Aerospace

Adhesively bonded carbon-fiber-reinforced polymer (CFRP) joints offer efficient load transfer and weight-saving potential in aerospace structures. The simple geometry of single-lap joints (SLJs) makes them useful for examining bond durability, although the effects of hygrothermal aging on their performance have not been sufficiently investigated. This research systematically integrates moisture absorption experiments, mechanical testing, finite element modeling (FEM), and deep neural network (DNN) modeling to provide a comprehensive analysis of moisture absorption behavior, strength degradation, and the evolution of failure modes within the adhesive layer. Initially, three types of adhesives were aged under various hygrothermal aging conditions to investigate their moisture absorption behavior and mechanical performance after aging. The tensile strength and modulus of the adhesives decreased linearly with increasing moisture uptake. In addition, hygrothermal aging tests were conducted on SLJs. Results demonstrated a significant reduction in joint shear strength during aging, accompanied by a transition in failure mode from cohesive to interfacial. Subsequently, a hygrothermally coupled FE model was developed using the experimental data and combined with a cohesive zone model to simulate joint strength evolution. The FE model achieved a calculation error within 5%. To address the high computational cost associated with finite element analysis of hygrothermal aging in SLJ structures and to enhance the physical interpretability of data-driven models, a novel prediction strategy was introduced. A three-stage serial neural network model was constructed using experimental and simulation data, with the quadratic stress criterion and power-law criterion embedded as physical constraints. Compared to unconstrained models, this physics-constrained neural network exhibited superior prediction accuracy and stability. The proposed method offers a valuable reference for the design and evaluation of the durability of CFRP bonded structures.

In time-marching simulation of airborne wind energy systems (AWESs), the tether is usually discretised into a series of lumped masses (i.e., nodes) connected by spring and damper elements. There is no consensus on the appropriate number of nodes for AWES applications, although it is known that using more nodes than necessary is computationally costly. In this work, we examine the trim solutions of a fixed-wing aircraft connected to the ground by a 500 m tether. A successive difference metric is proposed to quantify the convergence rate of the trim solutions as more nodes are added. We then compare this gain in accuracy to the simulation time and memory usage by plotting their Pareto fronts. Results reveal that using 6–8 tether nodes (i.e., 7–9 segments) is sufficient. Compared to using 15 nodes, 8 nodes keep the successive difference metric below 2%, run over 13 times faster, and require less than a quarter of memories. Beyond 8 nodes, the differential equation solver appears to enter a new stiffness regime, resulting in rapid rises in computation time and memory usage. These findings suggest that the conservative choices of 10–20 nodes can be relaxed, promising significantly lower computation costs in future studies.

Stall inception in high-speed counter-rotating axial compressors remains insufficiently understood because of the complex unsteady interactions between adjacent rotating blade rows. In this study, full-annulus unsteady Reynolds-averaged Navier–Stokes simulations combined with dense pressure monitoring, time-frequency analysis, and dynamic mode decomposition are used to investigate the evolution of a low-frequency stall precursor. A dominant disturbance at approximately 700 Hz in the stationary frame, corresponding to approximately 370 Hz in the rear-rotor-relative frame, is first detected in the rear-rotor region and subsequently appears at upstream and downstream monitoring stations. Its amplitude increases continuously over several rotor revolutions as the compressor approaches stall inception. Circumferential pressure signals exhibit an ordered phase progression around the annulus, indicating an annulus-scale, circumferentially organized disturbance rather than isolated local fluctuations. Dynamic mode decomposition associates the 370 Hz mode with periodic displacement and deformation of the rear-rotor shock system. Shock-position histories further reveal increasing oscillation amplitudes and circumferential phase shifts as stall is approached. Larger shock excursions are accompanied by stronger near-tip streamline deflection and precede substantial passage-blockage growth. These results identify the rear rotor as the earliest detected and primary amplification region of the precursor and support an interpretation involving progressively amplified shock-related unsteadiness and subsequent deterioration of passage flow capacity.