Scour Induced by Single and Twin Propeller Jets

Ong

et al. 2020

JMSE

Self Cite

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).

“…The clearance effect was reported in the works such as Ong et al [29]. The distance between propeller and sand bed was set same to Cui et al [30] without quay wall.…”

Section: Methodsmentioning

confidence: 99%

Section: Scour Patterns Between the External-rotating And Internal-rotating Systemsmentioning

confidence: 99%

Experimental Scours by Impinging Twin-Propeller Jets at Quay Wall

Ong

et al. 2020

JMSE

Self Cite

“…Previous research on twin-propeller induced scour is insufficient to estimate the scour depth for twin-propeller ship. Cui et al [16] stated that most ships used the external rotating system (turning outward over the top), and therefore the experimental data of external rotating system is used to establish the empirical model for twin-propeller. The twin-propeller scour has two connected scour holes, which can be described as the combination of two single-propeller scour holes in the preliminary stage.…”

Section: Methodsmentioning

confidence: 99%

Temporal Model for Ship Twin-Propeller Jet Induced Sandbed Scour

Zhang

et al. 2019

JMSE

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This research paper proposes the use of empirical equations to estimate the temporal maximum scour that is induced by twin-propeller ( ε t w i n = Ω t [ l n ( t ) ] Γ t ) when acting over non-cohesive bed materials. A purpose built experimental apparatus is used to obtain the measurement data required for the calculation of the empirical constants. The output from rigorous experimental investigations demonstrates that the maximum scour depth produced from the operation of twin-propeller ( ε t w i n ), within the confines of a harbour basin, varies as a logarithmic function of time. A dimensional analysis of the standard single propeller configuration is used as the foundation upon which the scour equation is postulated. This is extended to include the influence of the operating distance between the twin-propeller configurations for the first time. The division of scours by twin-propeller and single-propeller ( ε twin / ε m ) enables the establishment of mathematical relation to calculate C1, C2, A, and B. The constants are C 1 = 366.11, C 2 = 0.3376, A = 0.859, and B = 0.1571. The proposed scour equation is more reliable within the time zone up to two hours based on the experimental data.

“…Local scour is a well-defined term in river engineering and is described as the removal of sediment particles from the alluvial streams. It is recognized as the main reason for the failure of hydraulic structures [5][6][7][8]. Figure 1 shows an actual picture of the failure of a vertical spur dike in the river Gaula near Haldwani, Uttrakhand in India.…”

Section: Introductionmentioning

confidence: 99%

Scour around Spur Dike in Sand–Gravel Mixture Bed

Pandey

et al. 2019

Water

Self Cite

Scour is the main cause of failure for spur dike. The accurate prediction of scour around spur dike is essential to design a spur dike. The present study focuses on the maximum scour depth in equilibrium condition and parameters, which influence it in a sand–gravel mixture bed. Outcomes of the present experimental study showed that the non-dimensional maximum equilibrium scour depth increases with critical velocity ratio (U/Uca), water depth-armour particle ratio (h/da), Froude number for sediment mixture (Frsm), water depth-spur dike length ratio (h/l), and decreases with increase in armour particle-spur dike length ratio (da/l). The maximum scour depth is proportional to dimensionless parameters of U/Uca, h/da, Frsm, h/l, but the scour depth is inverse proportional to da/l. Scour around spur dike in a sand–gravel mixture is mainly influenced by the property of the sediment mixture. The scour increases with decrease in non-uniformity of the sediment mixture. A non-linear empirical equation is proposed to estimate the maximum scour depth at an upstream nose of rectangular spur dike with a maximum error of 15%. The sensitivity analysis indicates that the maximum non-dimensional equilibrium scour depth depends on Frsm, followed by the secondary sensible parameters da/l, h/l, and h/da.