Investigation of Sonar Stabilisation Method for Improved Seafloor Image Quality - Geoinformatics for Intelligent Transportation - page 13

1

0.5

0

-0.5

-1

0 3 6 9 12 15 18

Time, s

Fig. 12 Filtered accelerometer parameters. Second test, Z axis

To calculate the speed the following equation was used:

ð a n þ a n þ 1 Þ

v n þ 1 ¼

D t þ ð 17 Þ

v n

2

Here: v n þ 1 — is the current speed; a n+1 — is the current acceleration; a n — is the

acceleration, measured during the previous measurement; ʔ t — is the measurements

frequency, 0.05 s; V n — is the speed, during the previous measurement. Accelera-

tions of the axis Z and the calculated speed of the heaving are presented in the
Fig. 13 .
The researcher operating the system, determines the required length of the cable
h. Taking into account the heaving of the ship, the provided stabilization system can
change the length of the cable. However, the length of the cable must remain at
similar approximate value ( ± 0.5 2 m). The operator can set the maximal allowable

-

change of the cable ' is length. In the calculations the cable ' is length is marked as h n .

The starting settings of the system are: D t ¼ 0 : 0125 s; h n ¼ 0m

To calculate the general change of the cable ' s length h n+1 the following

equation was used ( 18 ):

ÞD t 2

h n þ 1 ¼ h n þ D t v n þ ð a n þ a n þ 1 ð 18 Þ

1 0.3

0.5 0.2

0 0.1

0

-0.5

-1 -0.1

-1.5 -0.2

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

Time, s

Fig. 13 Ship accelerations and speed