Local scour of bridge piers is one of the main threats responsible for bridge damage. Adopting scour countermeasures to protect bridge foundations from scour has become an important issue for the design and maintenance of bridges located in erodible sediment beds. This paper focuses on the protective effect of one active countermeasure named an “anti-scour collar” on local scour around the commonly used cylindrical bridge pier. A cylindrical pier model was set up in a current flume. River sand with a median particle size of 0.324 mm was selected and used as the sediment in the basin. A live-bed scour experimental program was carried out to study the protective effect of an anti-scour collar by comparing the local scour at a cylindrical bridge pier model with and without collar. The effects of three design parameters including collar installation height, collar external diameter and collar protection range, on the scour depth and scour development were investigated parametrically. According to the experimental results, it can be concluded that: the application of an anti-scour collar alleviates the local scour at the pier effectively; and the protection effect decreases with an increase in the collar installation height, but increases with an increase in the collar external diameter and the protection range. Design suggestions for improving the scour protective effect of the anti-scour collar are summarized and of great practical guiding significance to the development of anti-scour collars for bridge piers.
To more comprehensively explore the mechanism of the active freezing and thawing process of a new tube–curtain freezing method in construction, the temperature field of the new tube–curtain freezing process is analyzed using finite element software to establish a numerical model. Six paths were set up upstream and downstream of the model and around the top steel tube to analyze the development of frozen soil curtains during active freezing and forced thawing. The results show that, due to the effect of seepage, the cold energy generated by the upstream frozen pipe will be carried to downstream by water, which leads to the asymmetry of the frozen soil curtain. A greater seepage rate leads to a more pronounced the influence on the development of the temperature field. During the process of forced thawing, the first 15 days of the frozen soil curtain heating rate are fastest; thus, it is necessary to monitor the thawing settlement intensively during this period. By comparing different heads of water and different forced thawing temperatures, it was found that a bigger head of water results in a longer thawing time. At a constant head of water, a higher thawing temperature results in a shorter thawing time, with the thawing time at 50 °C being about 0.5 times that at 5 °C. Low-temperature thawing can be chosen to control the cost; however, when the head of water is large, high-temperature thawing can significantly shorten the thawing time. In addition, the new tube–curtain freezing method has little influence on the surrounding environment, along with a short construction period and low construction cost, in accordance with the concept of sustainable development.
Local scour around caissons under currents has become one of the main factors affecting the safety of foundation construction and operation in coastal and offshore bridge engineering. Local scour occurs not only in the operation stage, when the caisson has settled into the sediment, but also in the construction stage, when the caisson is suspended in water. In this study, the local scour induced by unidirectional and tidal currents around settled caissons with different cross-sections (circular, square, and diamond) was experimentally investigated. Circular and square caissons were selected to investigate the difference in local scour of suspended caissons under unidirectional and tidal currents. The main findings from the experimental results were: (1) the temporal development of scour under tidal current was slower than that of unidirectional current; (2) the effect of current type can significantly influence the size and location of maximum scour depth around circular and square caissons; (3) the appropriate choice of cross-section could reduce the maximum scour depth around the settled caisson; (4) the maximum scour depth of tidal current was smaller than that of unidirectional current when the caisson was settled into the sediment, while the opposite effect occurred when the caisson was suspended in water.
The weight function method that uses a known weight function has been a general tool for the signal analysis of the electromagnetic flowmeter(EMF). However, it is difficult to solve the voltage equation directly by analytical method in order to get weight function for the partially filled pipe electromagnetic flowmeter(EMF-PF). The finite element numerical analysis method is tried to solve the weight function for the EMF-PF in this paper. The results show that weight function for EMF-PF relates to fill height of liquid in partially filled pipes, and there is a nonlinear function relationship between weight function for EMF-PF and fullness degree of liquid in the pipe.
Low speed and high angle of attack are problems that must be faced in vertical launching missiles. A natural asymmetric vortex phenomenon occurs at a low speed and high angle of attack of a slender body. In this paper, the Detached Eddy Simulation (DES) method is adopted to simulate the asymmetric flow of a slender body at a high angle of attack. The influence of roughness is analysed from the flow field and pressure distribution. And the DES method is verified by comparing it with the wind tunnel test results. The flow fields of the four models with the surface roughness of 0, 0.8, 5, and 100 are compared. The downstream flow still appears asymmetric when the surface is smooth, indicating that the stability of the flow field is not enough to maintain the symmetry of the flow field. The simulation results show that the adverse pressure gradient increases in the region where the boundary layer separates with the roughness greatly increasing, but the structure of the flow field at the head is slightly different. On the whole, the surface pressure and lateral force per unit length ( C f z p m ) transform alternately along the axial direction, and the period of alternating reverses increases with the increase of roughness. Finally, the pressure tends to be in equilibrium, and C f z p m approaches zero. It should be noted that the distribution of C f z p m is slightly different on the head, indicating that the asymmetry of pressure on the cylinder section is an important factor controlling the magnitude and the direction of lateral force. The influence of roughness on the flow around a slender body is acquired in this paper, and it has reference significance to the roughness problem of the actual missile.
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