Full-scale Sea Trials Research Articles

Evaluation of the powering extrapolation of a ship with a gate rudder system, including ageing and fouling effects

This paper is based on the evaluation results of the calm water powering extrapolation of a 90-m general cargo vessel, originally built with a conventional rudder system (CRS) and later retrofitted with an innovative energy-saving device (ESD) known as the Gate Rudder System® (GRS), as part of the EU H2020 Project GATERS. The power estimation of the vessel was conducted using an adapted extrapolation procedure based on the scaled model tests of the vessel in a towing tank, validated by the three sets of sea trials. The first sea trial was performed when the ship was new, while the latter two were conducted during the project timeline, before and after the GRS retrofit. This paper aims to adapt the ITTC-78 power extrapolation method to predict the power performance of a ship retrofitted with the GRS for the first time in the maritime industry. Within this framework, the specific objectives of the paper are to describe and validate the proposed method using relevant power-speed data of the GATERS project target vessel (M/V ERGE) initially equipped with the CRS and later replaced by the retrofit GRS to achieve the project objective. Due to the real-world circumstances of retrofitting a 13-year-old ship with a novel energy-saving device, investigating the effects of ageing, hull roughness, and fouling has also become one of the key objectives of the paper. The findings demonstrate the ageing effect on the target ship's powering performance after retrofitting with GRS, highlighting the need for special consideration of power extrapolation alongside the hull fouling effects. The paper also demonstrates that the GRS is an emerging ESD, as a retrofit beside newly built ships with GRS, which improved the powering performance of the project target vessel, achieving a remarkable 25% power saving based on the comparative full-scale sea trials.

Spreading a demersal trawl without otter boards: A proof of concept using flexible foils

This manuscript documents an engineering proof of concept. We demonstrate that a deep-water demersal trawl targeting northern shrimp (Pandalus borealis) can be spread without otter boards using nothing more than flexible foils (i.e., kites) mounted near the wings of the trawl. A combination of numerical simulation, physical modeling in a flume tank, and full-scale sea trials were used to optimize the horizontal spreading of the demersal trawl. Spacing between the foils and the angle of attack to the direction of tow were found to be important parameters. To our knowledge this is the first successful attempt to spread a demersal trawl full-scale at-sea using nothing but flexible foils.

Influence of strain-rate on the interaction between towed fishing gears and the seabed

The ability to predict the seabed penetration and the drag force of the gear components of demersal trawlers is of significant benefit to the fisheries industry. It allows for the design of gears of reduced environmental impact and of improved fuel efficiency. This study presents a single-phase strain rate dependent soil model that can accurately predict deformation of a saturated granular soil. Elements of an otter trawl system are modelled as simplified discs which are then translated across a seabed at given speed where horizontal drag force and vertical penetration is measured. This is facilitated using an explicit Finite Element (FE) model developed in ABAQUS alongside a Coupled Eulerian-Lagrangian (CEL) mesh. Comparisons against laboratory experiments showed that the model was correctly able to capture the increase in drag force with towing speed. Further comparisons against full scale sea trials indicated the model generally compared well against test data and correctly identified the trends and magnitudes of drag force against towing speed. From these results, the influence of strain rate in the soil was studied in detail and conclusions drawn on the resultant drag force and penetration of towed fishing gears on the seabed.

Slam and wave load response reconstruction in high speed catamarans using transmissibility on full scale sea trials

In-service measurement of slam and wave load responses provide valuable information in the structural design and weight optimisation of high-speed catamarans. However, a limited number of measurements may be possible due to cost, and data may sometimes be lost or noise contaminated. This paper uses the transmissibility concept to reconstruct a set of unknown responses using a different set of known responses. Transmissibility functions and a transmissibility matrix based on linear response theory are derived from less than 12% of available data. The method is applied to full scale sea trials data on a 98 m high speed catamaran HSV 2 Swift, on which strain, acceleration, and angular velocity were measured. Responses are reconstructed for different vessel headings (head, port bow and starboard seas), speeds (15–35 knots), and sea states. The transmissibility matrix is tested on data from unseen sea states. Excellent agreement is achieved, particularly for larger loading events that would be of interest to structural designers. The study demonstrates the possibility to significantly reduce or build redundancy into the instrumentation.

Marine propeller underwater radiated noise prediction with the FWH acoustic analogy Part 2: Assessment of model scale propeller hydroacoustic performance under non-uniform flow conditions

This study presents the model scale benchmark, The Princess Royal, propeller's hydrodynamic performance, including cavitation extensions and URN operating in a non-uniform wake field. The developed V-AMR technique was used in the numerical calculations to accurately solve the tip vortex flow and better representation the tip vortex cavitation (TVC) in the propeller slipstream. The sheet and tip vortex cavitation was modelled using the Schnerr-Sauer cavitation model. A hybrid method, combining the DES and permeable formulation of the FWH equation, was used for predicting the propeller URN at four different operating conditions corresponding to full-scale operating conditions. The numerical results were first validated with the experimental data obtained in the cavitation tunnel through the propeller hydrodynamic characteristics, cavitation extension and URN in model scale. Then, the propeller URN predictions using a hybrid method were extrapolated to full-scale with the ITTC extrapolation procedure to compare the numerical results with the extrapolated experimental data and full-scale measurements. The results showed that the cavitation extensions on and off the blades were satisfactorily predicted in the numerical calculations compared to the model-scale campaigns and full-scale sea trial observations. However, the same cavitation dynamics and TVC could not be predicted in conditions where the weak and incipient TVC were present between the numerical calculations and model-scale test campaign. Also, the numerical calculations underpredicted the model scale propeller URN at certain frequencies compared to model scale experimental data, except for the highest loading condition. Akin to the comparisons of model scale propeller URN between the numerical calculations and model-scale test data, the extrapolated propeller URN was generally underpredicted at a certain frequency range of the noise spectrum in the numerical calculations compared to the full-scale measurements. This underprediction in the numerical calculations can be associated with the lack of cavitation dynamics, especially TVC, compared to experimental and full-scale observations.

Development of a Structural-Functional Approach for Heterogeneous Glider-Type Marine Robotic Complexes’ Group Interaction to Solve Environmental Monitoring and Patrolling Problems

Glider-type autonomous underwater vehicles are today one of the most promising areas of marine robotics. This is confirmed by the frequent and remarkable results of various research missions and projects. The cumulative group application of underwater and no less innovative wave gliders can significantly reduce the time of obtaining oceanographic data. Together with wave gliders, one group of such robotic objects can significantly increase the efficiency, time and volume of obtaining oceanographic data. There is big interest in increasing the functionality of such a group. This article presents one of the possible alternatives to increase the functionality of a group of underwater and waveguide hang gliders. We present the process of upgrading the existing design, control algorithms and software of the SHADOW underwater glider, which was developed by the teams of the St. Petersburg State Marine Technical University (SMTU) and Okeanos JSC in order to jointly study the monitoring of underwater potentially dangerous objects with the St. Petersburg State Fire Service EMERCOM of Russia. A structural-functional approach to the group application of underwater and waveguides is also proposed, which is capable of providing oceanographic, meteorological and environmental monitoring data online, based on the developed multilayer system for planning the trajectories of group movement of objects. The results of full-scale sea trials and the developed algorithms are demonstrated.

CFD Aided Ship Design and Helicopter Operation

In support of Canadian industrial and defence ship design and offshore helicopter operations, a series of Ship–Helicopter Operational Limits Analysis and Simulation (SHOLAS) projects are being conducted at the National Research Council Canada (NRC) in collaboration with Defence Research and Development Canada (DRDC). This study presents a brief overview of a Canadian in-house ship airwake simulation capability combining in-house high-fidelity wind-tunnel tests, full-scale sea trials, high-order computational fluid dynamics (CFD) tools, and realistic engineering-oriented flight simulators. This paper reports challenges and lessons learned during the course of the study, discusses the current capabilities and limitations of the CFD tools and the infrastructure required, and evaluates the gaps and barriers in industry adoption by focusing on how they could be overcome based on our current practice. After validating the CFD results of an updated version of a simplified frigate shape (SFS2) and the real-world Canadian Patrol Frigate (CPF), which are in reasonable agreement with the available in-house wind-tunnel and sea-trial data, the developed approach was recently applied to the design of an undisclosed Canadian ship. Among other applications, CFD airwake results were used with confidence as input to produce representative airwake features in industrial high-fidelity piloted flight simulators.

Nonlinear hydrodynamic model based course control and roll stabilization by taking rudder and propeller actions

The aim of this study is to control the course and roll motion for ships advancing in a seaway through taking the rudder and propeller actions. A high-fidelity model of the container ship is adopted and validated by using the data of the free-running model test. The full-scale sea trial data are analyzed to improve the simulation characteristics of the actuator to avoid the severe wear problem caused by overusing of the steering machine. In the present study, the adaptive robust controllers are designed for the nonlinear hydrodynamic model to achieve the overall optimal control performances of the course and roll motion. Results show that the course performance can be tuned quantitatively to satisfy the different engineering requirements. For the combined system of the course and roll motion, it is found that the course control and roll stabilization performances conflict with each other due to their coupling. The adaptive robustness controllers can easily make a tradeoff between them due to a controller only with an adjustable parameter. Simulation shows that under the premise of the good course performance, the roll reduction rate (RRR) can decrease by nearly 32% through taking the rudder and propeller actions.

A Persistent Sea-Going Platform for Robotic Fish Telemetry Using a Wave-Propelled USV: Technical Solution and Proof-of-Concept

Over the last few decades, acoustic fish telemetry has developed into a viable approach for remote monitoring of fish behaviour in the marine environment. Simultaneously, unmanned surface and underwater vehicles have found extensive use as scalable, persistent and cost-effective platforms for ocean observation. Equipping such robotic vehicles with fish telemetry receivers constitutes an emerging approach with the potential to significantly push the current operational limits of fish movement studies at sea. Here, we present an energy-autonomous robotic fish telemetry platform realised through the integration of a real-time acoustic receiver into an ocean-going wave- and solar-powered unmanned surface vehicle. The vehicle frame and energy harvesting solutions are based on the commercially available AutoNaut USV, while the vehicle’s control and communication systems were developed using open-source software and standard hardware components. The open architecture permitted deep integration of the acoustic receiver as a system-level payload making fish detections and other sensor data available in real-time to the vehicle’s onboard control system. The vehicle is thus prepared with local situational awareness to support autonomous control during vehicle-fish encounters, as well as conventional interfaces for remote piloting and data management through long-range wireless communication links and the Internet. The vehicle concept was investigated theoretically and experimentally in an acoustic range test and a full-scale sea trial. When driven passively by waves, tag detection performance was comparable to that of traditional moored receivers, while activation of the auxiliary electric thruster caused a reduction in detection radius of more than 50%, confirming wave-power as the ideal mode of propulsion. Finally, by deploying the AutoNaut over a period of several days at the outskirts of a Norwegian fjord during the seaward migration of Atlantic salmon post-smolts, we demonstrated that the vehicle was able to detect an acoustically tagged post-smolt into the open ocean beyond the reach of the fjord’s stationary receiver grid, while using only wave- and solar energy harvesting to power its operation. The ability to observe small individual fish in the ocean environment using an energy-autonomous robotic vehicle creates novel and unprecedented opportunities for scientific inquiry in fish behaviour and movement ecology studies at sea.

THE DESIGN AND HYDRODYNAMIC ASSESSMENT OF A SUBMARINE CONCEPT WITH OFF-AXIS RESOLVING THE IMPACT OF SHIP’S DESIGN ON DECK AND WELL-DECK LAUNCH AND RECOVERY OPERATIONS BY APPLYING OF QUIESCENT PERIOD PREDICTION (QPP)

One of the most challenging tasks in the deployment of ship-based manned and unmanned VTOL aviation is the launch and recovery and deck handling operational performance on smaller ship platforms. The same may be said of ship Well-deck-based surface boats, like Rhib and LCACs. Awareness and prediction of the ship’s position and movement in the ocean is key to ship-based air operations by targeting the right time to deploy and recover. The ships above waterline design coupled by the propulsion systems, affects ship’s motion and ship motion induced air wake behaviour. MoD/University of Exeter’s Quiescent Period Prediction (QPP) Program Aims to deliver technologies which support launch and recovery from Naval assets, particularly in higher sea states. The Quiescent Period Prediction (QPP) system achieves this by using a wave sensor system to measure the sea surface several hundred meters in advance of the ship. From the measured sea surface, a short-term deterministic wave model can be constructed allowing the wave system to be propagated to the ship's location. The ship's response to the wave spectrum is calculated to determine the level of quiescence at the time of encounter. The results are mapped dynamically on speed-polar visual graphics providing the ship’s best course to steer to ensure encountering the quiescent zone in a timely manner. The ability to fully define a ship’s motion as a function of a recovery device, greatly enhances the overall system operational capability whilst fundamentally reducing the inherent risks associated with platform manipulation in high sea conditions. The use of simulation, routinely considered in the UK, as an alternative to traditional approaches such as scale model testing and fullscale sea trials, to predict the safety and performance envelopes of platforms and systems, is discussed. Operating over deck whilst the ship is experiencing a quiescent period normally has the secondary effect of reduced air wake confusion. This is owing to fewer ship structure excursions into and out of the air flow. To better define off deck airflow around the ship a future QPP improvement will be the development and installation of a Doppler LiDAR federate. The objective of this work is to define ship-helicopter operational deck limits (SHOL), and then to safely expand ship operating deck limits. This article discusses the background to aircraft/ship operations in relation to QPP and goes on to consider both short term implementations (the Landing Period Designator System) and longer horizon deterministically predictive forms of QPP. This article describes the development of the QPP System concentrating on test procedures, timely seaway mapping and ship motion characteristics to complete specific motion sensitive task. An overview of the theory and application is provided concerning dynamic interface analysis with the focus on encountered forces and vehicle to platform response stability.

Experimental investigations into the effect of at-sea conditions on ship airwake characteristics

Shipboard helicopter operations are significantly impacted by the characteristics of the ship airwake which depend on environmental conditions in addition to the ship superstructure. In this paper, the effect of free stream turbulence, wind speed and ship motion on the airwake frequency spectra of two 1:50 scaled ships with stern flight-decks was investigated using wind tunnel testing. Results from a full-scale sea trial are also presented. Using both the wind tunnel and the sea trial data in ship motion conditions corresponding to medium sea states, results showed the ship motion energy was transmitted to the ship airwake at the motion frequencies. For single-frequency ship motions, the energy transfer occurred at the motion frequency only, whereas for more realistic at-sea ship motions with a range of frequency components the energy was transferred at a broadband of frequencies corresponding to the motion frequency range. The way in which realistic motion component effects combine at sea and the amount of energy added to the airwake in realistic conditions is presented. The impact of incoming atmospheric turbulence was also examined.

HIGH-SPEED WAVE-PIERCING CATAMARAN GLOBAL LOADS DETERMINED BY FEA AND SEA TRIALS

Wave-piercing catamaran hull forms are widely used for high-speed ferry applications due to the hull slenderness, suitable for achieving high speeds. The global loads acting on these craft are of great interest as there is limited knowledge on determining the magnitude of the loads, in particular when operating in random sea conditions. Longitudinal and transverse bending moments as well as pitch connecting moments and hull torsion loads act on the hull simultaneously. This paper investigates the estimation of these global loads from full-scale catamaran sea trials strain gauge data using finite element methods. Det Norske Veritas (DNV) load cases are applied to a finite element model in order to determine the conversion between local strain values observed during sea trials and prevailing global loads. Comparisons are thus made of global loads determined from strain data collected from sea trials with DNV global load cases. The results show that this method is relatively reliable for the prediction of hull global loads in the absence of slamming. Comparisons have been made for different heading angles. The quasi-static design loads are important during the ship design stage, as they are good proxies in wavelengths comparable to the hull length for rationally determined loads obtained from a first-principles dynamic analysis. The broad aims here are to demonstrate the use of strain sensor data obtained during sea trials for determination of global sea loads, to reconcile the loads thus determined with DNV load cases and thereby to improve the accuracy of the predicted loads used in design to increase the structural efficiency of vessel design.

PERFORMANCE PREDICTION OF A 112M WAVE-PIERCING CATAMARAN

The prediction of power required to propel a high-speed catamaran involves the hydrodynamic interactions between the hull surface and the surrounding fluid that may be difficult to compute numerically. In this study model-scale experiments are used as a basis for comparison to full-scale sea trials data measured on a 112m Incat wave-piercing catamaran to predict the full-scale powering requirements from model-scale testing. By completing water jet shaft power measurements on an Incat vessel during sea trials, comparison of these results was made to model-scale test results to provide good correlation. The work demonstrates that the International Towing Tank Conference (ITTC) extrapolation techniques used provide a good basis for extrapolating the data from model-scale to full-scale to predict the power requirements for the full-scale catamaran vessel operating at high Froude Number with water jet propulsion. This provides a useful tool for future designers and researchers for determining the power requirements of a catamaran vessel through model tests.

МАТЕМАТИЧНЕ МОДЕЛЮВАННЯ РОБОТИ СУДНОВИХ ГВИНТІВ ПРИ РІЗНИХ РЕЖИМАХ МАНЕВРУВАННЯ

In the study of ship maneuvers, in the development of ship's autopilots and simulators, the availability of adequate mathematical models of the ship’s propulsion complex, which would describe with high accuracy the dynamics of the ship for the widest ranges of phase coordinates, plays a decisive role. Mathematical models of ship dynamics consist of mathematical models of inertial and non-inertial forces and moments on the ship's hull. The latter include hydrodynamic and aerodynamic forces and moments on the ship's hull, forces and moments caused by the operation of propellers, rigging, ship rudders. For the adequacy of the general mathematical model of the ship's dynamics, the adequacy of the mathematical models of all components of non-inertial forces and moments on the ship's hull is necessary. Mathematical models of non-inertial forces and moments on a ship's hull are usually empirical and made by processing data from experimental tests in ship model basin or in full-scale sea trials. In particular, this applies to the forces and moments caused by the operation of the propeller. In the mathematical modeling of the indicated forces and moments, the rectilinear movement of the vessel, or movement at small values of the drift angles, is usually considered. In this case, only the longitudinal action of the propeller is usually considered, and the transverse component of the force and the moment on the ship's propeller are unreasonably neglected. In addition, well-known mathematical models usually contain coefficients and functions that are difficult to determine using tables and graphs, which is inconvenient for numerical modeling. This work is intended to somewhat eliminate the indicated disadvantages. In particular, it was investigated how the curvilinear movement of the ship affects the operation of the propeller, analyzed the existing mathematical models, and new effective mathematical models of the longitudinal and transverse components of the force and moment caused by the operation of the ship's propeller in dimensional and dimensionless forms were proposed. In particular, representations are obtained for the dimensionless coefficients of the propeller stop and the moment on the propeller shaft, the wake fraction coefficient, the thrust-deduction factor, and skew of the flow on the propeller. It is shown how these parameters change for all possible values of the drift angle and angular velocity. For a number of commercial vessels of various types, technical characteristics are given, and parameters for constructing mathematical models of the dynamics of the propeller are calculated.

Niche Applications and Flexible Devices for Wave Energy Conversion: A Review

We review wave energy conversion technologies for niche applications, i.e., kilowatt-scale systems that allow for more agile design, faster deployment and easier operation than utility scale systems. The wave energy converters for niche markets analysed in this paper are classified into breakwater-integrated, hybrid, devices for special applications. We show that niche markets are emerging as a very vibrant landscape, with several such technologies having now achieved operational stage, and others undergoing full-scale sea trials. This review also includes flexible devices, which started as niche applications in the 1980s and are now close to commercial maturity. We discuss the strong potential of flexible devices in reducing costs and improving survivability and reliability of wave energy systems. Finally, we show that the use of WECs in niche applications is supporting the development of utility-scale projects by accumulating field experience, demonstrating success stories of grid integration and building confidence for stakeholders.

Model tests and full-scale sea trials for drag force and deformation of a marine aquaculture net cage

In this study, we investigated the hydrodynamic characteristics of marine aquaculture net cages used for farming silver salmon (Oncorhynchus kisutch). Two sets of experiments were conducted: model-scale testing, which was used to measure the drag force and deformation of a model net cage at different current velocities, and full-scale testing, which involved a sea trial at a silver salmon farm site. In the sea trial, an acoustic wave and current meter was deployed to record the current velocities around the net cage, and the cage deformation was estimated from the several vertical positions of net using 13 depth sensors. The precision of estimating the cage deformation using only the depth information was evaluated by comparing the estimated cage deformation with that determined from the images in model-scale testing. Comparing the model-scale and full-scale testing results showed that only the bottom netting was found to be deformed under lower water currents. The trends observed for the drag force, cage deformation, and cross-section area estimated from the depth data in full-scale testing were generally consistent with those converted from the model-scale testing using Tauti's similarity law. However, the drag force values of a full-scale net cage converted from the model-scale testing were higher than those estimated from the depth data in the full-scale testing. In contrast, the converted cross-sectional areas from model-scale testing were smaller than the estimated values in full-scale testing. In future, the cage deformation should be examined under higher current velocities, and the drag force should be measured in the full-scale testing to validate the results of the model-scale testing and the hydrodynamic model.

Full-Scale Measurements of the Propeller Thrust during Speed Trials Using Electrical and Optical Sensors

Full-scale sea trials demonstrate a ship’s performance under real operating conditions to confirm whether a ship meets its specifications and requirements. The determination of the performance through a sea trial is the most important stage in the ship design cycle. If one is relying on measurements of propeller shaft power or fuel consumption, the distinction between the propeller and hull efficiencies may not be made. In order to be able to identify the propeller efficiency separate from the hull, full-scale propeller thrust should be accurately measured. In this study, full-scale measurements of the propeller thrust, torque, and revolution for a series of crude oil tankers and twin-skeg LNG carrier were conducted during the speed trials. Two different measuring systems, strain gauge and optical type, were implemented to compare the performance of sensors. As a result, it was shown that the strain gauge type-measuring device matched the model test results relatively well compared to the optical device. Above all, in the case of the optical device, it has been demonstrated that the zero setting is important to increase the accuracy of the full-scale measurements.

Using acoustically visible gillnets to reduce bycatch of a small cetacean: first pilot trials in a commercial fishery

Bycatch of protected species, particularly small cetaceans, in gillnets is a worldwide concern. One hypothesis for this is that echolocating cetaceans entangle because they do not perceive conventional gillnets as impenetrable barriers, owing to the gillnet’s faint echo. A gillnet modified for improved acoustical visibility was tested in a first pilot trial in a commercial gillnet fishery targeting turbot (Scophthalmus maeoticus) on the Turkish Black Sea coast. This study is the first demonstration of the viability of using a gillnet equipped with small acrylic glass spheres to reduce bycatch of harbor porpoises in a commercial fishery and provides the basis for full-scale sea trials of the gear in commercial fisheries through a power analysis. In these pilot experiments, the focus lied on the handling of the gear and identification of requirements for a full-scale trial, but results include promising bycatch data for an endangered echolocating marine mammal (Phocoena phocoena) and no reduction in catch efficiency of a bottom-dwelling, vulnerable species (Raja clavata).

Serviceability of the IAMSAR standard man overboard recovery maneuvers: A case-study of full-scale sea trials

In light of the proposal of the International Civil Aviation Organization and International Maritime Organization joint working group on harmonization of aeronautical and maritime search and rescue (ICAO/IMO JWG-SAR) 27th meeting, which points out that the current International Aviation and Maritime Search and Rescue (IAMSAR) standard man overboard (MOB) maneuvers may not be suitable for very large carriers, the authors briefly summarize the research on the MOB recovery maneuvers in recent years and conduct an investigation on the serviceability of these maneuvers by a series of full-scale sea trials. The sea trial results indicate that the standardized recovery maneuvers are serviceable to the employed oil/chemical tanker. However, similar to the simulation results obtained in the previous studies, there is a deviation in the Scharnov turn.

Flume tank testing, computer simulation and full-scale sea trials of a modified bottom trawl made of ultra-high-molecular-weight polyethylene twine for pair trawl fishery off Shimane Prefecture

島根県沖合底びき網漁業を対象として，現用網の袖網および身網の一部に超高分子量ポリエチレン繊維製網地を導入して網糸直径を細くした改良網1，さらに天井部の目合を拡大した改良網2について，模型実験と数値解析によって抵抗削減効果を推定した。現用網から改良網2に変更することで網抵抗は29.6％，網抵抗と海底との摩擦抵抗の合計は9.9％減少し，網形状はほとんど変化しないと考えられた。実物網を用いた海上実験では，通常の曳網速力3ノットで改良網2では現用網と比べてハンドロープ張力が19.3％減少した。