A three-dimensional nonlinear numerical model, that has been extensively used previously to predict environmental water flows, was applied to predict the flow over an isolated hill, Askervein. Predictions are reported for winds approaching the hill from 210 ° and 180 ° clockwise from north, both under almost neutral atmospheric conditions.The model predictions were compared with data collected during a major field study in 1983. From the comparisons it was concluded that the model predicts the mean flow variables with good accuracy. Larger discrepancies were found for quantities related to the turbulence, pointing to deficiencies in the turbulence model, and perhaps in some of the measurements. 相似文献
The Ordovician sedimentary rocks of the southeastern Lachlan Fold Belt in the Mystery Bay area are folded into two approximately coaxial and subhorizontally plunging fold series: F1 and F2. Regional domains with internally consistent F1 and F2 trends are juxtaposed along strike‐slip faults. Locally developed kink bands commonly have a close spatial relationship with the domain boundaries. A faulted domain boundary is exposed in coastal rocks at Mystery Bay between north‐northeasterly trending turbidites and northwesterly trending complexly deformed cherts and pelites of the Wagonga Beds. South of the boundary fault, F1 and F2 trends in the turbidite succession exhibit a segmented 75° counterclockwise rotation about a near‐vertical axis within a 750 m wide zone parallel with the coast, relative to regional trends preserved farther south. The rotation zone hosts prolific subvertical kink bands and crenulations. The turbidite succession youngs towards the east and hence its present position is incompatible with its projected along‐strike position on the western limb of a major anticline exposing the older Wagonga Beds. At least three generations of faulting are recognized. Within the coastal Wagonga Beds, a set of post‐F1 faults is subparallel to the tectonic grain and probably had vertical motion. Two systems of post‐F2 strike‐slip faults include a conjugate system in coastal outcrops, with offsets indicative of layer‐normal shortening; and a series of northerly trending faults, with probable sinistral displacements, recognized from inland exposures. 相似文献
Exploration within the Slave craton has revealed clusters of kimberlite intrusions, commonly with internally consistent geochemical and temporal characteristics. Translation diagrams (“Fry analysis”) allow an unbiased geometrical examination of the distance and direction between each kimberlite occurrence and all others in the database. Recurrent patterns are visually accentuated due to the square function in data density. Circular histograms quantify the azimuthal density of kimberlite at various distances. For this study, the database comprises the geographic position of 212 kimberlite occurrences of which 70% are from the Lac de Gras field (LDG). Analyses are presented separately for the LDG data and for all non-LDG data in order to test for regional variations and to avoid overwhelming the craton-scale studies by the high density of LDG data.
Empirical grouping of kimberlite locations results in delineation of five elliptical clusters that encompass all but four kimberlite occurrences. Clusters within the western part of the craton are elongate to the north–northeast and align within a narrow zone (“Western Corridor”). Elsewhere, the clusters are elongate to the northwest or west–northwest and appear to be arranged en echelon within a poorly defined north–northwest trending zone (“Central Corridor”). Geometrical spatial analyses of kimberlite locations highlight the craton-scale pattern of emplacement within the two main corridors. At regional and local scales, individual intrusions are preferentially located towards the west–northwest (ca. 280°) and north–northeast (ca. 015°) of other intrusions, and these orientations are interpreted to reflect upper mantle trends in magma generation. At local scales (10–25 km), kimberlite of the central and southern craton tends to be located to the northeast (ca. 045°), and possibly weakly to the east–northeast (ca. 070°), of other intrusions, and these orientations correspond to major crustal fractures systems. It is proposed that kimberlite emplacement is controlled primarily by the interaction of elongate 280° and 015° source regions with near-surface deviations influenced by crustal fracture systems.
The 015° trend evident at craton, regional, and local scales is parallel to a swarm of alkaline diabase dykes that are concentrated in a ca. 30-km-wide corridor passing through Lac de Gras. A profound spatial association between significantly diamondiferous kimberlite and the margins of the dyke corridor suggests the corridor is the surface expression of a mantle-depth structure. It remains unclear whether the proposed mantle structure coincides with a diamond-rich zone near the base of the lithosphere, or delineates pathways favorable for diamond preservation during emplacement. The linear array of kimberlite within the western craton forms a parallel corridor that may be an analogous mantle structure, but which to date has failed to yield economic diamond concentrations. 相似文献
A conjugate set of subvertical kink bands is exposed in coastal outcrops of well-foliated Ordovician turbidites near Mystery Bay, Australia. All kink bands with widths exceeding 3 cm have complex internal structures including compound and parasitic kinks, stepped kink boundaries, internal crenulations, variable kink angles and prismatic voids. The kink bands are interpreted to result from rotation of short foliation segments between fixed kink planes with subsequent widening and modification by layer-parallel shear external to the kink band. Layer-parallel shear of both sinistral and dextral sense accompanied kinking and indicates a variable stress system during kink band development.Conjugate kink bands are abundant and are used to estimate bulk strain orientations. In general, the dominant kink set of a conjugate pair is inclined at a lower angle to the external foliation than the weaker set and this angular disparity increases with increasing dominance of one set. These observations are at variance with relationships described from experimental bulk pure shear deformation of anisotropic materials. It is suggested that orthogonal constraints in these experiments restrict layer-parallel shear to within a developing kink band and are, therefore, unlike many natural kink systems. Simple shear experiments can produce structures geometrically similar to natural kink bands. 相似文献
The Leipzig wind profile recorded in 1931 has long been considered representative of the wind profile expected in a steady, barotropic flow in the planetary boundary layer over a flat homogeneous surface. As such, the Leipzig data set has been extensively used in the development of computational models for planetary boundary-layer flows. To date, workers have assumed that the effect of stable stratification in the atmosphere over Leipzig was negligible. In the present work, a second-order turbulence closure that explicitly accounts for the effects of stable stratification is used to analyse the Leipzig data. The importance of stable stratification in this near-neutral data set is demonstrated. 相似文献
The Kennady North Project kimberlites (Northwest Territories of Canada) comprises multiple shallow dipping dykes and several volcaniclastic bodies that have an unusual shallow plunging geometry and complex “pipe” shapes that are termed chonoliths. The detailed exploration of the entire system provides exceptional evidence for subterranean volcanic conduit growth processes. The possible processes leading to the development of the kimberlite bodies are discussed, with emphasis on the importance of the subsurface intrusive system geometry and the local stress tensor. Emplacement into a locally compressive stress regime (i.e. σ1 and σ2 inclined at a low angle to surface) could change the kimberlite emplacement geometries to that observed at Kennady North. Models are proposed for the development of the chonoliths, to emphasize aspects of the growth of kimberlite systems that are not well understood. The conclusions challenge or evolve current emplacement models and should influence kimberlite exploration and resource definition assumptions.
The influence of baroclinicity on the structure and levels of turbulence in the convective boundary layer depends on both the magnitude and orientation of geostrophic wind shear and the level of convection. The geostrophic Richardson number, a Richardson number defined in the present work and based on the geostrophic wind shear, is shown to be a single non-dimensional parameter which determines the influence of baroclinicity on convective turbulence structure. 相似文献
The planetary boundary layer (PBL) differs from other simple boundary layers in that it forms on the earth's rotating surface. While the effect of the earth's rotation on the mean wind vector of the PBL is well known, the rotational influence on PBL turbulence is not yet established. In the present work, the latter effect is investigated using numerical models that account for the influence of the earth's rotation on the turbulence. It is found that the earth's rotational influence on PBL turbulence is negligible, and therefore does not need to be included in turbulence models used to simulate PBL flows. 相似文献
While the importance of baroclinicity in determining the structure of the planetary boundary layer (PBL) is well recognized, the actual effect of baroclinicity on the structure is not well understood. Results based on simulations obtained using the turbulent kinetic energy-dissipation rate of turbulent kinetic energy closure model of the turbulent flow in a neutral baroclinic PBL provide additional insight into the role of baroclinicity. The baroclinic PBL is characterized by significant shear production of turbulent kinetic energy throughout the complete boundary-layer depth. The turbulent mixing length is bounded by the presence of a stable temperature inversion layer indicating that the depth of the baroclinic PBL is determined by the inversion height. Significant turbulent shear stresses exist throughout the baroclinic PBL and the air is relatively well-mixed except in the surface layer. 相似文献
