Bulk Carrier Update No. 1 2011

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Practical example

Return on investment tool

Guideline onfuel saving measures

NEWS FROM DNV TO THE BULK CARRIER INDUSTRY No 01 2011

bulk carrierupdate

SPEC

IAL E

DITION

FUEL SAVING MEASURES

2 | BULK CARRIER UPDATE NO. 1 2011

CONTENTS

Photos: front cover ©Getty Imagespages 8–9:Mewis Duct from Becker Marine SystemsPropeller Boss Cap Fin – MOTech, Mitsui O.S.K Techno-Trade, Ltd.Pre-swirl Stator – Daewoo Shipbuilding and Marine EngineeringPropeller nozzle – SDARIContra-rotating propeller – Wärtsilä and IHI Marine UnitedPropeller rudder transition bulb – ENERGOPAC from WärtsiläPre-duct – WED from Schneekluth

Return on investment tool ›› How to use the guideline for fuel saving measures and the return on investment tool ››

Guideline on fuel saving measures for bulk carriers ››

141004

GUIDELINE ON FUEL SAVING MEASURES FOR BULK CARRIERS ...........................................................4

SCOPE OF GUIDELINE ........................................................8

RETURN ON INVESTMENT TOOL ..................................10

HOW TO USE THE GUIDELINE FOR FUEL SAVING MEASURES AND THE RETURN ON INVESTMENT TOOL ..................................14

VALIDATION ON FUEL SAVINGS ....................................18

bulk carrier update

WE WELCOME YOUR THOUGHTS!

Published by DNV Global Governance, Market Communications.

Editorial committee: Michael Aasland, Business Director, Bulk CarriersMagne A. Røe, EditorLisbeth Aamodt, Production

Design and layout: Coor Service Management/Design Dept. 1104-011Print: Grøset Trykk AS, 6,000/05-2011

Please direct any enquiries to [email protected]

Online edition of bulk carrier update:www.dnv.com/bulkupdate

DNV (Det Norske Veritas AS)NO-1322 Høvik, NorwayTel: +47 67 57 99 00Fax: +47 67 57 99 11

© Det Norske Veritas AS www.dnv.com

BULK CARRIER UPDATE NO. 1 2011 | 3

EDITORIAL

The cost of fuel is increas-ing. Although we will most probably see large fluctua-tions in the future, most indicators point towards even higher fuel prices in the long term. Fuel costs already make up a large percentage of ship owners’ operating costs, and this percentage will most likely grow in the future.

Our industry is currently facing difficult times, with an oversupply of tonnage in the market depressing charter rates. The very large order book will further increase the supply side, so most analysts predict low to moderate rates in the short

to medium term. In this sit-uation, it will be even more important to reduce costs.

Much has been said about the importance of saving fuel from not only a financial but of course also an environmental point of view. However, we recognise that it is not easy to save fuel – if it was easy, it would have been done already!

Research has shown that the use of so-called propul-sion efficiency devices has a great fuel-saving potential. However, even in this area there is a lot of confusion. How do the various devices actually work? Which devices will work together?

What is the estimated effect of the device? And, most importantly, how can the return on the investment in such a device be calculated? Some ship owners do not have the necessary resourc-es to investigate these com-plex issues.

SDARI and DNV have worked together to address these complex issues. In a joint project, we have prepared a comprehensive guideline covering fourteen fuel-saving measures which are highly relevant today. For each measure, we have discussed how the measure or device works, the range of expected fuel savings and

the approximate cost of each device. We have also developed a unique return on investment calculator into which ship owners can enter possible future developments in fuel costs and interest rates as well as data for the relevant device and thus easily calculate the predicted cost effectiveness of each device.

We believe this guideline and the return on invest-ment calculator will be useful in endeavours to save fuel and reduce shipping’s environmental impact, and we therefore offer it free of charge to our clients.

COST OF FUEL

Michael AaslandBusiness Director, Bulk [email protected]

Executive summaryFuel is one of the major cost elements for a ship owner/operator and by reducing fuel consumption an owner/ operator will reduce both his costs and the environmental impact from his ship. The use of devices that increase propulsion efficiency has been shown to have a great potential to save fuel, however such devices are still not very common due to limited knowledge about them and their cost-effectiveness.

SDARI and DNV have worked together to prepare a guideline and a return on investment tool to deal with this issue. The guideline addresses how the devices work, their compatibility with other devices, the complexity of manufacturing and the classification requirements. It also gives ranges of expected fuel savings and indicates the price ranges for each device.

Various scenarios for fuel prices, interest rates, payback times, estimated fuel savings and costs can be entered in the return on investment tool in order to easily calculateboth the environmental impact and the cost/benefit.


‹‹ Olav Rognebakke

A NEED IN THE MARKET A joint project between Shanghai Merchant Ship Design & Research (SDARI) and Det Norske Veritas (DNV) is ongoing with the objec-tive of providing an overview of relevant fuel saving measures for bulk carriers to be built in China, and of developing a frame-work for return on investment calculations. This provides a practical approach to meet the needs of the cost-aware bulk carrier owner, as well as of designers and yards.

Implementing fuel saving measures can be challenging. The bulk carrier is the workhorse of the sea, and its design and outfitting are based on a long history of focusing on cost and optimisation. Bulk carriers are also traditionally relatively ‘low tech’ and even small investments are scru-tinised. However, the lower rates and high

HFO price predicted for the next couple of years will make cost reductions even more important. The typical bulk carrier owner is also reputed to be conservative; he requires a relatively short payback timeon any investment and accepts a limited risk.

On the other hand, a typical bulk carri-er with a traditional aft ship, propeller and rudder will have a large potential to save fuel by adding different devices. There is also an increasing trend for new bulk carri-ers to install fuel saving devices. For exam-ple, Mitsui claims that it has installed more than 1,700 of its Propeller Boss Cap Fins.

However, the owner has a variety of fuel saving devices to choose from, and selecting the appropriate one is a chal-lenge. It is sometimes possible to combine

different devices, but they need to be compatible to provide a total saving that is significantly larger than that from each individual device. Other factors further complicate the picture, and a number of questions need to be addressed: What will be required from the yard in order to install the fuel saving device? What will be required from classification in way of approval? How much fuel is the device esti-mated to save? What are the maintenance needs? And how much will the device cost? Some owners have limited technical resources to evaluate these issues, and may need assistance to choose the right means to save fuel.

Finally, the cost/benefit of the invest-ment in a fuel saving device may be difficult to calculate. Which factors

DNV presented MACC trend curves at Nor-Shipping two years ago. They showed a large fuel saving potential, which could be achieved by, for example, improving the hull and propeller

design, using various fuel saving devices and optimising machinery and outfitting.

To point out a great savings potential a is good start, but it must be followed up by providing the means to achieve change.

TEXT: OLAV ROGNEBAKKE, DNV

GUIDELINE

Guideline on fuel saving measures for bulk carriers


›› Mewis Duct. Courtesy of Becker Marine Systems

should be taken into account and how? Although saving fuel will naturally have a positive impact on the environmental footprint, the decision to invest must still be based on sound return on investment calculations.

A CONTRIBUTION FROM SDARI AND DNV To address this perceived need for objective information and guidance, SDARI and DNV defined a project aim-ing to: Provide ship owners with advice regarding the available technology and cost-effectiveness of fuel saving measures which are relevant for bulk carriers to be built in China.

The project has two main deliverables: A guideline on fuel saving measures A return on investment tool for

calculating the cost/benefit of the investment

This project benefits from the complemen-tary knowledge and experience of SDARI and DNV. SDARI mainly provides cost estimates and explains the manufacturing complexity. DNV is responsible for the detailed description of each fuel saving measure, including compatibility issues, classification requirements, the range of expected savings and the expected main-tenance during operation. DNV is also responsible for the return on investment tool.

OVERVIEW OF THE GUIDELINE The scope of the guideline is to provide a ship owner with an overview of the most

relevant fuel saving measures available for bulk carriers to be built in China.

The guideline provides the necessary input for a return on investment analysis of selected fuel saving measures. This document is available upon request from SDARI and DNV, together with the return on investment tool.

The guideline starts out with a general description of the selected evaluation parameters. A basic introduction to ship resistance and propulsion helps the reader understand more about how each measure works. Different ways of validating savings are also discussed.

The bulk of the guideline consists of sections giving a detailed evaluation of the various fuel saving measures. Each section describes the measure, including

GUIDELINE


›› Propeller (PBCF). Courtesy of MOTech, Mitsui O.S.K Techno-Trade, Ltd

compatibility issues, lists classification requirements and discusses manufacturing issues. The range of expected fuel savings is an important point which, together with the expected investment and maintenance costs, creates the basis for a cost/benefit analysis.

Finally, the fuel saving and cost factors for the fuel saving measure are listed in a table. The compatibility between different fuel saving devices is also presented in a matrix.

PHYSICAL EFFECTS Most of the fuel sav-ing devices work by reducing the energy loss from the propeller. There will be losses due to friction on the propeller blades and the generation of hub and tip vortices as well as axial and rotational losses. The effective wake is the velocity field in the plane of the propeller, and the characteristics of this wake influence the propeller efficiency. In addition, some devices improve the wake. The 22nd Inter-national Towing Tank Conference (ITTC) issued a document entitled “The specialist

committee on unconventional propulsors”, which categorises energy saving devices as “pre-swirl”, “post-swirl” or “pre- and post-swirl”. These devices create one or more of the energy saving mechanisms in the following list: Pre-rotation to the propeller inflow Improve propeller inflow Alleviate flow separation Recover rotational energy from downstream

Decrease viscous loss after propeller cap Decrease eddy after propeller cap

GUIDELINE


›› Mewis Duct. Courtesy of Becker Marine Systems

Produce additional thrust

PUTTING NUMBERS ON FUEL SAVINGSIt is necessary to present ranges of expect-ed fuel savings, since the actual reduction in the required engine power for a fixed speed depends on the ship size and the design of the hull, propeller and append-age. A highly optimised design will have less margin for fuel savings. Another topic is the individual adaptation of the cho-sen measure. The performance generally increases with the amount of effort put

into the design of a fuel saving device. Typ-ically, a supplier operates with an item cost as well as a design package cost. The latter will only be incurred once for a series of identical vessels.

THE IMPORTANCE OF VALIDATIONThe validation of the expected fuel sav-ings is important and challenging. Ideally, validation should be based on a compari-son between two ships that are identical except for the fuel saving measure in question. However, even two sister vessels

straight out from newbuilding dock may experience a few per cent difference in required power, which implies great uncertainty in a savings estimate. An alter-native is to conduct model tests in which the towing tanks have long experience in conducting accurate repeatability tests in accordance with the guidelines issued by the ITTC. In recent years, computational fluid mechanics has become a viable vali-dation option.

GUIDELINE


The guideline contains a detailed description of 14 different fuel saving measures, briefly described here. There are many other good candidates for fuel saving devices. This selection

consists of popular ones intended to be representative of typical main categories.


Scope of guideline

SCOPE OF GUIDELINE

Rudder profileThinner rudder profiles have less drag but are more likely to develop separated flow and cavitation. The twisted leading edge rudder from Becker Marine Systems is a more refined profile. High lift profiles can give significant power savings.

Mewis DuctThe MD is a combination of a vertically offset mounted duct positioned right in front of the propeller and an integrated asymmetric fin arrangement. For full-form slower ships. Combines the effect of a wave equalizing duct and pre-swirl fins.

Propeller designThe main propeller characteristics determining the open water efficiency are the diameter, rotational speed, pitch ratio, number of blades and blade area ratio. The main parameters may be optimised and selected on the basis of experimental data from propeller series such as the Wageningen B-series. High efficiency is achieved by a large diameter, low number of blades, low blade area ratio and low RPM.

Propeller Boss Cap FinThe PBCF consists of small fins attached to the propeller hub. The number of fins equals the number of propeller blades. The aim is to reduce the energy loss due to hub vortices.

Hull shapeThe hull lines and ship speed determine the lower limit of the vessel’s resistance. Traditionally there has been a large focus on design speed in the optimisation of hull lines, but new flexibility requirements mean that a vessel must perform well over a range of drafts and speeds. For low Froude number bulk carriers, a high block and maximum draft help reduce the dominating viscous resistance. Detailed aft ship optimisation that takes the propeller into consideration is required to achieve maximum performance.

Pre-Swirl StatorThe PSS is a set of blades positioned right in front of the propeller, with an asymmetric configuration. It works by introducing pre-swirl ahead of the propeller to reduce rotational losses and thus improve propulsion efficiency.


SCOPE OF GUIDELINE

Waste heat recovery systemWaste heat recovery has the largest potential to improve the efficiency of traditional two-stroke engines, but there are challenges related to exploiting this potential. Both the complexity and cost of the system have made these types of systems rare on bulk carriers.

Pre-ductA pre-duct is fitted to optimise the propulsion properties by improving the flow into the propeller. It can also improve manoeuvrability and reduce hull vibrations. Some pre-ducts also produce thrust.

Main engineGenerally, larger bulk carriers have two-stroke diesel engines installed. The most common type of engine is mechanically controlled, while electronically controlled engines are becoming more common for newer vessels. Typically the de-rating of the main engine, engine control tuning for electronically controlled engines and low load optimisation using the variable turbine area and exhaust gas bypass can be done to reduce the specific fuel oil consumption (SFOC).

Contra-Rotating PropellerA CRP is a highly efficient means of propulsion, but is also complex and costly. A two-digit improvement in efficiency is possible compared to a traditional propeller.

Propeller nozzleAn efficiency improving propeller nozzle changes the flow field in and around the propeller and divides the thrust force between itself and the propeller. A nozzle can also be used to improve cavitation and noise properties.

Openings – arrangement and design

Openings in the hull are needed for sea chests and bow/stern thrusters. The detailed configuration of these openings is important for resistance and possibly noise and vibration. The efficiency of the thrusters depends on the shape of the tunnel.

Auxiliary engineAuxiliary engines on board bulk ships that are not geared usually mainly supply electrical power to the accommodation and machinery systems when under way. The most common setup is to have three auxiliary engines of the same size. This allows one engine to be out for maintenance while still complying with the redundancy requirements. Generally all the measures that may be applied to the main engine in order to reduce the SFOC may be applied to the auxiliary engines.

Propeller rudder transition bulbThere is a variety of solutions involving bulbs fitted to the rudder in order to reduce hub vortex losses. Such solutions are typically a central part of a modern high efficiency rudder.


– a tool to analyse the cost effectiveness of fuel saving measures

TEXT: EIVIND NEUMANN-LARSEN, DNV

Return on investment tool

ROI TOOL


›› Figure 2: Operating profile

›› Figure 1: Methodology

FINANCIAL ANALYSIS FRAMEWORK When evaluating a fuel saving measure, several issues should be considered, such as the technical maturity, complexity of manufacturing and implementation, complexity of operation and classifica-tion requirements. These and other issues are covered in the Guideline and are not addressed in this tool, which is purely a financial tool that evaluates the cost/ben-efit of the fuel saving measures. According-ly, the tool provides a framework for finan-cial analysis, leaving it to the ship owner to enter the variable parameters into the calculation based on information included in the Guideline, as shown in Figure 1.

FUEL SAVING MEASURE AND INVEST-MENT PARAMETERS The starting point is to enter the investment cost and addi-tional maintenance costs (if relevant) due

to the new fuel saving measure. Some measures are quite costly and might have an impact on the second-hand value of the vessel. In these cases, this is also to be taken into consideration. Once the initial and annual costs have been estimated, the fuel consumption and corresponding costs are calculated. Fuel price developments are a major uncertainty when calculating operational costs, but at the same time fuel costs typically amount to 30–40% of a vessel’s total running costs. The fuel price can be stated as a fixed price throughout the investment period in the tool, but dif-ferent fuel price development scenarios, typically a high, medium and low price scenario, can also be analysed. In this way, it is possible to evaluate a fuel saving meas-ure’s fuel price sensitivity and its effect on profitability.

OPERATING PROFILE AND FUEL CON-SUMPTION A vessel’s annual fuel con-sumption is calculated based on the daily consumption in tonnes and total days at sea. However, it is also possible to define a detailed operating profile with different sailing conditions or operating states, e.g. sailing ballast, sailing laden, cargo han-dling in port, etc. The different operating states are specified in more detail with average engine load and specific fuel oil consumption, as shown in Figure 2. The reduction potential for each measure will vary depending on aspects like ship size, operation and engine load, and the fuel savings potential needs to be estimated for each operating state.

FINANCIAL MEASURES General invest-ment parameters must be decided upon (i.e. investment period, discount rate and

ROI TOOL


›› Figure 3: Cash flow and present value profile

fuel price scenario) and the given cash flow is then generated by the tool. The fuel savings are set as incomes and the initial and maintenance costs as costs. Common financial figures are calculated automatically, such as: Net Present Value (NPV): the present value of discounted benefits and discounted costs minus the investment cost

Payback period: the time span required to recover the cost of an investment

Internal Rate of Return (IRR): the discount rate at which the benefits (inflows) equal the costs (outflows)

Profitability Index (PI): the present value of the future cash flows divided by the initial investment (also known as the cost/benefit ratio)

As shown in Figure 3, the expected cash flow and profit are visualised in differ-ent charts, and changes in investment

parameters are updated instantly to allow easy evaluation of the effect.

ENVIRONMENTAL BENEFITS There is currently a high focus on green ship designs, and the environmental benefits should be taken into consideration in the evaluation. It is probable that stricter envi-ronmental regulations will be enforced in the foreseeable future, and fuel savings measures can reduce the burden of such

ROI TOOL


›› Figure 4: Reduced emissions

›› Figure 5: Fuel price and initial cost sensitivity

regulations. Figure 4 shows how the tool estimates the environmental benefits due to the reduced fuel consumption, includ-ing the reduction in CO2, SOx, NOx, and particulate matter..

COST/BENEFIT EVALUATION The finan-cial tool also has features to investigate the initial cost sensitivity, as shown in Figure 5. This is particularly relevant in order to evaluate the effect of any budget over-runs,

and is also relevant when evaluating meas-ures on a series of ships where quantity discounts may come into effect.

Several fuel saving measures are pro-moted by different vendors and shipyards, and ship owners need to obtain a general overview and evaluate the cost effective-ness of these measures for their bulk car-riers. The return on investment tool com-bined with the Guideline should provide an overview of the fuel saving measure’s

potential, cost efficiencies and fuel and emission reductions, as well as the number of years needed to recover the initial costs and the measure’s sensitivity to changes in fuel price. In that way, the tool will help reduce the risk of making a wrong invest-ment decision.

ROI TOOL


We assume a project under evaluation with the following initial data: Fuel Oil Consumption: 32 MT/day laden and 28 MT/day in ballast

Operational profile: Laden 150 days, Ballast 150 days, Manoeuvring 10 days, Cargo Handling 40 days, Idle 10 days.

First of all, it will be useful to understand the basic principles of propulsion and resistance. Chapter 2 of the guideline, “Physical Description of the Fuel Efficiency Measures”, provides an overview of the physics of ship powering and resistance and groups the issues into three areas: Resistance components Propeller characteristics, propulsive effi-ciencies and related losses

Machinery

All these areas are important and should be considered in detail. Chapter 5 is help-ful in this respect, as it gives a detailed

evaluation of the most common measures in the three areas: Mewis duct Propeller boss cap fins Pre-swirl stator Propeller nozzle Contra-rotating propeller Propeller rudder transition bulb Rudder profile Pre-duct Propeller design Hull shape Openings – arrangement and design Main engine Auxiliary engine Waste heat recovery system

Each of these measures is evaluated with respect to the following parameters: Description, including compatibility Requirements from Classification Manufacturing complexity Range of expected fuel savings

The device’s expected maintenance needs when in operation

Rough indication of price range

In this example, we will for simplicity focus on one measure only, and we have selected the propeller boss cap fins (PBCF).

The section of the guideline covering the PBCF starts off by describing how the device works, with references to further reading on the topic. The guideline also covers class requirements and finally describes the complexity of manufactur-ing and installing the PBCF. Based on the information provided in the guideline, it is concluded in this example that the device is of interest for further evaluation. The main reasons for this conclusion are: Simple concept, relatively common device, limited or no effect on the rest of the ship, and it does not place high demands on the shipyards’ installation capabilities.

In this article, we will illustrate the use of the SDARI-DNV Guideline for Fuel Saving Measures and the Return on Investment Tool by using

an example. We will in the example assume the role of a technical manager in a typical ship owner organisation. It should be noted

that the values used here have been selected to illustrate the process only, and reference is made to the guideline for further details.

TEXT: MICHAEL AASLAND, DNV

How to use the guideline for fuel saving measures

and the return on investment tool

HOW TO USE


HOW TO USE

››Propeller Boss Cap Fins. Courtesy of MOTech, Mitsui O.S.K Techno-Trade, Ltd


HOW TO USE

›› Figure 3: Financial results.

›› Figure 2: Fuel consumption results.

The section on PBCF goes on to describe the maintenance needs and pro-vide ranges of expected fuel savings as well as indications of the price of the device from a number of sources.

In this example, the following values have been selected with regard to the PBCF: Expected saving of 3% at full draught and 2% at ballast draught. These values are rough indications, and the guideline explains how they can be verified

Cost of maintenance estimated to be USD 5,000/year

Cost of design package estimated to be USD 28,000 – to be split between four ships – and cost of PBCF including installation, USD 40,000, i.e. a total cost of USD 47,000 per ship

We further assume that there is no impact on the resale of the ship, which is a conservative assumption.

The following variables are also assumed: Investment period of three years Discount rate of 8%

Fuel price developments will of course have a large impact on the cost/benefit analysis of the fuel saving device. The tool allows for several alternatives: Using a fixed price in USD/ton for the whole period

Using one of four scenarios: Low, Medi-um, High or Custom.

In this example, we have for illustration purposes selected the custom scenario option, with a starting price of USD 550 and a 2% year-on-year increase (Figure 1).

With the above assumptions entered into the return on investment tool, we obtain the following results (Figure 2).

Based on the assumed input, we achieve estimated fuel savings of 228 tons/year due to the reduced consumption on laden and ballast voyages.

We also achieve the following financial results presented in Figure 3.

The net present value of the USD 47,000 investment is calculated to be more than USD 250,000 (Figure 4).

The return on investment tool also gen-erates plots indicating the sensitivity of the investment for various fuel price scenarios entered, as well as its sensitivity to cost overruns. The latter is very useful, since the percentage overrun can be entered and the results plotted graphically (Figure 5).

Finally, the tool calculates the environ-mental impact of the fuel saving measure and plots the result as shown in Figure 6.

In this example, we have shown how the SDARI-DNV Guideline for Fuel Saving Measures and the Return on Investment Tool can be used when evaluating the cost/benefit of fuel saving devices.


›› Figure 5: Investment cost sensitivity – cumulative discounted cash flow.

HOW TO USE

›› Figure 6: CO2 reductions.

›› Figure 4: Cumulative discounted cashflow.

›› Figure 1: Various fuel price scenarios.

›› Figure 7: SOx, NOx, and particulate matter reductions.


The ship owner would like an accurate estimate of the fuel savings before deciding to purchase. After installation, it is valuable to know the actual savings. The effect of each measure varies

depending on ship characteristics like size, hull lines, speed, propeller and rudder configuration. The reduction in power usage reported by suppliers may well be validated for certain designs, but

some of the fuel saving devices should be optimised for each new vessel. Optimisation requires a means to estimate savings. Validation also becomes important when different devices are

combined, as compatibility issues may reduced the overall effectiveness. The performance of a fuel saving measure may be validated by full-scale measurements, model tests or numerical analyses.


FULL-SCALE MEASUREMENTSFuel savings measured by full-scale trials might appear to provide the best valida-tion of a device’s performance. However, full-scale measurements are subject to limited measurement accuracy, poor con-trol of the environment, and the effect of unexpected or unknown changes to the vessel between tests.

When conducting measurements, it is common to make use of the onboard sen-sor system. However, the quality of such a system may vary significantly. If the sensor is not intended to provide high precision measurements, the accuracy may be insuf-ficient. Since fuel saving measures often produce small gains, this uncertainty may be enough to disrupt the identification of any fuel saving.

When predicting the performance based on a sea trial, correcting for environ-mental effects like wind, waves and current is a challenging task. How these correc-tions are conducted may have a significant effect, and will probably represent a major source of uncertainty.

High quality validation data are obtained from full-scale measurements by good planning and execution combined with careful post-processing and analysis.

›› Illustration of speed power curve – measured data in blue and corrected data in red. The dots indicate the measured points while the lines are the smoothed results.

Validation of fuel savings

VALIDATION

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1500010.0 11.0

Speed [knots]

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12.0 13.0 14.0 15.0


COMPUTATIONAL FLUID DYNAMICSUnsteady RANS codes can now be used to accurately predict turbulent flow at real-istic Reynolds numbers for ship powering applications. Computational Fluid Dynam-ics (CFD) has become a standard tool for yards, research institutes, designers and classification societies.

Similar to model tests, CFD simulations allow for precise control of the measure-ments and environment. Since CFD simu-lations can be conducted at full scale, the scaling problem inherent in model tests is avoided.

When conducting CFD simulations, it is important to have a firm understanding of the physics to be investigated. This is necessary in order to include the appropri-ate numerical models in the simulations. When addressing new topics, model tests should be conducted and simulations performed in either model or full scale

to confirm the physical models. A mesh convergence study and sensitivity study may also be necessary. ITTC has issued recommendations on how to perform such studies.

CFD may be a cost effective means of validating savings, but typical analyses are still demanding in terms of both required man-hours and computational resources. In addition, software licences are expen-sive. Assuming that the hull shape is fixed and that reliable extrapolation methods exist for the fuel saving device in ques-tion, model tests may be cheaper if many parameter variations are needed. In CFD, meshing typically takes up most of the time, and this is in general required for new speeds and drafts.

All photos are courtesy of MOTech, Mitsui O.S.K Techno-Trade, Ltd

›› Without PBCF.

›› With PBCF.

›› Without PBCF.

›› With PBCF.

VALIDATION

MODEL TESTSThe International Towing Tank Confer-ence (ITTC) 1999 report on unconvention-al propulsion addresses the issue of using model tests to assess the performance of various fuel saving devices. Towing tank organisations typically use extrapolation methods based on modifications of the ITTC 1978 approach. Some have devel-oped a new methodology for each particu-lar type of unconventional propulsor. The report explains that extreme cases, such as

integrated ducted propulsors, cannot be adequately studied using the ITTC 1978 methodology, while for example pre- and post-swirl vanes, ducts and propeller pods have been dealt with by appropriate modi-fications. The standard correlation proce-dure fails to scale and predict the energy saving due to laminar flow on some devices at normal towing speeds.

For some devices, reliable full-scale esti-mates of savings depend strongly on achiev-ing the Froude and Reynolds number

similarity. Partial ducts are reported to result in energy savings in full-scale trials, but the ITTC report concludes that this probably cannot be proven by model tank towing tests at Froude speed. Even cavita-tion tunnel tests at higher speeds may show uncertain trends.

New testing procedures and the applica-tion of large high-Reynolds number water tunnels promise to improve fuel saving estimates.

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Bulk Carrier Update No. 1 2011

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Transcript of Bulk Carrier Update No. 1 2011