Publications of Eric Delhez     Results 1-20 of 92. 1 2 3 4 5   Age of Water Particles as a Diagnosis of Steady-state Flows in Shallow Rectangular ReservoirsDewals, Benjamin ; Archambeau, Pierre ; Bruwier, Martin et alin Water (2020), (12), 2819The age of a water particle in a shallow man-made reservoir is defined as the time elapsed since it entered it. Analyzing this diagnostic timescale provides valuable information for optimally sizing and ... [more ▼]The age of a water particle in a shallow man-made reservoir is defined as the time elapsed since it entered it. Analyzing this diagnostic timescale provides valuable information for optimally sizing and operating such structures. Here, the constituent-oriented age and residence time theory (CART) is used to obtain not only the mean age, but also the water age distribution function at each location. The method is applied to 10 different shallow reservoirs of simple geometry (rectangular), in a steady-state framework. The results show that complex, multimodal water age distributions are found, implying that focusing solely on simple statistics (e.g., mean or median age) fails to reflect the complexity of the actual distribution of water age. The latter relates to the fast or slow pathways that water particles may take for traveling from the inlet to the outlet of the reservoirs. [less ▲]Detailed reference viewed: 52 (18 ULiège) Hydrodynamic variability in the Southern Bight of the North Sea in response to typical atmospheric and tidal regimes. Benefit of using a high resolution modelIvanov, Evgeny ; Capet, Arthur ; Barth, Alexander et alin Ocean Modelling (2020), 154In this paper, the hydrodynamics of the Southern Bight of the North Sea (SBNS) and in particular, the Belgian Coastal Zone (BCZ) is investigated on daily to seasonal time scales using a high resolution ... [more ▼]In this paper, the hydrodynamics of the Southern Bight of the North Sea (SBNS) and in particular, the Belgian Coastal Zone (BCZ) is investigated on daily to seasonal time scales using a high resolution hydrodynamical model. The Regional Ocean Modeling System (ROMS) is implemented over the SBNS with 5 km resolution and downscaled at 1 km resolution over the BCZ in a two-way nesting configuration run over a three years period (i.e. 2006–2008). The benefit of using a high resolution model over the BCZ is assessed through an extensive comparison of model results with data from satellite and in-situ fixed platforms as well as reference products available for the region. The validation exercise and the results analysis are conducted with a particular focus on hydrodynamic features that are expected to impact the sediment transport. We find that despite the validation procedure does not allow to clearly demonstrate better performance of the high resolution model compared to the coarse resolution model in terms of overtidal circulation, sea surface temperature (SST) and salinity (SSS), the high resolution model resolves additional details in the variability of residual circulation and Scheldt salinity plume dynamics. The analysis of the response of the simulated hydrodynamics to atmospheric regimes for neap and spring tide highlights the major role played by the wind direction on the averaged currents and plume extension. The strongest currents and minimum plume extension are obtained under southwestern winds and neap tide while when northeastern winds prevail, the plume extension is at its maximum and the circulation is the weakest. We show that while neap tides allow the establishment of streamlined circulation, the spring tides induce more turbulent circulation which can favor the retention of transported elements. This latter property could not be resolved with the 5 km resolution model. [less ▲]Detailed reference viewed: 25 (4 ULiège) Modelling the hydrodynamics of the Southern Bight of the North Sea: Skills assessment of different configurations (i.e. nesting) in the perspective of coupling with sediment transportIvanov, Evgeny ; Capet, Arthur ; Barth, Alexander et alPoster (2018, May)The impact of offshore wind farm installation and dredging activities on the spatial distribution and dynamics of sediment grain size, biogeochemistry and biodiversity will be estimated in the Southern ... [more ▼]The impact of offshore wind farm installation and dredging activities on the spatial distribution and dynamics of sediment grain size, biogeochemistry and biodiversity will be estimated in the Southern Bight of the North Sea (SBNS) with a focus on the Belgian Coastal Zone (BCZ) in the frame of the FaCE-It research project (Functional biodiversity in a Changing sedimentary Environment: Implications for biogeochemistry and food webs in a managerial setting). The three-dimensional hydrodynamical model ROMS-COAWST was implemented for simulation of the complex hydrodynamics of SBNS and sediment transport. The first level of nesting with the resolution of 1 km was used in the area of Belgian Economical Zone. In order to reach a fine resolution of 250 m in the BCZ, the second level of nesting will be used. Six-hourly ECMWF ERA-interim meteorological data was used to force the model at the sea-air boundary and the coarse resolution model results available from Copernicus Marine Environment Monitoring Service were used to force the model at the open boundaries. Tides and rivers were also considered. Next types of long-run simulations have been conducted: a 10-years climatological simulation and an interannual simulation over 2004-2013 in order to investigate the interannual dynamics. The model accuracy was evaluated through validation of its outputs against observed salinity, temperature and currents data (remote sensing and in-situ). Results validation of currents and temperature and salinity horizontal fields and vertical profiles against available satellite fields and in-situ data, i.e. from the project field campaign, is conducted and discussed. Application of the nested grid and its benefits for results accuracy is also presented. [less ▲]Detailed reference viewed: 162 (24 ULiège) Hydrodynamic and sediment transport modelling in the North Sea. Assessment of wind farms impactIvanov, Evgeny ; Capet, Arthur ; Barth, Alexander et alScientific conference (2018, April 26)Detailed reference viewed: 82 (11 ULiège) Application of two way nesting model to upscale sediment processes of the Southern Bight of the North Sea: full model validationIvanov, Evgeny ; Capet, Arthur ; Barth, Alexander et alPoster (2018, March)The BRAIN project FaCE-iT (Functional biodiversity in a Changing sedimentary Environment: Implications for biogeochemistry and food webs in a managerial setting) funded by BELSPO aims at evaluating the ... [more ▼]The BRAIN project FaCE-iT (Functional biodiversity in a Changing sedimentary Environment: Implications for biogeochemistry and food webs in a managerial setting) funded by BELSPO aims at evaluating the influence of offshore wind farms settlements and dredging activities on the distribution of sediment grain size over the Southern Bight of the North Sea (SBNS) and the Belgian Coastal Zone (BCZ), as well as associated impacts on biodiversity and biogeochemistry.In this framework an implementation of the tri-dimensional hydrodynamical and sediment transport model ROMS-COAWST was set-up to conduct scenario experiment relating offshore activities to resulting alteration of the seafloor structure. This implementation combines high resolution nested grids covering the Belgian Coastal Zone, embedded into a coarser grid covering the Southern Bight of the North Sea and is forced by ECMWF ERA-Interim data at the air-sea interface, CMEMS data at the open boundaries, TPXO data to introduce/force the tidal impact, and consider the discharge of four main rivers. Currently, the work focuses on assessing the skills of this modelling system to resolve the dynamics of the complex shallow and highly tidal region. The 3-year climatological run for 2006-2009 was performed to test the model ability to simulate the interannual dynamics. The model skills were evaluated by validation against remote-sensing temperature fields, tidal elevations and currents at the Meetnet pylons, and in situ temperature and salinity data provided by the Lifewatch network. We evaluate how grid refinement and different set-up of the nesting strategy enhance essential model skills in relation with sediment transport The further step will be to confront the sediment transport dynamics stemming from the nested system to that resolved from the coarser parent alone. A diagenetic model developed in the frame of FaCE-iT will be joint with the sediment model in order to upscale locally derived alteration of the biogeochemistry and benthic functionality stemming from seafloor texture alteration. [less ▲]Detailed reference viewed: 51 (7 ULiège) Three-dimensional modelling of the hydrodynamics of the Southern Bight of the North Sea: first resultsIvanov, Evgeny ; Capet, Arthur ; Barth, Alexander et alPoster (2017, April 28)In the frame of the Belgian research project FaCE-It (Functional biodiversity in a Changing sedimentary Environment: Implications for biogeochemistry and food webs in a managerial setting), the impact of ... [more ▼]In the frame of the Belgian research project FaCE-It (Functional biodiversity in a Changing sedimentary Environment: Implications for biogeochemistry and food webs in a managerial setting), the impact of dredging activities andoffshorewindfarminstallationonthespatialdistributionofsedimentgrainsize,biodiversityandbiogeochemistry will be estimated in the Southern Bight of the North Sea (SBNS) with a focus on the Belgian Coastal Zone (BCZ). To reach this goal, the three-dimensional hydrodynamical model ROMS-COAWST is implemented in the SBNS in order to simulate the complex hydrodynamics and sediment transport. Two levels of nesting are used to reach a resolutionof250mintheBCZ.Themodelisforcedattheair-seainterfacebythe6-hourlyECMWFERA-interim atmospheric dataset and at the open boundaries by the coarse resolution model results available from CMEMS (Copernicus Marine Environment Monitoring Service), and also considers tides and 4 main rivers (Scheldt, Rhine with Maas, Thames and Seine). Two types of simulations have been performed: a 10-years climatological simulation and a simulation over 20032013toinvestigatetheinterannualdynamics.Themodelskillsareevaluatedbycomparingitsoutputstohistorical data (e.g. salinity, temperature and currents) from remote sensing and in-situ. The sediment transport module will then be implemented and its outputs compared to historical and newly collected (in the frame of FaCE-iT) observations on grain size distribution as well as with satellite Suspended Particulate Matter (SPM) images. This will allow assessing the impact of substrate modiﬁcation due to offshore human activities at local and regional scales. [less ▲]Detailed reference viewed: 78 (18 ULiège) Three-dimensional modelling of the Southern Bight of the North Sea: first results and perspectivesIvanov, Evgeny ; Capet, Arthur ; Barth, Alexander et alPoster (2017, March 03)The impact of offshore wind farm installation and dredging activities on the spatial distribution and dynamics of sediment grain size, biogeochemistry and biodiversity will be estimated in the Southern ... [more ▼]The impact of offshore wind farm installation and dredging activities on the spatial distribution and dynamics of sediment grain size, biogeochemistry and biodiversity will be estimated in the Southern Bight of the North Sea (SBNS) with a focus on the Belgian Coastal Zone (BCZ) in the frame of the FaCE-It research project (Functional biodiversity in a Changing sedimentary Environment: Implications for biogeochemistry and food webs in a managerial setting). The three-dimensional hydrodynamical model ROMS-COAWST was implemented for simulation of the complex hydrodynamics of SBNS and sediment transport. The first level of nesting with the resolution of 1 km was used in the area of Belgian Economical Zone. In order to reach a fine resolution of 250 m in the BCZ, the second level of nesting will be used. Six-hourly ECMWF ERA-interim meteorological data was used to force the model at the sea-air boundary and the coarse resolution model results available from Copernicus Marine Environment Monitoring Service were used to force the model at the open boundaries. Tides and rivers were also considered. Next types of long-run simulations have been conducted: a 10-years climatological simulation and an interannual simulation over 2004-2013 in order to investigate the interannual dynamics. The model accuracy was evaluated through validation of its outputs against observed salinity, temperature and currents data (remote sensing and in-situ). Results validation of currents and temperature and salinity horizontal fields and vertical profiles against available satellite fields and in-situ data, i.e. from the project field campaign, is conducted and discussed. Application of the nested grid and its benefits for results accuracy is also presented. [less ▲]Detailed reference viewed: 62 (7 ULiège) Developing a hydrodynamical model of the Southern Bight of the North Sea for impact studiesIvanov, Evgeny ; Capet, Arthur ; Barth, Alexander et alPoster (2016, November 08)In the frame of the Brain FaCE-It project (Functional biodiversity in a Changing sedimentary Environment: Implications for biogeochemistry and food webs in a managerial setting), the impact of fining and ... [more ▼]In the frame of the Brain FaCE-It project (Functional biodiversity in a Changing sedimentary Environment: Implications for biogeochemistry and food webs in a managerial setting), the impact of fining and hardening resulting from dredging and wind farms installation on the sediment grain size distribution has to be assessed at the scale of the Southern Bight of the North Sea (SBNS) with a particular focus on the Belgian Coastal Zone (BCZ). With this aim, the ROMS-COAWST tri-dimensional (3D) hydrodynamic model is implemented to simulate the hydrodynamics in the SBNS. At its open boundaries with the Atlantic Ocean and the North Sea, the model is forced with the results of a coarse resolution model available from Mercator. A high resolution of 250 m is used in the area of the BCZ where the accuracy of model predictions needs to be refined. Model currents, tides, temperature and salinity fields will be described and first validation exercises with satellite and local data will be presented and discussed in regards with the objectives of FaCE-It. In a next step, the model will be coupled with a sediment transport in order to describe the dynamics of suspended particulate materials (SPM) and the distribution of the seafloor sediment grain size. When finalized the hydrodynamic model will be coupled with a diagenetic model and will provide environmental conditions for scaling up local foodweb studies that are performed in the frame of FaCE-iT. The final aim is to assess the impact of substrate modifications due to aggregate extraction and wind farms on the biogeochemistry, benthic functionality and food webs at local (around the wind farm) and regional scales (SBNS). [less ▲]Detailed reference viewed: 49 (9 ULiège) Partial ages: diagnosing transport processes by means of multiple clocks.Mouchet, Anne ; Cornaton, Fabien; Deleersnijder, Eric et alin Ocean Dynamics (2016), 66Detailed reference viewed: 90 (16 ULiège) Benthic-Planktonic age biases: theoretical and modeling studiesMouchet, Anne ; Deleersnijder, Eric; Delhez, Eric et alConference (2015, June 25)Detailed reference viewed: 53 (6 ULiège) Optimizing Perfectly Matched Layers in Discrete ContextsModave, Axel ; Delhez, Eric ; Geuzaine, Christophe in International Journal for Numerical Methods in Engineering (2014), 99(6), 410437Perfectly Matched Layers (PMLs) are widely used for the numerical simulation of wave-like problems defined on large or infinite spatial domains. However, for both the time-dependent and the time-harmonic ... [more ▼]Perfectly Matched Layers (PMLs) are widely used for the numerical simulation of wave-like problems defined on large or infinite spatial domains. However, for both the time-dependent and the time-harmonic cases, their performance critically depends on the so-called absorption function. This paper deals with the choice of this function when classical numerical methods are used (based on finite differences, finite volumes, continuous finite elements and discontinuous finite elements). After reviewing the properties of the PMLs at the continuous level, we analyse how they are altered by the different spatial discretizations. In the light of these results, different shapes of absorption function are optimized and compared by means of both one- and two-dimensional representative time-dependent cases. This study highlights the advantages of the so-called shifted hyperbolic function, which is efficient in all cases and does not require the tuning of a free parameter, by contrast with the widely used polynomial functions. [less ▲]Detailed reference viewed: 175 (37 ULiège) Factors influencing radiocarbon-based estimates of ocean ventilation: theory and modelsMouchet, Anne ; Beckers, Jean-Marie ; Deleersnijder, Eric et alConference (2014, May 29)Detailed reference viewed: 31 (2 ULiège) The concept of partial age, a generalisation of the notion of age: theory, idealised illustrations and realistic applicationsDeleersnijder, Eric; Mouchet, Anne ; Debrauwere, Anouk et alConference (2014, May 12)Detailed reference viewed: 45 (3 ULiège) Processes affecting radiocarbon estimates of ocean ventilation: theory and modelsMouchet, Anne ; Deleersnijder, Eric; Delhez, Eric et alConference (2014, May 07)Detailed reference viewed: 30 (0 ULiège) Residence time vs influence timeDelhez, Eric ; de Brye, Bejamin; de Brauwere, Anouk et alin Journal of Marine Systems (2014), 132The concepts of age, residence time, exposure time and influence time provide space and time dependent quantitative measures of the rate at which watermasses and pollutants enter and/or leave a control ... [more ▼]The concepts of age, residence time, exposure time and influence time provide space and time dependent quantitative measures of the rate at which watermasses and pollutants enter and/or leave a control domain. To help avoid confusion between these concepts, this paper provides clear definitions of the residence time and the influence time. The similarities and differences between them are illustrated using both a simplified 1D advection–diffusion model and a realistic two-dimensional model of the Scheldt Estuary (Belgium and the Netherlands). The residence time of a water parcel in a control domain is the time taken by this parcel to leave the control domain for the first time. The influence time is the time required to replace the water in the domain of interest by renewing water. For steady flows, the influence time is numerically identical to the age of the renewing water, but the two timescales differ for unsteady flows. The residence timemeasures the influence of a hypothetical point discharge on a control domain. In environmental studies, it provides a measure of the effectiveness of hydrodynamic processes at helping a semi-enclosed basin to recover froma local pollution event. The influence time quantifies the local influence of a tracer that would be uniformly distributed in the control domain at the initial time. It is therefore a relevant diagnostic tool in impact studies focusing on the local persistence of a pollution problem. [less ▲]Detailed reference viewed: 97 (26 ULiège) Diagnosis of the transport of adsorbed material in the Scheldt estuary: A proof of conceptDelhez, Eric ; Wolk, Frank in Journal of Marine Systems (2013), 128Many contaminants can attach to suspended particles. Their transport differs therefore from the transport of dissolved substances, especially in highly turbid environment like estuaries. In this paper, we ... [more ▼]Many contaminants can attach to suspended particles. Their transport differs therefore from the transport of dissolved substances, especially in highly turbid environment like estuaries. In this paper, we show how the Constituent Age and Residence time Theory (CART — www.climate.be/CART) can be adapted to quantify in a rigorous manner the transport rate of contaminants that are present in both the dissolved and adsorbed phases. On the basis of numerical experiment using a 1D model of the Scheldt estuary, it is shown that the interaction with suspended particles significantly affects the transport of contaminants with partition coefficients larger than 1000 ml/g. The mean transit time from Ghent to Vlissingen of such contaminants can reach 160 days while it is only 60 days for water and dissolved constituents. This increase of the transit time is mainly due to the fact that adsorbed constituents spend long periods of time on the bottom. Surprisingly, the downstream transport of adsorbed constituents in the water column appears more effective than that of dissolved constituents. This transport affects however a small fraction of the adsorbed constituent and is therefore not sufficient to compensate for the long resting phase on the bottom of the bulk of the constituent. The concept and methodology introduced in this paper are easily applicable to most model studies and provide powerful and flexible tools for the detailed understanding of the transport of contaminants in estuaries. In particular, the concept of age and modified ages taking into account specifically the time spent in the water column or in the bottom provide new diagnostic tools to understand and quantify the dynamics of contaminants. [less ▲]Detailed reference viewed: 174 (42 ULiège) Modelling phytoplankton succession and nutrient transfer along the Scheldt estuary (Belgium, The Netherlands)Gypens, N.; Delhez, Eric ; Vanhoutte-Brunier, A. et alin Journal of Marine Systems (2013), 128Detailed reference viewed: 25 (2 ULiège) An optimum PML for scattering problems in the time domainModave, Axel ; Kameni, Abelin; Lambrechts, Jonathan et alin European Physical Journal: Applied Physics (2013), 64(2), 24502In electromagnetic compatibility, scattering problems are defined in an infinite spatial domain, while numerical techniques such as finite element methods require a computational domain that is bounded ... [more ▼]In electromagnetic compatibility, scattering problems are defined in an infinite spatial domain, while numerical techniques such as finite element methods require a computational domain that is bounded. The perfectly matched layer (PML) is widely used to simulate the truncation of the computational domain. However, its performance depends critically on an absorption function. This function is generally tuned by using case-dependent optimization procedures. In this paper, we will present some efficient functions that overcome any tuning. They will be compared using a realistic scattering benchmark solved with the Discontinuous Galerkin method. [less ▲]Detailed reference viewed: 137 (37 ULiège) A PML for convex truncated domains in time-dependent acoustics with a DG-FE discretizationModave, Axel ; Lambrechts, Jonathan; Delhez, Eric et alin Proceedings of the 11th International Conference on Mathematical and Numerical Aspects of Waves (WAVES 2013) (2013, June 03)A new perfectly matched layer (PML) is proposed for convex truncated domains in the context of time-dependent acoustics. With this formulation, the size of the computational domain can be reduced when ... [more ▼]A new perfectly matched layer (PML) is proposed for convex truncated domains in the context of time-dependent acoustics. With this formulation, the size of the computational domain can be reduced when classical shapes of truncated domains are less appropriate. A numerical discretization based on the discontinuous Galerkin method is then described and validated. An example of realistic three-dimensional application is finally proposed. [less ▲]Detailed reference viewed: 138 (37 ULiège) On the concept of exposure timeDelhez, Eric in Continental Shelf Research (2013), 71The concept of exposure time offers an interesting alternative to the residence time for the quantitative assessment of the water renewal of estuaries and semi-enclosed basins. It can cope with the ... [more ▼]The concept of exposure time offers an interesting alternative to the residence time for the quantitative assessment of the water renewal of estuaries and semi-enclosed basins. It can cope with the oscillations or meandering of the flow around the boundary of the control domain and is therefore particularly suited for tidal seas and sub-basins with strong mesoscale activity. We show however that the exposure time in a control domain \omega cannot be properly defined if \omega is part of a larger bounded system unless some removal process is taken into account. It is therefore suggested to revise and extend the definition of the exposure time by including a first order decay : the exposure time for the rate constant \lambda is the total time spent in a control domain \omega by particles subject to a first order decay with a rate constant $\lambda$, irrespective of their possible excursions in and out the control domain''. The exposure time revised in this way is well-defined in all circumstances provided that the decay rate differs from zero but depends on the rate constant \lambda. Alternatively, in order to diagnose the movement of water masses, the first order decay can be considered only outside the control domain. [less ▲]Detailed reference viewed: 90 (24 ULiège) 1 2 3 4 5