Time filter

Source Type

Maderich V.,Institute of Mathematical Machine and System Problems | Ilyin Y.,Ukrainian Hydrometeorological Institute | Lemeshko E.,Marine Hydrophysical Institute
Mediterranean Marine Science

chain of simple linked models is used to simulate the seasonal and interannual variability of the Turkish Straits System. This chain includes two-layer hydraulic models of the Bosphorus and Dardanelles straits simulating the exchange in terms of level and density difference along each strait, and a one-dimensional area averaged layered model of the Marmara Sea. The chain of models is complemented also by the similar layered model of the Black Sea proper and by a one-layer Azov Sea model with the Kerch Strait. This linked chain of models is used to study the seasonal and interannual variability of the system in the period 1970-2009. The salinity of the Black Sea water flowing into the Aegean Sea increases by approximately 1.7 times through entrainment from the lower layer. The flow entering into the lower layer of the Dardanelles Strait from the Aegean Sea is reduced by nearly 80% when it reaches the Black Sea. In the seasonal scale, a maximal transport in the upper layer and minimal transport in the bottom layer are during winter/spring for the Bosphorus and in spring for the Dardanelles Strait, whereas minimal transport in upper layer and maximal undercurrent are during the summer for the Bosphorus Strait and autumn for the Dardanelles Strait. The increase of freshwater flux into the Black Sea in interannual time scales (41 m3s-1 per year) is accompanied by a more than twofold growth of the Dardanelles outflow to the North Aegean (102 m3s-1 per year). Source

Maderich V.,Institute of Mathematical Machine and System Problems | Bezhenar R.,Ukrainian Center of Environmental and Water Projects | Heling R.,Nuclear Research and Consultancy Group | de With G.,Nuclear Research and Consultancy Group | And 5 more authors.
Journal of Environmental Radioactivity

The compartment model POSEIDON-R was modified and applied to the Northwestern Pacific and adjacent seas to simulate the transport and fate of radioactivity in the period 1945-2010, and to perform a radiological assessment on the releases of radioactivity due to the Fukushima Dai-ichi accident for the period 2011-2040. The model predicts the dispersion of radioactivity in the water column and in sediments, the transfer of radionuclides throughout the marine food web, and subsequent doses to humans due to the consumption of marine products. A generic predictive dynamic food-chain model is used instead of the biological concentration factor (BCF) approach. The radionuclide uptake model for fish has as a central feature the accumulation of radionuclides in the target tissue. The three layer structure of the water column makes it possible to describe the vertical structure of radioactivity in deep waters. In total 175 compartments cover the Northwestern Pacific, the East China and Yellow Seas and the East/Japan Sea. The model was validated from 137Cs data for the period 1945-2010. Calculated concentrations of 137Cs in water, bottom sediments and marine organisms in the coastal compartment, before and after the accident, are in close agreement with measurements from the Japanese agencies. The agreement for water is achieved when an additional continuous flux of 3.6TBqy-1 is used for underground leakage of contaminated water from the Fukushima Dai-ichi NPP, during the three years following the accident. The dynamic food web model predicts that due to the delay of the transfer throughout the food web, the concentration of 137Cs for piscivorous fishes returns to background level only in 2016. For the year 2011, the calculated individual dose rate for Fukushima Prefecture due to consumption of fishery products is 3.6μSvy-1. Following the Fukushima Dai-ichi accident the collective dose due to ingestion of marine products for Japan increased in 2011 by a factor of 6 in comparison with 2010. © 2013 Elsevier Ltd. Source

Maderich V.,Institute of Mathematical Machine and System Problems | Konstantinov S.,Institute of Hydromechanics
Fluid Dynamics Research

The asymptotic behavior of turbulent axisymmetric and plane momentumless wakes was studied using the Reynolds-averaged momentum equations and the second-order model of turbulence. The similarity solutions were obtained analytically and the process of transition to self-similarity was studied numerically. It was found that a single-point spectrum of the solutions of the corresponding eigenvalue problem for turbulent energy and dissipation rate existed. However, the spectra of solutions for the normal components of the anisotropy tensor and for the mean velocity defect were discrete. The numerical solution of a non-self-similar problem shows, in accordance with experiments and analytic solutions, that mean and fluctuating velocities decay with different rates, shear stresses decay faster than normal stresses and the anisotropic component of normal stresses decays faster than the isotropic component. The analysis of solutions for a full system of the Reynolds stress equations showed the presence of 'partial similarity' of the turbulent momentumless wake when some variables (velocity defect and shear stress) remain non-similar in flow that is self-similar as a whole. © 2010 The Japan Society of Fluid Mechanics and IOP Publishing Ltd. Source

Perianez R.,University of Seville | Bezhenar R.,Ukrainian Center of Environmental and Water Projects | Iosjpe M.,Norwegian Radiation Protection Authority | Maderich V.,Institute of Mathematical Machine and System Problems | And 4 more authors.
Journal of Environmental Radioactivity

Four radionuclide dispersion models have been applied to simulate the transport and distribution of 137Cs fallout from Chernobyl accident in the Baltic Sea. Models correspond to two categories: box models and hydrodynamic models which solve water circulation and then an advection/diffusion equation. In all cases, interactions of dissolved radionuclides with suspended matter and bed sediments are included. Model results have been compared with extensive field data obtained from HELCOM database. Inventories in the water column and seabed, as well as 137Cs concentrations along 5 years in water and sediments of several sub-basins of the Baltic, have been used for model comparisons. Values predicted by the models for the target magnitudes are very similar and close to experimental values. Results suggest that some processes are not very relevant for radionuclide transport within the Baltic Sea, for instance the roles of the ice cover and, surprisingly, water stratification. Also, results confirm previous findings concerning multi-model applications. © 2014 Elsevier Ltd. Source

Maderich V.,Institute of Mathematical Machine and System Problems | Talipova T.,Institute of Applied Physics | Grimshaw R.,Loughborough University | Terletska K.,Institute of Mathematical Machine and System Problems | And 3 more authors.
Physics of Fluids

This paper is devoted to the study of the transformation of a finite-amplitude interfacial solitary wave of depression at a bottom step. The parameter range studied goes outside the range of weakly nonlinear theory (the extended Korteweg-de Vries or Gardner equation), and we describe various scenarios of this transformation in terms of the incident wave amplitude and the step height. The dynamics and energy balance of the transformation are described. Several numerical simulations are carried out using the nonhydrostatic model based on the fully nonlinear Navier-Stokes equations in the Boussinesq approximation. Three distinct runs are discussed in detail. The first simulation is done when the ratio of the step height to the lower layer thickness after the step is about 0.4 and the incident wave amplitude is less than the limiting value estimated for a Gardner solitary wave. It shows the applicability of the weakly nonlinear model to describe the transformation of a strongly nonlinear wave in this case. In the second simulation, the ratio of the step height to the lower layer thickness is the same as that in the first run but the incident wave amplitude is increased and then its shape is described by the Miyata-Choi-Camassa solitary wave solution. In this case, the process of wave transformation is accompanied by shear instability and the billows that result in a thickening of the interface layer. In the third simulation, the ratio of the step height to the thickness of the lower layer after the step is 1.33, and then the same Miyata-Choi-Camassa solitary wave passes over the step, it undergoes stronger reflection and mixing between the layers although Kelvin-Helmholtz instability is absent. The energy budget of the wave transformation is calculated. It is shown that the energy loss in the vicinity of the step grows with an increase of the ratio of the incident wave amplitude to the thickness of the lower layer over the step. © 2010 American Institute of Physics. Source

Discover hidden collaborations