Delefortrie, Guillaume

Lataire, Evert

Vantorre, Marc

English

Ghent University Academic Bibliography

Impact of banks on ship squat

Hydraulic Engineering Repository

Conference Paper, Published VersionLataire, Evert; Delefortrie, Guillaume; Vantorre, MarcImpact of Banks on Ship SquatZur Verfügung gestellt in Kooperation mit/Provided in Cooperation with:Flanders Hydraulics Research, Ghent University, Maritime TechnologyVerfügbar unter/Available at: https://hdl.handle.net/20.500.11970/99858Vorgeschlagene Zitierweise/Suggested citation:Lataire, Evert; Delefortrie, Guillaume; Vantorre, Marc (2016): Impact of Banks on Ship Squat.In: Uliczka, Klemens; Böttner, Carl-Uwe; Kastens, Marko; Eloot, Katrien; Delefortrie,Guillaume; Vantorre, Marc; Candries, Maxim; Lataire, Evert (Hg.): 4th MASHCON -International Conference on Ship Manoeuvring in Shallow and Confined Water with SpecialFocus on Ship Bottom Interaction. Karlsruhe: Bundesanstalt für Wasserbau. S. 115-121.https://dx.doi.org/10.18451/978-3-939230-38-0_15.Standardnutzungsbedingungen/Terms of Use:Die Dokumente in HENRY stehen unter der Creative Commons Lizenz CC BY 4.0, sofern keine abweichendenNutzungsbedingungen getroffen wurden. Damit ist sowohl die kommerzielle Nutzung als auch das Teilen, dieWeiterbearbeitung und Speicherung erlaubt. Das Verwenden und das Bearbeiten stehen unter der Bedingung derNamensnennung. Im Einzelfall kann eine restriktivere Lizenz gelten; dann gelten abweichend von den obigenNutzungsbedingungen die in der dort genannten Lizenz gewährten Nutzungsrechte.Documents in HENRY are made available under the Creative Commons License CC BY 4.0, if no other license isapplicable. Under CC BY 4.0 commercial use and sharing, remixing, transforming, and building upon the materialof the work is permitted. In some cases a different, more restrictive license may apply; if applicable the terms ofthe restrictive license will be binding.IMPACT OF BANKS ON SHIP SQUAT E Lataire, Ghent University, Belgium G Delefortrie, Flanders Hydraulics Research, Belgium M Vantorre, Ghent University, Belgium SUMMARY In a restricted channel the hydrodynamic behaviour of a sailing vessel is affected by both the vertical and horizontal boundaries. The restricted space underneath and alongside a vessel has a noticeable influence on both the running sink-age and trim of a vessel, also known as squat. A different bank geometry will obviously change the available space around the vessel. To assess these influences an extensive model test program has been carried out in the Towing Tank for Manoeuvres in Shallow Water (cooperation Flanders Hydraulics Research – Ghent University) in Antwerp, Bel-gium. The tests were performed with 11 different ship models (both seagoing as inland vessels) along 25 different bank geometries and cross section areas. Systematic model tests were carried out along vertical quay walls, constant sloped banks (from full depth to free surface) and banks with a submerged sloped part and a horizontal submerged area (semi submerged banks). Also rectangular cross sections with a range of widths and water depths were tested in the towing tank. During the model tests the models were free to heave and trim and the running sinkage was measured at four dis-crete positions of the ship model (fore-aft / starboard-port side). In this article the executed model tests are described and the impact of different bank geometries on the squat of the vessel is discussed. The change in squat for different slopes of the bank as well as the bank type (quay wall/surface piercing) and cross section areas is shown. NOMENCLATURE AM Midship section area (m²) B Breadth of ship (m) CB Block coefficient (-) CM Midship coefficient AM/(BT) (-) Frh Froude number based on water  depth h (-) h Water depth (m) LPP Length between perpendiculars (m) LOA Length over all (m) m Blockage ratio (-) Re Reynolds number (-) T Draft (m) V Velocity (m/s) Vship Ship’s velocity (m/s) δV Return flow (m/s) W Width of the cross section (m) Wh Width of the section at full water depth (m) x Longitudinal position from FPP (m) y Lateral position from the centre  line (m) yinfl Influence width (m) ysmall Closest distance between ship andbank (m) zVA Running sinkage at the aft  perpendicular (mm) zVF Running sinkage at the fore  perpendicular (mm) zVM Running sinkage at the midship (mm) δ Thickness of the boundary layer (m) λ Scale factor (-) θV Running trim (m/m) ξ Coefficient of the mathematical model (-) ν Kinematic viscosity (m²/s) Ω Canal cross section area (m²) APP Aft perpendicular FPP Fore perpendicular FHR Flanders Hydraulics Research LNG Liquefied Natural Gas RoRo Roll on/Roll off UKC Under Keel Clearance Subscripts: m at model scale M at midship s at full scale 1 INTRODUCTION The dynamic under keel clearance of a sailing ship is affected by the changed pressure distribution around the ship’s hull. As a consequence the ship will move verti-cally downwards and will mostly trim as well due to the asymmetry between the fore and aft part of the ship. This phenomenon is commonly referred to as squat. The mag-nitude of this squat is affected by different parameters, among which the ship’s speed, the propulsion of the ship and the available water depth. These effects have already been the subject of numerous literature e.g. [1]. Figure 1. Ship and water at rest (1.1), return flow induced free surface water level depression (1.2), the sailing ship displacing the same volume of water as in 1.1 but having less under keel clearance (1.3). 4th MASHCON, Hamburg - Uliczka et al. (eds) - © 2016 Bundesanstalt für Wasserbau ISBN 978-3-939230-38-0 (Online) DOI: 10.18451/978-3-939230-38-0_15     115In open and unrestricted conditions, the water displaced by a sailing vessel can travel almost without restriction underneath and along the ship’s hull. In more shallow sailing conditions this water will rather be deviated around the hull, due to the limited space available be-tween the ship’s keel and the bottom of the waterway. This will result in higher velocities of the return flow travelling along the hull. This return flow will generate a pressure drop around the ship (Bernoulli’s principle) and because of that, the free surface of the water will go down compared to the situation at rest. As such, the run-ning sinkage or squat of a vessel should not be interpret-ed as an increase in the draft of the vessel but rather as a local decrease of the water depth around the ship.   Figure 2. Two pairs of parameters to express the running sinkage: sinkages at the fore and at the aft perpendiculars (zVF ; zVA), or trim (θV) and mean sinkage zVM.  In fact not only the water depth, but the entire cross sec-tion of the navigation channel affects the pressure distri-bution and the resulting squat. In general a more con-fined area will lead to larger squat for a given speed. In this article the attention will be put on the horizontal boundaries of a canal or fairway on the ship’s squat. The effect of the bank geometry on the squat will be dis-cussed based on an analysis of the database of captive model tests that have been carried out in the Towing Tank for Manoeuvres in Shallow Water at Flanders Hy-draulics Research (FHR).  Banks with varying geometries are frequently built into this towing tank to investigate ship-bank interactions. The test results used for the present paper are acquired in the frame of different projects. As such a database is acquired with model tests with as much as 11 different ship models and about 25 different bank geometries. The database consists of more than 14 000 different test con-ditions (ship, draft, water depth, bank geometry, relative position, drift angle, speed, propeller action). A limited selection of these model tests has been made public as benchmark data in [2].  The running sinkage can be expressed as either the com-bination of the mean sinkage and the trim or as the sink-age at the fore and aft perpendiculars. The latter will be used in this article with a positive sign convention in case of a downwards motion. 2 MODEL TESTS  2.1 TOWING TANK  The model tests under consideration are a selection of the model tests performed over the last 10 years in the fully automated towing tank at FHR. A technical overview of this facility can be found in [3]; its main dimensions are listed in Table 1.  Table 1. Main dimensions of the towing tank at FHR  Total length 87.5 m Useful length 68.0 m Width 7.0 m Maximum water depth 0.50 m   2.2 SHIP MODELS  Tests have been carried out with eleven different ship models of about 4m long (2 container carriers, 4 tankers, 3 RoRo-vessels, 1 inland vessel, 1 Wigley hull), some of them at different loading conditions. Detailed infor-mation on the ships’ hulls is available in [4], the proper-ties of the four ship models, used in this article, are shown in Table 2.  Table 2. Main properties of the ship models       KVLCC2 T0H LNG RoRo λ [ ] 75 75 70 50 Lpp [m] 4.267 2.210 3.809 3.800 LOA [m] 4.448 2.316 4.000 4.060 B [m] 0.773 0.296 0.594 0.620 TM [m] 0.277 0.178 0.157 0.148 CB [ ] 0.81 0.85 0.77 0.62   2.3 BANK GEOMETRIES  In present article only a selection of tests in a steady state regime condition are considered to check the influence of the bank geometry on the running sinkage of the vessel. Therefore, the installed cross section did not change in geometry for a significant amount of ship lengths (at least six ship lengths) before the ship model decelerates or another bank geometry initiates. When two geometries are installed consecutively in the tank, the transition zone of one bank to another is constructed in such a way to create a smooth change in geometry, this is to avoid abrupt and long lasting transition effects.  In the past tests have been carried out with surface pierc-ing banks (a constant slope from the bottom of the tow-ing tank up to the highest water level tested, Figure 3) and semi submerged banks (a sloped under water part in      116The viscosity of the water will influence the squatting behaviour of the ship when sailing very close to the bot-tom or bank. Because of the scale effects, this influence is more pronounced on model scale than at the full scale vessel.  5 REFERENCES  1. Briggs, M.J ., Vantorre, M., Uliczka, K., Debaillon, P., 2009. Prediction of Squat for Underkeel Clearance. Handbook of Coastal and Ocean Engineering. Edited by: Young C Kim (California State University, Los Angeles, USA)  2. Lataire, E.; Vantorre, M.; Eloot, K., (2009). Systematic Model Tests on Ship-Bank Interaction Effects, Ship Manoeuvring in Shallow Water with Ship-Bank Interaction Effects. In International Conference on Ship Manoeuvering in Shallow and Confined Water: Bank Effects 2009, Antwerp, Belgium  3. Delefortrie, G.; Geerts, S.; Vantorre, M. (2016). The Towing Tank for Manoeuvres in Shallow Water. MASHCON 2016, Hamburg, Germany.  4. Lataire, E. (2014) Experiment Based Mathematical Modelling of Ship-Bank Interaction, PhD thesis, Ghent University, Ghent.   5. Lataire, E.; Vantorre, M. ; Delefortrie, G. (2012). A Prediction Method for Squat in Restricted and Unrestricted Rectangular Fairways. Ocean Engineering, 55, pp.71–80.  dx.doi.org/10.1016/j.oceaneng.2012.07.009  6. Lataire, E., Vantorre, M. & Delefortrie, G., (2015). Longitudinally Directed Bank Effects. In MARSIM 2015. Newcastle.  7. Lataire, E.; Vantorre, M.; Laforce, E.; Eloot, K.; Delefortrie G.; (2007). Navigation in Confined Waters: Influence of Bank Characteristics on Ship-Bank Interaction. Proceedings of the 2nd International Conference On Marine Research And Transportation, Ischia, Naples, Italy  8. White, F.M. (2003). Fluid Mechanics Third Edit., McGraw-Hill, Inc. 6 AUTHORS’ BIOGRAPHIES  Evert Lataire is currently assistant at the division of Maritime Technology at Ghent University. He has made a PhD on the topic of bank effects mainly based upon model tests carried out in the shallow water towing tank of FHR. His ten year experience includes research on ship manoeuvring in shallow and confined water such as ship-ship interaction, ship-bottom interaction and ship-bank interaction  Guillaume Delefortrie is expert nautical research at Flanders Hydraulics Research. He is in charge of the research in the Towing Tank for Manoeuvres in Shallow Water (cooperation Flanders Hydraulics Research – Ghent University) and is secretary of the 27th and 28th ITTC Manoeuvring Committee.  Marc Vantorre, naval architect, is full senior professor of marine hydrodynamics and head of the Maritime Technology Division at Ghent University, Belgium. His research focuses on ship behaviour in shallow and con-fined waters, mainly in close co-operation with Flanders Hydraulics Research in Antwerp. He is member of PI-ANC Working Groups and former member of the ITTC Manoeuvring Committee.        121

Impact of Banks on Ship Squat

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Impact of banks on ship squat

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