Sea Trial Test Research Articles

Sea trials vs prediction by numerical models—Uncertainties in the measurements and prediction of WASP performance

Accurately predicting the power saving from wind-assisted ship propulsion is one of the most discussed topics in alternative and complementary propulsion methods. Aero- and hydrodynamic interactions between the sails and the ship increase the difficulty of modelling the propulsion contribution theoretically, but the sensibility of sail performance on the wind conditions increases the demands on measurement accuracy if the performance is to be measured in sea trials. This paper analyses and compares the uncertainties of sea trial tests and model predictions by means of parameter variation and Monte Carlo simulations. The results show that sea trials have an uncertainty of 23 %, well above 100 % of the measured savings, if performed using normal onboard equipment. Model uncertainties were found to be between 6 % and 17 % of the predicted savings.

Effect of Sampling Rate in Sea Trial Tests on the Estimation of Hydrodynamic Parameters for a Nonlinear Ship Manoeuvring Model

This paper explores the impact of sampling rates during sea trials on the estimation of hydrodynamic parameters in a nonlinear manoeuvring model. Sea trials were carried out using an offshore patrol vessel and test data were collected. A nonlinear manoeuvring model is introduced to characterise the ship’s manoeuvring motion, and the truncated least squares support vector machine is employed to estimate nondimensional hydrodynamic coefficients and their corresponding uncertainties using the 25°–25° zigzag test. To assess the influence of the sampling rates, the training set is resampled offline with 14 sampling rates, ranging from 0.2 Hz to 5 Hz, encompassing a rate 10 times the highest frequency component of the signal of interest. The results show that the higher sampling rate can significantly diminish the parameter uncertainty. To obtain a robust estimation of linear and nonlinear hydrodynamic coefficients, the sampling rate should be higher than 10 times the highest frequency component of the signal of interest, and 3–5 Hz is recommended for the case in this paper. The validation is also carried out, which indicates that the proposed truncated least square support vector machine can provide a robust parameter estimation.

Target positioning of dual forward looking sonars based on orthogonal detection

Accurate positioning of underwater targets is an important basis for many underwater tasks. As an imagery equipment, forward-looking sonar (FLS) can overcome the problem of poor brightness in underwater environment, and has a longer detection distance than the camera, which plays an important role in oceanic target positioning. However, there remain two challenging problems: (1) due to the complex underwater environment and the propagation characteristics of sound waves in the water, there are a lot of noises in the FLS images, which impair the accuracy of positioning; (2) FLS can only obtain two-dimensional information, which is insufficient for target positioning. Aiming at these two problems, a three-dimensional underwater target positioning algorithm based on dual FLSs is proposed in this paper. Firstly, a Threshold-Mask-Guided Filter (TMGF) image denoising algorithm is designed to deal with the obvious background noises and same-pitch noises in FLS images, which greatly improves the denoising effect compared with the original guided filter algorithm. Secondly, a target positioning algorithm based on orthogonal vertical placement of dual sonars is proposed to calculate the three-dimensional position of the target. Finally, pool experiments and sea trial tests are carried out respectively to verify the effectiveness of TMGF algorithm in denoising and the accuracy and stability of positioning algorithm.

Effect of Propeller Pitch on Ship Propulsion

The appropriate choice of a marine engine identified by using self-propulsion model tests is compulsory, in particular with respect to the improvement of vessel performances. Numerical simulations or experimental methods provide insight into the problem of flow, where fixed pitch propellers or controllable pitch propellers are preferred. While calculation methods are time consuming and computationally demanding for both propeller types, hydrodynamic performance assessment has more workload in controllable pitch propellers. This paper aims to describe and demonstrate the practicability and effectiveness of the self-propulsion estimation (SPE) method in understanding the effect of propeller pitch on ship propulsion. Technically, the hydrostatic and geometric characteristics of the vessel and open-water propeller performances are the focal aspects that affect the self-propulsion parameters estimated by the SPE method. The input coefficients for SPE have been identified using a code that generates propeller open-water performance curves. The propellers utilized to study pitch variations have been based on the Wageningen B-series propeller database. The method was first validated on the full size Seiun Maru ship whose sea trial tests are available in literature. After extensive calculations for full size KCS and DTC at service speeds, the study focused on the effect of the Froude number on propulsion parameters. These calculations have demonstrated that greater propeller pitch does not improve propulsion efficiency, and that maximum propeller efficiency changes with a ship's forward speed.

Sea-trial research on natural product-based antifouling paint applied to different underwater sensor housing materials

Biofouling is a common challenge for underwater sensors, especially for long-term in situ monitoring in marine environments. In this study, we assessed the antifouling efficacy of a paint containing a natural product camptothecin (CPT) on six materials (316 L stainless steel, TC4 titanium alloy, 7075 aluminum alloy, polyoxymethylene, polyvinyl chloride, and Teflon), which are frequently used in the construction of underwater sensor housings. Additionally, a buoy-based sea-trial was performed to test the antifouling performance of the CPT-based paint on housings of three in situ sensors used for practical seawater monitoring applications, namely a spectrophotometer for chemical oxygen demand (COD) measurements and two fluorimeters for biochemical oxygen demand (BOD) and chlorophyll a (Chl a) concentration measurements. The results showed significantly lower macrofouling coverage on the areas painted with the CPT-based paint compared to the unpainted areas for each tested material over 9 months of seawater immersion. The CPT-based paint exhibited different antifouling performance for the different materials; in particular, it exhibited better antifouling performance on the plastic materials compared to the metal materials. Furthermore, when applied on submersible sensor housings in the sea-trial test, the CPT-based paint kept the housings of the COD sensor and the Chl a sensor clean for over 4 months. In addition, the paint prevented fouling of the BOD sensor housing even after 6 months of seawater immersion. Thus, our results suggest that the CPT-based paint could be used as a potential solution to control the biofouling of sensor housings for long-term in situ applications in marine environments.

Classification of Underwater Target Based on S-ResNet and Modified DCGAN Models.

Underwater target classification has been an important topic driven by its general applications. Convolutional neural network (CNN) has been shown to exhibit excellent performance on classifications especially in the field of image processing. However, when applying CNN and related deep learning models to underwater target classifications, the problems, including small sample size of underwater target and low complexity requirement, impose a great challenge. In this paper, we have proposed the modified DCGAN model to augment data for targets with small sample size. The data generated from the proposed model help to improve classification performance under imbalanced category conditions. Furthermore, we have proposed the S-ResNet model to obtain good classification accuracy while significantly reducing complexity of the model, and achieve a good tradeoff between classification accuracy and model complexity. The effectiveness of proposed models is verified through measured data from sea trial and lake tests.

Numerical assessment of the scale effects on the propulsive performance of a ship with gate rudder system

Several energy-saving methods have been implemented on ships to improve propulsion efficiency, reducing fuel consumption and carbon dioxide emissions. The Gate Rudder System, as a novel energy-saving and maneuvering device, reduces fuel consumption by up to 14% compared to the conventional flap rudder system, as confirmed by the sea trial test of a container ship with a gate rudder system. The power savings achieved by the ship with the Gate Rudder system exceeded projections based on model tests. With the motivation of evaluating this discrepancy, this research aims to investigate the propulsive performance of a cargo ship with a gate rudder system as well as the scale effects on its performance, considering two different models of 3 m and 6 m in length, as well as a full-scale ship of 69 m in length. RANSE-based CFD analyses with the Shear Stress Transport (SST) k-ω turbulence model were performed to investigate the ship's propulsive performance and power savings at full load and sea trial conditions with both conventional and gate rudder arrangements. For multi-phase flows, the volume of fluid method (VOF) was used to account for free surface effects, and the model was unconstrained by heave and pitch. Grid convergence, verification, and validation studies were carried out to ensure the accuracy of the numerical studies. Improved propulsive performance and more than 12% power savings for the ship with the gate rudder system have been achieved at both loading conditions compared to the conventional rudder for the selected cargo ship. The study also observes scale effects, which reveal that the gate rudder of the larger model generates more thrust compared to the smaller one.

Sea trial test on offshore integration of an oscillating buoy wave energy device and floating breakwater

Wave energy has not yet been commercialized due to its high cost and low efficiency. The combination of wave energy devices and breakwaters can greatly improve the utilization of breakwaters and also reduce the cost of wave power generation devices. In this paper, four oscillating buoy wave energy devices with different geometries are proposed, where a kind of dolphin buoy design method with excellent energy harvesting mechanism is formed. And the integrated method of wave energy device and floating breakwater is proposed and the integrated model is tested in the tank, and on the basis of that a one-year sea trial test of the prototype was carried out in the real sea area, and the power generation performances of the wave energy device under different sea conditions are analyzed. The sea trial results show that the average energy conversion efficiency of wave energy device can reach more than 18% when the significant wave height is from 0.5 m to 2 m and an average period is from 2 s to 6 s, and that can even reach 27.2% under the optimal sea state. The research and manufacturing process of sea trial prototype and the sea trial operation of the prototype show that the combination of oscillating buoy wave energy device and floating breakwater can reduce the construction cost of wave energy device and also improve reliability and energy conversion efficiency of that. The research results of this paper are of great significance for the further commercialization of wave energy devices.

Prediction of Significant Wave Height in Korea Strait Using Machine Learning

The prediction of wave conditions is crucial in the field of marine and ocean engineering. Hence, this study aims to predict the significant wave height through machine learning (ML), a soft computing method. The adopted metocean data, collected from 2012 to 2020, were obtained from the Korea Institute of Ocean Science and Technology. We adopted the feedforward neural network (FNN) and long-short term memory (LSTM) models to predict significant wave height. Input parameters for the input layer were selected by Pearson correlation coefficients. To obtain the optimized hyperparameter, we conducted a sensitivity study on the window size, node, layer, and activation function. Finally, the significant wave height was predicted using the FNN and LSTM models, by varying the three input parameters and three window sizes. Accordingly, FNN (W48) (i.e., FNN with window size 48) and LSTM (W48) (i.e., LSTM with window size 48) were superior outcomes. The most suitable model for predicting the significant wave height was FNN(W48) owing to its accuracy and calculation time. If the metocean data were further accumulated, the accuracy of the ML model would have improved, and it will be beneficial to predict added resistance by waves when conducting a sea trial test.

Slam load estimation for high-speed catamarans in irregular head seas by full-scale computational fluid dynamics

Global loads acting on high-speed wave-piercing catamarans are investigated using computational fluid dynamics (CFD). Catamaran vessels are subjected to load cases that are not present on mono-hull vessels, such as transverse bending moment, pitch connecting moment and splitting force. As the speed and size of a catamaran increases the severity of loads rises with slam induced effects. Full-scale CFD simulation is undertaken to investigate the pressure distributions and resultant global loads acting on the 98 m INCAT wave-piercer catamaran HSV2 Swift, validated against sea trial tests. Rigid body dynamics are then applied to estimate the internal loads at different sections of the vessel based on the relative hydrodynamic and inertial force distributions. The estimated global loads are then checked according to DNV GL rules by comparing “design load limits”. Global loads are estimated for the 98 m INCAT HSV2 Swift catamaran in headseas at a forward speed of 20 knots. Splitting forces are found to have a longitudinal distribution along the catamaran hull, which causes prying moments. Peak values for LBM are examined relative to corresponding instantaneous wave height prior to the slam event. In addition, it is found that pitch acceleration has a linear correlation with LBM slam loads.

Evaluation of S-100 ECDIS Based on S-10X Digital Maritime Safety Information

The IMO has established a regulation for the ECDIS installation on ships based on the IHO S-57 standards. The ECDIS supports sailors in achieving a safe voyage by using ENCs and monitoring the information of their ship. However, the S-57 standards were developed as edition 3.1 and prohibited revision for more than 20 years. So, the IHO developed a new standard as S-100 into the hydrography and maritime field instead of updating the S-57 to edition 4.0. In this study, the new S-100 ECDIS was developed and verified with ENCs and the digital maritime safety information by using a ship steering simulator and by conducting an on-board sea-trial test. It evaluated the impact on ship operations if the next-generation navigation support system is introduced. Based on this research, the S-100 ECDIS will generate improvements such as safe voyages by providing various of real-time safety information and up-to-date data to ship and sailors.

The Effect of Uncertainty in Sea Trial Measurement System on Speed-Power Performance

Sea trial tests are necessary to verify speed-power performance, and are an import contract between ship owners and shipyards. The International Organization for Standardization (ISO) published ISO 15016:2015, which specifies the correlation method between model and full-scale ships. The results of sea trials have been questioned because of the uncertainty of speed and power measurements, especially when sea conditions differ from ideal calm water conditions. In this paper, such uncertainties were investigated by utilizing the standard speed-power trial analysis procedure defined in ISO 15016:2015 through Monte Carlo simulations. It was found that the expanded uncertainty of the delivered power (PDid) at 95 % confidence interval (k = 2) was ±1.5 % under 75 % MCR conditions.

Analysis of seafloor reverberation related characteristics based on sea trial data

Ocean reverberation is one of the main factors affecting sonar performance. Studying the spatio-temporal correlation statistical characteristics of reverberation is of great significance for sonar detection and suppress reverberation, and is a problem that sonar designers have always been concerned about. This paper first gives an overview of the sea trial test; and analyzes the signal strength of the reverberation signals with different frequencies under different terrain conditions, which proves the reliability of the sea trial data. By processing the time-space correlation characteristics of the seabed reverberation data, the relationship between time-space correlation characteristics of the seabed reverberation data and the frequency and form of the transmitted signal and the seabed topography is obtained, which provides a theoretical reference for reverberation suppression and application.

Simulation and Statistical Modeling of Acoustic Scattering of Bubble Wakes

Ship wakes are large, exist for a long time, and are difficult to disguise or conceal. These characteristics can be used as an important basis for ship tracking and recognition. However, distinguishing between wakes, underwater targets, and sea surface is a difficult problem that currently limits acoustic wake homing technology. To solve this problem, in this study, from the viewpoint of feature recognition, the effects of bubble radius, air volume fraction, frequency, depth, and other parameters on the group bubble were first investigated. The volume scattering intensity of acoustic wakes at different frequencies and depths was also calculated and analyzed, and the results of our theoretical calculations were verified through an experiment using a multifrequency single wave sonar dock. Subsequently, through the single frequency and multibeam sonar sea trial test, a statistical model of target characteristics with a clear physical mechanism was developed. The developed model can be utilized for the guidance and recognition of acoustic wake targets. Thus, this study lays the foundation for the practical application of acoustic wake guidance.

Development of an evaluation method to determine cavitation inception speed with aft hull vibration using kurtosis of the DEMON spectrum

The cavitation inception speed (CIS) is very important capability for a navy vessel because the underwater radiated noise dramatically increases when cavitation occurs. Therefore, the CIS has been severely restricted and evaluated at sea trial test steps in the shipbuilding process. After a naval vessel is delivered to the navy, CIS can vary according to the propeller and sea state conditions. However, inspection of CIS cannot be performed frequently due to time and expense limitation. Therefore, real time monitoring of CIS is urgently required by navy personnel. In order to inspect CIS with real time monitoring technique, the measuring method detecting fluctuation pressure of the propeller in a ship at sailing state should be developed. In this research, CIS monitoring techniques using acceleration on the hull above the propeller that can measure the fluctuation pressure of the propeller indirectly are suggested and verified experimentally. In addition, the evaluation algorithm of CIS using the kurtosis of the Detection of Envelope Modulation on Noise (DEMON) spectrum is used to determine the CIS quantitatively.

The Experimental Study on Inland Electric Propulsion Cruise Maneuverability

Through the Century myth of the electric propulsion ship trial experiment was carried out, respectively for the type of ship's turning performance, braking performance, and steady performance are analyzed in aspects of research, through comparing with other ways with traditional propulsion ship, according to the results above all aspects of performance is superior to the traditional ship propulsion mode. Excellent maneuverability and airworthiness, the ship for the research and development of green ships in inland water provides the research direction and development train of thought. At the same time, the type of ship's sea trial test for inland river ships new revision of the specification provides a reliable and objective data, the new specification and standard come on stage has played a great role in promoting.

Development of the USV ‘JingHai-I’ and sea trials in the Southern Yellow Sea

Shanghai University has developed an unmanned survey vehicle (USV) named JingHai-I. The mission of JingHai-I is to work as a test bed USV for the development and validation of various algorithms. One main innovation of the USV is the capability to achieve hydrographic surveying and charting in nearshore shallow waters. The highly resistant overturning ability and low draft (0.43m) enables the USV to move safely in shallow waters. Moreover, the USV can sail on a setting track and automatically avoid obstacles. This paper presents a review of our research work on the development of the USV, with a performance evaluation by a series of tests. In addition, the system design and implementation of the USV is detailed in the introduction. In order to get better control effects, a numerical model for the USV was built and a GPC-PID cascade controller was proposed, which combines generalized predictive control and PID control. A series of test results and discussions of the results are presented. Compared with the actual sea trial test data, the results show that the USV offers good maneuverability.

Application of a Winch-type Towed Acoustic Sensor to a Wave-powered Unmanned Surface Vehicle

Although many countries have focused on anti-submarine warfare for several decades, underwater submarines can hardly be detected by current assets such as patrol aircraft, surface ships and fixed underwater surveillance systems. Due to the difficult conditions of the oceanic environment and the relative quietness of submarines, existing acoustic surveillance platforms are not able to fully cover their mission areas. To fill in the gaps, a winch-type towed acoustic sensor system was developed and integrated into a wave-powered unmanned surface vehicle by the Korea Institute of Ocean Science and Technology. In June 2015, sea trial tests were conducted to verify maneuvering, acoustic signal detection, and communication capabilities. During the maneuvering test, the wave-powered glider successfully moved along programmed waypoints. Despite towing the acoustic sensor system, only 20% of initial electricity was consumed in 20 days. The acoustic sensor was lowered to depths of 100–150 m by the winch system, and received signals from an acoustic simulator lowered to depths of 50–100 m by RV Jangmok. Simulated submarine noises that were refracted downward could be clearly received and classified by the hydrophone system, from distances of 2–8 km, while it was being towed silently and deeply. In addition, an optical camera provided high-resolution images of surface vessels, allowing integration with acoustic detection of underwater objects. In conclusion, this new platform using a deeply towed hydrophone system is worthy of consideration as an underwater surveillance asset. Future work is required to strengthen inter-asset communication and obstacle avoidance, and to overcome strong currents to make this technology a reliable part of the underwater surveillance network.

Development of 6-DOF Equations of Motion for a Planning Boat Based on the Results of Sea Trial Tests

In general, the attitude of a high-speed planning boat changes following a speed change. Since the hydrodynamic forces acting on a ship differ according to the change of its underwater shape, it is difficult to estimate its hydrodynamic force compared to that of a large commercial ship. In this paper, 6 Degrees Of Freedom (DOF) equations of motion that express the maneuvering motion of a planning boat are modeled by analyzing its motion characteristics based on various sea trial tests. Finally, a maneuvering simulation is carried out and a validation of the equations of motion is confirmed with the results of sea trial tests.

Carboxyl-modified multi-walled carbon nanotubes-filled PDMS nanocomposites for anti-biofouling applications

In the current study, six carboxyl-modified multi-walled carbon nanotubes (cMWNTs)-filled PDMS nanocomposites (CPs) were successfully prepared, respectively. The antifouling (AF) properties of the CPs surfaces were evaluated via the long-term field immersion assays. The effects of the CPs surfaces on the attachment and colonization of the pioneer biofilm communities were investigated using the single-strand conformation polymorphism (SSCP) technique via the comparison of the diversity indices. Different CPs surfaces (i.e. the P1–P6 surfaces) have exhibited differential and excellent AF properties in the sea trial test as compared to that of the unfilled PDMS (P0) surface, indicating that the six cMWNT nanoparticles (i.e. the C1–C6 fillers) have demonstrated better AF properties, when used as reinforcing fillers in the PDMS matrix. The only reinforcing cMWNT filler (i.e. the C3 filler, 50 nm diameter, 10–20 μm length) has been identified and determined in the field. In addition, the partially aggregated cMWNT filler in the PDMS matrix was found to contribute to the improved AF properties of the CPs. The CPs surfaces can significantly reduce the adherent pioneer eukaryotic community diversity and richness, which may have dramatically modulating effect on the attachment and colonization of pioneer eukaryotic microbes. In contrast, most CPs (i.e. the P1–P5 surfaces) can only exert slight perturbation effect on the pioneer prokaryotic communities. Only the P6 surface can exert significant perturbation effect on the adherent pioneer prokaryotic and eukaryotic communities at the same time. The functionalized CPs surfaces may have the potential to be used for future maritime applications.