I outline a modified rotating shallow water model to represent an idealised atmosphere with moist... more I outline a modified rotating shallow water model to represent an idealised atmosphere with moist convection for use in inexpensive data assimilation experiments. By combining the nonlinearity due to advection in the shallow water equations and the onset of precipitation, the proposed model captures two important dynamical processes of convecting and precipitating weather systems. The model is a valid non-conservative hyperbolic system of partial differential equations and is solved numerically using a shock-capturing finite element framework which deals robustly with the high nonlinearity and so-called non-conservative products.
We outline a straightforward and creative methodology that offers both (i) a complementary diagno... more We outline a straightforward and creative methodology that offers both (i) a complementary diagnostic for classifying flood events (from gauge data and/or simulations) and (ii) a protocol to optimise the assessment of flood-mitigation measures via concise cost-effectiveness analyses. It is based on the concept of flood-excess volume (FEV), namely the volume of water exceeding a threshold and generating flood damage, and is exemplified for recent extreme-flood events in the UK and France. We are motivated by, and address herein, the following questions: (i) how can we express FEV (which is typically many million cubic metres) in a comprehensible way? and; (ii) what fraction of FEV is reduced, and at what cost, by a particular flood-mitigation measure? Our methodology allows direct comparison of the technical efficacy of a suite of measures, typically nature-based (e.g., tree planting, flow-attenuation features) or civil engineering-based (e.g., flood-storage basins, walls), that cons...
A two-layer Hamiltonian toy model consisting of two isentropic stratospheric layers is simplified... more A two-layer Hamiltonian toy model consisting of two isentropic stratospheric layers is simplified using perturbation analysis while preserving the Hamiltonian structure. These two layers are neutrally and stably stratified. The first approximation applies when the Froude number of the upper isentropic layer is small, such that the upper surface is approximately rigid, and this upper layer is much thicker than the lower layer. A conservative 1.5-layer isentropic model emerges when leading-order perturbation theory is used in the Hamiltonian formulation of the isentropic two-layer model. Furthermore, Hamiltonian theory directly leads to (Salmon's) L1-dynamics for the 1.5-layer model, following a more concise derivation than shown before, when the Rossby number in the upper stratospheric layer is small and leads to a geostrophic constraint.
We present a novel approach to fluid-structure interactions (FSI) that preserves energy and phase... more We present a novel approach to fluid-structure interactions (FSI) that preserves energy and phase-space structure owing to the variational and Hamiltonian techniques used. We posit a variational principle (VP), for nonlinear potential-flow wave dynamics coupled to a nonlinear hyperelastic mast, and derive its linearization. Both linear and nonlinear formulations can then be discretized in a classical-mechanical VP, using nite element expansions.
I outline a modified rotating shallow water model to represent an idealised atmosphere with moist... more I outline a modified rotating shallow water model to represent an idealised atmosphere with moist convection for use in inexpensive data assimilation experiments. By combining the nonlinearity due to advection in the shallow water equations and the onset of precipitation, the proposed model captures two important dynamical processes of convecting and precipitating weather systems. The model is a valid non-conservative hyperbolic system of partial differential equations and is solved numerically using a shock-capturing finite element framework which deals robustly with the high nonlinearity and so-called non-conservative products.
We outline a straightforward and creative methodology that offers both (i) a complementary diagno... more We outline a straightforward and creative methodology that offers both (i) a complementary diagnostic for classifying flood events (from gauge data and/or simulations) and (ii) a protocol to optimise the assessment of flood-mitigation measures via concise cost-effectiveness analyses. It is based on the concept of flood-excess volume (FEV), namely the volume of water exceeding a threshold and generating flood damage, and is exemplified for recent extreme-flood events in the UK and France. We are motivated by, and address herein, the following questions: (i) how can we express FEV (which is typically many million cubic metres) in a comprehensible way? and; (ii) what fraction of FEV is reduced, and at what cost, by a particular flood-mitigation measure? Our methodology allows direct comparison of the technical efficacy of a suite of measures, typically nature-based (e.g., tree planting, flow-attenuation features) or civil engineering-based (e.g., flood-storage basins, walls), that cons...
A two-layer Hamiltonian toy model consisting of two isentropic stratospheric layers is simplified... more A two-layer Hamiltonian toy model consisting of two isentropic stratospheric layers is simplified using perturbation analysis while preserving the Hamiltonian structure. These two layers are neutrally and stably stratified. The first approximation applies when the Froude number of the upper isentropic layer is small, such that the upper surface is approximately rigid, and this upper layer is much thicker than the lower layer. A conservative 1.5-layer isentropic model emerges when leading-order perturbation theory is used in the Hamiltonian formulation of the isentropic two-layer model. Furthermore, Hamiltonian theory directly leads to (Salmon's) L1-dynamics for the 1.5-layer model, following a more concise derivation than shown before, when the Rossby number in the upper stratospheric layer is small and leads to a geostrophic constraint.
We present a novel approach to fluid-structure interactions (FSI) that preserves energy and phase... more We present a novel approach to fluid-structure interactions (FSI) that preserves energy and phase-space structure owing to the variational and Hamiltonian techniques used. We posit a variational principle (VP), for nonlinear potential-flow wave dynamics coupled to a nonlinear hyperelastic mast, and derive its linearization. Both linear and nonlinear formulations can then be discretized in a classical-mechanical VP, using nite element expansions.
Uploads
Papers by Onno Bokhove