AUV Control during cable or pipeline inspection

The AUV control during inspection phase supposes: a) time minimization of object search; b) data gathering about the object and surrounding environment (using video and echo-sounder information). Thus, it is possible to choose the following requirements to AUV movement organization:

1. During initial search stage it is necessary to use the object detection systems possessing the least probability of false operations and to move so that to maximize object detection probability.

2. After detection of any object it is necessary to make sure that the given object is required and proceed to its tracking.

3. AUV tracking trajectory should stretch above the object while there is a steady contact from identification systems.

4. When steady state contact is lost it is necessary to carry out a search trajectory (e.g. "divergent zigzag") to guarantee the return to the object.

4.1 Search the communication line

So, AUV behavior (Inzartsev & Pavin, 2006) during pipeline or cable search and detection is similar in many respects and consists of three steps (fig. 7).

f Pipeline has been detected => I tracki ng yes

f Pipeline has been detected => I tracki ng

Fig. 7. Flowchart of preliminary phase of inspection

1. Execution of the search trajectory (meander) in prospective area of the object laying-out as long as crossing with the object looking like the lengthy.

2. Attempt to receive two more confirming contact from the object. For this purpose AUV changes motion direction on the opposite at each point of crossing (contact), i.e. goes by "zigzag". The primary goal of this maneuver is elimination of false contacts and calculation of approximate object direction (qwan).

3. If the number of crossing points is three, they lay on the straight line and the direction of this line coincides with the direction of the required object - then object is considered as found out and the stage of its tracking begins. Otherwise contacts are considered as false and the AUV returns to execution of the search trajectory (1).

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