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Fuping Gao - One of the best experts on this subject based on the ideXlab platform.
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Physical modelling of local Scour at twin piles under combined waves and current
Coastal Engineering, 2019Co-Authors: Fuping GaoAbstract:Abstract Under the actions of ocean waves and current, severe local Scour can be induced around pile groups, significantly compromising the safety of marine structures. A series of flume tests were conducted for physical modelling the local Scouring process around twin piles in the cohesionless soils under combined waves and currents, and compared with the pure current case. The effects of non-dimensional pile spacing (G/D) and flow skew angle (α) on the Scour Depth and time scale of Scour around twin piles are intensively examined. The experimental observations indicate that the influence of pile spacing on the Scour Depth development is much more significant for the side-by-side (α = 90ο) arrangement than that for the tandem arrangement (α = 0°). With the increase of flow skew angle α, the maximum Scour Depth is remarkably enhanced within the examined range 0 ≤ G/D ≤ 3.0. When G/D = 3.0, the pile group effect on the time scale is generally negligible for pure current cases, whereas a prominent pile-group effect can still be observed for combined wave-current cases, especially for the side-by-side arrangement. A parameter of "equivalent pile diameter" is then introduced for evaluating the maximum Scour Depth at the twin piles with the previous formulas for the single pile. Based on the existing and present experimental data, the empirical formula of dimensionless equivalent pile diameter as the function of G/D and α is established to predict the maximum Scour Depth at the twin piles.
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equilibrium Scour Depth at offshore monopile foundation in combined waves and current
Science China-technological Sciences, 2014Co-Authors: Fuping GaoAbstract:Unlike the pier Scour in bridge waterways, the local Scour at offshore monopile foundations should take into account the effect of wave-current combination. Under the condition of wave-current coexistence, the water-soil interfacial Scouring is usually coupled with the pore-pressure dynamics inside of the seabed. The aforementioned wave/current-pile-soil coupling process was physically modeled with a specially designed flow-structure-soil interaction flume. Experimental results indicate that superimposing a current onto the waves obviously changes the pore-pressure and the flow velocity at the bed around the pile. The concomitance of horseshoe vortex and local Scour hole around a monopile proves that the horseshoe vortex is one of the main controlling mechanisms for Scouring development under the combined waves and current. Based on similarity analyses, an average-velocity based Froude number (Fr (a)) is proposed to correlate with the equilibrium Scour Depth (S/D) at offshore monopile foundation in the combined waves and current. An empirical expression for the correlation between S/D and Fr (a) is given for predicting equilibrium Scour Depth, which may provide a guide for offshore engineering practice.
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physical modeling of local Scour development around a large diameter monopile in combined waves and current
Coastal Engineering, 2014Co-Authors: Fuping GaoAbstract:In most of the previous studies on local Scour around pile foundations, wave-induced pore pressure response has not been taken into account. The local-Scour and pore-pressure responses around a large-diameter monopile in combined waves and current have been physically modeled with a specially-designed flow-structure-soil interaction flume. In the series of experiments, the time developments of the Scour-Depth and the pore-pressure in the proximity of the model pile were measured simultaneously. Experimental results indicate that the wave-induced upward seepage under the wave troughs may weaken the buoyant unit weight of the surrounding sand, which brings the sand-bed more susceptible to Scouring. The superimposition of the waves on a current has much effect on the time-development of local Scour and the resulting equilibrium Scour-Depth, which is particularly obvious when the sand-bed is in the clear-water regime under the current or waves alone respectively. It is observed that the maximum flow velocity at the boundary layer for the following-current case is larger than that for the opposing-current case, which further results in faster time development of Scour Depth and greater equilibrium Scour Depth for the following-current case.
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local Scour and pore water pressure around a monopile foundation under combined waves and currents
The Twenty-second International Offshore and Polar Engineering Conference, 2012Co-Authors: Fuping Gao, Qixia GongAbstract:A series of experiments were conducted in a large flow-structure-soil interaction flume to analyze the Scour development and pore-water pressure response around a monopile foundation under the action of combined waves and currents. In the experiments, the Scour Depth and pore pressure response around the pile were measured simultaneously. The experimental results indicate that the maximum equilibrium Scour Depth due to waves plus currents is greater than a linear sum of those caused by waves and currents respectively. This nonlinearity effect is particularly obvious when the sand-bed condition under currents or waves alone is in clear-water regime. The maximum equilibrium Scour Depth normalized with pile diameter is closely dependent on the Froude number with increasing the wave-induced water particle velocity meanwhile the current velocity keeping constant. The wave-induced pore pressure gradient around the monopile under the wave trough weakens the buoyant unit weight of the surrounding sand and induces the sand-bed more susceptible to Scouring.
Dongsheng Jeng - One of the best experts on this subject based on the ideXlab platform.
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estimation of clear water local Scour at pile groups using genetic expression programming and multivariate adaptive regression splines
Journal of Waterway Port Coastal and Ocean Engineering-asce, 2019Co-Authors: S Bateni, Hamid Reza Vosoughifar, B Truce, Dongsheng JengAbstract:The physical process of Scour around pile groups is complex. Due to economical and geotechnical considerations, multiple pile bridge piers have become more common in bridge designs. Various empirical models have been developed to estimate Scour Depth at pile groups. However, these models are mostly based on the conventional statistical regression approaches and are not able to adequately capture the highly nonlinear and complex relationship between Scour Depth and its influential factors. In this study, genetic expression programming (GEP) and multivariate adaptive regression splines (MARS) were utilized to estimate clear-water local Scour Depth at pile groups using the flow, sediment, and pile characteristics. Two combinations of data were used to train the GEP and MARS models. The first combination included dimensional variables (e.g., mean flow velocity and Depth, mean grain diameter, pile diameter). The second combination contained nondimensional parameters. Results indicated that GEP and MARS can accurately estimate Scour Depth. Both models yielded better results when the dimensional data were used. In addition, the MARS model with a root mean square error (RMSE) of 0.0220 m and correlation coefficient (R2) of 0.902 outperformed the GEP model with an RMSE of 0.0285 m and R2 of 0.834. Performance of the GEP and MARS models was compared with that of the existing equations. The comparison showed that both models perform better than the regression-based empirical equations. Finally, a sensitivity analysis showed that pile diameter has the most significant impact on equilibrium Scour Depth.
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neural network and neuro fuzzy assessments for Scour Depth around bridge piers
Engineering Applications of Artificial Intelligence, 2007Co-Authors: S M Bateni, S M Borghei, Dongsheng JengAbstract: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 modeled as a function of five variables; flow Depth, mean velocity, critical flow velocity, mean grain diameter and pier diameter. The time variation of Scour Depth was also modeled in terms of equilibrium Scour Depth, equilibrium Scour time, Scour time, mean flow velocity and critical flow velocity. The training and testing data are selected from the experimental data of several valuable references. Numerical tests indicate that MLP/BP model provide a better prediction of Scour Depth than RBF/OLS and ANFIS models as well as the previous empirical approaches. Finally, sensitivity analysis shows that pier diameter has a greater influence on equilibrium Scour Depth than the other independent parameters.
Bruce W. Melville - One of the best experts on this subject based on the ideXlab platform.
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time scale for local Scour at bridge piers
Journal of Hydraulic Engineering, 2000Co-Authors: Yee-meng Chiew, Bruce W. MelvilleAbstract:The temporal development of clear-water local Scour Depth at cylindrical bridge piers in uniform sand beds is considered. New data are presented and used to quantify the influence of flow duration on the Depth of local Scour. An equilibrium time scale (t*) is defined. The data show that both t* and the equilibrium Scour Depth (dse) are subject to similar influences of flow and sediment parameters, as might be expected because they are inherently interdependent. A method is given for determination of the time for development of dse for a given pier, sediment, and approach flow velocity and the concomitant estimation of the Scour Depth at any stage during development of the equilibrium Scour hole. The results show that the Scour Depth after 10% of the time to equilibrium is between about 50% and 80% of the equilibrium Scour Depth, depending on the approach flow velocity. of local Scour d se is rapidly attained in live-bed conditions, but rather more slowly in clear-water conditions (Fig. 1). Clear- water Scour occurs for mean flow velocities up to the threshold velocity for bed sediment entrainment, i.e., V # Vc, while live- bed Scour occurs for V > Vc. The maximum equilibrium Scour Depth dse)max occurs at V = Vc. In armored cobble or cohesive sediment bed streams, multiple flood events may be required before the maximum clear-water Scour is reached. This may take many years. The equilibrium Scour Depth in live-bed con- ditions fluctuates due to the effects of bed form migration. The dashed lines in Fig. 1 represent the temporal average Scour Depth under live-bed conditions. The diagram also shows the time taken, te, for the equilibrium Scour Depth to develop. The equilibrium time, te, is the focus of this paper. It increases rapidly with flow velocity under clear-water conditions, but then decreases rapidly for live-bed Scour. Existing equations for Depth of local Scour at bridge piers give the equilibrium Depth and are therefore conservative re- garding temporal effects. For the live-bed conditions that typ- ically pertain in floods, equilibrium Scour Depths are appro- priate. However, where clear-water Scour conditions exist, the equilibrium Depth of Scour may be overly conservative. Peak flood flows may last only a number of hours or a few days in the field, and short floods have insufficient time to generate equilibrium Depths. For example, bridge piers situated on the floodplain may be wet for periods of less than one day during a flood; typically, clear-water conditions pertain at such sites. The actual Scour may be only a small fraction of the equilib- rium Scour Depth, which could take weeks to fully develop. Johnson and McCuen (1991) developed an analytical model to simulate the temporal process of local Scour at piers. The model was applied to a hypothetical bridge pier using a gen- erated sequence of flood flows over a 75 year period, the in- dividual storms being of 24 h duration. At the end of the 75 year period, the Scour Depth was still increasing.
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maximum local Scour Depth at bridge piers and abutments
Journal of Hydraulic Research, 1998Co-Authors: Jaya Kandasamy, Bruce W. MelvilleAbstract:Results of recent laboratory investigations of local Scour at bridge piers and abutments are presented. Similarities between the principal vortex occurring in local Scour holes at abutments and the horseshoe vortex and downflow at piers are highlighted. Pier and abutment laboratory data, collected near the threshold conditions for sediment movement, display similar trends in the variation of Scour Depth with length and flow Depth. This variation is best described in a three dimensional plot. A simple equation, that can be used to predict the maximum local Scour Depth at either piers or abutments aligned perpendicular to the flow, is presented and compared with field data.
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local Scour at bridge abutments
Journal of Hydraulic Engineering, 1992Co-Authors: Bruce W. MelvilleAbstract:Laboratory data for local Scour Depth at bridge abutments are presented. These include sufficient data to demonstrate the effects on Scour Depth of abutment length, flow Depth, and abutment shape and alignment. In addition, some data for the effects of sediment characteristics, flow intensity, and approach channel geometry are given. The data are rationalized in terms of the ratio of abutment length to flow Depth, L/y. Two limiting cases are identified. For large and small values of L/y, the abutments are termed long and short, respectively, and it is shown that the maximum Scour Depths measured in the laboratory for these cases are 2L and 10 y. Most actual cases of abutment Scour lie between the limiting cases, and it is demonstrated that, in such situations, Scour Depth is proportional to the square root of the product L/y. These relationships are formulated in a simple design method, which is used on some illustrative examples. Limitations to the design method are discussed.
Pezhman Taherei Ghazvinei - One of the best experts on this subject based on the ideXlab platform.
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a hybrid intelligence approach to enhance the prediction accuracy of local Scour Depth at complex bridge piers
Sustainability, 2020Co-Authors: Dieu Tien Bui, Ataollah Shirzadi, Ata Amini, Himan Shahabi, Nadhir Alansari, Shahriar Hamidi, Sushant K Singh, Binh Thai Pham, Baharin Bin Ahmad, Pezhman Taherei GhazvineiAbstract:Local Scour Depth at complex piers (LSCP) cause expensive costs when constructing bridges. In this study, a hybrid artificial intelligence approach of random subspace (RS) meta classifier, based on ...
Mohammad Najafzadeh - One of the best experts on this subject based on the ideXlab platform.
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prediction of local Scour Depth downstream of sluice gates using data driven models
ISH Journal of Hydraulic Engineering, 2017Co-Authors: Mohammad Najafzadeh, Ali Tafarojnoruz, Siow Yong LimAbstract:AbstractNumerous investigations have already been conducted to characterize the effects of influencing parameters on Scouring process in order to derive an accurate predictive equation of local Scour Depth downstream of a sluice gate. However, due to the complexity of the Scour phenomena, available empirical equations, originally derived on the basis of regressive methods, do not always offer accurate Scour Depth prediction. Previous studies have clarified that artificial intelligence techniques may be alternatively considered to solve a complex phenomenon like local Scouring. In present study, Gene-Expression Programming, Model Tree (MT), and Evolutionary Polynomial Regression approaches, which are among the newest artificial intelligence approaches, were evaluated for prediction of local Scour Depth downstream of sluice gates with an apron. The input variables affecting the Scour Depth are sediment size and its gradation, apron length, sluice gate opening, and the flow conditions downstream of the sluic...
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prediction of local Scour Depth downstream of sluice gates using data driven models
ISH Journal of Hydraulic Engineering, 2017Co-Authors: Mohammad Najafzadeh, Ali Tafarojnoruz, Siow Yong LimAbstract:Numerous investigations have already been conducted to characterize the effects of influencing parameters on Scouring process in order to derive an accurate predictive equation of local Scour Depth...
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neurofuzzy based gmdh pso to predict maximum Scour Depth at equilibrium at culvert outlets
Journal of Pipeline Systems Engineering and Practice, 2016Co-Authors: Mohammad NajafzadehAbstract:AbstractIn this study, the neurofuzzy-based group method of data handling (NF-GMDH) as an adaptive learning network was utilized to predict the maximum Scour Depth at equilibrium downstream of culvert outlet structures. The NF-GMDH network was developed using particle swarm optimization (PSO). Effective variables on the maximum Scour Depth at equilibrium included those of sediment size downstream of culvert outlets, the geometry of culvert outlets, and the flow characteristics upstream and downstream of the culvert. Training and testing performances of the NF-GMDH-PSO network were carried out using nondimensional data sets that were collected from the literature. The testing results of the NF-GMDH-PSO model were compared with the gene-expression programming (GEP) and traditional equations. The NF-GMDH-PSO network produced a lower error of maximum Scour Depth at equilibrium prediction than those obtained using the other models. Also, the most effective parameter on the maximum Scour Depth at equilibrium wa...
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evaluation of gmdh networks for prediction of local Scour Depth at bridge abutments in coarse sediments with thinly armored beds
Ocean Engineering, 2015Co-Authors: Mohammad Najafzadeh, Gholamabbas Barani, Masoudreza HessamikermaniAbstract:Protection of the bridge abutment in waterways against Scour phenomena is a very significant issue in hydraulic engineering fields. Several field and experimental investigations were carried out to produce a relationship between the abutment Scour Depth due to thinly armored bed and the governing variables. However, existing empirical equations do not always provide accurate Scour prediction due to the complexity of the Scour process. In the present study, group method of data handling (GMDH) networks are utilized to predict abutments Scour Depth in thinly armored beds. GMDH network is developed using evolutionary and iterative algorithms included those of gravitational search algorithm (GSA), particle swarm optimization (PSO), and back propagation (BP). The sediment size properties, bridge abutments geometry, and approaching flow are considered as effective parameters on the abutment Scour Depth. Training and testing stages of the models are carried out using experimental data sets. Performances results for alternative GMDH networks are compared with those obtained using traditional equations. A sensitivity analysis is also performed to determine the most important parameter in predicting the abutment Scour Depth in thinly armored beds.
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Prediction of pipeline Scour Depth in clear-water and live-bed conditions using group method of data handling
Neural Computing and Applications, 2014Co-Authors: Mohammad Najafzadeh, Gholamabbas Barani, Hazi Mohammad AzamathullaAbstract:In the present study, the Group method of data handling (GMDH) network was utilized to predict the Scour Depth below pipelines. GMDH network was developed using back propagation. Input parameters that were considered as effective parameters on the Scour Depth included those of sediment size, geometry of pipeline, and approaching flow characteristics. Training and testing performances of the GMDH networks have been carried out using nondimensional data sets that were collected from the literature. These data sets are related to the two main situations of pipelines Scour experiments namely clear-water and live-bed conditions. The testing results of performances were compared with the support vector machines (SVM) and existing empirical equations. The GMDH network indicated that using of back propagation produced lower error of Scour Depth prediction than those obtained using the SVM and empirical equations. Also, the effects of many input parameters on the Scour Depth have been investigated.