Search

This study investigates the spontaneous ignition of high-pressure hydrogen-enriched methane in air within a rectangular tube. A computationally efficient approach has been adopted, utilizing a reduced reaction mechanism and ignition delay model within a 3D Large Eddy Simulation (LES) framework. This approach overcomes the limitations of traditional 1D and 2D simulations with detailed chemistry models, which are unable to accurately reproduce the complex 3D shock wave structures within the tube. The simulated shock wave behavior during 9 MPa hydrogen leakage (case 1) and 11 MPa 90 vol% hydrogen/10 vol% methane mixture leakage (case 2) are found to agree well with experimental observations. In case 2, the hot spots generated by reflected shock waves and Mach reflections ignite the hydrogen/methane-air mixture, resulting in three sequential spontaneous ignitions. The flame is observed to primarily propagate along the tube corners and wall centers, with the central ignition spreading across the entire cross-section. For the 25 MPa 24 vol% hydrogen/76 vol% methane mixture leakage (case 6), the shock intensity is significantly reduced due to the increased methane proportion, leading to spontaneous ignition only at the tube corners when the hemispherical shock wave reflects from the wall. The flame predominantly forms downstream along the tube corner, gradually spreading along the tube wall. It is indicated that while the probability of spontaneous ignition decreases with increasing methane content, the risk remains significant under sufficiently high pressures. To the best our knowledge, this study represents the first 3D large eddy simulation of spontaneous ignition for high-pressure hydrogen-enriched methane leakage into air, providing valuable insights into the underlying physical phenomena. [ABSTRACT FROM AUTHOR]

Nitrogen-doped carbon monoliths can be prepared from liquid, deep eutectic mixtures of urea and hexaketocyclohexane octahydrate, which are structured by chitosan as a natural in-situ scaffold and support. The as-formed polymer monolith can then be transformed into the respective nitrogen-doped carbon monolith with a high surface area, high mesoporosity and high nitrogen-content. The surface functionality as well as the access to the internal pore structure were demonstrated by carbon dioxide and dye sorption experiments. The applied synthetic procedure is simple, does not require additional activation steps and uses cheap and naturally abundant compounds avoiding typical and hazardous formaldehyde resins. Eventually, this offers a safe and sustainable alternative to current carbon monolith synthesis. [ABSTRACT FROM AUTHOR]

Abstract: This study geospatially analyzes beach availability for global recreational tourism management with focus on a case study of Jekyll Island off the coast of Georgia, USA. Aerial digital imagery in combination with Light Detection and Ranging (LiDAR) data and geographic information system (GIS) mapping and analysis are employed to delineate accurate shorelines with regard to accessible and available beach area. This analysis demonstrates geospatial techniques for the identification, delineation, qualification and geovisualization of dry beaches, a popular tourist destination worldwide that is subjected to diurnal flooding by tides. The accurate depiction of shorelines using remotely sensed differences in Mean Higher High Water (MHHW) and Mean Lower Low Water (MLLW) levels is required to identify dry beach areas available for coastal tourism and management. Such information allows tourists to choose beach areas suitable for recreational or ecological activities. Dry beach availability also assists coastal restoration managers to plan and implement beach conservation measures. Results predict shoreline changes and dry beach access while promoting minimal impacts by tourists on fragile coastal dune ecosystems. [Copyright &y& Elsevier]

Abstract: Demarcation of upland and water/marsh boundary is a critical issue for management and protection of barrier island ecosystems. Most accurate, precise and confident approaches are required to resolve conflicts related to developable lands and conservation area. Barrier islands are especially prone to these conflicts because they are highly dynamic systems that are formed and reformed by rise and fall of tides and seal levels. In response, this research analyzes the demarcation of Jekyll Island State Park, Georgia, USA that is faced with management issues of balancing tourism and development with resource conservation. Questions addressed by this research include: (1) What are the standard sea levels used to demarcate barrier islands? (2) What are the best methods for most accurately estimating the total area of coastal barrier islands? (3) Do differences in tide elevations between back-barrier and ocean-front shorelines of barrier islands exist? Specifically, this research considers a number of environmental policies, regulations, and laws along with geospatial data such as aerial photography, Light Detection and Ranging (LiDAR) and GIS shapefiles. These data are used to define sea levels and outline of Jekyll Island State Park based on Mean High Water (MHW) levels with respect to 0.79-m, 0.85-m, 0.94-m, 1.00-m, and 1.49-m for the entire Jekyll Island State Park. The demarcations of different back-barrier marshland and ocean-front side of the island were also considered. Results indicate that the total area of Jekyll Island State Park may vary by as much as 3.31-km2 or 7.2% depending on the jurisdictional sea level that is used to demarcate the island boundary. [Copyright &y& Elsevier]

Abstract: The purpose of this study was to evaluate the radiographic changes of the tibiofibular position and the ankle mortise after removal of trans-syndesmotic fixation to determine if there is loss or maintenance of correction. In addition, the effect of the type of rotational injury, early weight bearing, and the number of trans-syndesmotic screws used on the integrity of the inferior tibiofibular articulation or ankle mortise after screw removal were evaluated. An analysis was conducted of 86 patients, with an unstable rotational ankle fracture requiring open reduction with syndesmosis screw stabilization. Routine radiographic parameters were measured just after open reduction and just before syndesmotic screw removal. There was a high correlation of loss of the integrity of the syndesmotic parameters after screw removal. However, the medial clear space of the ankle changed an insignificant amount, suggesting that although there appears to be some loss of maintenance, the talus did not shift laterally at the expense of a mobile syndesmosis. Ankle injuries requiring stabilization of syndesmotic instability with use of temporary trans-syndesmotic fixation achieve a stable ankle mortise after removal. Tibiofibular diastasis is commonplace upon removal of the syndesmotic hardware, but the ankle mortise remains unchanged. Based on the radiographic criteria described in this study, the postoperative change in medial clear space or tibiofibular diastasis has no bearing on fracture type, deltoid injury, or the use of 1 or 2 cortical screws. As such, other unknown mechanisms affecting the integrity of the syndesmosis after screw removal are in place. [Copyright &y& Elsevier]

Abstract: Medial column arthrodesis and calcaneal osteotomies are commonly used for adult acquired flatfoot surgical reconstruction. In this retrospective study, 41 patients (47 feet) with a mean age of 55 ± 13.5 years underwent a medial column arthrodesis, with or without calcaneal osteotomy, between 1999 and 2007. The indication for surgery was a painful flatfoot deformity with peritalar subluxation, and a fault in the naviculocuneiform joint. At a mean of 9.6 (range 3–43) months postoperatively, in patients who underwent a medial column arthrodesis, radiographs showed a mean decrease in the talonavicular coverage angle of 10.2° ± 8.7° (P < .001), and mean increases in the lateral talometatarsal and calcaneal inclination angle of 10.7° ± 5.1° (P < .001) and of 3.2° ± 2.7° (P < .001), respectively. In patients who underwent a combined medial column arthrodesis and a medializing calcaneal osteotomy, the talonavicular coverage angle decreased by a mean of 12.1° ± 6.1° (P < .001), while the lateral talometatarsal angle and calcaneal inclination angle increased by a mean of 12.3° ± 6.1° (P < .001) and 3.1° ± 2.7° (P < .001), respectively, from preoperative values. Four nonunions (4 of 47, 8.51%) occurred at the naviculocuneiform joint and 1 nonunion (1 of 32, 3.13%) occurred at the tarsometatarsal joint. These findings demonstrate marked improvement of radiographic flatfoot parameters following a medial column arthrodesis with or without a medializing calcaneal osteotomy. [Copyright &y& Elsevier]

Abstract: An example shows that weak decoherence is more restrictive than the minimal logical decoherence structure that allows probabilities to be used consistently for quantum histories. The probabilities in the sum rules that define minimal decoherence are all calculated by using a projection operator to describe each possibility for the state at each time. Weak decoherence requires more sum rules. They bring in additional variables, that require different measurements and a different way to calculate probabilities, and raise questions of operational meaning. The example shows that extending the linearly positive probability formula from weak to minimal decoherence gives probabilities that are different from those calculated in the usual way using the Born and von Neumann rules and a projection operator at each time. [Copyright &y& Elsevier]

For a single object, the Poisson bracket relations for the Galilei group or the Poincare´ group and the bracket relations that describe how the position should be changed by space translations, rotations, and either Galilei transformations or Lorentz transformations, imply that if the canonical coordinates are the position coordinates, the generators of the relativity group can be put in their familiar forms by a canonical transformation of the canonical momentum, which is a gauge transformation. In particular, the form of the Hamiltonian as a function of the canonical momentum, and the implied relation of the canonical momentum to the velocity and interpretation of the canonical momentum and Hamiltonian as physical quantities, are made more specific and unique by relativity; if Galilei or Lorentz transformations were not used, the Hamiltonian could be any function of the canonical momentum magnitude. Conversely, the same two sets of bracket relations imply that if the generators have their familiar forms, the canonical coordinates must be the position coordinates. [Copyright &y& Elsevier]

Abstract: Examples of repeatable procedures and maps are found in the open quantum dynamics of one qubit that interacts with another qubit. They show that a mathematical map that is repeatable can be made by a physical procedure that is not. [Copyright &y& Elsevier]

The provincial government of Nova Scotia, Canada, has provided numerous incentives for developing in-stream tidal energy projects since 2009. These incentives include co-operatively funding the development of the Fundy Ocean Research Centre for Energy with the Canadian federal government and industry partners, extensive funding of environmental impacts monitoring research for tidal energy projects, and offering direct financial incentives for tidal power produced and sold to the grid via feed-in tariffs. However, the provincial government has not treated all scales and types of tidal energy projects equally. Until recently, ambitious targets for hundreds of MW of tidal development by 2020–2025 led to tidal support policies focusing on large, utility-scale projects, with little evidence the tidal energy sector was prepared to pursue such projects in Nova Scotia or elsewhere. Some support was offered to smaller-scale, community-oriented tidal energy projects, but the rules and regulations for such projects were repeatedly changed (and sometimes revoked) between 2012 and 2018. Since the provincial legislature passed the revised Marine Renewable-electricity Act of 2018, a potentially more coherent and consistent tidal energy policy consensus appears to be forming in the province. This paper provides a review of the policies introduced, projects approved and canceled, and sectoral outlook for tidal energy development in Nova Scotia for the period 2009–2018. [ABSTRACT FROM AUTHOR]

Safety of the hydrogen refueling station under a postulated accident (e.g. leakage) is of great importance in hydrogen energy. The predictive CFD tool GASFLOW-MPI is utilized to simulate the full-scale hydrogen refueling station deflagration experiments with premixed H 2 -air cloud and high-pressure H 2 jet. The overpressures are predicted for an ignition between two dispensers in the premixed trial and a spark in the engine bay in the jet trial, which agree with the experimental data and validate the GASFLOW-MPI as well. Five turbulent burning velocity models are involved to investigate the explosion of the premixed H 2 –air cloud. The Zimont correlation is recommended for the combustion simulation of engineering full-scale H 2 refueling station. The turbulent flame speed is predicted after an ignition resulting in 50–200 m/s, and the flame acceleration happens due to the turbulence effect by obstacles. The developments of the pressure, temperature and H 2 concentration of premixed H 2 -air deflagration, indicate the pressure wave propagates with the reflections on obstacles, and the flammable H 2 cloud is enlarged by the push of combustion product. Moreover, the standard k − ε and DES model are adopted on the jet dispersion analysis. The local flow variables show some differences, but the global properties of average hydrogen concentration, the shape and size of the burnable cloud are similar, which indicates the hydrogen dispersion transient computed by k − ε turbulence model provides a reliable basis for estimating the combustion process. The evolutions of the jet resulting burnable H 2 -air mixture in the domain in terms of H 2 velocity field, concentration and mass are evaluated. The velocity field in jet trial explains that the momentum dominates hydrogen dispersion and result in a corresponding hydrogen concentration, however a large zone with high turbulence forms after combustion. The analysis of H 2 dispersed in the engine bay shows the growth and decay of the hydrogen concentration above some specified value of interest (4 and 10 vol% H 2). Most dispersed H 2 cloud is burnable, and half of the mass distributed in the cloud above 10 vol% may accelerate the flame to sonic. The comparison of the overpressure in k − ε and DES turbulence models with real and ideal gas release sources, shows in general no significant difference. The hydrogen release jet with higher turbulence generates the hydrogen cloud that can result in a large overpressure. • GASFLOW-MPI is validated comprehensively against the H2 deflagration experiments of a full-scale H2 refueling station. • Turbulent burning velocity correlations are investigated in the explosion of the premixed H 2 –air cloud. • Turbulence models are adopted and discussed in the analysis of the high-pressure H 2 jet release and dispersion. • Explosion overpressure and flame propagation in cases of both premixed H 2 –air cloud and high-pressure H 2 jet are presented. [ABSTRACT FROM AUTHOR]

• Droplet heat transfer model is extended with new features and coupled in Lagrangian approach for droplet-tracking in containment atmosphere. • Model validations against single droplet experiments show good agreements on droplet motion and condensation/evaporation. • The higher gas temperature is, the more significant it reduces the droplet evaporation heat transfer. • Solute effect is significant for the small droplet evaporating and the dry aerosol growth, which dominates the droplet equilibrium diameter. Spray droplet dynamics are expected to significantly affect steam condensation, droplet evaporation, and global gas mixing in the containment atmosphere. During severe accidents, droplets may evaporate under high gas temperatures (>200 °C) such as hydrogen fire radiation, and water-soluble aerosols such as CsI and CsHO may dissolve in droplets. An extension of the droplet heat transfer model was conducted to account for these conditions and coupled with a Lagrangian approach for droplet tracking. The approach was comprehensively validated through single droplet experiments, demonstrating the feasibility of this new approach. Analyses of the effects of high atmosphere temperature, droplet curvature, and aerosol solute indicate that, 1) High gas temperature significantly reduces heat transfer, with the effect increasing at higher gas temperatures; 2) Droplet curvature enhances droplet evaporation, but this effect is limited to tiny droplets (<100 nm) compared to other effects; 3) The solute effect significantly impacts small droplet evaporation and dry aerosol growth, dominating the final equilibrium droplet diameter. The extended droplet/aerosol heat transfer model fills a gap in the knowledge of containment spray under severe accidents. A feasible way to approximate the minimum spray droplet size in the heat transfer model is to truncate or initialize the small droplet by the equilibrium diameter. [ABSTRACT FROM AUTHOR]

Deterministic risk assessment for hydrogen installations offers an integrated solution for H 2 risk assessment, incorporating a hydrogen release model, a site-specific 3D geometry model, a Computational Fluid Dynamics (CFD) tool, and a consequence analysis methodology. Empirical engineering models expedite the preparation of source terms and harm evaluations, while CFD generates 3D contours of radiation and overpressure loads. A case study is provided by investigating a gaseous hydrogen leak of a truck in a refueling station with a large roof. The effects of leak diameters, roof configurations, and ignition locations on hydrogen dispersion, combustion, and hazard analysis are examined. Results indicate that the majority of the burnable cloud accumulates in a half-meter layer under the ceiling, diminishing within a minute. The impact of thermal radiation on individuals is insignificant, but overpressures increase the likelihood of structure failures, indirectly affecting human fatality. These findings inform the optimization of refueling station design and safety management. • CFD-based Deterministic Risk Assessment approach to assess the safety of hydrogen installations. • Addressing potential hydrogen explosions due to the current ceiling design. • Minimal injury likelihood from hydrogen flame contact or thermal radiation. • Revealing insights for optimizing ceiling design and hydrogen risk mitigation strategies. [ABSTRACT FROM AUTHOR]

Abstract: The mapping of coral reefs may be efficiently accomplished by the use of airborne laser bathymetry. However, there are often data holes within the bathymetry data which must be filled in order to produce a complete representation of the coral habitat. This study presents a method to fill these data holes through data merging and interpolation. The method first merges ancillary digital sounding data with airborne laser bathymetry data in order to populate data points in all areas but particularly those of data holes. What follows is to generate an elevation surface by spatial interpolation based on the merged data points obtained in the first step. We conduct a case study of the Dry Tortugas National Park in Florida and produced an enhanced digital elevation model in the ocean with this method. Four interpolation techniques, including Kriging, natural neighbor, spline, and inverse distance weighted, are implemented and evaluated on their ability to accurately and realistically represent the shallow-water bathymetry of the study area. The natural neighbor technique is found to be the most effective. Finally, this enhanced digital elevation model is used in conjunction with Ikonos imagery to produce a complete, three-dimensional visualization of the study area. [Copyright &y& Elsevier]

: BackgroundElderly patients undergoing pancreatic resection present unique challenges in postoperative care. Although mortality rates among elderly patients after pancreatectomy at high-volume centers is known to be low, the anticipated decline in functional status and nutritional parameters has received little attention. Functional decline is an unrecognized but critically important consequence of pancreatic resection in older patients.: Study designThis study is a retrospective review, validation cohort, of older and younger patients undergoing major pancreatic resection. The setting is the state of California (database of all hospitals in the state) and The University of California, San Francisco (UCSF; a tertiary care referral center). The study population is a consecutive sample of older (greater than or equal to 75 years) and younger (16 to 74 years) patients from California (January 1990 to December 1996; n = 3,113) and UCSF (January 1993 to November 2000; n = 218), who underwent radical pancreaticoduodenectomy, distal pancreatectomy, or total pancreatectomy for neoplasia. The main outcomes measures were length of stay, complications, mortality, discharge disposition, supplemental nutrition requirement, and readmissions.: ResultsElderly patients had higher mortality rates than the young statewide (10% versus 7%, p = 0.006). Although the 3% mortality at UCSF was the same for both groups, older patients were more often admitted to the ICU (47% versus 20%, p = 0.003), treated for major cardiac events (13% versus 0.5%, p < 0.001), discharged with enteral tube feedings (48% versus 16%, p < 0.001), or malnourished on readmission (17% versus 2%, p < 0.005). Older patients were more frequently discharged to skilled nursing facilities (17% versus 1% at UCSF; 24% versus 7% in California; p < 0.001, both groups).: ConclusionsOlder patients are more likely than younger patients to require an ICU stay, suffer a cardiac complication, and experience compromised nutritional and functional status after major pancreatic resection. [Copyright &y& Elsevier]

An accurate prediction of the hydrogen behaviors in the accident and management process is a crucial topic for both the hydrogen safety assessment and safety analysis in the confined enclosure like the containment of the nuclear power plant (NPP). Hence, the hydrogen behaviors including the transient light gas release, stratification and dissolution in the TH22 test facility for the NPP containment are analyzed and compared using the 3-D CFD code GASFLOW-MPI in this study. In this paper, the light gas helium is adopted as a substitute for the hydrogen in the calculations in accordance with the experiment. Firstly, the detached eddy simulation (DES) turbulence model, 3-D numerical model and experiment setup are introduced. Then, the hydrogen behaviors with the GASFLOW-MPI including the light gas release, stratification and dissolution are analyzed and validated with the experiment data. In addition, the velocity profiles, light gas concentrations, dimensionless numbers and temperature distributions are evaluated for the characteristics of the hydrogen behaviors. The results indicate that the calculation results agree well with the experiment data. Foremostly, the relative errors between the calculation results and experiment data during the phase of the dissolution of the light gas cloud are within 11.9%. Meanwhile, the relative errors of the time for the complete dissolution during the phase of the dissolution of the light gas cloud are within 5.0%. For the light gas release and stratification phase, the jet flow dominates as the Froude (Fr) number exceeds 10 during the time t = 600 s–800 s. Additionally, the time averaged centerline velocity and light gas concentration after the potential core region decay with a slop of 1/ z which coincide with the theoretical jet limit. Lastly, the light gas concentrations and temperature distributions in all three phases are captured clearly with the GAFLOW-MPI. It demonstrates that the GASFLOW-MPI can accurately described the details of the related hydrogen behaviors in the accident and management process in the confined enclosure like the NPP. This paper can provide guidance for the numerical computation of the hydrogen safety issues in the confined space. [Display omitted] • Light gas behaviors are evaluated with the 3-D CFD code GASFLOW-MPI. • The analysis includes the transient light gas release, stratification and dissolution. • Calculation results are compared and validated with the experiment data. • It demonstrates an integral method for the hydrogen safety in the confined space. [ABSTRACT FROM AUTHOR]

Hydrogen energy is expanding world-widely in recent years, while hydrogen safety issues have drawn considerable attention. It is widely accepted that accidental hydrogen release in an open-air environment will disperse quickly, hence not causing significant hydrogen hazards. A hydrogen hazard is more likely to occur when hydrogen is accidentally released in a confined place, i.e. parking garages and tunnels. Prediction the main accident process, including the hydrogen release, dispersion, and combustion, is important for hydrogen safety assessment, and ensuring the safety installations during accidents. Hence, a postulated accident scenario induced by the operation of Thermal Pressure Relief Device in a tunnel is analysed for hydrogen fuel cell vehicles with GASFLOW-MPI in this study. GASFLOW-MPI is a well validated parallel CFD code focusing on the transport, combustion, and detonation of hydrogen. It solves compressible Navier-Stokes equations with a powerful all-speed Arbitrary-Lagrangian-Eulerian (ALE) method; hence can cover both the non-compressible flow during the hydrogen release and dispersion phases, and the compressible flow during deflagration and detonation. In this study, a 3D model of real-scaled tunnel is modelled, firstly. Then the hydrogen dispersion in the tunnel is calculated to evaluate the risk of Flame acceleration and the Deflagration-Detonation Transient (DDT). The case with jet fire is analysed with assuming that the hydrogen is ignited right after being injected forming a jet fire in the tunnel, the consequence of this case is limited considering the small hydrogen inventory. The detonation in the tunnel is calculated by assuming a strong ignition at the top of the tunnel at an unfavourable time and location. The pressure loads are calculated to evaluate the consequence of the hazard. The analysis shows that the GASFLOW-MPI is applicable at a widely range for tunnel accidents, meanwhile, the safety issues related to tunnel accidents is worthy further study considering the complexity of tunnels. • A tunnel accident of HFCVs is analysed with parallel CFD code GASFLOW-MPI. • The analysis includes the hydrogen release, dispersion, jet fire and detonation. • This study demonstrates an integral method for the tunnel safety issue of HFCVs. [ABSTRACT FROM AUTHOR]