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Marine Science At Its Best


Human activities are creating tremendous amounts of underwater noise, effecting marine environment dramatically.


Marine researchers in Eckernförde, Germany, and at the Maritime Research Institute “Marin” in the Netherlands, are analyzing underwater sound  --- with the best equipment available in the market: the LTT24, a high precision, and high bandwidth data acquisition system that outperforms all competitors.

In recent years, a lot of international attention has been paid to the underwater noise of shipping and its influence on life in the sea. For example, the European Union has specifically named underwater noise as one of the 'descriptors' for 'Good Environmental Status' in the 'Marine Strategy Framework Directive' (Source). That is not yet a tough regulation, but it is likely that it will be put in place. Several classification societies now offer 'silent ship' notations. Once a ship has such a notation, the operator receives a discount on the port fees in the Port of Vancouver, Canada (Source). This is also a financial incentive for silent ships. In addition, there is also a lot of attention from the media on this topic (Source).

Cavitation (explained below) is, as soon as it occurs, the main source of underwater noise of a ship. Because it is difficult to remedy this when the ship is built, it is wise to verify that the ship meets the set noise requirements during the design of the ship. Moreover, measuring on a model scale is much more practical than full size. In recent years, the number of sound measurements in MARIN's DWB (Source) has increased considerably.

 

Cavitation is the effect of vapor-gas-bubbles that get created by the strong negative pressure on the suction side of a propeller of a ship.

The water simply vaporizes partially at these pressure conditions just before it passes the propeller.

With crossing the side of the propeller, the pressure increases immediately and the just created bubbles get compressed down to the point where they finally collapse.

The shrinking bubble size increases the internal pressure of theses bubbles dramatically so that the collapsing bubbles create a high-pressure shock wave.

These shock waves not only affect the noise level generated. They are also capable of “biting” tiny pieces out of the propeller if the cavitation occurs in close proximity to the propeller itself. Strong cavitation will therefore limit the service life of the propeller. (Video)

 

The special thing about this effect:
the generated noise bandwidth ranges up to several hundred Kilohertz  -- far beyond human hearing, but well within the most sensitive frequency spectrum of whale and dolphin communication. 

 

Detecting these high frequencies, as well as noise from low-frequency sources, places extreme demands on the data acquisition systems.

These demands are getting to the limits of feasible performance levels, getting even more critical if the sound measurements are to be used to determine the 3D-location of the source of the sound under water.

The data acquisition systems of type LTT24 (link einfügen) are the world’s best devices to fulfil these demanding tasks:

  • flat and wide bandwidth
  • ultralow distortion
  • ultralow noise
  • no phase differences between channels
  • ruggedized design.

 

Scientists around the globe show increasing activities in this field of science, defining the LTT24 as the new must-have of performance and reliability.

 

Further applications are:

  • Violent wave impacts measurement on model scale (Video)
  • Slamming measurement on model scale (Video)
  • Hybrid drive systems: measurement of switching behaviour
  • And many others

 

Contact our experts to learn more about our high performance data acquisition system LTT24 – your solution for marine research measurements.