Richard Burrows

The management of sediment in combined sewers

Abstract Sediments in sewers are ubiquitous because of the diverse nature of the inputs. Over the past decade or so, new understanding of the provenance, behaviour and nature of sewer solids is now allowing more effective means for solids management. Whilst current computer models are good at representing the hydraulic performance of sewer systems, their handling of sewer solids and associated processes is still embryonic. Hence any attempts to manage in-sewer solids more effectively require a diversity of approaches, both for any modelling studies and for the selection of the most appropriate option. Little information currently exists on which to draw to determine cost-effective or wholelife solutions. Nonetheless significant advances have been made in enhancing the traditional approaches to sewer solids management which have been in use for more than a century.

Lattice Boltzmann model for shallow water flows in curved and meandering channels

Meandering channel flows are simulated using two-dimensional lattice Boltzmann models (LBM) for the shallow water equations. A boundary approach is designed for curved boundary treatment, which is applicable to no-slip, semi-slip and slip boundaries at a second-order accuracy. The large eddy simulation model is added in the lattice Boltzmann model, so that the turbulence can be taken into account and modelled efficiently. The model is verified by three numerical tests: the first two involve flows in meandering channels with 60° and 90° consecutive bends; the third is a 180° sharply curved channel. The numerical results are compared with available experimental data, showing good agreement. This provides a second-order accurate scheme for the LBM to simulate complex flows with curved boundaries.

Morison wave force coefficients for application to random seas

Abstract Results are presented from the analysis of the data collected from the Christchurch Bay Tower Compliant Cylinder when tested in random waves in the De Voorst flume in The Netherlands during 1987. Attention is focused on the use of rigid and flexible member (relative motion) forms of Morisons equation for the estimation of drag and inertia forces under random wave excitation. Notwithstanding some inconsistencies, many attributable to the ill-conditioning of much of the data for Cd determination, the coefficients show reasonable agreement to values obtained from earlier studies. The work suggests that Cd and Cm coefficients from large scale measurements may not be so sensitive to their method of estimation as has previously been thought and that they are applicable to the relative velocity form of the loading mechanism. For non-deterministic analyses, Morisons equation is found to reproduce well the probability distribution of loading associated with given sea state conditions. Furthermore, no simple expansion/extension to the equation has been forthcoming and no mechanistic allowance for history effects or vortex shedding has been found.

Modeling Free-Surface Flow in Rectangular Shallow Basins by Using Lattice Boltzmann Method

The free-surface flows in rectangular basins are studied by the lattice Boltzmann model for shallow-water equations including flow turbulence (LABSWE). Asymmetrical flows occurring in the basins with different ratios of length to width are simulated. The predicted results are compared with corresponding experiments and show reasonable agreement. This indicates that the present model can produce solutions with accuracy similar to the conventional method with an algebraic model for flow turbulence. Furthermore, the effects of the Froude number and bed friction on flow asymmetry and reattachment length are investigated. The results show that the flow becomes less asymmetrical and the reattachment length grows with the increase of either the Froude number or bed friction.

Appraising the extractable tidal energy resource of the UK's western coastal waters

A two-dimensional west coast tidal model, built on the ADCIRC platform (an unstructured grid two-dimensional depth-integrated shallow water model), has been developed to examine the scope for reliable and fully predictable electricity generation from UK coastal waters using an ambitious combination of estuary barrages, tidal lagoons and tidal stream generator arrays. The main emphasis has been towards conjunctive operation of major estuary barrages, initially including the presence of pilot-scale tidal stream developments, though ambitious exploitation of extensive tidal streams has also been explored.

Expected value analysis for the quasi-static response of offshore structures

Abstract A probabilistic description of the quasi-static response of offshore structures to random wave loading has been developed recently in terms of the cross-covariance statistics of the mean-zero and Gaussian distributed particle kinematics at an array of locations beneath the water surface. Implementation of this model was initially restricted by the computational requirements associated with evaluation of certain high order expectations. However, approximations for these expectations have now been developed which enable some relaxation in these restrictions. The procedure employed makes use of standard properties of mean-zero Gaussian random variables and, in particular, application of Prices theorem. The paper presents, for the first time, the complete description of the expected value analysis upon which the model is based.

STATISTICAL MODELLING OF LONG-TERM WAVE CLIMATES

More than 150 tests have been analyzed in order to describe the dynamically stable profiles of rock slopes and gravel beaches under wave attack. Relationships between profile parameters and boundary conditions have been established. These relationships have been used to develop a computer program. This program is able to predict the profiles of slopes with an arbitrary shape under varying wave conditions, such as those found in storm surges and during the tidal period.This paper investigates the utility of winds obtainable from a numerical weather prediction model for driving a spectral ocean-wave model in an operational mode. Wind inputs for two operational spectral wave models were analyzed with respect to observed winds at three locations in the Canadian east coast offshore. Also, significant wave heights obtainable from the two spectral models were evaluated against measured wave data at these locations. Based on this analysis, the importance of appropriate wind specification for operational wave analysis and forecasting is demonstrated.

The UK Christchurch Bay Compliant Cylinder Project : analysis and interpretation of Morison wave force and response data

Abstract The main purpose of the Project was to investigate wave loading on and dynamic response of a compliant (flexible) cylinder in real sea conditions, at a sufficiently large scale (Re>100,000 with Kc

Quasistatic response of offshore structures using probabilistic methods

Abstract Recent research has developed probabilistic descriptions of wave loading on short sections of offshore structure members subject to random wave loading. These descriptions include both short and long term distributions of loading and their peak and extreme values, a knowledge of which is required for the structural design of members. Unfortunately, such a single component of loading is inadequate to effectively model all but the simplest of structural members and an extension of the probabilistic techniques is required to describe structural response, such as stress or deformation, for systems of a large number of loading components. For structures not subject to high dynamic response, there is evidence that the quasistatic response variables are distributed with a similar form to the wave loading, which, in the short term and in the absence of uni-directional currents, is fully described by its second and fourth statistical moments. This paper derives expressions for these moments of the response variables which then enables a similar treatment of response as has been applied to the loading on short sections of structural members. A simple example of a possible application of the method is included.

Management of point source discharges into rivers: Where do environmental quality standards in the new EC‐water framework directive apply?

Abstract The “combined approach” in the new EC‐Water Framework Directive (WFD) consisting of environmental quality standards in addition to emission limit values promises improvements in the quality characteristics of surface waters. However, the specification of where in the water body the environmental quality standards apply is missing in the WFD. This omission will limit its administrative implementation. A clear mixing zone regulation is needed so that the quality objectives of the WFD are not jeopardized. This need is demonstrated using the examples of point source discharges into rivers. Furthermore, water authorities will have to make increased use of predictive modeling techniques for the implementation of the “combined approach”.