Search Results (21)

Modernizing irrigation systems (ISs) from traditional gravity methods to sprinkler and drip technologies has significantly improved water use efficiency. However, it has simultaneously increased electricity demand and operational costs. Integrating photovoltaic generators into ISs represents a promising solution, as solar energy availability typically aligns with peak irrigation periods. Despite this potential, photovoltaic pumping systems (PVPSs) often face reliability issues due to fluctuations in solar irradiance, resulting in frequent start/stop cycles and premature equipment wear. The IEC 62253 standard establishes procedures for evaluating PVPS performance but primarily addresses steady-state conditions, neglecting transient regimes. As the main contribution, the current paper proposes a non-intrusive, high-resolution monitoring system and a methodology to assess the performance of an isolated, high-power PVPS, considering also transient regimes. The system records critical electrical, hydraulic and environmental parameters every second, enabling in-depth analysis under various weather conditions. Two performance indicators, pumped volume efficiency and equivalent operating time, were used to evaluate the system’s performance. The results indicate that near-optimal performance is only achievable under clear sky conditions. Under the appearance of clouds, control strategies designed to protect the system reduce overall efficiency. The proposed methodology enables detailed performance diagnostics and supports the development of more robust PVPSs. Full article

The automated guided vehicle (AGV) is widely used in industrial environments for goods transportation. However, issues such as mechanical wear, reduced battery life, navigation error accumulation, and decreased operational efficiency caused by frequent starts and stops need to be addressed. This paper proposes an improved Autonomous Emergency Braking (AEB) algorithm to tackle these problems. The algorithm employs a stepwise deceleration strategy, effectively reducing the frequency of sudden stops and enhancing the system’s operational smoothness. The AEB algorithm not only considers straight-line driving scenarios but also optimizes deceleration strategies for turning scenarios, adjusting the deceleration detection range according to the turning trajectory. Additionally, a velocity smoothing algorithm is designed to ensure that speed changes during deceleration are gradual, avoiding abrupt speed variations that could impact the system. The feasibility of the AEB algorithm is validated through testing on actual equipment, and its performance is compared to that of a conventional emergency stop strategy. Experimental results show that the AEB algorithm significantly reduces the number of sudden stops, improves the AGV’s operational smoothness and safety, and demonstrates excellent adaptability and robustness across different operational conditions. Full article

Improving the capabilities of online condition monitoring systems, able to detect arising of catastrophic wear on cutting tools, has been an important target to be pursued for the metal cutting industry. Currently, different systems have been proposed, moved by the rising need of part quality improvements and production cost control. Despite this, cutter wear development, being related to several process variables and conditions, is still really difficult to be predicted accurately. This paper presents a detection wear method based on the time-domain analysis of vibro-acoustic signals. Specifically, cutter wear monitoring, using sound signals of a milling process, was performed at a laboratory level in a well-isolated working room. Sound signals were recorded at fixed main machining parameters, i.e., cutting speed, feed rate and depth of cut. The tests were carried out starting with a new set of inserts with significant wear conditions for the investigated process configuration. Results showed a consistent overlapping between the beginning of the catastrophic wear and an evident increment in the trend of the root mean square of the monitored acoustic signal, showing the potential of the methodology in detecting a suitable time to stop the milling process and to change the worn-out cutters. Full article

The present study aims to efficiently predict the wear volume of a journal bearing under start–stop operating conditions. For this purpose, the wear data generated with coupled mixed-elasto-hydrodynamic lubrication (mixed-EHL) and a wear simulation model of a journal bearing are used to develop a neural network (NN)-based surrogate model that is able to predict the wear volume based on the operational parameters. The suitability of different time series forecasting NN architectures, such as Long Short-Term Memory (LSTM), Gated Recurrent Unit (GRU), and Nonlinear Autoregressive with Exogenous Inputs (NARX), is studied. The highest accuracy is achieved using the NARX network architectures. Full article

Modern engine bearing materials encounter the challenge of functioning under conditions of mixed lubrication, low viscosity oils, downsizing, start–stop engines, potentially leading to metal-to-metal contact and, subsequently, premature bearing failure. In this work, two types of polymer overlays were applied to the bearing surface to compensate for extreme conditions, such as excessive loads and mixed lubrication. Two different polymer overlays, created through a curing process on a conventional engine bearing surface with an approximate thickness of 13 µm, were investigated for their friction and wear resistances under a 30 N load using a pin-on-disc setup. The results indicate that the newly developed polymer overlay (NDP, PAI-based coating) surface has a coefficient of friction (COF) of 0.155 and a wear volume loss of 0.010 cm³. In contrast, the currently used polymer overlay (CPO) in this field shows higher values with a COF of 0.378 and a wear volume loss of 0.024 cm³, which is significantly greater than that of the NDP. It was found that, in addition to accurately selecting the ratios of solid lubricants, polymer resins, and wear-resistant hard particle additives (metal powders, metal oxides, carbides, etc.) within the polymer coating, the effective presence of a transfer film providing low friction on the counter surface also played a crucial role. Full article

One route to reducing global CO₂ emissions is to improve the energy efficiency of machines. Even small improvements in efficiency can be valuable, especially in cases where an efficiency improvement can be realized over many millions of newly produced machines. For example, conventional passenger car combustion engines are being downsized (and also downspeeded). Increasingly, they are running on lower-viscosity engine lubricants (such as SAE 0W-20 or lower viscosity grades) and often also have stop–start systems fitted (to prevent engine idling when the vehicle is stopped). Some of these changes result in higher levels of mixed and boundary friction, and so accurate estimation of mixed/boundary friction losses is becoming of increased importance, for both estimating friction losses and wear volumes. Traditional approaches to estimating mixed/boundary friction, which employ real area of contact modelling, and assumptions such as the elastic deformation of asperities, are widely used, but recent experimental data suggest that some of these approaches underestimate mixed/boundary friction losses. In this paper, a discussion of the issues involved in reliably estimating mixed/boundary friction losses in machine elements is undertaken, highlighting where the key uncertainties lie. Mixed/boundary lubrication losses in passenger car and heavy-duty internal combustion engines are then estimated and compared with published data, and a detailed description of how friction is related to fuel consumption in these vehicles, on standard fuel economy driving cycles, is given. Knowing the amount of fuel needed to overcome mixed/boundary friction in these vehicles enables reliable estimates to be made of both the financial costs of mixed/boundary lubrication for today’s vehicles and their associated CO₂ emissions, and annual estimates are reported to be approximately USD 290 billion with CO₂ emissions of 480 million tonnes. Full article

A dedicated test bench is employed to record acoustic emission signals from dry gas seals under various operating conditions. Time-domain and frequency-domain analysis methods are utilized to process and analyze the acoustic emission signals during start/stop, stable operation, and two common fault states (end-face defects and compensation spring failure). Furthermore, feature recognition research is conducted. A method for identifying the operational states of seals (low-speed friction, gradual detachment, stable operation) based on the root mean square (RMS) was established, with transition points at speeds of 100 and 1000 RPM, respectively. Additionally, spectral analysis is conducted using Fourier transform to determine the frequency band of acoustic emission signals (240–320 kHz) generated during contact wear of dry gas seals. Investigation into two typical faults of dry gas seals reveals that the RMS value of the acoustic emission signal gradually increases with the rotational speed during the operation of dry gas seal end-face defects. This is attributed to the insufficient dynamic pressure effect on the end face, resulting in long-term wear and tear. When the dry gas seal compensates for spring failure, the RMS value of the acoustic emission signal initially increases, then decreases, and finally increases again as the speed increases. It reaches the stable operating inflection point when the end-face speed is 800 r/min. Full article

During the start-up process, air foil thrust bearings (AFTBs) come into contact and are prone to localized overheating and even failure. Frequent starts and stops are the major sources of wear. In this study, a transient mixed lubrication model considering the air rarefaction effect is established. In the model, asperity contact between the top foil of the air foil thrust bearing (AFTB) and the rotor surface is considered using a deterministic approach, and the deformation of the foil structure is considered using the elastic-aerodynamic coupling. The influences of bearing compliance, external load, acceleration time and contact stiffness on the tribological properties during the start-up process are investigated. The results show that the lift-off speed increases with the increase of the bearing compliance and of the external load. Specifically, the lift-off speed of AFTBs increases from 1950 rpm to 5325 rpm when the bearing compliance increases linearly from 0.2 to 1.0. When the external load increases from 10 N to 80 N, the lift-off speed is increased by approximately 30 times, from 450 rpm to 13,575 rpm. Furthermore, a decrease in the acceleration time of the rotor generates a decrease in the lift-off time and an increase in the contact stiffness of the bearing leads to a decrease in the lift-off speed of the bearing. By exploring the effects of the bearing parameters and working conditions on the tribological performance of AFTBs during start-up, the results presented in this study can provide theoretical support for improving start-up performance and designing high-reliability and long-life AFTBs. Full article

This article deals with methods and measurements related to environmental pollution and analysis of particle distribution in urban and suburban landscapes. Therefore, an already-invented sampling method for tyre road wear particles (TRWP) was used to capture online emission factors from the road. The collected particles were analysed according to their size distribution, for use as an input for particle distribution simulations. The simulation model was a main traffic intersection, because of the high vehicle dynamic related to the high density of start–stop manoeuvres. To compare the simulation results (particle mass (PM) and particle number (PN)) with real-world emissions, measuring points were defined and analysed over a measuring time of 8 h during the day. Afterwards, the collected particles were analysed in terms of particle shape, appearance and chemical composition, to identify the distribution and their place of origin. As a result of the investigation, the appearance of the particles showed a good correlation to the vehicle dynamics, even though there were a lot of background influences, e.g., resuspension of dust. Air humidity also showed a great influence on the recorded particle measurements. In areas of high vehicle dynamics, such as heavy braking or accelerating, more tyre and brake particles could be found. Full article

The next few years will be marked by major changes in the mobility sector in order to come closer to CO${}_2$ neutrality. Especially in the commercial vehicle sector, fuel cells can make an important contribution. In order to achieve this, the efficiency of all subcomponents of a vehicle has to be improved. This also includes the bearings in the electrical air compressors. The frequent start–stop cycles are critical, as they can lead to higher wear and thus a shorter service life. One solution is a prototype that can actively switch between a triangular profile and a round bearing shape. In this work, the two switching states are investigated experimentally. Instead of the thin bearing sleeve of the prototype, rigid sleeves are used for each switching shape. This allows the shape itself to be studied without the contribution of the stiffness of the thin bearing sleeve along with the actuators. The examination includes static load tests and run-out tests in the range of the lift-off speed. Alongside this, the difficulties of the bearing production and the improvement of the test rig used are pointed out. Full article

Faced with the biggest virus outbreak in a century, world governments at the start of 2020 took unprecedented measures to protect their healthcare systems from being overwhelmed in the light of the COVID-19 pandemic. International travel was halted and lockdowns were imposed. Many nations adopted measures to stop the transmission of the virus, such as imposing the wearing of face masks, social distancing, and limits on social gatherings. Technology was quickly developed for mobile phones, allowing governments to track people’s movements concerning locations of the virus (both people and places). These are called contact tracing applications. Contact tracing applications raise serious privacy and security concerns. Within Europe, two systems evolved: a centralised system, which calculates risk on a central server, and a decentralised system, which calculates risk on the users’ handset. This study examined both systems from a threat perspective to design a framework that enables privacy and security for contact tracing applications. Such a framework is helpful for App developers. The study found that even though both systems comply with the General Data Protection Regulation (GDPR), Europe’s privacy legislation, the centralised system suffers from severe risks against the threats identified. Experiments, research, and reviews tested the decentralised system in various settings but found that it performs better but still suffers from inherent shortcomings. User tracking and re-identification are possible, especially when users report themselves as infected. Based on these data, the study identified and validated a framework that enables privacy and security. The study also found that the current implementations using the decentralised Google/Apple API do not comply with the framework. Full article

A critical review of recent work on fuel lubricant interactions is undertaken. The work focusses on liquid fuels used in diesel and gasoline vehicles. The amount of fuel that contaminates the lubricant depends on driving conditions, engine design, fuel type, and lubricant type. When fuel contaminates a lubricant, the viscosity of the lubricant will change (it will usually decrease), the sump oil level may increase, there may be a tendency for more sludge formation, there may be an impact on friction and wear, and low speed pre-ignition could occur. The increased use of biofuels (particularly biodiesel) may require a reduction in oil drain intervals, and fuel borne additives could contaminate the lubricant. The move towards the active regeneration of particulate filters by delayed fuel post-injection and the move towards hybrid electric vehicles and vehicles equipped with stop-start systems will lead to increased fuel dilution. This will be of more concern in diesel engines, since significant fuel dilution could persist at sump oil temperatures in the range of 100–150 °C (whereas in gasoline engines the more volatile gasoline fuel will have substantially evaporated at these temperatures). It is anticipated that more research into fuel lubricant interactions, particularly for diesel engines, will be needed in the near future. Full article

Improving fuel economy and reducing emissions is nowadays more important than ever. Apart from powertrain electrification, automotive manufacturers have constantly been seeking to improve the efficiency of the internal combustion engine. Downsizing and boosting have become common practice in the internal combustion engine (ICE) design. Increased power density and torque output of modern boosted engines, in combination with the introduction of automatic stop-start systems and ultralow viscosity lubricants tends to stress the engine beyond the limits foreseen in the classical design. This leads to wear problems. Each engine component comes with a unique landscape of competing manufacturing technologies, among which advanced surface finishing and coating methods play an important role. This presentation provides an overview of different industrial trends related thereto. The role of lubricant on the engine tribology is studied for different engine designs. The importance of in-design “pairing” of low-viscosity motor oils with the engine characteristics is highlighted filling the gap in the understanding of complex interactions between the crankcase lubricant and engine mechanics. Full article

The COVID-19 pandemic has placed an unprecedented burden on public health and strained the worldwide economy. The rapid spread of COVID-19 has been predominantly driven by aerosol transmission, and scientific research supports the use of face masks to reduce transmission. However, a systematic and quantitative understanding of how face masks reduce disease transmission is still lacking. We used epidemic data from the Diamond Princess cruise ship to calibrate a transmission model in a high-risk setting and derive the reproductive number for the model. We explain how the terms in the reproductive number reflect the contributions of the different infectious states to the spread of the infection. We used that model to compare the infection spread within a homogeneously mixed population for different types of masks, the timing of mask policy, and compliance of wearing masks. Our results suggest substantial reductions in epidemic size and mortality rate provided by at least 75% of people wearing masks (robust for different mask types). We also evaluated the timing of the mask implementation. We illustrate how ample compliance with moderate-quality masks at the start of an epidemic attained similar mortality reductions to less compliance and the use of high-quality masks after the epidemic took off. We observed that a critical mass of 84% of the population wearing masks can completely stop the spread of the disease. These results highlight the significance of a large fraction of the population needing to wear face masks to effectively reduce the spread of the epidemic. The simulations show that early implementation of mask policy using moderate-quality masks is more effective than a later implementation with high-quality masks. These findings may inform public health mask-use policies for an infectious respiratory disease outbreak (such as one of COVID-19) in high-risk settings. Full article

In the gas-turbine research field, superalloys are some of the most widely used materials as they offer excellent strength, particularly at extreme temperatures. Vital components such as combustion liners, transition pieces, blades, and vanes, which are often severely affected by wear, have been identified. These critical components are exposed to very high temperatures (ranging from 570 to 1300 °C) in hot-gas-path systems and are generally subjected to heavy repair processes for maintenance works. Major degradation such as abrasive wear and fretting fatigue wear are predominant mechanisms in combustion liners and transition pieces during start–stop or peaking operation, resulting in high cost if inadequately protected. Another type of wear-like erosion is also prominent in turbine blades and vanes. Nimonic 263, Hastelloy X, and GTD 111 are examples of superalloys used in the gas-turbine industry. This review covers the development of hardface coatings used to protect the surfaces of components from wear and erosion. The application of hardface coatings helps reduce friction and wear, which can increase the lifespan of materials. Moreover, chromium carbide and Stellite 6 hardface coatings are widely used for hot-section components in gas turbines because they offer excellent resistance against wear and erosion. The effectiveness of these coatings to mitigate wear and increase the performance is further investigated. We also discuss in detail the current developments in combining these coating with other hard particles to improve wear resistance. The principles of this coating development can be extended to other high-temperature applications in the power-generation industry. Full article