Civil Engineering Reference
In-Depth Information
Soliton currents
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Longshore currents
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Wind-generated currents are caused by wind stress and the atmospheric
pressure gradient during a storm.
Tidal currents are regular and follow the harmonic astronomical motions of
the planets. The maximum tidal current precedes or follows the highest and low-
est astronomical tides, HAT and LAT, respectively. Tidal currents are generally
weak in deep water, but they are strengthened by shoreline configurations. Strong
tidal currents exist in inlets and straits in coastal regions.
Circulational currents are steady, large-scale currents of the general oceanic
circulation (i.e., the Gulf Stream in the Atlantic Ocean). Parts of circulation cur-
rents may break off from the main circulation to form large-scale eddies. Current
velocities in such eddies (loop and eddy currents) can exceed the velocity of the
main circulation current (i.e., loop current in the GoM).
Soliton currents are due to internal waves generated by density gradients.
Loop/eddy currents and soliton currents penetrate deeply in the water column.
Longshore currents in coastal regions run parallel to the shore as a result of
wavesbreakingatanangleontheshore;theyarealsoreferredtoaslittoral
currents.
Earthquakes can cause unstable deposits to run down continental slopes and
thereby set up gravity-driven flows. Such flows are called turbidity currents.
Sediments in the flow have a higher density than the ambient water. Such cur-
rents should be accounted for in the design of pipelines crossing a continental
slope with unstable sediments. Strong underwater earthquakes can also lead to
the generation of tsunamis, which in coastal regions behave like a long, shallow
water wave similar to a strong horizontal current.
The effects of currents on ships and offshore structures should be considered
in their design, construction and operation. The effects of currents that should
be considered in the design of offshore structures include:
Currents can cause large, steady excursions and slow drift motions of
moored platforms.
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Currents can create drag and lift forces on submerged structures.
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Currents can cause vortex-induced vibrations of slender structural elements
and vortex-induced motions of large-volume structures.
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Interaction between strong currents and waves leads to change in wave
height and wave periods.
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Currents can create seabed scouring around bottom-mounted structures.
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Information on the statistical distribution of currents and their velocity pro-
file is generally scarce for most areas of the world. Current measurement cam-
paigns are recommended during the early phases of an offshore oil exploration
development.
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