## About

207

Publications

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Introduction

Prof Tanyimboh's research focuses on novel computational solution methods for water and environmental systems, e.g. urban drainage, combined sewers, water distribution, water resources, infrastructure resilience and climate adaptation. Uncertainty, risk and systems-oriented methods are addressed also. Pioneering research on water distribution networks includes design optimization, pressure-driven analysis, reliability, failure tolerance and information-theoretic flow entropy methods.

Additional affiliations

March 1993 - September 2005

Education

October 1989 - July 1993

October 1984 - July 1988

## Publications

Publications (207)

The application of the analytic hierarchy process (AHP) to help select the best option for the long-term design and upgrading of a water distribution network is described and applied to a real-world network. The main criteria used are: reliability-based network performance; present value of construction, upgrading, failure, and repair costs; and so...

Finding low-cost designs of water distribution systems (WDSs) which satisfy
appropriate levels of network performance within a manageable time is a complex problem
of increasing importance. A novel multi-objective memetic algorithm (MA) is introduced as a
solution method to this type of problem. The MA hybridises a robust genetic algorithm (GA)
wit...

Water quality models are increasingly being routinely used to help ascertain the quality of water in drinking water
distribution systems for design and operational management purposes. Conventional water quality models are
demand driven and consequently do not incorporate the effects of any deficiency in pressure on the water quality
throughout the...

Several hydraulic modelling approaches have been proposed previously to simulate pressure-deficient operating conditions in water distribution networks more realistically. EPANET-PDX is a pressure-driven extension of the EPANET 2 hydraulic simulation model that has an embedded logistic nodal head-flow function. The pressure-driven analysis algorith...

The informational entropy model for flow networks was formulated over 30 years ago by Tanyimboh and Templeman (University of Liverpool, UK) for a single discrete operating condition that typically comprises the maximum daily demands and was undefined for water distribution networks (WDNs) under multiple operating conditions. Its extension to includ...

Evolutionary algorithms (EAs) have been used extensively for the optimal design of water distribution networks (WDNs). There is evidence in the literature that search space reduction is highly effective. However, practical methods that do not introduce extra computational requirements are lacking. A dynamic search space reduction methodology is pro...

Water distribution network optimization problems have been solved previously for hydraulic and cost efficiency. However, more researchers are attempting to include other important design objectives. This, however, further increases the complexity of these problems. For example, there are multiple water quality parameters in various locations over v...

EPANET 2.2 is a newly introduced upgraded version of EPANET 2 that can be used for both pressure-driven analysis (PDA) and demand-driven analysis (DDA) of water distribution networks. Moreover, it has certain limitations concerning the minimum and required pressure head parameters used for PDA, which leads to inaccurate simulation results. Another...

The article is concerned with the holistic assessment of the effectiveness of source and regional control measures
for sustainable stormwater management in a residential development in Johannesburg.

Research was carried out to assess changes in extreme rainfall properties over time for the area surrounding the National Route 1 Section 29 (N1-29), located in Limpopo, South Africa. The study examined the changes in return levels for 1920-1970 and 1969-2019. The analysis showed that there is substantial change in the intensity of extreme rainfall...

Conventional stormwater management removes runoff from developed areas as quickly as possible. It does not consider possible reduction of runoff at source or water pollution control, and sustainability aspects cannot be incorporated in the management of stormwater by following this practice. This article describes the design, hydraulic simulation a...

Rigorous system-wide aggregated water quality performance indices for water distribution networks are lacking in the literature due to complexities associated with high dimensional spatial and temporal water quality data. Water quality considerations unavoidably increase performance evaluation difficulties considerably. The formulation developed in...

While analysing a real network, the assumption of zero minimum pressure head as the elevation of demand node may lead to unrealistic results as some residual pressure is necessary to derive any outflow at the node. A more realistic minimum pressure head plays an important role for analysis of an existing or proposed network. The present study exten...

Construction sector plays a key role in the economic development of a country. The management of this sector is thus crucial to maximise the performance of the sector and of the economy. This paper explores entry requirements that could be considered in the South African construction sector for contractor grading, to help improve the sectors perfor...

Genetic algorithms have been shown to be highly effective on optimization problems in various disciplines, and binary coding is generally adopted as it is straightforward to implement and lends itself to problems with discrete-valued decision variables. However, a difficulty associated with binary coding is the existence of redundant codes that do...

The City of Johannesburg’s latest stormwater management by-laws encourage the use of Sustainable Drainage Systems (SuDS) and rainwater harvesting (RWH) is one of the proposed SuDS options for residential complexes. Also, RWH is an essential element of effective water conservation where stormwater is utilised to augment water supply. However, the ex...

Water distribution systems are an integral part of the economic infrastructure of modern-day societies. However, previous research on the design optimization of water distribution systems generally involved few decision variables and consequently small solution spaces; piecemeal-solution methods based on pre-processing and search space reduction; a...

The use of water quality indices to aggregate pollution loads in rivers has been widely researched with researchers using various sub-indices and aggregation methods. These have been used to combine various quality variables at a sampling point in a river into an overall water quality index to compare the state of water quality in different river r...

EPANET 2 software is widely used among researchers and practitioners from its inception for hydraulic analysis. This article presents a method to simulate pressure-dependent volume-based demands in a single extended period simulation run of EPANET 2. In the proposed method, artificial strings made up of a pipe with a minor loss, pressure-sustaining...

The authors’ assessment of the common surrogate measures appeared promising at first glance but proved to be disappointing ultimately on multiple levels. Fundamentally, the hypothesis of the article is questionable in the sense that surrogate measures are not accurate reliability measures. In other words, by definition, they are indicative rather t...

Discharges from urban wastewater systems are the main source of pollution for inland and coastal waters, and intermittent unsatisfactory discharges from combined sewer systems have been recognized as a major environmental concern. The aim of the research was to investigate active system control of an interceptor sewer system. The dynamic multiobjec...

The use of water quality indices to aggregate pollution loads in rivers has been widely researched with researchers using various sub-indices and aggregation methods. These have been used to quantify various quality variables at a sampling point in a river into an overall water quality index to compare the state of water quality in different river...

The stormwater from urban catchments is often managed as a potential flood hazard and is disposed of as rapidly as possible; in so doing quantity is managed whilst quality is ignored. This is the widely used stormwater management approach in South Africa, which is based on the conventional drainage system. There is, however, a growing movement to t...

Design optimization procedures for water distribution systems generally assume that the nodal demands follow the same diurnal pattern, which implies that the demands are fully synchronised and perfectly correlated. However, it is well known that in practice the spatial correlation of the demands is not perfect; i.e. the cross-correlation is less th...

The flow entropy, when increased, has been revealed to: produce designs with improvements in the hydraulic reliability; make use of the arrangements of the flow paths in layout optimization; produce high uniformity of the pipe diameters in line with increase in the reliability; provide strong positive correlation with hydraulic reliability and fail...

The design of water distribution networks (WDNs) is a complex problem that has been the focus of computational optimization research over many decades. However, the optimization procedures generally have not incorporated water quality objectives in the design optimization of WDNs explicitly. This is thought to result in potentially negative effects...

The optimal design of water distribution networks involves minimizing the cost of the network subject to the constraints of satisfying the pressure requirements at all the nodes. In genetic algorithm (GA)-based optimal design, such constrained problems are generally converted to unconstrained ones using penalty methods. The penalty is applied for n...

Evolutionary optimization approaches such as genetic algorithms are being used increasingly in the optimization of water distribution networks. The number of hydraulic simulations required to find good solutions can be extremely large and time-consuming. It is, therefore, highly desirable to reduce the search or solution space to speed up the optim...

Service reservoirs are an essential component of water distribution networks. More often, research is being expanded to include the optimisation of not only the pipe elements of a water distribution network but also the service reservoirs that may exist in the system. This is done since service reservoirs contribute to the head that drives the syst...

Genetic algorithms have been effective on optimization problems in various disciplines, and binary coding is often adopted as it is straightforward and lends itself to problems with discrete-valued decision variables. However, a challenge associated with binary coding is the existence of redundant codes. Redundant binary codes are commonly discarde...

The flow from urban catchments is often managed as a potential flood hazard and is disposed of as rapidly as possible; in so doing quantity is managed whilst quality is ignored. This is the widely used conventional stormwater management approach. There is, however, a growing movement to treat stormwater as a renewable resource as opposed to a nuisa...

An effective way to improve the computational efficiency of evolutionary algorithms is to make the solution space of the optimization problem under consideration smaller. A new reliability-based algorithm that does this was developed for water distribution networks. The objectives considered in the formulation of the optimization problem were minim...

It is essential to consider resilience when designing any water distribution network and surrogate measures of resilience are used frequently as accurate measures often impose prohibitive computational demands in optimization algorithms. Previous design optimization algorithms based on flow entropy have essentially employed a single loading conditi...

The optimal design of Water Distribution Network (WDN) involves minimizing the cost of network subjected to the constraints of satisfying the pressure requirements at all the nodes. In Genetic Algorithm (GA) based optimal design, such constrained problems are converted to unconstrained one using penalty methods. The penalty is applied for not meeti...

Simulation models for water distribution networks are used routinely for many purposes. Some examples are planning, design, monitoring and control. However, under conditions of low pressure, the conventional models that employ demand-driven analysis often provide misleading results. On the other hand, almost all the models that employ pressure-driv...

Water distribution systems are key components of public infrastructure and it is essential to design, manage and rehabilitate them economically without compromising the required performance and regulatory standards. Evolutionary optimization algorithms such as genetic algorithms have become popular in providing optimal and near optimal solutions to...

Evolutionary algorithms are used widely in optimization studies on water distribution networks. The optimization algorithms use simulation models that analyse the networks under various operating conditions. The solution process typically involves cost minimization along with reliability constraints that ensure reasonably satisfactory performance u...

Water distribution systems are key components of public infrastructure and it is essential to design, manage and rehabilitate them economically without compromising the required performance and regulatory standards. Evolutionary optimisation algorithms such as genetic algorithms have become popular in providing optimal and near optimal solutions to...

In steel portal frames, cold-formed steel channel sections are increasingly used as the primary framing components, in addition to the secondary members e.g. purlins and side rails. For such framing systems, the stiffness of the joints at the eaves and apex affects the bending moment distribution, as well as the frame deflections. This paper invest...

Evolutionary algorithms are used widely in optimization studies on water distribution networks. The optimization algorithms use simulation models that analyse the networks under various operating conditions. The solution process typically involves cost minimisation along with reliability constraints that ensure reasonably satisfactory performance u...

In this research, a significant improvement in reservoir operation was achieved using a state-of-the-art evolutionary algorithm named Borg MOEA. A real-world multipurpose dam was used to test the algorithm’s performance, and the target of the reservoir operation policy was to fulfil downstream water demands in drought condition while maintaining a...

The complexity of water resources management problems, especially for multipurpose reservoirs, increases the
motivation to find a robust method to overcome this challenge. Evolutionary optimization algorithms are used widely to handle reservoir management problems. In this research, one of the competitive methods of optimization named Borg MOEA was...

This paper describes the development and application of a new multi-objective evolutionary optimization approach for the design and upgrading of water distribution systems with multiple pumps and service reservoirs. The optimization model employs a pressure-driven analysis simulator that accounts for the minimum node pressure constraints and conser...

This article investigates the computational efficiency of constraint handling in multi-objective evolutionary optimization algorithms for water distribution systems. The methodology investigated here encourages the co-existence and simultaneous development including crossbreeding of subpopulations of cost-effective feasible and infeasible solutions...

An investigation into the effectiveness of surrogate measures for the hydraulic reliability and/or redundancy of water distribution systems is presented. The measures considered are statistical flow entropy, resilience index, network resilience and surplus power factor. Looped network designs that are maximally noncommittal to the surrogate reliabi...

A new multi-directional search approach that aims at maximizing the flow entropy of water distribution systems is investigated. The aim is to develop an efficient and practical maximum entropy based approach. The resulting optimization problem has four objectives, and the merits of objective reduction in the computational solution of the problem ar...

Evolutionary algorithms are a commonly applied optimisation approach in water distribution systems. However, the algorithms are time consuming when applied to large optimisation problems. The aim of this paper is to evaluate the application of a penalty-free multi-objective evolutionary optimisation algorithm to solve a real-world network design pr...

A structural design optimisation has been carried out to allow for asymmetry and fully tapered portal frames. The additional weight of an asymmetric structural shape was found to be on average 5 to 13% with additional photovoltaic (PV) loading having a negligible effect on the optimum design. It was also shown that fabricated and tapered frames ach...

EPANET 2 has been used previously to simulate pressure-deficient operating conditions in water distribution systems by: (a) executing the algorithm repetitively until convergence is achieved; (b) modifying the source code to cater for pressure-dependent outflows; or (c) incorporating artificial elements e.g., reservoirs in the data input file. This...

This paper describes a stressed-skin diaphragm approach to the optimal design of the internal frame of a cold-formed steel portal framing system, in conjunction with the effect of semi-rigid joints. Both ultimate and serviceability limit states are considered. Wind load combinations are included. The designs are optimized using a real-coded niching...

Evolutionary algorithms are a commonly applied optimisation approach in water distribution systems. However, the algorithms are time consuming when applied to large optimisation problems. The aim of this paper is to evaluate the application of a penalty-free multi-objective evolutionary optimisation algorithm to solve a real-life network design pro...

This paper presents a novel multi-objective evolutionary optimization approach for the active control of intermittent unsatisfactory discharges from combined sewer systems. The procedure proposed considers the unsteady flows and water quality in the sewers together with the wastewater treatment costs. The distinction between the portion of wastewat...

There is a growing body of evidence that, on average, hydraulic reliability of water distribution systems increases in line with entropy of the pipe flows. Motivated by the existence of large sets of flow directions in looped water distribution systems along with the computational simplicity of the informational entropy function, a multi-directiona...

Combined sewer overflows (CSOs), during storm weather periods, are frequent in many cities. Many proposed engineering solutions are based on structural measures. However, they are not the best solutions since most of these measures require new structural components. Therefore, control of existing combined sewer networks show a great potential in mi...

A new multi-objective evolutionary optimization approach for joint topology and pipe size design of water distribution systems is presented. The algorithm proposed considers simultaneously the adequacy of flow and pressure at the demand nodes; the initial construction cost; the network topology; and a measure of hydraulic capacity reliability. The...

This paper considers the optimal design of fabricated steel beams for long-span portal frames. The design 18
optimisation takes into account ultimate as well as serviceability limit states, adopting deflection limits recom- 19
mended by the Steel Construction Institute (SCI). Results for three benchmark frames demonstrate the efficiency 20
of the o...

For small to modest frame spans, cold-formed steel portal frames are a popular and efficient form of construction which can be used for low-rise commercial, light industrial and agricultural buildings. Such buildings are lightweight, have ease of installation and erection, as well as economy. However, in cold-formed steel portal framing systems, th...

Combined sewer networks carry wastewater and stormwater together. Capacity limitation of
these sewer networks results in combined sewer overflows (CSOs) during high-intensity
storms. Untreated CSOs when directly discharged to the nearby natural water bodies cause
many environmental problems. Controlling existing urban sewer networks is one possible...

Water storage tanks or service reservoirs are key components of water distribution systems but
often pose water quality problems. This paper assesses the effects of service reservoirs on water
quality by comparing two new feasible solutions for the ‘Anytown’ network that are cheaper
than previous solutions in the literature. The recently developed...

Nodal outflows in a pressure deficient water distribution network depend on available nodal heads. Thus, node-head flow
relationship exists at each node which are solved along with other appropriate equations for simulation. While using EPANET for
such simulation, source code needs to be modified to obtain direct solution. The other way is to use E...

This paper describes a penalty-free multi-objective evolutionary optimization approach for the phased whole-life design and rehabilitation of water distribution systems. The optimization model considers the initial construction, rehabilitation and upgrading costs. Repairs and pipe failure costs are included. The model also takes into consideration...