Residual Load Research Articles

Hybrid Salp Swarm and Improved Whale Optimization Algorithm‐based clustering scheme for improving network lifespan in wireless sensor networks

SummaryWireless sensor networks (WSNs) represent the collection of restricted energy sensor nodes that are deployed in an area of target for gathering potential environment data for decision‐making with respect to their objective of application. However, the implementation of energy‐effective data gathering strategies in large‐scale WSNs is the most challenging due to the limited energy resources. Clustering‐based data gathering strategies are identified to be quite effective for energy saving that directly attributes to extended network lifetime. Moreover, optimal path amid the cluster head (CH) and sink node needs to be selected for sustaining energy efficiency and improving network lifespan. In this article, Hybrid Salp Swarm and Improved Whale Optimization Algorithm (HSSIWOA)‐based clustering scheme is proposed for improving the network lifetime and routing optimization with maximized energy efficacy. It integrated the exploration capability of Salp Swarm Optimization Algorithm (SSOA) with exploitation benefits of Improved Whale Optimization Algorithm (IWOA) for balancing the trade‐off between the rate of exploration and exploitation during CH selection process. It utilized the parameters of residual energy, load balance, intra‐cluster distance, inter‐cluster distance, and node centrality into account during the process of fitness evaluation. It performed well by constructing an optimized number of clusters, such that energy stability and network lifetime are maintained in the network. The experimental results of the proposed HSSIWOA scheme confirmed extended network lifetime of 21.64%, minimized energy utilization of 23.42%, and maximized throughput of 18.56%, better than the baseline approaches.

Quantitative assessment of the extent of damage to timber structures during the full course of a real fire using the energy equivalence method

In this study, an innovative method, the Energy Equivalence Method (EEM), is proposed in the context of the Performance-Based Fire Engineering (PBFE) framework for quantitatively assessing the degree of damage of timber structures during the full process of a real fire. To verify the validity of the method, glued laminated timber (GLT) specimens and GLT columns were selected as the subjects of fire action, and a series of equivalent fire experiments were conducted by using a parametric fire model (referred to as the DNI fire model), which is currently used in Germany, to simulate real fire scenarios. By comparing the equivalence of charring depth (CD), pyrolysis zone temperature, and residual load-carrying capacity of the test specimens after the action of the DNI fire and its equivalent standard fire, the validity of the EEM in quantifying the degree of damage to timber members after the DNI fire was fully verified. Subsequently, based on the fire experimental data, accurate thermal and structural models were developed, and these models were utilized to further validate the effectiveness of the EEM in quantifying the extent of damage to timber members under the action of a DNI fire over an arbitrary time period. The results of the study show that the proposed EEM not only can be used to assess the extent of structural damage during fire action and the residual load carrying capacity of the structure after fire action, but also promotes the transition from standard fire safety design to the PBFE design.

Maximizing self-sufficiency and minimizing grid interaction: Combining electric and molecular energy storage for decentralized balancing of variable renewable energy in local energy systems

The increase of renewable electricity from variable sources, such as solar PV and wind turbines, leads to increasing need for energy storage to maintain balance between demand and supply, and decrease peak load on electricity grids. Energy storage options to achieve this include electric energy storage such as batteries, and molecular energy storage such as hydrogen. In this research, we use a model to simulate the behavior of a local residential grid in the Netherlands supplied exclusively by decentralized solar PV and wind energy. Our model includes combinations of batteries and hydrogen as energy storage options to investigate synergies between them. The simulation results indicate that combining the characteristics of battery and hydrogen energy storage in a single grid leads to a more resilient and flexible system compared to one in which only one of the two technologies is deployed. In our simulations of combined storage options, local demand can be met with less installed capacity, and less energy exchange with external grid takes place. However, we also conclude that diversity of storage options alone is insufficient to reduce the highest peak load on external grids, and additional measures are required to ensure net residual load remains within specific bandwidths.

Seismic performance of flexural reinforced concrete columns subjected to varying axial forces

This paper examines the influence of variable axial force on the seismic performance of flexural domain reinforced concrete (RC) columns through experimental testing of five full-scale specimens. The test results demonstrate that fluctuating axial force, when combined with simulated cyclic seismic loading, significantly impacts the flexural behavior of RC columns. The behavior of RC columns under fluctuating axial loads was markedly different from that of columns under constant axial loads. A notable observation was that the failure mode of the columns transitioned from ductile flexural failure to flexure-shear failure when comparing columns subjected to constant axial loads to those subjected to fluctuating axial loads that alternated between compression and tension. This study further demonstrated that the lateral load capacity of the columns, along with their deterioration, was significantly influenced by both the fluctuating pattern and intensity of the axial forces, as well as the displacement ductility. An empirical equation was proposed to estimate the residual lateral load capacity of flexural domain RC columns under varying axial forces, providing a practical tool for designers to assess the behavior of columns under different loading conditions. To corroborate the conclusions drawn from the experimental investigation and gain further insights into the influence of fluctuating axial force on the seismic behavior of flexural domain columns, this study additionally proposes a finite element (FE) model. According to the experimental and numerical results, an empirical equation to estimate the ultimate drift capacity of RC columns subjected to varying axial force is also proposed.

Residual loads from tilapia farming on the sediment of a Brazilian reservoir

This study investigated the sediment geochemistry of a fish farming area in net cage tanks in the Rosário reservoir, Brazil. Three areas were investigated: reference (RA), fish farming (FFA), and dispersion (DA). The results were analyzed through correlation, similarity, principal component analysis, comparison with legislation, sediment quality guidelines, and sediment pollution indices. The mean concentrations for RA, FFA, and DA areas were respectively: Cu (mg.kg−1) 37.74, 62.23, and 71.83; Mn (mg.kg−1) 22.55, 66.48, and 55.90; Zn (mg.kg−1) 9.13, 114.83, and 94.27; Fe (%) 0.28, 0.40, and 0.43; OM (%) 15.84, 21.95, and 18.45; TOC (%) 1.86, 3.69, and 6.05; TN (mg.kg−1) 2365.00, 5015.00, and 3447.51; TP (mg.kg−1) 780.00, 6896.00, and 2585.50; ORP (mV) −95.50, −135.20, and −127.10; pH 6.60, 6.58, and 6.05; <63 μm 90.59, 78.68, and 87.30. Statistically, the influence of fish farming on sediment, organic matter, and pollutant sedimentation was demonstrated. Cu and Zn concentrations were below sediment quality guidelines. Regarding legal limits (resolution 454/2012/CONAMA), nutrients in the FFA area exceeded by 60% (TN) and 100% (TP), while in DA and RA areas they were 100% lower. TOC was 100% lower in all areas. Organic matter exceeded the limit by 100% in all areas. Pollution indices resulted in: low contamination factor 78%; unpolluted for 87% of pollution load and 83% of combined pollution; moderately polluted for 75% of the Nemerow index. The greatest impacts and influence of farming on pollutant sedimentation were more concentrated in the fish farming area. In terms of legal aspects and pollution indices, fish farming produced low levels of trace metal pollution and nutrient concentrations exceeded legal limits.

Study on the influencing factors of impact resistance of shear thickening fluids filled foam

PurposeThe present study assesses the impact resistance of the shear thickening fluids-filled (STFs-filled) foam through drop-hammer impact tests.Design/methodology/approachThe maximum residual impact load and specific impact energy absorption rate of STF-filled foam are studied with varying thickness (4–14 mm), densities (0.35–0.6 g/cm3) and hardness (40–50 Rockwell Hardness C Scale (HRC)) under different ambient temperatures (−20−20 °C) and impact energies (25–75 J).FindingsThe following conclusions are obtained from this study: (1) the higher the impact energy, the greater the maximum residual impact force and energy absorption efficiency of the material; (2) the impact resistance of STF-filled foam can be improved with the decrease of ambient temperature, achieving the highest energy absorption rate at −10?. (3) STF-filled foam substrate has the highest impact resistance, the lowest maximum residual impact force and the highest energy absorption coefficient when the density is 0.35 g/cm3, the hardness is 45HC and the thickness is 10 mm.Originality/valueThis is the first paper to analyze the impact of both environmental factors and material properties on the impact resistance of STF-filled foam. The results show that the decrease in temperature and the increase in hardness can enhance the impact resistance of STF-filled foam.

Flexibility Potential in the Austrian Building Sector

What would happen if 15% of the Austrian building stock in 2030 – both refurbished and newly-built – would use flexible heating/cooling systems to offer their flexibility on a market? How much annual residual loads from volatile renewable energy sources (RES) could be absorbed? Our simple agent-market model says: ~5% of RES surpluses and around 2% of RES residual loads. The cost of this operation is additional energy demand of about 30%, indicating an efficiency of approx. 70% in using these volatile supply peaks in flexible building operation. In this model, buildings are agents offering additional electricity consumption from pre-emptive HVAC operation, effectively using the building mass as storage, their energy demand is modelled in a simple thermal RC model. The grid flexibility demand is derived from future residual load scenarios and the offered flexibility depends both on signal parameters, mainly signal frequency and duration, and on key building parameters indoor temperature comfort bounds, building mass and thermal envelope quality.

Geospatial optimisation of wind and solar energy generation: A framework for optimised resource allocation

Wind and solar power generation profiles exhibit a high degree of power output variability and uncertainty compared to conventional fossil fuel generation plants. However, it is generally accepted that this variability and uncertainty can be mitigated by geographic siting and dispersion of the renewable energy plants, particularly with the view to leverage aggregation effects. In this context, this paper proposes a framework for the geospatial optimisation of wind and solar PV generation for scenarios with a high penetration of wind and solar renewable energy. The proposed optimisation framework represents a probabilistic risk-based approach that seeks to minimise the number of events where high residual load values require ancillary service interventions to maintain power balance. In this approach, the wind and solar resources are categorised in terms of the statistical properties of the associated spatiotemporal wind and solar power profiles for a given set of daily and seasonal Time of Use periods. It is thereby recognised that the resource characteristics and grid impact of wind and solar generation profiles can be interpreted with reference to the daily and seasonal cycles exhibited by the demand profiles, wherein some Time of Use periods are more important than others. The proposed framework is implemented for a number of baseline case studies and optimisation case studies, using wind and solar resource data sets covering South Africa. Overall, it is concluded that this approach can leverage geospatial site optimisation to substantially reduce the risks associated with high residual load events. Furthermore, the proposed framework is highly flexible in that the formulation of the minimum and maximum allocation constraints allows application for real-world scenarios whereby stringent capacity allocation constraints can be applied.

Variable renewable energy modeling system to study challenges that impact electrical load at different penetration levels: A case study on Kuwait's load profile

The transitioning from conventional power systems to variable renewable energy (VRE) could impose significant challenges on transmission, short-term balancing requirements, and more cycling to ramp conventional plants. Kuwait's government has set a target of 15% of electricity generation from renewable resources by 2030 and more in the following years. This ambitious target requires close collaboration between researchers and decision-makers to overcome the upcoming challenges. The current study comes in the context of this objective to support decision-makers technically during planning and deploying VRE plats in various parts of the country. An in-house simulation modeling system for solar photovoltaic (PV) and wind power based on high-quality weather data has been developed. The system can model centralized or decentralized VRE scenarios. Several load characteristics have been used to examine the output of the scenario, such as the residual load, impact on the peak, and baseload due to changes in VRE penetration level. Other parameters, including capacity credit, full load hours, ramping power magnitude and rate, and overproduction of resources, are also outputs of the system. The output results of the modeling system have been validated against two years of operational solar PV and wind Shagaya power plants data. The results show combining solar PV with wind could dramatically increase the capacity credit, reduce overproduction, and reduce ramping power. The authors will continue evolve and improve this in-house modeling system to support research in this field and for the upcoming future RE projects instead of relying on commercial software.

Experimental study and theoretical analysis of fire resistance properties of prestressed glued laminated timber beams

The addition of prestressing not only improves the force resistance of glulam beams, but also provides a potential solution to improve their fire resistance. An in-depth study of the fire behavior of prestressed glulam beams (PGBs) under fire and the force behavior after fire is essential for their fire resistance design and evaluation. In this paper, fire tests and post-fire four-point bending experiments were conducted on the PGBs aiming to investigate the thermal response of the PGBs as well as their force resistance after fire. The results showed that fire significantly affected the mechanical properties of the PGBs, not only reducing the prestressing force during the fire, but also decreasing the residual load carrying capacity after the fire. After 60 min of standard fire exposure, the prestress and load capacity of the PGBs decreased by 10 % and 33.33 %, respectively. Increasing either prestress or reinforcement ratio can effectively improve the resistance performance of the PGBs after fire. In the same fire action time, if the prestress was increased by 59.46 % or the reinforcement ratio was increased by 0.53 %, the residual ultimate load capacity of the PGBs was increased by 17.14 % and 22.19 %, respectively. The study also indicates that fully utilizing the synergistic effect of prestressing and reinforcement ratio enhancement can significantly improve the overall performance of the PGBs. In addition, a theoretical calculation model is proposed to accurately predict the residual flexural capacity of the PGBs after fire, which provides a theoretical support for the fire-resistant design of the PGBs before fire and the assessment of residual load capacity after fire.

The potential of decentral heat pumps as flexibility option for decarbonised energy systems

Decarbonising the energy system requires high shares of variable renewable generation and sector coupling like power to heat. In addition to heat supply, heat pumps can be used in future energy systems to provide flexibility to the electricity system by using the thermal storage potential of the building stock and buffer tanks to shift electricity demand to hours of high renewable electricity production. Bridging the gap between two methodological approaches, we coupled a detailed building technology operation model and the open-source energy system model Balmorel to evaluate the flexibility potential that decentral heat pumps can provide to the electricity system. Austria in the year 2030 serves as an example of a 100% renewable-based electricity system (at an annual national balance). Results show that system benefits from heat pump flexibility are relatively limited in extent and concentrated on short-term flexibility. Flexible heat pumps reduce system cost, CO2 emissions, and photovoltaics and wind curtailment in all scenarios. The amount of electricity shifted in the assessed standard flexibility scenario is 194 GWhel and accounts for about 20% of the available flexible heat pump electricity demand. A comparison of different modelling approaches and a deterministic sensitivity analysis of key input parameters complement the modelling. The most important input parameters impacting heat pump flexibility are the flexible capacity (determined by installed capacity and share of control), shifting time limitations, and cost assumptions for the flexibility provided. Heat pump flexibility contributes more to increasing low residual loads (up to 22% in the assessed scenarios) than decreasing residual load peaks. Wind power integration benefits more from heat pump flexibility than photovoltaics because of the temporal correlation between heat demand and wind generation.

Finite element model analysis of long-term performance of composite anchorage based on double-material parameters

Carbon fibre-reinforced polymer (CFRP) tendons demonstrate the advantages of light weight, high strength, and superior corrosion resistance and have broad application prospects for long-span cable structures. However, given the low transverse shear strength of CFRP tendons, how to achieve long-term and reliable anchorage for CFRP tendons is a critical issue. The long-term performance (LTP) of a novel composite anchorage for CFRP tendon was assessed in this study. Then, a finite element model (FEM) with double-material creep parameters was established to reliably model the LTP experiment according to the creep parameters of the bonding medium and CFRP tendon. Finally, the effects of the free section tendon length, pre-tightening force, over-tensioning force, and elastic modulus of the bonding medium were analysed using the established FEM with double-material creep parameters. Results revealed no visible damage to the CFRP tendon and anchorage after the LTP experiment. The maximum tendon slippage was 0.054 mm, and the residual load ratio was 0.826. These phenomena indicate that the novel composite anchorage has excellent LTP. The FEM modelling results based on double-material creep parameters were in good agreement with the experiment results. The residual load ratio calculated by the FEM was 1% lower than the experimental value. Through the parameter analysis, the residual load ratio of the specimen was effectively improved under longer free section tendon condition, but tendon slippage increased to a certain extent. In addition, the LTP of the composite anchorage can be effectively improved by appropriately decreasing pre-tightening force and over-tensioning force. When the over-tensioning force was 1.4 times the test load, the tendon slippage was reduced by 34.2%, and the residual load ratio increased by 4.8%. The greater elastic modulus of the bonding medium in the range of 2.1 GPa–3.1 GPa, the worse the LTP of the composite anchorage.

Evaluation of future renewable energy drought risk in China based on CMIP6

With the growing share of the climate-sensitive renewable energy market supply in China, estimating future energy drought risk (ED) is essential. In this paper, based on CMIP6, energy demand and power generation are estimated from 2023 to 2100 under SSP2-4.5 and SSP5-8.5 climate scenarios, and ED is defined from high demand (HD), low wind-solar generation (LWS), and residual load (RL). The results show that the ED exacerbation is relatively high under the SSP5-8.5. Between 2023 and 2100, the duration and severity of HD and RL notably increase, while LWS changes are relatively weak. We find that HD and RL exhibit high summer risks in the south and high winter risk in the north. The return periods vary significantly and extends over time in most regions. Moreover, there are few ED when the installed power generation capacity (IPGC) is increased. When the IPGC increases by 2%–5%, the LWS will decrease at least 20%–72%. With a 10% increase, the LWS will be mitigated by at least 80%, whereas the mitigation for RL is limited, approximately 3–17% at different rates. This work performs the first evaluation of future ED and provides the useful references for risk mitigation in China based on CMIP6.

Low velocity impact and compression after impact of thin and thick laminated carbon fiber composite panels

This study explores the impact behavior of thin and thick composite panels, yielding insights into their behavior under increasing impact energies. Thin composite specimens demonstrated limited surface damage tolerance, while thicker panels remained visually intact but suffered internal damage, adversely affecting their compressive load capacity. The study shows a robust correlation between impact energy and key measurements, including dent depth, bottom surface matrix splitting, and internal delaminations. Moreover, the research identified a consistent pattern in damage initiation, showing that the onset of matrix splitting and delamination remained relatively constant regardless of increasing impact energy, emphasizing the predictability of damage initiation. Compression after impact study showed distinctive responses between thin and thick composites. Thin composites exhibited global buckling before final failure, with a gradual reduction in peak load-carrying capability as damage escalated. In contrast, thick composites suffered substantial damage and delamination at higher impact energies, leading to significant losses, up to 60%, in residual compressive load capacity. The study introduces a simplified quasi-static model to capture delamination effects on panel responses to low-velocity impacts. This study contributes significantly to understanding composite materials’ impact behavior, providing essential knowledge for practical applications and future research endeavors.

Experimental Study on the Flexural Properties of Steel-Fibre-Reinforced Concrete Specimens with Different Heights

Flexural strength is an important mechanical property of steel-fibre-reinforced concrete. By designing three-point bending tests of concrete with five specimen heights, three steel fibre types, and two steel fibre mixing methods, the effects of the specimen height, steel fibre mixing method, and steel fibre type on the peak load, effect of size, section characteristics, strain characteristics, and characteristics of the load–displacement curve of concrete specimens were studied. The results show that the peak load of the control group is basically linear with the height of the specimen. After adding three kinds of steel fibres, the peak load of the specimen is greater than that of the control group in the same case. The peak load of the specimen increases by adding three kinds of steel fibres, and the increase is closely related to the height of the specimen. The residual stage of the load–displacement curve of the milling steel fibre and the end hook steel fibre are relatively flat, while the residual stage of the load–displacement curve of the shear steel fibre is relatively large, and the residual load is also greater than the residual load of the shear steel fibre. The specimens in the control group show brittle failure characteristics. As the height of the specimens increases, the failed section of the specimens is smoother. The development of cracks in the steel fibre specimens is more tortuous than that of the control group, showing ductile failure characteristics. Some tensile failure zones are still present where the fibres are densely distributed, and the failure characteristics of the specimens are further explained and proven by the strain characteristics.

Consideration of Multi-Objective Stochastic Optimization in Inter-Annual Optimization Scheduling of Cascade Hydropower Stations

There exists a temporal and spatial coupling effect among the hydropower units in cascade hydropower stations which constitutes a complex planning problem. Researching the multi-objective optimization scheduling of cascade hydropower stations under various spatiotemporal inflow impacts is of significant importance. Previous studies have typically only focused on the economic dispatch issues of cascade hydropower stations, with little attention given to their coupling mechanism models and the uncertainty impacts of inflows. Firstly, this paper establishes a coupled optimization scheduling model for cascade hydropower stations and elaborates on the operational mechanism of cascade hydropower stations. Secondly, according to the needs of actual scenarios, two types of optimization objectives are set, considering both the supply adequacy and peak-shaving capacity as indicators, with the total residual load and the peak-valley difference of the residual load as comprehensive optimization objectives. Subsequently, considering the uncertainty impact of the inflow side, a stochastic optimization model for inflow is established based on a normal distribution probability. Finally, case study analyses demonstrate that the proposed model not only effectively achieves supply stability but also reduces the peak-valley difference in load, and can achieve optimized scheduling under the uncertain environment of inflow.

Fatigue performance of ECC link slab incorporated full RC girder joint-free bridges

The use of link slab (LS) made of Engineered Cementitious Composite (ECC) in the construction of joint-free bridge deck can meet structural performance requirements and enhance durability to minimize life cycle costs. Studies documented in the literature to date have been limited to composite steel-concrete I-deck girder bridges despite their commonly used reinforced concrete (RC) girder counterparts in construction. This paper deals with two span full RC deck girder joint-free bridges with ECC link slab (ECC-LS) constructed and tested under static and fatigue loading up to 1,000,000 cycles at 4 Hz subjected to mean stress level of 40% of girder ultimate load, followed by post-fatigue static loading to failure. Residual load, deflection, moment, rotation, stiffness, and energy absorbing capacity of fatigued bridge specimens are compared with its virgin (non-fatigued) counterparts to assess structural performance. Experimental moment capacities are compared with those obtained from existing analytical equations. The comparative performance of joint-fee bridge with RC deck girder is compared with its composite steel-concrete I-girder counterpart to assess its feasibility of construction.

A convergence‐enhanced Timoshenko beam element for the stochastic nonlinear analysis of reinforced concrete components

AbstractAn effective and precise physical model is generally required for the performance assessment of reinforced concrete (RC) components. In this study, a convergence‐enhanced Timoshenko beam element considering finite deformation is proposed for the stochastic nonlinear analysis of RC components. The unified framework of the rank 2 correction matrix is obtained by approximating the iterative matrix through the linearly independent basis vectors, and two types of Broyden–Fletcher–Goldfarb–Shanno (BFGS) operators are constructed. Then, a consistent solution scheme with superior numerical stability and efficiency is proposed based on the second kind of BFGS operator and improved quasi‐Newton method. Accurate discretization of the displacement fields and description of nonlinear sectional behavior are achieved by the high‐order Lagrangian interpolation functions, concrete damage‐plasticity model and J2 plasticity model. In an updated Lagrangian formulation, these shape functions and constitutive relationships are used to develop a complete secant stiffness with higher‐order terms in the strain tensor and residual force vector. To validate the proposed Timoshenko beam element, numerical applications involving material nonlinearity and geometrical nonlinearity are conducted. The numerical stability and efficiency of the solution scheme, the shear‐locking free technique, and the oscillation of axial force are thoroughly examined and discussed by solution of RC columns, cantilever beam and progressive collapse of planar RC frame. Finally, the parametric study considering the geometric and material randomness indicates that the RC column designed for flexural failure mode suffered considerable degradation of loading capacity and a larger scatter of residual load.

Impact of a High Penetration of Electric Vehicles and Photovoltaic Inverters on Power Quality in an Urban Residential Grid Part I – Unbalance

This paper presents a measurement-based assessment of the impact of a high penetration of plug-in electric vehicles with on-board charger (EVC) and photovoltaic inverters (PVI) on Power Quality in a public low voltage (LV) network. The paper consists of two parts. This first part is focused on the impact on unbalance, the second part is related to harmonics. The results are based on extensive measurements in an urban residential grid with almost 100 households (HH), 43 PVIs and 36 EVCs. The impact of PVI and EVC on unbalance at different levels of aggregation is described in detail. At first the individual impact of a single PVI and EVC is discussed for different operating conditions. In particular, a sunny day, a cloudy day and hours during the night are used for PVI, while periods of charging and periods of no charging are considered for EVC. Next sections analyse the interaction between PVI, EVC and residual load at household level as well as the overall impact of PVIs and EVCs in the low voltage grid. The analysis considers current unbalance and voltage unbalance.

The Residual Load Duration Curve (rLDC) to model an energy system

This paper develops a framework to represent the action of different generation and balancing technologies based on the statistics of the demand and generation using the concept of the Load Duration Curve (LDC). The aim is to capture the statistics in terms of energy and power provision from a generation type given by its inherent resource, technical and economic constraints. This paper provides a brief overview of the fundamental types of generation and balancing, and how their action modifies the load duration curve to eventually arrive at a balanced system. Based on empirical data from the UK National Grid, the statistical properties of renewable energy sources and of the energy and power capacities of energy storage technologies, different basic functional relationships between the residual Load Duration Curves (rLDC) will be derived for these technologies.