The following are summaries of papers published in other parts of ICE Proceedings during 2008 that readers of Engineering and Computational Mechanics may find of interest. Summaries of all papers in ICE journals are freely available and fully searchable at the ‘journals on-line’ section of the ICE website. See www.ice.org.uk/journals for details
Pedestrian-induced vibrations of the Clifton Suspension Bridge, UK
J. H. G. Macdonald
Proceedings of the Institution of Civil Engineers, Bridge Engineering, 161, No. 2, June, 69–77, doi: 10.1680/bren.2008.161.2.69
Detailed vibration measurements were taken on the Clifton Suspension Bridge in Bristol, England to define its basic dynamic characteristics in normal conditions and then to assess its dynamic response to crowd loading; 27 vibration modes were identified with natural frequencies below 3 Hz. When subject to crowd loading, quite large lateral vibrations occurred in two modes, with sudden onset. This phenomenon, often termed ‘synchronous lateral excitation’ or ‘pedestrian lock-in’, is similar to the behaviour observed on the London Millennium Bridge and a number of other bridges. Data analysis showed the behaviour to be consistent with the pedestrian negative damping model proposed by Arup in developing a solution for the Millennium Bridge. This model does not, however, explain the underlying mechanism causing the excitation, and a number of observations of the behaviour of the Clifton Suspension Bridge suggest that significant synchronisation of pedestrians did not actually occur. Although synchronisation may occur for large-amplitude vibrations on some bridges, the observations challenge the commonly held view that this mechanism is responsible for the initial rapid onset of lateral vibrations due to crowd loading.
Assessment of concrete half-joints using non-linear analysis
D. Boothman, S. Leckie, I. MacGregor and A. Brodie
Proceedings of the Institution of Civil Engineers, Bridge Engineering, 161, No. 3, September, 141–150, doi: 10.1680/bren.2008.161.3.141
The Kingston Bridge in Glasgow carries traffic across the River Clyde. Carrying an average of around 180 000 vehicles per day, it is one of the busiest bridges in Europe. The approach ramps to the Kingston Bridge include numerous half-joint geometries. These joints were designed in accordance with standards current in the late 1960s. A recent assessment to more onerous modern codes showed that some of the half-joints were not code compliant. In light of this theoretical inadequacy, a destructive load test was undertaken on a typical half-joint on one of the approach ramps that was being demolished and replaced. The data obtained fromthe tested half-joint demonstrated significant capacity above that predicted by the assessment codes. The results of the load tests were used to calibrate a non-linear finite-element model of the tested half-joint. Once confidence in the reliability of the non-linear model was established, various derivative models were used to reassess the half-joints in the Kingston Bridge Complex. This approach justified confidence that the half-joints' actual capacities were significantly greater than those calculated from the assessment codes and that they were sufficient to sustain the assessment loading.
Performance-based seismic design of a continuous bridge
G. Ghosh, Y. Singh and S. K. Thakkar
Proceedings of the Institution of Civil Engineers, Bridge Engineering, 161, No. 4, December, 177–182, doi: 10.1680/bren.2008.161.4.177
Performance-based design (PBD) provides an insight into the expected performance of a designed structure during an earthquake. Over recent decades, considerable development on the PBD of buildings has taken place, but studies regarding the PBD of bridges are limited. This paper examines the estimated performance of a three-span continuous bridge designed using a codal procedure for the site-specific design response spectrum. A three-dimensional model of the bridge was developed using nonlinear modelling of the piers. The response of the bridge was estimated using non-linear static and dynamic procedures. The effect of loading patterns and the accuracy of different pushover analysis methods were examined, and Fema-356 performance levels compared with limit states defined by Kowalsky. The performance of the bridge was studied for different values of the response reduction factor used in the design. The paper also discusses the advantages of PBD and pushover analysis.
Non-linear and linear models in design of retaining walls
A. Grammatikopoulou, H. D. St John and D. M. Potts
Proceedings of the Institution of Civil Engineers, Geotechnical Engineering, 161, No. 6, December, 311–323, doi:10.1680/geng.2008.161.6.311
This paper compares non-linear and linear elasto-plastic models in the numerical analyses of a retaining wall in stiff clay. The paper aims to be applicable to routine design, where often a non-linear elasto-plastic model is not available and instead a linear elasto-plastic model is used. Current guidelines suggest deriving the appropriate linear elastic stiffness from the non-linear soil behaviour, on the basis of the expected straining in the ground. However, it is not always straightforward to choose a representative strain level. The paper presents profiles of linear elastic stiffness, back-calculated to match the maximum wall deflection of the nonlinear analyses in the short term. On the basis of the non-linear soil stiffness–strain curve, the paper then derives a corresponding strain level for each linear elastic stiffness profile. Three different support systems are examined: a single-propped wall, a double-propped wall, and a topdown construction. A number of non-linear stiffness– strain curves are considered for the stiff clay and two K0 profiles are examined.
Stochastic response of underground structures
K. Haciefendioǧlu and A. Bayraktar
Proceedings of the Institution of Civil Engineers, Geotechnical Engineering, 161, No. 6, December, 325–339, doi: 10.1680/geng.2008.161.6.325
This investigation uses a linear elastic finite-element method to analyse the stochastic dynamic response of the Bolu tunnel in Turkey when subjected to spatially varying earthquake ground motion. The research conducts a parametric study to discover the critical magnitude of earthquake ground motion that causes tensile cracking in the reinforced concrete tunnel lining. The Drucker–Prager yield criterion determines the forces that cause cracking of reinforced elements of three cross-sections of the tunnel system subjected to spatially varying seismic ground motion. The study applies spatially varying ground-motion models, wave passage, incoherence and site response as well as the uniform ground-motion model to three cross-sections of the tunnel–soil deposit interaction system. The purpose is to determine the stochastic seismic behaviour of the tunnel. Of particular emphasis is the importance of the site response effect that arises from the difference in the local soil conditions at the different support points of the tunnel–soil deposit interaction system. The results of the analyses demonstrate that the number of cracked elements increases as the amplitude of earthquake ground motion increases. In addition, the means of the maximum values obtained from the spatially varying ground-motion case are compared with those of specialised earthquake ground-motion models. The result is proof that variations in local soil conditions have important effects on the stochastic response of tunnels.
Modelling embankments reinforced with sand columns
M. Sathishbalamurugan and B. Muhunthan
Proceedings of the Institution of Civil Engineers, Ground Improvement, 161, No. 2, May, 71–78, doi: 10.1680/grim.2008.161.2.71
Numerical simulation of the deformation characteristics of an embankment on weak clay reinforced with stone columns was carried out using FLAC 3D software. The problem was also analysed by using equivalent critical-state parameters of the composite ground. The results of the equivalent parameter model are found to correlate well with the analysis of the original configuration. The numerical analyses show that improvement in vertical as well as lateral displacement of the embankment is very much dependent on the location and extent of the sand columns. The displacement pattern of unimproved ground is shown to be useful for economical placement of the sand columns in this regard. The numerical results also show that, beyond 40% improved area ratio, very little improvement in displacement is achieved.
Modelling and acoustic monitoring of grout propagation in sands
N. Saiyouri, L. Jason, O. Chupin and P. Y. Hicher
Proceedings of the Institution of Civil Engineers, Ground Improvement, 161, No. 3, August, 143–152, doi: 10.1680/grim.2008.161.3.143
Grouting is generally used for ground reinforcement or for reducing soil permeability. However, choosing grouting parameters or predicting improvements is at present rather empirical. A numerical approach may therefore enable grouting to be more efficient. The purpose of this paper is to model the evolution, in time and space, of two major variables: grout concentration and fluid pressure in grouted soil. After a brief description of a first tried diffusive model, this study aims to describe the performance of a software program, Athos. This program was initially developed for the oil industry and uses a piston model. Results are given in one- and three-dimensional approaches. They underline a rapid evolution of concentration from grout-saturated zones to non-saturated zones. The evolution of pressure depending on this degree of saturation is also highlighted. The second part of the paper compares the numerical model with a series of experiments carried out on grouted sand columns and in saturated sand tanks. In the latter tests, the grout is injected into the sand using a sleeved grout pipe, and the progress of grout propagation in the soil is monitored by acoustic emission (AE). This comparison shows the validity of the chosen model. The permeation distance detected by AE is compared with that predicted by simple grout propagation models.
Modelling effects of realignment of Keelung River, Taiwan
W.-C. Liu, W.-B. Chen and C. H. Wu
Proceedings of the Institution of Civil Engineers, Maritime Engineering, 161, No, 2, June, 73–87, doi: 10.1680/maen.2008.161.2.73
A three-dimensional hydrodynamic model was implemented and applied to the Danshuei River estuarine system and its adjacent coastal sea in northern Taiwan. The model was calibrated and verified with the available hydrological data measured in 2000. A detailed model calibration and verification was performed using field data which consisted of the measured amplitudes and phases of five tidal constituents, water surface elevations, tidal current and salinity distributions. The overall performance of the model was in qualitative agreement with the field data. The validated model was then used to investigate the changes in salt water intrusion and residual circulation as a result of channel regulation in the Keelung River. The residual circulations before channel regulation differed slightly from those after channel regulation and the result for the limits of salt intrusion before channel regulation were only slightly different from those after channel regulation. At the Kuan-Du wetland, the saline difference was only 0·3 parts per thousand. These results suggest that the channel regulations for flood control in the Keelung River made no substantial contribution to the expansion of the mangrove areas and disappearance of freshwater marshes in the the Kuan-Du wetlands.
Finding safe routes to school using optimisation methods
P. Wackrill and C. Wright
Proceedings of the Institution of Civil Engineers, Municipal Engineer, 161, No. 2, June, 117–127, doi: 10.1680/muen.2008.161.2.117
Encouraging children to walk to school has become an important issue. Government agencies are therefore keen to reduce child pedestrian casualties associated with the school journey. One way forward is to provide each catchment area with a system of designated routes that minimise road accident risk for pupils on foot. However, there is no accepted modelling procedure for identifying safe routes. This paper reviews the obstacles and assesses the potential for ad hoc solution methods, using the road network surrounding a primary school in north London as a test bed. Solutions close to the optimum were obtained by transforming the network to a simpler form and by modifying the objective function, which effectively linearised the problem. This paper assesses the sensitivity of the results to various assumptions and uncertainties in the data, and concludes with a brief comment on the prospects of finding safe routes on a routine basis at local authority level.
Dweller perception using fuzzy logic for slum upgrading
O. B. Moraes and A. K. Abiko
Proceedings of the Institution of Civil Engineers, Municipal Engineer, 161, No. 3, September, 151–161, doi: 10.1680/muen.2008.161.3.151
A large number of initiatives in cities in Brazil—including slum clearance and upgrading—have been undertaken over the years in an effort to ameliorate the problems arising from informal occupation; unfortunately, however, little is known about the related performance outcomes. Careful appraisal of the results of such initiatives is thus called for, covering evaluations of dwellers' perceptions of the upgraded environments. Among the available evaluation methods, post-occupancy evaluation (POE) is commonly employed, although it fails adequately to reflect prevailing subjective concepts of quality. The present paper contains the partial findings of a research exercise aimed at developing an original method, using fuzzy logic, for urban environmental quality evaluation in informally occupied areas on the basis of combining quantitative indicators and dweller perception. It combines POE with fuzzy logic in order to develop tools that can better model the uncertain information that emerges from that kind of study. This paper aims to introduce an uncertainty measure used in order to identify the strengths and weaknesses of slum upgrading projects. The results show that it is possible to quantify certainty degrees in the findings and to define if additional information is needed.
Neural network modelling of RC deep beam shear strength
K.-H. Yang, A. F. Ashour, J.-K. Song and E.-T. Lee
Proceedings of the Institution of Civil Engineers, Structures and Buildings, 161, No. 1, February, 29–39, doi: 10.1680/stbu.2008.161.1.29
A9 × 18 × 1 feed-forward neural network (NN) model trained using a resilient back-propagation algorithm and early stopping technique is constructed to predict the shear strength of deep reinforced concrete beams. The input layer covering geometrical and material properties of deep beams has nine neurons, and the corresponding output is the shear strength. Training, validation and testing of the developed neural network have been achieved using a comprehensive database compiled from 362 simple and 71 continuous deep beam specimens. The shear strength predictions of deep beams obtained from the developed NN are in better agreement with test results than those determined from strut-and-tie models. The mean and standard deviation of the ratio between predicted capacities using the NN and measured shear capacities are 1·028 and 0·154, respectively, for simple deep beams, and 1·0 and 0·122, respectively, for continuous deep beams. In addition, the trends ascertained from parametric study using the developed NN have a consistent agreement with those observed in other experimental and analytical investigations.
Statistical analysis of structural vibrations due to crowd jumping loads
J. Sim, A. Blakeborough and M. S. Williams
Proceedings of the Institution of Civil Engineers, Structures and Buildings, 161, No. 2, February, 65–75, doi: 10.1680/stbu.2008.161.2.65
This paper presents an analysis method for the response of an assembly structure such as a grandstand to simulated crowd jumping loads. The structure is initially modelled as a single-degree-of-freedom (SDOF) system and then modified by the addition of a two-degree-offreedom (2DOF) model of a passive standing crowd. A statistical approach is used in order to represent realistically the natural variability in the jumping loads. The paper outlines how to simulate individual jumping loads based on a statistical model developed elsewhere. The response of the joint crowd–structure system to the jumping loads is then obtained and presented in graphical form. These results give a first estimate to the response of cantilever grandstands due to crowd jumping loads. An example is presented, the various factors affecting the structural response owing to crowd jumping loads are discussed and the limitations of the results considered.
The continuous strength method
L. Gardner
Proceedings of the Institution of Civil Engineers, Structures and Buildings, 161, No. 3, June, 127–133, doi: 10.1680/stbu.2008.161.3.127
Many of the principal concepts that underpin current metallic structural design codes were developed on the basis of bilinear (elastic, perfectly-plastic) material behaviour; such material behaviour lends itself to the concept of section classification. The continuous strength method represents an alternative treatment to crosssection classification, which is based on a continuous relationship between slenderness and (inelastic) local buckling and a rational exploitation of strain hardening. The development and application of the continuous strength method to structural steel design is described herein. Materials that exhibit a high degree of nonlinearity and strain hardening, such as aluminium, stainless steel and some high-strength steels, fit less appropriately into the framework of cross-section classification, and generally benefit to a greater extent from the continuous strength method. The method provides better agreement with test results in comparison to existing design codes, and offers increases in member resistance and a reduction in scatter of the prediction. An additional benefit of the proposed approach is that cross-section deformation capacity is explicitly determined in the calculations, thus enabling a more sophisticated and informed assessment of ductility supply and demand. Further developments to the method are under way.
A new lateral force distribution formula for base isolated structures
F. Khoshnoudian and S. Esrafili
Proceedings of the Institution of Civil Engineers, Structures and Buildings, 161, No. 5, October, 277–297, doi: 10.1680/stbu.2008.161.5.277
It has been suggested that the static lateral response procedure for a base-isolated structure presented in the International Building Code (IBC) somewhat overestimates the seismic storey force. In this paper an IBC-equivalent static method for base-shear distribution of seismic isolated structures is evaluated. The results of the equivalent static procedure in the vertical distribution of base shear are compared with results obtained from dynamic linear and nonlinear analysis and the efficiency of its application is studied. In general, the results of the equivalent lateral response procedure in the proposed triangular distribution of base shear are somewhat conservative. Based on linear and nonlinear analysis results of isolated structures, therefore, two new formulae are proposed for the vertical distribution of the base shear. The proposed linear formula is based on the first mode shape of the isolated structure and the nonlinear formula follows three first mode shapes, which imply contribution of higher modes in a more realistic nonlinear analysis. The accuracy of the new formulae is examined by comparing the results obtained from this study with those calculated from linear and nonlinear time history analysis.
Modelling of bonded post-tensioned concrete slabs in fire
E. A. M. Ellobody and C. G. Bailey
Proceedings of the Institution of Civil Engineers, Structures and Buildings, 161, No. 6, December, 311–323, doi: 10.1680/stbu.2008.161.6.311
This paper presents a finite element model highlighting the behaviour of bonded post-tensioned one-way spanning concrete slabs in fire conditions. The model was verified against ten fire tests on bonded post-tensioned concrete slabs at ambient and elevated temperatures. The slabs were simply supported and post-tensioned with 15·7 mm nominal diameter seven-wire mono-strand tendons. The mechanical and thermal material non-linearities of the entire slab's components, consisting of the concrete, plastic and galvanised steel ducts, prestressing tendon and the anchorages, have been carefully inserted into the model. The interface between the tendon and surrounding grout was also considered, allowing the bond behaviour to be modelled and the tendon to retain its profile shape during the deformation of the slab. The temperature distributions throughout the slab, together with the slab's development of displacement and stress, as it was heated, were predicted by the model and verified against test data. A parametric study was conducted to investigate the effects on the global structural behaviour owing to the change in the aggregate type, duct type, load ratio, boundary conditions and different fire scenarios. The study has shown that the bonded post-tensioned concrete slabs investigated in this study are capable of achieving the designed 90 min fire resistance. It is also shown that the fire resistance given by BS 8110–2 and BS EN 1992–1–2 are acceptable for the design of bonded post-tensioned one-way spanning concrete slabs under fire conditions.
Probabilistic analysis of train–track vertical impact forces
J. Leong and M. H. Murray
Proceedings of the Institution of Civil Engineers, Transport, 161, No. 1, February, 15–21, doi: 10.1680/tran.2008.161.1.15
As part of a project developing a new limit states design method for prestressed concrete railway sleepers, extensive measurements were conducted of vertical impact forces exerted by trains on track. The vertical impact forces due to defects in the train wheels were found to occur randomly and followed an exponential distribution with time. This distribution is used to predict return periods for various levels of impact forces, needed for limit states design of sleepers. The effect of train speed was studied and showed that doubling the speed of a train would increase impact forces by about 140% for a wide range of return periods, but increasing the return period from 25 years to 200 years increased the impact force by only 10 to 15%. Applying a proposed cumulative damage model to the Monte Carlo method, it was found that the return period used for potential design of sleepers had little effect on the rate of sleeper failure in the period up to 20 years sleeper age, but that the return period had a large effect after that time.
An optimisation model for prioritising transport projects
A. Ahern and G. Anandarajah
Proceedings of the Institution of Civil Engineers, Transport, 161, No. 3, November, 221–230, doi: 10.1680/tran.2008.161.4.221
The decision of how much to invest in the development of transportation projects is very important. Optimisation tools are commonly used to prioritise investment in transportation networks. The objective of this study was to develop an optimisation model that will prioritise and rank investment in transportation infrastructure. The model was developed using data from the Department of Transport in Ireland. The concept of the ideal solution has been used. This is a multi-objective model, giving more than one optimal solution. The research concludes that weighting assigned by the user to the attributes is crucial in the prioritisation process when the attributes are numerous.
A simulation model for generating alternative scenarios
J. R. Ottensmann
Proceedings of the Institution of Civil Engineers, Urban Design and Planning, 161, No. 3, September, 131–140, doi: 10.1680/udap.2008.161.3.131
The luci2 urban simulation model simulates new urban development for a large region in central Indiana (USA) that includes multiple metropolitan areas. The model has been developed for use by persons without specialised expertise. It is freely distributed and may be downloaded from the Internet. Land use data for the model have been estimated from satellite imagery. Aggregate logit models have been estimated and are used to predict the probabilities of land being converted from non-urban to residential and employment-related uses for 1609-meter grid cells. A key feature of the model is the capability to generate alternative development scenarios reflecting a range of policy choices and assumptions regarding future development, ranging from the imposition of development restrictions to changes in densities of development to different overall rates of population growth. The model and its capabilities to produce alternative scenarios have been applied in a variety of planning contexts.
Simulation of municipal solid waste reactors using Moduelo
A. Lobo, A. López, N. Cobo MEng and I. Tejero
Proceedings of the Institution of Civil Engineers, Waste and resource management, 161, No. 3, August, 99–104, doi: 10.1680/warm.2008.161.3.99
The biodegradation and settlement of two consolidating municipal solid waste (MSW) anaerobic reactors operated at Southampton University, UK, were modelled with the Moduelo landfill simulation tool. This paper presents the fundamental concepts of the model, the difficulties found in its application to the studied case and the simulation results obtained. The significant difference found between the rates of anaerobic processes that took place in the field in relation to those in the laboratory required the reduction of the default simulation time step of the model and the introduction of a new parameter to represent the delay in the onset of methanogenesis so that it became predominant after rapid hydrolysis was experienced. Once calibrated by fitting the evolution of the organic content of the leachate during the start-up period (the first 77 days), the model was used to predict leachate concentration, gas generation and composition and settlement of the waste mass throughout the experimental period (919 days). The predicted results will be compared with actual data and discussed in another paper. The exercise here constitutes a basis for reflection on the model's structure and applicability, and serves as a reminder of the difficulty of representing field (landfill) conditions in a laboratory.
Modelling the landfill process using GasSim2
H. Clewes, E. Fuggles and R. G. Gregory
Proceedings of the Institution of Civil Engineers, Waste and resource management, 161, No. 3, August, 105–111, doi: 10.1680/warm.2008.161.3.105
The prediction of landfill gas generation is an important exercise for both operators and regulators of landfill sites. The GasSim2 model, developed for this purpose by Golder Associates (UK) Ltd on behalf of the Environment Agency, is used to predict gas generation and subsequent emissions to air and land in order to assess whether emissions exceed acceptable limits. A number of other models for the prediction of landfill processes exist, and they have evolved significantly over the last decade. In order to compare individual models' strengths and weaknesses and therefore enable further development, a formal framework was designed by researchers at Southampton University. A challenge was set to modelers to predict the performance of a laboratory experiment on biodegradable waste. The data provided, including waste composition, cellulose and hemicellulose content, leachate recirculation and experimental layout, were manipulated to fit into GasSim2. A number of difficulties were experienced in modelling, including scaling the laboratory experiment to the required scale of the model, categorisation of the waste stream and the length of the model timestep. Model results indicate a potential for gas production of 17·7–47·6m3/t dry waste per year initially, decreasing over time.
Modelling decomposition of MSW using genetic algorithms
T. Reichel and A. Haarstrick
Proceedings of the Institution of Civil Engineers, Waste and Resource Management, 161, No. 3, August, 113–120, doi: 10.1680/warm.2008.161.3.113
This paper arose in response to the challenge to landfill modellers developed by the waste management research group of the school of civil and environmental engineering of the University of Southampton (WMRG). Data on the setup and operational procedures of the experiment were provided to modellers; the aim was to make predictions over time of different topics. The model POSE (parametric optimization and simulation of emission) was used to accomplish the task. This model is focused on local reaction processes governed by environmental factors in wastes to predict gas production and evolution of leachate chemistry. The paper provides an overview of the modelling approach and explains the basics of genetic algorithms used in the model. The use and modelling of input data are described and the obtained simulation results are presented. Based on this, predictions of gas formation and leachate chemistry evolution are shown. A comparison of the predicted and monitored data was performed by WMRG and is reported elsewhere.
The application of LDAT to the HPM2 challenge
J. K. White
Proceedings of the Institution of Civil Engineers, Waste and Resource Management, 161, No. 4, November, 137–146, doi: 10.1680/warm.2008.161.4.137
The challenge laid down to landfill modellers at the 4th Intercontinental Landfill Research Seminar in June 2006 was to see to what extent modellers could predict experimental results from a closely monitored anaerobic degradation laboratory experiment when given only the initial conditions. This paper presents results from the University of Southampton landfill degradation and transport (LDAT) model. The LDAT model uses chemical pathways for degradation of carbohydrates, fats and protein. When waste solids are described using the descriptors food, green waste, paper and textiles, LDAT converts these into carbohydrates, fats and protein. LDAT also accommodates pathways that proceed at different rates. The stoichiometric equations on which the LDAT degradation chemistry is currently based are used independently of LDAT to predict the gas yield that might be expected from the data that have been derived for the carbohydrate, protein and fat components. The more difficult question of estimating the timescale over which the gas emerges is also addressed. The paper gives details of the bacteria population growth rates, half-saturation constants, yield coefficients and initial bacteria masses used to obtain the reaction rates for the degradation pathways. LDAT tracks the depth of the sample which reduces with time in response to the degradation of the solids. These results are given and compared with the settlement implied by the gas yield calculations.
CFD modelling of meandering channel during floods
D. R. Shukla and K. Shiono
Proceedings of the Institution of Civil Engineers, Water Management, 161, No. 1, February, 1–12, doi: 10.1680/wama.2008.161.1.1
The three-dimensional Reynolds-averaged Navier–Stokes (RANS) and continuity equations are solved using a standard computational fluid dynamics (CFD) solver to predict flow in a compound meandering channel. Highquality experimental data from the UK Flood Channel Facility (FCF) are used to validate the computational results. The flow velocities, free-surface elevation, bed shear stress and turbulent kinetic energy are predicted reasonably well. The measured and predicted flows are analysed qualitatively and quantitatively to improve further understanding of mean flow, turbulence and secondary flow structures in a compound meandering channel. The streamwise component of the mean vorticity equation is used to quantify the behaviour of secondary flow circulations in terms of their generation, development and decay along the meandering channel. The turbulent kinetic energy equation is used to understand energy expenditure mechanisms of secondary flow circulations. The numerical results show that one of the shear stresses significantly contributes towards the generation of the streamwise vortex and the production rate of turbulent kinetic energy.
Benchmarking 2D hydraulic models for urban flooding
N. M. Hunter, P. D. Bates, S. Neelz, G. Pender, I. Villanueva PhD, N. G. Wright, D. Liang, R. A. Falconer, B. Lin PhD, S. Waller, A. J. Crossley and D. C. Mason
Proceedings of the Institution of Civil Engineers, Water Management, 161, No. 1, February, 13–30, doi: 10.1680/wama.2008.161.1.13
This paper describes benchmark testing of six two dimensional (2D) hydraulic models (DIVAST, DIVASTTVD, TUFLOW, JFLOW, TRENT and LISFLOOD-FP) in terms of their ability to simulate surface flows in a densely urbanised area. The models are applied to a 1·0km_0·4 km urban catchment within the city of Glasgow, Scotland, UK, and are used to simulate a flood event that occurred at this site on 30 July 2002. An identical numerical grid describing the underlying topography is constructed for each model, using a combination of airborne laser altimetry (LiDAR) fused with digital map data, and used to run a benchmark simulation. Two numerical experiments were then conducted to test the response of each model to topographic error and uncertainty over friction parameterisation. While all the models tested produce plausible results, subtle differences between particular groups of codes give considerable insight into both the practice and science of urban hydraulic modelling. In particular, the results show that the terrain data available from modern LiDAR systems are sufficiently accurate and resolved for simulating urban flows, but such data need to be fused with digital map data of building topology and land use to gain maximum benefit from the information contained therein. When such terrain data are available, uncertainty in friction parameters becomes a more dominant factor than topographic error for typical problems. The simulations also show that flows in urban environments are characterised by numerous transitions to supercritical flow and numerical shocks. However, the effects of these are localised and they do not appear to affect overall wave propagation. In contrast, inertia terms are shown to be important in this particular case, but the specific characteristics of the test site may mean that this does not hold more generally.
Determining water surface elevation in tidal rivers by ANN
A. Adib
Proceedings of the Institution of Civil Engineers, Water Management, 161, No. 1, February, 83–88, doi: 10.1680/wama.2008.161.1.83
Fluvial flows and tidal flows are governing on tidal rivers while fluvial flows are governing on non-tidal rivers alone. In addition to analytical and numerical models, stochastic methods must be considered to determine water surface elevation at the tidal limit of tidal rivers because hydraulic routing of this reach is very complex. In the present research, the neural network method was considered for determination of water surface elevation at the tidal limit of tidal rivers. The artificial neural network (ANN) method was trained using results from a suitable numerical model. The results of the ANN method were compared with results for the governing regression relation for water surface elevation at the tidal limit of tidal rivers. The ANN method was applied to the Karun river in Iran and the River Severn in the UK. The ANN method was found to produce water surface elevations for different combined return periods in the Karun river and the River Severn.
Modelling of lake–groundwater interaction in Turkey
I. I. Soyaslan, A. Dogan and R. Karaguzel
Proceedings of the Institution of Civil Engineers, Water Management, 161, No. 5, October, 277–287, doi: 10.1680/wama.2008.161.5.277
A regional steady state groundwater flow model was developed for the Yalvac basin located in the watershed of Lake Egirdir, the second largest freshwater lake in Turkey. Determination of lake–groundwater interaction is an important step in taking proactive measures for optimal and beneficial use of water resources from the water management perspective. The geological structure around the lake and its surrounding aquifer system makes the modelling challenging. The hydrogeologic units in the groundwater system exhibit both confined/unconfined conditions: they are not horizontal, yet some of them are nearly vertical, which does not allow use of the ‘horizontal-layer’ concept of Modflow. The model demonstrated that it is a useful tool for planning and managing the water resources in the region by determining immeasurable components of classical water budget calculations, the groundwater inflow/outflow components, which are generally required for management of lakes. The groundwater discharge to Lake Egirdir through the Yalvac basin was estimated by means of the model. Two scenarios of hypothetical drought and wet conditions were simulated and evaluated from water resources management and groundwater–lake interaction perspectives.
Computer modelling of graded sediments in rivers
A. B. Shvidchenko and G. Pender
Proceedings of the Institution of Civil Engineers, Water Management, 161, No. 5, October, 289–297, doi: 10.1680/wama.2008.161.5.289
This paper reports on current engineering capability to simulate the behaviour of graded sediments in rivers using one-dimensional computer models. Emphasis is placed on non-equilibrium conditions when the bedload transport rate, bed elevation and composition of the bed material are changing with time. The model used is typical of those available to practicing engineers. A general description is given and comparisons are made of the model's ability to reproduce available laboratory and field data. The performance of four sediment transport equations (Ackers and White, Meyer-Peter and Muller, White and Day, Parker) in predicting graded sediment movement is assessed by comparison with the measured data. Of these equations, the first two were originally developed for application to uniform sediment and do not account for size fraction interaction, while the other two take account of sediment grading. The test simulations demonstrate that the use of the Parker equation provides the best overall agreement with the measured data, while the use of the other equations provides inadequate prediction in the case of graded sediments. It is concluded that an adequate computer simulation of long-term trends in the behaviour of graded sediments is only possible if size fraction interaction in the sediment mixtures is accounted for in the sediment transport equation used.
