Francois Clemens

Bio: Francois Clemens is an academic researcher from Delft University of Technology. The author has contributed to research in topics: Sanitary sewer & Combined sewer. The author has an hindex of 23, co-authored 170 publications receiving 2032 citations. Previous affiliations of Francois Clemens include Norwegian University of Science and Technology & City University of New York.

Wastewater System Optimisation Using Genetic Algorithms

Abstract: The optimi.~ation of complete wastewater systems receives more and more attention, since it has become clear that the current apptczeh of optimising the subsystems of sewerage and was~water treatment separately often results in sub-optimal solutions. This optimisation, however, shows to be very troublesome in practice due to its complexity. The complexity of a wastewater system opthuisafion problem is related to the many variables involved (multi-dimensional search) and to the optimisation goal, defined by an objective fuuetien~ Optimi.xation with respect to multiple objectives, e.g. overall costs as well as environmental performance, is often suggested but increases the complexity. One of the optimisation or search techniques which is capable of dealing with such a complex surrounding is a genetic algorithm (GA). This paper discusses the potential of the use of genetic algorithm~ for opfimisation of wastewater systems. The definition of the objective function and the characteristics of the GA, especially mutation probability, proved to be key-elements for a successful application of a GA for this type of problems. Finally, it is concluded that GAs are capable of solving the very complex opfimisation problems related to improvement of total wastewater systems.

Interactions Within the Wastewater System: Modeling of Sewer Processes

Abstract: Since the beginning of the last decade, an integrated approach towards the urban water system has often been advocated. From a scientific point of view, this approach is preferable, but in day-to-day engineering practice the problem arises to what extent the interactions, and sewer processes, within the wastewater system should be included in wastewater system optimisation studies. This paper briefly describes the methodology applied to evaluate the relative importance of each sewer process with respect to the interactions within the wastewater system and, subsequently, the possibility to model the, in this respect, most important sewer processes.

Quantifying the effect of proactive management strategies on the serviceability of gully pots and lateral sewer connections

Abstract: Gully pots and lateral connections represent the anterior part of the sewer infrastructure responsible for the majority of flooding events in public areas. This study provides a statistical procedure to quantify the effectiveness of proactive management strategies to improve their performance. The first part consists of non-parametric methods to determine the evolution of gully pot blockages. The second part presents a Bayesian approach to quantify the development of reported flooding events when lateral connections are subject to proactive strategies. To this end, call data were collected from areas that were maintained proactively instead of reactively. Application of the procedure revealed a significant call decrease in one area. In addition, an increasing blockage likelihood over time indicated cyclic cleaning to be effective to improve sewer serviceability. By linking management strategies to performance, this flexible procedure can support sewer managers to balance the merits of proactive an...

Air pocket removal from downward sloping pipes

Abstract: Air-water flow is an undesired condition in water pipelines and hydropower tunnels. Water pipelines and wastewater pressure mains in particular are subject to air pocket accumulation in downward sloping reaches, such as inverted siphons or terrain slopes. Air pockets cause energy losses and an associated capacity reduction. Despite its practical relevance, many phenomena associated with airwater flow in downward sloping pipe reaches are still poorly understood. Deltares and Delft University of Technology have investigated the co-current flow of air and water in twelve different large-scale facilities. Pothof and Clemens have recently developed a numerical model for the total air discharge by flowing water in downward sloping pipes. The model has been validated against the experimental data on co-current air-water flow and available literature. This paper presents new experimental data on the breakdown and removal of large air pockets. The experimental results are compared with the numerical model. The observed disagreement is analysed and discussed. The main conclusion is that the numerical model predicts the air pocket breakdown rate with reasonable accuracy.

THE CHARACTERISTICS OF AN IN-SEWER EROSION EVENT ? OBSERVATIONS FROM ENVIRONMENTALLY CONTROLLED ANNULAR FLUME - op internet

Abstract: This paper provides an overview of a collaborative project recently completed at WL Delft Hydraulics. It describes tests in an annular flume, in which sewer sediment deposits could be formed under carefully controlled and monitored environmental conditions and then subjected to a test series in which the bed shear stress was progressively increased. The characteristics of the eroded sediment were then closely monitored. The sediment deposits were formed using two different types of sewer sediment. The deposits in the reported experiments were formed using real in-sewer sediments, from a catchment in the UK (Dundee) and from a catchment in the Netherlands (Loenen). During the erosion tests, total and volatile suspended solids concentration, particle size distribution of the eroded sediment, and COD and DO levels were all recorded. In addition, the biodegradability of the eroded sediments were also analysed using a respirometric method. This provided the most detailed data set covering the physical and biochemical aspects of an erosion event associated with insewer sediments ever recorded. The bed surface topography was also measured so that the influence of the deposit formation condition on bedforms could also be examined.

Climate Change 2007: The Physical Science Basis.

Abstract: Cause, conseguenze e strategie di mitigazione Proponiamo il primo di una serie di articoli in cui affronteremo l’attuale problema dei mutamenti climatici. Presentiamo il documento redatto, votato e pubblicato dall’Ipcc - Comitato intergovernativo sui cambiamenti climatici - che illustra la sintesi delle ricerche svolte su questo tema rilevante.

Boundary Layer Theory

Abstract: The boundary layer equations for plane, incompressible, and steady flow are $$\matrix{ {u{{\partial u} \over {\partial x}} + v{{\partial u} \over {\partial y}} = - {1 \over \varrho }{{\partial p} \over {\partial x}} + v{{{\partial ^2}u} \over {\partial {y^2}}},} \cr {0 = {{\partial p} \over {\partial y}},} \cr {{{\partial u} \over {\partial x}} + {{\partial v} \over {\partial y}} = 0.} \cr }$$