While ships are at sea, they are continuously exposed to varying loads from waves that subject the vessel to rigid body motions and deformations. A distinction is made between two types of deformation: the quasi-static response and the dynamic response. A vessel's dynamic response can be characterized by its modal parameters. Springing and whipping are two of the relevant dynamic responses for ships. Springing is the steady-state resonant vibration of the two-node flexural mode in response to continuous wave loading. Whipping is the transient elastic vibration of the ship's hull girder. Whipping vibrations typically result in higher accelerations that may produce higher stresses and increased fatigue.
Marine modal and structural analysis: accelerometers and modal sensors
Structural vibrations and related damage can affect ship structure, crew comfort and lifetime of the vessel's equipment. Measurement technology from Kistler supports engineers with obtaining the necessary data for marine modal and structural analysis – enabling a definitive description of the structure's response, which can then be evaluated against design specifications.
Waterproof, compact and low noise solutions
Accelerometers are the means of choice when it comes to measuring the dynamic response signal while a ship is navigating. For this kind of operational modal analysis (OMA), both standard and IP68 waterproof accelerometers are used. But they must meet several key technical requirements: watertightness (sometimes up to 10 bar/150 psi), small size and lightweight design (to avoid mass loading effects), wide frequency range, and low noise specifications to measure very small signals.
The low-noise performance of ceramic-based acceleration sensor families allows measurement of the very small signals often encountered during modal analysis investigations.
Flat frequency response
IEPE Modal sensors from Kistler are characterized by a flat and repeatable frequency response, especially towards low frequencies. We also provide specific low-frequency calibration certificates and phase response characterizations on request. Kistler offers MEMS capacitive accelerometers for investigations of modal parameters toward the lowest frequencies.
Easy handling for fast and simple installation
For fast and simple installation, special clips or housings are available allowing for flexible orientation of the sensitive axis.