Load Curve Research Articles

Fracture behavior of concrete made with sintered fly ash lightweight coarse aggregate in comparison to normal weight concrete

Sintered fly ash lightweight aggregate based concrete has been reported to give mechanical and durability properties similar to conventional concrete. But concrete made up of lightweight aggregate possesses lower stiffness and shear strength resulting into a brittle mode of failure due to crack propagating directly inside aggregate which is weak in nature. The study presents findings from the experimental investigation of fracture behavior of concrete made with sintered fly ash lightweight coarse aggregate in comparison to normal weight concrete (NWC) at w/b ratio of 0.5, 0.4 and 0.3. The mixes have been tested for compressive and split tensile strength for both concrete types. On notched beams of size 100x 100 x 500 mm, a three-point bend test has been carried out for both lightweight and normal weight concrete to evaluate fracture parameters. The results of split tensile strength test indicated that the split tensile to compressive strength ratio lies in the range of 5-8% for lightweight concrete and this ratio lies between 5-10% for normal weight concrete. The study indicates comparable fracture behavior for both lightweight and normal weight concrete. The non-linear ascending and descending branches in load vs deflection curve of concrete with sintered fly ash lightweight coarse aggregate can be linked with the non-linearity in tensile type stress-strain behavior and formation of the fracture zone in front of the initial notch. The modulus of elasticity of lightweight concrete is significantly lower than normal concrete. The modulus of elasticity, area under the load deflection curve, tensile strength, fracture behavior etc. needs to be considered appropriately in the non-linear analysis of lightweight concrete.

A Market Strategy for Joint Profitability of Electric Vehicle Charging Stations and Retailers: Considering Electricity Price Fluctuations and Users’ Service Fee Response

With the introduction of the “carbon peaking and carbon neutralizing” initiative, China is undergoing a positive energy transition, emphasizing the replacement of traditional fossil fuels with clean energy sources. As part of this transition, numerous megacities are progressively endorsing electric vehicles (EVs) as substitutes for traditional fuel‐based vehicles. The expanding use of EVs, however, has presented challenges related to the randomness and volatility of EV charging. In response to this, many regions in China have mandated the implementation of the time‐of‐use (ToU) scheme. This scheme divides the day into distinct periods such as “valley,” “flat,” “peak,” and “critical peak,” each associated with varying charging prices. According to the management regulations, the fees collected from vehicle owners at the charging station are divided into two parts: ToU electricity value and service fees. The former is jointly determined by the power company and the government, while the latter is set by the charging station operator. To overcome the limitation on profitability, this paper proposes a scheme enabling charging stations and retailers to participate in the day‐ahead (DA) market. The proposed approach involves a two‐stage decision‐making method. By analyzing the charging habits of local residents, the paper constructs a quadratic curve for dynamic service fees and charging rates. The objective function is then utilized to adjust the anticipated charging load curve. Prior to the DA‐bidding process, an uncertain set of scenarios for electricity prices and charging loads is generated. The conditional value‐at‐risk (C‐VaR) method is employed to balance expected benefits and risks amid uncertain scenarios.

Analysis of total nitrogen pollution load and identification of key pollution sources in Futuan River basin based on SWAT model

In order to identify the key source area of the Futuan River basin, the Futuan River basin is taken as the target area, establishes the Soil Water Assessment Tool (SWAT) model, simules the runoff and total nitrogen pollution process in the basin, and analyzes the spatiotemporal characteristics of total nitrogen pollution. The key source areas of total nitrogen pollution in the basin were identified by the cumulative load curve method. The results show that the total nitrogen pollution load in the Futuan River basin presents obvious seasonal distribution characteristics. The subbasins with high load intensity of total nitrogen into the river are mainly in the middle and upper reaches of the Futuan River.

Electricity Pricing with Continuous-time Commodity Model and Non-monotonic Load Curve

Electricity Pricing with Continuous-time Commodity Model and Non-monotonic Load Curve

Classification Method of Load Pattern Based on Load Curve Image Information

Classification Method of Load Pattern Based on Load Curve Image Information

Modelling of fire behavior of RC girders strengthened by external prestressing

Since the 1950s, external post-tensioning has been a powerful tool for retrofitting existing bridges. In unbonded prestressing, the post-tensioning tendons are positioned outside the concrete cross-section, and the prestressing forces are transferred to the girder through end anchorages, deviators, or saddles. This implies that these could be critical elements for the bridge performance against fire. This paper examines reinforced concrete bridges strengthened by external prestressing and subjected to fire, using a mixed experimental and analytical approach. Initially, load tests are conducted on a model of a bridge beam strengthened by external prestressing to assess the effectiveness of the intervention until failure. The ultimate limit state (ULS) capacity of the beam is then evaluated both before and after rehabilitation. Subsequently, the fire performance is investigated through different scenarios defined by the fire load curves of Eurocode, evaluating the cross-sectional temperatures resulting from fire, estimating the loss of external prestressing efficiency, and assessing the beam’s overall fire resistance. This methodology is then applied to a real girder bridge with adjacent beams of the same type, extending the approach used on the experimental scaled beam to an actual bridge deck. Results are presented in terms of performance levels for different traffic load values and residual capacity over time from fire ignition, providing a safety assessment of girder bridges under fire exposure. The procedure is straightforward and immediately applicable to many existing reinforced bridges. The findings demonstrate how quickly external prestressing degrades, leaving the beam unprotected, and highlight the fundamental importance of the protective sheath for external tendons in limiting this degradation. Evaluating load levels based on exposure time also allows engineers to estimate the service time before rescue arrives, given the expected traffic level.

Calculation of Power Purchase Imbalance Costs for Grid Enterprises’ Agents Considering Uncertainty of Supply and Demand and Price Fluctuations in the Context of Beijing-Tianjin-Tangshan Unified Spot

Abstract The regional unified electricity spot market plays an important role in promoting the optimal allocation of power resources over a wider range and cross-regional consumption of renewable energy. This paper examines the supply and demand uncertainty and price volatility of power grid agency power purchases in the context of the Beijing-Tianjin-Tangshan unified spot purchase. It delves into the specific mechanism of unbalanced costs in agency power purchase decisions and investigates the specific channeling methods of unbalanced costs in the dual-track system. Based on the dual-track unbalanced cost under the unified spot market, a dual-track power balance model is proposed based on the typical daily load curve, and a time-based unbalanced cost calculation model is designed. Using the typical daily electricity load data from the power supply enterprise in X province as an example, the calculation and simulation of unbalanced costs are carried out. The spot electricity price fluctuates between 0.25 yuan/(kW•h) and 0.45 yuan/(kW•h) in different periods. The overall unbalanced power purchased by the power grid in the load trough stage is only 6.24% of the total monthly electricity consumption. Still, the unbalanced cost in the study period is of a deficit nature, and its average value reaches −268 million yuan. The calculation method of unbalanced costs caused by agency power purchases clearly reveals the unbalanced cost-sharing mechanism in the context of the unified spot.

A Novel Dynamic Pricing Time‐Based Demand Response Program for Net‐Load Flexibility of Microgrids

In recent years, concerns about electrical energy supply have led to the extensive use of renewable energy sources (RESs). In addition to all the benefits and reasons that justify the unlimited use of RESs, the unplanned exploitation of these sources can challenge the reliability indices of the power system. Demand‐side management (DSM) by demand response programs (DRPs) is one of the most effective and powerful measurements to provide flexibility for the system. DRPs can change the pattern of customer consumption as well as the shape of the load curve. In this study, a novel time‐based demand response model is proposed to control the slope of demand changes. Consequently, dynamic/fixed pricing models with a controllable time step are extracted. These models are implemented on experimental networks, and the results are analyzed and presented for three cases. According to the desired model, the electricity price management at particular hours of the day affects the behavior of the consumers, and it reduces the steep slope in the net‐load ramping curves (62.5% and 50% reduction in peak to valley (P2V) distance for hourly curve and daily curve, respectively).

Indigenous resources contribution and influence of load curve shapes in the optimal growth of Bangladesh electricity sector

The diminishing natural gas resource has turn out to be a severe energy concern for Bangladesh. This study conducts a detailed evaluation of potential pathways for the development of Bangladesh's electricity sector as an emerging economy by developing a capacity expansion model capable of capturing the hourly operational characteristics of diverse power generators and storage technologies, while also identifying the optimal utilization of limited resources. The simulation results indicate that nuclear energy stands out as the most cost-effective option for achieving sustainable development goals in the absence of substantial opportunities for widespread deployment of renewable energy sources in Bangladesh. However, a significant deployment of solar PV and the incorporation of battery storage could reduce the reliance on nuclear power, contingent on a revision of current land-use policies. The construction of cross-border transmission lines for importing surplus electricity is economically advisable and considering the load curve shape change is found to have significant impact on capacity mix.

Cost-efficiency based residential power scheduling considering distributed generation and energy storage

The permeation of renewable energy into smart house is a key characteristic of the future power system that brings a significant challenge to the peak load management in the power sector. In this paper, we propose cost-efficiency based residential power scheduling scheme considering distributed generation and energy storage. In which, a cost-efficiency model designed by the ratio of consumption benefit to its cost is introduced to capture the residential users' electricity consumption behaviors and reflect their economic efficiency. A discomfort cost is constructed to represent the losses associated with power scheduling when facing the incentives given by the smart grid. Specially, not only residential load consumption utility, but also that of the renewable energy generation and energy storage devices are applied to compose the consumption benefit，and an energy storage model to be established to plan the charging and discharging of energy storage batteries. Day-Ahead Bidding Price and Real-time consumption management models are introduced to test the performance of the proposed scheduling scheme. Simulation results demonstrate that the proposed method increases the residential consumer's daily cost efficiency by 1.5834, and reduces its daily electricity bill by 38.43 % and that about 36.86 % of energy is saved in the smart grid while the proposed scheduling strategy for energy consumption can effectively smooth the load curve in smart grid.

Lüders and Portevin–Le Chatelier processes in austenitic-martensitic TRIP steel

The authors studied the nature of mobile fronts of localized deformation that generate and propagate during deformation of metastable austenitic-martensitic TRIP steel VNS9-Sh along the entire length of the loading curve from the yield point to fracture. A joint research of the nature of the deformation fronts movement and kinetics of the magnetic phase accumulation made it possible to establish that the fronts under consideration are the fronts of the thermoelastic phase transformation of metastable austenite into martensite. This transformation is realized firstly by formation of the Chernov–Lüders bands and then the Portevin–Le Chatelier bands. Both processes are consistent with staging of the deformation curve, which contains a pseudo-plateau, a section with an increasing hardening coefficient, and a section with a decreasing hardening coefficient. It is shown that the deformation-induced phase transformation corresponds to the fronts propagating on the pseudo-plateau and on the section of loading curve with an increasing hardening coefficient. The Portevin–Le Chatelier bands, which are formed in the section of the loading diagram with a decreasing hardening coefficient, are not associated with “austenite-martensite” transformation and have a twin nature. The kinetics of thermoelastic transformation fronts, as well as deformation fronts in materials with a shear mechanism of shaping, can be described in terms of the autowave concept. On the yield plateaus, the phase transformation occurs through generation and propagation of localized plasticity switching autowaves. In the section with an increasing hardening coefficient, it continues through generation and movement of excitation autowaves. The propagation regions of excitation autowaves are limited in the sample space. They are set by the zones of origin and annihilation of primary switching autowaves which were formed on the yield plateau.

Optimizing Distributed Generation Resources for Power Grid Quality Improvement Using Hybrid Optimization Technique

Distributed generation (DG) integration is a critical requirement in modern distribution networks to enhance power grid quality. An essential aspect of this endeavor involves strategically placing and sizing various DG resources optimally. The primary objective of this study is to determine an efficient approach for allocating Photovoltaic (PV) and Wind Turbine resources to minimize overall power losses within the grid. To achieve this goal, we introduce a novel hybrid optimization technique that combines Particle Swarm Optimization (PSO) with Genetic Algorithms (GAs). Furthermore, we explore the influence of factors such as variations in PV daily consumption, load profile fluctuations, penetration levels, and changing climatic conditions on the optimization process across two comprehensive case studies presented in this research. Our modeling results reveal that the hybrid PSO-GA approach outperforms traditional PSO in terms of integration speed, power loss reduction, and enhancements to grid quality, including voltage and frequency profiles. Additionally, this study highlights the dynamic impact of load curve fluctuations and climate changes on the optimal location and capacity of DG resources, leading to a substantial reduction in grid power losses.

Multiscale dynamic time‐domain simulation of regional integrated energy considering seasonal load difference

AbstractTo improve the multiscale dynamic dispatching and distribution capacity of regional integrated energy, a multiscale dynamic time‐domain dispatching model of regional integrated energy with seasonal load difference is proposed. The master–slave game coordination planning model of regional comprehensive energy multiscale dispatching is constructed, and the difference fusion model of regional comprehensive energy multiscale dynamic dispatching is established by using the active and reactive power coordination control method according to the influence factors of voltage deviation and line overload absorption. Maximize the weight factors of the positive contribution of distributed photovoltaic (PV) power to the active distribution network. On the basis of the quantitative regulation analysis method of demand response power based on the equivalent slope of the load curve, establish an energy absorption capacity analysis model of seasonal load differentiation. On the basis of the dynamic interaction between different systems, a multiscale dynamic time‐domain analysis and dynamic simulation model of regional integrated energy is constructed by using the method of PV absorptive capacity assessment on both sides of demand uncertainty, to achieve multiscale dynamic time‐domain feature extraction of integrated energy and integrated scheduling of seasonal load differences. The simulation results show that the multiscale dynamic time‐domain allocation of regional comprehensive energy using this method improves the energy dispatching and balanced allocation capability, and the time‐domain dynamic allocation capability is good. Considering the terminal load demand and the electricity price demand formulated by the distribution network investment operators, the seasonal load response and comprehensive dispatching capability are improved.

Features of interaction bored pile with the soil base in the presence of structurally unstable soils

During the construction of pile foundations, the pile testing process is necessary and mandatory. Therefore, there is a need for a correct assessment of the interaction elements of the "foundation-pile" system with the provision of a reliable and effective design solution.
 If the soil parameters provided in the reports on engineering and geological searching are used without their prior refinement, this leads to a significant discrepancy in the results of numerical modeling of the interaction of piles with the base and data from field tests. In this regard, there is a need to identify the design parameters of the adopted soil model in order to match the modeling results with the results of experimental studies in a wide range of loads.
 The Hardening Soil Model was chosen to describe the interaction behavior of the elements of base-pile system in this study. The nature of the influence of the three modules identified in the above model was investigated: modulus deformation at 50% of the base strength ( ); compressive strain module ( ); strain module at unloading ( ). The influence of the effect of dilatancy of the sand base was also analyzed.
 At the initial stage of loading, the values of the and modules make a significant contribution to its performance. With further increased loads in the soil, significant plastic shear deformations occur, and accordingly, the parameters of soil strength (c, φ) are the leading parameters. Due to the fact that the upper part of the bored pile is located in structurally unstable soils (bulk soil and plastic sandy loam), and the lower part of the pile is located within sandy soil for a significant part of its length, it is also important to take into account the effect of soil dilatancy (ψ).
 It was found that an increase in the unloading module ( ) reduces not only the settlement along the unloading curve, but also along the load curve.
 The results of comparison of full-scale testing of a bored pile and its numerical modeling of interaction with structurally unstable and sandy soils are presented, and the design parameters of the soil environment model are identified in order to match the modeling results with experimental data at the corresponding specified loads.
 The obtained convergence is within 5% in a wide range along the curve of the load on the bored pile.

Joint operation of mobile battery, power system, and transportation system for improving the renewable energy penetration rate

Future energy system will feature in a high-share of renewable energies (REs), which poses huge challenges to obtain full utilization of renewable power generation. To solve the problem, this paper presents a joint-operation two-stage mixed integer linear programming model to coordinate the power system and train transportation system by optimizing the logistics of mobile batteries and real-time charge/discharge in cities. The full/empty batteries are transported through the train transportation system between the load side and the renewable energy station, which improves renewable energy penetration, economics, and mobilities. The first-stage model deals with the preliminary logistic optimization of batteries including routes, time and capacities of transportation, and the second-stage model optimizes real-time schedule of charge/discharge of batteries. The aim of the proposed model is to minimize the transportation cost, maximize the utilization rate of renewable energy in an energy system and smooth the daily load curve. The proposed model considers technical constraints such as railway transportation capacity, load demand satisfaction and renewable energy consumption in the power system. The optimal logistics plan and real-time charging and discharging plan can be obtained for both full and empty battery transportation. The validity of the method is verified with real data from Northeast China and Northern China, including railway routes, renewable energy output, and load profiles. The results show that the renewable energy penetration rate increases from 84.4% to 95.3% in Northeast China and from 42.7% to 78.2% in Northern China under the 2050 scenario with the proposed method. The peak-to-valley difference in the daily load curve decreases by 84% and 100% in Northeast China and Northern China, respectively. Meanwhile, the case study shows that the costs of battery transportation decrease from 0.398 CNY/kWh and 0.377 CNY/kWh to 0.252 CNY/kWh and 0.254 CNY/kWh when energy density of battery increases from 0.170 kWh/kg to 0.250 kWh/kg. This indicates that mobile energy storage has great economics. Moreover, renewable energy penetration rate is increased and peak-to-valley difference of daily load curve is decreased with no additional transmission lines.

Study on multi-type flexible load control method of active distribution network based on dynamic time-sharing electricity price

Accurate load control is the basis of safe operation and optimal dispatching in active distribution network, and the demand response system of flexible electricity price mechanism and incentive mechanism is the premise of load control. Aiming at the complexity increase of load control caused by the integration of conventional loads, electric vehicles, and micro-grid multi-type user loads in the existing active distribution network, this study comprehensively takes the power consumption willingness of multiple typesof users in active distribution network into account for the first time. This study dominated by the user willingness selects a typical active distribution network load-related data onto a certain area to conduct a calculation example analysis. Firstly, a multi-type user load demand response model of active distribution network is constructed. Then, in order to achieve flexible control of active distribution network loads, a dynamic time-of-use electricity price game model considering the target function and the willingness of multiple usersis proposed, in order to achieve the maximum of user satisfaction and interests of power supply enterprises. Furthermore, the example results are compared with the intrinsic electricity price.Finally, the simulation results show that the time-of-use price established by the multi-type user load game is effective inguiding users to adjust their power consumption habits, making the load curve shift, controlling the electricity load within the maximum power supply limit, and thus alleviating the pressure of power grid expansion.

The effect of varying stress intervals on fatigue of rock salt

The surrounding rock of underground energy storage salt caverns is subjected to periodic loading with stress intervals during actual operation. To study the fatigue behavior of rock salt with such stress intervals, one conventional fatigue test and three fatigue tests with multi-step varying stress intervals (MVSIs) were conducted. The results show that the circumferential deformation first decreases and eventually becomes similar to the axial deformation in fatigue tests with MVSIs, as the interval duration increases. Both the dissipated energy and the spacing between the loading and unloading curves of a single cycle first decreased, then remained constant, and finally increased sharply as the stress interval increased. When the stress intervals corresponded to the elastic phase of loading (between 20% and 40% of the uniaxial compressive strength), the rock salt was subjected to the minimum damage. Based on the Bauschinger effect and dislocation internal friction theory, the micromechanism of rock salt fatigue was further explained.

Low-carbon optimal scheduling for multi-source power systems based on source-load matching under active demand response

To reduce the source-load uncertainty and carbon emission levels of the power system, this study proposes a novel low-carbon economic stochastic optimization scheduling model. Firstly, to partially compensate for the instability of wind power (WP) and photovoltaic power (PV) generation, enhance energy efficiency, and reduce system carbon emissions, the introduction of concentrating solar power (CSP) as one of the power sources on the generation side. Secondly, to optimize load characteristics, a peak–valley time period division method based on fuzzy theory and an active demand response model for electric load using the Logistic fuzzy function are introduced on the load side. Thirdly, taking into account the role of the carbon trading market, a ladder-type carbon trading mechanism (LCTM) is introduced to control carbon emissions and reduce overall economic costs. Finally, considering WP-PV output fluctuations, the degree of matching between power output and load, WP-PV utilization, system economic efficiency, and carbon trading factors, with the objective of maximizing the tracking of the load curve and minimizing comprehensive system economic costs, a multi-objective stochastic optimized scheduling model for power systems is established. A multi-objective Runge–Kutta algorithm based on a population-based parallel search mechanism (PSMORUN) is proposed to solve the active demand response model and the low-carbon stochastic optimization scheduling model. Additionally, constraint repair techniques are employed to handle the complex constraints of the models. To verify the effectiveness of the proposed model, a 10-generator power system, including a WP farm, a PV plant, and a CSP plant, is used as a test case for simulation experiments and compared with other multi-objective scheduling models. The experimental results show that the proposed stochastic optimal scheduling model has higher safety, better economy, and lower carbon emissions.

Deep neural network aided cohesive zone parameter identifications through die shear test in electronic packaging

AbstractThe die shear test is a feasible and conventional method to characterize the shear strength of die‐attaching layer materials in electronic packaging. A new method for determining cohesive zone model (CZM) parameters using deep neural networks (DNN) and die shear tests is proposed, different from classical fracture framework or lap shear test‐based methods. With the sintered nano‐silver die shear test, the results show that the bilinear CZM inversion results agree well with the experimental results. It is found that the DNN model has high accuracy in predicting and identifying the maximum shear traction strength τmax, separation displacement of the interface δf, and the interface stiffness k1 of CZM parameters for sintered nano‐silver adhesive layer through die shear test load versus displacement curves. The presented DNN‐aided inverse identifying method through the die shear test in this paper could provide an alternative and convenient method for extracting CZM parameters of various kinds of adhesive materials in electronic packaging.

Experimental investigation on low-velocity impact behavior of glass, Kevlar, and hybrid composites with an elastomeric polyurethane matrix

Low-velocity impacts represent a critical dynamic condition for engineering structures. Combining two reinforcing fibers in a single matrix, i.e., hybridization, is considered a feasible way to improve composite performance. In this context, this paper presents an experimental work on composites with Kevlar and glass fabrics and a novel thermoset polyurethane matrix. The coupons are manufactured by vacuum infusion technique and low-velocity impact tests are carried out. First, the impact behavior of Kevlar and glass laminates of different thicknesses is assessed, and then impact tests are performed on different configurations of hybrid laminates, both symmetric and non-symmetric. For the non-symmetric specimens, impact tests were conducted on both sides of the stack. Load vs displacement curves are reported along with absorbed energy. To investigate the damage mechanism, the front, back, and cross-section views of the specimens are analyzed, and features related to the stacking sequences are discussed. Thermographic analyses are carried out on the impacted specimens to further analyze damage. The failure mechanisms are different from traditional epoxy composites and a hybridization effect is reported. The results evidence that the hybrid coupons are viable for structural applications, being capable of absorbing high-impact energies, in particular, non-symmetric hybrid laminates outperformed the Kevlar, glass, and symmetric ones, absorbing roughly 15% less energy for the highest energy impact.