Captive Model Tests Research Articles

Practical 6-DoF Manoeuvring Simulation of a BB2 Submarine Near the Free Surface

It is necessary to predict the manoeuvring performance of a submarine accurately at the early design stage for its safe and effective operations. In this paper, the practical 6-DoF simulation models of an X-form stern plane submarine operating near the free surface are proposed. A 1/15 scaled model of ‘BB2 submarine’ is constructed, the captive model tests are performed in a towing tank of Korea Research Institute of Ships and Ocean Engineering (KRISO) at the full-scale depths, 30, 15.4 (snorkel depth), and 4.5 metres (surfaced depth). Resistance and propulsion tests are performed at the deepest depth, 30 metres. The vertical planar motion mechanism (PMM) tests including the forced rolling motions are also carried out at the depth of 30 metres. The horizontal PMM tests are conducted at three kinds of depths, respectively. The depth-varying horizontal plane coefficients in the model are identified, and the coefficients which are little influenced by the depths are treated as the constant values for the practical purpose. Some of velocity coupled terms are approximated by using the added mass coefficients on the assumption that the viscous components are negligible. In addition, the resistance increases, vertical suction forces and moments are measured in the straight-ahead tests with varying the submergence depths. The free surface effects are considered as the exponential function terms in the proposed models. Based on the present tests and the previous studies about the free surface effects on the submerged bodies, it is practically assumed that the free surface effects are exponentially decayed with the depths, and are already negligible when the submergence depth is 30 metres, approximately three times the hull depth. Horizontal and vertical plane manoeuvring motions as well as the neutral flights are simulated with the control plane deflections less than 15 degrees. The present simulations are in good agreements with existing free-running model test results.

Determination of Propeller-Rudder-Hull Interaction Coefficients in Ship Manoeuvring Prediction

Abstract The assessment of ship manoeuvring properties is a crucial part of the process of ship design and is usually first carried out during the model test phase of the project. According to the International Maritime Organisation (IMO), the manoeuvrability of the ship can be assessed on the basis of the standard trial manoeuvres. In order to do this, free running model tests or captive model tests are used, in conjunction with a mathematical model of ship motion; this is considered to be a reliable prediction method. In recent years, numerical-based methods have also been widely used in ship hydrodynamics and constantly improving computing power and more accurate fluid dynamics models have made the simulation of more complex cases possible. The study presented in this paper focuses on the determination of propeller-rudder-hull interaction coefficients based on the Mathematical Modelling Group (MMG) standard method in ship manoeuvring prediction. The identification of the parameters uses both captive model tests and a simplified numerical method, as well as regression formulas. The results of 35° turning and 10°/10° zig-zag manoeuvres, obtained with the use of each prediction method, are then compared. The test case used in the study is the container type cargo ship equipped with a single propeller and rudder. The model scale, for which the referenced model tests were carried out, is equal to 1:25 and a NACA 0020 rudder profile was used. This research highlights the advantages and disadvantages of each presented prediction method and their potential for future improvement.

Rans investigation on the hydrodynamic performance of a ship moving obliquely in shallow and narrow channel

ABSTRACT The ship traveling in restricted waterways often experiences larger hydrodynamic forces and moments, together with larger sinkage, trim and heel, compared with that in open water. The hydrodynamic performance of an oil tanker moving obliquely in a shallow and narrow channel is investigated by using a RANS (Reynolds-Averaged Navier-Stokes) method in this work. The effects of ship-bank distance, water depth, etc. on hydrodynamic performance are analysed. When the ship gets closer to the channel bank or the inclination of the channel bank becomes steeper, the blockage effects due to the channel become more considerable. The effects of shallow water and ship drift motion will augment bank effects. The captive model test for a ship moving obliquely in a shallow and narrow channel are numerically carried out in both Circulating Water Channel (CWC) and Towing Tank (TT). The bank effects showed by TT are more considerable than that by CWC.

Integrating Computational Fluid Dynamics for Maneuverability Prediction in Dual Full Rotary Propulsion Ships: A 4-DOF Mathematical Model Approach

To predict the maneuverability of a dual full rotary propulsion ship quickly and accurately, the integrated computational fluid dynamics (CFD) and mathematical model approach is performed to simulate the ship turning and zigzag tests, which are then compared and validated against a full-scale trial carried out under actual sea conditions. Initially, the RANS equations are solved, employing the Volume of Fluid (VOF) method to capture the free water surface, while a numerical simulation of the captive model test is conducted using the rigid body motion module. Secondly, hydrodynamic derivatives for the MMG model are obtained from the CFD simulations and empirical formula. Lastly, a four-degree-of-freedom mathematical model group (MMG) maneuvering model is proposed for the dual full rotary propulsion ship, incorporating full-scale simulations of turning and zigzag tests followed by a full-scale trial for comparative validation. The results indicate that the proposed method has a high accuracy in predicting the maneuverability of dual full-rotary propulsion ships, with an average error of less than 10% from the full-scale trial data (and within 5% for the tactical diameters in particular) in spite of the influence of environmental factors such as wind and waves. It provides experience in predicting the maneuverability of a full-scale ship during the ship design stage.

Assessment of Numerical Captive Model Tests for Underwater Vehicles: The DARPA SUB-OFF Test Case

During the early design stage of an underwater vehicle, the correct assessment of its manoeuvrability is a crucial task. Conducting experimental tests still has high costs, especially when dealing with small vehicles characterized by low available budget. In the current investigation, virtual towing tank tests are simulated using the open-source OpenFOAM library in order to assess the reliability of CFD methods for the prediction of hydrodynamic forces and moments. A well-known case study, the Defence Advanced Research Projects Agency (DARPA) SUB-OFF model, is used, and the outcomes are compared to the experimental results available in the literature. Five different configurations are investigated for pure drift tests, rudder tests and pure rotation in both vertical and horizontal plane. The results show an overall good agreement with the experimental data with a quite low demanding mesh arrangement of 3M cells, a favourable balance between accuracy and computational time. In more detail, the expected error in the most significant forces during manoeuvres is less than 2% for the fully appended configuration (the submarine real operative condition), whereas the accuracy is moderately reduced for the barehull configuration (a case not representative of a real hull) with an expected error of 15%. A possible reason for the differences observed could be attributed to the description of the two streamwise vortices generated when manoeuvring. Apart from the lateral force and yaw moment, the results of the longitudinal force are also presented, having a greater disparity when compared to the experimental data. Nevertheless, the longitudinal force has no important role for the purpose of making stability and control predictions. The study contributes to the validation and consolidation of CFD methods, offering insights into their accuracy and limitations for practical applications in underwater vehicles.

Estimation of linear hydrodynamic derivatives of a 37000 tdw chemical tanker using virtual captive model tests

Forecasting the hydrodynamic properties of a ship is crucial for assessing its maneuvering capabilities. This study presents the results of static drift and circular motion simulations conducted on a 37000 tdw chemical tanker. The calculations were carried out using the ISIS-CFD solver, accessible through the FineTM/Marine academic license provided by NUMECA. The flow solution was obtained by numerically solving the Reynolds-Averaged Navier Stokes equations, employing the k-ω Shear Stress Transport (SST) model to represent turbulence. The simulation results were used to determine the linear hydrodynamic derivatives, which were then compared with hydrodynamic derivatives estimated with empirical formulas proposed by Clarke et. al. [1] and Tribon Initial Design module in the absence of experimental results.

Effects of strut cover and lower vertical fin in podded propulsion units on ship maneuverability

To investigate the effects of a strut cover and lower vertical fin in podded propulsion units (POD units) on the maneuverability of a POD-driven ship, free-running model tests (turning test, spiral/revers spiral test, and zig-zag maneuver test) were conducted for three different profiles of the POD units: only a vertical strut without the strut cover or fin (F0), smaller strut cover and smaller fin (FS), and larger strut cover and larger fin (FL). The profile area increases in the order of F0, FS, and FL. The tests were conducted using two propeller positions: one with a propeller equipped in front of the POD units (PULL position) and another with the propeller equipped behind the POD units (PUSH position). The steady turning performance at a steering angle of 35° in the PULL position deteriorated in the order of F0, FS, and FL. In contrast, in the case of the PUSH position, the turning performance improved in the order of F0, FS, and FL. Thus, the PULL and PUSH positions demonstrated different tendencies. The non-dimensional steady yaw rate exceeded 1.0 in all cases, which indicates that the present ship has an excellent turning performance. Furthermore, captive model tests (the POD steering force test in straight towing, oblique towing test, and circular motion test) were conducted to determine the effects of the strut cover and lower vertical fin on the lateral force and yaw moment acting on the ship model. It was found that the large strut cover and fin increase the steering force and improves the course stability of the ship in both the PULL and PUSH positions.

Unsteady ship–bank interaction: a comparison between experimental and computational predictions

ABSTRACT A collaborative exercise is presented where different numerical methods were used to recreate the forces acting on a ship model while executing captive model tests along a channel which has an unsteady cross section (dock opening). Such a layout is typical for a harbour environment. The unsteady nature of the cross section leads to peak values in forces, sinkage and free surface deformations. Experimental tests were conducted by Flanders Hydraulics (with the co-operation of Ghent University). Numerical contributions involve three potential flow methods (Strathclyde University and Pinkster Marine Hydrodynamics) and one RANS method (Federal Waterways Engineering and Research Institute of Germany). All methods are capable of qualitatively predicting the water level variations and sinkage and trim of the vessel. RANS has a better capability of predicting the unsteady sway force and yaw moment acting on the ship including sinkage and trim, but it comes at a much higher computational cost.

Estimation of steady wave forces and moment acting on an obliquely moving ship in short waves, and its application in a manoeuvring simulation

In this study, we propose a prediction method for steady wave forces acting on an obliquely moving ship in short waves. Particularly, we enhance an existing method that focuses on refraction of flow and waves in the vicinity of ship's waterline, in terms of the wave amplitude in the near region of the ship and the flow velocity. The former is theoretically modified by deriving an advection equation for wave energy on a ship-fixed frame, and the latter is improved by reflecting the results of computational fluid dynamics that automatically includes viscous effects. A comparison between the prediction and published captive model test results shows that the present method can more adequately capture the variation of the steady wave forces owing to the ship advancing speed and lateral drift than the original method, although the prediction accuracy is not necessarily improved under all conditions. To confirm the applicability of the present method for steady wave forces to ship manoeuvring problems, we predict course-keeping manoeuvres of a ship in regular short waves through a numerical simulation that considers only the steady wave forces in the equation of motion in calm water. The manoeuvring simulation results are validated using previously published free-running model test results, involving various rudder effectiveness conditions for the ship model and full-scale ships, both with and without engine limits. The comparison shows that the present method for steady wave forces is effective in predicting the course-keeping manoeuvres under rudder effectiveness conditions for a ship model in regular short waves. Nonetheless, the present method is insufficiently practical in terms of the manoeuvring simulation under rudder effectiveness conditions for a full-scale ship that is relatively more susceptible to waves. We confirm that an empirical correction for the computed steady wave surge forces based on the discrepancy between the measured and computed values under the ship resting enables the approximate prediction of the course-keeping manoeuvres even under the rudder effectiveness conditions for the full-scale ship.

Mathematical modeling of shallow water effects on ship maneuvering

An Abkowitz-type model was extended to improve the prediction of maneuvering dynamics of inland ships in deep and shallow waters. First, additional coupled rudder and speed related hydrodynamic derivatives were added to better capture hydrodynamic forces and moments. Second, higher order drift related hydrodynamic derivatives were implemented to more reliably predict longitudinal forces. Steady RANS-based captive model tests were performed to estimate speed-dependent hydrodynamic derivatives. Unsteady captive model tests, based on applying a novel Euler equations based numerical approach, were carried out to determine acceleration-dependent zero-frequency hydrodynamic derivatives. Executed were propulsion tests, rudder tests, coupled propulsion and rudder tests, rotating arm tests, drift tests, and coupled rotating arm and drift tests, all at five water depths to draft ratios of 1.43, 1.79, 2.00, 4.00, and 8.00. Tests at the ratio 1.79 were validated against physical captive model tests, and regression analyses estimated the hydrodynamic derivatives. At each water depth, a 45 deg turning circle test, a 35/10 zigzag test, and a 45/110 evasive action test were carried out. Turning circle maneuvers were significantly influenced by shallow water. Compared to deep water, in shallow water the tactical diameter increased from 1.6L to 2.6L, and the drift angle decreased from 21 deg to about 4 deg. Compared to turning circles maneuvers, effects on the zigzag and evasive action maneuvers were relatively small in shallow water. Drift angles and yaw rates in the simulated 45 deg turning circle and a 35/5 zigzag tests agreed favorably with full-scale trials of a similar ship; however, scale effects and the slightly different hull shapes led to different speed losses.

Maneuvering simulations at large drift angles of a ship with a flapped rudder

In this paper, a simulation method is presented for calculating the ship maneuvering motions at large drift angles, including acceleration turning and stopping. For the ship hull force model, a method to use directly the hydrodynamic force data at large drift angle conditions without a mathematical expression is employed. The hydrodynamic forces are obtained using captive model tests. The rudder force is modeled based on existing tank test results. The present models are applied to the maneuvering simulations for an inland container ship equipped with a bow thruster and flap rudder. In addition to the ordinary maneuvering motions such as turning and zig-zag maneuvers, the low-speed maneuvering motions such as acceleration turning by steering, acceleration turning using the bow thruster, and propeller reverse stopping are simulated. The simulation results are compared with the free-running model test results to validate the present method. As a result, we found that the present method can simulate not only ordinary maneuvering motions but also low-speed maneuvering motions with a large drift angle with practical accuracy.

A study on interaction among hull, diesel engine and propellers of a twin-screw ship during turning circle maneuver

A marine propulsion plant will experience power fluctuations during ship maneuvers. In the turning circle maneuver, the propulsive load increases significantly, and the power required by the two shafts of a twin-screw ship may be completely inconsistent. To protect the propulsion plant, the interaction between the engine and the propellers should be studied in depth. In this paper, the twin-screw ONRT ship and the 16PA6-STC diesel engine are selected as the study objects. A series of captive model tests are simulated by using CFD method to obtain the hydrodynamic derivatives and hull-propeller-rudder interaction coefficients in the MMG model. The effective wake fraction is computed under the maneuvering conditions. Turning circle maneuver of the ship is predicted by using the established MMG model, and the predicted ship maneuvering characteristics show good agreement with the available experimental results, which verifies the CFD-based modeling method. Finally, a dynamic model of hull-engine-propeller system is established on the simulation platform for evaluating the operating characteristics of propulsion plant. The propeller loads are predicted and the interaction among hull, engine and propellers is investigated. This study helps to provide a deeper insight into the engine operation behaviors during turning circle maneuver of a ship.

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 numerical study on the ship-bank interaction at various water depths of a surface ship.

Ship maneuvering in restricted waters is a significant challenge in navigation safety due to the complex flow around the ship. In particular, when a ship travels close to a lateral bank and shallow water, the hydrodynamic interaction forces significantly influence the maneuvering motion of the ship. Maneuverability in restricted water is even more difficult for an autonomous surface ship. Therefore, it is necessary to assess the effects of maneuvering near a bank and in shallow water for an autonomous surface ship. In this study, maneuvering simulations considering the bank effect at various water depths are implemented based on hydrodynamic forces estimated using computational fluid dynamics simulation. First, virtual captive model tests at various water depths and simulations of various lateral distances to the banks are performed to estimate the hydrodynamic forces using computational fluid dynamics simulation. The simulation method is validated by comparing the simulation results of the static drift test in deep water with the measured one in the experimental method. Second, the maneuvering simulations for the turning circle test and zig-zag test at various water depths are conducted using the obtained hydrodynamic coefficients. Then, the maneuvering simulations in deep water are compared with the experiment results, and a good agreement is observed. Finally, the simulation considering the bank effects at various water depths is evaluated and discussed.

추력편향방식 AUV의 직진안정성 개선을 위한 고정핀 설계

AUVs (Autonomous Underwater Vehicles) have been widely used for various underwater survey missions. In general, cruising type AUVs have torpedo-shaped hull forms for minimizing the hull resistances. It is necessary to ensure there are sufficient straight-line stabilities for a cruising type AUV in order to maintain its desired courses and depths with minimum controls during operations. In this study, vertical and horizontal plane straight-line stabilities of a designed AUV are analyzed based on the captive model tests. VPMM (Vertical Planar Motion Mechanism) tests are carried out to obtain hydrodynamic coefficients of the designed AUV. The AUV shows both vertical and horizontal plane instabilities, its stability margin indices are unsatisfying when compared with the recommended values. But the recommended vertical plane stability margins are subject to very high-speed conditions, so the characteristic equations of the AUV are reconsidered to investigate low-speed vertical plane stabilities in more detail. Next, a pair of horizontal and vertical fins are respectively designed to improve the vertical and horizontal plane stabilities of the AUV. The AUV with fixed fins shows improved stability margin indices within the recommended levels. In addition, the shape of the horizontal fins is properly modified for safe operations. The AUV with the designed vertical fins shows good horizontal plane stability in straight run simulations with step disturbances. And the effects of the horizontal fins are investigated through depth control simulations with biased random disturbances.

Full-scale URANS prediction of a vessel's transverse stability in wind and waves under lifting condition

Predicting a vessel’s motion response is important for the design as well as evaluating its operability and sustainability. This is often performed in towing tanks through captive model tests in towing tanks. However, discrepancies exist between model-scale and full-scale results. Besides, quite often, the wind is not included in the test, resulting in unrealistic assumptions of static pressure and constant heeling lever from the wind. This paper presents a study on transverse stability under wind, waves, and lifting conditions, incorporating several series of URANS-based simulations in model-scale and full-scale. According to the results, scaling effects accounts for about 3~15% in terms of roll amplitudes and it seems to be both frictional-force-related and wave-frequency-dependent. Wind force exerts limited influence on the vessel’s transverse stability, however, in waves especially for longer wavelength, a wind of 25 m/s increases the roll amplitude up to 53% and it appears to be wave frequency-dependant. The correlation between roll motion and wind/waves/lifting is complicated but their combination produces way more influence than any individual factor alone, indicating none of them should be neglected.

Research on the influence of trimaran side hull layout on its manoeuvrability

In this paper, the numerical simulation method is used to calculate the hydrodynamics of the trimaran under different longitudinal and lateral side hull positions to predict the maneuvering motion, and then analyze the influence of the side hull layout on its Manoeuvrability. Firstly, based on the finite volume method (FVM),numerical simulation of the Captive Model Tests such as towing tests, circular motion tests, static heel tests, and roll decay motion tests are carried out by solving the 3-D unsteady Reynolds-Averaged Navier-Stokes (URANS) equations to determine the hydrodynamic coefficients for a mathematical model of the ship maneuvering motion, and to explore the hydrodynamic performance changes of trimaran under different working conditions and side hull layouts. Next, the turning maneuvering motion and Zig-zag maneuvering motion of the trimaran were predicted by combining with the 4-degree-of-freedom MMG model. Finally, the influence of different side hull layouts on the trimaran's maneuvering performance and the hull's heeling attitude under maneuvering motion was explored by comparing the maneuvering motion parameters.

KCS 선형의 규칙파 중 구속모형시험에 대한 연구

In order to investigate maneuvering characteristics of KCS in waves, captive model test in regular waves was conducted. Purpose of the test is measuring maneuvering hull forces when ship is maneuvering in waves. Model test was carried out using CPMC (Computerized Planar Motion Carriage) of ocean engineering basin in KRISO (Korea Research Institute of Ships and Ocean engineering). Total 6 degrees-of-freedom motion were fixed by two points supporting captive model test device, which is specially designed for this test. This system estimates 6 degrees-of-freedom forces and moments through 12 strain gauge signals. Mapping matrix from strain gauge signals to 6 degrees-of-freedom forces and moments was derived by a well-organized calibration test. Static drift test was conducted in calm sea and in regular waves with various wave conditions. Hydrodynamic coefficients related to drift angle were extracted for each wave conditions, and the effect of waves on course stability was analyzed.

자유수면 근처에서 직진하는 BB2 잠수함의 심도별 유체력과 중립운항에 대한 구속모형시험 연구

In this study, the force and moment acting on a Joubert BB2 submarine model at depths near the free surface were measured through a captive model test with the scale ratio of 1/15. Based on the experiment, the pitch moment and heave force due to the

The heel influence on ship manoeuvrability: Single and twin-screw surface vessels

Low transverse metacentric height and high speed are peculiar destabilising factors in ship manoeuvrability according to the attainable large heeling angles. The phenomenon indeed occurs in the case of vessels characterised by loading conditions with low transverse stability — e.g. high centre of mass of container vessels and RoRos. Starting from Kijima’s single-screw container vessel evidence, an extension of the study to twin-screw ferry vessels is undertaken, with the scope of quantifying its effect in terms of turning and zig-zag IMO margins at an early design stage. Given the relevant impact, an enlarged captive model testing campaign executed on a sample of reference vessels was analysed to further characterise and extend the concepts to a broader class of modern single and twin-screw vessels, thus motivating the study. As a further result, this analysis allowed to underline the need of a review of the IMO intact stability code when dealing with heeling angle during a turn.