University of Southern Brittany

Thrust allocation is one of the key technologies in dynamic positioning (DP) systems. Accurately allocating the thrust and angle of each thruster will achieve the desired force and moment of the ships, which is crucial for improving the positioning accuracy and positioning performance of marine ships. This paper develops an improved Non-dominated Sorting Genetic Algorithm (NSGA-II) to handle thrust allocation problem of dynamic positioning (DP) system in rough sea conditions. Firstly, the multi-objective optimisation model is built considering the thrust prohibited area, output angle, output thrust, angle change rate and thrust change rate as the constraints, and considering the power consumption, thrust error and thruster wear, and singular structure penalty term as the optimisation objectives simultaneously. Then, an improved NSGA-II algorithm is proposed to optimise the selection process of Pareto-optimal solution. Finally, multiple simulation results show that improved NSGA-II has better optimisation performance compared with basic NSGA-II. All of the comparisons could fully be conducted to demonstrate the effectiveness and advantages of the proposed algorithm.

Since 10 May, 2018, a significant number of volcanic and seismic events have been recorded in Mayotte, in the Comoros Archipelago of the Indian Ocean. Detailed bathymetry of Mayotte′s eastern regions has uncovered steep underwater slopes. A recent study in the area investigated liquefaction-prone layers associated with low sea-level depositions. However, the reason for the presence of such ‘weak zones’ remained unknown. In the present study, we examined samples from Mayotte’s slopes to investigate the reason for liquefaction at the particle-scale of such layers. Our results show that biogenic particles in naturally sedimented environments can crush under cyclic or static loading even with large amounts of fines. In the case of Mayotte’s slopes, the external loading threshold was found to be 500 kPa under K 0 -conditions. Our findings highlight the complex behavior of biogenic-dominant sediments, their impact on classification and overall behavior, and their potential implications for the design of wind farms.

This paper introduces a novel type of sequences called C4-sequences. C4-sequences share similar optimal auto-correlation properties with Zadoff-Chu sequences. However, C4-sequences offer the additional advantage of being also optimal (in the sense of minimal Euclidean distance between sequences) for four truncation lengths, providing flexibility in adapting to different channel conditions without compromising performance. Moreover, unlike Zadoff-Chu sequences, the points of a constellation associated with a C4-sequence are not limited to the unit circle. This opens up possibilities for achieving shaping gain, leading to enhanced spectral efficiency. By combining a truncated C4-sequence modulation as an inner code with a fixed-rate non-binary outer code, flexible and performant rate-adaptive communication systems can also be achieved. Finally, the notion of C4-sequences can be generalized.

In order to reduce the contamination of marine ecosystems by plastic materials, the scientific community is engaged in the development of biodegradable substitutes for conventional plastics. While certain candidates have been successfully tested in coastal marine environments, the degradation process in deep-sea environments remains poorly understood. This study examined the degradation of two industrial biopolyesters, a poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) and a polybutylene-succinate (PBS), in two deep marine environments of the Middle and Eastern Atlantic, at depths of 780 and 1740 m, as well as under laboratory conditions under hydrostatic pressure and without micro-organisms. The findings reveal a considerable biodeterioration of PHBV and a pronounced influence of flax fibre reinforcement on the degradation mechanisms. Conversely, PBS exhibits minimal to no indications of degradation. Additionally, the results confirm that biotic factors are the primary determinants of the degradation processes, with no degradation observed under abiotic conditions.

Recently, Younes et al. (2024) proposed an efficient multi-party semi-quantum secret sharing (SQSS) scheme that generalizes Tian et al.’s three-party protocol (Tian et al. Quantum Inf. Process. 20(6), 2021) to accommodate multiple participants. This scheme retains the original advantages, such as high qubit efficiency and allowing the secret dealer, Alice, to control the message content. However, (He et al. Quantum Inf. Process 23(2), 2024) identified a vulnerability in Tian et al.’s protocol to the double CNOT attack (DCNA), which also affects the generalized scheme. In response, He et al. proposed an improved protocol to address this issue. Despite these improvements, their protocol is limited to two participants and remains a primarily two-way communication scheme, which does not fully prevent the Trojan horse attack without expensive quantum devices such as photon number splitters (PNS) and wavelength filters (WF). To address these issues, this paper develops a novel multi-party SQSS scheme using the quantum property between Bell states and the Hadamard operation to detect eavesdroppers. This new scheme is secure against the DCNA, intercept-resend attack, and collective attack. It employs a fully one-way communication scheme, entirely preventing the Trojan horse attack without costly quantum devices, aligning with the semi-quantum environment’s original intent. This new protocol also offers better qubit efficiency and allows Alice to share specific secrets.

The aim of this paper is to design and Finite Element Analysis (FEA) of a novel rotor topology for a permanent magnet synchronous reluctance machine. According to the advantages and drawbacks of the PMSyncRM and the SPMSM, a conventional PMSyncRM rotor design combined with sur‐face‐mounted magnets is introduced as the SPMSyncRM. The surface‐PM arc size is investigated, so that it is considered as multiplication of an integer coefficient and the angle between two adjacent slots of the stator. The analysis involves simulation of the electromagnetic characteristics and the numerical model of each structure using finite element method. Each E‐Magnetic character is calculated for a better understanding of the benefits of the SPMSyncRM. Applying 2D FEA, the optimised surface‐PM arc size is calculated and the static and dynamic operational behaviour of the SPMSyncRM is simulated. Moreover, short circuit analysis is performed to study the demagnetisation of magnets. All results are reported comparatively considering a conventional PMSyncRM, so that the proposed SPM‐SyncRM topology presents high torque‐power density, lower values of cogging torque, higher values of power factor and efficiency, better static and dynamic performance, and robustness towards demagnetisation.

Axial compressible strength is a key design parameter of CFRP laminate structures, especially for Aerospace where maximum flexure on wings is driven by the global margin of safety on compressive loads. One of its main limiting contributors is the non-linear shear behaviour of the unidirectional ply. This shear response can be predicted by using generated (quasi-)random microstructures set within representative volume elements (RVE). Different microstructures with or without clusters of fibres (resulting from manufacturing processes) are necessary to quantify the mechanical variability. The variability of the microstructures is characterised by the variation of the arrangement, the volume fraction and the misalignment of the fibres. This leads to significant variations in the mechanical performance, in particular for the shear behaviour. In this study, we propose a unified algorithm that makes it possible to generate all the different positions of fibres in microstructures with very high fibre volume fractions. The microstructural parameters responsible for variations in mechanical behaviour are identified to establish a correlation between fibre distribution and the mechanical response. Finally, a composite cross-section is analysed to estimate the local non-linear shear behaviour as well as the compressive strength as an example to illustrate the benefit of complex microstructures modelling.

Surface tension of metals is a data of interest for the simulation of welding or additive manufacturing. In this regard, surface tension of three steels has been measured with an experimental device of aerodynamic levitation with the well-known oscillating drop method (observation of the resonance frequency of the drop). Steel can be very sensitive to evaporation that occurs above melting point which can lead to the modification of the chemical composition and thus of the thermophysical properties. One option to limit evaporation is to reduce the duration of the experiment. In this perspective, a new acoustic method has been tested, which consists in exciting the sample with a frequency close to the resonance frequency for a fraction of second and then observing the frequency naturally adopted by the drop during a short relaxation time. This reduces the time of the experiment to less than 1 s, against about 10 s with the frequency sweep method previously used. Both methods are used and discussed in this article. The solicitation-relaxation method is found to significantly reduce the evaporation and thus provides more consistent results at high temperatures. For the steel on which this new method has been tested, the characteristic increasing–decreasing surface tension with temperature has been observed, which can have an impact on the melt pool dynamic in welding or additive manufacturing and should be considered in numerical simulation for better results.

The log-TGARCHX model is less restrictive in terms of the inclusion of exogenous variables and asymmetry lags compared to the GARCHX model. Nevertheless, adding less (or more) covariates than necessary may lead to under- or overfitting, respectively. In this context, we propose a new algorithm, called VS-LTGARCHX, which incorporates a variable selection procedure into the log-TGARCHX estimation process. Furthermore, the VS-LTGARCHX algorithm is applied to extremely volatile BTC markets using 42 conditioning variables. Interestingly, our results show that the VS-LTGARCHX models outperform benchmark models, namely the log-GARCH(1,1) and log-TGARCHX(1,1) models, in one-step-ahead forecasting.

Industry 4.0 comes with the human-autonomy teaming (HAT) paradigm. Autonomous agents and operators are working as teammates with complementary competencies. Agents can make proposals thanks to new sensor technologies and data analyzing methods. The operator’s new task is to accept or reject these proposals. Consequently, trust is central in an HAT environment. This experiment aims to understand the effects of agent-generated information on the operators’ decision-making, trust, and risk perception during cooperation operations. This cooperation aims to help operators to manage maintenance dates in a maritime context. To this end, participants formed a team with a predictive maintenance system that provided them with proposals for modifying the schedule. In each situation, participants had to decide whether to comply with the proposal or not. The variables modified were agent transparency (transparency about analytical uncertainty and/or environmental projections) and situation criticality (moderate or high). The participants’ trust, risk perception, and compliance were measured. The results show that trust is a predictor of decision-making and risk perception is a moderator of trust. Transparency and situation criticality, and their interaction, influence participants’ trust and risk perception. These effects are also present in participants’ compliance. Notably, transparency in the environmental projections with a high-criticality situation leads to lower compliance. Agent transparency and situation criticality play an important role in operator decision-making and trust building. As transparency helps improve HAT, situation criticality must be taken into account for a better understanding of its effects.

In material extrusion, while maintaining a constant mass flow rate, operations involving temperature-sensitive expandable materials show an increase in the volumetric flow rate at the nozzle exit. This research uses foamable filaments made of thermoplastic elastomers and thermally expanded microspheres (TEMs) to examine this phenomenon and focuses on continuous 3D printing of hybrid thermoplastic elastomer foam samples with density gradients. This is achieved by real-time adjustments to printing temperatures and layer heights. Using TEMs with a higher initial expansion temperature provides a linear density decline from 200 to 240 ∘$^{\circ }$C, allowing for the fabrication of gradient density structures by controlling 3D printing parameters. The pressure–volume–temperature investigation indicates that the expansion ratio of the foamable filament increases with TEM weight percent and a reduction in pressure, but the mass remains the same. Based on the volume conservation principle, custom G-codes are developed for strand analysis and hybrid cube production. It is observed that the layer height has a linear connection with flow rate, which increases with temperature. The material flow rate is key to controlling the foamable filament expansion, through which parts with gradient properties are produced. Finally, hybrid cubes made of filament containing 4 wt% of TEMs have been successfully fabricated.

The agricultural sector plays a crucial role in sustaining population growth and ensuring our well-being. However, as this sector faces numerous challenges due to environmental conditions and the increasing population, it is essential to identify natural alternatives that promote sustainable farming practices and protect the environment. Seaweed-based extracts have gained popularity in agriculture because of their numerous benefits for plant growth and health. This study focuses on Fucus vesiculosus Linnaeus, a prevalent brown seaweed species found along the Brittany coast. The research involved comparing Enzyme-Assisted Extraction (EAE) with conventional aqueous extraction methods for the purpose of determining the effectiveness of EAE in producing enriched extracts that could have an interesting agricultural application. The results indicates that enzymatic extraction of Fucus vesiculosus significantly increased the content of neutral sugars by 34% and reducing sugars by 21% in the extracts, compared to conventional aqueous extraction (WE). Regarding Plant Growth Regulators, the levels of Isopentenyladenosine (iPR) and Cis zeatin (cZ) were enhanced by 6 times and 28 times, respectively, when using EAE instead of WE. Additionally, the total phenolic content was notably higher in EAE extracts, showing a twofold increase over WE extracts. Furthermore, the various extracts demonstrated superior antioxidant activity compared to raw Fucus vesiculosus powder. Thus, this study confirms that EAE is an effective method for enriching Fucus vesiculosus extracts with various compounds that can play a vital role in agriculture.

This study aims at presenting a new proposal to perform the water capillary absorption test of hemp concretes, and to establish the parameters useful for analyzing the obtained results. Based on the standards of traditional materials, such as concrete and mortar, a protocol was proposed and executed by 8 laboratories through a round robin test. Homogeneous hemp concrete cubic specimens of edge 150 mm were cast, distributed to the laboratories, where they were conditioned before being submitted to the test. By adopting the new test procedure, it was possible to obtain consistent results after analyzing in both square root of time and log-time regimes. For each regime, two parameters couples CA and k (square root of time regime), IRA and K1 (log-time regime) were used to compare the obtained data, and validate successfully the round robin test.

Accurately measuring the velocity field (VF) of liquid metals is essential for optimizing and controlling high-temperature industrial processes, yet remains a challenging task despite the numerous existing velocimetry techniques. In this paper, a methodology for estimating the VF of a liquid metal pool is proposed. The experimental set-up used here to heat the metal sample up to the liquid state and collect data is presented. This set-up primarly intented to perform flash experimetns on liquid metals, allows contactless heating and data measurements by a high speed camera. The proposed methodology for estimating the VF consists then in implementing a Non-Rigid Registration between the different frames of the recorded temperature fields (TFs). This method is applied on TFs resulting from multiple experimental tests conducted on iron samples in the temperature range of 1850−2100 K. The consistency of the results is put to test via multiple validation tests. The influence of the main parameters is also evaluated. The results show that the proposed methodology allows a fine experimental quantification of liquid metal VFs with an estimated error of 8% and confirm the feasibility of the proposed approach.

The present research investigates the influence of chemical modifications on the surface of Diss fibers ( Ampelodesmos mauritanicus ) as an effective reinforcing agent for biocomposites based on poly (3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBV). The Diss fiber surface underwent three different chemical treatments: alkaline, alkaline/peroxide, and alkaline/silane. Changes in morphology, mechanical properties, thermomechanical behavior, and contact angle measurements of the biocomposite materials were studied according to the following weight ratio PHBV/Diss fibers 80/20. Scanning electron microscopy (SEM) analysis of the fractured surface of the biocomposite samples revealed improved adhesion between Diss fibers and the PHBV matrix after surface modification, compared with the unmodified sample. The study demonstrated that the incorporation of Diss fibers leads to an enhancement in the mechanical performances of PHBV‐based biocomposites. The tensile properties of the modified biocomposites showed a significant increase in Young's modulus compared with the biocomposites with untreated fiber. Similar trends were observed in the data obtained from dynamic mechanical analysis (DMA) and contact angle measurement. Overall, the study highlights the beneficial effects of Diss fibers modification, particularly with the alkali–silane combination, in enhancing the properties of PHBV biocomposites, there by broadening their potential application fields. Highlights The study explores the potential of Diss fibers as an effective reinforcement for PHBV‐based biocomposites. Fully biodegradable biocomposites based on PHBV/Diss fibers are melt‐compounded. Diss fibers are chemically modified by alkaline, alkaline/peroxide, and alkaline/silane. The chemical treatment has considerably enhanced the properties and morphology of the biocomposites, being however much higher for alkaline/silane treatment. The method can be used for specific applications and large‐scale production.