna (at right). (From Sfakiotakis et al., 1999, © IEEE.)

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FIG. 5.10 Drag on a fish is affected greatly by streamlining. (a) If a fish is well streamlined, the wake is reduced, streamlines are maintained behind the fish, and the drag is much reduced. (b) If a fish is poorly streamlined, a wake is created at the rear, producing a pressure gradient and drag

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FIG. 8.10 The overall form of fishes can represent an intermediate among the end-member forms that would be ideal for the separate activities of accelerating, steady cruising, and maneuvering.