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.

Influence of Surface Tension on Air-Water Flows

Abstract: Stricter environmental regulations have led to new wastewater treatment plants and a centralization of existing wastewater treatment plants. Therefore, pressurized wastewater mains have become an indispensable link between the collection systems and the treatment plants. In urban areas in particular, these pipelines include many inverted siphons to cross other infrastructure, like railways, motorways, other pipelines, and buildings. Accumulation of air in downward sloping sections of these wastewater mains reduces the transport capacity significantly. A dominant air transport mechanism is the air-entraining hydraulic jump at the tail of an accumulated air pocket. The novelty of this paper is a systematic investigation of the influence of surface tension on the air discharge in downward sloping pipe sections. Experiments have been performed with clean water, surfactant-added water, and wastewater. The experiments with surfactant-added water confirm that the air discharge increases significantly at ...

Intelligent SUBsurface Quality: Intelligent use of subsurface infrastructure for surface quality

Abstract: This project focuses on the urban renewal of (delta) metropolises and concentrates on the question how to design resilient, durable (subsurface) infrastructure in urban renewal projects using parameters of the natural system – linking in an efficient way (a) water cycle, (b) soil and subsurface conditions, (c) soil improvement technology, and (d) opportunities in urban renewal (e.g. urban growth or shrinkage). The subsurface is the technical space, the engine room of a city, housing the vital functions of water, electricity, sewers and drainage, but also housing the natural system that is crucial for a stable, green, healthy and livable city. Especially the effects of climate change, the boosts for an energy transition and the fact that there are less financial mean makes the intelligent use of the subsurface more important. This prublication reprots on the explorative method to get insight and design methods for the urban renewal of (delta) metropolises where resilient, durable (subsurface) infrastructure is carefully balanced out with parameters of the natural system. The question “how can the different technological artefacts in the subsurface be synchronized offering more space and adding to a better urban quality?” is answered by taking procedural steps from the technology (the knowledge of) to the design of public space and urban main structures. In each step the translation from the engineering language to the language of the urban designer (and vice-versa) is done producing an informative and useful overview in how to relate technological artefacts to urban quality. In order to reach interdisciplinary design, explorative research is used for creating a shared language. Explorative research has been useful because the problems at hand are wicked problems that has not been clearly defined. The exploration was framed by co-creation in workshops and later a more precise elaboration of these results in the working group.

A coupled hydro-mechanical model for subsurface erosion with analyses of soil piping and void formation

Abstract: Abstract A coupled hydro-mechanical erosion model is presented that is used for studying soil piping and erosion void formation under practical, in-situ conditions. The continuum model treats the soil as a two-phase porous medium composed of a solid phase and a liquid phase, and accounts for its elasto-plastic deformation behaviour caused by frictional sliding and granular compaction. The kinetic law characterizing the erosion process is assumed to have a similar form as the type of threshold law typically used in interfacial erosion models. The numerical implementation of the coupled hydro-mechanical model is based on an incremental-iterative, staggered update scheme. A one-dimensional poro-elastic benchmark problem is used to study the basic features of the hydro-mechanical erosion model and validate its numerical implementation. This problem is further used to reveal the interplay between soil erosion and soil consolidation processes that occur under transient hydro-mechanical conditions, thereby identifying characteristic time scales of these processes for a sandy material. Subsequently, two practical case studies are considered that relate to a sewer system embedded in a sandy soil structure. The first case study treats soil piping caused by suffusion near a sewer system subjected to natural ground water flow, and the second case study considers the formation of a suffosion erosion void under strong ground water flow near a defect sewer pipe. The effects on the erosion profile and the soil deformation behaviour by plasticity phenomena are elucidated by comparing the computational results to those obtained by modelling the constitutive behaviour of the granular material as elastic. The results of this comparison study point out the importance of including an advanced elasto-plastic soil model in the numerical simulation of erosion-driven ground surface deformations and the consequent failure behaviour. The numerical analyses further illustrate that the model realistically predicts the size, location, and characteristic time scale of the generated soil piping and void erosion profiles. Hence, the modelling results may support the early detection of in-situ subsurface erosion phenomena from recorded ground surface deformations. Additionally, the computed erosion profiles may serve as input for a detailed analysis of the local, residual bearing capacity and stress redistribution of buried concrete pipe systems.

Decision tree analysis of factors influencing rainfall-related building damage

Abstract: The aim of this paper is to investigate a wide range of damage-influencing factors and their relationships with rainfall-related damage, using decision tree analysis. For this, district-aggregated claim data from private property insurance companies in the Netherlands were analysed, for the period of 1998–2011. The databases include claims of water-related damage, for example, damages related to rainwater intrusion 10

Uncertainty in risk analysis of urban pluvial flooding: a case study.

Abstract: The interest in urban flood risk is growing steadily over the last decades. Still, in the Netherlands no data is available to quantify urban flood risk. In this paper an estimation of urban flood frequencies is made in a detailed analysis of an urban catchment. Calculation results from a theoretical model are compared with data from a complaint register. The analysis in the case study shows that insufficient system maintenance condition is an important potential cause of urban flooding. The estimated flood frequency caused by severe rainfall is 4 events in 7 years or 0.6 per year, while the flood frequency caused by maintenance problems is 13 in 4 years or 3.3 per year. This includes 2 flood events that are caused by heavy rainfall and 11 events that are related to maintenance problems. The number of locations that suffer flooding caused by severe rainfall is more than 3 or 4 per event, while the number of locations that suffer flooding caused by maintenance problems is not more than 2 per event. It is expected that these numbers are representative for the rest of the Netherlands. Further research and data collection will very this assumption.

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 $$\matrix{ {u{{\partial u} \over {\partial x}} + v{{\partial u} \over {\partial y}} = - {1 \over \varrho }{{\partial p} \over {\partial x}} + v{{{\partial ^2}u} \over {\partial {y^2}}},} \cr {0 = {{\partial p} \over {\partial y}},} \cr {{{\partial u} \over {\partial x}} + {{\partial v} \over {\partial y}} = 0.} \cr }$$