Experimental Scours by Impinging Twin-Propeller Jets at Quay Wall

Abstract

Experiments were conducted to investigate the seabed scour holes due to the interaction between the twin-propeller jet and quay wall. Vertical quay wall was modelled by using a polyvinyl chloride (PVC) plastic plate in a water tank. The relationship between the positions of the propeller and the vertical quay wall was designed according to the actual working conditions of a ship entering and leaving a port. Propeller-to-wall distance and rotational speed were changed to observe the various scour conditions. The scour depth was measured by using an Acoustic Doppler Velocimeter (ADV). Primary scour hole was found within the jet downstream and secondary scour hole occurred beneath of the propeller. Third scour hole was found close to the quay wall due to horseshoe vortices. The maximum scour position of this third scour hole was found at the jet centre near the quay wall. Temporal formation of scour holes can be divided into three stages: axial scour formation, obstructed scour expansion and equilibrium stages. The quantitative relationships for six characteristic parameters of the scour pit were established including the maximum scour depth (εmax,q), maximum scour depth position (Xm，q), maximum scour width (Wm，q), length of main scour pit (XS，q), maximum deposition height (ZD，q), and location of maximum deposition height (XD，q).

Ship propeller induced scour of non-cohesive sediment in low bed-clearance conditions

“…Therefore, considering a no-scour threshold at X w = 7D p in their experiments, performed over a sandy bed of d 50 = 0.2mm and with a twin-propeller of D p = 55mm rotating at 500rpm, the obtained wall Froude number is Fr w = 0.24. This result is slightly below the threshold obtained in this article, probably due to the slightly lesser sediment diameter used by Cui et al (2020b) in comparison with the present study. This difference points to a partial agreement and to the need to consider different sediment diameters to obtain a clear threshold of the wall Froude number to prevent scour over non-protected beds in case of confined twin propeller jets.…”

“…This threshold is found at Fr w ≈ 0.25. In the same line, Cui et al (2020b) reported no scour near the quay wall in the test experiments at X w = 9D p , although with wall clearance of X w = 7D p scour was visible. Therefore, considering a no-scour threshold at X w = 7D p in their experiments, performed over a sandy bed of d 50 = 0.2mm and with a twin-propeller of D p = 55mm rotating at 500rpm, the obtained wall Froude number is Fr w = 0.24.…”

“…However, the existing models to obtain the time-dependent scour depth may be applied. Cui et al (2020b) proposed an empirical model for inwards rotating twin propellers in confined scenarios, following the previous study of unconfined twin 3.8 to simply obtain the maximum scour due to a confined twin propeller jet (S con f ), from the more complex Eq. 3.5 in Cui et al (2019), focused on the time evolution of the maximum scour depth in case of unconfined twin propeller jets (S uncon f ).…”

“…The propeller jet properties and their effects over to confined propeller jets have received much less attention, and not many articles are found in literature about the topic. In case of confinement by a closed quay wall, only Hamill, Johnston, and Stewart (1999) and Cui et al (2020b) proposed an expression to determine the expected scour depth due to single and twin propeller jets, respectively.…”

Structural health monitoring of inland navigation structures and ports: a review on developments and challenges

“…For example, core samples are extracted from the concrete structures to evaluate the reasons for deterioration and estimate the remaining service life. 32,33 Other major factors urging for frequent assessments of INS are as follows: (i) changing weather patterns causing floods and droughts, 34 (ii) a rise in extreme weather events like storm surges 35 , and (iii) an increase in the inland water traffic and size of vessels, 36 which may causes misuse of the navigation structures. These factors compromise the integrity of INS and their service life.…”