Having gained extensive experience in the design, construction and maintenance of highly complex vessels since the ‘90s, the marine arm…
System Engineering Approach for Conceptual Design of USV
This paper presents a system engineering approach for conceptual design of Unmanned Surface Vessel (USV) as shown in Figure 1. This approach provides ship designers guidance to establish the CONOPS, requirement analysis and eventually how to develop a feasible conceptual design study and cost estimation.
New USV designs are usually created in response to needs, such as the onset of new technologies and new operational requirements. These needs are identified by the stakeholders and are used as a basis for new USV design development. Defining the problem statement was the crucial first step in establishing the design’s purpose and direction. Finalizing the statement created several combinations and revisions. Similarly, the scope of effort required a careful analysis of the problem space to determine the boundaries of the design. USV designers will deal with a variety of stakeholders’ requirements, and operating and maintenance concepts.
With the clearly defined effective needs, CONOPS development shall be performed and discussed by all the stakeholders to determine what are the operational requirements, operating scenarios and profiles and suitable payload configurations for the USV. The CONOPS describes the use of system solution and its context. The CONOPS of USV can be for Maritime Security, Mine Counter-Measures (MCM) and Anti-Submarine Warfare (ASW). The USV which is specifically configured for the maritime security role needs to meet the operational requirements of patrol and surveillance. Some of the key design considerations will definitely be the surveillance sensors and weapon suite of the USV. The primary sensors can be one surveillance radar for search and detection of threats and one electro optical sensor (EOS) for precise target tracking purposes. The weapon system can range from a small to medium caliber remote weapon system. UAV can be a modular payload to enhance the USV’s situational awareness.
After understanding the needs, CONOPs, and constraints of the stakeholders, requirement analysis has to be performed for the operational requirements of the USV to be translated into desired functional requirements. The requirement analysis phase of the systems engineering process allows individual component functions of a concept to be determined and then later developed further into the means to execute the functions in an operational environment. Functional decomposition is performed to breakdown the functional requirements into sub-function forms. The functional architecture of the system is, first, defining all the pertinent high-level functions; second, decomposing the functions into logical groupings of “high-level” and “derived” functions; third, organizing the functions into appropriate model diagrams e.g. functional flow block diagram (FFBD; Blanchard and Fabrycky 2011) that indicate the logical ordering or relation of functions; and fourth, performing an analysis of the functional architecture in order to understand what would need to be accomplished by the entire system of systems to make the solution concept valid. By decomposing the functions, many pertinent features of the USV could be derived and these insights can be used to generate accurate system requirements and performance.
Conceptual Design Studies
The design process is iterative, like a spiral model (Evans 1959), towards an efficient USV design. The capabilities of the USV have already been identified in the previous stages and the design is refined to meet the requirements as the concept design develops. During the conceptual design study stage, the preliminary USV weight, dimensions, and topside area can be approximated and determined based on the payload configuration, such as sensors, communication system and weaponry. Based on the specific mission needs, different sets of payload configurations can be inserted and evaluated using design methodology to derive satisfactory conceptual USV designs. It is also important to conduct the overall USV designs in conjunction with such analyses as ship hull, seakeeping, stability, speed, power and system availability & redundancy studies to demonstrate the feasibility of the design. Some constraints faced by USV designers are limited real estate, EMI/EMC issues and payload capacity of the USV.
Verification and Validation (V&V)
The conceptual design led to a model of the system. Verification and Validation (V&V) reviews ensured the model accurately and effectively reflected the USV functional architecture and its system performance e.g. navigation autonomy system performance. Thus after conceptual design stage, USV designers proceed to apply modelling and simulation for better understanding of how USV behaves and functions in different operation scenarios and the results help them to iterate a more effective and robust design, evaluation and operation of the USV.
After conceptual design and V&V stage, the designers should have developed the required design and system specifications information. This technical information will assist the cost estimators to accurately estimate costs. Cost estimation is necessary for tender process and for trade off studies.
Evaluation of Design
The USV designers must take all of these stakeholders’ feedbacks and inputs into their design considerations, explore alternatives, and later demonstrate to stakeholders their proposed design alternatives that meet the required operational requirements and profiles. In the process, the designers will explain to the stakeholders the trade-offs, limitations and feasible design boundaries. The stakeholders and designers can apply sensitivity analysis on various USV parameters. However, they must keep in mind that any upgrades to the parameters e.g endurance and payload configuration, it will result in a larger USV and higher cost. Lastly and most importantly, the overall USV design must be able to converge and achieve an acceptable optimized performance of all the autonomy system and weaponry suites in order to meet the USV’s operational requirements.
At times during designing of USV, the designers lose sight of the overall big picture, functionalities, and the mission needs of the vessel. The naval architects concentrate on the speed, endurance, displacement and ship stability calculation. The autonomy system designers are more concerned with the placement, feasibility checks, and optimization of the location of perception sensors and communication systems. The designers are designing in “silos,” and thus the design of the USV is not well integrated. At the conceptual phase, ship designers can apply systems engineering approach for the conceptual design of a USV. The designers can be brought together to understand the big picture and work towards a common set of functions and meet the overall requirements.