Gaurav Savant

Efficient Implicit Finite-Element Hydrodynamic Model for Dam and Levee Breach

This technical paper presents the development and application of a pseudo-transient continuation (PTC)– inspired flow model for the simulation of dam and levee failure. The unstructured, implicit, Petrov-Galerkin finite-element model relies on computed residuals to automatically adjust the time-step size. The implicit time integration, together with the automatic time-step size selection through PTC, makes the model computationally efficient. The model is verified and applied to several analytic and real-world test cases that exercise model behavior and accuracy for several critical, transcritical, and subcritical flows. The result is an efficient and accurate prediction of both the speed and depth of shock waves as the dam-break flow passes over initially dry and wet land.

Two-Dimensional Numerical Model of the Gulf Intracoastal Waterway near New Orleans

AbstractTwo-dimensional tidal flows within the Lake Pontchartrain–Lake Borgne area (Louisiana) are simulated to assess the effects of the surge protection structure on the Gulf Intracoastal Waterway (GIWW) on navigation conditions. The region of interest is modeled with a shallow-water, depth-averaged, finite-element model. The water levels and discharge are analyzed at a location in the GIWW to ascertain model behavior. It is shown that the presence of the structure produces infrequent increases in velocities in the GIWW, which can be mitigated by a proposed structure near Lake Pontchartrain.

Hydrodynamics of Knik Arm: Modeling Study

An adaptive hydraulics (AdH) model was applied to lower Knik Arm near the Port of Anchorage, Alaska, to assess its ability to model a macrotidal system with complex hydrodynamics, including the formation and evolution of numerous gyres that are prominent at this site. Lower Knik Arm is an ideal system for this model evaluation because of the large tide range (approximately 10 m at Anchorage) and complex geometry of the system, which results in high velocities and the formation of numerous eddies throughout the study area. One eddy of primary importance is the one generated by Cairn Point, which occurs near the Port of Anchorage. Limitations of previous modeling studies and the availability of recent field data enabled this evaluation. The AdH results were compared with field data (water surface elevations, fluxes, and velocities) collected in August of 2002 and 2006, and favorable comparisons obtained for tidal amplification and eddy generation indicate that AdH reasonably reproduces the complex hydrodynamic conditions in lower Knik Arm. Simulations were also performed to investigate the importance of eddy viscosity specification, frictional specification, and bathymetry on the generation/evolution of eddies present in the system. Upon completion of the model validation, simulations were performed with modified Cairn Point configurations to investigate the impact to the eddy generated at the port. These results illustrate the variation in eddy generation through lengthening, lowering/reducing, or raising Cairn Point.

Rapid Response Numerical Modeling of the 2010 Pakistan Flooding

AbstractLate summer 2010 saw record flooding of the Indus River in Pakistan. In response to requests by the U.S. Army, the writers provided flood extents to aid humanitarian assistance in the affected areas. Numerical modeling provided the best way to compute the flooding in this situation, but with limited bathymetric, topographic, and inflow information, assumptions had to be made; timelines were of significantly higher importance than complete accuracy. The writers developed an adaptive hydraulics (AdH) model of the Indus River from Sukkur to the Arabian Sea covering approximately 180,000 km2 of Pakistan. Based on aerial images taken during the flood, the writers later compared the model results to the flood extents to determine the level of accuracy of the model. The AdH model results approximately reproduced the area of flooding for initial emergency operations, even with little knowledge of the area and the inflow conditions. The results of this exercise show that rapid modeling of large-scale flood...

Refinement Indicator for Dynamic-Mesh Adaption in Three-Dimensional Shallow-Water Equation Modeling

AbstractOne of the basic articles of discretization-based numerical modeling of three-dimensional shallow water equations is the spatial convergence of the mesh utilized. The process of creating a ...

Tidal Hydrodynamics in the Lower Columbia River Estuary through Depth Averaged Adaptive Hydraulics Modeling

The adaptive hydraulics (AdH) numerical code was applied to study tidal propagation in the Lower Columbia River (LCR) estuary. The results demonstrate the readiness of this AdH model towards the further study of hydrodynamics in the LCR. The AdH model accurately replicated behavior of the tide as it propagated upstream into the LCR system. Results show that the MSf tidal component and the M4 overtidal component are generated in the middle LCR and contain a substantial amount of tidal energy. An analysis was performed to determine the causes of MSf tide amplification, and it was found that approximately 80% of the amplification occurs due to nonlinear interaction between the M2 and the S2 tidal components.

AMass Conservation AlgorithmFor Adaptive Unrefinement Meshes Used By Finite Element Methods

Abstract The AdaptiveHydraulics (ADH) model is an adaptivefinite element method to simulate three-dimensional Navier-Stokes flow, unsaturated and saturated groundwater flow, overland flow, and two-or three-dimensional shallow-water flow and transport. In the shallow-water flow and transport, especially involving multispecies transport, the water depth (h), the product of water depth and velocities (uh and vh), as well as water depth and chemical concentration (hc) are dependent variables of fluid-motion simulations and are often solved at various times. It is important for the numerical model to predict accurate water depth, velocity fields, and chemical distribution, as well as conserve mass, especially forwater quality applications. Solution accuracydepends highly on mesh resolution. Adaptive mesh refinement (AMR), particularly the h-refinement, is often used to add new nodes in the region where they are needed and to remove others where they are no longer required during the simulation. The AMR is proven to optimize the performance of a computed solution. However, mass withgain or loss can occur when elements are merged due to removing a node at mesh coarsening. Therefore, we develop and implement the mass-conservative unrefinement algorithm to ensure the mass conserved in a merged element in which a node has been removed. This study describes the use of the Galerkin finite element method to redistribute mass to nodes comprising a merged element. The algorithmwas incorporated into the ADH code. This algorithm minimizes mass error during the unrefinement process to conserve mass during the simulation for two-dimensional shallow-water flow and transport. The implementation neither significantly increases the computational time nor memory usage. The simulation was runwithvarious numbersof processors.The resultsshowedgoodscalingof solutiontimeasthenumberof processors increases.

Modeling Flap Gate Culverts in Adaptive Hydraulics (AdH)

PURPOSE: This Coastal and Hydraulics Engineering Technical Note (CHETN) describes the methodology and implementation of flap gate culverts in the 2-D Shallow Water (SW2D) version of Adaptive Hydraulics (AdH). See Figure 2 for an example of this type of structure. This technical note will outline how to calculate the culvert coefficient (K) for flap gate culverts for use in AdH and present a test case detailing the implementation of the structure into AdH input files. A synopsis of the test case results is also presented.

Numerical framework to link the Adaptive Hydraulics (AdH) code to the Nutrient Simulation Module-I (NSMI)

BACKGROUND: The AdH hydrodynamic code is a linear element-based finite element code that is capable of solving the saturated/unsaturated groundwater equations, the Reynolds Averaged Navier-Stokes equations, Diffusive Wave equations as well as the two/three-dimensional (2D/3D) Shallow Water Equations (SWE). This CHETN provides the framework for linking NSMI to the AdH-2D/3D SWE code (hereafter referred to as AdH).

A Library of Two Turbulence Closure Schemes

Two two-equation turbulence closure models are implemented in a three dimensional (3D) hydrodynamic model (Adaptive Hydraulics; ADH). The implementation is in the form of a modular library that can in effect be called from any 3D hydrodynamic model. The models incorporated into this library consist of the two equation MellorYamada level 2.5 and the κ−e model. The two equation models have the capability to represent several real world phenomenons such as density stratification, flow separation and suspended sediment transport. The presence of multiple turbulence closure models, of varied complexity from one equation to two equations, allows for the selection of a model best suited for the problem at hand. The implementation of this library was tested using a vertical backstep problem.