Showing papers by "Francois Clemens published in 2017"
TL;DR: A discussion is thus presented on the uncertainty estimation of interpolated/extrapolated data and some suggestions for further research and a new method are proposed.
Abstract: A thorough review has been performed on interpolation methods to fill gaps in time-series, efficiency criteria, and uncertainty quantifications. On one hand, there are numerous available methods: interpolation, regression, autoregressive, machine learning methods, etc. On the other hand, there are many methods and criteria to estimate efficiencies of these methods, but uncertainties on the interpolated values are rarely calculated. Furthermore, while they are estimated according to standard methods, the prediction uncertainty is not taken into account: a discussion is thus presented on the uncertainty estimation of interpolated/extrapolated data. Finally, some suggestions for further research and a new method are proposed.
144 citations
TL;DR: In a case study for a combined sewer system with limited discharge to a WWTP, it is demonstrated that the successful application of RTC and the possibility to determine a significant effect is very much dependent on the goal and the need for taking uncertainties into account is demonstrated.
Abstract: Real time control (RTC) is generally viewed as a viable method for optimising the performance of urban wastewater systems. A literature review on the performance evaluation of RTC demonstrated a lack of consensus on how to do this. Two main deficiencies were identified: omitting uncertainty analysis and applying limited evaluation periods. A general methodology to evaluate the performance of RTC in practice, that takes into account these deficiencies, is proposed. The methodology is either data or model driven and the (dis)advantages of each are discussed. In a case study for a combined sewer system with limited discharge to a WWTP, it is demonstrated that the successful application of RTC and the possibility to determine a significant effect is very much dependent on the goal. It also clearly illustrates the need for taking uncertainties into account and that careful consideration in the chosen evaluation period is required.
41 citations
TL;DR: In this article, the laser-scanning device presented by Stanic, Lepot, Catieau, Langeveld and Clemens has been used for sewer inspections: displaced joints, cracks, deposits can be accurately measured without any bias by comparison to CCTV.
28 citations
TL;DR: IR frame analysis and 2D temperature mapping demonstrate that: i) the detection limit is very low (ratio between lateral and main discharges: 0.025) and ii) the quantification of the lateral discharge is impossible.
23 citations
TL;DR: In this paper, an improved laser profiler was developed to improve the accuracy of collected data by using more accurate equipment (lasers and cameras) and by improving the methodologies applied (e.g. removing the last bias image distortion by camera calibration).
19 citations
TL;DR: In this paper, the authors proposed a model to calculate water temperature in free-surface flow with two main innovations: the convective heat transfer occurs only at the wetted perimeter of pipes, and the model was integrated to commercial software used for hydraulic calculations in drainage systems.
Abstract: This paper presents a model (inspired by another model) to calculate water temperature in free-surface flow with two main innovations: the convective heat transfer occurs only at the wetted perimeter of pipes, and the model was integrated to commercial software used for hydraulic calculations in drainage systems. Given these innovations, we could reduce the number of modeling input data to calculate the temperature of water and soil in the radial and tangential directions along the pipes, with the advantages of using industry-standard software. To test the performance of the model, it was firstly calibrated in two sets of experiments (to calibrate the hydraulic and the thermal parameters separately), and benchmarked with a third controlled discharge against the case model. The results indicate that in unsteady-state situations the parsimonious model can be twice as accurate as the underlying model because the parsimonious model considers the hydraulic influence of sewer infrastructure.
16 citations
TL;DR: In this article, a game Maintenance in Motion is introduced, aiming at investigating the influence of information quality on rehabilitation decisions, for single and multi-actor decision-making, for drinking water, gas, sewer and street infrastructures.
Abstract: Operational decision-making processes for networked infrastructure management often occur as a multi-actor planning problem, implying these are based on negotiations between different stakeholders in addition to available system quality information. As such, does more accurate data about actual structural condition lead to other or better decision-making? A serious game is introduced, Maintenance in Motion, aiming at investigating the influence of information quality on rehabilitation decisions, for single- and multi-actor decision-making. Players manage drinking water, gas, sewer and street infrastructures. They are to balance their individual goal, cost-effectiveness, with their team utility, increasing overall infrastructure quality to minimise failure while minimising overall public costs. The game design, calibration and solution space are presented.
13 citations
TL;DR: In this article, the results of core samples are compared with results of full-scale pipe cracking lab experiments, and it is concluded that tensile splitting strength and the carbonation depth are two material property parameters of core sampling with a sufficiently high correlation with the structural strength of the p...
Abstract: Drill core samples are taken in practice for an analysis of the material characteristics of concrete pipes in order to improve the quality of the decision-making on rehabilitation actions. Earlier research has demonstrated that core sampling is associated with a significant uncertainty. In this paper, the results of core samples are compared with the results of full-scale pipe cracking lab experiments. It is shown that the concrete of deteriorated sewer pipes shows a significant variability in material characteristics. Further it is shown that the formation of ettringite due to biochemical sulphuric corrosion is not necessarily limited to the crown of the pipe and also degradation of pipe material, measured by the carbonation depth, is occurring at the inside and outside of the pipe. It is concluded that tensile splitting strength and the carbonation depth are the two material property parameters of core sampling with a sufficiently high correlation (R2 > .90) with the structural strength of the p...
12 citations
TL;DR: In this paper, the authors investigate the influence of information quality about structural condition on replacement decisions for single and multi-actor decision-making in Maintenance in Motion, a game where players are challenged to balance their individual goal, cost-effectiveness, with their team utility, increasing overall infrastructure quality to minimize failure while minimising overall public costs.
Abstract: Operational decision processes for networked infrastructure management often occur as a multi-actor planning problem, implying these are partly based on negotiations between different stakeholders. The starting point for negation for each stakeholder is the available information about the structural condition of his infrastructure. In this respect, this leads to the question: ‘does more accurate data about actual structural condition lead to other or better decision-making?’ A serious game is introduced, ‘Maintenance in Motion’, aiming at investigating the influence of information quality about structural condition on replacement decisions, for single and multi-actor decision-making. Players are challenged to balance their individual goal, cost-effectiveness, with their team utility, increasing overall infrastructure quality to minimise failure while minimising overall public costs. Results show that if players are presented with perfect instead of imperfect information, in a single player environ...
10 citations
TL;DR: In this paper, the concept of hydraulic fingerprinting based on model calibration is introduced to identify in-sewer defects affecting hydraulic performance, which enables detection of changes in hydraulic properties of the sewer system each model calibration results in a set of model parameters, their uncertainties and residuals.
Abstract: Sewer performance is typically assessed using hydrodynamic models assuming the absence of in-sewer defects As a consequence, hydraulic performance calculated by models is likely to be overestimated, while the real hydraulic performance of the sewer system remains unknown This article introduces the concept of ‘hydraulic fingerprinting’ based on model calibration to identify in-sewer defects affecting hydraulic performance Model calibration enables detection of changes in hydraulic properties of the sewer system Each model calibration results in a set of model parameter values, their uncertainties and residuals The model parameter values also incorporate the antecedent condition of the catchment of the event calibrated and are therefore less suitable to identify in-sewer defects The residuals on the other hand, and more specifically their absolute values, statistical properties and the correlation between residuals at different monitoring locations are suitable as indicators of the occurrence
9 citations
TL;DR: In this paper, the potential of laser scanning methods for accurate, noninvasive, and nonintrusive assessment of the hydraulic roughness of concrete sewer pipes is described, demonstrated, and discussed.
Abstract: In sewer asset management, decision making on rehabilitation or replacement should preferably be based on the actual functionality of a sewer system. In order to judge the ability of a sewer system to transport wastewater, hydrodynamic models are used; in these, hydraulic roughness is one of the key parameters. For new pipes, this is well known, but for aged pipes with uneven deterioration along the cross section, information on the hydraulic roughness is lacking. In this article, the potential of laser scanning methods for accurate, noninvasive, and nonintrusive assessment of the hydraulic roughness of concrete sewer pipes is described, demonstrated, and discussed. Processing of raw scanned data consists of two steps: (1) spatial interpolation with uncertainty analysis, and (2) statistical analysis for estimating the hydraulic roughness. Moreover, a statistical analysis was carried out to determine the minimal scanning resolution required in order to yield results accurate enough for subsequent m...
TL;DR: In this paper, the authors used a statistical procedure to support proactive strategies by analyzing spatial blockage patterns to identify system parts with higher blockage incidences, which justifies the identification of explanatory factors by means of a bootstrapped generalised additive model.
Abstract: The performance of lateral house connections has a direct impact on sewer serviceability. Despite the potential consequences of a blockage, these components are generally maintained with a reactive approach. As inspection data on the condition of lateral house connections are scarce, this study adopts a statistical procedure to support proactive strategies by analysing spatial blockage patterns to identify system parts with higher blockage incidences. First, a Monte Carlo simulation test provides insight into whether the spatial variation of the blockage likelihood is significant. This justifies the identification of explanatory factors by means of a bootstrapped generalised additive model. Application of the procedure to two databases containing 10 years of lateral house connection blockage data, revealed factors such as building age, sewer system type and ground settlement rate to explain spatial differences in the blockage likelihood. Furthermore, a likelihood ratio test demonstrated that the addition of a spatial smoother improved model performance. This smoother was able to account for additional spatial variation caused by explaining factors for which no data were available. The procedure provides key information for inspection and rehabilitation strategies by taking into account the model performance in assessing the trade-off between costs and benefits in terms of serviceability.
TL;DR: In this paper, the authors investigated the effect of the characteristics of rainfall inputs on a large-scale integrated catchment simulator for dissolved oxygen predictions in the River Dommel (The Netherlands).
Abstract: Integrated Catchment Modelling aims to simulate jointly urban drainage systems, wastewater treatment plant and rivers. The effect of rainfall input uncertainties in the modelling of individual urban drainage systems has been discussed in several studies already. However, this influence changes when simultaneously simulating several urban drainage subsystems and their impact on receiving water quality. This study investigates the effect of the characteristics of rainfall inputs on a large-scale integrated catchment simulator for dissolved oxygen predictions in the River Dommel (The Netherlands). Rainfall products were generated with varying time-aggregation (10, 30 and 60 min) deriving from different sources of data with increasing spatial information: (1) Homogeneous rainfall from a single rain gauge; (2) block kriging from 13 rain gauges; (3) averaged C-Band radar estimation and (4) kriging with external drift combining radar and rain gauge data with change of spatial support. The influence of the different rainfall inputs was observed at combined sewer overflows (CSO) and dissolved oxygen (DO) dynamics in the river. Comparison of the simulations with river monitoring data showed a low sensitivity to temporal aggregation of rainfall inputs and a relevant impact of the spatial scale with a link to the storm characteristics to CSO and DO concentration in the receiving water.
TL;DR: In this article, the applicability of computational fluid dynamics (CFD) simulations for deriving reliable discharge relationships for weirs where the weir chamber geometry limits the discharged flow is investigated.
TL;DR: In this paper, a statistical procedure to quantify the effectiveness of proactive management strategies to improve the performance of gully pots and lateral connections is presented, where call data were collected from areas that were maintained proactively instead of reactively.
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...
01 Dec 2017
TL;DR: This study compares two approaches – principal component analysis and data depth theory – to identify outliers and select the most representative spectrum (MRS) among the repetitively recorded spectra.
Abstract: UV/Vis spectrophotometers have been used to monitor water quality since the early 2000s. Calibration of these devices requires sampling campaigns to elaborate relations between recorded spectra and measured concentrations. In order to build robust calibration data sets, several spectra must be recorded per sample. This study compares two approaches – principal component analysis and data depth theory – to identify outliers and select the most representative spectrum (MRS) among the repetitively recorded spectra. Detection of samples that contain outliers is consistent between the methods in more than 70% of the samples. Identification of spectra as outliers is consistent in more than 95% of the cases. The identification of MRS differs depending on the approach used. In their current form, both of the proposed approaches can be used for outlier detection and identification. Further studies are suggested to combine the methods and develop an automated ranking and sorting system.