Question

An underwater sensor is mounted below the keel
of the fast patrol boat shown in Figure 10.29. The
supporting bracket is of cylindrical cross-section
(diameter 0.04 m), and so is subject to an oscillating
side-force due to vortex shedding. The bracket is
of negligible mass compared with the sensor itself,
which has a mass of 4 kg. The bracket has a tip
displacement stiffness of 25 000Nm−1. The
frequency of the oscillating side-force is SU/d,
where U is the speed of the vessel through the
water, d is the diameter of the supporting bracket
and S is the Strouhal number for vortex shedding
from a circular cylinder. S has the value 0.20
approximately. At what speed will the frequency of
the side-force coincide with the natural frequency
of the sensor and mounting?

MODERN ENGINEERING MATHEMATICS, GLYN JAMES 5TH ED, CHP10.10

71 An underwater sensor is mounted below the keel of the fast patrol boat shown in Figure 10.29. The supporting bracket is of cylindrical cross-section (diameter 0.04 m), and so is subject to an oscillating side-force due to vortex shedding. The bracket is of negligible mass compared with the sensor itself, which has a mass of 4 kg. The bracket has a tip displacement stiffness of 25 000 Nm. The frequency of the oscillating side-force is SUld, where Uis the speed of the vessel through the water, d is the diameter of the supporting bracket and Sis the Strouhal number for vortex shedding from a circular cylinder. S has the value 0.20 approximately. At what speed will the frequency of the side-force coincide with the natural frequency of the sensor and mounting? Figure 10.29 An underwater sensor mounting

Answer 1

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