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Preventing Collisions at Sea
Published in David House, Seamanship Techniques, 2019
Special features of certain types of craft also bring with them inherent problems. Hovercraft, for instance, generate considerable noise and as such operators of these craft may not readily hear sound manoeuvring signals made by other vessels. They also exhibit a flashing yellow light at 120 flashes or more per minute. A similar flashing yellow light, at a slower frequency, is relevant to some submarine types when navigating on the surface. Little wonder, then, that watch officers may be confused with what type of vessel they are dealing with.
Observation reconstruction and disturbance compensation-based position control for autonomous underwater vehicle
Published in Systems Science & Control Engineering, 2022
Wanping Song, Zengqiang Chen, Mingwei Sun, Qinglin Sun
As a classic nonlinear control technology, active disturbance rejection control (ADRC) was first proposed by Han (1998). The basic idea of ADRC is to observe and compensate the nonlinear dynamics, model uncertainties, and external disturbances in the system in real-time through the extended state observer (ESO) (Han, 2008). Gao linearized the ESO (LESO), and simplify the original ADRC into the Linear ADRC (LADRC) Gao (2003). The excellent performance of ADRC has been verified in many aspects, such as an aerial vehicle, hovercraft, and power systems (Morales et al., 2015; Zhao et al., 2020; Zheng et al., 2020). In recent years, disturbance rejection has become a research hotspot in the field of control (Chen et al., 2016). It is hoped that there will have better estimation and compensation methods to make the controller have the good capability. Fischer et al. (2014) developed a nonlinear control method using a continuous robust integral of the sign of the error (RISE) to compensate for disturbance and uncertainty for a fully-actuated AUV. Fang et al. (2018) combined ADRC with fractional-order–proportional–integral–derivative (FOPID), the ADRC-FOPID control scheme for hydro turbine speed governor system was proposed, and the proposed control scheme has the strong anti-disturbances capability and better performance. To improve the robustness of the controller, Chen et al. (2020) and Khodayari and Balochian (2015), respectively, used reinforcement learning and fuzzy rules to realize the real-time adjustment of controller parameters according to the state of the controlled object.
Additive manufacturing of a shift block via laser powder bed fusion: the simultaneous utilisation of optimised topology and a lattice structure
Published in Virtual and Physical Prototyping, 2020
Sang Hoon Kim, Si-Mo Yeon, Jae Hyang Lee, Young Won Kim, Hyub Lee, Jiyong Park, Nak-Kyu Lee, Joon Phil Choi, Clodualdo Aranas, Yong Jin Lee, Seouk An, Kyunsuk Choi, Yong Son
The Republic of Korea Navy has been required to rapidly supply shift blocks mounted on crankshafts to support each of the five turbine blades in a hovercraft used offshore. The hovercraft is typically operated in extreme conditions, and disruptions occur frequently due to the ongoing demand for vehicle parts. A shift block consists of several components with both precise and irregular geometries that are achieved using complex cutting and milling, and are difficult to fabricate using conventional methods. Furthermore, the setup processes involve a high cost for designing a mould for a limited number of parts, a certified degree of forging, and machining the as-prepared substance by a skilled person. Subsequently, the part should be replaced annually to ensure good durability and thus cannot be fabricated using high-performance metals and alloys such as Ti–Al, Co–Cr, Cr–V, etc., except for stainless-steel types. In the worst case, manufacturers would stop the production of outdated parts that are profitless, thus discarding their blueprint. In practice, the original equipment manufacturer no longer produces specific parts for the air-cushioned hovercraft assault vehicle that is still in use by the Republic of Korea Navy. Hence, laser powder bed fusion (LPBF)-based additive manufacturing is an effective method for rapidly and accurately producing the part in one step that can serve as a replacement part in situ without requiring expensive moulds, fitting tools, or frequent cutting and complicated milling processes (Kim et al. 2017a; Martin et al. 2017; Post et al. 2019; Ryabokon 2017; Sutton et al. 2017; Wang et al. 2018b).
Cooperative vehicular platooning: a multi-dimensional survey towards enhanced safety, security and validation
Published in Cyber-Physical Systems, 2023
Ênio Vasconcelos Filho, Ricardo Severino, Pedro M. Salgueiro dos Santos, Anis Koubaa, Eduardo Tovar
Several testbeds have been developed to evaluate autonomous vehicles, but they have limitations regarding Co-VP analysis. For example, the authors of [153] developed a low-cost testbed that can be implemented in different vehicle models to test different control algorithms for autonomous trajectory following. However, this testbed lacks V2× communications support and uses onboard sensors for platooning testing. Two other testbeds for platooning that do not support V2V communication are presented in [155] and [154]. The latter uses the HoTDeC hovercraft, which provides greater flexibility but has significantly different vehicle dynamics from a traditional car.