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Free accessIntroductionFirst published June 22, 2017pp. 85-86
Available accessResearch articleFirst published June 22, 2017pp. 87-107In an early design stage of ship and propeller or in a propeller retrofit case one may consider a pre-swirl stator (PSS) to recover rotational energy.
A model for the working principle of a PSS was to be developed and then to be applied for power saving estimates. This model should also support the PSS design procedure.
The PSS ‘working principle model’ is based on a very fundamental quantity related to a propellers characteristic, namely the circulation distribution. An extended model addresses hub vortex contraction losses. In specific cases a BEM (Boundary Element Method) based propeller analysis is performed. To confirm actual PSS designs, a RANS/BEM coupling method is invoked.
Global parameters as
The simple PSS ‘working principle model’ delivers very reasonable predictions. RANS results and available full scale trial measurements can be reproduced using this approach.
Available accessResearch articleFirst published June 22, 2017pp. 109-136The technological advancement in the equipment used in ships and emission restrictions from the classification societies forces the ship owners to periodically perform retrofitting on their ships. Therefore, ship owners today plan to utilise the docking downtime of a ship at a shipyard to its maximum potential. During this docking period in the shipyard, they would plan to perform all the retrofitting activities as well as any maintenance activities required for the ship equipment. In order to execute all the activities within the minimum downtime, a thorough and careful planning of the activities is required. With the ship under continuous operation before its docking at the shipyard, it could be possible that all the required documents for planning activities are not available for the shipyards. In order to tackle this problem, in the European Commission (EC) funded project GRIP – Green Retrofitting through Improved Propulsion, the use of Simulation Tools and Reverse Engineering was executed and tested, and so to perform the retrofitting activities more effectively and efficiently. Of the different Green technologies accessed by the GRIP Consortium, the retrofitting of Pre-Swirl Stator Fins was selected as the prototype study for testing and validating the Simulation Tools and Reverse Engineering Technologies proposed in GRIP. Tools developed in the Simulation Toolkit for Shipbuilders (STS) and newly developed planning tool anteSIM were used by CMT to perform simulation of retrofitting activities and thereby provide planning recommendations to the shipyard. IMAWIS used Laser Scanning as the Reverse Engineering technologies studied in the project to perform measurements and dimensional accuracy comparison after the assembly process of the Pre-Swirl Stator Fins. The methodologies and results from the execution of the Simulation Tools and Reverse Engineering Technology are satisfactory in order to provide beneficial recommendations for efficient planning of retrofitting activities in the shipyards.
Available accessResearch articleFirst published June 22, 2017pp. 137-168In this paper the hydrodynamic design procedure for Energy Saving Devices (ESDs) developed in the FP7 EU project GRIP is applied to full scale validation vessel – a newly built handymax Bulk carrier by Uljanik shipyard in Croatia. Three ESDs such as a Pre-Swirl Stator, a Pre Duct and a Rudder Bulb have been designed for this ship by three partner – HSVA, MARIN and VICUS respectively. From the three ESD designs that were submitted, the most promising alternative was selected via a thoroughly performed cross check by all participating partners. For the ESD selection, the hydrodynamic performance of the ESD is the most but not the only important factor; other aspects, such as cavitation risk, structural, manufacture and installation aspects have also been considered, but will not be covered in this paper. The finally selected ESD was HSVA’s Pre-Swirl Stator, which has been developed further and successfully tested during the trials of the full scale ship. In this paper only the conceptual design of PSS during the ESD hydrodynamic design phase and the results of the cross check which has been performed for the selection of ESDs will be presented.
Available accessResearch articleFirst published June 22, 2017pp. 169-195Energy saving devices (ESD)s designed to improve the propulsive efficiency of a ship are often designed and validated using CFD tools and model tests. Evaluation at full scale is however still required to understand extrapolation methods and scale effects. This paper describes the evaluation of an ESD by means of dedicated speed/power trials just prior and directly after the installation of the device in dry dock. The energy saving device is in the form of three stator fins located at the port side just ahead of the propeller creating a pre-swirl in the flow into the propeller which reduces rotational losses of the propulsion. The stator was build and retrofitted by Uljanik shipyard in Croatia on a new build 52,000 DWT bulk carrier. Trials were done prior and after retrofitting of the ESD in almost ideal weather conditions. Comparison of the trial results revealed a fuel saving effect of 6.8% in power. Cavitation observations of the stator and propeller showed a removal of the cavitating hub vortex of the propeller after the installation of the fins. This can be detected and confirmed in the CFD computations as well. Full scale CFD investigation employing the RANS-BEM coupling method to simulate the propeller effect gives a power saving of more than 5%, which is in good agreement with the trial results. The geometry used in the CFD simulation is based on the 3D in-situ geometry measured via laser scan technique after the retrofitting of the fins.
Available accessResearch articleFirst published June 22, 2017pp. 197-210Within GRIP, ESD (Energy Saving Device(s)) are installed on existing vessels. Installation of an ESD can influence the neighbouring hull outfitting elements.
The influence of ESD installation on the hull outfitting elements have been investigated.
The classification rules have been studied to identify all parameters and subjects that could be influenced by installation of an ESD.
A selection of subjects is further investigated to provide an estimation of the magnitude of the impact.
Five example ESD’s have been investigated. The influence on the neighbouring hull outfitting elements has been determined by comparison of results of hydrodynamic calculations without and with an ESD.
For two cases, the effect on propeller cavitation behaviour has been investigated.
The possible effects of an ESD on the requirements according class rules (overview table).
For selected subjects, the magnitude of influence is defined in relation to the change of a directly influenced parameter.
For the example cases, the influence on the neighbouring hull outfitting elements and on propeller cavitation behaviour has been reported.
Installation of an ESD affects indeed the neighbouring hull outfitting elements and their compliance with class rules in certain cases. The possible effects of an ESD on the compliance to class rules requirements are summarized in Table 1. Most significant impact can be expected for up-stream installed ESD and ESD directly mounted on the propeller. The addition of an ESD to a propeller has a linear influence on torsional frequency and stress as well as whirling frequency, bearing load and mis-alignment. Adding 10% MOI (of total propeller MOI) results in 3% decrease of torsional frequency, 10% increase of torsional stress, decrease of 2.5% of natural critical whirling speed. Addition of 10% mass results in a decrease of 1.7% of critical whirling speed. The influence of an ESD on alignment are shown in Table 3.
Available accessResearch articleFirst published June 22, 2017pp. 211-226The FP7 project GRIP deals with Energy Saving Devices (ESDs). These are devices placed in front, or aft of the propeller with the aim to reduce the fuel consumption of the vessel. VICUS has worked on a hydrodynamic design procedure and had the opportunity to apply it to a validation vessel: a new-build handymax Bulk carrier by Uljanik shipyard in Croatia. VICUS has selected a downstream device, named Rudder Bulb, for this application case: it is positioned aft of the propeller and allows for a reduction of the rotational energy of the outflow. Two other partners within GRIP have also been developing their own methodology for the hydrodynamic design of an ESD. MARIN have worked on a Pre-Duct and HSVA on a Pre-Swirl Stator. Each partner has designed its ESD according to its own procedure for the Uljanik bulk carrier. From these three ESD, a cross check was carried out in order to select the device that will be manufactured on the full scale vessel. HSVA’s Pre-Swirl Stator was chosen and was been installed on the ULJ vessel. Full scale trials were carried out on the vessel, giving satisfactory results (see (Xing-Kaeding
Available accessResearch articleFirst published June 22, 2017pp. 227-253One of the first stages during the evaluation of the viability of an Energy Saving Devices (ESDs) for existing ships is a global scan of the field of application, performance and the required investment. Based on this preliminary data the Return on Investment (RoI) for an ESD retrofit can be estimated, which is a key figure in decision making processes. To this end an Early Assessment Tool (EAT) is developed, containing a database of reliable performance data, a patent database, a benefit tool, cost model and an economical tool.
The EAT is compatible with container vessels, bulk carriers, tankers, ferries/RoPax vessels and short sea shipping cargo vessels. Integrated ESDs are the pre duct, pre swirl stator, PBCF, rudder fin, rudder bulb-hub cap system, ducts surrounding the propeller, hull fin and the combination of a pre duct and pre swirl stator.
The benefit tool calculates the power reduction at a given sailing mode by application of a specific ESD type. The cost tool determines approximate ESD costs, broken down into design, material and installation costs. The economical tool combines output from the benefit and cost tools and calculates the RoI.
A web-based EAT for public use and an extensive EAT for project members have been created.
Available accessResearch articleFirst published June 22, 2017pp. 255-290Throughout the years, many types of Energy Saving Devices (ESDs) have been introduced to the naval industry, each claiming to achieve several percent of power reduction. Although their commercial success is undeniable, there has always been much controversy regarding the assumed working principles of ESDs. Therefore, the basis of this paper is a comprehensive explanation of the hydrodynamic working mechanism of an Energy Saving Device known as the Blade efficiency improving Stator Duct (BSD). Using knowledge of this working principle, an alternative way of analysing propulsion efficiency dedicated to pre-swirl devices has been developed. The working mechanism of the BSD and the assessment of its performance is subsequently demonstrated at model scale by means of RANS simulations.
Another topic of discussion regarding ESDs are the scaling procedures used in model testing to predict the full scale performance, which possibly lead to exaggerated claims. The scale effect on the performance of the BSD is therefore addressed in the final part of this paper, also based on numerical simulations.
Available accessResearch articleFirst published June 22, 2017pp. 291-314In order to design an Energy Saving Device (ESD), shipyards need to know the forces applied on the structure.
The objective is to develop a methodology able to evaluate the forces applied on an ESD in navigation conditions.
From existing hydrodynamic potential codes, such as HydroStar, and tools developed by Bureau Veritas, the forces applied on an ESD have been evaluated and the methodology has been tested on a Pre-Swirl Stator structure.
The design process for an ESD has been described and tested including static analysis, dynamic analysis and fatigue analysis.
The forces applied on an ESD can be estimated following a design process and a methodology developed in GRIP.
Free accessOtherFirst published June 22, 2017pp. 315-316