Hydroelastic analysis of flexible floating interconnected structures

We present the methodology, algorithms, system design, and experiments addressing the self-assembly of large teams of autonomous robotic boats into floating platforms. Identical self-propelled robotic boats autonomously dock together and form connected structures with controllable variable stiffness. These structures can self-reconfigure into arbitrary shapes limited only by the number of rectangular elements assembled in brick-like patterns. An $O(m^{2})$ complexity algorithm automatically generates assembly plans which maximize opportunities for parallelism while constructing operator-specified target configurations with $m$ components. The system further features an $O(n^{3})$ complexity algorithm for the concurrent assignment and planning of trajectories from $n$ free robots to the growing structure. Such peer-to-peer assembly among modular robots compares favorably to a single active element assembling passive components in terms of both construction rate and potential robustness through redundancy. We describe hardware and software techniques to facilitate reliable docking of elements in the presence of estimation and actuation errors, and we consider how these local variable stiffness connections may be used to control the structural properties of the larger assembly. Assembly experiments validate these ideas in a fleet of 0.5 m long modular robotic boats with onboard thrusters, active connectors, and embedded computers.

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Automated Self-Assembly of Large Maritime Structures by a Team of Robotic Boats

Hydroelastic analysis of a flexible mat-shaped floating breakwater under oblique wave action

Response Analysis and Optimum Configuration of a Modular Floating Structure with Flexible Connectors

This paper addresses the self-assembly of a large team of autonomous boats into floating platforms We describe the design of individual boats, the systems concept, the al- gorithms, the software architecture and experimental results with prototypes that are 1:12 scale realizations of modified ISO shipping containers, with the goal of demonstrating self- assembly into large maritime structures such as air strips, bridges, harbors or sea bases Each container is a robotic module capable of holonomic motion that can dock in a brick pattern to form arbitrary shapes Over 60 modules were built of varying capability The docking mechanism is designed to be robust to large disturbances that can be expected in the high seas The docking mechanism also incorporates adjustable stiffness so that the conglomerate can comply to waves representative of sea state three, and have the ability to dynamically stiffen as required The component modules for autonomous assembly, docking and simultaneous collision-free planning as well as the software architecture are presented along with the description of experimental verification

/pdf/self-assembly-of-a-swarm-of-autonomous-boats-into-floating-482yj879iv.pdf

Self-assembly of a swarm of autonomous boats into floating structures

A comparative study of RMFC and FEA models for the wave-induced response of a MOB

The linear, wave-induced response of a 5-module, 1500-m-long mobile offshore base (MOB) is investigated. Each module is a 2-pontoon, 8-column semisubmersible, and the MOB is represented by the lumped-parameter rigid module-flexible connector model. An extensive parametric study is carried out to determine the impact of the stiffness on the motions and connector loads. Results show that the hydrodynamic interaction between modules is relatively small. Although the response is a complicated function of the connector stiffness, the maximum extreme connector forces for hinged modules are often a result of horizontal bending induced by oblique waves. Also, it is shown that resonance can be a significant problem, especially for lower stiffnesses. *ISOPE Member. Received July 6, 1998: revised manuscript received by the editors January 25, 1999. The original version (prior to the final revised manuscript) was presented at the Eighth International Offshore and Polar Engineering Conference (ISOPE-98), Montréal, Canada, May 24-29, 1998.

T.R.J. Mills

Papers

A comparative study of RMFC and FEA models for the wave-induced response of a MOB

Impact of Stiffness On the Response of a Multimodule Mobile Offshore Base

Impact of Connector Stiffness On the Response of a Multi-Module Mobile Offshore Base