An Adaptable Walking-skid for Seabed ROV under Strong Current Disturbance

School of Marine Science and Technology,Newcastle University, Newcastle upon Tyne, NE1 7RU, United Kingdom

An Adaptable Walking-skid for Seabed ROV under Strong Current Disturbance

Jianting Si and Chengsiong Chin＊

School of Marine Science and Technology,Newcastle University, Newcastle upon Tyne, NE1 7RU, United Kingdom

This paper proposed a new concept of an adaptable multi-legged skid design for retro-fitting to a remotely-operated vehicle (ROV) during high tidal current underwater pipeline inspection. The sole reliance on propeller-driven propulsion for ROV is replaced with a proposed low cost biomimetic solution in the form of an attachable hexapod walking skid. The advantage of this adaptable walking skid is the high stability in positioning and endurances to strong current on the seabed environment. The computer simulation flow studies using Solidworks Flow Simulation shown that the skid attachment in different compensation postures caused at least four times increase in overall drag, and negative lift forces on the seabed ROV to achieve a better maneuvering and station keeping under the high current condition (from 0.5 m/s to 5.0 m/s). A graphical user interface is designed to interact with the user during robot-in-the-loop testing and kinematics simulation in the pool.

ROV;hexapod; multi-legged; skid; seabed; tidal current;

1 Introduction

Most underwater robots (Corradiniet al., 2011) use propellers for their propulsion and its theoretical mechanism is well-established. However, there exist a few difficulties to conduct pipeline inspection work because of disturbances caused by the high tidal current. Flow from the propellers causes disturbance on the seabed, stirring up soft sediment that impairs visibility. Efficiency of seabed operation is compromised as the operator will have to depend on the ocean current to carry away or clear the suspended particles. This effect magnifies when thrusters are actively used for discrete adjustment of the ROV (Chinet al.,2011; Enget al.,2008) or to provide downward thrust for a positively buoyant vehicle on a soft seabed to achieve desired position. Effects of such propeller action are also detrimental to the marine environment and undesirable to activities such as underwater archaeology as it disturbs the natural state of the subject to be observed (Rife and Rock, 2006; Tsusakaet al., 1986). In addition, shallow waters usually present a plethora of marine growth such as corals and seaweeds, which may be drawn into the suction stream of the thrusters and causefouling on mechanical propeller.

Furthermore, ROVs have difficulties in getting precise positioning, accurate manipulation and clear acoustic image particularly in high current environment (Junet al., 2011). It is also not easy to achieve fine attitude control due to the highly non-linear dynamic characteristics caused by dead zone, delay and saturation. Although, the propellers have high efficiency when performing underwater flight, it is obviously ineffective in partially submerged or out of water condition. For the tasks that require amphibious capabilities in shallow water, reliance on propellers as the sole mode of propulsion will severely limit the ROV’s range of effectiveness. Besides, thrusters are expensive and have limited service life due to the seals and oil compensation system for watertight integrity.

In addition to propeller-based propulsion, other methods of ROV locomotion could be found. A tracked-based category is a subset of ROVs commonly known as crawlers. They move on seabed via belted threads, or in combination with the thrusters. The belted threads have a large contact surface area with contact on the seabed to provide sufficient traction for benthic maneuvers for ROV (Inoueet al., 2013; Herzoget al., 2007). However, it caused stirring up of large clouds of sediment, sinkage due to thixotropic behavior of seabed. A wheel-based locomotion is another type of crawlers (Waldmann and Bergenthal, 2010; Nowaket al., 2008) developed to perform underwater intervention by direct contact with the seabed. A new type of compound-mobile mechanism (Yuet al., 2010) achieves amphibious ability by a wheel-propeller-leg driving method was proposed. It is apparent that characteristics of wheel-based locomotion are very much similar to the track-based. Wheels have less direct contact area with the terrain that minimizes the impact of disturbance. But the wheels’ ability to tackle irregularity may be slightly inferior to the tracked design. Compound-driven mechanisms may be novel and effective, but combination of different mechanisms can be quite difficult.

In addition, a body undulation ROVs based on different modes of locomotion and hyper-redundant mechanisms were also used. Example of this type of vehicles are the AmphiBot I and II (Crespiet al., 2005; Yuet al., 2011; Zuoet al., 2009), which are both snake-like and achieves motion using linked non-linear oscillators to produce travelling waves both on land and in open water (McIsaacet al.,2003).Besides, various swimming modes of fish are enumerated and the analytical method for their propulsive mechanism was reviewed (Sfakiotakiset al., 1999). The advantage of these robots is their dexterity in a highly unstructured environment that makes them ideal for search and rescue operations. The modularity of such robots makes reconfiguration easy and mitigates the risk of the vehicle loss due to damage such as water ingress. However, due to the inherent shape and construction of these robots, they have limited payload capacity and are incapable of tool utilization other than basic camera and lights for search and observation operations. Also, the poor power efficiency and the requirement of complex kinematics and dynamics result in undulating locomotion.

Recently, a multiple-legged underwater robot (Junet al., 2012) was then designed for high tidal current. The kinematic structure and gait of lobster were analyzed but the studies on the hydrodynamic on a ROV platform during testing were not performed. This spurred a further development of an amphibious six-legged underwater robot (Tanakaet al., 2004; Christinaet al., 2009; Theberge and Dudek, 2006)that they focused on the watertight technologies for the robot in underwater. Unfortunately, the six-legged design does not allow adaptability to other robots platform. The graphical-user-interface (GUI) for simulation and experimental testing of the seabed ROV are not available in the robot-in-the-loop testing. To best of our knowledge, the design and robot-in-the-loop simulation of an adaptable hexapod walking-skid for a seabed ROV has not been shown in a single publication.

Hence, this paper will develop a low cost biomimetic solution using an attachable hexapod walking skid on a ROV platform. The biomimetic lobster-like seabed ROV is designed to improve the maneuvering and station keeping on seabed under turbulent environment. A simplified kinematic model to develop a ROV’s simulation and prototype control program using the GUI during the robot-in-the-loop testing will be presented. The drag and lift forces (and its coefficients) acting on the seabed ROV’s body and legs compensation postures will be determined using the computer software under the sea current disturbances (from 0.5 m/s to 5.0 m/s).

This paper is organized as follows: The concept of the adaptable hexapod walking skid is addressed in Section 2. It is followed by kinematic modelling and simulation in Section 3. In Section 4 and 5, the computer simulation and experimental tests on the seabed ROV are presented respectively. Lastly, the conclusions are drawn.

2 Design of adaptable hexapod walking skid

Generally, legged locomotion refers to the conventional way of walking on the seabed or in the form of paddling of legs to result in vehicular displacement. Taking inspiration from nature, these bio-mimetic robots strive to emulate nature’s using locomotion to achieve proficiency on the seabed. In order for the body of the vehicle to be entirely decoupled from the irregularities of the seabed environment, the legs should be independently controlled in three degrees of freedom (DOF). A six-legged walking machine (hexapod) (Shimet al., 2013) was used for modeling, based on the criteria of a statically stable means of locomotion, and simplicity. Bottom dwelling marine creatures such as lobsters and crabs have evolved around the conditions of heavy turbulence caused by tides, current and wave action. Lobsters for example use their abdomen and appendages to create hydrodynamic adaptable shapes to cope with directional high velocity water flow (Maude and Williams, 1983). The resultant hydrodynamic translational forces allow them to achieve stability on the seabed even with a buoyant body and avoid negative lift that will sweep those away (Martinez, 2001). In addition, the hydrodynamic thrust achieved by body posture adjustment pushes their legs further into the substrate, increasing traction (Junet al., 2012) without the need to adjust body weight.

To achieve the proposed legged form of locomotion on the seabed ROV, the attachable hexapod walking skid will be fitted onto existing ROV that has thrusters as its main propulsion. As such, the scope of the conventional propeller-driven ROV can be extended with the added range of motion to operate efficiently on the seabed and achieve amphibious ability to travel from deep to shallow water. The attachable hexapod walking skid as seen in Fig. 1 will be designed and prototyped in a small scale and constructed using readily available components.

The mechanical system design for the seabed ROV can be seen in Fig. 1 (with no thrusters installed). To support development of the seabed ROV, a test-bed vehicle (weighted 3.5kg in air with a dimension of approximately 0.25 m×0.25 m×0.25 m at its full extended position) dedicated for the test-bedding of the attachable skid and control subsystems was developed by the Newcastle University. The seabed ROV is positively buoyant by design. The robot enclosure design is pressure tested at 50m. The maximum walking speed is not more than 1m/s. For initial prototype design, the payload (i.e. weight carrying capacity) should not be more than 2kg due to the servomotors used and the dimension of the prototype. The attachable skid will be attached to a small-size ROV platform with minimal modification.

The ROV is equipped with 7.4 V 5.2 Ah lithium polymer battery power supply for up to 50 m for testing and initial deployment purpose. The key components are servomotors and electronics casing containing electronics circuit boards. The electronics casing was used to represent a solely propeller-driven ROV in which the hexapod walking skid will be attached. Four hexapod walking skids (or legs) are shown in Fig.1. Each leg consists of three servomotors, brackets and metal parts that come into contact with the ground. The two remaining legs were used as manipulator that consists of five servomotors, brackets and a gripper mechanism. The completed mechanical subsystems of theadaptable hexapod walking skid can be seen in Fig. 2. Besides, the mechanical subsystems, the buoyancy of the seabed ROV need to be adjusted. Due to the considerable volume of the casing which represents the ROV that is mounted on the skid, the entire prototype is positively buoyant as it displaced more water than its own weight.

A microcontroller was used to control the actuators for moving the attachable hexapod walking skid. Four Seeeduino Mega microcontrollers were used in the project. The seabed ROV is connected to the computer via a RS232 communication. Each microcontroller takes 5 V 500 mA power from the lithium-polymer battery. The microcontrollers control the 22 servomotors (each sealed with silicone grease, Nitrile rubber o-ring and adhesive) attached to its legs and manipulators of the seabed ROV. The robot-in-the-loop testing and robot’s kinematic simulation is accomplished through the MATLABTMGUI software.

Fig. 1 3D models of attachable walking skid fixed on a ROV (right)

Fig. 2 Actual fabricated walking skid (left) and seabed ROV prototype (center & right)

3 Kinematics of hexapod walking skid

There are many methods used in robotics to describe the position and orientation of robotic links in Euclidean space(Zhu, 2001; Junet al., 2011). The approach taken in the kinematic derivation of the hexapod walking skid in this project differs slightly and undertakes the use of homogenous coordinates and application of corresponding homogenous transformation matrices in relation to a single absolute reference point, namely the point of origin. The four legs and two manipulators of the hexapod walking skid are each simplified into two-link three degree of freedom (DoF) linkages (see Fig. 3). The manipulators consist of five DoF, the remaining two DoF (the translational opening/closing of the gripper and the rotation of the gripper’s wrist) are omitted to reduce the complexity of the simulation.

For brevity, only the derivation of one appendage, the front left manipulator (see Fig. 4) is shown as the rest are similar.

Fig. 3 Overview definition of the coordinate system of the hexapod walking skid

Fig. 4 Top view of the front left manipulator’s coordinate system and notation

The point vectors are named with capital letters, which in the case of the front left manipulator – the capital letter ‘A’, and the lengths of legs or manipulator links with the capital letter ‘L’. Joint angles are preceded with the particular vector notation of interest, followed by ‘J’ and then the corresponding angle notation (See Fig.5). CP stands for controlling point that indicates the location of the hexapod skid in three-dimensional (3D) space. The rest of the coordinates of the model are then calculated based on CP. The length and width of the skid are represented by BL and BW, respectively. The lengths of the two link manipulator are assigned asL1andL2, respectively in Fig.5, with one end ofL2in contact with the ground and the other end ofL1to the skid.L3AandL4Aare virtual lengths, used to calculate the joint angles (AJa,AJb,AJcandAJd) betweenL1,L2, ground and skid, respectively.

Fig. 5 Detailing of the front left manipulator’s coordinate system and notation

With the knowledge ofCP,BL,BW, the vectors for all of the left manipulator can be found as follows: where OFF represents the linear distance ofA3from the skid’s edge in length and breadth-wise.

With specification of the skid’s locating pointCPby (1), the ends of the manipulator links can be located by (2) and (3). The required angles for determination of the joint vectorA2between the two manipulators links are determined as follows:

As shown in (1) to (10), specification of CP takes precedence before the determination ofA1andA3, which ultimately leads to calculation ofA2. The equations are applicable to all the appendages in the hexapod skid. For convenience of handling the equations, vectors representing the connection of the appendages’ link to the side of skid and vectors represent the other end of the appendages’ link to the ground are combined as follows:

For manipulating the vectors in 3D space, the canonical transformation matrices are used. The below shown the steps applied in MATLABTMto obtain the desired control of the hexapod walking skid. For example, consider having the hexapod walking skid start at the coordinates of (0,0,50). Using (1), the CP corresponds to:

Applying (2) to all the six legs of the skids from A1 to F1, with BL = 175, BW = 105, L1 = 63 and L2 = 77, the Body matrix is achieved with the following value:

To achieve a desired elevation of 20 units in the direction of the Z-axis, the following translation operation is used.

To simplify the mathematical complexities when performing arbitrary rotations that involve various reference frames and orientations, the following is used. If the location of the skid is not at the point of origin and a rotation about an arbitrary axis is required, CP (which represents the location of the skid) is first translated to the point of origin, where the required matrix operations are performed with the canonical rotation matrices. CP is then translated back to its initial position to achieve a similar result as a rotation about an arbitrary axis.

whereToriis translation back to origin,Tiniis translation back to original position before rotation andRxis the rotation matrix about x-axis. The above equations illustrates the basic kinematics for positioning the components such as the‘spine’, attached legs and manipulators of the hexapod walking skid in 3D space.

4 Computational fluid dynamic (CFD) simulation tests

The SolidWorks Flow Simulation was used to simulate the seabed ROV under the strong current speed. It solves the basic equations that govern the fluid motion using the Finite Volume (FV) method. SolidWorks Flow Simulation solves the full Navier-Stokes equations while also applying fluid state equations that define the nature of the fluid, and also by other empirical laws for the dependency of viscosity and thermal conductivity. SolidWorks Flow Simulation begins by analyzing the model geometry and the computational domain. Boundary conditions such as fluid properties, pressure, and temperature must be given to the computational domain before solving for the solution. However, the smaller the mesh size implies greater computational domain or processing power and time to obtain the flow solution. As such, compromises need to be made during the setting up of the boundary conditions and the mesh size. The initial conditions are based on the flow study in 10 m depth of water measuring at 20?C with flow velocity of 1 m/s. The input temperature and pressure are set to 293 K and 199 249 Pa, respectively. The turbulence parameters are automatically calculated by the software and its recommended values are used. The ideal mesh level was determined for every individual flow study. For example, instead of computing the drag force at different mesh levels over the velocity range of 0 to 5 m/s, intermediate values of 1.0 m/s, 3.0 m/s and 5.0 m/s were used at incremental mesh levels. The deviation of values between each level was calculated and compared when the deviation drops below ±5%. This implies that the flow studies at higher mesh level have no significant changes to the simulation results besides having a longer computation time. As such, the full set of velocities from lowest to highest (0.5 m/s to 5.0 m/s) were computed at the mesh level.

The computational domain is defined as the geometric area around the ROV. To obtain a complete flow study for analyzing the external flow characteristics, the size of the computational domain is shown in Fig. 6. The external flow boundary was set to five times the size of the ROV. In total, around 750 000 tetrahedral elements were built. The region of disturbed flow (usually turbulent) occurred at downstream of the ROV body. This region creates high velocity (or low pressure) region at the rear end, and thus low velocity (or high pressure) in the front to resist the ROV motion.

Fig. 6 Computational domain for seabed ROV

SolidWorks Flow Simulation runs the flow studies to derive the forces over the external surface of the 3D model. The aim of the sequence simulations is to determine the magnitude of the additional drag and lift force (and it corresponding drag and lift coefficients) when the hexapod walking skid is attached to the seabed ROV during maneuvering and on the seabed (with/without skid and at different seabed ROV’s body postures).

4.1 Flow Simulation during underwater maneuvering

There are many posture that the legs and manipulator of the hexapod walking skid can be positioned during maneuvering. The two main configurations are considered here. Configuration 1 (see Fig. 7 in the center) has the legs of the skid kept as close to the body of the ROV, with the aim of reducing frontal projection area against the current flow. By keeping the legs and manipulators retracted and close to the sides of the ROV, the servomotors at the joints do not have to strain as much against the flow of the current to maintain the position of the appendages. Configuration 2 (see Fig. 7 on the right) has the legs/manipulators of the hexapod walking skid spread out laterally to create a more streamlined vehicle, much like the shape of the fins of a stingray. Both configurations have similar frontal projected area, with Configuration 2’s area greater than Configuration 1 by approximately 8.6 %. Besides, the drag and lift forces in the flow direction were computed. The corresponding drag and lift coefficients (and Reynolds number) were determined using the highest flow velocities. The corresponding graphs were generated.

(a) Model of the propeller-driven ROV only;

(b) Model of the propeller-driven ROV with skid attached (Configuration 1);

(c) Model of the propeller-driven ROV with skid attached in more compact posture (Configuration 2).

Fig. 7 Underwater flight flow studies for without skid (left), configuration 1(center) and 2 (right)

The derived values of drag force of underwater flight with/without the skid attached with both configurations are shown in Fig. 8. As observed, the attachment of the hexapod walking skid caused the overall drag of the vehicle to increase by approximately four times at the highest simulation stream velocity ?5 m/s. This is expected as the skid contributes to the higher frontal projected area. However, it is also observed that Configuration 1, which has a slightly smaller frontal projection area, actually incurred 14.3 % more drag than Configuration 2. This may be due to the free stream flow trajectories of the models, which the Configuration 1 presents a much more streamlined exterior with a lesser turbulent vortices around the vehicle than Configuration 2.

Fig. 8 Drag force of ROV’s underwater flow studies

4.2Flow simulation on seabed with body compensation postures

The series of flow studies in this section attempts to determine the drag force under different body compensation postures (see Fig. 9) under the high tidal current on the seabed.

(a) Model of the propeller-driven ROV with skid-attached in 10°compensation posture;

(b)Model of the propeller-driven ROV with skid-attached in 20°compensation posture;

(c)Model of the propeller-driven ROV with skid-attached in 30°compensation posture;

(d) Model of the propeller-driven ROV with skid-attached in 40°compensation posture.

The derived values of drag/lift force and coefficients of the model on the seabed at various compensation postures are shown in Fig. 10. As compared with the four compensation postures, it shows that the degree of tilt increases with reference to the flat seabed. The drag force on the model increases due to the negative lift on the model. The result implies that the tilting of the model in the current flow creates a downward force that is significant at compensation postures above 20°. Fig. 10 also included data for the model with the skid attached with legs and manipulators in default position. It can be seen that the incurred drag force on the model is less than the rest of the postures when compared with the default position (except at 40° posture). All the compensation postures results in much greater negative lift than the default position.

In summary, the numerical flow studies indicated that the hexapod walking skid results in increased drag force, and a higher negative lift force (by the compensation postures) to adhere the ROV onto the seabed in the midst of a considerable current flow (from 0 to 5 m/s).

Fig. 9 Compensation postures flow studies and actual implementation for configuration (a) to (d) - starting from top

Fig. 10 Drag and lift coefficients compensation postures from 10 to 40 degrees

Fig. 11 MATLABTMGraphics User Interface

5 Experimental tests in air and water

The movement of the hexapod walking skid was simulated using the GUI in MATLABTM. The object-oriented programming (OOP) design approach was taken in developing the MATLABTMscripts to support the GUI. The OOP allows modularization of the codes for easier management. It also allows concepts such as encapsulation, inheritance and polymorphism to be exploited in order to optimize both the development and execution of the program. As shown in Fig. 11, GUI was created to interact with the user during the dry and water testing. The user has a choice of performing simulation of the hexapod walking skid and/or real- time control of the actual prototype.

The GUI provides access to methods such as manipulator direction controls together with planar and angular controls of the skid. There are three types of walking gaits (see Fig. 12), each with a different characteristic as follows. Metachronal wave gait is the slowest but most stable out of the three gaits, suited for traversing uneven terrains. Only one leg (usually from the rear) is raised, moved forward and lowered at single time before the next leg on the same side is moved in a similar manner. A five-point contact with the ground is made at all times that is more stable but slow. However, it has a good load carrying capability as the weight is distributed equally on the ground. Ripple gait is similar to the metachronal wave except the two legs are diagonally across each other are lifted to move forward. It is slightly less stable but faster than the metachronal wave gait. On the other hand, tripod gait is the fastest and least stable of the three gaits. It is suitable for traversing on flat and even terrains. The middle leg on one side of the body is lifted together with the front and rear legs of the other side to move forward, before the remaining legs in the first sequence are repeated with the same motions. Load carrying capability is weaker than the previous gaits as the load is distributed among the three legs only.

Fig. 12 Screenshot of metachronal wave gait (left), ripple gait (center) and tripod gait (right)

Fig. 13 depicts a block diagram of the MATLABTMGUI interface for the seabed ROV attached with a hexapod walking skid. After the user has selected the choice, the commands go into the serial communications on the four Seeeduino microcontrollers. Each microcontroller uses the arduino interactive development environment (IDE) to provide basic interface between the Arduino microcontroller, as well as to control the servomotors interactively from the MATLABTMcommand window, without having to write, debug, compile, upload and run the C programs. However, the Arduino IO can only control up to two servomotors connected to the microcontroller, whereas a total of 22 servomotors are required for the control of the hexapod walking skid. With that, the Arduino IO package code was modified and extended.

The constructed seabed ROV prototype will be tested to verify the derived kinematic simulations and software/hardware interfacing. All tests were conducted with the help of the GUI. For clarity, only the GUI for the robot-in-the-loop testing is shown in Fig. 14. Initially, the stationary planar and angular motion were performed under the dry condition. The purpose is to verify basic coordination of the servomotors and identify any faulty servomotors or GUI interfacing error.

During the pool test, it was observed that seabed ROV prototype and the GUI displayed some correlation. Besides, it was found that the coordination of servomotors is generally acceptable except the jerkiness when performing slow motion. The jerkiness was due to the analogue servomotors programmed to move in a fixed series incremental steps. This can be minimized by decreasing the step size, but it would affect the speed or rotation of the servomotor’s output shaft. With that, the digital servomotors were used and the parameters were programmed into the servomotor’s control board.

Fig. 13 MATLABTMGUI for seabed ROV with attachable hexapod walking skid

Fig. 14 Dry test showing correlation of both prototype and simulation on GUI

Fig. 15 Test of prototype in the midst of yaw rotation underwater (left) and metachronal wave gait (right)

In addition, the stationary planar, angular motion and metachronal wave gait (see Fig. 15) were conducted in a swimming pool. The prototype performed quite well in water and exhibit stability during the walking gait. The legs were able to achieve traction despite the slippery tiles on the swimming pool. Due to the deliberately slow and minimal accelerated motions, the underwater performance of the prototype barely differed from the one tested in dry condition.

The testing of feasibility of compensation postures was performed. The ppol test verified the feasibility of implementing the compensation postures on the ROV. The prototype was able to achieve the various degrees of compensation postures (except for the 40?compensation posture). It was due to the fabrication fault that caused the top of the leg collided with the servomotor brackets of the hind legs. As a result, only a maximum of 35° compensation posture could be achieved. In summary, the waling skid on the seabed ROV is able to perform the required postures and maneuvering that give an increase on the drag and negative lift force required to sustain on the seabed under the high tidal current.

6 Conclusions

A new concept of an adaptable multi-legged skid design that could be retro-fitted to an existing remotely-operated vehicle (ROV) for high tidal current underwater pipeline inspection was proposed. The advantage of this concept is the ROV is able to have a higher stability during positioning on seabed than the one using propellers only. A simplified kinematic model and hydrodynamic simulation of the seabed ROV was presented. The computational-fluid dynamic (CFD) flow studies shown that the skid attachment provides an increase in overall drag and negative lift force of the vehicle at a maximum speed of 5m/s at certain body compensation postures. Hence, the hexapod walking skid at different posture provides a better maneuvering and station keeping on seabed under the sea current condition. With the graphics user interface using MATLABTM, it allows user to interact with the seabed robot during the robot-in-the-loop testing both in wet and dry condition. For the future works, the sensor such as gyroscope, altimeter, force sensors and accelerometer will be included in the seabed ROV for feedback control and comparisons with the simulated results. Lastly, actual implementation on the existing ROV (mounted with thrusters) for underwater pipeline inspection will be performed.

Acknowledgment

The authors would like to thank Newcastle University in United Kingdom (project account number:C0570D2330) and Ngee Ann Polytechnic (in Singapore) for providing laboratory space, and the reviewers for their valuable comments, which improve the readability of this paper significantly.

Christina G, Meyer N, Martin B (2009). Simulation of an underwater hexapod robot.Ocean Engineering,36, 39-47.

Chin C, Lau M, Low E (2011). Supervisory cascaded controllers design: experiment test on a remotely-operated vehicle.Proceedings of the IMechE Part C: Journal of Mechanical Engineering Science, 225(3), 584-603.

Corradini ML, Monteriù A, Orlando G (2011). An actuator failure tolerant control scheme for an underwater remotely operated vehicle.IEEE Transactions on Control Systems Technology, 19(5), 1036-1046.

Crespi A, Badertscher A, Guignard A, Ijspeert AJ (2005). AmphiBot I: an amphibious snake-like robot.Robotics and Autonomous Systems, 50, 163-175.

Eng YH, Lau WS, Low E, Seet GL, Chin CS (2008). Estimation of the hydrodynamic coefficients of an ROV using free decay pendulum motion.Engineering Letters, 16(3), 326-331.

Herzog K, Schulte E, Atmanand MA, Schwarz W (2007). Slip control system for a deep-sea mining machine.IEEE Transactions on Automation Science and Engineering, 4, 282-286.

Inoue T, Shiosawa T, Takagi K (2013). Dynamic analysis of motion of crawler-type remotely operated vehicles.IEEE Journal of Oceanic Engineering, 38(2), 375-382.

Jun BH, Lee PM, Baek H, Lim YK (2011). Approximated modeling of hydrodynamic forces acting on legs of underwater walking robot. IEEE OCEANS 2011, Spain, 1- 6.

JunBH, ShimH, ParkJY, KimB, LeePM (2011). A new concept and technologies of multi-legged underwater robot for high tidal current environment.IEEE Symposium on Underwater Technology (UT) and Workshop on Scientific Use of Submarine Cables and Related Technologies (SSC), Tokyo, Japan, 475-479.

Jun BH, Shim H, Kim B, Park JY, Baek H, Lee PM, Kim WJ, Park YS (2012). Preliminary design of the multi-legged underwater walking robot CR200. OCEANS 2012, Yeosu, South Korea, 1-4.

Martinez MM (2001). Running in the surf: hydrodynamics of the shore crab Grapsus tenuicrustatus.Journal of Experimental Biology, 204, 3097-3112.

Maude SH, Williams DD (1983). Behavior of crayfish in water currents: hydrodynamics of eight species with reference to their distribution patterns in southern Ontario.Canadian Journal of Fisheries and Aquatic Sciences, 40, 68-77.

McIsaac KA, Ostrowski JP (2003). Motion planning for anguilliform locomotion. IEEE Transactions on Robotics and Automation, 19(4), 637-652.

Nowak BM, Whitney T, Ackley SF (2008). Analysis of ROV video imagery for krill identification and counting under Antarctic sea ice.IEEE/OES Autonomous Underwater Vehicles, 1-9.

Rife JH, Rock SM (2006). design and validation of a robotic control law for observation of deep-ocean Jellyfish.IEEE Transactions on Robotics, 22(2), 282-291.

Sfakiotakis M, Lane, DM, Davies JBC (1999). Review of fish swimming modes for aquatic locomotion. IEEE Journal of Oceanic Engineering, 24, 2, 237-252.

Shim H, Jun BH, Kang H, Yoo S, Lee GM, Lee PM (2013). Development of underwater robotic arm and leg for seabed robot, CRABSTER200.MTS/IEEE OCEANS, Bergen, Norway, 1-6.

Tanaka T, Sakai H, Akizono J (2004). Design concept of a prototype amphibious walking robot for automated shore-line survey work. MTS/IEEE Techno-Ocean ′04, 834-839.

Theberge M, Dudek G (2006).Gone swimmin’[seagoing robots].IEEE Spectrum, 43(6), 38-43.

Tsusaka Y, Ishidera H, Itoh Y (1986). MURS-300 MK II: a remote inspection system for underwater facilities of hydraulic power plants.IEEE Journal of Oceanic Engineering,11(3), 358-363.

Waldmann C, Bergenthal M(2010). CMOVE-a versatile underwater vehicle for seafloor studies.OCEANS 2010, Seattle, USA, 1-3.

Yu JC, Tang YG, Zhang XQ, Liu CJ (2010). Design of a wheel-propeller-leg integrated amphibious robot.11th International Conference on Control Automation Robotics & Vision (ICARCV), 1815-1819.

Yu S, Ma S, Li B, Wang Y (2011). An amphibious snake-like robot with terrestrial and aquatic gaits.IEEE International Conference on Robotics and Automation (ICRA), 2960-2961.

Zhu WH (2005). On adaptive synchronization control of coordinated multirobots with flexible/rigid constraints.IEEE Transactions on Robotics, 21(3), 520-525.

Zuo Z, Wang Z, Li B, Ma S (2009). Serpentine locomotion of a snake-like robot in water environment.IEEE International Conference on Robotics and Biomimetics, 25-30.

Author biographies

Jianting Siisthe assistant superintendent for technical services at POSH Fleet Services Pte Ltd. He has been working in maritime industry for few years. He worked in Lloyd’s Register UK for his internship and has a few years of experience as a marine engineer with Neptune Orient Lines (NOL) and American President Lines (APL) Technical Service Department. He has a degree of bachelor of Engineering with First Class Honours in Marine Engineering. He received the school prize for Best Performance in Bachelor of Engineering with Honours in Marine Engineering, RINA-Keppel Student Naval Architect award for the Best Final Year Project, SIT-Keppel Gold Medal, SNAMES award and IMAREST award. His research interests are in the robotics, systems integration and hardware-in-the-loop testing

Chengsiong Chinisa senior lecturer at Newcastle University (Singapore). He received the Ph.D from Nanyang Technological University (NTU) in 2009 and a M.Sc. from Control System Centre in The University of Manchester in 2001 after completed his B.Eng. at NTU in 2000. He worked in industry for 6 years before moving into academia. He currently holds 3 U.S. Patents, 2 provisional US patent applications and 2 Trade Secrets. In 2013, he obtained a research grant from Singapore Maritime Institute (SMI) on High Performance Lithium-Ion Battery Power System for Long Endurance Deep Water Operation (worth S$0.59M) and EDB-IPP on noise and vibration prediction. He is the FHEA, FIMarEST, SIEEE, CEng, Eur.Ing and MIET. He is also a Member of the Editorial Advisory Board of The Mediterranean Journal of Measurement and Control. Recently, he becomes a member of the IMarEST′s Biofouling Management Expert Group. He had authored a book entitled Computer-aided Control Systems Design: Practical Applications using MATLABTMand SimulinkTMpublished by CRC Press, USA in 2012. His research interests are in the marine mechatronic systems design.

1671-9433(2014)03-0306-10

Received date:2014-02-03.

Accepted date:2014-06-05.

Foundation:Suuported by Newcastle University in United Kingdom (Project account number:C0570D2330).

＊Corresponding author Email: cheng.chin@ncl.ac.uk

? Harbin Engineering University and Springer-Verlag Berlin Heidelberg 2014