A high-speed on/off valve (HSV) is generally the core component of a digital hydraulic transmission system. Therefore, its dynamic characteristics often restrict the overall performance of the digital hydraulic system. Most of the current studies focus on the optimization on the dynamic characteristics or the energy characteristics, few studies have comprehensively considered the two characteristics of the valve together. In this paper, a pre-existing control algorithm (PECA) is proposed to improve the dynamic characteristics of the HSV, and simultaneously optimize the power losses of the HSV to improve its energy conversion efficiency. The results show that, compared with the traditional single-voltage driven strategy, the opening time of the PECA decreases by 29.4%, the closing time decreases by 59.6%, and the energy conversion rate increases by 7.9%.

The integration of an electrical storage system (ESS) into a DC microgrid using a bidirectional DC/DC converter provides substantial benefits but requires careful design. Among such converter topologies, the Split-pi converter presents several merits at the cost of non-isolated operation. However, the few works in the literature on the Split-pi presented only closed-loop control with a single control loop; furthermore, they neglected the reactive components’ parasitic resistances and did not perform any experimental validation. This work aimed at investigating the use of the Split-pi converter as a power interface between an ESS and a DC microgrid. Five typical microgrid scenarios are presented, where each of which requires a specific state-space model and a suitable control scheme for the converter to obtain high performance. In this study, two different state-space models of the converter that consider the parasitic elements are presented, the control schemes are discussed, and crite... [more]

In this paper, an automated umbilical system based on a 6-dof (degree of freedom) hydraulic parallel mechanism is proposed to automate the rocket propellant loading process. The mechanical structure, vision acquisition algorithm, and control algorithm used in the system are described in detail in the paper. To address the fluid nonlinearity problem of the hydraulic drive system, nonlinear compensation and three-state feedback control are used in the paper to enhance the performance of the hydraulic system. For the problem of force tracking during the docking process between the umbilical system and the rocket, an adaptive impedance control algorithm based on the online environmental parameter estimation is proposed in the paper, which effectively reduces the contact force during the docking process. The dynamic tracking and docking experiments indicate that this automated umbilical system features rapid reaction speed, high measurement precision, and good flexibility, which can be used... [more]

Phase change dispersions are useful for isothermal cooling applications. As a result of the phase changes that occur in PCDs, they are expected to have greater storage capacities than those of single-phase heat transfer fluids. However, for appropriate heat exchanger dimensions and geometries for use in phase change dispersions, knowledge about the convective heat transfer coefficients of phase change dispersions is necessary. A test unit for measuring the local heat transfer coefficients and Nusselt numbers of PCDs was created. The boundary condition of constant heat flux was chosen for testing, and the experimental heat transfer coefficients and Nusselt numbers for the investigated phase change dispersion were established. Different experimental parameters, such as the electrical wall heat input, Reynolds number, and mass flow rate, were varied during testing, and the results were compared to those of water tests. It was found that, due to the tendency of low-temperature increases in... [more]

The article discusses the findings related to the calorific value as well as the explosion and combustion parameters of dust from the raw biomass of fruit trees, i.e., apple, cherry, and pear branches, and from biochars produced using this type of biomass during pyrolysis processes conducted under various conditions. The plant biomass was thermally processed at 400, 450, or 500 °C for a duration of 5, 10, or 15 min. The study aimed to identify the calorific value of the biomass obtained from waste produced in orchards and to estimate the explosion hazard during the processing of such materials and during the storage of the resulting solid fuels. Tests were conducted to assess the total contents of carbon, ash, nitrogen, hydrogen, and volatile substances as well as the calorific value. The findings show a significant effect of the thermal transformation of fruit tree branches on the calorific value of the biochars that were produced. It was found that the mean calorific value of all of... [more]

Spatial heating and cooking account for a significant fraction of global domestic energy consumption. It is therefore likely that hydrogen combustion will form part of a hydrogen-based energy economy. Catalytic hydrogen combustion (CHC) is considered a promising technology for this purpose. CHC is an exothermic reaction, with water as the only by-product. Compared to direct flame-based hydrogen combustion, CHC is relatively safe as it foregoes COx, CH4, and under certain conditions NOx formation. More so, the risk of blow-off (flame extinguished due to the high fuel flow speed required for H2 combustion) is adverted. CHC is, however, perplexed by the occurrence of hotspots, which are defined as areas where the localized surface temperature is higher than the average surface temperature over the catalyst surface. Hotspots may result in hydrogen’s autoignition and accelerated catalyst degradation. In this review, catalyst materials along with the hydrogen technologies investigated for CH... [more]

Ocean energy is a promising source of clean renewable energy, with clear development targets set by the European Commission. However, the ocean energy sector faces non-technological challenges and opportunities that are frequently overlooked in deployment plans. The present study aimed to provide a critical evaluation of the ocean energy sector’s legal, institutional, and political frameworks with an identification and analysis of both barriers and enabling features for the deployment of ocean energy. In the first stage, a literature review on the current political and regulatory frameworks of a set of European countries was carried out, setting the basis for the main challenges and enabling factors faced by the sector. Secondly, a critical analysis of the main non-technological barriers and enablers was performed, which was supported by questionnaires sent to regulators, technology developers, and test-site managers. This questionnaire allowed us to collect and integrate the views, pe... [more]

Anaerobic Digestion (AD) is a well-established process that is becoming increasingly popular, especially as a technology for organic waste treatment; the process produces biogas, which can be upgraded to biomethane, which can be used in the transport sector or injected into the natural gas grid. Considering the sensitivity of Anaerobic Digestion to several process parameters, mathematical modeling and numerical simulations can be useful to improve both design and control of the process. Therefore, several different modeling approaches were presented in the literature, aiming at providing suitable tools for the design and simulation of these systems. The purpose of this study is to analyze the recent advancements in the biomethane production from different points of view. Special attention is paid to the integration of this technology with additional renewable energy sources, such as solar, geothermal and wind, aimed at achieving a fully renewable biomethane production. In this case, au... [more]

Research work on the air flow in mine workings frequently utilises computer techniques in the form of numeric simulations. However, it is very often necessary to apply simplifications when building a geometrical model. The assumption of constant model geometry on its entire length is one of the most frequent simplifications. This results in a substantial shortening of the geometrical model building process, and a concomitant shortening of the time of numerical computations; however, it is not known to what extent such simplifications worsen the accuracy of simulation results. The paper presents a new methodology that enables precise reproduction of the studied mine gallery and the obtaining of a satisfactory match between simulation results and in-situ measurements. It utilises the processing of data from laser scanning of a mine gallery, simultaneous multi-point measurements of the velocity field at selected gallery cross-sections, unique for mine conditions, and the SAS turbulence mo... [more]

The droop control scheme based on Q − ω and P − V characteristics is conventionally employed to share the load power among sources in an islanded low-voltage microgrid with resistive line impedances. However, it suffers from poor active power sharing, and is vulnerable to sustained deviations in frequency and voltage. Therefore, accurate power sharing and maintaining the frequency and voltage in the desired ranges are challenging. This paper proposes a novel microgrid control strategy to address these issues. The proposed strategy consists of a virtual flux droop and a model predictive control, in which the virtual flux is the time integral of the voltage. Firstly, the novel virtual flux droop control is proposed to accurately control the power sharing among DGs. Then, the model predictive flux control is employed to generate the appropriate switching signals. The proposed strategy is simple without needing multiple feedback control loops. In addition, pulse width modulation is not req... [more]

The popularity of climate neutral new energy vehicles for reduced emissions and improved air quality has been raising great attention for many years. World-wide, a strong commitment continues to drive the demand for zero-emission through alternative energy sources and propulsion systems. Despite the fact that 71.27% of hydrogen is produced from natural gas, green hydrogen is a promising clean way to contribute to and maintain a climate neutral ecosystem. Thereby, reaching CO2 targets for 2030 and beyond requires cross-sectoral changes. However, the strong motivation of governments for climate neutrality is challenging many sectors. One of them is the transport sector, as it is challenged to find viable all-in solutions that satisfy social, economic, and sustainable requirements. Currently, the use of new energy vehicles operating on green sustainable hydrogen technologies, such as batteries or fuel cells, has been the focus for reducing the mobility induced emissions. In Europe, 50% of... [more]

Short-term electric load forecasting plays a significant role in the safe and stable operation of the power system and power market transactions. In recent years, with the development of new energy sources, more and more sources have been integrated into the grid. This has posed a serious challenge to short-term electric load forecasting. Focusing on load series with non-linear and time-varying characteristics, an approach to short-term electric load forecasting using a “decomposition and ensemble” framework is proposed in this paper. The method is verified using hourly load data from Oslo and the surrounding areas of Norway. First, the load series is decomposed into five components by variational mode decomposition (VMD). Second, a support vector regression (SVR) forecasting model is established for the five components to predict the electric load components, and the grey wolf optimization (GWO) algorithm is used to optimize the cost and gamma parameters of SVR. Finally, the predicted... [more]

This paper reports the results of heat transfer during refrigerant flow in rectangular mini-channels at stationary conditions. The impacts of selected parameters on boiling are discussed, i.e., thermal and flow parameters, dimensions and orientation of the channels. Four refrigerants (FC-72, HFE-649, HFE-7000 and HFE-7100) were used as the working fluid. Research was carried out on the experimental set-up with the test section with a single rectangular mini-channel of 180 mm long and with a group of five parallel mini-channels, each 32 mm long. The temperature of the mini-channel’s heated wall was measured by infrared thermography. Local values of the heat transfer coefficient at the contact surface between the fluid and the plate were calculated using the 1D mathematical method. The results are presented as the relationship between the heat transfer coefficient and the distance along the mini-channel length and boiling curves. Two-phase flow patterns are shown. Moreover, the results c... [more]

Public transport (PT) service disruptions are common and unexpected events which often result in major impediment to passengers’ typical travel routines. However, attitudes and behavioural responses to unexpected PT disruptions are still not fully understood in state-of-the-art research. The objective of this study is to examine how PT users adapt their travel choices and what travel information sources they utilize once they encounter sudden PT service disruptions. To this end, we conduct a passenger survey among PT users in the city of Kraków (Poland), consisting of a series of stated- and revealed-preference questions. Results show that passengers’ reported choices during past PT disruptions mostly involve adjusting the current PT travel routine, exposing a certain bias with their stated choices (which tend to overestimate the probability of modal shifts). Factors influencing travel behaviour shifts include frequency and recency of PT disruption experience, as well as propensity to... [more]

Induction machines have been key components in the industrial sector for decades, owing to different characteristics such as their simplicity, robustness, high energy efficiency and reliability. However, due to the stress and harsh working conditions they are subjected to in many applications, they are prone to suffering different breakdowns. Among the most common failure modes, bearing failures and stator winding failures can be found. To a lesser extent, High Resistance Connections (HRC) have also been investigated. Motor power connection failure mechanisms may be due to human errors while assembling the different parts of the system. Moreover, they are not only limited to HRC, there may also be cases of opposite wiring connections or open-phase faults in motor power terminals. Because of that, companies in industry are interested in diagnosing these failure modes in order to overcome human errors. This article presents a machine learning (ML) based fault diagnosis strategy to help m... [more]

The principal goal of this paper is to investigate the views of local government officials on revitalisation priorities in Polish municipalities. To accomplish this, the perception of revitalisation objectives by local government representatives (who, according to Polish regulations, are responsible for revitalisation planning and carrying it out) was examined. A catalogue of revitalisation objectives, which were assessed by the respondents, was drawn up on the basis of a review of research on the conceptualisation and measurement of sustainable revitalisation and social sustainability at the local level. Exploratory factor analysis was the method used in the study. In total, the list of the examined revitalisation objectives includes 26 objectives related to the following revitalisation dimensions: infrastructure, community, economy, environment, space, co-governance, and inclusion. A survey of the executive bodies of 573 municipalities in Poland revealed a discrepancy between the sus... [more]

Two phase flow and horizontal well completion pose additional challenges for rate-transient analysis (RTA) techniques in under-saturated coal seam gas (CSG) reservoirs. To better obtain reservoir parameters, a practical workflow for the two phase RTA technique is presented to extract reservoir information by the analysis of production data of a horizontal well in an under-saturated CSG reservoir. This workflow includes a flowing material balance (FMB) technique and an improved form of two phase (water + gas) RTA. At production stage of a horizontal well in under-saturated CSG reservoirs, a FMB technique was developed to extract original water in-place (OWIP) and horizontal permeability. This FMB technique involves the application of an appropriate productivity equation representing the relative position of the horizontal well in the drainage area. Then, two phase (water + gas) RTA of a horizontal well was also investigated by introducing the concept of the area of influence (AI), which... [more]

In this study, uncertainty and sensitivity analyses were performed with MELCOR 2.2.18 to study the hydrogen generation (figure-of-merit (FoM)) during the in-vessel phase of a severe accident in a light water reactor. The focus of this work was laid on a large generation-III pressurized water reactor (PWR) and a double-ended hot leg (HL) large break loss of coolant accident (LB-LOCA) without a safety injection (SI). The FPT-1 Phebus integral experiment emulating LOCA was studied, where the experiment outcomes were applied for the plant scale modelling. The best estimate calculations were supplemented with an uncertainty analysis (UA) based on 400 input-decks and Latin hypercube sampling (LHS). Additionally, the sensitivity analysis (SA) utilizing the linear regression and linear and rank correlation coefficients was performed. The study was prepared with a new open-source MELCOR sensitivity and uncertainty tool (MelSUA), which was supplemented with this work. The FPT-1 best-estimate mod... [more]

A key question for European energy transition is which forms of renewable energy technologies will play a central role in this process. The recent dynamic growth in offshore wind power together with the vast wind energy potential of the European seas, including the Baltic Sea, make this technology an increasingly attractive and viable option. Considering the high installation and connection costs, government support is considered essential for the development of offshore wind power. The aim of this article is to analyze Poland’s public policy tools, which govern offshore wind farm development, and to present them from a wider geostrategic perspective. Authors identify, classify, and evaluate individual public policy tools with the use of multi-criteria and multi-dimensional methods while explaining their impact on offshore wind development in Poland. The analysis of the individual tools has shown that the currently applied tools give a high probability of achieving public policy object... [more]

Fracture-driven interactions (FDIs) in unconventional reservoirs significantly affect well production and have thus garnered extensive attention from the scientific community. Furthermore, since the industry transitioned to using large completion designs with closer well spacing and infill drilling, FDIs have occurred more frequently and featured more prominently, which has primarily led to destructive interference. When infill wells (i.e., “child” wells) are fractured, older, adjacent producing wells (i.e., “parent” wells) are put directly at risk of premature changes in production behavior. Some wells may never fully recover following exposure to severe FDIs and, in the worst case scenario, will permanently stop producing. To date, previous investigations into FDIs have focused mainly on diagnosis and detection. As such, their formation mechanism is not well understood. To address this deficiency, a three-dimensional, multi-fracture propagation simulator was constructed based on the... [more]

The study was based on saline soils with surface mineral layers impacted by the waste produced by the soda plant in Poland. The activity of selected enzymes (catalase CAT, alkaline AlP, and acid phosphatase AcP), pH in KCl, content of the clay, total organic carbon (TOC), total nitrogen (TN), total exchangeable bases (TEB), electrical conductivity (ECe), CaCO3, and concentration of available phosphorus AP were investigated in the soil next to the soda plant. Based on the enzyme activity, the following were calculated: enzymatic pH indicator AlP/AcP, the resistance index (RS), resilience index (RL), relative changes (RCh), and the time index (TI). The soil was sampled from the mineral horizon in spring and autumn from eight (S1−S8) soil sampling sites in the area of the soda plant and from the control point (C). Soil is characterized by alkaline reaction. Statistical analysis (ANOVA, η2 effect size) showed significant variation in parameters under the influence of different sites next t... [more]

The emergence of smart sensors has had a significant impact on the utility industry. In particular, it has made the planning and implementation of demand-side management (DSM) programmes easier. Nevertheless, for various reasons, some users may not implement smart meters for load monitoring. This paper addresses such cases, particularly large-scale industrial users, which, despite heavy electrical loads coming from many different processes, implement only simple energy measuring equipment for billing purposes. This necessitates the utilisation of novel methodologies for load disaggregation, often referred to as nonintrusive load monitoring (NILM). The availability of such tools can create multifold benefits for industrial park management, utility service providers, regulators, and policymakers. Here, we introduce an optimisation algorithm for nonintrusive load disaggregation that is low-cost, speedy, and acceptably accurate. As a case study, we used real network data of three industria... [more]

In the current context of transition from the powertrains of cars equipped with internal combustion engines to powertrains based on electricity, there is a need to intensify studies and research related to the command-and-control systems of electric vehicles. One of the important systems in the construction of an electric vehicle is the thermal management system of the battery with the role of optimizing the operation of the battery in terms of performance and life. The article aims to critically analyze the studies and research conducted so far related to the type, design and operating principles of battery thermal management systems (BTMSs) used in the construction of various shaped Li-ion batteries, with focus on cooling technologies. The advantages and disadvantages of the individual components, as well as of the proposed BTM solutions, are extensively investigated, with regard also to the adaptability of these systems to the different Li-ion battery shapes. The information thus sy... [more]

The purpose of study was to find out how electric bikes are perceived in Poland, a country with a high level of motorisation and a low cycling culture. A key question was to investigate whether differences in perceptions between traditional (unassisted) and electrically assisted bicycles could bring about greater interest in bicycle transport. The analysis was based on the results of a CAWI survey analysing the perception of the electric bicycle in comparison with the traditional bicycle and the car. Its undoubted advantages are marginalised (only 14% of respondents considered it more practical). The position of the electric bicycle seemed to increase in the opinion of the surveyed only when used by elderly people with poorer fitness, as something that can encourage them to cycle. In general evaluations, it was the traditional bicycle that was seen as better for health. The presented results may serve as a signal that electric bicycles need more promotion in Poland, especially in terms... [more]

Islanding detection needs are becoming a pivotal constituent of the power system, since the penetration of distributed generators in the utility power system is continually increasing. Accurate threshold setting is an integral part of the island detection scheme since an inappropriate threshold might cause a hazardous situation. This study looked at the islanding conditions as well as two transient faults, such as a single line to ground fault and a three-phase balance fault, to assess the event distinguishing ability of the proposed method. Therefore, the goal of this research was to determine the threshold of the island if the distributed generator (DG) capacity is greater than the connected feeder load, which is the over-frequency island condition, and if the DG capacity is less than the connected feeder load, which is the under-frequency island condition. The significance of this research work is to propose a new island detection threshold setting method using the slip angle and ac... [more]