ROV (Remotely Operated Vehicles) is a kind of robot tool for conducting underwater searches equipped with sonar and cameras. ROV has the ability to observe objects in the ocean and is controlled by remote control directly from the surface of the water.
ROV (Remotely Operated Vehicle) operational system according to Hydrovision Inc. consists of :
- Free Swimming System.
- Tether Management System
• Garage TMS
• TopHat TMS
1. Free Swimming System.
ROV operational system that uses cables as a direct link between the ROV and the existing control room at sea level without any additional system between the two. This system is the cheapest operating system and the least equipment to support ROV operations. Based on research results from Hidrovision Inc. Free Swimming system is suitable for operations in shallow water to a depth of 600 m. For more depth than that, the system will cause various problems, including the cable being longer and heavier, so that it will add power burden for the ROV drive, besides that the long cable can cause the cable to be difficult to handle and also will limit the ROV maneuver. With this cable, the supply of power from the surface becomes infinite, only if the power transferred to the ROV is greater, then the diameter of the cable becomes large so that the power supply can run properly, then this will increase the drag force on the cable.
Usually in the operation of this system using cables with layers of umbilical polyurethane sheathed lifting material. The advantages of the Free Swimming system are as follows :
- Not too complex.
- Not too heavy.
Easy operation and control.
2. Tether Management System (TMS).
ROV operational system that provides an additional system that is placed between the ROV with the control room that is above sea level. The addition of this system means that it will increase investment costs. This system is very suitable to be operated in deep waters to a depth of 6000 m.
TMS system (Tether Management System) consists of 2 types of systems, namely :
- Garage / cage TMS.
- Top hat TMS.
Benefits of Tether Management System :
– Eliminates the effect of drag force on the cable.
– Provides ROV protection during launch and withdrawal.
– Increase the speed of movement to and from work sites.
– Being able to move to work properly.
– Provides a safe place to stop ROY under the sea.
Garage Tether Management System (TMS).
For operations in deep water, ROV can use the TMS garage. This system consists of a garage that connects the ROV with the control room on the surface, where the ROV with the garage is connected by a cable tether stored on the winch in the garage, while the garage with the control room is connected with the cable umbilical. The function of this cable in addition to being a lifting cable also functions as a power cable and signal cable. In the garage operation was reduced to reach operational depth, then the ROV was removed from the TMS garage to the workplace. In most TMS systems, the cable is stored on the winch inside the TMS and this cable will be stretched, when the ROV moves away from the TMS. This system is better because the garage is able to provide protection to the vehicle.
This Free Swimming system is preferred by operators because of its ability to change the weight of the garage for a variety of different tasks. Garage can be modified to suit the movement characteristics of the existing surface and overall environmental conditions by using a thruster placed on the vehicle and the TMS garage. The Oceaneering Company has developed a cage system with a thruster for the operation of high ocean currents. They have developed a system called vectored orientation system. Systems that use cage and thruster integration. Thruster is placed on the cage and integrated with the gyro compas mounted on the cage. The system is controlled with a separate joystick in the control room. Cage can maneuver freely or adjust to the ROV movement. The thruster is designed to be strong enough to not only prevent the influence of horizontal drag forces on the vehicle, but also protect the cage or ROV from the rig structure during launch and withdrawal in high ocean currents. When lowered and in an underwater installation, a VOS (Vectored Orientation System) system is used to attach the cage to an operation that is continuously monitored if necessary.
ROV is lowered to the bottom of the sea in its cage. The vehicle then exits the cage. The ROV is connected to the cage with armor fiber for direct communication. Direct communication is achieved for the ROV system by connecting the vehicle to the cage with an optical fiber cable and cage to the ship on the surface with the power / communication cable. This connector gives the operator control of the vehicle directly. The reduced diameter of the cable will affect the reduction in drag force. As stated, the cage will function as a TMS and the vertical forces can be ignored on the fiber optic cable connecting the vehicle to the cage. In addition horizontal forces are also ignored because of the small diameter of the cable. The tether cable is used in connection with a vehicle that is derived from a TMS or cage system or directly from the surface to the ROV. TMS or cage provides protection to the ROV when passing through air or water and allows the ROV to be connected via a tether cable from moving vesels on the surface by wave motion.
This tether cable planning must pay attention to the high level of flexibility, reliability, neutral buoyancy, minimum drag force and easy maneuverability for the ROV. To connect the ROV to the cage, it is connected by a fiber optic cable that can transfer communication signals, the ROV uses batteries on the mother ship as a power supply. With optical fiber will reduce the diameter of the tether so that it can reduce the drag induction force. With a TMS or a stop, it can extend the operating range. The reason for using fiber optic cable is that the bandwidth capacity is large, the reduction is low, the outer diameter is small and free from interference. To get the best dynamic performance and prevent stress on the outermost components during bending, all units must be arranged in a helical manner with cable construction that can rotate fully 360 degrees.
Garage TMS consists of a garage with a side entry, made with a certain size to accommodate the size of the installed ROV. The height of the garage is adjusted so that it can accommodate the ROV. The upper part of the garage contains a winch and slip ring or a bobin and bale arm mechanism to control the ROV tether spooling. An umbilical lifting winch is used to lower the TMS garage to the work site. Umbilical steel is passed on an umbilical beam that is mounted on both the frame and the crane. During launches and withdrawals, ROVs are Arnan in TMS with an open-close mechanism. After reaching the required operational depth, the ROV can be moved safely out of the TMS to the worksite within the maximum operating radius of the tether. Pilots on aircraft carriers can adjust the length of the tether through the ROV control unit.
The benefits of TMS garage are as follows :
– Greater stability during launch and withdrawal.
– Easier to dug under the sea.
– The possibility of damage to the tether cable during dosing is small.
– Able to stop at the bottom of the sea in calm sea conditions.
Top Hat Tether Management System (TMS).
The Top Hat Tether Management System (TMS) has an operational system similar to the TMS garage operating system, but the ROV is not placed in the garage, but is connected to the top hat system via a tether cable hanging down. This tether cable is stored in a winch that is in a top hat.
The advantages of Top Hat TMS are as follows:
– The room is bigger.
– The design is more compact.