Stability of stones in the top layer of a granular filter: Literature survey

In order to understand the processes involved in damaging a granular filter, the behaviour of the separate particles it is made of must be known. The hydrodynamic forces on the particles are very important for understanding this behaviour. These forces have been examined by many researchers. Chapter 2 deals with that aspect. The characteristics of stones, like shape, size and orientation influence these forces, so definitions of these characteristics, as well as their influence on stone stability are treated at the end of this chapter. The 3rd chapter of this report focuses on the stability of an entire bed, consisting of the particles that have been described in the first chapter. The stability is discussed first, followed by a description of some bed-lead transport formulas. Several basic aspects of the influence of turbulence on stone stability and transport are treated as well. The final chapter deals with flow characteristics in general. First of all boundary layer flow, especially over rough walls, will be treated. Research on turbulence-induced wall pressures-which might be used to correlate flow properties to stone stability-is a separate field which generated a lot of research over the last decades. A model for calculating pressure fluctuations on the bed that can be related to stone stability-is discussed. As it is expected that experiments with a backward-facing step will be executed, this flow configuration is described. The chapter will be extended with other configurations when it becomes clear which flow configurations will be used for experiments to come.Hydraulic EngineeringCivil Engineering and Geoscience

Polder Halsteren, schade en herstel 1953

Foto's van de schade in 1953 bij Halsteren, de noodmaatregelen en het herstel daarna. Beschrijving en tekeningen van de situatie uit het Verslag van de Stormvloed

Report on measurements: Pressure and velocity fluctuations around a granular-bed element

The second chapter describes the general methodology of the research. It presents the key questions about the entrainment of stones from granular filters that are as yet unanswered. It also describes the aspects that are being regarded in the analysis in this report. In chapter 3 the measuring set-up is described. The following two chapters present the experimental results. Chapter 4 describes the pressures on and flow around a solitary bed-mounted cube. This configuration can be regarded as a model for a very exposed stone, subject to a flow with low turbulence intensities. This simple configuration (already with a complicated flow-field) can also be calculated relatively easily. This generates the possibility to obtain even more information about the entire velocity and pressure field. Chapter 5 presents the measurements that have been done on the bed-mounted cube as part of a (one layer thick) granular filter. The protrusion of the cube has been varied in order to examine the influence of the stone position on stability. In chapter 6 some further possible analyses on the measurements are described. Finally, in chapter 7 some conclusions are drawn from the results that have been gathered so far. SOME RELEVANT CONCLUSIONS - It was shown that both the fluctuating and the mean pressures are influenced by the position of the cube. This cube can be regarded as a model of a stone. - The average pressures on the bed mounted cube follow the p = Cpü^2 law, with a positive C for the upstream side and a negative C for the top and the lee-side. - Pressure on top of solitary bed-mounted cube has a very high intensity and a maximum at u/f = 15.Hydraulic EngineeringCivil Engineering and Geoscience

Veiligheidsrapport voor de PIV-goot in het Laboratorium voor Vloeistofmechanica

Bevat een veiligheidsvoorschrift voor de PIV (particle-image velocimetry) goot. Het rapport is vooral gericht op het gebruik van de krachtige Nd: YAG laser (veiligheidsklasse 4) die gebruikt wordt voor de PIV techniek.Hydraulic EngineeringCivil Engineering and Geoscience

Rock and roll: Turbulence-induced damage to granular bed protections

Layers of stone or rock are often applied around hydraulic structures to protect the sand bed from scouring. Determining the size of the rocks is complicated by the fact that the flow over a bed protection usually is non-uniform. This thesis describes two experimental series in which the stability of a single stone under non-uniform flows is studied in detail. From these experiments more understanding in the process of damage to bed protections is obtained. It is seen that besides the classical form drag, also small-scale accelerations in the flow attribute to the stone movement. In the last chapter a new stability model is developed for practical use.Civil Engineering and Geoscience

Pressure Sensors and Filtering Techniques for Stone Stability Assessment

This report is structured as follows: In chapter 2 the importance of wall pressures with respect to the present research is described. The literature on wall pressures that was used, and some general features of wall pressure fluctuations are subsequently described in chapter 3. Chapter 4 deals with the pressure sensors. It begins with a brief description of some general features of pressure sensors. Then the criteria for the required pressure sensor are given. This is followed by a description of the two types of pressure sensors, which were acquired from commercial companies. The character of the noise that is present in the measured pressure signal is described in chapter 5. This chapter ends with a list that comprises numerous possible sources of noise. A few dedicated filtering techniques that can be used to attenuate the vibrational and acoustical noise are described in the next chapter (chapter 6). Several experiments were executed in order to get a further idea of the possibilities of the sensors, and the nature of the noise that will be present in the measured signal. The set-up of these experiments is described in chapter 7. An analysis of the tests that were executed is given in chapter 8. In this chapter the nature and magnitude of the various sources of noise are described. Chapter 9 presents the conclusions of the report. Based on these conclusions the requirements for the experimental facilities that are needed for the final experiments, and the choice of the best suited pressure sensor are given. MOST RELEVANT CONCLUSIONS - The pressure sensors seem to work satisfactorily regarding the accuracy and the frequency range they can cover. - Of the two types of pressure sensors tested, the Honeywell sensors are found to be more precise, as their range is better suited for the present application. - The temperature of the water must be kept constant, as the Honeywell sensor is influenced by it.Hydraulic EngineeringCivil Engineering and Geoscience

Nauwkeurigheid van ZSTEEN bij golfklappen

In deze studie wordt geevalueerd hoe goed het programma ZSTEEN de stijghoogtes onder een steenzetting, die wordt belast met golfklappen, berekent. Verschillende berekeningen zijn uitgevoerd van de stijghoogtes onder een relatief open toplaag voor reeds gedane proeven in de Deltagoot. Voor 9 extreme golfklappen worden de berekende stijghoogtes vergeleken met de metingen. In de metingen zijn er momenten waarin de stijghoogte op het talud, Phi', onder het taludoppervlak komt. In ZSTEEN wordt als minimale Phi' het taludoppervlak aangehouden. Dit is een foutieve modelaanname. Verder blijkt de exacte spleetpositie geen noemenswaardige invloed te hebben op de berekende stijghoogtes, terwijl het wel een invloed heeft op de blokbeweging. Tevens zijn er nevenconclusies getrokken over de invloed van het 3D karakter van de klappen, de invloed van de geinterpreteerde golf (het aangenomen stijghoogteverloop buiten het meetgebied), oscillaties van de stijghoogtes na de golfklap (waarschijnlijk ten gevolge van het trillen van het talud), de invloed van de traagheid, eventuele hysterese in de weerstandsterm, en de resolutie. De onnauwkeurigheid van de formules waarmee de doorlatendheid van het filter en de toplaag bepaald wordt blijkt een belangrijke bron van fouten te zijn. In de onderzochte golfklappen komen stijghoogteverschillen voor tot 1,0 - 1,4 m, voor golfhoogtes van Hs = 0,94.1 - 1,07 m. De verschillen tussen meting en gekalibreerde berekening hebben een standaardafwijking van 0,13 m. Op basis van deze resultaten kan geconcludeerd worden dat ZSTEEN het vrij goed doet, mits het aangepast wordt zodat rekening gehouden wordt met de mogelijkheid van Phi'-waarden onder het taludoppervlak.Steenzettinge

The current deflecting wall in a tidal harbour with density influences

Siltation is a serious problem for harbours situated on tidal rivers and estuaries. Maintenance dredging is necessary on a regular basis to guarantee safe navigation and is often a large cost factor. A means to prevent sediment from entering a harbour is the Current Deflecting Wall (CDW), which passively alters the water exchange at the harbour entrance. The established beneficiary effects ofthe CDW during rising tide under tidal conditions with homogeneous density are: 1) The mixing exchange between harbour and river is reduced. 2) The water needed for tidal filling is captured by the CDW from the top layer of river water, which contains less sediment. 3) An over-capture of water by the CDW pushes the mixing layer away from the harbour basin. This final thesis presents the findings ofthe experiments on the effect of a Current Deflecting Wall on siltation reduction in harbours. The experiments were executed in the tidal flume at Delft Hydraulics. The experiments were conducted in the framework ofthe European Community's LIP III program. Aim of the study The thesis work had the following objectives: 1) Quantification ofthe effect of a CDW on water exchange between harbour and river under quasi-tidal flow and homogeneous conditions (constant water density, constant discharges through the flume and the harbour). These tests were performed during Phase 1. 2) Investigation ofthe influence of a CDW on water exchange between harbour and river under tidal flow and inhomogeneous conditions (salinity gradients). These tests were performed during Phase 2. 3) Development of the experimental measurement techniques Dye Concentration Measurements (DCM) and Particle Tracking Velocimetry (PTV) for quantification of water exchange between harbour and river. The emphasis ofthe current study was on the second objective because the CDW had not been studied under inhomogeneous conditions before.Hydraulic EngineeringCivil Engineering and Geoscience