As transoceanic flight missions become more common, different aircraft types face an increased risk of emergency ditching. The complex hydrodynamic loads during ditching can severely threaten aircraft structural integrity and passenger safety. Therefore, considering ditching under various scenarios, this study selects typical commercial, transport, and specialized amphibious aircraft fuselages as research objects. A 6-DOF motion simulation method was used, combining the VOF and global moving mesh method. The motion characteristics of the three fuselage types were investigated during ditching at five initial horizontal velocities. The effects of bottom forces were examined by analyzing pressure distributions at 40 monitoring points. The conclusion of this paper analyzed the motion differences of the different fuselages, discussed the evolution of negative pressure at the bottom of the fuselages and its influence on the motion process. The findings of this study provide valuable references for the design of transoceanic aircraft.

Abstract The breathing oscillation of cross parachutes has received limited attention in previous studies, although it represents a physically important transitional state between stable inflation and severe deployment instabilities such as canopy collapse or inversion. In this study, the inflation dynamics and breathing oscillation behavior of a small cross parachute are investigated using a three-dimensional fluid-structure interaction simulation based on the Arbitrary Lagrangian-Eulerian (ALE) framework. The aerodynamic response and structural deformation of the canopy are analyzed under two representative inflow velocities of 20 m/s and 40 m/s to evaluate the influence of inflow conditions on unsteady loading characteristics. The results show that at 20 m/s the parachute undergoes a smooth inflation process and reaches a quasi-steady post-inflation state, with the axial aerodynamic force stabilizing at approximately 101.2 N. At 40 m/s, pronounced breathing oscillations are observed during both the inflation and post-inflation stages, characterized by periodic expansion and contraction of the canopy. The axial force exhibits large-amplitude oscillations with a mean value of 444.6 N, a maximum of 650.4 N, and a minimum of 293.4 N. The time-averaged force accounts for about 94% of the mid-oscillation level, indicating a clearly asymmetric oscillatory behavior. Further analysis of velocity fields demonstrates that this response is closely related to a strongly unsteady wake, in which a periodically varying axial jet and recurrent low-velocity and recirculation regions develop downstream of the canopy. These results elucidate the fluid-structure interaction mechanisms responsible for breathing oscillation and establish a theoretical basis for evaluating the aerodynamic response and deployment stability of cross parachutes under high inflow velocities.

This study addresses the safety and attitude stability issues associated with the separation of internal loads from missile warheads under tractor parachute drag by employing a dynamic nested mesh method combined with a penalty function to numerically simulate the separation process, accounting for collisions between the load and the adapter within the warhead. In contrast to previous studies, this method shifts the aerodynamic computation during the separation process from steady-state to transient computation, and the collision calculation from characteristic point estimation to precise node-surface computation, achieving a coupled solution of the unsteady flow field and multi-body collisions with enhanced fidelity. Firstly, the calculation method employed in this study is introduced in detail. Subsequently, a simulation model of the separation process was developed, and the flow field and motion characteristics of the missile warhead, internal load, and tractor parachute during separation were analyzed. The research method employed in this study provides novel insights for the engineering development of air separation systems.

With the increasing number of trans oceanic flight missions, different types of aircraft have the possibility of emergency water landings, and the complex hydrodynamic loads during the water landing process will greatly threaten the structural safety of the aircraft and the passenger’s lives. Therefore, this paper selects three typical fuselage as the object of study. The CFD method was used to conduct research on it, and the finite volume method and overall dynamic mesh technology were employed. The conclusion of this paper analyze the differences in motion and force of each fuselage, the impact of velocity changes on the motion trends during calm water ditching was analyzed by changing the initial forward speed.

ABSTRACT Bolted joints are widely used in aerospace composite structures for assembly and maintenance, but stress concentration and bearing damage can limit reliability. The behavior of joints in hybrid plain‐satin woven glass fiber‐reinforced polymer (GFRP) laminates remains insufficiently understood, particularly when countersunk fasteners, insert‐containing designs, joint geometry, and hygrothermal conditioning are coupled. This study investigates single‐shear bolted joints in such laminates using seven room‐condition configurations and one conditioned counterpart. The effects of bolt‐head geometry, complete insert‐containing joint design, aperture‐based edge‐distance ratio (), and conditioning were evaluated through load–displacement response, nominal bearing strength, secant stiffness, failure morphology, and micro‐CT observations. For insert‐free joints, protruding‐head bolts provided higher peak load, nominal bearing strength, and displacement tolerance than countersunk‐head bolts. The insert‐containing designs increased peak load for both bolt types, especially countersunk joints, but reduced nominal bearing strength because the laminate aperture and nominal bearing area were enlarged. Their stiffness effect depended on bolt‐head geometry: secant stiffness increased in protruding‐head joints but decreased in countersunk‐head joints. For insert‐containing countersunk joints, gave the highest peak load among the tested ratios, indicating a non‐monotonic edge‐distance effect. Hygrothermal conditioning reduced the peak load by 19.8%, while the conditioned insert‐containing countersunk joint retained a stable post‐peak load‐carrying plateau. Overall, joint performance is governed by coupled interactions among bolt‐head geometry, insert‐mediated confinement, aperture size, edge distance, and environmental degradation.

To address the structural deformation and mechanism jamming frequently observed in critical linkages during retraction and extension of door-coupled landing gear systems, this study proposes a rigid–flexible coupled dynamic modeling approach. A representative landing gear system was studied, and a high-fidelity rigid–flexible multibody dynamics model was developed based on a conventional rigid-body framework. The left linkage, which was prone to failure, was modeled as a flexible finite element component, while the remaining parts were treated as rigid bodies. A multibody dynamics method based on nonlinear finite element was adopted, incorporating elastoplastic constitutive relations and Lagrange constraint equations. Two materials, ultra-high-strength 300M steel and high-strength 7075-T6 aluminum alloy, were evaluated to investigate the influence of structural stiffness on critical linkage stress and door kinematics during deployment. Results showed that maximum stress occurred at the hinge joint, identified as the critical region for strength assessment. The peak stress for 300M reached approximately 168 MPa, about 8.4% higher than that of 7075-T6. However, 7075-T6 exhibited lower stress oscillation frequency and superior damping performance, which helped suppress high-frequency vibration. Material selection had negligible influence on door centroid displacement, velocity, and opening angle, and the motion trajectories remained highly consistent.

In the field of aerospace, the structural integrity analysis of the revolution body, such as those dominated by missiles and rockets, is becoming increasingly important. However, addressing the water entry problem in water-gas two-phase structures presents a complex fluid-structure interaction challenge. The intricate shapes and internal configurations of these structures further complicate the analysis of water and structural loads. In this paper, a multi-stage revolution model comprising internal and external compartments is established, based on the SPH-FEM (coupling Smoothed Particle Hydrodynamics method and the Finite Element Method) numerical calculation method. The study examines water inflow scenarios for revolution structures under three different working conditions. Various results, including velocity, overload, pressure, cross-sectional force, and stress, are analyzed. The comparison results indicate that the maximum bending moment in the multi-stage revolution body typically occurs near the support connection between the internal and external compartments. As the water entry height and pitching angular velocity increase, the water load grows larger, the center of action shifts backward, and the maximum bending moment in the critical cross-section rises, leading to potential collisions between the internal and external compartments.

This study addresses critical engineering challenges associated with safe stratospheric deployment of tethered balloons through the development of a spring-damper mass element for tether dynamics based on the Arbitrary Lagrangian-Eulerian (ALE) method. Integrated with the Newton-Euler formulation, a comprehensive multibody dynamic model is established for stratospheric tethered balloon systems. The proposed ALE cable element’s computational accuracy and efficiency are systematically validated via three numerical benchmarks: cable pendulum, a constant-period pendulum with time-varying cable and a suspended cable with a moving lumped mass. Focusing on characteristic operational regimes, this investigation examines balloon dynamics during station-keeping and ascent phases, elucidating coupling mechanisms within the winch-tether-balloon multibody system. The presented methodology enables rigorous evaluation of dynamic response characteristics for tethered balloon systems operating in complex wind environments during both ascent and station-keeping missions. Derived analytical conclusions provide substantive references for engineering deployment and airworthiness certification of stratospheric tethered systems. Finally, a novel tether tension control strategy is proposed, which achieves stable tension regulation through Proportional-Integral-controlled thrust vector modulation. The effectiveness of the controller is validated under step and sinusoidal wind disturbances, demonstrating a significant improvement in the overall safety margin of the system.

Aircraft structural strength test is the most important verification method of aviation structure at present, and it is an indispensable and important link in the aircraft development process. At present, the measurement method of aircraft structural strength test is relatively simple, and only limited and discrete response data can be obtained, and it is difficult to obtain information during the whole process and the whole field of the test, which limits the comprehensive analysis and processing of data. In view of this, this paper proposes a data-driven virtual-real fusion algorithm to construct a digital twin model suitable for structural strength test by fusing simulation data and test data, so as to achieve high-precision prediction of the mechanical properties of test objects. The algorithm is divided into two stages: pre-training and real-time prediction. In the pre-training stage, the simulation data is used to train the Particle Swarm Optimization Random Forest (PSO-RF) model. In the real-time prediction stage, based on the error between the trained PSO-RF model and the experimental data, the Radial Basis Function Multi-Fidelity Surrogate (RBF-MFS) model is trained. Finally, by fusing the PSO-RF model and the RBF-MFS model, a digital twin model of the test object is constructed. The results show that the accuracy of the model on the test set is basically about R2=0.97, and the calculation time on the 330 000 grid nodes is only 0.8 s, and the prediction error of the model is less than 10% for the danger area of the wing box segment, which meets the needs of practical engineering applications and provides a reference for the digitization of aircraft structural strength tests.

Abstract In order to obtain the tensile properties of metal honeycomb sandwich structures with single-sided panel damage and single-sided panel / honeycomb core damage after bonding repair, tensile tests and finite element simulations were carried out. Firstly, the failure mode and load displacement curve of the repaired structure are obtained through the test. Compared with the tensile strength of the intact structure, the strength recovery rates of the two repaired structures are 99.4% and 94.4%, respectively. Secondly, the corresponding finite element model is established. Combined with the test results, the engineering effectiveness of the model is verified. Finally, through the research of experiment and finite element simulation, it is shown that the bonding repair technology in this paper can be fully applied to the engineering practice of civil aircraft maintenance.

A phase-field framework is proposed for simulating intralaminar mixed-mode fracture in fiber-reinforced composites. Within this framework, the LaRC04 failure criteria serve as activation indicators for the different failure modes, which affect the anisotropic phase-field formulation through the effective structural tensor and the crack driving force. Crack initiation and propagation are governed by a unified phase-field model. When multiple failure mechanisms are activated simultaneously, the crack propagation direction emerges naturally as a result of their combined energetic contributions, rather than being restricted to a single limiting direction. From this perspective, intralaminar mixed-mode fracture is interpreted as an evolving interaction between competing failure mechanisms, with the crack propagation direction adjusting continuously as a consequence.Analytical expressions for the critical crack initiation stress and the crack bandwidth are derived, revealing a theoretical decoupling between the material failure strength and the phase-field length scale. The theoretical predictions are verified numerically. The proposed model is further assessed through a set of representative benchmark problems, including open-hole tension, single-edge-notched tension, tow-steered laminates, and asymmetric three-point bending. The results demonstrate that the proposed approach retains the computational efficiency of a single phase-field formulation while providing a physically consistent description of competing intralaminar failure mechanisms.

In recent years, with the rapid development of the aerospace industry, precise airdrop and recovery system have gradually received more widespread attention. Due to the main working environment of the parafoil in the troposphere, the air flow situation is relatively complex. Therefore, it is necessary to study the aerodynamic performance of parafoil in complex flow field environment. In this paper, the incoming flow is decomposed into two factors: speed and direction, and the influence of continuous change of incoming flow direction on the aerodynamic performance of parafoil is mainly considered. Using the method of computational fluid dynamics, the finite volume method is used to discretize the Reynolds time-averaged stress equation. In this paper, the spatial discretization of 16 m2 parafoil is carried out by overset grid. The aerodynamic performance of parafoil is solved when the incoming flow direction changes 100°, 10°and 1° per second, and compared with the results of steady calculation. The results show that with the increasing of the change rate of the incoming flow direction, the lift and drag coefficient of the parafoil will gradually increase, reaching the maximum at 100°per second. When the rate of change of direction is 10°/s and 1°/s, the lift and drag coefficient are almost the same as those in the steady state. When the rate of change of direction reaches 100°per second, the lift coefficient and drag coefficient increase significantly. It can be proved that when the direction of the incoming flow changes slowly, the aerodynamic performance of the parafoil gliding will not be affected in any way.

This study investigates the aerodynamic performance degradation of semi-rigid parafoils caused by canopy bulging during inflation. Wind tunnel tests and numerical simulations, including Computational Fluid Dynamics (CFD) for rigid parafoil model and Fluid-Structure Interaction (FSI) for semi-rigid parafoil model, were conducted to analyze the aerodynamic effects of flexible canopy deformation. Experimental and numerical results consistently show that canopy bulging in semi-rigid parafoils leads to a reduction in the lift-curve slope, decreasing from K1 = 0.044 to K2 = 0.032. This degradation is primarily attributed to two mechanisms: (1) increased curvature near the leading edge of the upper surface slows the upper-surface flow and elevates static pressure; and (2) localized flow separation on the lower surface reduces static pressure beneath the canopy. These effects jointly diminish the pressure differential between the upper and lower surfaces of the parafoil, thereby reducing lift. Moreover, the semi-rigid parafoil shows greater susceptibility to large-scale flow separation at high angles of attack. These findings provide critical insights into the design and optimization of parafoil-based recovery systems in aerospace applications.

In aeronautical engineering, the structural safety and seakeeping are of principal importance in the assessment of amphibious aircraft during planing and landing in wave. However, the structural integrity of the wings is significantly challenged by slamming loads generated in such environments. Therefore, it is crucial to comprehensively understand the transient dynamic response of the wing structure under hydrodynamic excitation. To systematically investigate the structural dynamic performance of the wing, a high-fidelity two-way fluid-structure interaction (FSI) numerical framework is established in this study. The variations in aircraft body loads across different planing velocities and wavelengths were systematically evaluated, and their consequent effects on wing structural vibrations were elucidated. The kinematic and dynamic characteristics of the aircraft are analyzed in detail through its pitch angle, accelerations, structural response, and stress distributions. The water-exit phenomenon at high planing velocities and short-wavelength encounters are both observed to result in water-entry slamming. In these cases, a sudden increase in transient vertical acceleration is observed. Furthermore, free vibrations of the wing are directly induced by such slamming loads. As a result, significant large-amplitude variations in wingtip displacement are generated. Concurrently, the number of stress cycles is significantly increased by the high-frequency and large-amplitude vibrations of the wing. Such vibrations are identified as the fundamental cause of damage within the wing structure.

The deployment of ships into water involves complex multi-body dynamics and fluid–structure coupling phenomena, which are inherently interdisciplinary. To effectively analyze the motion and force variations of the parachute rope during the ship’s entry into the water, the calculation of the ship’s water immersion is divided into three phases. In the airdrop phase, the 9-DOF multi-body dynamics equations governing the parachute system of the ship are formulated to determine the forces acting on the parachute and the ship’s attitude. In the water entry phase, a numerical model of ALE fluid–structure coupling is developed for the ship’s entry into the water, with LS-DYNA employed to calculate the attitude and water load of the ship during and after entry. Finally, the motion trajectory of the ship during the immersion phase is substituted into the 9-DOF dynamic equation derived in the airdrop phase to obtain the force curve of the parachute rope throughout the immersion phase. The work presented in this paper offers valuable insights for the comprehensive motion analysis and parachute rope strength validation of the airdrop system for ships.

Current passive anti-rollover systems exhibit inadequate adaptability to complex operational environments. Additionally, due to unidentified critical factors driving rollover incidents during landing, the design of active anti-tipping systems for airdrop remains constrained. Given the foregoing circumstances, this paper divides the landing impact process of the vehicle into the airbag cushioning stage and the rigid collision stage. In the airbag cushioning stage, a vertical impact test bench and a fluid–structure interaction (FSI) model is built up to obtain the terminal impact velocity when the airbag’s touching down speed is set as around 8 m/s. An oblique impact test bench and a dynamic model are proposed to investigate the influence of terminal sideslip angles and impact velocities on the vehicle’s roll/pitch stability during the rigid collision phase. Experimental and numerical analyses reveal that the peak overload during the airbag cushioning stage reaches approximately 11 g while the terminal impact velocity in this stage is around 2 m/s. In the rigid collision stage, higher initial descent velocities amplify the peak roll angles and significantly compromise the roll stability. Notably, adjusting the terminal sideslip angle from 90° to 0°/180° triples the critical horizontal velocity threshold from 5.3 m/s to 14.7 m/s which markedly enhances the vehicle’s stability. To address this, an active sideslip angle control system activated at a 250 m altitude is developed to align the vehicle’s horizontal velocity vector with its longitudinal axis to nearly 0°/180° and thus improves the roll/pitch stability. This study establishes a technical foundation for the design of a highly reliable anti-rollover device for the airdrop vehicle.

The unpredictability of crack initiation and propagation in aircraft structures with multiple site damage (MSD) and widespread fatigue damage (WFD) presents significant challenges for maintaining the structural integrity of aircraft under fatigue loading. This paper presents a probabilistic analysis model for riveted lap joints with MSD. The probabilistic analysis model leverages a secondary customization of ABAQUS, enabling parametric modeling of penetration cracks with varying lengths. In this model, the stochastic processes of crack initiation, propagation, and failure are simulated through a Monte Carlo framework, incorporating the theories of fracture mechanics and fatigue statistics. In addition, a group of riveted lap joint tests are carried out to verify the accuracy of the calculation results. The simulated results are in good agreement with the mean experimental fatigue life. However, the model underestimates the dispersion observed in the experimental data in the current study, primarily due to the lack of extensive experimental data needed for further calibration. Overall, the developed model can capture the complex, interdependent mechanisms of fatigue damage in riveted lap joints with MSD.

This study investigates the compression-after-impact (CAI) performance of carbon fiber-reinforced polymer (CFRP) laminates containing pre-embedded delamination and subjected to low-velocity impact (LVI). Experimental tests were conducted on various laminate configurations, including intact, delaminated, and bolted-repaired specimens. Bolted repairs were found to significantly enhance compressive strength across all configurations, with improvements ranging from 5.8% to 12.2% compared to undamaged specimens, highlighting their effectiveness in restoring load-bearing capacity. Experimental analysis also showed that delamination depth critically affected CAI strength, with near-surface delaminations causing the greatest performance degradation. Furthermore, stacking sequence architecture-especially the distribution of 0 degrees unidirectional and woven fabric plies-proved more influential than overall symmetry in determining residual strength. A finite element model was developed to complement the experiments by combining Puck failure theory for intralaminar damage with a cohesive zone model (CZM) for interlaminar delamination. The simulation results showed excellent agreement with the experimental data, confirming the accuracy and reliability of the numerical framework. Based on this validated approach, the model was further applied to investigate the effects of delamination size at mid-thickness in symmetric laminates and stacking sequence asymmetry. The results successfully captured the transition from global to localized buckling as delamination size increased and reproduced the strength degradation observed in reversed asymmetric configurations (A- and B-), which were affected by unfavorable surface ply layouts. These outcomes demonstrate the effectiveness of the model in evaluating impact-induced damage and CAI performance in composite laminates.

This study investigates the failure behavior of open-hole Variable-Stiffness Composite (VSC) laminates. A fiber placement path was fitted based on the distribution of principal stresses, and an anisotropic and quasi-brittle phase-field model was developed to predict the damage evolution in VSCs. First, a direction-dependent crack surface density function was introduced into the unified phase-field framework to capture the anisotropic characteristics during crack propagation. Then, a phase-field driving force and damage constitutive relationship suitable for mixed failure modes were constructed, enabling the model to analyze coupled failure mechanisms. By implementing an alternate solution scheme and a layered element structure in the UEL subroutine, the phase-field model was numerically solved using ABAQUS. To verify the accuracy and applicability of the model, damage and failure analyses were conducted on single-edge-notched plates made of straight-fiber and curved-fiber composites, respectively. The results indicate that the model can reasonably predict the mechanical behavior and crack propagation paths of composite laminates. Finally, the model was used to simulate the tensile failure and damage evolution of open-hole plates with constant and variable stiffness. The results show that the predicted crack paths agree well with experimental observations, and the tensile strength of the variable stiffness plate is significantly improved compared to that of the constant stiffness plate.

With the development of the low - altitude economy and the growth of the small unmanned aerial vehicle (UAV) market, rotary wing UAVs have limitations in flight speed and stability, while tilt rotor aircraft, with their unique advantages, have become a research hotspot. Thus, it’s important to design a tilt rotor UAV with excellent performance and stability. This paper used commercial software for structural strength and aerodynamic numerical simulations, conducted wind tunnel force measurement experiments, and designed a tilt servo rotor coordinated heading enhancement control strategy and an airspeed - based tilt transition control strategy. Through these theoretical methods and simulations/tests, it was obtained that the designed twin tail beam tilt rotor UAV shows good maneuverability, wind resistance, and smooth mode transition without altitude loss, verifying the effectiveness of the control strategy and the reliability of the overall layout. This paper will give a reference to the design of small UAVs and composite thrust technology aircraft in the future work.