Elliptical ring distribution probability-based damage imaging method for complex aircraft structures

In engineering applications, the robustness and effectiveness of damage diagnostic imaging for guided wave-based structural health monitoring could be affected by the complexity of structures. In this study, an elliptical ring distribution probability-based diagnostic imaging algorithm is proposed to mitigate this effect using the estimated wave velocity and damage index. This algorithm improves the ability of damage localization by modifying the defect distribution probability of probability-based diagnostic imaging. The elliptical ring distribution probability of the presence of defect is used for each sensing path in the algorithm. The width of the elliptical ring distribution probability is determined by the range of estimated wave velocity. The amplitude of the elliptical ring distribution probability is determined by the damage index. The damage location is determined by the cross region of different elliptical rings for different sensing paths. The capability of the algorithm is validated by identifying damages at different locations on a complex composite fuselage panel. The results show that the proposed algorithm can identify a single damage accurately and it can identify multiple damages effectively as well

Arresting-Cable System for Robust Terminal Landing of Reusable Rockets

Recent successful recovery techniques for rockets require that rockets maintain a vertical configuration with zero vertical and lateral velocities; otherwise, landings may fail. To relax this requirement, a new active-arresting system (inspired by the arresting gears used on aircraft carriers) is proposed herein to achieve a robust landing, even if the rocket deviates from the target position or has notable residual velocities and inclinations. The system consists of four deployable onboard hooks above the rocket’s center of mass, an on-ground apparatus containing four arresting cables forming a square capture frame, and four buffer devices to actively catch and passively decelerate the landing rocket. To catch the rocket, the capture frame was controlled by servo motors via a simple proportional–derivative controller. After catching, the buffer devices generate decelerating forces to stop its motion. A flexible multibody model of the proposed system was built to evaluate its robust performance under various combinations of multiple uncertainties, such as noise measurement, time delay in the motor, initial conditions, and wind excitation. Using a quasi-Monte Carlo method, hundreds of deviated landing cases were generated and simulated. The results confirmed the robustness of the proposed system for achieving successful terminal landings

Modeling and Simulation of Arresting Gear System with Multibody Dynamic Approach

The arresting dynamics of the aircraft on the aircraft carrier involves both a transient wave propagation process in rope and a smooth decelerating of aircraft. This brings great challenge on simulating the whole process since the former one needs small time-step to guarantee the stability, while the later needs large time-step to reduce calculation time. To solve this problem, this paper proposes a full-scale multibody dynamics model of arresting gear system making use of variable time-step integration scheme. Especially, a kind of new cable element that is capable of describing the arbitrary large displacement and rotation in three-dimensional space is adopted to mesh the wire cables, and damping force is used to model the effect of hydraulic system. Then, the stress of the wire ropes during the landing process is studied. Results show that propagation, reflection, and superposition of the stress wave between the deck sheaves contribute mainly to the peak value of stress. And the maximum stress in the case of landing deviate from the centerline is a little bit smaller than the case of landing along centerline. The multibody approach and arresting gear system model proposed here also provide an efficient way to design and optimize the whole mechanism

Baseline Signal Reconstruction for Temperature Compensation in Lamb Wave-Based Damage Detection

Temperature variations have significant effects on propagation of Lamb wave and therefore can severely limit the damage detection for Lamb wave. In order to mitigate the temperature effect, a temperature compensation method based on baseline signal reconstruction is developed for Lamb wave-based damage detection. The method is a reconstruction of a baseline signal at the temperature of current signal. In other words, it compensates the baseline signal to the temperature of current signal. The Hilbert transform is used to compensate the phase of baseline signal. The Orthogonal matching pursuit (OMP) is used to compensate the amplitude of baseline signal. Experiments were conducted on two composite panels to validate the effectiveness of the proposed method. Results show that the proposed method could effectively work for temperature intervals of at least 18 °C with the baseline signal temperature as the center, and can be applied to the actual damage detection

A multibody dynamic model of the drilling system with drilling fluid

This article is intended to present a multibody dynamic model of the drilling system, consisting of drillstring and drilling fluid. The drillstring is a complex rigid–flexible coupling system, including rigid bodies, Euler–Bernoulli beam elements, constraints and dynamic loads, and its dynamic model is established using the absolute nodal coordinate formulation. The drilling fluid, composed of internal, annulus, and under-bit fluids, is modeled as one-dimensional compressible fluid; the relative flow of the drilling fluid is modeled using the Arbitrary Lagrangian–Eulerian description; the force of the drillstring acting on the drilling fluid is introduced through the drilling fluid transport motion; meanwhile, the reaction force acting on the drillstring is taken as an external load. The contact between the drillstring and drilling fluid is simulated based on Hertz contact theory, and the rock penetration model is built based on the rock-breaking velocity equation. Based on this model, the coupled vibration of the drillstring and the effects of the drilling fluid flow rate and density on the drilling process are investigated through several examples