Aircraft Vibration Research Articles

Nonlinear metamaterial enabled aeroelastic vibration reduction of a supersonic cantilever wing plate

The violent vibration of supersonic wings threatens aircraft safety. This paper proposes the strongly nonlinear acoustic metamaterial (NAM) method to mitigate aeroelastic vibration in supersonic wing plates. We employ the cantilever plate to simulate the practical behavior of a wing. An aeroelastic vibration model of the NAM cantilever plate is established based on the mode superposition method and a modified third-order piston theory. The aerodynamic properties are systematically studied using both the timedomain integration and frequency-domain harmonic balance methods. While presenting the flutter and post-flutter behaviors of the NAM wing, we emphasize more on the pre-flutter broadband vibration that is prevalent in aircraft. The results show that the NAM method can reduce the low-frequency and broadband pre-flutter steady vibration by 50%–90%, while the post-flutter vibration is reduced by over 95%, and the critical flutter velocity is also slightly delayed. As clarified, the significant reduction arises from the bandgap, chaotic band, and nonlinear resonances of the NAM plate. The reduction effect is robust across a broad range of parameters, with optimal performance achieved with only 10% attached mass. This work offers a novel approach for reducing aeroelastic vibration in aircraft, and it expands the study of nonlinear acoustic/elastic metamaterials.

Investigating Flow-Induced Vibration by Regarding the Alignment of Flow Modes and Structural Modes

In this work, a modal matching approach is developed to investigate the impact of the spatial correlation of wall pressure fluctuations on structural vibration and its role in suppressing flow-induced vibration in aircraft. The modal matching method defines the wavelength ratio between the convection wave and the flexural wave to capture the spatial characteristics of both the flow mode and the structural mode. In comparison to conventional methods such as the finite element method and analytical method, the proposed modal matching approach allows for obtaining the vibration response in the spatial–wavenumber domain. To validate the spatial correlation effect on structural vibrations obtained with the modal matching approach, a wind tunnel test was conducted to measure flow-induced vibrations. The calculated spatial–wavenumber data for flow-induced vibrations reveal that the crests and troughs of the vibration velocity alternate periodically as the wavelength of the wall pressure fluctuations changes. At the resonance frequency, a vibration velocity trough can be observed when the spatial correlation of wall pressure fluctuations aligns with the structural mode. Additionally, the concept of resonance independence of flow-induced vibrations is introduced to describe the phenomenon where the most severe structural vibration, determined by the matching value between the aerodynamic mode and the structural mode, does not always occur at the resonance frequency. The modal matching approach effectively suppresses structural vibration by utilizing the spatial correlation of wall pressure fluctuations, offering a new perspective on controlling flow-induced vibrations.

Vibration analysis and control of aircraft landing systems using proposed neural controllers

Nowadays, landing gears used in aircraft are the basic systems that carry the weight of aircraft systems and provide them to move on the ground. During the landing of aircraft, big and sudden vibrations occur as soon as the wheels come into contact with the runway. This situation negatively affects human safety, comfort and also the life of the landing gear system. Therefore, it is important to keep this vibration at permissible levels. This paper presents an improved vibration control method that controls the amplitudes of vibrations of landing systems. This paper presents proposed vibration control method that controls the angular position variables of the landing gear mechanism to control the vibrations occurring during landing. For different runway conditions and 200 km/h landing speed, the angular joint variables of the landing gear mechanism links are controlled using standard controller and a proposed neural controller structure. The simulation results are shown that the proposed neural controllers have better performance at vibration control of landing systems during landing.

Optimization of landing gear under consideration of vibration comfort for civil aircraft

Purpose This study aims to investigate the design and optimization of landing gear buffers to improve the landing-phase comfort of civil aircraft. Design/methodology/approach The vibration comfort during the landing and taxiing phases is calculated and evaluated based on the flight-testing data for a type of civil aircraft. The calculation and evaluation are under the guidance of the vibration comfort standard of GB/T13441.1-2007 and related files. The authors establish here a rigid-flexible coupled multibody dynamics finite element model of one full-size aircraft. Furthermore, the authors also implement a dynamic simulation for the landing and taxiing processes. Also, an analysis of how the main parameters of the buffers affect the vibration comfort is presented. Finally, the optimization of the single-chamber and double-chamber buffers in the landing gear is performed considering vibration comfort. Findings The double-chamber buffer with optimized parameters in landing gear can improve the vibration comfort of the aircraft during the landing and taxiing phases. Moreover, the comfort index can be increased by 25.6% more than that of a single-chamber type. Originality/value To the best of the authors’ knowledge, this study first investigates the evaluation methods and evaluation indexes on the aircraft vibration comfort, then further conducts the optimization of the parameters of landing gear buffer with different structures, so as to improve the comfort of aircraft passengers during landing process. Most of the current studies on aircraft landing gear have focused on the strength and safety of the landing gear, with very limited research on cabin vibration comfort during landing and subsequent taxiing because of the coupling of runway surface unevenness and airframe vibration.

Validation of a turboprop cabin demonstrator

Turboprop aircraft should be improved as they are more environmentally friendly aircraft compared to turbojet aircraft but noise and vibration are often too high for passengers. A simple and uncomplicated way to carry out experiments is using a demonstrator. To determine whether the demonstrator represents the reality, it must be validated. In this project, real flights were first conducted in a turboprop aircraft. During two 70-minute flights, 94 subjects answered questions about symptoms, mood or comfort levels related to noise and vibration, among other things. In the next step, investigations will be carried out in the demonstrator under the same conditions as the real flights. Both results will be compared with each other. If the data from the demonstrator corresponds to that of the real flights, the demonstrator is considered to have been successfully validated. The requirement for this is that the demonstrator data lies within the confidence intervals of the results from the real flights. The aim is to validate a full-scale on-ground demonstrator of a regional turboprop aircraft cabin that will be used for multiple tests like subject tests and comfort evaluation, composite materials and structures, systems and energy consumption.

Vibration Response Analysis of a Main Landing Gear System for High In-Flight Dynamic Loadings

The prediction of aircraft vibrations is necessary for identifying possible design optimization points of each on-board system. In this context, the authors investigated the dynamic response of a Main Landing Gear (MLG) conceived for a fast helicopter when exposed to flight vibrations arisen from the engine propellers. The research activity falls within the Racer program of Clean Sky 2 framework, which aims to develop a novel high-speed rotorcraft. Relying on Airbus Helicopters operative requirements, this paper deals with the numerical procedure description of the MLG dynamic response assessment (resonance frequencies, accelerations amplitude, generalized masses) with respect to the expected in-flight vibrations levels. In particular, an equivalent combined load (sine and random spectrum) based on the normal modes and the corresponding modal mass distribution is employed for investigating the relevant effects on structural endurance. The central themes focus on the possible numerical modelling strategies and vibration loads analysis, which led safely to the qualification. This method could allow for performing sensitivity dynamic analyses in case of further design stiffness or weight changes.

Computational Investigation of a Flexible Airframe Taxiing Over an Uneven Runway for Aircraft Vibration Testing

<div>Ground vibration testing (GVT) is an important phase of the development, or the structural modification of an aircraft program. The modes of vibration and their associated parameters extracted from the GVT are used to modify the structural model of the aircraft to make more reliable dynamics predictions to satisfy certification authorities. Due to the high cost and the extensive preparations for such tests, a new method of vibration testing called taxi vibration testing (TVT) rooted in operational modal analysis (OMA) was recently proposed and investigated by the German Institute for Aerospace Research (DLR) as alternative to conventional GVT. In this investigation, a computational framework based on fully coupled flexible multibody dynamics for TVT is presented to further investigate the applicability of the TVT to flexible airframes. The time domain decomposition (TDD) method for OMA was used to postprocess the response of the airframe during a TVT. The framework was then used to examine the impact of the taxiing speed, shock absorber damping coefficient, and bump geometry on the outcome of the computational TVT. It was found that higher taxiing speed does not necessarily mean a better quality TVT, and one must find the optimal speed using the computational framework presented herein. A higher shock absorber damping coefficient was found to increase the amplitude of the response during the TVT without significantly impacting the extracted modes and their frequencies. Also, the quality of the TVT was found to be inversely proportional to the curvature of the bump cross section. The proposed TVT computational framework is validated against the normal modal analysis technique and certain experimental data.</div>

The vibration reduction index allocation method for aircraft vibration comfort design

A two-level vibration reduction index (VRI) allocation method is proposed to guide aircraft vibration comfort design. Firstly, using grey theory and transfer path analysis, the reduced total vibration at the target point is allocated to vibration contributions from main sources. Secondly, the VRI assigned to each dominant contribution is allocated to dampers at critical locations according to generalized costs. Finally, the method is demonstrated through cockpit vibration comfort design. The effective loads transferred from engine mounts are reduced by over 49.17%, and the effective accelerations from these loads through seat-floor dampers are decreased by over 53.95% for a discomfort-free experience.

Vibration response analysis of a two-stage vibration isolation system for large airborne equipment

PurposeThis paper aims to propose a two-stage vibration isolation system for large airborne equipment to isolate aircraft vibration load.Design/methodology/approachFirst, the vibration isolation law of the discrete model of large airborne equipment under different damping ratios, stiffness ratios and mass ratios is analyzed, which guides the establishment of a three-dimensional solid model of large airborne equipment. Subsequently, the vibration isolation transfer efficiency is analyzed based on the three-dimensional model of the airborne equipment, and the angular and linear vibration responses of the two-stage vibration isolation system under different frequencies are studied.FindingsFinally, studies have shown that the steady-state angular vibration at the non-resonant frequency changes little. In contrast, the maximum angular vibration at the resonance peak reaches 0.0033 rad, at least 20 times the response at the non-resonant frequency. The linear vibration at the resonant frequency is at least 2.14 times the response at the non-resonant frequency. Obviously, the amplification factor of linear vibration is less than that of angular vibration, and angular vibration has the most significant effect on the internal vibration of airborne equipment.Originality/valueThe two-stage vibration isolation equipment designed in this paper has a positive guiding significance for the vibration isolation design of large airborne equipment.

Prestressed Multilayer Structures from Polymer Composites for Vibration and Noise Control of Aircraft

Prestressed Multilayer Structures from Polymer Composites for Vibration and Noise Control of Aircraft

Evaluation of aircraft random vibration under roughness excitation during taxiing

The assessment of runway smoothness or roughness is intimately tied to the vibrational response of aircraft during taxiing. In this study, employing the pseudo excitation method (PEM) based on random vibration analysis, we unearthed the relationship between the random vibrations of five distinct aircraft types and runway irregularities. Initially, we established two three-dimensional (3D) models of aircraft taxiing vibration and derived the response output under roughness excitation. Subsequently, we employed MATLAB to analyze the power spectral characteristics of the vibrational response in different parts of the aircraft. Lastly, we examined the effects of taxiing speed, aircraft type, runway roughness, and lift on the aircraft's vibration. Our findings indicate that the distribution of vibration power spectral density (PSD) exhibits multiple peaks, correlating with the degrees of freedom of the aircraft. We further note that the frequency that aligns most closely with the response peak should be the focus of investigation. High-frequency excitation impacts the pilot and nose landing gear more significantly than the passenger and main landing gear. Absent the consideration of lift, increased taxiing speed amplifies the impact of roughness excitation on aircraft taxiing safety. Larger aircrafts are more sensitive to long-wave roughness. With lift in consideration, all aircraft types exhibit a speed sensitivity to vibration, which should be the primary concern in runway roughness evaluations.

Vibration Response Law of Aircraft Taxiing under Random Roughness Excitation

Understanding the vibration response patterns of aircraft taxiing under runway roughness excitation is crucial for aircraft design and runway performance evaluation. In this paper, we establish pavement roughness models for both asphalt and concrete surfaces, taking into account their unique structural characteristics. We construct a six-degrees-of-freedom aircraft model using multi-rigid-body system dynamics theory and employ the pseudo-excitation method to examine the influence of pavement roughness types on the steady vibration response of aircraft taxiing at constant speeds. Furthermore, we analyze the non-stationary vibration response patterns of aircraft during takeoff and landing taxiing using the method of instantaneous frequency response function with space frequency. Lastly, we explore the effect of stochastic structural parameters on aircraft vibration response using the Monte Carlo method. Our findings reveal that the roughness power spectrum differs between asphalt and concrete pavements, and the established roughness models in this paper demonstrate a strong fit (R2 > 0.95). The type of pavement roughness has a relatively minor impact on the power spectral density distribution of the aircraft vibration response, suggesting that the same roughness model can be used for both asphalt and concrete pavements when high accuracy is not required. The power spectral density distribution of aircraft vibration response varies across different motion attitudes, with the vibration response during landing being significantly larger than that during takeoff. Among the aircraft structural parameters, the randomness of the sprung mass has the most substantial effect on the aircraft vibration response, potentially causing the variation coefficient of dynamic load on the front landing gear to exceed 0.11. Tire stiffness comes next, which can lead to the variation coefficient of dynamic load on the main landing gear reaching 0.07. The results have a guiding role in optimizing aircraft structure design and ensuring pavement performance.

Improving Accuracy of Airfoil Trailing Edge Noise Models with Turbulent Flow Anisotropy for Cambered Airfoil

In turbomachinery applications such as wind turbines, and aircraft airframe, flow-induced noise and vibration are significant noise sources. There are five main types of airfoil self-noise, with trailing edge noise (TEN) being the most dominant high-frequency broadband noise. The Amiet TE noise model is a low-order analytical model that requires the surface pressure (SP) near the trailing edge for TEN modelling. The accuracy with which the SP spectrum is calculated determines the accuracy of the TEN modelling. The SP spectrum is calculated using the physics-based TNO-Blake (TB) Model and its recently produced improved version. Most studies have focused on using the TB model for symmetric airfoil, with little attention paid to modelling the TEN of cambered airfoil. We use TB model variants on the SP spectrum prediction in this study, which are enforced with the Amiet TEN model for far-field noise modelling. The SP models' source comes from a high-fidelity Large-Eddy-Simulation simulation (LES) based on CABARET method. The simulation is carried out using the NACA65410 airfoil with a chord length of 0.3m and an angle of attack of 0,2, 4, 6, and 8 degrees at a Reynolds number of 5.2e5. The SP spectrum and velocity spectrum used to improve the TEN model's accuracy for cambered airfoil.

Vibration Reduction Design and Test of UAV Load Radar

It is challenging to design complex structures and calculate their dimensions only on the basis of theory. This issue was resolved efficiently by the FEM. Using the applicable test, the mechanical properties of the materials used in the damper are estimated, effectively guiding the design of the device and boosting its vibration-reducing performance. A large-load unmanned aerial vehicle (UAV) airborne radar is the subject of this research article. According to particular use case, vibration dampers for the radar-mounting platform are designed using passive vibration isolation technology to reduce aircraft vibration transmission to the radar. A conference paper has already presented prior research on the same topic. Earlier research confirmed the vibration-isolating efficacy of the T-type rubber isolator, which can greatly improve the operational conditions of the airborne radar. In contrast, earlier studies relied more on experimental validation and did not use numerical simulations. This research’s primary objective is the development of a T-type rubber isolator, whose vibration reduction performance is proven using FEM and experiments. Utilizing a suitable simulation analysis method to investigate the vibration reduction of an unmanned aerial vehicle’s (UAV) airborne component is a crucial technical task. By comparing multiple material models, a more precise model for characterizing rubber was developed.

Comprehensive Engineering Frequency Domain Analysis and Vibration Suppression of Flexible Aircraft Based on Active Disturbance Rejection Controller.

The crash of an aircraft with an almost vertical attitude in Wuzhou, Guangxi, China, on 21 March 2022, has caused a robust discussion in the civil aviation community. We propose an active disturbance rejection controller (ADRC) for suppressing aeroelastic vibrations of a flexible aircraft at the simulation level. The ADRC has a relatively simple structure and it has been proved in several fields to provide better control than the classical proportional-integral-derivative (PID) control theory and is easier to translate from theory to practice compared with other modern control theories. In this paper, the vibration model of the flexible aircraft was built, based on the first elastic vibration mode of the aircraft. In addition, the principle of ADRC is explained in detail, a second-order ADRC was designed to control the vibration model, and the system’s closed-loop frequency domain characteristics, tracking effect and sensitivity were comprehensively analyzed. The estimation error of the extended state observer (ESO) and the anti-disturbance effect were analyzed, while the robustness of the closed-loop system was verified using the Monte Carlo method, which was used for the first time in this field. Simulation results showed that the ADRC suppressed aircraft elastic vibration better than PID controllers and that the closed-loop system was robust in the face of dynamic parameters.

Fuzzy control of a landing gear system with oleo-pneumatic shock absorber to reduce aircraft vibrations by landing impacts

PurposeThe purpose of this paper is to control a landing gear system with an oleo-pneumatic shock absorber with the fuzzy controller.Design/methodology/approachThe landing gear system with an oleo-pneumatic shock absorber is modeled mathematically. A fuzzy controller is designed for reducing aircraft vibrations. Stroke velocity and main mass velocity parameters were used to decide variable gas pressure with the fuzzy controller.FindingsThe fuzzy controller, designed according to stroke velocity and main mass velocity, reduces aircraft vibrations by the landing impacts. The controller can provide strong robustness because it shows similar good performance for different descent speeds.Research limitations/implicationsThis study was carried out through simulations in a computer environment and has not been experimentally tested in a real environment. In addition, signal and measurement delays are not taken into account. In future models, the effects of these signal delays can be added, and the controller can be tested on a real model.Originality/valueIn this study, to the best of the authors’ knowledge, for the first time, the gas pressure for the landing gear system using an oleo-pneumatic shock absorber was controlled by a fuzzy controller that adjusts the stroke velocity and the main mass velocity. Although the oleo-pneumatic shock absorber model contains high nonlinearities, the designed fuzzy controller gave successful results as robust.

A new look at the Birnbaum–Saunders regression model

AbstractMotivated by problems of vibration in commercial aircraft that caused fatigue in materials, Birnbaum and Saunders (1969a,b) proposed a family of two‐parameter distributions to model failure time due to fatigue under cyclic loading and the assumption that failure follows from the development and growth of a dominant crack. This article is cited in at least 930 scientific articles. After the work of Birnbaum and Saunders (1969a,b), the Birnbaum–Saunders model is one of the most important and used models for analyzing lifetime data. Regression analysis is commonly used when covariates are involved in the life test. In this article, we provide a comprehensive review of Birnbaum–Saunders regression models based on parameterizations of the Birnbaum–Saunders distribution in terms of central tendency measures. In particular, we propose a new and straightforward reparameterization of the Birnbaum–Saunders distribution based on an approximation to its mode. In contrast to the original parameterization, the proposed parameterization leads to regression coefficients directly associated (approximately) with the mode of the response variable. We discuss the estimation of model parameters by maximum likelihood, hypothesis testing, and residual analysis. Furthermore, we show that the proposed regression model and other parameterized Birnbaum–Saunders models have the same log‐likelihood function estimate when no covariates are used to model the shape parameter. Additionally, we propose a simple script in the R software to solve numerical problems in the Fisher information matrix for some values of the shape parameter. Finally, we present and explore two empirical applications to compare the investigated regression models.

Whole-Body Vibration Experienced by Pilots, Passengers and Crew in Fixed-Wing Aircraft: A State-of-the-Science Review

Before the coronavirus pandemic, there were 4.5 billion passenger movements by aircraft annually; this is expected to recover after the pandemic. Despite the large numbers of flights per year, there are few reports of whole-body vibration in fixed-wing aircraft. This paper reports a review of literature intended to collate reported data related to exposure to whole-body vibration. Following a filtering process to select relevant articles, a literature search elicited 26 papers reporting measurements of vibration. These included measurements made in the cockpit and cabin, and for pilots, crew and passengers. Aircraft included military, commercial and passenger aircraft, turboprops, jets and piston prop aircraft. There was a lack of consistency on measurement method and analysis, and few met the full requirements of ISO 2631-1. However, measurements showed significant components of vibration at frequencies largely attenuated by the ISO frequency weighting filters, but have been shown to be important in terms of human vibration perception. Propeller aircraft showed strong tonal components in vibration frequency spectra. There was also a significant effect of the flight phase in the vibration exposure. It is recommended that the body of literature related to human response to whole-body vibration on aircraft is augmented with further studies in order to understand in-flight experiences and to optimize human health, wellbeing, comfort and performance.

Low-frequency bandgaps and sound isolation characteristics of a novel Helmholtz-type phononic crystal

In recent years, the vibration and noise reduction performance of military aircraft has become an important index to measure its performance. In order to solve the problem of low-frequency noise generated by military aircraft, a novel Helmholtz two-dimensional phononic crystal is constructed in this paper. The structure adopts maze-shaped air channel and adds rigid oscillators. On condition that the lattice constant is 62 mm, the lower limit of the first band gap is reduced to about 15 Hz. The structure has four complete band gaps in a range of 0–500 Hz, specifically, they being 15.223–17.464 Hz, 107.46–200.68 Hz, 231.18–310.68 Hz, and 341.14–404.49 Hz. In addition, the sound reduction index of the structure reaches 25 dB at 15 Hz, and two peaks higher than 150 dB appear at about 107 Hz and 231 Hz. which shows distinct sound insulation capability in the low-frequency range. It has engineering significance in controlling the low-frequency noise in the aircraft cabin. The cause of the band gap is explored by analyzing the vibration mode and sound pressure field. The “spring-oscillator” of the structure model is established by the method of “Mechanical-acoustic analogy”. The finite element method and transfer matrix method are used to calculate the upper limit and the lower limit of the first band gap. It is shown that for the first gap of the structure, the results obtained by the two methods are similar, which indicates the correctness of the model hypothesis. Secondly, the effects of structural parameters such as the lattice constant, the length of the air channel and the oscillator material on the first band gap are investigated by finite element method and equivalent model method. It is obtained that the increase of the length of air channel and lattice constant will reduce the lower limit of the first band gap, with other structural parameters remaining unchanged. Moreover, the increase of the density of the oscillator material can effectively reduce the upper limit and lower limit of the second band gap, which further reveals the essence of the formation of the band gap of the structure and verifies the accuracy of the equivalent model. This study provides theoretical support for low frequency noise control and broadens the design of low-frequency phononic crystals.

АДАПТИВНЫЙ ПСЕВДОГРАДИЕНТНЫЙ АЛГОРИТМ ОБНАРУЖЕНИЯ СИГНАЛОВ НА ФОНЕ КВАЗИПЕРИОДИЧЕСКИХ ПРОЦЕССОВ

Some parameters of many objects in practical situations are quasi-periodic, or there is a noticeable repeatability with random variations. Such parameters can be represented by random quasiperiodic processes, for example speech signals, aircraft engine noise and vibration, etc. From time to time, against the background of this process, special structures (signals) may appear that arise due to the influence of internal or external factors on the object, for example, impacts of external objects. In this article an autoregressive model is used to represent quasi-periodic processes. It is assumed that the detected signals interact additively with the background (process) and have a known shape. The detection algorithm is based on the classical likelihood ratio. In this case, the statistics of the decision rule is represented through the compensation of the background ‘to the point’, that is, through the subtraction from the observation at the point of its forecast for all other observations. The parameters of the background model may be unknown; therefore, an adaptive pseudogradient algorithm for optimizing the parameters of the background compensator is applied. In the case of homogeneous processes, the compensator converges to the optimal one, constructed with known background parameters, and in the case of inhomogeneity, compensation and detection are carried out that are close to optimal. The results of statistical tests of the developed algorithm are presented.