Search Results (252)

This paper presents a methodology to evaluate the entire process of thermal evolution and fracture failure within stay cables subjected to sheath fires. Computer software FDS 2021 and ABAQUS 2021 are applied to build a sequentially thermos–mechanics coupled method integrating thermal, structural, and fracture dynamic analyses in stay cables under sheath fire exposure conditions. Herein, three representative fire scenarios including full-circumferential, top-side, and bottom-side ignition are reconstructed. Further, 127 individual wires, accounting for interstitial cavity radiation and contact heat transfer, are utilized to perform analysis on sectional temperature in stay cables. The results indicate that the ignition mode dictates the cross-sectional temperature gradient, with localized ignitions inducing highly asymmetric thermal fields and pronounced internal bending moments. Elevated temperatures trigger a progressive load redistribution from the degraded fire-facing wires to cooler internal layers. Ultimately, abrupt global fracture occurs when the residual ultimate load-carrying capacity intersects with the actual applied tension, resulting in a fracture morphology that closely corresponds to the spatial thermal distribution. Furthermore, the structural capacity degradation exhibits three distinct time-dependent stages: a slow degradation stage, a sharp decline stage, and a recovery stage. Among the analyzed scenarios, full-circumferential ignition induces the most drastic overall capacity reduction, while bottom-side ignition poses a markedly greater rupture risk than top-side ignition. Full article

Recycled polymer-rich residues can alter several functions of wood-based panels, but claims of multifunctionality require property-specific evidence and transparent treatment of replication. Three-layer spruce particleboards were therefore prepared with 10 wt.% painted or unpainted polypropylene bumper granules, high-density polyethylene fuel-tank granules, tire rubber, seal-and-carpet residues, or electrical-cable fractions in the core layer. Two hybrid formulations contained 10 wt.% recycled rubber-rich filler plus 10 wt.% expandable graphite. Transient plane source measurements were evaluated at the specimen-pair level (two pairs per formulation); normal-incidence sound absorption and radiant-heat mass loss were complementary descriptive screens because the archived datasets contained one spectrum or one exposed specimen per formulation. Mean thermal conductivity varied only from 0.1908 to 0.2075 W m⁻¹ K⁻¹ (−5.3% to +3.0% relative to the reference). The graphite hybrids showed the clearest change in transient response: thermal diffusivity increased by 19.6–20.1%, whereas volumetric heat capacity decreased by 14.5–16.7% and thermal effusivity by 6.5–8.7%. SC10G10 had the highest mean absorption coefficient over 126–6400 Hz (0.210; +46.2%) and the lowest mass loss after 600 s at 30 kW m⁻² (37.48%; −17.72%). Macroscopic and polarizing optical images showed formulation-dependent filler distribution and visible interfacial spaces, but they did not establish bonding mechanisms or quantify porosity. The results identify promising formulation-dependent responses while also defining the replication and structural measurements needed before application-level claims can be made. Full article

The temperature field of a high-voltage direct-current (HVDC) cable governs its current rating and insulation lifetime and must therefore be predicted accurately across diverse operating conditions. Finite-element (FE) simulation is accurate but too costly for repeated evaluation, whereas data-driven reduced-order models (ROMs) often extrapolate poorly beyond the training-current range. This paper proposes a physics-structured POD–neural ROM to address this limitation. Specially, proper orthogonal decomposition (POD) compresses the three-dimensional temperature-rise field into a few modal coefficients, which are predicted from the operating conditions by a neural network. The key innovation is to embed the Joule-heating law directly into the architecture: the leading coefficient is represented as a current-squared factor multiplied by a learned current-independent shape. This construction guarantees the correct current scaling of the dominant mode, including its zero-current limit and extrapolation beyond the training range. On FE data for an eight-layer cross-linked polyethylene cable, the model achieves 2.4% mean relative error under current extrapolation and remains below 5% at twice the maximum training current, outperforming Gaussian-process, dynamic-mode-decomposition, autoregressive, and black-box baselines. The full field is evaluated in approximately one millisecond per condition, with a cost independent of the training-set size. Controlled ablations show that the improvement arises from structurally enforcing the scaling law rather than merely supplying $I^2$ as an input feature. Embedding known physical scaling into a surrogate architecture therefore provides a principled route to reliable extrapolation. Full article

The conductor temperature of cross-linked polyethylene (XLPE) high-voltage direct-current (HVDC) cables governs ampacity assessment and insulation life management, yet it cannot be measured in service, and finite-element simulation is too expensive for real-time use. This paper presents a physics-informed neural network (PINN) that embeds the transient heat-conduction equation, a temperature-dependent Joule source, and the boundary and initial conditions into the training loss of a neural surrogate. Three ingredients adapt the framework to power cables: a layer-aware material mapping over the eight heterogeneous cable layers; an electro-thermal coupling through the temperature dependence of the conductor conductivity, handled during training by a convergent Picard-type evaluation of the Joule source; and a condition-embedding input treating the load current and ambient temperature as continuous parameters so that a single network covers the admissible current–ambient envelope of the studied cable configuration. Validated against finite-element references under fifteen operating conditions, the model attains a root-mean-square error of $0.0024$ K (mean over five training seeds) on a held-out condition relative to a finite-element reference whose mesh-discretization error a refinement study bounds at about $0.04$ K while reducing the governing-equation residual by approximately 28-fold relative to an identically sized data-driven network at statistically indistinguishable pointwise accuracy. The physics prior also renders degradation under training-data reduction more graceful and improves extrapolation to unseen ambient temperatures, whereas current extrapolation remains the most challenging transfer. The differentiable surrogate identifies the load current and the unmeasurable conductor hotspot from ten surface sensors within seconds, at below 9 ms per ${10}^5$ queries. A loss-weight sensitivity study and a three-dimensional cable-end-effect case on a second material configuration are also reported. All reference data are numerical; experimental cable-loop validation remains for future work. Full article

Given the modernization of power systems in recent years, the quality of electrical energy is changing. With the increasing prevalence of harmonic components and rising current densities, conductor efficiency has become critically important. This study investigates the skin effect as a function of conductor geometry within the framework of electromagnetic field theory. Classical circular cross-section cable geometries and rectangular busbar systems were compared under an AC current of 1350 A (peak) across a frequency range of 50–500 Hz. The findings are comparatively presented, and their electromagnetic and thermal implications are discussed. Numerical modeling and simulation studies were performed using the Finite Element Method. COMSOL Multiphysics^® software AC/DC Module 6.2 version was used for the analyses. In the simulation studies, the magnetic flux density distribution within the conductor and the current concentration induced by eddy currents were analyzed. Frequency-dependent behavioral characteristics were examined in the analyses. The results revealed that the conductor with circular geometry exhibited a more severe skin effect. The rectangular conductor used in busbar systems was found to effectively distribute the current density across its surface area. Thus, rectangular geometry optimizes AC resistance. The analysis results revealed that conductor design and material selection depend not only on the cross-sectional area but also on the geometric shape factor. In this context, it was determined that conductor design has a decisive effect on electromagnetic power losses, which directly govern the heat generation potential within high-current systems. This study serves as a technical guide to evaluate frequency-dependent electromagnetic performance across a 50–500 Hz range—reflecting frequencies relevant to harmonic components—to assist in the design and optimization of high-current energy distribution systems. Full article

This study evaluates high-silica fiber/silica aerogel composites (HSFACs) for the passive fire protection of bridge cables. The primary objective is to reveal the high-temperature degradation mechanism of HSFAC and quantitatively determine a reliable thickness scheme for long-term hydrocarbon-fire protection of bridge cables. HSFAC specimens were heat-treated and characterized by thermal conductivity, tensile testing, SEM/TEM, FTIR, and TG analysis. A self-built furnace was used to assess an HSFAC-based cable protection system under hydrocarbon-fire exposure. Increasing heat-treatment temperature enlarged the pore and particle sizes of HSFAC and reduced its thermal-insulation performance. During 120 min of fire exposure, the cable protected by a single 5 mm HSFAC layer reached 300 °C within 45 min, whereas the cable protected by a double-layer 5 + 5 mm HSFAC system remained below 300 °C throughout the test. Finite element simulations validated against the experimental results confirmed that increasing HSFAC thickness improved thermal protection. After 90 min, the predicted cable-surface temperatures were 556 °C and 314 °C for HSFAC thicknesses of 5 mm and 10 mm, respectively. By integrating high-temperature material characterization, HC-fire testing, and thickness-dependent numerical analysis, this study links material degradation to system-level fire performance and provides a quantitative basis for HSFAC thickness design. Full article

To address the discrepancy between the constant-power fire sources currently used in cable fire-related research and cable fire protection product testing and actual cable fires, this paper proposes a cable equivalent combustion simulation method based on electrical fault fires. The cable tunnel experiment platform was built and, based on energy equivalence, used an igniter to simulate a fault arc’s thermal effect and ignite the cable, obtaining the temperature rise characteristics at multiple points in the fire source area. Based on the experimental data, a simulation model for the mixed combustion of multiple cable materials was established and revised, and the heat release rate (HRR) under different fire scenarios was calculated. Then, an equivalent fire source device capable of simulating the aforementioned HRR curve was designed. The results indicate that under ignition conditions with an igniter power of 400 kW and duration of 90 s, the cable fire development exhibits nonlinear dynamic evolution, with a flame height of 0.63 m. The peak temperature rise rate and peak temperature at the measurement point reach 3.27 °C/s and 926 °C, respectively. When 39.4% of the insulation layer material of the cable participates in combustion, and the fuel molecular formula is C_2.28H_5.70O_1.42N_0.08Si_0.65, the relative error between simulated and experimental temperatures during stable combustion is 3.0%. Heat release rates for mild, moderate, and severe fires stabilize near 350 kW, 420 kW, and 530 kW under this calibrated cable model. The relative error between the temperature curve from the fire source device during the stable combustion stage and that from the actual combustion experiment is 3.4%, indicating favorable equivalence. Full article

Overheating of polymeric cable materials is a major contributor to insulation aging, electrical failure, and fire risk in power systems, particularly in densely installed urban underground cable corridors where heat dissipation is limited and early-stage defects are difficult to identify. Although gas-detection approaches are promising for non-invasive overheating monitoring, their practical value depends on identifying material- and lay-er-specific volatile products and clarifying how their release evolves with temperature and time. Herein, volatile products released from the PVC outer jacket of a YJV22-8.7/15 kV-3 × 185 medium-voltage cable were investigated using headspace gas chromatography–mass spectrometry (GC-MS). Temperature- and time-dependent evolution was estimated for selected marker species, and the associated degradation behavior was correlated with chemical/structural and electrical changes using ATR-FTIR, KPFM, and dielectric measurements. The number and observed headspace levels of organic components increased substantially with severe overheating, reaching more than 20 dominant components at 200 °C. 2-Ethylhexanol (2-EH) was observed across the studied range and reached approximately 300 × 10⁻⁶ (volume fraction) at 200 °C for 60 min while remaining at or below approximately 50 × 10⁻⁶ at temperatures up to 140 °C. Benzene was observed mainly at severe overheating, whereas DOTP was first observed at 140 °C among the tested conditions, reaching approximately 40 × 10⁻⁶ at 140 °C for 5 min and exceeding 300 × 10⁻⁶ under more severe conditions. KPFM showed surface roughness increasing from 7.70 to 43.39 nm, and the real permittivity increased by up to 13.9% at 50 Hz. These results provide a temperature- and time-resolved headspace dataset for the tested cable outer jacket and relate its organic-gas profile to surface and dielectric changes. Full article

To improve the stability and controllability of narrow-gap welding (NGW) and systematically elucidate the mechanism by which pre-embedded cold wire modulates arc behavior and metal transfer, this study investigated the arc characteristics and metal transfer behaviors in thick-wire narrow-gap gas metal arc welding (GMAW) with a swing arc and pre-embedded cold wire. Two types of thick wires, single-strand welding wire (SWW) and cable-type welding wire (CWW), were compared under different numbers of pre-embedded cold-wire layers (n = 0, 1, 2). The results indicate that during arc swinging, the average arc spreading angle at the sidewalls is consistently smaller than that at the groove center for both wire types. For SWW, the sidewall arc spreading angle decreased by 13.1% and 18.4% with n = 0 and n = 2, respectively, compared with the groove center; for CWW, the reductions were 24.6% and 20.2%. Moreover, pre-embedded cold wire significantly increased the arc spreading angle (by up to 15.8% for SWW at the groove center) and induced deflection of arc cathode spots toward the cold wire, thereby improving heat distribution on the sidewalls and promoting sidewall penetration. In terms of droplet transfer, SWW exhibited stable spray transfer at the sidewalls and globular spray transfer at the groove center, while CWW showed rotating spray transfer at the sidewalls and a unique hanging droplet transfer mode at the groove center. The average droplet diameter of CWW at the groove center is 17% larger than that of SWW. Pre-embedded cold wire also significantly improved arc stability for both wire types, as indicated by a more concentrated voltage–current distribution, with CWW showing superior stability in the absence of cold wire, whereas no clear regularity was observed in its effect on droplet transfer. The findings suggest that pre-embedded cold wire is beneficial for applications requiring reliable sidewall fusion, as it improves heat distribution while maintaining droplet transfer stability. Further optimization of cold-wire layer number and positioning is recommended for enhanced weld quality. Full article

Steam-assisted gravity drainage (SAGD) is constrained in deep heavy-oil reservoirs by wellbore heat losses, delayed steam-chamber development and high steam–oil ratio (SOR). This study develops an experimentally parameterized reduced-order screening framework for thermocable-assisted SAGD, formulated as a digital-twin prototype that couples heat transfer, temperature-dependent viscosity, chamber-growth geometry and energy-efficiency indicators. The formulation is evaluated within an experimentally parameterized screening matrix covering steam temperature, oil viscosity, permeability, depth, cable power and early heating time. The graphical dependencies are presented in a unified publication format and supplemented by heat-balance, chamber-field, sensitivity and operating-window analyses. For the reference experimental case, thermocable support increases oil rate from 84.1 to 96.1 t/day and reduces SOR from 2.70 to 2.30 t/t. The cable heat input is small relative to useful steam heat; therefore, its effect is interpreted through local compensation of downstream heat deficit and longitudinal temperature stabilization rather than through bulk energy addition. The strongest sensitivity is associated with steam rate, oil viscosity and depth, whereas cable power shows a beneficial but saturating effect. The proposed reduced-order digital-twin prototype is intended for feasibility screening, preliminary operating-window selection and prioritization of candidate regimes for detailed thermal-reservoir simulation and subsequent field-scale validation. Full article

To systematically examine the effects of ambient wind speed on the fire behavior of inclined tunnel cables, this paper determines the combustion characteristics of ZR-RVV cable combustion parameters using synchronous thermal analysis and cone calorimetry. A 1:20 scaled tunnel platform was established based on Froude similarity criterion to conduct combustion experiments under varying wind speeds (0–0.7 m/s) and inclination angles (−30°–30°). Results indicate the ignition time of the cable decreases gradually with increasing external heating radiation intensity (25–50 kW/m²), with ignition at 295.1 °C. A modified Richardson number (Ri*) is introduced to quantitatively identify the dominant flow regime. It is confirmed that when |θ| ≈ 20°, Ri* ≈ 1, and the fire behavior transitions from “domination” (Ri* < 0.5) to “buoyancy-driven stack effect domination” (Ri* > 2). This critical inclination angle provides decisive guidance for fire source localization, smoke control, and exhaust design. Increasing ambient wind speed significantly reduces the fire temperature and dilutes the smoke; at a wind speed of 0.7 m/s, the maximum temperature drop at the ceiling monitoring point reaches 67%, while CO/CO₂ concentrations decrease correspondingly. The findings provide a theoretical basis for smoke exhaust design and fire monitoring in tunnel fire protection. Full article

Steam-assisted gravity drainage (SAGD) remains one of the most energy-intensive technologies for heavy-oil recovery because production response is controlled not only by injected heat but also by spatial heat delivery, wellbore losses, viscosity reduction and steam chamber geometry. This paper develops a physics-guided digital twin for SAGD with distributed thermocable assistance and a bounded residual machine learning correction layer. The framework combines a heat-delivery model, temperature-dependent oil mobility, scenario analysis and decision-oriented visualization within a reproducible computational experiment. A reference operating envelope was formulated for heavy-oil reservoirs, including depth, horizontal well length, permeability, porosity, oil viscosity, steam temperature, injection rate, thermocable power and cable coverage. The analysis includes sensitivity testing, cumulative-production/SOR dynamics and Pareto-type operating-window mapping. In the reference computational scenario, which is treated as an illustrative screening case rather than as field-history validation, the thermocable-assisted hybrid configuration changed the model-calculated eight-year cumulative oil from 452.5 × 10³ m³ to 615.2 × 10³ m³ and the mean SOR from 3.17 to 2.72 t/t relative to the conventional SAGD physics-core case. The largest sensitivities were associated with steam rate, steam temperature, initial viscosity and permeability. Within the declared operating envelope, the results support the use of the framework as a pre-field screening tool and indicate that thermocable assistance should be interpreted primarily as spatial heat distribution control rather than as a field-validated production-improvement guarantee. Full article

Addressing issues such as corrosion and the eccentric wear of metal tubing strings, low heating efficiency, and high operation and maintenance costs of lifting systems in heavy-oil extraction, core equipment comprising carbon-fiber-reinforced PEEK (Polyetheretherketone) multi-layer composite continuous tubing has been developed. This equipment integrates an embedded cable-laying system and an intelligent regulation module, establishing a rodless oil-extraction technology system suitable for heavy-oil reservoirs. This article systematically describes the process structure, preparation principle, core characteristics, and key parameters of this composite continuous tubing. By deriving an equivalent thermal-resistance model for the multi-layer structure and an unsteady-state heat-transfer equation, precise regulation of the wellbore temperature field is achieved. Combined with field tests at Well A in Jinghe Oilfield, the tubing’s effectiveness in reducing viscosity, increasing production, saving energy, and extending the operational cycle in heavy-oil extraction is verified. The results show that the carbon-fiber-reinforced PEEK composite continuous tubing possesses characteristics such as high strength, strong corrosion resistance, low friction, and high thermal insulation. When paired with a viscosity–temperature coupling regulation algorithm, the heating efficiency is improved by 40% compared to traditional electric heating rods. The efficiency ranges from 37% to 43% when the formation thermal conductivity fluctuates by ±20%. Field applications have achieved a 230% increase in daily oil production, a 30% reduction in system energy consumption, and an extension of the hot washing cycle to over 180 days. The development of this tubing breaks through the technical bottleneck of traditional metal tubing, providing a new material solution for the efficient and intelligent development of heavy-oil extraction, and has broad promotional value. Full article

In hot and humid regions, urban underground utility tunnels are susceptible to high temperature and humidity due to moist inlet air, cable heat dissipation, and limited ventilation jointly affecting the internal environment. To address this issue, an alternating ventilation strategy, in which fan operation is periodically reversed to switch between air supply and exhaust, is proposed. Compared to conventional mechanical ventilation, this strategy overcomes the constraints of unidirectional airflow and mitigates thermal and humidity stratification, with low retrofit requirements and good adaptability. Ventilation performance was evaluated using non-guarantee rates for temperature and relative humidity, i.e., the ratio of the number of measurement points where the temperature/relative humidity exceeds 40 °C/65% to the total number of measurement points in the utility tunnel (TNGR and RHNGR), non-uniformity coefficients (K_T and K_RH), and mean temperature (T_m). The alternating mode outperformed the conventional mode, reducing TNGR by 6.0% and Tm by 0.3 °C while improving temperature and humidity distributions and lowering cable temperatures. Although the reduction in T_m appears modest, it is practically meaningful because it helps weaken thermal stratification and local overheating, improves cable operating conditions, and may reduce the need for high-airflow operation when tunnel temperatures approach the permissible limit. Response surface methodology was further used to optimize the alternating ventilation parameters, indicating that the recommended fan commutation frequency is 2 under different inlet air temperatures. CFD validation confirmed the effectiveness of the optimized scheme. At an inlet air temperature of 35 °C, KRH decreased from 11.9% to 11.0% and Tm decreased from 37.5 °C to 36.9 °C. 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