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Stone Stability Under Non-uniform Flow- Sự ổn định của viên đá gia cố đáy dưới tác động của dòng chảy không đều
Stone StabilityUnder Non-uniform Flow Stone StabilityUnder Non-uniform FlowProefschriftter verkrijging van de graad van doctoraan de Technische Universiteit Delft,op gezag van de Rector Magnificus prof.dr.ir. J.T. Fokkema,voorzitter van het College voor Promoties,in het openbaar te verdedigenop maandag 3 november 2008 om 12.30 uurdoorNguyen Thanh Hoanciviel ingenieurgeboren te Nam Dinh, Vietnam Dit manuscript is goedgekeurd door de promotor:Prof.dr.ir. M.J.F. StiveCopromotor:Ir. H.J. VerhagenSamenstelling promotiecommissie:Rector Magnificus voorzitterProf.dr.ir. M.J.F. Stive Technische Universiteit Delft, promotorIr. H.J. Verhagen Technische Universiteit Delft, copromotorProf.dr.ir. H.H.G. Savenije Technische Universiteit DelftProf.dr.ir. J.A. Roelvink UNESCO-IHE Institute for Water EducationProf.dr.ir. J. de Rouck Universiteit GentDr.ir. W.S.J. Uijttewaal Technische Universiteit DelftDr.ir. B. Hofland DeltaresProf.dr.ir. G.S. Stelling Technische Universiteit Delft, reservelidDrs. R. Booij has provided substantial guidance and support in the preparationof this thesis.This research has been financially supported by the Ministry of Education andTraining of Vietnam and Delft University of Technology.Keywords: Stone stability, stone transport, stone entrainment, incipient motion,threshold condition, bed protection, bed damage, non-uniform flow, turbulentflow, decelerating flow.This thesis should be referred to as: Hoan, N. T. (2008). Stone stability under non-uniform flow. Ph.D. thesis, Delft University of Technology.ISBN 978-90-9023584-4Copyrightc 2008 by Nguyen Thanh HoanPrinted by PrintPartners Ipskamp B.V., the Netherlands.All rights reserved. No part of the material protected by this copyright noticemay be reproduced or utilized in any form or by any means, electronic or me-chanical, including photocopying, recording or by any information storage andretrieval system, without written permission of the author. To my family ContentsSummary vSamenvatting ixTom tat xiii1 Introduction 11.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2 Objectives of this study . . . . . . . . . . . . . . . . . . . . . . . . . . 21.3 Research methodology . . . . . . . . . . . . . . . . . . . . . . . . . . 31.4 Outline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 Literature review 72.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72.2 Turbulence and flow properties . . . . . . . . . . . . . . . . . . . . . 72.2.1 Uniform open-channel flow over a rough bed . . . . . . . . 72.2.2 Non-uniform open-channel flow . . . . . . . . . . . . . . . . 112.3 Hydrodynamic forces on a single stone . . . . . . . . . . . . . . . . 132.4 Stability parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162.4.1 Governing variables . . . . . . . . . . . . . . . . . . . . . . . 162.4.2 The Shields stability parameter . . . . . . . . . . . . . . . . . 182.4.3 The Jongeling et al. stability parameter . . . . . . . . . . . . 182.4.4 The Hofland stability parameter . . . . . . . . . . . . . . . . 192.5 Mobility parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . 202.6 Methods for stone stability assessment . . . . . . . . . . . . . . . . . 212.6.1 The stability threshold concept . . . . . . . . . . . . . . . . . 212.6.2 The stone transport concept . . . . . . . . . . . . . . . . . . . 262.6.3 Comparison and selection of methods . . . . . . . . . . . . . 292.7 Concluding remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . 303 Experimental arrangement and data processing methods 333.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 333.2 Experimental configuration . . . . . . . . . . . . . . . . . . . . . . . 343.2.1 Geometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34i ii Contents3.2.2 Instrumentation . . . . . . . . . . . . . . . . . . . . . . . . . . 363.3 Stones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 383.4 Test program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 393.4.1 Hydraulic conditions . . . . . . . . . . . . . . . . . . . . . . . 393.4.2 Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . 423.5 Selected time series . . . . . . . . . . . . . . . . . . . . . . . . . . . . 433.6 Data processing methods . . . . . . . . . . . . . . . . . . . . . . . . . 453.6.1 Velocity and turbulence data . . . . . . . . . . . . . . . . . . 453.6.2 Stone entrainment rate data . . . . . . . . . . . . . . . . . . . 463.6.3 Correlation analysis . . . . . . . . . . . . . . . . . . . . . . . 474 Flow characteristics 494.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 494.2 Flow quantities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 504.3 Shear velocity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 524.4 Mean flow velocity . . . . . . . . . . . . . . . . . . . . . . . . . . . . 534.5 The eddy viscosity and mixing length . . . . . . . . . . . . . . . . . 554.6 Turbulence intensity data . . . . . . . . . . . . . . . . . . . . . . . . 594.7 Reynolds shear stress data . . . . . . . . . . . . . . . . . . . . . . . . 634.8 Concluding remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . 655 Stone transport formulae 675.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 675.2 The proposed stability parameter . . . . . . . . . . . . . . . . . . . . 685.3 Final formulation of the proposed stability parameter . . . . . . . . 705.4 Evaluation of the available stability parameters . . . . . . . . . . . . 725.4.1 The Shields stability parameter . . . . . . . . . . . . . . . . . 725.4.2 The Jongeling et al. stability parameter . . . . . . . . . . . . 735.4.3 The Hofland stability parameter . . . . . . . . . . . . . . . . 755.5 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 765.5.1 Comparison of the stability parameters . . . . . . . . . . . . 775.5.2 Sensitivity analysis of key parameters . . . . . . . . . . . . . 785.5.3 Entrainment correction . . . . . . . . . . . . . . . . . . . . . . 805.5.4 Data comparison . . . . . . . . . . . . . . . . . . . . . . . . . 815.6 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 846 Estimation of stone entrainment using numerical flow modeling 876.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 876.2 Flow conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 886.3 Numerical model set-up . . . . . . . . . . . . . . . . . . . . . . . . . 886.3.1 Grid . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 896.3.2 Boundary condition . . . . . . . . . . . . . . . . . . . . . . . 916.3.3 Model validation . . . . . . . . . . . . . . . . . . . . . . . . . 92 Contents iii6.3.4 Model calibration and verification . . . . . . . . . . . . . . . 946.4 Computation results . . . . . . . . . . . . . . . . . . . . . . . . . . . 956.5 Estimation of bed damage . . . . . . . . . . . . . . . . . . . . . . . . 976.6 Conclusions and recommendations . . . . . . . . . . . . . . . . . . . 997 Conclusions and recommendations 1017.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1017.2 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1027.3 Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104References 106A Stones 115A.1 Artificial stones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 115A.2 Stone gradation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116B Data 117B.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117B.2 Velocity and turbulence data . . . . . . . . . . . . . . . . . . . . . . . 117B.3 Governing variables . . . . . . . . . . . . . . . . . . . . . . . . . . . 124C Numerical flow modeling 129C.1 Turbulence modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . 129C.1.1 Mean-flow equations . . . . . . . . . . . . . . . . . . . . . . . 129C.1.2 The two-equation k-ε model . . . . . . . . . . . . . . . . . . . 130C.2 Deft input files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132C.2.1 Mesh description . . . . . . . . . . . . . . . . . . . . . . . . . 132C.2.2 Problem description . . . . . . . . . . . . . . . . . . . . . . . 136C.2.3 Typical sequence of an Deft session . . . . . . . . . . . . . . 139List of symbols 141List of figures 145List of tables 148Acknowledgements 151Curriculum Vitae 153 iv Contents [...]... studies on the stability of stones in bed protections under owing water have been conducted, our knowledge is still far from advanced and reliable Issues like how to quantify the hydraulic loads exerted on the stones on a bed and how to assess the stability of the stones are central and most challenging in stone stability research Firstly, it is important that the hydraulic forces exerted on the stones in... fact that much research on stone stability has been accumulated over the years, our knowledge is still far from advanced and reliable The above discussion has focussed on the stability of stones in bed protections under owing water, which is also central in this study Aspects like the inuence of turbulence uctuations, the quantication of hydraulic loads exerted on the stones and stone transport formulae... expanding open-channels and its inuence on stone stability were focused on because under these conditions the turbulence intensity is high In the experiments, both the bed damage and the ow quantities (velocity and turbulence intensity) are measured A new stability parameter is formulated to better describe the impact of hydraulic parameters on stone stability This new stability parameter together with those... physical models obsolete Surprisingly, most of the previous studies on stone stability are re1 2 Chapter 1 Introduction stricted to the stability threshold concept and few have attempted to derive stone transport formulae Examples of the investigations that use a stone transport approach are Paintal (1971, for uniform ow) and Hoand (2005, for non-uniform ow) However, still no generic physical relationship... exerted on the bed for non-uniform ow Secondly, the method with which the stability of stones is assessed also plays an important role Available stability formulae used to determine the required stone sizes and weights are mainly based on the concept of incipient motion of bed material Due to the stochastic nature of bed material movement, a robust ow condition at which the stones begin to move does... This study focuses on stability or damage formulations for granular bed protections under owing water An important investigated aspect is the effect of turbulence uctuations of the ow on the stability of stones The objectives of this study are: (i) to increase insight into the effect of hydraulic parameters, such as the velocity and the turbulence uctuations, on the stability of stones in bed protections;... as stone transport formulae - has been established for non-uniform ow Since a good collapse of the data is obtained for a variety of stone densities (varying from 1320 to 1970 kg/m3 ), the inuence of stone density is well incorporated into the formulae Therefore, the newly-developed stone transport formulae are likely to be valid for other bed materials with different densities, including natural stones... is essential for studying the interaction between ow and stone stability The governing equations of turbulent ow and stone stability are presented The physical meaning of various terms in the equations is discussed, indicating the importance to measure them As a result, the requirements for the development of new stone transport formulae for non-uniform ow are derived The ow congurations used in the... discussed instead (Section 2.2) In Section 2.3 the physical concepts of stability of a single stone are treated, focusing on the hydrodynamic forces on the stones The parameters used to quantify the ow forces acting on a bed are treated in Section 2.4 Several aspects that play a role in stone stability like turbulence effects and stone characteristics are discussed It is followed by a discussion on how... hydraulic load and the bed response is available for non-uniform ow In the authors opinion, the most challenging issue in stone stability research is how to quantify the hydraulic loads exerted on the stones on a bed The bed shear stress is widely used as the only hydraulic quantity for this purpose ever since it was introduced by Shields (1936) The Shields stability parameter, however, does not explicitly . định củacác khối gia cố đáy dưới tác động của dòng chảy. Trong hai vấn đề trên, việc định lượng tác động của dòng chảy lên các viên á gia cố đáy có ý nghĩa. để định lượng hóa tác động của dòng chảylên lòng dẫn. Do tính rối động của dòng chảy có tác động lớn đến sự ổn địnhcủa đá gia cố đáy nên ảnh hưởng đó cần