Spread Distance Research Articles

Study on suppression of bituminous coal explosion by inert powder in cylindrical space

In order to understand how to control the spread of bituminous coal explosion, a cylindrical explosion tube is used for research. The results indicate that within 60 ms, the flame develops to the top of the tube. When 10 % inert powder is mixed in, the flame spreads to 1.2 cm at 10 ms, which is 0.4 cm shorter than the spread distance without adding inert powder. The time point for ending preheating and entering heating will be advanced with the increase of the mass of inert dust added. As the proportion of inert dust mixed decreases, the maximum impact airflow velocity of explosion gradually increases, the acceleration time interval gradually extends. When 10 % inert powder is mixed in, the maximum impact airflow velocity is 17 m/s, but it is delayed to 52 ms. The mixing of inert dust can reduce the mass fraction of CO inside the tube without changing the mass fraction of other gases, especially O2. As the mass of inert dust increases, the mass fraction of CO2 gradually increases and the range gradually expands.

A Study on the Influence of Mobile Fans on the Smoke Spreading Characteristics of Tunnel Fires

Mobile fans, as flexible and convenient new longitudinal ventilation and smoke extraction equipment for tunnels, demonstrate more significant effectiveness in an emergency response to tunnel fires compared to traditional smoke extraction methods. This study employs computational fluid dynamics simulation methods, selecting two fire scenarios to investigate the effects of fan inclined angles and fan airflow volumes on the longitudinal temperature distribution and smoke back-layering length in tunnels. The results indicate that when using mobile fans for longitudinal ventilation in tunnels, at a lower fan airflow volume, the temperature distribution along the longitudinal axis is nearly symmetrical. The fire source and the fan installed in the upstream are within a certain range, and it is more effective to use the horizontal angle for longitudinal ventilation. As the fan airflow volume increases, the back-layering length significantly decreases (210,000 m3/h < V < 270,000 m3/h). However, as the fan flow volume continues to increase (270,000 m3/h < V < 300,000 m3/h), the reduction in the back-layering length becomes less pronounced, the smoke spread distance of the latter is only 11% of that of the former. Therefore, selecting appropriate fan airflow volumes and fan inclined angles them can effectively enhance the performance of tunnel smoke extraction systems. Moreover, by comparing with traditional fans, we find that mobile fans provide an alternative effective strategy during firefighting by allowing adjustments in distance from the fire source and fan inclination angles, enhancing fire suppression effectiveness while reducing energy losses. The research findings can serve as a reference for tunnel fire prevention design.

An explicit incompressible scheme based on the MPS method to simulate slump flow

AbstractIn this study, an explicit incompressible scheme based on the Moving Particle Semi-implicit method (MPS) is applied to simulate slump flow. In the numerical method, the pressure Poisson equation is explicitly solved to obtain the pressure field. In simulating slump flow caused by fresh concrete, the fluid is treated to be non-Newtonian fluid and a regularized Bingham model is employed to calculate the viscosity. Flow characteristics in the slump flow are reproduced by the numerical method, and in good agreement with experimental measurements. The parameters including the rheological regularized parameter, yield stress, plastic viscosity, and particle distance, are examined in the simulations. It is found that the explicit incompressible scheme can well reproduce the concrete spreading. The yield stress in the rheology model affects the spreading distance significantly while the plastic viscosity plays an important role in the acceleration stage of the material spreading.

Development on Surrogate Models for Predicting Plume Evolution Features of Groundwater Contamination with Natural Attenuation

Predicting the key plume evolution features of groundwater contamination are crucial for assessing uncertainty in contamination control and remediation, while implementing detailed complex numerical models for a large number of scenario simulations is time-consuming and sometimes even impossible. This work develops surrogate models with an effective and practicable pathway for predicting the key plume evolution features, such as the distance of maximum plume spreading, of groundwater contamination with natural attenuation. The representative various scenarios of the input parameter combinations were effectively generated by the orthogonal experiment method and the corresponding numerical simulations were performed by the reliable Groundwater Modeling System. The PSO-SVM surrogate models were first developed, and the accuracy was gradually enhanced from 0.5 to 0.9 under a multi-objective condition by effectively increasing the sample data size from 54 sets to 78 sets and decreasing the input variables from 25 of all the considered parameters to a smaller number of the key controlling factors. The statistical surrogate models were also constructed with the fitting degree all above 0.85. The achieved findings provide effective generic surrogate models along with a scientific basis and investigation approach reference for the environmental risk management and remediation of groundwater contamination, particularly with limited data.

On gravity-driven liquid nitrogen jets reach and horizontal spread for extinction of ground fires by aerial means

This paper describes experimental and numerical results on the reach and the spread of gravity-driven jets of liquid nitrogen (LN2) on the ground for applications to fire extinction by aerial means. A series of experiments released LN2 jets from different elevations in ambient air to measure their reach and spread distances upon the impingement. A numerical model was developed to simulate the behavior of such jets. Upon validation, the numerical model was used to further predict the LN2 pool mass and spreading distances under various release configurations. Results showed that the LN2 survivability is greatly affected by the release height of the cryogen, since the LN2 quantity reaching the ground decreases as the release height increases. Moreover, releasing larger initial LN2 quantities and, most importantly using larger nozzle diameters, both the LN2 pool mass and spreading diameter can be extended. Additional experiments were conducted where cryogen jets were released onto small (∼300 cm2) alcohol pool fires; results showed that only limited quantities of the LN2 evaporated in transit to the fire, and small amounts of the cryogen expediently snuffed the fires. A simplified model also suggested that in fire supression/extinction by LN2 the fuel cooling mechanism is of secondary importance compared to the mechanism of separating the fuel from oxygen.

An analytical heat transfer model for transient Raman thermometry analysis.

Transient Raman thermometry improves on its steady-state counterpart by eliminating the error-prone steps of temperature calibration and laser absorption measurement. However, the accompanying complex heat transfer process often requires numerical analysis, such as the finite element method, to decipher the measured data. This step can be time-consuming, inconvenient, and difficult to derive a physical understanding of the heat transfer process involved. In this work, the finite element method is replaced by fitting the measured data to an analytical three-dimensional heat transfer model. This process can be completed in a few seconds. Using this approach, the in-plane thermal conductivity of two bulk layered materials and the interfacial thermal conductance between two-dimensional materials and quartz have been successfully measured. Based on our model, we performed an analytical quantitative sensitivity analysis for transient Raman thermometry to discover new physical insights. The sensitivity of the in-plane thermal conductivity of bulk layered materials is dictated by the ratio between the spot radius and heat spreading distance. The sensitivity of the interfacial thermal conductance between two-dimensional materials and quartz is determined by its conductance value. In addition, the uncertainty of the measured value contributed by the uncertainty of the input parameters can be efficiently estimated using our model. Our model provides an efficient data and sensitivity analysis method for the transient Raman thermometry technique to enable high throughput measurements, facilitate designing experiments, and derive physical interpretations of the heat transfer process.

Monitoring and Evaluation of Debris Flow Disaster in the Loess Plateau Area of China: A Case Study

The Loess Plateau area, with complex geomorphological features and geological structure, is highly prone to geologic disasters such as landslides and debris flow, which cause great losses. To investigate the initiation mechanism of landslide and debris flow disasters and their spreading patterns, historical satellite images in the Laolang gully were collected and digitized to generate three-dimensional topographic and geomorphological maps. Typical landslides were selected for landslide thickness measurement using a standard penetrometer and high-density electrical method. Numerical models were established to simulate the occurrence and development of landslides under different working conditions and to evaluate the spreading range based on the propagation algorithm and friction law. The results show that the 10 m resolution DEM data are well matched with the potential hazard events observed in the field site. The smaller the critical slope threshold, the greater the extent and distance of landslide spreading. The larger the angle of arrival, the greater the energy loss, and therefore the smaller the landslide movement distance. The results can provide scientific theoretical guidance for the prevention and control of rainfall-induced landslide and debris flow disasters in the Loess Plateau area.

Evaluation of the Potential Flight Ability of the Casuarina Moth, Lymantria xylina (Lepidoptera: Erebidae).

Lymantria xylina Swinhoe (Lepidoptera: Erebidae) is a potentially invasive pest, similar to Lymantria dispar asiatica Vnukovskij and Lymantria dispar japonica Motschulsky (Lepidoptera: Erebidae). To evaluate its potential for spread and flight distance related to egg deposition on vessels at ports, we employed a flight mill to assess the flight capabilities of its adults under varying conditions. Our findings revealed that females primarily flew short distances and ceased flying after 3:00 AM, whereas males covered much longer distances throughout the day. Sex, age, and flight duration significantly influenced flight ability. Females exhibited weaker flight capability than males, and their ability declined with increasing age or flight duration. Notably, 1-day-old moths displayed the strongest flight ability, with average flight distances of up to 3.975 km for females and 8.441 km for males. By the fifth day, females no longer flew, and males experienced reduced flight ability. After continuous hanging for 16 h, females lost most of their flight capacity, while males remained capable of flight even after 32 h. Additionally, female flight ability decreased significantly after mating, possibly due to factors such as egg-carrying capacity, weight, and load ratio. This study provides a foundation for assessing the risk of long-distance dispersal of L. xylina via ocean-going freighters, considering female moths' phototactic flight and oviposition.

Complete coding sequence of an Aedes flavivirus strain isolated from Aedes albopictus collected in Northern Italy.

Complete genome data for the globally distributed Aedes flavivirus (AEFV) is scarce. We analyzed a new Italian AEFV strain isolated from Aedes albopictus. The results demonstrated genetic diversity among Italian AEFVs. The high similarity between AEFV genomes across geographically distant regions suggests long distance spreading via invasive host mosquito species.

Analysis of the spread distance of dandelion and invasive species

This paper aims to investigate the distance of seed dispersal in diverse environments and explore the intricate relationship between invasive species and dandelions. Specifically, this paper intends to focus on the scenario where a single dandelion, in its puffball stage, is situated within an open one-hectare plot of land. The objective is to develop a mathematical model capable of predicting the dissemination of dandelions throughout 1, 2, 3, 6, and 12 months. This model will help people understand the temporal dynamics of dandelion expansion in a controlled setting. Furthermore, for the invasive species model, this paper proposes to initially identify and select several species known for their invasive properties. Subsequently, we will utilize modeling techniques to calculate an impact factor, which quantifies the extent to which these invasive species affect their environment.

Analytical solutions for airborne droplet trajectory: Implications for disease transmission

Airborne droplets containing viruses from infected persons can present long range disease transmission risks. In this study, we examine the trajectory of an airborne droplet based on a point force model. The interplay between gravity, drag, inertia and deformation are factored in, for drop sizes ranging from micrometer to millimeter size. In particular, we propose an expression for the drag force which enables analytical solutions for cases of practical interest, such as the transient velocity behavior and spreading distances. This allows us to obtain physical insights which are not obvious from direct numerical simulations. Effects such as droplet deformation, breakup and evaporation are also considered. Our analytical solutions compare favorably with numerical and experimental data. The evaporation rate was determined experimentally with a levitating device and some experimental drop velocity versus time data were obtained with falling millimeter sized droplets.

PostBP: A Python library to analyze outputs from wildfire growth models

Wildfire is an important natural disturbance agent in Canadian forests, but it has also caused significant economic damage nationwide. Spatial fire growth models have emerged as important tools for representing wildfire dynamics across diverse landscapes, enabling the mapping of key wildfire hazard metrics such as location-specific burn probabilities or likelihoods of fire ignition. While these summary metrics have gained popularity, they often fall short in capturing the directional spread of wildfires and their potential spread distances. The metrics depicting the directional spread of wildfire can be derived from raw outputs generated with fire growth models, such as the perimeters and ignition locations of individual fires, but extracting this information requires complex data processing. To address this data gap, we present PostBP, an open-source Python package designed for post-processing the raw outputs of fire growth models — the ignition locations and perimeters of individual fires simulated over multiple stochastic iterations — into a matrix of fire spread likelihoods between all pairs of forest patches in a landscape. The PostBP also generates several other summary outputs, such as the source-sink ratio and the fire spread rose diagram. We provide an overview of PostBP's capabilities and demonstrate its practical application to a forested landscape.•Wildfire growth models generate large amounts of outputs, which are hard to summarize for practical decision-making.•The PostBP package calculates the summary metrics characterizing the directional spread of wildfires.•The fire risk summaries generated with PostBP can support the assessments of wildfire risk and mitigation measures.

A new-proposed triangular- prism flame radiation model of large-scale spilling fire to subsurface convection flow area

The usage of liquid fuel is commonly subjected to a spilling fire due to the accidental leakage. The flame radiation is the primary heat transfer mode in supporting the advancement of large-scale spilling fire. In this work, spilling fires are carried out based on a 6 m × 0.8 m × 0.1 m tray, and the spilling fire performance and flame radiation are examined. The instantaneous flame height and mass burning rate versus fire spread distance are examined. The radiation heat flux of large-scale spilling fire to subsurface flow area is obtained by dividing the flame configuration into a triangular-prism flame and a cuboid flame. The multi-cuboid flame equivalent-division method is proposed to estimate the radiation heat flux of leading triangular-prism flame, finding that the maximal 70 equivalent divisions are sufficiently accurate. The proportion of triangular-prism flame radiation to total heat flux reduces from 100 % to 50 % during spilling fire propagation. The triangular-prism flame radiation plays a dominant role in heat transfer to the subsurface flow area while the cuboid flame radiation plays a secondary role. The current research is of great significance for revealing heat transfer mechanism and predicting rate of spilling fire.

Molecular Dynamics Simulation of Dual Nanodroplet Impacts on a Cylindrical Surface.

Droplet impact behavior is ubiquitous in various fields. However, the dynamics and spreading mechanisms of micro- and nanoscale droplet impact on curved surfaces, particularly in the case of multiple droplets, have yet to be fully elucidated. In this study, molecular dynamics (MD) methods are employed to investigate the dynamic evolution of double nanodroplet impact on a nano cylindrical wall. The effects of droplet spacing, initial impact velocity, and wall wettability on droplet impact characteristics are analyzed. The results demonstrate that there are five impact modes of nanoscale double-droplet impacts with nanocylinders: spreading-partial wrapping-splitting-complete detachment (SPSC), spreading-complete wrapping-complete attachment (SCC), spreading-partial wrapping-complete attachment (SPC), spreading-partial wrapping-partial attachment (SPP), and spreading-partial wrapping-fragmentation-partial attachment (SPFP). The droplet spacing has an insignificant effect on the impact modes but affects the droplets' spreading shape in both the axial and radial directions. The initial velocity and wall wettability have significant impacts on the droplet impact modes and liquid film spreading characteristics. As the initial velocity increases, the liquid film's radial and axial spreading distances gradually increase. Under hydrophobic conditions, the spreading of the droplet is dominant in the radial direction, while under hydrophilic conditions, the spreading is dominant in the axial direction. Properly reducing the droplet spacing, increasing the impact velocity, and enhancing the wall hydrophobicity can promote detaching the droplet from the cylindrical wall.

Wild Oat ( Avena fatua ): Crop Mimicry and Herbicide Resistance

Abstract Wild oat ( Avena fatua ) is a weed species that through crop mimicry survive in conventional managed farmlands, particularly in cereal crops such as wheat and barley. Adaptation of wild oat likely dates back around 9000 years when domestication of cereal species began in the Fertile Crescent and around the Mediterranean Sea. So far, wild oat has been described as a troublesome weed in 44 countries across temperate parts of the world. Wild oat reduces crop yields due to its competition for nutrients, water and light. Variable seed dormancy results in early maturing plants that add to the soil’s seed bank, and later maturing plants that contaminate the harvested grain. Since wild oat seeds resembles cereal grain, they are difficult to remove by mechanical seed cleaning. Seed lots contaminated with wild oat seeds are downgraded since it reduces the suitability as food and feed. Contaminated seedlots used for planting is a source of long distance spread of the weed. Herbicide application is an important part of wild oat control in areas with intensive wheat and barley production. Herbicide labels typically recommend the optimal size of wild oat seedlings and crop plants for best control. However, timing of an application can be difficult when wild oat plants are at different growth stages. The majority of herbicides are grouped according to the mode-of-action in cells of weed plants either inhibiting specific enzymes or entire metabolic pathways. Repeated use of herbicides with the same mode-of-action creates a selection pressure that can result in development of wild oat populations resistant to these herbicides. There is a direct relationship between the number of wild oat plants treated with herbicides and the risk of selecting for resistant plants. Thus, best management practices (BMP) aim to reduce the number of wild oat seed in the field, and include rotating between herbicides with different mode-of-action, and following recommendations on herbicide labels regarding plant growth stages and dosage. Cultural practices include rotating crop species and optimizing crop health, planting of weed-free seed, and cleaning of machinery between fields. Wild oat’s adaptations for crop mimicry and herbicide resistance make it problematic to manage but incorporating BMPs into an integrated approach can help. Information © His Majesty the King in Right of Canada, as represented by the Minister of Agriculture and Agri-Food Canada.

Modeling the Interaction of Proximal Fragments for Destructive Atmospheric Entry Analysis

The destructive atmospheric entry process is distinguished by the formation of several fragments due to the severe aerothermal loads encountered during the descent. The proximity of debris leads to shock wave interactions and collisions between bodies, influencing the overall dynamics of the fragments and affecting the prediction of demise and ground impact location. To account for these effects, the use of computational fluid dynamics is introduced to resolve the shock interaction patterns by employing a quasi-steady approach, and the use of a simple rigid-body collision model is introduced to represent the dynamics of fragments in the cloud of debris. The quasi-steady approach is assessed and validated by comparative analysis with a few studies in the literature. One of these examples is the rebuilding of the VKI’s experiment of a free-flying ring crossing a shock wave generated by the presence of a stationary cylinder. The impact of explicitly modeling collision dynamics in the trajectory of fragments and ground spread distance is validated by considering a set of relevant test cases from the literature and tested them for destructive atmospheric reentry of the Attitude Vernier Upper Module, the launcher VEGA upper stage.

Experimental study of smoke characteristics in a double-deck tunnel with multiple point extraction using a branch pipe

A reduced scale 1:8 double-deck tunnel model was built to study smoke control performance of a semi-transverse ventilation system using a branch pipe to connect the lower deck tunnel to the upper smoke duct. 41 experiments were conducted to analyze the effects of different activation modes of smoke vents, heat release rate (HRR), and exhaust smoke rates on smoke spread distance. An optimum smoke control mode was found by activating two vents near the fire source when the heat release rate was 44.19 kW (8 MW at full scale) and the fan's extraction rate was 0.66 m3/s (120 m3/s at full scale) using a branch pipe. Results showed that as HRRs rise, the smoke spread distance first increases and then remains constant. The ratio of the smoke spreading distance on the upstream side of the fire to the total smoke spreading distance was 0.4 in this experimental setup. Furthermore, fire smoke spread characteristics were quantified for a typical ventilation design.

Shaping a Surface Microdroplet by Marangoni Forces along a Moving Contact Line of Four Immiscible Phases

AbstractThe ability to transfer microdroplets between fluid phases offers numerous advantages in various fields. This study focuses on the stability and morphology of a sessile oil microdropletduring the transfer from underwater to air. A distinct transition in microdroplet dynamics is observed, characterized by a shift from a scenario dominated by Marangoni forces to one dominated by capillary forces. In the former regime, the oil microdroplets spread in response to the contact between the water‐air interface and the water‐oil interface. The spreading distance follows a power law relationship of t3/4, reflecting the balance between Marangoni forces and viscous forces. On the other hand, in the capillarity‐dominated regime, the oil microdroplets remain stable at the contact line and after being transferred into the air. The crossover between these two regimes is identified in the parameter space defined by three factors: the approaching velocity of the solid‐water‐air contact line (vcl), the radius of the oil microdroplet (ro), and the radius of the water drop (rw). Furthermore, how to use the four‐phase contact line for shaping oil microdroplets is demonstrated using a full liquid process by the contact line lithography.

Mapping the distance between fire hazard and disaster for communities in Canadian forests.

Communities interspersed throughout the Canadian wildland are threatened by fires that have become bigger and more frequent in some parts of the country in recent decades. Identifying the fireshed (source area) and pathways from which wildland fire may ignite and spread from the landscape to a community is crucial for risk-reduction strategy and planning. We used outputs from a fire simulation model, including fire polygons and rate of spread, to map firesheds, fire pathways and corridors and spread distances for 1980 communities in the forested areas of Canada. We found fireshed sizes are larger in the north, where the mean distances between ecumene and fireshed perimeters were greater than 10 km. The Rayleigh Z test indicated that simulated fires around a large proportion of communities show significant directional trends, and these trends are stronger in the Boreal Plains and Shields than in the Rocky Mountain area. The average distance from which fire, when spreading at the maximum simulated rate, could reach the community perimeter was approximately 5, 12 and 18 km in 1, 2 and 3 days, respectively. The average daily spread distances increased latitudinally, from south to north. Spread distances were the shortest in the Pacific Maritime, Atlantic Maritime and Boreal Plains Ecozones, implying lower rates of spread compared to the rest of the country. The fire corridors generated from random ignitions and from ignitions predicted from local fire history differ, indicating that factors other than fuel (e.g. fire weather, ignition pattern) play a significant role in determining the direction that fires burn into a community.

Modeling of jet spreading and flame hazard distances for high pressure hydrogen releases

Hydrogen is a promising clean and sustainable energy carrier. Hydrogen is usually stored at high pressure due to its low density. Hydrogen releases from high pressure storage can result in underexpanded jets that will mix with air, forming a large combustible cloud. If the jets are ignited, jet flames will form with a large hazard area. This study simulated hydrogen jets and jet flames for storage pressures of 1~70 MPa and nozzle diameters of 1~2 mm using the HyRAM software. The results show that the jet diffusion distance increased with the hydrogen stagnation pressure and the nozzle diameter. The diffusion distances were correlated with the nozzle diameter and the hydrogen stagnation pressure. The jet flames and thermal radiations were then analyzed to show that the flame length and hazard distance both increased with the stagnation pressure and nozzle diameter. Correlations for radiation major harm distance, harm distance and no harm distance were developed to predict the jet flame hazard range. The present study can provide references for the safety design of hydrogen applications.