Ata Bilgili - Academia.edu (original) (raw)
Papers by Ata Bilgili
Regional Studies in Marine Science
WIT transactions on engineering sciences, 1970
Current, sea level and bed load transport are investigated in the Great Bay Estuary, New Hampshir... more Current, sea level and bed load transport are investigated in the Great Bay Estuary, New Hampshire, U.S.A. a well-mixed system with low freshwater flow and having main channel tidal currents over 2 m/sec. Current and sea level forced by the Mi-Mi-Ma tide at the estuary mouth are simulated by a vertically averaged, nonlinear, time-stepping, finite-element model. The hydrodynamic model uses a fixed boundary computation domain and accounts for flooding-dewatering over tidal flats by making use of a groundwater component. Inertia terms are neglected in comparison with pressure gradient and bottom friction terms, which is consistent with the observed principal dynamic balance for this system. The accuracy of the hydrodynamic predictions is demonstrated by comparison with 5 tidal elevation stations and 2 cross-sectional ly averaged current measurements. Simulated current and bottom stress are then used to model bed load transport in the vicinity of a rapidly growing shoal located in the m...
The formation of a shoal was investigated in the Piscataqua River, New Hampshire, which is a well... more The formation of a shoal was investigated in the Piscataqua River, New Hampshire, which is a well-mixed channel with low freshwater flow and tidal currents up to 2.3 m s-1. Observations of sediment characteristics, bathymetry, and bottom current were made, and theory was used to predict bedload transport. Sediment sampling showed the bottom material to be coarse sand and gravel, and sidescan sonar revealed large sand waves directed upriver at the shoal. Bottom current measurements were made along transects upriver and downriver of the shoal and downriver of an adjacent deep- water area that was also studied for comparison. Bedload flux inferred from current measurements using the Brown- Einstein theory indicated that transport is generally directed upriver. Sediment budget calculations showed the shoal area to be depositional before, immediately after, and subsequent to a dredging operation at rates of 0.36 m yr-1, 1.06 m yr- , and 0.35 m yr-1, respectively. Predredge and subsequent...
Environmental Problems in Coastal Regions VI, 2006
A 2-D hydrodynamic finite element model with a Lagrangian particle module is used to investigate ... more A 2-D hydrodynamic finite element model with a Lagrangian particle module is used to investigate the effects of dredging on the horizontal dilution of pollutant particles originating from a Wastewater Treatment Facility (WWTF) in a tidal river. The model is driven by the semi-diurnal (M 2) tidal component and includes the effect of flooding and drying of mud flats. The particle tracking method consists of tidal advection plus a horizontal random walk model of subgrid scale turbulent processes. Our approach is to perform continuous pollutant particle releases from the outfall, simulating three different scenarios: a basecase representing the present conditions and two different dredged channel / outfall location configurations. Lagrangian particle concentrations are simulated on finite elements and dilution improvement ratios are presented for both scenarios. Results show that although no particles leave the river in a single M 2 cycle, flushing takes place in longer time scales. Simulated dilution maps show that relocation of the WWTF outfall into the dredged main channel is required for increased dilution performance. The addition of a pool at the head of the river also improves dilution by adding to the tidal volume. Case oriented short-term investigations of coastal hydrodynamic problems suitable for Lagrangian particle methods should be encouraged to improve our knowledge of estuarine processes and how we model them while providing solutions to the management community in time and budget constrained decision making.
Journal of Environmental Management, 2016
A 2-D hydrodynamic finite element model with a Lagrangian particle module is used to investigate ... more A 2-D hydrodynamic finite element model with a Lagrangian particle module is used to investigate the effects of dredging on the hydrodynamics and the horizontal dilution of pollutant particles originating from a wastewater treatment facility (WWTF) in tidal Oyster River in New Hampshire, USA. The model is driven by the semi-diurnal (M2) tidal component and includes the effect of flooding and drying of riverine mud flats. The particle tracking method consists of tidal advection plus a horizontal random walk model of sub-grid scale turbulent processes. Our approach is to perform continuous pollutant particle releases from the outfall, simulating three different scenarios: a base-case representing the present conditions and two different dredged channel/outfall location configurations. Hydrodynamics are investigated in an Eulerian framework and Lagrangian particle dilution improvement ratios are calculated for all cases. Results show that the simulated hydrodynamics are consistent with observed conditions. Eulerian and Lagrangian residuals predict an outward path suggesting flushing of pollutants on longer (>M2) time scales. Simulated dilution maps show that, in addition to dredging, the relocation of the WWTF outfall into the dredged main channel is required for increased dilution performance. The methodology presented here can be applied to similar managerial problems in all similar systems worldwide with relatively little effort, with the combination of Lagrangian and Eulerian methods working together towards a better solution. The statistical significance brought into methodology, by using a large number of particles (16000 in this case), is to be emphasized, especially with the growing number of networked parallel computer clusters worldwide. This paper improves on the study presented in Bilgili et al., 2006b, by adding an Eulerian analysis.
Oceans '04 MTS/IEEE Techno-Ocean '04 (IEEE Cat. No.04CH37600)
Most data visualization systems only show static data or produce "canned" movies of time-varying ... more Most data visualization systems only show static data or produce "canned" movies of time-varying data. Others incorporate visualization in real-time monitoring but these are generally customized to the particular application. The ability to interactively navigate through geospatial data is common but interactive navigation along the time dimension is not. And yet, visualization of data from interacting dynamic systems is increasingly necessary to interpret biological process, physical oceanographic processes, the motion of instrument platforms (such as ships, ROVs and AUVs), and the interactions between all of these. To address this need, we have enhanced our GeoZui3D system so that it seamlessly handles multiple time varying data sets: anything can be handled that can be represented through time varying surfaces, curved colored lines, curved colored tubes, arrow arrays, or color-, shape-, and size-coded points. The system can be used in both real-time and replay modes and data sets that have different sampling rates can still be visualized together. GeoZui3D can visualize events over a wide range of time scales from sensor readings at the millisecond scale to glacial movements evolving over tens of thousands of years. The system is illustrated with examples from collaborative research projects including modeled ocean and estuarine currents, tides, ship movements, changes in surface topography, AUV and ROV movements and the movements of marine mammals.
Water Quality, Exposure and Health, 2014
The establishment of numeric nutrient criteria for the Great Bay Estuary System (GBES) to improve... more The establishment of numeric nutrient criteria for the Great Bay Estuary System (GBES) to improve water quality used a computer modeling approach to determine how much of the waste water treatment facility (WWTF) discharges were responsible for nitrogen entering GBES. The Great Bay Estuary, located in southeastern New Hampshire, is a relatively shallow (a tidal amplitude to mean depth ratio of 0.18), well-mixed tidal estuary with a wet area of 24 km 2 and a main channel length of approximately 26 km. The dominant tide is the principal lunar (M2). The modeling approach includes both a finite element, two-dimensional, vertically averaged, time stepping circulation model, and a Lagrangian particle tracking module. The spatial discretization uses finite element triangles with a characteristic length (√ 2 A where A is the triangle area) of roughly 3 m in the estuary. The time discretization uses a time step of 99.36 s. The particle model does not include vertical motion, and the particles are neutrally buoyant passive particles. Several WWTF discharges were selected and run separately as a continuous release of conservative particles. The percentages of particles residing in each region at the end of the simulation time (65 days) from each source were summarized to allow comparison. In addi-C. Swanson (B) RPS ASA,
Computational Methods in Water Resources: Volume 2, Proceedings of the XVth International Conference on Computational Methods in Water Resources, 2004
A Lagrangian particle method which has been parallelized and embedded within a 2-D finite element... more A Lagrangian particle method which has been parallelized and embedded within a 2-D finite element code is used to study the transport and fate of contaminant plumes and ocean-estuary exchange processes in a well-mixed Gulf of Maine estuary. The particle method has been extended to include a random walk model in the horizontal that simulates sub-grid scale turbulent transport processes. This module has been formulated to allow for spatial variability in the diffusivity. The 2-D finite element model includes a porous medium transport module to treat the effects of wetting and drying of estuarine tidal flats. Due to the highly-complex, spatially dependent nature of tidal mixing and shear dispersion, contaminant transport is most naturally addressed through the Lagrangian methodology. Our approach involves instantaneous, massive particle releases that enable the quantification of ocean-estuary and inter-bay exchange along with the associated residence time. The results show that estuary-ocean exchange is significantly enhanced, and hence residence times reduced, by the presence of turbulent mixing, which combines with the effects of the sheared tidal currents to drive strong interbay exchange, and/or river input, which drives a mean throughflow. The particle approach helps to uncover the strong spatial dependent nature of the residence time within the estuary which has important ramifications for local water quality. The interbay exchanges are considered as a Markov process as discussed by Thompson et al. [11] and this framework is found to be useful.
Estuarine and Coastal Modeling (2005), 2006
Hog Island Bay, Virginia, is a shallow back barrier lagoon that is subject to seasonal inputs of ... more Hog Island Bay, Virginia, is a shallow back barrier lagoon that is subject to seasonal inputs of inorganic nitrogen and related episodes of hypoxia. Numerical simulations were carried out to estimate the importance of physical flushing times relative to biochemical turnover times known to be a few days or less within the system. A 2D vertically averaged finite element hydrodynamic model, which was designed to accommodate regular flooding and dewatering of shallow flats and marshes, was coupled with a particle tracking model to estimate median lagoon residence time and the spatial distribution of local residence time in the lagoon. The model was forced with observed tidal elevations and winds from the end of the growing season when hypoxia tends to occur. The median residence time estimated by numerical modeling is on the order of weeks (358 hours), and variations in tidal stage, tidal range and wind produced deviations in median residence time on the order of days. Residence times near the inlets were very short, while those near the mainland were long, showing that (i) horizontal mixing in the Bay is insufficient to successfully apply integral methods to obtain residence times, and (ii) residence times near the mainland are long compared to timescales of biologically driven chemical transformations.
Particles in the Coastal Ocean Theory and Applications
Particles in the Coastal Ocean Theory and Applications
Particles in the Coastal Ocean Theory and Applications
Particles in the Coastal Ocean Theory and Applications
Particles in the Coastal Ocean Theory and Applications
Particles in the Coastal Ocean Theory and Applications
Particles in the Coastal Ocean Theory and Applications
Particles in the Coastal Ocean Theory and Applications
Particles in the Coastal Ocean Theory and Applications
Particles in the Coastal Ocean Theory and Applications
Particles in the Coastal Ocean Theory and Applications
Regional Studies in Marine Science
WIT transactions on engineering sciences, 1970
Current, sea level and bed load transport are investigated in the Great Bay Estuary, New Hampshir... more Current, sea level and bed load transport are investigated in the Great Bay Estuary, New Hampshire, U.S.A. a well-mixed system with low freshwater flow and having main channel tidal currents over 2 m/sec. Current and sea level forced by the Mi-Mi-Ma tide at the estuary mouth are simulated by a vertically averaged, nonlinear, time-stepping, finite-element model. The hydrodynamic model uses a fixed boundary computation domain and accounts for flooding-dewatering over tidal flats by making use of a groundwater component. Inertia terms are neglected in comparison with pressure gradient and bottom friction terms, which is consistent with the observed principal dynamic balance for this system. The accuracy of the hydrodynamic predictions is demonstrated by comparison with 5 tidal elevation stations and 2 cross-sectional ly averaged current measurements. Simulated current and bottom stress are then used to model bed load transport in the vicinity of a rapidly growing shoal located in the m...
The formation of a shoal was investigated in the Piscataqua River, New Hampshire, which is a well... more The formation of a shoal was investigated in the Piscataqua River, New Hampshire, which is a well-mixed channel with low freshwater flow and tidal currents up to 2.3 m s-1. Observations of sediment characteristics, bathymetry, and bottom current were made, and theory was used to predict bedload transport. Sediment sampling showed the bottom material to be coarse sand and gravel, and sidescan sonar revealed large sand waves directed upriver at the shoal. Bottom current measurements were made along transects upriver and downriver of the shoal and downriver of an adjacent deep- water area that was also studied for comparison. Bedload flux inferred from current measurements using the Brown- Einstein theory indicated that transport is generally directed upriver. Sediment budget calculations showed the shoal area to be depositional before, immediately after, and subsequent to a dredging operation at rates of 0.36 m yr-1, 1.06 m yr- , and 0.35 m yr-1, respectively. Predredge and subsequent...
Environmental Problems in Coastal Regions VI, 2006
A 2-D hydrodynamic finite element model with a Lagrangian particle module is used to investigate ... more A 2-D hydrodynamic finite element model with a Lagrangian particle module is used to investigate the effects of dredging on the horizontal dilution of pollutant particles originating from a Wastewater Treatment Facility (WWTF) in a tidal river. The model is driven by the semi-diurnal (M 2) tidal component and includes the effect of flooding and drying of mud flats. The particle tracking method consists of tidal advection plus a horizontal random walk model of subgrid scale turbulent processes. Our approach is to perform continuous pollutant particle releases from the outfall, simulating three different scenarios: a basecase representing the present conditions and two different dredged channel / outfall location configurations. Lagrangian particle concentrations are simulated on finite elements and dilution improvement ratios are presented for both scenarios. Results show that although no particles leave the river in a single M 2 cycle, flushing takes place in longer time scales. Simulated dilution maps show that relocation of the WWTF outfall into the dredged main channel is required for increased dilution performance. The addition of a pool at the head of the river also improves dilution by adding to the tidal volume. Case oriented short-term investigations of coastal hydrodynamic problems suitable for Lagrangian particle methods should be encouraged to improve our knowledge of estuarine processes and how we model them while providing solutions to the management community in time and budget constrained decision making.
Journal of Environmental Management, 2016
A 2-D hydrodynamic finite element model with a Lagrangian particle module is used to investigate ... more A 2-D hydrodynamic finite element model with a Lagrangian particle module is used to investigate the effects of dredging on the hydrodynamics and the horizontal dilution of pollutant particles originating from a wastewater treatment facility (WWTF) in tidal Oyster River in New Hampshire, USA. The model is driven by the semi-diurnal (M2) tidal component and includes the effect of flooding and drying of riverine mud flats. The particle tracking method consists of tidal advection plus a horizontal random walk model of sub-grid scale turbulent processes. Our approach is to perform continuous pollutant particle releases from the outfall, simulating three different scenarios: a base-case representing the present conditions and two different dredged channel/outfall location configurations. Hydrodynamics are investigated in an Eulerian framework and Lagrangian particle dilution improvement ratios are calculated for all cases. Results show that the simulated hydrodynamics are consistent with observed conditions. Eulerian and Lagrangian residuals predict an outward path suggesting flushing of pollutants on longer (>M2) time scales. Simulated dilution maps show that, in addition to dredging, the relocation of the WWTF outfall into the dredged main channel is required for increased dilution performance. The methodology presented here can be applied to similar managerial problems in all similar systems worldwide with relatively little effort, with the combination of Lagrangian and Eulerian methods working together towards a better solution. The statistical significance brought into methodology, by using a large number of particles (16000 in this case), is to be emphasized, especially with the growing number of networked parallel computer clusters worldwide. This paper improves on the study presented in Bilgili et al., 2006b, by adding an Eulerian analysis.
Oceans '04 MTS/IEEE Techno-Ocean '04 (IEEE Cat. No.04CH37600)
Most data visualization systems only show static data or produce "canned" movies of time-varying ... more Most data visualization systems only show static data or produce "canned" movies of time-varying data. Others incorporate visualization in real-time monitoring but these are generally customized to the particular application. The ability to interactively navigate through geospatial data is common but interactive navigation along the time dimension is not. And yet, visualization of data from interacting dynamic systems is increasingly necessary to interpret biological process, physical oceanographic processes, the motion of instrument platforms (such as ships, ROVs and AUVs), and the interactions between all of these. To address this need, we have enhanced our GeoZui3D system so that it seamlessly handles multiple time varying data sets: anything can be handled that can be represented through time varying surfaces, curved colored lines, curved colored tubes, arrow arrays, or color-, shape-, and size-coded points. The system can be used in both real-time and replay modes and data sets that have different sampling rates can still be visualized together. GeoZui3D can visualize events over a wide range of time scales from sensor readings at the millisecond scale to glacial movements evolving over tens of thousands of years. The system is illustrated with examples from collaborative research projects including modeled ocean and estuarine currents, tides, ship movements, changes in surface topography, AUV and ROV movements and the movements of marine mammals.
Water Quality, Exposure and Health, 2014
The establishment of numeric nutrient criteria for the Great Bay Estuary System (GBES) to improve... more The establishment of numeric nutrient criteria for the Great Bay Estuary System (GBES) to improve water quality used a computer modeling approach to determine how much of the waste water treatment facility (WWTF) discharges were responsible for nitrogen entering GBES. The Great Bay Estuary, located in southeastern New Hampshire, is a relatively shallow (a tidal amplitude to mean depth ratio of 0.18), well-mixed tidal estuary with a wet area of 24 km 2 and a main channel length of approximately 26 km. The dominant tide is the principal lunar (M2). The modeling approach includes both a finite element, two-dimensional, vertically averaged, time stepping circulation model, and a Lagrangian particle tracking module. The spatial discretization uses finite element triangles with a characteristic length (√ 2 A where A is the triangle area) of roughly 3 m in the estuary. The time discretization uses a time step of 99.36 s. The particle model does not include vertical motion, and the particles are neutrally buoyant passive particles. Several WWTF discharges were selected and run separately as a continuous release of conservative particles. The percentages of particles residing in each region at the end of the simulation time (65 days) from each source were summarized to allow comparison. In addi-C. Swanson (B) RPS ASA,
Computational Methods in Water Resources: Volume 2, Proceedings of the XVth International Conference on Computational Methods in Water Resources, 2004
A Lagrangian particle method which has been parallelized and embedded within a 2-D finite element... more A Lagrangian particle method which has been parallelized and embedded within a 2-D finite element code is used to study the transport and fate of contaminant plumes and ocean-estuary exchange processes in a well-mixed Gulf of Maine estuary. The particle method has been extended to include a random walk model in the horizontal that simulates sub-grid scale turbulent transport processes. This module has been formulated to allow for spatial variability in the diffusivity. The 2-D finite element model includes a porous medium transport module to treat the effects of wetting and drying of estuarine tidal flats. Due to the highly-complex, spatially dependent nature of tidal mixing and shear dispersion, contaminant transport is most naturally addressed through the Lagrangian methodology. Our approach involves instantaneous, massive particle releases that enable the quantification of ocean-estuary and inter-bay exchange along with the associated residence time. The results show that estuary-ocean exchange is significantly enhanced, and hence residence times reduced, by the presence of turbulent mixing, which combines with the effects of the sheared tidal currents to drive strong interbay exchange, and/or river input, which drives a mean throughflow. The particle approach helps to uncover the strong spatial dependent nature of the residence time within the estuary which has important ramifications for local water quality. The interbay exchanges are considered as a Markov process as discussed by Thompson et al. [11] and this framework is found to be useful.
Estuarine and Coastal Modeling (2005), 2006
Hog Island Bay, Virginia, is a shallow back barrier lagoon that is subject to seasonal inputs of ... more Hog Island Bay, Virginia, is a shallow back barrier lagoon that is subject to seasonal inputs of inorganic nitrogen and related episodes of hypoxia. Numerical simulations were carried out to estimate the importance of physical flushing times relative to biochemical turnover times known to be a few days or less within the system. A 2D vertically averaged finite element hydrodynamic model, which was designed to accommodate regular flooding and dewatering of shallow flats and marshes, was coupled with a particle tracking model to estimate median lagoon residence time and the spatial distribution of local residence time in the lagoon. The model was forced with observed tidal elevations and winds from the end of the growing season when hypoxia tends to occur. The median residence time estimated by numerical modeling is on the order of weeks (358 hours), and variations in tidal stage, tidal range and wind produced deviations in median residence time on the order of days. Residence times near the inlets were very short, while those near the mainland were long, showing that (i) horizontal mixing in the Bay is insufficient to successfully apply integral methods to obtain residence times, and (ii) residence times near the mainland are long compared to timescales of biologically driven chemical transformations.
Particles in the Coastal Ocean Theory and Applications
Particles in the Coastal Ocean Theory and Applications
Particles in the Coastal Ocean Theory and Applications
Particles in the Coastal Ocean Theory and Applications
Particles in the Coastal Ocean Theory and Applications
Particles in the Coastal Ocean Theory and Applications
Particles in the Coastal Ocean Theory and Applications
Particles in the Coastal Ocean Theory and Applications
Particles in the Coastal Ocean Theory and Applications
Particles in the Coastal Ocean Theory and Applications
Particles in the Coastal Ocean Theory and Applications