Design and testing of underwater thruster for SHRIMP ROV-ITB
Muljowidodo K.1, SaptoAdiN.2, Nico Prayogo2, and Agus Budiyono3*
1Mechanical Engineering Program, Mechanical Engineering and Aeronautics Faculty, InstitutTeknologi Bandung (ITB). Ganesha 10, Bandung, West Java, Indonesia
[E-mail: muljo@bdg.centrin.net.id]
2Center for Unmanned System Studies (CentrUMS), InstitutTeknologi Bandung (ITB), Ganesha 10, Bandung, West Java, Indonesia [E-mail:sapto131@students.itb.ac.id, prayogo_nico@yahoo.co.id]
3Department of Aerospace Information, Smart Robot Center, Konkuk University, 1 Hwayang-Dong, Seoul 143-701, Korea [E-mail: budiyono@alum.mit.edu]
Received 26 July 2009, revised 11 September 2009
Shrimp ROV is the most recent underwater vehicle that has been developed at Center for Unmanned System Studies (CentrUMS)-ITB. This type of vehicle is typically designed for environmental or scientific surveillance mission as well as for Small Observation ROV with military functions. One of them is Minesweeper ROV. The present study consists the thruster design of ITB SHRIMP-ROV as its main propulsion device. In the thruster design, we used and applied Finite Element Analysis for calculating structural strength and Computational Fluid Dynamics (CFD) for identification of fluid characteristic on thruster. All the testing at this stage is performed in the laboratory.
[Keywords: ROV, Surveillance, Thruster, Mine sweeper, Finite Element Analysis, Computational Fluid Dynamics]
Introduction
The needs for main component of underwater vehicle have been growing in line with increasing demand for the underwater vehicle for various missions. Thruster is one of the most critical underwater technology that defines vehicle overall performance. Thruster is commonly used as underwater vehicle’s main propulsion device. It enables the vehicle to perform desired maneuver in horizontal (forward-backward maneuver) or vertical axis (up and down movement). Despite its importance, only a few papers on this subject have been published in the literature such as Refs. [1] and [2]. Present study comprises the design of the thruster based on technical requirement specified for Shrimp underwater vehicle. The efforts include all phases of design, manufacturing and testing of the thruster as propulsive component of the vehicle.
There are six major steps for design of this thruster.
They are enumerated as follows:
1. Determination of Technical requirement, 3D CAD Drawing, 2. CFD Analysis for performance prediction, 3. Finite Element Analysis for construction strength, 4. Detail drawing and manufacture, 5. Testing.
The best way for determination of technical requirement is by considering the dynamics characteristic of the vehicle, i.e. the capability of the vehicle to perform some desired maneuver in six degrees of freedom. After determining the technical requirement, we can start working on 3D CAD Drawing for candidate of propulsion device.
Specification of SHRIMP ROV – ITB, detail component shown in Fig. 1 and Fig. 2 are ROV Surveillance Test Bed, Dimension : 600mm × 610mm
×740mm, Weight on air : 30 Kg, Max operating depth : 100 msw.
The following information has been gathered from the results of Computational Fluid Dynamics before for Shrimp ROV:
For each mode of movement (3 knot forward shown on Fig. 3 and 1 knot backward shown on Fig. 4) we have used different types and con- figurations of thrusters:
3 knot forward; For forward movement we have used two thruster configurations. The thrust requirement is therefore around 49.62 divided by two for each thruster. Thus, each thruster minimum requirement 49.62/2 = 24.81 N.
1 knot downward; Downward movement just required one thruster. So the minimum thrust that must produced by this thruster is approximately 35.4 N.
——————
Author for correspondence
Materials and Methods
The propeller and nozzle type that has been used for this thruster design was the modified Wagenigen standard series ducted propeller4. There are Ka series for propeller and 19A series for the Nozzle.
The geometr of Ka Series Propeller
The propellers of the Ka series are operating in an accelerating duct and have a wide blade tip.
Systematic series are available of four nozzles, designated Ka3-65, Ka4-55, Ka4-70, and Ka5-75.
One of the important parameter of the duct isthe length ratio, expressed Ld/D, where Ld is the length of the duct and D is the inner diameter the duct at the location of the propeller. The geometry of an arbitrary duct section is shown in Fig.5. Another important parameter is the contraction ratio, the ratio between the inflow area and the exit area. This can also expresses by the angle αd of the duct section. The third important parameter is the geometry of the duct section, which is characterized by its maximum thickness and maximum camber. The section of a duct is adapted to its application, although Oosterveld tested many duct with NACA section5.
A general purpose duct for application at heavy screw loads is nozzle 19A. This is a nozzle with a cylindrical inner side. The outside of the nozzle is straight and the trailing edge is relatively thick. The nozzle is practical from a view point of construction due to its straight parts and it is strong due to its thick tail. The profile of nozzle 19A is given in Fig. 6. The length ratio of nozzle 19A is 0.5. The geometry of this nozzle is given in Table 1. The percentage of the nozzle length L. the Straight part in the outer contour of the nozzle has been indicated with ‘S’. Nozzle 22 and 24 have a larger length ratio than nozzle 19A.
This may be attractive for cases where a very large bollard pull is required, such as for tugs. The length ratio of nozzle 22 and 24 is 0.8 and 1.0, respectively.
The backing characteristics of these nozzles are rather
Figure 1—Detail main component of SHRIMP ROV-ITB
Figure 2 — Dimension of SHRIMP ROV- ITB
Figure 3 — 3 knot forward CFD results of SHRIMP ROV
Figure 4 — 1 knot downward CFD results of SHRIMP ROV Figure 5 — The geometry of duct section
poor. The geometry of nozzle 22 and 24 can be found from Table 1 with the proper length diameter ratio.
When bollard pull is of the almost importance not only in ahead but also is astern direction, a more symmetrical nozzle has to be used. The nozzle designed for this condition is nozzle 37. Its profile is given in Fig. 7. This Nozzle has a length diameter ratio of 0.5. The geometrical data are given in Table 2. The propeller used in the nozzles has a wide blade tip. The contour is symmetrical from 0.76 R to tip. From 0.6R to the hub the leading edge is
shifted a few percent in forward direction. A sketch of the propeller geometry is given in Fig. 8
Similarly as with the B-series the contour can expressed as:
Z xDxEAR r
r K
c ( )
)
( =
… (1) The factor Kr is given in Table 3, together with the skew, the skew is given non-dimensionally as skew/cr.
The geometry of the blade sections of the Ka- series has been defined similarly as the geometry of the B-series, that is with reference to the pitch line.
through the pressure side of the blade (see Fig.9).
Figure 7 — Geometry of nozzle 37.
Table 2 — Ordinates of nozzle 37.
x/L y inner/L y outer/L
0 18.25 -
1.25 14.66 20.72
2.5 12.8 21.07
5 10.87 20.8
7.5 8 -
10 6.34 -
15 3.87 -
20 2.17 -
25 1.1 -
30 0.48 -
40 0 -
50 0 -
60 0 -
70 0.29 -
80 0.82 -
90 1.45 -
95 1.86 -
100 2.36 6.36
Figure 6 — Geometry of nozzle 19A Table 1 — Coordinate of 19A, 22 and 24 Nozzle
x/L y inner/L y outer/L
0 18.25 -
1.25 14.66 20.72
2.5 12.8 21.07
5 10.87 20.8
7.5 8 s
10 6.34 s
15 3.87 s
20 2.17 s
25 1.1 s
30 0.48 s
40 0 s
50 0 s
60 0 s
70 0.29 s
80 0.82 s
90 1.45 s
95 1.86 s
100 2.36 6.36
The contour is again given in coordinates relative to the location of maximum thickness, where the maximum thickness is at 0% . The blade section are given in Table 3 and Table 4.
The distance to the reference line is given as a percentage of the maximum thickness tmax. The section geometry of the Ka series depends on the maximum thickness tmax and on the position of the maximum thickness Xtmax/cr. Table 5 consists the maximum thickness and its position. The maximum thickness is made non dimensional with the propeller diameter, the position of maximum thickness is made non dimensional with the sectional chord-length.
Similar with the B series propeller, the maximum chamber of the Ka series is half the maximum thickness from 0.6 R to the tip. At inner radii the maximum chamber is reduced due to the rise of the pressure side of the profile and the maximum chamber can be written by :
max max
max t2 K xt
f − − f … (2)
the value of Kf is given in Table 6.
The Ka series propeller has no rake. The hub diameter of the Ka series propeller is 1/6 of the diameter.
Approach
To know the propeller and nozzle performance results of the modification, we’ve used CFD analysis software (Fluent 6,2). The above will enable to analysis results we could prediction of flow condition, pressure distribution of the propeller blade, thrust and moment requirement to rotate the propeller itself. In order to catch the swirling phenomena and tip vortex, we must choose the correct turbulence model for this analysis.
The RNG k-e model on Fluent 6.2 had used to catch the turbulence flow phenomena6. Turbulence flow could be detected by fluctuation flow field. With this fluctuation the value of momentum, energy and species concentration are also in fluctuation state.
The RNG k-e model was derived using a rigorous statistical technique (called renormalization group theory)9. It is similar in form to the standard k-e model, but includes the following refinements:
The RNG model has an additional term in its equation that significantly improves the accuracy for rapidly strained flows.
The effect of swirl on turbulence is included in the RNG model, enhancing accuracy for swirling flows.
The RNG theory provides an analytical formula for turbulent Prandtl numbers, while the standard k-e model uses user-specified, constant values.
While the standard k-e model is a high-Reynolds- number model, the RNG theory provides an analytically-derived differential formula for effective viscosity that accounts for low-Reynolds-number effects. Effective use of this feature does, however,
Figure 8 — Blade plan form of the Ka- series
Table 3 — Suction side section geometry from position of maximum thickness to the leading edge.
r/R 20% 40% 60% 80% 90%
0.2 97.92 90.83 77.19 55 38.75
0.3 97.63 90.06 75.62 53.02 37.87
0.4 97.22 88.89 73.61 50 34.72
0.5 96.77 87.1 70.46 45.84 30.22 0.6 96.47 85.89 68.26 43.58 28.59 0.7 96.58 86.33 69.24 45.31 30.79 0.8 96.76 87.04 70.84 48.16 34.39 0.9 97.17 88.09 72.94 51.75 38.87
1 97 88 73 52 39.25
Figure 9 — Definition of blade section of Ka series.
Table 4 — pressure side section geometry from position of maximum thickness to the trailing edge.
r/R T.E 80% 60% 40% 20%
0.2 20.21 7.29 1.77 0.1 0
0.3 13.85 4.62 1.07 0 0
0.4 9.17 2.36 0.56 0 0
0.5 6.62 0.68 0.17 0 0
depend on an appropriate treatment of the near-wall region. With this preliminary design, we can continues with the detail of thruster itself.
These features make the RNG k-e model more accurate and reliable for a wider class of flows than the standard k-e model.
From graphical observation on Fluent CFD analysis we have:
• Static Pressure distribution on pressure side and suction side of propeller. Pressure increased on pressure side and decreasing pressure on suction side, these results can be seen on the contour graphics. The decreasing pressure at propeller wall still out of cavitations tendency. The minimum pressure at operating depth still higher if compare with water vapor pressure at 27°C Celsius around 1700 Pascal.
• Fluid flow pattern around propeller and nozzle, Pressure distribution and velocity contour on propeller and nozzle include with influenced environment.
Results & Discussion
The thruster which has been designed has the follow parameters:
• Propeller type that have used was modified Wagenigen Ka series propeller and 19A nozzle type;
•Propeller diameter : 161 mm; • Hub Diameter: 50 mm; • Blade Number :5; • pitch/diameter = 0,6; • Nozzle inner diameter : 163 mm; • Outer Nozzle Diameter: 220 mm; • Nozzle Length: 82 mm; • Propeller Speed= 1300 rpm; • Propeller Motor Power= 400 watt
The thruster performance one from design results and further analyzed by computational fluid dynamics Software. 3D design results until contour of static pressure on pressure side suction side of propeller’s blades shown on Fig. 10, Fig. 11, and Fig. 12. The propeller rotation varied at several level of speed in order to observe produced thrust. The results of this testing is shown in Table 7. The thruster performance results at speed 1 and 3 knot (Table 8), shows that’s propeller design have met of SHRIMP ROV maneuver thrust requirement. After the analysis process, we need to validate the results by several testing as follows: 1. Hydrostatic pressure testing resistance, 2. Magnetic coupling Torque testing, 3. Static Bollard Pull Testing (the illustration of testing installation shown on Fig. 13).
There are 3 steps for these testing procedures, viz:
• Thruster testing without propeller (out of water), to check motor and control with just coupling load (for illustration see Fig. 14), • Thruster testing with propeller (out of water), to check the vibration and mechanical load ( friction, misalignment , etc),for illustration see Fig. 15, • Thruster testing full throttle (underwater), to check thrust, power, and speed maximum (for illustration see Fig. 16).
With all the testing, we obtained power requirement correlation at each rotation speed on three different conditions above. The results are shown on Table 9, Table 10 and Table 11 respectively. From the testing results, we can observe the comparison between testing and simulation results. The detail of comparison results are shown on Table 12.
Table 5 — Maximum thickness and position of maximum thickness.
r/R tmax/D Xtmax/cr
0.2 0.004 0.35
0.3 0.0352 0.398
0.4 0.03 0.46
0.5 0.0245 0.491
0.6 0.019 0.5
0.7 0.0138 0.5
0.8 0.0092 0.5
0.9 0.0061 0.5
1 0.005 0.5
Table 6— Correction for maximum chamber
r/R Kf
0.2 0.287
0.3 0.183
0.4 0.115
0.5 0.072 Figure 10—Hruster 3d design results.
Conclusion
The paper presents the design and testing phase of the underwater thruster for the ROV Shrimp ROV developed at Institut Teknologi Bandung (ITB). Both
Figure 11 — Contour pressure on pressure side thruster.
Figure 12 — Contour pressure on Suction side thruster.
Table 7— Variation speed, thrust and Torque of thruster.
Rotation (rpm) Thrust (N) Torque (Nm)
1300 4.34 0.1047
600 14.45 0.382
900 37.5 0.817
1300 74.4 1.56
Table 8 — Variation speed, rotation, thrust and torque of analysis results.
Advanced Speed (knot)
Rotation speed (rpm)
Thrust (N) Torque (Nm)
1 1300 67.19 1.25
3 1300 22.93 0.97
Figure 13— Bollard testing construction and setup schematics.
Figure 14 — Thruster testing out of water.
mechanical and electrical design aspects are properly considered. The electrical design considerations are expressed in terms of the specifications of the electrical motor (power, operating speed and torque).
An appropriate electrical motor can then be identified from this requirement. The thruster design has been conducted by an intensive use of Computational Fluid Dynamic (CFD) simulation. The differences between CFD and testing results at bollard Pull conditions fall in the range of 0 – 6.25% of error. The results show that thruster design methods with CFD modeling is effective and the approach can be used for more general thruster design.
Acknowledgements
The work was supported by DIKTI, LPPM, and Automation and Robotics Laboratory. The authors would like to thank to the technical team involved in through the design process, manufacturing and testing of the entire thruster. The corresponding author was supported by the MKE (Ministry of Knowledge Economy), Korea, under the ITRC (Information Tecnology Research Centre) support program supervised by IITA (Insititute for Information Technology Advancement) (IITA-20096-1090-0902- 0026).
Table 10— Testing Results of Thruster with propeller (out of water)
Rotation Speed (rpm) Power (Watt)
300 54.288
600 105.876
900 139.986
1300 159.933
Table 11— Testing Results of Thruster complete (underwater).
Rotation Speed (rpm) Power (Watt) Thrust (N)
300 60.48 5
600 132.762 17.5
900 239.44 40
1300 393.84 75
Table 12— Testing comparison results between CFD analysis and The real Testing.
Rotation Speed (rpm)
Power (Watt)
Thrust from Testing (N)
Thrust from CFD simulation
(N)
Error (%)
300 60.48 4.5 4.34 3.555556
600 132.762 15 14.45 3.666667
900 293.44 40 37.5 6.25
1300 393.84 75 74.4 0.8
Figure 15—Thruster testing without propeller
Figure 16—Thruster complete underwater testing.
Table 9—Testing results of Thruster without propeller (out of water)
Rotation Speed (rpm) Power (Watt)
300 46.398
600 95.17
900 124.64
1300 138.92
References
1 Abu Sharkh S., Harris M. R., Crowder R. M., Chappell P. H.
& Stoll R. L. & Sykulski, J. K., Design considerations for electric drives for the thrusters of unmanned underwater vehicles, 6th European Conference on peer Electronics and Applications, Sevilla.
2 Changzhi Sun, Zhifei Chen & Hongyan Shi, Optimal design of thruster motor for underwater robot, Fifth World Congress on Intelligent Control and Automation, 2004.
WCICA 2004.
3 Muljowidodo K., Sapto Adi N, Agus Budiyono & Nico Prayogo, Design of SHRIMP ROV for Surveillance and Mine
Sweeper, The 2nd International Conference on Underwater System Technology: Theory and Application, USYS08, Bali, Indonesia, November 4-5, 2008
4 Kuiper G, The Wagenigen propeller series, MARIN Publication 92-001, May, 1992.
5 Muljowidodo K, Sapto Adi N., Said D. Jennie & Agus Budiyono, Design, Development and Testing Underwater Vehicle: ITB Experience, In Proceeding of International Conference On Underwater System Technology: Theory and Applications, Penang Malaysia,2006.
6 Fluent Incorporated, Fluent 5 and Gambit User Guide, Lebanon, 1998.
