Wake Fraction Research Articles

NUMERICAL STUDY ON PROPULSIVE FACTORS IN REGULAR HEAD AND OBLIQUE WAVES

This paper applies Reynolds-averaged Navier-Stokes (RANS) method to study propulsion performance in head and oblique waves. Finite volume method (FVM) is employed to discretize the governing equations and SST k-ω model is used for modeling the turbulent flow. The free surface is solved by volume of fluid (VOF) method. Sliding mesh technique is used to enable rotation of propeller. Propeller open water curves are determined by propeller open water simulations. Calm water resistance and wave added resistances are obtained from towing computations without propeller. Self-propulsion simulations in calm water and waves with varying loads are performed to obtain self-propulsion point and thrust identify method is use to predict propulsive factors. Regular head waves with wavelengths varying from 0.6 to 1.4 times the length of ship and oblique waves with incident directions varying from 0° to 360° are considered. The influence of waves on propulsive factors, including thrust deduction and wake fraction, open water, relative rotative, hull and propulsive efficiencies are discussed.

Discussion of the Fluid Acceleration Quality of a Ducted Propulsion System on the Propulsive Performance

This paper focuses on the ducted propulsion with the accelerating nozzle, and discusses the influence of its fluid acceleration quality on its propulsive performances, including the hull efficiency, the relative rotative efficiency, the effective wake, and the thrust deduction factor. An actual ducted propulsion system is used as an example for computational analysis. The computational conditions are divided into four combinations, which are provided with different propeller pitches, cambers, and duct lengths. The method applied in this study is the Computational Fluid Dynamics (CFD) technology, and the contents of the calculation include the hull's viscous resistance, the wave-making resistance, the propeller performance curve, and the self-propulsion simulation in order to obtain the ship's effective wake, thrust deduction factor, hull efficiency, and relative rotative efficiency. The performance curve of the propeller and resistance estimation results are compared with the experimental values for determining the correctness of the self-propulsion simulation. According to the computational analysis, it is known that increasing the propeller pitch cannot effectively increase the hull efficiency. The duct acceleration quality can be reduced by shortening the duct length; hence, when the effective wake fraction and thrust deduction factor decrease, the hull efficiency is increased. In addition, the pressure inside the duct is relatively low if the acceleration quality of the duct is too high, which is unfavorable for controlling the propeller cavitation. Moreover, if the hull bottom in front of the propeller is tapered up from the front to the back at an overly steep angle, the thrust deduction factor will be too large and lead to a relatively low hull efficiency.

Prediction of resistance and propulsion performances using calm-water and resistance tests in regular head waves of a 1,800 TEU container ship

This paper predicts resistance and propulsion performances in regular and irregular head waves of a 1800 TEU container ship. ‘Calm-water tests’ and ‘resistance test in regular waves’ have been performed. Methods applied are the LVM-W and the revised ITTC-78. Added propeller revolution, thrust, and torque in waves linearly increase as added resistance does. The relative contributions of added propulsion performances in waves have been evaluated using the logarithmic derivative. The spectral method in operating sea states has been applied. The response spectra of added propeller revolution, thrust, and torque show similar characteristics to those of added resistance. The FSEM, LVM-IR, ITTC78-IR, DPM, RTIM, QNM, and TNM are useful to predict added delivered power and propeller revolution in irregular waves when SS < 5. These differences between the DPM/RTIM/QNM/TNM and the Spectral(LVM-W) are dependent on the linearity of fitting line for overload factor. The TNM underpredicts added delivered power due to the lower wake fraction in waves.

Numerical study of nominal wake fields of a container ship in oblique regular waves

Accurate estimation of the actual nominal wake behind the ship in waves is important for propeller designers when improving efficiency and minimizing cavitation. The present CFD study investigates the nominal wake fields of the Kriso Container Ship (KCS) in regular waves with wavelength equal to the ship length in five different headings. The ship is sailing at design speed and the wave steepness is 1/60. The results show that when sailing in the studied waves, the nominal wake fraction fluctuate up to 39% of the mean nominal wake fraction. The mean nominal wake fraction is higher than in calm water for all headings besides head sea waves. The maximum mean nominal wake fraction is found to occur in stern quartering sea waves, with a 16% higher mean nominal wake fraction than in calm water. It is also found that the transient bilge vortex and shadow from the skeg have a significant influence on the nominal wake field. Finally the study shows that the modified advance angle on the r/R=0.7 circle in the propeller plane varies 3.5 degrees more in port stern quartering than in calm water, increasing the risk of cavitation.

Resistance and wake distortion optimization of JBC considering ship-propeller interaction

In this paper, the self-propulsion performance of a full formed hull is optimized by the in-house hull form optimization software OPTShip-SJTU 2.1. In the field of hull form optimization, complex hull optimizations such as hull-propeller interaction optimization have not launched a full investigation. To break through this limitation, the hull-propeller interaction module is brought into the software. We conduct a hull-propeller interaction design optimization of Japan Bulk Carrier (JBC) with an actual propeller (AP) based on CFD considering ship resistance and propeller wake distortion at Fr = 0.142. Hull form deformation module is applied to change the stern shape of the JBC. The in-house CFD software naoe-FOAM-SJTU is applied to calculate the hull resistance and wake fraction. The dynamic overset grid method is used to achieve the interaction between hull and propeller and obtain the high-fidelity flow field during the optimization processing. A multi-objective genetic algorithm (NSGA-II) is applied to obtain the optimized hull forms based on the Kriging surrogate model. The influences of propeller for the flow field around stern are also studied. Results indicate: (I) OPTShip-SJTU 2.1 can optimize the coupled hydrodynamic performance in complex hull form optimization. (II) The hull resistance and wake fraction have a strong positive correlation under the deformation setting in this paper. (III) Contraction of hull line at the stern can suppress the flow separation around the stern which is benefit for reducing the pressure resistance and improving the propeller wake distortion. (IV) It is necessary to consider the interaction between propeller and hull together in hull form optimization. The interactions between the shape of stern, propeller performance, and flow field around stern are discussed preliminary, which provide several references for the subsequent research.

COMPARISON OF UNSTEADY REYNOLDS-AVERAGED NAVIER-STOKES PREDICTION OF SELF-PROPELLED CONTAINER SHIP SQUAT AGAINST EMPIRICAL METHODS AND BENCHMARK DATA

The demand to increase port throughput has driven container ships to travel relatively fast in shallow water whilst avoiding grounding and hence, there is need for more accurate high-speed squat predictions. A study has been undertaken to determine the most suitable method to predict container ship squat when travelling at relatively high speeds (Frh ≥ 0.5) in finite water depth (1.1 ≤ h/T ≤ 1.3). The accuracy of two novel self-propelled URANS CFD squat model are compared with that of readily available empirical squat prediction formulae. Comparison of the CFD and empirical predictions with benchmark data demonstrates that for very low water depth (h/T &lt; 1.14) and when Frh &lt; 0.46; Barass II (1979), ICORELS (1980), and Millward’s (1992) formulae have the best correlation with benchmark data for all cases investigated. However, at relatively high speeds (Frh ≥ 0.5) which is achievable in deeper waters (h/T ≥ 1.14), most of the empirical formulae severely underestimated squat (7-49%) whereas the quasi-static CFD model presented has the best correlation. The changes in wave patterns and effective wake fraction with respect to h/T are also presented.

МАТЕМАТИЧНЕ МОДЕЛЮВАННЯ РОБОТИ СУДНОВИХ ГВИНТІВ ПРИ РІЗНИХ РЕЖИМАХ МАНЕВРУВАННЯ

In the study of ship maneuvers, in the development of ship's autopilots and simulators, the availability of adequate mathematical models of the ship’s propulsion complex, which would describe with high accuracy the dynamics of the ship for the widest ranges of phase coordinates, plays a decisive role. Mathematical models of ship dynamics consist of mathematical models of inertial and non-inertial forces and moments on the ship's hull. The latter include hydrodynamic and aerodynamic forces and moments on the ship's hull, forces and moments caused by the operation of propellers, rigging, ship rudders. For the adequacy of the general mathematical model of the ship's dynamics, the adequacy of the mathematical models of all components of non-inertial forces and moments on the ship's hull is necessary. Mathematical models of non-inertial forces and moments on a ship's hull are usually empirical and made by processing data from experimental tests in ship model basin or in full-scale sea trials. In particular, this applies to the forces and moments caused by the operation of the propeller. In the mathematical modeling of the indicated forces and moments, the rectilinear movement of the vessel, or movement at small values of the drift angles, is usually considered. In this case, only the longitudinal action of the propeller is usually considered, and the transverse component of the force and the moment on the ship's propeller are unreasonably neglected. In addition, well-known mathematical models usually contain coefficients and functions that are difficult to determine using tables and graphs, which is inconvenient for numerical modeling. This work is intended to somewhat eliminate the indicated disadvantages. In particular, it was investigated how the curvilinear movement of the ship affects the operation of the propeller, analyzed the existing mathematical models, and new effective mathematical models of the longitudinal and transverse components of the force and moment caused by the operation of the ship's propeller in dimensional and dimensionless forms were proposed. In particular, representations are obtained for the dimensionless coefficients of the propeller stop and the moment on the propeller shaft, the wake fraction coefficient, the thrust-deduction factor, and skew of the flow on the propeller. It is shown how these parameters change for all possible values of the drift angle and angular velocity. For a number of commercial vessels of various types, technical characteristics are given, and parameters for constructing mathematical models of the dynamics of the propeller are calculated.

PENGARUH THRUST DEDUCTION FACTOR DAN WAKE FRACTION TERHADAP EFISIENSI PROPULSI AKIBAT PERUBAHAN DRAFT KAPAL

This study is to investigate propulsion efficiency due to changes in draught of ship using data series and theoretical approach. A hard chain rescue boat with triplet screw was used for the study and to examine the effect of thrust deduction factor and wake fraction due to changes in draught of ship and its relevance to propulsion efficiency by observing hull and propeller interaction based on openwater test by Wageningen Data Series with cavitations analysis has been neglected. The study is done using hydrodynamics analysis for planning hull and using intersection between thrust characteristic curve with openwater test data series for fixed pitch propeller. The result indicated that the changes in ship draught are very influential on the changes in thrust deduction factor and wake fraction value which is one of the contributing factor to change the propulsion efficiency value 1% - 5%.

통계적 접근 방법을 이용한 저속비대선 및 컨테이너선의 동력 성능 추정

In this study, we introduce the prediction of brake power for low-speed full ships and container carriers using the linear regression and a machine learning approach. The residual resistance coefficient, wake fraction coefficient, and thrust deduction factor are predicted by regression models using the main dimensions of ship and propeller. The brake power of a ship can be calculated by these coefficients according to the 1978 ITTC performance prediction method. The mean absolute error of the predicted power was under 7%. As a result of several validation cases, it was confirmed that the machine learning model showed slightly better results than linear regression.

Assessment of full-scale KCS free running simulation with body-force models

Self-propulsion free running ship simulation is most closely similar to the running ship for different operating condition without any simplification of the ship hull and appendages. Accurate evaluations of self-propulsion performance are vitally important in the design of hull–propeller systems. This paper describes unsteady Reynolds-averaged Navier–Stokes (RANS) simulations to determine the self-propulsion performance of a full-scale container ship with a KP505 propeller. An inhouse code is used to solve the RANS equations with a discretized propeller, descriptive body-force, OUM (Osaka University Method) and modified OUM body-force methods selected as the propulsion models. The modified OUM body-force method couples blade element momentum theory, considering the three-dimensional viscous effects, with the RANS solver. Before the full-scale self-propulsion simulations, uncertainty analyses are performed on the full-scale hull and the propeller. The effect of roughness on the full-scale simulations is also studied. We discuss how the modified OUM body-force method can be used for full-scale self-propulsion simulations, and show that the model-scale body force can be substituted into the full-scale rough propeller in the self-propulsion simulations. The body-force results are compared with extrapolated experimental data, full-scale simulation results from the literature, and simulation results with the discretized propeller. In this paper, the modified OUM shows higher accuracy for full-scale self-propulsion simulation than other two body forces for inhouse URANS solver. Moreover, the scale effect is discussed by comparing open-water, resistance, and self-propulsion simulations at different scales. The open-water and resistance results show that the propeller scale effect can be ignored, whereas both the wake flow and skin friction correction have large scale effects. The self-propulsion scale effect is mainly reflected in the wake factor, thrust deduction factor, and rotation speed. For the container ship considered herein, the full-scale wake fraction is smaller than the model-scale prediction, whereas the rotational speed and thrust deduction factor are greater.

An investigation of scale effects on the self-propulsion characteristics of a submarine

This study's main objective is to investigate the scale effect on the benchmark DARPA Suboff submarine hull form's resistance and self-propulsion characteristics. The study's secondary objective is to explore the feasibility of the 1978 ITTC performance prediction method for submarines' power prediction. In achieving both objectives, the CFD solver is utilised. Hence, the flow around the three different scales of the DARPA submarine forms and its propellers, including a full-scale one, is first solved using the steady RANS method with the k-ω SST turbulence model. Verification studies are conducted to determine the uncertainty level of the numerical computations for each scale. The hull resistance, propeller open water and self-propulsion performances are validated with the available experimental data and other numerical studies in the literature for the widely used benchmark submarine model. In the self-propulsion simulations, the propeller flow is modelled using the discretised propeller geometry with the Moving Reference Frame (MRF) approach. Also, the Proportional Integral (PI) controller is adopted to find the self-propulsion point efficiently. The scale effects on the hull resistance and its components, nominal wake fraction and self-propulsion characteristics, are explored at two different velocities. The extrapolated numerical results obtained by the 1978 ITTC procedure show that the scale ratio decrease enables better prediction of the self-propulsion characteristics compared to the full-scale CFD predictions. As well as this, the extrapolated self-propulsion characteristics using the model scale results, which are obtained by the CFD computations, are found to be in good agreement with those of the full-scale CFD results. The study, therefore, suggests that the 1978 ITTC performance prediction method can be used in some confidence to extrapolate the performance results from the model to full-scale for the submerged bodies, similar to the surface ships. This study also presents the full-scale self-propulsion characteristics of the benchmark DARPA Suboff form for the first time in the literature using the CFD tool over a realistic range of submarine forward speeds.

Comparison of self-propulsion performance between vessels with single-screw propulsion and hybrid contra-rotating podded propulsion

The present work compares the self-propulsion performance between vessels with single-screw propulsion and hybrid contra-rotating podded propulsion. The viscous flow fields of 4000 TEU container vessels with single-screw, single-rudder propulsion and hybrid contra-rotating propeller (CRP) podded propulsion systems were solved numerically by the Reynolds-averaged Navier–Stokes equations (RANS), the shear stress transport (SST) k−ω turbulence model, and the sliding mesh method. Numerical uncertainty analysis of the resistance and self-propulsion factor were employed according to ITTC Quality Manual 7.5-03-01-01. Self-propulsion factor, viscous flow field, and pressure distribution at the stern of the vessels were analyzed in detail. Numerical results suggested that the vessel with the hybrid CRP podded propulsion showed a 17.59% larger effective wake fraction, a 40.2% smaller thrust deduction fraction, a 15.1% higher hull efficiency, and a 4.12% higher overall propulsive efficiency compared with the single-screw vessel. In addition, the vessel with the hybrid CRP podded propulsion showed a basically symmetric, smaller velocity gradient and more uniform flow field at the stern, resulting in a much smaller propeller-induced fluctuating pressure on the hull, compared with the single-screw vessel. In conclusion, the hybrid CRP podded propulsion system exhibited high efficiency and low vibration levels.

CFD study of hull wakes in oblique flow at model and full scales

The characteristic of hull wake for a ship operating in oblique flow significantly affects the ship performance at off-design conditions. This paper presents a numerical study on the hull wakes under oblique flow conditions and analyzes the scale effect. RANS method combined with SST k-ω turbulence model is adopted and an international benchmark ship, Japan Bulk Carrier (JBC), is computed. Drift angles ranging from 0° to 20° with an interval of 5° are considered. Results show that the oblique flow considerably changes the hull wake field. Unlike a left-right symmetric pattern at zero drift angle, the nominal wake in oblique flow conditions shows a strong asymmetry since the flow at the windward side is close to the incoming flow whereas the flow at the leeward side is featured by the vortices detached from the hull. It is also revealed that the mean wake fraction decreases as the drift angle increases. Both model and full scales are simulated and the comparison between them shows significant differences in the wake pattern on the leeward side and the magnitude of the mean wake fraction. Compared with the model scale, the full scale has a stronger aft-body vortex and a smaller mean wake fraction.

Experimental measurements of propulsive factors in following and head waves

The results from resistance measurements in calm water and load-varying self-propulsion tests in calm water and regular head and following waves are presented. The experimental campaign is conducted in the large towing tank at SINTEF Ocean (formerly MARINTEK). The openly accessible hull of the single screw Duisburg Test Case is selected as the test case. The wave added resistance, ship motions RAOs, axial wake fraction, thrust deduction fraction, relative rotative efficiency, hull efficiency, propeller open-water efficiency, propeller efficiency behind ship, and propulsive efficiency are determined.Regarding the calculation of the thrust deduction fraction, the results of the experiments show the effect of utilizing the bare hull resistance instead of the linearly extrapolated ship resistance at zero propeller thrust. If the former is applied, the thrust deduction fraction will be dependent on the load of the propeller. If the latter is utilized, the thrust deduction fraction will be independent of the propeller loading. As expected, the wave added resistance is lower in following waves than in head waves. The heave and pitch motions are larger in head waves, whereas the surge motion is higher in following waves. The effective wake fraction is affected by both the propeller loading and the ship motions. In the case of the former, the higher the propeller loading, the lower the effective wake fraction. For the latter, a general decrease in effective wake fraction is noticed in head waves compared to calm water. On the contrary, the effective wake fraction is higher in following waves in comparison to calm water. The thrust deduction fraction computed with the extrapolated ship resistance appears to be slightly affected by the ship motions. However, a final conclusion was not drawn because of the large uncertainties in the measurements of this propulsive coefficient. The variation in propeller open-water efficiency is mainly related to the change in propeller loading. The relative rotative efficiency is barely affected by both the propeller loading and the motions of the ship. Except in the case of very large wave amplitudes, the hull efficiency is hardly influenced by the ship motions. The propulsive efficiency is primarily affected by the change in propeller open-water efficiency.Based on the results of the experimental campaign, overload tests in calm water provide a good estimation of the propulsion efficiency in waves for the selected case vessel.

A study on ship performance in waves using a RANS solver, part 1: Comparison of power prediction methods in regular waves

Numerical analyses were performed on a KVLCC2 (Korea Research Institute of Ships and Ocean (KRISO) Very Large Crude oil Carrier 2) at Fr = 0.092 and 0.037 in regular wave conditions. A Reynolds averaged Navier-Stokes (RANS) solver was applied with the finite volume method and a realizable k-ε model as a turbulence model. The Volume of Fluid (VOF) equation was solved to implement the free surface. The body-force propeller method of the Virtual Disk model was used to represent the effect of the propeller and reduce the computation time significantly. Resistance and self-propulsion computations were carried out in calm water and regular head waves, and the results were verified by comparing them to the added resistance and motions from experiments. To find the trend of the delivered horsepower (DHP) in regular waves, regular head waves from the short wave to long wave conditions with two different wave steepness were considered. The load variation method was also performed using the obtained added resistance, and the resulting self-propulsion points were compared with the CFD results. In each wave case, the propulsive coefficients and DHP were also compared, and we discuss the relationship between the thrust deduction factor and wake fraction factor according to the wave conditions.

A CFD study: Influence of biofouling on a full-scale submarine

The aim of this study is to investigate the effect of biofouling related hull roughness on a full-scale submarine by taking into consideration the resistance components, effective power, and nominal wakefield using a Computational Fluid Dynamics (CFD) solver. The validation study was first performed for the model scale submarine form in hydraulically smooth (reference) condition with the available experimental data. Following that, roughness functions, representing the different biofouling conditions, were obtained from the literature and then employed in the wall function of a RANS solver. Later on, the full-scale submarine form was investigated both in the smooth and different grades of biofouling related roughness conditions. The scale effects were examined between the model and full-scale submarine forms through the total resistance components and nominal wake fraction in the smooth reference condition. In rough cases, the frictional resistance values of the full-scale submarine form obtained by RANS solver were compared with those of predicted using Granville`s similarity law analysis based on the flat plate approach. The numerical results showed that the roughness causes a substantial increase in effective power, ranging from ∼36% to ∼112% depending on the roughness height and submarine speed. Furthermore, with an increasing boundary layer thickness (due to the impact of increasing roughness heights), the mean nominal wake fraction values increase ranging from ∼25% to ∼68 compared to the reference wake fraction values in the axial direction at the stern.

Modification and Analysis of Twin Screw Ship Stern for Optimizing Propulsive Coefficient Values in Propulsive System

Twin-screw ship has the advantage of being able to reduce the diameter of propeller by using the same rotation and engine power as a single-screw ship. With the result that twin-screw ship can be operated in areas with lower water depth. However, the type of twin-screw ship has a deficiency in the value of hull efficiency ( ) and the relative rotative efficiency ( ). This occurs because of the propeller position which is far from the field of the flow of the ship’s hull speed (V). So that the value of the water flow to the propeller (advance velocity/) becomes low. Various studies have been conducted to increase wake fraction (w) and reduce the thrust deduction factor (t) values some of which are by modifying the shape of the ship’s stern parts bossing to increase the water speed to the propeller (advance velocity/) which will have a large effect on the wake fraction (w) and thrust deduction factor (t). Among them is by modifying the shape of the ship’s stern bossing so that it can increase the speed of water to the propeller (advance velocity/) which will greatly affect the value of the wake fraction (w) and thrust deduction factor (t) to increase the propulsive coefficient (PC). In this study, it is known that the QPC value for the ship model tested in the Hydrodynamics Laboratory Indonesia (LHI) is 0.54 while for the four models tested using the CFD method is model one 0.63, model two 0.55, model three 0.63, and model four amount 0.51. Based on the above test it can be concluded that the third hull model has the highest QPC. be in ALARP compared to acceptance criteria.

Analysis of Stern Shape Effect on Pre-Duct Propeller Performance Based on Numerical Simulation

In process and development of ship building, it always lead to the design that is environmentally friendly and has high efficiency values on the energy and economic side. The factor is the selection and determination of the propulsion system. In propulsion system, propeller and its flow is very influential, such as flow at the stern, the flow that will enter the propeller, and the propeller design used. This can increase the propulsive coefficient of the propulsion system. For single screw ship, the hull efficiency is usually between 1.1 - 1.4, while for twin-screw with conventional hull forms, the hull efficiency is around 0.95 - 1.05. The value of relative rotative efficiency is between 1.0 - 1.07 and the efficiency of the shaft is between 0.96 - 0.995. Meanwhile, the value of open water efficiency and hull efficiency greatly affect to ship performance. From the simulation, with the additional of pre-duct The hull efficiency value has increased by 2.2% - 4.3%, this is due to the increase of wake fraction value higher than the thrust deduction value. The relative rotative efficiency also increases by 0.8% - 1% for each variation of the block coefficient or type of ship. But, for the propulsive coefficient, the resulting gap was decreasing by 2% - 6%. Because of that the distance between the hull and the pre-duct, the design of the propeller, the distance between the pre-duct and the propeller, and the shape of the stern are important references for the pre-duct design.

Prediction of Resistance and Self-Propulsion Characteristics of a Full-Scale Naval Ship by CFD-Based GEOSIM Method

Resistance and self-propulsion characteristics of a naval ship at full scale have been investigated by using Telfer’s GEOmetrically SIMilar (GEOSIM) method based on the computational fluid dynamics (CFD) approach. For this purpose, first, the resistance forces of the Office of Naval Research Tumblehome (ONRT) hull have been computed at different three model scales by using the overset mesh technique. The full-scale resistance and nominal wake fraction of the ONRT hull have been estimated by using Telfer’s GEOSIM method. Resistance and nominal wake fraction have then been compared with those of CFD at full scale. Later, the self-propulsion characteristics of the ONRT hull have been examined using Telfer’s GEOSIM method based on the CFD approach. Self-propulsion factors at the full-scale hull have been predicted by using the SST k–x turbulence model to involve 2-degrees of freedom ship motions (heave and pitch). Rotational motion of the propeller has also been simulated by using the rigid body motion technique. The results calculated by Telfer’s GEOSIM method and the 1978 International Towing Tank Conference (ITTC) extrapolation technique have been compared with each other and discussed with those of the CFD approach at full scale. It was found that the full-scale results (both resistance and self-propulsion factors) predicted by Telfer’s GEOSIM method are closer to those of the CFD approach than those of the 1978 ITTC technique. It can be noted that Telfer’s GEOSIM method is fast, robust, and reliable and can be used as an alternative to the 1978 ITTC method for predicting the self-propulsion performance of a full-scale ship. Introduction Resistance and self-propulsion characteristics of a surface ship should be known properly in the design stages. For this purpose, model tests and numerical methods are used together to determine the resistance and self-propulsion performance of a ship. However, model tests are expensive and time-consuming, and the accuracy of the International Towing Tank Conference (ITTC) extrapolation technique from model scale to full scale may not have in a satisfactory level. On the other hand, Telfer’s GEOmetrically SIMilar (GEOSIM) method based on computational fluid dynamics (CFD) can overcome these difficulties.

Effective wake estimation of KCS hull at full-scale by GEOSIM method based on CFD

In this study, the effective wake factors of a self-propelled container ship were investigated by Telfer's GEOSIM method based on CFD (Computational Fluid Dynamics). For this purpose, the self-propulsion characteristics of KCS (KRISO Container Ship) at three different model scales and full-scale were determined at Fr = 0.26 by unsteady RANS (Reynolds Averaged Navier-Stokes) solver. All scales corresponded to a wide range of Reynolds numbers. Turbulent flow around the KCS hull has been investigated by the k-ε turbulence model. Heave and pitch motions of KCS hulls have been modeled with the DFBI (Dynamic Fluid Body Interaction) method and overset mesh technique. The rotational motion of KP505 propeller has been simulated using the RBM (Rigid Body Motion) approach. The result obtained by the extrapolation of the effective wake fraction with the GEOSIM method was compared with the full-scale ones of CFD and ITTC methods. The results by the GEOSIM method are more compatible with those of full-scale CFD than the results of 1978 ITTC method. In the wake region, where viscous effects are predominant, the change of effective wake fraction with Reynolds number has been successfully represented by the GEOSIM method, thus more robust and reliable results have been found.