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FEM3A simulations of selected LNG vapor barrier verification field tests

Description: In order to evaluate and eventually predict the possible mitigating effects of vapor fences on the dispersion of the vapor cloud resulting from an accidental liquefied natural gas (LNG) spill in storage areas, a research program was initiated to evaluate methods for predicting LNG dispersion distances for realistic facility configurations. As part of the program, Lawrence Livermore National Laboratory (LLNL) conducted a series of large-scale field experiments called the LNG Vapor Barrier Verification Field Trials (also referred to as the Falcon Series) at the Liquefied Gaseous Fuels Spill Test Facility (LGFSTF), Nevada. Objectives were (1) to provide a data base on LNG vapor dispersion from spill involving complex field obstacles to assist in validation of wind tunnel and mathematical models, and (2) to assess the effectiveness of vapor fences for mitigating LNG vapor dispersion hazards in the events of an accidental spill. Five spill experiments were conducted on water in order to generate vapor at rates equivalent to the liquid spill rates. In this study, the FEM3A model was applied to simulate four of the Falcon experiments. The objectives of this study were, through numerical modeling and a detailed model-data comparison: (1) to improve our understanding of LNG vapor dispersion involving vapor barriers, (2) to assess FEM3A in modeling such complex vapor dispersion scenarios, and (3) to complement the results of field and wind tunnel tests, such as providing plausible explanations for unexpected results and filling in data gaps due to instrument failure or limited array size. Toward these goals, the relevant field measurements were analyzed and several series of 2-D and 3-D simulations were carried out. 11 refs., 93 figs., 11 tabs.
Date: October 1, 1990
Creator: Chan, S.T.
Partner: UNT Libraries Government Documents Department

Recent upgrades and enhancements of the FEM3A model

Description: In 1984, the US Army Edgewood Research, Development and Engineering Center began to fund Lawrence Livermore National Laboratory to further develop FEM3, a fully three-dimensional heavy-gas dispersion model, as a research tool for studying the atmospheric transport and diffusion of certain chemical systems. As a result, a significantly improved version of the model, called FEM3A, was delivered to ERDEC in 1988. During the past few years, two more major improvements have been developed and tested. They are: improved mass conservation for treating dispersion scenarios with large density variations, and the addition of an advanced turbulence submodel based on the k-{var_epsilon} transport equations. These enhancements have resulted in substantial improvements in the dispersion simulations of heavy-gases and can greatly extend the range of applicability of the model, including the ability to treat problems with large density variations and dispersion scenarios of much greater complexities. Documented in this report are the new features and some of the improvements obtained with the new model.
Date: December 1, 1994
Creator: Chan, S.T.
Partner: UNT Libraries Government Documents Department

Three-dimensional model for simulating atmospheric dispersion of heavy-gases over complex terrain

Description: To help understand heavy gas releases and simulate the resultant dispersion, we have developed a three-dimensional finite element model called FEM3 and an improved version names FEM3A for solving the time dependent conservation equations based on generalized anelastic approximation. Recent enhancements to the model to include the treatment of dispersion scenarios involving density variations much larger than the liquefied natural gas range and an advanced turbulence submodel based on the buoyancy-extended transport equations. This paper presents the main features of the present model FEM3C and numerical results from the simulations of a field-scale LNG spill experiment.
Date: September 1, 1997
Creator: Chan, S.T.
Partner: UNT Libraries Government Documents Department

Numerical simulation of the mitigating effects of an LNG vapor fence

Description: FEM3A, a fully three-dimensional numerical model for simulating the atmospheric dispersion of heavy gases involving complex geometry, has been used to investigate the mitigating effects of a vapor fence for LNG storage areas. In this paper, a brief description of the numerical model used to perform such calculations is given, the problem being simulated is described, and an intercomparison among the results from numerical simulations (with and without the vapor fence) and field data (with vapor fence) is made. The numerical results indicate that, with the present fence configuration, the maximum concentration on the cloud centerline was reduced by a factor of two or more within 250 m behind the fence, and the downwind distance to the 2.5% concentration was reduced from 365 m to 230 m. However, a vapor fence could also cause the vapor cloud to linger considerably longer in the source area, thus increasing the potential for ignition and combustion within the vapor fence and the area nearby over time. 8 refs., 10 figs.
Date: May 1, 1990
Creator: Chan, S.T.
Partner: UNT Libraries Government Documents Department

Recent progress in modeling the atmospheric dispersion of heavy gases over variable terrain using the three-dimensional conservation equations

Description: In this paper, a three-dimensional, conservation equation model for simulating the atmospheric dispersion of heavy gases has been briefly described; the model was successfully applied and assessed via simulating three distinctly different LNG spill experiments. These experiments involve approximately 30 m/sup 3/ LNG spills, with atmospheric conditions ranging from slightly stable to slightly unstable (ambient wind speed from about 2 m/s to 10 m/s). In general, good agreement between model predictions and field measurements was observed in all cases based on comparing, among others, the maximum concentrations as a function of downwind distance, the maximum downwind distances to the LFL, time histories of concentration at specific locations, and concentration contours on certain horizontal and crosswind surfaces. In particular, the overall results obtained in the model calculations with the simulated actual topography were shown to correlate much better with the field data in that many important features of the vapor cloud observed under the light wind conditions of Burro 8 were successfully reproduced. These include the spreading of vapor cloud in all directions (in upwind direction as well), the vortex-induced high concentration regions, the bifurcation of the NG cloud, and the deflection of the NG cloud due to sloping terrain. Through the present numerical simulations, the effects of variable terrain on the dispersion of heavy gases have been clearly demonstrated. Even with the relatively mild terrain at the test site and under a moderately high wind speed of approx. 6 m/s (Burro 9), the resulting vapor cloud dispersion was seen to differ noticeably from that using a flat terrain assumption. The combined effects of large gravity-flow (relative to the mean wind) over variable terrain and under light wind conditions (Burro 8) were shown to be even more profound. In such gravity-flow dominated regimes, proper treatment of the terrain, if present, is ...
Date: August 1, 1983
Creator: Chan, S. T. & Ermak, D. L.
Partner: UNT Libraries Government Documents Department

Meteorological data assimilation for real-time emergency response

Description: The US Department of Energy`s Atmospheric Release Advisory Capability (ARAC) provides real-time dose assessments of airborne pollutant releases. Diverse data assimilation techniques are required to meet the needs of a new generation of ARAC models and to take advantage of the rapidly expanding availability of meteorological data. We are developing a hierarchy of algorithms to provide gridded meteorological fields which can be used to drive dispersion codes or to provide initial fields for mesoscale models. Data to be processed include winds, temperature, moisture, and turbulence.
Date: November 1, 1996
Creator: Sugiyama, G. & Chan, S.T.
Partner: UNT Libraries Government Documents Department

New meteorological data assimilation model for real-time emergency response

Description: We are developing a new meteorological data assimilation model for the Atmospheric Release Advisory Capability (ARAC) project at Lawrence Livermore National Laboratory, which provides real-time dose assessments of airborne pollutant releases. The model, ADAPT (Atmospheric Data Assimilation and Parameterization Techniques), builds three-dimensional meteorological fields, which can be used to drive dispersion models or to initialize or evaluate mesoscale models. ADAPT incorporates many new features and substantial improvements over the current ARAC operational models MEDIC/MATHEW, including the use of continuous-terrain variable-resolution grids, the ability to treat assorted meteorological data such as temperatures, pressure, and relative humidity, and a new algorithm to produce mass-consistent wind fields. In this paper, we will describe the main features of the model, current work on a new atmospheric stability parameterization, and show example results.
Date: September 1, 1997
Creator: Sugiyama, G. & Chan, S.T.
Partner: UNT Libraries Government Documents Department

New model for generating mass-consistent wind fields over continuous terrain

Description: Based on a mixed variational principle and the finite element method, a model for efficiently generating mass-consistent wind fields over continuous terraing has been developed. Two numerical examples are presented to demonstrate the applicability of the model.
Date: November 1, 1996
Creator: Chan, S.T. & Sugiyama, G.
Partner: UNT Libraries Government Documents Department

An update on projection methods for transient incompressible viscous flow

Description: Introduced in 1990 was the biharmonic equation (for the pressure) and the concomitant biharmonic miracle when transient incompressible viscous flow is solved approximately by a projection method. Herein is introduced the biharmonic catastrophe that sometimes occurs with these same projection methods.
Date: July 1, 1995
Creator: Gresho, P.M. & Chan, S.T.
Partner: UNT Libraries Government Documents Department

A Model for Flow and Dispersion Around Buildings and Its Validation Using Laboratory Measurements

Description: Numerical modeling of airflow and pollutant dispersion around buildings is a challenging task due to the geometrical variations of buildings and the extremely complex flow created by such surface-mounted obstacles. The airflow around buildings inevitably involves impingement and separation regions, a multiple vortex system with building wakes, and jetting effects in street canyons. The interference from adjacent buildings further complicates the flow and dispersion patterns. Thus accurate simulations of such flow and pollutant transport require not only appropriate physics submodels but also accurate numerics and significant computing resources. We have developed an efficient, high resolution CFD model for such purposes, with a primary goal to support incident response and preparedness in emergency response planning, vulnerability analysis, and the development of mitigation techniques.
Date: May 17, 2000
Creator: Chan, S. T.; Stevens, D. & Lee, R.
Partner: UNT Libraries Government Documents Department

Model Validation of Flow and Dispersion Around a Cube

Description: This paper compares results for flow over a cube between laboratory experiments and two numerical simulations. One of the simulations is a Reynolds-averaged Navier-Stokes (RANS) calculation, the other a large eddy simulation (LES). Both the structure of the flow and dispersion of a source behind the cube are compared. It was found that both simulations performed well when mean flows are compared. For dispersion, the LES performed better than the RANS simulation in that it was able to capture the effect of vortex shedding and produce a wider dispersion pattern. The plume in the RANS simulation is very similar to instantaneous realizations of the plume in the LES. Near the cube, the results were very similar. This model validation study suggests that the high cost of LES computations may be warranted when detailed time-varying solutions are of high interest, However the high fidelity RANS approach is a cost-effective alternative to LES in obtaining time-average mean field results.
Date: January 20, 2000
Creator: Lee, R. L. & Chan, S. T.
Partner: UNT Libraries Government Documents Department

An Evaluation of Two Advanced Turbulence Models for Simulating the Flow and Dispersion Around Buildings

Description: Numerical modeling of airflow and pollutant dispersion around buildings is a challenging task due to the geometrical variations of buildings and the extremely complex flow created by such surface-mounted obstacles. The airflow around buildings inevitably involves impingement and separation regions, building wakes with multiple vortices, and jetting effects in street canyons. The interference from adjacent buildings further complicates the flow and dispersion patterns. Thus accurate simulations of building-scale transport phenomena requires not only appropriate physics submodels but also significant computing resources. They have developed an efficient, high resolution CFD model for simulating chemical and biological releases around buildings. The primary goal is to support incident response and preparedness in emergency response planning and vulnerability analysis.
Date: March 14, 2000
Creator: Chan, S.T. & Stevens, D.E.
Partner: UNT Libraries Government Documents Department

Air quality modeling for emergency response applications. [MATHEW; ADPIC; FEM3]

Description: The three-dimensional diagnostic wind field model (MATHEW) and the particle-in-cell transport and diffusion model (ADPIC) are used by the Atmospheric Release Advisory Capability (ARAC) for real-time assessments of the consequences from accidental releases of radioactivity into the atmosphere. For the dispersion of hazardous heavier-than-air gases, a time-dependent, three-dimensional finite element model (FEM3) is used. These models have been evaluated extensively against a wide spectrum of field experiments involving the release of chemically inert tracers or heavier-than-air gases. The results reveal that the MATHEW/ADPIC models are capable of simulating the spatial and temporal distributions of tracer concentration to within a factor of 2 for 50% of the measured tracer concentrations for near surface releases in relatively flat terrain and within a factor of 2 for 20% of the comparisons for elevated releases in complex terrain. The FEM3 model produces quite satisfactory simulations of the spatial and temporal distributions of heavier-than-air gases, typically within a kilometer of the release point. The ARAC consists of a centralized computerized emergency response system that is capable of supporting up to 100 sites and providing real-time predictions of the consequence of transportation accidents that may occur anywhere. It utilizes pertinent accident information, local and regional meteorology, and terrain as input to the MATHEW/ADPIC models for the consequence analysis. It has responded to over 150 incidents and exercises over the past decade.
Date: December 1, 1985
Creator: Gudiksen, P.H.; Chan, S.T.; Knox, J.B.; Dickerson, M.H. & Lange, R.
Partner: UNT Libraries Government Documents Department

Simulation of three-dimensional, time-dependent, incompressible flows by a finite element method

Description: A finite element model has been developed for simulating the dynamics of problems encountered in atmospheric pollution and safety assessment studies. The model is based on solving the set of three-dimensional, time-dependent, conservation equations governing incompressible flows. Spatial discretization is performed via a modified Galerkin finite element method, and time integration is carried out via the forward Euler method (pressure is computed implicitly, however). Several cost-effective techniques (including subcycling, mass lumping, and reduced Gauss-Legendre quadrature) which have been implemented are discussed. Numerical results are presented to demonstrate the applicability of the model.
Date: January 1, 1981
Creator: Chan, S.T.; Gresho, P.M.; Lee, R.L. & Upson, C.D.
Partner: UNT Libraries Government Documents Department

An Evaluation of Boundary Conditions for Modeling Urban Boundary Layers

Description: Numerical modeling of the urban boundary layer is complicated by the need to describe airflow patterns outside of the computational domain. These patterns have an impact on how successfully the simulation is able to model the turbulence associated with the urban boundary layer. This talk presents experiments with the model boundary conditions for simulations that were done to support two Department of Energy observational programs involving the Salt Lake City basin. The Chemical/Biological Non-proliferation Program (CBNP) is concerned with the effects of buildings on influencing dispersion patterns in urban environments. The Vertical Transport and Mixing Program (VTMX) investigating mixing mechanisms in the stable boundary layer and how they are influenced by the channeling caused by drainage flows or by obstacles such as building complexes. Both of these programs are investigating the turbulent mixing caused by building complexes and other urban obstacles.
Date: May 18, 2000
Creator: Calhoun, R.J.; Chan, S.T. & Lee, R.L.
Partner: UNT Libraries Government Documents Department

Building Scale Simulation in Support of Field Experiments around Salt Lake City

Description: Numerical modeling of the urban boundary layer is complicated by the need to describe airflow patterns outside of the computational domain. These patterns have an impact on how successfully the simulation is able to model the turbulence associated with the urban boundary layer. This talk presents experiments with the model boundary conditions for simulations that were done to support two Department of Energy observational programs involving the Salt Lake City basin. The Chemical/Biological Non-proliferation Program (CBNP) is concerned with the effects of buildings on influencing dispersion patterns in urban environments. The Vertical Transport and Mixing Program (VTMX) investigating mixing mechanisms in the stable boundary layer and how they are influenced by the channeling caused by drainage flows or by obstacles such as building complexes. Both of these programs are investigating the turbulent mixing caused by building complexes and other urban obstacles.
Date: May 30, 2000
Creator: Stevens, D.; Calhoun, R.J.; Chan, S.T.; Lee, R.L.; Leone, J. & Shinn, J.
Partner: UNT Libraries Government Documents Department

Falcon series data report: 1987 LNG vapor barrier verification field trials

Description: A series of five Liquefied Natural Gas Spills up to 66 m{sup 3} in volume were performed on water within a vapor barrier structure at Frenchman Flat on the Nevada Test Site as a part of a joint government/industry study. This data report presents a description of the tests, the test apparatus, the instrumentation, the meteorological conditions, and the data from the tests. 16 refs., 27 figs., 8 tabs.
Date: June 1, 1990
Creator: Brown, T.C.; Cederwall, R.T.; Chan, S.T.; Ermak, D.L.; Koopman, R.P.; Lamson, K.C. et al.
Partner: UNT Libraries Government Documents Department