Ship Model Experiment Research Articles

A true double-body method based on porous media model for simulation and froude scaling verification of an aquaculture vessel resistance

A blueprint of a novel aquaculture vessel composed of rectangular cylinders, pontoons, and nets with the capacity for self-propulsion was drawn. However, when completely different flow features are caused by non-stream shapes, resistance prediction cannot be accurately performed through conventional ship model experiments as the existing scale rules may be invalid. Besides, the existence of nets creates obstacles not only in model tests but also in numerical simulations. Therefore, resistance evaluation of the vessel with nets is very challenging. Porous media model for nets is one of feasible solutions and was validated by previously published experimental results, although a control volume was required. However, porous media model is incompatible with volume of fluid multiphase, which makes the double-body method adopted inevitably. A literally true double-body method based on porous media model was proposed. The comparison of vessels with and without a net exhibited a beneficial interaction between the net and the vessel hull, especially for nets with higher solidity. Furthermore, the Froude scaling law was adopted based on the hypothesis of Reynolds number invariance. All the full-scale resistances predicted by it in seven scale ratios demonstrated satisfactory consistency, and the relative errors grew with the increase of the scale ratios.

Research on the design of a novel composite solenoid model ship simulation magnetic source based on DTW

In order to study the simulation ability of a solenoid on a ship magnetic field, a new composite model based on a double row magnetic dipole array model with an ellipsoid was designed. The time-domain characteristics, such as magnetic field characteristics, magnetic inclination cosine, magnetic field scalar gradient, and magnetic field spatial distribution characteristics, were extracted. It was verified that the model can accurately simulate the magnetic field characteristics of ships through ship model experiments and simulation analysis. To further quantitatively and accurately analyze the simulation ability of the composite model for ship magnetic fields, a dynamic time wrapping measurement method based on one-dimensional time series was adopted to calculate the similarity of four characteristic quantities: magnetic field vector, magnetic field modulus, magnetic inclination cosine, and magnetic field scalar gradient. The results showed that the composite model has high simulation ability for ship magnetic fields.

Reconstruction and prediction of global whipping responses on a large cruise ship based on LSTM neural networks

This study presents a model based on Long Short-Term Memory (LSTM) neural networks for the reconstruction and prediction of global whipping responses using ship motion data. The model is fine-tuned and trained based on a dataset of heave, pitch, surge motion data, vertical acceleration data, and vertical bending moments (VBM) from a large cruise ship model experiment by utilizing 5-fold cross-validation. The established model is tested with a pre-split test dataset and used to carry out reconstruction and multi-step prediction of the VBM amidship in following and head seas. The reconstructed results demonstrate a high degree of fit with the measured VBM amidship under both regular and irregular wave cases, indicating the model's ability to capture whipping responses. The findings of multi-step prediction indicate that the prediction accuracy and the model's ability to capture whipping responses decrease as the horizon increases, and the model is more accurate in predicting whipping responses when they are stronger.

Experiment and numerical simulation study on resistance performance of the shallow-water seismic survey vessel

In this paper, a new type of shallow-water seismic survey vessel is proposed to solve the problem that the traditional seismic survey vessels cannot satisfy the requirements of the shallow-water marine resources exploration. To reveal the influence of shallow water effect on resistance and flow field, this research is to obtain the resistance and shallow-water characteristics of this shallow-water seismic survey vessel through ship model experiments and numerical methods. Firstly, the ship model experiment predicted the resistance at different speeds in shallow water and obtained the benchmark data to validate numerical methods. Then, the CFD methods were used to calculate the resistance of the ship in deep and shallow water. The numerical results are in good agreement with the experimental results. Finally, this paper provided details of the distribution of wave, pressure and flow fields at different water depth conditions in order to explain the causes of increased resistance in shallow water, providing a reference for the shallow-water seismic survey vessel design.

Electrical signal reconstruction method of target-simulated minesweeper based on small unmanned boat platform

In recent years, with the continuous development of military unmanned boat technology, there has been a significant increase in interest in small unmanned boat-based minesweeper hunting technology. In this paper, an electrical signal reconstruction method based on time–frequency characteristics and used for small minesweeping gear is proposed. Compared with the existing methods, the method does not require measurement to obtain the complete electrical signal of the distribution and is applicable to both surface ships and submarines for signal reconstruction, which can complete the reconstruction of the original signal with high accuracy in the case of incomplete signal acquisition and can be applied to the signal reconstruction under the harsh marine acquisition environment or strong electromagnetic interference. In this paper, the mathematical model between the maximum sampling interval and the captain is established by extracting the time–frequency features of large ships, and the optimal size of the minesweeper and the optimal parameters of the point charge model are obtained based on the point charge model, and the performance of the method under low signal-to-noise ratio conditions is evaluated by depth permutation. Under the challenging signal-to-noise ratio conditions, the proposed method can accomplish the high-precision reconstruction of the electrical signal distribution of a large ship with the passage data collected by only one measurement node. From the results of simulation and ship model experiments, it can be seen that the electric signal can be simulated with a series unmanned boat array of one-tenth the size of a large ship, and the amplitude error of the reconstructed signal is less than 0.2 mV, the inversion error of EF(Electrostatic Field) is less than 10%, and the inversion error of SEF(shaft-frequency electric field) is less than 12%.

Mixed Electric Field of Multi-Shaft Ship Based on Oxygen Mass Transfer Process under Turbulent Conditions

The theoretical basis for a multi-physics coupling modeling involving a turbulence flow field and a ship’s electric field was analyzed using the principles of electrochemistry and hydrodynamics. Considering the mass transfer of oxygen in the cathode reaction of electrochemical corrosion, the boundary element method was adopted to construct a corrosion electric field model for a multi-shaft ship under navigation. After dissecting the equivalent circuit resistance of the mechanical structure of a ship’s shaft, the initial phase difference of the equivalent resistance between different shafting systems of a multi-shaft ship was analyzed to reveal the regularity of variation of the ship corrosion mixed electric field, when the contact positions of the shaft grounding device were different. A ship model experiment was conducted to verify the correctness of the simulation model. As shown in the results, when the initial phase difference of two-shaft ship shafting equivalent resistance increased from 0° to 45°, 90°, 135°, and 180°, the amplitude of the ship’s mixed electric field varied by less than 3.7%, which was practically negligible. However, the amplitude of the ship’s shaft-rate electric field decreased by 8.30%, 25.4%, 50.2%, and 88.0%, respectively. Moreover, the minimum value of the shaft-rate electric field accounted for 4.11% of the maximum value. This significantly increased the difficulty of marine target detection based on electric field sensors.

Comparative study on the applicability of regularization method in ship’s magnetic signature modeling based on monopole array

In this paper, we first study the applicability and stability of the Tikhonov regularization method (TRM) and the truncated singular value decomposition method in ship’s magnetic signature inversion modeling. To further improve the noise immunity and robustness of the model, we apply an iterative regularization algorithm based on the conjugate gradient least squares (CGLS) method. Numerical simulation shows that the proposed algorithm is more applicable and can obtain better results of ship’s magnetic field extrapolation under different noise backgrounds. In the ship model experiment, the errors of the TRM and CGLS method for magnetic signature extrapolation are, respectively, 4.77% and 3.67%, showing that the proposed algorithm can improve the inversion effect of the ship model magnetic field.

Barrel Distortion Correction for Digital Optic-Based Motion Tracking in Ship Hydrodynamic Model Experiments

In hydrodynamic ship-model experiments, motion tracking of ship model trajectory is employed to predict the maneuverability of the ship when operating in its actual environment. There are some systems for motion tracking, such as inertial measurement unit, radar, laser, and infrared sensors. The system has proven reliable, however, the disadvantage is that they are all relatively expensive. This paper proposes a low-cost digital optic-based motion tracking system using consumer-grade video camera. In order to examine the accuracy of the system, some experiments to apply the method were carried out in maneuvering offshore engineering basin at the Indonesian Hydrodynamics Laboratory, The National Agency for Research and Innovation. To cover a broader area of the trajectory, a wide-angle camera lens was utilized, consequently, the image recorded by the camera experienced a barrel distortion. As a reference for the measurements, gridlines spaced 2 meters apart were drawn on the floor of the basin. Using the grid pattern, the distortion was corrected by finding the relationship between the grid pattern in the object space and in the distorted image. A fourth-order polynomial regression was applied to solve the problem. The results showed that the method was effective for correcting distorted images with a relative standard error of 0.42%.

Analysis of static electric field characteristics of ships in flowing medium

At present, the model of ship corrosion electrostatic field mainly analyzes the electrostatic field distribution in the static medium under the given boundary conditions, without considering the actual corrosion of the metal on the ship’s surface in the flowing seawater, and the relationship between the electrochemical corrosion of the metal and the flow of the medium is very large, which results in a large error between the simulation results and the actual measurement results. In this paper, the relationship between corrosion electrostatic field and flow rate in flowing medium is theoretically deduced. Firstly, the distribution of liquid flow rate is analyzed, the thickness of boundary layer on the surface of metal plate is calculated, then the mass transfer process in flowing electrolyte is calculated by combining the flow rate distribution of metal surface medium, and the corrosion current density on the metal surface under the control of mass transfer process is calculated. Finally, the corrosion current density on the metal surface under the control of mass transfer process is calculated. The equivalent source model of electric field is established based on the current density, and the distribution of corrosion electrostatic field in the medium is analyzed. The correctness of the conclusion is verified by the finite element simulation and the ship model experiment.

Resistance reduction technology research of high speed ships based on a new type of bow appendage

A new type of bow appendage is proposed to reduce resistance of high-speed ship with a Froude Number of 0.4–0.5 in this paper. The ship bow appendage can restrain the bow waves of high-speed ships, thus enabling to decrease the principal wave-making resistance significantly. In this study, resistance experiments and numerical simulation calculations on a ship model were carried out. This new type of bow appendage was designed according to wave pattern of the ship model at the Froude Number of 0.45, aiming to restrain the peak of bow wave. Numerical calculation shows that the bow appendage can affect the wave-making state and reduce the resistance of ship model at high speed, and the effect of the bow appendage is sensitive to its installation position and the model speed. The ship model experiments were conducted to verify the effects of the bow appendage on reducing the resistance of ship model. Experiment results show that this bow appendage is able to restrain bow wave of the ship model and reduce the total resistance by more than 8% to the maximum extent. The water spray induced by the bow appendage can be improved by optimization of the shape.

Experimental Study of Air Layer Drag Reduction with Bottom Cavity for A Bulk Carrier Ship Model

Air lubrication by means of a bottom cavity is a promising method for ship drag reduction. The characteristics of the bottom cavity are sensitive to the flow field around the ship hull and the effect of drag reduction, especially the depth of the bottom cavity. In this study, a ship model experiment of a bulk carrier is conducted in a towing tank using the method of air layer drag reduction (ALDR) with different bottom cavity depths. The shape of the air layer is observed, and the changes in resistance are measured. The model experiments produce results of approximately 20% for the total drag reduction at the ship design speed for a 25-mm cavity continuously supplied with air at Cq = 0.224 in calm water, and the air layer covers the whole cavity when the air flow rate is suitable. In a regular head wave, the air layer is easily broken and reduces the drag reduction rate in short waves, particularly when λ/Lw1 is close to one; however, it still has a good drag reduction effect in the long waves.

The Influences of Lengthening Dimension of Ro-Ro Ferry Toward the Considerations of Hydrodynamics Characteristic and Loading Capacity Aspect

The ferry business has become an important business segment for ship designers, builders and operators. Therefore, many ways have been done in order to increase ferry business through the proper design or converting ships by lengthening. This research is focused on the influences of lengthening a Ro-Ro ferry to hydrodynamics characteristic and loading capacity aspects. Moreover, the ships also are fixed in the same width and draft dimensions. The difference of the Ro-Ro ferries length is indicated by the addition of one column of car space where one column car space is given by car size including distance between car columns spaces which is an increment of every 5.88 meter. The total resistances of Ro-Ro ferries are obtained by ship model experiment in towing tank. There are 4 ship models that are made. The lengthening a Ro-Ro ferry is described into non-dimensional parameter by the ratio of ship length and displacement volume (L/V1/3). The hydrodynamics and the loading capacity of carried car aspects could be described into the ratio of resistance and loading capacity of carried car (RT/SUK) with ship speed. The research result shows that the lengthening of a Ro-Ro ferry affects on total resistance, speed, and loading capacity of carried car. The increase of total resistance is caused by higher residual resistance at high speeds and this is experienced by small length size. Therefore by lengthening the Ro-Ro ferry it could reduce total resistance in the same speed especially the residuary resistance but eventhough lengthening Ro-Ro ferry the effective speed should be considered. In additions, the effective speed for actual ships dimension in the same Rt/SUK 0.05 i.e. B5L10 is about 13.85 knot, B5L11 14.33 knot, B5L12 14.94 knot, and B5L13 15.45 knot respectively.

Inversion of UEP signatures induced by ships based on PSO method

Abstract To model the underwater electric potential (UEP) of ships, a multiple point-electrodes method is commonly used. However, it is difficult to determine the total number of point-electrodes, their respective positions and current values. In this paper, the particle swarm optimization (PSO) method is applied to solve the number, positions and current values of these point-electrodes according to the UEP distribution at a known depth below the keel of a ship. A scaled ship model experiment is carried out to determine the effectiveness of the method. The results show that for hulls in a natural corrosion or cathodic protection state, the UEP inversion accuracy can reach 85% at different depths below the keel. This method is suitable for software implementation and can help the simulation and prediction of UEP signatures.

The application of a smartphone in ship stability experiment

The inclining experiment is the only regulatory tool to assess ship stability. This experiment is a time consuming process for both real-life tests and ship model experiments. The difficulty is mainly due to a bias in the measurement of heel angle. Nowadays, digital inclinometers are available but they are expensive. In this study, the use of a smartphone application is presented for ship inclination and rolling-period tests. The idea consists of using accelerometer and gyroscope sensors built into the current smartphones for the measurements. Therefore, some experiments are carried out on an example trawler model to exhibit the uses and advantages of this method. The obtained results are in good agreement with those provided from the pendulum method and natural roll-period test. This application is new, easy, and more accurately assesses metacentric height during the inclining and rolling-period tests.

Operational modal analysis of a ship model in the presence of harmonic excitation

A ship is operated under an extremely complex environment, and waves and winds are assumed to be the stochastic excitations. Moreover, the propeller, host and mechanical equipment can also induce the harmonic responses. In order to reduce structural vibration, it is important to obtain the modal parameters information of a ship. However, the traditional modal parameter identification methods are not suitable since the excitation information is difficult to obtain. Natural excitation technique-eigensystem realization algorithm (NExT-ERA) is an operational modal identification method which abstracts modal parameters only from the response signals, and it is based on the assumption that the input to the structure is pure white noise. Hence, it is necessary to study the influence of harmonic excitations while applying the NExT-ERA method to a ship structure. The results of this research paper indicate the practical experiences under ambient excitation, ship model experiments were successfully done in the modal parameters identification only when the harmonic frequencies were not too close to the modal frequencies.

Numerical Simulation Calculation of Hydroplane Direct Route Motion Based on FLUENT

Aiming at hydrodynamic performance prediction for hydroplane motion, numerical simulation calculation for direct route motion of a hydroplane was carried out under FLUENT software platform by using VOF method and RNG k-ε model and solving Navier-Stokes equation. Evolution of ship resistance was obtained as the velocity change, and flow field situation and dynamic pressure variation of hydroplane hull bottom were reflected intuitively. By comparing the results of FLUENT calculation and ship model experiment and theoretical estimation, analyzing, especially wake current, it was verified that numerical simulation calculation of hydroplane direct route motion and hydrodynamic performance prediction based on FLUENT are feasible and precise enough.

The Marker-density method in cartesian grids applied to nonlinear ship waves

A numerical simulation method is presented for nonlinear waves generated by advancing ships. The nonlinear free surface is determined by a modified Marker-density method. Pressures and velocities in body boundary cells and free surface cells are calculated through a simultaneous iterative method. The filtered Navier–Stokes equations and filtered continuity equation are used as governing equations. The equations are solved by using a finite difference method in a Cartesian grid system. The body boundary is defined by the line segments connecting the points where grid lines and body surface meet. Pressures are coupled with velocities through two-step projection method in the present approach. The governing equations are approximated in finite difference form using a forward time centered space (FTCS) scheme except convection terms. The convection terms are approximated in finite difference form employing third order upwind scheme in space and Adams–Bashforth scheme in time. For the verification of the present numerical simulation, a numerical computation is carried out with Series-60 cargo ship. For the grid convergence test, three grid levels are selected with a constant grid refinement ratio. For the purpose of understanding spilling type breaking waves near a ship bow, a wedge shape model is selected, and its numerical simulation is performed using the computational fluid dynamics program developed during the present research. For a specific case, plunging type breaking bow waves with scars which are frequently generated by a planing hull type patrol ship, are numerically simulated at several different speeds. In addition, the pressure resistance coefficients from the numerical computations are investigated in detail with respect to the residual resistance coefficients from the corresponding ship model experiments.

タグボートの曳引力に及ぼすプロペラ没水深度と波浪の影響に関する模型実験

The tow force of tugboat has been brought through the bollard pull test, it execute under the condition of calm water and no forward speed. However, since the tugboat usually works in waves, the towing ability has to be examined in waves. In case of shallow propeller immersion depth I/D (Immersion depth/ Propeller diameter ratio), it will be supposed that a tugboat caused the tow force reduction due to the propeller racing in waves. In this paper, we examine the characteristics of mean tow force of tugboat for various factors, such as I/D ratio, wave height, wave direction, towing speed, wave length/ship length ratio X/L, through ship model experiment. In the water tank experiment, two types of ship models are used, which equipment a single kort nozzle Propeller or twin Azimuth Drive Propeller (A.D.P), respectively. Main results are as follows; 1) The mean tow force Tm in calm water and in wave clearly decreased with shallow I/D ratio. 2) Concerning with the influence of wave direction, the mean tow force Tm decreased with the wave height in head waves, but Tm increased in follow waves. 3) The influence of the wave length/ship length ratio X/L and towline length on Tm was slight.

Broaching prediction in the light of an enhanced mathematical model, with higher-order terms taken into account

We have attempted to develop a more consistent mathematical model for capsizing associated with surf-riding in following and quartering waves by taking most of the second-order terms of the waves into account. The wave effects on the hull maneuvring coefficients were estimated, together with the hydrodynamic lift due to wave fluid velocity, and the change in added mass due to relative wave elevations. The wave effects on the hydrodynamic derivatives with respect to rudder angles were estimated by using the Mathematical Modelling Group (MMG) model. Then captive ship model experiments were conducted, and these showed reasonably good agreements between the experiments and the calculations for the wave effects on the hull and the rudder maneuvring forces. It was also found that the wave effects on restoring moments are much smaller than the Froude–Krylov prediction, and the minimum restoring arm appears on a wave downslope but not on a wave crest amidship. Thus, an experimental formula of the lift force due to the heel angle of the ship is provided for numerical modelling. Numerical simulations were then carried out with these second-order terms of waves, and the results were compared with the results of free-running model experiments. An improved prediction accuracy for ship motions in following and quartering seas was demonstrated. Although the boundaries of the ship motion modes were also obtained with both the original model and the present one, the second-order terms for waves are not so crucial for predicting the capsizing boundaries themselves.

Stern Flap Powering Performance on a Spruance Class Destroyer: Ship Trials and Model Experiments

ABSTRACT Model and full scale testing by the U. S. Navy indicate substantial powering improvements due to the installation of a stern flap on Spruance Class (DD 963) Strike Destroyers, and Ticonderoga Class (CG 47) AEGIS Cruisers. An appropriate stern flap design was determined through model scale experimentation, and full scale powering improvements were predicted. The destroyer Arthur W. Radford (DD 968) was then fitted with a prototype stem flap in order to demonstrate full scale performance improvements. Speed/power ship trials indicate considerable performance improvements due to the stern flap: reduction in power of 6% to 14%, resulting in an 11.7% time‐averaged powering reduction 0.75 knot increase in top speed $240K annual fuel cost avoidance (savings) retrofit cost amortized in less than one year The flap design on the A. W. Radford, and the associated fuel savings, can be applied to each ship of the DD 963 and CG 47 Classes, for a multi‐million dollar life cycle fuel cost savings.An economic cost analysis was performed on the stern flap installation for both the Spruance and Ticonderoga Classes. The stern flap fuel cost avoidance and retrofit costs place the Net Present Value at $60 million. The internal rate of return on investment may reach as high as 262%.The physics surrounding the operation of a stern flap on this combatant, and some identified mechanisms that account for the improved performance, are also discussed.