Study of the Bed Velocity Induced by Twin Propellers

Mujal-Colilles, Anna; Gironella, X.; Crespo, A. J. C.; Sánchez‐Arcilla, Agustín

doi:10.1061/(asce)ww.1943-5460.0000382

Cited by 17 publications

(15 citation statements)

References 6 publications

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“…Water 2018, 10, x FOR PEER REVIEW 5 of 14 According to the results obtained from the experiments, maximum eroded depth, εmax, is located at the symmetry plane between the propellers, regardless of the engine order (ahead/forward or astern/backward direction). When a twin propeller model rotates inward in the ahead direction (forward scenario), the left-hand propeller rotates to starboard and the right hand to port, and the flux at the symmetry plane between propellers is towards the bed [13], increasing the action of a single propeller due to the sum of each propeller flow. On the contrary, if the twin propeller model is rotating outwards in the astern direction (backward scenario), the right hand propeller rotates to starboard and the left hand to port; thus, the flux at the symmetry plane is moving upwards, and the maximum scouring action should be concentrated below each propeller.…”

Section: Resultsmentioning

confidence: 99%

“…In particular, the focus of this study has tried to reproduce the consequences of this jet flow with the influence of a vertical wall simulating the berthing infrastructures during docking and undocking maneuvers. It is important to outline that the width and length of the LaBassa tank were large enough to avoid the influence of the lateral walls and the opposite vertical wall, as concluded by [13]. Moreover, the experimental facility only allowed a fixed configuration with respect to the vertical wall and the sediment bed.…”

Section: Discussionmentioning

confidence: 99%

“…However, the former equations were developed considering a single propeller. The guidelines published in [12] proposed two mathematical methods to extrapolate the efflux velocity of a single propeller to twin propellers, but [13] demonstrated that the empirical formulas to compute efflux velocity clearly overestimated the experimental results of a twin propeller model.The maximum erosion can be computed either (i) using the efflux velocity to obtain the bed velocity [7,8,14] and then computing the Shields parameter; or (ii) using empirical formulas developed in physical experiments with a single propeller model [15][16][17][18][19][20][21][22]. For the first case, ref.[13] found that bed velocity for twin propellers was estimated properly if the formulation proposed by [8] was used, but [13] did not compute the maximum erosion.…”

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Stern Twin-Propeller Effects on Harbor Infrastructures. Experimental Analysis

Mujal-Colilles

Castells

Marroig

et al. 2018

Water

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The growth of marine traffic in harbors, and the subsequent increase in vessel and propulsion system sizes, produces three linked problems at the harbor basin area: (i) higher erosion rates damaging docking structures; (ii) sedimentation areas reducing the total depth; (iii) resuspension of contaminated materials deposited at the seabed. The published literature demonstrates that there are no formulations for twin stern propellers to compute the maximum scouring depth. Another important limitation is the fact that the formulations proposed only use one type of maneuvering during the experimental campaign, assuming that vessels are constantly being undocked. Trying to reproduce the real arrival and departure maneuvers, 24 different tests were conducted at an experimental laboratory in a medium-scale water tank using a twin propeller model to estimate the consequences and the maximum scouring depth produced by stern propellers during the backward/docking and forward/undocking scenarios. Results confirm that the combination of backward and forward scenario differs substantially from the experiments performed so far in the literature using only an accumulative forward scenario, yielding deeper scouring holes at the harbor basin area. The results presented in this paper can be used as guidelines to estimate the effects of regular vessels at their particular docking location. reducing its operability for larger draft vessels and the area has to be dredged often enough for safe navigation (with sufficient keel clearance). Moreover, an environmental problem can also arise from the scouring effects of stern twin propellers of the vessels, and the increase in marine traffic in ports is also increasing the accumulation of heavy contaminants in some areas of the harbor. One of the engineering solutions to improve the water quality of the harbor is to trap the contaminated sediment below a layer of coarser gravel [2]. However, as reported by [3,4], the action of stern propellers over the seafloor can negate the solution and free the contaminated sediment creating an important issue that correlates sediment resuspension of contaminants due to the stern propellers' effects and water quality requirements of the cruise shipping industry.Therefore, the growth of marine traffic in harbors and its subsequent increase in vessel and propulsion system sizes produces three linked problems at the seabed of the harbor basins: (i) higher erosion rates damaging docking structures; (ii) sedimentation areas reducing the total depth of the harbor basin and its operability; and (iii) resuspension of contaminated materials deposited at the seabed.The formulation published and used so far to investigate the erosion rates of ship's propellers is based on empirical equations with a dependent variable named efflux velocity, V 0 . Efflux velocity is defined as the average velocity of the flux nearby a single propeller in a plane parallel to the propeller blades. The first empirical equation for V 0 was developed by [5,6], and detailed the expression ...

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Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Stern Twin-Propeller Effects on Harbor Infrastructures. Experimental Analysis

Mujal-Colilles

Castells

Marroig

et al. 2018

Water

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“…Hamill et al (2016) proposed the semi-empirical equations to determine the location, magnitude and distribution of the axial velocity within a free expanding propeller jet. Mujal-Colilles et al (2017) measured the velocity distribution within a twin-propeller jet using Acoustic Doppler Profiler (ADP) and suggested Blaauw et al's (1978) equation well agreed with the experimental results.…”

Section: Introductionmentioning

confidence: 67%

Ship Twin-propeller Jet Model used to Predict the Initial Velocity and Velocity Distribution within Diffusing Jet

et al. 2019

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The current research proposed the theoretical model for ship twin-propeller jet based on the axial momentum theory and Gaussian normal distribution. The twin-propeller jet model is compared to the more matured single propeller jet model with good agreement. Computational Fluid Dynamics (CFD) method is used to acquire the velocity distribution within the twin-propeller jet for understanding of flow characteristics and validation purposes. Efflux velocity is the maximum velocity within the entire jet with strong influences by the geometrical profiles of the blades. Twin-propeller jet model showed four-peaked profile at the initial plane downstream to the propeller compared to the two-peaked profile from a single-propeller. The four-peaked profile merges to be two-peaked velocity profile and then one-peaked profile due to the fluid mixing. Entrainment occurs between the ambient still water outside and the rotating flow within jet due to the high velocity gradient. The research proposes a twin-propeller jet theory with a serial of equations enabling the predictions of velocity magnitude within the jet.

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