Problems of designing stand-alone power supply systems using renewable energy sources

The paper considers the problems of designing autonomous power supply systems using the renewable energy resources. The efficiency of using energy resources in conditions of growing prices for electricity brings significant saving of both energy and financial factors. The analyses show that the main losses of energy resources are the result of inefficient use, distribution and consumption of electrical energy. There has been stated one of the most important problems of energy saving: many existing consumers are located at a significant distance from centralized power supply systems. Today connecting such consumers to large power grids is economically inexpedient. These facilities are supplied from the stand-alone power plants. According to the program of energy saving and energy efficiency improvement of FGC UES, PJSC, reducing electricity consumption for auxiliary needs of transformer substations is one of the main mechanisms for the program implementation.

Missing two key parameters in the pooled testing strategy

The pooled testing strategy [1] misses two key parameters, the infection prevalence p and its variance mentioned many times in the paper as the key determinants of any pooled testing strategy. For illustrating their methods, the authors used p from other studies that employed individual tests. It turned that that no statistical estimators for p and its variance have ever been derived for testing data of pooled samples since the first formulation of testing strategies based on pooled sampled in 1943 [2]. Here I derive the maximum likelihood estimators for p and its variance based on tests of pooled samples. This should result in significant saving in time, resource, and costs.

Event-triggered adaptive control for upper-limb robot-assisted passive rehabilitation exercises with input delay

In this article, an adaptive tracking control strategy is designed for uncertain electrically driven end-effector type upper-limb rehabilitation robots subject to an input delay and a limited bandwidth channel. This control scheme is implemented to perform upper-limb passive rehabilitation training for different subjects. Primarily, dynamic analysis of the rehabilitation robot is carried out using the Euler–Lagrange principle, which incorporates motor dynamics to allow the voltage-based control commands as desirable in practical implementations. Thereafter, an adaptive backstepping control law with input delay compensation is designed to estimate the unknown dynamical parameters of the rehabilitation robot during the training sessions. Furthermore, a Lyapunov-based triggering mechanism is developed to deal with the limited bandwidth challenge and reduce the transmissions over the network. The experimental validation is conducted for different scenarios, and a comparison study is carried out with two time-triggered control schemes to investigate the potential of the proposed approach. From the experimental runs and the comparative analysis, the proposed control scheme is found to achieve a promising tracking performance with input delay compensation. Moreover, a significant saving in the network resources is attained during the passive rehabilitation training of the subjects.

Mixed Scheduling Model for Limited-Stop and Normal Bus Service with Fleet Size Constraint

Limited-stop service is useful to increase operation efficiency where the demand is unbalanced at different stops and unidirectional. A mixed scheduling model for limited-stop buses and normal buses is proposed considering the fleet size constraint. This model can optimize the total cost in terms of waiting time, in-vehicle time and operation cost by simultaneously adjusting the frequencies of limited-stop buses and normal buses. The feasibility and validity of the proposed model is shown by applying it to one bus route in the city of Zhenjiang, China. The results indicate that the mixed scheduling service can reduce the total cost and travel time compared with the single scheduling service in the case of unbalanced passenger flow distribution and fleet constraints. With a larger fleet, the mixed scheduling service is superior. There is an optimal fleet allocation that minimizes the cost for the system, and a significant saving could be attained by the mixed scheduling service. This study contributed to the depth analysis of the relationship among the influencing factors of mixed scheduling, such as fleet size constraint, departure interval and cost.

Downhole Monitoring of Fractures in a Waterflood Development – Part II

For maintenance of the reservoir pressures and enhanced oil recovery in oil producing formations, waterflooding is often implemented by the Operators. This is achieved by drilling injection wells or converting the oil producing wells into injectors. The injection wells are located at carefully selected points in the oilfield so that the water displaces as much oil as possible to the production wells before the water starts to break through. A significant saving in an oilfield development can be obtained by reducing the actual number of injecting wells and increasing each of the injector wells’ capacity for injection. Balancing the injection and produced volumes often involves injecting at high pressures leading to the fracture of the reservoir rocks along a plane intersecting the wellbore. This happens when injection pressure exceeds the minimal principal stress and the tensile strength of the rock, thereby creating a hydraulic fracture. With continuous injection, these fractures start propagating into the reservoir and may reach the reservoir caprock, which may decrease the integrity and possibly lead to out of zone injection. The study of evaluation of downhole fracture monitoring is divided into two parts. In the first part of the paper (Kohli, et al., 2021), a downhole verification approach to identify the fracture initiation point(s) is the focus. It describes the planning, execution and interpretation of the downhole data. This includes spectral acoustic monitoring and modelling of the temperature responses to quantify the injectivity profile. In this second part of the paper, the direct business impact is discussed by further integration of acoustic monitoring and temperature modeling data with detailed results from of fracture dimension (height) measurement by means of pressure fall off tests. Combined, both studies form an integrated approach that the operator took to prove that the fracture network propagation remains within the reservoir and that the top seal integrity is maintained.

Downhole Monitoring of Fractures in a Waterflood Development – Part 1

When an oilfield is exploited by simply producing oil and gas from a number of wells, the reservoir pressure in many circumstances drops quicker than normal impacting the production rates (Koning, 1988) and well performance. To maintain the pressures in the oil producing formations, waterflooding enhancement method is implemented by the Operators. This is achieved by drilling injection wells or converting the oil producing wells into injectors. The injection wells are located at carefully selected points in the oilfield so that the water displaces as much oil as possible to the production wells before the water starts to break through. A significant saving in an oilfield development can be obtained by reducing the actual number of injecting wells and increasing each of the injector wells' capacity for injection. Balancing the injection and produced volumes often involves injecting at high pressures leading to the fracture of the reservoir rocks along a plane intersecting the wellbore. This happens when injection pressure overcomes the rock stress and its tensile strength, thereby creating an induced fracture network. With continuous injection, these fractures start propagating into the reservoir and may reach the reservoir caprock. Continuing to inject further in such a fracture system may breach the top seal integrity of the caprock leading to uncontrolled out of zone injection. The study of evaluation of downhole fracture monitoring is divided into two parts. In this paper a downhole verification approach to identify the fracture initiation point(s) is the focus. It describes the planning, execution and interpretation of the downhole data. This includes spectral acoustic monitoring and modelling of the temperature responses to quantify the injectivity profile. In paper (Kohli, Kelder, Volkov, Castelijns, & van Eijs, 2021), the direct business impact and regulatory requirements are discussed by further integration of acoustic monitoring and temperature modeling data with detailed results from downhole measurements of fracture dimensions by means of pressure fall off tests. Combined, both studies form the integrated approach that the Operator took to meet the regulatory requirements proving that the fracture network propagation remains within the reservoir and that the top seal integrity is maintained.

Optimized Nitriding for Subsequent Induction Heat Treatment

Nitriding is used to achieve a high hardness in the surface layer through the precipitation of nitrides. However, to realize high nitriding hardness depths, treatment times of many hours are necessary, which usually also result in a decrease in strength within the nitrided layer and base material. With induction heat treatment, on the other hand, high hardness depths can be achieved in a very short time. However, the maximum hardness increase is limited by the alloy content of the material. By combining nitriding and induction hardening, high hardness depths can be achieved in short treatment times as an alternative to deep nitriding. In addition to a significant saving in process energy surface layer properties that cannot be achieved with the individual processes are expected. In order to fully exploit the potential of the combination treatment, at first suitable conditions must be set during nitriding for the subsequent induction hardening. In the present work, nitriding layers with low-porosity compound layers as well as only diffusion layers were produced and analyzed on typical nitriding and tempering steels for this purpose.

Public Transport Fleet Replacement Optimization Using Multi-Type Battery-Powered Electric Buses

To achieve a green and sustainable public transit system, most transit agencies plan to completely replace current diesel and hybrid buses with battery-powered electric buses (EBs) in the decades ahead. Based on performances of EBs in practical operations, this study develops a transit fleet replacement model using multi-type EBs to determine an optimal fleet replacement plan in a cost-effective manner, considering associated diesel–electric replacement rates and in-vehicle crowd costs for passengers. Multi-type EBs include small EBs with fast charging technique, and large EBs with fast and slow charging techniques. The proposed model is applied to a real-life case study of the transit system in Qingdao, China. The results obtained indicate that large EBs with a high price tag are preferentially purchased in the first few years of the analysis period, whereas small EBs with a low price tag are favored in the latter years. The use of multi-type EBs results in a significant saving of the total cost, compared with the use of single-type EBs. Interestingly, with the increase of passenger demand, a large EB with a fast charging method presents more benefits than others. In contrast, a small EB has more advantages in a transit system with low demand.

Insights and experiences from assessing the added value of PROSNOW, a prediction system to support snow management in Alpine ski resorts

<p>Within the H2020 project PROSNOW (www.prosnow.org), a demonstrator of a forecasting system that aims at increasing the anticipatory power of ski resorts in the field of snow management has been developed and tested. The PROSNOW® demonstrator, which includes a web-based user interface, represents a meteorological prediction and snow management system with the aim to provide improved anticipation capabilities at various time-scales, spanning from a few days to the seasonal scale of several months. The system holds significant potential to increase the resilience of socio-economic stakeholders and support their real-time adaptation. However, it is expected to take some time until users will gain confidence with the service, completely realize its power and its limitations, and learn to use it in the most effective way to exploit its potential. Although the final actual added value of the PROSNOW® prediction and snowmaking system can thus only be assessed several years after its initial implementation, some ex-ante and preliminary ex-post valuations have already been carried out following the real-time testing of the demonstrator in nine Alpine pilot ski resorts in the winter season 2019/20.</p><p>We applied two different approaches to assess the added value of PROSNOW®: (i) a simulation-based approach and (ii) a survey-based approach. The simulation-based approach consisted of the ex-ante valuation of PROSNOW®’s cost saving potential in the field of snowmaking, using meteorological hindcast data and simulations from snowpack models. The approach is based on decision theory and aims at estimating the cost savings achievable by using the PROSNOW® system to support a ski resort’s daily and strategic snowmaking decisions, compared to the information sources and strategies used so far. In the survey-based approach, which included both ex-ante and ex-post elements, pilot ski resorts were asked to (e)valuate the PROSNOW® demonstrator, based on their experiences from the real-time testing in the winter season 2019/20. The survey included questions about the perceived forecasting accuracy, observed positive impacts, the experienced as well as expected usefulness of the PROSNOW® demonstrator for different areas of application within the ski resort, and the ski resort’s willingness to pay (WTP). For the latter, both direct and indirect stated preference methods (e.g. limit conjoint analysis) were applied.</p><p>Both, simulations and survey results revealed that increases in the ability to anticipate weather and snow conditions bear significant saving potentials for some ski resorts. Areas of application for which PROSNOW® is considered particularly useful include snowmaking decisions for the upcoming hours and days, the optimization of water and energy use and avoidance of snow overproduction. Even though some pilot ski resorts experienced problems with the demonstrator, the majority indicated to be willing to pay a non-zero price for the service, ranging from 2,500€ to 12,700€ per season.</p>

Improvement of load-bearing capacity of arched support using rolled steel reinforcement in mines

The economic efficiency of coal mining at the reduced cost is directly related with maintenance of operation conditions in temporary roadways. This article proposes a method of increasing the loadbearing capacity of the three-link arched support made of a special rolled profile (SRP) by increasing the stiffness moments of arched support sections subjected to the greatest bending moments. It is determined to be necessary to install the same size SPR in the support sections exposed to the greatest bending moments. Mathematical modeling of the reinforcement shows that the sufficient length of SRP segments is 30 cm. The calculations show that SRP 27 is replaceable by SRP 17 with the same size inserts, which allows saving of 10 kg of steel per each meter of the arched support. The proposed method of increasing the load-bearing capacity of the support will reduce the specific content of steel in the mine support manufacture and, thereby, will enable significant saving of material and labor resources. The studies conducted to substantiate the proposed solution include: determination of bending moments and normal forces in the three-link steel arched support by the computer-aided procedure of VNIMI (All Union Research Institute of Mining Geomechanics and Mine Surveying) for the specific existing conditions, with the subsequent choice of the required size of the support; stress–strain analysis of rock mass and mine support in ANSYS environment; economic calculation of the proposed solution effectiveness. The implemented researches give grounds to believe that the proposed variant of increasing the loadbearing capacity of the support made of the rolled steel profile can significantly improve stability of mine roadways. It is possible to strengthen the support without reducing the metal content in cases of expected deformation of the support under the influence of the confining pressure, when the other methods of maintenance-free support in roadways are ineffective or require a lot of time, materials and labor.