Design optimization of offshore wind turbine (OWT) monopiles presents a high-dimensional challenge, as the pile is discretized into multiple segments (typically 2–3 m in length), each with independent diameter and wall thickness. Furthermore, the optimization is governed by various design constraints (ultimate, fatigue, and serviceability limit states), numerous design load cases (DLCs), and complex multi-physics involving aero-hydro-servo-elastic-soil interactions. These factors necessitate computationally expensive time-domain simulations. Conventional optimization methods are susceptible to local optima and struggle with the high-dimensionality, multiple constraints, and numerous load cases inherent to this problem. Moreover, current monopile designs are seldom optimized using integrated multi-physics simulations, which can lead to suboptimal or potentially over-conservative designs. This study proposes an efficient global optimization framework for high-dimensional, multi-constrained, integrated design of monopiles under various load cases. The framework comprises three key components: (i) an integrated aero-hydro-servo-elastic-soil model for providing high-fidelity dynamic responses; (ii) the subset simulation optimization (SSO) algorithm for efficient global exploration of the high-dimensional design space; and (iii) a high-fidelity multivariate metamodel based on Gaussian process regression (GPR) for accelerating the optimization process. The effectiveness of the proposed framework is demonstrated by optimizing a monopile for a 15 MW OWT. Benchmarking against a suite of optimization algorithms (GD, GA, PSO, SA) demonstrated the superiority of SSO, which achieved a 9% reduction in mass and reduced the required computational time by 38%. The results identify fatigue, rather than ultimate strength, as the governing constraint for monopile optimization. The framework equips designers with a computationally efficient, globally optimal route to lighter offshore wind turbine foundations, cutting costs while sustaining structural integrity.
Water hammer protection design for long-distance water conveyance systems faces two major challenges: the high computational cost of transient simulations and the difficulty of accurately characterizing safety boundaries. To overcome these limitations, we propose a systematic framework that integrates active-learning-based surrogate modeling with closed-loop progressive optimization for robust cost reduction in air-vessel design under multiple hydraulic safety constraints. To reduce the arbitrariness of high-dimensional optimization, the air vessel installation location and the initial parameter search space are first derived from the propagation mechanism of water hammer waves. An active learning strategy combining query-by-committee with hybrid sampling is then developed to progressively characterize the non-convex feasible domain by adaptively enriching high-value samples in constraint-sensitive regions. A closed-loop optimization procedure centered on FAR-constrained calibration is further established, through which the epistemic uncertainty of the surrogate model is transformed into an explicit feasibility margin, thereby improving the reliability of feasibility screening near the hydraulic constraint boundary. Finally, we employ SHAP analysis to reveal the nonlinear coupled contributions of key variables to extreme pressure responses. Application to a real-world water conveyance project demonstrates that the proposed method achieves substantial cost reduction and improved computational efficiency while satisfying the prescribed hydraulic safety constraints.
Abstract Dike failure is a disaster that brings extensive damage. Studying the characteristics of breach flow is of great practical significance for breach closure and reducing flood damage. However, experimental research on the surface morphology and velocity field of breach flow during the process of dike-break remains relatively limited. In this study, a large-scale experimental model of instantaneous dike-break induced flow under various flow conditions was conducted. The simultaneous measurement of water surface morphology and surface velocity fields near the breach was achieved using three-dimensional surface particle tracking velocimetry measurement technology. Based on the morphological evolution of the breach water surface, the dike-break process was divided into three stages: initial stable water tongue formation, gradual submergence, and eventual disappearance. The dimensionless water surface profile elevation along the breach centerline during the first stage exhibited similar characteristics under varying experimental conditions. The surface velocity also exhibited relatively stable distribution patterns along the breach centerline during this stage. The dimensionless water-level difference between the main channel side and floodplain side decreased with increasing initial water depth. However, the water-level difference between the downstream and upstream sides within the main channel increased with higher initial river velocities. The surface velocity of breach flow exhibited an initial increase to a peak followed by a decline, with the peak value showing a positive correlation with the initial channel depth. These findings revealed the evolution of breach flow surface morphology and velocity field, enhancing understanding of hydrodynamic processes of dike failure.
High penetration of renewable energy is transforming modern power systems into low-inertia and weak-grid networks, where frequency and voltage no longer respond independently to active and reactive power disturbances. Under such conditions, the conventional decoupled paradigm, which assigns active power mainly to frequency regulation and reactive power mainly to voltage control, may overlook cross-channel interactions and lead to inaccurate security assessment. To address this problem, this paper proposes an analytical framework for quantifying frequency-voltage coupling strength and assessing the corresponding joint security region in renewable-dominated power systems. First, a quasi-steady-state linearized coupling model is established by integrating source-side regulation, load response, and network impedance characteristics. Based on this model, a frequency-voltage coupling matrix is derived to explicitly map active-reactive power disturbances to coupled frequency and voltage deviations. Then, the relative gain array theory is introduced to construct a dimensionless interaction factor for evaluating coupling strength and identifying strongly coupled buses. Furthermore, the coupled response is reformulated as a linear mapping problem, through which equal-power disturbance boundaries are transformed into frequency-voltage response trajectories and regions. Finally, prescribed frequency and voltage security limits are inversely mapped to the active-reactive power input space to obtain a joint input power perturbation security region. Case studies show that frequency-voltage coupling is more pronounced at load and passive connection buses and in weak-grid areas. Stronger coupling rotates the response trajectory, deforms the coupled response region, and compresses the security input power disturbance region.
To achieve efficient resource utilization and harmless disposal of shield tunnel muck, a shield tunnel section of Nanjing Metro Line 6 was selected as the engineering case. A novel grouting material was prepared by replacing all bentonite and part of the sand with on-site muck, and the effects of multi-component substitution and mix proportions on grout performance were investigated. For large-scale, high-dimensional multi-objective optimization, a mix proportion optimization method based on multi-criteria decision-making was proposed, integrating NSGA-II genetic algorithm optimization with entropy-weighted TOPSIS selection to determine the recommended baseline mix. The field application benefits of the proposed material were further evaluated from multiple perspectives, including pollution characteristics. The results indicate that the adsorption of clay particles in the muck improves the electric double-layer compression effect within the system, thereby generating electrostatic repulsion between particles that densifies the microstructure and significantly reduces the bleeding rate; the adhesion-filling effect also enhances the compressive strength. The recommended on-site baseline mix proportion is as follows: water-to-binder ratio of 0.888, binder-to-sand ratio of 0.738, muck-to-water ratio of 0.521, and fly ash-to-cement ratio of 1.223. With this mix, the bleeding rate is only 0.81%; the setting time is shortened by 3 h compared with the conventional on-site grouting material, the 28 d UCS increases by approximately 10%, and the migration and release of heavy metals in the muck are effectively inhibited. Producing 1 m3 of this grout reduces costs by 26.1%, while recycling 1 m3 of muck yields a carbon-reduction benefit of 57.45 kg CO2e. Field tests further confirm its superior performance in controlling ground settlement and segment uplift.
