Analysis of the 3D zone of flow establishment from a ship’s propeller

Lam, Wei-Haur; Hamill, Gerard; Robinson, D. J.; Raghunathan, Srinivasan; Song, Yongchen

doi:10.1007/s12205-012-1256-7

Cited by 13 publications

(6 citation statements)

References 17 publications

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“…In this area, the boundary between the jet flow and the ambient water is found, and higher values of turbulence intensity may be caused by the increased mixing and higher shear forces in the flow. This results are in good agreement with the expected behavior and literature (Lam et al, 2012), where higher values of TI were found both at the outer and inner jet layers through LDA measurements of the propeller jet velocity distribution. To provide further insight to the punctual velocity measurements, the energy spectra analysis is presented herein, through the Power Spectral Density (PSD) of each measurement within a radial distance in the range of 0.15D p < R m < 0.3D p .…”

Section: Axial Velocity Distribution At the Propeller Facesupporting

confidence: 93%

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

Llull Marroig

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Ships maneuvering in low bed clearance conditions induce sediment scour due to the high speed jet generated by a rotating propeller. Sediment scour is known to cause instability to quay structures, damage to the bed protection and may create huge accretion areas reaching extremely low depths, preventing the free passage of large ships. This on-going problem is linked to the constant increase in commercial ship sizes and is widely recognized in current harbor management guidelines. This thesis presents in the first place the experimental work carried out to study the effects of two common propeller systems over the sediment bed: single and twin propellers. Next, the analysis of a case study is used to evaluate the impact of ship maneuvers over the seabed in a particular harbor basin. The first part of the thesis presents a set of experiments in propeller jet velocity and bed shear stresses. By measurements performed in a point-by-point grid, with a Pitot-static tube coupled to differential pressure sensors, the axial velocity distribution at the so-called efflux plane is characterized. After that, direct measurements of bed shear stress are performed at several speeds of rotation and two bed-clearance distances with a shear plate. Velocity and bed shear stress measurements are related by an empirical friction coefficient, which is dependent on the bed clearance. A new empirical model is presented to estimate the mean shear stress in case of unconfined ship propeller jets in low bed clearance conditions. The second part of this work shows the results of a new set of experiments in local scour due to confined twin propeller jets. The maximum scour depth is studied as a function of the bed clearance, the wall clearance and the efflux velocity of the jet. Aiming to reproduce more realistic maneuvers, scour due to forward and backward rotation of the propellers is analyzed, showing a different behavior compared to the traditional experiments with only forward rotation. The obtained results are compared to the existing formulae and later used to propose two different empirical models, one for each regime of rotation. A new non-dimensional parameter obtained from the Buckingham Pi analysis, proposed as Wall Froude number, is used to find a threshold triggering the scouring mechanism. The experimental results show that the distance to the vertical wall is the main contributor to the higher scour depths rather than the bed clearance. The last part of the thesis presents a case study that is used to relate the maneuvers of the ship with the scour observed in an inner basin of the port. The study ship characteristics are obtained from the port statistics. The morphological evolution of the seabed is analyzed through hydrographic surveys of the last decade, which allows characterizing the erosion pattern. Through AIS data, the maneuver of the study ship is analyzed and used as an input maneuver in a simulator. The maneuver is reproduced to obtain the behavior of the main engines and bow thrusters. The maneuvering pattern and the behavior of the engines are used to assess the most damaging maneuvering sections, which turns out to be the ship's lateral approach to the berth, during the arrival maneuver, and the early stages of the departure maneuver. Els vaixells que maniobren en condicions de calat reduït poden provocar erosió local del llit de sediments a causa del raig d'aigua d'alta velocitat generat per les hèlix. L'erosió causa inestabilitat en les estructures dels molls, danys a la protecció del llit i pot crear grans àrees d'acreció, posant en risc la seguretat en la navegació. Aquest fenòmen està relacionat en gran mesura amb l'augment de les dimensions dels vaixells comercials en les darreres dècades i és àmpliament reconegut en les guies actuals de gestió portuària. Aquesta tesi presenta, en primer lloc, el treball experimental realitzat per estudiar els efectes erosius provocats per dos dels sistemes de propulsió més comuns: hèlix convencional i sistema de doble hèlix. A continuació, s'utilitza l'anàlisi d'un cas pràctic per avaluar l'impacte de les maniobres dels vaixells sobre el fons marí en una dàrsena portuària concreta. A la primera part de la tesi es presenten i s'analitzen en un conjunt de mesures experimentals de velocitat del flux d'aigua a la sortida de l'hèlix i de tensions de tall sobre un llit horitzontal. La distribució de velocitats axials es caracteritza a partir de mesures puntuals preses amb un sistema de tub de Pitot-estàtic acoblat a sensors de pressió diferencial. Posteriorment es realitzen mesures directes de les tensions de tall al llit amb una placa de tensions (shear plate) a tres velocitats de rotació de l'hèlix i dues distàncies verticals sobre el llit. Les mesures de la velocitat i la tensió de tall es relacionen amb un coeficient de fricció empíric que és dependent de la distància al llit. A la segona part d'aquest treball es presenta un nou conjunt d'experiments en erosió local per sistemes de doble hèlix confinats. La profunditat màxima d'erosió s'estudia en funció de la distància al sòl, la distància a la paret i la velocitat de sortida del raig d'aigua. Amb l'objectiu de reproduir maniobres de vaixells en entorns portuaris, s'analitza l'erosió generada pels sistemes de doble hèlix en règim combinat, és a dir, avant i invertit. Els resultats mostren diferències respecte els experiments tradicionals en què només es considera la rotació avant. Per estimar l'evolució temporal de la màxima profunditat d'erosió es proposen dos models empírics, un per a cada règim de rotació. De l'anàlisi de Pi de Buckingham s'obté un nou paràmetre adimensional que, proposat com a nombre de Froude del mur, permet establir un llindar d'erosió. Els resultats experimentals també mostren que la distància al mur vertical està més relacionada amb les majors profunditats d'erosió que amb la distancia al sòl. La darrera part de la tesi presenta un cas d'estudi en què les maniobres del vaixell es relacionen amb els canvis en la morfologia portuària observada al llarg del temps. El vaixell d'estudi s'obté a partir de les estadístiques d'ús de les dàrsenes portuàries. L'evolució morfològica del fons marí s'analitza mitjançant estudis hidrogràfics de la darrera dècada, que permet caracteritzar el patró d'erosió. A través de dades AIS, s'analitza la maniobra del vaixell d'estudi i s'utilitza com a model de maniobra en un simulador. La maniobra es reprodueix al simulador, d'on se n'extreu el comportament dels motors principals i de les hèlix de maniobra. El patró de maniobra i el comportament dels motors s'utilitzen per avaluar les seccions de maniobra més perjudicials, que resulten ser l'aproximació lateral del vaixell al moll d'atrac, durant la maniobra d'arribada, i les primeres etapes de la maniobra de sortida.

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Section: Axial Velocity Distribution At the Propeller Facesupporting

confidence: 93%

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

Llull Marroig

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“…The earliest investigations on this topic were focused on the velocity characteristics within a ship propeller jet using the axial momentum theory and a plain water jet, as it was documented by Ozan and Yüksel (2010), Yeh et al (2009) and Yüksel et al (2005). Actually, the velocity characteristics of a ship propeller jet are more complicated than those of a plain water jet (Lam et al, 2012) and, therefore, also the resulting scour holes are far different. Several researchers focused their work on the prediction of the maximum scour depth in the absence of berthing structures (e.g., Blaauw and van de Kaa, 1978;Hamill, 1987;Hong et al, 2013;Tan and Yüksel, 2018), considering the efflux velocity as the main driving force for scouring.…”

Section: State Of the Artmentioning

confidence: 99%

Three-dimensional analysis of local scouring induced by a rotating ship propeller

et al. 2019

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“…It can be seen from the figure that the speed of the water body due to rotation on the propeller surface is the highest on the outflow plane, and then it begins to decay. In 2012, Lam [9][10] systematically summarized the flow characteristics of the propeller jet without boundary effects by using physical experiments and numerical simulation methods, analyzed the three components of the jet velocity (axial, radial, and tangential) and discussed the attenuation and distribution of turbulence intensity in a propeller jet. Although previous studies have studied the effect of the propeller jet shape and the bottom boundary on the initial flow velocity, the effect of the bottom boundary on the propeller jet shape has not been specifically studied.…”

Section: Introductionmentioning

confidence: 99%

Numerical simulation of propeller jet field based on Star-ccm+

Li¹

2020

AJSRE

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During the ship's voyage, the propeller jet affects the movement of silt at the bottom of the bed. To research the influence of the bottom boundary on the propeller jet field, this paper takes the standard propeller DTRC4119 propeller as the research object and uses the CFD software Star-ccm+ to carry out a numerical simulation of the propeller jet under uniform flow. The flow velocity distribution of the jet under four operating conditions is mainly analyzed, including the axial velocity, tangential velocity and radial velocity of the jet. The results show that the distance between the propeller and the boundary does not affect the magnitude and distribution of the velocity on the initial plane but affects the shape of the axial velocity and the velocity on the central axis in the development zone; The closer to the bottom boundary, the greater the disturbance of tangential velocity and radial velocity, the peak value of tangential velocity will be affected and changed from central symmetry of velocity to unanimous trend earlier. The radial velocity contributes less to the overall velocity and can be ignored.

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Analysis of the 3D zone of flow establishment from a ship’s propeller

Cited by 13 publications

References 17 publications

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

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

Three-dimensional analysis of local scouring induced by a rotating ship propeller

Numerical simulation of propeller jet field based on Star-ccm+

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