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第六届国际流体力学会议

作者： C.Zeng C.W.Li Department of Civil and Structural Engineering The Hong Kong Polytechnic University Hong Kong China

A Reynolds-averaged Navier-stokes equations（RANS） model using the body force method（BFM） has been developed to simulate open-channel flows over gravel *** momentum equation is modified by introducing the form drag as an extra body force term to represent the gravel-bed *** applying the body force within the roughness layer of the flow over small-scale roughness,it is found that the body force coefficient f rk varies inversely with the roughness length scale k *** method is robust,not sensitive to mesh resolution and is easily extended to deal with large scale roughness.

关键词： open-channel flows RANS modeling turbulent flows gravel beds body force method

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A combined tectono-climatic control on Holocene sedimentation in Ladakh Himalaya,India: Clues from Anisotropy of Magnetic Susceptibility(AMS) of lake sediments

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Journal of Palaeogeography 2024年第4期13卷 738-753页

作者： B.V.Lakshmi K.Deenadayalan Md.Mujahed Baba Saumitra Misra Indian Institute of Geomagnetism Discipline of Geological Sciences SAEESUniversity of Kwa Zulu-Natal

Anisotropy of Magnetic Susceptibility(AMS) data from a ～27.8 m thick soft sedimentary mud sequence(～10.5-3.25 k yrs) from the Spituk Palaeolake Sequence(SPSS) of Holocene age, located in the northern bank of the Indus River in the Leh-Ladakh Himalaya, show effects of tectonic versus climate dynamics responsible for the Himalayan sedimentation. The sedimentary sequence, consisting of alternating of aeolian sand and glacio-fluvial mud flow deposits, has been subdivided into an older Last Glacier Phase I(LGP 1) and a younger Last Glacier Phase II(LGP 2), where the termination of each phase is marked by the occurrence of gravel beds of thickness ≤1 m, which were deposited due to glacial melting. The present AMS data along with previously published information on sedimentology confirm that the mudflow deposits of the LGP 1 and LGP 2phases were deposited in a lacustrine environment under glacio-fluvial conditions. However, a weak fluvial flow towards NW and NE could have existed for the LGP 1 and LGP 2, respectively. The glacial beds terminating LGP 1 and LGP 2 appear to have formed by climatic warming and tectonic activity, respectively. Hence, the Holocene Himalayan sedimentation was influenced by both climatic and tectonic activities. However, the thickness of the gravel bed(～0.8 m) terminating LGP 2 occupies only ～ 2.8 vol % of the total studied thickness～28 m, of the SPSS in the present study, which indicated a lesser control of tectonism in the growth of the Himalaya in and around the study area.

关键词： Holocene palaeolake sequence AMS studies gravel beds Deglaciation Tectonic instability

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A comparison between different methods for determining grain distribution in coarse channel beds

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International Journal of Sediment Research 2016年第2期31卷 97-109页

作者： Alessio Cislaghi Enrico Antonio Chiaradia Gian Battista Bischetti Department of Agricultural and Environmental Sciences(DiSAA) Universita degli Studi di Milano

The determination of grain size distribution in alluvial channels plays a crucial role in understanding fluvial dynamics and processes(e.g.,hydraulic resistance,sediment transport and erosion,and habitat suitability).However,to determine an accurate distribution,tremendous field efforts are often ***,the grain size distribution of channel beds have been obtained by manually counting a set of randomly selected stones(the "pebble count").Based on this elementary principle,many authors have proposed different adaptations to overcome weaknesses and problems with the original method;with the development of digital technology,photographic methods have been developed in order to significantly reduce the time spent in the *** of these "image-assisted" methods include Automated Grain Sizing,ACS,and Manual Photo Sieving,*** this study,AGS and MPS were applied under ideal laboratory conditions,to be used as reference,and in two field conditions with different degrees of difficulty in terms of visual determination of the grain size distribution;these included an artificial unlined channel and two natural mountainous *** results were compared with those obtained with the pebble-count *** general,strong agreement between the methods was found when they were applied under favorable conditions( "the laboratory"),and the differences between the imageassisted and pebble count methods were similar to those found in previous *** being more time consuming,MPS was deemed preferable to AGS when conditions are not optimal;in these cases,the time spent on image elaboration significantly increased in the AGS method(approximately three-fold),but the estimation error of the median grain size decreased by approximately 37%.The use of imageassisted analysis has proven to be robust for characterizing sediment in watercourse beds and reducing fieldwork time,but because field conditions can significantly affect the accuracy of results,the method

关键词： Grain size distribution curve Grain size analysis Image analysis gravel beds Segmentation

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