Search Results (513)

This study investigates the residual web crippling behavior of pultruded glass fiber-reinforced polymer (P-GFRP) hollow sections after exposure to elevated temperatures. The primary objective is to evaluate the combined influence of temperature and loading configuration on web crippling capacity, failure mechanisms, and structural performance, and to develop practical prediction models for engineering applications. A total of twenty pultruded GFRP hollow section specimens were exposed to temperatures of 24 °C, 200 °C, 250 °C, 300 °C, and 350 °C and tested under four loading configurations: End Ground (EG), Interior Ground (IG), End Two Flange (ETF), and Interior Two Flange (ITF). In addition to web crippling tests, tensile, SEM-EDS, TGA-DSC, DMA, and FT-IR analyses were conducted to investigate the mechanical, thermal, and microstructural degradation mechanisms. The results showed that elevated temperatures significantly reduced the web crippling capacity, with strength losses reaching up to 80% at 350 °C due to matrix degradation, fiber–matrix debonding, and loss of structural integrity. Among the investigated loading configurations, IG exhibited the highest load-carrying performance, whereas ETF experienced the greatest capacity reduction. A temperature-dependent reduction factor and unified empirical prediction equations were developed and demonstrated good agreement with the experimental results, with experimental-to-predicted ratios ranging from 0.97 to 1.15. The findings provide valuable insight into the post-fire behavior of pultruded GFRP hollow sections and offer practical guidance for the design, assessment, and fire safety evaluation of GFRP structural members exposed to elevated-temperature environments. Full article

Spacecraft are evolving toward larger scales and higher performance, enabling widespread application of sophisticated space structures such as space antennas and flexible solar arrays. Such structures may experience thermally induced vibration (TIV) due to the influence of sudden solar radiation heat flows when it enters and leaves the Earth’s shadow in orbit. This paper focuses on a space thin-walled tube structure as the test specimen, and conducts ground-based TIV experiments in a vacuum environment, comparing the results with numerical simulations. The numerical simulation results for various key parameters show good agreement with the experimental data. The relative errors of average temperature, quasi-static displacement, and vibration frequency are approximately 5%, while the relative error of vibration amplitude is around 10%. Leveraging the validated numerical model, this study further investigates the influence of gravity on the TIV of large space structures. The results indicate that the TIV response amplitude under orbital conditions is significantly larger than that obtained from ground-based experiments. Full article

The synergistic utilization of post-mining spaces and geothermal energy through underground seasonal thermal energy storage (USTES) provides a promising pathway for sustainable heating and the low-carbon redevelopment of mining regions. To advance the thermal management and reveal the thermo-hydraulic evolution patterns within these repurposed environments, this study proposes an integrated approach that utilizes post-mining roadways as heat storage reservoirs, within the scope of a single idealized case study. A comprehensive USTES heating system model was established to systematically evaluate operational characteristics and environmental impacts under diverse conditions assuming homogeneous rock properties and idealized thermal boundaries. Results demonstrate that the surrounding ground temperature and the low thermal conductivity of the rock mass contribute to limiting heat dissipation and maintaining stable seasonal storage performance. For a roadway with a 20,000 m³ water storage capacity and an optimal 3900 m² solar collector area, the system successfully satisfies the thermal demand of 30,000 m² of building area. The configuration achieves 1239 MWh of cumulative heat storage over a 245-day cycle, maintaining a direct heating-to-heat-pump-upgraded heating ratio of 1.02. Furthermore, the implementation of variable-frequency thermal management strategies demonstrates remarkable economic and environmental superiority, yielding a 35.8% cost reduction compared to coal-fired heating, an overall energy saving rate of 77.5% relative to electric heating systems and a 13.5% decrease in CO₂ emissions relative to gas-fired systems. This research provides fundamental design parameters for the synergistic exploitation of mineral and geothermal resources, advancing the development of green heating and the sustainable utilization of post-mining spaces. Full article

Open-cathode Proton Exchange Membrane Fuel Cells (PEMFCs) are a promising technology for increasing the endurance of small Unmanned Aerial Vehicles (UAVs), ground robots, e-bikes, and light electric vehicles. However, their performance under realistic operating conditions is strongly influenced by rapid variations in load, temperature, and ambient pressure, which are often neglected in design-oriented or quasi-steady-state analyses. This study experimentally investigates a 1 kW open-cathode PEMFC system, including its balance of plant and a passive supercapacitor buffer, under a representative UAV flight power profile. Steady-state and dynamic tests were conducted to assess polarization characteristics, thermal behavior, parasitic power consumption, and hydrogen utilization. Results revealed significant thermal inertia and hysteresis effects during load transients, causing voltage deviations from steady-state performance and stabilization times exceeding 90 s. The supercapacitor effectively reduced stack current ramp rates, although some high-frequency oscillations remained. Under flight-representative conditions, the system achieved stable operation with average voltaic efficiency ranging from 55.3% to 60.7% and net efficiency ranging from 50.2% to 54.2%. Auxiliary components had a measurable impact on overall performance: cooling fans accounted for 2–6% of stack power during steady operation and approximately 2.5% of total mission energy, while hydrogen purge losses can significantly reduce vehicle endurance. The findings demonstrate the importance of energy-based performance assessment, including auxiliary loads and purge losses, to obtain realistic estimates of efficiency and endurance in dynamic PEMFC-powered applications. Full article

The present study investigates the synergistic effects of incorporating natural alkali-treated Alfa fibers, lime, and ground granulated blast-furnace slag (GGBS) on the physical and mechanical performance of compressed earth blocks. Laboratory tests were conducted using locally sourced earth material, reinforced with two lengths of alkali-treated Alfa fiber—F1 (3–9 mm) and F2 (20–25 mm)—and stabilized with lime (4, 8%) and GGBS (4, 8, 12%). Tests included wet and dry compressive strength, capillary absorption, linear shrinkage, abrasion resistance and thermal conductivity. Results show that the incorporation of Alfa fibers, particularly when combined with lime and GGBS, significantly enhanced wet compressive strength and abrasion resistance, while the initial reduction in dry compressive strength due to fibers was effectively offset by GGBS. The combination of longer Alfa fibers (F2) with lime and GGBS provided the best overall performance, producing compressed earth blocks with superior mechanical strength, durability, and thermal efficiency. Full article

The incorporation of ground tire rubber (GTR) into elastomeric compounds offers a sustainable route for recycling end-of-life tires; however, its effect on the structure–property relationships governing mechanical and dielectric performance remains insufficiently understood. In this study, NR/SBR composites containing 0–50 phr of devulcanized GTR were prepared and characterized through Fourier-transform infrared spectroscopy (FTIR), swelling analysis, thermogravimetric analysis (TGA), mechanical testing, and broadband dielectric spectroscopy. FTIR and swelling results revealed enhanced matrix–GTR interaction at intermediate GTR loadings (10–20 phr), evidenced by an increased intensity of sulfur-related bands and reduced swelling degree, indicating partial chemical integration of the recycled phase into the elastomer network. Mechanical testing showed that increasing GTR content increased stiffness at high loadings, while tensile strength, elongation at break, and toughness progressively decreased due to interfacial debonding mechanisms. TGA demonstrated that the main degradation temperature of the NR/SBR matrix remained essentially unchanged (418–425 °C) across all formulations, confirming preservation of thermal stability despite increasing structural heterogeneity. Dielectric spectroscopy (10⁻²–3 × 10⁶ Hz, 40–120 °C) revealed pronounced Maxwell–Wagner–Sillars interfacial polarization and thermally activated charge transport, with conductivity increasing with GTR content without evidence of electrical percolation, even at 50 phr. The results demonstrate that the performance of NR/SBR/GTR/SiO₂ composites is primarily controlled by the interfacial structure generated by the recycled phase. Intermediate GTR contents (10–20 phr) provide the most effective matrix–GTR interaction, while higher loadings mainly affect mechanical integrity and dielectric response through increased structural heterogeneity. These findings provide practical guidelines for designing sustainable elastomeric compounds with high recycled content while maintaining thermal stability and controlled electrical insulation properties. Full article

In the severely cold regions of northern China, large-scale clean heating retrofits in rural areas face critical problems, including substandard indoor thermal environments, excessive energy consumption, and prohibitive operating costs. To address these challenges, this study focuses on rural residences in Hohhot as the research subject. Field measurements were conducted throughout the heating season in a typical rural house in Hohhot, a representative city with severe cold weather, to collect indoor/outdoor thermal parameters and real-time operational data of an air-source heat pump (ASHP). A dynamic simulation platform was established using TRNSYS 18. The optimization scheme integrates passive envelope retrofitting (ground insulation improvement and energy-efficient windows) with the active optimized control of the ASHP system. Indoor thermal comfort was evaluated using the Predicted Mean Vote (PMV) index. The results show that the ASHP exhibits excellent heating effectiveness and economic viability, making it the preferred technology for rural residences in Hohhot and similar regions. After implementing the active–passive scheme, the proportion of time with comfortable indoor conditions in rural houses surges from 34.1% to 84.1%, while during the severe cold period, this proportion increases from 16.97% to 61%. The indoor thermal comfort index shifts from its previous state to the baseline comfort range of −1.0 to 0. The total heating energy consumption decreased from 18,646 kWh to 15,861 kWh, and the seasonal operating cost dropped from 3207 to 2579.3 RMB, achieving an overall reduction of 19.6% in both energy and costs. The proposed active–passive synergistic optimization scheme simultaneously improves the indoor thermal environment and reduces heating energy consumption, overcoming the limitations of single-measure retrofits. This study fills the research gap on the quantitative evaluation of active–passive synergy for rural clean heating in severely cold regions, providing a theoretical basis and technical support for clean heating retrofits in Hohhot and Inner Mongolia, facilitating low-carbon and efficient rural clean heating in northern China. Full article

This study focuses on optimizing backfill materials to enhance the heat transfer performance of ground heat exchangers (GHEs) in ground source heat pump (GSHP) systems. A series of composite phase change material/original sand soil (CPCM/OSS) backfill materials was prepared using capric acid–myristic acid/expanded graphite (CA-MA/EG) at mass ratios of 5%, 10%, 15%, and 20%. Thermal conductivity testing, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), laboratory heat transfer tests, and 3D numerical simulations under typical intermittent summer conditions were systematically conducted. The results show that thermal conductivity, specific heat capacity, and thermal storage coefficient all increase with rising moisture content and CPCM dosage. The newly developed CPCM/OSS backfill material significantly improves the heat transfer performance of GHEs. Comprehensive thermophysical characterization indicates that the 10 wt% CPCM sample is the optimal formulation. Laboratory tests demonstrate that, relative to pure OSS backfill, the 10 wt% CPCM-doped CPCM/OSS raises the average soil temperature by approximately 2.5–2.8 °C. Numerical simulations over three consecutive days show that, relative to pure OSS backfill, the 10 wt% CPCM-doped composite enhances the heat exchange capacity per linear meter of the GHEs by 8.8%. The newly developed CPCM/OSS backfill material significantly improves the heat transfer performance of GHEs. It provides a feasible material solution and technical reference for GSHP system design. Full article

The growth of the global population has led to increased demand for agricultural products, resulting in greater agricultural waste production. One sustainable response to this challenge is using agricultural waste as raw material in building materials. This study examines the potential for partial replacement of natural aggregates in concrete with agricultural waste from typical Mediterranean fruits: sour cherry pits, grape seeds, ground olive pits, and carob seeds. To evaluate the effect of treatment on the behavior of agro-waste aggregates, ground olive pits were used untreated, treated with ash water, or treated with seawater. Carob seed concrete deteriorated during water curing due to seed swelling and tannin-related degradation, revealing its unsuitability without prior stabilization. Partial replacement of natural aggregates with agricultural waste resulted in decreased density, ultrasonic pulse velocity (UPV), dynamic elastic modulus, compressive strength, and thermal conductivity, while increasing saturated water absorption. Treatment with ash water on ground olive pits improved the interfacial transition zone (ITZ), resulting in 29% increase in compressive strength relative to untreated ground olive pits. Concrete with ash water treated ground olive pits demonstrated the highest practical potential among all tested agro-waste concretes. Full article

The energy transition of district heating systems in Poland requires the simultaneous consideration of energy efficiency, operating costs, technical feasibility, and local environmental constraints. This study addresses an identified gap in the literature by combining real operational time series from a municipal district heating system with time-resolved market signals and site-specific resource constraints in a single OPEX-based operational screening framework. A case study is conducted for the city of Ustka using a configuration-based comparison of hybrid supply systems that include a gas-fired combined heat and power (CHP) unit, air-source and ground-source heat pumps, thermal energy storage, and a peak-load boiler. The optimisation model was implemented in MS Excel using the GRG Nonlinear algorithm (Solver) and was driven by the district heating operational data for 2021–2022 together with electricity and natural gas prices from the Polish Power Exchange day-ahead market (TGE RDN), evaluated under both hourly and daily settlement assumptions. The results indicate an optimal capacity split of 1.2 MWel/1.3 MWth for the CHP unit and 1.5 MWel/3.0 MWth for the heat pump system, supported by a required peak boiler capacity of 8.23 MWth. Within the adopted OPEX-based assessment, the lowest value of the unit heat generation indicator was obtained for the CHP-led configuration with combined ground-source and air-source heat pumps (38.45–38.55 PLN/GJ). A distinctive element of the study is the explicit verification of whether an operationally favourable configuration remains practically feasible when local resource constraints are considered. The site assessment indicates limited practical feasibility of the borehole heat exchanger at the analysed location in Ustka, showing that the lowest OPEX result should not be interpreted as a final investment recommendation. The study provides a replicable approach for the Polish district heating operators to screen hybrid transition pathways under real market conditions and to avoid technology choices that are favourable in dispatch models but constrained in practice. From a sustainability perspective, the proposed framework supports more energy-efficient, resilient, and locally feasible district heating transition planning in municipal heat systems. Full article

Frost heave in cold-region pavements is governed by coupled heat and moisture migration, but the specific contribution of vapour transport in multilayer subgrades remains poorly constrained. This study combines field temperature monitoring with analytical modelling to estimate effective thermal conductivities of pavement structural layers and to evaluate vapour-driven moisture fluxes during seasonal freezing. A vertical thermistor array beneath a two-lane highway near Astana (Kazakhstan) and in the adjacent snow-covered ground is used to back-calculate layer-specific conductivities from midwinter temperature gradients by applying Fourier’s law under quasi-steady conditions. Vapour migration is then assessed by two complementary approaches. A diffusion-based formulation, which couples measured vapour-density gradients with air-filled porosity, provides a conservative lower bound and yields very small fluxes, with maximum daily ice deposition of 8.17 × 10⁻⁵ kg·m⁻²·day⁻¹ beneath the pavement and cumulative seasonal masses of order 10⁻² kg·m⁻² (10⁻³ kg·m⁻² under snow). An energy-balance approach, which relates conductive heat flux to latent heat of vapour–ice phase change and introduces an efficiency parameter α, supplies a physically constrained upper envelope. For a central scenario with α = 0.6, daily deposition in the 0.60–1.00 m layer reaches 0.0961 and 0.0330 kg·m⁻²·day⁻¹ beneath pavement and snow, respectively, yielding seasonal totals of 12.1 and 4.1 kg·m⁻². Together, these bounds indicate that vapour migration beneath pavements, although unlikely to be the dominant driver of frost heave, can be substantially more intense than under adjacent snow-covered ground due to steeper temperature gradients in the upper subgrade. Full article

Rockfall events are significant natural hazards on fractured rock cliffs, often driven by environmental forcing, including thermal variations that induce stress and fatigue in rocks. This study presents the first application of Ground-Based Interferometric Synthetic Aperture Radar (GB-InSAR) for high-resolution monitoring of sub-millimeter thermally induced displacements on a rock slope. An eight-day pilot experiment conducted at the La Cornalle molasse cliff (Vaud, Switzerland) revealed cyclic displacement signals with a clear 24 h periodicity, identified through Fourier and wavelet analyses, with a mean amplitude of 5 × 10⁻⁴ m. Simultaneously, infrared thermography (IRT) and a weather station recorded rock surface and air temperature variations, allowing a first estimation of the time lag between thermal forcing and mechanical response, with delays of 1–8 h relative to air temperature and 1–6 h relative to solar radiation. An analytical deformation model based on thermal diffusion predicts a daily displacement amplitude of 4.2 × 10⁻⁵ m, highlighting a significant difference with GB-InSAR observations and emphasizing the influence of structural complexity and thermo-hydro-mechanical processes in rock slopes. These results demonstrate the capability of combined high-resolution remote sensing techniques to quantify thermo-mechanical behavior in rock masses and provide a methodological framework for future investigations of rockfall-prone slopes. Full article

The submarine cable installed in the directional drilling pipeline may face constrained ampacity due to the narrow air gap and complex thermal environment. The current studies have overlooked the axial heat transfer caused by variable burial depth and the influence of deep ground temperature, resulting in inaccurate assessment of the hot spot temperature and hot spot location of submarine cable in the directional drilling pipeline. To address this issue, the distributed parameter electrical circuit model for long-distance submarine cable and the three-dimensional thermal simulation model for the submarine cable landing section were developed to analyze the heat generation and dissipation characteristics of submarine cable in the directional drilling pipeline. Then, the hot spot location of submarine cable in the directional drilling pipeline was identified. Subsequently, an improved thermal rating method based on the quasi-three-dimensional thermal model was proposed to rapidly assess the hot spot temperature for the submarine cable in the directional drilling pipeline. The accuracy of the improved thermal rating method was verified by comparison with the simulation method. Finally, implementation of water circulation was conducted to resolve the overheating issue in the directional drilling pipeline. The investigations in this paper can provide support for the efficient utilization of submarine cable. The improved evaluation method for submarine cable in a directional drilling section proposed in this paper can be regarded as the supplement to the traditional IEC method. Full article

This investigation aims to experimentally evaluate the thermal performance of plasters reinforced with bio-based materials and to assess their contribution to sustainable construction and the reduction in the environmental footprint of building materials by simulating their impact on the thermal behavior of a building in different Moroccan climates using TRNSYS software. Three types of samples were investigated: pure plaster and two others strengthened by 4% of alfa fibers and 6% of coffee grounds. Each model was produced with the following different water-to-plaster ratios (W/P): 0.5, 0.6, and 0.7. The results demonstrated that the inclusion of aggregates and the increase in water content improved the thermal qualities of the composites. A combination of 4% alfa fibers and a W/P ratio of 0.7 significantly reduced thermal conductivity by 32.24%, decreased density by 26.82%, and lowered the decrement factor by 21.67%. Additionally, a composite containing 6% coffee grounds and a W/P ratio of 0.7 demonstrated a reduction in thermal amplitude by 15.61% and decreases in both thermal conductivity and density by 26.05% and 22.23%, respectively. Dynamic simulation indicated that these designs reduced greenhouse gas emissions and energy loads. However, energy gains using optimal configurations were considerable and similar in the following locations: Agadir (16.3%), Tangier (14%), Meknes (13.5%), Ifrane (13.42%), Marrakech (13.6%), and Er-rachidia (12.5%). Full article

The aim of this research was to evaluate the efficacy of water-soluble epoxy resin (ER) in regard to stabilising clay soils, specifically for the design of column-type reinforcement in soft ground. An extensive laboratory program was conducted to assess the mechanical enhancement of a silty clay soil via ER, both as a standalone stabiliser and in combination with cement, bentonite, and sodium polyacrylate (PA). In addition, the study investigated the impacts of thermal stabilisation and electro-osmotic dewatering on resin–soil specimens. Specimens stabilised solely with ER exhibited poor strength development due to the inhibition of polymerisation by water. The addition of bentonite at low concentrations resulted in low early strength development and a moderate increase in the final strength. The use of cement provided the most significant strength gains, which were further enhanced by optimising the dosage of PA, although an excessive PA content significantly reduced the strength properties. In terms of physical treatments, thermal stabilisation at an optimal temperature of 60 °C for 24 h substantially improved the performance of ER. Electro-osmotic treatment accelerated the development of early strength but failed to provide appreciable strength improvement, and resulted in brittle behaviour and reduced toughness in the later stages (90–180 days). These findings offer critical guidelines for optimising mix designs and treatment protocols for geotechnical ground improvement projects. Full article