transducer is normally fixed on each hydraulic cylinder that provides the movement . A pressure sensor is normally installed to identify the outlet pressure from the water pump .
The most important aspect of a jetting unit is the nozzle design . Suitable nozzle design selection is done by CFD . In practice , a few nozzle designs are prepared and tested during sea trials . Figures 3.4.3 and 3.4.4 show the CFD analysis of the flow through the jetting sword and its nozzle performed by the Korean Institute of Robotics and Technology Convergence [ 16 ].
In a common design approach , the required exit pressure is dependent on the nozzle diameter , the number of nozzles , and the nozzle factor determining the jet velocity , output flow , and the reaction force of the nozzle . See Figure 3.4.5 for an example of different internal configurations of jetting nozzles . These differences result in a variety of jetting performances .
Note that the material used also plays an important role in determining the nozzle ’ s durability because the internal surface experiences a high friction rate caused by the sea water . Soft material tends to deteriorate with time so SS304 , 17-4PH , titanium or ceramic are usually used for nozzles . Depending on how much money a company can afford to spend in developing a trenching machine , the chosen material will impact the results .
The typical design of the ROV jetting device fundamentally has two jetting arms , three jetting directionals and three cavities , as illustrated in Figure 3.4.6 . The twin jetting arms are used for straddling cables or pipelines and breaking the soil in advance of the trenching vehicle . The inner width between the arms should thus be larger than the diameter of the cable to be buried . It is also observed that the jetting nozzles arranged on the ‘ arms ’ typically conform to a three directional configuration . High-pressure cutting nozzles are regularly placed on the principal face of the jet arms , while their inner side is equipped with large flow-breaking nozzles and the bottom side with large flow-conveying nozzles . The corresponding nozzles in each direction are denoted as ( 1 ), ( 2 ), ( 3 ), respectively , in the section view A-A ’ ( see Figure 3.4.6 ). Furthermore , the three-cavity design of the jet arms is to fulfil the function of breaking the soil at different levels by supplying ( independently ) each type of nozzle with water . It should , however , be emphasised that the crosssectional area of the water supply chamber is normally designed to match the pressure , flow rate and the number of nozzles required by the jet arm . The sectional view B-B ’ ( see Figure 3.4.6 ) shows the water supply chamber , while the cavities of interest are respectively labelled I , II , and III . [ 6 ]
CONCLUSION
The trenching ROV has huge potential in the current global situation where digital communications is crucial for accurate and fast data transmission or reception . There is no denying that every country in the world is racing to achieve up to 100 % network coverage so that all citizens may be informed of the policies of their ruling Government .
One of our neighbouring countries , Indonesia , which is popularly known as the country of a thousand islands is busy connecting each and every island to their main capital city with communication and electrical cables . This will definitely greatly benefit the islanders as well as businesses .
With fast communication systems , virtual meetings can be held anywhere , allowing for effective decision-making so projects can be finalised quickly . All documentation can be digitised and accessed anywhere by the authorities , making workforces or resources management very efficient and cutting bureaucratic delay .
It is hoped that our country can develop our own trenching equipment without having to rely on European , American , Chinese or other countries . There is no doubt that our cable lay contractors are still using foreign trenchers to bury the subsea cables because none are made in Malaysia . If we want to be classified as a developed country , we have to be able to make our own high-tech equipment .
We have the resources , thinkers , technical expertise , and with the Internet at our fingertips , we should be able to develop our own vehicle of interest . Price is of course an important element but with the intervention and support from the Government , and with proper project leaders , planners , and the right teams , everything is possible .
73