Traditional Calculation Method Research Articles

Cost Analysis of Synchronous Condenser Transformed from Thermal Unit Based on LCC Theory

With the development of large-scale renewable energy consumption and multi-infeed high voltage direct current (HVDC) systems, the demand of a system for the synchronous condensers with a strong dynamic reactive power support capacity and a strong short-time overload capacity is increasing. Meanwhile, with the reuse of a large number of retired thermal units, the most practical and economic way is to transform thermal units into synchronous condensers. The cost difference in the life-cycle of the synchronous condenser transformed from a thermal unit (SCTTU) and the newly established synchronous condenser (NESC) is a key factor that affects the decision-making and construction of the transformation from thermal unit to synchronous condenser. However, the life-cycle cost (LCC) of the synchronous condenser transformed from a thermal unit and the newly established synchronous condenser contains many uncertain factors, which affect the accuracy of the LCC estimation value. In order to quantify the impact of the blind information on the cost of the synchronous condenser station, blind number theory is introduced to establish the blind number model of the LCC of the synchronous condenser transformed from a thermal unit and the newly established synchronous condenser. Additionally, the LCC of the NESC and SCTTU with a different life-cycle under the capacity of 2 × 300 MVar are estimated. The results show that the cost of the SCTTU with a long service life of more than 15 years is significantly lower than that of the NESC and, thus, the SCTTU has better economic performance. The economic performance of the SCTTU with a life-cycle of less than 15 years is not better than that of the NESC. Compared with the traditional calculation method of a single cost value, the blind number model can obtain the possible distribution interval of LCC and the reliability of the corresponding interval, which makes the estimation results more valuable for practical engineering reference.

Study on the slope dynamic stability considering the progressive failure of the slip surface under earthquake

The strength of a rock-soil mass shows complex and obvious weakening characteristics under seismic dynamic load. The previous stability analysis methods of a seismic slope do not fully depict the attenuation law of geotechnical materials and cannot truly reflect the stable state of a slope under earthquake action. Based on the theoretical analysis of the progressive failure mechanism and the evolution law of a seismic slope, the adverse effect of progressive failure on slope stability is clarified. According to the progressive failure process of a slope under dynamic load, the strain-softening model and vibration deterioration model are introduced to represent the attenuation law of rock strength parameters, and a calculation method of seismic slope stability coupled with vibration disturbance and progressive failure is proposed. The method considers the strength parameter characteristics of a rock-soil mass in different stages and is combined with the vector sum method to obtain the time-history curve of the slope safety factor under earthquake action, which makes the evaluation result of slope stability more accurate and reliable. The numerical examples show that this method can effectively reflect the dynamic stability of seismic slopes, and solve the problem that the traditional calculation methods are difficult to characterize the strength attenuation characteristics of rock and soil mass. If these characteristics are not considered, the calculation results will be unsafe.

Second-Order Model-Based Predictive Control of Dual Three-Phase PMSM Based on Current Loop Operation Optimization

To reduce the amount of computation in traditional model predictive current control, to improve the flexibility in choosing the direction and amplitude in the voltage vector synthesis of a dual three-phase motor by two degrees of freedom, and to reduce the output torque ripple and current ripple, this paper proposes a dual second-order model predictive control algorithm based on current loop operation optimization. Compared with the conventional speed loop using the PI control algorithm and the traditional MPC control algorithm, the proposed algorithm adopts the second-order MPC control mode in the speed loop, which decreases the speed regulation time and increases motor immunity. Meanwhile, the second-order MPC control mode is adopted in the current loop, and the traditional iterative calculation method is improved to calculate the direction and amplitude of the output voltage vector through the analytic function, which increases the flexibility of the output voltage vector. Additionally, a four-vector SVPWM is employed to modulate the voltage vector to reduce the current amplitude in the harmonic subspace. The simulation results indicate that the algorithm proposed in this paper can significantly reduce the torque ripple and the current ripple as well as increase the transient performance of the motor.

A novel method for calculating distributed water depth and flow velocity of stormwater runoff during the heavy rainfall events

• Traditional calculation method of runoff depth and flow velocity is inefficient. • The proposed novel method fully couples hydrological model and hydrodynamic model. • Runoff depth can be simplified as a power function of the catchment area. This work presents a novel method to calculate the distributed water depth and flow velocity of heavy rainfall-induced stormwater runoff. Although the shallow water equations or other numerical models are often employed to deal with the calculation of distributed water depth and flow velocity of runoff, it still suffers from low computational efficiency due to low convergence. This restricts its applicability to early warning of geological disasters (floods and debris flows). The novel method proposed in this work fully integrates the conceptual hydrological model and hydrodynamic model and gives full play to the advantages of both. In the novel method, based on the two equivalence relations between the hydrological model and the hydrodynamic model, i.e., the discharge at the boundary of the catchment and the total water storage in the catchment calculated by the two models should be equal at all times, a governing equation in Ordinary Differential Equation (ODE) form of stormwater runoff simulation is obtained, named distributed runoff model (DRM). The effectiveness and practicality of the DRM have been verified by three validation systems. Results indicate that the DRM can calculate distributed water depth and flow velocity of heavy rainfall-induced stormwater runoff with a low degree of difficulty and a high degree of accuracy and efficiency.

An optimization model for rescuer assignments under an uncertain environment by using Dempster–Shafer theory

Emergency decision making and disposal are significant challenges faced by the international community. To minimize the emergency casualties, and reduce probable secondary disasters, it is necessary to immediately dispatch rescuers for emergency rescue in calamity prone areas. The abruptness, destructiveness, and uncertainty of emergencies, the rescue team often faces challenges of pressing time, scattered calamity locations, and diverse tasks. This necessitates the effective organization of rescuers, for their swift dispatch to the areas requiring rescue. A valuable research problem is how to group and dispatch rescuers reasonably and effectively according to the actual needs of the emergency rescue task and the situation to achieve the best rescue effect. This study establishes a dispatch model for rescuers in multiple disaster areas and rescue points. First, this paper combines the Dempster–Shafer theory (DST) and linguistic term set, to propose the concept of an evidential linguistic term set (ELTS), that can flexibly and accurately describe the subjective judgment of emergency decision-makers. It not only lays a theoretical foundation for establishing the rescuers’ dispatch model, but also aids in expressing information in uncertain linguistic environments of decision-making and evaluation. Second, to determine the weight of ability-based rescuer evaluation criteria, this study adopted the evidential best–worst method, combining it with DST to compensate for the limitations of the traditional weightage calculation method in expressing uncertainty. Third, to effectively dispatch rescuers to multiple disaster areas, modeling is carried out based on the above methods to maximize the competence of rescuers and the satisfaction of rescue time, and the best scheme for the allocation of rescuers is determined by solving the model. Finally, the advantages of the constructed model in emergency multitasking group decision-making are demonstrated through an empirical analysis.

Inclined Layer Method-Based Theoretical Calculation of Active Earth Pressure of a Finite-Width Soil for a Rotating-Base Retaining Wall

In this study, we evaluated the active earth pressure on a retaining wall with a narrow cohesive fill under the rotation about the base mode. Under these conditions, Rankine’s and Coulomb’s earth pressure theories are not strictly effective. To improve the traditional earth pressure calculation methods (Rankine and Coulomb methods) and deduce the active earth pressure under the rotation about the base mode, here, we propose a new calculation method that incorporates the effects of wall displacement, soil arching and soil cohesion using inclined thin-layer elements. The calculation results are in good agreement with the model test data. Based on the parameter analysis, a critical aspect ratio of B/H = cotβ is determined along with a detailed elucidation of the various influencing factors (such as aspect ratio, cohesion and friction angle). The paper presents several solutions to improve the stability and lower the costs of retaining walls.

A New Method to Calculate the Relative Permeability of Oil and Water in Tight Oil Reservoirs by Considering the Nonlinear Flow

The theoretical research on the percolation mechanism and oil-water relative permeability of low-permeability oil reservoirs is the focus and hotspot of international researchers. Oil-water relative permeability is an important parameter that describes the characteristics of oil-water two-phase flow and is widely used in the dynamic analysis of development and numerical simulation technology in the reservoir. The traditional calculation method of oil-water relative permeability (i.e., the JBN method) is based on the Darcy flow law. When the velocity and the displacement pressure gradient do not follow the linear flow law, there are some errors in the results of oil-water relative permeability calculated by the JBN method. In this paper, the traditional JBN method is improved, and we establish a new processing method of experimental data for oil-water relative permeability considering the effects of nonlinear flow, capillary pressure, and gravity in tight oil reservoirs. The experiments on the flow characteristics of single-phase oil and oil-water relative permeability under nonsteady-state conditions were carried out. The flow velocity and displacement pressure gradient show nonlinear characteristics when single-phase oil is passed through a tight core. At the same time, when the air permeability decreases from 1.92 × 10 − 3 μ m 2 to 0.1 × 10 − 3 μ m 2 , the nonlinear characteristics are becoming more and more obvious. Compared with the traditional JBN method, when the nonlinear flow characteristics are considered, the oil phase relative permeability increases, and the water phase relative permeability is slightly lower. If nonlinear flow characteristics are considered, when the water saturation increases from 0.605 to 0.699, the difference of oil phase relative permeability calculated by the JBN method and this method is gradually decreasing and, with the increase of water saturation, decreases from 0.0029 to 0.0001. In addition, the effects of capillary pressure, gravity, and the nonlinear flow coefficient on the oil-water relative permeability in tight oil reservoirs are studied. The capillary pressure also has a great influence on the relative permeability of the oil phase, and the relative permeability of the oil phase increases with the increase in capillary pressure. In the development process of the low-permeability reservoir, the seepage characteristics of each flow area are different, and the oil-water relative permeability is also different. Therefore, the research results play an important role in guiding the understanding of seepage characteristics of low permeability of tight oil reservoirs.

Equivalent modeling for a finite element analysis of the mechanical properties of a bolted joint with a superelastic shape memory alloy

In this study, a beam element model with tension–compression asymmetry is constructed by using the improved Brinson model. A comparison between the calculated and experimental results verifies the computational effectiveness of the beam element. Then, a new mechanical property analysis model of a shape memory alloy (SMA) bolted joint based on the beam element model is proposed. Combined with a constructed convergence function, the mechanical equilibrium state of the SMA bolted joint under preload and external load is solved iteratively by the bisection method. Consequently, the stress–strain response curve of the SMA bolt rod and the root of the first thread, the deformation law of each thread and the separation conditions of the contact surface of members are analyzed by the proposed model. It is shown that the new proposed method can greatly improve the calculation efficiency with high calculation precision compared with the traditional calculation method.

Fractal of the Gobi surface sediment components and its variability characteristics

The surface sediment components of the Gobi are extremely complex, and the content has a “multimodal” distribution. Additionally, the gravel content, cover degree, and gravel distribution have shown significant spatial heterogeneity. Traditional fractal theory has limitations in the multimodal component fractal calculation, and the physical meaning remains unclear. In this study, we modified the traditional fractal calculation method according to a segmented weighted averaging method and quantitatively expressed spatial heterogeneity features, such as the Gobi surface, using the fractal dimension and its variation parameters. The results showed that the surface sediment component of Gobi was fractal, the fractal dimensions were between 2.23 and 2.84, and the average value was 2.56. Both the sediment component content and the granularity composition distribution structure (unimodal, bimodal, and multimodal state) had a significant influence on the fractal dimension values. The fractal dimensions of the medium-gravel Gobi sediment had a large local variability but less spatial variability. The fractal dimension degree of local variation of the sandy gravel Gobi sediment was low, but had a large range of spatial variation and a large spatial variability. The local variation and spatial variability of fine-gravel Gobi sediment were both small.

Novel method for an optimised calculation of modal analysis of girder bridge decks

A correct modal analysis of girder bridge decks requires a correct characterisation of the deformation of their cross-section, governed by the longitudinal bending of the girders and the transverse bending of the slab. This paper presents a novel method that allows the modal analysis of girder bridge decks by applying a matrix formulation that reduces the structural problem to one degree of freedom for each girder: the deflection at the centre of the beam span. A parametric study is presented that analyses the structural response of 64 girder bridge decks. The study compares the dynamic structural response obtained by the proposed method with that obtained by traditional grillage calculation methods. The method is experimentally contrasted by a dynamic load test of a full-scale girder bridge. As a result of the analysis, the proposed method reflects adequate convergence with the experimental dynamic structural response. The use of the proposed novel analysis method contributes to the intelligent modelling process for the analysis of the dynamic behaviour of bridges opening the way to easily feed a Digital Twin accelerating the demands of the Decision Support System in real time.

Continuous Line Loss Calculation Method for Distribution Network Considering Collected Data of Different Densities

In order to find the causes of statistical line loss abnormalities and propose better loss reduction strategies, it is necessary to improve the accuracy of theoretical line loss calculations. Since Distributed Generation (DG) access to the distribution network causes variability of power flow in the distribution network within a short period, the error of the traditional line loss calculation method increases. For the line loss calculation of medium-voltage distribution networks containing DGs with high-density collection data, a continuous line loss calculation method for the distribution network was proposed, aiming at improving the accuracy compared with the traditional line loss calculation method. The proposed method makes full use of the high-density collection data on the dispatch side and DG side, distributing the supply power to each load node by power to calculate real-time power flow, thus obtaining a more credible line loss value. The effectiveness and accuracy of the proposed method were verified in the IEEE 17-node distribution system.

Reliability analysis of reinforced concrete beams based on the stochastic model of resistance calculation

Abstract As a basic place for human daily life, the safety performance of architectural structure in practical application directly determines the future trend of social economy and urban construction development. By understanding the relationship between the internal and external environment of the structure and using advanced theoretical knowledge to evaluate the effectiveness of the structure, we can find effective countermeasures to solve the problem. Therefore, on the basis of defining the stochastic process model of resistance, this paper uses the reliability period analysis method to compare the structural effectiveness indicators of the proposed structure and the existing structure, and thus makes clear the differences between the traditional reliability calculation method and the time period analysis method, and analyzes the particularity of different structures.

Method for Solving the Microwave Heating Temperature Distribution of the TE10 Mode

Microwave heating is a process in which the electric, magnetic, and temperature fields are coupled with each other and are characterised by strong non-linearity, high time variability, and infinite dimensionality. This paper proposes a method for predicting the microwave heating temperature distribution of the TE10 mode, because the traditional numerical calculation method is not conducive to designing microwave controllers. First, the spatial distribution of the main electromagnetic mode TE10 waves in a rectangular waveguide was analysed using the principal mode analysis method. An expression for the transient dissipated power and a heat balance equation with infinite-dimensional characteristics were constructed. Then, the microwave heating model was decomposed into electromagnetic and temperature field submodels. A time discretization approach was used to approximate the transient constant dielectric constant. The heating medium was meshed to solve the electric field strength and transient dissipated power in discrete domains, and the temperature distribution was obtained by substituting this value into the finite-dimensional temperature field submodel. Finally, the validity of the proposed numerical model was verified by comparing the results with the numerical results obtained with the conventional finite element method. The methodology presented in this paper provides a solid basis for designing microwave heating controllers.

A Method of Winding Fault Classification in Transformer Based on Moving Window Calculation and Support Vector Machine

Winding fault is one of the most common types of transformer faults. The frequency response method is a common diagnosis method for winding fault detection. In order to improve the feature extraction ability of the frequency response curve before and after the winding fault, this paper proposes a winding fault feature extraction method based on the moving window algorithm to improve the Euclidean distance and correlation coefficient and uses a support vector machine to diagnose winding fault. “Moving window meter algorithm” refers to the fixed moving window width and window moving interval, scanning the entire frequency response curve from the initial point to the end point of the frequency response curve, using the correlation coefficient (CC) and Euclidean distance (ED) to calculate the mathematical index of each window. The mathematical index of each window is used as the characteristic quantity of fault type classification. Finally, the grid search algorithm is used to optimize the support vector machine to classify and identify the type of winding fault. At the same time, the standard support vector machine s(SVM) and back propagation neural network algorithm (BPNN) are compared with the support vector machine optimized by the grid search method to diagnose the fault type. The research shows that the improved correlation coefficient and Euclidean distance using the moving window algorithm are more sensitive to winding faults than the traditional calculation methods. The combination of the two calculation methods makes up for the shortcomings of their respective methods. The fault features obtained meet the requirements of the support vector machine for fault diagnosis, and the grid search method-optimized support vector machine classification algorithm has a good classification and recognition effect on the identification of fault types. The effectiveness and superiority of this method are further illustrated.

Portfolio value-at-risk estimation for spot chartering decisions under changing trade patterns: A copula approach.

Evolving geopolitical relationships between countries (especially between China and the United States) in recent years have highlighted dynamically changing trade patterns across the globe, all of which elevate risk and uncertainty for transport service providers. In order to mitigate risks, shipowners and operators must be able to estimate risks appropriately; one potentially promising method of doing so is through the value-at-risk (VaR) method. VaR describes the worst loss a portfolio is likely to sustain, which will not be exceeded over a target time horizon at a given level of confidence. This article proposes a copula-based GARCH model to estimate the joint multivariate distribution, which is a key component in VaR estimation. We show that the copula model can capture the VaR more successfully, as compared with the traditional method of calculation. As an empirical study, the expected portfolio VaR is examined when a shipowner chooses among Panamax soybean trading routes under a condition of reduced trade volumes between the United States and China due to the ongoing trade turmoil. This study serves as one of the very few papers in the literature on shipping portfolio VaR analysis. The results have significant implications for shipowners regarding fleet repositioning, decision making, and risk management.

North/South Station Keeping of the GEO Satellites in Asymmetric Configuration by Electric Propulsion with Manipulator

Geosynchronous orbit (GEO) is a very important strategic resource. In order to maximize the utilization of the GEO resources, the use of all-electric propulsion GEO platforms can greatly extend the service life of satellites. Therefore, this paper proposes a control scheme of the north/south station keeping (NSSK) by using electric propulsion with a manipulator. First, on the basis of the traditional calculation method of the semi-diurnal period of the orbital inclination, the calculation method of the semi-monthly period and the semi-annual period of the orbital inclination are proposed. The new method can reduce the fuel consumption and reduce the control amount and control frequency of the station keeping (SK). Secondly, a fuel-optimized NSSK algorithm by using electric propulsion with a manipulator is proposed. The algorithm can not only be applied to a large initial orbital inclination but also can unload the large angular momentum of the asymmetric satellites while keeping the north/south station, thereby avoiding the loss of control of the satellite’s attitude. The research results of this paper provide a new idea for the SK control of the GEO satellites and have great engineering application value.

Multiple Open-Circuit Fault Diagnosis Method in NPC Rectifiers Using Fault Injection Strategy

This article proposes an open-circuit fault diagnosis method in power semiconductors of three-level neutral-point-clamped (3L-NPC) rectifiers by using a fault injection strategy. To enhance the anti-interference ability of the diagnosis method, an improvement is made in the traditional calculation method of phase-to-phase pole voltage residuals by selectively adopting the quantifying operation according to the current level. Then, the normalized and quantified residuals are obtained as the diagnosis variables. All signals for calculations are derived from the controller and pre-existing sensors, avoiding the requirement of extra hardware. To improve the diagnosis accuracy and speed, a fault injection strategy is designed. A preidentification method provides guidance for choosing the type of fault to inject. On this basis, the fault injection is implemented by revising the switching signals sent from the modulation module for a short time. In this way, inner-switch faults and outer-switch faults are easier to be differentiated, and the misdiagnosis of simultaneous multiple-switch faults is avoided. Therefore, the proposed diagnosis method is accessible to detect single-switch faults as well as multiple-switch faults in 3L-NPC rectifiers more accurately and fast. The experiments are carried out to confirm the effectiveness and the robustness of the proposed fault diagnosis method.

Research on algorithms of flicker detection and calculation methods in power system

This paper mainly introduces the detection method and calculation method of load flicker signal. Firstly, the commonly used detection methods are theoretically analyzed, their advantages and disadvantages are pointed out, and a fundamental effective value detection method is proposed. Then the flicker calculation method is studied. The traditional flicker calculation method is complex and needs the design of some filters. Based on the traditional algorithm, the flicker calculation method is improved, and the accuracy and rapidity of the algorithm are verified by simulation.

The real cost of deep peak shaving for renewable energy accommodation in coal-fired power plants: Calculation framework and case study in China

To fulfill the commitment to carbon emission reduction, the grid penetration rate of renewable energy in China has increased rapidly. High penetration of renewable energy brings a significant challenge to the peaking ancillary services providers. In northern China, coal-fired units still play a significant role in peak-shaving, especially in areas where pumped hydropower, gas-fired power, and controllable load are limited. The current peaking ancillary service market in China cannot effectively mobilize the enthusiasm of peaking power plants. Fair calculation of the peak-shaving costs of coal-fired power plants is significant for formulating an ancillary service market mechanism. Current research on peak-shaving costs calculation of coal-fired power fleets is limited to the operating coal consumption costs, wear-and-tear costs, and the additional environmental costs (do not contain pollutant tax and ashes treatment). However, this costs calculation lacks consideration of the additional peaking coal consumption costs, the additional peaking environmental costs with pollution tax and ashes treatment, and the power output loss caused by the peak-shaving process. Therefore, this study proposes a novel calculating framework that includes all the potential peak-shaving costs of the coal-fired generating units mentioned above. To evaluate the proposed framework, a case study was conducted in a coal-fired power plant in Dalian City, Liaoning Province, China, in 2020. The results show that the total costs of peak-shaving in 2020 was only 4.96 million Yuan according to the existing method. However, according to the proposed costs calculation framework, the peak-shaving costs in 2020 should be 16.97 million Yuan. The power grid compensated 12.83 million Yuan to the power plant, and the real peaking net profits was -4.14 million Yuan, which means coal-fired power units are unprofitable under the current peaking compensation mechanism. Compared with the existing traditional costs calculation method, the proposed method could provide a more comprehensive and accurate costs accounting for the deep peak-shaving process of coal-fired units. This study may help formulate the benchmark and reasonable compensation in the peak-shaving ancillary service market.

Fractal Description of Rock Fracture Networks Based on the Space Syntax Metric

Fractal characteristics and the fractal dimension are widely used in the description and characterization of rock fracture networks. They are important tools for coal mining, oil and gas transportation, and other engineering problems. However, due to the complexity of rock fracture networks and the difficulty in directly applying the limit definition of the fractal dimension, the definition and application of the fractal dimension have become hot topics in related projects. In this paper, the traditional fractal calculation methods were reviewed. Using the traditional fractal theory and the head/tail breaks method, a new fractal dimension quantization model was established as a simple method of fractal calculation. This simple method of fractal calculation was used to calculate the fractal dimensions of three rock fracture networks. Through comparison with the box-counting dimension calculation results, it was verified that the model could calculate the fractal dimension of the fracture length of rock fracture networks, as well as quantify it accurately and effectively. In addition, we found a number of similarities between rock fracture networks and urban road traffic networks in GIS. The application of the space syntax metric to rock fracture networks prevents controversy with respect to the definition of the axis and it showed a good effect. Using the space syntax metric as a parameter can better reflect the space relationship of rock fractures than length. Through the calculation of the fractal dimension of the connection value and control value, it was found that the trend of the length fractal dimension was the same as that of the control value, whereas the fractal dimension of the connection value was the opposite. This further verifies the applicability of the space syntax metric in rock fracture networks.