Remote Operated Vehicles (ROVs) are inevitable components in deepwater exploration and operation. Integrity and stability of ROV when it is passing through the splash zone is one of the main engineering tasks in the design of an ROV-umbilical system. To keep the tension during deepwater operation below the safe working load of its umbilical, a deepwater work class ROV is usually designed with neutral buoyancy. Due to the lightweight nature of ROV in water, the umbilical experiences repetitive transitions between slack and taut condition as the ROV travels through the splash zone. A rapid transition from slack to taut induces a tension spike in the umbilical that can endanger the deployment and recovery of an ROV. It is important to ensure that the emerged tension spike does not exceed the safe working load of the umbilical when an ROV is deployed or recovered from ship to water or vice versa.Due to the ROV’s irregular shape, the interaction between ROV and wave around the splash zone is hard to model accurately with a simple mathematical formulation. In addition, the inclusion of flexible umbilical to the problem increases the difficulty of representing the whole process accurately. By using a model test, a better representation of the process can be achieved and the tension on the umbilical when the ROV located in the splash zone can be measured accurately.&nbsp;In this study, deployment and recovery of a deep-water work class ROV were experimentally investigated using a 1:10 scaled ROV model through a series of wave flume tests. Different regular and irregular waves were generated in the flume while the ROV model was hanged over the flume in four different positions relative to the water surface: just above water surface, half-submerged, just below water surface, and fully submerged with certain distance to water surface. For all experiments, the tension time-history in the line was measured and recorded through a load cell at the end of the line. The effects of different wave conditions and ROV’s relative positions to the tension in the umbilical were analyzed. The worst-case condition was selected and a mitigation option to reduce the tension spike was tested. A simplified numerical model for launch and recovery of the ROV was then developed and the experimental test results for the line tension were used for calibration of the model. It was shown that the presented model with special considerations when tension spikes occur in the line can be accurately used for launch and recovery of the ROV.

Experimental Wave Flume Tests in Rov-Wave Interaction Effects on the Line Tension for a Work Class Rov in Splash Zone

Paper Proceedings: https://asmedigitalcollection.asme.org/OMAE/OMAE2021/volume/85116

OMAE 2021

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