Seakeeping Tests Research Articles

Experimental modelling of a novel concrete-based 15-MW spar wind turbine

Physical model testing is a crucial step in the validation process of floating offshore wind concepts that can be used to contribute to the worldwide decarbonization objectives. It is also important to understand the coupled performance of all the sub-systems that conform to a floating wind concept: wind turbines, mooring systems or floating platform hydrodynamic responses. Few experimental tests had been conducted, and no real-time hybrid modelling had been performed in these tests. In this paper, an open-source experimental dataset is presented, and the dynamics of a concrete spar-based floating concept withstanding the IEA 15-MW Reference Wind Turbine are investigated. An experiment on a 1:55 scale concrete-based spar (WindCrete) at IHCantabria's ocean basin was developed by means of the hardware-in-the-loop technique under the COREWIND EU-H2020 project. The available data consist of the hydrodynamic characterizations and seakeeping tests with a total of 57 available datasets. The proper behaviour of the WindCrete platform and the designed mooring system is confirmed by the maximum motion values and accelerations below the established acceptance criteria defined. Moreover, this test program identifies the importance of the wind loads over the dynamic performance of the concept.

Uji Performa Model Batam Marine Ambulance Sebagai Armada Pendukung Medis dan Logistik

This study aims to test the performance of the Batam Marine Ambulance model as a medical and logistics support fleet using the comparison ship method. A series of stability and motion analysis processes were carried out, then the results were assessed to determine the best design among the proposed design options. Performance tests used three ship models (Model I, Model II, and Model III). It is known that in the stability test, the tilt angle of model III is 33.63° and the maximum GZ value is 4.673 cm. Then, in the resistance test, Model I has a lower resistance of 87.29 N and the required power is 1496.93 W compared to the other proposed models. In the seakeeping test, Model III was found to be more stable or less affected on all surface conditions because the RAO value was relatively lower, namely 90o in terms of heaving, rolling, and pitching at 135o and 180o then had lower additional resistance. The Model III design has good ship stability, drag, and seakeeping characteristics.

Hydrodynamic Tests of Innovative Tourist Submarine

This paper deals with the resistance, towing, seakeeping, and open water propeller tests of an innovative tourist submarine model. Tests were performed in a 276 m long towing tank. As the submarine model is a complex structure composed of various parts attached to the pressure hull, the largest possible model, in the scale of 1:5.0, was produced, considering the towing tank depth and the capabilities of the measurement equipment. Resistance tests were performed in deep water and on the surface in calm water. The tested speed range in both cases was up to 5.5 knots. To ensure the avoidance of free surface effects, resistance tests in deep water were performed for different draughts and then extrapolated to infinite water depth. Smaller effective powers were found for the surface condition. The results are compared to an independently performed computational fluid dynamics (CFD) analysis using OpenFOAM. A fair agreement between the experimentally and numerically predicted effective power is found, while the reasons for the differences found are explained. The free submarine model was towed with a rope performed for the speed range 1.7 kn–3.5 kn, and the towing force in the rope was measured. Seakeeping tests in irregular beam waves at zero speed were performed to check the flooding risk on open hatches. Open water tests of the main thrusters for propelling the submarine were conducted, indicating that both power demand and propeller thrust are slightly larger compared to the initial estimates.

Development of Low-Cost Wave Measurement Model Using Ultrasonic Sensor JSN-SR04T for Supporting Seakeeping Test in the Maneuvering and Engineering Ocean Basin (MOB)

Development of Low-Cost Wave Measurement Model Using Ultrasonic Sensor JSN-SR04T for Supporting Seakeeping Test in the Maneuvering and Engineering Ocean Basin (MOB)

Regular Wave Seakeeping Analysis of a Planing Hull by Smoothed Particle Hydrodynamics: A Comprehensive Validation

In this work, the dynamics of a planing hull in regular head waves was investigated using the Smoothed Particle Hydrodynamics (SPH) meshfree method. The simulation of the interaction of such vessels with wave trains features several challenging characteristics, from the complex physical interaction, due to large dynamic responses, to the likewise heavy numerical workload. A novel numerical wave flume implemented within the SPH-based code DualSPHysics fulfills both demands, guaranteeing comparable accuracy with an established proprietary Computational Fluid Dynamics (CFD) solver without sharpening the computational load. The numerical wave flume uses ad hoc open-boundary conditions to reproduce the flow characteristics encountered by the hull during its motion, combining the current and waves while adjusting their properties with respect to the vessel’s experimental towing speed. It follows a relatively small three-dimensional domain, where the potentiality of the SPH method in modeling free-surface flows interacting with moving structures is unleashed. The results in different wave conditions show the feasibility of this novel approach, considering the overall good agreement with the experiments; hence, an interesting alternative procedure to simulate the seakeeping test in several marine conditions with bearable effort and satisfying accuracy is established.

Study on the Measured Signal Analysis Method Based on Sine Curve-fit Method for Ship Model Seakeeping Test

Ship model seakeeping test measure data included frequency ponderances of syntonic waves, mixed waves, and white noise, which affect the test result. Heave time series and pitch time series of planning hull model seakeeping test are calculated by the three-parameter sine wave curve-fit method. Amplitude, angular frequency, and phase angle are obtained. The result shows that the distortion degrees of heave and pitch decrease gradually with an increase in wavelength; when the test wavelength is 8.8m, the distortion degrees of heave and pitch are the smallest, which reach 2.79% and 4.69%; however, at a wavelength of 11m, the distortion degrees of heave and pitch increase.

Разработка формы обводов носовой оконечности судов типа «река – море» повышенной мореходности

Object and purpose of research. The purpose of this study was to develop a bow shape with increased block coefficient for river-sea vessels so as to improve their seakeeping at high sea states. Subject matter and methods. This paper qualitatively analyses the physics of wave effects upon a moving ship, ranking the contribution of specific factors and solving the task of improving the seakeeping performance through optimization of hull lines. Main results. The study highlighted the peculiarities of intense wave effects upon ship bow and suggested the hull lines offering a good seakeeping performance for a hull with high block coefficient. Seakeeping tests of initial and modified hull models at Krylov State Research Centre Seakeeping Basin have confirmed the theoretical results. Conclusion. The study outlined one of the ways to improve seakeeping performance of river-sea ships with increased block coefficient at high sea states.

Robust Laboratory Scale Seakeeping Test Wave Measurement Method Use Ultrasonic Sensor

The seakeeping test is one of the tests done in the Indonesia Hydrodynamic Laboratory (IHL) test tank on a model ship or floating unit. In the test tank, a wave can be generated by using electric and mechanic wave flaps that are pre-programmed on a certain condition of the wave, i.e. different frequencies and amplitude. To measure waves, produced by a wave generator, a wave measuring instrument is needed that can measure changes in water level in the test tank. The current wave measuring instrument is in the form of a 600 mm twin wire wave probe. This instrument is can be used to measure waves in the test tank but has limitations because it is only placed in one location without being moved. Another method is developed to be used in making alternative measuring instruments using ultrasonic sensors. In this paper, this alternative wave measuring instrument shows that measuring waves even when moving the measurement point to a new point location or following a towing carriage can be done and gives better measurement results. Based on these results, this new measuring instrument can be used in a more complex configuration test in the tank.

Uncertainty Analysis Study on Seakeeping Tests of Benchmark Model

Experimental uncertainty and measurement, particularly in engineering, have been increasingly emphasized over the last 20 years. Uncertainty analysis of ship model testing in seakeeping experiments based on International Organization for Standardization, Guide for Uncertainty of Measurements (ISO-GUM), report with recommendations published by ITTC (2008). In this paper, the uncertainties for free-running tests were performed for a model scale 1:62 as a benchmark model test at the Indonesian Hydrodynamic Laboratory (IHL). The benchmark model is representative of a full scale of 186 meters. The model has full appendages as well as a rudder and propellers to allow for free-running tests, natural roll period, free roll decay, and swing tests. Factors of basic uncertainty (type A and type B) are estimated using model tests. The standard deviation of the mean value of a repeated measurement is uncertainty type A. However, Type B uncertainty is estimated from manufacturing specifications. The uncertainty components resulting from both types are quantified by standard deviations. The uncertainty value of Type B is approximated by a corresponding variance. This study helps to understand the underlying uncertainty associated with this research, which resulted in a total geometry uncertainty value (Lpp, B, T, H, , and kyy) of 0.17598% and the total uncertainty value of the instrument calibration results (wave height sensor and qualysis motion tracking) is 0.01161%. The results of this study are expected to minimize the impact of sources of uncertainty and allow the potential for underlying uncertainty to be corrected for the next seaworthiness test.

Experimental parametric study on hydroelastic behaviour of a 15000-TEU container ship based on segmented ship model

ABSTRACT Large-scale ships with high elasticity and low natural frequency, behave high dynamic response amplitude under impulsive wave loads (whipping) and short period waves (springing), which could result in serious ultimate loads and fatigue damage. The segmented model test is a more powerful approach for the ship hydroelastic analysis compared with ship seakeeping test. However, the effect of some test parameters on the hydroelastic responses is still not a clear statement. Therefore, the number of segments, propulsion mode and backbone form are chosen for the parametric study on ship hydroelastic behaviour. A three-dimensional (3-D) nonlinear time-domain hydroelastic method is developed, in which the nonlinearity of instantaneous wetted surface and slamming force are considered. Through the analysis of natural frequencies and vertical bending moments (VBM), the impact on hydroelastic behaviour is discussed. Results show that self-propelling models with variable cross-section backbones are more suitable and reliable in studying nonlinear hydroelastic behaviour.

Estimating wave spectra from the motions of dynamically positioned vessels: An assessment based on model tests

Alternatives for estimating the directional wave spectrum from the motions of a vessel have been evaluated over the past years considering different statistical approaches. This paper discusses the application of the motions of a dynamically positioned platform supply vessel to perform inferences by means of a Bayesian method. The method was formulated considering a methodology for hyperparameter calibration based on an optimization process, and the definition of an iterative estimation scheme. Small-scale seakeeping tests in irregular waves were carried out with the model of a platform supply vessel (PSV) equipped with a dynamic positioning (DP) system, which was calibrated to be consistent with a typical real system. For evaluating any possible influence the DP responses might have had on the motion-based wave estimations, the same test conditions were also performed with the model moored by means of an equivalent soft-mooring configuration. Estimation results were obtained from the motions measured in the experiments, showing that wave parameters could be computed with good precision in both arrangements, with overall average errors, in moored and DP configurations, respectively, of: 5.54% and 5.47% for significant height, 0.76% and 0.75% for peak period, and 1.25° and 1.46° for direction. A further analysis with the comparison of the estimated wave spectra attested the correspondence with the expected values and the similarities between the estimations obtained in the two different scenarios.

水圧計測による波浪中船体構造応答の推定手法

It is important for the design of the safe hull structure to grasp the hull structural response in waves. A seakeeping test by using a flexible ship model is carried out to clarify hull structural response in waves. But it is difficult to design and deal with a flexible ship model. In this study, the estimation method available to a rigid ship model for hull structural response is proposed. First, hydrodynamic pressure in the hull surface is measured by conducting a seakeeping test. Next, the hydrodynamic pressure is interpolated in the whole hull surface considering the hydrodynamic pressure distribution near the draft. Finally, the hydrodynamic pressure distribution is used as load and finite element analysis (FEA) is carried out. Inertial force is considered by using the inertia relief method. The hull structural response in waves can be obtained from FEA results. In this 1st report, a seakeeping test is carried out, and the vertical bending moment (VBM) is estimated by using the proposed method. An acrylic flexible ship model is used in the test to measure the hydrodynamic pressure on the hull outer surface and hull strains at many points by using the fiber Bragg gratings sensors. VBM obtained by the proposed method is good agreement with one obtained by the measured strains.

Experimental study of the state-of-the-art offshore system integrating a floating offshore wind turbine with a steel fish farming cage

An innovative offshore system integrating a floating offshore wind turbine with a steel fish farming cage (FOWT-SFFC) has recently been developed by the two leading authors for offshore wind and aquaculture industry. The purpose of this paper is to investigate the dynamic responses of FOWT-SFFC subjected to simultaneous wind and wave actions in the harsh South China Sea environment by a series of model tests. The tests are conducted at the Tsinghua Ocean Engineering Basin with Froude scale of 1:30. In this paper, the similarity law and setup of model tests are given first. Then a series of calibration tests and identification tests are carried out to validate the capacity of wind generator and wave maker, and to identify the vibration frequencies of tower, the stiffness of mooring system, natural periods and system damping, motion response amplitude operators (RAOs) of FOWT-SFFC, and thrust-speed performance of the turbine in wave basin. After that, seakeeping tests are implemented for random waves, followed by a sequence of load cases including normal operating and extreme conditions. Constant wind speeds and random wind speeds are respectively considered in load combinations. The experimental results affirm the excellent seakeeping and dynamic performance of FOWT-SFFC. Existence of metal fish nets increases the damping of foundation's 6 degree-of-freedoms motions. Generally, the influence of nets on the dynamic responses is insignificant in wind sea states.

Numerical investigation of side-wall effects on the seakeeping performance of a ship advancing in waves

During seakeeping tests of a ship model in a towing tank, the hydrodynamics will show discrepancies when compared to the open-sea results because of side-wall effects. Here, a three-dimensional panel method based on a Rankine-type tank-wall Green function is proposed to solve this problem. This tank-wall Green function, which satisfies the non-penetration condition on the side walls, is in the form of an infinite series, which has slow convergence. Therefore, an approximate computation method is established, and this is found to have satisfying efficiency and accuracy. The present numerical results are compared to the corresponding experimental results from a floating spheroid of beam–length ratio 1/5 and a Lewis-form ship, both advancing with forward speed at Froude number 0.1. Good agreement between the test measurements and the numerical results is obtained in all cases, indicating that the present panel method is useful and applicable. According to the propagation characteristics of the three-dimensional translating–pulsating source Green function, an approximate discrimination method is proposed for identifying side-wall effects. The present numerical method can be further extended to investigate the interactions between side-wall effects and shallow-water effects.

Validation of vessel seakeeping model tuning algorithm based on measurements at model scale

Wave-induced vessel motion prediction plays a critical role in ensuring safe marine operations. The operational limiting criteria can usually be calculated by applying presumed linearized vessel motion transfer functions based on the specified vessel loading condition, which may deviate from the real vessel condition when the operation is executed. Reducing the uncertainties of the onboard vessel loading condition can therefore improve the accuracy of vessel motion prediction and hence improve the safety and cost-efficiency for marine operations. However, parameters related to the onboard vessel loading condition can be difficult to measure directly, such as the center of gravity and moments of inertia. In addition, the hydrodynamic viscous damping terms are always subject to significant uncertainties and sometimes become critical for accurate vessel motion predictions. A very promising algorithm for the tuning of these important uncertain vessel parameters based on the unscented Kalman filter (UKF) that uses onboard vessel motion measurements and synchronous wave information was proposed and demonstrated previously by application to synthetic data. The present paper validates the UKF-based vessel seakeeping model tuning algorithm by considering measurements from model-scale seakeeping tests. Validation analyses demonstrate rational tuning results. The observed random errors and bias in relation to the measurement functions due to the applied simplification and linearization in the seakeeping simulations can lead to biased tuning. The importance of designing the state space and the measurement space is demonstrated by case studies. Due to the nonlinear relationship between the uncertain vessel parameters and the vessel motions, the tuning is shown to be sensitive to the mean state vector and selection of the surrounding sigma points.

An Experimental Analysis of Active Pitch Control for an Assault Amphibious Vehicle Considering Waterjet-Hydrofoil Interaction Effect

The present study aims to reduce the pitch motion of an assault amphibious vehicle system in seaways by waterjet impeller revolution rate control. A series of seakeeping tests were performed in a towing tank with a 1/4.5-scale model. This vehicle is manufactured as a box-shaped hull, and since an appendage that generates lift force is attached, the amount of change in pitch motion is large according to the forward speed. For pitch motion reduction, the impeller revolution rate and resultant pitch moment were controlled through a proportional-integral-derivative controller. Improvements in seakeeping performance were examined in both regular and irregular conditions by the model tests in terms of root mean square of pitch motion. The tuned controller decreased pitch motion by more than 60%.

Towing-tank measurement of unsteady wave elevation around two ships in head sea condition and comparison with computational results

Many studies on ship wave elevation measurement have been performed focusing on steady waves in calm water and unsteady wave-cut analysis near ships, and a reliable experimental database of unsteady wave elevation with incident waves is not enough for the validation of numerical computations. In this study, a non-contact scheme for capturing the instantaneous free surface near two ships is adopted to avoid any disturbance caused by measuring equipment. The applicability of the newly established unsteady measurement technique is examined during a standard seakeeping test with various wave amplitudes. Heave and pitch motions are set free, while the soft spring system is used for surge motion. The instantaneous free surface elevation is obtained on equally spaced positions. The mean value and higher harmonic components of measured wave elevation clearly show nonlinear characteristics for various incident wave amplitudes. Snapshots at several time instants and the magnitude of the first harmonic components of unsteady wave elevation are compared with those of numerical computations based on a Rankine panel method. The overall trend shows fair correspondence, whereas the detailed local flows are somewhat different because of the nonlinearity of waves.

Steering model identification and control design of autonomous ship: a complete experimental study

ABSTRACT Steering ship models are important for the study of autonomous ship manoeuverability and design of ship motion control system. It is always a difficult task to find the mathematical model by first principle as it needs prior knowledge of hydrodynamic derivatives. The input–output-based system identification theory can be used to establish system mathematical models. A solution is offered by developing a Wi-Fi-based self-propelled, autonomous system for a ship model with Internet of Things (IoT) capabilities to perform manoeuvering and seakeeping tests in indoor environment without any complex mechanical structure, viz. following bridge. The developed autonomous on-board system equipped with main computer, suitable electronics, sensors, data acquisition system and Wi-Fi-based communication system. The developed system offers a cost effective, modular and portable solution to perform hydrodynamic studies of different hull form without incorporating major changes in the system. The use of IoT makes the data accessible to a naval architecture in real-time to analyse the motion response of the ship in different wave conditions and enables to implement the digital twin to simulate the real field scenario. Input–output-based model identification experiments such as turning circle and zig-zag tests are conducted to estimate the first-order steering model parameters and is further extended to design and implementation of a classical proportional–derivative-based steering control. The design is described in this paper with details of implementation on a demonstration oceanographic coastal research vessel. It illustrates the excellent communication between shore station computer and the on-board system on a wire-free model with robust control and exhibiting all the motion behaviour and dynamic effects. Experiments performed in wave basin in different wave conditions validate the efficacy of the proffered method.

Model scale prediction of seakeeping and global bending moment on a high speed craft

Estimating the forces acting on a high speed craft for structural assessment purposes is challenging due to the complex combination of hydrodynamic loads. These include wave pressures, slamming pressures and their load effects at a global ‘hull girder’ level. An experimental approach to validate the use of established strip theory methods for predicting the hydrodynamic wave pressure loads is presented here. A series of regular wave seakeeping tests on a small scale segmented hull model of a high speed craft were completed and compared to equivalent seakeeping calculations. Experiments were conducted with a 1:13.5 scale hull model of a 17-metre all weather lifeboat, which is typical of a high speed watercraft capable of operating in severe weather at exposed locations. The model is segmented into four sections, rigidly held together by an instrumented backbone beam which can measure shear force and bending moments at the segmentation points. The model was tested over a full range of operating speeds and wave encounter frequencies. Results are compared with two strip theory calculations, the first using a zero speed Green function and the second using a Rankine source method with a forward speed correction term. It is shown that the Green function strip theory provides better correlation at lower speeds (up to a Froude number of 0.4) and the Rankine source method is more appropriate at higher speeds. The experiments generally show good equivalence to calculations and demonstrate that strip theory gives reasonable predictions of the global bending moment assuming linearity with the wave height. Equivalently, this suggests that strip theory is an appropriate method to predict the hydrodynamic wave induced load component in displacement and semi-planing regimes. This unlocks the potential for strip theory to be used as part of a complete assessment of the seakeeping loads on a high speed craft by combining the wave induced loads with the other significant load components, which include the local hydrodynamic wave pressures and the transient loads caused by slamming impacts. This may be applied as part of an analysis to determine a craft’s safe operating envelope or for interpreting component loads within full scale trial data.

CFD prediction of stern flap effect on Catamaran seakeeping behavior in long crest head wave

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.