Glenn P. Forney

A reactive molecular dynamics model of thermal decomposition in polymers: I. Poly(methyl methacrylate)

The theory and implementation of reactive molecular dynamics (RMD) are presented. The capabilities of RMD and its potential use as a tool for investigating the mechanisms of thermal transformations in materials are demonstrated by presenting results from simulations of the thermal degradation of poly(methyl methacrylate) (PMMA). While it is known that depolymerization must be the major decomposition channel for PMMA, there are unanswered questions about the nature of the initiation reaction and the relative reactivities of the tertiary and primary radicals formed in the degradation process. The results of our RMD simulations, performed directly in the condensed phase, are consistent with available experimental information. They also provide new insights into the mechanism of the thermally induced conversion of this polymer into its constituent monomers.

Improved Radiation And Combustion Routines For A Large Eddy Simulation Fire Model

Improvements have been made to the combustion and radiation routines of a large eddy simulation fire model maintained by the National Institute of Standards and Technology. The combustion is based on a single transport equation for the mixture fraction with state relations that reflect the basic stoichiometry of the reaction. The radiation transport equation is solved using the Finite Volume Method, usually with the gray gas assumption for large scale simulations for which soot is the dominant emitter and absorber. To make the model work for practical fire protection engineering problems, some approximations were made within the new algorithms. These approximations will be discussed and sample calculations presented.

Development and Validation of Corridor Flow Submodel for CFAST

The modeling of fire and smoke spread is an evolvingfield. As knowledge is acquired and resources become available, models are enhanced to make their predictions more accurate and/or their computations faster. This paper will discuss the Consolidated Fire and Smoke Transport (CFAST) zone fire model, developed by the National Institute of Standards and Technology (NIST), and a recent addition to that model, referred to as the Corridor Flow Submodel. The goal of this new submodel is to more accurately predict the flow of smoke down a corridor which has an impact on fire protection issues such as detection and escape time. Prior to the addition of this new submodel, CFAST assumed that smoke traveled instantly from one side of a compartment to another. Development of the submodel will be discussed and then the enhanced CFAST, Version 4.0.1 (executable dated 3/8/00), will be used to model a real-scale experiment conducted onboard the ex-USS SHADWELL, the Navys R&D Damage Control platform.

Computational fluid dynamics modelling of fire

An overview of a methodology for simulating fires and other thermally-driven, low-speed flows is presented. The model employs a number of simplifications of the governing equations that allow for relatively fast simulations of practical fire scenarios. The hydrodynamic model consists of the low Mach number large-eddy simulation subgrid closure with either a constant or dynamic coefficient eddy diffusivity. Combustion is typically treated as a mixing-controlled, single-step reaction of fuel and oxygen. The radiation transport equation is written in terms of a spectrally-averaged grey gas. Applications of the model include the design of fire protection systems in buildings and the reconstruction of actual fires.

Spectroscopic Quantitative Analysis of Strongly Interacting Systems: Human Plasma Protein Mixtures

Blood plasma protein infrared spectra, while qualitatively very similar, display subtle differences in the frequencies and intensities of absorption bands. These small differences are sufficient to permit an accurate quantitative analysis of mixtures of these proteins. In this paper we examine the performance of some alternative methods of spectroscopic quantitative analysis in determining the concentrations of proteins in aqueous solutions. The widely-used K matrix method, using sloping baselines and intercept functions, was found to be inadequate for these determinations. In contrast, a method based on the little-known Q matrix approach, augmented by a robust equation solver, yielded results with a sufficient degree of accuracy to make it a viable tool for use in the study of proteins at solid interfaces and for more general applications in the field of protein chemistry.

Understanding fire and smoke flow through modeling and visualization

Computer modeling and visualization are important tools for understanding the processes of fire behavior. Fire models range in complexity from simple correlations for predicting quantities such as flame heights or flow velocities to moderately complex zone fire models for predicting time-dependent smoke layer temperatures and heights. Zone fire model calculations can run on todays computers within minutes because they solve only four differential equations per room. Zone models approximate the entire upper layer with just one temperature. This approximation works remarkably well but breaks down for complicated flows or geometries. For such cases, computational fluid dynamics (CFD) techniques are required.

Improvement in predicting smoke movement in compartmented structures

This paper describes improvements which have been made in the CFAST model of fire growth and smoke transport for compartmented structures. In particular, we are interested in the ability to model the movement of toxic gases from the room of origin of a fire to a distant compartment. The newest phenomena in the model are vertical flow and mechanical ventilation. Finally, we have improved the radiation transport scheme which affects energy distribution, and therefore the buoyancy forces. These are very important in actual situations relevant to fire growth and smoke propagation, as is demonstrated.

Developing detector siting rules from computational experiments in spaces with complex geometries

Abstract The National Institute of Standards and Technology (NIST) is conducting a 4-year research project wherein a computational fluid dynamics (CFD) computer code is utilized to map temperature, flow velocities, and particle densities in spaces with complex ceiling geometries. Through parametric variation of independent variables for the fire and the space, the number and location of smoke or thermal sensors required to assure response prior to a critical fire size is determined. The first year addressed horizontal ceilings with open beams or joists, and the second year adds sloped ceilings. In addition to the geometric studies, several special studies have been conducted. These include detection of low energy fires (as low as 100 W), stratification of fire gases in spaces with a vertical thermocline which exceeds the plume temperature, and obstructions which do not come, completely to the ceiling. A unique method of relating the response of detectors to the predicted conditions has been developed which can be utilized with any CFD model or with experimental data. The data analysis is being used to produce siting rules for inclusion directly into existing codes. The paper will review the results of the first 2 years of the project and present some thoughts on the potential for these techniques to greatly improve the technical basis for the utilization of fire sensors in complex installations.

Modeling Solid Sample Burning.

Black PMMA was burned in the cone calorimeter in two orientations (horizontal and vertical), at imposed radiant heat fluxes of (0, 5, 10, 25, 50, and 75) kW/m 2 , and the visual appearance, flame size, heat release rate, and mass loss rate were recorded. Various other experimental parameters were varied. The topography of the burned samples was also recorded, and the heat flux to the sample was inferred from the variation of the mass loss over the surface of the sample. The burning was subsequently modeled using a computational fluid dynamics (CFD) model, and various experimental, numerical, and physical parameters were varied in the simulations. The results provide an indication of the ability of the fire model to predict the burning of a simple solid sample, and also provide guidance concerning the importance of various experimental and numerical parameters for accurate simulation.

Modeling Of Sprinkler, Vent And Draft Curtain Lnteraction

The International Fire Sprinkler, Smoke & Heat Vent, Draft Curtain Fire Test Project organized by the National Fire Protection Research Foundation (NFPRF) brought together a group of industrial sponsors to support and plan a series of large scale tests to study the interaction of sprinklers, roof vents and draft curtains of the type found in large warehouses, manufacturing facilities, and warehouse-like retail stores. In conjunction with the large scale tests, NIST developed a numerical model based on large eddy simulation techniques, the Industrial Fire Simulator (IFS), that could be used to plan, analyze and supplement the test results. A series of bench scale experiments was conducted to develop necessary input data for the model. These experiments generated data describing the burning rate and flame spread behavior of the cartoned plastic commodity, thermal response parameters and spray pattern of the sprinkler, and the effect of the water spray on the burning commodity.