1642 research outputs found
Sort by
Sandwaves and megaripples at Race Bank (UK) Offshore Wind Farm
Get PDFThe Race Bank Offshore Windfarm is part of the UK Round 2 extension. The windfarm comprises 91 6.3 MW turbines and two substations with total installed power of 573 MW. Construction work is scheduled for 2016/17. The windfarm is located in UK waters in the southern part of the North Sea about 30 km north of the Norfolk coastline and 30 km east of Lincolnshire. The Race Bank site has a diverse morphology located on large sandbanks with mobile sandwaves and megaripples and intersected by deeper featureless swales where clay soil formations are found close to or at the sea floor. The morphological complexity of the site was recognised early in the project development and numerous bathymetric surveys have been undertaken to help quantify sandwave migration rates and expected seabed variability. Morphological seabed assessments have been conducted by ABPmer throughout the project development. In the detailed design phase the ABPmer assessments have been combined with in-house DONG Energy analysis to provide design seabed levels and anticipated ranges of natural seabed changes within the lifetime of the windfarm. The paper presents an overall morphological characterisation of the windfarm site and provides examples of the very diverse seabed morphology encountered. When quantified, the morphological diversity can be absorbed in the monopile foundation design and cable installation contractors can select appropriate installation tools. The paper thus comes with a recommendation to ensure that bathymetric surveys in morphological active sites are carried out early and repeatedly during the project development stages
Suffusion susceptibility characterization by triaxial erodimeter and statistical analysis
Get PDFSuffusion process corresponds to the coupled processes of detachment-transport-filtration of the soil’s fine fraction within the voids between the coarse fraction. Because of the great length of earth structures and because of the heterogeneities of soils, it is very difficult to characterize the suffusion susceptibility of soils all along the earth structures. So, a statistical analysis can be performed in order to optimize the experimental campaign. By using a specific triaxial erodimeter, an experimental program was setup to study suffusion susceptibility of thirty two specimens. The suffusion susceptibility is determined by the erosion resistance index. Ten physical parameters are determined and a statistical analysis is performed in order to identify the main parameters for a correlation with erosion resistance index. The multivariate statistical analysis leads to an expression of the erosion resistance index as a function of eight physical parameters, and by distinguishing the gap-graded and widely-graded soils, another new correlation is obtained with five physical parameters
Determination of optimum wave reflection of seawalls via experimental modeling
Get PDFThis paper presents and discusses the results of experimental investigations using both vertical and sloping seawalls configurations to determine the optimal wave reflection characteristics of seawalls for protecting beaches against erosion under a variety of hydrodynamic conditions. The different experiments include both of rectangular or triangular serrated blocks and slotted seawalls with or without triangular serrations as energy dissipaters. The linear wave theory is utilized. Moreover, the Dalrymple method is considered to predict the ordinates of the resultant standing wave due to the partial wave reflection. The study shows that the usage of slotted seawall with triangular serrations is superior compared to the other suggested energy dissipaters in reducing wave reflection whenever the waves become longer. The findings of the present investigation could be applied to optimize the design criteria of shore protection structures
Development and verification of a finite volume model for hydraulics over multi-layered erodible beds
Get PDFThe accuracy and efficiency of a class of finite volume methods are investigated for numerical solution of morphodynamic problems in multi-layered beds. The governing equations consist of two components, namely an hydraulic part described by the shallow water equations and a sediment part described by the transport and suspended sediments equations. To allow exchange between layers in the bed we propose an equation of balance laws for the bed elevation. As a numerical solver we consider a modified Roe method in the finite volume framework. A well balanced discretization is also used for the treatment of the source terms. The method is well-balanced, non-oscillatory and suitable for both near- and far-bed simulations in sediment transport. The proposed model is verified for a dam-break problem over erodible multi-layered bed and the obtained results demonstrate it abilities to resolve the vertical features in multi-layered sediment transport problems
Scour patterns below pipelines and scour hole expansion rate
Get PDFThis paper presents the results of an experimental study on the onset of scour and the propagation of scour hole on the cross-section of a partially buried pipeline under a unidirectional current with uniform sediment. A specially designed device including a transparent pipeline with a mini underwater camera installed inside it is utilized to observe and record the whole scour process. The scour below the pipeline can be divided into an integral scour pattern and a partial scour pattern. In both patterns, the seepage force is the main cause of the onset of scour. However, the scour hole expansion process is driven by the seepage force in the integral scour pattern, while in the partial scour pattern it is driven by the bed shear stress. The effects of pipeline embed-ment, flow depth and the averaged flow velocity on the averaged cross-section expansion rate of the scour hole are also evaluated
Scour and Erosion: Proceedings of the 8th International Conference on Scour and Erosion (Oxford, UK, 12-15 September 2016)
No full textThe 8th International Conference on Scour and Erosion (ICSE 2016) was organised by HR Wallingford, Oxfordshire, UK and held at the Mathematical Institute, Andrew Wiles Building, The University of Oxford from 12 to 15 September 2016. Contributions were received across eight principal themes: internal erosion, sediment transport, grain scale to continuum scale, advanced numerical modelling of scour and erosion, terrestrial scour and erosion, river and estuarine erosion including scour around structures, coastal and offshore scour and erosion and, management of scour/erosion and sediment (including hazard management and sedimentation in dams and reservoirs). The conference included four keynote lectures from world leading academics and practitioners cutting across the themes of scour and erosion, together with 132 peer-reviewed papers from 34 countries
25 years of fixing bridges on gravel mined rivers in California (Keynote)
Get PDFThe degradation caused by instream and off channel gravel mining and its resultant impact on bridges is investigated. Three case studies in California are utilized to illustrate the cost of fixing bridges impacted by channel bed degradation. Revisions to California regulations are suggested to increase awareness and decrease taxpayer costs
Putting fish in the tank: An Agent Based Model with flow interaction
Get PDFAn Agent Based Model (ABM) coded in Matlab is described in which fish (or other marine creatures) are introduced into the 3D underwater flow domain modelled by TELEMAC. The released fish individuals are preassigned a set of physiological characteristics and behavioural traits and are then free to swim and interact with each other in the flow field environment. The model is particularly designed to model potential impacts on marine organisms due to anthropogenic induced stresses, such as caused by underwater noise and/or interaction with power station intakes or hydro-power turbines. A description of the algorithms is given followed by an example of how the ABM can be used to assess the potential stress exerted on fish populations due to underwater noise generated from pile driving during construction of a hypothetical offshore windfarm. Future developments of the model will also be described
Rock scour in Australia: some latest Queensland experiences
Get PDFFrom 2010, a succession of floods in eastern Australia, and particularly in Queensland, brought about spillway operation at high head dams with return periods in the region of Annual Exceedance Probabilities (AEP) of up to 1 in 2,000 years. As such, a number of spillways experienced extensive scour of rock downstream – including Boondooma Dam and Paradise Dam – the subject of the present paper. For both dams, part of the scour assessment process has been to utilise a large-scale physical model to obtain transient data which, together with the detailed geologic assessment, have been incorporated into the numerical scour modelling procedures developed by Dr Erik Bollaert. This paper will first of all describe the features of the 2011 and 2013 flood events at both dams, as well as the resulting rock scour and damage on both spillways and the geology of the rock area below. The paper will then go on to describe the computational scour modelling procedures of calibration and application, used in conjunction with a large-scale physical model of both dam and spillway, demonstrating a “system” approach to spillway scour analysis for plunge pools and similar situations with energy dissipation on natural materials
The human factor in an effective structure management system
Get PDFThis paper demonstrates that while an effective structure monitoring system benefits strongly from the integration of modern technologies, human experience and oversight remain the essential component. The myriad of technologies available for structure monitoring and management are improving at a great rate. These technologies provide analysis and oversight at levels which historically have been uneconomical or unachievable. A single instance of the DamWatch application is providing real-time, always-on monitoring of 12,000 dam structures for 3,000 users in the United States (Caldwell, Scannell, & Herbert, 2014). Automated systems can tirelessly monitor data feeds, rapidly perform complex calculations and dispatch notifications. However, this paper argues that the impacts of this growing role for technology, while powerful, is still superseded by the impacts of the human input in structure management systems. An optimal structure management system should be designed with this in mind. This includes ensuring data is complete and accurate, easily accessible and understandable for users. User contribution and involvement in structure management systems should not be limited by an individual’s computer literacy. Users should be trained and supported to ensure they are able to react to and leverage data provided by information systems. Clearly defined protocols allow individuals to make informed decisions and organizations to respond promptly to developing situations. To assess these arguments we will examine a number of case studies. These case studies will focus on hydrologic events which affected bridge and dam structures in the care of multiple, unrelated managing authorities. By exploring the incidents, the responses and the eventual outcomes, we will weigh the role of human data in the effective management of structures exposed to the natural environment