Journal of Marine Science, Engineering & Technology Webpage: https://jmset.rina-imarest-mjbsc.org JMSET 2018, Vol. 1 DEVELOPMENT OF REMOTELY OPERATED VEHICLE UNDERWATER ROBOT Aminuddin, M. H., Md Zain, M. Z., Nor, N. S. M., Mastura, A. W. 1 Department of Applied Mechanics, School of Mechanical Engineering, Faculty of Engineering, Universiti Teknologi Malaysia, 81310 Skudai, Johor Bahru. ABSTRACT Nowadays, Remotely Operated Vehicle (ROV) robot has been widely used in industry especially in oil and gas sector. It has been used to do a task inside the sea water environment besides has a capability to perform a deep sea rescue operation and recover objects from the ocean floor. Development on the design of the ROV underwater robot is done to increase the performance of the robot in the ocean. This project will discuss the steps from designing the ROV until its prototype construction. There are several steps need to be followed in order to produce efficient mechanical structure or design of the ROV underwater robot. In this project it consist three preliminary designs and one final design. The final design is produced through evaluation process of three preliminary designs of ROV. Computational fluid dynamic (CFD) software is used in order to analyse and identify the drag coefficient of the ROV underwater robot structure. Other than that, other software and calculation is used to determine the behaviour of the robot inside the water. This thesis also will provide the overview of the process in designing, constructing and testing the ROV with respect to mechanical part only. The main material used for this ROV is Aluminium square hollow and Acrylonitrile butadiene styrene (ABS). Entire joint and holder used in this ROV is custom made in order to maintain the originality of the ROV design. All the steps are carefully conducted in order to design and construct an effective structure for underwater robot in term of its drag coefficient and stability performance. Keywords : Acrylonitrile butadiene stryrene (ABS), Aluminium hollow bar, Ocean. 1.0 INTRODUCTION Nowadays, it is common for remotely operated vehicle or ROV are used to extract images from the sea and solve environmental problems such as removing the waste that can cause water pollution. A tether is used as signal transmitting between the operator and robot since radio signal cannot be used to any depth of water greater than 1m. In recent years, ROV become popular due to replacement human role in work at dangerous underwater condition for a specific task. The Remotely Operated Vehicles (ROVs) received increasing attention because of its significant impact in several underwater operations. Examples are in monitoring and maintenance of off shore structure or pipeline or the exploration of the sea bottom. Skilled human operator is needed to operate, control and in charge of command vehicle; a failure detection strategy will help in human decision making. However, ROV system will not completely replace divers in the near future due to the weaknesses and lack of the sensory feedback needed to complete a task. But the ROV, in many cases, *Corresponding author: zarhamdy@utm.my 9
can replace the putting a human in dangerous condition or environment. Other than that, using the ROV also can simplify the human work. Human only needed to searching and monitoring the ROV thus require less effort as well as less risk for human when using the ROV [1-7]. 2.0 PROJECT METHODOLOGY There are few steps in order to achieve the objective that is to build the efficient structure of the ROV underwater robot. The efficient structure means the robot has the ability to move smoothly and also high stability when it going into the sea water. Other than that, it also must have enough strength to experience the sea water pressure at the required depth. In this case, material selection is important aspect to ensure the frame do not deform plastically when it performs in the required depth due to the high pressure inside the sea water. Next step is to understand the function of every compulsory part in the ROV underwater robot. The knowledge on function of every compulsory part will guide to the effective usage on every part. Besides, studies about previous design is also important because it can avoid from doing the same mistakes or weaknesses that has be made on previous design. For example, the usage of welding and rivet as a joining part will make the robot is fixed and cannot be adjustable. Besides that, it can make the robot became difficult to undergo maintenance process. This mistakes had been applied on robot ROV RECFRS when it entering the ROV competition. Research background on ROV is studied in detail after the analysis on design weaknesses and strength is completed. The purpose for this step is to determine the components that are needed in the ROV. ROV is used in the water so that there are several equipment needed to make sure our robot stable when it operates in order to complete the task. This step will show the importance of every part needed in the ROV mechanical design. This is the step where all the data or knowledge from previous step is needed to apply it into the design. This step is called design process. This step required SolidWork software. This software is used as a 3D-drawing tool to draw the ROV design. In this stage, team member is required to give any idea about the design that compatible to do the task given. In design process also require other software to check the drag force occur to the robot during the movement in the water despite to check the stability of the robot during movement. The software is called ANSYS 16.0. This software is the computational fluid dynamic software and used to check the behaviour of our robot in the water theoretically. In order to produce accurate data, there are several tests that are conducted to get the correct parameter. The tests are grid independent test, solver test and turbulence model test. Last step is the construction of the ROV. This step required the skill of construction of team member. Team work among team member also important to make sure the prototype design construction follow the Gantt Chart. In this stage also it is critical where problem will appear. All the technical knowledge and experience is needed to solve the problem during prototype design construction of ROV. After the construction process, there are several tests are conducted to make sure the efficiency of the robot in term f stability and maneuvering system of the robot. The main purpose of conducting the tests is to ensure some development on ROV underwater robot has been made to achieve the objective of this study. 3.0 DEVELOPMENT OF ROV In this section, it will explain the steps before the construction of the ROV underwater robot. There are a few process involved in this section that are design specification, ROV s final design and analysis of the design. The final design produced based on three preliminary designs evaluation. Entire analysis is used to check the behaviour of the ROV in the water. 3.1 Design specification There are few important aspects need to be in a ROV. The specifications of the ROV were listed before proceed to the design process and construction of the ROV. The specification is based on the design requirement and it is different compared to standard industry s ROV due to money and time 10
constraint to build the ROV. Developments of the ROV also need to be included in the design specification. The specification of the ROV has been listed below: 1. Maximum operating depth must be 30m 2. The weight of the ROV must be less than 30kg 3. Length of tether must be at more than 30m 4. Electrical tank must be in the robot. 5. The part of the robot must be easily attached and detached 6. Shape of the robot must be hydrodynamic shape 3.2 Final Design concept Final design is chosen based on evaluation on three preliminary designs. In final design, it can be divided into three four structures: Frame, holder, electrical tank and manipulator arm. All of the materials were used without further purification. 3.2.1 Frame Design Figure 1 shows the frame of the robot. Frame is used as a base to install all the components or parts of the robot. The body frame of our ROV was built using Aluminium hollow bar. The aluminium hollow bar was used to make sure our ROV has the ability to float and sink easily. The dimension of Aluminium hollow bar used in the frame is 30 cm x 40 cm. All the joint and connection of the frame use the custom made joint that made from 3D print technique. Joint made up from 3D print technique to make sure our joint easy to re-changeable and replaceable. This because almost failure is occurs at the joint of the robot. 3.2.2 Customize joint and holder Figure 1: Final design frame Figure 2 shows several joint and holder that had been used in the ROV. All the joint and holder were custom made to maintain the originality of the ROV design. This will make the ROV different compared to other ROVs. Joint and holder used were made from ABS material. 3D printer was used to produce all the parts that use ABS material. The most important mechanical properties of ABS are impact resistance and the toughness. This will make this material suitable to be used as a joint and holder of the ROV. Other than that, ABS also has a strength, flexibility and machinability that make it a preferred plastic for ROV application. 11
Figure 2: The customize holder at ROV. 3.2.3 Electrical tank Figure 3 is the container that acts as electrical tank of the ROV underwater robot. All the electric circuit that cannot be exposed to the water is placed at one aluminum container with the dimension 30 cm x 40 cm. In this container, there were several holes used for the wire to give the signal to motor and sensor. The electrical tank was closed with Perspex plate. Between Perspex plate and the container there was rubber to seal the gap between the Perspex plate and the aluminum container to prevent the water from leaking. All the electronic par including lighting, power, LAN, motor and the signal cables are installed within a PVC cylinder. Epoxy was used to seal the PVC fitting wires together. 3.2.4 Customize joint and holder Figure 3: The electrical tank Figure 4 shows the manipulator arm design at the ROV. Another feature that ROVs should have is the manipulators. Manipulators are mechanical arms that are able to perform various jobs underwater. Because the underwater environment is not suitable and very dangerous to humans, using remotely manipulated mechanical arms is a natural way to perform subsea work. The main objective behind creating the ROV is so it would complete the tasks given by interacting with some objects inside the pool such as pick up and handle various objects that need to be moved while competing. The actuator chosen for the manipulators was a pneumatic cylinder. Pneumatic cylinder was chosen due to its advantage in reducing the complexity of the manipulator design, as well as simpler electronic circuit to be used for controlling it. This manipulator was positioned on the lower front of the ROV in order to attach a flange, install the cap over the flange and insert the cable connector into the port on the power and communication hub. By putting some rubbers at the hand grip, the ability to grip can be improved. 12
Figure 4: Manipulator arm 3.3 Design Analysis After completing the design process, the design was analysed using SolidWork simulation and Computational Fluid Dynamic software. Other than that, some calculations also need to be conducted to make sure the design fulfil all design requirements. The analysis was needed to ensure effective and workable design after construction process and this will prevent from built the design that has not fulfilled the design requirements. In this section, SolidWork simulation and Computational Fluid Dynamic software have been used to analyse the behaviour of the robot inside the water. Calculation on maximum depth which the robot can withstand also was calculated to make sure the design requirement had been fulfilled. 3.3.1 Solidwork Simulation The objective of Solidwork simulation is to determine the behaviour of the frame in the water with 30m-depth. Solidwork Simulation is used to make sure the frame of the robot can withstand the high pressure in 30m depth in the water. The change the depth will increase the pressure exerted at the frame. Frame is the critical part in the 30m-depth due to high pressure of water exerted most is at the frame. Other than that, frame also is the place where all the parts is placed and it must be strong to stand in the depth and suitable to hold the part. The detail parameter used in this simulation is shown at table below. Table 1: Parameter of Solidwork analysis Material of the parts Aluminium 6061 alloy Acrylonitrile butadiene styrene (ABS) Connection Global Contact (-Bonded) Fixture Fixed on the leg of the robot External Load Pressure on the frame : 402879 Pa Force at electrical tank holder : 150N Gravity with 9.81 m/s^2 Mesh detail 13
3.3.2 Solidwork Result Analysis Figure 5 shows the effect of pressure inside the water of 30m depth. In this figure, it shows that there is no critical part experience the load inside the sea water. The most critical load exerted at the frame is 2.134 10 7 Pa which is lower compared to modulus elasticity of the ABS and aluminium 6061alloy. The safety factor of ABS due to the load or pressure at 30m depth can be calculated as below: From the calculation, it shows that the ABS and aluminium alloy material used at the frame is suitable to use and safe to withstand high pressure inside the sea water. It shows also there is no plastic deformation of the ABS material when it exerted the pressure at the depth of 30m. Figure 5: The result analysis on SolidWork software 3.3.3 Computational Fluid Dynamic Simulation The objective of this study is to measure the drag forces on underwater robot when changing the motion speed in the horizontal direction at a constant wave speed (5 knot) at 30m depth. In this problem, the enclosure was used to limit the observation area of the model. The enclosure was used to define the inlet of the outlet of the problem. The type of enclosure used in this problem was a rectangular shape and its inlet and outlet were placed at the front and back of the model. Inlet speed used to solve the problem is 5 knot with the pressure 402879 Pa. The speed of the inlet is referring to the ocean wave speed and the pressure is referring the pressure of the sea at the 30m depth. The reference line use is between the inlet and the outlet. Reference line is chosen to show the reaction of the water flow toward the ROV underwater robot. The model used in this analysis was a simplified model from the actual model to reduce the computational time for the analysis. The final parameters were obtained after conducting several tests: Grid Independent test, Solver test and Turbulence model test. 14
Table 2: Parameter for CFD analysis Grid size 0.015m Pressure-velocity coupling SIMPLE Pressure Second order upwind Momentum Second order upwind Turbulence model K-Epsilon 3.3.4 Computational Fluid Dynamic Result analysis The Ansys Fluent software is used to find the drag coefficient exerted at the design body of the ROV. There are two velocities used in this test which are when the robot in stationary and when robot is move (0.5m/s). The drag coefficient of the ROV underwater robot design is 0.0813.The data shows that the drag coefficient remains constant although the speed is changing. The drag coefficient is depending on the shape of the structure of the ROV underwater robot. Next step is to change the drag coefficient to drag force by using drag equation. Drag equation is a formula used to calculate the force of drag experienced by design body due to the movement through a fully enclosing fluid. Drag force was calculated based on drag coefficient produced all the data. In order to validate the result, journal with title Verification of CFD analysis method for predicting the drag force and thrust power of an underwater disk robot that have been done by Tae-Hwan Joung et al. [3]. In this journal, it shows that when speed increasing, the drag forces exerted at the ROV also will increase. It is similar with the data produced using CFD analysis. Table 3 shows the drag force produced when the robot in stationary and in motion. Table 3: Result of CFD analysis Design condition Drag force (N) During robot in Stationary ( 0 m/s ) 23.29 During robot move ( 0.5 m/s) 33.24 3.3.5 Buoyancy of the robot analysis The objective is to identify the mass need to be placed at the robot so that the robot can submerge in the water. One of the important aspects is the buoyancy of the ROV underwater robot. Since it needs to float and sink at the water at the same time, the buoyancy is needed to make sure the robot can float using a minimum amount of thrust. Too heavy will make the robot cannot float on the surface while if it too light, it will make the robot difficult to be submerged in the water. So calculation is needed to make sure the robot was not too heavy and not too light so that the robot can float and submerged easily in the water. In the ROV, air is trapped in the electrical tank that gives the ability for robot to float. Calculation is needed to make sure the robot can submerge by counter back effect of air in the tank by adding the mass on the robot [6-7]. 15
(Sea water density) The weight need to be placed at the robot including the frame weight must be more than 8.21 kg for robot to submerge in the water. Too much buoyancy force exerted in the robot also will cause difficulty for robot to submerge. 4.0 DISCUSSION This is the section to discuss all the result taken before and after the construction of the robot. Every decision is made to make sure the robot can perform during operation under the water. The underwater test for performance evaluation for the ROV is conducted in UTM marine laboratory s towing tank. The test is conducted to ensure the robot has high stability to perform the task and can move smoothly inside the water. 4.1 Construction of ROV Underwater Robot There are many criteria need to be considered during choosing the suitable material for ROV underwater robot. The consideration taken in chooses the materials are the corrosion resistance, weight, strength to high pressure inside the water and oxidation resistance. So that, some analysis of the material is taken and Aluminium 6061 alloy hollow bar and acrylonitrile butadiene styrene (ABS) is chosen as a main material for ROV underwater robot. These materials are chosen due to the strength of the material that can withstand with the high pressure besides has the good corrosion resistance. Hollow bar is chosen as the shape for aluminium alloy due to the light weight of the material and easy for machining process. The pneumatic system was used in controlling the vertical movement of the robot. In fact, pneumatic system more reliable compared to the actuator system. In Malaysia, it s hard to find the suitable motor or thruster for ROV underwater robot which a powerful thruster is needed to control the ROV s movement. Combination of actuator system and pneumatic system was used in the ROV to control the vertical movement of the robot. These combination make the robot more unique compared to other industrial ROVs. Figure 6 shows the robot after construction process. 4.2 Submerge depth of the ROV underwater robot ROV is able to submerge into 30 metre based on analysis conducted by using SolidWork software. Practically, the ROV had been tested in 5 metre below bottom of swimming pool successfully without any leaking problem and able to perform perfectly. Other than that, the electrical tank in the ROV can withstand the pressure with the depth of 30 metre under the water. The tank was made up from stainless steel and it has high tensile strength while for the lid was made from thick Perspex that can withstand high pressure in water. Tank is the most critical part due to its function to place all the microcontroller and electronic parts that are sensitive to the water. Practically, the tank had been tested in 5m-depth of water without any leaking as a result of the test. 16
4.3 Stability of the ROV Underwater robot Figure 6: Final ROV Design The ballast tank is inserted in the ROV underwater robot to be functioned as a stabilizer of the robot. It is used to make sure the robot to be in correct orientation besides to prevent the robot from inverted during operation of a task inside the water. The ROV frame initially show positive buoyancy of the ROV means that the ROV unable to submerge in the water but this problem has been solved by placing weightage to make sure the ROV can submerge easily. The weightage is used to make sure robot can submerge and float easily. The ROV become stable and able to submerge, float and successfully perform forward and reverse motion. The stability because of the design has symmetry in axis that makes the robot become more stable. Figure 7 shows the ROV stability while moving in the water. Figure 7: ROV stability in water 5.0 CONCLUSION Design and prototype construction of an underwater robot with manipulator arm according to the design specification that has been made require careful analysis during the design and fabrication phase. Entire decision is selectively made because it may affect the performance result of underwater robot as well as delay the process. Simulation has been conducted to measure the efficiency of the design performance of underwater robot in the sea water. Computational fluid dynamic software was used to calculate the drag coefficient of the design. For a result, drag coefficient for the design is 0.0813 is similar to the half streamlined body and it also shows that the shape of the design is hydrodynamic shape. Besides, SolidWork simulation also was conducted to make sure the frame has the ability to withstand the pressure at 30m depth. The efficient design had been made based on 17
several simulations and design performance analysis after the prototype s design developement process. REFERENCES 1. Muhammad Zuhdi bin Mohd Zin. Design and construction of remotely operated underwater vehicle with manipulator arm. Undergraduate Project Report. Universiti Teknologi Malaysia. 2014 2. Tae-Hwan Joung, Hyeung-Sik Choi, Sang-Ki Jung, Karl Sammut and Fangpo He. Verification of CFD analysis methods for predicting the drag force and thrust power of an underwater disk robot. Int. J. Nav. Archit. Ocean Eng. 269 281; 2014 3. Tomoya Inoue, Hiroyoshi Suzuki, Risa Kitamoto, Yoshitaka Watanabe, Hiroshi Yoshida. Hull Form Design of Underwater Vehicle Applying CFD (Computational Fluid Dynamics). JAMSTEC (Japan Agency for Marine-Earth Science and Technology) Yokosuka; 2010 4. Team Genesis, Washington State University. Sea Tech 4H Team Genesis Technical Report. MATE. 2009 5. Team Aftershock, Bristol Community College. Bristol Community College AfterShock Al Technical Report. MATE. 2010 6. Robert D. Christ, Robert L. Wernli Sr. The ROV Manual- A User Guide For Observation- Class Remotely Operated Vehicle. First Edition. Butterworth-Heinemann. 2007. 7. Robert D. Christ, Robert L. Wernli Sr. The ROV Manual- A User Guide for Remotely Operated Vehicle. Second Edition. Butterworth-Heinemann. 2013. 18