Large-scale Transport Research Articles

Enhancing safety in hydrogen storage: Understanding the dynamic process in hydrogen-methane mixtures during the pressurized leakage

Using natural gas pipelines for hydrogen-doped transportation represents a cost-effective solution for large-scale and long-distance hydrogen transport. However, concerns have been raised regarding the potential for leakage under high-pressure conditions, which could result in the spontaneous combustion of the leaking hydrogen. It is, therefore, imperative to understand the gas dynamics involved in methane-hydrogen mixtures during high-pressure leaks to ensure the safety of hydrogen storage. In the present work, the release process and the spontaneous ignition of hydrogen/methane mixtures with a hydrogen blending ratio from 0.1 to 1.0 from pressurized storage containers (20 MPa) have been numerically studied upon validated models. The findings indicate that spontaneous ignition occurs in the mixtures with any hydrogen blending ratios under the releasing pressure of 20 MPa, but the methane component is not involved in the initial combustion if the hydrogen blending ratio is less than 0.5. As the hydrogen blending ratio increases, more combustible components are involved in the initial ignition, and the location of the initial ignition turns closer to the leakage port. Meanwhile, as the hydrogen blending ratio rises from 0.1 to 1.0, the shockwave propagation is accelerated with the moment the shockwave first reflects is advanced from 58 to 60 μs to 22–24 μs, and the maximum temperature in the early leakage will exceed 3000 K. Furthermore, a higher hydrogen blending ratio leads to a more rapid pressure rise in the external space (reaching peak pressure at 191 μs for pure hydrogen) and forming a Mach disk structure with higher Mach numbers (around 7). These findings provide critical insights for understanding the combustion behavior of hydrogen/methane mixtures in high-pressure pipelines and offer valuable guidance for developing safety protocols and infrastructure designs.

Random nonequilibrium Green's function method for large-scale quantum transport simulation

Random nonequilibrium Green's function method for large-scale quantum transport simulation

Flows, circulations, and energy transport in the outer and deep atmospheres of synchronous and non-synchronous hot Jupiters

Recent studies have shown that vertical enthalpy transport can explain the inflated radii of highly irradiated gaseous exoplanets. Simultaneously, they have also shown that rotation can influence this transport, leading to highly irradiated, rapidly rotating objects that are uninflated. Here we explore the flows that underpin this transport, including the impact of synchronous or non-synchronous rotation. We used DYNAMICO to run a series of long timescale HD209458b-like atmospheric models at various rotation rates. For models that are tidally locked we considered rotation rates between $1/16^ th $ and $40$ times the rotation rate of HD209458b, whilst for non-synchronous models, we considered the range one-eighth to four times HD209458b. We find that our synchronous models fall into one of three Omega -dependent regimes. At low Omega , we find that the outer atmosphere dynamics are driven by a divergent day-night wind which drives weak vertical transport and can lead to the formation of a night-side hot-spot. At intermediate Omega , we find classical hot Jupiter dynamics, whilst at high Omega we find a strong Coriolis effect that suppresses off-equator dynamics, including the jet-driving standing waves, thus also reducing vertical transport. As for non-synchronicity, when small, we find that it has little effect on the dynamics. However as it grows, we find that temporal variations prevent the formation of the persistent structures that drive large-scale dynamics and transport. We find that rotation can significantly impact the atmospheric dynamics of irradiated exoplanets, including vertical enthalpy advection, which may help explain the scatter in the hot Jupiter radius-irradiation relation. We have also identified a seemingly robust atmospheric feature at slow rotation: a night-side hot-spot. As this may have important implications for both the phase curve and atmospheric chemistry, we suggest that this study be followed up with next-generation global circulation models (GCMs) that robustly model radiation and chemistry.

Broadband large-scale acoustic topological waveguides

The acoustic topological waveguide (ATW) hosting topologically protected waveguide modes provides a unique opportunity for achieving large-scale sound transport with robustness. However, prevailing ATWs are typically designed by forward-designed sonic crystals (SCs) based on physical intuitions, unavoidably leading to restricted bandwidths. Here, using the inverse-designed SCs with maximized topological bandgaps, we construct broadband ATWs based on both the quantum spin Hall effect and the quantum valley Hall effect. Broadband large-scale transportation, spin-locked one-way transportation, and the squeezing effect of acoustic waves are demonstrated. This study ushers a new path for designing topological devices with broadband performance for large-scale acoustic wave transportation.

High-performance porous 3D Ni skeleton electrodes for the oxygen evolution reaction

A key component of green hydrogen production technologies is the fabrication of large-scale porous transport layer (PTL) for use in anion electrolyte membrane water electrolysers (AEMWEs). One strategy to achieve that goal is to manufacture Ni-based 3D electrode skeletons that can be further catalyzed to achieve high current densities at low overpotentials. In the present work, shock-wave induced spray (SWIS) and cold spray (CS) deposition techniques were used to prepare 20 cm2 Ni-based electrode skeletons. In our experimental conditions, the porosity of coatings prepared using the SWIS deposition system and Ni powders with particle sizes D50 = 32 and 75 μm never exceeded 28%. Higher porosity could only be achieved using the CS deposition system and a spheroidal Ni–Al powder, whose particles consist of an aluminum core encapsulated in a nickel shell. After Al leaching in an alkaline solution, the resulting electrodes showed good mechanical and structural integrity with up to 41% porosity. The electrochemical active surface area of the most porous electrodes is a factor of 2100 larger than a polished Ni plate, and it has superaerophobic properties with a captive air bubble contact angle of 151°. During 1 h of electrolysis, the overpotential at 100 mA cm−2 of the most active leached Ni–Al cold spray deposited electrode was 330 mV, compared to 380 mV for a Ni foam electrode.

The role of green ammonia in meeting challenges towards a sustainable development in China

The shift to a sustainable development has become an important issue in China. This paper discusses the role of green ammonia in promoting China's energy, environmental and economic sustainability which has not drawn enough attention. First, key challenges in China's energy transition, decarbonisation and regional sustainable development are explored. The coal-dominated energy consumption has placed great obstacles in achieving energy transition and led to massive CO2 emission since the large-scale industrialization. The high dependency on oil and gas import has threatened China's energy security. Imbalanced and unsustainable regional development is identified with data envelopment analysis. Second, the potential of green ammonia in meeting these challenges is analysed. Ammonia is examined to be a flexible and economic option for large-scale hydrogen transport and storage. Co-firing ammonia in coal power generation at 3 % rate is evaluated as an option for achieving low-carbon transition by 2030. Benefits of developing a green ammonia economy is discussed from energy, environmental and economic aspects. The practice can decline fossil energy consumption, enhance energy security, and facilitate renewable energy delivery and storage, industry decarbonisation, and regional development. We assume the findings and results contribute to addressing sustainability challenges and realizing a hydrogen economy in China.

Precursor boundary layer conditions for shallow and deep convection: inferences from CAIPEEX field measurements over the Indian Peninsula

The diurnal cycle of environmental conditions for shallow and deep convection regimes within the Indian monsoon environment is investigated using comprehensive observations from the surface, boundary layer, and cloud layers. For shallow convection (SC) and deep convection (DC) in the afternoon hours, thermodynamics, moisture convergence, and several other environmental variables provide information on the factors that control the vertical extent of convection in both regimes. The SC regime is characterized by high sensible heat flux, leading to stronger boundary layer turbulence, a higher mixed layer, and increased dry air entrainment from the free troposphere. Evaluation of several pre-conditioning parameters with T-test statistics suggests that stronger mid-level meridional wind shear and lack of mid-level moistening are detrimental to the growth of clouds in the SC regime. Conversely, the DC regime is driven by low surface fluxes and low surface-level buoyancy, with higher boundary layer and mid-layer moisture and more mid-layer instability, supporting larger Convective Available Potential Energy (CAPE). Morning precursor conditions for the preference of SC versus DC regime in the afternoon reveal that total column water vapor, relative humidity and CAPE are significantly higher on DC days. Large-scale moisture transport in the early morning within and above the boundary layer, driven by stronger westerly winds, is a key factor for the development of DC later in the day. This investigation enhances our understanding of boundary layer controls on shallow and deep convection within the Indian Monsoon environment.

Advancements in Cooperative Mobile Robots Control Strategies for Large-Scale Material Transport

This paper explores groundbreaking advancements in control strategies for cooperative mobile robots used in large-scale material transport, a critical aspect of modern industrial, manufacturing, logistics, and construction sectors. It delves into the development of sophisticated systems that enable seamless coordination among multiple mobile robot systems. The research presents a novel hierarchical finite state automaton for dynamic mission adaptation and a null space-based control scheme for precise task execution and enhanced system resilience. The introduction of Mecanum wheels facilitates flexible movement and manipulation of materials, thereby increasing operational efficiency and safety. Cutting-edge sensory technology, including LiDAR, and the implementation of the Robot Operating System are highlighted for their roles in enhancing autonomous navigation and intelligent operation. Additionally, the paper discusses the impact of centralized and decentralized control methods in ensuring safe, cooperative object transport. The findings contribute to the vision of Industry 4.0 by promoting the integration of automation and robotic cooperation in complex environments and present a foundational blueprint for further research. Challenges for future work such as scalability, communication efficiency, collision avoidance, and energy efficiency are also considered, underscoring the need for ongoing development of robust and scalable robotic systems to address modern transport challenges.

A High-Resolution, Large-Scale Agent-Based Transport Model for Health Outcomes Evaluation from Policy Changes

A High-Resolution, Large-Scale Agent-Based Transport Model for Health Outcomes Evaluation from Policy Changes

Mercury compound distribution and stable isotope composition in the different compartments of seabird eggs: The case of three species breeding in East Greenland

Mercury (Hg) is a toxic contaminant of global concern and the impact on Arctic ecosystems, particularly in seabirds, is critical due to large-scale Hg transport towards polar regions and its biomagnification in marine trophic systems. While the adverse effects of Hg on reproductive processes in seabirds are established, the understanding of Hg maternal transfer pathways and their control on Hg reproductive toxicity is limited. The combination of Hg compounds speciation (inorganic mercury and monomethylmercury MMHg) and Hg stable isotope composition in the different egg compartments (yolk, albumen, membrane, and shell) before embryo development was investigated to provide information on (i) Hg maternal transfer mechanisms, (ii) influence of egg biochemical composition on Hg organotropism and (iii) proxies of inputs of Hg contamination. Eggs of three seabird species (the common eider, the black-legged kittiwake and the little auk) collected within the same breeding period (summer 2020) in East Greenland were investigated. For all seabirds, albumen and membrane, the most protein-rich compartments, were the most contaminated (from 1.2 to 2.7 μg g−1 for albumen and from 0.3 to 0.7 μg g−1 for membrane). In these two compartments, more than 82% of the total Hg amount was in the form of MMHg. Additionally, mass-dependent fractionation values (δ202Hg) were higher in albumen and membrane in the three species. This result was mainly due the organotropism of MMHg as influenced by the biochemical properties and chemical binding affinity of these proteinous compartments. Among the different egg compartments, individuals and species, mass-independent fractionation values were comparable (mean ± sd were 0.99 ± 0.11‰, 0.78 ± 0.11‰, 0.03 ± 0.05‰, 0.04 ± 0.10‰ for Δ199Hg, Δ201Hg, Δ200Hg and Δ204Hg, respectively). We conclude that initial MMHg accumulated in the three species originated from Arctic environmental reservoirs exhibiting similar and low photodemethylation extent. This result suggests a unique major source of MMHg in those ecosystems, potentially influenced by sea ice cover.

Interannual Fluctuations and Their Low-Frequency Modulation of Summertime Heavy Daily Rainfall Potential in Western Japan

Heavy rainfall under the conditions of the changing climate has recently garnered considerable attention. The statistics on heavy daily rainfall offer vital information for assessing present and future extreme events and for clarifying the impacts of global climate variability and change, working to form a favorable background. By analyzing a set of large-ensemble simulations using a global atmospheric model, this study demonstrated that two different physical processes in global climate variability control the interannual fluctuations in the 99th- and 90th-percentile values of summertime daily rainfall (i.e., the potential amounts) on Kyushu Island in western Japan. The 90th-percentile values were closely related to large-scale horizontal moisture transport anomalies due to changes in the subtropical high in the northwestern Pacific, which was usually accompanied by basin-scale warming in the Indian Ocean subsequent to the wintertime El Niño events. The contributions of the sea surface temperatures over the northern Indian Ocean and the eastern tropical Pacific Ocean showed low-frequency modulations, mainly due to the influences of the global warming tendency and the interdecadal variability in the climate system, respectively. In contrast, tropical cyclone activity played a major role in changing the 99th-percentile value. The potentials of both the tropical cyclone intensity and the existence density fluctuated, largely owing to the summertime sea surface temperature over the tropical Pacific, which can be modulated by the El Niño diversity on interdecadal timescales.

Performance analysis of coaxial shear static mixer for hydrogen blending into natural gas

Blending a specific proportion of hydrogen into a natural gas (NG) pipeline network is an effective strategy for achieving long-distance, large-scale, and cost-effective hydrogen transport. Static mixers played a crucial role in this process. In this study, a coaxial shear static mixer with ring-shaped structures instead of turbulence elements is proposed. The mixer exhibited favorable mixing performance and low pressure loss. The flow characteristics of NG and hydrogen within the mixer were investigated with computational fluid dynamics (CFD) methods. The effects of the number of cavities, hydrogen pipe diameter, hydrogen blending ratio and pressure on the mixer performances were investigated, taking into account both mixing uniformity and pressure loss. When the number of cavities in the coaxial shear mixer increases to 48, the mixing uniformity reaches 95.43% (SMX is 95%), and the pressure loss is 67.02 Pa (SMX is 500 Pa).

Lagrangian Perspectives on the Small-scale Structure of Alfvénic Turbulence and Stochastic Models for the Dispersion of Fluid Particles and Magnetic Field Lines in the Solar Wind

Lagrangian perspectives on the small-scale structure of anisotropic Alfvénic turbulence are adopted. We are interested in relating the statistical properties of the Eulerian field increments evaluated along the fluid particle trajectories, in the direction perpendicular to the guiding magnetic field and along the magnetic field lines. We establish the basis for a unified multifractal phenomenology of Eulerian and Lagrangian Alfvénic turbulence. The critical balance condition is generalized to structure functions of an order different than 2. A Lagrangian perspective is not only useful for investigating the small-scale structure of Alfvénic turbulence, it is also tailored to the modeling of large-scale turbulent transport. Therefore, we develop Lagrangian stochastic models for the dispersion of fluid particles and magnetic field lines in the solar wind. The transport models are based on the integrated Ornstein–Uhlenbeck process that is not Markov, yielding smooth stochastic fluid particle trajectories and magnetic field lines. Brownian diffusion is recovered by tending the integral scale parameter to zero while keeping the diffusivity finite.

Computational thermal fluid enabled multi-physics transport processes analysis of ceramic hollow fiber membrane for oxygen separation

A comprehensive hollow fiber membrane model is developed using an experimental system as a physical base, where Multiphysics transport processes in the membrane are coupled with a large-scale thermal fluid transport processes in the test assembly and furnace. Systematic parametric studies are carried out to understand fundamental mechanisms and membrane performance. Results indicate that oxygen partial pressure at the permeate side asymptotically increases from the inlet toward the outlet of hollow fiber membrane. Longitudinal distribution of oxygen vacancy concentration follows the opposite trend to that of oxygen partial pressure at the permeate side while oxygen flux distribution follows the profile of oxygen vacancy distribution at the permeate surface. High air pressure at the feed side and low gas pressure at the permeate side facilitate to enhance oxygen permeation performance. Surface exchange resistance at the permeate side dominates the total resistance of the membrane while the bulk diffusion resistance accounts for the minimum contribution in substrate-supported thin film hollow fiber membrane. The modeling study may obtain an insightful understanding of fundamental mechanisms and can provide guidance for membrane design and operations to achieve better performance for oxygen production.

Activity-based and agent-based transport model of Melbourne: an open multi-modal transport simulation model for Greater Melbourne

Activity- and agent-based models for simulating transport systems have attracted significant attention in recent years. However, building these types of models at a city-wide level and including motorized (i.e. cars and public transport) and non-motorized (i.e. walk and bicycle) modes of transport is a complicated and involved task. This paper presents an open workflow for creating large-scale multi-modal agent-based transport simulation models. The workflow brings together a number of external tools, for example, an activity-based demand generation tool and a road network generation tool, and a set of tools developed for the agent-based model parameter estimation, calibration, and simulation post-processing. We used this workflow to create an activity- and agent-based model for Melbourne and compared the output of the simulation model with observations from the real world in terms of mode share, road volume, travel time, and travel distance. Through these comparisons, we showed that our model is suitable for studying mode choice and road usage behavior of travelers. The calibrated model could be used to test road network change interventions. In addition, a similar workflow can be applied for building simulation models for other cities or could be expanded to include more complicated travel behaviors.

Efficient self-organization of informal public transport networks

The Global South, encompassing more than 80% of the world population, heavily relies on informal paratransit services with ad-hoc routes. Yet, it remains unclear how efficiently such informal public transport services organize and operate. Here, we analyze and compare the structural efficiency of more than 7000 formal and informal bus service routes in 36 cities across 22 countries globally. Intriguingly, informal transport self-organizes in ways at or above efficiency levels of centralized services. They exhibit fewer detours, more uniform paths, and comparable interconnectivities, all while remaining profitable without the major subsidies common in the Global North. These insights challenge the global perception of informal transport as an inferior alternative to centrally organized services. More generally, analyzing large-scale microscopic transport data and condensing them into informative macroscopic observables may qualitatively improve system understanding and reveal specific options to create more accessible, efficient, and sustainable public transport solutions.

Spatial distribution of small microplastics in the Norwegian Coastal Current

High concentrations of microplastic (MP) particles have been reported in the Arctic Ocean. However, studies on the high-resolution lateral and vertical transport of MPs from the European waters to the Arctic are still scarce. Here, we provide information about the concentrations and compositions of MPs in surface, subsurface, and deeper waters (< 1 m, ∼ 4 m, and 17–1679 m) collected at 18 stations on six transects along the Norwegian Coastal Current (NCC) using an improved Neuston Catamaran, the COntinuos MicroPlastic Automatic Sampling System (COMPASS), and in situ pumps, respectively. FTIR microscopy and spectroscopy were applied to measure MP concentration, polymer composition, and size distribution. Results indicate that the concentrations of small microplastics (SMPs, <300 μm) varied considerably (0–1240 MP m−3) within the water column, with significantly higher concentrations in the surface (189 MP m−3) and subsurface (38 MP m−3) waters compared to deeper waters (16 MP m−3). Furthermore, the average concentration of SMPs in surface water samples was four orders of magnitude higher than the abundance of large microplastics (LMPs, >300 μm), and overall, SMPs <50 μm account for >80 % of all detected MPs. However, no statistically significant geographical patterns were observed in SMP concentrations in surface/subsurface seawaters between the six sampling transects, suggesting a relatively homogeneous horizontal distribution of SMPs in the upper ocean within the NCC/Norwegian Atlantic Current (NwAC) interface. The Lagrangian particle dispersal simulation model further enabled us to assess the large-scale transport of MPs from the Northern European waters to the Arctic.

A Tempered Fractional Kinetic Transport Theory for Energetic Particle Interaction with Quasi-two-dimensional Turbulence in the Large-scale Solar Wind

Observational evidence is accumulating that turbulence in the solar wind is intermittent (non-Gaussian) because of the strong presence of a quasi-two-dimensional (quasi-2D), low-frequency turbulence component containing nonpropagating, closed, small-scale magnetic flux ropes with open meandering field lines in between. le Roux & Zank showed how one can derive fractional focused and Parker-type transport equations that model large-scale anomalous transport in the solar wind as the outcome of energetic particle interaction with quasi-2D turbulence. In this follow-up paper this theory is developed further to address certain limitations. (i) The second moment of the Lévy probability distribution function (PDF) specified in the theory for the particle step size is infinite, indicating unphysical transport. (ii) The expected transition of energetic particle transport from anomalous to normal diffusion beyond a certain critical transport distance was not included. (iii) The competition between anomalous diffusion and advection is not properly sustained at late times. Shortcomings (i) and (ii) are addressed by introducing an exponentially truncated Lévy PDF for the energetic particle step size in the theory, resulting in revised tempered fractional focused and Parker-type transport equations featuring tempered fractional derivatives that enable modeling of tempered Lévy flights. Furthermore, these equations are cast in a tempered fractional telegrapher form to investigate whether the fractional wave equation part of the equation can restore causality in unscattered particle transport during early times and in Lévy flights during intermediate times (Lévy walks). They are also transformed into a tempered fractional Fokker–Planck form to overcome limitation (iii).

Externalities from the confinement of a railway: Analysis of the barrier effect

In this paper, we present a mixed qualitative-quantitative approach to analyse the multiple dimensions of the barrier effect caused by the removal of all at-level pedestrian crossings on a railway in a residential area of Santiago, Chile, as part of a new suburban rail service. A set of interviews with a wide range of stakeholders is followed by a quantitative analysis of time delays and extra discomfort for pedestrians, as we measure both the horizontal and vertical detours on walking distance and time, due to having to cross on pedestrian overpasses and underpasses. We find that (i) the new suburban rail service is a source of social inclusion on a metropolitan scale (accessibility gains) and of social exclusion on a more local scale, due to a barrier effect (ii) the confinement of the railway produces strong negative impacts on pedestrians that need to cross the railway, by increasing walking times and by worsening their perception of security and comfort (iii) underpasses and overpasses increase between twofold and fourfold the time needed to cross the railway on average, relative to the case of at-level crossings, (iv) taking into account the increased physical burden and insecurity perceived on overpasses and underpasses, weighted walking times increase up to ten times relative to at-level crossing, and (v) women, elderly people and pedestrians with heavy luggage are more affected by the increased walking time. Traditional methods employed to analyse large-scale transport projects should assess the negative implications of the barrier effect on local communities, as well as the relief measures designed to reduce local segregation, especially in vulnerable communities. The results of this study are useful to quantify the social value of such relief measures, particularly in highly unequal urban settings.

A new multi-input multi-output control design method for a large-scale web transport system

The paper introduces an innovative multi-input multi-output (MIMO) control design approach tailored for the complex dynamics of large-scale web transport systems in printed electronics manufacturing technology. First, a novel hybrid control design is proposed to a MIMO strict-feedback nonlinear dynamic system, in which a modified tracking error is introduced in term of a sliding surface for design purpose. Then, a combined use of Lyapunov-based control design and sliding mode control is employed to formulate a novel control law, called Backstepping Sliding Mode Control (BSMC) and a BSMC based control structure is provided. Second, application of this control strategy is implemented to control web tension and velocity of a three-span web transport system. In this study, a series of assumptions are provided to transform an original system dynamics of web transport system into a standard strict-feedback form. Then, the proposed theory is applied for the achieved system, a BSMC for the system is synthesized for simulation study. Finally, numerical simulations are conducted under different operating conditions to validate the effectiveness, reliability, and robustness of the proposed control method.