This paper presents a series of experiments focused on the displacement of viscoplastic fluids by various Newtonian and non-Newtonian fluids from a long horizontal, eccentric annulus. The flow regimes range from high Reynolds number laminar regimes through to fully turbulent. These experiments represent the primary cementing operation in a horizontal well. The main objective of our experiments is to gain insight into the role of the flow regime in the fluid-fluid displacement flows of relevance to primary cementing. We study strongly eccentric annuli and displaced fluids with a significant yield stress, i.e., those scenarios where a mud channel is most likely to persist. For fully eccentric annuli, the displacements are uniformly poor, regardless of regime. This improves for an eccentricity of 0.7. However, at these large eccentricities that are typical of horizontal well cementing, the displacement is generally poor and involves a rapid “breakthrough” advance along the wide upper side... [more]

The concept of high-voltage DC transmission using a multiterminal configuration is presently a central topic of research and investment due to rekindled interest in renewable energy resource integration. Moreover, great attention is given to fault analysis, which leads to the necessity of developing proper tools that enable proficient dynamic simulations. This paper leverages models and control system design techniques and demonstrates their appropriateness for scenarios in which faults are applied. Furthermore, this paper relies on full-bridge submodule topologies in order to underline the increase in resilience that such a configuration brings to the multiterminal DC network, after an unexpected disturbance. Therefore, strong focus is given to fault response, considering that converters use a full-bridge topology and that overhead power lines connect the terminals.

The effects of two pilot injections on combustion and emissions were evaluated in a single−cylinder turbocharged diesel engine, which operated in premixed charge compression ignition (PCCI) modes with multiple injections and heavy exhaust gas recirculation under the low load by experiments and simulation. It was revealed that with the delay of the start of the first pilot injection (SOI−P1) or the advance of the start of second pilot injection (SOI−P2), respectively, the pressure, heat release rate (HRR), and temperature peak were all increased. Analysis of the combustion process indicates that, during the two pilot injection periods, the ignition timing was mainly determined by the SOI−P2 while the first released heat peak was influenced by SOI−P1. With the delay of SOI−P1 or the advance of SOI−P2, nitrogen oxide (NOx) generation increased significantly while soot generation varied a little. In addition, increasing Q1 and decreasing the second pilot injection quantity (Q2) can manipul... [more]

Extensive surfaces of land are currently under-utilized, marginal and/or contaminated (MUC) in many EU and neighbouring countries. In the past few years, scientific research has demonstrated that bioenergy crops can potentially render this land profitable, generating income for the local populations and, at the same time, reaching the goals of the new Renewable Energy Directive (REDII) without interfering with food production. The main purpose of this paper is to measure net economic returns by computing benefits and costs of low indirect Land Use Change (iLUC) biofuel production on MUC land from the perspective of both the private investors and social welfare. A standard cost-benefit technique was applied to analyse and compare net returns of different advanced bioenergy value-chains in monetary terms. Productivity, economic feasibility and green-house gas (GHG) emissions impact were assessed and considered for the economic analysis. The considered pathways were cellulosic or second g... [more]

Early prediction of thermal loads plays an essential role in analyzing energy-efficient buildings’ energy performance. On the other hand, stochastic algorithms have recently shown high proficiency in dealing with this issue. These are the reasons that this study is dedicated to evaluating an innovative hybrid method for predicting the cooling load (CL) in buildings with residential usage. The proposed model is a combination of artificial neural networks and stochastic fractal search (SFS−ANNs). Two benchmark algorithms, namely the grasshopper optimization algorithm (GOA) and firefly algorithm (FA) are also considered to be compared with the SFS. The non-linear effect of eight independent factors on the CL is analyzed using each model’s optimal structure. Evaluation of the results outlined that all three metaheuristic algorithms (with more than 90% correlation) can adequately optimize the ANN. In this regard, this tool’s prediction error declined by nearly 23%, 18%, and 36% by applying... [more]

Economic analysis allows for determining the required daily output under certain natural and mining conditions based on the costs of the production process in a particular mine infrastructure. Therefore, there is a need to determine the potential daily output of a longwall using the technical equipment at the disposal of the mine. In the case of mines, when exploiting a few longwalls simultaneously in the conditions of bumping hazards, it is indispensable to ensure safety. Due to a necessity of keeping a safe distance among the longwall fronts, when planning their exploitation, developing a prediction of the longwalls in advance during the planning period is needed. To predict the daily production from a longwall and daily advance of the longwall in the analyzed period, it is necessary to know the current operating time of machines and the capacity of the shearer under given conditions. The current working time of machines results from the available time and the degree of its utilizati... [more]

Reducing greenhouse gas emissions in the transport sector is known to be an important contribution to climate change mitigation. Some parts of the transport sector are particularly difficult to decarbonize; this includes the heavy-duty vehicle sector, which is considered one of the “hard-to-abate” sectors of the economy. Transitioning from diesel trucks to hydrogen fuel cell trucks has been identified as a potential way to decarbonize the sector. However, the current and future costs and efficiencies of the enabling technologies remain unclear. In light of these uncertainties, this paper investigates the investments required to decarbonize New Zealand’s heavy-duty vehicle sector with green hydrogen. By combining system dynamics modelling literature and hydrogen transition modelling literature a customized methodology is developed for modelling hydrogen transitions with system dynamics modelling. Results are presented in terms of the investments required to purchase the hydrogen product... [more]

Increasing traffic volumes in cities leads to common traffic congestions building up, especially during peak hours. To protect city dwellers from excessive fuel exhaust and traffic noise and to prevent drivers from time loss due to overloaded routes, it is important to inform them about real-time traffic conditions and possible delays in advance. Effectively influencing drivers’ decisions to divert from an original route choice in case of traffic hinderance is essential, and application of dynamic travel information in the form of variable message signs (VMSs) is believed to be effective in these terms. The paper examines drivers’ willingness to divert from an initial route choice due to the information provided on VMS boards. Their behavior was analyzed in terms of their response to everyday and artificially elongated travel times displayed on the VMSs. Maximum simulated elongation reached 200% and 300% of the initial state, depending on the characteristics of the pre-peak conditions.... [more]

The cuttings transport efficiency of various drilling fluids has been studied in several approaches. This is an important aspect, since hole cleaning is often a bottleneck in well construction. The studies so far have targeted the drilling fluid cuttings’ transport capability through experiments, simulations or field data. Observed differences in the efficiency due to changes in the drilling fluid properties and compositions have been reported but not always fully understood. In this study, the cuttings bed, wetted with a single drilling fluid, was evaluated. The experiments were performed with parallel plates in an Anton Paar Physica 301 rheometer. The results showed systematic differences in the internal friction behaviors between tests of beds with oil-based and beds with water-based fluids. The observations indicated that cutting beds wetted with a polymeric water-based fluid released clusters of particles when external forces overcame the bonding forces and the beds started to bre... [more]

We present a novel indicator for the effectiveness of longitudinal, convecting-radiating fins to dissipate heat. Starting from an analysis of the properties of the entropy rate of the steady state, we show how it is possible to assess the efficiency of such devices by looking at the amount of entropy produced in the heat transfer process. Our study concerns both purely convective fins and convection-radiant fins and takes advantage of explicit expressions for the distribution of heat along the fin. It is shown that, in a suitable limit, the standard definition of efficiency and the entropic definition coincide. The role of the fluid temperature is explicit in the new definition and in the purely convective case. An application to an aluminium fin is given. Analytical and numerical results are discussed.

Taking into account the impact of the COVID-19 and adopting the assessment optics of students from Generation Z currently entering the labor market, we have made the aim of this article to provide better insight into the relationship between Industry 4.0 and corporate social responsibility. The survey was conducted in the form of an online survey in two leading universities in Poland in the field of economic education. 646 students took part in the survey. The data were analyzed using logit regression models. The results of the study suggest that the increase in the use of management solutions supporting Industry 4.0 in the wake of the COVID-19 crisis will increase the importance of the economic, social, and environmental dimensions of corporate social responsibility. Pointing to the forecasted increase importance of corporate social responsibility, we suggest linking management solutions supporting Industry 4.0 with corporate social responsibility. However, we also draw attention to t... [more]

To utilize the rapidly refreshed operating data of power systems fully and effectively, an integrated scheme for inter-area oscillatory stability assessment (OSA) is proposed in this paper using a compositive feature selection unit and random bits forest (RBF) algorithm. This scheme consists of offline, update, and online stages, and it can provide fast and accurate estimation of the oscillatory stability margin (OSM) by using the real-time system operating data. In this scheme, a compositive feature selection unit is specially designed to realize efficient feature selection, which can significantly reduce the data dimensionality, effectively alleviate feature redundancy, and provide accurate correlation information to system operators. Then, the feature set consisting of the selected pivotal features is used for the RBF training to build the mapping relationships between the OSM and the system operating variables. Moreover, to enhance the robustness of the scheme in the face of variab... [more]

Substantial insight into the effect of ultrasound disintegration on the changes in biochemical parameters of manure digestate and digestate age is needed to understand the potential of digestate treatment. To address this knowledge gap, in this study, the effect of digestate age on the efficiency of ultrasound (US) disintegration was investigated. In this scope, dairy manure digestate samples were incubated in an oven at 37 °C for a predetermined amount of time to obtain simulated digestate ages of 15, 22, 29, 36 and 43 days. The results showed that US disintegration efficiency significantly affected the initial biochemical characteristics of digestate and that the digestate age had a significant effect on the US disintegration efficiency. This effect diminished when the applied specific energy (SE) was higher than 3000 kJ/kg total solids (TS). A numerical partial least squares (PLS) model was constructed to investigate the relative influences of the initial biochemical parameters on t... [more]

Covid-19 affects the personal lives of millions and led to an economic crisis. Changed behavioral patterns and a reduction of industrial activity result in a reduction in power demand, and thus Covid-19 impacts the power systems around the world. Bottom-up mapping of the effect of Covid-19 on the energy demand is challenging, if not impossible. In order to analyze the impact of the pandemic on power demand, we instead propose a simplified approach based on an econometric analysis that quantifies the country-wide load reduction of Covid-19, using the number of active cases as well as the specific lockdown period as proxies. The time span covered is from 1 January 2016 to 31 August 2020. This long time span allows us to investigate the effect of Covid-19 on the power demand. We find that in Germany (DE) and Great Britain (GB) the power demand is reduced by about 1−1.7 MW per case, while in France the demand increased by 1 MW per case during times outside of the lockdown. On the other han... [more]

In this article, the authors analyzed two extreme investment variants considering the installed capacity of Poland’s residential pv installation: (a) pv installation meets electricity demand only in the first year of operation, and in each subsequent year it is necessary to purchase electricity at market prices; (b) installation meets electricity demand even in the last year of operation, and in each previous year, the excess of generated electricity needs to be transferred back to the grid, with the limited (by law) right of drawing it from the grid for free in the future. In the article, a sensitivity analysis was performed, and profitability changes were established based on the NPV value, depending on case (a) or (b). The performed analyses showed that the pv installation profitability should not be analyzed, assuming only one moment when it meets 100% of the household’s electricity demand. It was shown that the choice of such a moment, depending on the value of particular technica... [more]

Reactivity control compression ignition engines illustrated suitable abilities in emission reduction beside high thermal efficiency. In this research, nine various direct fuel injection strategies were studied numerically: three cases with single injection strategy and six cases with split injection and different start of injection (SOI). In all simulated cases, equivalence ratio kept constant (i.e., 0.3). Among various strategies, single injection showed higher IMEP as a factor of efficiency with about 5.39 bar that occurred at SOI = 60 before top dead center (bTDC), while lower efficiency was observed for split injection case with 50%-50% injections of fuel in each injection stage. Start of combustion (SOC), burn duration and CA50 as factors for combustion characteristics were affected with SOI changes. In single SOI strategies, more advanced injection caused more advanced SOC where there was about 1.3 CAD advancing from 40 to 80 bTDC injection. Spilt SOI showed more advanced SOC, wh... [more]

The Polish government has made a decision to build a nuclear power plant (NPP) in the South Baltic coastal zone. This means that three major types of structures will be located in the nearshore: (1) breakwaters and a wharf where ships may dock to load and unload cargo (harbor), (2) seawalls protecting the shore against erosion and storm surge floods, and (3) an underwater piping system for cold water intake and heated water discharge. This study determines the dominant directions and rate of sediment transport for the coastline section in the vicinity of the projected Polish NPP (ca. 100,000 m3/year), as well as assesses current changes at this coastline location on the basis of field measurements and mathematical modeling.

Hydraulic fracturing is usually employed to create a complex fracture network to enhance heat extraction in the development of an enhanced geothermal system. The heat extraction depends on the heat conduction from the rock matrix to the flowing fractures and the heat convection through a complex fracture network. Therefore, the geometries of the fracture network have important influences on the thermal breakthrough. In this paper, a hydro-thermal coupling mathematical model considering a complex fracture network is established. The embedded discrete fracture model is adopted to explicitly model the individual fracture on the mass flow and heat transfer. The model is validated by analytical solutions. Fracture network parameters are changed systematically to investigate the effects of fracture network distribution including regular and complex shape on the thermal production performance. The results show that the increase of producing pressure differential, fracture number, and conducti... [more]

In the present era, electrical power system is evolving to an inverter-dominated system from a synchronous machine-based system, with the hybrid power systems (HPS) and renewable energy generators (REGs) increasing penetration. These inverters dominated HPS have no revolving body, therefore, diminishing the overall grid inertia. Such a low system inertia could create issues for HPS with REG (HPSREG) such as system instability and lack of resilience under disturbances. A control strategy, therefore, is required in order to manage this task besides benefitting from the full potential of the REGs. A virtual inertia control for an HPSREG system built with the principle of fractional order (FO) by incorporation of proportional-integral-derivative (PID) controller and fuzzy logic controller (FLC) has been projected. It is utilized by adding virtual inertia into HPSREG system control loop and referred to as FO based fuzzy PID controller for this study. Simulation outcomes states that the advo... [more]

The COVID-19 pandemic is having a strong impact on the economies of all countries, negatively affecting almost all sectors. This paper compares Spanish electricity and natural gas prices in the first half-year of 2020 with the prices expected for that period at the end of 2019. The half-year of 2020 selected coincides with the period of greatest impact of COVID-19 on Spanish society. Expected prices and their future probability distributions are calculated using a stochastic model with deterministic and stochastic parts; the stochastic part includes mean-reverting and jumps behaviour. The model is calibrated with 2016−2019 daily spot prices for electricity and with day-ahead prices for natural gas. The results show large monthly differences between the prices expected at the end of the year 2019 and the actual prices for the half-year; in May 2020, wholesale electricity prices are found to be EUR 31.60/MWh lower than expected, i.e., 60% lower. In the case of natural gas, the prices in... [more]

Photovoltaic (PV) modules suffer from a reduction of electric conversion due to the high operating temperatures of the PV cells. Hybrid photovoltaic/thermal (PV/T) technology represents an effective solution for cooling the PV cells. This paper discusses a theoretical study on a novel bi-fluid PV/T collector. One dimensional steady-state numerical model is developed, and computer simulations are performed using MATLAB. This numerical model is based on a pilot PV/T plant, installed in the Campus of the University of Catania, and was experimentally validated. The design of the proposed bi-fluid PV/T is based on a commercial WISC PV/T collector, to which are added an air channel, an aluminum absorber with fins, and a layer of thermal insulation. The analysis of the thermal behavior of the proposed collector is carried out as a function of the flow rate of the two heat transfer fluids (air and water). Finally, the comparative analysis between the conventional water-based PV/T collector, na... [more]

Solar energy planning becomes crucial to develop adaptive policies ensuring both energy efficiency and climate change mitigation. Cities, particularly building’s rooftops, constitute a promising infrastructure for enabling the use of locale solar resources. This study proposes a combined engineering−statistical methodology to assess the photovoltaic potential of residential rooftops. Using validated algorithms for solar simulation and geographical information system (GIS) for spatial dissemination, the proposed methodology deals with the lack of data and allows an accurate investigation of the geographical and technical potential. Applied to the municipality of Laghouat, the results reveal that suitable rooftops areas for PV installations in the examined typologies were approximately between 18 and 35%. Moreover, the deployment of distributed PV systems on residential rooftops provides significant technical potential, which could cover up to 55% of the annual electricity needs. These o... [more]

The problem of global warming and the related climate change requires solutions to reduce greenhouse gas emissions, in particular CO2. As a result, newly manufactured cars consume less fuel and emit lower amounts of CO2. In terms of exhaust emissions and fuel consumption, old cars are significantly inferior to the more recent models. In Poland, for instance, the average age of passenger cars is approximately 13 years. Therefore, apart from developing new solutions in the cars produced today, it is important to focus on measures that enable the reduction in CO2 emissions in older vehicles. These methods include the adaptation of used cars to run on gaseous fuels. Natural gas is a hydrocarbon fuel that is particularly preferred in terms of CO2 emissions. The article presents the results of research of carbon oxides emission (CO, CO2) in the exhaust gas of a passenger car fueled by petrol and natural gas. The emissions were measured under the conditions of the New European Driving Cycle (... [more]

Leading edge erosion (LEE) repairs of wind turbine blades (WTBs) involve infield application of leading edge protection (LEP) solutions. The industry is currently aiming to use factory based LEP coatings that can applied to the WTBs before they are shipped out for installation. However, one of the main challenges related to these solutions is the choice of a minimum LEP application length to be applied in the spanwise direction of the WTBs. Generally, coating suppliers apply 10−20 m of LEP onto the blades starting from the tip of the blade using the “rule of thumb”, and no studies in the literature exist that stipulate how these LEP lengths can be calculated. In this study, we extend the scope of a recently developed long-term probabilistic framework to determine the minimum LEP application length required for WTBs to combat rain-induced erosion. A parametric study is performed where different wind turbines with varying power ratings of 2.1 MW to 15 MW at different Dutch sites ranging... [more]

Stator winding faults are one of the most common faults of permanent magnet synchronous motors (PMSMs), and searching for methods to efficiently detect this type of fault and at an early stage of damage is still an ongoing, important topic. This paper deals with the selected methods for detecting stator winding faults (short-circuits) of a permanent magnet synchronous motor, which are based on the analysis of the stator phase current signal. These methods were experimentally verified and their effectiveness was carefully compared. The article presents the results of experimental studies obtained from the spectral analysis of the stator phase current, stator phase current envelope, and the discrete wavelet transform. The original fault indicators (FIs) based on the observation of the symptoms of stator winding fault were distinguished using the aforementioned methods, which clearly show which symptom is most sensitive to the incipient fault of the stator winding of PMSMs.