Discrete simulations of a triaxial compression test for sand by DEM

A quasi‐static homogeneous drained triaxial compression test on cohesionless sand under constant lateral pressure was simulated using a three‐dimensional discrete element method. Grains were modelled by means of particle clusters composed of rigid spheres or spheres with contact moments imitating irregular particle shapes. Attention was paid to the effect of initial void ratio and grain shape mixture on the shear strength, volume changes, force chains, kinetic, elastic and dissipated energies. In addition, the effect of the mean grain size, grain size distribution, grain size range, specimen size and roughness and stiffness of boundaries was numerically analysed in initially dense sand. Some numerical results were compared with available experimental results. Copyright © 2014 John Wiley & Sons, Ltd.     

Geothermal Energy for Northern Canada: Is it Economical?

We examined the potential of geothermal energy development in northern Canadian communities to support local energy demand, along with providing an initial assessment of the economic viability of geothermal energy resources for (a) low enthalpy heating systems and (b) electrical power generation from high temperature resources. We estimate yearly energy production and cost per kWh for geothermal systems using scenarios for thermal and electrical production sustained over 15 years from temperatures reached in the 2–6-km depth range. All the calculations are based on a borehole fluid productivity of 30 kg/s. We assume this to be feasible in sedimentary aquifers and through fractured granites. Under such an assumption and assumptions made on the efficiency of heat exchangers, our modeling shows that thermal energy output for 120°C from 3- to 5-km wells can be as low as 5–8 cents/kWh thermal. For a 6 km depth, the cost of thermal energy can be as low as 1–2 cents/kW thermal for thermal energy production of 100–200 MWh annually.     

Regional variations of heat flow differences with depth in Alberta, Canada

Summary. Differences between estimated average heat flow values for the Mesozoic and Cenozoic formations ( Q ₁) and estimated average heat flow values for the Palaeozoic formations below the erosional unconformity ( Q ₂) are calculated for the Alberta part of the western Canadian sedimentary basin. Significant heat flow differences exist for these two intervals and the map of Δ Q = Q ₁– Q ₂ shows that Q ₂ is generally greater than Q ₁ in the western and south-western part of Alberta, while in the northern part of the province Q ₂ is generally less than Q ₁. The regional variations of Δ Q are large, with standard deviation of 26 mW m⁻² and average value –13.5 mW m⁻². A regional trend of Δ Q correlates with topographic relief and the hydraulic head variations in the basin. It is shown that there is a heat flow increase with depth in water recharge areas and a decrease in heat flow with depth in the low topographic elevation water discharge areas when comparing the average heat flow in Mesozoic + Cenozoic and Palaeozoic formations.     

Evolution of depressions on Comet 67P/Churyumov-Gerasimenko: Role of ice metamorphism

This work is intended to investigate the influence of temperature-dependent metamorphism of ice on the shape of small depressions in the surface of cometary nuclei. We are mainly interested in the role of initial cohesivity of a nucleus. For this purpose we simulate sublimation of ice from the facets of initially cylindrical depressions in ice of different initial structure. The simulations account for the diurnal and orbital changes of insolation and its dependence on the current shape of the depressions. Our model includes heat transport in the cometary material and metamorphism of ice. We present the results obtained for the nucleus of the Comet 67P/Churyumov-Gerasimenko, target of the ESA cornerstone mission Rosetta.     

Impact Break-Up of Cometary Nuclei – Conclusions from Impact Experiments

Experiments of impact-generated break-up of icy and icy/mineral targets were performed. Formulae for the velocity of ejecta and for energy of disruption were fitted to the experimental data. An assumption that these formulae can be extrapolated for kilometer-size bodies enabled us to discuss the consequences of impacts on cometary nuclei and on planetesimals. It was found that the porosity of the targets as well as their composition (mineral to total mass ratio), are the crucial parameters.     

Potential causes of differences between ground and surface air temperature warming across different ecozones in Alberta, Canada

Analysis and modelling of temperature anomalies from 25 selected deep wells in Alberta show that the differences between GST (ground surface temperature) warming for the northern Boreal Forest ecozone and the combined Prairie Grassland ecozone and Aspen Parkland transition region to the south occur during the latter half of this century. This corresponds with recent changes in surface albedo resulting from permanent land development in the northern areas and also to increases in natural forest fires in the past 20 years. Differences between GST and SAT (surface air temperature) warming are much higher in the Boreal Forest ecozone than in the Prairie Grassland ecozone and Aspen Parkland transition region. Various hypotheses which could account for the existing differences between the GST and SAT warming in the different ecozones of Alberta, and western Canada in general, are tested. Analysis of existing data on soil temperature, hydrological piezometric surfaces, snowfall and moisture patterns, and land clearing and forest fires, indicate that large areas of Alberta, characterised by anomalous GST warming, have experienced widespread changes to the surface landscape in this century. It is postulated that this has resulted in a lower surface albedo with a subsequent increase in the absorption of solar energy. Heat flow modelling shows that, after climatic SAT warming, permanent clearing of the land is the most effective and likely cause of the observed changes in the GST warming. The greater GST warming in the Boreal Forest ecozone in the latter half of this century is related to landscape change due to land development and increasing forest fire activity. It appears to account for a portion of the observed SAT warming in this region through a positive feedback loop with the overlying air. The anthropogenic effect on regional climatic warming through 20th century land clearing and landscape alteration requires further study. In future, more accurate quantification of these various forcings will be necessary in order to distinguish between, and to detect, the variety of natural and anthropogenic influences and on climate.