2011 DP Conference Cover Page Format - Dynamic Positioning · Web viewAuthor Liz Stanfield / Richard Simpson Created Date 09/20/2019 04:24:00 Title 2011 DP Conference Cover Page Format

Author’s Name Name of the Paper Session

DYNAMIC POSITIONING CONFERENCEOctober 15 - 16, 2019

THRUSTERS SESSION

System integration: from single unit thrust to total vessel DP-performance

By Norbert BultenWärtsilä

Norbert Bulten Thrusters System integration: from single unit thrust to total vessel DP-performance

AbstractDuring the evaluation process of a vessel’s Dynamic Positioning (DP) capability, the actual propulsion performance of the propulsion units have typically been implemented based on a simplified constant Thrust/Power ratio approach, showing a fair prediction of the resulting vessel DP-capability. However, in order to gain better insight into the added value of tilted-thruster benefits, the overall calculation methodology for DP-capability requires an upgrade to a higher level of accuracy. In this paper a new modular approach is introduced, based on the 360°-circumferential performance of each propulsion unit, which can be either an azimuth thruster, main CPP propeller or transverse/tunnel thruster. The performance of the different propulsors has been determined based on full-scale CFD simulations and interaction effects between the hull and other propulsors are taken into account in the Thrust-Allocation-Logic (TAL). Comparisons with available DP-calculation results from industry are shown for a semi-submersible drill-rig and a drill-ship. Furthermore a comparison is made of the DP performance of a drill-rig equipped with 8°-tilted shaft thruster and with an industry standard unit, showing significant gains in DP performance for the modern tilted units under both all units intact and single unit failure modes.

Abbreviation / Definition CFD Computational Fluid DynamicsCPP Controllable pitch propellerQP Quadratic ProgrammingTAL Thrust Allocation Logic

1. Introduction

During the evaluation process of a vessel’s Dynamic Positioning (DP) capability, the actual propulsion performance of the propulsion units have typically been implemented based on a simplified constant Thrust/Power ratio approach, showing a fair prediction of the resulting vessel DP-capability. From a propulsion point of view there are aspects in such methodology that have room for improvement, which should lead to a more accurate description of the vessel’s actual DP-performance. A major step which has to be made is the transition from a constant-performance factor of a thruster, to an actual 360°-circumferential performance description of each thruster-unit. This performance depends on the design of the thruster unit and the interaction with its surrounding, being the vessel geometry and the other thruster units. Interaction with the vessel geometry is expressed in the hull-thrust-deduction factor and interference with other thrusters is managed by the so-called forbidden zones. Full scale CFD simulations can be used to determine the various performance factors within acceptable time and cost nowadays, and provide more detailed performance characteristics of azimuth thrusters, transverse tunnel thrusters or main propulsion propellers resulting in a performance polar plot for each separate unit. The next step in the process of upgrading the DP-capability methodology is to implement the unit specific 360°-circumferential performance into the Thrust Allocation Logic (TAL). Existing allocation methods are typically based on Quadratic Programming (QP) approaches, such as those described by Leavitt [1] and De Wit [2] or on an improved Lagrange multiplier method [3]. Implementation of any arbitrary performance polar plot into the QP-methodology might not be straight forward however, in the new approach outlined here, a system simulation approach is used, which can read any polar performance data set and removes the limitation with regards to the input performance data. The problem of defining the individual thrust vectors (magnitude and angle) of all units remains however. For vessels with multiple thruster units, the target is to get the maximum thrust in the desired direction, whilst minimizing the resultant yaw-moment and side force (perpendicular to the target heading). An iterative method has been

MTS DP Conference - Houston October 15 - 16, 2019 Page 1


programmed in the system simulation methodology, which takes care of elimination of the yaw-moment. Once the thrust vectors from each individual thruster have been defined, the total force can be checked as well as the remaining yaw-moment and side-forces resulting in a Thrust-availability polar plot. In case a vessel experiences significant yaw-moments from environmental loads, a compensating yaw-moment should be targeted at. With such a plot, the performance of different thruster configurations and/or power ratings can be compared and explored.

In order to transfer the thrust-availability to a DP-capability plot, the impact of the environmental forces on the vessel from wind, waves and current need to be included. Data from literature, such as those given in Brix [4] may be used to determine the wind-force coefficients of the vessel in question, such as a drill-ship used for this case-study and, shown in Figure 1. Similar data sets are available for current and wave forces. Review of the current literature and DP-capability calculation methodologies, reveal the simplicity of the underlying formulas for many components, where the application of full-scale CFD calculations for wind-forces and current forces are appropriate nowadays, given the limited required effort and time.

Figure 1: drill-ship geometry from Brix as used for wind-coefficients

In this paper a new approach for determination of DP-capability is discussed in which the method is based on the polar performance data of each individual thruster. In the following section a number of offshore vessels are discussed, which vary from a drill-rig with a homogeneous set of azimuth thrusters to a supply vessel with a large variation in propulsion units onboard. With the new methodology, a similar DP-capability evaluation can be made for all vessels, since the propulsion unit specific polar thrust performance data is read as input data.

2. Vessel types and propulsion unit lay-outThe vessels discussed in this section are the commonly equipped with azimuth thrusters, some of which can be executed by a retraction mechanism in case the units are not allowed to protrude below the vessel base line. It is acknowledged that this is by far not a complete list of vessels which are currently equipped with DP-systems.

2.1 Semi-submersible drill-rig

Semi-submersible drill-rigs are generally known for flat, 2 pontoons underside. In the era before the 8°-tilted thrusters, quite significant thruster-hull interaction phenomena with such an underside were presented with such typical thruster-hull interaction given by various researchers [5, 6] however, with the introduction of tilted thrusters, exceeding a 7 degree tilt angle, the flow is deflected significantly downward and eliminating hull-thruster interaction. This positive impact of thruster-tilt angle on DP-performance has been acknowledged by ABS and implemented in their guidelines [7].



When looking at the lay-out of the thrusters on a semi-submersible rig, two variants can be distinguished, which are a circular and a cross layout, as shown in Figure 2. In the circular layout the forward-most units are placed on the inner side of the pontoons, where as in the cross layout the most forward units are placed on the outer side. The choice for the thruster arrangement will have an impact on the sectors of the forbidden zones. For the drill rig configurations shown, the main forbidden zone is dictated by the thruster unit which is closest. Two forbidden zones are indicated for the most-forward port thruster, showing the difference in orientation.

Figure 2: thruster configurations for semi-submersible drill-rig, left cross layout, right circle layout. Forbidden zones are indicated for the most forward port thruster unit.

2.2 Semi-submersible crane-vessel

At first glance, The Heerema built semi-submersible crane vessel, Sleipnir, might look comparable to a semi-submersible drill-rig with 8 thruster units (see Figure 3). However, the crane vessel has a more pronounced aft-ship shape on the two pontoons, where 4 thruster units are located. With the asymmetrical shape of the pontoons, the vessel can achieve a significant transit speed which reduces the time to sail from one lifting operation site to another. These units are located above the vessel base line, which allow for operation in shallow water. Another 4 retractable tilted thruster units are located in the forward part of the vessel to have optimum DP-capability in offshore lifting operations. The forward thrusters have similar low hull-interaction factors as seen for the semi-sub rigs whereas the aft thrusters will only have slight interaction losses when operating in astern mode.

Figure 3: Heerema Sleipnir semi-submersible crane vessel



2.3 Drill-ship

Drill-ships are generally equipped with 6 units, 3 in the bow and 3 in the stern. The horizontal distance between the various units in either bow or stern is rather small, certainly when compared to a drill-rig with thrusters on 2 separate pontoons. Due to the smaller distance between the units, drill-ships tend to have relatively higher interaction effects than drill-rigs with possible overlapping zones between the three units [8]. In addition to this, the interaction effects of the aft thrusters with the aft-ship hull-shape are more pronounced. Apart from having higher interaction effects than the drill-rigs, the higher aspect ratio between vessel length and beam leaves a drill ship significantly more vulnerable to environmental forces from the sides. A typical DP-capability plot for this vessel type has critical operational characteristics at 90 and 270 degrees.

2.4 Offshore construction vessels / windfarm installation vessels

Whereas the drill rigs and drill ships are characterized by a limited number of propulsion equipment lay-outs, the group of offshore construction vessels (OCV) have a larger variety. Depending on the operational profile, both shaft-line driven propellers and azimuth thrusters can be selected in the design, in combination with transverse tunnel thrusters and/or retractable thrusters.

2.5 Pipe laying & cable laying vessels

Pipe and cable laying vessels are often equipped with a large number of propulsion units. In operation, the vessels have to follow the intended route with Dynamic Tracking, which is a derivative of the normal Dynamic Positioning operation. For these vessels, no generic propulsion lay-out can be distinguished, similar to the offshore construction vessels.

2.6 Offshore / platform supply vessels (OSV / PSV)

On the smaller thruster side the offshore and platform supply vessels (OSV & PSV) are equipped with DP systems. These vessels have different propulsion products on board, which can be azimuth thrusters, retractable thrusters and transverse tunnel thrusters. Main propulsion configuration can be based either on azimuth thrusters or shaft-line driven propellers with rudders. Supply vessels have both efficient transit sailing characteristics and DP capabilities in their operational scenario therefore, trade-offs between both free sailing ahead and DP in the selection of equipment have to be made. Compared to the vessel types discussed above, supply vessels are clear outliers with their variety of propulsion configurations. A clear difference in the power levels of various propulsion units are also present, whereas one single thruster-type is seen on drill-rigs and drill-ships.

2.7 AHTS

Anchor handler vessels are designed for maximum bollard pull force. In order to achieve this force, two shaft-driven ducted propellers or ducted azimuth thrusters are installed. Bollard pull forces of 300 tonnes can be reached with such equipment. For DP operation, additional tunnel thrusters and retractable azimuth thrusters are typically installed.

2.8 Summary

The main drivers determining the interaction between the vessel and various other thrusters have been discussed for different ship types with findings summarized in Table 1 below. From Table 1 it can be



concluded that the number of variables is increasing when going from a drill-rig to a supply vessel or anchor handler.

Verification of the new DP-capability methodology will focus on drill-rigs and drill-ships in the first phase, which are equipped with identical units. Extensions to other thruster types, transverse tunnel thrusters and shaft-line driven propellers are anticipated to be incorporated into the architecture of the methodology.

Type Hull-interaction Thruster-thruster interaction Propulsion layoutDrill rig limited for 8° tilt forbidden zones required identical unitsCrane vessel aft ship units forbidden zones required identical unitsDrill ship aft ship units forbidden zones required identical unitsOCV aft ship units design dependent different units & powerPipe/cable laying aft ship units design dependent different units & powerSupply vessels main propulsion forbidden zones required different units & power AHTS main propulsion limited different units & power

Table 1: overview of main propulsion performance interaction factors

3. Hydrodynamics / propulsion performance

3.1 Performance prediction methodology

Detailed performance of any of the propulsion products are determined with full scale CFD simulations where the calculation of generated thrust using Simcenter StarCCM+ has been described in more detail in [9]. Hull resistance and propeller-hull interaction can be calculated with CFD within reasonable timeframes as well. An example of such a CFD simulation is shown in Figure 4, where the performance of an AHTS vessel’s ducted propellers in transit are analysed.

The numerical flow simulations have been validated extensively with available model scale measurement data however. analysis of performance data at model scale and full scale revealed significant differences in case of ducted propellers. The physics behind this large Reynolds scaling effect (up to 10% for ducted propellers and 15% for ducted azimuth thrusters) have been revealed based on more detailed analysis of the occurring flow phenomena in [10].

Figure 4: AHTS vessel with calculated free surface and streamlines from full scale CFD

Once the isolated azimuth thruster unit performance has been calculated (open water performance data), the various interaction losses have to be determined. The losses due to thruster-hull interaction depend on the direction of the jet out of the thruster and once this jet of accelerated water hits the hull, reduction of



net thrust is to be expected. For 8°-tilted thrusters it has been confirmed that the jet is deflected sufficiently downwards, as shown in Figure 5, so that no interaction with a horizontal hull surface is expected. Thrusters with smaller tilt angles can still suffer from thruster-hull interaction losses when the diverging jet interferes with the hull further downstream. Once the flow of the jet interferes with the hull, the well-known Coanda effect will be triggered, which introduces further losses. This can be recognized in Figure 5 by the yellow/orange area on the hull surface. Another major thrust loss phenomenon occurs when the jet interacts with the second pontoon, in case of a crabbing operation. This net thrust loss can be up to 50% higher when the jet hits the second pontoon. The differences with between tilted and un-titled units are significant in such a case as when the jet stays beneath the second pontoon and no measurable loss is visible [6].

Figure 5: comparison of conventional thruster (left) and 8°-tilted thruster. Colors of the particles indicate distance from the hull surface, yellow/orange color on the hull indicates increased friction

Thruster units in the stern of a drill-ship can suffer from thruster-hull interaction losses, when operating in astern mode as the jet is then directed towards the ship-body and reduction of overall thrust occurs in that segment. This kind of interaction loss cannot be eliminated by the tilt angle and it has to be accepted for all thruster types.

Performance prediction and interaction losses of tunnel thrusters with the hull are mainly related to the local hull-tunnel interfacing geometry and the presence of grid-bars [4]. In case the edge between the hull plating and the tunnel becomes too sharp, flow separation inside the tunnel might occur [11] which will result in a reduction of the flow through the tunnel and consequently a reduction in net thrust. When grid bars are placed at the entrance of the tunnel, they will also result in a reduction in flow rate and thus thrust.

3.2 Actual thruster performance

Actual performance determination (real, full-scale vessel) of equipment remains a challenging topic. Vessels with smaller thrusters, such as tugs, can execute bollard pull tests to verify the performance. Even for vessels with two azimuth thrusters with bollard pull up to 100 tonnes, this measurement can become challenging Furthermore, vessels with azimuth thrusters in the range of 4000-6500kW can produce such thrust values with a single unit. For these offshore vessels it is impractical to perform similar bollard-pull tests.

An alternative approach could be to measure the thruster performance at full power in transit. The vessel speed which can be achieved can be compared to the predicted vessel speed providing an indirect way to



verify the thruster performance of the larger units. Apart from vessel speed comparisons, the required power can be compared to the measurement of the absorbed power. Once both vessel speed and power absorption of the simulations match the measurements, it can be concluded that the full scale thruster performance data is accurate.

3.3 Drill rig system simulation model

In order to evaluate the full-scale performance prediction of an 8°-tilted thruster unit, a system simulation model has been made in Simcenter Amesim, as shown in Figure 6. In this model the performance of 8 azimuth thruster units is modelled in combination with the vessel hydrodynamic resistance in transit mode. The actual operational data of all thruster units has been measured onboard of the rig together with the vessel speed. In the transient simulation, the thruster propeller RPM and thruster azimuth angle are read from the monitoring data and the full-scale thruster unit performance curve has been calculated with CFD as previously mentioned. Based on initial vessel speed and propeller RPM, the unit thrust is calculated. As long as the resultant force of all 8 units exceeds the hull resistance, the vessel will accelerate. The higher vessel speed will have impact on the actual propeller loading (both thrust and torque).

Figure 6: system simulation model of drill rig with 8 azimuth thrusters

The data from the sea trials shows quite large variations in both thruster RPM and steering angle, resulting in a vessel speed and the shaft torque that do not reach a steady-state value, as shown in Figure 7 and the comparison between the measured and calculated ship speed shows that the overall agreement is good. The system simulation model takes both the vessel inertia and the resistance into account. As seen in Figure 7, at approximately t=1300 seconds, the thrusters are shutdown and the vessel takes a few minutes to decelerate due to its inertia. During the acceleration of the vessel, started at approximately t=1700 seconds, the majority of the thrust is used to overcome the inertia of the rig. The measured and calculated torque show good agreement as well, with similar results obtained for all 8 units. The torque signal shows a number of steps in the signal during acceleration (between t=1700 and t=3000 seconds) which are directly related to the steps in propeller RPM. The impact of vessel speed



increase can be observed by the small negative slope in the torque signal and due to higher inflow speed, the propeller loading reduces slightly, which results in a small reduction of torque.From the results from the system simulations it is concluded that the full scale thruster input performance data can be regarded as accurate. Similar results from CFD simulations will be used in following analyses, when thruster performance data is used.

Figure 7: comparison of measured and calculated ship speed (left) and thruster shaft torque (right)

4. Thruster Allocation Logic for DP

4.1 Environmental force impact

In the previous section the hydrodynamic performance of the propulsion system has been discussed. It has been shown that the generated thrust from the azimuth thrusters balance the hull resistance in transit condition well. The hull resistance in both water and wind is aligned with the vessel surge direction in such condition However, for the development of the methodology to calculate the DP-capability, the impact of environmental forces need to be considered over the complete 360° circumference. These environmental forces are split into the contributions from wind, waves and current in general. Once the environmental forces and moments are determined, the Thrust Allocation Logic (TAL) has to be applied to the available thruster unit performance data to find a balance with the environmental forces. For the TAL different targets can be defined, depending on the life-cycle phase. Two defined targets are:

Maximum achievable dynamic positioning thrust, including failure cases (early design phase) Economic part load operation (fuel saving modes)

In order to get a good thrust allocation, all aspects of the net-thrust generation have to be taken into account. This means that the unit performance over its complete 360° circumference including the specific thrust-deduction for each operating angle have to be considered. Apart from this, all possible forbidden zones have to be complied with when selecting thruster azimuth angles. Forbidden zones are mainly related to the drop in performance when the jet of one thruster interacts with another downstream unit. These aspects are covered in the far left arrow as shown in Figure 8



Figure 8: Thrust Allocation Logic (TAL) input drivers

The arrow on the right side of Figure 8 represents the impact of the environmental forces. A significant contribution to the environmental forces and moments arises from the wind forces, acting on the vessel superstructure. Relations between wind force and wave height, wave period and current are given in the DNVGL document ST-0111: Assessment of station keeping capability of dynamic positioning vessels [12], and reproduced in Table 2.

Beaufort (BF) number

DP-capability number

Beaufort description Wind speed [m/s]

Significant wave

height [m]

Peak wave period [s]

Current speed [m/s]

0 0 Calm 0 0 NA 01 1 Light air 1.5 0.1 3.5 0.252 2 Light breeze 3.4 0.4 4.5 0.503 3 Gentle breeze 5.4 0.8 5.5 0.754 4 Moderate breeze 7.9 1.3 6.5 0.755 5 Fresh breeze 10.7 2.1 7.5 0.756 6 Strong breeze 13.8 3.1 8.5 0.757 7 Moderate gale 17.1 4.2 9.0 0.758 8 Gale 20.7 5.7 10.0 0.759 9 Strong gale 24.4 7.4 10.5 0.7510 10 Storm 28.4 9.5 11.5 0.7511 11 Violent storm 32.6 12.1 12.0 0.7512 NA Hurricane force NA NA NA NA

Table 2: wind speed, significant wave height, peak wave height and current speed as function of Beaufort scale (from DNVGL ST-0111)

The DNVGL document also provides formulae for the calculation of various environmental forces. Figure 9 shows a comparison between wind forces and moments acting on both a drill-ship and a semi-submersible drill-rig, based on those formulae providing frontal (Fx) and longitudinal (Fy) force curves in line with expectations. A reasonable resemblance is given in the longitudinal force, whereas the impact of the difference in frontal area can be seen in the diagram for the frontal force. From the two forces, the resultant force vector can be calculated and the direction of this total wind force can be compared to the angle of the wind. The difference between these two angles is shown in the bottom left picture. A clear difference is observed for the two vessels, for example at a wind-angle of 30°, the resultant wind force on the drill-rig retains an angle of about 30°, where the total force on the drill-ship already has an angle of about 60°. A similar trend is shown when the yaw-moment (Mz) is evaluated. In this example, the maximum yaw-moment acting on the drill-ship is about 3 times the yaw-moment of the drill-rig. Balancing this vessel yaw-moment is a key-target of the algorithm in the TAL, along with maximization of the thrust-force in the target direction of the total combined environmental forces.

4.2 Verification of DP-capability for the drill-rig



The developed DP-capability calculation method has been verified with available data from a semi-submersible drill-rig. The environmental forces as reported, have been used to ensure identical situations for both calculation methods. The thruster-hull interaction losses are based on the 8°-tilted thrusters, which are small over the complete 360° circumference. Forbidden zones are also based on the 8°-tilted thrusters performance data. The thruster-utilization rate is shown in Figure 10 for the rig, for both the reference DP-capability method as well as for the Wärtsilä DP-capability method showing good agreement between the two methods. The averaged difference between the two methods is only 1.3%.

Figure 9: Comparison of wind forces and moments of drill-ship and drill-rig, top left frontal forces, top right longitudinal forces, bottom left total force angle deviation, bottom right hull yaw moment



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Figure 10: verification of DP-capability calculation method for semi-submersible drill-rig based on thrust utilization polar plot

4.3 Verification of DP-capability method for the drill-ship

The developed DP-capability method has been compared to the DNV GL DP-Cap web-app [13] as well, with results of the calculation presented in Figure 11, as a wind limit plot in Beaufort or DNVGL scale. The input data for the vessel and the thruster units are identical for both calculation methods. The proposed forbidden zones from the DNVGL DP-Cap tool are used in the new calculation method, even though the standard Wärtsilä calculation method for tilted thrusters expect smaller forbidden zones. Standard operational margins, such as a dynamic factor of 25% and reserved power of 10% are taken into account. Good agreement is observed over the whole 360° circumference for the maximum predicted wind speed under the all units in operation condition (left) and for a single failure mode of thruster unit 2. Full scale measurements on the Maersk Venturer drill ship have been compared with DP simulation tools of DNVGL [14]. Good agreement between measurements and simulations have been found, which are another indicator of the accuracy of the applied simulation tools and full scale thruster performance.



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Figure 11: verification of DP-capability calculation method for drill ship based on maximum wind polar plot. Left side all units intact, right single failure of thruster 2

5. Evaluation of tilt-benefits on DP performance In the previous section the development and verification of the DP-capability calculation method has been discussed. In this section the developed calculation tool will be used to evaluate DP-performance for different thruster-units. Isolated thruster performance and thruster-hull interaction effects for different tilt-angles have been determined before [5, 6] and these results are used as input for the DP-capability calculations. Since the calculations focus on a single drill-rig, the environmental forces and moments remain the same for both thruster configurations (the far-right arrow in Figure 8). The results of the DP-capability calculation are shown in Figure 12, for the all-intact and a single unit failure mode and are presented as thruster utilization plots, which indicate feasible operation as long as the utilization values remain below 100%. Constant wind speed of 32.6 m/s is selected, which is equivalent to DNVGL scale 11 (see Table 2). With all eight units intact, this harsh condition can be handled by both the thruster units with 8°-tilted thrusters (Wärtsilä units) and units with 5°-tilted nozzle (industry reference) However the performance differences are clearly visible. The significance of the differences can be seen in the plots, where a single failure mode is calculated (right image in figure 12). Performance with 8°-tilted thrusters is just at the limit, where the units with tilted nozzle fail to produce sufficient thrust in the sectors from 60°-110° and 250°-300°. The difference in DP-performance for failure of either thruster unit 1 or 2 is negligible. An additional calculation has been made, where the wind speed has been reduced until the thrusters with tilted-nozzles provide allowable operation with a single failure where it has been found that the maximum wind speed needs to be reduced from 32.6 m/s (scale 11) to 30.0 m/s. This is a reduction in wind speed of about 8%, which translates into a difference in environmental force of about 16%, which is quite significant for thruster units operating at the same design power.



Figure 12: DP-capability comparison of Wärtsilä 8°-tilted thruster with 5°-tilted nozzle industry reference based on thrust utilization polar plot. Left side all units intact, right side single unit failure (unit 1 solid line, unit 2 dotted line)

7. ConclusionThe benefits of tilted-thrusters for dynamic positioning have been acknowledged by the maritime and offshore industry however, the true merits of the improved performance cannot be based on the individual unit performance or the net-thrust generation only, but together in an interacting system. Here, full-scale thruster unit performance determination is based on CFD simulations nowadays and the accuracy of such full-scale performance has been verified, based on monitoring data from a drill-rig in transit sailing condition. In order to show the actual performance of a modern azimuth thruster in DP-operation a new DP-capability calculation method has been developed. The methodology is based on the actual hydrodynamic performance of the propulsion units in their 360° circumferential operation. This approach is valid for azimuth thrusters, but also for transverse tunnel thrusters and propeller-rudder propulsion units. Interaction with the ship-hull structure is implemented over the 360° circumference as well. Furthermore, the number and size of forbidden zones are left unlimited. The thrust allocation logic (TAL) algorithm ensures that the environmental forces and moments are balanced in the proper way whilst the methodology has been verified with available data, covering both a semi-submersible drill-rig and a drill-ship layout. Good agreement between the calculated results is found. The DP-calculation method has been used to determine the DP-utilization plots of a drill-rig equipped with 8°-tilted thruster units and 5°-tilted nozzle units. Clear difference in performance in favour of the 8°-tilted thruster units is shown, both for the situation with all units intact and for the single failure case. The vessel specific wind and current forces values need attention as well. Often very simplistic formulas are used, where full scale CFD simulations with the actual vessel geometry are appropriate, considering developments in software which have made it possible to carry out such flow analyses within limited effort and time.



References[1] J.A. Leavitt, ‘Optimal Thrust Allocation in a Dynamic Positioning System’, SNAME transactions paper,

2009

[2] C. De Wit, ‘Optimal Thrust Allocation Methods for Dynamic Positioning of Ships’, MSc-thesis Technical University of Delft, 2009

[3] E.F.G van Daalen, J.L. Cozijn, C. Loussouarn, P.W. Hemker, ‘A Generic Optimization Algorithm for the Allocation of DP Actuators", OMAE2011-49116, OMAE Conference, Rotterdam, 2011.

[4] J. Brix,’Manoeuvring Technical Manual’, Seehafen Verlag, Hamburg, 1993

[5] D. Jürgens, M. Palm, A. Amelang, T. Moltrecht, ’Design of reliable steerable thrusters by enhanced numerical methods and full scale optimization of thruster-hull interaction using CFD”, Dynamic Positioning Conference, Houston, 2008

[6] N. Bulten, P. Stoltenkamp, ‘DP-capability of tilted thrusters’, Dynamic Positioning Conference, Houston, 2013

[7] ABS, Guide for Dynamic Positioning Systems, Houston, 2012

[8] N. Bulten, P. Stoltenkamp, ’Improved DP-capability with tilted thruster units and smart controls algorithms’, Dynamic Positioning Conference, Houston, 2016

[9] N. Bulten, R. Suijkerbuijk, ‘Full scale thruster performance and load determination based on numerical simulations’, International Symposium on Marine Propellers smp’13, Launceston, Tasmania, 2013

[10] N. Bulten, P. Stoltenkamp, ‘Full scale CFD: the end of the Froude-Reynolds battle’, Proceedings of Fifth International Symposium on Marine Propulsion SMP’17, Espoo, Finland, 2017

[11] N. Bulten, ‘The journey to new tunnel thrusters, the road so far and what is still going to come’, Proceedings of IMDC conference, Helsinki, Finland, 2018

[12] https://rules.dnvgl.com/docs/pdf/DNVGL/ST/2016-07/DNVGL-ST-0111.pdf

[13] https://dpcapability.azurewebsites.net/

[14] L. Pivano, M. Poirier, P. Frederiksen, K. Eide, Ø. Smogeli, ‘Planning of drilling operations in extreme ocean currents: experience from time-domain simulations and full-scale validation on Maersk Venturer’, Dynamic Positioning Conference, Houston, 2016


https://dpcapability.azurewebsites.net/

https://rules.dnvgl.com/docs/pdf/DNVGL/ST/2016-07/DNVGL-ST-0111.pdf

2011 DP Conference Cover Page Format - Dynamic Positioning · Web viewAuthor Liz Stanfield / Richard Simpson Created Date 09/20/2019 04:24:00 Title 2011 DP Conference Cover Page Format

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