Abstract: Coiled tubing fishing operation is a major technical challenge in petroleum engineering. Especially for high-strength materials such as N80, conventional direct pulling is often limited by the bearing capacity limit of the tubing. In this study, an innovative fishing process combining perforation weakening and axial fracture is proposed. Based on the finite element method of ANSYS software, the influence of tool geometry on perforation load and residual strength of tubing string is systematically investigated. The explicit dynamics method is adopted to simulate the dynamic process of the punch piercing the pipe wall and fracturing the tubing. Meanwhile, the Johnson-Cook damage model is introduced to characterize the failure behavior of N80 material under complex stress triaxiality. The results show that compared with the circular cutter head, the optimized diamond cutter head reduces the piercing load by approximately 45.3% and the fracture load by about 23%, and induces obvious stress concentration zones on the pipe wall. This research provides a theoretical basis for the design of downhole perforation fishing tools. Read More

Abstract: To investigate the local flash temperature, stress oscillations, and elastoplastic energy dissipation induced by asperity interactions on both sides of a high-speed train disc brake, a three-dimensional transient thermo-mechanically coupled finite element model of a dual-roughness disc-pad interface was established. A fixed Weierstrass-Mandelbrot fractal morphology was used to evaluate temperature, von Mises stress, thermal penetration depth, thermoelastic power, plastic dissipation, and frequency-domain responses. The peak temperatures of the brake disc and brake pad reached 1409.5 °C and 1571.9 °C, respectively, and the corresponding peak von Mises stresses were 1079.4 MPa and 1024.6 MPa. The dominant stress frequency was 3395.6 Hz, with a relative oscillation amplitude of 312.10%. Plastic power accounted for approximately 32% and 37% of the theoretical input power in the disc and pad, respectively. Misaligned asperity contact and repeated jumps in contact stiffness jointly caused near-surface heat accumulation, high-frequency instability, and synergistic plastic dissipation. Read More

Abstract: High penetration of distributed energy resources (DERs)—photovoltaics, wind, storage, and flexible demand—is reshaping distribution networks. Bidirectional power flows, tighter voltage limits, and higher uncertainty make traditional passive operation inadequate. Flexible distribution systems (FDSs) address this by coordinating flexibility across source–grid–load–storage. This review synthesizes core FDS work through a three-layer lens: (i) structural flexibility (reconfiguration and controllable interconnection) that expands feasibility; (ii) real-time control (local, distributed/hierarchical, and predictive) that enforces constraints; and (iii) multi-timescale scheduling that allocates resources under forecasts and uncertainty. We emphasize cross-layer alignment—structure shapes controllability, and schedules must preserve regulation margins—and summarize open challenges in uncertainty propagation, scalability, and deployable hybrid (model + data) methods. Read More

Abstract: To reveal the differences in local thermal instability at rough braking interfaces under different load and rotational-speed conditions, a three-dimensional transient thermo-mechanically coupled finite element model was established. A 5×5×1 mm³ single-sided rough surface region containing 496 asperities was used as the computational domain. Temperature, stress, affected depth, energy dissipation, and frequency-domain fluctuations were compared under three operating conditions. The results show that, when the load increases from 12 kN to 16 kN, the maximum temperature rises from 957.03 °C to 993.10 °C, and the plastic-dissipation depth increases from 0.204 mm to 0.300 mm. Under a 16 kN load, reducing the rotational speed from 48 rad/s to 42 rad/s lowers the maximum temperature to 709.20 °C, but increases the root-mean-square stress amplitude to 265.79 MPa. Lowering the rotational speed can alleviate thermal concentration, but it cannot eliminate contact reconstruction and stress fluctuation induced by high load. Braking risk should therefore be evaluated jointly using the dual indicators of temperature concentration and stress fluctuation. Read More

Abstract: The paper explores the use of a combined approach of computational fluid dynamics and genetic algorithm in improving the performance of airfoils in subsonic sub-flows to achieve high lift and low-drag ratios. Airfoil shapes are modeled with the use of PARSEC geometric parameterization with eleven design variables, which allows exploring the design space systematically and with physical realizations. Simulations of Reynolds-Averaged Navier-Stokes with Spalart-Allmaras turbulence models offer aerodynamic performance analysis at Reynolds number at Re = 3×10⁶ over angles of attack between -4° to 16°. The genetic algorithm optimization model, which uses tournament selection, simulated binary crossover, and polynomial mutation operators, used populations of 50 individuals which evolved over 100 generations to maximize the lift-to-drag ratio at cruise conditions (α = 4°). The findings show that peak L/D = 98.5, which is equivalent to an increase of 26.5% over NACA 2412 base level and 38.7% over NACA 0012. The streamlined design has lift coefficient Cₗ = 0.52 and drag coefficient Cⴅ = 0.00528 by optimized pressure distribution with increased suction peak and better aft pressure recovery. The results of the computational predictions are in great agreement with the experimental validation data with mean absolute error of 2.8% and 4.2% mean error of lift coefficient and drag coefficient respectively, as well as correlation coefficients higher than R² = 0.99. The study lays down systematic optimization procedures that can be used in the design of unmanned aerial vehicles, general aviation purposes, and wind turbine blades to give the aerospace engineers a solid computational foundation of aerodynamic performance improvements Read More