Marcel Zijlema

Hurricane Gustav (2008) Waves and Storm Surge: Hindcast, Synoptic Analysis, and Validation in Southern Louisiana

AbstractHurricane Gustav (2008) made landfall in southern Louisiana on 1 September 2008 with its eye never closer than 75 km to New Orleans, but its waves and storm surge threatened to flood the city. Easterly tropical-storm-strength winds impacted the region east of the Mississippi River for 12–15 h, allowing for early surge to develop up to 3.5 m there and enter the river and the city’s navigation canals. During landfall, winds shifted from easterly to southerly, resulting in late surge development and propagation over more than 70 km of marshes on the river’s west bank, over more than 40 km of Caernarvon marsh on the east bank, and into Lake Pontchartrain to the north. Wind waves with estimated significant heights of 15 m developed in the deep Gulf of Mexico but were reduced in size once they reached the continental shelf. The barrier islands further dissipated the waves, and locally generated seas existed behind these effective breaking zones.The hardening and innovative deployment of gauges since Hur...

Performance of the Unstructured-Mesh, SWAN+ADCIRC Model in Computing Hurricane Waves and Surge

Coupling wave and circulation models is vital in order to define shelf, nearshore and inland hydrodynamics during a hurricane. The intricacies of the inland floodplain domain, level of required mesh resolution and physics make these complex computations very cycle-intensive. Nonetheless, fast wall-clock times are important, especially when forecasting an incoming hurricane.We examine the performance of the unstructured-mesh, SWAN+ADCIRC wave and circulation model applied to a high-resolution, 5M-vertex, finite-element SL16 mesh of the Gulf of Mexico and Louisiana. This multi-process, multi-scale modeling system has been integrated by utilizing inter-model communication that is intra-core. The modeling system is validated through hindcasts of Hurricanes Katrina and Rita (2005), Gustav and Ike (2008) and comprehensive comparisons to wave and water level measurements throughout the region. The performance is tested on a variety of platforms, via the examination of output file requirements and management, and the establishment of wall-clock times and scalability using up to 9,216 cores. Hindcasts of waves and storm surge can be computed efficiently, by solving for as many as 2.3⋅1012 unknowns per day of simulation, in as little as 10 minutes of wall-clock time.

Invariant discretization of the - model in general co-ordinates for prediction of turbulent flow in complicated geometries

Abstract An invariant formulation and finite volume discretization of the standard k-ϵ turbulence model in general curvilinear co-ordinates is presented. The k-ϵ model is implemented together with the incompressible Navier-Stokes equations on staggered grids with contravariant flux components as unknowns. A proof that k and ϵ are non-negative is given. Positive schemes in the implementation of the k-ϵ model are evaluated. Discretization of boundary conditions is considered. The numerical method is applied to a turbulent flow across a staggered tube bank.

Higher-Order Flux-Limiting Schemes for the Finite Volume Computation of Incompressible Flow

Numerical modelling of convection suitable for cell-centred finite volume methods for incompressible flow is considered. Higher-order accurate and oscillation-free solutions are obtained through flux limiting, Two improvements are discussed: the enhancement of accuracy at smooth extrema of the TVD solution, and the construction of flux limiters, which is based on polynomial interpolants in the normalized variable space. Some implementation issues are outlined. Numerical examples are provided to illustrate these advancements.

Infragravity-wave dynamics in a barred coastal region, a numerical study

This paper presents a comprehensive numerical study into the infragravity-wave dynamics at a field site, characterized by a gently sloping barred beach. The nonhydrostatic wave-flow model SWASH was used to simulate the local wavefield for a range of wave conditions (including mild and storm conditions). The extensive spatial coverage of the model allowed us to analyze the infragravity-wave dynamics at spatial scales not often covered before. Overall, the model predicted a wavefield that was representative of the natural conditions, supporting the model application to analyze the wave dynamics. The infragravity-wave field was typically dominated by leaky waves, except near the outer bar where bar-trapped edge waves were observed. Relative contributions of bar-trapped waves peaked during mild conditions, when they explained up to 50% of the infragravity variance. Near the outer bar, the infragravity-wave growth was partly explained by nonlinear energy transfers from short waves. This growth was strongest for mild conditions, and decreased for more energetic conditions when short waves were breaking at the outer bar. Further shoreward, infragravity waves lost most of their energy, due to a combination of nonlinear transfers, bottom friction, and infragravity-wave breaking. Nonlinear transfers were only effective near the inner bar, whereas near the shoreline (where losses were strongest) the dissipation was caused by the combined effect of bottom friction and breaking. This study demonstrated the models potential to study wave dynamics at field scales not easily covered by in situ observations.

WAVE PHYSICS IN A TIDAL INLET

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Three‐dimensional dense distributed temperature sensing for measuring layered thermohaline systems

Distributed temperature sensing has proven a useful technique for geoscientists to obtain spatially distributed temperature data. When studies require high-resolution temperature data in three spatial dimensions, current practices to enhance the spatial resolution do not suffice. For example, double-diffusive phenomena induce sharp and small-scale temperature patterns in water bodies subject to thermohaline gradients. This article presents a novel approach for a 3D dense distributed temperature sensing setup, the design of which can be customized to the required spatial resolution in each dimension. Temperature is measured along fiber-optic cables that can be arranged as needed. In this case, we built a dense cage of very thin (1.6 mm) cables to ensure that interference with flow patterns was minimal. Application in water bodies with double-diffusion induced sharp temperature gradients shows that the setup is well able to capture small-scale temperature patterns and even detects small unsuspected seeps and potential salt-fingers. However, the potential effect of the setup on the flow patterns requires further study. This article is protected by copyright. All rights reserved.

Computing Incompressible Flows in General Domains

We describe a generalization of the classical staggered grid discretization of the incompressible Navier-Stokes equations to general coordinates, using the coordinate-invariant tensor formulation of the equations of motion. Provided a certain choice is made for the dependent variables and for the computation of the geometric quantities, satisfactory accuracy is obtained on fairly non-uniform grids. The pressure-correction method is used to solve the time-dependent equations with preconditioned GMRES and multigrid methods. Turbulent and three-dimensional applications are presented.

Numerical Modeling of Wave Propagation, Breaking and Run-Up on a Beach

A numerical method for free-surface flow is presented to study water waves in coastal areas. The method builds on the nonlinear shallow water equations and utilizes a non-hydrostatic pressure term to describe short waves. A vertical boundary-fitted grid is used with the water depth divided into a number of layers. A compact finite difference scheme is employed that takes into account the effect of non-hydrostatic pressure with a small number of vertical layers. As a result, the proposed technique is capable of simulating relatively short wave propagation, where both frequency dispersion and nonlinear shoaling play an important role, in an accurate and efficient manner. Mass and momentum are strictly conserved at discretelevel while themethod only dissipates energy in the case of wave breaking.A simple wet-dry algorithm is applied for a proper calculation of wave run-up on the beach.The computed results show good agreement with analytical and laboratory data for wave propagation, transformation, breaking and run-up within the surf zone.

Chapter 26 – Parallelization of a nearshore wind wave model for distributed memory architectures

Publisher Summary This chapter discusses parallelization of the sequential code SWAN (simulating waves nearshore) on distributed memory architectures using MPI for simulating wind-generated waves in coastal regions. Efficient parallel algorithms are required to calculate spectra of random short-crested, wind-generated waves in coastal regions using the third-generation wave model SWAN. The propagation schemes used in SWAN are fully implicit, so that they can be utilized for computing waves in shallow water. Two strategies for parallelizing these schemes are presented: (1) the block Jacobi approximation with a high degree of parallelism, and (2) the block wavefront approach that is to a large extent parallelizable. Contrary to the first one, the latter has the same behavior as the sequential method with respect to convergence. Numerical experiments are run on a dedicated Beowulf cluster with a real-life application. They show that good speedups have been achieved with the block wavefront approach, as long as the computational domain is not divided into too thin slices. Concerning the block Jacobi method, a considerable decline in performance is observed, which is attributable to the numerical overhead arising from tripling the number of iterations.