The objective of this study was to analyze the unwinding motion of a fiber-optic cable by considering the effect of flexural rigidity, to predict dynamic load at connection part that plays a role to connect flexible hose with underwater vehicle while an underwater vehicle was launched from a mother ship, and to predict the dynamic motion of flexible hose by evasive maneuvering of a mother ship.
An unwinding system for describing the motion of the fiber-optic cable was defined in the orthogonal coordinate system because of the merit that the independence of each basis enables the simple derivation of scalar equations. Hamilton's principle for an open system was employed to represent the phenomenon that the mass of cable changes continuously in the control volume by the unwinding velocity and initial tensile force at a guide-eyelet point. The 4th order transient-state unwinding equation of motion was able to derive from using Hamilton's principle. To numerically solve the transient-state unwinding equation of motion, Newmark implicit integration was utilized with the central finite-difference approximation for spatial variables. The unwinding velocity and initial tensile force that are dominant factors in forming the balloon shape were retained from the lab-based experiment in water. The fiber-optic cable did not have the unwinding problem at selected unwinding velocities 5kn, 10kn and 15kn and the simulation result was verified with experiment result. Therefore, it was able to infer that there was no unwinding problem at increased velocity of 25kn.
Dynamic load on shear pin of connection part that connects the underwater vehicle with flexible hose is essential to control the initialpose of underwater vehicle. Thus, it was important to predict the dynamic load on shear pin of connection part. The total mass of flexible hose had been distributed by using rigid body modeling. Gravity, buoyancy, contact force, normal and tangential fluid resistance were considered as the external force working in flexible hose. Tensile forces at the maximum unwinding velocities of 25kn and 15kn were verified with experiment result. From the examined result, the angular velocity on shear pin and hinge, the dynamic load on shear pin, and the motion that is formed in the process of unwinding of flexible hose were predicted.
It was important to analyze and predict the motion of underwater flexible hose because the motion of flexible hose connected with the mother ship was continually changed by the evasive maneuvering. In this study, the flexible hose was formulated with flexible body by using absolute nodal coordinate formulation. Four kinds of longitudinal stiffness matrices were derived based upon strain assumptions and two kinds of transverse stiffness matrices were developed by curvature assumptions. The dimensional equation of motion was converted into the non-dimensional equation of motion to enhance the efficiency of analysis time. Considering straight-line and turning evasive maneuvering, the motion of flexible hose was analyzed by time of evasive maneuvering, propulsion velocity, and winding velocity. Therefore, it was possible to predict the height of end point of flexible hose by propulsion velocity for straight-line and turning evasive maneuvering.
The followings are the originalities of this study:
1) The analysis of unwinding motion of fiber-optic cable by considering the effect of flexural rigidity
2) Verification the unwinding motion of fiber-optic cable with lab-based experiment and prediction of the unwinding motion in increased unwinding velocity
3) Prediction of dynamic load acting on shear pin of connection part and verification the result with lab-based experiment
4) Modeling the flexible hose by using absolute nodal coordinate formulation and shorten of analysis time through the use of non-dimensional equation of motion
5) Prediction of dynamic motion of flexible hose by straight-line and turning evasive maneuvering and winding velocity