Experimental and numerical analysis of the squat and resistance of ships advancing through the new Suez Canal

Student thesis: Doctoral Thesis

Abstract

When a ship is sailing in shallow and restricted waters such as harbours and canals, it is usually accompanied by obvious sinkage and trim, called squat. The ship squat has important influences on ship hydrodynamic performance in shallow and restricted water such as ship resistance. Squat is caused by the drop in pressure under the bottom of the ship, where the relative speed of the water is higher. Due to the squat effect, the hydrodynamic forces on the ship will increase largely, ship control will become difficult and risks of grounding may increase. A new division of the Suez Canal is called New Suez Canal, recently opened for international navigation. It is important to obtain accurate prediction data for ship squat to minimise the risk of grounding in this canal. Accurate prediction of the squat is of great significance to correctly evaluate ship hydrodynamic performance and to ensure navigation safety in the New Suez Canal. In this study, various methods for prediction of shi p squat were conducted and introduced. A series of experiments were conducted with a model scale of the KRISO Container Ship (KCS) at 1:75 scale. The squat of the KCS was examined by measuring its sinkage, trim and resistance. The influences of ship speed, water depth, ship-bank distance on the squat and blockage effect were analysed. The results indicated that for Froude’s number based on depth (Fnh) below 0.4, measured squat values do not change with either Fnh or depth to draft ratio (H/T). The squat increases with H/T values for the depth Froude numbers higher than 0.4. Moreover, a ship’s speed can be increased to up to 9 knots inside the New Suez Canal with no adverse effects, thus significantly reducing the time for a ship to pass through the Canal. Next, the study of reduced the Canal width to 62.5% of its real-life cross sectional area, no significant effect was observed on ship squat. Moreover, a series of experimental tests were conducted at loading conditionsunder diffe rent trimming angles to examine the range of ship trim for safe and efficient sailing in canals. to detect the best trim angle for ships during sailing in restricted waters to reduce resistance and therefore fuel consumption.The results show that for depth Froude’s numbers higher than 0.4, the ship model sinkage is less for aft trim than for level trim or forward trim. Concurrently, it can be observed that there is less water resistance for aft trim than for forward trim, albeit level trim shows the least resistance. Furthermore, the present study combines numerical, analytical and empirical methods for a holistic approach in calm water. As a case-study, the KCS hullform is adopted, and analysed experimentally, via Computational Fluid Dynamics, using the slender body theory, and empirical formulae. The results reveal strong effect between the canal’s cross section and all examined parameters. In addition, CFD calculations proved to be a reliable tool for predicting ship performance while navigating shallow and restricted waters. CFD simulations in multiphase and double body regime are performed to reveal the form factor and wave resistance of the KCS. This is performed in two different canals while varying the depth Froude number. The results suggest a dependency of the form factor on ship speed. Analytical and empirical methods were used for comparison, the slender body theory, provided good predictions in the low speed range, but did not agree well with the experimental data at high speeds. To model the sloping canal sides of the Suez Canal via the slender body theory, a rectangular canal with equivalent blockage was constructed, which may have influenced the accuracy of the theory.
Date of Award14 Feb 2020
Original languageEnglish
Awarding Institution
  • University Of Strathclyde
SupervisorTahsin Tezdogan (Supervisor) & Atilla Incecik (Supervisor)

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