Wildfire Spreading: a new application of the Beta distribution

This dissertation is in the mathematical physics area, more specifically, applications in the statistics field. The thesis, under the supervision of Dr. Gianni Pagnini, was carried out at the BCAM - Basque Centre for Applied Mathematics in Bilbao, Spain. It is the result of the continuous interaction with the team of Statistical Physics, characterised by an international, stimulating and constantly growing environment. The subject of this thesis is PROPAGATOR: a stochastic cellular automaton model for forest fire spread simulation, conceived as a rapid method for fire risk assessment. The reason behind the popularity of cellular automata can be traced to their simplicity, and to the enormous potential they hold in modeling complex systems, in spite of their simplicity. Cellular automata can be viewed as a simple model of a spatially extended decentralized system made up of a number of individual components: cells. The communication between constituent cells is limited to local interaction. PROPAGATOR is a cellular automata model which simulates wildfire spread through empirical laws that guarantee probabilistic outputs. This algorithm, whose first version was released in 2009, is currently in use, along with other software, although it is constantly being updated. In fact, the first version was requested by the Italian Civil Protection, but later it became part of the ANYWHERE project. This project, active from June 2016 to December 2019, was funded under the EU’s research and innovation funding program Horizon 2020 (H2020), which aimed to improve emergency management and response to high-impact weather and climate events such as floods, landslides, swells, snowfalls, forest fires, heat waves and droughts. As part of the ANYWHERE project, Propagator was rewritten in Python. The version we worked with is the 2020 version, but an updated 2022 version is already available. The main aim of this work was to understand the distribution of the wildfire propagation. As can be seen from Propagator input parameters, the propagation depends on different factors: ignition point, wind speed and direction, as well as fuel moisture content and firebreaks-fire fighting strategies. Wind is recognized to be by far the most important factor in the entire problem of forest fire propagation. In this paper, we analyzed four different situations varying initial conditions, in particular we changed wind speed: 0 km/h, 10 km/h, 20 km/h, 30 km/h. However, the phenomenon of fire spotting and firebreaks-fire fighting strategies were not taken into consideration. By modifying the code, it was possible to obtain the output required to achieve the desired result. The conclusion we came to is that the distribution of a wildfire spreading is described by the beta distribution. This allows us, for the first time, to attribute a new application of the beta function: describing the propagation of a process studied using a cellular automaton algorithm. The thesis is organised as follows: In the first chapter, there is an introduction to special functions. In particular, their role in applied mathematics is analyzed, followed by a discussion of the two most commonly used special functions: the Gamma function and the Beta function. • In the second chapter, the PROPAGATOR model was introduced following the article "PROPAGATOR: An Operational Cellular-Automata Based Wildfire Simulator" by A. Trucchia. • The third chapter contains the analysis carried out on the output data. A discussion of the obtained results and suitable observations can be found in the conclusions. • There are three appendixes containing: – Appendix A: the lines of code we wrote to carry out the analysis. – Appendix B: explanation of the software, apps and routines used, with particular reference to the Hypathia server. – Appendix C: discussion on stochastic processes carried out as an approach and preparation for the subsequent work with Propagator

Publications of the Jet Propulsion Laboratory, July 1961 through June 1962

Jpl bibliography on space science, 1961-196

Innovation: Key to the future

The NASA Marshall Space Flight Center Annual Report is presented. A description of research and development projects is included. Topics covered include: space science; space systems; transportation systems; astronomy and astrophysics; earth sciences; solar terrestrial physics; microgravity science; diagnostic and inspection system; information, electronic, and optical systems; materials and manufacturing; propulsion; and structures and dynamics

Multi-dimensional simulations of mixing in classical novae

Classical nova explosions are stellar explosions that take place in close binary systems with an energy release only exceeded by gamma-ray bursts and supernova explosions. Matter from the white dwarf flows through the inner lagrangian point and spirals in towards the white dwarf for about 10^4-10^5 years, forming an accretion disk around it. Ultimately, part of this hydrogen-rich matter piles-up on top of the compact object and becomes partially degenerate due to the high densities attained. Consequently, temperature is allowed to rise, but the envelope does not experience any expansion. Actually, this is the key mechanism that controls the subsequent phases and powers a thermonuclear runaway, which is followed by an ejection of part of the accreted envelope. The ejecta are enriched with the products from the nuclear processes, presenting a final metallicity much above solar. This model, introduced in the early 70s, is a solid theory that can account for the gross scenario of nova explosions. Nevertheless, the theory relies on the fact that a mixing episode with matter from the white dwarf core has to take place at the core-envelope interface to successfully account for the high metallicities inferred from observations. During the past 40 years, theoreticians have performed many one-dimensional simulations, which can reproduce the abundances in the ejecta and other important observational properties. However, these calculations performed in spherical symmetry cannot study the mixing process, since they exclude a suite of very important multi-dimensional effects, such as convection. Therefore, multi-dimensional calculations are required to shed light into the mixing episode. In this thesis we have performed two- and three- dimensional simulations of CO novae to study the mixing mechanisms operating at the core-envelope interface, how convection sets in and how the deflagration spreads over the domain, by means of the Eulerian, parallelized, hydrodynamical FLASH code. The two-dimensional results show how convection sets in at the innermost envelope layers, after the appearance of temperature fluctuations that arise from the interface. Convection, in turn, powers the formation of kelvin-Helmholtz instabilities, which efficiently dredge-up 12C from the core and carry it into the envelope, reproducing correctly the high metallicity found in the ejecta. This result solves the controversy generated by the two existing two-dimensional calculations up-to-date. We have also realized a sensitivity study to analyze the impact of some initial parameters, such as the temperature perturbation, resolution of the simulations and the size of the computational domain. The results point out that these parameters have a negligible impact on the degree of mixing and, therefore, the calculations are not affected by numerical artifacts. Although two-dimensional calculations can quantitatively reproduce the mixing episode, they cannot describe correctly the convective pattern due to conservation of vorticity, which translates into recombination of the convective cells. Therefore, we have extended the work to three dimensions and performed the first three-dimesional model of mixing in classical novae up-to-date. These calculations can successfully reproduce the intermittency present in turbulent convection, with an energy cascade into smaller scales which clearly fulfills the Kolmogorov theory, while the thermonuclear runaway continues propagating with almost spherical symmetry. Mixing proceeds through the filamentary structure powered by robust kelvin-Helmholtz instabilitites that arise from the interface, resulting in a CNO enhancement which agrees with observations. This convective profile also generates density contrasts that could be the origin of the inhomogeneous distribution of chemical species.Les explosions de noves tenen lloc en un sistema estel.lar binari, on un dels estels ha arribat a la fi de la seva vida convertit en una nana blanca. En sistemes binaris molt propers, l'estel acompanyant cedeix part del seu gas (material ric en hidrogen), el qual s'arremolina al voltant de la nana blanca durant prop de 10^4 - 10^5 anys. Una fracció d'aquest material acaba apilant-se a la superfície de l'objecte compacte i esdevé parcialment degenerat com a conseqüència de l'elevada densitat. Aquest fet és clau en el procés, ja que permet que la temperatura augmenti sense que es produeixi una expansió de l'embolcall, desencadenant un allau termonuclear i finalment, l'ejecció de matèria. El material ejectat està enriquit amb els isòtops processats en les reaccions nuclears, presentant una metal.licitat molt superior a la solar. Aquest model, presentat a principis dels anys 70, és una teoria sòlida que explica raonablement l'explosió de noves. No obstant, la teoria rau en el fet que s'ha de produir un procés de barreja entre el material de la nana blanca i el material de les capes més internes de l'embolcall per poder explicar l'alta metal.licitat que s'observa en el material ejectat. Durant els últims 40 anys, s'han fet molts estudis en una dimensió que aconsegueixen reproduir correctament les abundàncies del material ejectat i altres importants propietats observacionals, però que no poden explicar com es produeix el procés de barreja, ja que aquests càlculs amb simetria esfèrica exlouen tota una sèrie d'importants fenòmens multidimensionals. Per tant, per estudiar aquests aspectes de la teoria es requereixen estudis multidimensionals. En aquesta tesi hem realitzat simulacions en dues i tres dimensions de noves de CO per estudiar els mecanismes de barreja que es produeixen a la interfície del nucli de la nana blanca i l'embolcall, com s'estableix la convecció i com es propaga el front deflagratiu, mitjançant el codi hidrodinàmic FLASH, que és Eulerià i està paral.lelitzat. Els resultats en dues dimensions mostren com es genera convecció a les capes més internes de l'embolcall, després de la formació de fluctuacions de temperatura a la interfície. La convecció, al seu torn, origina inestabilitats Kelvin-Helmholtz que transporten eficientment 12C del nucli cap a l'embolcall, aconseguint reproduir correctament el grau de metal.licitat observat. Aquest resultat resol la controvèrsia generada pels dos estudis en dues dimensions realitzats fins ara. També hem realitzat un estudi per analitzar l'impacte dels paràmetres inicials tals com la perturbació inicial, la resolució de les simulacions o les dimensions del domini computacional. Els resultats indiquen que cap d'aquests paràmetres influeix en el grau de barreja final i, per tant, que els càlculs no estan condicionats per aspectes numèrics. Finalment, hem presentat el primer model tridimensional de barreja de noves fet fins ara. Aquest càlcul és necessari, ja que les simulacions bidimensionals, tot i que quantitativament reprodueixen la barreja esperada, no poden representar el patró convectiu correctament, degut a la conservació de la vorticitat, fent que les cel.les convectives esdevinguin cada cop més grans. El nostre càlcul aconsegueix reproduir el comportament intermitent de la turbulència, amb una cascada d'energia que flueix cap a escales cada cop més petites, tal i com prediu la teoria de Kolmogorov, alhora que el front convectiu avança pràcticament amb simetria esfèrica. La barreja procedeix a través de l'estructura filamentosa originada per l'aparició de potents inestabilitats Kelvin-Helmholtz a la interfície, obtenint-se una metal.licitat final a l'embolcall que concorda amb els valors observacionals. Aquest patró convectiu també genera contrastos de densitat que podrien ser l'origen de la distribució inhomogènia que presenten les espècies químiques.Postprint (published version

Direct Numerical Simulation of supercritical CO2 mixing and combustion

The supercritical CO2 power cycle (sCO2 ) is a relatively new technology, which promises to reduce CO2 emissions with potentially higher efficiencies. However due to challenging conditions posed by supercritical pressures, the mixing and ignition phenomena in sCO2 combustion is relatively less understood and studied. The primary objective of the current study is to investigate these fundamental processes using homogeneous ignition calculations (HMI) and direct numerical simulations (DNS). Broadly, the study is divided into two major parts. In the first part supercritical mixing in sCO2 relevant conditions is investigated. To achieve this, DNS of temporally developing, three dimensional, CH4 /CO2, CH4 /O2 and CO2 /O2 mixing layers, are conducted at a supercritical pressure of 300 atm. To effectively model the supercritical regime, the employed formulation includes the compressible form of the governing equations, the cubic Peng-Robinson equation of state and a generalized formulation for heat and mass flux vectors derived from non-equilibrium thermodynamics and fluctuation theory. A linear inviscid stability analysis is also performed for each case, to determine its most unstable wavelength. Flow visualizations reveal the presence of high density gradient magnitude regions for all three mixing layers, with conditional averages indicating increased presence of heavier fluid species within these regions. No significant departures are observed from perfect gas behavior, with compressibility factors very close to unity for all three mixing cases. Applicability of presumed probability density function methods (PDF) is examined for the three supercritical mixing layers. An a priori analysis is also conducted to investigate various simplifying assumptions employed in modeling various subgrid scale (SGS) flux models. Two additional terms are identified in the large eddy simulations (LES) equations, the gradient of SGS contribution of pressure in the momentum equation and the gradient of SGS contribution of heat flux in energy equation, whose magnitudes are similar and comparable with their respective resolved terms. The performance of the scale similarity model to represent these additional terms is investigated. The performance of Smagorinsky, gradient and scale similarity models is also investigated to model the conventional SGS fluxes. In the second part, the ignition process in sCO2 combustion is investigated using homogeneous ignition calculations (HMI) and two-dimensional direct numerical simulations (DNS). For selection of a suitable chemical mechanism, HMI calculations are first employed, to investigate the performance of existing skeletal mechanisms against shock- tube experimental data. The chemical characteristics of ignition are further studied using path-flux and sensitivity analysis, with CH3O2 chemistry exhibiting the largest effect on accelerating the ignition process. Different chemical pathways of fuel breakdown are also discussed to aid in interpretation of subsequent DNS case. In the DNS case, autoignition of a two dimensional mixing layer perturbed with pseudo-turbulence is simulated. The ignition is found to be delayed compared to the HMI case, with the ignition kernels forming in a spotty manner. The two phenomena are primarily attributed to variation of scalar dissipation within the mixing layer. The ignition kernels expand and evolve into a tribrachial edge flame propagating along the stoichiometric isosurface. Further investigation on the structure of edge flame revealed an asymmetrical structure, with CH4 molecules being entirely consumed in the triple point region of the flame along the stoichiometric isosurface, and more stable fuels like CO burning in the non-premixed branch of the edge flame. The edge flame propagation speeds are also calculated, with variations found to be correlated with scalar dissipation and upstream progress variable of the reacting mixture

Annual Report 2016 of the Institute for Nuclear and Energy Technologies (KIT Scientific Reports ; 7742)

The annual report of the Institute for Nuclear and Energy Technologies of KIT summarizes its research activities and provides some highlights of each working group, like thermal-hydraulic analyses for nuclear fusion reactors, accident analyses for light water reactors, and research on innovative energy technologies: liquid metal technologies for energy conversion, hydrogen technologies and geothermal power plants. The institute has been engaged in education and training in energy technologies

Optical spectroscopy of HMX reaction regimes

A detailed study on the visible light emission from multiple granular HMX reactions has been completed. New techniques for measuring the reaction properties were devised, both directly and indirectly from the results gained from using optical spectroscopy. Two different impact initiated deflagration reactions were performed. Improvements were made to the fallhammer sensitivity test to allow for more quantitative measurements, and the Split Hopkinson Pressure Bar (SHPB) was used for the first time to purposely initiate deflagration, providing better measurements of the energy present during initiation. Using the greybody emission, the temperatures of these reactions were measured as 3900 ± 400 K and 2900 ± 200 K respectively. Building a time-dependent pyrometer showed a constant temperature throughout the main reaction period. The significant difference between the two temperatures inspired the addition of a mass spectrometer to investigate the products from each reaction. The results showed the two reactions did not resemble variants of an ‘ideal’ deflagration reaction, and so identical chemistry should not be assumed to be present in both. Optical spectroscopy also showed the existence of a spectral peak in deflagration due to emissive sodium impurities. The peak was red-shifted under the pressures of the reaction, and the calibration curve of the red-shift was calculated. The functional form of the shift has a dependence on pressure and temperature in agreement with Lindholm-Foley collisional theory, allowing the pressure to be calculated optically from position of the shift. This was achieved with a streak spectrometer, where time-dependent measurements of the temperature (using greybody emission) and pressure (using the sodium peak) from the same source of light were made. Finally, detonation of HMX was examined. The detonation pressure and velocity were measured as a function of initial density, and found consistent with models of shock conservation and Group Interaction Modelling. High temperatures of 7000 K were recorded from the greybody emission, with the light emitted from mechanical high pressure void collapse dominating over the heat produced from the chemical reaction. These temperatures were not affected by the density of the HMX bed, but instead the size of the voids present. Larger particles increased the size of the voids, leading to higher temperatures and decreased light scattering, with the inclusion of sodium absorption features.Emmanuel college Avik Chakravarty Memorial fun

The 1991 Marshall Space Flight Center research and technology

A compilation of 194 articles addressing research and technology activities at the Marshall Space Flight Center (MSFC) is given. Activities are divided into three major areas: advanced studies addressing transportation systems, space systems, and space science activities conducted primarily in the Program Development Directorate; research tasks carried out in the Space Science Laboratory; and technology programs hosted by a wide array of organizations at the Center. The theme for this year's report is 'Building for the Future'

Combustion Characteristics of Methane, Ethane, Propane, and Butane Blends Under Conditions Relevant of a Dual-Fuel Diesel and Natural Gas Engine

As natural gas production infrastructure is already in place in most of the world and will continue expanding for the foreseeable future, natural gas is an alternative to traditional liquid petroleum fuels in heavy-duty engines. Dedicated natural gas or dual-fuel diesel-natural gas heavy-duty engines are alternatives to diesel-only power generation equipment. One challenge is the large variation in the natural gas composition available for such applications, which is known to significantly affect engine’s combustion characteristics and the emissions composition. As the literature on dual-fuel combustion under low load engine operating conditions that use more realistic natural gas mixtures (i.e., mixtures that, in addition of methane (C1;the most abundant natural gas component), also contain ethane (C2), propane (C3), and butane (C4)) is limited, this study evaluated the combustion characteristics of a variety of C1-C4 mixtures using three different experimental platforms: a 4.5-L 4-cylinder heavy-duty production diesel engine modified for dual-fuel diesel-natural gas engine operation, a prototype 1.125-L single-cylinder engine with extended optical access that was based on the same production diesel engine, and a laminar flame burner. Experiments in the heavy-duty production engine under low load dual-fuel diesel-natural gas operating conditions (6 bar break mean effective pressure at 1000 RPM, 1000 bar diesel injection pressure, and 40% diesel substitution ratio) showed that gas composition affected the diesel fuel ignition delay and combustion phasing, which are known to affect both engine performance and emissions. As in-cylinder pressure correlated with the autoignition temperature of the gaseous mixture, mixtures with higher C2-C4 content produced the best engine performance and emissions compared to using 100% C1, suggesting that the addition of C2-C4 content benefits low load dual-fuel combustion. For example, brake specific carbon dioxide and nitrogen oxides emissions reduced up to 6.6% and 20%, respectively. In addition, gas mixtures containing C3 and C4 reduced the brake specific carbon dioxide equivalent by up to 50 g/kWh compared to the C1-only case. Experiments in the prototype single cylinder optical engine employed imaging diagnostics to better understand the C1-C4 effects observed in the production engine experiments. High boost and high intake temperature were used to create in-cylinder conditions similar to those in the production engine at the start of combustion. To enhance the visual differences between the natural gas components, only one component was used at a time instead of a multicomponent mixture as in the production engine experiments, and difficulties in accurately controlling the C4 flow resulted in using only C1-C3. Experiments were performed at similar low load dual fuel operating conditions (~ 6.6 bar indicated mean effective pressure at 1000 RPM, 500 bar diesel injection pressure, and ~ 63% diesel substitution ratio), using both traditional and advanced diesel injection timing (i.e., conventional mixing-controlled compression ignition or MCCI compared to reactivity-controlled compression ignition or RCCI). Natural luminosity data showed that C3 RCCI had a more advanced combustion phasing despite an increased ignition delay and higher spatially-integrated natural luminosity compared to C1 RCCI and C2 RCCI. An earlier premixed combustion and a smaller phasing difference between the apparent heat release and spatially-integrated natural luminosity was seen for MCCI compared to RCCI. The results suggested that the C1-C3 content indeed affected the diesel gas mixing and stratification of the low load dual-fuel operation, hence the differences in engine performance and emissions observed in the production engine experiments. As a result, the findings in this study can be used for modeling the dual-fuel combustion of C1-C4 blends and can help industry in utilizing more efficiently natural gas with higher C2-C4 content

Annual report of the South Carolina Experiment Station

The South Carolina Agricultural Experiment Station annual report provides information on agricultural advancements, pest control, food, crop, and livestock development, and evaluation of soils, plants, and water resources