Wyniki wyszukiwania - Biblioteka Nauki

1

A review on hydrodynamics of horseshoe vortex at a vertical cylinder mounted on a fat bed and its implication to scour at a cylinder

100%

Gazi A. H. , Afzal M. S.

Acta Geophysica

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2020

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tom Vol. 68, no. 3

861--875

EN

A comprehensive review of the local scour due to vortical fow around a cylindrical bridge pier under steady current is presented in this paper. The mechanism of the formation of vortices, the size, velocity and strength of horseshoe vortex (HSV), formation of the HSV by the separation of laminar and turbulent boundary layer and the scour around a cylindrical pier due to vortices have been presented. The complexity involved in the scour-related calculations, and the scope for future research are discussed in the last section.

2

Experimental study of debris-induced scour around a slotted bridge pier

100%

Hamidifar H. , Nezhadian D. M. A. , Carnacina I.

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tom Vol. 70, no 5

2325--2339

EN

One of the most common problems for river engineers is the accumulation of waterborne debris upstream of the bridge piers. In addition to reducing the cross-sectional flow area, debris increases the drag force exerted to the pier and contributes to scour. Several studies have been carried out by previous researchers to examine the usefulness of different types of countermeasures. The effectiveness of these countermeasures is not well understood when debris accumulation occurs. In this study, the effect of debris accumulation on the efficiency of a bridge pier slot, as scour countermeasure, is investigated experimentally. A total of 54 experiments were carried out under different hydraulic and debris geometrical conditions. The results showed that slots were effective in protecting bridge piers against scouring in presence of debris. Depending on the debris shape, the reduction efficiency may increase or decrease for a slotted pier in presence of debris accumulation when compared to the standard pier conditions without debris accumulation. Except for the inverse pyramid shape, the maximum scour is generally more reduced due to sheltering effect when the debris is located on the bed. While debris accumulation can lead to a reduction of the slot efficiency, the slot can be considered a reliable countermeasure against scouring. The outcome of this study can help the design of new bridges affected by large wood debris accumulations.

3

Splitter plate as a flow-altering pier scour countermeasure

80%

Khaple S. , Hanmaiahgari P. R. , Gaudio R. , Dey S.

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tom Vol. 65, no. 5

957--975

EN

Results of an experimental study on the countermeasure of scour depth at circular piers are presented. Experiments were conducted for pier scour with and without a splitter plate under a steady, uniform clear-water flow condition. The results of pier scour without splitter plate were used as a reference. Different combinations of lengths and thicknesses of splitter plates were tested attaching each of them to a pier at the upstream vertical plane of symmetry. Two different median sediment sizes (d50 = 0.96 and 1.8 mm) were considered as bed sediment. The experimental results show that the scour depth consistently decreases with an increase in splitter plate length, while the scour depth remains independent of splitter plate thickness. In addition, temporal evolution of scour depth at piers with and without a splitter plate is observed. The best combination is found to be with a splitter plate thickness of b/5 and a length of 2b. Here, b denotes the pier diameter. An empirical formula for the estimation of equilibrium scour depth at piers with splitter plates is obtained from a multiple linear regression analysis of the experimental data. The flow fields for various combinations of circular piers with and without splitter plate including plain bed and equilibrium scour conditions were measured by using an acoustic Doppler velocimeter. The turbulent flow fields for various configurations are investigated by plotting the velocity vec-tors and the turbulent kinetic energy contours on vertical and horizontal planes. The splitter plate attached to the pier deflects the approach flow and thus weakens the strength of the downflow and the horseshoe vortex, being instrumental in reducing the equilibrium scour depth at piers. The proposed method of pier scour countermeasure is easy to install and cost effective as well.

4

On the resistance of concrete hollow thin-walled high piers to rock collisions

80%

Huang Y.

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tom Vol. 69, nr 3

187--197

EN

Concrete hollow thin-walled high piers (CHTWHPs) located in mountainous areas may be destroyed by the huge impact force of accidental rocks. The study focuses on analyzing the effects of rock impact on the pier, including its impact force, pier damage, dynamic response, and energy dissipation characteristics. The results show that: (1) Increasing the impact height led to a decrease in the peak impact force. Specifically, 15.5% decrease in the peak collision force is induced when the height of rock collision rises from 10 m to 40 m. (2) The damage mode of the pier’s collision surface is mainly oval damage with symmetrical center, radial damage on the side surface, and corner shear failure on the cross section. (3) The peak displacement of bridge pier increases with the increase of collision height. As the collision height increased from 10 m to 40 m, the bridge pier’s peak displacement also increased, rising by 104.2%. (4) The concrete internal energy gradually decreased with increasing collision height, dropping by 36.9% when the height of rock collision rises from 10 m to 40 m. The reinforcement internal energy showed an increase of 78%. The results of this study may provide reference for the rock collision resistance design of CHTWHPs.