Current Calculation Method Research Articles

A new calculation method of mean skin temperature for assessment of thermal comfort

The current calculation methods of mean skin temperature did not work so well in some thermal comfort evaluations, especially under local thermal stimulation or uniform thermal environment. In this paper, a new calculation method for mean skin temperature was established, at the same time, distribution of receptors, gender difference, ambient temperature and local thermal stimulation spots. A subject experiment was conducted to validate the new method. In three conditions with different indoor air temperatures, local stimulation of different temperatures was given to the forehead, back and sole of the feet of 10 subjects in winter and 24 subjects in summer, respectively. Results showed that the current method showed much higher accuracy in predicting subjects’ thermal comfort than conventional methods, especially for females. This new calculation method provides an improved tool for thermal comfort assessment, and it has guiding significance for future research on thermal comfort.

Start-up and shut-down strategies of DR-based hybrid DC converter for offshore wind power transmission system

The diode rectifier (DR) based hybrid dc converter can significantly increase the economy of the offshore wind power transmission system comparing with the traditional modular multilevel converter (MMC). However, the start-up and shut-down methods of this hybrid dc converter are not studied. In this paper, the start-up and shut-down strategies of the hybrid dc converter are proposed. The start-up process can be divided into two stages: uncontrollable precharging stage and controllable precharging stage. In the uncontrollable precharging stage, the calculation method of the precharging current is given and the design method of the current limiting resistor is presented. In the controllable precharging stage, a circulating current control strategy is proposed to balance the inner energy of the converter and charge the submodule capacitors to the rated value. Besides, the corresponding shut-down strategy is also introduced. Simulation results based on MATLAB/Simulink and hardware-in-the-loop experiment results based on the RT-LAB are provided to support the proposed strategies. The proposed start-up and shut-down strategies can charge and discharge the submodules of the hybrid DC converter safely and cheaply.

An Improved Critical Current Calculation Method of HTS Field-Excitation Coil for Double-Stator HTS Generator With Stationary Seal

In this article, a calculation method for critical current of high-temperature superconducting (HTS) excitation coils made by Bi-2223 tapes is proposed, which can provide a reference for the design and manufacture of HTS excitation coils. Based on the test data provided by the manufacturer, the suppression effect of the applied parallel and perpendicular magnetic field on the critical current density is separately described by the proposed Jc-B model of the Bi-2223 tapes. Then, taking a 10 kW double-stator HTS machine (DS-HTSM) as an example, the target excitation magnetomotive force (MMF) required to meet its designed electromagnetic properties is obtained. After then, the turns number and the critical current of the HTS excitation coils required to meet the target MMF are calculated by the finite element analysis (FEA). Further, the FEA model of the DS-HTSM will be built by using the homogenization modeling method of HTS coils, and the influence of the armature reaction magnetic field on the critical current of the HTS excitation coils is analyzed. Finally, the correctness and effectiveness of the proposed improved critical current calculation method is verified by fabricating the 10 kW DS-HTSM prototype and conducting experimental test.

Research on the influence of distributed generation on the calculation of closed-loop current in distribution network

The closed-loop operation is frequently used in the distribution network to realize maintenance and loading transfer uninterruptedly, and the access of distributed generation (DG) changes the structure and the operation modes of the distribution network, which affects the closed-loop operation. Firstly, the paper analyzes the calculation method of closedloop stable current and closed-loop surge current of distribution network with DG. Then, according to the types of utility interface of distributed photovoltaic power, the equivalent model of PI type and PV type of photovoltaic power is given, and the calculation process of loop current is analyzed. Finally, the validity of the closed-loop current calculation method is verified by a 15-node example, and the influence of the capacity and location of the distributed photovoltaic power on the calculation of closed-loop current in the distribution network is analyzed.

Computational Analysis of Tube Wall Temperature of Superheater in 1000 MW Ultra-Supercritical Boiler Based on the Inlet Thermal Deviation

Local over-temperature is one of the main reasons for boiler tube failures (BTF). By accurately monitoring and controlling tube wall temperature, local over-temperature can be avoided. Based on the measured flue gas parameters and numerical simulation, a method of thermal deviation calculation is proposed in this study for the on-line calculation of the tube wall temperature of boiler superheaters. The full-size three-dimensional numerical simulation was presented on the combustion in a pulverized coal-fired boiler of 1000 MW ultra-supercritical (USC) unit. A difference in the thermal deviation of the vertical direction was innovatively introduced into a segmented discrete model, and the thermal deviation condition conforming to reality was introduced into the calculation. An on-line calculation system developed based on the current calculation method was applied in a 1000 MW USC unit. The calculated local high-temperature zone was consistent with the actual over-temperature position and conformed to the law of the allowable metal temperature of the final superheater (FSH) serpentines segment. The comparison results showed that the calculated data by this method were more reflective of tube wall temperature change with boiler loads than the measured data. According to the calculated local over-temperature zone, the immediate warning response can effectively reduce the possibility of over-temperature BTF.

YOLOCa: Center aware yolo for dense object detection

In this report, we propose a fully convolutional one-stage object detector (YOLOCa) with a novel decoupled head, an improved label assignment strategy, and a new loss computation method for dense object detection. By comprehensively considering the IoU, score and position connection between the prediction frame and the ground truth in the sample allocation, and by introducing some current mainstream loss function calculation methods such as Focal loss, DIOU nms, etc. Through the above techniques, we have effectively improved the AP. We conduct experiments on the global wheat detection dataset, and as shown in figure 1, our method achieves an AP of 49.9%, which is a 14.5% improvement over the baseline yolov3 (35.4%). This is still 0.8% AP higher than yolox which also uses the advanced label assignment strategy, and we still maintain the speed efficiency of the first-level object detector. We hope our work can provide some useful tips for developers and researchers, the source code is at https://github.com/gaozixiang13/YOLOCa.

Short Circuit Current Algorithm and Software Design Based on IEC60909 Standard

With the continuous growth of load and the enhancement of grid structure, the problem of excessive short circuit current has become a key factor affecting the safe operation of the China Southern Power Grid. The comparison of measured data shows that the short circuit current calculation results of China Southern Power Grid are optimistic based on the existing short circuit current calculation method. It brings difficulties to the arrangement of the power grid operation mode. This paper first briefly introduces the calculation principle of the IEC60909 Standard (short for IEC60909 Short Circuit Current Calculation Standard). And based on this standard, an improved algorithm for short-circuit current calculation is proposed. FCAP (short for Fault Current Analysis Program), a newly developed software based on the improved algorithm, is compared with other similar software being popular in domestic and foreign to prove its engineering practical value.

Let the data speak about the cut-off values for multidimensional index: Classification of human development index with machine learning

The Human Development Index (HDI) classification is essential as it relates to international aid policies and business strategies. Although the existing literature has criticized the arbitrariness of cut-off values of the HDI, few proposed an ideal approach to overcome this drawback. This paper first employs the unsupervised machine learning techniques, the K-means clustering and Partitioning Around Medoids algorithms, to cluster the HDI and offers more reasonable cut-off values for classifying countries in combination with the current HDI calculation method. The results indicate that we can group the countries worldwide into three clusters, given the 2018 HDI dataset. We suggest cut-off values of 0.65 and 0.85 to classify low, medium, and high human development countries. This paper provides a new perspective to classifying the HDI based on the similarity of countries’ development but not subjective judgments.

An investigation of the customer baseline load (CBL) calculation for industrial demand response participants –A regional case study from Iran

In today's power systems, performing demand response (DR) programs is considered a solution for sustainable operation, carbon reduction, and facilitating renewable energy integration. Currently in Iran, several DR programs are available to industrial customers. Moreover, the design of a market-based DR has recently been considered by the power system operator. In DR programs, customer baseline load (CBL) is used to determine the level of customers’ demand reduction and is key to the billing process; thus, the CBL calculation methodology can directly affect the efficiency of these programs. This paper investigates the current CBL calculation method in Iran's power system and, as its main contribution, proposes some effective methods to reduce the probable incentives for CBL manipulation. In order to show the effectiveness of the methods, a real study case is considered based on the historical load data of the industries in the Khorasan region.

Methods and tools of a construction cost management system at the pre-project lifecycle stage of a construction facility

Introduction. The cost of construction is the most important indicator of any investment and construction project which is subject to change at every stage of its lifecycle due to the influence of many internal and external factors. Creation of an effective integrated construction cost management system, which allows controlling changes in construction costs in the process of developing a construction facility, is relevant for all participants of investment and construction processes. Certain methods and tools are applied at every lifecycle stage of a construction facility; they solve construction cost management problems. At the stage of capital investment planning and preliminary design, the main task is to determine trustworthy construction costs and possible limits of their change, taking into account any risks and uncertainties. This task turns more complex due to the lack of initial data about the facility and tight deadlines. This article is focused on the system of methods and practical tools used to determine construction costs at the stages of capex planning and preliminary design of a construction facility.
 Materials and methods. In the course of the study, current construction cost calculation methods were analyzed. Methods of analysis, synthesis, expert and comparative evaluation were applied.
 Results. As a result of the analysis the main principles of this methodological approach and a set of practical tools were developed to find reliable construction costs.
 Conclusions. The proposed methods and practical construction cost management tools can be applied in the process of implementation of investment and construction projects of any complexity.

GCN-Based Short-Circuit Current Calculation Method for Active Distribution Networks

GCN-Based Short-Circuit Current Calculation Method for Active Distribution Networks

Brain-Inspired Spike Echo State Network Dynamics for Aero-Engine Intelligent Fault Prediction

Aero-engine fault prediction aims to accurately predict the development trend of the future state of aero-engines, so as to diagnose faults in advance. Traditional aero-engine parameter prediction methods mainly use the nonlinear mapping relationship of time series data but generally ignore the adequate spatio-temporal features contained in aero-engine data. To this end, we propose a brain-inspired spike echo state network (Spike-ESN) model for aero-engine intelligent fault prediction, which is used to effectively capture the evolution process of aero-engine time series data in the framework of spatio-temporal dynamics. In the proposed approach, we design a spike input layer based on Poisson distribution inspired by the spike neural encoding mechanism of biological neurons, which can extract the useful temporal characteristics in aero-engine sequence data. Then, the temporal characteristics are input into a spike reservoir through the current calculation method of spike accumulation in neurons, which projects the data into a high-dimensional sparse space. In addition, we use the ridge regression method to read out the internal state of the spike reservoir. Finally, the experimental results of aero-engine states prediction demonstrate the superiority and potential of the proposed method.

Проблемы моделирования незадымляемых лестничных клеток в высотных зданиях

Introduction. Within the framework of this article, the main problems associated with modeling the operation of the supply smoke-free ventilation of pressurized stairwells in high-rise buildings are formulated. Taking into account the identified problems, the first numerical experiments were carried out to study the operation of the supply smoke ventilation system in the volume of the pressurized stairwell with a distributed supply of outdoor air. Purpose and objectives. Analysis of the main problems related to the modeling and design of the operation of the plenum smoke ventilation of pressurized stairwells in high-rise buildings. Conducting numerical experiments to study the distribution of pressure in the volume of pressurized stairwells. Methods. Using the Fire Dynamics Simulator software used to simulate the fire process, numerical experiments were carried out to study the pressure distribution in the volume of pressurized stairwells with a distributed external air supply device. Results and discussion. Based on the analysis of the main problems related to the modeling and design of the operation of the plenum smoke ventilation of pressurized stairwells in high-rise buildings, the mathematical models of such systems were tested and adapted taking into account the accepted assumptions. Evaluation of the results of the calculations showed satisfactory convergence of the results of numerical experiments with the results obtained on the basis of the current calculation methods. Conclusions. Data were obtained on the distribution of pressure in the volume of the stairwell when arranging a distributed external air supply. The optimal number and location of the air distribution devices of the plenum smoke ventilation is determined. To assess the possibility of using supply smoke ventilation systems when arranging a distributed external air supply, as well as to develop a design method for determining the performance of ventilation equipment with this method of ensuring smoke-free stairwells in high-rise buildings, taking into account the provisions of existing methods, further studies will be carried out, including using computer modeling methods. Keywords: pressurized stairwell; air overpressure; supply smoke ventilation; smoke protection; high-rise buildings.

무기체계 국산화 평가방안의 한계와 발전방안

Currently, overseas exports of domestic defense products are gaining momentum starting with the Ukraine-Russia war. The way to continuously improve the competitiveness of domestic defense products is to utilize localization evaluation measures as a key tool to promote substantial localization advancement. This study aims to contribute to innovation in the way of working in the defense industry by inducing the level of localization to continuously upgrade by improving the evaluation plan for localization. First, the scope of the study is to understand the limitations of the current localization evaluation. Second, the effect on the total life cycle is analyzed when the localization evaluation is distorted. Third, finally, it seeks development solitions that can practically carry out localization. Qualitative research methodology is applied for the effective performance of this study. The opinions of various interest groups are collected and analyzed through the f irst and second Delphi surveys and in-depth interviews. Conflicting opinions are agreed through expert discussions in in-depth interviews. As a result of the performance of this study, it was analyzed that the current localization rate calculation method has a high possibility of abuse or distortion. In order to solve this problem, an agreement was reached that it was necessary to expand the scope of calculation to the 1st or 2nd partner companies. It was partially confirmed that when the result of calculating the localization rate is distorted, the effect is increased as the total life cycle progresses. However, in order to reduce the distortion effect of the localization rate at the operation maintenance stage, it was confirmed that it is not reasonable to convert the operational maintenance cost into the present value and reflect it in the localization rate. In summary, the current localization evaluation relies only on measuring the simple cost performance of calculating the localization rate, and there is a limitation that the possibility of abuse or distortion is high due to the limitation of the scope of calculating the localization rate to primary suppliers. In order to improve this, a model that comprehensively evaluates not only cost performance but also various performance is needed, but in the short term, it is realistic to maintain the current cost-related performance measurement method and expand the scope of localization rate calculation. The expected effect of this study is to seek ways to continuously promote localization by raising the need for improvement of localization evaluation measures, and furthermore, localization evaluation is used as a key tool to secure the external competitiveness of domestic defense products. In addition, various stakeholders may have conflicting opinions in various fields in the defense sector, and the introduction of qualitative research methodology can help each other share various perspectives and come up with solutions through discussions and agreements.

Protection of Multi-Terminal HVDC Grids: A Comprehensive Review

Multi-terminal HVDC grids facilitate the integration of various renewable resources from distant locations; in addition, they enhance the reliability and stability of the grid. Protection is one of the major obstacles in realizing reliable and secure multi-terminal HVDC grids. This paper presents a comprehensive review of the existing protection schemes for multi-terminal HVDC grids. First, DC fault current stages are demonstrated; in addition, fault analysis studies and the existing fault current calculation methods are reviewed. Then, HVDC grid protection requirements including multi-vendor interoperability conditions are extensively discussed. Furthermore, primary protection algorithms are classified into single- and double-ended schemes, and a detailed comparison between each category is presented such that the distinctive algorithms from each group are highlighted. Moreover, the recent DC reclosing schemes are reviewed highlighting their role in enhancing grid stability and ensuring supply continuity. Finally, available standards for HVDC protection systems alongside their design considerations and procedures are thoroughly outlined. This paper focuses on the recently proposed methods to design reliable protection schemes for multi-terminal HVDC grids and highlights the main advantages and disadvantages associated with them; thus, it offers a beneficial guide for researchers in the HVDC protection field.

A Strategy to Quantify Water Supply of an Agricultural Reservoir for Integrated Water Management Policy

A data-driven approach is required to scientifically manage agricultural water resources in accordance with the integrated water management policy of South Korea. In this study, a quantification strategy is presented to calculate reservoir supply by comparing the results with the actual reservoir water storage. Strategies considering current calculation methods were divided into canal flow measurement (S1), theoretical flow rate (S2), water storage decrease in field practice (S3), and water demand in design practice (S4), utilizing water levels of the reservoir and its canal and the level–flow rate curve obtained from surveying the canal flow. Each strategy was assessed through hydrological verification of reservoir water balance modeling. Based on the determination coefficient (R2), Nash–Sutcliffe efficiency (NSE), and relative error (RE) values, the S1 method was found to be the most suitable. S2 had lower reliability than S1, while S3 and S4 satisfied neither R2 nor NSE and had a larger RE than S1 and S2. To accurately quantify agricultural water supplies, the importance of directly measuring reservoir canal flows must be emphasized using automatic water level and flow gauges in canals. This study provides insights into more scientific management of agricultural reservoir water supplies and more effective monitoring of agricultural water usage.

Considerations of a thick lens formula for intraocular lens power calculation

BackgroundIn recent years, some lens manufacturers have committed to providing lens shape data for some of their lens models. The purpose of this study is to present a strategy for prediction of intraocular lens power and residual refraction based on a pseudophakic model eye containing 5 refractive surfaces and to show its applicability using worked examples. MethodsA pseudophakic model eye with a thin spectacle correction, a thick cornea (radius of curvatures for both surfaces and central thickness) and a thick IOL (either radius of curvatures RLa and RLp for front and back surface or equivalent power PL and Coddington factor CL; and either central thickness LT or edge thickness and optic diameter) was set up. Calculations were performed based on linear Gaussian optics (vergence formulae). Formulae were provided to derive the lens power/shape and the residual equivalent spectacle refraction SEQ. From the lens shape the location of the haptic plane HP, the image sided principal plane of the lens HL, and the ocular magnification OM were extracted. ResultsThe calculation of a thick intraocular lens and the prediction of residual refraction is presented with reference to 3 working examples: A) lens varied in PL and shifted with its haptic plane keeping the CL constant, B) lens varied in CL and shifted with its haptic plane keeping PL constant, and C) CL and PL of the lens varied keeping its haptic plane position in the eye constant. For each combination of parameters (PL, CL, or haptic plane shift) the parameters influencing SEQ, OM and HL-HP were analysed. ConclusionSome modern optical biometers currently on the market provide the radii of curvature of both corneal surface and all relevant distances in the eye. With additional data on the lens shape, it would be possible to improve lens power calculations by switching from thin to thick lens models for the cornea and for the lens. This would overcome one of the major drawbacks of current lens power calculation methods.

A software-based method for energy losses decreasing in cascaded buck + boost DC-DC converter

A MOSFETs switching times calculation method for the known modulation strategy for bidirectional buck + boost DC-DC converter is presented. A former low-loss, constant-frequency modulation strategy based on a negative inductor offset current takes place at the beginning of each conversion period which provides the ability to turn on converter’s MOSFET switches under zero-voltage and zero current switching (ZVS/ZCS) condition. Time interval between switching times of half-bridge MOSFETs is needed to provide the ability to turn on the MOSFET under ZVS/ZCS due to its antiparallel diode takes over an inductor current. Described method based on a switching delay time estimation for the worst case of converter’s circuit components spread which allows to calculate proper MOSFETs switching times by Digital Control Unit (DCU). The article describes in detail the switching of the input half-bridge MOSFETs at first switching time. The clarified offset current calculation method, based on an estimated switching delay and converter’s input voltage is presented.

Active torsional vibration suppression of integrated electric drive system based on optimal harmonic current instruction analytic calculation method

Torque fluctuation caused by flux harmonics in a permanent magnet synchronous motor (PMSM) leads to torsional vibrations in vehicle-integrated electric drive systems. To resolve this fluctuation, the coupling relationship between the torque fluctuation and harmonic current of the PMSM was analyzed by establishing an analytical model of the instantaneous torque of the PMSM. The analysis was performed considering the harmonic and saturation characteristics of the flux chain. An analytical calculation method for the reference harmonic-current instruction was proposed to suppress torque fluctuation. The proportional integral resonant (PIR) controller was designed to accurately control the actual current to follow the reference harmonic-current command. Thus, an active torsional vibration suppression method was developed. Simulation and experimental results showed that the proposed method can effectively reduce the amplitude of the 6th and 12th harmonic torque of the PMSM. The amplitude of each axis torque and gear-meshing force, corresponding to the harmonic frequency of the transmission system, is considerably reduced. The transmission stability is also significantly improved.

Experiments on local–distortional interaction buckling of cold-formed steel three-limbed built-up open-section columns

Cold-formed steel built-up open-section members, which are widely used in doorways, window frames, and corners, exhibit low torsion stiffness and high susceptibility to the deformation of the cross-section. Extensive research has been conducted on the pure buckling behaviour of cold-formed built-up members. However, few studies have investigated the local–distortional buckling interaction behaviour of complex built-up sections. This study aims to obtain a thorough understanding of the mechanics of three-limbed built-up open-section columns undergoing local–distortional interaction buckling through experiments and numerical simulations. Six lipped channels and 18 built-up columns were axially compressed under fixed boundary conditions. Finite element models were established and verified. Detailed parametric studies were conducted on the validated finite element models by varying the web height–thickness ratio, screw spacing, and slenderness ratio. The experimental results indicate that the studied built-up section had an evident assembly effect, and the bearing capacity of the built-up open-section column was sensitive to the web height–thickness ratio. Additionally, the numerical results show that, under local–distortional interaction buckling, the screw spacing had a minor influence on the ultimate bearing capacity of the three-limbed built-up open-section columns. The columns buckled in local–distortional interactions, with slenderness ratios ranging from 12.73 to 36.30. Finally, the validity and accuracy of the local–distortional​ interaction buckling calculation methods considering three-limbed built-up open-section columns were evaluated. With the current calculation methods, the prediction of the local–distortional buckling capacity of three-limbed open-section built-up columns is conservative.