Shahrouz Aliabadi

A fully automated and integrated multi-scale forecasting scheme for emergency preparedness

In this paper, we present one multi-scale integrated simulation technology for emergency preparedness with a holistic approach in hurricane, related storm surge and flood forecasting; infrastructure assessment; and emergency planning. This is an emergency management tool to aid the decision-makers and first responders in preparation for the appropriate response to an impending hurricane disaster. Three primary models, hurricane forecasting, storm surge, and overland flooding, are executed in sequence to generate the necessary results for the proposed integrated emergency planning and preparedness tool. Two of these are open source codes in the public domain and the overland flooding model is an in-house code developed by the authors. Using the results of the primary models, two secondary models are executed to assess local infrastructure vulnerability and to determine the optimal evacuation routes for impacted inhabitants. The results from each model are post-processed and saved as Keyhole Markup Language (KML) files that are viewable in Google Earth for overlay analysis and decision-making. Hurricane Katrina (2005) in the Mississippi coastal area is chosen as a case study to validate the developed tool. The models are run in sequence to generate the layers of data necessary during an actual event. The sequence is fully automated using Python and Shell scripts, which allow users to interact with each model through a series of Graphical User Interfaces. The development of technology described here would not only satisfy the scope of the project, but also be of great significance to national homeland security in the area of emergency preparedness and response.

Integrated high performance computational tools for simulations of transport and diffusion of contaminants in urban areas

Rapid analysis of transport and diffusion of chemical and biological aerosols and contaminants in an urban environment is a critical part of any homeland security response team. High performance computing (HPC) is a valuable technique for such analysis. The time constraint needed to create fully developed complex 3D city terrain models to support such dispersion simulations requires a task of converting agency data to the format necessary on the simulation platform. Numerous data sets have been employed in the development of complex 3D city models. Such data include the use of multi-layer building morphology data, the use of geographic information system (GIS) based shapefiles and digital elevation models (DEM), and the use of remote sensing data such as Light Detection and Ranging (LIDAR). The constructed geometry models are used to generate large-scale computational domains on a platform that supports our HPC tools. These tools include fully automated unstructured mesh generation, parallel and scalable flow solvers based on stabilized finite element formulations and a remote client-server environment for large-scale flow visualization. The stabilized finite element formulations, which are based on the SUPG and PSPG techniques, are parallelized and vectorized on the Cray X1. The 3D validation problem involves transient simulation of flow past a building with a source point releasing traces. A 3D application problem is presented to demonstrate the capability of the integrated HPC tools.

Hybrid numerical methods to solve shallow water equations for hurricane induced storm surge modeling

In this paper an efficient numerical method based on hybrid finite element and finite volume techniques to solve hurricane induced storm surge flow problem is presented. A segregated implicit projection method is used to solve the 2D shallow water equations on staggered unstructured meshes. The governing equations are written in non-conservation form. An intermediate velocity field is first obtained by solving the momentum equations with the matrix-free implicit cell-centered finite volume method. The nonlinear wave equation is solved by the node-based Galerkin finite element method. This staggered-mesh scheme is distinct from other conventional approaches in that the velocity components and auxiliary variables are stored at cell centers and vertices, respectively. The present model uses an implicit method, which is very efficient and can use a large time step without losing accuracy and stability.The hurricane induced wind stress and pressure, bottom friction, Coriolis effect, and tidal forcing conditions are implemented in this model. The levee overtopping option is implemented in the model as well. Hurricane Katrina (2005) storm surge has been simulated to demonstrate the robustness and applicability of the model.

Simulation of Hydrodynamic Cavitating Flows Using Stabilized Finite Element Method

This paper reports our progress on the simulation of cavitating ∞ows using the stabilized flnite element method. The solver is modifled from our incompressible free-surface ∞ow solver where the volume-of-∞uid (VOF) concept is applied. The liquid-vapor phase interface is treated as an internal interface captured by an interface function. The vapor bubble boundary can be located according to the value of the volume fraction of vapor. Source terms based on the bubble dynamics are added to the incompressible Navier-Stokes equations to model the physical phase change process (vaporization and condensation) due to cavitation. The discretization is based on the flnite element method stabilized using the Streamline-Upwinded/Petrov Galerkin (SUPG) method. The matrix-free GMRES solver together with block diagonal preconditioning are used to solve the large sparse linear system resulting from the flnite element discretization. The Message Passing Interface (MPI) functions are called to parallelize the code for large-scale applications on distributed memory computers. Preliminary results are presented to demonstrate the capability of our solver in simulating cavitating ∞ows.

Hybrid finite element/volume method for 3D incompressible flows with heat transfer

An implicit hybrid finite element (FE)/volume solver has been extended to incompressible flows coupled with the energy equation. The solver is based on the segregated pressure correction or projection method on staggered unstructured hybrid meshes. An intermediate velocity field is first obtained by solving the momentum equations with the matrix-free implicit cell-centred finite volume (FV) method. The pressure Poisson equation is solved by the node-based Galerkin FE method for an auxiliary variable. The auxiliary variable is used to update the velocity field and the pressure field. The pressure field is carefully updated by taking into account the velocity divergence field. Our current staggered-mesh scheme is distinct from other conventional ones in that we store the velocity components at cell centres and the auxiliary variable at vertices. The Generalized Minimal Residual (GMRES) matrix-free strategy is adapted to solve the governing equations in both FE and FV methods. The presented 2D and 3D numerical examples show the robustness and accuracy of the numerical method.

Variable Intensity Computational Mesh And Data Technique: A Practical Approach For Large-Scale Flow Simulation and Visualization

In this paper, we report the development of a parallel program to isotropically subdivide a coarse 3-D hybrid unstructured mesh to obtain a finer mesh. The main motivation is to generate very fine meshes, a task which is impossible using a sequential mesh generator on a single machine due to the memory limitation and algorithm scalability. We first generate a coarse mesh using any sequential unstructured mesh generator. We then subdivide the coarse mesh to obtain a finer one on a parallel computer platform. The new mesh obtained from the isotropic subdivision does not alter the quality of the original coarse mesh. Test cases, a generic reentry vehicle and an Army projectile, show that this program is a useful and an alternative tool to generate extremely large unstructured meshes. We have presented meshes and flow solutions at each subdivision. Flow solutions are obtained using CaMEL Aero, a compressible Navier-Stokes flow solver with the Detached Eddy turbulence model. Flow solutions and mesh subdivisions are performed in the ARL HPC cluster, Harold.

Overland Flow Modeling of Mississippi Coastal Region Using Finite Element Method

In this paper we describe the implementation and discussion of overland flow models using finite element method. The results of our overland flow simulations coupled with storm surges initiated with hurricanes in coastal regions are integrated into geographical information systems for visualization, analysis and decision-making. As a case study, we have modeled the overland flow caused by hurricane Katrina. Our computational domain starts from the Mississippi shoreline to about 75 kilometers inland. First we have run fully nonlinear, two-dimensional, barotropic hydrodynamic model ADCIRC with appropriate data and tidal information to simulate storm surge in the Gulf of Mexico. The ADCIRC simulation results in the boundary close to the shoreline are then used as driving force in our overland flow analysis. The overland simulation results are compared with available observed data from Katrina.

Numerical Simulation of a Spinning Projectile Using Parallel and Vectorized Unstructured Flow Solver

The finite volume method (FVM) is the most widely used numerical method by computational fluid dynamics (CFD) researchers to solve the compressible Navier-Stokes equations. A successful FVM solver should be accurate, efficient and robust. High-order spatial discretization must be used for accuracy. Implicit time integration is usually adopted to obtain better efficiency, especially for high Reynolds number flows. For large-scale applications, the solver should be parallelized and even vectorized to be able to run on parallel and vector computer platforms.

Development of an ESRI ArcToolBox for semi-automated building modeling from multipatch features

This paper briefly describes the development of an ESRI ArcToolBox that leverages commercial-off-the-shelf (COTS) software for the semi-automated generation of Open Geospatial Consortium (OGC) CityGML standard level of detail one (LoD1) and two (LoD2) building models from high resolution imagery and digital elevation models (DEM) for use in blast analysis applications. The ArcToolBox consists of Overwatch Systems Feature Analyst (v4.2), ESRI ArcGIS (v9.2) ModelBuilder, and the Safe Software Feature Manipulation Engine (v2010). This work is part of an on-going project to improve the blast damage predictions and calculation of evacuation distances for explosions in urban environments through development of a fast-running, easy-to-use desktop tool that would combine updated correlation modeling for urban blast and fragmentation with improved semi-automated geometry modeling techniques.

Hybrid Finite Element and Finite Volume Methods for Two Immiscible Fluid Flows

We have successfully extended our implicit hybrid finite element/volume solver to flows involving two immiscible fluids. The solver is based on the segregated pressure correction or projection method on staggered unstructured hybrid meshes. An intermediate velocity field is first obtained by solving the momentum equations with the matrix-free implicit cell-centered finite volume method. The pressure Poisson equation is solved by the node-based Galerkin finite element method for an auxiliary variable. The auxiliary variable is used to update the velocity field and the pressure field. The pressure field is carefully updated by taking into account the velocity divergence field. This updating strategy can be rigorously proven to be able to eliminate the unphysical pressure boundary layer and is crucial for the correct temporal convergence rate. Our current staggered-mesh scheme is distinct from other conventional ones in that we store the velocity components at cell centers and the auxiliary variable at vertices. The fluid-interface is captured by solving an advection equation for the volume fraction of one of the fluids. The same matrixfree finite volume method as the one used for momentum equations is used to solve the advection equation. We will focus on the interface sharpening strategy to minimize the smearing of the interface over time. We have developed and implemented a global mass conservation algorithm which enforces the conservation of the mass for each fluid. ecently, we developed a hybrid finite element/volume (FE/FV) solver [1] for incompressible flows. The hybrid solver is based on the well-known pressure correction (projection) method [2, 3]. The solution procedure follows a segregated approach to decouple the pressure from the velocity. The velocity field is updated by solving the momentum equation provided that a known pressure field is given as a source term, through a cell-centered finite volume (FV) discretization. The pressure does not directly enter the momentum equation. Instead, an auxiliary variable, which is closely related to the pressure, takes the place of pressure in the momentum equation, providing pressure gradient information. We put the auxiliary variable on the vertices of cells. This deployment provides a convenient way to evaluate the pressure gradient using the local finite element basis functions. The incremental value of the auxiliary variable is computed by solving a Poisson equation using the Galerkin finite element (FE) method. The auxiliary variable is then used to update the velocity field. After the final velocity field is determined, the pressure can be updated using the auxiliary variable and the velocity divergence field. The pressure is updated in such a way that the pressure field is free of unphysical conditions in the boundary layer. Our hybrid finite volume/element solver is aimed to take advantage of the merits of both the FV and the FE methods and avoid their shortcomings. For example, highly-stretched cells (also known as high-aspect-ratio cells) are commonly used inside the boundary layer for high Reynolds number flows to resolve the boundary layer and reduce the number of cells. The stabilization parameters in the stabilized FE based flow solvers [4, 5] are related to the characteristic element length that is not well defined for high-aspect-ratio mesh elements. Due to this, it is very difficult to control the numerical dissipation of stabilized finite element solvers. By contrast, the finite volume flow