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51.
We present a two-dimensional, two-phase model for non-cohesive sediment transport. This model solves concentration-weighted averaged equations of motion for both fluid and sediment phases. The model accounts for the interphase momentum transfer by considering drag forces. A collisional theory is used to compute the sediment stresses, while a two-equation (k–ε) fluid turbulence closure is implemented. A benchmark sediment transport problem concerning the scouring downstream of an apron is carried out as an example and numerical results agree with existing experimental data. 相似文献
52.
This paper presents the first large‐scale British study of the impacts of commercial forest cutting on stream‐flow regimes. The 70% forested headwaters of the River Severn are part of the intensively instrumented long‐term Plynlimon catchment study into the impact of land use on stream flow. The forest area, comprising predominantly Sitka spruce (Picea sitchensis), was planted mainly in the 1930s and 1940s. Harvesting commenced in the mid‐1980s and over the study period about half the forest has been felled. Changes in annual water yield and extreme flows were studied in four nested catchments ranging in area from about 1 to 10 km2 and compared with an adjacent benchmark grassland catchment. As expected from earlier process studies the cutting of the forest increased total annual flows. Less expected was the clear evidence that the felling augmented low flows. This informs a long‐standing debate whether upland forestry increases or reduces baseflows. A particularly notable result was the lack of impact of the harvesting on storm peak flows. This may result from the application of forest management guidelines designed to reduce soil damage and erosion during the harvesting, and indicates that the forest itself has a limited impact on flooding. These findings are timely because British forest expansion peaked in the 30 years following the Second World War, and large areas of these woodlands are now approaching economic maturity and will be harvested in the next two decades. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
53.
R. García Díaz 《水文研究》2005,19(16):3221-3233
The limitations of Manning's formula are analysed when it is in extreme conditions, and more specifically with small‐depth flows on natural‐vegetation beds. A thorough analysis is made of research carried out on macro‐rough beds, placing particular emphasis on vegetated beds. Research carried out to date on the roughness of vegetated beds and macro‐roughness is commented on, including that carried out at the Laboratory of Hydraulics and Hydrology of the Forestry Engineering Faculty (Polytechnic University of Madrid). The work was done in two phases, the first in a laboratory channel with artificial vegetation and the second in natural beds. The results of the experimental research allow the development of a new approximate method of determining Manning coefficient according to the Froude number. This method may be applied in extreme conditions, both in small depths and steep slopes. It was proved that the Manning coefficient depends not only on roughness height, but also on depth and slope values; thus, it is advisable to choose the appropriate method for its calculation. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
54.
E. Knobloch 《地球物理与天体物理流体动力学》2013,107(1-4):105-116
Abstract Unbounded stratified plane Couette flow is shown to be stable against small amplitude disturbances. The Brunt-Väisälä frequency is assumed to be constant. Both viscosity and thermal diffusion are included, and shown to be stabilizing. 相似文献
55.
Abstract Accretion discs in astrophysics are fundamental for converting gravitational binding energy into observed electromagnetic radiation. We study the behavior of waves in a two dimensional supersonic Keplerian flow inside a given gravitational potential. We present the effects of shearing and rotation on short waves, and the numerical study of the dynamical stability of such flows with respect to various perturbations. We show that a large class of dynamical effects, due to pressure and associated to short time scales, may be excited. 相似文献
56.
Boris Moro 《地球物理与天体物理流体动力学》2013,107(3-4):209-225
Abstract Who show through numerical experiments that friction may enhance westward motion of vortices on the beta-plane and establish a relation betwen the dissipation coefficients and westward aceleration. This suggests an explanation fot the dunamics of westward intensification. 相似文献
57.
Xia Zhenhuan. Professor Dept. Hydraulic Engineering. Tsinshua University. Song Genpei. Lecturer. kept. Hydraulic Engineering. Tsinghua University. Chen Yiping. Assistant. Dept. Hydraulic Engineerins Tsomghua University Wang Gang. Engineer. Research institute of Naval Engineering. PLA 《国际泥沙研究》1990,(1)
1. INTRODUCTIONAs a wide range of size distirbution including usually a certain POrtion of cohesive material is thecommon feature of the sediment constituting hyperconcentrated flows. it is desirable to study the settling properties of mixtures of cohesive and non--cohesjve sediment particles at high concentrations.Past studies on the settling of discrete particles in a suspension of fine cohesjve sediment is scarcein the literature. The Sediment Research Laboratory of Tsinghua Universi… 相似文献
58.
K. Stingl 《International Journal of Earth Sciences》1994,83(4):811-821
The Eibiswald Bucht is a small subbasin of the Western Styrian Basin exposing sediments of Lower Miocene age. In the past the entire sequence exposed in the Eibiswalder Bucht has been interpreted as being of fluvial/lacustrine origin; here, results are presented of detailed sedimentological investigations that lead to a revision of this concept. The lowermost siliciclastic sedimentary unit of the Eibiswalder Bucht sequence is the Radl Formation. It is overlain by the Eibiswald Beds, which are subdivided into the Lower, Middle and Upper Eibiswald Beds. The Radl Formation and the Lower Eibiswald Beds are interpreted as a fan delta complex deposited along NNW-SSE striking faults. Based on the sedimentary facies this fan delta can be subdivided into a subaerial alluvial fan facies group, a proximal delta facies group and a distal delta/prodelta facies group. The Radl Formation comprises the alluvial fan and proximal delta facies groups, the Lower Eibiswald Beds the distal delta/prodelta facies group. The alluvial fan and the proximal delta consist of diverse deposits of gravelly flows. The distal delta/prodelta consists of wave-reworked, bioturbated, low density turbidites intercalated with minor gravelly mass flows. The prodelta can be regarded as as the basin facies of the small and shallow Eibiswalder Bucht, where marine conditions prevailed. The basin was probably in part connected with the Eastern Styrian Basin, the contemporary depositional environment of the Styrian Schlier (mainly turbiditic marine offshore sediments in the Eastern Styrian Basin). Analysis of the clast composition, in conjunction with the paleotransport direction of the coarse delta mass flows of the Radl Formation, shows that the source rocks were exclusively crystalline rocks ranging from greenschists to eclogites. 相似文献
59.
60.
John L. Innes 《地球表面变化过程与地形》1983,8(6):579-588
Debris-flow deposits, dated by lichenometry, indicate that the majority of hillslope debris flows in Scotland have occurred within the last 500 years. Progressive weathering and climatic change can be discounted as the prime cause of the increase in the incidence of debris flows. The timing of the increase suggests that it is related to landuse changes in the Scottish Highlands during the 19th and early 20th centuries. Both burning and overgrazing can be cited as potential causal factors. 相似文献