Self-propulsion Point Research Articles

Influence of energy-saving devices on the hydrodynamic characteristics of a waterjet-propelled ship: Experimental and numerical investigation

Installing stern energy-saving devices can help conserve energy and enhance ship speed, particularly for medium-to-high-speed ships. This study focuses on a waterjet-propelled ship and examines the performance of two energy-saving devices: the interceptor and stern flap. The investigation involves conducting a comparative analysis through towing-tank experiments and utilising Reynolds-averaged Navier–Stokes (RANS) numerical methods. The findings suggest that incorporating energy-saving devices alters the capture flow of the waterjet-propelled ship. Furthermore, these devices reduce ship resistance, resulting in a maximum decrease in the impeller speed of the self-propulsion point up to 5%. Following the installation of energy-saving devices, the propulsion efficiency of the waterjet-propelled ship demonstrates an enhancement ranging from 0.5% to 5.7%. This increase in propulsion efficiency emerges as a principal factor contributing to the energy savings facilitated by the stern energy-saving device. Upon comparison, it was found that within the Fr range of 0.3–0.5, the stern flap exhibited a superior energy-saving effect. Conversely, when Fr exceeded 0.5, the interceptor demonstrated a more pronounced energy-saving effect. Finally, the mechanisms of the stern energy-saving devices are elucidated based on the momentum velocity coefficient, thrust deduction fraction, and changes in the internal and external flow fields of the waterjet-propelled ship.

Numerical investigation on steady turning motion of a generic submarine near the free surface

This study investigated the steady turning motion of a generic submarine near the free surface using computational fluid dynamics (CFD) methods. The Joubert BB2 submarine and Marine 7371R propeller models were employed as the subjects of this research. The analysis utilized the Reynolds-averaged Navier-Stokes (RANS) equations with the SST k-ω turbulence model to capture turbulent flows, and the volume of fluid (VOF) method to capture the free surface dynamics. A mesh convergence study was conducted with three different mesh resolutions to ensure the accuracy of the simulations. An overset mesh method was used to control the submarine and its four control surfaces, while a sliding mesh approach simulated the propeller rotation. The self-propulsion point of the submarine was determined at a fixed speed using a PI controller. Subsequently, rudder maneuvers were executed to replicate a steady 20-degree turning motion. The study examined the effects of submergence depth and speed on the flow field. Results indicated an approximate 15% variation in turning parameters between the maximum and minimum submergence depths at the same speed, with force and torque differences around 30%. Additionally, the study explored the impact of the free surface on hydrodynamic forces, pressure distribution, free surface wave patterns, and vortex structures during turning maneuvers.

Effect of pre-swirl stator angles on broadband noise considering hydrodynamic performance of pump-jet propeller

A pump-jet propeller is composed of a rotor, stator, and duct. A pre-swirl stator is employed to optimize flow into the rotor. The hydrodynamic and noise performances of pump-jet propellers vary with the stator angles. In this study, the hydrodynamic performance of a full-scale submarine and pump-jet propeller is assessed by conducting computational fluid dynamics simulations based on the Reynolds-averaged Navier–Stokes equation. Additionally, broadband noise, blade-passing frequency noise, and a significant factor, that is, underwater radiated noise are predicted using Lighthill’s equation, Green’s function, and wall pressure spectrum. Unsteady forces were extracted from the flow field to obtain the blade-passing frequency noise. Broadband noise could not be calculated directly from the flow field owing to the absence of small eddies, and wall pressure spectrum was used to obtain high-frequency broadband noise. The overall noise, including broadband noise and blade-passing frequency noise, was evaluated. The optimal stator angle for the rotor at the self-propulsion point was determined considering the propulsion efficiency and noise level of the pump-jet propeller.

Impacts of regular head waves on thrust deduction at model self-propulsion point

The results obtained from the self-propulsion simulations using Computational Fluid Dynamics (CFD) in the current study, for a ship free to heave, pitch and surge with the means of a weak spring system, are combined with the formerly executed CFD results of the bare hull and propeller open water simulations to investigate the impacts of regular head waves on the propeller-hull interactions in comparison to calm water, at the self-propulsion point of the model. Despite a rather significant dependency of the nominal wake on the wave conditions, the Taylor wake fraction remains almost unchanged in different studied waves which is around 12% lower than the calm water value. The thrust deduction factor in waves is reduced (12.8%–26.1%) in comparison to the calm water value. The change of thrust deduction factor is found to be associated with the boundary layer contraction/expansion and vortical structure dynamics, originating from the wave orbital velocities as well as the significant shaft vertical motions and accelerations that resulted in a modified propeller action, and consequently diminished suction effect on the aft ship. The altered thrust deduction factor and wake fraction in waves in comparison to calm water underlines the significance of waves on the propulsive factors and propeller design.

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.

Numerical simulations of submarine self-propulsion flows near the free surface

Submarine needs to complete more tasks near the free-surface area in modern war. When sailing near the free surface, the self-propelled characteristics of the submarine and its nearby flow field will be affected by the free surface. This paper presents the research on the self-propulsion submarine near the free surface with computational fluid dynamics (CFD) method. We take the generic Joubert BB2 submarine and Marine 7371R propeller models as the research objects. The RANS method and SST k-ω turbulence model are selected to solve the turbulent flows. The volume of fluid (VOF) method is used to capture the free surface. Grid convergence study is performed based on three sets of grids with different resolution. Numerical simulations are performed under the self-propulsion cases with different submergence depths and velocities. The proportional integral (PI) controller method is proposed to obtain the self-propulsion point. The results are more accurate compared with the traditional one. It is found that with the decrease of the submergence depths, the rotating speed of the self-propelled point and the corresponding thrust increase. The study also explores the free surface effect on flow field characteristics, wave-making characteristics and vortex structures. The scientific findings provide some useful results for the self-propulsion submarines near the free surface and support the further research in the future.

Numerical Investigation of Self-Propulsion Performance and Noise Level of DARPA Suboff Model

Propulsion noise is an enduring problem of significant military and environmental importance. Hence, it is crucial to investigate propeller noise characteristics. In this study, the hydrodynamic performance and noise level of the DARPA (Defense Advanced Research Projects Agency) Suboff submarine with the E1619 propeller were analyzed. The hull resistance and propeller hydrodynamics were studied separately, and the numerical results were validated using available experimental values. The self-propulsion point was determined by matching the hull resistance and propeller thrust following ITTC (International Towing Tank Conference) convention. Based on hydrodynamics and acoustic Ffowcs Williams–Hawkings (FW–H) models, the underwater-radiated noise characteristics in the self-propulsion state were simulated. The calculations indicated that the contribution of the quadrupole term in the FW–H equation is not negligible in the high-frequency band. Compared with the noise of open-water propellers, the spectrum of the E1619 propeller in its self-propulsion state is more complex, and the upstream noise is amplified.

Experimental study of the hydrodynamic maneuvering coefficients for a BB2 generic submarine using the planar motion mechanism

In this study, a series of captive model tests were conducted to obtain the reference dataset of hydrodynamic coefficients and experimental data for the BB2 generic submarine model with a scale ratio of 35.1. A mathematical model was constructed using the dataset, and validated against a model scale free-running experiment conducted by MARIN for scale ratio of 18.341. The experiments used vertical planar motion mechanism equipment in the model basin at Pusan National University and included resistance, static drift, static control plane deflection, and dynamic tests. Horizontal planar motion mechanism tests were performed by rotating the model by 90° about the propeller shaft axis. Subsequent combination tests—horizontal static with rudder tests and pure yaw with rudder tests—were performed to evaluate the effects between the hull and control planes. The tests were performed under the model self-propulsion point to consider the effects of the propulsor on the maneuvering characteristics of the vehicle. The obtained results were compared with those of numerical studies owing to the absence of open-experimental captive test data for the scaled BB2 model.

A study on PID controlled self-propulsion and turning simulations based on the URANS CFD free running approach

In this study, the proportional, integral, and differential control constants for a self-propulsion point search were investigated using free running Computational Fluid Dynamics (CFD) simulations. The experimental data obtained using a 1/100 scale model of KVLCC2 were used to verify the calculation results. A range of initial propeller rotational speeds from 30% to 140% of the self-propulsion point of the experiment was considered. The controller constants were estimated using the trial-and-error and the Ziegler-Nichols methods, and the two results were similar. As a result, a robust numerical result was obtained within a 0.01% difference of the target speed, and a 0.5% difference of the self-propulsion point of the experiment with P and I constants of 180/m and 30 RPS/m, respectively, for a straight-ahead time of 12.5 L/V. Under the straight-ahead condition, a time step of 0.005 L/V was sufficient. However, in the turning simulation, a time step of 0.0025 L/V or less was required. The key findings obtained from this study are believed to provide a practical guideline for self-propulsion and maneuvering simulation using CFD.

구속모형시험을 통한 잠수함 선형의 수상 조건 조종성능 추정 연구

In this paper, the results of Planar Motion Mechanism (PMM) test for a 1/15 scaled model of the MARIN Joubert BB2 submarine is dealt with to derive the maneuvering coefficients for surface condition. For the depth of surface navigation, the top of the sail was exposed 0.46 m above the water surface in the model scale, and it corresponds to 6.9 m in the full scale. The resistance and self-propulsion tests were conducted, and the model’s self-propulsion point was obtained for 1.328 ㎧, which corresponded to 10 knots in the full scale. The maneuvering tests were performed at the model’s self-propulsion point, and the maneuvering coefficients were obtained. Based on the maneuvering coefficients, a turning simulation was performed for starboard 30 degree of stern fins. The straight-line stability and control effectiveness in the horizontal plane were analyzed using the maneuvering coefficients and compared with the appropriate range. For the analysis of the neutral fin angle of the X-type stern fin, the stern fin test with drift angles was carried out. As a result, the flow straightening effect at lower and upper parts of the stern fin was discussed.

UNCERTAINTY QUANTIFICATION OF SELF-PROPULSION ANALYSES WITH RANS-CFD AND COMPARISON WITH FULL-SCALE SHIP TRIALS

RANS-CFD is a well-established tool with widespread use in maritime industry and research. Valuable information might be extracted from the results of such simulations in terms of ship resistance and flow field variables. With recent advancements in computational power, it became possible to investigate the performance of ships in self-propulsion conditions with RANS method. This paper presents the results of a study in which self-propulsion analyses of a small size product/oil tanker has been carried out at ship scale. The methodology proposed in this study makes use of open water propeller performance predictions, resistance analyses at model scale and self-propulsion computations at ship scale for a minimum of 2 different propeller loadings to obtain the self-propulsion point and respective performance parameters. In order to speed up the time-consuming self-propulsion computations, these cases have been solved with a single-phase approach. Resistance predictions have been compared with experimental findings. Uncertainty associated with prediction of resistance and thrust has been quantified. Additionally, sea trials have been conducted on the subject vessel and its two sisters and measured delivered power data have been used for evaluating the capability of the numerical method in self-propulsion predictions. Comparison of results indicate that the proposed self-propulsion computation methodology with RANS CFD at ship scale is capable of predicting delivered power with sufficient accuracy at an acceptable computational cost.

Enhanced body-force propeller model for non-uniform inflow flow and application to turning circle test of KCS in calm water

An enhanced body-force propeller model is developed to consider propulsion effects without solving the actual propeller geometry in ship maneuvering problems. Application to the KCS turning circle test in calm water (starting at the self-propulsion point) is conducted using the computational fluid dynamics solver, snuMHLFoam, which was developed on OpenFOAM-plus. Based on the original Hough and Ordway model, the non-uniform advance velocity of the propeller is considered using the local velocity on the inflow plane, to compute the local advance coefficient for different parts of the propeller disk when the propeller works behind a hull. The original overset algorithm is revised by introducing more flexible hole-patch definitions for the hole-cutting procedure and an iterative procedure for the donor-searching procedure to remove invalid donors. The motion decomposition of ship and rudder motions with the revised overset is implemented in order to handle body motions effectively. Self-propulsion and turning circle tests for KCS ships are successfully conducted in calm water. The predicted results, including the PI control results, turning trajectory and parameters, ship motions and velocities, forces and moments, and flow and vortical structures are illustrated and compared with the benchmark experimental data, as well as the numerical results obtained using the Maneuvering Modeling Group (MMG) model. The results indicate that the developed body-force propeller model can provide more reasonable predictions of the propulsive performance when the propeller works behind a hull. The snuMHLFoam solver, which is coupled with motion decomposition using the revised overset grid methodology, is validated to be effective and reliable.

The hydrodynamic performance analysis of a submarine with new pump-jet propulsor

A new type of pump-jet propulsor (PJP) was designed and installed on the DARPA Suboff. The installation position of this new PJP is different from the traditional PJP, which gives more possibilities to improve the comprehensive performance of submarine. The duct of PJP has been automatically modeled based on pumped rotor, stator and hull shape. The rotor of PJP has been modeled as an actuator disc based on body force method coupled with the experimental open water data. The hydrodynamic performance analysis was applied on the self-propulsion point, and the self-propulsion characteristics were estimated by the thrust identity method. Moreover, the pressure and velocity distribution for different duct geometric parameters have been compared and discussed. The results indicate that the size of the duct has an impact on the generation of negative pressure zone and the wake distribution. When the geometric parameters of duct are equal to r = 0.75R, L = 3.5D and H = 0.8D, the overall performance is superior. The new pump jet destroys the circumferential correlation of the duct vortex and accelerates the dissipation of the vortex.

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.

Моделирование самоходных характеристик натурного судна с дискретным гребным винтом

A comparison between towing tank testing and full-scale CFD simulations is presented at three different target speeds. For the current self-propulsion simulation, the self-propulsion point was obtained using polynomial interpolation. The studies of boundary layer thickness, a basic grid uncertainty assessment and verification were performed to give some confidence of grid application to current self-propulsion simulation. All simulations are performed using a commercial CFD software STAR-CCM+. It is concluded that with high-fidelity numerical methods, it’s possible to treat hull roughness and directly calculate full-scale flow characteristics, including the effects of the free surface, none-linearity, turbulence and the interaction between propeller, hull and the flow field.

THE STUDY ABOUT THE IMPACT OF THE FREE-SURFACE ON THE PERFORMANCE OF THE PROPELLER ATTACHED AT THE STERN OF A SUBMARINE

The performance of the propeller attached at the stern of the submarine navigating under limited depths is affected obviously by the free-surface, duo to the changes of the flow field characteristics around this vehicle. And what mentioned above will greatly threaten the security of the maneuverability of the submarine. To figure out the effect of the free-surface on the performance of the propeller attached at the stern of the submarine. In this paper, the URANS (unsteady Reynold average Navier−Stokes) equations coupled with \begin{document}$ k - \omega $\end{document} turbulence model are used for the numerical simulations about performance of the self-propulsion model (the standard Sub-off geometry and the E1619 propeller). At first, the experimental data available including the resistance tests of the submarine with all appendages under total submergence, the resistance tests of the revolution with different navigating depths and the OWC (open water curve) of the propeller, is used for the validation of the numerical method adopted in this paper. Next, the correctness of the numerical method is acquired based on three sets of grids with different spatial resolutions. Finally, the performance of the self-propulsion model navigating under two depths and three different velocities is simulated carefully to figure out the effect of the free-surface on the performance of the self-model. The numerical results show that the exitance of the free surface increases the rotational speed of the propeller at a specific navigating speed, which corresponds to the self-propulsion point. The increment mentioned above is related to the wave pattern induced by the submarine. The wave pattern will cause the nozzle-like flow between submarine and free-surface. The nozzle-like flow and the suction of the propeller change the angle of attack of the blade profile at different radial sections. Meanwhile, approaching and getting away from free surface will also significantly change the hydrodynamic loads of the propeller.

Effect of biofouling roughness on the full-scale powering performance of a submarine

The aim of this study is to investigate the impact of barnacle type biofouling roughness on the full-scale powering performance of a submarine in calm seas. The importance of the diversified biofouling accumulations in terms of hull location is also examined over the submarine hull by implementing homogeneous and heterogenous roughness distribution. In this study, a Reynolds Averaged Navier Stokes (RANS) based CFD model was used for predicting the effects of biofouling roughness on the self-propulsion characteristics for the full-scale submarine form. The powering performance analyses are performed with discretised propeller geometry, and the Moving Reference Frame approach is used to model the rotational motion of the propeller. A proportional-integral (PI) approach is adopted to obtain the self-propulsion point efficiently by modifying the propeller's rotational speed. First, the resistance and the self-propulsion characteristics of the model scale submarine are validated with the experimental and other numerical studies in the literature. Following this validation task, a roughness function model is employed within a CFD software's wall function to represent the rough surfaces over the submarine hull. The results showed that although roughness has a varying effect on the submarine's self-propulsion characteristics depending on the roughness distribution, it increases the hull resistance and, hence, the delivered power overall. Roughness on the forward section of the hull has a more pronounced effect on the resistance and delivered power. The study demonstrated that the presence of partial hull fouling should not be ignored, and required precautions should be taken to prevent losses in submarine performance, especially for the fouling at the forward section of the submarine.

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.

A comparative investigation of fixed and free-running CFD self-propulsion models on a waterjet-propelled trimaran

The numerical method for self-propulsion (SP) point prediction is an essential part of ship hydrodynamics. However, comprehensive investigations on different CFD SP model characteristics are rare, especially for the high-performance waterjet-propelled trimarans. This paper proposes four types of overset mesh-based CFD SP numerical models on a waterjet-propelled trimaran model: two PID-controlled free-running SP models with/without a moving background and two surge-fixed SP models with/without the propulsor PID controller. The URANS CFD simulations are conducted by following the Verification and Validation (V&V) procedure to investigate the four SP models' characteristics. The four computed model SP points agree well with the experimental result, and both the finest grid relative errors are within 1.5%. A comprehensive comparison of the consumed computing resources, surge freedom, control strategy, simulation scheme, V&V result, simulated flow field, simulation accuracy, and calculation efficiency of the four SP models are analyzed. Both the PID-controlled free-running SP model with a moving background and the PID-controlled surge-fixed SP model show advantages in terms of computing resource consumption, propulsor control strategy, accuracy, and efficiency. In particular, compared with the conventional fixed SP model, the computational efficiency could be promoted up to 150%, and the time consumption could decrease up to 60%. Furthermore, the PID-controlled free-running CFD model with moving background shows its advantages and potential in directly simulating the ship's real-time motion in various complex environments.

Impact of Hard Fouling on the Ship Performance of Different Ship Forms

The successful optimization of a maintenance schedule, which represents one of the most important operational measures for the reduction of fuel consumption and greenhouse gas emission, relies on accurate prediction of the impact of cleaning on the ship performance. The impact of cleaning can be considered through the impact of biofouling on ship performance, which is defined with delivered power and propeller rotation rate. In this study, the impact of hard fouling on the ship performance is investigated for three ship types, keeping in mind that ship performance can significantly vary amongst different ship types. Computational fluid dynamics (CFD) simulations are carried out for several fouling conditions by employing the roughness function for hard fouling into the wall function of CFD solver. Firstly, the verification study is performed, and the numerical uncertainty is quantified. The validation study is performed for smooth surface condition and, thereafter, the impact of hard fouling on resistance, open water and propulsion characteristics is assessed. The differences in the impact of biofouling on the ship performance are noticed amongst different ship forms. They are mainly influenced by the portion of viscous resistance in the total resistance, relative roughness, roughness Reynolds number and advance coefficient for the self-propulsion point.