Position Of Front Research Articles

Spatially resolved investigation of flame particle interaction in a two dimensional model packed bed

This study investigates the interaction between a premixed methane-air flame and particles inside a model packed bed. The opacity of the spherical packed beds to visible light poses a major barrier to the implementation of highly resolved optical diagnostics, so that no detailed experimental data were so far available for the validation of numerical simulation. Here, a two-dimensional cylindrical packed bed design is set up, which enables direct line-of-sight optical measurements without loss of spatial resolution over the fluid region between the particles. In this study, the case of cold metallic cylindrical particles (T = 377 K) relevant to start-up of a reactor is investigated using internal particle cooling, which also allows cylinder specific heat transfer rate measurements by differential temperature measurements on the coolant streams. The two dimensional assumption is first verified by measuring the inflow velocity and cylinder temperature profile along the cylinders. Chemiluminescence imaging is then performed using a telecentric lens to observe the position and geometry of the two-dimensional flame front with respect to the surrounding cylinders without loss of resolution. Simultaneously, the cylinder-specific flame to cylinder heat transfer rates and cylinder surface temperature are measured. As the flame is closely surrounded by the three cooled cylinders, intense heat transfer is observed in this region corresponding to 25 ± 2.5% of the flame thermal power. Flames were stabilised at different positions depending on inflow velocity and equivalence ratio, and a direct correlation between flame to cylinder stand-off distance and the heat transfer rate normalised to the flame thermal power was found for both top and side cylinders. Also, sidewall quenching distances to the curved cylinder surfaces were evaluated, and seem to be influenced by the presence of a warm recirculation zone behind the cylinders. This investigation provides fully resolved flame front position and heat transfer rates for a known geometry and cylinder thermal boundary conditions, and provides validation data for numerical simulations of this high flame particle coupling case.

Pore-scale Numerical Simulations on the Lean Concentration Methane Combustion in Porous Medium with Gyroid Triply Periodic Minimal Surfaces Structures

ABSTRACT In this work, a series of porous medium with Gyroid Triply Periodic Minimal Surfaces (G-TPMS) structures were established for lean concentration methane combustion. Based on pore-scale numerical simulations, the influence of TPMS parameters on porous media combustions, as well as the shape of flame surface in different TPMS structures, heat transfer characteristics between solids and fluids, the radiation characteristics and heat flux on the solid surface were investigated. Results show that, under the same inlet flow rate and equivalence ratio, the value and axial location of the maximum average fluid temperature will be changed due to the difference in porosity and flow resistance of each structure. For the G-TPMS structures’ porous medium, the change of structure period had a greater impact on the combustion compared with the wall thickness. And, in the G-TPMS structures’ porous medium, the flame surface always shows a finger structure. The flow rate that shows the same increase trend with the fluid temperature in the preheating region, which has a periodic change like the porosity in the axial direction. Based on the results, it can be seen that the region of solid-to-solid surface radiative heat transfer and fluid-solid heat flux on the interface was also changed due to the influence of flame front position.

Co-evolutionary algorithm based on problem analysis for dynamic multiobjective optimization

Dynamic multiobjective optimization problems (DMOPs) vary over time, requiring an optimization algorithm to track the position of Pareto-optimal front (PF) in a dynamic environment. To achieve that, a novel co-evolutionary algorithm based on problem analysis (CAPA) is proposed in this paper. CAPA is designed to solve DMOPs from decision space and objective space simultaneously, which is achieved by the combination of adjustable prediction (AP) and precise mapping strategy (PM). In decision space, the proposed multi-model prediction can estimate the location of new population based on the historical median points. In objective space, a novel sampling method is developed to search for sample points with better convergence or diversity. Then, mapping these sample points back to decision space based on inverse model. Through the problem analysis mechanism, the proportion of the new solutions produced by each strategy changes adaptively. CAPA is incorporated into the dynamic multiobjective evolutionary algorithm (DMOEA) based on decomposition (MOEA/D) to construct a novel algorithm. The efficacy of CAPA is validated by comparison with five state-of-the-art algorithms on 28 benchmarks. Experimental results show that CAPA has the ability to generate high quality population uniformly along PF.

IceLines – A new data set of Antarctic ice shelf front positions

The frontal position of an ice shelf is an important parameter for ice dynamic modelling, the computation of mass fluxes, mapping glacier area change, calculating iceberg production rates and the estimation of ice discharge to the ocean. Until now, continuous and up-to-date information on Antarctic calving front locations is scarce due to the time-consuming manual delineation of fronts and the previously limited amount of suitable earth observation data. Here, we present IceLines, a novel data set on Antarctic ice shelf front positions to assess calving front change at an unprecedented temporal and spatial resolution. More than 19,400 calving front positions were automatically extracted creating dense inter- and intra-annual time series of calving front change for the era of Sentinel-1 (2014-today). The calving front time series can be accessed via the EOC GeoService hosted by DLR and is updated on a monthly basis. For the first time, the presented IceLines data set provides the possibility to easily include calving front dynamics in scientific studies and modelling to improve our understanding about ice sheet dynamics.

Data‐based learning control for optimization of nonlinear systems

Data‐based learning control for optimization of nonlinear systems

Theoretical model of radiation heat wave in two-dimensional cylinder with sleeve

A semi-analytical model is constructed to investigate two-dimensional radiation heat waves (Marshak waves) in a low-Z foam cylinder with a sleeve made of high-Z material. In this model, the energy loss to the high-Z wall is regarded as the primary two-dimensional effect and is taken into account via an indirect approach in which the energy loss is subtracted from the drive source and the wall loss is ignored. The interdependent Marshak waves in the low-Z foam and high-Z wall are used to estimate the energy loss. The energies and the heat front position calculated using the model under typical inertial confinement fusion conditions are verified by simulations. The validated model provides a theoretical tool for studying two-dimensional Marshak waves and should be helpful in providing further understanding of radiation transport.

Investigating the DDT of H2-Air Mixture in a Rectangular Channel using RANS-Based Numerical Analysis

In this study, a numerical code based on Reynolds-Averaged Navier-Stokes (RANS) method was developed using OpenFOAM to investigate the deflagration to detonation transition (DDT) phenomenon in hydrogen-air mixture gas inside a rectangular channel. The channel was modeled with a thickness of 80 mm and a length of 2000 mm. The numerical simulations were compared with the experimental results and it was found that the developed code qualitatively well simulated the transition process from deflagration to detonation. It was also found that the pressure distribution and reaction progress variables can be useful indicators to understand the instant and location of DDT occurrence. The location of DDT was found to be at the point where the shock wave and the position of the flame front matched. Furthermore, it was observed that the higher the height of the obstacle, the earlier the DDT occurred, but the magnitude of pressure after the DDT did not correlate with the height of the obstacle.

Comparison of the Determination of Some Antihypertensive Drugs in Clinical Human Plasma Samples by Solvent Front Position Extraction and Precipitation Modes.

The determination of the selected antihypertensive drugs in human plasma samples with the novel solvent front position extraction (SFPE) technique is presented. The SFPE procedure combined with LC-MS/MS analysis was used for the first time to prepare a clinical sample containing the drugs mentioned above from different therapeutic groups. The effectiveness of our approach was compared with the precipitation method. The latter technique is usually used to prepare biological samples in routine laboratories. During the experiments, the substances of interest and the internal standard were separated from other matrix components using a prototype horizontal chamber for thin-layer chromatography/high-performance thin-layer chromatography (TLC/HPTLC) with a moving pipette powered by a 3D mechanism, which distributed the solvent on the adsorbent layer. Detection of the six antihypertensive drugs was performed by liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) in multiple reaction monitoring (MRM) mode. Results obtained by SFPE were very satisfactory (linearity R2 ≥ 0.981; %RSD ≤ 6%; LOD and LOQ were in the range of 0.06-9.78 ng/mL and 0.17-29.64 ng/mL, respectively). The recovery was in the range of 79.88-120.36%. Intra-day and inter-day precision had a percentage coefficient of variation (CV) in the range of 1.10-9.74%. The procedure is simple and highly effective. It includes the automation of TLC chromatogram development, which significantly reduced the number of manual operations performed, the time of sample preparation and solvent consumption.

Sound-space symbolism: Associating articulatory front and back positions of the tongue with the spatial concepts of forward/front and backward/back

The study investigated whether the concepts of forward/front and backward/back are associated with the vocalizations requiring the front/back position of the tongue. In Experiment 1, the participants were visually presented with a forward or backward-directed movement. They were asked to vocalize the front ([i]) or back ([o]) vowel based on whether the stimulus moved forwards or backwards. Vocal responses were produced faster when the required response was hypothetically congruent with the movement direction (e.g., [i] – forward-directed movement) in comparison to incongruent conditions. In Experiment 2, the same effect was observed when these vocal responses were performed based on whether the target object was at the front of or back of the reference object. These observations present a novel sound-space symbolism phenomenon, which associates spatial concepts of forward/front and backward/back with particular speech sounds. We propose that this finding might contribute to an understanding of cognitive mechanisms in sound–space associations and more generally in sound symbolism.

Analytical study on an oscillating buoy integrated with a perforated structure with a quadratic pressure drop condition: A case study on a WEC-perforated breakwater integration system

A general analytical method for solving the linear wave interactions with the integration systems comprising an oscillating buoy and perforated structure is presented, with a quadratic pressure drop condition on the perforated surface. Using the method of variable separation and eigenfunction expansion, the motion response of the buoy and total velocity potential can be solved using a two-loop iterative method. The method is validated against the published results. The integration system with a heaving WEC arranged inside a perforated breakwater was investigated particularly. Under the quadratic pressure drop condition, the symmetry of the hydrodynamic coefficients and Haskind relation, are found no longer satisfied, and the dissipation through the perforated wall also contribute to the damping coefficient. Effects of the damping of the power take-off system, front wall porosity, wave amplitude, and position of the WEC are investigated in particular. It was found that the horizontal and vertical wave forces on the WEC increase significantly as wave amplitude increases; however, the hydrodynamic efficiency decreases. When the WEC is near the solid rear wall, the horizontal wave forces on the WEC and solid rear wall increase significantly at the frequencies of piston mode gap resonance and heave motion resonance.

Experimental Study of Stretched Premixed Flame Stabilized in a Flat Channel near a Heated Wall

In this work, the behavior of a lean premixed stretched flame stabilized in a flat channel near a heated wall was studied. Dependences of the flame front position on the stretch rate parameter at temperatures of the heated wall of 1000 and 1200 K and the combustible mixture composition (ϕ = 0.7 and 0.6) were obtained experimentally. The reduced thermal diffusive model was used in numerical simulation for an explanation of obtained experimental results. Theoretical estimates are in qualitative agreement with the experiment. The performed qualitative analysis may be useful in estimation of the combustion product temperature and the residence time of the nanoparticles forming in combustion products before their impact with the hot wall.

Flame oscillation instability of H2/CO/air at different ignition positions in an open-ended vertical narrow channel

ABSTRACT The propagation instability of a premixed H2/CO/air mixture flame in an open-ended vertical narrow channel was investigated in this paper. The mixture was ignited at five different ignition positions: IP-50, IP-250, IP-500, IP-750, and IP-950. This paper presents a new method for flame image processing. The flame front curve is generally an exponential outflow from the ignition to the top opening at any ignition. The oscillation frequency increases with the increase of flame front curvature. The flame front curvature fluctuates with time when the oscillation propagation occurs, and the flame decelerates and inverts when the curvature is larger. The dominant frequencies are different depending on ignition position, which has a certain effect on frequency. Five different ignition positions of dominant frequency are 78.00 Hz, 125.07 Hz, 170.5 Hz, 125.1 Hz, 170.7 Hz, respectively. Interestingly, IP-500, IP-750 and IP-950 have secondary frequency values of 356.9 Hz, 357.1 Hz and 331.8 Hz, respectively. The secondary frequency is about twice the dominant frequency, and it is caused by parametric instability. Flame oscillation propagation is affected by dimensionless temperature and Lewis value. The interaction between flame and overpressure wave promotes the deformation and oscillation of the flame front. The overpressure, flame front position, flame front curvature, and flame speed coupled oscillation.

The Gibraltar slab dynamics and its influence on past and present-day Alboran domain deformation: Insights from thermo-mechanical numerical modelling

The origin and tectonic evolution of the Gibraltar Arc system is the result of a complex geodynamic evolution involving the convergence of the Eurasian and African plates and the dynamic impact of the Gibraltar slab. Although geologic and geophysical data collected in the last few years have increased our knowledge of the Gibraltar Arc region, it is still unclear which are the mechanical links between the Gibraltar slab and the past deformation of the overriding Alboran lithosphere, as well as to which degree this subduction system is presently active. In this study, we use 2D numerical modelling to investigate the impact of the Gibraltar slab dynamics on the deformation of the overriding Alboran lithosphere. Our model simulates a WE generic vertical section at an approximate latitude of 36°N and considers an initial setup at about Burdigalian times (∼20 Ma), when the subduction front position is relatively well constrained by recent tectonic reconstructions. Our modelling shows a switch in the overriding plate (OP) stress state from extensional stresses during the slab rollback to compressional stresses near the trench when the rollback velocity decreases, caused by the change in slab-induced mantle flow. We also find that much of the crustal and lithospheric deformation occur during fast slab rollback and OP extension in the first 10 Myr of evolution, while after that only moderate deformation associated with subduction is predicted. Finally, we find that despite the subduction rollback ceases, the ongoing motion of the deeper portion of the slab induces a mantle flow that causes some amount of west-directed basal drag of the Alboran lithosphere. This basal drag generates interplate compresional stresses compatible with the distribution of intermediate-depth earthquakes in western Alboran.

Liquid film and heat transfer characteristics during superheated wall cooling via pulsed injection of a liquid jet

Pulse firing is one of the major operation modes of bipropellant thrusters for the attitude control of small-scale spacecrafts. In the pulse-firing mode, the operational range of the thruster depends on the deterioration of liquid film cooling performance. Because cooling performance is determined by the balance of heat removed by the liquid film and transferred to the manifold, the behavior and heat transfer characteristics of liquid films under the intermittent injection of liquid jets must be understood to enable a wider range of operational patterns. We conducted cooling tests on a superheated metal plate via the pulsed injection of a liquid jet for better understanding of the pulsed cooling process. Different injection patterns, including continuous injection, with the same injection quantity were examined on two types of metal plates (aluminum alloy and copper), because the thermal properties of metal plates affect both the heat transfer characteristics of the liquid film and temperature rise of the plate during the inter-pulse duration. The cooling process was evaluated based on the evolution of the liquid film on the metal plate and rear-side temperature of the metal plate. The evolution and temperature were simultaneously visualized using a high-speed camera and infrared camera, respectively. To link the liquid film state to the heat transfer process, the temperature and heat flux on the cooled surface were estimated by solving the inverse problem of three-dimensional transient heat conduction. The results indicate that the wetting front position corresponds to the position of the maximum temperature gradient. Additionally, the residual liquid film is consumed through the evaporation and the droplet dispersion related to the nucleate boiling. The effects of thermal inertia and diffusivity of the metal plate highlight the differences in the amount of heat removed by the liquid film. The heat removed by the liquid film during pulsed cooling exhibited a peak and was higher than that removed by continuous injection on the aluminum alloy plate. Less heat was removed under low-duty-cycle conditions, and the amount of heat removed by the liquid film was lower than that removed by continuous injection on the copper plate.

Motion leadership and local interaction in two species of freshwater fish (Danio rerio and Hyphessobrycon herbertaxelrodi).

The authors studied momentary motion leadership in small groups of black neon tetra (Hyphessobrycon herbertaxelrodi) and zebrafish (Danio rerio), its relationship with local interaction parameters, such as the acceleration and turning angle of the individuals, and the relative locations of the individuals within the group. The purpose was to know whether leadership tended to be monopolised by certain individuals or whether it was equitably shared between them and if there were differences in leadership sharing between these two species, which are known to have different degrees of cohesion and polarisation. The authors filmed groups of two, three, four and eight fishes of each species and tracked their individual motion by image analysis and trajectory extraction. In both species, motion leadership was not monopolized but egalitarian and very short lived, with leadership shifts distributed randomly over time. The duration of leadership episodes decreased as group size increased and was longer in black neon tetra than in zebrafish. Momentary leaders did not tend to be in the front positions, but closer to the centre of the group. Acceleration and turning angle were more extreme in zebrafish than in black neon tetra and in the momentary leaders than the followers in both species. In general, these differences between species and between leaders/followers were qualitatively similar with some differences in detail, indicating that the relationship between motion leadership and local interaction parameters is likely to conform to a general physical law.

Modeling of solidification processes under consideration of particle transport in the melt under terrestrial and microgravity conditions

In this work the interaction of solid particles with the moving water-ice solidification front under terrestrial and microgravity conditions is studied by numerical simulations as well as by experiments. A global, three-dimensional, time-dependent model is used to simulate the solidification processes taking into account buoyant convection and the injection of the particles, their transport through the fluid and their interaction with the moving interface. In basic parameter studies without considering any particle transport and interaction, the thermal conditions of the solidification processes in the module were systematically varied and their influence on the position and shape of the solidification front investigated. It was found that there is only a minor influence on the pure solidification process whether the experiments are carried out under terrestrial or microgravity conditions. Also, the orientation of gravity relative to the solidification direction plays only a minor role. For the simulation of the TEXUS 56 sounding rocket experiment, the injection of the particles, their transport through the fluid and their interaction with the interface were considered in the simulations. The simulation results of the TEXUS 56 experiment agree reasonably to the experimental data. In both cases, a transition from a convex to a concave solidification front is observed. The calculated and measured growth rates are also in the same range and finally it was confirmed by the model that the injection of the particles causes a forced flow, which disturbs the solidification process for a short time period. Once the injection process is stopped, the forced flow decays quickly. The resulting particle distribution is comparable in experiment and simulation and no significant particle movement in the fluid is observed.

Diapycnal and isopycnal mixing along the continental rise in the Australian–Antarctic Basin

Shipboard measurements of temperature, salinity and horizontal current velocity were used to estimate diapycnal and isopycnal diffusivities in the Australian sector of the Southern Ocean between 120∘E and 150∘E near 64∘S, along the climatological positions of the Southern Antarctic Circumpolar Current Front and the Southern Boundary. The diapycnal diffusivities estimated by the finescale parameterization on the neutral density surfaces of 1028.05, 1028.2, and 1028.3 kg m−3 are (9.5±6.8)×10−5, (10.7±2.6)×10−5, and (13.8±3.7)×10−5 m2s−1, respectively (mean ± one standard deviation). At these densities, salinity and temperature decreased with depth but salt fingering was unlikely. Using the water mass transformation framework and a box inverse model, the isopycnal diffusivities were estimated from the diapycnal diffusivities. Climatological estimates of the isopycnal diffusivities in the density ranges of Upper Circumpolar Deep Water, Lower Circumpolar Deep Water, and Antarctic Bottom Water were −30±116, 16±319, and −30±83 m2s−1, respectively. These diffusivities were likely underestimates by 10 to 20 m2s−1 because eddy transport could not be considered in the climatological data. The weak isopycnal diffusivities were not inconsistent with diffusivity suppressed by the frontal jets. The large uncertainties were caused by the uncertainty in the box inverse model and the fact that the size of the box was comparable to the advection speed times the diffusion time scale.

Numerical study on non-premixed combustion characteristics of NH3/O2 in multi-inlet micro combustor

In recent years, Micro Thermophotovoltaic (MTPV) devices using NH3 have attracted much attention due to their high energy density, small size and carbon-free. A novel micro non-premixed combustor with multi-inlet is presented. A 2D model of non-premixed micro combustion in multi-inlet micro combustor coupled with NH3/O2 mechanism was established. The ignition position and flame front position of non-premixed flame were discussed. The effect of inlets arrangement, total flow velocity, diameter ratio, and transverse distance of each fuel inlets on the thermal and emission performance was numerically investigated. The results showed that the flame position and flame temperature are the two main factors affecting NO emissions. Increasing the ignition point and ignition area can make the flame more uniform with lower temperature, which aids in NO emission reduction. However, the average temperature of the outer wall decreases. The average wall temperature in the multi-inlet combustor increases by 6.72 % from 1324 K to 1413 K when compared to the literature. The mass fraction of NO in the exhaust decreases by 14.46 % from 2.35 × 10-2 kmol/m3 to 2.01 × 10-2 kmol/m3. The total radiation energy of outer wall increases from 63.9 W to 75.7 W.

Freezing process of nanomaterial inside thermal storage tank with amelioration in geometry utilizing Galerkin modeling

In the current attempt, the numerical technique (Galerkin method) has been implemented to scrutinize the solidification within the sustainable energy unit involving elliptic and sigma shaped cylinders. The domain is full of water and due to the cold condition of complex walls, the liquid water converts to solid and the rate of process was enhanced with addition alumina nanomaterial. The concentration and shapes of additives have been assumed as variables in this study. Mesh has been adopted with a position of solid front and validation test proved the correctness of modeling. The period for water is 1.36 times superior than that of NEPCM. The required time changes form 1144.04 s to 837.44 s with loading nanoparticles. As particles with greater shape factor have been utilized, the needed time declines around 6.98 %.

Glaciological history and structural evolution of the Shackleton Ice Shelf system, East Antarctica, over the past 60 years

Abstract. The discovery of Antarctica's deepest subglacial trough beneath the Denman Glacier, combined with high rates of basal melt at the grounding line, has caused significant concern over its vulnerability to retreat. Recent attention has therefore been focusing on understanding the controls driving Denman Glacier's dynamic evolution. Here we consider the Shackleton system, comprised of the Shackleton Ice Shelf, Denman Glacier, and the adjacent Scott, Northcliff, Roscoe and Apfel glaciers, about which almost nothing is known. We widen the context of previously observed dynamic changes in the Denman Glacier to the wider region of the Shackleton system, with a multi-decadal time frame and an improved biannual temporal frequency of observations in the last 7 years (2015–2022). We integrate new satellite observations of ice structure and airborne radar data with changes in ice front position and ice flow velocities to investigate changes in the system. Over the 60-year period of observation we find significant rift propagation on the Shackleton Ice Shelf and Scott Glacier and notable structural changes in the floating shear margins between the ice shelf and the outlet glaciers, as well as features indicative of ice with elevated salt concentration and brine infiltration in regions of the system. Over the period 2017–2022 we observe a significant increase in ice flow speed (up to 50 %) on the floating part of Scott Glacier, coincident with small-scale calving and rift propagation close to the ice front. We do not observe any seasonal variation or significant change in ice flow speed across the rest of the Shackleton system. Given the potential vulnerability of the system to accelerating retreat into the overdeepened, potentially sediment-filled bedrock trough, an improved understanding of the glaciological, oceanographic and geological conditions in the Shackleton system are required to improve the certainty of numerical model predictions, and we identify a number of priorities for future research. With access to these remote coastal regions a major challenge, coordinated internationally collaborative efforts are required to quantify how much the Shackleton region is likely to contribute to sea level rise in the coming centuries.