IJAV site directory











Published Articles


The Volume 21, No 3, September 2016



Display the cover:

Display the full text:

Display the Editorial file:

http://dx.doi.org/10.20855/ijav.2016.21.1E81

«« Back to the List of the Articles



Investigation on a High-Frequency Controller for Rotor BVI Noise Alleviation

Alessandro Anobile, Giovanni Bernardini and Massimo Gennaretti


https://doi.org/10.20855/ijav.2016.21.3416


Among the several sources of acoustic annoyance produced by rotorcraft in operating conditions, blade-vortex interactions (BVIs) capture the interest of much of the current research. This paper deals with the reduction of BVI noise from helicopter main rotors by application of the active twist rotor concept (ATR), exploiting smart materials for twisting blades through higher-harmonic torque loads. An optimal, multi-cyclic, control approach is applied to identify the control law driving the ATR actuation during the occurrence of severe BVI events. Numerical predictions are obtained through a computational tool that is able to predict the aeroelastic response of the rotor blades and the emitted noise in arbitrary steady flight conditions. The approach for the control law identification is described and numerical results concerning aeroelastic and aeroacoustic performance of the controlled rotor are presented to assess the cbox{proposed} methodology.


Display the first page:

Display the full text:





Reliability-Based Optimization of Coupled Structural-Acoustic System with Random Parameters

Xiaojun Wang, Yunlong Li, Zhiliang Ma and Zhiping Qiu


https://doi.org/10.20855/ijav.2016.21.3417


Structural noise is an important factor that endangers aircraft fatigue life and flight safety. It also has a negative effect on aircraft stealth performance and noise navigability. An optimal design of a structure-acoustic coupled system is an effective way to reduce noise and vibration. Due to the uncertainties that exist in the structural and acoustical parameters, the traditional deterministic optimization method may be unfeasible when the parameters are subject to fluctuations. This means that when the parameters are uncertain, the results obtained from the deterministic optimization method may be beyond their constraints. This paper proposes to apply the stochastic reliability-based optimization method to the design optimization of the coupled structural-acoustic system with random parameters. A comparison between the results of the stochastic reliability-based method, the safety factor-based method, and the deterministic method show that the first two methods can effectively consider the dispersion of the parameters.


Display the first page:

Display the full text:





Frequency Identification of Flexible Hub-Beam System Using Control Data

Xie Yong, Liu Pan, and Cai Guo-Ping


https://doi.org/10.20855/ijav.2016.21.3418


This paper studies the parameter identification of a flexible hub-beam system based on the input-output data. Firstly, the first-order approximation coupling (FOAC) model is presented. Then, active position control for the system is studied using optimal tracking control theory. Finally, the observer/Kalman filter identification (OKID) and eigensystem realization algorithm (ERA) method are applied to identify the frequency of the system. In the simulations, the effectiveness of the identification method presented in this paper is verified by comparing the identification results of several different external excitations. Simulation results indicate that the anticipated position of the system may be traced by the proposed controller, and the residual vibration of the beam may be suppressed as well. The frequency of the system can be effectively identified using OKID and ERA. It is feasible and effective to identify the frequency using the control data.


Display the first page:

Display the full text:





Exact Solution for a Free Vibration of Thermoelastic Hollow Cylinder Under GNIII Model

Ibrahim A. Abbas


https://doi.org/10.20855/ijav.2016.21.3419


The exact analytic solutions are obtained with the use of the eigenvalue approach for a free vibration problem of a thermoelastic hollow cylinder in the context of Green and Naghdi theory (GNIII). The dispersion relations for the existence of various types of possible modes of vibrations in the considered hollow cylinder are derived in a compact form and the validation of the roots for the dispersion relation is presented. To illustrate the analytic results, the numerical solution of various relations and equations has been carried out to compute the frequency, thermoelastic damping and frequency shift of vibrations in a hollow cylinder of copper material with MATHEMATICA and MATLAB software.


Display the first page:

Display the full text:





The Effect of Crack Geometry on the Nondestructive Fault Detection in a Composite Beam

Sadettin Orhan, Murat Lüy, M.Hüsnü Dirikolu, and G.Mustafa Zorlu


https://doi.org/10.20855/ijav.2016.21.3420


Defects in structures may be inherited from materials and manufacturing or they develop during service. Defects may cause catastrophic failure, which is why their detection and classification are important issues. Many aspects of defects have already been dealt with, but with wider applications of non-destructive testing methods to composite materials. However, the effect of arbitrary and random defect geometry on the applicability of these methods has been overlooked. In order to investigate this issue, this study carries out a free vibration analysis of a specially orthotropic cracked cantilever beam that was manufactured by Pultrusion. A new crack model, unlike the widely known V-shaped crack, is introduced and the effect of crack depth on the natural frequency is investigated, both experimentally and numerically. The results obtained from both the new- and the V-shaped models are compared with each other, and it is revealed that the results are not sensitive to the geometry change.


Display the first page:

Display the full text:





Fault Diagnosis For Exhaust Fan Using Experimental Predictive Maintenance Method

Hamdi Taplak, Emrah Kurt and Mehmet Parlak


https://doi.org/10.20855/ijav.2016.21.3421


Unexpected machine failures cause decreasing of production and increasing of cost so that predictive maintenance methods have importance day by day. The main principle of predictive maintenance methods is to decide maintenance time of machines by monitoring machine performance during operations and after that resolving the failure when the machines stop. In this study, failures of exhaust fan system used in Afsin-Elbistan B Thermal Power Plant were diagnosed by using predictive maintenance method rely on vibration analysis. It has been periodically measured from totally four points on the bearings of fan and motor with vibration analyzer. Identified failures on the system have been respectively removed with analysis of measurements. After all failures have been removed, it has been seen that vibration values decreased when it had been measured again from four points mentioned before. With using the predictive maintenance method, failures can be identified before the failures cause negative results whereby both unnecessary machine stops can be prevented and cost of operation can be decreased.


Display the first page:

Display the full text:





Dynamic Analysis of Draft Gear and Draft Pad of Freight Wagon due to Localized Defects using FEM

Sachin S. Harak, Satish C. Sharma and Suraj P. Harsha


https://doi.org/10.20855/ijav.2016.21.3422


The present work investigates the effect of a crack on the modal frequency of a draft pad. Initially, the first five mode shapes of a healthy draft pad and the first seven mode shapes of healthy draft gear considering compressed draft pads are determined using the finite element approach. A mathematical model of the draft pad is formulated to predict the effect of the crack on its modal frequency. A semi-elliptical shaped crack is modelled in the lateral and longitudinal direction of the draft pad. It is observed that if the crack lies in the zone of minimum modal displacement, then the frequency drop is minimal, and if the crack lies in the zone of maximum modal displacement, then the frequency drop is significant. Various damage scenarios are simulated by varying the width and aspect ratio of the crack in order to identify its effect on the modal frequency. It is seen that if the aspect ratio is varied while the crack's width is maintained constant, then the frequency drop is linear, whereas if the crack's width is varied while the aspect ratio is maintained constant, then the frequency drop is parabolic. This study provides a tool for monitoring exciting frequencies of draft gear and shows how each modal frequency is affected by the crack due to parameters like aspect ratio, crack width, and crack location/orientation.


Display the first page:

Display the full text:





Effects of Young's Modulus on Disc Brake Squeal using Finite Element Analysis

Ali Belhocine and Nouby M. Ghazaly


https://doi.org/10.20855/ijav.2016.21.3423


This paper is concerned with the disc brake squeal problem of passenger cars. The objective of this study is to develop a finite element model of the disc brake assembly in order to improve the understanding of the influence of Young's modulus on squeal generation. A detailed finite element model of the whole disc brake assembly that integrates the wheel hub and steering knuckle is developed and validated by using experimental modal analysis. Stability analysis of the disc brake assembly is conducted to find unstable frequencies. A parametric study is carried out to look into the effect of changing Young's modulus of each brake's components on squeal generation. The simulation results indicate that Young's modulus of the disc brake components plays an important role in generating the squeal noise.


Display the first page:

Display the full text:





Acoustic Characteristic Analysis of Prestressed Cylindrical Shells in Local Areas

Lu-yun Chen and Yong Liu


https://doi.org/10.20855/ijav.2016.21.3424


The influence of prestress on dynamic responses and acoustic radiation for thin cylindrical shells is analyzed in this study. The strain-displacement equation of cylindrical shells with prestress in local areas is established based on the Fl"{ugge theory. The structural-acoustic radiation formulation for prestressed cylindrical shells in local areas is instituted by using the variational principle. A numerical analysis is then carried out. The numerical results are validated by comparing the influence of prestress on acoustic radiation power and directivity. This study shows that prestress significantly affects the dynamic characteristics of cylindrical shells.


Display the first page:

Display the full text:





Nonlinear Vibrations and Chaos in Rectangular Functionally Graded Plates with Thermo-mechanical Coupling

Seyedeh Elnaz Naghibi and Mojtaba Mahzoon


https://doi.org/10.20855/ijav.2016.21.3425


We analyze the nonlinear dynamics of a simply supported, rectangular, and functionally graded plate in terms of a newly derived coupled system of thermo-elasticity and energy equations, which is then expanded here in derivations and explored for chaotic responses through a parameter study in the state space. The plate properties vary linearly in thickness. Three-dimensional stress-strain relations are considered in general case and nonlinear strain-displacement relations are deployed to account for the plate's large deflection. A lateral harmonic force is applied on the plate, and there is a heat generation source within it and the surfaces are exposed to free convection. By integrating over the thickness, four new thermal parameters are introduced, which together with the mid-plane displacements constitute a system of seven partial differential equations. These equations are changed into ordinary differential equations in time using Galerkin's approximation and solved by using the 4th order Runge-Kutta method. Finally, a parameter study is performed and the appropriate conditions resulting in chaotic solutions are determined by using numerical features such as the Lyapunov exponent and power spectrum.


Display the first page:

Display the full text:





Response of a Cylindrical Shell with Finite Length Ring Stiffeners

Andrew J. Hull and Geoffrey R. Moss


https://doi.org/10.20855/ijav.2016.21.3426


This paper derives a spatial domain wave propagation solution of a cylindrical shell that contains periodically spaced ring stiffeners. Previous work in this area has modeled the stiffeners as having a very short or very long length. This paper models the stiffeners as finite length inclusions with forces that have spatial extent in three-dimensions. Furthermore, there is a well-defined separation distance between each stiffener. The new model uses Donnell shell equations with the stiffener forces applied in three-dimensions using Heaviside step functions. These equations of motion are orthogonalized in both the angular and longitudinal directions resulting in a double fixed index matrix equation. These indices can be varied which yields a set of double indexed matrix equations that are written together as a single global matrix. This global matrix can be solved, which results in a solution to the system displacements. Two specific external loading cases are investigated and convergence criteria are discussed. One of the models is verified with a comparison to finite element analysis.


Display the first page:

Display the full text:





Aeroelastic Analysis of Unrestrained Aircraft Wing with External Stores Under Roll Maneuver

Seyed Ahmad Fazelzadeh, Amir Hosein Ghasemi, and Abbas Mazidi


https://doi.org/10.20855/ijav.2016.21.3427


This paper discusses our study on the flutter of an unrestrained aircraft wing carrying a fuselage at its semispan and arbitrary placed external stores under roll maneuver. Maneuver terms are combined in the governing equations which are obtained using the Hamilton's principle. The wing is represented by a classical beam and incorporates bending-torsion flexibility. Theodorsen unsteady aerodynamic pressure loadings are considered to simulate the aeroelastic loads. The Galerkin method is subsequently applied to convert the partial differential equations into a set of ordinary differential equations. Numerical simulations are validated against several previous published results and good agreement is observed. In addition, simulation results are presented to show the effects of the roll angular velocity, fuselage mass, external stores mass, and their locations on the wing flutter of an aircraft in free-flight condition. Parametric studies show that the predicted flutter boundaries are very sensitive to the aircraft rigid body roll angular velocity, fuselage mass and external stores mass and locations.


Display the first page:

Display the full text:





Research on Fault Feature Extraction of Rubbing Rotor Based on Vector-Bispectrum Energy

Zhang Chao


https://doi.org/10.20855/ijav.2016.21.3428


Signals collected from dual-channel sensors contain abundant fault characteristic information when the rub-impact fault occurs in a rotor system. As a combination of bispectrum and vector-spectrum analisys, vector-bispectrum analysis can achieve an effective elimination of Gaussian noise and accurate analysis on quadratic phase coupling in signals by combining dual-channel information. However, it has been found in the slight rubbing experiment that part of the fault information is lost by simply using the bispectrum or vector-bispectrum method. In order to resolve this problem, a new fault feature extraction approach for the rubbing rotor based on the energy index of vector-bispectrum is proposed and used in the experimental test to obtain typical characteristics of the full annular rub-impact fault. It is shown that this novel method of feature extraction inherits the advantages of vector-spectrum analysis. The features of the rub-impact fault based on the energy index of vector-bispectrum has been extracted successfully, and the result of classification through SVM illustrates that the extracted features are very noticeable, and the proposed method can comprehensively reflect nonlinear information of the rubbing rotor.


Display the first page:

Display the full text:





Performance of Sound Insulation in Buildings - A Case Study

Marcus Vinicius Manfrin de Oliveira Filho and Paulo Henrique Trombetta Zannin


https://doi.org/10.20855/ijav.2016.21.3429


The purpose of this study is to recognize usual facade sound insulation problems that affect a construction's acoustical quality by measuring the facade's sound insulation. Thirteen different situations were evaluated through in situ measurements in Curitiba, Brazil. By measuring buildings in different locations with constructive materials and different designs, this research found that the performance of the majority of evaluated facades did not reach the minimum proposed by both Brazilian and Portuguese standards. These results indicate that the sound insulation quality in Brazilian buildings is low and is mainly due to constructive imperfections and the use of materials with unfavorable acoustical properties.


Display the first page:

Display the full text:





Dynamic Feature Extraction for Speech Signal Based On MUSIC and Modulation Spectrum

Han Zhiyan and Wang Jian


https://doi.org/10.20855/ijav.2016.21.3430


A novel dynamic feature extraction algorithm is proposed to help improve speech recognition robustness in noise environmental conditions. Owing to the modulation spectrum having time-frequency agglomeration performance, according to different reflections in the modulation spectrum for interference and speech signals, we first calculate the Multiple Signal Classification (MUSIC) spectrum and then get the modulation spectrum. We then filter the modulation spectrum signal. For the filter signal, use a 32 frames signal is used as a processing unit to get the modulation spectrum energy vector. This reveals the close correlation between the speech signal frames and can well reflect speech dynamic characteristics. Finally, the cepstrum coefficients are extracted as the feature parameter. It not only adequately reflects speech dynamic characteristics, but also has lower sensitivity for the speech environment. The effectiveness of the feature is discussed in view of the class separability and speaker variability properties. We evaluated the feature under different kinds of noise (white noise, pink noise, street noise, and panzer noise) and different signal-to-noise ratios (-5~dB, 0~dB, 5~dB, 10~dB, and 15~dB). The experimental results show that the novel feature has good robustness and computational efficiency under low signal-to-noise ratios and plays a very good foreshadowing role in latter speech research.


Display the first page:

Display the full text:





«« Back to the List of the Articles