A Quantitative Parametric Study on Output Time Delays for Autonomous Underwater Cleaning Operations

Abstract

Offshore pipelines and structures require regular marine growth removal and inspection to ensure structural integrity. These operations are typically carried out by Remotely Operated Vehicles (ROVs) and demand reliable and accurate feedback signals for operating the ROVs efficiently under harsh offshore conditions. This study investigates and quantifies how sensor delays impact the expected control performance without the need for defining the control parameters. Input-output (IO) controllability analysis of the open-loop system is applied to find the lower bound of the H-infinity peaks of the unspecified optimal closed-loop systems. The performance analyses have shown that near-structure operations, such as pipeline inspection or cleaning, in which small error tolerances are required, have a small threshold for the time delays. The IO controllability analysis indicates that off-structure navigation allow substantial larger time delays. Especially heading is vulnerable to time delay; however, fast-responding sensors usually measure this motion. Lastly, a sensor comparison is presented where available sensors are evaluated for each ROV motion’s respective sensor-induced time delays. It is concluded that even though off-structure navigation have larger time delay tolerance the corresponding sensors also introduce substantially larger time delays.

A Review of Underwater Robot Localization in Confined Spaces

“…In confined underwater spaces, robots are often subject to environmental constraints, requiring precise operation. This makes it crucial to minimize the delays in controlling sensors [42,43] and output signals [44]. Due to the working characteristics of acoustic sensors, which collect information through sound waves, similar to DVL, acoustic sensors often face issues with delays [45].…”

Formation control of multiple autonomous underwater vehicles: a review

“…By assuming that the delays of propagation are bounded and the bounds on delays are less than the sampling period of AUVs, it was shown [164] that the leader-following based formation system can tolerate the delays and still achieve the formation stabilization, although it takes a longer time to stabilize than the case without delays. To provide a lower bound on control performance of an inspection ROV with sensor time delays, the authors employed an input-output controllability analysis to show that at which amount of delays the ROV system can tolerate irrespective of the forms of designed controllers, while the results are obtained based on an approximated linear model of the ROV [165] . As well, the researchers demonstrated by experiments that there exists a dominant time delay in the underwater acoustic positioning system powered by the short baseline (SBL) with four transducers, and that the traditional Smith predictor failed to estimate due to the time-varying properties.…”

“…Therefore, we believe that incorporating delay estimation and compensation techniques into formation control or designing delay-tolerant formation systems is of great significance in practice. • While there are some primary proposals that provide several delay compensating strategies [165][166][167][168] , most of them may be lack practicality due to the employment of an unrealistic delay model. Thus, more practical delay models are required, and then can be used to compensate for the impacts of the propagation delays.…”

Design of an Autonomous ROV for Marine Growth Inspection and Cleaning

“…It should be noted that this paper is intended to present the PT design considerations. The algorithms needed for localization and mapping and control are currently ongoing where preliminary results may be found in [5], [6] II. FEASIBILITY STUDIES Prior to the development of the prototype described in this work, several feasibility studies were performed to delimit the solutions, investigated through a rapid prototype (RPT) development, cleaning tool investigation, and sensor-technology review, which are summarized in the following sections.…”