Thrust Losses on Underwater Snake Robots with Thrusters
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- Institutt for marin teknikk 
The main motivation behind this thesis is to study the effects from different thrust losses on an underwater snake robot (USR) with thrusters. In-line velocity fluctuations, transverse velocity fluctuations, thruster-thruster interactions, thruster-hull interactions, thurster-nearby structure interactions and ventilation are studied. First, an extensive literature study is done for the modeling of underwater snake robots with and without thrusters, propeller characteristics and thrust losses. In-line and transverse velocity fluctuations are simulated in MATLAB. It is shown that the smaller the model is and the higher the shaft speed is, the bigger the thrust losses become. In-line velocity fluctuations are present as long as thrust is given from at least one of the thrusters, while transverse velocity fluctuations are present as long as there is a normal velocity component close to the thruster. The influence of the $K_T$-value (non-dimensional thrust coefficient) is also studied. A smaller $K_T$-value, gives a larger effect from the thrust losses. By adding current it is shown that the current changes the velocities in the x- and y-directions of the robot, which leads to the thrust losses increasing or decreasing in the respective directions. Observations are done using the USR at Eelume %in order to do observations to study the rest of the thrust losses. When the configuration is as given in this thesis, the effects from the thruster-thruster interactions, thruster-hull interactions and thurster-nearby structure interactions seem to be negligible. Ventilation is present when the USR is near the water surface.