Idealized Model

14,000,000 Leading Edge Experts on the ideXlab platform

Scan Science and Technology

Contact Leading Edge Experts & Companies

Scan Science and Technology

Contact Leading Edge Experts & Companies

The Experts below are selected from a list of 249 Experts worldwide ranked by ideXlab platform

Pieter C. Roos - One of the best experts on this subject based on the ideXlab platform.

  • Three-dimensional semi-Idealized Model for estuarine turbidity maxima in tidally dominated estuaries
    Ocean Modelling, 2017
    Co-Authors: Mohit Kumar, Henk M. Schuttelaars, Pieter C. Roos
    Abstract:

    Abstract We develop a three-dimensional Idealized Model that is specifically aimed at gaining insight in the physical mechanisms resulting in the formation of estuarine turbidity maxima in tidally dominated estuaries. First, the three-dimensional equations for water motion and suspended sediment concentration together with the so-called morphodynamic equilibrium condition, are scaled. Next, surface elevation, velocity and sediment concentration are expanded in a small parameter ϵ = A ¯ M 2 / H , where A ¯ M 2 is the mean amplitude of the M2 tide and H is the mean water depth at the seaward side. This results in a system of equations at each order in this small parameter. This ordering allows solving for the vertical structure of the velocity and suspended sediment concentration, independently of the horizontal dimension. After obtaining these vertical structures, the horizontal dependencies of the physical variables follow from solving a two-dimensional elliptic partial differential equation for the surface elevation. The availability of fine sediments in the estuary follows from a two-dimensional elliptic partial differential equation which results from requiring the system to be in morphodynamic equilibrium, and prescribing the total amount of easily erodible sediments available in the estuary. These elliptic equations for the surface elevation and sediment availability are solved numerically using the finite element method with cubic polynomials as basis functions. As a first application, the Model is applied to the Ems estuary using a simplified geometry and bathymetric profiles characteristic for the years 1980 and 2005. The availability of fine sediments and location of maximum concentration are investigated for different lateral depth profiles. In the first experiment, a uniform lateral depth is considered. In this case, both the sediment availability and suspended sediment concentration are, as expected, uniform in the lateral direction. In 1980, the sediment is mainly trapped near the entrance, while in 2005, the sediment is mostly trapped in the freshwater zone. In the next experiment, the lateral bathymetry is varied parabolically while keeping the mean depth unchanged. In this case, the fine sediment is mainly found at the shallow sides, but the maximum sediment concentration is found in the deeper channel where the bed shear stress is much larger than on the shoals. As a final experiment, a more realistic (but smoothed) geometry and bathymetry for the Ems estuary are considered, showing the possibilities of applying the newly developed Model to complex geometries and bathymetries.

  • Three-dimensional semi-Idealized Model for tidal motion in tidal estuaries
    Ocean Dynamics, 2016
    Co-Authors: Mohit Kumar, Henk M. Schuttelaars, Pieter C. Roos, Matthias Möller
    Abstract:

    In this paper, a three-dimensional semi-Idealized Model for tidal motion in a tidal estuary of arbitrary shape and bathymetry is presented. This Model aims at bridging the gap between Idealized and complex Models. The vertical profiles of the velocities are obtained analytically in terms of the first-order and the second-order partial derivatives of surface elevation, which itself follows from an elliptic partial differential equation. The surface elevation is computed numerically using the finite element method and its partial derivatives are obtained using various methods. The newly developed semi-Idealized Model allows for a systematic investigation of the influence of geometry and bathymetry on the tidal motion which was not possible in previously developed Idealized Models. The new Model also retains the flexibility and computational efficiency of previous Idealized Models, essential for sensitivity analysis. As a first step, the accuracy of the semi-Idealized Model is investigated. To this end, an extensive comparison is made between the Model results of the semi-Idealized Model and two other Idealized Models: a width-averaged Model and a three-dimensional Idealized Model. Finally, the semi-Idealized Model is used to understand the influence of local geometrical effects on the tidal motion in the Ems estuary. The Model shows that local convergence and meandering effects can have a significant influence on the tidal motion. Finally, the Model is applied to the Ems estuary. The Model results agree well with observations and results from a complex numerical Model.

  • Three-dimensional semi-Idealized Model for tidal motion in tidal estuaries An application to the Ems estuary
    Ocean Dynamics, 2015
    Co-Authors: Mohit Kumar, Henk M. Schuttelaars, Pieter C. Roos, Matthias Möller
    Abstract:

    In this paper, a three-dimensional semi-Idealized Model for tidal motion in a tidal estuary of arbitrary shape and bathymetry is presented. This Model aims at bridging the gap between Idealized and complex Models. The vertical profiles of the velocities are obtained analytically in terms of the first-order and the second-order partial derivatives of surface elevation, which itself follows from an elliptic partial differential equation. The surface elevation is computed numerically using the finite element method and its partial derivatives are obtained using various methods. The newly developed semi-Idealized Model allows for a systematic investigation of the influence of geometry and bathymetry on the tidal motion which was not possible in previously developed Idealized Models. The new Model also retains the flexibility and computational efficiency of previous Idealized Models, essential for sensitivity analysis. As a first step, the accuracy of the semi-Idealized Model is investigated. To this end, an extensive comparison is made between the Model results of the semi-Idealized Model and two other Idealized Models: a width-averaged Model and a three-dimensional Idealized Model. Finally, the semi-Idealized Model is used to understand the influence of local geometrical effects on the tidal motion in the Ems estuary. The Model shows that local convergence and meandering effects can have a significant influence on the tidal motion. Finally, the Model is applied to the Ems estuary. The Model results agree well with observations and results from a complex numerical Model.

  • An Idealized Model of tidal dynamics in semi-enclosed basins online: the effects of a mega-scale sand extraction trench in the North Sea
    Coastal Engineering Proceedings, 2011
    Co-Authors: Wiebe P. De Boer, Pieter C. Roos, Suzanne J.m.h. Hulscher, Ad Stolk
    Abstract:

    We investigate the effects of a mega-scale sand extraction trench (length ~200 km, width ~10 km, depth ~10 m, located in front of the Dutch coast) on tidal dynamics in the Southern North Sea. To this end, an Idealized Modeling approach is adopted, extending the classical problem of Kelvin wave reflection in rectangular semi-enclosed basins to account for lateral depth variations and the presence of a trench. The Model results indicate changes in tidal range (zones of decrease and increase of the order of several cm), phase and currents (order cm/s) throughout the whole basin, which emphasizes the importance of a Model domain on the scale of the basin. The changes in currents may structurally change sediment transport rates by several percents, which is relevant to coastal morphology. It is argued that this Idealized Model can be used to support a companion study carried out with a more detailed numerical engineering Model. This is because of its ability to (1) provide insight into the physical mechanisms, (2) reveal the order of magnitude and area of influence of the effects and (3) allow for a quick sensitivity analysis with respect to trench geometry.

  • Impact of mega-scale sand extraction on tidal dynamics in semi-enclosed basins An Idealized Model study with application to the Southern North Sea
    Coastal Engineering, 2011
    Co-Authors: Wiebe P. De Boer, Pieter C. Roos, Suzanne J.m.h. Hulscher, Ad Stolk
    Abstract:

    Long-term considerations of repeated and increasing sand extraction on the Netherlands Continental Shelf (North Sea) may lead to the creation of a mega-scale extraction trench in front of the Dutch coast (length hundreds of km, width over 10 km, depth several m). We investigate the impact of such a huge topographic intervention on tidal dynamics, which is a key aspect in hydrodynamics, and indirectly also affecting morphodynamics and ecology. Because of the unprecedented extent of the extraction scenario, we follow a generic approach aimed at understanding the physical mechanisms behind the changes, the orders of magnitude and area of influence. Hence, rather than applying an existing numerical Model, we develop an Idealized Model for tide propagation in semi-enclosed rectangular basins. The Model geometry consists of three adjacent compartments with a realistic cross-basin depth profile, the trench being located in the second compartment, while assuming along-basin uniformity of depth within each compartment. The problem is forced by an incoming Kelvin wave. The solution in each compartment, satisfying the linear depth-averaged shallow water equations on the f plane including bottom friction, is written as the superposition of semi-numerically obtained wave solutions. A collocation technique is employed to satisfy no-normal flow across the basin's closed end as well as continuity of elevation and flux across the interfaces between the compartments. The results indicate changes in tidal range, phase and currents throughout the whole basin, which shows the importance of a Model domain on the scale of the basin. Changes in coastal tidal range show zones of decrease and increase (order cm). Changes in coastal shore-parallel tidal current amplitudes are of the order of cm s− 1. A sensitivity analysis for various trench geometries shows that the hydrodynamic impact generally increases with increasing extraction volume, being more sensitive to trench depth and width than trench length. The changes in tidal currents may structurally alter sediment transport rates with several percents. As the bathymetry and coastal morphology result from subtle balances in long-term sediment transport, the trench may indirectly affect various user functions and values (coastal safety, navigation, marine ecology, cables and pipelines) and, hence, be of concern to coastal management.

Henk M. Schuttelaars - One of the best experts on this subject based on the ideXlab platform.

  • Three-dimensional semi-Idealized Model for estuarine turbidity maxima in tidally dominated estuaries
    Ocean Modelling, 2017
    Co-Authors: Mohit Kumar, Henk M. Schuttelaars, Pieter C. Roos
    Abstract:

    Abstract We develop a three-dimensional Idealized Model that is specifically aimed at gaining insight in the physical mechanisms resulting in the formation of estuarine turbidity maxima in tidally dominated estuaries. First, the three-dimensional equations for water motion and suspended sediment concentration together with the so-called morphodynamic equilibrium condition, are scaled. Next, surface elevation, velocity and sediment concentration are expanded in a small parameter ϵ = A ¯ M 2 / H , where A ¯ M 2 is the mean amplitude of the M2 tide and H is the mean water depth at the seaward side. This results in a system of equations at each order in this small parameter. This ordering allows solving for the vertical structure of the velocity and suspended sediment concentration, independently of the horizontal dimension. After obtaining these vertical structures, the horizontal dependencies of the physical variables follow from solving a two-dimensional elliptic partial differential equation for the surface elevation. The availability of fine sediments in the estuary follows from a two-dimensional elliptic partial differential equation which results from requiring the system to be in morphodynamic equilibrium, and prescribing the total amount of easily erodible sediments available in the estuary. These elliptic equations for the surface elevation and sediment availability are solved numerically using the finite element method with cubic polynomials as basis functions. As a first application, the Model is applied to the Ems estuary using a simplified geometry and bathymetric profiles characteristic for the years 1980 and 2005. The availability of fine sediments and location of maximum concentration are investigated for different lateral depth profiles. In the first experiment, a uniform lateral depth is considered. In this case, both the sediment availability and suspended sediment concentration are, as expected, uniform in the lateral direction. In 1980, the sediment is mainly trapped near the entrance, while in 2005, the sediment is mostly trapped in the freshwater zone. In the next experiment, the lateral bathymetry is varied parabolically while keeping the mean depth unchanged. In this case, the fine sediment is mainly found at the shallow sides, but the maximum sediment concentration is found in the deeper channel where the bed shear stress is much larger than on the shoals. As a final experiment, a more realistic (but smoothed) geometry and bathymetry for the Ems estuary are considered, showing the possibilities of applying the newly developed Model to complex geometries and bathymetries.

  • Three-dimensional semi-Idealized Model for tidal motion in tidal estuaries
    Ocean Dynamics, 2016
    Co-Authors: Mohit Kumar, Henk M. Schuttelaars, Pieter C. Roos, Matthias Möller
    Abstract:

    In this paper, a three-dimensional semi-Idealized Model for tidal motion in a tidal estuary of arbitrary shape and bathymetry is presented. This Model aims at bridging the gap between Idealized and complex Models. The vertical profiles of the velocities are obtained analytically in terms of the first-order and the second-order partial derivatives of surface elevation, which itself follows from an elliptic partial differential equation. The surface elevation is computed numerically using the finite element method and its partial derivatives are obtained using various methods. The newly developed semi-Idealized Model allows for a systematic investigation of the influence of geometry and bathymetry on the tidal motion which was not possible in previously developed Idealized Models. The new Model also retains the flexibility and computational efficiency of previous Idealized Models, essential for sensitivity analysis. As a first step, the accuracy of the semi-Idealized Model is investigated. To this end, an extensive comparison is made between the Model results of the semi-Idealized Model and two other Idealized Models: a width-averaged Model and a three-dimensional Idealized Model. Finally, the semi-Idealized Model is used to understand the influence of local geometrical effects on the tidal motion in the Ems estuary. The Model shows that local convergence and meandering effects can have a significant influence on the tidal motion. Finally, the Model is applied to the Ems estuary. The Model results agree well with observations and results from a complex numerical Model.

  • Three-dimensional semi-Idealized Model for tidal motion in tidal estuaries An application to the Ems estuary
    Ocean Dynamics, 2015
    Co-Authors: Mohit Kumar, Henk M. Schuttelaars, Pieter C. Roos, Matthias Möller
    Abstract:

    In this paper, a three-dimensional semi-Idealized Model for tidal motion in a tidal estuary of arbitrary shape and bathymetry is presented. This Model aims at bridging the gap between Idealized and complex Models. The vertical profiles of the velocities are obtained analytically in terms of the first-order and the second-order partial derivatives of surface elevation, which itself follows from an elliptic partial differential equation. The surface elevation is computed numerically using the finite element method and its partial derivatives are obtained using various methods. The newly developed semi-Idealized Model allows for a systematic investigation of the influence of geometry and bathymetry on the tidal motion which was not possible in previously developed Idealized Models. The new Model also retains the flexibility and computational efficiency of previous Idealized Models, essential for sensitivity analysis. As a first step, the accuracy of the semi-Idealized Model is investigated. To this end, an extensive comparison is made between the Model results of the semi-Idealized Model and two other Idealized Models: a width-averaged Model and a three-dimensional Idealized Model. Finally, the semi-Idealized Model is used to understand the influence of local geometrical effects on the tidal motion in the Ems estuary. The Model shows that local convergence and meandering effects can have a significant influence on the tidal motion. Finally, the Model is applied to the Ems estuary. The Model results agree well with observations and results from a complex numerical Model.

  • Channel and shoal development in a short tidal embayment: an Idealized Model study
    Journal of Fluid Mechanics, 2011
    Co-Authors: M.c. Ter Brake, Henk M. Schuttelaars
    Abstract:

    In many tidal embayments, complex patterns of channels and shoals are observed. To gain a better understanding of these features, an Idealized Model, that describes the interaction of water motion, sediment transport and bed evolution in a semi-enclosed, rectangular basin, is developed and analysed. To explain the initial formation of channels and shoals, two-dimensional perturbations superposed on a laterally uniform equilibrium bottom are studied. These perturbations evolve due to convergences of various residual suspended sediment fluxes: a diffusive flux, a flux related to the bed topography, an advective flux resulting from internally generated overtides and an advective flux due to externally prescribed overtides. For most combinations of these fluxes, perturbations start to grow if the bottom friction is strong enough. Their growth is mainly a result of convergences of diffusive and topographically induced sediment fluxes. Advective contributions due to internally generated overtides enhance this growth. If only diffusive sediment fluxes are considered, the underlying equilibrium is always unstable. This can be traced back to the depth dependence of the deposition parameter. Contrary to the results of previous Idealized Models, the channels and shoals always initiate in the shallow, landward areas. This is explained by the enhanced generation (compared to that in previous Models) of frictional torques in shallow regions. The resulting initial channel–shoal formation compares well with results found in complex numerical Model studies. The instability mechanism and the location of the initial formation of bottom patterns do not change qualitatively when varying parameters. Changes are mainly related to differences in the underlying equilibrium profile due to parameter variations.

  • Lateral entrapment of sediment in tidal estuaries: an Idealized Model study
    Journal of Geophysical Research, 2006
    Co-Authors: K. M. H. Huijts, Henk M. Schuttelaars, H. E. Swart, Arnoldo Valle-levinson
    Abstract:

    Two physical mechanisms leading to lateral accumulation of sediment in tidally dominated estuaries are investigated, involving Coriolis forcing and lateral density gradients. An Idealized Model is used that consists of the three?dimensional shallow water equations and sediment mass balance. Conditions are assumed to be uniform in the along?estuary direction. A semidiurnal tidal discharge and tidally averaged density gradients are prescribed. The erosional sediment flux at the bed depends both on the bed shear stress and on the amount of sediment available in mud reaches for resuspension. The distribution of mud reaches over the bed is selected such that sediment transport is in morphodynamic equilibrium, that is, tidally averaged erosion and deposition of sediment at the bed balance. Analytical solutions are obtained by using perturbation analysis. Results suggest that in most estuaries lateral density gradients induce more sediment transport than Coriolis forcing. When frictional forces are small (Ekman number E 0.02), the lateral density gradient mechanism dominates and entraps sediment in areas with fresher water. Results also show that the lateral sediment transport induced by the semidiurnal tidal flow is significant when frictional forces are small (E ? 0.02). Model predictions are in good agreement with observations from the James River estuary.

Matthias Möller - One of the best experts on this subject based on the ideXlab platform.

  • Three-dimensional semi-Idealized Model for tidal motion in tidal estuaries
    Ocean Dynamics, 2016
    Co-Authors: Mohit Kumar, Henk M. Schuttelaars, Pieter C. Roos, Matthias Möller
    Abstract:

    In this paper, a three-dimensional semi-Idealized Model for tidal motion in a tidal estuary of arbitrary shape and bathymetry is presented. This Model aims at bridging the gap between Idealized and complex Models. The vertical profiles of the velocities are obtained analytically in terms of the first-order and the second-order partial derivatives of surface elevation, which itself follows from an elliptic partial differential equation. The surface elevation is computed numerically using the finite element method and its partial derivatives are obtained using various methods. The newly developed semi-Idealized Model allows for a systematic investigation of the influence of geometry and bathymetry on the tidal motion which was not possible in previously developed Idealized Models. The new Model also retains the flexibility and computational efficiency of previous Idealized Models, essential for sensitivity analysis. As a first step, the accuracy of the semi-Idealized Model is investigated. To this end, an extensive comparison is made between the Model results of the semi-Idealized Model and two other Idealized Models: a width-averaged Model and a three-dimensional Idealized Model. Finally, the semi-Idealized Model is used to understand the influence of local geometrical effects on the tidal motion in the Ems estuary. The Model shows that local convergence and meandering effects can have a significant influence on the tidal motion. Finally, the Model is applied to the Ems estuary. The Model results agree well with observations and results from a complex numerical Model.

  • Three-dimensional semi-Idealized Model for tidal motion in tidal estuaries An application to the Ems estuary
    Ocean Dynamics, 2015
    Co-Authors: Mohit Kumar, Henk M. Schuttelaars, Pieter C. Roos, Matthias Möller
    Abstract:

    In this paper, a three-dimensional semi-Idealized Model for tidal motion in a tidal estuary of arbitrary shape and bathymetry is presented. This Model aims at bridging the gap between Idealized and complex Models. The vertical profiles of the velocities are obtained analytically in terms of the first-order and the second-order partial derivatives of surface elevation, which itself follows from an elliptic partial differential equation. The surface elevation is computed numerically using the finite element method and its partial derivatives are obtained using various methods. The newly developed semi-Idealized Model allows for a systematic investigation of the influence of geometry and bathymetry on the tidal motion which was not possible in previously developed Idealized Models. The new Model also retains the flexibility and computational efficiency of previous Idealized Models, essential for sensitivity analysis. As a first step, the accuracy of the semi-Idealized Model is investigated. To this end, an extensive comparison is made between the Model results of the semi-Idealized Model and two other Idealized Models: a width-averaged Model and a three-dimensional Idealized Model. Finally, the semi-Idealized Model is used to understand the influence of local geometrical effects on the tidal motion in the Ems estuary. The Model shows that local convergence and meandering effects can have a significant influence on the tidal motion. Finally, the Model is applied to the Ems estuary. The Model results agree well with observations and results from a complex numerical Model.

Mohit Kumar - One of the best experts on this subject based on the ideXlab platform.

  • Three-dimensional semi-Idealized Model for estuarine turbidity maxima in tidally dominated estuaries
    Ocean Modelling, 2017
    Co-Authors: Mohit Kumar, Henk M. Schuttelaars, Pieter C. Roos
    Abstract:

    Abstract We develop a three-dimensional Idealized Model that is specifically aimed at gaining insight in the physical mechanisms resulting in the formation of estuarine turbidity maxima in tidally dominated estuaries. First, the three-dimensional equations for water motion and suspended sediment concentration together with the so-called morphodynamic equilibrium condition, are scaled. Next, surface elevation, velocity and sediment concentration are expanded in a small parameter ϵ = A ¯ M 2 / H , where A ¯ M 2 is the mean amplitude of the M2 tide and H is the mean water depth at the seaward side. This results in a system of equations at each order in this small parameter. This ordering allows solving for the vertical structure of the velocity and suspended sediment concentration, independently of the horizontal dimension. After obtaining these vertical structures, the horizontal dependencies of the physical variables follow from solving a two-dimensional elliptic partial differential equation for the surface elevation. The availability of fine sediments in the estuary follows from a two-dimensional elliptic partial differential equation which results from requiring the system to be in morphodynamic equilibrium, and prescribing the total amount of easily erodible sediments available in the estuary. These elliptic equations for the surface elevation and sediment availability are solved numerically using the finite element method with cubic polynomials as basis functions. As a first application, the Model is applied to the Ems estuary using a simplified geometry and bathymetric profiles characteristic for the years 1980 and 2005. The availability of fine sediments and location of maximum concentration are investigated for different lateral depth profiles. In the first experiment, a uniform lateral depth is considered. In this case, both the sediment availability and suspended sediment concentration are, as expected, uniform in the lateral direction. In 1980, the sediment is mainly trapped near the entrance, while in 2005, the sediment is mostly trapped in the freshwater zone. In the next experiment, the lateral bathymetry is varied parabolically while keeping the mean depth unchanged. In this case, the fine sediment is mainly found at the shallow sides, but the maximum sediment concentration is found in the deeper channel where the bed shear stress is much larger than on the shoals. As a final experiment, a more realistic (but smoothed) geometry and bathymetry for the Ems estuary are considered, showing the possibilities of applying the newly developed Model to complex geometries and bathymetries.

  • Three-dimensional semi-Idealized Model for tidal motion in tidal estuaries
    Ocean Dynamics, 2016
    Co-Authors: Mohit Kumar, Henk M. Schuttelaars, Pieter C. Roos, Matthias Möller
    Abstract:

    In this paper, a three-dimensional semi-Idealized Model for tidal motion in a tidal estuary of arbitrary shape and bathymetry is presented. This Model aims at bridging the gap between Idealized and complex Models. The vertical profiles of the velocities are obtained analytically in terms of the first-order and the second-order partial derivatives of surface elevation, which itself follows from an elliptic partial differential equation. The surface elevation is computed numerically using the finite element method and its partial derivatives are obtained using various methods. The newly developed semi-Idealized Model allows for a systematic investigation of the influence of geometry and bathymetry on the tidal motion which was not possible in previously developed Idealized Models. The new Model also retains the flexibility and computational efficiency of previous Idealized Models, essential for sensitivity analysis. As a first step, the accuracy of the semi-Idealized Model is investigated. To this end, an extensive comparison is made between the Model results of the semi-Idealized Model and two other Idealized Models: a width-averaged Model and a three-dimensional Idealized Model. Finally, the semi-Idealized Model is used to understand the influence of local geometrical effects on the tidal motion in the Ems estuary. The Model shows that local convergence and meandering effects can have a significant influence on the tidal motion. Finally, the Model is applied to the Ems estuary. The Model results agree well with observations and results from a complex numerical Model.

  • Three-dimensional semi-Idealized Model for tidal motion in tidal estuaries An application to the Ems estuary
    Ocean Dynamics, 2015
    Co-Authors: Mohit Kumar, Henk M. Schuttelaars, Pieter C. Roos, Matthias Möller
    Abstract:

    In this paper, a three-dimensional semi-Idealized Model for tidal motion in a tidal estuary of arbitrary shape and bathymetry is presented. This Model aims at bridging the gap between Idealized and complex Models. The vertical profiles of the velocities are obtained analytically in terms of the first-order and the second-order partial derivatives of surface elevation, which itself follows from an elliptic partial differential equation. The surface elevation is computed numerically using the finite element method and its partial derivatives are obtained using various methods. The newly developed semi-Idealized Model allows for a systematic investigation of the influence of geometry and bathymetry on the tidal motion which was not possible in previously developed Idealized Models. The new Model also retains the flexibility and computational efficiency of previous Idealized Models, essential for sensitivity analysis. As a first step, the accuracy of the semi-Idealized Model is investigated. To this end, an extensive comparison is made between the Model results of the semi-Idealized Model and two other Idealized Models: a width-averaged Model and a three-dimensional Idealized Model. Finally, the semi-Idealized Model is used to understand the influence of local geometrical effects on the tidal motion in the Ems estuary. The Model shows that local convergence and meandering effects can have a significant influence on the tidal motion. Finally, the Model is applied to the Ems estuary. The Model results agree well with observations and results from a complex numerical Model.

Carlos Luna - One of the best experts on this subject based on the ideXlab platform.

  • Formally Verified Implementation of an Idealized Model of Virtualization
    2014
    Co-Authors: Gilles Barthe, Gustavo Betarte, Juan Diego Campo, Jesús Mauricio Chimento, Carlos Luna
    Abstract:

    VirtualCert is a machine-checked Model of virtualization that can be used to reason about isolation between operating systems in presence of cache-based side-channels. In contrast to most prominent projects on operating systems verification, where such guarantees are proved directly on concrete implementations of hypervisors, VirtualCert abstracts away most implementations issues and specifies the effects of hypervisor actions axiomatically, in terms of preconditions and postconditions. Unfortunately, seemingly innocuous implementation issues are often relevant for security. Incorporating the treatment of errors into VirtualCert is therefore an important step towards strengthening the isolation theorems proved in earlier work. In this paper, we extend our earlier Model with errors, and prove that isolation theorems still apply. In addition, we provide an executable specification of the hypervisor, and prove that it correctly implements the axiomatic Model. The executable specification constitutes a first step towards a more realistic implementation of a hypervisor, and provides a useful tool for validating the axiomatic semantics developed in previous work.

  • TYPES - Formally Verified Implementation of an Idealized Model of Virtualization.
    2013
    Co-Authors: Gilles Barthe, Gustavo Betarte, Juan Diego Campo, Jesús Mauricio Chimento, Carlos Luna
    Abstract:

    VirtualCert is a machine-checked Model of virtualization that can be used to reason about isolation between operating systems in presence of cache-based side-channels. In contrast to most prominent projects on operating systems verification, where such guarantees are proved directly on concrete implementations of hypervisors, VirtualCert abstracts away most implementations issues and specifies the effects of hypervisor actions axiomatically, in terms of preconditions and postconditions. Unfortunately, seemingly innocuous implementation issues are often relevant for security. Incorporating the treatment of errors into VirtualCert is therefore an important step towards strengthening the isolation theorems proved in earlier work. In this paper, we extend our earlier Model with errors, and prove that isolation theorems still apply. In addition, we provide an executable specification of the hypervisor, and prove that it correctly implements the axiomatic Model. The executable specification constitutes a first step towards a more realistic implementation of a hypervisor, and provides a useful tool for validating the axiomatic semantics developed in previous work.

  • cache leakage resilient os isolation in an Idealized Model of virtualization
    IEEE Computer Security Foundations Symposium, 2012
    Co-Authors: Gilles Barthe, Gustavo Betarte, Juan Diego Campo, Carlos Luna
    Abstract:

    Virtualization platforms allow multiple operating systems to run on the same hardware. One of their central goal is to provide strong isolation between guest operating systems, unfortunately, they are often vulnerable to practical side-channel attacks. Cache attacks are a common class of side-channel attacks that use the cache as a side channel. We formalize an Idealized Model of virtualization that features the cache and the Translation Look aside Buffer (TLB), and that provides an abstract treatment of cache-based side-channels. We then use the Model for reasoning about cache-based attacks and countermeasures, and for proving that isolation between guest operating systems can be enforced by flushing the cache upon context switch. In addition, we show that virtualized platforms are transparent, i.e. a guest operating system cannot distinguish whether it executes alone or together with other guest operating systems on the platform. The Models and proofs have been machine-checked in the Coqproof assistant.

  • CSF - Cache-Leakage Resilient OS Isolation in an Idealized Model of Virtualization
    2012 IEEE 25th Computer Security Foundations Symposium, 2012
    Co-Authors: Gilles Barthe, Gustavo Betarte, Juan Diego Campo, Carlos Luna
    Abstract:

    Virtualization platforms allow multiple operating systems to run on the same hardware. One of their central goal is to provide strong isolation between guest operating systems, unfortunately, they are often vulnerable to practical side-channel attacks. Cache attacks are a common class of side-channel attacks that use the cache as a side channel. We formalize an Idealized Model of virtualization that features the cache and the Translation Look aside Buffer (TLB), and that provides an abstract treatment of cache-based side-channels. We then use the Model for reasoning about cache-based attacks and countermeasures, and for proving that isolation between guest operating systems can be enforced by flushing the cache upon context switch. In addition, we show that virtualized platforms are transparent, i.e. a guest operating system cannot distinguish whether it executes alone or together with other guest operating systems on the platform. The Models and proofs have been machine-checked in the Coqproof assistant.

  • formally verifying isolation and availability in an Idealized Model of virtualization
    Formal Methods, 2011
    Co-Authors: Gilles Barthe, Gustavo Betarte, Juan Diego Campo, Carlos Luna
    Abstract:

    Hypervisors allow multiple guest operating systems to run on shared hardware, and offer a compelling means of improving the security and the flexibility of software systems. We formalize in the Coq proof assistant an Idealized Model of a hypervisor, and formally establish that the hypervisor ensures strong isolation properties between the different operating systems, and guarantees that requests from guest operating systems are eventually attended.