Water Density Fields Research Articles

Modeling microstructural mechanical behavior of expansive soil at various water contents and dry densities by molecular dynamics simulation

Microstructural behaviour plays an important role in building up the constitutive model of expansive soil. However, the responses of microstructural mechanical behaviour of expansive soil subjected to different water contents under varying dry densities are still poorly understood. In this study, we computed the bulk modulus and shear modulus of montmorillonite under various water contents and dry densities through molecular dynamics (MD) simulations. The mechanism that controls the changing of elastic properties subjected to water content and dry density changes was revealed by energy variation and water density field evolution. Results show that the microscopic bulk modulus is strongly influenced by dry density and water content while the dependence of shear modulus with water content and dry density is not as significant as bulk modulus. The comprehensive micromechanical studies demonstrate the critical water contents identified from either energies (bond, angle, and interfacial energies) or bulk/shear modulus are all highly related to the water content with full microscopic water filling ratio. The microscopic water filling ratio of the interlayer space thus can be considered as the key fundamental factor to control the variation of bulk/shear modulus through changing the energies in clay-water system.

Numerical simulation of temperature field and pressure field of the fracture system at Zhangzhou geothermal field

Zhangzhou geothermal field is one of the highest temperature in southeastern coastal areas in China. Zhangzhou geothermal field is an uplift-fracture type geothermal resource, and there are several deep fractures in the geothermal field, controlling water flow and heat transfer. Presently there is no systematic study of the characteristics of the temperature field, pressure field and water density distribution in the geothermal field, and there is no systematic analysis of the main factors affecting the temperature field. In this work, geological features of the fracture system are considered, and a conceptual model of the fracture system is established. Based on these, the distribution of the temperature field, pressure field and water density field at Zhangzhou geothermal field are numerically studied, the controlling effect of the fracture system on the temperature field is analyzed, and the main factors affecting the temperature field, pressure field and water density field are discussed. The results indicate that the temperature field and water density field at Zhangzhou geothermal field are strongly controlled by the fracture system, and the zone of high-temperature and low-density is confined within the fracture system. Main factors affecting the temperature field and water density field include the permeability of the fracture zone, the thermal conductivity of rocks and the water recharge rate. Higher fracture zone permeability will reduce the temperature and increase the water density in the center of the fracture system. Higher water recharge rate will increase the temperature and reduce the water density in the center of the fracture system.

A spatio-temporal process data model for characterizing marine disasters

Marine disasters are a more prevalent problem in China than in many other countries. Based on the development of a status quo of China's marine disaster the space-time process model is used. The model uses the ocean's temperature field, salinity field, water density field, surface wind field, wave field and other four-dimensional spatio-temporal quantities. This paper studies that model in detail. This study aims at using the theory to provide support during marine disasters in an effort to prevent or decrease their frequency in the future.

Modeling study of seasonal and inter-annual variability of circulation in the coastal upwelling site of the El Loa River off northern Chile

A three-dimensional numerical model using the Finite Element Method (FEM) was used to diagnose coastal currents off the El Loa River (21° S) in the northern upwelling region of Chile. This site has been recognized as an important spawning zone of the southern anchovy Engraulis ringens. Diagnostic current fields were obtained for summer and winter during the 1997–1998 El Nino conditions and during a “normal” upwelling year. The results show this site as an efficient retention area in the nearshore, because of a reduced cross-shelf flow, a strong alongshore flow and presence of several anticyclonic eddies. A simulated Lagrangian experiment indicated that retention within the nearshore (<10 km) may last for more than 4 days under a steady-state wind condition. Wind regimes and water density fields during 1997–1998 (El Nino) and 1995–1996 (“normal” upwelling) did not cause differences in the general pattern of coastal circulation. However, the magnitudes of both the alongshore and the cross-shelf flows are substantially reduced during El Nino in the nearshore spawning zone, possibly as a consequence of an anomalous water mass in the coastal area. This altered condition may limit the transport and dispersion of anchovy spawning products.

Understanding upwelling circulation off Antofagasta (northern Chile): A three-dimensional numerical-modeling approach

A three-dimensional (3D) numerical model using the finite element method was used to diagnose coastal currents off Antofagasta, in the upwelling region of northern Chile. The diagnosis was emphasized in the nearshore zone off Peninsula Mejillones (23°S), a well-known upwelling site off northern Chile. Water density fields, available from seasonal climatologies of the region, were used to predict currents for the austral winter, and summer conditions. Steady-state conditions were simulated under absence of wind, with a constant southwest wind of 10 knots (5.14 m s −1), which is the dominant upwelling-favorable wind in the zone, and with a constant north wind of 10 knots. Spatial variability of winds was examined by using historical wind fields for the region. A 3D particle tracking program was further used to diagnose expected particle trajectories over a 72 h steady-state period. Coastal circulation was dominated by alongshore currents, and presence of reversal currents and coastal eddies. Wind forcing accelerated the flow of the nearsurface layer in most cases, but did not considerably alter the circulation pattern of the average water column. Simulation of passive particle drift showed that the whole nearshore zone might act as an efficient retention area. It was concluded that, as a result of the interactions among distinct water masses, upwelling plumes, and alongshore currents, physical barriers may develop and give rise to semi-enclosed habitats. Physical structuring may have important ecological implications for the upwelling ecosystem.

The physical environment of Kongsfjorden–Krossfjorden, an Arctic fjord system in Svalbard

Kongsfjorden-Krossfjorden and the adjacent West Spitsbergen Shelf meet at the common mouth of the two fjord arms. This paper presents our most up-to-date information about the physical environment of this fjord system and identifies important gaps in knowledge. Particular attention is given to the steep physical gradients along the main fjord axis, as well as to seasonal environmental changes. Physical processes on different scales control the large-scale circulation and small-scale (irreversible) mixing of water and its constituents. It is shown that, in addition to the tide, run-off (glacier ablation, snowmelt, summer rainfall and ice calving) and local winds are the main driving forces acting on the upper water masses in the fjord system. The tide is dominated by the semi-diurnal component and the freshwater supply shows a marked seasonal variation pattern and also varies interannually. The wind conditions are characterized by prevailing katabatic winds, which at times are strengthened by the geostrophic wind field over Svalbard. Rotational dynamics have a considerable influence on the circulation patterns within the fjord system and give rise to a strong interaction between the fjord arms. Such dynamics are also the main reason why variations in the shelf water density field, caused by remote forces (tide and coastal winds), propagate as a Kelvin wave into the fjord system. This exchange affects mainly the intermediate and deep water, which is also affected by vertical convection processes driven by cooling of the surface and brine release during ice formation in the inner reaches of the fjord arms. Further aspects covered by this paper include the geological and geomorphological characteristics of the Kongsfjorden area, climate and meteorology, the influence of glaciers, freshwater supply, sea ice conditions, sedimentation processes as well as underwater radiation conditions. The fjord system is assumed to be vulnerable to possible climate changes, and thus is very suitable as a site for the demonstration and investigation of phenomena related to climate change.