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The article shows the performance comparison between two marine engines, fuelled by diesel oil and natural gas respectively. Two different simulation codes, each for engine type, have been developed to extend the comparison to the whole working area of the examined engines. Although the maximum continuous power is very similar (about 2 MW at the same rotational speed), some differences exist in size, efficiency and pollutant emissions. The reasons are investigated through a specific thermodynamic analysis, by comparing the respective real cycles at several power and revolution values. In detail, the two combustion modes are analysed to explain the main differences that are found mostly in nitrogen oxides emissions

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The paper presents a path planning algorithm for ship guidance in presence of obstacles, based on an ad hoc modified version of the Rapidly-exploring Random Tree (RRT*) algorithm. The proposed approach is designed to be part of a decision support system for the bridge operators, in order to enhance traditional navigation. Focusing on the maritime field, a review of the scientific literature dealing with motion planning is presented, showing potential benefits and weaknesses of the different approaches. Among the several methods, details on RRT and RRT* algorithms are given. The ship path planning problem is introduced and discussed, formulating suitable cost functions and taking into account both topological and kinematic constraints. Eventually, an existing time domain ship simulator is used to test the effectiveness of the proposed algorithm over a number of realistic operation scenarios. The obtained results are presented and critically discussed.

While collisions and groundings still represent the most important source of accidents involving ships, autonomous vessels are a central topic in current research. When dealing with autonomous ships, collision avoidance and compliance with COLREG regulations are major vital points. However, most state-of-the-art literature focuses on offline path optimisation while neglecting many crucial aspects of dealing with real-time applications on vessels. In the framework of the proposed motion-planning, navigation and control architecture, this paper mainly focused on optimal path planning for marine vessels in the perspective of real-time applications. An RRT*-based optimal path-planning algorithm was proposed, and collision avoidance, compliance with COLREG regulations, path feasibility and optimality were discussed in detail. The proposed approach was then implemented and integrated with a guidance and control system. Tests on a high-fidelity simulation platform were carried out to assess the potential benefits brought to autonomous navigation. The tests featured real-time simulation, restricted and open-water navigation and dynamic scenarios with both moving and fixed obstacles.

Intelligent and/or autonomous vehicle technologies are rapidly growing to meet the needs of marine safety and transport efficiency. One of the requirements to manage autonomous vehicles includes the integration between route planning and automatic motion control. In the authors' opinion, the latter could be sketched in three different layers: obstacle detection, planning and actuation. Moreover, the three layers should be able to interact in real-time. Dealing with such a challenging task, one of the best techniques to develop and test the logic is the use of the time-domain simulation. In the present work, a simulation model, integrating a path planning algorithm in the presence of obstacles with a track keeping controller, is developed. The path planning is based on a modified version of the Rapidly-exploring Random Tree (RRT*) algorithm. The track keeping is based on the Line-of-Sight (LOS) waypoints navigation for underactuated vessels. To achieve more reliable results, a detailed ship simulation model is used as a benchmark. Different scenarios and navigation modes are successfully tested, and the results are presented and analysed.

From the working data of a dual-fuel marine engine, in this paper, we optimized and compared two waste-heat-recovery single-pressure steam plants—the first characterized by a saturated-steam Rankine cycle, the other by a superheated-steam cycle–using suitably developed simulation models. The objective was to improve the recovered heat from the considered engine, running with both heavy fuel oil and natural gas. The comparison was carried out on the basis of energetic and exergetic considerations, concerning various aspects such as the thermodynamic performance of the heat-recovery steam generator and the efficiency of the Rankine cycle and of the combined dual-fuel-engine–waste-heat-recovery plant. Other important issues were also considered in the comparison, particularly the dimensions and weights of the steam generator as a whole and of its components (economizer, evaporator, superheater) in relation to the exchanged thermal powers. We present the comparison results for different engine working conditions and fuel typology (heavy fuel oil or natural gas).