Browse ORBi by ORBi project

- Background
- Content
- Benefits and challenges
- Legal aspects
- Functions and services
- Team
- Help and tutorials

Residual circulation and thermohaline distribution of the Ria de Vigo: a 3-D hydrodynamical model ; ; Delhez, Eric in Scientia Marina (2001), 65(Suppl. 1), 277-289 A three-dimensional, non-linear, baroclinic model is described and tested for the first time to study the residual circulation and the thermohaline distribution of the Ria de Vigo (NW Spain) at short time ... [more ▼] A three-dimensional, non-linear, baroclinic model is described and tested for the first time to study the residual circulation and the thermohaline distribution of the Ria de Vigo (NW Spain) at short time scales and under different wind stress regimes. Two markedly different realistic scenarios were chosen: northerly upwelling-favourable winds and southerly downwelling-favourable winds. The numerical experiments carried out indicate that the hydrodynamic regime of the Ria de Vigo is mostly a consequence of wind events. As could be expected, moderately strong North winds reinforce the normal (positive) Ria circulation, while winds blowing from the South, when sufficiently strong, reverse the typical circulation pattern and reduce the characteristic outgoing velocities and the flushing time inside the Ria. The temperature and salinity fields generated by the model in both situations were compared with observations and found to be in qualitatively good agreement, supporting the 3D velocity field distribution. [less ▲] Detailed reference viewed: 8 (2 ULg)The concept of age in marine modelling I. Theory and preliminary model results ; ; Delhez, Eric in Journal of Marine Systems (2001), 28(3-4), 229-267 The age of a particle of a seawater constituent is defined to be the time elapsed since the particle under consideration left the region, in which its age is prescribed to be zero. An Eulerian theory of ... [more ▼] The age of a particle of a seawater constituent is defined to be the time elapsed since the particle under consideration left the region, in which its age is prescribed to be zero. An Eulerian theory of the age is presented, in which advection, diffusion, production and destruction phenomena are properly accounted for. The key hypothesis is that the mean age of a set of particles is to be evaluated as the mass-weighted average of the ages of the particles under study. The basic variable is the concentration distribution function, representing, at a given time and location, the distribution over the age of the concentration of the constituent being considered. This function satisfies a partial differential equation, which, upon appropriate integration over the age, yields the equations, in flux form, governing the evolution of the concentration and the age concentration. The ratio of the latter variable to the former is the mean age. Further theoretical developments are presented, including a thought experiment showing that mixing processes cause the ages of various constituents to be different from each other. The potential of the age as a tool for understanding complex marine flows is briefly demonstrated by analysing the results of two numerical models. The ages of a passive tracer, a radioactive tracer and the water are computed, along with a suitably defined radio-age. First, the fate of tracers released into the English Channel at La Hague is simulated. Then, ages are computed in the World Ocean as a measure of the time that has elapsed since leaving the surface layers. A theorem is demonstrated, which specifies that the age of the radioactive tracer must be smaller than the relevant radio-age, the latter being smaller than the age of the passive tracer, which, under appropriate hypotheses, can be seen to be equivalent to the age of the water. These inequalities seem to be remarkably robust, since they are found to hold valid in most of the numerical and analytical results examined in the present study. On the other hand, a dimensionless number is highlighted, which is believed to play an important role in the scaling of the differences between ages. (C) 2001 Elsevier Science B.V. All rights reserved. [less ▲] Detailed reference viewed: 67 (22 ULg)Integrated modelling of the Belgian Coastal Zone Delhez, Eric ; in Estuarine Coastal & Shelf Science (2001), 53(4), 477-491 The management of the water resources in coastal or delta plains asks for an integrated modelling of the water system at a regional scale. In the SALMON project, detailed descriptions of the groundwater ... [more ▼] The management of the water resources in coastal or delta plains asks for an integrated modelling of the water system at a regional scale. In the SALMON project, detailed descriptions of the groundwater, river and marine domains are provided by coupling appropriate numerical models of these different sub-systems. The application of this three-fold model to the Scheldt and Belgian Coastal Zone reveals a marked river plume extending along the Belgian Coast with strong offshore gradients. This plume cannot be explained by the Eulerian residual transport velocity field but requires Lagrangian aspects to be taken into account. The computation of the age of this water mass shows that the different parts of the coastal zone are influenced by a discharge in the Grote Schijn River after a delay that varies between a few days (for the marine part of the estuary) to about 100 days (for the centre of the residual gyre). The computation shows also that the groundwater around Antwerp can also be contaminated by a pollution in the river but the resulting mass loss from the river does not lead to a significant reduction of the flux to the coastal zone. (C) 2001 Academic Press. [less ▲] Detailed reference viewed: 21 (10 ULg)Synthesis of water balance data and simulation of the shrinking process of the Aral Sea. Sirjacobs, Damien ; Grégoire, Marilaure ; Delhez, Eric et al Conference (2001) Detailed reference viewed: 27 (1 ULg)Some properties of generalized age-distribution equations in fluid dynamics Beckers, Jean-Marie ; Delhez, Eric ; in SIAM Journal on Applied Mathematics (2001), 61(5), 1526-1544 The concept of age in fluid dynamics is analyzed in the case of a tracer advection-diffusion equation. From the general solution in a uniform velocity field, it is shown that unexpected symmetry ... [more ▼] The concept of age in fluid dynamics is analyzed in the case of a tracer advection-diffusion equation. From the general solution in a uniform velocity field, it is shown that unexpected symmetry properties arise for the age field. In particular, for a point release, the age field is isotropic, regardless of the direction of the ow and the value of the diffusion coefficient. The analysis is then extended to situations with time-varying currents, where the symmetry can be broken under some circumstances. Finally, we show a method by which a time-dependent problem can be used to assess a stationary concentration distribution function, providing details about the propagation of younger and older material at a given location. [less ▲] Detailed reference viewed: 32 (13 ULg)On the symmetry of the age field of a passive tracer released into a one-dimensional fluid flow by a point-source ; Delhez, Eric ; et al in Bulletin de la Société Royale de Liège (2001), 70 Tracer is released from a point-source into an incompressible, one-dimensional fluid flow, with constant velocity and diffusivity. The age of a tracer parcel, which is defined as the time elapsed since ... [more ▼] Tracer is released from a point-source into an incompressible, one-dimensional fluid flow, with constant velocity and diffusivity. The age of a tracer parcel, which is defined as the time elapsed since leaving the source, may be evaluated as the ratio of the age concentration to the tracer concentration. The latter are governed by two partial differential equations. Time-dependent analytical solutions are derived, which show that the age is symmetric with respect to the source. This is astonishing, since it could have been expected that the age would reflect somehow the strong asymmetry of the tracer concentration, which tends to be much larger on the downstream side of the source than on the upstream side. Some finite-difference counterparts of this problem are seen to lead to age fields which, in their steady-state limit, are also symmetric with respect to the source. This is believed to be helpful to interpret the results of numerical models of complex fluid flows in which the age is introduced as a diagnostic variable. [less ▲] Detailed reference viewed: 17 (4 ULg)The age, a tool for understanding complex fluid flows ; Beckers, Jean-Marie ; et al Conference (2000, May) Detailed reference viewed: 8 (3 ULg)Some theoretical and modelling aspects of the age as a tool for understanding marine flows ; ; Beckers, Jean-Marie et al in Alonso Del Rosario, J. L.; Gallego, F. O. (Eds.) Actas de la II Jornadas de análisis de variables y simulación numérica del intercambio de masas de agua a través del estrecho de Gibraltar (2000) The age of a parcel of a constituent of seawater is defined to be the time elapsed since the parcel under consideration left the region where its age is prescribed to be zero. Estimating the age is thus ... [more ▼] The age of a parcel of a constituent of seawater is defined to be the time elapsed since the parcel under consideration left the region where its age is prescribed to be zero. Estimating the age is thus an invaluable tool for understanding complex oceanic flows and the functioning of the numerical models used for representing them. In this paper, a general theory of the age is presented, in which advection, diffusion, production and destruction are properly accounted for. The partial differential equations used for the rigorous computation of the age as a function of space and time are established. This general theory is applied to the computation of the ventilation rates in the World Ocean. The results are compared with those of widely used carbon-14-like dating techniques. Using both numerical simulations and analytical developments, it is shown that the age of the radioactive tracer is smaller than the carbon-14-like age, which is larger than that of the passive tracer. The latter is equivalent to the ventilation or water age. The difference between the various ages, which is essentially due to the influence of mixing processes, increases as the timescale of decay of the radioactive tracer decreases [less ▲] Detailed reference viewed: 21 (2 ULg)Dissection of the GHER turbulence closure scheme Delhez, Eric ; Grégoire, Marilaure ; Nihoul, Jacques et al in Journal of Marine Systems (1999), 21(1-4), 379-397 In this paper, the turbulence closure scheme implemented in the GHER hydrodynamic model is described in detail. Two case studies carried out in two contrasting conditions-one in the shallow, tide ... [more ▼] In this paper, the turbulence closure scheme implemented in the GHER hydrodynamic model is described in detail. Two case studies carried out in two contrasting conditions-one in the shallow, tide dominated, north-western European continental shelf, and the other in the deep Mediterranean Sea-are used to identify the dominant terms of the equation for the turbulent kinetic energy, first theoretically, secondly from the results of the simulations. In both domains, the dominant terms are the local destruction and production terms, the vertical diffusion term and to a smaller degree, the time derivative. Advection and horizontal diffusion turn out to be negligible in most of the relevant cases for such large scale studies. This opens the way to simplifications and optimisations of the numerical models. (C) 1999 Elsevier Science B.V. All rights reserved. [less ▲] Detailed reference viewed: 67 (12 ULg)Dissection of the GHER Turbulence Closure Scheme Delhez, Eric ; Grégoire, Marilaure ; Nihoul, Jacques et al Poster (1998, May) Detailed reference viewed: 5 (0 ULg)Toward a general theory of the age in ocean modelling Delhez, Eric ; ; et al in Ocean Modelling (1998), 1 Detailed reference viewed: 9 (0 ULg)Modelling Hydrodynamically Dominated Marine Ecosystems Delhez, Eric in Journal of Marine Systems (1998), 1-2 Detailed reference viewed: 18 (0 ULg)Macroscale ecohydrodynamic modeling on the Northwest European Continental Shelf Delhez, Eric in Journal of Marine Systems (1998), 16(1-2), 171-190 A 3D coupled hydrodynamic-biological model is applied to the simulation of the biological processes on the Northwest European Continental Shelf. The model operates in the macroscale spectral window (time ... [more ▼] A 3D coupled hydrodynamic-biological model is applied to the simulation of the biological processes on the Northwest European Continental Shelf. The model operates in the macroscale spectral window (time scales of a month or a season) without explicit description of the higher frequency processes but with an adequate modeling of their influence on larger time scales. The hydrodynamic sub-model is 3D, baroclinic and includes a refined turbulence closure. The non-linear interactions of mesoscale fluctuations are described by means of the generalized mesoscale Reynolds stresses and the Stokes drift transport velocity field. The biological sub-model describes the nitrogen and carbon cycles through the food web with 17 state variables representing 9 compartments: inorganic nutrients, small phytoplankton, large phytoplankton, dissolved organic matter, pelagic bacteria, heterotrophic flagellates, pelagic detritus, zooplankton and benthic organic detritus. The simulation emphasizes the strong influence of the local depth and of the stability of the water column on the whole annual cycle of phytoplankton. In well-mixed shallow areas, the chlorophyll concentration increases in early spring and the primary production occurs steadily until October. In deeper areas, the spring bloom is much sharper and appears later, after the set up of the seasonal stratification. The main part of the primary production happens during the bloom period. The macroscale approach provides results that are comparable with observations and results of other more classical models describing explicitly the higher frequency processes. The current method allows, however, a more direct insight into the dynamics of the system and into the interactions between the hydrodynamics and the biology. Also, it greatly reduces the CPU requirements and is therefore particularly suited for repeated or long term simulations. (C) 1998 Elsevier Science B.V. All rights reserved. [less ▲] Detailed reference viewed: 49 (11 ULg)La modélisation de la circulation résiduelle sur le Plateau Continental Nord-Ouest Européen dans la perspective d'applications pluridisciplinaires Delhez, Eric Book published by Université de Liège (1997) Detailed reference viewed: 28 (5 ULg)Sea air land modelling operational network ; ; Beckers, Jean-Marie et al in Lecture Notes in Computer Science (1997), 1225 The purpose of the SALMON project is to develop a single model from three previously existing models (ocean, river and groundwater) for the description of environment quality in a whole system of regional ... [more ▼] The purpose of the SALMON project is to develop a single model from three previously existing models (ocean, river and groundwater) for the description of environment quality in a whole system of regional scale including marine, river, groundwater and atmospheric inputs. The connection of the different models is done through a specific interface, a junction, designed to allow the data exchange between models based on different numerical methods. The software is developed on IBM RS/6000 computers (the SP2 parallel machine). [less ▲] Detailed reference viewed: 98 (49 ULg)Mécanique Rationnelle - Modèle Mathématique de Newton Delhez, Eric ; Nihoul, Jacques Book published by Etienne Riga (1996) Detailed reference viewed: 131 (12 ULg)Modelling the North Sea hydrodynamics in a management perspective Djenidi, Salim ; Delhez, Eric ; Martin, Géraldine et al in Bulletin de la Société Royale des Sciences de Liège (1996), 65 Detailed reference viewed: 15 (5 ULg)Reconnaissance of the general circulation of the North-Western European Continental Shelf by means of a three-dimensional turbulent closure model Delhez, Eric in Earth-Science Reviews (1996), 41(1-2), 3-29 The general circulation of the North-Western European Continental Shelf is investigated by means of a three-dimensional macroscale mathematical model. Results corresponding to typical winter and summer ... [more ▼] The general circulation of the North-Western European Continental Shelf is investigated by means of a three-dimensional macroscale mathematical model. Results corresponding to typical winter and summer conditions are described in detail. Prominent features are explained from a dynamic point of view by referring to the main forcing factors of the macroscale circulation on the North-Western European Continental Shelf: seasonal mean wind stress and atmospheric pressure, large a scale sea surface slope, non-linear interactions of the higher frequency processes and density differences. The role of the bottom topography is also highlighted. The largest seasonal variations are mainly due to the occurrence of a thermal stratification in summer over large parts of the shelf. In such conditions, there is only a weak interaction between the surface and bottom layers that have therefore significantly different dynamics. [less ▲] Detailed reference viewed: 23 (4 ULg)On the residual advection of passive constituents Delhez, Eric in Journal of Marine Systems (1996), 8(3-4), 147-169 In this paper, the different approaches used to simulate the long-term advection of passive constituents on tidal shelves are discussed in the framework of large scale hydrodynamic modelling. The direct ... [more ▼] In this paper, the different approaches used to simulate the long-term advection of passive constituents on tidal shelves are discussed in the framework of large scale hydrodynamic modelling. The direct approach in which the unsteady mesoscale (tides and storm surges) and macroscale (monthly or seasonal mean processes) currents are used is very demanding in computer resources (CPU and memory). On the other hand, the use of residual velocities gives a larger understanding of the long-term transport processes and simplifies numerical treatments. However, the definition of such appropriate velocities is still an open question. In the context of large scale models, Lagrangian residuals are not applicable. Eulerian residual transport velocities fail to represent long-term motions when tidal non-linearities are important. The first order Lagrangian residual velocity introduced by Feng et al. (1986a) and generalized here is shown to be a very good solution. The North-Western European Continental Shelf (NWECS) is used as an example to compare the numerical solutions obtained with the different approaches. [less ▲] Detailed reference viewed: 33 (11 ULg)La modélisation de la circulation résiduelle sur le Plateau Continental Nord-Ouest Européen dans la perspective d'applications pluridisciplinaires Delhez, Eric Doctoral thesis (1995) Detailed reference viewed: 21 (8 ULg) |
||