The unit commitment problem has been a very important problem in the power system operations, because it is aimed at reducing the power production cost by optimally scheduling the commitments of generation units. Meanwhile, it is a challenging problem because it involves a large amount of integer variables. With the increasing penetration of renewable energy sources in power systems, power system operations and control have been more affected by uncertainties than before. This paper discusses a stochastic unit commitment model which takes into account various uncertainties affecting thermal energy demand and two types of power generators, i.e., quick-start and non-quick-start generators. This problem is a stochastic mixed integer program with discrete decision variables in both first and second stages. In order to solve this difficult problem, a method based on Benders decomposition is applied. Numerical experiments show that the proposed algorithm can solve the stochastic unit commitment problem efficiently, especially those with large numbers of scenarios.
As a first step in developing better molecular scale understanding of the effects of organic additives on the adsorption and mobility of radionuclides in cement under conditions of geological nuclear waste repositories, two complementary approaches, wet chemistry experiments and molecular dynamics (MD) computer simulations, were applied to study the sorption behaviour of two simple model systems: gluconate and uranyl on calcium silicate hydrate phases (C-S-H) - the principal mineral component of hardened cement paste (HCP). Experimental data on sorption and desorption kinetics and isotherms of adsorption for gluconate/C-S-H and U(VI)/C-S-H binary systems were collected and quantitatively analysed for C-S-H samples synthesised with various Ca/Si ratios (0.83, 1.0, 1.4) corresponding to various stages of HCP aging and degradation. Gluconate labelled with 14C isotope was used in order to improve the sensitivity of analytical detection technique (LSC) at particularly low concentrations (10(-8) -10(-5) Â mol/L). There is a noticeable effect of Ca/Si ratio on the gluconate sorption on C-S-H, with stronger sorption at higher Ca/Si ratios. Sorption of organic anions on C-S-H is mediated by the presence of Ca(2+) at the interface and strongly depends on the surface charge and Ca(2+) concentration. In parallel, classical MD simulations of the same model systems were performed in order to identify specific surface sorption sites most actively involved in the sorption of gluconate and uranyl on C-S-H and to clarify molecular mechanisms of adsorption.
The paper presents the results of research that can be put into the development and research of non-contact rapid method for assessing the quality of the assembly and installation of EM designs. To achieve the objectives, studied the behavior of the mechanical connection of the contact pairs, namely the definition of the contribution of R,L,C parameters contact joints in the modulation level and the spectral composition of the electromagnetic radiation mechanical contact pair
In this paper we propose a method for solving systems of nonlinear inequalities with predefined accuracy based on nonuniform covering concept formerly adopted for global optimization. The method generates inner and outer approximations of the solution set. We describe the general concept and three ways of numerical implementation of the method. The first one is applicable only in a few cases when a minimum and a maximum of the constraints convolution function can be found analytically. The second implementation uses a global optimization method to find extrema of the constraints convolution function numerically. The third one is based on extrema approximation with Lipschitz under- and overestimations. We obtain theoretical bounds on the complexity and the accuracy of the generated approximations as well as compare proposed approaches theoretically and experimentally.
A new interatomic potential for a uranium–molybdenum system with xenon is developed in the framework of an embedded atom model using a force matching technique and a dataset of ab initio atomic forces. The verification of the potential proves that it is suitable for the investigation of various compounds existing in the system as well as for simulation of pure elements: U, Mo and Xe. Computed lattice constants, thermal expansion coefficients, elastic properties and melting temperatures of U, Mo and Xe are consistent with the experimentally measured values. The energies of the point defect formation in pure U and Mo are proved to be comparable to the density-functional theory calculations. We compare this new U–Mo–Xe potential with the previously developed U and Mo–Xe potentials. A comparative study between the different potential functions is provided. The key purpose of the new model is to study the atomistic processes of defect evolution taking place in the U–Mo nuclear fuel. Here we use the potential to simulate bcc alloys containing 10 wt% of intermetallic Mo and U2Mo.
In coming years residential consumers will face real-time electricity tariffs with energy prices varying day to day, and effective energy saving will require automation - a recommender system, which learns consumer's preferences from her actions. A consumer chooses a scenario of home appliance use to balance her comfort level and the energy bill. We propose a Bayesian learning algorithm to estimate the comfort level function from the history of appliance use. In numeric experiments with datasets generated from a simulation model of a consumer interacting with small home appliances the algorithm outperforms popular regression analysis tools. Our approach can be extended to control an air heating and conditioning system, which is responsible for up to half of a household's energy bill.
The motion of a heavy bead on the surface of a parabolic bowl rotating at a constant angular velocity about its axis, which coincides with the vertical, is considered. It is assumed that the dry friction force acts between the bead and the bowl. The sets of nonisolated relative equilibria of the bead on the bowl are determined, and their dependence on the problem parameters is studied. The results are illustrated in the form of bifurcation diagrams.
Dynamics of a massive point on a rotating wire or surface under dry friction force action is considered. Existence, stability and bifurcations of non-isolated relative equilibria sets of the point located - on a sphere uniformly rotating about an inclined fixed axis; - on a thin circular hoop rotating about an inclined fixed axis; - on a paraboloidal bowl uniformly rotating about its axis are studied. The results are represented in the form of bifurcation diagrams.
The sliding of a heavy bead, threaded on a thin circular hoop, rotating with a constant angular velocity around a vertical axis, situated in its plane and, in the general case, not passing through its vertical diameter, is considered. It is assumed that dry friction acts between the bead and the hoop. A set of unisolated positions of relative equilibrium of the bead on the hoop is obtained, and their dependence on the problem parameters is investigated. The results are presented in the form of bifurcation diagrams. The stability properties of the unisolated relative equilibria obtained are discussed.
One of the most important key factors for the development of non-urban areas is infrastructure, and energy generation is one of the fundamental infrastructure elements. This paper provides a new solution for energy generation based on wood chips which has a multi-sector effect because the authors offer to combine planning of forest cleaning cutting with bioenergy generation in one complex project, which will have socio-economic and ecological effects. The situation with forest fires makes the authors’ idea more attractive because after forest fires the problem of cleaning cutting in forest becomes very important and urgent by ecological and economical points: after cleaning cutting there are a lot of low quality wood which can be recycled into chips for the production bioenergy by the authors’ idea. This enriched methodology has successfully been applied into the regional strategical planning in the field of bioenergy and forestry of the Ural region of Russia; however, it is suitable for applications in regional development in any non-urban forested region of the world.
The article focuses on corporate information systems intended for management accounting and budgeting (MAB) in projectized construction companies. The author argues that the successful implementation of such systems requires a comprehensive approach involving the development or the adaptation of MAB philosophy taking into account the software functionality and related business processes. The author demonstrates that ERP software is the most effective technological platform for corporate MAB systems of projectized companies. This is explained by the fact that the ERP systems have both sufficient functionality for project management automation and appropriate tools for management accounting and budgeting. Relying on this analysis, a comprehensive approach and appropriate solutions for developing corporate MAB systems in projectized construction companies are proposed. The methodological solutions proposed in the field of MAB design take into account the specific nature of a contractor who carries out construction projects for external customers. In particular, the following methodological solutions are presented: establishing temporary project-based profit centers in the construction company’s financial structure; using administrative quasi-projects and the “direct costing” method for fixed overheads costing in certain departments; establishing temporary profit centers related to production departments (internal subcontractors). This paper also shows how such a financial structure may be used in the SAP ERP system relying on the end-to-end “project” attribute. A budgeting structure with two versions of the corporate master budget is proposed. The first version of the structure is based on the contracting plans and the second – on the last approved project budget versions. The paper shows that monitoring implementation is necessary for both master budget versions. The main assertions and results of the paper are applied in the implementation of a corporate MAB information system based on SAP ERP in a construction company. The results of the system’s implementation and operation have shown significant improvement in the key financial indicators of the company, including profits, rate of return and net cash flow.
This paper reviews atomistic force field parameterizations for molecular simulations of cementitious minerals, such as tricalcium silicate (C3S), portlandite (CH), tobermorites (model C-S-H). Computational techniques applied to these materials include classical molecular simulations, density functional theory and energy minimization. Such simulations hold promise to capture the nanoscale mechanisms operating in cementitious materials and guide in performance optimization. Many force fields have been developed, such as Born–Mayer–Huggins, InterfaceFF (IFF), ClayFF, CSH-FF, CementFF, GULP, ReaxFF, and UFF. The benefits and limitations of these approaches are discussed and a database is introduced, accessible via a web-link (http://cemff.epfl.ch). The database provides information on the different force fields, energy expressions, and model validations using systematic comparisons of computed data with benchmarks from experiment and from ab-initio calculations. The cemff database aims at helping researchers to evaluate and choose suitable potentials for specific systems. New force fields can be added to the database.
It has been investigated the corrosion resistance, strength and plasticity of vanadium-based ternary (V-Ti-Cr) alloys in a steam–water medium. It has been found the optimum compositions with the best properties.
This article aims to identify effects of client orientation on business models of central power generation companies.
Five major Russian wholesale electricity market players were selected for the analysis conducted applying A. Osterwalder and Y. Pigneur’s ‘Business Model Canvas’. To identify the changes induced by client orientation, the progress of companies’ business models was traced over 6 years; from 2009 to 2015.
Five major trends in business model changes due to client orientation were identified:
1. Declaration of client orientation and adoption of client service standards;
2. Advent of business diversification in favor of engineering, construction, service, operation and maintenance of generating facilities;
3. Increase in vertical integration;
4. Increase in diversity of communication channels with consumers;
5. Increase in diversity of customer relationships.
The results were compared with those obtained in international studies. Conclusions about international and local character of the trends are presented.
The study contributes to knowledge of current and upcoming changes in the business of central power generation triggered by the advent of electricity prosumers. It is valuable both for management decision makers and theorists.
Using molecular dynamics simulations, we study the transient response of a binary Lennard-Jones glass subjected to periodic shear deformation. The amorphous solid is modeled as a three-dimensional Kob-Andersen binary mixture at a low temperature. The cyclic loading is applied to slowly annealed, quiescent samples, which induces irreversible particle rearrangements at large strain amplitudes, leading to stress-strain hysteresis and a drift of the potential energy towards higher values. We find that the initial response to cyclic shear near the critical strain amplitude involves disconnected clusters of atoms with large nonaffine displacements. In contrast, the amplitude of shear stress oscillations decreases after a certain number of cycles, which is accompanied by the initiation and subsequent growth of a shear band.
The article deals with issues of technical and economic substantiation of priorities and scopes of modernizing the existing thermal power plants (TPPs) in Russia to work out long-term forecasts of the development of the industry. The current situation in the TPP modernization trends is analyzed. The updated initial figures of the capital and operation costs are presented and the obtained estimates of the comparative efficiency of various investment decisions on modernization and equipment replacement at gas-and-oil-burning and coal-fired TPPs with regard to the main zones of the national Unified Power System (UPS) of Russia are cited. The results of optimization of the generating capacity structure underlie a study of alternative TPP modernization strategies that differ in the scope of switching to new technologies, capital intensity, and energy efficiency (decrease in the average heat rate). To provide an integral economic assessment of the above strategies, the authors modified the traditional approach based on determination of the overall discounted costs of power supply (least-cost planning) supplemented with a comparison by the weighted average wholesale price of the electricity. A method for prediction of the wholesale price is proposed reasoning from the direct and dual solutions of the optimization problem. The method can be adapted to various combinations of the mechanisms of payment for the electricity and the capacity on the basis of marginal and average costs. Energy and economic analysis showed that the opposite effects of reduction in the capital investment and fuel saving change in a nonlinear way as the scope of the switch to more advanced power generation technologies at the TPPs increases. As a consequence, a strategy for modernization of the existing power plants rational with respect to total costs of the power supply and wholesale electricity prices has been formulated. The strategy combines decisions on upgrade and replacement of the equipment at the existing power plants of various types. The basic parameters of the strategy for the future until 2035 are provided.
The paper describes the method for modeling of nanostructure polymerizable multicomponent oxide melts, which can be used for systems of type Me2O-SiO2 (Me = monovalent cation), with the results of a molecular dynamics simulation as input. The models of the short-range and medium-range orders taking into account dual behavior of monovalent alkali metal cations able to form stable groups with oxygen atoms are built. The melt structure is described with help of heterogeneous descriptors which are constructed using the polymer models and molecular dynamics results. The model is a heterogeneous graph which is built with gradually increasing of mapping levels (from selection heterogeneous graph vertices associated with individual particles, to forming connected components of vertices corresponding polyanionic complexes and rings in the melt. Quantitative calculations of the structure associated characteristics are carried out using the distribution function of graph vertices. We have modeled nanostructure and studied polymerization processes in the system SiO2-Na2O in the range of five compositions by the above method. In particular, we calculated the radial and angular distribution, the distribution of the coordination numbers, the bond lengths, the mole portions of different types of oxygen atoms, the complex anions in the model system taking into account sodium ions, the proportion of flat rings in polyanionic complexes, as well as the average connection factor. The obtained results give a satisfactory agreement with the characteristics in the range having experimental data. A number of results the structure modeling has a scientific novelty and practical significance.
The use of gas-turbine plants (GTPs) in the power industry of Russia is analyzed. Attention is paid to microturbines and low-, medium-, high-, and superhigh-power GTPs. The efficiency of the gas-turbine plants of domestic and foreign manufacture is compared. The actual values of the installed capacity utiliza- tion factor and the corresponding efficiency values are calculated for most GTPs operating in the country. The long-term demand of the country’s electric power industry for GTPs for the period until 2040 is deter- mined. The estimates have been obtained for three basic applications of the gas turbines, viz., for replacement of the GTPs that have exhausted their lifetime, replacement of outdated gas-turbine plants at gas-and-oil- burning power plants, and construction of new thermal power plants to cover the anticipated growing demand for electric power. According to the findings of the research, the main item in the structure of the demand for GTPs will be their use to replace the decommissioned steam-turbine plants, predominantly those integrated into combined-cycle plants. The priority of the reconstruction of the thermal power plants in operation over the construction of new ones is determined by the large excess of accumulated installed capacities in the country and considerable savings on capital costs using production sites with completed infrastructure. It is established that medium- and high-power GTPs will be the most in-demand plants in the electric power in- dustry. The demand for low-power GTPs will increase at high rates. The demand for microturbines is expect- ed to be rather great. The demand for superhigh-power plants will become quantitatively significant after 2025 and grow rapidly afterwards. The necessity of accelerated development of competitive domestic GTPs with a wide range of capacities and mastering of their series manufacture as well as production of licensed gas tur- bines at a high production localization level on the territory of the country is shown. Considerable home de- mand for the power-generating GTPs and vast external markets will make the development of efficient do- mestic GTPs economically viable.
Uniaxial tensile testing is a most common way of obtaining the information about the constitutive behavior of a material during gas forming. At the same time for industrial applications it is important to know the material behavior in a biaxial tension mode, which is much closer to the one realized in a shell during forming process. The paper focused on the investigation of the differences between the gas forming technologies designed in FEM based CAE system using the material parameters obtained in conditions of uniaxial and biaxial tension. The rheological characteristics of AMg6 aluminum alloy obtained by tensile and free bulging testing are analyzed and compared. The comparison shows that the constitutive data obtained by these methods are different. The effect which these differences could provide to the design of a gas forming technology was studied. A pressure regime for an aircraft part forming which maintains the maximum strain rate at constant level was calculated using finite element simulation for the both sets of constitutive constants. The calculated pressure regimes were then realized experimentally and the differences between the deformed specimens were analyzed.
This study proposes a method for determining the material constitutive equations and optimal forming conditions on the basis of free bulging tests. The blow-forming tests were carried out at the temperature of 420 °C using aluminum alloy (AMg-6) sheets of a 1 mm thickness. Each test was performed at constant pressure. For each fixed value of the pressure, a series of experiments was carried out with different forming times to obtain evolutions of dome height H and thickness s. These data were processed by the proposed method to obtain the flow stress dependence on the effective strain rate. The constitutive equations were obtained by least squares minimization of deviations between the experimental variations of H and s and ones predicted by a simplified engineering model. On the basis of the obtained data, the optimum strain rate for AMg-6 processing was determined as one corresponding to the maximum strain rate sensitivity.