New formulations for prediction of velocity at limit of deposition in storm sewers based on a stochastic technique.

AbstractSedimentation in storm sewers strongly depends on velocity at limit of deposition. This study provides application of a novel stochastic-based model to predict the densimetric Froude number in sewer pipes. In this way, the generalized likelihood uncertainty estimation (GLUE) is used to develop two parametric equations, called GLUE-based four-parameter and GLUE-based two-parameter (GBTP) models to enhance the prediction accuracy of the velocity at the limit of deposition. A number of performance indices are calculated in training and testing phases to compare the developed models with the conventional regression-based equations available in the literature. Based on the obtained performance indices and some graphical techniques, the research findings confirm that a significant enhancement in prediction performance is achieved through the proposed GBTP compared with the previously developed formulas in the literature. To make a quantified comparison between the established and literature models, an index, called improvement index (IM), is computed. This index is a resultant of all the selected indices, and this indicator demonstrates that GBTP is capable of providing the most performance improvement in both training () and testing () phases, comparing with a well-known formula in this context

New stochastic modeling strategy on the prediction enhancement of pier scour depth in cohesive bed materials

Abstract Scouring around the piers, especially in cohesive bed materials, is a fully stochastic phenomenon and a reliable prediction of scour depth is still a challenging concern for bridge designers. This study introduces a new stochastic model based on the integration of Group Method of Data Handling (GMDH) and Generalized Likelihood Uncertainty Estimation (GLUE) to predict scour depth around piers in cohesive soils. The GLUE approach is developed to estimate the related parameters whereas the GMDH model is used for the prediction target. To assess the adequacy of the GMDH-GLUE model, the conventional GMDH and genetic programming (GP) models are also developed for evaluation. Several statistical performance indicators are computed over both the training and testing phases for the prediction accuracy validation. Based on the attained numerical indicators, the proposed GMDH-GLUE model revealed better predictability performance of pier scour depth against the benchmark models as well as several gathered literature studies. To provide an informative comparison among the proposed techniques (i.e. GMDH-GLUE, GMDH, and GP models), an improvement index () is employed. Results indicated that the GMDH-GLUE model achieved = 6% and = 3%, demonstrating satisfying performance improvement in comparison with the previously proposed GMDH model

Sensitivity analysis of bridge pier scour depth predictive formulae

Sensitivity analysis is an approach to recognising the behaviour of models and relative importance of causative factors. In this paper, behaviours of six pier scour depth empirical formulae are evaluated on the basis of an analytical method. The sensitivity of predicted scour depth is analysed with respect to the following independent parameters: approach flow depth, riverbed slope and median sediment size. Also their combined influence is studied examining the relative importance of each parameter with respect to the total variation of the maximum scour depth. Results show that: (1) sensitivity significantly depends on flow intensity for most of the selected formulae, whereas for the others it is a constant value or depends on other influencing parameters; (2) different formulae demonstrate various level of sensitivity to the input variables, so that, for a certain error in the input variables, the error in the results may vary consistently; (3) some formulae are very sensitive to the input parameters under some conditions, hence an error in an input variable may be amplified in the output results; and (4) most of the formulae are more sensitive to the variations of the influencing parameters in clear-water than in live-bed conditions

Application of nature-inspired optimization algorithms to ANFIS model to predict wave-induced scour depth around pipelines

Wave-induced scour depth below pipelines is a physically complex phenomenon, whose reliable prediction may be challenging for pipeline designers. This study shows the application of adaptive neuro-fuzzy inference system (ANFIS) incorporated with particle swarm optimization (ANFIS-PSO), ant colony (ANFIS-ACO), differential evolution (ANFIS-DE) and genetic algorithm (ANFIS-GA) and assesses the scour depth prediction performance and associated uncertainty in different scour conditions including live-bed and clear-water. To this end, the non-dimensional parameters Shields number (θ), Keulegan–Carpenter number (KC) and embedded depth to diameter of pipe ratio (e=D) are considered as prediction variables. Results indicate that the ANFIS-PSO model (R 2 live bed ¼ 0:832 and R 2 clear water ¼ 0:984) is the most accurate predictive model in both scour conditions when all three mentioned non-dimensional input parameters are included. Besides, the ANFIS-PSO model shows a better prediction performance than recently developed models. Based on the uncertainty analysis results, the prediction of scour depth is characterized by larger uncertainty in the clear-water condition, associated with both model structure and input variable combination, than in live-bed condition. Furthermore, the uncertainty in scour depth prediction for both live-bed and clear-water conditions is due more to the input variable combination (R-factor ave ¼ 4:3) than it is due to the model structure (R-factor ave ¼ 2:2)

Experimental and Numerical Study of Free-Surface Flows in a Corrugated Pipe

A new discharge computational model is proposed on the basis of the integration of the velocity profile across the flow cross-section in an internally corrugated pipe flowing partially full. The model takes into account the velocity profiles in the pressurised pipe to predict the flow rate under free-surface flow conditions. The model was evaluated through new laboratory experiments as well as a literature datasets. The results show that flow depth and pipe slope may affect the model accuracy; nevertheless, a prediction error smaller than 20% is expected from the model. Experimental results reveal the influence of the pipe slope and flow depth on the friction factor and the stage-discharge curves: the friction factor may increase with pipe slope, while it reduces as flow depth increases. Hence, a notable change of pipe slope may lead to the variation of the stage-discharge curve. A part of this study deals with numerical simulation of the velocity profiles and the stage-discharge curves. Using the Reynolds-Averaged Navier-Stokes (RANS) equations, numerical solutions were obtained to simulate four experimental tests, obtaining enough accurate results as to velocity profiles and water depths. The results of the simulated flow velocity were used to estimate the flow discharge, confirming the potential of numerical techniques for the prediction of stage-discharge curves

Large eddy simulation of the turbulent flow field around a submerged pile within a scour hole under current condition

Coastal finite structures, bridge piers, and bank protection structures may become submerged during storm surges. In the present study, a turbulent flow field around a submerged pile within a scour hole is numerically simulated considering a very fine mesh in the order of 50 million cells distributed within a relatively small computational domain. Necklace vortices, including two horseshoe vortices (HVs) and a junction vortex (JV), are detected upstream from the cylinder. In many snapshots, the tails of the HVs stretch in the flow direction, while their size and length change considerably over time. Downstream of the cylinder, the influence of the trailing vortex from the cylinder roof is mainly limited to a zone near the cylinder top, whereas the effect of the separated shear layers (SSLs) from the cylinder sides is dominant within a larger region. The strength of vorticity associated with the trailing vortex is mainly notable within the “very near wake” area, where the strength of the upward velocity component of the wake vortices generated from the cylinder sides mitigates. This paper describes the distribution and origin of streaks and rollers on the scoured bed, i.e. the main cause of sediment transported downstream of the cylinder

Flow-altering countermeasures against local scour at bridge piers

Scuola di Dottorato "Pitagora" in Scienzae Ingegneristiche, Ciclo I, a.a.2007-2010The ability to protect bridge piers and abutments against scour is critical to bridge safety. Excessive pier scour can cause high maintenance costs or even bridge collapse resulting in the interruption of traffic and possibly death. Up to now, various types of countermeasures have been recommended to reduce scouring around pier foundations. The countermeasures against pier scour can be broadly classified into two categories: (1) flow-altering and (2) bed-armouring countermeasures. This thesis focuses on the first category of countermeasures. Based on a comprehensive review of the up-to-date studies on various types of flow-altering countermeasures, these can be classified into four main groups based on their shapes and performances: (1) openings through piers, (2) pier attachments, (3) bed attachments and (4) other devices. After evaluation and considering all the countermeasures, a few countermeasures were recommended for further investigations. Among them, five countermeasures were selected for analysis in the present thesis. They are transverse sacrificial piles, collar, threading, pier slot and bed-sill. The first part of the experiments, were performed in clear-water scour condition, near threshold condition of sediment movement. In this part, countermeasures were tested individually. Afterwards, countermeasures that showed appropriate efficiency in scour depth reduction were combined one by one. Results of this part showed that a collar, pier slot and sacrificial piles may show efficiency of about 30% in scour depth reduction; however, threading cannot be assumed as a reliable pier scour countermeasure. Results show that the blockage ratio of sacrificial piles is an important parameter, since by increasing the number of piles from three to five, the efficiency reduces. In this part also optimum size and location of a pier slot were criticised and best configuration based on previous and present studies was proposed. In fact, the best configuration can be suggested as a pier slot half as long as the flow depth plus maximum scour depth. In this case, the pier slot near the water surface may not significantly increase the efficiency. A combination of sacrificial piles with a collar and sacrificial piles with a slot showed that they cannot reduce the scour depth significantly with respect to each individual countermeasure. In particular, a combination of a collar and sacrificial piles increases the rate of scouring with respect to a single collar. At the end of this part, a combination of a bed-sill and cut-collar was selected as the best configuration. Two forms of this countermeasure were proposed for further studies. In the first proposed countermeasure, the use of a sill as wide as the channel width was recommended. This form, although reliable to prevent souring at the upstream part of the bed-sill, may not be applicable for some practical purposes. Therefore, in another attempt, a shorter bed-sill was also proposed, protected with two side-walls, in order to reduce the risk of scour intrusion in front of the bed-sill. These two proposed countermeasures showed efficiencies of 68.5% and 64.5% in scour depth reduction, however owing to the use of a border around the collar rim, the scour did not reach the pier body. In next part, the later form of proposed countermeasure that consists of a shorter bed-sill and seems to be more practical, was evaluated in unsteady flow tests with the peak flow intensity slightly greater than the threshold for the inception of sediment movement. In this section of the thesis, circular and round nose and tail rectangular piers were tested in both configurations of single and two in-line piers. The results of unsteady flow tests also show that the proposed combined countermeasure can protect pier foundation during a flood event. Specifically, it seems that the proposed countermeasure is more effective when it is applied to round nose and tail rectangular piers than circular onesUniversità degli Studi della Calabri

Flow-altering countermeasures against scour at bridge piers: a review

During the past decades, several investigations were conducted to assess the adequacy of countermeasures against local scour at bridge piers. The countermeasures can be broadly classified into two categories: (1) flow-altering and (2) bed-armouring countermeasures. Flow-altering countermeasures, as treated herein, can be classified into four main groups based on their shapes and performances. A comprehensive review of the up-to-date studies on various types of flow-altering countermeasures is presented, placing special emphasis on recently proposed methods while also revisiting studies of former methods. Experimental conditions of different studies under which the tests were performed are critically examined. A preliminary evaluation of the previously conducted experiments indicates that the results of several tests were influenced by side-wall, sediment size, flow shallowness and temporal effects. Experimental results on the combinations of different countermeasures, including their limitations and difficulties in field applications, are also discussed. Finally, suggestions are presented for further research on selected countermeasures

Escavazione localizzata a valle di strutture trasversali in fondo incoerente o coesivo: osservazioni sperimentali e modellazione numerica

Dottorato di Ricerca in Ingegneria Idraulica per l’Ambiente e il Territorio Ciclo XXV, a.a.2013Università della Calabri