Abstract Bushfires pose a significant threat to numerous countries, often causing vast property damages and loss of lives. Efforts to combat and manage these fires heavily rely on predicting the ...fires' rate of spread and intensity. A significant component of these predictions involves understanding the thermophysical characteristics of vegetative fuels. The accuracy of predictive models (especially physical models) also depends on obtaining precise thermophysical and combustion parameters. This research aims to provide a comprehensive set of thermal degradation and combustion parameters for surface and near‐surface fuel samples collected during prescribed fire experiment conducted in April 2022 in Little Desert National Park, Victoria, Australia. Firstly, fuel properties like fuel height, moisture content, bulk density, fuel load and heat of combustion were meticulously characterized for both surface and near‐surface samples. Then activation energies for degradation reactions were determined using the Flynn–Wall–Ozawa method and for the determination of pre‐exponential factors, in most cases these reactions closely aligned with a Second order model. This was followed by determination of other parameters such as heat of reaction, specific heat and conductivity. It was found that the density, activation energy and heat of combustion did not vary significantly across the six samples under question. The comprehensive set of obtained parameters will likely help to facilitate better predictions in fire propagation modelling.
Exposure of liquid steel to air, consequent re-oxidation as well as nitrogen absorption are common in steelmaking and produce unacceptable variations in product chemistry. The phenomena, during ...continuous casting of the lead or first heat, have been investigated in a full-scale water model of a two-strand, bloom casting shroud-tundish system. Physical modelling results supported by industrial scale measurements have demonstrated that exposure of liquid steel to tundish atmosphere during initial period of ladle teeming and consequent nitrogen absorption, manifest over substantial period, influencing predominantly the first three blooms.
To elucidate the early stages of heave, settlement and fracture of intact frost-susceptible rock by temperature cycling above and below 0°C, two physical modelling experiments were performed on 10 ...rectangular blocks 450mm high of fine-grained, soft limestone. One experiment simulated 21cycles of bidirectional freezing (upward and downward) of an active layer above permafrost, and the other simulated 26cycles of unidirectional freezing (downward) of a seasonally frozen bedrock in a non-permafrost region. Heave and settlement of the top of the blocks were monitored in relation to rock temperature and unfrozen water content, which ranged from almost dry to almost saturated.
In the bidirectional freezing experiment, heave of the wettest block initially occurred abruptly at the onset of freezing periods and gradually during thawing periods (summer heave). After the crossing of a threshold marked by the appearance of a macrocrack in the upper layer of permafrost, summer heave increased by an order of magnitude as segregated ice accumulated incrementally in macrocracks, interrupted episodically by abrupt settlement that coincided with unusually high air temperatures. In the unidirectional freezing experiment, the wet blocks heaved during freezing periods and settled during thawing periods, whereas the driest blocks showed the opposite behaviour. The two wettest blocks settled progressively during the first 15 freeze-thaw cycles, before starting to heave progressively as macrocracks developed.
Four processes, operating singly or in combination in the blocks account for their heave and settlement: (1) thermal expansion and contraction caused heave and settlement when little or no water-ice phase change was involved; (2) volumetric expansion of water freezing in situ caused short bursts of heave of the outer millimetres of wet rock; (3) ice segregation deeper in the blocks caused sustained heave during thawing and freezing periods; and (4) freeze-thaw cycling caused consolidation and settlement of wet blocks prior to macrocracking in the unidirectional freezing experiment. Rock fracture developed by growth of segregated ice in microcracks and macrocracks at depths determined by the freezing regime. Overall, the heave, settlement and fracture behaviour of the limestone is similar to that of frost-susceptible soil.
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•Freeze-thaw experiments recorded heave, settlement and fracture of chalk.•Heave varied with freezing regime and water content.•Thermal expansion and contraction controlled heave of dry chalk.•Volumetric expansion, ice segregation and consolidation occurred in wet chalk.
Human habitats on the lunar surface have been planned and designed already since the beginning of the space age in the early 1960's, long before the successful Apollo missions, which for the first ...time brought humans to the Moon and safely back to Earth. While existing plans for manned lunar stations were postponed for a long time for various reasons, the interest in building permanent research stations on the surface of the Moon re-awoke in the late 1990s and early 2000s. Hereby, the focus turned more and more towards the lunar poles, where strong indications for the existence of water ice inside permanently dark craters were found. In this study we present a design for a lunar habitat, which makes maximal use of the natural resources available on the Moon, in particular in the vicinity of the poles, while at the same time the necessary material transfer from Earth to the lunar surface is minimized. We identify and study the sites around the lunar poles (both north and south pole) and present a design for a lunar habitat consisting of up to 16 greenhouses suitable for permanently housing and nourishing up to 32 humans. The greenhouses have a toroidal shape and are connected by tunnels. The horizontally incident sunlight is re-directed by a rotating mirror towards an artificial crater and from there through a transparent foil to the interior of the greenhouses. The main feature of our design is that the walls of the greenhouses as well as the attached rooms and tunnels are made of extremely light-weight materials, which are inflated to their final size simply by applying air pressure. Effective protection against harmful cosmic radiation is reached by covering greenhouses, living areas and connecting tunnels with a several metres thick layer of loose regolith. This cover ensures also a high level of thermal isolation, which helps to avoid too fast cooling of the interior during phases of total darkness. Finite element models of the thermodynamic behaviour of the suggested design confirm that life-friendly conditions can be created and kept over long time spans by using only the available solar illumination as power source and installing a state-of-art cooling system for the interior. In contrast to other concepts, the basic building blocks of this habitat design could be transported to the lunar surface by existing rocket systems offering a medium transport capacity, like Ariane 64, in combination with the planned European Large Logistics Lunar Lander Finally, various safety issues that might occur during setup and operation of such a lunar habitat, are discussed.
•Low weight lunar habitats.•Thermo-physical modelling.•Inflatable membranes as building elements.•Mirror membranes for use of natural sunlight.•Loose regolith for protection against cosmic radiation and micro-meteorites.
Effects of slag layer thickness on the fluid dynamics of liquid steel in gas-stirred ladles by bottom injection of argon was studied through water modeling experiments and numerical simulations. ...Mixing times increase considerably with thicker slag layers and decrease of gas flow rates. The physical properties of the system have a smaller influence on mixing time. Slag Eye Opening (SEO) area is increased under thin slag layers, increase of gas flow rates, and denser and less viscous slags. The planes close to the metal-slag interface, under the presence of thick slag layers for a given gas flow rate, are split in subregions of small velocities with different orientations making the lower fluid to come close to a stagnant condition. The presence of, either, thick or thin slag layers does not influence the axial velocity along the plume height for a fixed flow rate of gas. The SEO area follows a linear relationship with the square root of the densiometric Froude number based on the slag layer thickness.
Dual-ion batteries are being considered a feasible approach for electrochemical energy storage. In this battery technology both cations and anions are involved in the redox reactions, respectively, ...at the anode and the cathode. However, the participation of both ions in the redox reactions means that enough salt must be added in the electrolyte to ensure proper battery functioning, which present a limiting factor in battery design. Herein, a modified version of the standard pseudo-2D Doyle-Fuller-Newman model is proposed to account for the different redox reactions that occur in dual-ion batteries and simulate the variation of average salt concentration in the electrolyte during charging and discharging. The model has been validated against galvanostatic cycling and electrochemical impedance spectroscopy experimental data from dual-ion batteries based on poly(2,2,6,6-tetramethyl-1-piperidinyloxy methacrylate) (PTMA). Such a model can be helpful to design practical dual-ion batteries that respect the constraints imposed by their working mechanism and maximize the obtainable capacity and energy density.
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•Physical model for dual-ion batteries.•Simulations of electrolyte salt concentration variations during charge and discharge.•Experimental validation of simulations with PTMA-lithium battery.•Influence of the geometry and electrolyte salt concentration on dual-ion battery performance.
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•Development of a 3D model adapted to the ballast and slab tracks’ physical models.•Implementation of a permanent deformation model into the numerical model.•Calibration of numerical ...models to improve reliability prediction.•Calibration’s results show good agreement between numerical and experimental data.•Sensitivity analysis shows importance of effective cohesion in subgrade’s long-term behaviour.
Ballast and slab railway track structures are constructed from different materials, thus requiring different maintenance strategies. Therefore, this paper compares the settlement performance of both structures using laboratory experiments, and calibrates numerical models based upon the results. Firstly, a comparison of the short and long-term behaviour of ballasted and slab tracks under cyclic loading is performed at full-scale. Both tracks have the same track foundation but a different track superstructure, and are subject to 3 million cycles of loading. The results are used to develop and calibrate the short-term response of a 3D finite element model of both track structures. They are also used to calibrate an empirical permanent deformation model for the track foundation, where the number of load cycles and stresses are the main inputs. A strong agreement is found between the numerical and experimental results. This justifies the track modelling approach in predicting the long-term behaviour of track structures where the subgrade is influential.
The article presents the results of modeling research of hydrodynamic phenomena occurring in the oxygen converter during the addition of SLCF while blowing the liquid bath. The water physical model ...of the oxygen converter was used for the research. The oxygen lance of the model was equipped with a head with five nozzles at an angle to the lance axis. The research was aimed at determining the most favorable process parameters for the use of lump fuel in the oxygen converter.
Cyclic loading features in many applications. Questions important for design include: Does the monotonic capacity increase or decrease following cyclic loading? How does foundation rotation, ...stiffness and damping evolve? This is investigated here for suction caissons in sand, looking to applications as foundations for offshore wind turbines where changing stiffness, capacity and accumulated rotation can be critical, and soil damping is being looked at more closely. The problem is investigated experimentally through a series of single gravity monopod caisson tests in saturated sand subjected to unidirectional or multidirectional cyclic loading with between 360,000 and 106 cycles applied in each test. Results from the unidirectional tests are consistent with previous experimental studies, whilst also demonstrating the expected changes in damping ratio during cyclic loading for a monopod caisson in sand. The multidirectional tests reveal more significant and potentially important findings, particularly on the very significant increases in unloading stiffness and damping ratio associated with load direction changes.
•Lateral cyclic loading of suction caissons in sand leads to moderate improvements in moment capacity.•Suction caisson rotation accumulates during cycling by an amount that is mainly controlled by the cyclic load amplitude.•Accumulated rotation for multi-directional loading is bounded by the response measured in unidirectional tests.•Multi-directional loading leads to significant increases in unloading stiffness and damping ratio.
Although solidification crack susceptibility modelling has been a point of interest for many years in fusion welding of aluminum alloys, the underlying mechanism of solidification crack elimination ...is not yet fully understood. To contribute in closing this knowledge gap, the present study investigates and proposes a new modified Rappaz-Drezet-Gremaud (RDG) physical model in autogenous and heterogeneous TIG welding of Al7075 sheets. The core novelty of the new model is that it includes the shrinkage strain rate, which allows to better capture the effects of capillary pressure, coherency point, as well as final dendrite or grain size in the fusion zone. In agreement with the experimental results and previous models, the new model shows that the defining mechanism of eliminating solidification cracks in heterogeneous joints is the capacity of nanoparticles to initiate heterogeneous grain nucleation, altering the fusion zone grain morphology from dendritic to fine equiaxed, with only little impact of the resulting grain size. This leads to two main effects causing reduced solidification crack susceptibility: (1) a reduction in coherency point by about 15 % from 902 K to 879 K, which reduces strain accumulation on the coherent solid network; (2) a considerable increase in capillary pressure across the entire mushy zone, allowing to maintain the total pressure at void/liquid interfaces in the positive range, which prevents the growth of potentially formed voids between grains at any temperature during solidification. In contrast, dendrite widths below 68 μm are required to prevent solidification cracks in autogenous joints without TiC nanoparticles, indicating a greater role of grain refinement. Overall, the proposed model highlights the more determinant role of the temperature-dependent solidification shrinkage strain rate in solidification crack susceptibility as it is an order of magnitude greater compared to the temperature-independent thermal contraction strain rate that has been the main or sole focus of previous models.
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