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1.
The paper presents a semi-analytical method for predicting the flow rate hydrograph due to a hypothetical sudden and total dam failure in a natural valley. The method generalizes the approach proposed by Hunt for the dam-break problem in a rectangular frictionless sloping channel to a valley with a cross-section area expressed by a power-law function of water depth, in order to take into account the most common shapes of natural valleys. The parameters of the deriving model can be set by exploiting data usually available concerning the dam section geometry and the reservoir storage-depth curve. The application of the technique to three different reservoirs is discussed. The results show that the flow rate hydrographs obtained at the dam site agree with the ones calculated by means of a finite volume numerical code based on two-dimensional shallow water equations. The method requires moderate computational and data collecting effort, so it can be regarded as a useful alternative to other procedures commonly adopted in the practice. 相似文献
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The Gulf of Cadiz is swept by the strong saline Mediterranean Outflow Water (MOW). On the Algarve Margin (South Portugal), this current has constructed fine-grained contourite drifts. This margin is dissected by the Portimao Canyon and three short channels that only incise the upper slope, and are absent on a terrace located at mid-slope depths along the Algarve Margin. High-resolution seismic profiles and sediment cores highlight the original architecture of the sedimentary deposits on this terrace. Coarse-grained lenticular chaotic bodies formed during major relative sea-level lowstands are intercalated within the drift. The lobate shape and sandy nature of the lenticular chaotic bodies and their location at the mouths of the three short channels suggest they are gravity-generated deposits that are perched on the middle continental slope.In the Gulf of Cadiz, the interaction between contour current and gravity processes is strongly controlled by climatic variations and relative sea-level changes during the late Quaternary. During cold periods when sea-level was low, erosion intensified on the continental shelf and the deepest part of MOW was active. Sediment was transported downslope through the channels and deposited on sedimentary lobes perched on the mid-slope terrace. During warm periods when relative sea-level was high, the supply of sediment from the shelf was shut off and the shallowest part of MOW was more active. Contourite drifts fill the channels and bury the sandy lobes. 相似文献
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Christopher M. Wright 《Astrophysics and Space Science》2007,311(1-3):47-55
The position angle of mid-infrared polarisation can be directly related to the magnetic field direction projected onto the
plane of the sky. Such observations, from both ground and space-based platforms, have been used to investigate the relation
between the magnetic field and other “symmetry axes” associated with embedded young stars, such as the interstellar magnetic
field, bipolar outflow and disk/toroid axes. Interpretation of the results in terms of hydromagnetic driving mechanisms of
bipolar outflow is discussed. 相似文献
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N. Mangold V. Ansan D. Baratoux F. Costard L. Dupeyrat H. Hiesinger Ph. Masson G. Neukum P. Pinet 《Planetary and Space Science》2008,56(7):1030-1042
Syrtis Major Planum is a volcanic plain dominated by lava flows. High resolution stereo camera (HRSC) images of the northern Syrtis Major region display erosional features such as grooves, teardrop-shaped islands and valleys. These landforms are characteristics of outflow channels seen on Mars, therefore implying that a flood event took place in this region. The flow of 100 km long and a few kilometer wide followed the local slopes in most locations. Maximum flood discharges estimated from images and topography vary from about 0.3×106 to 8×106 m3/s, and therefore are in the range of terrestrial mega-floods in the Scablands or Lake Bonneville. In North Syrtis Major, the relationships with surrounding lava flows and the timing of the flood coeval to Syrtis Major volcanic activity suggest that it could be related to the subsurface water discharge mobilized by the volcanic activity. The proximity of Noachian age basement rocks 20 km away from the flood and below lava flows might have played a role in its formation and water presence. 相似文献
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E. N. Parker 《地球物理与天体物理流体动力学》2013,107(3-4):165-189
Abstract The mean-field effects of cyclonic convection become increasingly complex when the cyclonic rotation exceeds ½-π. Net helicity is not required, with negative turbulent diffusion, for instance, appearing in mirror symmetric turbulence. This paper points out a new dynamo effect arising in convective cells with strong asymmetry in the rotation of updrafts as against downdrafts. The creation of new magnetic flux arises from the ejection of reserve flux through the open boundary of the dynamo region. It is unlike the familiar α-effect in that individual components of the field may be amplified independently. Several formal examples are provided to illustrate the effect. Occurrence in nature depends upon the existence of fluid rotations of the order of π in the convective updrafts. The flux ejection dynamo may possibly contribute to the generation of field in the convective core of Earth and in the convective zone of the sun and other stars. 相似文献
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童双立 《CT理论与应用研究》1997,6(1):11-14
本文讨论了血液流动对MR成像的影响。它们是图像为影的来源,在血管造影中,它们用于显示血管和提供关于血液流动速度的信息。流动两个方面的影响敏感,第一质子群的流入和注出。第二流动产生的相位移。本文也介绍了流动补偿技术。 相似文献
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The sandy channel-lobe depositional systems in the Gulf of Cadiz: Gravity processes forced by contour current processes 总被引:1,自引:0,他引:1
The sedimentation in the Gulf of Cadiz (NE Atlantic Ocean) is significantly controlled by the Mediterranean Outflow Water (MOW). Along its pathway onto the continental slope, the MOW is canalized by contourite channels, some of them feeding gravity sandy channel-lobe depositional systems firstly recognized in previous study [Habgood et al., 2003. Deep-water sediment wave fields, bottom current sand channels and gravity flow channel-lobe systems: Gulf of Cadiz, NE Atlantic. Sedimentology 50(3), 483-510.].Using very high resolution acoustic data and cores, a detailed characterization and a new evolution pattern of these channel-lobe depositional systems is established. Complex internal geometry of the lobes shows several depositional units revealing a polyphase evolution of these systems, with a general progradation punctuated by retrogradation and avulsion phases. A gravity origin controlled by contouritic processes and climatic changes is demonstrated for the feeding and the evolution of these sandy channel-lobe depositional systems. Climate oscillations, via the MOW variations, act as a major forcing of the activity of the channel-lobe depositional systems during the Late Quaternary. 相似文献
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In the Gulf of Cadiz, the hydrodynamic process acting on particle transport and deposition is a strong density-driven bottom current caused by the outflow of the saline deep Mediterranean water at the Strait of Gibraltar: the Mediterranean Outflow Water (MOW). New high resolution acoustic data including EM300 multibeam echo-sounder, deep-towed acoustic system SAR and very high resolution seismic, completed by piston cores collected during the CADISAR cruise allow to improve the understanding of the hydrodynamics of the MOW in the eastern part of the Gulf of Cadiz. Interpretation of data corrects the previous model established in this area and allows, for the first time, the accurate characterization of various bedforms and erosive structures along the MOW pathway and the precise identification of numerous gravity instabilities. The interaction between the MOW, the seafloor morphology and the Coriolis force is presently the driving force of the sedimentary distribution pattern observed on the Gulf of Cadiz continental slope. 相似文献