Lateral Spread Rate Research Articles

Experimental study of smouldering combustion and transient emissions from forest duff with dual layers

Smouldering combustion in wildfires is responsible for large amounts of carbon emissions and regional haze episodes. In the wildland, there are dual or multiple layers of forest duff with varying particle sizes, forming a non-homogeneous fuel system. However, understanding of the effects of the fuel heterogeneity on smouldering combustion is limited. In this study, we experimentally investigated the smouldering behaviour and gas emissions of forest duff consisting of dual layers with particle diameters ranging in three sizes (1 mm ≤ d1 < 2 mm, 0.425 mm ≤ d2 < 1 mm, and d3 < 0.425 mm). A comprehensive smouldering combustion rig was designed and built to simultaneously measure the mass loss, temperature profile, time-resolved gas concentration for 20 species, and visual and infrared imaging for 6 dual-layered duff samples (d1 - d1, d1 - d2, d1 - d3, d2 - d2, d2 - d3, d3 - d3) under a controlled environment. A terrace smouldering front structure was observed for dual-layered fuel beds with coarse duff particle (d1 and d2) staying in the upper layer (50% of the volume of an open-top reactor with dimensions of 20 × 20 × 10 cm), while a surface cracking phenomenon was observed for sample consisting of fine duff particles d3 - d3. Increases in the particle size at the lower-layer with a fixed d1 upper-layer particles were found to have a greater impact on the oxygen supply, leading to a higher lateral spread rate, a higher modified combustion efficiency (MCE), and a lower fire-averaged CO/CO2. In contrast, changes in the upper-layer particle size with a fixed d3 lower-layer particles have a greater impact on the heat transfer. These findings advance the scientific understanding of smouldering fires spreading in dual forest fuel system, ultimately contributing to the development of wildfire mitigating technologies.

Computational study of the multidimensional spread of smouldering combustion at different peat conditions

Smouldering combustion is the slow, low-temperature, flameless burning of porous fuels, which propagate both laterally and in-depth. In this study, we build a physics-based two-dimensional model to simulate lateral and in-depth smouldering spread simultaneously based on open-source code Gpyro. We first validate the model against a shallow-reactor experiment (of 1.6 cm thickness) in the literature. Based on the validated model, we then investigate 2D smouldering in a 3 times deeper peat layer at different soil conditions. We found that lateral and in-depth spread rates depend on the organic density and the Oxygen supply. Because of the larger Oxygen supply close to the free surface, the lateral spread is 10 times faster than in-depth spread. In addition, for lateral spread the influence of inorganic density and moisture can be explained by a unified parameter, heat sink density, agreeing with previous experimental results. The model predicts the effects of peat conditions on multidimensional smouldering spread and reveals the controlling mechanisms both lateral and in-depth spread, providing a better understanding of this complex phenomenon.

Freezing propagation of condensate droplets at early stage of frosting on vertical hydrophobic surface

As condensate droplets formed at the early stage of frosting are the foundation of frost layer growth, to study the freezing propagation of condensate droplets is of great significance to understand the frosting process. In this paper, the influencing factors of lateral spreading of frost crystals and freezing propagation modes of condensation droplets were discussed by visualization experiments, and the propagation mechanism was revealed combined with theoretical analysis. It is observed that condensate droplets relies on the lateral spreading of frost crystals to realize the freezing propagation and frost crystals diffuse to the center of the cold surface with the help of freezing droplets. The lateral spreading of frost crystals is the key to achieve freezing propagation of condensate droplets, which is accompanied by the evaporation of droplets with small size. The freezing propagation of condensate droplets is affected by the lateral spreading rate of frost crystals and the droplet spacing. Increasing the contact angle of the cold surface reduces the freezing propagation rate and delay frost formation. Interestingly, two freezing propagation modes, “contact-freeze” and “absorption-freeze”, are observed when the frost crystals contact the subcooled droplets. Increasing the surface contact angle or reducing the contact angle hysteresis can increase the frequency of the “absorption-freeze” mode, which helps to reduce the freezing propagation rate of condensate droplets.

CFD Simulations of Fire Propagation in Horizontal Cable Trays Using a Pyrolysis Model with Stochastically Determined Geometry

In this paper, a pyrolysis model for a PVC cable is constructed using results from thermogravimetric analysis, microscale combustion calorimeter and cone calorimeter experiments. The pyrolysis model is used to simulate fire propagation in horizontal cable trays. The simulated arrangement corresponds to a cable tray fire experiment from OECD PRISME 2 project. As laying the cables loosely along the horizontal trays is a random process, a novel stochastic method is developed for making the simplified cable tray geometries for the computational fluid dynamics model. In addition, as the simplified cable tray geometry has significantly smaller surface area than a real tray full of cables, the surface area was parametrically adjusted. In contrast to most of the earlier published numerical approaches for simulating cable tray fires, the presented approach does not use empirical correlations for predicting fire propagation and does not require any results from full-scale experiments for calibrating the model. The simulation results are compared to experimental results in terms of heat release rate, mass loss, tray ignition times and lateral flame spread rates. The maximum heat release rate was overpredicted by 8% on average.

Plant life‐history traits rather than soil legacies determine colonisation of soil patches in a multi‐species grassland

Abstract Interactions between plants and soil biota are increasingly shown to play critical roles in plant species coexistence processes. Plant species coexistence is thought to be promoted via biotic legacies that plant species leave behind in the soil after a plant disappears. These soil legacies are hypothesised to supress colonisation success when the preceding plant is of the same species, that is, when a plant species encounters its own, species‐specific soil antagonists. However, colonisation of vacant spots in plant communities is in the first place determined by the ability of plants to reach such vacant locations. We currently lack an understanding of the explicit role of soil legacy effects and their relative contribution to colonisation processes in plant communities consisting of plant species inherently differing in colonisation ability. In experimental, outdoor plant communities consisting of eight grassland species, we tested the effect of five differently conditioned soil patches on plant species colonisation success over three consecutive growing seasons. We found that colonisation success was largely determined by the species' reproductive strategy, lateral spread and growth rate, and not by the plant species that conditioned the soil patch. Fast spreading, clonal plant species reached the soil patches first and initially attained the highest biomass inside the patch. One year later, slower spreading plant species colonised the patch via seedlings. Species with intrinsically high growth rates attained the highest biomass, decreasing biomass of the initial colonisers. While subtle differences between conditioned soil patches did occur, these were not strong enough to overcome the inherent differences in colonisation ability between the various plant species. Synthesis. Our results reject the hypothesis that colonisation of vacant soil patches in plant communities is strongly affected by the legacy that is left behind by the preceding plant species. Instead, plant species life‐history strategy plays a prominent role, driving sequential plant species replacements. Based on our results and recent accounts in literature we present a conceptual model for local cyclic dynamics in grassland communities, where soil legacy plays a role in affecting the performance of established plant species rather than colonisation of vacant patches.

Mechanisms of Lateral Spreading in a Near-Field Buoyant River Plume Entering a Fjord

Observations collected from a fast-flowing buoyant river plume entering the head of Doubtful Sound, New Zealand, were analysed to examine the drivers of plume lateral spreading. The near-field plume is characterised by flow speeds of over 2 ms−1, and strong stratification (N2 &amp;gt; 0.1 s−2), resulting in enhanced shear which supports the elevated turbulence dissipation rates (ϵ &amp;gt; 10−3 W kg−1). Estimates of plume lateral spreading rates were derived from the trajectories of Lagrangian GPS surface drifters and from cross-plume hydrographic transects. Lateral spreading rates derived from the latter compared favourably with estimates derived from a control volume technique in a previous study. The lateral spreading of the plume was driven by a baroclinic pressure gradient toward the base of the plume. However, spreading rates were underestimated by the surface drifters. A convergence of near-surface flow from the barotropic pressure gradient concentrated the drifters within the plume core. The combination of enhanced internal turbulence stress and mixing at the base of the surface layer, and the presence of steep fjord sidewalls likely reduced the rate of lateral spreading relative to the theoretical spreading rate. The estimates of plume width from the observations provided evidence of scale-dependent dispersion which followed a 4/3 power law. Two theoretical models of dispersion, turbulence and shear flow dispersion, were examined to assess which was capable of representing the observed spreading. An analytical horizontal shear-flow dispersion model generated estimates of lateral dispersion that were consistent with the observed 4/3 law of dispersion. Therefore, horizontal shear dispersion appeared to be the dominant mechanism of dispersion, thus spreading, in the surface plume layer.

The dynamics of cable bacteria colonization in surface sediments: a 2D view

Cable bacteria that are capable of transporting electrons on centimeter scales have been found in a variety of sediment types, where their activity can strongly influence diagenetic reactions and elemental cycling. In this study, the patterns of spatial and temporal colonization of surficial sediment by cable bacteria were revealed in two-dimensions by planar pH and H2S optical sensors for the first time. The characteristic sediment surface pH maximum zones begin to develop from isolated micro-regions and spread horizontally within 5 days, with lateral spreading rates from 0.3 to ~ 1.2 cm day−1. Electrogenic anodic zones in the anoxic sediments are characterized by low pH, and the coupled pH minima also expand with time. H2S heterogeneities in accordance with electrogenic colonization are also observed. Cable bacteria cell abundance in oxic surface sediment (0–0.25 cm) kept almost constant during the colonization period; however, subsurface cell abundance apparently increased as electrogenic activity expanded across the entire surface. Changes in cell abundance are consistent with filament coiling and growth in the anodic zone (i.e., cathodic snorkels). The spreading mechanism for the sediment pH–H2S fingerprints and the cable bacteria abundance dynamics suggest that once favorable microenvironments are established, filamentous cable bacteria aggregate or locally activate electrogenic metabolism. Different development dynamics in otherwise similar sediment suggests that the accessibility of reductant (e.g., dissolved phase sulfide) is critical in controlling the growth of cable bacteria.

Convection beyond the Steam Chamber Interface in the Steam-Assisted-Gravity-Drainage Process.

In the steam-assisted-gravity-drainage (SAGD) process, heat energy is transferred from the steam chamber to the farther cold reservoir by conduction and convection mechanisms, so as to reduce the oil viscosity. In previous research works, although it was proved that convection is an indispensable part of the heat-transfer process, there is still a controversy about the formation mechanism of heat convection. In this study, an analytical mathematic model was proposed to explore the convective heat transfer in SAGD operation. Typically, this model integrates three heat convection forms that are generated by pressure difference, gravity, and thermal expansion of connate water,. Subsequently, the simulation results are compared with field data to evaluate the accuracy of the new model, and they are reasonably consistent with UTF field data. The results indicate that convective heat transfer plays a predominant role in the immediate vicinity of the steam chamber interface. Furthermore, this paper derives a mathematic model of oil production to explore the effect of heat convection on oil production under different operation conditions. The results demonstrate that heat convection has an adverse impact on oil production, but it is inevitable. This study also displays that some parameters, such as the lateral spreading rate, the thermal diffusivity, the viscosity coefficient, and the curvature of oil relative permeability curve, can significantly affect the oil production rate. Based on this study, the effect of convection mechanism on the heat-transfer process and oil production will be further clarified, and the parameters in the SAGD process can be optimized, so as to effectively enhance and predict oil production.

A numerical study of a rectangular jet along a shear free boundary: Surface jet

A numerical simulation of a rectangular surface jet is performed at a Reynolds number of Rej=4400. The global parameters of the jet e.g. maximum velocity decay, jet surface normal and lateral spread rates, entrainment, jet momentum flux and turbulent momentum flux are in agreement with several other studies reported in the literature. It is shown that the mean velocity and Reynolds stress profiles scale with the maximum local streamwise velocity and jet half width in the surface normal and lateral directions. The current simulation provides balance, explicitly calculated budgets for the turbulence kinetic energy, Reynolds normal and shear stresses. The surface jet develops a thin layer of fast moving fluid in the lateral direction near the surface. This layer is called the ‘surface current’. It has been suggested that the surface current arises due to the Reynolds stress anisotropy in the near surface region. The current study shows that this explanation is incomplete. The turbulence production for the Reynolds stress in the lateral direction is negative, which can drive the mean flow in the lateral direction. The higher level of negative production in the near surface region is responsible for the development of the surface current.

Influence of Wind Direction on Fire Spread on the Exposed XPS insulation Wall

Medium-sized wall fire experiments were carried out using extruded polystyrene (XPS) panels to build an insulation layer to simulate the flame spread over the exterior thermal insulation system during the exposed stage. During the experiments, the influences of the wind direction on the lateral and vertical flame spread speed without fire barrier designs under the wind speed of 2.5m/s were studied quantitatively and qualitatively. According to the experimental results, it is found out the averaged peak lateral flame spread rate increases and the averaged peak vertical flame spread rate decreases when the angle between the wind direction and the wall increases from 0° to 60°. It can be seen from the analysis that the largest average lateral flame spread rate and the largest average vertical flame spread rate also show regular changes at same wind direction. This study results can provide valuable references for optimizing the fire safety design of exterior insulation system.

Influence of soil conditions on the multidimensional spread of smouldering combustion in shallow layers

Smouldering peatland fires are capable of burning vast amounts of organic soils, resulting in the release of greenhouse gases into the atmosphere, as well as a significant deterioration of air quality causing in major regional crises known as haze events. Fundamental understanding of smouldering fire spread is essential for the development of mitigating technologies. In this paper, we have systematically conducted 63 experiments studying the individual and combined influence of two key factors affecting multidimensional smouldering spread in organic soils: moisture content (MC) and inorganic content (IC). Both lateral and in-depth smouldering spread were investigated using a novel shallow reactor. This shallow depth allows a greater number of experiments to be performed in a short period of time compared to deeper samples. Lateral spread was found to decrease linearly with moisture content (R2 > 90%); while in-depth spread rate increased linearly up to 300% from moisture content of 0% to 140%. Increased inorganic content linearly decreased the lateral spread rate but had little influence on in-depth spread in drier samples. Interestingly, in wetter samples, in-depth spread was in fact sensitive to inorganic content. A novel approach combining lateral and in-depth spread rates as vector components, revealed that the global spread is independent of moisture content, with an average spread rate of 8.7 and 8.4 cm/h for 2.5 and 40% IC, with changes in direction according to moisture content; going in-depth for wet soils, and laterally for dry soils. Similarly, increasing the IC encouraged downward spread for wet samples. We also report observations of a bifurcation of lateral spread, where spread would locally extinguish where the in-depth spread was greater than the lateral spread. These findings provide previously unknown insight into the relationship between lateral and in-depth spread in smouldering fires, ultimately improving the fundamental understanding of such fires.

Lateral Flame Spread over PMMA Under Forced Air Flow

In wildland and other flame spread scenarios a spreading fire front often forms an elliptical shape, incorporating both forward and lateral spread. While lateral flame spread is much slower than forward rates of spread, it still contributes to the growth of the overall fire front. In this work, a small-scale experiment is performed to investigate the mechanisms causing this lateral spread in a simple, small-scale configuration. PMMA strips with thicknesses ranging from 1 mm to 3.1 mm and widths of 5 cm and 10 cm were ignited under forced flow in a laminar wind tunnel. Unlike traditional concurrent or opposed flame spread experiments, flames were allowed to progress from one side of the sample to the other, perpendicular to the wind direction. An infrared camera was used to track the progression of the pyrolysis front by estimating the surface temperature of the PMMA. The flame spread rate, depth of the burning region, thermal diffusion length, and radiant heat flux were determined and analyzed. Based on a theory of heat and mass transfer for a laminar diffusion flame, a thermal heat transfer model was developed for the preheating region to predict the lateral flame spread rate. Results show that the thermal diffusion length decreases with wind velocity, ranging from 4.5 mm to 3 mm. Convection dominates the flame-spread rate, accounting for more than 80% of the total heat flux. The theoretical flame spread rate agrees well with experimental data from all but the thinnest samples tested, overpredicting the lateral flame spread rate for 1 mm thick samples. The resulting model for lateral flame spread under concurrent flow works for forced-flow dominated flame spread over thermally-thin fuels and helps provide physical insight into the problem, aiding in future development of two-dimensional, elliptical fire spread models.

The Effect of Microstructural Refinement on the Localized Corrosion of Model Zn-Al-Mg Alloy Coatings on Steel

A combination of in-situ Scanning Vibrating Electrode Technique (SVET) and time-lapse immersion optical microscopy (TLM) is used to investigate the effect of microstructural refinement on patterns of localized corrosion affecting zinc-aluminum-magnesium (ZAM) galvanized coatings on steel. Model ZAM coatings comprising Zn-2.7 wt% Al-1.5 wt% Mg are produced on 0.7 mm mild steel sheet by hot dipping, and the resulting coating microstructure is systematically refined by increasing the cooling (solidification) rate from 5°C.sec−1 to 1000°C.sec−1. The intact ZAM coated surface is immersed in 0.17 M aqueous NaCl, and SVET and TLM are used to follow the resulting localized corrosive attack. TLM shows that corrosion initiates preferentially within MgZn2 and spreads laterally over the ZAM surface by preferentially following MgZn2 rich phases. In coarse microstructures, large primary zinc grains tend to deflect and constrain lateral spreading whereas in fine microstructures the smaller primary zinc grains do not. Consequently, lateral spreading rate increases with microstructural refinement. SVET shows that global corrosion rates are similar for all the ZAM coatings but that increased lateral spreading results in lower rates of through-coating penetration for the refined microstructures. These findings are explained in terms of the lateral diffusion of aggressive anolyte species.

Hydraulics and mixing in a laterally divergent channel of a highly stratified estuary

AbstractEstuarine mixing is often intensified in regions where topographic forcing leads to hydraulic transitions. Observations in the salt‐wedge estuary of the Connecticut River indicate that intense mixing occurs during the ebb tide in regions of supercritical flow that is accelerated by lateral expansion of the channel. The zones of mixing are readily identifiable based on echo‐sounding images of large‐amplitude shear instabilities. The gradient Richardson number (Ri) averaged across the mixing layer decreases to a value very close to 0.25 during most of the active mixing phase. The along‐estuary variation in internal Froude number and interface elevation are roughly consistent with a steady, inviscid, two‐layer hydraulic representation, and the fit is improved when a parameterization for interfacial stress is included. The analysis indicates that the mixing results from lateral straining of the shear layer, and that the rapid development of instabilities maintains the overall flow near the mixing threshold value of Ri = 0.25, even with continuous, active mixing. The entrainment coefficient can be estimated from salt conservation within the interfacial layer, based on the finding that the mixing maintains Ri = 0.25. This approach leads to a scaling estimate for the interfacial mixing coefficient based on the lateral spreading rate and the aspect ratio of the flow, yielding estimates of turbulent dissipation within the pycnocline that are consistent with estimates based on turbulence‐resolving measurements.

Large-scale fire suppression modeling of corrugated cardboard boxes on wood pallets in rack-storage configurations

In this study, the fire growth and suppression models in FireFOAM were validated for rack-storage commodities consisting of two solid fuels, namely corrugated cardboard boxes and hardwood pallets, which are referred to as Class 2 commodity. Validation experiments included two fire-growth and two fire-suppression configurations with different rack-storage array heights (3 and 5 tiers). In the suppression study, standard-response upright ceiling sprinklers (K-factor of 160lpm/bar1/2) were used. The time-resolved chemical heat release rates obtained from the experiments were used to validate the fire growth model. The observed sprinkler activations and fire-spread patterns were used to validate the suppression model. This study identified that lateral flame spread is primarily enabled by flames impinging on the commodity's bottom surfaces. This study also showed that obstructions, such as wood pallets, can significantly impede convective and radiative heat transfer to the underside of the commodity, reducing the lateral flame spread rate. Fire-suppression modeling revealed that both surface water transport and lateral flame spread rates are important when predicting fire-suppression behavior. Therefore, as the rack-storage array height increases, so does the water transport time, which results in the fire becoming more difficult to control. Likewise, as the lateral spread rate increases, e.g., as occurs in the absence of wood pallets, fire-suppression also becomes more difficult.

Kinetic Model for Layer-by-Layer Crystal Growth in Chain Molecules

A kinetic model is proposed to describe the structure and rate of advancement of the growth front during crystallization. Solidification occurs through the mechanisms of surface nucleation and lateral spreading of the solid phase within layers in the vicinity of the growth front. The transformation from liquid to solid within each layer is described by an equation similar to the two-dimensional variant of the Johnson–Mehl–Avrami (JMA) equation, but in which the finite size and shape of the critical nucleus and the dynamic evolution of the solid fraction of the underlying layers are taken into account. Connection to the regime theory of Hoffman and co-workers, for surface nucleation and spreading in one or two dimensions, is also made. Given only molecular level information regarding surface nucleation rates, lateral spreading rates, and critical surface nucleus geometry, the resulting set of coupled nonlinear equations for solidification in each layer is numerically integrated in time to obtain the struct...

Observed and modeled drifters at a tidal inlet

Material transport and dispersion near the mouth of a tidal inlet (New River Inlet, NC) are investigated using GPS-tracked drifters and numerical models. For ebb tide releases, velocities are largest (>1 m s−1) in two approximately 30 m wide channels that bisect the 1–3 m deep ebb shoal. In the channels, drifter and subsurface current meter velocities are similar, consistent with strong vertical mixing and 2-D hydrodynamics. Drifters were preferentially entrained in the channelized jets where drifter cluster lateral spreading rates μin were small ( μin≈0.5 m2 s−1). At the seaward edge of the ebb shoal, jet velocities decrease linearly with distance (to ≤0.2 m s−1, about 1 km from shore), and cluster spreading rates are larger with μout≈3 m2 s−1. Although the models COAWST and NearCom generally reproduce the observed trajectory directions, certain observed drifter properties are poorly modeled. For example, modeled mean drifter velocities are smaller than observed, and upon exiting the inlet, observed drifters turn north more than modeled drifters. The model simulations do reproduce qualitatively the spreading rates observed in the inner inlet, the flow deceleration, and the increase in μout observed in the outer inlet. However, model spreading rates increase only to μout<1 m2 s−1. Smaller modeled than observed μout may result from using unstratified models. Noncoincident (in space) observations show evidence of a buoyant plume ( Δρ=1 kg m−3) in the outer inlet, likely affecting drifter lateral spreading. Generally, drifter-based model performance is good within the inlet channels where tidal currents are strongest, whereas model-data differences are significant farther offshore.

Flow characteristics within the recirculation region of three-dimensional turbulent offset jet

ABSTRACTThe present study investigates the flow characteristics within the recirculation region of three-dimensional offset jets using a particle image velocimetry technique. Measurements were performed for four nozzle offset height ratios of 0, 2, 4 and 8. The discharged jet entrained the ambient fluid as depicted by streamlines superimposed on the mean velocity contours. Analysis of the flow field showed that the maximum streamwise mean velocity decay rate increased with increasing offset height ratio. Wall-normal spread rates of 0.066 and 0.016 were obtained for jets with offset height ratios of 0 and 2, respectively, and lateral spread rates of 0.116, 0.114 and 0.096 for jets with offset height ratios of 0, 2 and 4, respectively. The reattachment lengths of the jets increased with increasing offset height ratio. Profiles of the mean velocities, Reynolds stresses and some of the budget terms (specifically, production, diffusion and convective terms) of the turbulent kinetic energy have been investigated. It was observed that increasing the offset height ratio influenced the distribution of these quantities within the recirculation region. A two-point velocity correlation analysis was performed to analyse the flow structures within the recirculation region. The two-point correlation revealed some large-scale structures which were observed to increase in size as the offset height ratio increased. The two-point correlation analysis also revealed that the estimated integral length scales within the recirculation region of the flow increased with increasing offset height ratio.

Sm–Nd geochronology of the Erro-Tobbio gabbros (Ligurian Alps, Italy): Insights into the evolution of the Alpine Tethys

article The Alpine-Apennine ophiolites are considered analogs of the oceanic lithosphere formed at ocean-continent transition zones and very slow oceanic spreading centers. They are lithospheric remnants of the Jurassic Piedmont-Ligurian ocean, a branch of the Mesozoic Tethys separating the European and Adriatic continental margins. Previous geochronological studies on gabbroic rocks of the Alpine Tethys indicated a rather large time span of crust formation. In this paper, we present Sm-Nd geochronological data on well-preserved olivine gabbros intruded in mantle peridotites from the Erro-Tobbio ophiolitic unit (Ligurian Alps, Italy). Borghini et al. (2007) documented that these gabbros crystallized at low-P conditions (b5 kb) from primitive N-MORB melts, similar to many gabbroic rocks from Alpine-Apennine ophiolites. Here four plagioclase-clinopyroxene internal Sm-Nd isochrons are presented, yielding equivalent ages and initial eNd values. The ages are 177 ± 7 Ma, 179 ± 7 Ma, 178 ± 21 Ma and 182 ± 19 Ma, reflecting a weighted mean age of 178 ± 5 Ma with initial eNd of 9.2 ± 0.4 (2SD). Similar ages are only recorded in gabbroic rocks from the External Liguride Units (Northern Apennines) and represent the oldest ages available for the gabbroic crust of the Alpine Tethys. These Mg-rich gabbros can therefore be considered as representative of early (syn-rift) melt intrusions in thinned lithospheric mantle exhumed at ocean-continent transition domains, likely close to Adria's continental margin, similar to the hyper-extended Western Iberian Margin. Our new results together with previous ages of the Tethys oceanic crust allow for the reconstruction of the spatial distribution of oceanic gabbros over time, and evaluation of the spreading and propagation rates of this paleo-ocean. The northward propagation rifting velocity, estimated at ~5 cm/year, is presumably higher than the lateral spreading rate of ~2 cm/year. Our rate estimates suggest that the Red Sea is a present-day analog for the evolution of the Piedmont-Ligurian ocean. © 2014 Elsevier B.V. All rights reserved.

3D thermomechanically coupled FEM analysis of large disk rolling process and trial production

Recently, rolling technique used to manufacture rings with various dimensions, shapes, and materials is innovated to a revolutionary technique for the fabrication of large disks. In this paper, in order to study the forming capability of this novel method, its principle was introduced, and the 3D thermomechanically coupled FE model was established using the dynamic explicit code ABAQUS/Explicit. Considering the adaptive treatment of boundary conditions, the user subroutines of ABAQUS were explored based on the movement law of the guide rolls and profiled axial rolls, and contacts between these rolls and the disk component. And the reliability of the FE model was verified theoretically and experimentally. Furthermore, the extending rule of plastic deformation zone and the effect of feed speed on the size of both the outer and inner diameters were investigated. The main results show that (1) the smallest equivalent plastic strain (PEEQ) occurs at the hub of the disk and the junction of the rim and the web, and the larger PEEQ appears on the outer surface of the rim and the web of disk. (2) Both the outer and inner diameters of the disk increase gradually at the beginning stage and more and more rapidly at a later stage. With the increase of the feed rate, the increase rate of both the outer diameter and inner diameter will decrease and the lateral spread rate will increase. And trial production of the large disk based on the analysis had been carried out successfully on the revamped Wagner RAW500/400 radial-axial ring rolling mill.