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

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 ship 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 conditions under different 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.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 ship 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 conditions under different 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

Experimental analysis of the squat of ships advancing through the New Suez Canal

As a ship travels forward, squat of the ship may occur due to an increase in sinkage and trim. Squat is a crucial factor that restricts ship navigation in shallow water. A new division of the Suez Canal, the 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. To provide guidance for shipping in canals a series of experiments was conducted on a model scale of the Kriso Container Ship (KCS). The squat of the KCS was examined by measuring its sinkage and trim. A wide range of water depth to ship draft ratios at various ship speeds was investigated. Additionally, the blockage effect was studied by varying the canal width, and deep water tests were performed. The results indicated that for Froude's number based on depth (Fnh) below 0.4, measured squat value do not change with either Fnh or depth to draft ratio (H/T). The squat increases with H/T values for Froude numbers higher than 0.4. Moreover, a canal with reduced width had a negligible effect on squat, suggesting that the next segment of the Suez Canal can be built to a narrower width

Influence of scale effect on flow field offset for ships in confined waters

To investigate the flow field characteristics of full-scale ships advancing through confined waters, the international standard container ship (KRISO Container Ship) was considered as a research object in this study. Using the RANS equation, the volume of fluid method and the body force method were selected to investigate the hydrodynamic characteristics of a model-scale ship (the model-scale ratio λ=31.6) and a full-scale ship advancing through confined waters at low speed. A virtual disk was used in the full-scale model to determine the influence of the propeller on the ship’s flow field. First, the feasibility of the numerical calculations was verified. This proves the feasibility of the numerical and grid division methods. The self-propulsion point of the full-scale ship at Fr=0.108 is determined. The calculation cases of model-scale and full-scale ships (with or without virtual disks) at different water depths and distances between the ship and the shore were calculated, and the changes in the hull surface pressure, the flow field around the ship, and the wake fraction near the ship propeller disk in different calculation cases were determined and compared. The variations in the surge force, sway force, and yaw moment between the model- scale and full-scale ships were generally consistent. In very shallow water (H/T=1.3), the non-dimensional force and moment coefficients for model-scale ships increase more rapidly with decreasing distance from shore, suggesting that using model-scale ships to investigate the wall effect in very shallow water will result in predictions that are biased towards safety. By comparing full-scale ships with and without propellers, it was discovered that the surge force, sway force, and yaw moment were marginally greater in the propeller-equipped ship due to the suction effect, and the accompanying flow before and after the propeller was slightly smaller, with less asymmetry

Influence of the canal width and depth on the resistance of 750 DWT Perintis ship using CFD simulation

Investigation of hydrodynamic interaction between the vessel and the seabed when entering shallow water is considered one of the most critical considerations of inland waterway transport. There are many investigations into the behavior of ships in restricted waters, such as ships traveling in different forms of canal cross-sections. The present study aims to evaluate the hydrodynamic interaction of the 750 DWT Perintis Ship moving through the different canal types to determine the relative effects of limiting the width and depth cross section on the ship\u27s resistance. Two different canals with different cross sections, including canal bank and rectangular canal, were evaluated to investigate the influence of canal width (Wb), depth ratio (hw/T), and blockage ratio function (As/Ac). The Computational Fluid Dynamic (CFD) method with Reynolds-averaged Navier–Stokes (RANS) solver and turbulent model − were used to predict the total resistance of the ship. The proposed numerical simulation was initially validated with an experimental towing tank test in the error range of 0.11-7.74%. The results indicated similar phenomena were found both in rectangular and canal banks. The case with a shallower (lower hw/T) and a narrower (lower Bc/Bs) canal dimension has a higher resistance value. Backflow and subsidence of free surface became significant around the ship\u27s hull in more restricted water, changing the ship\u27s hydrodynamic characteristics and increasing resistance. It can be found that the higher the blockage ratio (mb), the higher the total resistance value in both canal types, which proved that ships with higher speeds were more sensitive to changes in waterway restrictions

Virtual replica of a towing tank experiment to determine the Kelvin half-angle of a ship in restricted water

The numerical simulation of ship flows has evolved into a highly practical approach in naval architecture. In typical virtual towing tanks, the principle of Galilean relativity is invoked to maintain the ship as fixed, while the surrounding water is prescribed to flow past it. This assumption may be identified, at least partly, as being responsible for the wide-scale adoption of computational solutions within practitioners' toolkits. However, it carries several assumptions, such as the levels of inlet turbulence and their effect on flow properties. This study presents an alternative virtual towing tank, where the ship is simulated to advance over a stationary fluid. To supplement the present work, the free surface disturbance is processed into Fourier space to determine the Kelvin half-angle for an example case. The results suggest that it is possible to construct a fully unsteady virtual towing tank using the overset method, without relying on Galilean relativity. Differences between theoretical and numerical predictions for the Kelvin half-angle are predominantly attributed to the assumptions used by the theoretical method. The methods presented in this work can potentially be used to validate free-surface flows, even when one does not have access to experimental wave elevation data

Experimental and numerical study of an obliquely towed ship model in confined waters

In this study, the forces and moments acting on the KCS ship model as a result of oblique towing at 10 and 20 degrees drift angles are evaluated experimentally and numerically via a commercial Reynolds averaged Navier-Stokes solver. For the purposes of this work, the KCS hull is modelled both experimentally and numerically at a scale factor of 1:75. The adopted case-studies feature both horizontal and vertical restrictions. Thus, the subject of this work is the oblique motion of a ship in a narrow canal with a depth of h/T=2.2. The relative impact of turbulence modelling is assessed by comparing the computed integral quantities via several eddy-viscosity closure strategies. These include significant variants of the k-ϵ and k-ω models as well as a widely used one-equation closure. Multiphase numerical simulations are performed at several of the experimentally investigated depth Froude numbers for each drift angle condition in order to fully capture the physics of the problem at hand. The present study aims to provide a quantitative evaluation of the performance of the adopted turbulence models and recommended the best closure strategy for the class of investigated problems

Numerical investigation of depth-varying currents on ship hydrodynamics in confined water

Vessels can operate in unpredictable environments depending on the geographical area and weather conditions. One example of conditions a vessel might not be assessed against is the presence of depth-varying currents, which are particularly relevant in confined waters where currents can be created due to tidal influences, or short fetches in inland waterways. The possible presence of depth-varying currents motivates a numerical assessment of the effects of sheared currents on the hydrodynamic performance of the KRISO Container Ship (KCS) in confined waters. The results highlight that exploiting currents, such as those generated by tides could be used to improve the energy efficiency of vessels considerably. These currents present significant possibilities for voyage optimisation based on geographical and meteorological conditions. The results specific for the KRISO container ship point to resistance reductions when the current assists ship motions, accompanied by considerable decreases in sinkage and trim. Conversely, when currents oppose ship motion, resistance, sinkage and trim can increase by a factor of 3 depending on the strength and shape of the depth-varying current. The results also show that a current with constant vorticity, a case frequently used in the literature to investigate the impact of sheared currents, creates the biggest increase and decrease for inhibiting and assisting currents, respectively

Investigating the influence of sheared currents on ship hydrodynamics in confined water using Computational Fluid Dynamics

The field of ship hydrodynamics in confined water has received increased attention by the academic community in recent years. Nevertheless, a number of phenomena occurring in confined waters are yet to be examined using high fidelity Computational Fluid Dynamics (CFD) or experimentally. One particular case is the presence of sheared currents and their impact on the performance of a ship. Such currents can be generated in confined waters as a result of the natural flow of water in rivers or due to the action of tidal influences in long canals. Alternatively, due to the short fetch of many inland waterways, the action of wind may result in the production of a sheared current. This work aims to investigate these effects by making use of a commercially available Reynolds Averaged Navier-Stokes (RANS) solver. A number of current profiles are numerically modelled to determine their influence on ship performance and the manner in which ship waves interact with the background current. The present study will contribute to the understanding of restricted water effects by revealing the impact of shear currents on ship performance

Experiment based mathematical modelling of ship-bank interaction

The forces and moments induced by the vicinity of banks on a sailing vessel are known as bank effects. An extensive set of model tests have been carried out in a towing tank to investigate bank effects induced by irregular bank geometries. Tests along sloped surface-piercing as well as submerged banks are carried out. A mathematical model (for the longitudinal force and sway forces) found on these tests is formulated