1,720,972 research outputs found
Development of a novel hybrid field and zone fire model
Full text linkThis thesis describes the design and implementation of a novel hybrid field/zone fire model, linking a fire field model to a zone model. This novel concept was implemented using SMARTFIRE (a fire field model produced at the University of Greenwich) and two different zone models (CFAST which is produced by NIST and FSEG-ZONE which has been produced by the author during the course of this work). The intention of the hybrid model is to reduce the amount of computation incurred in using field models to simulate multi-compartment geometries, and it will be implemented to allow users to employ the zone component without having to make further technical considerations, in line with the existing paradigm of the SMARTFIRE suite.
In using the hybrid model only the most important or complex parts of the geometry are fully modelled using the field model. Other suitable and less important parts of the geometry are modelled using the zone model. From the field model‘s perspective the zone model is represented as an accurate pressure boundary condition. From the zone model‘s perspective the energy and mass fluxes crossing the interface between the models are seen as point sources.
The models are fully coupled and iterate towards a solution ensuring both global conservation along with conservation between the regions of different computational method. By using this approach a significant proportion of the computational cells can be replaced by a relatively simple zone model, saving computational time. The hybrid model can be used in a wide range of situations but will be especially applicable to large geometries, such as hotels, prisons, factories or ships, where the domain size typically proves to be extremely computationally expensive for treatment using a field model. The capability to model such geometries without the associated mesh overheads could eventually permit simulations to be run in ‘faster-real-time’, allowing the spread of fire and effluents to be modelled, along with a close coupling with evacuation software, to provide a tool not just for research objectives, but to allow real time incident management in emergency situations.
Initial ‘proof of concept’ work began with the development of one way coupling regimes to demonstrate that a valid link between models could allow communication and conservation of the respective variables. This was extended to a two-way coupling regime using the CFAST zone model and results of this implementation are presented. Fundamental differences between the SMARTFIRE and CFAST models resulted in the development of the FSEG-ZONE model to address several issues; this implementation and numerous results are discussed at length. Finally, several additions were made to the FSEG-ZONE model that are necessary for an accurate consideration of fire simulations.
The test cases presented in this thesis show that a good agreement with full- field results can be obtained through use of the hybrid model, while the reduction in computational time realised is approximately equivalent to the percentage of domain cells that are replaced by the zone calculations of the hybrid model
Domain partitioning and software modifications towards the parallelisation of the buildingEXODUS evacuation software
Full text linkThis thesis presents a parallel approach to evacuation modelling in order to aid real-time, large-scale procedure development. An extensive investigation into which partitioning strategy to employ with the parallel version of the software was researched so as to maximise its performance.
The use of evacuation modelling is well established as part of building design to ensure buildings meet performance based safety and comfort criteria (such as the placements of windows or stairs so as to ease people‘s comfort) . A novel approach to using evacuation modelling is during live evacuations from various disasters. Disasters may be fast developing in large areas and incident commanders can use the model to plan safe escape routes to avoid danger areas. For this type of usage, very fast results must be obtainable in order for the incident commanders to optimise the evacuation plan along with the software‘s capability to simulate large-scale evacuation scenarios.
buildingEXODUS provides very fast results for small-scale cases but struggles to give quick results for large-scale simulations. In addition, the loading up of large-scale cases are dependent on the specifications of the processor used thus making the problem case unscalable. A solution to address these shortcomings is the use of parallel computing. Large-scale cases can be partitioned and run by a network of processors, thus reducing the running time of the simulations as well as the ability to represent a large geometry by loading parts of the domain on each processor. This scheme was attempted and buildingEXODUS was successfully parallelised to cope with large-scale evacuation simulations.
Various partitioning methods were attempted and due to the stochastic nature of every evacuation scenario, no definite partitioning strategy could be found. The efficiency values ranged from 230% (with both cores being used from 10 dual-core processors) when an idealised case was run to 23% for another test case. The results obtained were highly dependent on the test case‘s geometry, the scenario being applied, whether all the cores are being used in case of multi-cores processors, as well as the partitioning method used.
However, the use of any partitioning method will produce an improvement from running the case in serial. On the other hand, the speedups obtained were not scalable to warrant the adoption of any particular partitioning method. The dominant criteria inhibiting the parallel system was processor idleness or overload rather than communication costs, thus degrading the performance of the parallel system. Hence an intelligent partition strategy was devised, which dynamically assesses the current situation of the parallel system and repartitions the problem accordingly to prevent processor idleness and overloading. A dynamic load reallocation method was implemented within the parallelised buildingEXODUS to cater for any degradation of the parallel system. At its best, the dynamic reallocation strategy produced an efficiency value of 93.55% and a value of 36.81% at its worse.
As a direct comparison to the static partitioning strategy, an improvement was observed in most cases run. A maximum improvement of 96.48% was achieved from using the dynamic reallocation strategy compared to using a static partitioning approach. Hence the parallelisation of the buildingEXODUS evacuation software was successfully implemented with most cases achieving encouraging speedup values when a dynamic repartitioning strategy was employed
GPGPU enabled CFD simulation for fully coupled fire and evacuation modelling
Full text linkTraditionally fire and evacuation models are run independently of one another to ascertain two key building safety parameters: ASET (available safe evacuation time) determined by the fire spread; RSET (required safe exit time) determined by the evacuation model. A building can be deemed to be safe if RSET <ASET. A more advanced method is to couple the models together to give a dynamic fire environment superimposed on the evacuation. This has typically been achieved using a one way couple where the fire is predetermined prior to the evacuation. A more advanced two-way couple can be used in scenarios, where the evacuation behaviour effects the fire environment, e.g. opening/closing doors by agents, extinguishment of fire by agents etc. Presently the time taken to run these simulations is dominated by the CFD fire model.
The problem with two-way coupling is that every change requires a recalculated CFD environment and as the evacuation simulation is based on Monte Carlo methods this leads to multiple calculations to achieve statistically significant results. A complete GPGPU implementation (solver, coefficients and other dependent variables) of the CFD based fire model has been developed which leads to a substantial execution speed-up. Many previously reported implementations are limited to the matrix solver and are thus limited to the speed of the host calculating the coefficients and thereby returning modest overall speedups.
The speed-up gained through the parallel implementation enables the practical use of the two way coupling. The key point of the two way coupling is that the agents in the evacuation model dictates the way the CFD code calculates its values. By letting the agents directly interact with the geometry it eliminates the element of making assumptions when events happen and drastically reduces the number of required simulation runs for all permutations
Improving the regulatory acceptance and numerical performance of CFD based fire-modelling software
Full text linkThe research of this thesis was concerned with practical aspects of Computational Fluid Dynamics (CFD) based fire modelling software, specifically its application and performance. Initially a novel CFD based fire suppression model was developed (FIREDASS). The FIREDASS (FIRE Detection And Suppression Simulation) programme was concerned with the development of water misting systems as a possible replacement for halon based fire suppression systems currently used in aircraft cargo holds and ship engine rooms.
A set of procedures was developed to test the applicability of CFD fire modelling software. This methodology was demonstrated on three CFD products that can be used for fire modelling purposes. The proposed procedure involved two phases.
Phase 1 allowed comparison between different computer codes without the bias of the user or specialist features that may exist in one code and not another by rigidly defining the case set-up.
Phase 2 allowed the software developer to perform the test using the best modelling features available in the code to best represent the scenario being modelled. In this way it was hoped to demonstrate that in addition to achieving a common minimum standard of performance, the software products were also capable of achieving improved agreement with the experimental or theoretical results.
A significant conclusion drawn from this work suggests that an engineer using the basic capabilities of any of the products tested would be likely to draw the same conclusions from the results irrespective of which product was used. From a regulators view, this is an important result as it suggests that the quality of the predictions produced are likely to be independent of the tool used - at least in situations where the basic capabilities of the software were used.
The majority of this work has focussed on the use of specialised proprietary hardware generally based around the UNIX operating system. The majority of engineering firms that would benefit from the reduced timeframes offered by parallel processing rarely have access to such specialised systems. However, in recent years with the increasing power of individual office PCs and the improved performance of Local Area Networks (LAN) it has now come to the point where parallel processing can be usefully utilised in a typical office environment where many such PCs maybe connected to a LAN.
Harnessing this power for fire modelling has great promise. Modern low cost supercomputers are now typically constructed from commodity PC motherboards connected via a dedicated high-speed network. However, virtually no work has been published on using office based PCs connected via a LAN in a parallel manner on real applications. The SMARTFIRE fire field model was modified to utilise multiple PCs on a typical office based LAN. It was found that good speedup could be achieved on homogeneous PCs, for example for a problem composed of-100,000 cells would run on a network of 12 PCs with a speedup of 9.3 over a single PC. A dynamic load balancing scheme was devised to allow the effective use of the software on heterogeneous PC networks.
This scheme also ensured that the impact of the parallel processing on other computer users was minimised. This scheme also minimised the impact of other computer users on the parallel processing performed by the FSE
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Determining confidence intervals, and convergence, for parameters in stochastic evacuation models
Full text linkAn issue when using stochastic egress models is how many simulations are required to accurately represent the modelled scenario? Engineers are mostly interested in a representative Total Evacuation Time (TET). However, the convergence of the TET may not ensure that the full range of evacuation dynamics has been adequately represented. The average total egress curve (AC) has been suggested as an improved measure. Unfortunately, defining a confidence interval (CI) for the AC is problematic. CIs can robustly quantify the precision of many statistics and have been used to define convergence in egress modelling and other research fields. This paper presents a novel application of bootstrapping, functional analysis measures (FAMs), and a bisection algorithm, to derive three FAM-based CIs representing the precision of the AC. These CIs were tested using a theoretical model to demonstrate the consistency of the coverage probability, the actual percentage of CIs that contain the theoretical parameter, with the nominal 95% confidence level (NCL). For two of the FAM-based CIs, it was found that the coverage probability was between 94.2% and 95.6% for all tested sample sizes between 10 to 4000 simulations. The third FAM-based CI’s coverage probability was always greater than the NCL and was a conservative estimate, but this presented no problems in practice. A FAM-based CI may suggest if there is more or less variability in an earlier phase of the evacuation. A convergence scheme based on statistical precision, CI widths, is proposed and verified. The method can be extended to other statistics
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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