Vibration Control in Ship Structures

Abstract

The dominant sources of noise radiation in water are from ship engines and machinery—the propeller cavitation noise, the noise radiation from propeller blades, and the hydrodynamic pressure fluctuations induced by turbulent water flow along the ship's hull. At speeds below propeller cavitation inception, a ship's acoustic signature is generally dominated by structurally transmitted noise from onboard machinery. Reduction or control of ship noise has traditionally been implemented by passive means, such as by the use of vibration isolation mounts, flexible pipe‐work, and interior acoustic absorbing materials. However, these passive noise control techniques are effective mostly for attenuating high‐frequency noise; they are generally ineffective for controlling low‐frequency noise. There are, on the other hand, active noise control methods that have been proven to be effective in controlling low‐frequency and tonal noise. These active control methods could be used instead of, or in combination with, passive techniques, for controlling or reducing ship noise. Active noise control (ANC) involves the reduction or elimination of noise by modification of the dynamic properties of a system or by noise cancellation through linear superposition of a secondary noise field of equal but opposite strength. An active noise control system will typically consist of all or some of the following ingredients: sensors, actuators, and controllers.

A model of magnetostrictive actuators for active vibration control

“…Passive damping materials have been used effectively for a very long time but in many cases, especially for small amplitude and low frequency vibration, passive damping materials are inadequate and not effective [1,2]. Hence active vibration control (AVC) techniques with feedback control have begun to be used to meet performance requirements.…”

“…Moreover, they can be driven at high frequencies. These characteristics make them suitable for a variety of vibration control applications such as vibrations control of machine tools [1], of ship structures [2], of helicopter blades [3], of airplanes [4], of cylindrical [5] and linear [6] structures, of cables [7] and multi-dof systems [8].…”