Turbine blades (TBs) are widely regarded as the “jewel in the crown” of modern aeroengines, operating under extremely high temperatures, pressures, and loads. Investment casting (IC) remains the primary manufacturing process for these critical components. However, the increasingly intricate geometries of modern TBs, characterized by thin walls, curvature, twist, and multi-cavity hollow structures, pose persistent challenges in dimensional accuracy, defect control, and microstructural consistency. This review presents a comprehensive overview of recent advances in TB IC from the perspectives of process mechanisms, modeling, and intelligent manufacturing. The fundamental mechanisms governing multiscale deformation and dimensional evolution across the entire IC workflow are systematically examined, including die compensation strategies, wax/shell behaviors, and thermomechanical interactions during directional solidification and subsequent constraint removal. Progress in modeling methodologies is then reviewed, with particular attention to geometric modeling fidelity, the roles of process parameters and boundary conditions, and the evolution of multiphysics fields associated with stress, deformation, and solidification. Furthermore, emerging intelligent manufacturing paradigms are discussed, highlighting artificial intelligence (AI) assisted technologies for predicting temperature fields, deformation, and defects in TB casting, together with the role of 3D printing in enabling rapid and flexible fabrication of sacrificial tooling to support advanced internal cooling architectures for next-generation aeroengines. Overall, this work provides a systematic synthesis of the current research progress in TB IC and offers a systematic reference for future studies in this field.
The paper proposes a novel general definition of coherency among power system devices of any type. The proposed approach is thus not limited to synchronous machines. With this aim, the paper shows that coherency can be formally based on the difference in the complex frequency of the current injections of any two devices electrically connected to the same grid. The proposed definition is model-agnostic, making it general and suitable for modern power systems composed of a heterogeneous mix of technologies. The paper also provides a systematic analytical procedure to study the properties that specific device models must satisfy to be coherent. Time-domain simulations are conducted in three case studies whose results illustrate the ability of our definition to evaluate coherency among any type of device.
A precise estimation of the Rate of Change of Frequency (RoCoF) is crucial for secure power system operation. In fact, RoCoF is strictly related to the amount of the available physical and/or virtual inertia of the system and the severity of the active power unbalance following a disturbance. For this reason, it is widely exploited in different protection systems, e.g., Anti-Islanding, Under Frequency Load Shedding (UFLS) and wide-area protection systems. The new paradigm of modern power systems, with a low-inertia and converter-based generation assets, is increasing the transient severity, making the frequency and the RoCoF estimation more complex and less precise for the actual devices. This work addresses this issue by proposing a numerically robust approach based on concepts inherited from differential geometry and fluid mechanics. The proposed approach is then tested with high-sampling real experimental measurements and used to develop a faster control logic for a RoCoF-based UFLS control scheme. The proposed approach provides information to protections regarding the nature of the contingency which can be used to improve its response.
This paper examines defending the power grid against load-altering attacks using electric vehicle charging. It proposes to preventively segment the cyber infrastructure that charging station operators (CSOs) use to communicate with and control their charging stations, thereby limiting the impact of successful cyber-attacks. Using real German charging station data and a reconstructed transmission grid model, a threat analysis shows that without segmentation, the successful hack of just two CSOs can overload two transmission grid branches, exceeding the N-1 security margin and necessitating defense measures. A novel defense design problem is then formulated that minimizes the number of imposed segmentations while bounding the number of branch overloads under worst-case attacks. The resulting IP-MILP bi-level problem can be solved with an exact column and constraint generation algorithm and with heuristics for fast computation on large-scale instances. For the near-real-world Germany case, the applicability of the heuristics is demonstrated and validated under relevant load and dispatch scenarios. It is found that the simple scheme of segmenting CSOs evenly by their installed capacity leads to only 23% more segments compared to the heuristic optimization result, suggesting potential relevance as a regulatory measure.
The increasing demand for atomic and close-to-atomic scale manufacturing of advanced optical components poses significant challenges for polishing hard and brittle materials such as silicon carbide (SiC) ceramics. Photocatalysis-assisted polishing has demonstrated high efficiency and surface quality in planar processing, while its application to complex surfaces remains limited. To address this issue, a five-axis photocatalysis-assisted polishing system is developed to enable the machining of complex geometries. Two motion generation strategies are proposed based on this developed platform, namely a dimension-reduced motion generation approach for rotational-symmetrical surfaces and a homogeneous-transformation-based motion generation approach for freeform surfaces. Polishing experiments on complex surfaces are conducted and the results demonstrate stable material removal and satisfactory surface quality, with a surface roughness of 0.22 nm in Sa. The study shows that the proposed motion generation strategies, combined with photocatalysis-assisted polishing, provide an effective approach for high-precision finishing of complex SiC ceramic surfaces.
