Unstructured, anisotropic mesh generation for the Northwestern European continental shelf, the continental slope and the neighbouring ocean

in Continental Shelf Research (2007), 27(9), 1344-1356

A new mesh refinement strategy for generating high quality unstructured meshes of the Northwestern European continental shelf, the continental slope and the neighbouring ocean is presented. Our objective ... [more ▼]

A new mesh refinement strategy for generating high quality unstructured meshes of the Northwestern European continental shelf, the continental slope and the neighbouring ocean is presented. Our objective is to demonstrate the ability of anisotropic unstructured meshes to adequately address the challenge of simulating the hydrodynamics occurring in these three regions within a unique mesh. The refinement criteria blend several hydrodynamic considerations as the tidal wave propagation on the continental shelf and the hydrostatic consistency condition in steep areas. Several meshes illustrate both the validity and the efficiency of the refinement strategy. The selection of the refinement parameters is discussed. Finally, an attempt is made to take into account tidal ellipses, providing another cause for anisotropy in the mesh. (c) 2007 Elsevier Ltd. All rights reserved. [less ▲]

Three dimensional sediment transport model of the Belgian coastal zone: application of the CART theory

Conference (2006)

Suspended sediment processes in the Belgian coastal zone are discussed by presenting the first results given by a 3D coupled hydrodynamic-sediment transport model covering the Southern Bight in North Sea ... [more ▼]

Suspended sediment processes in the Belgian coastal zone are discussed by presenting the first results given by a 3D coupled hydrodynamic-sediment transport model covering the Southern Bight in North Sea. The hydrodynamic sub-model is three-dimensional, baroclinic and includes a refined turbulence closure. In the sediment transport sub-model, the dynamic of sediments is described by an evolution equation of the sediment concentration in the water column and an equation for the sediment load on the seabed. Sedimentation is modeled through the addition of a sedimentation velocity in the vertical advection term. For the evaluation of deposition and erosion terms, formu- lae based on the calculation of the bottom stress under the combined effect of prevailing currents and waves are used. For more realism, sediment loads has also been split into different sediment classes with different sedimentation, deposition and erosion characteristics. The equations are solved by a finite volume method based on an Arakawa C grid, using sigma-transform and mode-splitting numerical methods. The horizontal resolution is 500x500 m and 10 vertical sigma-layers are used. Advection is handled using a TVD scheme with superbee flux limiter. Boundary conditions are provided by coupling this model to a 3D coupled hydrodynamic-sediment transport model of the North-Western European Continental Shelf. The results are validated with measurements carried out by Haecon NV and are compared with those obtained with the MU-STM model. A sensitivity analysis of the model to critical parameters of erosion, deposition and sedimentation based on the concept of residence time was carried out. [less ▲]

On the behaviour of the residence time at the bottom of the mixed layer

in Environmental Fluid Mechanics (2006), 6(6), 541-547

To understand why the findings of Deleersnijder et al. [(2006), Environ Fluid Mech 6: 25-42]-the residence time in the mixed layer in not necessarily zero at the pycnocline-are consistent with those of ... [more ▼]

To understand why the findings of Deleersnijder et al. [(2006), Environ Fluid Mech 6: 25-42]-the residence time in the mixed layer in not necessarily zero at the pycnocline-are consistent with those of Delhez and Deleersnijder [(2006), Ocean Dyn 56:139-150]-the residence time in a control domain vanishes at the open boundaries of this control domain-, it is necessary to consider a control domain that includes part of the pycnocline, in which the eddy diffusivity is assumed to be zero. Then, depending on the behaviour of the eddy diffusivity near the bottom of the mixed layer, the residence time may be seen to exhibit a discontinuity at the interface between the mixed layer and the pycnocline. If such a discontinuity exists, the residence time is non-zero in the former and zero in the latter. This is illustrated by analytical solutions obtained under the assumption that the eddy diffusivity is constant in the mixed layer. [less ▲]

Study of the seasonal cycle of the biogeochemical processes in the Ligurian Sea using a ID interdisciplinary model

in Journal of Marine Systems (2005), 55(3-4), 177-203

A one-dimensional coupled physical-biogeochemical model has been built to study the pelagic food web of the Ligurian Sea (NW Mediterranean Sea). The physical model is the turbulent closure model (version ... [more ▼]

A one-dimensional coupled physical-biogeochemical model has been built to study the pelagic food web of the Ligurian Sea (NW Mediterranean Sea). The physical model is the turbulent closure model (version I D) developed at the GeoHydrodynamics and Environmental Laboratory (GHER) of the University of Liege. The ecosystem model contains 19 state variables describing the carbon and nitrogen cycles of the pelagic food web. Phytoplankton and zooplankton are both divided in three size-based compartments and the model includes an explicit representation of the microbial loop including bacteria, dissolved organic matter, nano-, and microzooplankton. The internal carbon/nitrogen ratio is assumed variable for phytoplankton and detritus, and constant for zooplankton and bacteria. Silicate is considered as a potential limiting nutrient of phytoplankton's growth. The aggregation model described by Kriest and Evans in (Proc. Ind. Acad. Sci., Earth Planet. Sci. 109 (4) (2000) 453) is used to evaluate the sinking rate of particulate detritus. The model is forced at the air-sea interface by meteorological data coming from the "Cote d'Azur" Meteorological Buoy. The dynamics of atmospheric fluxes in the Mediterranean Sea (DYFAMED) time-series data obtained during the year 2000 are used to calibrate and validate the biological model. The comparison of model results within in situ DYFAMED data shows that although some processes are not represented by the model, such as horizontal and vertical advections, model results are overall in agreement with observations and differences observed can be explained with environmental conditions. (c) 2004 Elsevier B.V. All rights reserved. [less ▲]

Influence of the Aral Sea negative water balance on its seasonal circulation patterns: use of a 3D hydrodynamic model

in Journal of Marine Systems (2004), 47(1-4), 51-66

A 3D hydrodynamic model of the Aral Sea was successfully implemented to address the complex hydrodynamic changes induced by the combined effect of hydrologic and climatic change in the Aral region. The ... [more ▼]

A 3D hydrodynamic model of the Aral Sea was successfully implemented to address the complex hydrodynamic changes induced by the combined effect of hydrologic and climatic change in the Aral region. The first barotropic numerical experiments allowed us to produce a comparative description of the mean general seasonal circulation patterns corresponding to the original situation (1956-1960) and of the average situation for the period from 1981 to 1985, a very low river flow period. The dominant anticyclonic circulation suggested by our seasonal simulation is in good agreement with previous investigations. In addition. this main anticyclonic gyre was shown to be stable and clearly established from February to September, while winter winds led to another circulation scenario. In winter, the main anticyclonic gyre was considerably limited, and cyclonic circulations appeared in the deep western basin and in the northeast of the shallow basin. In contrast, stronger anticyclonic circulation was observed in the Small Aral Sea during winter. As a consequence of the 10-m sea level drop observed between the two periods considered, the 1981-1985 simulation suggests an intensification of seasonal variability. Total water transport of the main gyre was reduced with sea level drop by a minimum of 30% in May and up to 54% in September. Before 1960, the study of the net flows through Berg and Kokaral Straits allowed us to evaluate the component of water exchange between the Small and the Large Seas linked with the general anticyclonic circulation around Kokaral Island. This exchange was lowest in summer (with a mean anticyclonic exchange of 222 m(3)/s for July and August), highest in fall and winter (with a mean value of 1356 m(3)/s from September to February) and briefly reversed in the spring (mean cyclonic circulation of 316 m(3)/s for April and May). In summer, the water exchange due to local circulation at the scale of each strait was comparatively more important because net flows through the straits were low. After about 20 years of negative water balance, the western Kokaral Strait was dried up and the depth of Berg Strait was reduced from 15 to 5 m. Simulation indicated a quasi-null net transport, except during the seasonal modification of the circulation pattern, in February and October. A limited, but stable, water exchange of about 100 m(3)/s remained throughout the year, as a result of the permanent superposition of opposite currents. (C) 2004 Elsevier B.V. All rights reserved. [less ▲]

Structural optimisation of steel frames for industrial applications

in Proceedings of the Inverse Problems Design and Optimization Symposium (2004)

The paper reports the first results of a work carried out in close collaboration between Astron Buildings SA, a manufacturer of industrial steel buildings, and different groups of civil engineers and ... [more ▼]

The paper reports the first results of a work carried out in close collaboration between Astron Buildings SA, a manufacturer of industrial steel buildings, and different groups of civil engineers and mathematicians of the University of Liège to develop an automatic design method for structures with tapered members. This research aims at improving the current method of trialerror followed by experienced engineers to optimize the frames constrained by a chosen national construction code and the technological constraints of the producer. The main benefit of this collaboration arises through the application of a mathematical algorithm based on the sequential quadratic programming method (SQP) in order to reduce, in the first step, the weight of the building, under the great number of constraints. The second step, not yet started, will be devoted to the minimization of the real cost of the frame. This report introduces the first results of this industrial application. [less ▲]

The age as a diagnostic of the dynamics of marine ecosystem models

in Ocean Dynamics (2004), 54(2), 221-231

The constituent-oriented age theory (CAT) worked out by Delhez et al. (1999) is a flexible tool that can be applied to diagnose complex models. It is shown here how this can be used to quantify the pace ... [more ▼]

The constituent-oriented age theory (CAT) worked out by Delhez et al. (1999) is a flexible tool that can be applied to diagnose complex models. It is shown here how this can be used to quantify the pace at which an ecosystem model works. At the cost of the introduction of one additional evolution equation for each compartment of the ecosystem model, the mean age of the biological material forming these compartments can be computed. The information obtained in this way complements the information provided by the concentration data; while the latter measures the standing stocks, the former provides an integrated assessment of the interaction rates and matter fluxes. The benefits of the method are demonstrated with a simple Lotka-Volterra system and a one-dimensional vertical model of the nitrogen cycle in the Ligurian Sea. The theory can be used to study the biological compartments individually or the ecosystem as a whole. In particular, the age is a valuable tool to quantify the overall cycling rate of nitrogen in the food web. [less ▲]

Symmetry and asymmetry of water ages in a one-dimensional flow

in Journal of Marine Systems (2004), 48(1-4), 61-66

Hall and Haine [J. Mar. Syst., in press] briefly addressed the problem of estimating the age of irreducible fluid elements or water parcels in a one-dimensional flow with constant velocity and diffusivity ... [more ▼]

Hall and Haine [J. Mar. Syst., in press] briefly addressed the problem of estimating the age of irreducible fluid elements or water parcels in a one-dimensional flow with constant velocity and diffusivity. Herein further developments are achieved on this subject. The age of every water parcel is set to zero at the moment it passes through the point x = 0, where x is an appropriate space coordinate. As time progresses, the age of the water is seen to increase unboundedly upstream of the point x = 0, and tend to the steady-state value \x/u\ downstream of the point x = 0, where a is the water velocity. By contrast, the age of the water parcels that have touched at least once the point x = 0 is symmetric with respect to the point x = 0 is smaller than the water age at any tune and position, and tends to \x/u\ as time progresses. Asymptotic expansions are derived for large times. (C) 2004 Elsevier B.V. All rights reserved. [less ▲]

Identification of elastoplastic model in large deformation problems

in Cinquini, Carlo (Ed.) Proceedings of the 5th World Congress of Structural and Multidisciplinary Optimization WCSMO5 (2003, May)

This paper reports on preliminary results of parameter identification problems in finite element non-linear analyses such as metal forming simulations. Two approaches are compared. The first one is the ... [more ▼]

This paper reports on preliminary results of parameter identification problems in finite element non-linear analyses such as metal forming simulations. Two approaches are compared. The first one is the classic Levenberg-Marquardt algorithm. The second one is a trust-region algorithm based on a quadratic model. The two algorithms are compared on two cases, one of them being an actual experiment. [less ▲]

Influence of the Aral Sea negative water balance on its seasonal circulation : use of a 3D hydrodynamic model

Conference (2003, May)