Search for: scour
Total 23 records
Scour hole depth prediction around pile groups: review, comparison of existing methods, and proposition of a new approach, Article Natural Hazards ; Volume 88, Issue 2 , 2017 , Pages 977-1001 ; 0921030X (ISSN) ; Beheshti, A. A ; Ataie Ashtiani, B ; Sharif University of Technology
A dataset of 365 laboratory tests for scour hole depth (SHD) around pile groups (PGs) under unidirectional aligned flow is compiled, and the performances of the existing equations are comparatively evaluated on the dataset using several statistical indices. A formulation based on a correction of HEC-18 equation provides the best estimate with a correlation factor of 0.58. The test durations of the considered data ranged between 4 and 389 h. A time factor (Kt) is proposed to take into account the temporal variation of the SHD around different PGs. Among the datasets, 51 long-duration experiments are scrutinized to show the temporal variation of scour depth toward equilibrium state. The time...
Article Journal of Hydroinformatics ; Volume 15, Issue 2 , September , 2013 , Pages 516-528 ; 14647141 (ISSN) ; Etemad-Shahidi, A ; Ataie-Ashtiani, B ; Sharif University of Technology
Scour phenomenon around piles could endanger the stability of the structures placed on them. Therefore, an accurate estimation of the scour depth around piles is very important for engineers. Due to the complexity of the interaction between the current, seabed and pile group; prediction of the scour depth is a difficult task and the available empirical formulas have limited accuracy. Recently, soft computing methods such as artificial neural networks (ANN) and adaptive neuro-fuzzy inference system (ANFIS) have been used for the prediction of the scour depth. However, these methods do not give enough insight into the generated models and are not as easy to use as the empirical formulas. In...
Discussion of “Neuro-fuzzy GMDH systems based evolutionary algorithms to predict scour pile groups in clear water conditions” by M. Najafzadeh, Article Ocean Engineering ; Volume 123 , 2016 , Pages 249-252 ; 00298018 (ISSN) ; Ataie Ashtiani, B ; Sharif University of Technology
The author utilized neuro-fuzzy based group method of data handling (NF-GMDH) to predict the local scour depth around pile groups under clear-water conditions. They collected the datasets from literature. To predict the local scour by using NF-GMDH, nine dimensional parameters were considered to define a functional relationship between input and output variables. The results of NF- GMDH networks were compared with that of the empirical equations. However, the collected datasets for pile group scouring, the method of implementing the empirical formula to calculate scour depth, and using the equation of Sheppard et al. (2004) suggested for single pier to predict local scouring around pile...
Article 23rd International Conference on Offshore Mechanics and Arctic Engineering, Vancouver, BC, 20 June 2004 through 25 June 2004 ; Volume 3 , 2004 , Pages 563-566 ; Jamali, M ; Sharif University of Technology
Scour is an important cause of instability of breakwaters. In case of vertical-wall breakwaters, toe scour can cause collapse of the whole structure. This paper is concerned with an experimental study of the effects of regular breaking waves on scour at toe of vertical-wall breakwaters. Experiments were carried out in a wave flume with regular waves for two cases of a beach with and without a breakwater. Bed profiles and scour depths for various wave heights, periods and depths were recorded. For the case of a beach without a breakwater, the observed bed profile types are compared to predictions. For the case of a beach with a breakwater, factors affecting the scour are investigated, and an...
M.Sc. Thesis Sharif University of Technology ; Abbaspour, Madjid
Regarding to significant role of marine pipelines in transferring oil, water and other products, a research was carried out to study the sediment transportation (Scouring) under pipelines which threaten pipelines. Interaction between fluid phase (flow field), structure phase (pipe) and sediment, determine scour profile shape and specifications of each phase which can change scour depth. In this research Flow-3D software was used to simulate scouring process under cylinder. First the flow field around cylinder near wall was studied and the scour depth under direct and oscillating flow was simulated. In addition, in next pace, the number of pipes and their distance were varied to measure...
Article Coastal Engineering ; Volume 133 , 2018 , Pages 43-58 ; 03783839 (ISSN) ; Ataie Ashtiani, B ; Beheshti, A ; Hadjzaman, M ; Jamali, M ; Sharif University of Technology
Elsevier B.V 2018
Complex piers (CPs), consisting of a column, pile cap and pile group, are commonly built as foundations for hydraulic and marine structures. Scour-hole development around CPs is studied in this paper. A total of 52 tests is carried out on 4 CP models, with experiments durations ranging from 24 to 120 h. All of the available experimental data for clear-water scour around CPs including the collected data of the present study and those previously published are reviewed and combined into a database. A special case of bridge piers with deep foundation or caisson instead of pile caps is also considered, which is herein called compound piers. The database contains 367 experiments for CPs and 162...
Article Journal of Hydraulic Engineering ; Volume 136, Issue 6 , June , 2010 , Pages 343-351 ; 07339429 (ISSN) ; Baratian Ghorghi, Z ; Beheshti, A. A ; Sharif University of Technology
Local scour around complex piers under steady clear-water condition was studied experimentally for a variety of configuration, including different sizes and shapes of complex piers. A total of 70 experiments were carried out. Three sets of experiments were performed over the entire range of possible pile cap elevations for complex piers with different geometrical characteristics. The collected data are used to quantify the pile cap elevations that maximize or minimize the local scour depth. Some of the available methodologies to estimate the maximum local scour depth around such complex piers are evaluated. The predictions of the scour depths improved by using the revised methods of...
M.Sc. Thesis Sharif University of Technology ; Jamali, Mirmosaddegh
In this study, the effect of submerged vanes on the bed erosion pattern at a 90° open-channel junction has been evaluated experimentally. In this study, 41 tests have been conducted in four different steps. In each test, the bed surface level has been measured at the end of 1st, 2nd and 24th hour. In the first step, the preliminary tests have been conducted. In this step, six different formations of submerged vanes have been selected and their performance has been evaluated and the most efficient formation, in the field of maximum scour depth reduction, has been selected. In the second step, six different formations of submerged vanes have been selected and their performance has been...
Investigation of the Effective Parameters on the Scouring Phenomenon of Seabed Pipelines by a Combination of Computational Fluid Dynamics and Discrete Elements Method, M.Sc. Thesis Sharif University of Technology ; Khorasanchi, Mahdi
Occurrence of scouring around the seabed pipelines can lead to pipe failure and pose a serious threat to the marine environment, economic losses and waste of oil and gas. Therefore, to prevent the occurrence of scouring, by simulating this phenomenon and identifying the parameters affecting it, we can help to design a more efficient placement of pipes in the seabed. Various methods such as potential flow theory and turbulent single-phase and two-phase models have been proposed to simulate this phenomenon. The purpose of this article is to simulate and investigate the effective parameters of this phenomenon by combining computational fluid dynamics and separate elements. The innovation of...
Experimental Study on Sediment Non-uniformity Effects on Local Scour Due to Hydraulic Jump Using Buried Plates, M.Sc. Thesis Sharif University of Technology ; Borghei, Mahmood
Local scour downstream of sluice gates in the erosive bed is one of the main concerns of hydraulic engineers, since it can cause serious damage to the structure. One of the ways to overcome this problem is the use of apron, or non-erosive bed. In order to shorten the apron or decrease the effect of the turbulence flow, different measures can be used. These approaches can be divided into two main branches, "Energy dissipating" and "bed reinforcement" measures. This study has investigated the scour phenomenon under the different conditions of the bed material gradation and bed reinforcement using vertical buried plates. The effect of sediment non-uniformity, unlike uniform sediment, has a...
Investigation of bed Stability in Downstream for the Diversion dam under Scour (Mill & Moghan case study), M.Sc. Thesis Sharif University of Technology ; Shamsai, Abolfazl
Numerical simulations and large eddy simulations (LES) of turbulent flow downstream of diversion dam , pool-riffle bedform in different geometrical ratios (different lengths of riffle and pool) with flow Reynolds number of 3.0 E+04 to 3.3E+04, downstream of special case study "Mill and Moghan diversion dam" with Froude number of 0.5 are presented The calculations are performed using a computational fluid dynamics model, FLOW-3D, which solves the Navier-Stokes equations in three dimensions with finite volume method. Numerical simulations are validated by comparing the numerical results of time-averaged flow patterns downstream of pool-riffle sequence with that of the experimental...
Estimation of current-induced scour depth around pile groups using neural network and adaptive neuro-fuzzy inference system, Article Applied Soft Computing Journal ; Volume 9, Issue 2 , 2009 , Pages 746-755 ; 15684946 (ISSN) ; Beheshti, A. A ; Ataie Ashtiani, B ; Sabbagh Yazdi, S. R ; Sharif University of Technology
The process of local scour around bridge piers is fundamentally complex due to the three-dimensional flow patterns interacting with bed materials. For geotechnical and economical reasons, multiple pile bridge piers have become more and more popular in bridge design. Although many studies have been carried out to develop relationships for the maximum scour depth at pile groups under clear-water scour condition, existing methods do not always produce reasonable results for scour predictions. It is partly due to the complexity of the phenomenon involved and partly because of limitations of the traditional analytical tool of statistical regression. This paper addresses the latter part and...
Article Proceedings of the Institution of Civil Engineers: Water Management ; Volume 165, Issue 9 , October , 2012 , Pages 473-480 ; 17417589 (ISSN) ; Kabiri-Samani, A ; Banihashem, S. A ; Sharif University of Technology
ICE Pub 2012
Accurate estimation of scour depth is needed for economic and safe determination of bridge pier foundation depth. Most design criteria are based on maximum scour depth due to the steady design discharge without flow time limit. In this paper, the results are presented of an experimental investigation on local scouring around a single bridge pier under steady and unsteady flow regimes. For unsteady flow, triangular shape hydrographs with repeatable peaks have been chosen. Results show that both sharp and flat increases to the peak of hydrographs have a negligible effect on scour depth for the same base time. An equation is obtained to compute the scour depth due to a specific triangular...
Article Journal of Hydraulic Research ; Volume 48, Issue 4 , Sep , 2010 , Pages 538-542 ; 00221686 (ISSN) ; Jabbari Sahebari, A ; Sharif University of Technology
High bed-shear stress resulting from secondary flows and velocity increase at a channel junction cause local erosion and deposition in natural rivers and earth-lined channels. Herein, the scour patterns at the junction of two loose bed channels were studied under clear-water conditions. The main dimensionless variables are the angle between the two approach flow branches, the discharge and width ratios of the tributary to the downstream channel branches, and the ratio of the mean downstream velocity to the threshold velocity. The results indicate that the position of the maximum scour depth temporally moves to the outer wall and upstream to the main channel, as affected by the dimensionless...
Article European Journal of Mechanics, B/Fluids ; Volume 36 , 2012 , Pages 152-166 ; 09977546 (ISSN) ; Aslani Kordkandi, A ; Sharif University of Technology
The present study provides the experimental results of the flow pattern around two-circular piers positioned in side-by-side arrangement. The experiments were performed for two bed configurations (with and without a scour hole). Velocities were measured by an Acoustic Doppler Velocimeter (ADV). Flat bed and scour hole were frozen by synthetic glue to facilitate the performance of the experiments. The contours and distributions of the time-averaged velocity components, turbulence intensities, turbulence kinetic energy, and Reynolds stresses at different horizontal and vertical planes are presented. Streamlines and velocity vectors obtained from time-averaged velocity fields are used to show...
M.Sc. Thesis Sharif University of Technology ; Borghei, Mahmood
Local scouring at the downstream of sluice gates in the erosive beds is one of the main concerns of hydraulic engineers because of the significant damage that it can cause to the hydraulic structures. It is important to control the local scour depth at downstream of hydraulic structures to ensure safety operation of these systems. Many researchers have conducted various studies to predict the maximum depth and diameter of scour hole and develop new methods in order to control this phenomenon. One way to overcome this problem is the use of apron, or non-erosive bed. In order to shorten the apron length or decrease the effect of the...
Experimental and Numerical Investigation of the Flow Field around Complex Bridge Piers with and without the Scour Hole, Ph.D. Dissertation Sharif University of Technology ; Ataie Ashtiani, Behzad
Local scour around bridge piers is one of the main causes of bridge failures Application of existing equations to complex flow patterns is problematic and often leads to questionable results in the field applications. A lack of understanding of the complex flow field and erosion mechanisms seems to be at least partly responsible for this state. Despite the rapid expansion of the literature on the flow around cylindrical piers, there are still challenges for flow field comprehension and estimating design scour depths around complex bridge piers. Due to geotechnical and economical reasons, bridge designs often leads to a complex foundation. Laboratory studies of local scour around complex...
M.Sc. Thesis Sharif University of Technology ; Ataie-Ashtiani, Behzad
The occurrence and development of scour hole around bridge pier are the main causes of bridge destruction. To predict manner, occurrence, development and final situation of scour hole around pier is the most important in the hydraulic design of bridges. A large number of studies have been performed to estimate the scour depth around piers at simplified laboratory conditions. The available equations from these studies do partly not present acceptable solutions. This issue is especially of great importance to the pile groups. For accurate determination of scour depth, it is required to get a better understanding of the flow and governing mechanism around pier. Although the flow pattern...
M.Sc. Thesis Sharif University of Technology ; Ataie-Ashtiani, Behzad ; Jamali, Mirmosaddegh
In this study, existing prediction methods of maximum scour depth around complex piers are studies using available experimental data and a new relationship for scour prediction is presented. Complex pier consists of a column, pile cap and pile group and is frequently used for foundation of bridge piers in hydraulic and marine structures. The results of 52 clear-water scour experiments on 4 CP models are reported which can be valuable to hydraulic design of a CP. The 4 models had different values of pile cap thickness and number of piles inline with the flow and were tested at different pile cap elevations. The duration of experiments ranged from 24 to 120 hours. Then a database of laboratory...
Article Engineering Applications of Artificial Intelligence ; Volume 20, Issue 3 , 2007 , Pages 401-414 ; 09521976 (ISSN) ; Borghei, S. M ; Jeng, D. S ; Sharif University of Technology
The mechanism of flow around a pier structure is so complicated that it is difficult to establish a general empirical model to provide accurate estimation for scour. Interestingly, each of the proposed empirical formula yields good results for a particular data set. Hence, in this study, alternative approaches, artificial neural networks (ANNs) and adaptive neuro-fuzzy inference system (ANFIS), are proposed to estimate the equilibrium and time-dependent scour depth with numerous reliable data base. Two ANN models, multi-layer perception using back-propagation algorithm (MLP/BP) and radial basis using orthogonal least-squares algorithm (RBF/OLS), were used. The equilibrium scour depth was...