Search Results (21)

This study proposes a bidirectional underwater optical wireless communication network that maximizes data transmission capacity by dynamically switching between underwater and aerial optical paths based on channel conditions. The proposed system employs adaptive modulation and beam steering techniques to address dynamic factors, such as turbidity and transmission distance, in underwater channels. The experimental results revealed that switching to the aerial optical path when the underwater transmission distance exceeded 1.8 m led to significant performance improvements, with consistent SNR and bit rates maintained in the aerial channel, unlike the exponential degradation observed underwater. Dynamic evaluations demonstrated that the system maintained high transmission capacity and SNR stability, even with incremental increases in underwater distances. In a 4K UHD video streaming experiment, switching from the underwater optical path to the aerial path reduced video quality degradation, delivering near-original video quality with latency as low as 20 ms. Furthermore, tolerance experiments for beam steering misalignment showed a sharp performance drop at a maximum misalignment of 2 degrees, with a 12 dB SNR loss and a reduction of 222 Mbps in transmission capacity. These findings suggest that selectively utilizing underwater and aerial optical paths based on channel conditions enables reliable and efficient data transmission, paving the way for next-generation underwater optical wireless communication networks. Full article

Power transformers are vital components of electrical power systems, ensuring reliable and efficient energy transfer between high-voltage transmission and low-voltage distribution networks. However, they are prone to various faults, such as insulation breakdowns, winding deformations, partial discharges, and short circuits, which can disrupt electrical service, incur significant economic losses, and pose safety risks. Traditional fault diagnosis methods, including visual inspection, dissolved gas analysis (DGA), and thermal imaging, face challenges such as subjectivity, intermittent data collection, and reliance on expert interpretation. To address these limitations, this paper proposes a novel distributed approach for multi-fault diagnosis of power transformers based on a self-organizing neural network combined with data augmentation and incremental learning techniques. The proposed framework addresses critical challenges, including data quality issues, computational complexity, and the need for real-time adaptability. Data cleaning and preprocessing techniques improve the reliability of input data, while data augmentation generates synthetic samples to mitigate data imbalance and enhance the recognition of rare fault patterns. A two-stage classification model integrates unsupervised and supervised learning, with k-means clustering applied in the first stage for initial fault categorization, followed by a self-organizing neural network in the second stage for refined fault diagnosis. The self-organizing neural network dynamically suppresses inactive nodes and optimizes its training parameter set, reducing computational complexity without sacrificing accuracy. Additionally, incremental learning enables the model to continuously adapt to new fault scenarios without modifying its architecture, ensuring real-time performance and adaptability across diverse operational conditions. Experimental validation demonstrates the effectiveness of the proposed method in achieving accurate, efficient, and adaptive fault diagnosis for power transformers, outperforming traditional and conventional machine learning approaches. This work provides a robust framework for integrating advanced machine learning techniques into power system monitoring, paving the way for automated, real-time, and reliable transformer fault diagnosis systems. Full article

As the main mechanical transmission parts, the gears are usually exposed to wear, corrosion, and fatigue; their failure in a poor working environment may cause a huge economic loss and waste of resources. Laser cladding (LC) has been proven to quickly repair parts at good metallurgical bonding performance and has flexible scanning strategies and a wide material selection. Therefore, LC technology can be considered an ideal approach to repairing damaged gear. However, the repair of damaged teeth by LC has not been systematically reported. In this paper, a series of progressive works have been carried out to systematically investigate the repair process of broken gears by LC. Firstly, process parameters, overlapping ratio, and Z-increment for Ni60 powder on 20CrMnTi were optimized. Secondly, the effects of deposition strategies on morphologies of single-layer and multi-layer multi-tracks were carefully analyzed. Then, the gear repair was successfully realized based on obtained optimized parameters. Finally, the phase composition, microstructure, hardness, and wear properties of the repaired gear tooth were analyzed by XRD, SEM, microhardness tester, and friction and wear tester. The results show that the remanufactured tooth can recover its appearance before breakage. The repaired zone is mainly composed of γ-Ni, Cr₇C₃, Cr₂₃C₆, and CrB phases. The micro-hardness and wear volume loss of the repaired zone is 60.63 ± 1.23HRC and 1674.983 μm², which are consistent with those of the other teeth. This study is expected to expand the application of LC technology and provide guidance to engineers in the repair of damaged parts. Full article

A novel, fully distributed controller with a rapid convergence rate is developed to ensure the optimal loading dispatch for interconnected DC MGs. It comprises local and global-control levels, handling the economic load allocations in a finite-time manner, for distinct MGs and cluster of MGs, respectively. The local-control layer guarantees MG’s economic operation by matching the incremental costs (ICs) of all DGs, respecting the power equilibrium among generations and demands, DGs’ generation limits, as well as the transmission line losses. Furthermore, the economic operation of battery energy sources is considered, in the optimization problem, to strengthen the overall reliability and maximize energy arbitrage. The global controller adjusts MGs’ voltage references to determine the optimal exchanged power, between MGs, for reducing the global total generation cost (TGC). A rigorous analysis is developed to confirm the stable convergence of the developed controller. Extensive simulation case studies demonstrate the superiority of the proposed control system. Full article

This study investigates the effects of face masks on physiological and voice parameters, focusing on cyclists that perform incremental sports activity. Three healthy male subjects were monitored in a climatic chamber wearing three types of masks with different acoustic properties, breathing resistance, and air filtration performance. Masks A and B were surgical masks made of hydrophobic fabric and three layers of non-woven fabric of 100% polypropylene, respectively. Mask S was a multilayer cloth mask designed for sports activity. Mask B and Mask S behave similarly and show lower sound attenuation and sound transmission loss and lower breathing resistance than Mask A, although Mask A exhibits slightly higher filtration efficiency. Similar cheek temperatures were observed for Masks A and B, while a significantly higher temperature was measured with Mask S at incremental physical activity. No differences were found between the masks and the no-mask condition for voice monitoring. Overall, Mask B and Mask S are suitable for sports activities without adverse effects on voice production while ensuring good breathing resistance and filtration efficiency. These outcomes support choosing appropriate masks for sports activities, showing the best trade-off between breathing resistance and filtration efficiency, sound attenuation, and sound transmission loss. Full article

This study aims to evaluate the effects of price liberalization on energy consumption intensity, because price liberalization leads to improved productivity, energy consumption management, and consumption reform. Although the energy consumption of large-scale factories and industries has increased dramatically, and the energies losses have an increment in the power transmission lines, this policy can result in decreasing the energy consumption intensity due to the changes in consumption patterns. If there is a correlation between two variables, the price can be a valid variable to control cost and increase consumption efficiency. The augmented Dickey–Fuller (ADF) and the Chi-squared tests are also employed to investigate the maneuverability of these variables in the first-order contrast. In this case study, the energy consumption intensity response to price changes using the data gathered between 1988–2020, has gained a confidence interval of these reactions at 95%. The proposed vector autoregressive (VAR) model has forecasted the action and reaction of the end-user, to investigate the future shocks between 2020–2050, considering a new price shock, in the Iranian energy market for the first time. The research findings have shown that energy price liberalization leads to the energy intensity improvement, however, the end-user (shocking) reactions should be investigated to implement a more sustainable policy that eases the new energy price rises. Full article

The paper shows a method of optimizing local initiatives in the energy sector, such as energy cooperatives and energy clusters. The aim of optimization is to determine the structure of generation sources and energy storage in order to minimize energy costs. The analysis is carried out for the time horizon of one year, with an hourly increment, taking into account various RES (wind turbines (WT), photovoltaic installations (PV), and biogas power plant (BG)) and loads (residential, commercial, and industrial). Generation sources and loads are characterized by generation/demand profiles in order to take into account their variability. The optimization was carried out taking into account the technical aspects of the operation of distribution systems, such as power flows and losses, voltage levels in nodes, and power exchange with the transmission system, and economic aspects, such as capital and fixed and variable operating costs. The method was calculated by sixteen simulation scenarios using Mixed-Integer Linear Programming (MILP). Full article

Digestate from biogas production can be recycled to the soil as conditioner/fertilizer improving the environmental sustainability of the energy supply chain. In a three-year maize-triticale rotation, we investigated the short-term effects of digestate on soil physical, chemical, and microbiological properties and evaluated its effectiveness in complementing the mineral fertilizers. Digestate soil treatments consisted of combined applications of the whole digestate and its mechanically separated solid fraction. Digestate increased soil total organic C, total N and K contents. Soil bulk density was not affected by treatments, while aggregate stability showed a transient improvement due to digestate treatments. A decrement of the transmission pores proportion and an increment of fissures was observed in digestate treated soils. Soil microbial community was only transiently affected by digestate treatments and no soil contamination from Clostridiaceae-related bacteria were observed. Digestate can significantly impair seed germination when applied at low dilution ratios. Crop yield under digestate treatment was similar to ordinary mineral-based fertilization. Overall, our experiment proved that the agronomic recycling of digestate from biogas production maintained a fair crop yield and soil quality. Digestate was confirmed as a valid resource for sustainable management of soil fertility under energy-crop farming, by combining a good attitude as a fertilizer with the ability to compensate for soil organic C loss. Full article

In recent years, multiple technologies have been proposed with the aim of combining the characteristics of traditional planar and non-planar transmission lines. The first and most popular of these technologies is the Substrate Integrated Waveguide (SIW), where rows of metallic vias are mechanized in a printed circuit board (PCB). These vias, together with the top and bottom metal layers of the PCB, form a channel for the propagation of the electromagnetic fields, similar to that of a rectangular waveguide, but through a dielectric body, which increases the losses. To reduce these losses, the empty substrate integrated waveguide (ESIW) was recently proposed. In the ESIW, the dielectric is removed from the substrate, and this results in better performance (low profile and easy manufacturing as in SIW, but lower losses and better quality factor for resonators). Recently, to increase the operational bandwidth (monomode propagation) of the ESIW, the ridge ESIW (RESIW) and a transition from RESIW to microstrip line was proposed. In this work, a new and improved wideband transition from microstrip line (MS) to RESIW, with a dielectric taper based on the equations of the superellipse, is proposed. The new wideband transition presents simulated return losses in a back-to-back transition greater than 20 dB in an 87% fractional bandwidth, while in the previous transition the fractional bandwidth was 82%. This is an increment of 5%. In addition, the transition presents simulated return losses greater than 26 dB in an 84% fractional bandwidth. For validation purposes, a back-to-back configuration of the new transition was successfully manufactured and measured. The measured return loss is better than 14 dB with an insertion loss lower than 1 dB over the whole band. Full article

Two low-C steels microalloyed with niobium (Nb) were fabricated by simulated strip casting, one with molybdenum (Mo) and the other without Mo. Both steels were heat treated to simulate coiling at 900 °C to investigate the effect of Mo on the precipitation behaviour in austenite in low-C strip-cast Nb steels. The mechanical properties results show that during the isothermal holding at 900 °C the hardness of both steels increases and reaches a peak after 3000 s and then decreased after 10,000 s. Additionally, the hardness of the Mo-containing steel is higher than that of the Mo-free steel in all heat-treated conditions. Thermo-Calc predictions suggest that MC-type carbides exist in equilibrium at 900 °C, which are confirmed by transmission electron microscopy (TEM). TEM examination shows that precipitates are formed after 1000 s of isothermal holding in both steels and the size of the particles is refined by the addition of Mo. Energy dispersive spectroscopy (EDS) and electron energy loss spectroscopy (EELS) reveal that the carbides are enriched in Nb and N. The presence of Mo is also observed in the particles in the Nb-Mo steel during isothermal holding at 900 °C. The concentration of Mo in the precipitates decreases with increasing particle size and isothermal holding time. The precipitates in the Nb-Mo steel provide significant strengthening increments of up to 140 MPa, higher than that in the Nb steel, ~96 MPa. A thermodynamic rationale is given, which explains that the enrichment of Mo in the precipitates reduces the interfacial energy between precipitates and matrix. This is likely to lower the energy barrier for their nucleation and also reduce the coarsening rate, thus leading to finer precipitates during isothermal holding at 900 °C. Full article

Two-way relaying channel (TWRC) improves the throughput of one-way relaying channel through network coding at the relay. Time division broadcast (TDBC) is one typical protocol for TWRC, but with three time slots for one round information exchange leading to throughput loss. To enhance throughput performance, incremental redundancy transmission is usually incorporated into TDBC (i.e., TDBC-IR) by one bit feedback, indicating the successful or failed transmission. Nevertheless, TDBC-IR still suffers in throughput since it cannot fully exploit and adapt to the varying channel dynamics. In the paper, we propose a dynamic TDBC protocol with incremental redundancy in the form of rateless coding (i.e., DTDBC-RC) to fully utilizing the varying channel dynamics. In DTDBC-RC, the two sources first transmit in rateless coding way with given maximum allowable transmission time, and then the relay retransmits or not based on its decoding results. To reveal the advantages of DTDBC-RC, we analyze its performance comprehensively in terms of outage probability, expected rate, and diversity-multiplexing trade-off (DMT). We also present a subslot realization scheme for DTDBC-RC (i.e., sub-DTDBC-RC) since the DMT of DTDBC-RC cannot be obtained directly. Simulation and numerical results show the performance advantage of DTDBC-RC (or sub-DTDBC-RC) over TDBC-IR in terms of both expected rate and DMT. Full article

Power transmission and protection of power electronics–electromagnetic actuators are crucial parts in renewable energy systems (energy management of photovoltaic, wind power, hybrid and electric vehicles). Consistency optimization of electromagnetic actuators has attracted extensive attention from corporations in competitive markets. Robust design has been widely applied for reducing the influence of uncertainties in the manufacturing process to improve the consistency of product quality. However, the cost factors of the actual manufacturing process are not fully considered in state-of-art methods. Although the consistency has been improved, the optimization scheme may not be optimal from the perspective of engineering applications, because unnecessary cost increments may be produced. In this paper, an application-oriented robust design method for consistency optimization is proposed. The impact of tolerance values on quality loss and manufacturing cost can be considered simultaneously to guide the tolerance optimization process. Thus, the optimal solution of total loss is obtained by optimizing the quality fluctuation to the design objective with the minimum increment of manufacturing cost. An example of the consistency optimization of an electromagnetic actuator used in the photovoltaic system is presented to illustrate the procedure and verify the effectiveness of the proposed method. Full article

We consider a Wireless Sensor Network (WSN) monitoring environmental data. Compressive Sensing (CS) is explored to reduce the number of coefficients to transmit and consequently save the energy of sensor nodes. Each sensor node collects N samples of environmental data, these are CS coded to transmit $M<N$ values to a sink node. The M CS coefficients are uniformly quantized and entropy coded. We investigate the rate-distortion performance of this approach even under CS coefficient losses. The results show the robustness of the CS coding framework against packet loss. We devise a simple strategy to successively approximate/quantize CS coefficients, allowing for an efficient incremental transmission of CS coded data. Tests show that the proposed successive approximation scheme provides rate allocation adaptivity and flexibility with a minimum rate-distortion performance penalty. Full article

Wireless Body Area Networks (WBANs) are single-hop network systems, where sensors gather the body’s vital signs and send them directly to master nodes (MNs). The sensors are distributed in or on the body. Therefore, body posture, clothing, muscle movement, body temperature, and climatic conditions generally influence the quality of the wireless link between sensors and the destination. Hence, in some cases, single hop transmission (‘direct transmission’) is not sufficient to deliver the signals to the destination. Therefore, we propose an emergency-based cooperative communication protocol for WBAN, named Critical Data-based Incremental Cooperative Communication (CD-ICC), based on the IEEE 802.15.6 CSMA standard but assuming a lognormal shadowing channel model. In this paper, a complete study of a system model is inspected in the terms of the channel path loss, the successful transmission probability, and the outage probability. Then a mathematical model is derived for the proposed protocol, end-to-end delay, duty cycle, and average power consumption. A new back-off time is proposed within CD-ICC, which ensures the best relays cooperate in a distributed manner. The design objective of the CD-ICC is to reduce the end-to-end delay, the duty cycle, and the average power transmission. The simulation and numerical results presented here show that, under general conditions, CD-ICC can enhance network performance compared to direct transmission mode (DTM) IEEE 802.15.6 CSMA and benchmarking. To this end, we have shown that the power saving when using CD-ICC is 37.5% with respect to DTM IEEE 802.15.6 CSMA and 10% with respect to MI-ICC. Full article

The presence of optimized distributed generation (DG) with suitable distribution network reconfiguration (DNR) in the electrical distribution network has an advantage for voltage support, power losses reduction, deferment of new transmission line and distribution structure and system stability improvement. However, installation of a DG unit at non-optimal size with non-optimal DNR may lead to higher power losses, power quality problem, voltage instability and incremental of operational cost. Thus, an appropriate DG and DNR planning are essential and are considered as an objective of this research. An effective heuristic optimization technique named as improved evolutionary particle swarm optimization (IEPSO) is proposed in this research. The objective function is formulated to minimize the total power losses (TPL) and to improve the voltage stability index (VSI). The voltage stability index is determined for three load demand levels namely light load, nominal load, and heavy load with proper optimal DNR and DG sizing. The performance of the proposed technique is compared with other optimization techniques, namely particle swarm optimization (PSO) and iteration particle swarm optimization (IPSO). Four case studies on IEEE 33-bus and IEEE 69-bus distribution systems have been conducted to validate the effectiveness of the proposed IEPSO. The optimization results show that, the best achievement is done by IEPSO technique with power losses reduction up to 79.26%, and 58.41% improvement in the voltage stability index. Moreover, IEPSO has the fastest computational time for all load conditions as compared to other algorithms. Full article