Revealing the Fluttering Motions of Mid-Water Trawl Codend Through Sea Trials:Case Study of Antarctic Krill Trawl Codend

The dynamic coupling between the fluttering motions and hydrodynamic characteristics of codend is essential in understanding the trawl selectivity through fish response and the drag force acting on the whole trawl.This study investigated the effect of towing speed,warp length,warp tension,and catch size on the fluttering motions of Antarctic krill trawl codend during net shooting,towing,and hauling by using sea trial data.The time-periodicity of codend oscillation was analyzed by the Morlet wavelet transform method.Results indicated that the period of codend oscillation was between 50 s and 90 s and showed an increasing trend with the warp tension but a decreased value at the towing stage.The coefficient amplitude of codend oscillation was between 0 and 4 at the net shooting and hauling stages,and between 0.2 and 0.6 at the towing stage.The amplitude of codend oscillation increased with the warp tension,towing speed,and catch size,but decreased with the increase of the warp length.In addition,the period of codend oscillation increased with the towing speed at the net shooting and hauling stages,but decreased at the towing stage.These results from codend fluttering motions can improve the understanding of fish behavior and gear shape that modify the hydrodynamic force on the codend instantaneously.

Validation of an Emission Model for a Marine Diesel Engine with Data from Sea Operations

In this study,a model is developed to simulate the dynamics of an internal combustion engine,and it is calibrated and validated against reliable experimental data,making it a tool that can effectively be adopted to conduct emission predictions.In this work,the Ricardo WAVE software is applied to the simulation of a particular marine diesel engine,a four-stroke engine used in the maritime field.Results from the bench tests are used for the calibration of the model.Finally,the calibration of the model and its validation with full-scale data measured at sea are presented.The prediction includes not only the classic engine operating parameters for a comparison with surveys but also an estimate of nitrogen oxide emissions,which are compared with similar results obtained with emission factors.The calibration of the model made it possible to obtain an overlap between the simulation results and real data with an average error of approximately 7%on power,torque,and consumption.The model provides encouraging results,suggesting further applications,such as in the study on transient conditions,coupling of the engine model with the ship model for a complete simulation of the operating conditions,and optimization studies on consumption and emissions.The availability of the emission data during the sea trial and validated simulation results are the strengths and novelties of this work.

Novel Gas-tight Multi-sampler for Discrete Deep-sea Water

The issues of how to quickly collect seawater samples and of how to make sure that those samples truly reflect the in-situ information on gas composition and concentration have therefore become a hot but difficult topic in the field of ocean technology.Most conventional seawater samplers only focus on collecting seawater itself,but take little consideration on gas preservation.A set of new oceanographic tools are presented for ocean resource exploration such as hydrothermal sulfide and gas hydrate,and for investigations on the processes and mechanisms of marine physical,chemical and biological evolutions.A gas-tight deep-sea water sampling system（GTWSS） is designed for the collection of deep-sea geochemical samples.This set of tools mainly consists of a conductivity temperature depth profiler（CTD）,release devices and gas-tight deep-sea water samplers（GTWS）.The GTWS is able to hold the gases in deep-sea water samples tightly,providing in-situ information on gas contents in the seawater samples and can be deployed on a routine wire-deployed CTD sampler for multi-layer discrete sampling of gas-tight seawater.Sea trials are performed successfully in 2008 and 2009,on a research vessel named HaiYang Si Hao in South China Sea,with the deepest trial depth 3 930 m.GTWSS is capable of quickly sampling 12 discrete gas-tight seawater samples（8.3 L per sample） during its single deployment.The head space method is employed to separate the gases from the seawater samples immediately after recovery of the seawater samples on the vessel.Field geochemical analysis is carried out by gaseous hydrocarbon sensors and an infrared gas analyzer.Results show that the concentrations of CH4 and CO2 in the seawater sampled by GTWSS are higher than those sampled by general non-gas-tight water samplers,thus confirming the gas tightness of GTWSS.Seawater samples can be collected quickly by using GTWSS,and GTWSS can keep the samples＇ integrity quite well.

Study and innovation of a flexible blade turbine,a new type of tidal current generating device

Utilization of tidal current is becoming a focus of marine energy research and development field. In this paper, a new type of tidal current power generating device which was called flexible blade turbine was put forward. A scale model testing was carried out, and results show that the models performed as expected with good hydrodynamic characteristics. Based on analysis of the results, a scale model turbine with a rated power of 5 kW was constructed, which was an optimal scheme of the flexible blade turbine having higher coefficient of power and power generation capacity. Sea trials were carried out in the Zhaitang Island Channel to evaluate the performance of the turbine. Results show that the turbine performed well, generating the power predicted.

Vibration Analysis for the Comfort Assessment of Superyachts

Comfort levels on modern superyachts have recently been the object of specific attention of the most important Classification Societies, which issued new rules and regulations for evaluating noise and vibration maximum levels. These rules are named "Comfort Class Rules" and set the general criteria for noise and vibration measurements in different vessels' areas, as well as the maximum noise and vibration limit values. As far as the vibration assessment is concerned, the Comfort Class Rules follow either the ISO 6954:1984 standard or the ISO 6954:2000. After an introduction to these relevant standards, the authors herein present a procedure developed to predict the vibration levels on ships. This procedure builds on finite element linear dynamic analysis and is applied to predict the vibration levels on a 60 m superyacht considered as a case study. The results of the numerical simulations are then benchmarked against experimental data acquired during the sea trial of the vessel. This analysis also allows the authors to evaluate the global damping ratio to be used by designers in the vibration analysis of superyachts.

Performance analysis of the mooring system of a two-module scientific research and demonstration platform

A mooring system has been designed for the position keeping of a two-module semi-submersible platform which is connected by hinge-type connectors.Under the excitation of ocean waves,the relative motion between the two modules can be significant.It is therefore no longer adequate to model the platform as a single rigid body in the analysis of the performance of the mooring system.In this study,an analysis method has been developed based on the three-dimensional frequency domain hydroelasticity theory in conjunction with the time domain quasi-static analysis method of mooring actions,which takes into account of the coupling effect of the platform motion and mooring tension.The proposed method is verified by comparing the numerical results with the measured data obtained from the on-site measurements.The comparison shows a good agreement,and demonstrates the feasibility and effectiveness of the proposed method for the analysis of the module responses and mooring tensions of multi-module floating platforms.

Energy saving by using asymmetric aftbodies for merchant ships–design methodology, numerical simulation and validation

The methodology and procedures are discussed on designing merchant ships to achieve fully-integrated and optimized hull-propulsion systems by using asymmetric aftbodies. Computational fluid dynamics （CFD） has been used to evaluate the powering performance through massive calculations with automatic deformation algorisms for the hull forms and the propeller blades. Comparative model tests of the designs to the optimized symmetric hull forms have been carried out to verify the efficiency gain. More than 6% improvement on the propulsive efficiency of an oil tanker has been measured during the model tests. Dedicated sea-trials show good agreement with the predicted performance from the test results.

Experimental study of hydrodynamic performance of full-scale horizontal axis tidal current turbine

In this paper, experiments of both the model turbine （1 kW） and the full scale （10 kW） turbine are carried out in a towing tank and a basin, respectively, and the test of the full scale turbine on the sea is conducted. By comparison between the model turbine （D = 0.7 m） and the full scale turbine （D = 2.0 m）, it is shown that the maximum power coefficient increases with the increase of the diameter of the turbine. The test results on the sea are used to study the hydrodynamic performances of the horizontal axis turbine, and provide a basis for the design. Experimental results can validate the accuracy of the numerical simulation results.

Design and friction loss study of full-ocean depth oil-filled direct current motor

In this study,we designed an oil-filled motor that can be used at full-ocean depths,and investigated the friction losses caused by the rotating seal and the properties of the oil.The direct current(DC)motor is encapsulated in an aluminum alloy housing.A rubber diaphragm is used to balance the internal and external pressures so that the motor can work on the seabed without pressure difference.To study the resistance caused by the rotating seal,a numerical model of the Glyd ring and the rotating shaft was established.Results from a rotational torque test agreed with those from numerical analysis.The kinematic viscosity of four oils was measured at 1-25℃.Oil bath experiments in an incubator showed that the resistance from oil is highly correlated with its dynamic viscosity.Dimethicone appears to be very suitable as an insulating oil for these motors.The working characteristics of the motor were tested in a high-pressure chamber.The results showed that the motor needs to overcome higher oil resistance under higher pressure.A prototype of a pressure-adaptive motor was designed and applied successfully in the hadal zone at a water depth of more than 10000 m.

Model Testing for Ship Hydroelasticity: A Review and Future Trends

Conducting model experiments is an effective and reliable way in the investigation of ship hydrodynamic and hydroelastic behaviors. A survey of model testing techniques for ship hydroelasticity and its prospect are presented in this paper. The research highlights with respect to ship hydroelasticity and key points in model testing are summarized at first. Then testing techniques including laboratory tank test and full-scale sea trial are reviewed, and both their advantages and disadvantages are analyzed comprehensively. Based on the conventional testing approaches, a state-of-the-art testing approach which includes performing tests using large-scale model at sea is proposed. Furthermore, recommendations towards the further development of ship hydroelasticity tests are forecasted and discussed.

Feasible study on full-scale delivered power prediction using CFD/EFD combination method

Three-dimensional(3-D)power prediction method from model test has been widely accepted and used for many years.Form factor k is the most important characteristics of 3・D method and very crucial to the accurate power prediction.However,it's rather difficult to get the accurate value of k for those ships with pronounced bulbous or large transom from model test.In this paper,a new method to predict power is proposed,using k from CFD while other data from model test(or experimental fluid dynamics(EFD)).Delivered power prediction using the combination of CFD/EFD method agrees well with sea-trial results.