KRISO Container Research Articles

Hydrodynamic shape optimization by high fidelity CFD solver and Gaussian process based response surface method

A computational framework for hydrodynamic shape optimization of complex ship hull form is proposed and applied to improve the calm water performance of the KRISO Container Ship (KCS). The framework relies on three key features: a novel shape morphing method based on a combination of subdivision surfaces and free form deformations, a robust three dimensional viscous computational fluid dynamic solver based on the openFOAM open-source libraries and a Gaussian process-response surface method (GP-RSM) based on ordinary Kriging model which has been created to speed-up the evaluation of the quantity of interest (QoI) of the design process.The accuracy of the hydrodynamic solver is proven by comparing the obtained results against available experimental measurements. A preliminary sensitivity analysis on the mesh size has been carried out aiming at reducing the computational burden required by the CFD predictions. Three GP-RSMs have been trained relying on increasing number of hull designs. Each surrogate model has been cross-validated by both leave-one-out and k-fold techniques. The behaviours of these multi-dimensional surfaces have been analyzed in details by sampling the investigated design space with 107 points according to a Full-Factorial algorithm, highlighting the regions of maximum deviation with respect to the resistance of the reference hull. The three optimum designs provided by the corresponding GP-RSM models have been verified by using high-fidelity CFD simulations with a refined mesh configuration. Calm water resistance, wave patterns and pressure distributions over the selected hull surfaces have been discussed in the light of the generated shape variations.

횡경사상태 선박의 조종성능변화에 관한 실험적 연구

Predicting ship manoeuvrability is attracting widespread interest in the field of analyzing maritime accident to simulate a highly accurate track of a ship in abnormal accident situations. This study investigated the manoeuvrability of a ship in abnormally heeled condition. Free Running Model Tests (FRMT) with 1/65.83 scaled KCS (KRISO container ship) were conducted in three heeled conditions; 35°turning circle tests and 20/20 zigzag manoeuvring tests were conducted in 0°, -10°, and –20° conditions. The test results showed that the heeled to port condition significantly affected starboard turning and zigzag characteristics; the tactical diameters in the turning circle tests decreased, and the first overshoot angles in the zigzag tests increased when the ship was in the larger heeled condition. These results indicate that the roll angle of the ship considerably affects yaw rate and speed decrease of the ship. The turning and zigzag indices from trajectory and navigation data in the study were provided for benchmark data sets.

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.

An Integrated Ship Re-Design/Modification Strategy

Herein, we present an integrated ship re-design/modification strategy that integrates the ‘Computer-Aided Design (CAD)’ and ‘Computational Fluid Dynamics (CFD)’ to modify the ship hull form for better performance in resistance. We assume a modular design and the ship hull form modification focuses on the forward module (e.g. bulbous bow) and aft module (e.g. stern bulb) only. The ship hull form CAD model is implemented with NAPA*TM and CFD model is implemented with Shipflow**TM. The basic ship hull form parameters are not changed and the modifications in some of the technical parameters because of re-designed bulbous bow and stern bulb are kept at very minimum. The bulbous bow is re-designed by extending an earlier method (Sharma and Sha (2005b)) and stern bulb parameters for re-design are computed from the experience gained from literature survey. The re-designed hull form is modeled in CAD and is integrated and analyzed with Shipflow**TM. The CAD and CFD integrated model is validated and verified with the ITTC approved recommendations and guidelines. The proposed numerical methodology is implemented on the ship hull form modification of a benchmark ship, i.e. KRISO container ship (KCS). The presented results show that the modified ship hull form of KCS - with only bow and stern modifications - using the present strategy, results into resistance and propulsive improvement.

An investigation into the effect of biofouling on the ship hydrodynamic characteristics using CFD

To reduce the fuel consumption and green-house gas emissions of ships, it is necessary to understand the ship resistance. In this context, understanding the effect of surface roughness on the frictional resistance is of particular importance since the skin friction, which often takes a large portion in ship drag, increases with surface roughness. Although a large number of studies have been carried out since the age of William Froude, understanding the roughness effect is yet challenging due to its unique feature in scaling. In this study, a Computational Fluid Dynamics (CFD) based unsteady Reynolds Averaged Navier-Stokes (RANS) resistance simulation model was developed to predict the effect of barnacle fouling mainly on the resistance and hull wake characteristics of the full-scale KRISO container ship (KCS) hull. Initially, a roughness function model was employed in the wall-function of the CFD software to represent the surface conditions of barnacle fouling. A validation study was carried out involving the model-scale flat plate simulation, and then the same approach was applied in full-scale flat plate simulation and full-scale 3D KCS hull simulation for predicting the effect of barnacle fouling. The increase in frictional resistance due to the different fouling conditions were predicted and compared with the results obtained using the boundary layer similarity law analysis of Granville. Also, a further investigation of the roughness effect on the residuary resistance, viscous pressure resistance and wave making resistance was carried out. Finally, the roughness effect on the wave profile, pressure distribution along the hull, velocity distribution around the hull and wake flows were examined.

Hydrodynamic Design Study on Ship Bow and Stern Hull Form Synchronous Optimization Covering Whole Speeds Range

The main objective of this article is to describe an innovative methodology of synchronous local optimization which considers the whole ship speed range being presented for a KRISO Container Ship (KCS). Parametric form approaches are adopted by employing a fairing B‐spline curve in order to generate variants of the bow and stern of forms using form design parameters modified, resulting in an optimization system based on NSGA‐II. The total resistance is calculated by the Rankine source panel method and the empirical formula which agrees well with the corresponding experimental data and further acquires validation with the overall error of 2.0%. Accordingly, the ship forepart and stern form have been optimized under conditions of the single design speed and whole speeds range based on the considerations of generally distributed and variable operational speeds for the operating characteristics of modern container ships synchronously. The optimized result presents well‐balanced drag reduction benefits which averagely remain above 4.0% of ship resistance decrease. Compared to the traditional optimization process which is based on a specific design speed, the newly developed method is more practical and effective in both automation and integration.

EFD and CFD Study of Forces, Ship Motions, and Flow Field for KRISO Container Ship Model in Waves

EFD and CFD Study of Forces, Ship Motions, and Flow Field for KRISO Container Ship Model in Waves

Coupled Ranse and Lifting Line Theory for Estimation of Ship Propulsion Factors

Advances in Computational Fluid Dynamics (CFD) techniques through the development of the Reynolds-Averaged Navier-Stokes Equations (RANSE) have assisted in estimation of resistance and propulsion characteristics of ships to a reasonable level of accuracy. The aim of this paper is to test and demonstrate the capabilities of the coupled RANSE and Lifting Line theory for undertaking ship resistance, propeller open-water and self-propulsion simulations. Further, parametric studies for generation of numerical propeller design sheets and optimisation of propulsive efficiency using the coupled simulation approach has been discussed. Commercial CFD solver “M/s Flowtech - Shipflow” has been used for the study. Initially, some benchmark experimental/numerical model results are validated with the results of the CFD simulations and then, further parametric analyses have been undertaken with the KRISO Container Ship and the KP505 Propeller. The numerical propeller series and the preliminary study methodology for optimization of location of propeller disc behind the ship’s hull are being proposed as an effective concept/feasibility design stage tool for estimation of ship propulsion characteristics.

Solid body motion prediction using a unit quaternion-based solver with actuator disk

A six-Dof motion solver based on unit quaternions and an actuator disk model are implemented for ship hydrodynamics predictions. The six-Dof module is tested using the water entry phenomenon of a free falling sphere. The displacement history and impacting forces are analyzed. A KCS (KRISO container ship) model with the allowances of sinkage and trim is then simulated and validated. The actuator disk model is used to replace a real propeller. The open-water test of a KP458 propeller is first carried out to obtain the thrust and torque coefficients, using both the multi-run and single-run approaches. Oblique Towing Tank (OTT) tests using the actuator disk are conducted at last and the results agree well with the experiments. These models can be used for simulating six-Dof motions and captive model tests of ships.

A numerical and experimental study on the performance of a twisted rudder with wavy configuration

In this paper, a Wavy Twisted Rudder (WTR) is proposed to address the discontinuity of the twisted section and increase the stalling angle in comparison to a conventional full-spade Twisted Rudder (TR). The wave configuration was applied to a KRISO Container Ship (KCS) to confirm the characteristics of the rudder under the influence of the propeller wake. The resistance, self-propulsion performance, and rudder force at high angles of the wavy twisted rudder and twisted rudder were compared using Computational Fluid Dynamics (CFD). The numerical results were compared with the experimental results. The WTR differed from the TR in the degree of separation flow at large rudder angles. This was verified by visualizing the streamline around the rudder. The results confirmed the superiority of the WTR in terms of its delayed stall and high lift–drag ratio.

Adjoint volume-of-fluid approaches for the hydrodynamic optimisation of ships

ABSTRACTThe paper is concerned with simulation-based shape optimisation in marine engineering flows. Attention is devoted to the derivation of an adjoint complement to two-phase flow finite-volume procedures. The strategy refers to an extension of a hybrid continuous/discrete adjoint method for volume-of-fluid (VoF) approaches. The study outlines means to formulate a discrete adjoint VoF scheme from the terms that originate from variations of the fluid properties. The adjoint solution is verified against results of a direct differentiation technique. The application is devoted to the drag optimisation of the Kriso container ship. A kernel-based self-parametrisation approach of the design surface is combined with mesh-morphing techniques to drive the 150,000 shape parameters of the vessel without the need to revisit or differentiate the CAD environment during the optimisation. The optimisation process obeys to practical constraints. The optimised vessel displays more than 5% reduction of total drag while maintaining main dimensions and displacement.

Numerical prediction analysis of the fluctuating pressure and rudder force of full-scale hull-propeller-rudder system

In order to analyze the fluctuating pressure and rudder force characteristics of a full-scale hull-propeller-rudder system, a hybrid structured/unstructured grid was combined with the Reynolds-averaged Navier-Stokes (RANS) and volume of fluid (VOF) methods to perform a numerical prediction of model and full-scale performance for the Kriso Container Ship (KCS) case. A numerical simulation for the self-propulsion test of a full-scale ship was first performed to obtain the propeller velocity under the self-propulsion point, the results of which indicated a notable wake fraction and velocity scale effect at the self-propulsion point. Transient two-phase flow calculations were then performed for the model and full-scale KCS hull-propeller-rudder systems. According to the monitoring data, the hull surface fluctuating pressure and rudder force fluctuated periodically over time and the full-scale fluctuating pressure exhibited a higher time-average value as compared to the model-scale pressure. The frequency spectrum curves were also generated by the fast Fourier transform algorithm. The analysis of the frequency spectrum data indicated that the peaks of the fluctuating pressure and rudder force reached their respective maximums at the blade passing frequency (BPF), after which the peak gradually decreased and the full-scale ship reduced more quickly. Furthermore, fluctuating amplitude of full-scale ship was bigger than model-scale.

부유체의 상하동요 고유진동수 예측

As the motion response of heave for floating bodies on the water surface is relatively large near the natural frequency, it is necessary to predict its value accurately from the stage of initial design. Bodies accelerating in fluid experience force acted upon by the fluid, and this force is quantified by using the concept of added mass. For predicting the natural frequency of heave we need to know the added mass, which is given as a function of frequency, and hence the natural frequency can be obtained through only by iteration process, as was pointed out by Lee (2008). His method was applied to circular cylinders, and two dimensional cylinders of Lewis form by making use of the Ursell-Tasai method in the previous works, Lee and Lee (2013), Kim and Lee (2013), and Song and Lee (2015). In this work, a similar algorithm employing the concept of strip method is adopted for predicting the heave natural frequency of KCS(KRISO Container Ship), and the obtained computational result was compared with other existing experimental data, and the agreement seems reasonable. Furthermore, through the error analysis, it is shown that why the frequency corresponding to the local minimum of the added mass and the natural frequency are very close. And it seems probable that we can predict the heave natural frequency if we know only the local minimum of added mass and the corresponding frequency under a condition, which holds for ship-like bodies in general.

Model experiments on the early detection and rudder stabilization of KCS parametric roll in head waves

Free running model experiments on the early detection and rudder stabilization of parametric roll in regular and irregular head waves are conducted in the towing tank of Yokohama National University. The KCS (KRISO Container Ship) containership model is used in the experiment. Parametric roll motions are observed in various ship speeds and wave lengths. The parametric roll early detection algorithm based on incremental real-time Hilbert–Huang transform (IR-HHT) technique is validated by the model experiments. Results show that the occurrence of parametric roll under different cases can be successfully detected through the detection algorithm when the roll amplitudes are still small. The rudder anti-roll control is applied for the stabilization of parametric roll in regular and irregular head waves. The rudder anti-rolling is activated when parametric roll is detected by the detection algorithm. It is found that the rudder anti-rolling can successfully stabilize parametric roll in regular and irregular head waves especially when the ship speed is high. However, the effectiveness of rudder anti-rolling is limited in severe parametric roll cases with roll amplitude larger than 25°.

An extensive analysis of numerical ship self-propulsion prediction via a coupled BEM/RANS approach

The paper deals with the self-propulsion problem, i.e. the solution of the flow around the hull that advances at uniform speed due to the action of its own propeller. A coupled BEM/RANS approach, previously proposed for a simpler case with only rudder and propeller, has been extensively analysed to highlight the strength and the weakness of the method. The proposed analyses consider the influence of different turbulence modelling, the role of the interpolating algorithm for the inclusion of body forces into the RANS domain, a mesh and simulation time step sensitivity study and the influence of the extrapolation procedure for the definition of the effective wake to the propeller in the light of the lightest and the most affordable computational setup for daily accurate calculations. At first, the well-known Kriso Container Ship (KCS) test case is considered. This ship has been widely investigated in the context of different research projects and a large amount of data (both measurements and numerical calculations) is available to validate the solution approach and to highlight the benefits, as well as the weaknesses, of the proposed coupled BEM/RANS approach versus established but computationally demanding calculations based only on RANS simulations. Once the approach has been developed and validated via the KCS test case, calculations have been repeated in the case of completely different ships, in order to evaluate its general applicability and to test the robustness and the reliability of the proposed procedure.

Predicting the effect of biofouling on ship resistance using CFD

This paper proposes a Computational Fluid Dynamics (CFD) based unsteady RANS model which enables the prediction of the effect of marine coatings and biofouling on ship resistance and presents CFD simulations of the roughness effects on the resistance and effective power of the full-scale 3D KRISO Container Ship (KCS) hull.Initially, a roughness function model representing a typical coating and different fouling conditions was developed by using the roughness functions given in the literature. This model then was employed in the wall-function of the CFD software and the effects of a typical as applied coating and different fouling conditions on the frictional resistance of flat plates representing the KCS were predicted for a design speed of 24 knots and a slow steaming speed of 19 knots using the proposed CFD model. The roughness effects of such conditions on the resistance components and effective power of the full-scale 3D KCS model were then predicted at the same speeds. The resulting frictional resistance values of the present study were then compared with each other and with results obtained using the similarity law analysis. The increase in the effective power of the full-scale KCS hull was predicted to be 18.1% for a deteriorated coating or light slime whereas that due to heavy slime was predicted to be 38% at a ship speed of 24 knots. In addition, it was observed that the wave resistance and wave systems are significantly affected by the hull roughness and hence viscosity.

Determination of ship maneuvering hydrodynamic coecients using system identication technique based on free-running model test

In the recent years, di erent mathematical models have been suggested for maneuvering of displacement vessels that are capable of estimation of vessel maneuvers with acceptable precision. These mathematical models are based on determined hydrodynamic coecients and their accuracy depends on the known coecients used to solve the mathematical model. System identi cation methods are developed to calculate these coecients utilizing input and output data obtained from di erent sources. In this research, a 4.36-m model of KRISO Container Ship (KCS) displacement vessel has been manufactured by berglass, and the maneuver turning tests have been carried by selfpropulsion method. A 3DM-GX1 sensor, together with a protractor and Global Positioning System (GPS), has been used to measure the yaw and rudder angle, position, linear accelerations, and angular velocities of the vessel in di erent times. The hydrodynamic coecients in the mathematical model are determined by the Extended Kalman lter method. Then, the mathematical model is solved and di erent maneuvers are simulated by coecients calculated from the experiments. Simulations are validated by model tests. The mathematical model and hydrodynamic coecients presented in this paper can be applied for optimization of ship maneuvering performance and course control purposes

Computations of linear and nonlinear ship waves by higher-order boundary element method

A practical method for computing ship waves accurately and efficiently is favorable for hull form optimization in early stage of ship design. In the present study, Rankine source method incorporated with high-order boundary element (HOBEM) discretization is applied to solve linear ship waves at first. Numerical implementation is described in detail. An incomplete LU factorization preconditioned Generalized Minimal Residual method (GMRES) is employed to solve the resulting boundary integral equation in order to improve efficiency. A corresponding Fortran program is developed for the validation study. It is applied to solve ship waves of different hulls, including slender Wigley hull, KRISO Container Ship (KCS) with relatively full form and a fishery patrol boat. Ship wave drag, sinkage, trim and wave pattern over a wide range of Froude numbers are all well predicted.In order to further investigate nonlinear effects on ship waves, a fully nonlinear potential flow method based on stationary iteration is proposed. The same numerical approach of HOBEM is employed. The combined nonlinear free surface condition is solved in each iteration to evaluate the free surface. Numerical investigation for Wigley and KCS hull shows the present nonlinear method are accurate. Comparison study with linear and partial nonlinear solution are also carried out and nonlinear effects on ship waves are detailedly discussed.

대한해협에서의 수온 및 염도변화를 고려한 선박의 저항성능 예측을 위한 기초 연구

Recently, shipping operators have been making efforts to reduce the fuel cost in various ways, such as trim optimization and bulb re-design. Furthermore, IMO restricts the hydro-dioxide emissions to the environment based on the EEDI (Energy Efficiency Design Index), EEOI (Energy Efficiency Operational Indicator), and SEEMP (Ship Energy Efficiency Management Plan). In particular, ship speed is one of the most important factors for calculating the EEDI, which is based on methods suggested by ITTC (International Towing Tank Conference) or ISO (International Standardization Organization). Many shipbuilding companies in Korea have carried out speed trials around the Korea Straits. However, the conditions for these speed trials have not been exactly the same as those for model tests. Therefore, a ship’s speed is corrected by measured environmental data such as the seawater temperature, density, wind, waves, swell, drift, and rudder angle to match the conditions of the model tests. In this study, fundamental research was performed to evaluate the ship resistance performance due to changes in the water temperature and salinity, comparing the ISO method and numerical simulation. A numerical simulation of a KCS (KRISO Container ship) with a free-surface was performed using the commercial software Star-CCM+ under three conditions that were assumed based on the water temperature and salinity data in the Korea Straits. In the simulation results, the resistance increased under low water temperature & high salinity conditions, and it decreased under high water temperature & low salinity conditions. In addition, the ISO method showed the same result as the simulation.

Dynamic overset grids in OpenFOAM with application to KCS self-propulsion and maneuvering

An implementation of the dynamic overset grid technique into naoe-FOAM-SJTU solver developed by using the open source code OpenFOAM is presented. OpenFOAM is attractive for ship hydrodynamics applications because of its high quality free surface solver and other capabilities, but it lacks the ability to perform large-amplitude motions needed for maneuvering and seakeeping problems. The implementation relies on the code Suggar to compute the domain connectivity information (DCI) dynamically at run time. Several Suggar groups can be used in multiple lagged execution mode, allowing simultaneous evaluation of several DCI sets to reduce execution time and optimize the exchange of data between OpenFOAM and Suggar processors. A towed condition of the KRISO Container Ship (KCS) are used for static overset tests, while open-water curves of the KP505 propeller and self-propulsion and zig-zag maneuvers of the KCS model are exercised to validate the dynamic implementation. For self-propulsion the ship model is fitted with the KP505 propeller, achieving self-propulsion at Fr=0.26. All self-propulsion factors are obtained using CFD results only, including those from open-water curves, towed and self-propulsion conditions. Computational results compare well with experimental data of resistance, free-surface elevation, wake flow and self-propulsion factors. Free maneuvering simulations of the HSVA KCS model appended with the HSVA propeller and a semi-balanced horn rudder are performed at constant self-propulsion propeller rotational speed. Results for a standard 10/10 zig-zag maneuver and a modified 15/1 zig-zag maneuver show good agreement with experimental data, even though relatively coarse grids are used. Grid convergence studies are performed for the open-water propeller test and bare hull KCS model to further validate the implementation of the overset grid approach.