Modeling of Unmanned Underwater Vehicle with Rotating Thrusters for Offshore Rig Inspection PDF

Preview

Summary

Proceedings of the 1st International Conference on Unmanned Vehicle Systems (UVS), Muscat, Oman, 5-7 February, 2019 Modeling of Unmanned Underwater Vehicle with Rotating Thrusters for Offshore Rig Inspection Alex Bernard Khalid Al Maawali Rakesh Sharma Department of Well Engineering Department of We...

Description

Proceedings of the 1st International Conference on Unmanned Vehicle Systems (UVS), Muscat, Oman, 5-7 February, 2019

Modeling of Unmanned Underwater Vehicle with Rotating Thrusters for Offshore Rig Inspection Alex Bernard Department of Well Engineering International College of Engineering and Mangement Seeb,Sulatanate of Oman [email protected]

Khalid Al Maawali Department of Well Engineering International College of Engineering and Mangement,Seeb,Sulatanate of Oman [email protected].

Abstract— the offshore rig preservation and inspection are critical tasks conducted to accomplish the safety standards followed by the rig contractors and operators. The underwater vehicles can help the oil companies to inspect and keep the system safe for operations and maintenances. Controllability and maneuverability of the vehicles depends on various forces including hydrodynamic forces applied on them. This paper investigates the modeling of an Unmanned Underwater Vehicle (UUV) in virtual 3D platform and conducts analysis on horizontal and vertical rotating thrusters. It also highlights the challenges involved in balancing the thrusters against the forces during execution of safety inspections. The Computational Fluid Dynamics (CFD) and Finite Element Method (FEM) were carried out in propellers to confirm the effect of forces. The structure of the full model of the thrusters was analyzed with and without nozzles. The thrust force generated by horizontal and vertical thrusters was compared to identify the optimum performance. The roles of vehicle size, weight and operating depth in the design of UUV were also considered. It was observed that UUV equipped with camera and sensor can detect any kind of oil spillage and monitor the health of the underwater structure of the offshore rigs. Keywords—Unmanned Underwater Vehicle, Maneuverability and Computational Fluid Dynamics.

I. INTRODUCTION An offshore drilling rig is a facility used to drill oil and natural gas from underground reservoirs. The primary function of the drilling rig is to create the opening so oil or gas can be produced. The type of offshore facility depends on the distance from shore and the depth of the water. Some facilities are mobile and can be floated or moved to various locations on the field area, whereas others are more permanently anchored to the sea [1]. Platform may have several well heads and can be connected to many subsea wells that are often miles away from the platform. Another important difference in offshore drilling is the relative motion between a floating rig and the wellbore. The rig is subjected to surface conditions such as tidal action, wind and weather effects. The offshore facility must have to maintain a positive connection with the wellbore and compensate for all other relative motion [2]. Oil rig accidents can quickly spill thousands of barrels of oil. For instance, in 2010, an explosion rocked an oil rig of Deepwater Horizon and as a result oil gushed from a well on the ocean floor for nearly three months and reached shores all along the Gulf of Mexico [3]. There are several complex and various nonlinear forces acting on an

Rakesh Sharma Department of Well Engineering International College of Engineering and Mangement Seeb,Sulatanate of Oman [email protected]

underwater vehicle. The forces such as hydrodynamic drag force, damping forces, lift, gravity force, buoyancy forces, thrust forces and environmental parameters affect the performance of the UUV [4]. The offshore rig inspections play vital role in managing safety in rigs [5]. Remotely operated vehicles and autonomous underwater vehicles are currently used for operation and inspection purpose. The implementation of these tools has already allowed moving rigs from shallow to deep waters. The CFD and FEM simulations can help the Underwater Vehicle designers to build the vehicles for better performance and reduce the operational disturbances [6]. The objective of the present study was, therefore, to determine the stability and oscillation of the UUV when inspection is carried out under the sea level [7]. The selection of the geometrical shape and position of the components were also reported after considering many factors discussed in the results section. II. MATERIALS AND METHODS The structure of the full model of the UUV not only had to provide the information about the effectiveness of the solutions but also make basis for analysis of the operational capacity of the rotating thrusters of UUV. Stability of the UUV Figure 1 shows the equilibrium and tilted positions of UUV. When both the UUV and the fluid are at rest it follows that the forces acting on the submarine are the weight, W and the buoyancy force, FB ,both of which at in a vertical direction. The weight acts vertically through centre of mass CM and buoyancy force acts vertically through centre of Volume CV. If the UUV is in equilibrium then these forces must be equal [8]. The tilted orientation of the right hand side of UUV, when CM is below CV and here the tilt leads to a moment which corrects the tilt as shown in Figure 1(b).

(a)

978-1-5386-9368-1/19/$31.00 ©2019 IEEE Authorized licensed use limited to: University of Central Lancashire. Downloaded on November 29,2020 at 14:03:23 UTC from IEEE Xplore. Restrictions apply.

Proceedings of the 1st International Conference on Unmanned Vehicle Systems (UVS), Muscat, Oman, 5-7 February, 2019

(b) Fig.1. Unmanned Water Vehicle: a) In equilibrium and b) In tilted position For FEM Analysis Software used –SolidWorks Simulation Xpress Name of blade material: AISI 1035 Steel (SS) Model type:

Linear Elastic Isotropic

Default failure criterion: Max von Mises Stress Yield strength: 2.82685e+008 N/m2 Tensile strength: 5.85e+008 N/m2 III. MODELING OF UNMANNED UNDER WATER VECHICLE Due to the various uncertainties in the underwater environment and dynamic behavior, modeling and analysis is a challenging task. Underwater vehicle employed for leakage detection of oil and gas from the underwater pipe lines requires consistency and efficiency [9]. A. The UVV modeling The UUV design was modeled by parts to facilitate the construction process [10]. All the individual parts were assembled using SolidWorks Software to complete the modeling of the Vehicle. Design of the assembled UUV with parts is shown in figure 3. Geometric Parameters UUV- Length: 800mm, Height: 600mm, Width: 600mm Propeller - Diameter: 100 mm, number of blades: 4, hub diameter 20mm

Fig. 3. Assembled UUV model C. Control system Controlling the UUV is not easy, mainly due to unknown non –linear hydrodynamics and difficulty in accurate estimation of parameter uncertainties. Most UUV require a cable to transfer the mechanical loads, power and communications to and from the underwater vehicle [12]. The present works considered the effect of thrust force on the performance of propeller. IV. OVERVIEW OF THE ANALYSIS The UUV is having propellers and rely on these to conduct stabilization, maneuvering and movement [13]. Propeller –driven electrical thrusters were selected for present study. Fixed pitch propellers were used for both vertical and horizontal movement and thrust force controlled by propeller speed [14]. To calculate the thrust force analytically, it follows the equation (1). F = meVe-moVo + (pe-po) Ae

(1)

B. Parts  Chassis: The design of the chassis considered the assembling easiness and stability factors. The remaining parts of the UUV are fixed on the Chassis

Where me and mo are the mass flow rate at the exit and free stream of the propulsion device, Ve and VO are the velocity at exit and free stream region ,pe and po are the pressure at exit and free stream and Ae is the area of the exit .

 Control Unit: Consists of camera, spillage sensor and lighting unit and connected to platform through umbilical code system [11]. The control unit sense if spillage occurs and provide underground images.

The thruster with free propeller and with nozzle was selected for the CFD analysis. The horizontal and vertical propellers were placed in the virtual model and the effects were compared. The FEM analysis considered the push and pull effect of the propeller for analysis [15]. The propeller undergoes a push and pull effect because of the pressure difference between the two sides of the blade, i.e., the pushing effect on underside of the propeller and pulling effect on the top side [16]. This action occurs on all the propellers around the full circle of rotation as the motor rotates the propeller [17]. Consequently, the propeller is both pushing and being pulled through the water.

 Thrusters: The design consists of six thrusters, such as four units for vertical movement and two units for horizontal maneuverability. The propeller consists of four blades aligned with motor.  Float: Two floats are provided on the upper part of the UUV to manage the submerging and lifting functions. The stability of the unit depends on the float positions too.

Authorized licensed use limited to: University of Central Lancashire. Downloaded on November 29,2020 at 14:03:23 UTC from IEEE Xplore. Restrictions apply.

Proceedings of the 1st International Conference on Unmanned Vehicle Systems (UVS), Muscat, Oman, 5-7 February, 2019

V. CFD ANALYSIS As already mentioned in the model with respect to the CFD, four models of varying degrees of sophistication were built. The propeller was mounted in a duct which increases the static and dynamic efficacy of the thruster [18]. The velocity of the fluid entering the thruster changes the angle of attack of the propeller which in turn alter the force produced [19]. Boundary conditions applied for all CDF analysis are similar. Inlet velocity of sea water to the propeller was assumed as 2 m/s2 entering into the fluid domain. The depth was assumed as 30 meter and pressure as 407,704 Pa. The propeller speed assumed as 200 rpm.

Fig.6. Free propeller with vertical flow domain. The analysis was carried out to simulate outlet velocity and exit pressure. The results are shown in Figure 7. The results shows velocity and pressure shows an increasing trend in the vertical position.

A. Free propeller in horizonal position Free propeller modeling keeps the propeller as open type and not having any nozzle surrounding it. Domain of the free propeller model is shown in Figure 4

Fig.7.Flow simulation a) Velocity profile b) Pressure profile

(a) (b) Fig.4. Free propeller Model a) Part diagram b) Analysis domain. The CFD analysis was done to simulate outlet velocity and exit pressure. The corresponding results are shown in figure 5. The results shows that velocity and pressure are increasing at exit point.

C. Propeller with nozzle in Horizonatal position The propeller was provided with a nozzle on the surface and covers the propeller. The motor shaft was directly coupled to propeller hub. Domain of the propeller with nozzle model is shown in Figure 8.

(a) (b) Fig.8. Propeller with nozzle Model a) Part diagram b) Analysis domain.

(a) (b) Fig.5.Flow simulation a) Velocity profile b) Pressure profile

Here also the outlet velocity and exit pressure were considered for simulation .The results are shown in Figure 9.

B. Free propeller in vertical position The free propeller was kept in vertical position resembling with the vertical thrusters. The analysis was carried out following the same boundary conditions used in horizontal position. The free propeller vertical flow domain is shown in Figure 6. (a) (b) Fig.9.Flow simulation a) Velocity profile b) Pressure profile

Authorized licensed use limited to: University of Central Lancashire. Downloaded on November 29,2020 at 14:03:23 UTC from IEEE Xplore. Restrictions apply.

Proceedings of the 1st International Conference on Unmanned Vehicle Systems (UVS), Muscat, Oman, 5-7 February, 2019

D. Propeller with nozzle in Vertical position The propeller with nozzle was kept in vertical position similar with vertical thruster positions in UUV. The analysis followed the same boundary condition followed in horizontal position. The propeller with nozzle flow domain is shown in Figure 10.

Fig. 10. Propeller with nozzle in Vertical flow domain The analysis was carried out to simulate outlet velocity and exit pressure. The results are shown in Figure 11. The result shows that the velocity and pressure are increasing at exit point.

(a) (b) Fig.11.Flow simulation a) Velocity profile b) Pressure profile

A. Free propeller from push side The free propeller with push side has positive pressure effect on the blade face. The stress and displacement simulation after the loading is shown in Figure 12.

(a) (b) Fig.12. Simulation a) Stress profile b) Displacement profile B. Free propeller from pull side The free propeller with pull side has negative effect on the blade back. The stress and displacement simulation after the loading is shown in Figure 13.

(a) (b) Fig.13. Simulation a) Stress profile b) Displacement profile C. Propeller with nozzle from push side

VI. FEM ANALYSIS The reason to create the FEM model for propeller loaded with pressure imported from the CFD model was to analyze the stress and displacement behavior. The propeller in this discussion rotates downward, it pushes water down. At the same time, water must rush in behind the blade to fill the space left by the downward moving part. This results in a pressure difference between the two sides of the blade: a positive pressure or pushing effect on the underside and a negative pressure or pulling effect on the top side. Hence, the propeller is pushing and being pulled through the water. The FEM analyses were carried out for both push and pull cases in free propeller and in propeller with nozzle. Boundary conditions applied for push and pull analysis were similar. The blade selected was conventional or eared type same as the one used for CFD analysis. The pressure applied on the walls of the propeller blades are 407704 Pa. The inner hub was constrained and pressure was applied to the leading and trailing edge of the propeller blades. The material used was same for all analysis and properties are given below.

The propeller with nozzle from push side has positive pressure effect on the blade face. The stress and displacement simulation after the loading is shown in Figure 14.

(a) (b) Fig.14. Simulation a) Stress profile b) Displacement profile D. Propeller with nozzle from pull side The propeller with push side has negative effect on the blade back. The stress and displacement simulation after the loading is shown in Figure 15.

Authorized licensed use limited to: University of Central Lancashire. Downloaded on November 29,2020 at 14:03:23 UTC from IEEE Xplore. Restrictions apply.

Proceedings of the 1st International Conference on Unmanned Vehicle Systems (UVS), Muscat, Oman, 5-7 February, 2019

pressure from the propellers are increasing and thereby increasing the thrust force. VIII .CONCLUSIONS

(a) (b) Fig.15. Simulation a) Stress profile b) Displacement profile VII. ANALYSIS OF SOLUTIONS The main purpose of the construction of CFD model and FEM was to gain knowledge on simulation behavior with theoretical results. The promising results of the analysis gave rise to the application of this method for modeling the phenomenon of UUV under varying parameters. The following section interprets the results obtained from simulations. The CFD results of the velocity profile of free propeller in horizontal and vertical position show an increase in outlet velocity and exit pressure. The results confirm with the theoretical values of thrust force under similar working environment shown in equation (1). The increase in pressure and velocity would lead to an increase in thrust force. The results from propeller with nozzle show marginally high values of pressure both in horizontal and vertical positions than free propeller. But the velocity was not increasing comparatively much in the propeller with nozzle type. So the CFD models infer that propeller with nozzle has high exist pressure than free propeller in horizontal and vertical positions. The exit velocity of propeller with nozzle type is comparatively low with horizontal type. It is because the weight of the fluid above the propeller might influence the velocity. It infers that providing more thrusters in vertical position for controlling the UUV would increase the thrust force thereby increasing the speed of reach. The FEM analysis of free propeller and propeller with nozzle were compared for stress and displacements. In the free propeller both push and pull side shows that stress accumulates at blade root. The modeling shows that proper blade thickness is important in propeller selection. The thickness near to the blade hub must be high and low as possible to the blade tip. The water pressure should be accommodated and infers that it can avoid stress concentration too. The results from simulations of displacement indicate that it is more in blade tip than at root. If the thickness is less at blade tip, less power is required from thruster to rotate it. The FEM stress analysis of propeller with nozzle shows that stress values are less at blade root when compared with the free propeller. This model also indicated that that chance of failure is less even though the pressure increases when UUV moves deeper. From the simulations it is better to select the propeller with nozzle as thrusters for better performance. If the pressure difference is not created the angle of attack will be zero and thrust will lead to zero. The pressure profiles generated for the thruster’s show that exit

This paper presents the modelling of unmanned water vehicle via CFD and FEM workbenches. It was found that propeller made from AISI 1035 Steel (SS) can safely transfer the dynamic load generated during UUV operation. It is also evident that a small deformation of the material should not affect efficiency of the propeller and change its hydrodynamic parameters. The velocity and pressure profiles from CFD analysis has proved the thrust force generated depends on these parameters. The analysis also infers that pressure at pull and push side of the propeller affects the thrust force of the UUV. The number of thrusters in vertical position should be more in the present model of the UUV when compared with that of the horizontal position. It was also evident from the result that the major forces influencing the UUV, which act along vertical position and movement to the depth of the sea level, require higher thrust force. The thruster in horizontal position maintains the UUV while tilting. These factors greatly influence the prototyping of the UUV in future experimental system testing. A conclusion from the modeling performed on UUV proposes to have more analysis to be carried out to decide the hydrodynamic behavior of the unit. The presently obtained results are satisfactory considering the further stages of the project which will include the full scale fabrication and testing of the unit in real environment. ACKNOWLEDGMENT Special appreciation and gratitude to International College of Engineering and Management for providing financial as well as moral support to complete this project successfully. The authors are thankful to Dr. Girma Chala for his valuable suggestions during the work. REFERENCES [1] [2] [3] [4]

[5] [6] [7] [8] [9]

[10]

Julia Ruggeri, “Rotary Drilling series,” 2nd ed., unit 5. Petroleum Extension Service, 2008, pp.46-51. Hugh McCrae, “Marine Riser Systems and subsea Blowout preventers.” Rotary drilling, Petroleum Extension service, 2003, pp 6875. Christine.A.Caputo, “Oil Spills,” Capstone press, 2011, pp.4-14. F. A. Aziz, M.S.M Aras, M.Z.A Rashid, M.N Othman, “Problem identification for underwater remotely operated vehicle (ROV): A case study,” International Symposium...