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| 2. |
- Feng, Na, et al.
(författare)
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Predictive compensator based event-triggered model predictive control with nonlinear disturbance observer for unmanned surface vehicle under cyber-attacks
- 2022
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Ingår i: Ocean Engineering. - : Elsevier. - 0029-8018 .- 1873-5258. ; 259
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Tidskriftsartikel (refereegranskat)abstract
- The trajectory tracking problem of unmanned surface vehicles (USVs) with external disturbances and input constraints, under denial of service (DoS) is addressed in this paper. We propose a predictive compensator based event-triggered model predictive control with nonlinear disturbance observer (PC-ETMPC with NDO) strategy. A model predictive controller (MPC) based on a nominal USV model is combined with a nonlinear disturbance observer (NDO) to estimate and compensate external disturbances. A predictive compensator (PC) is used to compensate network attack signals, which reduces the adverse impact of cyber-attack on the system, and an event-triggered mechanism is used to save computational resources of the calculation of the MPC. The proposed strategy is feasible for implementation, and its stability is proved to ensure the stable operation of the system. Numerical simulations and comparison are performed to demonstrate the effectiveness and superiority of the proposed control strategy.
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| 3. |
- Luo, Peng, et al.
(författare)
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Observer-based fixed-time dynamic surface tracking control for autonomous surface vehicles under actuator constraints and denial-of-service attacks
- 2024
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Ingår i: Applied Mathematics and Computation. - : Elsevier. - 0096-3003 .- 1873-5649. ; 465
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Tidskriftsartikel (refereegranskat)abstract
- This paper proposes a novel trajectory tracking control strategy for autonomous surface vehicles (ASVs), subject to actuator constraints and under denial-of-service (DoS) attacks. Firstly, a fixed-time disturbance observer (FTDO) is used to estimate and compensate unknown external disturbances, which enhances the robustness of the motion system. Secondly, a novel fixed-time filter is designed by combining dynamic surface technology with fixed-time control, which avoids the problem of differential explosion, and reduces the filtering error. Lastly, in order to address the effects of actuator constraints and DoS attacks, an auxiliary system (AS) and a compensation system (CS) are included in the fixed-time dynamic surface controller based on FTDO. The proposed method improves the robustness, stability and accuracy of the closed-loop system. Additionally, the reference tracking error converges to the neighborhood of the origin within a fixed-time. The superiority of the proposed control method over traditional control strategies from the existing literature is demonstrated in simulations.
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| 4. |
- McFiggans, Gordon, et al.
(författare)
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Secondary organic aerosol reduced by mixture of atmospheric vapours
- 2019
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 565:7741, s. 587-593
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Tidskriftsartikel (refereegranskat)abstract
- Secondary organic aerosol contributes to the atmospheric particle burden with implications for air quality and climate. Biogenic volatile organic compounds such as terpenoids emitted from plants are important secondary organic aerosol precursors with isoprene dominating the emissions of biogenic volatile organic compounds globally. However, the particle mass from isoprene oxidation is generally modest compared to that of other terpenoids. Here we show that isoprene, carbon monoxide and methane can each suppress the instantaneous mass and the overall mass yield derived from monoterpenes in mixtures of atmospheric vapours. We find that isoprene 'scavenges' hydroxyl radicals, preventing their reaction with monoterpenes, and the resulting isoprene peroxy radicals scavenge highly oxygenated monoterpene products. These effects reduce the yield of low-volatility products that would otherwise form secondary organic aerosol. Global model calculations indicate that oxidant and product scavenging can operate effectively in the real atmosphere. Thus highly reactive compounds (such as isoprene) that produce a modest amount of aerosol are not necessarily net producers of secondary organic particle mass and their oxidation in mixtures of atmospheric vapours can suppress both particle number and mass of secondary organic aerosol. We suggest that formation mechanisms of secondary organic aerosol in the atmosphere need to be considered more realistically, accounting for mechanistic interactions between the products of oxidizing precursor molecules (as is recognized to be necessary when modelling ozone production).
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| 5. |
- Sarrafzadeh, Mehrnaz, et al.
(författare)
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Impact of NOx and OH on secondary organic aerosol formation from β-pinene photooxidation
- 2016
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Ingår i: Atmospheric Chemistry and Physics. - 1680-7316 .- 1680-7324. ; 16, s. 11237-11248
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Tidskriftsartikel (refereegranskat)abstract
- In this study, the NOx dependence of secondary organic aerosol (SOA) formation from photooxidation of the biogenic volatile organic compound (BVOC) β-pinene was comprehensively investigated in the Jülich Plant Atmosphere Chamber. Consistent with the results of previous NOx studies we found increases of SOA yields with increasing [NOx] at low-NOx conditions ([NOx]0 < 30ppb, [BVOC]0 [NOx]0 > 10ppbCppb-1). Furthermore, increasing [NOx] at high-NOx conditions ([NOx]0 > 30ppb, [BVOC]0 [NOx]0 ∼ 10 to ∼ 2.6ppbCppb-1) suppressed the SOA yield. The increase of SOA yield at low-NOx conditions was attributed to an increase of OH concentration, most probably by OH recycling in NO+HO2 → NO2+OH reaction. Separate measurements without NOx addition but with different OH primary production rates confirmed the OH dependence of SOA yields. After removing the effect of OH concentration on SOA mass growth by keeping the OH concentration constant, SOA yields only decreased with increasing [NOx]. Measuring the NOx dependence of SOA yields at lower [NO] [NO2] ratio showed less pronounced increase in both OH concentration and SOA yield. This result was consistent with our assumption of OH recycling by NO and to SOA yields being dependent on OH concentrations. Our results furthermore indicated that NOx dependencies vary for different NOx compositions. A substantial fraction of the NOx-induced decrease of SOA yields at high-NOx conditions was caused by NOx-induced suppression of new particle formation (NPF), which subsequently limits the particle surface where low volatiles condense. This was shown by probing the NOx dependence of SOA formation in the presence of seed particles. After eliminating the effect of NOx-induced suppression of NPF and NOx-induced changes of OH concentrations, the remaining effect of NOx on the SOA yield from β-pinene photooxidation was moderate. Compared to β-pinene, the SOA formation from α-pinene photooxidation was only suppressed by increasing NOx. However, basic mechanisms of the NOx impacts were the same as that of β-pinene.
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| 7. |
- Zhang, Tengfei, et al.
(författare)
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A fault reconfiguration strategy based on adjustable space operator discrete state transition algorithm for ship microgrid system
- 2022
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Ingår i: Electric power systems research. - : Elsevier. - 0378-7796 .- 1873-2046. ; 205
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Tidskriftsartikel (refereegranskat)abstract
- As an independent power supply network, when the ship ring microgrid system (SRMS) fails or is damaged, the power-loss load can be reasonably distributed to other power sources through the control switch, thereby improving the reliability of the power grid. We consider the maximum power load, minimum switching action and generator efficiency as the reconfiguration goals. In order to complete the reconfiguration quickly, we present an optimization strategy based on an adjustable space operator (ASO) and the discrete state transition algorithm (DSTA), the ASODSTA. The main idea of DSTA is to use four spatial geometric operators to find the optimal solution. The optimization is completed by combining the operators with the sigmoid function, and an ASO is proposed as the variable of the sigmoid function. The spatial distribution of the candidate solutions is more widespread through the unification of the four operators. The introduction of the sigmoid function and the ASO improves the quality of the global optimal solution and shortens the running time of the algorithm. The simulation results show that the proposed method can solve the SRMS reconfiguration problem faster and more effectively by comparing with the algorithms EO, WOA, GWO and BPSO in the references.
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