USV is short for Unmanned Surface Vehicle. In a broad sense, unmanned ship refers to a kind of water robot which can perform a certain kind of assigned task and design functions and performances based on the purpose of the task; in a narrow sense, unmanned ship refers to the autonomous, semi-autonomous and remote control carrier of water surface with certain mobility.
2. Components of USV System
USV consists of platform system and task load system, which are integrated through one interfaces. Platform system includes platform ontology subsystem, dynamic/energy subsystem, perception subsystem, control subsystem, communication subsystem and interactive subsystem. The six systems together form the most basic units of USV, each of which is an independently-run subsystem designed to complete different tasks. The task load system includes loaded equipments that can perform tasks, as well as supporting servo mechanisms and devices. Different task load systems can be planned according to different mission purposes.
Among them, each subsystem of the platform system is defined as follows:
(1) Sub-system of platform body: including hull design and layout, material and structure and platform machinery. It is the most basic component of unmanned ship, providing buoyancy, space arrangement for the whole system, actuator and necessary protective conditions;
(2) Dynamic/energy subsystem: including propulsion system and power supply system, providing necessary water surface maneuvering ability for unmanned ships, and providing power support for control system and task load system, etc;
(3) Perception subsystem: including positioning and navigation system, external environment perception system and platform State perception system, providing necessary data sources, hardware and interface support for unmanned ship motion decision-making and control and self state monitoring;
(4) Control Subsystem: including the hardware and software of the control system. It is the “brain” of the unmanned ship, which is processed for the unmanned ship through the perception and control equipment of the whole ship, analyze the information of external space and internal environment, and realize the functions of autonomous navigation, autonomous obstacle avoidance and so on according to the core control algorithm;
(5) Communication subsystem: it includes communication equipment at the control end and the execution end, and builds the data link needed for the unmanned ship to perform the task;
(6) Interactive subsystem: including supporting equipment and interactive software, for the operators to control the unmanned ship, understand the state information, give autonomous instructions and other operations;
The definition of the task load system is as follows: the task load system refers to the instruments, equipment, weapons, supporting servo mechanism, devices and so on that unmanned ships carry out tasks, which are generally designed as plug-and-play modules. Different task load systems can be planned according to different task purposes and uses.
3. Key Technologies of USV
It is the product of marine technology development. The purpose of marine technology development is to improve the accuracy and continuity of data acquisition, and at the same time to improve the safety of data acquisition process and reduce its cost.
Marine Technology is divided into two major directions. One is platform technology or carrier technology, which mainly refers to the design, development and application of the carrier body. The other is sensor technology or load technology, it mainly refers to the design, development and analysis, storage and processing of obtained data of instruments and equipment. In terms of the division of discipline direction, the narrow sense of unmanned ship belongs to the platform technology, in the field of marine technology. Therefore, the core technology of unmanned ship is consistent with the core technology in the field of marine technology. The essence is to focus on the purpose of the task, the principle of loading and the characteristics of the working environment to apply and develop, the key technologies of the system design with function development as the main body mainly include the following aspects:
Special platform design
Focusing on the principle of task load, application requirements, operation methods and so on, the platform is designed specifically, such as noise suppression, weakening navigation disturbance, dynamic stability optimization, electromagnetic compatibility optimization and so on.
The instruments and equipments used in conventional ocean survey are mostly acoustic, optical and electrochemical contact sensors. The unmanned ship has shallow draft and compact layout space, so all kinds of instruments and equipment are vulnerable to platform vibration, self-noise, shaking in the navigation process and the generated splash, the influence of bubble surface layer, electromagnetic radiation and power system emission, etc., which causes decline of data quality and operation efficiency. Therefore, in the aspect of unmanned ship design, it is necessary to start from the perspective of system efficiency, focus on the principle of task load and the requirements of working environment, from the linear and structural design, load arrangement mode, and carry out targeted special design and treatment in aspects of power system selection, propulsion device optimization, motion control strategy design, power supply system design, etc.
4. Advantages of USV
As a kind of autonomous platform on the water surface, compared with traditional manned ships, USV carrying task loads features high flexibility, safety, strong concealment and low operation and maintenance costs, the scenarios that will play a role in the future mainly include the following three types: (1) replace the practitioners to carry out the work with high labor intensity and high safety risk; (2) replace the practitioners to carry out repetitive and long-term work; (3) replace the part with high construction cost, working mode or method with large human input.
To sum up, as USV technology develops these years and its tendency to prosper in the future, the technical maturity will gradually deepen and its application scope will gradually expand, especially in the fields of far-reaching sea investigation and engineering. Undoubtedly, USV will gradually replace some of the conventional means of ocean survey and ocean engineering. At the same time, the traditional ocean operation mode will undergo earthshaking changes.