Projects / Programmes
Erosion in Coastal Seas and Navigable Rivers
| Code |
Science |
Field |
Subfield |
| 2.20.00 |
Engineering sciences and technologies |
Hydrology |
|
| Code |
Science |
Field |
| T220 |
Technological sciences |
Civil engineering, hydraulic engineering, offshore technology, soil mechanics |
| Code |
Science |
Field |
| 2.07 |
Engineering and Technology |
Environmental engineering
|
sediment erosion, sediment resuspension, bottom stress, propeller's jet, ship waves, orbital
velocity of waves
Researchers (8)
Organisations (2)
Abstract
In coastal seas, as well as in navigable rivers, the issue of erosion of the bottom of
water bodies or their banks is one of the most important challenges in coastal and
riverine engineering. The basic principles of erosion of a substrate over which the
volume of fluid (water) flows have long been known and are grounded on a surpassing
of the bottom shear stress, a critical bottom stress value. The former is caused by the
vertical shear of the velocity of currents and waves while the latter depends heavily on
the nature of the substrate.
Three major possible mechanisms by which the moving vessels may erode sediments
ANG are: 1. erosion due to changes of a flow field by a ship’s movement in the absence of
propeller’s propulsion 2. erosion due to propeller wake that reaches the sea bottom or
near-shore area 3. erosion due to ship waves that reach near-shore zone.
We intend to complement field observations with state-of-the art equipment, e.g. Laser
In-Situ Scattering and Transmissometery (LISST) instruments operated by a Slovenian
and a Hungarian team to measure the size distribution of suspended sediments (and
their falling speeds)[1], and acoustic probes for the measurement of near-bottom
turbulence[2] and for acoustic current meter profilers (ADCP), with the addition of
turbidimeters. The microstructure probe[3] (Slovenian team) will make available vertical
profiles of density and turbulence. Field observations will also be complemented by
numerical modelling of fluid motion and sediment transport in the northern Adriatic[4]
and the River Danube[5]. Analytical expressions will also be utilized appropriately.
The original method of estimating bottom stress under the direct influence of vessel
passage over (nearby) a spot at depth will be applied. There have been numerous
research papers and reports stimulated by significant damage on moored vessels from
ship passage. To our knowledge, studies relating a velocity (near) field around the
vessel to bottom stress are extremely scarce, so this present study will thus be novel.
There have been many studies concerning propeller wash, relating the propeller’s
vorticity trail behind a ship, considered a jet, to bottom stress. Two aspects will be new
in this study: First, the numerical merge of a narrow jet structure with an ambient
velocity field due to circulation, which is feasible along the vessel’s path using the
adaptive mesh concept, or the one-way nesting concept within the fixed ‘hot-spot’
area. A second topic is more a conceptual one: an in-depth study should remove
doubts concerning tangential (and radial) velocity components in intertwined swirling
vorticity trails, generated by each of the propeller blades, on bottom stress.
The third element of the study, on ship waves affecting the bottom sediment (and
organisms on it) in a very-near-shore zone is also novel. It will combine video imaging of
the near-shore area where waves break, the high-frequency measurements of the
velocities near the bottom and the sophisticated numerical modeling in a model grid of
an order of 1 cm. Bottom stress will be calculated by several methods. The concept
developed for the calm areas on the Danube banks will also be directly applicable to
coastal sea problems.
The proposed project will explore all important mechanisms of ship-generated erosion of
sediments on the sea and river floor. This research of a broader picture of the effects of
ship motion will select from three major mechanisms the most important ones that
matter at a specific site.
[1] http://www.sequoiasci.com/product/lisst-100x/
[2] http://www.nortek-as.com/en/products/velocimeters/vector;
http://www.fondriest.com/pdf/sontek_adv_spec.pdf
[3] http://www.sea-sun-tech.com/marine-tech/offshore/mss-microstructureprobe/
mss-90-profiler-microstructure-probe.html
[4] http://www.ccpo.odu.edu/POMWEB/
http://www.hydroqual.com/ehst_ecomsed.html
[5] http://folk.ntnu.no/nilsol/ssiim/
Significance for science
State of the art field observations, numerical simulations and hydrodynamic analysis of
three key mechanisms (bypassing of vessels, the propellers jet during manoeuvring,
arrivals to and departures from ports/berths, and ship waves) that affect erosion of
shallow bottom will contribute to the development of engineering sciences in the field
of environmental fluid dynamics. We will also introduce novel methods in the
observation and analysis of these mechanisms. This seems to be one of first projects
that will embrace these different mechanisms. The assessment of their relative impact
on the erosion in specific coastal zones will represent a significant contribution to
science.
Significance for the country
State of the art field observations, numerical simulations and hydrodynamic analysis of
three key mechanisms (bypassing of vessels, the propellers jet during manoeuvring,
arrivals to and departures from ports/berths, and ship waves) that affect erosion of
shallow bottom will contribute to the development of engineering sciences in the field
of environmental fluid dynamics. We will also introduce novel methods in the
observation and analysis of these mechanisms. This seems to be one of first projects
that will embrace these different mechanisms. The assessment of their relative impact
on the erosion in specific coastal zones will represent a significant contribution to
science.
Most important scientific results
Interim report
Most important socioeconomically and culturally relevant results
