280 research outputs found
Experimental study of blockage of random waves by counter currents
No full textFrom February to April 1999, wave-blocking experiments have been conducted at the Laboratory of Fluid Mechanics of the Faculty of Civil Engineering and Geosciences, Delft University of Technology, The Netherlands as a part of the Ph.D. research of I.K. Suastika. Wave blocking is a special case of wave-current interaction. It can occur when waves are propagating against a counter of which the velocity is increasing in the wave propagation direction. Blocking occurs where the intrinsic wave group velocity (cg) is equal, but opposite in sign, to the mean velocity. The counter current velocity at the blocking point is called the blocking velocity. In this thesis the experiments are described and a part of the measurement data is analysed, especially the data concerning the blocking of irregular waves. The first objective of this research is to acquire quantitative data on partial and complete blocking. The second objective is to develop a model for wave blocking. The model should describe the wave field in a situation where blocking occurs. 80, for a given incoming (generated) wave field and counter current, the model should describe the wave field up to and at the blocking point. (And beyond, in cases of partial blocking.)Hydraulic EngineeringCivil Engineering and Geoscience
The isolation of novel Erwinia phages and their use in the study of bacterial phytopathogenicity
No full textSIGLEAvailable from British Library Document Supply Centre- DSC:D171630 / BLDSC - British Library Document Supply CentreGBUnited Kingdo
Evans blue removal from wastewater by rarasaponin-bentonite
No full textThe feasibility of natural bentonite and rarasaponin-bentonite for
Evans blue removal from aqueous solution was studied. Rarasaponin is a
natural surfactant obtained from Sapindus rarak DC was used as
modifying agent for natural bentonite modification. Adsorption
experiments were conducted in a batch system at various temperatures.
Several temperature-dependent isotherm models (Langmuir, Freundlich,
Sips and Toth) were used to represent equilibrium data. It was found
that Toth model represents the adsorption equilibrium data better than
other models. Kinetic data were best represented by the pseudo-first
order model. The controlling mechanism of the adsorption of Evans blue
onto natural bentonite and rarasaponin-bentonite was physical
adsorption
Experimental study of blockage of monochromatic waves by counter currents
No full textBlockage of waves by a current can occur if waves are propagating on a spatially varying opposing current in which the velocity is increasing in the wave propagation direction. The ongoing waves become shorter and steeper while they are propagating against the current. Blocking occurs at the location where the opposing current strength is the same as the effective wave energy transport velocity, the intrinsic wave group velocity. This implies that upstream of this location, the blocking point, there is no propagation of wave energy. A question that immediately arises is what happens with the ongoing wave energy. The theory suggests that the ongoing waves will break before reaching the blocking point due to steepening of the waves. However, other mechanisms than wave breaking may also play an important role in the wave energy dissipation such as energy dissipations due to wave interactions with the turbulence and due to viscous effects. Another possibility is that the ongoing wave energy may be partially reflected at the blocking point. Some earlier studies (e.g. Long et al [1993]) have reported some evidence of wave reflection in blocking situations. The present study aims to investigate experimentally the phenomena of wave breaking and/or wave reflection in blocking situations. For this purpose a novel experimental arrangement has been designed and implemented in a laboratory flume. Previous laboratory studies utilized a constant discharge (Q) and a varying cross section (A) to obtain a longitudinal velocity gradient. This has the disadvantage that the effects of non-uniform cross-section and non-uniform velocity are mixed. In the present study, it was decided to use a constant cross-section and a non-uniform discharge, to he obtained by withdrawal of water through a perforated false bottom. CONCLUSIONS The fitted model has shown to he capable to reproduce the wave field of monochromatic waves being blocked by a counter current reasonably well, allowing us to discriminate the reflected waves and the incoming waves. However, the model in its present form contains unknown calibration coefficients whose variation requires further study and most likely a reformulation of the dissipation model.Hydraulic EngineeringCivil Engineering and Geoscience
Viscous dissipation of monochromatic waves in still water of finite constant depth in a channel of finite width
No full textEnergy dissipation of water waves propagating in a smooth-walled channel of finite water depth and finite width is mainly due to viscous effects. Providing that the wave length is sufficiently large compared to the water depth and a finite channel width, wave energy is principally dissipated in the boundary layers on the bed and on the walls. Hunt [1952] studied the attenuation of periodic water waves travelling in shallow water in a channel of finite width. In the present study we investigate experimentally the wave attenuation of monochromatic waves travelling in still water of finite constant depth in a channel of finite width. In the experiments, we measured the water surface elevation at a number of locations along the flume. First, Fourier analysis is performed to the surface elevation data, in which the surface elevation is represented as a sum of many harmonic components. This analysis is performed to the surface elevation data obtained at each station, resulting in discrete values of wave amplitudes and phase shifts as function of wave travel distance. Next, the values of wave amplitudes and phase shifts so obtained are modelled by using a wave attenuation model in order to estimate the damping modulus K. Finally, the damping modulus K so determined is compared with that calculated using the formulation of Hunt. CONCLUSION The damping modulus representing the wave attenuation determined from the laboratory measurements of Auke - method gives on average slightly higher values of the damping modulus than the values from the theory by Hunt.Hydraulic EngineeringCivil Engineering and Geoscience
A pilot study to test a method to enhance the turbulence of a water flow in a laboratory flume
No full textIn this report we present some results of a laboratory pilot study which has been conducted to test a method to artificially enhance the turbulence of a water flow in a laboratory flume. The purpose of this test is to provide data which will be used to verify whether the method is suitable for the study of the dissipative effects of turbulence on surface waves. In order to study the dissipative effects of turbulence on the surface waves, it is essential to enhance the turbulent intensity of the flow. On the other hand, it is desirable to enhance the shear rates of mean flow, and to generate turbulence of relatively large length scales. A strong interaction between the turbulent motion and the surface waves might be expected in cases where the turbulent length scale is of the same order as the wave length of the surface waves. In this study, we investigate the feasibility of a method to intensify the turbulence of the flow and to establish larger structures ("turbulence") in the flow of length scale of order of the surface waves wave length. For this purpose, we disturb the flow in the flume of smooth walls by constructing a number of rectangular plates at the bottom of the flume. As first estimates, we use plates of height of about 20 percent of the water depth and width of about 20 percent of the flume width. The plates were fastened at the bottom on two rails by using T-shaped chords. It is possible to adjust the orientation of a particular plate by rotating it around the horizontal part of the T-chord and by rotating the T-chord itself on the rail around its vertical leg. Further, it is possible to adjust the distance between two subsequent plates on the rail. However, once the plates have been fastened on the rails, it is not possible to change their orientation and position during a particular test. In this series of experiments, we measured the flow velocity at a number of measurement points in a cross section of the flume. From the velocity measurement, a number of flow parameters are determined: mean velocity,standard deviation(r.m.s.-value of the velocity fluctuation),lateral shear stress and mean rate of shear. From the same measurement, we determine also the auto-correlation function of the flow velocity at each measurement point. In the analysis, these parameters and the plot of the auto-correlation function determined from the measurement in the presence of the plates are compared with those determined from a reference measurement, that is the measurement in the absence of the plates. CONCLUSIONS 1. The presence of the plates in the flume changes the mean longitudinal flow velocity; a decrease near the bottom and an increase at higher elevations. 2. The increase of turbulent intensity caused by the vertical plates is very much larger in the locations near the bottom, slightly smaller in the locations near the free surface and, over the whole cross section, very much larger than that caused by the tilted plates. 3. The increase of magnitude of the Reynolds stress caused by the vertical plates is larger than that caused by the tilted plates. 4. The increase of mean rates of shear caused by the vertical plates is smaller in the locations at higher elevations and larger in the locations near the bottom than that caused by the tilted plates. 5. The plates do not introduce turbulence of larger time scales.Hydraulic EngineeringCivil Engineering and Geoscience
Practising critical architecture
No full textI see architecture not as a property of an object, but as a practise. For this project I have looked critically at the origins of an architect's instruments, methods and notions, and hypothesized how changing these could make them more equipped to deal with my personal understandings of contemporary conditions. Main topics include: Bottom-up, participation, logistics, architect as curator, cultivation and public expression.ExplorelabArchitectureArchitecture and The Built Environmen
Long wave case study for Barbers Point Harbour, Hawaii
No full textThis master thesis project focusses on the numerical modelling of bound and free long wave action in two diffrent harbours. This model, called Surf Beat, is a time dependent generic numerical model for the simulation of generation and propagation of bound long wave energy generated by short carrier waves. This model has been developed by Delft Hydraulics and is part of the hydraulic modelling environment Delft 3D. The carrier wave energy and the corresponding bound wave is calculated at the boundary and transported into the computational domain. The effects generated by refraction and breaking of the carrier waves are all accounted for in the model. Some simulations were also done that also include diffraction of the short wave. The first harbour is located in the Pacific Ocean on the island of Oahu, Hawaii (US). The modelling of this harbour consisted of calibration of the model to this particular situation, sensitivity analysis and some mitigating measures.The second harbour is a bay in South Africa, where a jetty services bulk carriers. The modelling for this harbour consisted of the modelling of the long wave action during four selected storms. The sensitivity analysis done shows that the influence of the directional spreading of the short wave signal influences the results quite significantly. It also showed that bottom frictionHydraulic EngineeringCivil Engineering and Geoscience
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