Study of the jump fire produced by the interaction of two oblique fire fronts. Part 1. Analytical model and validation with no-slope laboratory experiments

2012 ◽  
Vol 21 (7) ◽  
pp. 843 ◽  
Author(s):  
Domingos X. Viegas ◽  
Jorge R. Raposo ◽  
David A. Davim ◽  
Carlos G. Rossa
Keyword(s):  
Analytical Model ◽  
Large Scale ◽  
Experimental Tests ◽  
Intersection Point ◽  
High Rate ◽  
Energy Concentration ◽  
Fire Behaviour ◽  
Rate Of Spread ◽  
In Fire ◽  
Intense Radiation

When two fires approach each other, convective and radiative heat transfer processes are greatly enhanced. The interaction between two linear fire fronts making an angle θoi between them is of particular interest as it produces a very rapid advance of their intersection point with intense radiation and convection activity in the space between the fire lines. This fire is designated here as a ‘jump fire’ for when the value of θoi is small, the intersection point of the fire lines can reach unusually high rate of spread values that decrease afterwards in the course of time. A very simple analytical model based on the concept of energy concentration between the fire lines is proposed to explain this behaviour, which in large-scale fires can be of great concern to personnel and property safety. Experimental tests performed at laboratory scale on a horizontal fuel bed confirmed the basic assumptions of the model and provide a framework to extend the present analysis to more general conditions, namely to explain the behaviour of real fires. Given the rapid changes in fire behaviour, ‘jump fires’ can be considered as a form of extreme fire behaviour.

Modelling the dynamic behaviour of junction fires with a coupled atmosphere–fire model

2017 ◽  
Vol 26 (4) ◽  
pp. 331 ◽  
Author(s):  
C. M. Thomas ◽  
J. J. Sharples ◽  
J. P. Evans
Keyword(s):  
Fire Spread ◽  
Community Safety ◽  
Fire Behaviour ◽  
Ambient Conditions ◽  
Fire Model ◽  
Fire Propagation ◽  
Dynamic Propagation ◽  
Rate Of Spread ◽  
Steady Rate ◽  
In Fire

Dynamic fire behaviour involves rapid changes in fire behaviour without significant changes in ambient conditions, and can compromise firefighter and community safety. Dynamic fire behaviour cannot be captured using spatial implementations of empirical fire-spread models predicated on the assumption of an equilibrium, or quasi-steady, rate of spread. In this study, a coupled atmosphere–fire model is used to model the dynamic propagation of junction fires, i.e. when two firelines merge at an oblique angle. This involves very rapid initial rates of spread, even with no ambient wind. The simulations are in good qualitative agreement with a previous experimental study, and indicate that pyro-convective interaction between the fire and the atmosphere is the key mechanism driving the dynamic fire propagation. An examination of the vertical vorticity in the simulations, and its relationship to the fireline geometry, gives insight into this mechanism. Junction fires have been modelled previously using curvature-dependent rates of spread. In this study, however, although fireline geometry clearly influences rate of spread, no relationship is found between local fireline curvature and the simulated instantaneous local rate of spread. It is possible that such a relationship may be found at larger scales.

Effects of fuel load and moisture content on fire behaviour and heating in masticated litter-dominated fuels

2013 ◽  
Vol 22 (4) ◽  
pp. 440 ◽  
Author(s):  
Jesse K. Kreye ◽  
Leda N. Kobziar ◽  
Wayne C. Zipperer
Keyword(s):  
Moisture Content ◽  
Fuel Load ◽  
Maximum Temperature ◽  
Fire Behaviour ◽  
Fuel Loading ◽  
Pine Flatwoods ◽  
Rate Of Spread ◽  
Soil Temperatures ◽  
Fuel Moisture Content ◽  
In Fire

Mechanical fuels treatments are being used in fire-prone ecosystems where fuel loading poses a hazard, yet little research elucidating subsequent fire behaviour exists, especially in litter-dominated fuelbeds. To address this deficiency, we burned constructed fuelbeds from masticated sites in pine flatwoods forests in northern Florida with palmetto-dominated understoreys and examined the effects of fuel load and fuel moisture content (FMC) on fire behaviour. Flame lengths (49–140 cm) and fireline intensity (183–773 kJ m–1 s–1) increased with loading (10–30 Mg ha–1) and were reduced by 40 and 47% with increasing FMC from 9 to 13%. Rate of spread was not influenced by fuel load, but doubled under drier FMC. Fuel consumption was >90% for all burns. Soil temperatures were influenced by both fuel load and FMC, but never reached lethal temperatures (60°C). However, temperatures of thermocouple probes placed at the fuelbed surface reached 274–503°C. Probe maximum temperature and duration at temperatures ≥60°C (9.5–20.0°C min) both increased with fuel load, but were unaffected by FMC. The fire behaviour observed in these unique litter-dominated fuelbeds provides additional insight into the burning characteristics of masticated fuels in general.

Analysis of the physical processes associated with junction fires at laboratory and field scales

2018 ◽  
Vol 27 (1) ◽  
pp. 52 ◽  
Author(s):  
J. R. Raposo ◽  
D. X. Viegas ◽  
X. Xie ◽  
M. Almeida ◽  
A. R. Figueiredo ◽  
...  
Keyword(s):  
Boundary Conditions ◽  
Large Scale ◽  
Symmetry Plane ◽  
Initial Boundary ◽  
Fire Spread ◽  
Intersection Point ◽  
Deceleration Phase ◽  
Rate Of Spread ◽  
Wide Range ◽  
Fire Front

Junction fires, which involve the merging of two linear fire fronts intersecting at a small angle, are associated with very intense fire behaviour. The dynamic displacement of the intersection point of the two lines and the flow along the symmetry plane of the fire are analysed for symmetric boundary conditions. It is observed that the velocity of displacement of this point increases very rapidly owing to strong convective effects created by the fire that are similar to those of an eruptive fire. The change of fire geometry and of its associated flow gradually blocks the rate of spread increase and creates a strong deceleration of the fire, which ends up behaving like a linear fire front. Results from laboratory and field-scale experiments, using various fuel beds and slope angles and from a large-scale fire show that the processes are similar at a wide range of scales with little dependence on the initial boundary conditions. Numerical simulation of the heat flux from two flame surfaces to an element of the fuel bed show that radiation can be considered as the main mechanism of fire spread only during the deceleration phase of the fire.

scholarly journals DESCRIBING FOREST FIRES — OLD WAYS AND NEW

1965 ◽  
Vol 41 (3) ◽  
pp. 301-305 ◽  
Author(s):  
C. E. van Wagner
Keyword(s):  
Forest Fires ◽  
Quantitative Measure ◽  
Verbal Description ◽  
Energy Output ◽  
Fire Behaviour ◽  
Fire Control ◽  
Linear Rate ◽  
Rate Of Spread ◽  
Fire Front ◽  
In Fire

This article deals with several ways of describing forest fires and their limitations. The simplest and oldest way is by simple verbal description. Then came the combination of rate of spread and resistance to control. The best quantitative measure of fire behaviour, however, is the rate of energy output per unit of fire front, quoted in conjunction with the linear rate of spread. If the full benefits of advances in fire control technology are to be realized, wider use of the energy output concept will probably be necessary, first among fire researchers and eventually among fire control people.

Transient creep analytical modeling for shear endplate assemblies in fire

2020 ◽  
Vol 11 (3) ◽  
pp. 289-309
Author(s):  
Hadi O. Al Haddad ◽  
Elie G. Hantouche
Keyword(s):  
Analytical Model ◽  
Design Procedure ◽  
Experimental Tests ◽  
Thermal Creep ◽  
Geometrical Parameters ◽  
Content Type ◽  
Axial Forces ◽  
Creep Effect ◽  
Fire Scenarios ◽  
In Fire

Purpose The purpose of this study is to develop an analytical model that is capable of predicting the behavior of shear endplate beam-column assemblies when exposed to fire, taking into account the thermal creep effect. Design/methodology/approach An analytical model is developed and validated against finite element (FE) models previously validated against experimental tests in the literature. Major material and geometrical parameters are incorporated in the analysis to investigate their influence on the overall response of the shear endplate assembly in fire events. Findings The analytical model can predict the induced axial forces and deflections of the assembly. The results show that when creep effect is considered explicitly in the analysis, the beam undergoes excessive deformation. This deformation needs to be taken into account in the design. The results show the significance of thermal creep effect on the behavior of the shear endplate assembly as exposed to various fire scenarios. Research limitations/implications However, the user-defined constants of the creep equations cannot be applied to other connection types. These constants are limited to shear endplate connections having the material and geometrical parameters specified in this study. Originality/value The importance of the analytical model is that it provides a time-effective, simple and comprehensive technique that can be used as an alternative to the experimental tests and numerical methods. Also, it can be used to develop a design procedure that accounts for the transient thermal creep behavior of steel connections in real fire.

scholarly journals High-Rate Transition Metal-based Cathode Materials for Battery-Supercapacitor Hybrid Devices

2021 ◽  
Author(s):  
Cong Wang ◽  
Zehao Song ◽  
Pei Shi ◽  
Lin Lv ◽  
Houzhao Wan ◽  
...  
Keyword(s):  
Large Scale ◽  
Rapid Development ◽  
Electronic Devices ◽  
High Rate ◽  
Specific Power ◽  
Energy Storage Devices ◽  
Storage Devices ◽  
Electrochemical Devices ◽  
Hybrid Devices ◽  
Scale Grid

With the rapid development of portable electronic devices, electric vehicles and large-scale grid energy storage devices, it needs to reinforce specific energy and specific power of related electrochemical devices meeting...

scholarly journals Rapid evolution at the Drosophila telomere: transposable element dynamics at an intrinsically unstable locus

Genetics ◽  
2020 ◽  
Vol 217 (2) ◽  
Author(s):  
Michael P McGurk ◽  
Anne-Marie Dion-Côté ◽  
Daniel A Barbash
Keyword(s):  
Copy Number ◽  
Large Scale ◽  
Insertion Site ◽  
Rapid Evolution ◽  
Interspecific Variation ◽  
High Rate ◽  
Evolutionary Strategy ◽  
Control Mechanisms ◽  
Genetic Conflict ◽  
Number Variation

AbstractDrosophila telomeres have been maintained by three families of active transposable elements (TEs), HeT-A, TAHRE, and TART, collectively referred to as HTTs, for tens of millions of years, which contrasts with an unusually high degree of HTT interspecific variation. While the impacts of conflict and domestication are often invoked to explain HTT variation, the telomeres are unstable structures such that neutral mutational processes and evolutionary tradeoffs may also drive HTT evolution. We leveraged population genomic data to analyze nearly 10,000 HTT insertions in 85  Drosophila melanogaster genomes and compared their variation to other more typical TE families. We observe that occasional large-scale copy number expansions of both HTTs and other TE families occur, highlighting that the HTTs are, like their feral cousins, typically repressed but primed to take over given the opportunity. However, large expansions of HTTs are not caused by the runaway activity of any particular HTT subfamilies or even associated with telomere-specific TE activity, as might be expected if HTTs are in strong genetic conflict with their hosts. Rather than conflict, we instead suggest that distinctive aspects of HTT copy number variation and sequence diversity largely reflect telomere instability, with HTT insertions being lost at much higher rates than other TEs elsewhere in the genome. We extend previous observations that telomere deletions occur at a high rate, and surprisingly discover that more than one-third do not appear to have been healed with an HTT insertion. We also report that some HTT families may be preferentially activated by the erosion of whole telomeres, implying the existence of HTT-specific host control mechanisms. We further suggest that the persistent telomere localization of HTTs may reflect a highly successful evolutionary strategy that trades away a stable insertion site in order to have reduced impact on the host genome. We propose that HTT evolution is driven by multiple processes, with niche specialization and telomere instability being previously underappreciated and likely predominant.

Development and Modeling of a Highly-Adjustable Base Isolator Utilizing Magnetorheological Elastomer

2013 ◽  
Author(s):  
Yancheng Li ◽  
Jianchun Li
Keyword(s):  
Analytical Model ◽  
Seismic Isolation ◽  
Large Scale ◽  
Lateral Stiffness ◽  
Magnetorheological Elastomer ◽  
Isolation System ◽  
Vertical Loading ◽  
Base Isolator ◽  
Field Dependent ◽  
Dependent Property

This paper presents a recent research breakthrough on the development of a novel adaptive seismic isolation system as the quest for seismic protection for civil structures, utilizing the field-dependent property of the magnetorheological elastomer (MRE). A highly-adjustable MRE base isolator was developed as the key element to form smart seismic isolation system. The novel isolator contains unique laminated structure of steel and MRE layers, which enable its large-scale civil engineering applications, and a solenoid to provide sufficient and uniform magnetic field for energizing the field-dependent property of MR elastomers. With the controllable shear modulus/damping of the MR elastomer, the developed adaptive base isolator possesses a controllable lateral stiffness while maintaining adequate vertical loading capacity. Experimental results show that the prototypical MRE base isolator provides amazing increase of lateral stiffness up to 1630%. Such range of increase of the controllable stiffness of the base isolator makes it highly practical for developing new adaptive base isolation system utilizing either semi-active or smart passive controls. To facilitate the structural control development using the adaptive MRE base isolator, an analytical model was developed to stimulate its behaviors. Comparison between the analytical model and experimental data proves the effectiveness of such model in reproducing the behavior of MRE base isolator, including the observed strain stiffening effect.

Structural Post-Fire Behaviour of the Steel I-Shape Beams-to-Cylindrical Columns

2012 ◽  
Vol 249-250 ◽  
pp. 1057-1062
Author(s):  
M. Zeinoddini ◽  
S.A. Hosseini ◽  
M. Daghigh ◽  
S. Arnavaz
Keyword(s):  
Structural Damage ◽  
Elevated Temperatures ◽  
Small Scale ◽  
Fire Tests ◽  
Fire Behaviour ◽  
Fire Event ◽  
Rescue Workers ◽  
Left Behind ◽  
Oil Platforms ◽  
In Fire

Previous researchers have tried to predict the response of different types of structures under elevated temperatures. The results are important in preventing the collapse of buildings in fire. Post-fire status of the structures is also of interest for ensuring the safety of rescue workers during the fire and in the post-fire situations. Determining the extent of the structural damage left behind a fire event is necessary to draw up adequate repair plans. Connections play an important role on the fire performance of different structures. Due to the high cost of fire tests, adequate experimental data about a broad range of connections is not available. A vulnerable type of such connections to fire is the weld connections between I-shape beams and cylindrical columns in oil platform topsides. Considering the high probability of fire in oil platforms, study of the behaviour of these connections at elevated temperatures and in the post-fire, is of great importance. In the current study, eight small scale experimental fire tests on welded connections between I-shape beams and cylindrical columns have been conducted. Four tests are aimed at investigating the structural performance of this connection at elevated temperature. In other tests, post-fire behaviour of these connections has been studied to investigate their residual structural strength.

On the irreversibility of internal-wave dynamics due to wave trapping by mean flow inhomogeneities. Part 1. Local analysis

1993 ◽  
Vol 251 ◽  
pp. 21-53 ◽  
Author(s):  
Sergei I. Badulin ◽  
Victor I. Shrira
Keyword(s):  
Shear Flow ◽  
Internal Wave ◽  
Wave Field ◽  
Large Scale ◽  
Spatial Scales ◽  
Energy Concentration ◽  
Local Analysis ◽  
Mean Flow ◽  
Wave Trapping ◽  
Wave Dynamics

The propagation of guided internal waves on non-uniform large-scale flows of arbitrary geometry is studied within the framework of linear inviscid theory in the WKB-approximation. Our study is based on a set of Hamiltonian ray equations, with the Hamiltonian being determined from the Taylor-Goldstein boundary-value problem for a stratified shear flow. Attention is focused on the fundamental fact that the generic smooth non-uniformities of the large-scale flow result in specific singularities of the Hamiltonian. Interpreting wave packets as particles with momenta equal to their wave vectors moving in a certain force field, one can consider these singularities as infinitely deep potential holes acting quite similarly to the ‘black holes’ of astrophysics. It is shown that the particles fall for infinitely long time, each into its own ‘black hole‘. In terms of a particular wave packet this falling implies infinite growth with time of the wavenumber and the amplitude, as well as wave motion focusing at a certain depth. For internal-wave-field dynamics this provides a robust mechanism of a very specific conservative and moreover Hamiltonian irreversibility.This phenomenon was previously studied for the simplest model of the flow non-uniformity, parallel shear flow (Badulin, Shrira & Tsimring 1985), where the term ‘trapping’ for it was introduced and the basic features were established. In the present paper we study the case of arbitrary flow geometry. Our main conclusion is that although the wave dynamics in the general case is incomparably more complicated, the phenomenon persists and retains its most fundamental features. Qualitatively new features appear as well, namely, the possibility of three-dimensional wave focusing and of ‘non-dispersive’ focusing. In terms of the particle analogy, the latter means that a certain group of particles fall into the same hole.These results indicate a robust tendency of the wave field towards an irreversible transformation into small spatial scales, due to the presence of large-scale flows and towards considerable wave energy concentration in narrow spatial zones.

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