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[Objectives] The recovery of the dinghy is a typical dynamic problem of multi-body interaction,and the stern-slipway launch and retrieval system is widely used in that process. When the dinghy moves rapidly towards the capture devices which are located in the aft of the mother ship,it may be affected by the wake of mother ship which may cause overturn.[Methods] Numerical wave tank,overlapping grid technique and 6-DOF are mainly used and the interference motion of Fridsma planing in approaching the mother ship is simulated. The motion characteristics of planing vessel in waves are calculated and analyzed while the grid independence is verified. Then the simulation of small craft's motion in regular waves in the wake of mother ship is carried out.[Results] Comparison of computational and experimental results indicates that the calculation method is reliable. And the simulation results show that the influence from the mother ship is obvious.[Conclusions] When the direction of motion of planing deviated from the center line of the wake of mother ship,the pitch and roll angle of it will be significantly affected,eventually leading to the occurrence of capsizing.

Waterjet–hull interaction is the hot point and research focus in the research of waterjet-propelled crafts. This paper presents numerical studies on the interaction between a waterjet system and a catamaran. Numerical simulations of both bare hull and self-propulsion hull were carried out based on the URANS method. The SST k-ω model is selected for the closure of the URANS equations. The level set method together with the dynamic overset grid approach is used for the simulations. The body force model with the PI speed controller is used to simulate the rotational motion of the rotor in the simulations for the self-propulsion hull. Moreover, uncertainty analyses of the numerical method are conducted to verify the accuracy of the numerical solver. The numerical results of the bare hull and self-propulsion hull are compared in detail, such as the wave pattern, pressure distribution, hull attitude, and so on. The waterjet reduces the pressure on the hull surface near the stern and makes the height of the wave near the stern lower. This leads to a more violent change in hull attitude and the thrust deduction is positive, ranging from 0.1 to 0.2. The energy conversion is analyzed based on the ITTC recommended procedures, which shows the overall efficiency of the waterjet behind the hull is about 0.75~0.8 times the free stream efficiency. [ABSTRACT FROM AUTHOR]

To examine mechanisms of the high speed and efficiency of propulsion of aquatic animals and to apply the findings to the design of underwater vehicles, this study uses dolphins as an example. The motion of aquatic animals is divided into three stages for the convenience of analysis of bio-propulsion: the oscillation of one-third of the rear body, the oscillation of the caudal fin, and the deformation of the caudal fin. We call the case multi-stage propulsion when all the stages are contained in a bio-propulsion. We investigate the effects of the phase difference between oscillations of the first and second stages φ on hydrodynamic performance and the chordwise deformation factor δc0 on hydrodynamic performance. The results show that when the phase difference was 90°, the propulsion efficiency was the highest and an appropriate caudal chordwise deformation could increase the propulsion efficiency, which was consistent with the result of previous studies. The key part of this paper is the comparative study between different propulsion modes in terms of fluid mechanism from multiple perspectives, such as the force generated by the oscillating motion, the shedding frequency of the wake vortex, and the spacings of vortices induced by different propulsion modes. The aim of this paper is to understand the mechanism supporting a larger thrust and higher efficiency of multi-stage propulsion and provide reference for the improvement and optimization of bionic propulsion in the future. [ABSTRACT FROM AUTHOR]

International Maritime Organization (IMO) has stated that the direct assessment for the pure loss of stability, one of the typical stability failure modes, is necessary for ship designers and under development currently. In this study, extreme roll motions with large amplitudes, induced by the pure loss of stability, are predicted for a benchmark combatant ONR Tumblehome running in stern quartering waves by the computational fluid dynamics (CFD) simulations. An unsteady Reynolds-averaged Navier–Stokes (RANS) solver coupled with a dynamic overset grid approach is used to predict six degree of freedom (DOF) motions. The discretized propeller model is applied to the free-running model, along with a course keeping controller. Different speed conditions are considered for the ship to investigate the instability zone where the pure loss of stability occurs and the CFD results for the roll amplitude are compared with the experimental data, with an average difference less than 3%. In addition, it is observed that ship capsizing occurs coupled with a rapid increase of yaw angle, which is consistent with the phenomenon in the existed model tests. Overall, it indicates that this viscous simulation model is capable for the prediction of the extreme roll as well as the capsizing. • Numerical simulations were conducted by an unsteady RANS solver coupled with dynamic overset grid method. • The extreme roll induced by pure loss of stability for a free-running ONR Tumblehome was investigated in stern quartering seas. • The capsizing coupled with large yaw angle was accurately captured using this numerical method. • Similar method could be extended to investigate the IMO 2nd generation intact stability criteria. [ABSTRACT FROM AUTHOR]

Feng, D.; Wang, X.; Jiang, F., and Zhang, Z., 2015. Large eddy simulation of DARPA SUBOFF for Re = 2.65 × 107. Accurate simulation of the flow field around the hull is of great significance to predict hydrodynamic performances of a submarine. Judging by the resistance of the hull, researchers will be able to know whether the flow field was finely simulated. In this paper, LES (Large-Eddy Simulation) is used to predict the resistance and wake of a standard submarine model DARPA SUBOFF at a high Reynolds number of 2.65 × 107. The results of the simulation were analyzed in detail and compared with the experimental data; they showed satisfactory agreement with the experimental data both quantitatively and qualitatively. [ABSTRACT FROM AUTHOR]

Feng, D.; Wang, X.; Jiang, F., and Zhang, Z., 2015. Large eddy simulation of DARPA SUBOFF for Re = 2.65 × 107. Accurate simulation of the flow field around the hull is of great significance to predict hydrodynamic performances of a submarine. Judging by the resistance of the hull, researchers will be able to know whether the flow field was finely simulated. In this paper, LES (Large-Eddy Simulation) is used to predict the resistance and wake of a standard submarine model DARPA SUBOFF at a high Reynolds number of 2.65 × 107. The results of the simulation were analyzed in detail and compared with the experimental data; they showed satisfactory agreement with the experimental data both quantitatively and qualitatively. [ABSTRACT FROM AUTHOR]

Two propeller models of RANS tools for ship maneuvering predictions are recommended by ITTC committee: discretized propeller model and body force model. In this paper, discretized propeller model and three different body force models are selected to conduct the ship turning circle maneuvering simulations. The direct URANS (unsteady Reynolds-averaged Navier–Stokes) CFD (computational fluid dynamics) method is adopted to assess ship turning circle performance of the self-propelled KCS (KRISO Container Ship) with KP505 propeller model and rudder. Rudder deflection and propeller rotation are executed by the application of hierarchy of overset grids while the ship undertakes 6 DOF dynamic motions. According to the benchmark case, KCS 35 ° turning circle test is simulated at F r = 0.26 using four propulsion models (including the discretized propeller model (DPM), descriptive body-force method (DBM), OUM (Osaka University Method) and modified OUM (MOUM) body-force methods). The present numerical method for maneuvering simulations is verified and validated by conducting the uncertainty analyses. The ship turning circle computational results have been compared against experimental data from literature and with each other in detail. It is found that DPM is able to predict ship turning circle performance well. The difference between DPM and body-force approach become noticeable when the drift angle is larger than 10 deg. DBM is shown to under-predict the magnitude of propeller induced wake passing the rudder and over-predict the tactical diameter, which is consistent with the literatures. The iterative body forces (OUM and MOUM) are found to solve this problem better, especially, MOUM shows higher accuracy in predicting the turning circle characteristics. • The ability of different propulsion models to predict ship maneuvering are compared comprehensively. • The reasons for the differences in predicting ship turning performance using different propulsion models are analyzed. • The computational efficiency of discretized propeller model and body force models are compared. • The effects of the drift angle on ship turning prediction using body force models are discussed. [ABSTRACT FROM AUTHOR]

In this study, numerical simulations of the parametric roll of a ship coupled with liquid sloshing were performed. A model-scale ONR Tumblehome was used for the simulation, and the ship was equipped with a partially filled liquid tank. An in-house unsteady Reynolds-averaged Navier–Stokes solver was applied to the numerical simulation of the coupling effect between the sloshing and parametric roll of the ship in regular head waves. First, a validation study of the computational fluid dynamics (CFD) solver was conducted. Comparisons between the CFD and experimental results showed good agreement. Systematic grid and time-step convergence studies were performed to estimate the numerical uncertainty. The effect of liquid sloshing on the parametric roll of a ship was then investigated numerically with different liquid levels and different ship forward speeds. The results demonstrated that water sloshing could significantly decrease the natural roll frequency of the ship model, which led to a lower speed range where the parametric roll occurred compared with the model without sloshing. The phase difference between the total moment and sloshing-induced moment was close to 180°, resulting in a reduction of the parametric roll amplitude. Sloshing had slight effects on the amplitudes of the heave and pitch motions. • The coupling effect between the sloshing and parametric roll of the ONR Tumblehome was investigated. • Numerical simulations were conducted by an unsteady RANS solver with dynamic overset grid method. • The wave- and sloshing-induced loads were analyzed under the parametric roll condition. [ABSTRACT FROM AUTHOR]

Tank sloshing is widely present in many engineering fields, especially in the field of marine. Due to the trend of large-scale liquid cargo ships, it is of great significance to study the coupled motion response of ships with tanks in beam waves. In this study, the CFD (Computational Fluid Dynamics) method and experiments are used to study the response of a ship with/without a tank in beam waves. All the computations are performed by an in-house CFD solver, which is used to solve RANS (Reynold Average Navier-Stokes) equations coupled with six degrees-of-freedom solid-body motion equations. The Level Set Method is used to solve the free surface. Verification work on the grid number and time step size has been conducted. The simulation results agree with the experimental results well, which shows that the numerical method is accurate enough. In this paper, several different working conditions are set up, and the effects of the liquid height in the tank, the size of the tank and the wavelength ratio of the incident wave on the ship's motion are studied. The results show the effect of tank sloshing on the ship's motion in different working conditions. [ABSTRACT FROM AUTHOR]

The simulations of submarine sailing near the free surface with long-crested waves have been conducted in this study using an in-house viscous URANS solver with an overset grid approach. First, the verification and validation procedures were performed to evaluate the reliability, with the results showing that the generation of irregular waves is adequately accurate and the results of total resistance are in good agreement with EFD. Next, three different submerged depths ranging from 1.1D to 3.3D were selected and the corresponding conditions of submarine sailing near calm water were simulated, the results of which were then compared with each other to investigate the influence of irregular waves and submerged depths. The simulations of the model near calm water at different submerged depths demonstrated that the free surface will cause increasing resistance, lift, and bow-up moments of the model, and this influence decreases dramatically with greater submerged depths. The results of the irregular wave simulations showed that irregular waves cause considerable fluctuations of hydrodynamic force and moments, and that this influence remains even at a deeper submerged depth, which can complicate the control strategies of the submarine. The response spectrum of hydrodynamic forces and moments showed slight amplitudes in the high-frequency region, and the model showed less sensitivity to high-frequency excitations. [ABSTRACT FROM AUTHOR]

This study presents a numerical research on the open-water performance of a pumpjet propulsor at different scales. Simulations were performed by an in-house viscous CFD (Computational Fluid Dynamic) code. The Reynolds-averaged Navier–Stokes (RANS) method with SST k-ω turbulence model is employed. A dynamic overset grid is used to treat the relative motion between the rotor and other parts. The numerical results are compared with the model test data and they agree well. Comparisons for the open-water performance between the pumpjet propulsors with two scales are carried out. The results indicate that the total thrust coefficient of the large-scale pumpjet propulsor is greater than that of the small-scale one while the torque coefficient is smaller. Therefore, the efficiency of the large-scale pumpjet propulsor is about 8~10% higher than that of the small-scale pumpjet propulsor. The open-water performance of the rotor, pre-swirl stator and duct is obtained separately to estimate the discrepancies on the thrust and torque coefficients between different scales. To analyze the scale effect from different parts, the research on flow field and pressure distribution are carried out. The variation of total thrust and torque coefficient comes mainly from the rotor, which is caused by the flow field, influenced by the duct and stator. [ABSTRACT FROM AUTHOR]

• Wake flow is taken into account in new body force. • Open water results of the different methods are very close and new body force shows higher accuracy than other body forces regardless of flow field or open water results. • New body force results for open water and wake flow effect are in good agreement with discretized propeller and experiment. • New body-force is reliable and supports rapid and accurate prediction of self-propulsion. Body force propulsion model has been used for ship self-propulsion CFD simulation for a long time due to its higher computational efficiency and less computer source required. This paper presents a new body force method coupled the blade element momentum theory (BEMT) considering the three-dimensional viscous effects with the RANS solvers. In-house code HUST-Ship was used to solve RANS equations with finite difference method and PISO arithmetic for propulsion model and ship hydrodynamic simulation. KP505 propeller and KCS ship model were used as the numerical model for the studies. Open water characteristics of discretized propeller model were obtained after uncertainty analysis of CFD results. The lift coefficients C L and the drag coefficients C D of different radius sections on the propeller blade were obtained from CFD results of open water characteristics. The multivariate regression method was used to get the correlations between C L , C D and propeller parameters for a propeller model. Then the BEMT method would adopt the correlations with the local velocity at the virtual disk from CFD simulation results simultaneously to calculate the thrust and torque distributions on the blade and thrust and torque of the propulsion model were obtained with integration along the blade. The comparisons of open water characteristics of CFD results between three different body force models and discretized propeller model were performed. The CFD simulation for open water characteristics and velocity distribution around propulsion models are almost same for new body force model and discretized propeller model. The self-propulsion simulations of KCS with new body force model were performed. The comparisons of the KCS self-propulsion simulations results with new body force model, discretized propeller model and EFD results showed good matches with each other. [ABSTRACT FROM AUTHOR]

Estimating ship resistance accurately in different water depths is crucial to design a resistance-optimized hull form and to estimate the minimum required power. This paper presents a validation of a new procedure used for resistance correction of different water depths proposed by Raven, and it presents the numerical simulations of a Kriso container ship (KCS) for different water depth/draught ratios. Model-scale and full-scale ship resistances were predicted using in-house computational fluid dynamics (CFD) code: HUST-Ship. Firstly, the mathematical model is established and the numerical uncertainties are analyzed to ensure the reliability of the subsequent calculations. Secondly, resistances of different water depth/draught ratios are calculated for a KCS scaled model and a full-scale KCS. The simulation results show a similar trend for the change of model-scale and full-scale resistance in different water depths. Finally, the correction procedure proposed by Raven is briefly introduced, and the CFD resistance simulation results of different water depth/draught ratios are compared with the results estimated using the Raven method. Generally, the reliability of the HUST-Ship solver used for predicting ship resistance is proved, and the practicability of the Raven method is discussed. [ABSTRACT FROM AUTHOR]

Ship capsizing in stern quartering wave is very complicate with a strong correlation to the stability failure modes proposed in second-generation intact stability criteria. It is of great importance to shed some light on this complex phenomenon. In this study, the capsizing behavior of a free-running ONR Tumblehome model in stern quartering seas is investigated by an unsteady Reynolds-averaged Navier–Stokes (URANS) solver coupled with dynamic overset grid approach. Validation study of the URANS solver is performed for the prediction of extreme roll motion of the ship. The comparisons show satisfactory agreement, with an average difference less than 3% between the simulation and experimental results. The correlation between the occurrence of stability failure modes (surf-riding, pure loss of stability, and broaching) and ship capsizing is then assessed under different ship speed and heading angle conditions. It is concluded that the capsizing occurs as the free-running ship sailing with a high speed, which is caused by the interaction between the broaching and severe stability loss. In addition, influenced by the wave-induced moment, both the pure loss of stability and surf-riding modes may cause the broaching, indicating the similar occurring condition and strong relation between these stability failure modes. • Ship capsizing in stern quartering wave are directly simulated by an unsteady RANS solver. • Pure loss of stability, surf-riding, and broaching are observed for the ship in stern quartering waves. • Both the pure loss of stability and surf-riding may cause the broaching, closely coupled with ship capsizing. • Wave-induced yaw moment with a small heading angle is not enough to cause the broaching. [ABSTRACT FROM AUTHOR]

Submarine is easily disturbed by the passing surface ships when submarine sailing near the sea surface, the disturbance can greatly affect the hydrodynamic performance and sailing status of the submarine during navigation. In this study, A model-scale tanker (KVLCC2, L PP = 32m) and a model-scale submarine (SUBOFF, L o a = 6.534m) were used to study the hydrodynamic interaction to the submarine when the surface ship overtakes the submarine sailing below it. An in-house unsteady Reynolds-averaged Navier–Stokes solver was applied to the simulation. First, uncertainty analysis of the computational fluid dynamics (CFD) solver was conducted, and validation study based on available experimental data showed good agreement. The hydrodynamic interaction to the submarine during the overtaking process was then investigated numerically with different submarine forward speed, tanker forward speed and different tanker-submarine vertical distance. The results showed that the vertical distance between tanker and submarine has great influence on submarine, the peak values of vertical force and pitching moment of submarine were obviously affected by the forward speed of tanker and submarine, meanwhile, The interaction force on submarine resistance was less effected by submarine forward speed, but the forward speed of tanker was more effected. • A URANS computational model is developed to accurately study the hydrodynamic disturbance of the tanker to the submarine. • Numerical prediction of the sailing performance of SUBOFF during KVLCC2 overtaking the SUBOFF sailing below it. • Investigated the effects of vessel speed and the vertical distance between them on the performance of the submarine. [ABSTRACT FROM AUTHOR]

The complex sea states with the co-occurrence of swell and wind-sea conditions represent threats to sailing vessels. This study presents the computational fluid dynamics (CFD) simulations for a surface combatant model advancing in mixed seas combined with the swell and wind-sea components, aimed at estimating the swell impact on ship seakeeping performance. An in-house unsteady Reynolds-averaged Navier–Stokes solver coupled with an overset grid approach is applied to the numerical predictions, along with the assessment study for the model advancing in calm water and harmonic wave group based on the existed model tests, indicating the CFD results agree well with the experimental data. Irregular wave simulations are then conducted for the model advancing in head seas combined with different swell and wind-sea components. Comparisons of ship seakeeping behaviors for wind-sea dominated, energy equivalent, and swell dominated mixed seas are carried out with the statistical assessment and frequency analysis. Overall, both the heave and pitch amplitudes are larger as the ship is advancing in swell dominated sea than those in the other two seas. The ship motions are also predicted in wind sea and it indicates that the ship encounters the larger heave motion in mixed seas compared with that in wind sea. • Numerical wave tank is modeled based on an unsteady RANS solver to generate the mixed seas combined with the wind-sea and swell components accurately. • Seakeeping performance of DTMB5512 ship model advancing in the complex sea states is numerically predicted. • The influence of wind-sea and swell components on ship vertical motions is investigated with the statistical assessment and frequency analysis. • When advancing in mixed seas, the ship encounters the larger heave motion compared with that in wind sea. [ABSTRACT FROM AUTHOR]

An inhouse CFD code with ship-motion predicting model and dynamic overset grid method is used to evaluate the influence of stern flap's dimension on resistance and motions of the catamaran in long crest head wave. Presented numerical method is verified and validated by the uncertainty analysis for catamaran advancing in calm water and regular wave. Both model-scale and full-scale simulations are conducted to compare stern flap effect on the catamaran at model scale and full scale The paper presents the numerical studies of seakeeping behavior for a high-speed catamaran with stern flap advancing in long crest head wave. Both model-scale and full-scale simulations have been carried out in sea state 6 using unsteady Reynolds-averaged Navier-Stokes (URANS) solver. Uncertainty analyses were performed to verify the accuracy of the numerical solver. Model tests were conducted for the catamaran including resistance tests in calm water and seakeeping tests in regular waves to validate simulation results. The comparisons between simulation results and experimental results show good agreement. Seakeeping behaviors of models with/without stern flaps were predicted for the comparison and evaluation. Model-scale simulation results indicate that using stern flap could reduce catamaran's total resistance and the effects on heave and pitch motions are obvious in sea state 6. The installation of stern flap shows significant effect on the reduction of vertical acceleration's amplitudes, especially for reducing the occurrence of slamming impact due to the effective control of model's trim angle. Full-scale simulations have also been conducted and compared with results at model scale. Results show that effects of stern flap on heave and pitch motions are the same for both model-scale and full-scale catamaran. Residuary resistance coefficients on full-scale catamarans with/without stern flap are almost the same with model-scale simulations. [ABSTRACT FROM AUTHOR]