Design of Catamaran EU-MOP units for efficient oil spill confrontation

Design of Catamaran EU-MOP units for efficient oil spill confrontation

Boulougouris E.(1), Papanikolaou A.(1), Ghozlan F.(2), Turan O.(3), Kakalis N.(4), Fritsch D.(5)

(1) National Technical University of Athens (SDL), (2) SIREHNA, (3) Universities of Strathclyde & Glasgow (SSRC), (4) Oxford University, (5) Fraunhofer Gesell. z. Frderung der angew. Forschung (IPA)ABSTRACT: The paper presents the design of an autonomous oil-skimming catamaran unit developed within the EU-MOP (Elimination Units for Marine Oil Pollution) Research Project funded by the European Commission (FP6). The design was based on the requirements and specifications produced through the research in EU-MOP. The special operational features required for the units in order to fulfil adequately their missions resulted in designs with unique hullform properties, outside ordinary catamaran hull forms. The general arrangement, the energy source, the propulsion system, the artificial intelligence package, the robotics and the oil processing systems of the units are presented in the paper. Additionally, the performance characteristics with respect to the resistance, seakeeping and manoeuvring capabilities are outlined. The ultimate aim is the development of efficient, practicable and feasible designs that ensure adequate oil confronting records for the proposed units.1. INTRODUCTION

EU-MOP is the acronym for Elimination Units for Marine Oil Pollution project, supported by the European Commission under the Sustainable Development, Global Change and Ecosystems thematic area, Sustainable Surface Transport Programme of the 6th Framework Programme. The aim of the project is the design and proof of concept of autonomous EU-MOPs, capable of mitigating and eliminating the threat arising from oil spill incidents. The end-result will be the conceptual development and validation of low cost, possibly recyclable, autonomous vessels/drones that will be released in the oil spill area, will track the oil concentration specifics of the spill using proper sensors and will apply mechanical countermeasures locally. The confrontation of the entire spill requires a swarm of such units. In order to handle the variety of locations where oil spills could occur (ranging from open ocean to harbour or coastal areas), different sizes of such units are designed. The complete integrated system, including communication, logistical support and response management is analysed and assessed.The successful design of the EU-MOP units is a decisive part of the overall EU-MOP concept development. The ambition is to develop the best feasible Elimination Units within the design space defined by the requirements and the constraints of the EU-MOP concept. In this context, an initial feasibility study of various sizes and concepts and a first preliminary design loop has been performed. A second preliminary design loop is currently underway and finally, the selection of the most promising concept for materializing the EU-MOP concept is going to be made. In this paper the results of the first preliminary design loop will be presented.

2. BACKGROUND

Given the unique design challenges posed by the requirements of the EU-MOP concept, the following design scheme shown in Figure 1 was used.

Figure 1. EU-MOP unit(s) design scheme [1].

The EU-MOP design requirements were defined by its mission targets, namely the confrontation of seawater oil spills. These have been defined by formulating appropriate oil spill scenarios. In the context of the EU-MOP units, they have been classified in three groups [1]. The corresponding scenario characteristics are summarised as follows:Type of sea area: Open ocean area (sea type I), enclosed seas (sea type II, including the Mediterranean Sea with the possible exception of the sea area between Sardegna, France and the Balearic Islands, Baltic Sea and Black Sea) and shallow water areas (type III, estuaries, rivers, lakes, ambers, inlets).

Quantity: Small spills (less than 7 tons of oil), medium size spills (7 to 700 tons) and large spills (>700 tons).

Type of oil: Two basic types of oil were being examined: light oils (non persistent like diesel oil) and persistent oils (heavy fuel oil or crude oil).

Meteorological conditions: The variations on the wave height have been taken into account in the type of sea area. A working hypothesis for the EU-MOPs is to be operational 50% of the time on the winter season, which roughly represents 75% of the time year round, is used.

Using the available statistical wave data different seas around Europe three sea areas have been identified [1]:

Sea type I, considering three different areas in Atlantic Ocean, namely north of Ireland, English Channel and Baltic Sea. From the data on the Baltic Sea (highest annual mean value of significant wave height is approximately 1.4 m, similar to the Mediterranean values) we considered this area as sea type II. For the English Channel the highest annual mean value of significant wave height exceeds 1.7 m whilst for the open Ocean area the mean value reaches 3.6 m (minimum value is 1.3 m).

Sea type II, considering the Mediterranean Sea where the annual mean value of wind speed does not exceed 7.5 m/s and 8 m/s in the winter season. In the entire basin the highest annual mean value of significant wave height corresponds to the Gulf of Gascogne in France and is approximately 1.4 m and 2 m for the winter season.

Sea type III was considered as an area with no large waves (significant wave height less than 0.5 m). However, this type of sea area may be subject to strong tidal currents. It is stated that differences in the water temperature may also have significant effects on the spreading rate and weathering of the oil spill but it would be impossible to study all cases.

Working hypothesis: Considering the above classification oil spill conditions, three working hypotheses have identified for the size of EU-MOPs:

small model (S) for a response area of type III designed to operate in very shallow waters

medium model (M) for sea type II, that has the approximate size of a skimmer head

larger model (L) for open ocean type I, with assumed operational limits wave height 1.6. SEAKEEPINGMotion transfer functions were calculated at units CoG with the software AQUA+ [13], which is based on a 3D radiation - diffraction method using Kelvin sources. The criteria for the behaviour of the units are the limitation of motions for brush efficiency. Seakeeping calculations grid was:

Two speeds, 1 and 5 kts for the large units, 1 and 4 kts for the medium units

Five headings, 0 to 180 deg with 45 deg step

Three loading cases, departure condition with empty recovered oil tank, 50% load condition with the recovered oil tank half full and the arrival condition with the recovered oil tank full

Two brush positions, flat and inclined.

Statistical values of motions at CoG and relative brush tip position / sea surface were calculated for 4 sea states (1, 2, 3 and 4).

Sea State (SS)1234

Hs (m)0.050.300.881.88

Tpeak (s)2.07.57.58.8

The Tpeak value for sea state 1 was chosen close to the roll period of the unit in order to have a dimensioning value.

Since inertia (gyration) radius data were not available and since no classical formulas could be used to estimate their value, relevant data for the EU-MOP units were estimated using a module of AQUA+ software which assumes that the weight is equally distributed over the wetted surface of the hulls.

Roll and pitch viscous damping of the hull have been estimated using classical formulas:

B44H=2(I44+A44)*2/Tp B55H=2(I55+AI55)*2/Tpwhere:

= 0.10 empirical value

A44 =Roll added inertia from Aqua+

A55 =Roll added inertia from Aqua+

Tp = roll natural period from Aqua+Inertia and damping coefficients for the large unit are given in Table 11 while for the medium unit they are given in Table 12.Table 11. Inertia and roll and pitch damping for the Large unit

Table 12. Inertia and roll and pitch damping for the Medium unit

Indicative results for the large and the medium unit are shown in Figure 14 and Figure 15 respectively, whiles a set of results for the motions at CoG of the large unit are given in Table 13. The analysis for the location of the oil recovering brush tip has shown that: For the large unit, the RMS value of the relative position of brush tip to the sea surface is almost always negative (tip submerged) which ensures the proper function of the oil recovering device.

For the medium unit, only in the lightship condition, the brush tip is almost constantly above sea water. This could pose a problem of the initiation of the oil recovery. However, this condition is not a real operating condition because the unit has no fuel. The addition of even a small fuel weight (for few hours operation) will alleviate this problem.

Figure 14. Heave (left) and Roll (right) RAO for Large unit running at 5kts at full load condition

Figure 15. Heave (left) and Roll (right) RAO for Medium unit running at 4 kts at full load conditionTable 13. Motions at CoG for the large unit fully loaded running at 5 knots at sea state 4

7. PROPULSION AND STEERINGEvaluation of the propulsion system was made by SSRC [14], considering the initial & lifecycle costs, system reliability & performance, maintenance & manpower requirements, as well as vessel arrangement options. The mission profile of EU-MOP units is closer to a dynamically positioned vessel rather than a conventional sea-going ship, therefore the design of the EU-MOP unit propulsion system must be made with this in mind. For such a mission profile, the propulsion system must be able to generate counter forces against environmental forces such as wind, current and waves. Environmental forces are omni-directional, therefore, propulsion & steering system or devices must have the ability to perform station keeping operations under these conditions. The propulsion system must also be able to generate enough power in longitudinal direction to move the vessel from location to location.

In many aspects, the design of a propulsion system for dynamic positioning (DP) applications varies from that of a conventional propulsion system. A conservative design philosophy must be used. While the design objective for conventional propulsion system places peak efficiency on or near the systems maximum continuous rating, a propulsion system designed for DP service should be selected and sized to meet the absolute survival requirements, placing the system efficiency based on the anticipated average power level.The propulsion and energy system requirements for EUMOP units are indicated Table 14.Table 14. Propulsion requirements

PropulsionLarge UnitMedium Unit

Hull Weight (kg)150100

Total Weight (kg)278180

Volume (m3)0.400.30

Power at Thrust (kW)24.085.42

Three types of transmission systems were considered and are compared based on the point where the drive left the vessel:1. Mechanical Transmission Drive

2. Hydraulic Transmission Drive

3. Electrical Transmission Drive (Batteries + Engine or Fuel Cell Charging System)

Both the mechanical and the hydraulic transmission systems require a prime mover which would probably be a small reciprocating diesel powered internal combustion engine. At this relatively shallow draught, using a diesel engine as a prime mover has a number of disadvantages compared to a battery driven array. The ongoing need for fuel, running spares such as filters and lubricating oil and the near presence of seawater that may ingress into the engine are such distinctive disadvantages. A diesel driven unit would always find salt getting into the air inlet system. Onshore there would need to be adequate supplies of fuel, lubricating oil and filters as well as engine component spares and this cost should be factored into account.

The vessels judging from the performed analysis would require a much larger prime mover if a hydraulic drive was used. However when electric drives are used the efficiency increases over that of the hydraulic drive and therefore the electric drive could be better matched to the specification of power asked at the energy output. There then begs the question that if we use a generating set to power both the large and the medium units what the power utilization would be as the diesel engine operates best at 85%MCR and begins to coke up at 60% MCR. A comparison of the drive systems is shown in Table 15.The selected drive system is an electrical drive system, but a hybrid diesel-electrical system is also under investigation for the next preliminary design loop.

7.1 Propulsion Motors The propulsion motors for the large unit are 2 Tecnadynes Model 8020 which provides 12.9 kW for each propeller and operates at 150VDC. Table 15. Drive System Comparison [14]RED items inside/within sea borne side of thruster

BLACK items above waterlineMechanical Drive SystemHydraulic Drive SystemElectrical Drive System

Driven by direct drive or gearbox off diesel/LPG engineDriven by hydraulic power pack off diesel/LPG engineDriven by DC motor off batteries

REQUIREMENTS

Hub

Column

Thrust Faces

Propeller Hub Bearings

Power CharacteristicsScaled for PowerScaled for PowerScaled for Power

Mass CharacteristicsScaled for MassScaled for MassScaled for Mass

LubricationSealed Unit

FailsafeRelief ValveOverloads

SteeringOn VesselCan be OmittedCan be Omitted

Vertical Drive ShaftN/AN/A

FeedbackSupply PressureLine Current

C.P.P. PropellerLikelyN/AN/A

ControlsSwash PlateVarying Voltage

Vertical Drive Shaft BearingsN/AN/A

Horizontal Drive Shaft BearingsHydraulic MotorElectric Motor

Position & FlexibilityLikely to be fixedMovableMovable

Hydraulic Pump BearingsN/AN/A

Hydraulic HosesN/AN/A

Electrical Motor BearingsN/AN/A

Electrical MotorN/AN/A

Main AdvantageTried and TestedEasily AdaptableDoes Not Need Prime Mover

Main DisadvantageToo Many Moving PartsHydraulic Pressure Losses and NoiseNeeds Recharging/ Battery Weight

Figure 16 Tecnadyne's Model 8020 [15]For the medium unit, 2 Tecnadynes which provide 1.5 kW for each propeller and operates at 150VDC, were selected.7.2 Steering A steering column was used for both the large and the medium unit located outside the hull. Each of the steering column connection units is universal in design, application and interchangeable with every thruster, no matter the power or mass of the propulsion system. It is a resilient and robust steering system that resists propeller upthrust and at the same time is able to safely support the mass of the unit whilst combating the variation in propeller load.Locating the propeller under the after hull in the conventional manner was inappropriate as experience has shown it is better to initiate a swing transfer of an all-in-one replacement unit when required and accordingly, in such circumstances, the propeller and its steering column must be in a position where it can be easily removed.The propeller and the steering column were located outside the hull thus avoiding hull penetration(s) under the waterline and this gives two further advantages as follows:

1. Avoidance of taking the boat out of the water to remove the propeller for repair of replacement

2. Any damage to the propeller hub by collision or rope entwinement will not cause damage to the hull and leaks or a substantial ingress of water

Figure 17. Bearing location (left) and cross section showing DC motor connection (right) [14]8. MANOEUVRINGCurrent IMO Criteria were applied to assess the manoeuvring characteristics of EU-MOPs. Most up-to-date standards for ship manoeuvrability are set by the Resolution MSC.137(76) while detailed explanatory notes are given by MSC Circular 1053. Based on these criteria an initial manoeuvrability and directional stability assessment conducted for both catamaran units.

This was done by computer simulations using a manoeuvring mathematical model to assess the manoeuvring characteristics of large catamaran EU-MOP unit [16]. Since the units are not covered by IMO standards, the assessment was made for Lightship + 10% fuel condition and full weight condition. Environmental parameters such as wind and current were also investigated, defined according to mission objectives.8.1 Turning abilityFor the turning ability investigation the full nozzle deflection angle of 60 was used in each manoeuvre. The effect of speed and of the loading condition is shown in Figure 18 and Figure 19 respectively. It is obvious that as the load increases, the directional stability of the catamaran unit decreases. The existing numerical results have shown that the large catamaran unit initial turning ability is sufficiently within the IMO criteria.

However it should be noted that the hydrodynamic characteristics of the catamaran unit were calculated assuming there are no interaction effects for initial design. It is reminded here that for this assumption to be valid the ratio of hull separation to demihull beam should be greater than 1.6 and yaw angles should be small [17].

Figure 18. Effect of speed to turning ability of large unit at the Unloaded+10% fuel condition [14]

Figure 19. Effect of loading condition to turning ability for large units speed of 5 kts [14]8.2 Yaw checking abilityYaw checking ability of the large EUMOP unit was tested with different loading conditions at 5 knots. The performance of the catamaran satisfied the criteria for the maximum first overshoot is 10 and the maximum second overshoot is 25 for 10/10 Zig-Zag manoeuvre. An indicative result is shown in Figure 20.

Figure 20. 10/10 Zig-Zag Manoeuvre for large unit at the full load condition [14]8.3 Course-keeping and Directional Stability in Waves

The course-keeping and the direction stability due to the effects of environment such as winds, local currents and waves was investigated. The roughest environmental conditions the EU-MOPs will face apply the large models, therefore the analysis was limited to the large model only. Time domain motion simulations were made in six degrees of freedom, assuming a Ka-4-70 propeller series in the Nozzle 19A. The P/D ratio was chosen as 1.230 as a standard off-the-shelf application. A cavitation and efficiency analysis was not performed.

The directional control system was assumed to be governed by a Proportional-Differential controller. The tuning of the system is done by Ziegler-Nichols parameters [18]. Assessment of directional stability for the units was done in both operating speed and transit speed. The environmental conditions were 19 knots wind speed and an average speed of 0.8 knots current, which was modelled as a random walk in time, in differing directions. A one meter significant wave height was selected to observe the effect of waves on the system operability. The unit was given an initial 30 deviation from course and the autopilot was commanded to bring the unit back on course to assess the directional stability in different environmental scenarios. The results for the large unit running at 5 kts are shown in Figure 21.

Figure 21. Course-keeping Ability of the large unit at 5 kts [14]The results has shown that although the catamaran unit seemed to be within the operational limits, the effect of environment on directional stability was significant and a strategy to overcome these effects must be implemented to the governing mechanism. Additionally, the effect of the propellers on pitch motion was an issue requiring more thorough analysis.9. ELECTRONICSFour sensor configurations were investigated for the Large and Medium models. Among those configurations, one that best comply with the various Artificial Intelligence Architecture was selected. It is comprised by the following sensors for the Large and Medium EU-MOP units [19]:

a DGPS system,

an obstacle detection and collision avoidance system,

a depth sensor,

a compass,

an oil in water sensor,

level indicators for the fuel tank and the oil storage tank,

a radio-based communication system,

an embedded control processor / computer.

10. OIL SKIMMING DEVICEBoth large and medium catamaran units are using an Oleophilic belt type oil skimming device similar to the one shown in Figure 22.

Figure 22. Oleophilic belt type [1]11. HULL CONSTRUCTION MATERIALTwo materials have been identified as applicable for the units; namely FRP and aluminium. Initially, a detailed analysis for the selection of aluminium alloys was performed. Different grades of aluminium alloys were identified and total weight and thickness values were obtained using classification societys rules. The scantling determination covered two aspects for the selected rounded types aluminium alloys; plate thickness and addition to hull weight for the each stiffener spacing case, minimum thickness required for bottom and side shell in the hull and addition to hull weight. The findings from the analysis can be summarised as follows: Three types of 5xxx series were chosen, which are regularly used for similar types of small working boats in the marine industry; Aluminium Alloy Grade 5083, Aluminium Alloy Grade 5086, Aluminium Alloy Grade 5754.

From the selected grades, Grade 5083 has proven more suitable in terms of total weight with less thickness within the limits required by classification societies.In order to identify the required mechanical properties of selected aluminium alloys, the rules and estimation methods specified by classification societies have been followed. For this task, Lloyds Registers rules on hull construction in aluminium have been used (Lloyds Register, 2004).12. CONCLUSIONSThe conceptual design of autonomous oil-skimming catamaran units, developed within the EU-MOP (Elimination Units for Marine Oil Pollution) Research Project funded by the European Commission (FP6, Contact No. TST4-CT-2004-516221, Duration 2005-2008), has been presented. In particular, the designs and performance of a large and a medium size unit that fulfil the set requirements and specifications according to the EU-MOP operational concept have been analysed. The systems comprising the units have been outlined. The present findings suggest that the ultimate goal of this project to develop efficient, practicable and feasible designs that ensure adequate oil confronting records for the proposed units is achievable. Currently the second stage of the preliminary design is underway, along with model experiments to verify the hydrodynamic performance of the planned units in a rational way.REFERENCES

[1].Kakalis N.M.P., Ventikos Y.P., Ayaz Z. and Turan O., Deliverable D1.3 Technical Requirements, document 01-30-RD-2005-09-00-1f from the EU-MOP project, 31-10-2005.[2].Lemesle P., Kakalis N., Fritsch D. and Turan O., Design of Monohull EUMOP units to clean oil spills, Small Craft Conference, Bodrum, Turkey, November 2006.

[3].Lemesle P., Le Corre Y. and Ventikos Y.P., Deliverable D2.1 Integrated Design Initial phase, document 02-10-RD-2005-11-01-1 from the EU-MOP project, 30-11-2005.

[4].Ayaz Z., Armaoglu E., Turan O., Ghozlan F. and Lemesle P., Deliverable D.3.1 EU-MOP Energy Source and Propulsion-Initial Phase, document 01-20-REP-2005-01-00-0 from the EU-MOP project, 31-01-2006.

[5].Lewis E.V. (editor), Principles of Naval Architecture, Vol. II, Resistance, Propulsion and Vibration, 2nd Revision, ISBN 0-939773-01-5, SNAME 1988, pp. 106-108.

[6].Lamb T. (editor), Ship Design and Construction, Vol. II, SNAME 2004, Chapter 45.

[7].Papanikolaou A., Kaklis P., Koskinas C. and Spanos D., Hydrodynamic Optimisation of Fast-Displacement Catamarans, 21st Symposium on Naval Hydrodynamics (ONR), 1997, pp. 697-714.

[8].Holtrop J. and Mennen G.G.J., An Approximate Power Prediction Method, International Shipbuilding Progress, Vol. 89, 1982.

[9].Holtrop J., A Statistical Reanalysis of Resistance and Propulsion Data, International Shipbuilding Progress, Vol. 31, 1984.

[10].NAPA Oy (2005), NAPA software, http://www.napa.fi/[11].Kakalis N.M.P. and Ventikos Y.P., Deliverable D3.2 Engine Selection, document 03-20-RD-2006-09-00-1 from the EU-MOP project, 30-04-2006.

[12].http://iseek.com/solomontech/newsite/public_html/motordrive.htm, Solomon Technologies Inc.,

[13].AQUA+, http://www.ec-nantes.fr/Sirehna/products/products.htm, SIREHNA.[14].Armaoglu E., McNair B., Turan O., EU-MOP Energy Source and Propulsion, The Selection, document 01-20-REP-2005-01-00-0 from the EU-MOP project, 31-08-2006.[15].Tecnoval Inc., http://www.tecnadyne.com/thrusters.htm

[16].Armaoglu E., Ayaz Z., Turan O., Design of EU-MOP Units Integrated Characteristics, document 01-20-REP-2006-01-00-0 from the EU-MOP project, 01-06-2006.[17].Dubrovsky, V. A., Lyakhovitsky, A. A.,Multi-Hull Ships, Backbone Publishing, Fair Lawn, NJ, 2001.[18].Astrom K. J., Hagglund T., PID Controllers: Theory, Design, and Tuning, International Society for Measurement and Con; 2nd edition, 1995.[19].Fritsch D., Cellier N., Doucy O. and Vrhovac M., Artificial Intelligence Structure, rev.1", document 04-20-RD-2005-13-01-1 from the EU-MOP project, 24-01-2006.