Sea trial results of cable inspection

The first full-scale experiments were made with the use of VIC and EMS developed in the Institute of Marine Technology Problems. Both devices were installed aboard AUV MT-98 (Fig. 12) and used for automatic inspection of thin metallic cable, which was preliminary laid on the bay floor.

The described method was realized in a coordinating level of AUV control system. AUV sea trials were carried out in two stages (fig. 13):

1. EMS only was involved as a cable recognition system,,

2. EMS and VIC were used for cable detection simultaneously. Sea trial parameters and some results are summarized in table 1.

Parameter

Value

Cable diameter

12 mm

Cable length

800 m

Approx cable direction

180°

Average AUV altitude

1.7 m

Average AUV velocity

0.35 m/s

Average inspection speed (EMS only detection using)

0.2 m/s

Average inspection speed (EMS & VIC detection using)

0.3 m/s

AUV-cable offset dispersion (EMS only detection using)

1.5 m

AUV-cable offset dispersion (EMS & VIC detection using)

0.5 m

Maximal AUV-cable offset (EMS only detection using)

3 m

Maximal AUV-cable offset (EMS & VIC detection using)

1.5 m

Cable presence on photo images (EMS only detection using)

30%

Cable presence on photo images (EMS & VIC detection using)

90%

Table 1. Field Test parameters and Results

Table 1. Field Test parameters and Results

In both cases after first EMS-contact underwater vehicle made "zigzag" movement along a general cable direction to collect the contact statistic. As four minutes passed (from the first EMS contact) AUV started search movements guided by inspection zone borders. In the result all test part of the cable was inspected by AUV in autonomous mode (fig. 13, 14-left picture).

The second full-scale experiment was carried out during the inspection of real cable, which has been laid several years ago on bottom of Ussuriysky Bay of Japan Sea. The cable is partly silted and also surrounded by sea organisms (fig. 14 central pictures). AUV moved above silted cable fragments by "zigzag" and straight forward along well seen sites of cable. The total length of the surveyed fragment of the cable composed 13 km. The scheme of inspection consisted of two stages. At the first stage the AUV moved at height of 1.7 m with the use of EMS & VIC, specified cable position and carried out its photographing. The control system registered coordinates of intersection points with the cable. At the second stage the AUV rose on height of 5 m, departed aside from the cable approximately on 20-25 m and came back along the cable in an initial point (registered coordinates were used). At the same time HF SSS (fig. 14 right picture) survey of cable vicinities was being carried out (i.e. the motion was similar to inspection of pipeline freespan).

Search I zone 1 !

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