- Author
-
Prasad, K. R.
|
Patnaik, G.
|
Kailasanath, K.
- Title
- Advanced Simulation Tool for Improved Damage Assessment. Part 1. A Multiblock Technique for Simulating Fire and Smoke Spread in Large Complex Enclosures.
- Coporate
- Naval Research Laboratory, Washington, DC
Science Applications International Corp., VA
- Report
-
NRL/MR/6410-00-8428,
February 21, 2000,
30 p.
- Keywords
-
damage
|
simulation
|
fire spread
|
smoke
|
enclosures
|
flow fields
|
air entrainment
|
detonation
|
combustion
- Identifiers
- multiblock technique; complex enclosures
- Abstract
- Shipboard and submarine fires present a variety of novel problems for firefighters due to the unique nature of the environment. In particular, the enclosed spaces permit heat and smoke to build to levels far in excess of those found in most structural fires. Further aggravating the situation is the high rate of heat transfer through the steel bulkheads and decks, which contributes to rapid fire spread. Firefighting in cluttered machinery spaces has its unique challenges. A computer based model that can quickly and accurately estimate the impact of a fire, and the effectiveness of measures used to control the fire can be a valuable tool for firefighting. There are two major classes of computer models for analysing fire development in large enclosures. Stochastic or probabilistic models generally treat the fire growth as a series of sequential events or states. Mathematical rules are established to govern the transition from one event to another and probabilities are assigned to each transfer point based on analysis of relevant experimental data and historical fire incidence data. In contrast, deterministic models represent the processes encountered in a compartment fire by mathematical expressions based on physics and chemistry. The most common type of deterministic fire model is the "zone" or "control volume" based model. The zone model represents the system as a few distinct compartment gas zones resulting from thermal stratification due to buoyancy. The fire is represented as a source of energy and mass, and manifests itself as a plume, which acts as a pump for the mass from the lower zones to the upper zones. Zone models utilize equations employing empirical relationships and constants obtained from experiments. These empirical expressions will break down as the geometries become more complex. Any radical departure by the fire system from the basic concept of the zone model can seriously affect the accuracy and validity of the approach. The building block of the zone model is the conservation equations for the upper and lower gas zones. These equations are developed either by using fundamental equations of energy and mass transport in control volume form as applied to the zones or by using differential equations that represent the conservation laws and integrating them over the zones. The momentum equations are not explicitly used. Information needed to compute velocities and pressures is based on simplifying assumptions and specific applications of momentum principles at vent boundaries of the compartment. Fowkes in his work with Emmons appears to be the first to publish a basis for the zone model approach. Almost simultaneously, computer models based on the zone model approach were produced by Quintiere, Pape and Waterman and by Mitler working with Emmons. ASET, CFAST, FIRST and WPI/FIRE are some of the zone based computer models that are presently being used for studying fires in large enclosures.