Journal of Theoretical and Applied Vibration and Acoustics
Volume:6 Issue: 1, Winter & Spring 2020

Estimation of remaining useful life (RUL) of rolling element bearings (REBs) has a major effect on improving the reliability in the industrial plants. However, due to the complex nature of the fault propagation in these components, their prognosis is affected by various uncertainties. This effect is intensified when the recorded data is offline, which is very common for many industrial machines due to the lower cost rather than the online monitoring strategy. In the present paper, in order to overcome the shortcoming of the feed-forward neural network (FFNN) in REBs prognostics, a new method for considering two main uncertainties (caused by the measurement and process noises) is proposed, in the presence of offline data acquisition. Inthe proposed method, the primary RUL probability distribution corresponded to each offline measured data is predicted, utilizing the outputs of trained FFNNs. Then, the predicted RUL distribution will become more robust in confronting the temporal changes, by taking into account the approval of pervious stage predictions to the present prediction. As a result, the overall probability distribution of REBs RUL and also its confidence levels (CLs) areobtained. Finally, the evaluation of the proposed method is performed byutilizing bearing experimental datasets. The results show that the proposed method has the capability to express the estimated RUL CLs in the offline data acquisition method, effectively. By providing a probabilistic perspective, the proposed method can improve the reliability of the asset and also the decision-making about the future of the industrial plants.

A study on the dynamics of cantilever orthotropic plates under spinning conditions is presented in this article. The governing equations of motions are containing the centrifugal and Coriolis effects. Two approximation methods, the extended Galerkin method, and extended Kantorovich method, are utilized for the investigation of the mathematical model. The verification of the obtained results is conducted by comparing two methods that show good agreement. Thisinvestigation is concentrated on the time histories and the natural frequencies of the system. First, using time responses, the effects of different types and numbers of admissible functions used in the approximate solution are discussed.Next, the results are obtained to explore the impact of dimensionless parameters like material, hub radius ratio, stagger angle, etc. on the modal characteristics of the spinning structures. The results of the simulations exhibit the importance of the proper choice of both type and number for trial functions. Furthermore, the selection of orthogonal functions can be vital to guarantee the convergence speed of an approximate solution. Further discussion on the modal characteristic reveals that in different stiffness ratios of the plate, the centrifugal stiffening rate caused by spinning motion is affected by rotational speed. Moreover, this stiffening rate is depended on setting angle and hub radius ratio. Finally, the last part of the paper is devoted to the forced  response analysis of the rotating plate.

Nonlinear localization approaches are used not only for detecting the exact location ofthe nonlinear elements in mechanical structures, but they are also exploited in order to find any possible flaws such as cracks in Structural Health Monitoring (SHM) applications. This study aims to develop a localization method to determine the location of localized nonlinearities in dynamic structures utilizing the experimentally measured data obtained from the base excitation test. The nonlinear element in the experimental set-up is represented by a pair of permanent magnets placed on both sides on the free end of the cantilever, and a pair of electromagnets placed with equal distances on both sides of thepermanent magnets. The combination of permanent and electromagnets create andapply nonlinear electromagnetic force on the free end of the cantilever beam.Hence, stepped-sine vibration tests are carried out using constant accelerationbase excitation to measure the response of the nonlinear system. The linearresponse of the system obtained from the low amplitude test is used to updatethe Finite Element (FE) model of the underlying linear system of the structure.Then, the developed approach utilizes the updated linear model along with themeasured nonlinear dynamics of the experimental set-up obtained usinghigh-amplitude excitation to determine the location of nonlinearity. The results of the experimental study are demonstrated to show the performance ofthe presented method.

In the current study, the mechanical performance of functionally graded oscillating micro-plates bonded with piezoelectric layers is examined using the modified couple stress theory. The modified couple stress theory contains a length scale parameter that considers the size-effects of micro-plates. The various modified shear deformation theories are employed to represent the displacement field of micro-plate, such as exponential, parabolic, hyperbolic, trigonometric, and fifth-order shear deformation theories. The properties of FG micro-plate, such as Young’s modulus, density, and length scale parameter, are assumed to vary smoothly and across the micro-plate thickness based on the Power-law model. The governing equations of motion are obtained by Hamilton's principle and solved by a theoretical approach under various boundary conditions. The accuracy of the proposed model is validated based on a comparison of the results with the accepted studies. Computational analysis is carried out to clarify the impacts of mechanical and geometrical variables on the natural frequencies of micro-plates.

Ultrasonic evaluation of austenitic welds has long been considered to be difficult. Recent studies in this field have made it possible to inspect these welds in many cases. However, the ultrasonic inspection methods of austenitic steels are more complicated and limited than those of ferrite steels. The difficulty in ultrasonic testing of austenitic welds stems from the presence of anisotropic and expanded grains, which are usually in the form of columnar structures. These grain structures lead to local anisotropy in these types of welds. This paper aims to create a more thorough understanding of the propagation of ultrasonic waves in austenitic welds produced by gas tungsten arc welding and shielded metal arc welding processes. For this purpose, special finite element models are developed for these two types of welds. In these finite element models, the orientation of the structural domains in welds is accounted for in both SMAW and GTAW processes. Results are validated by comparison of the numerical models with theoretical predictions and experiments already reported in the literature. The numerical models provide a better understanding of how ultrasonic waves propagate in anisotropic structures of SMAW and GTAW welds.

This paper presents the effect of a magnetorheological (MR) damper in the aircraft seat system on the body's biodynamic response for different flight maneuvers. For this purpose, discrete models 4 and 7 degrees of freedom for human modeling and the Bouc-Wen model are used to model MR damper. In various flight maneuvers, the changes in acceleration g are recorded and applied to the desired models after processing. Models used for the human body and the MR damper are compared for validation with previously published researches. The dynamic responses of the human body to these inputs without MR dampers and with an MR damper are investigated. The transmissibility[1] of the seat to the human body is used as a parameter that is common in these types of analyses. The results show that the use of MR dampers has a significant effect on reducing the transmissibility in maneuvers with a sudden increase in acceleration and also significant changes in the frequency at which maximum transmissibility is achieved.

In the present study, the free vibration and aeroelastic problems of rectangular cantilever plates with varying aspect ratio have been investigated. The classical plate theories based on the Kirchhoff hypothesis have been adopted to simulate the structural response of the plate. The Peter’s theory is selected to model the aerodynamic pressure on the plate due to the incompressible air flow. To discretize the partial deferential equations of the system, the ayleigh-Ritz method has been applied and by using Lagrange equations, the mass, damping, and stiffness matrices have been derived. Various numbers of mode shapes are used to show the convergence of the response of the system . The theoretical results including the natural frequencies and flutter speed have been evaluated by using the experimental data obtained from the ground vibration experiment carried out at Duke University. It has been shown that fora relatively low aspect ratio rectangular cantilever plate, using some techniques in Rayleigh–Ritz method leads to an improvement of the results for both the natural frequencies and flutter speed. This technique ends up having two sets of decoupled equations and consequently, the number of equations that have to be solved simultaneously is divided by two. This could lead to a reduction of computational time significantly.

The architecture of the Jaame mosque, being the most important place for gathering and worship in the Islamic world, is detailed to the finest of building elements. Several activities take place inside the Jaame mosque in separate or connected order. These activities are the performing prayers led by the Imam, the preaching speech and the recitation of some of theverses of the holy Quran. Considering that, it is determiningto study the acoustics of Jaame mosques and how architects constructed the space to promote the words of God; hence, this paper analyzes the acoustic qualities of Jaame Mosque of Yazd, as one of the architectural and historical masterpieces in Iran. The decorative brickwork used in conjunction with tiles and the muqarnases, karbandies, and squinches adorning the dome, iwan, and their adjacent spaces, appear to have significant effects on the quality of sound in the building. In this study, we simulated the volume and interior surface of the space and conducted calculations of the reverberation time using EASE. Reverberation time shows a downward trend from lowto high frequencies, and is controlled in low frequencies to produce a preferable acoustic experience. The median of reverberation time shows 4.32-seconds without muqarnases. Thistime reduces to 3.33-seconds with the proper arrangement of muqarnases, squinches under thedome and their distance from the sound source, as well as the brickwork decorations and the configuration of the mortar joints to remarkable effect. The results showed an appropriate distribution of sound throughout the mosque.

The mechanisms involved in the operation of the wall-mounted boilers are the primary source of noise pollution, which bothers users while operating. One of the most basic solutions is to control the amount of noise by using insulator materials. The material must have acoustic absorption characteristics and high heat resistance. In this study, four acoustic materials based on polymer resins, glass wool and stone, and jute fabrics that have good degradability in nature have been studied as noise control materials. Based on the physical and chemical properties of the acoustic insulating polymers, high noise absorption is generated and flammability is preserved at high temperatures too. The nature of acoustic absorption and high degradability is also noticeable in jute fabrics. For the shell sound control tests, several wall-mounted boilers have been used in this study, and the sound waves have been measured using a B&K 2260 measuring device. The overall rate of noise reduction in monolayer and blended double-layer insulators has been compared. Although the monolayer or double-layer insulators perform better than jute ones, the acoustic absorption standard of the wall-mounted boilers can also be achieved by using jute. Therefore, due to environmental conditions, the jute is approved as a sound insulator.

Thorough knowledge of the wind turbine (WT) dynamics is necessary to efficiently improve its design, operation, and maintenance. Due to the wind turbine's large size, there are difficulties in measuring and excitation of full-scale WTs in general modal tests. Because of the issue, the designers may rely on finite elements and numerical models. Nevertheless, by considering the advantages of operational modal analysis relative to the experimental modal analysis, it is an efficient way to understand the dynamics behavior of WT based on the actual operation installed turbine at the site. With regard to performing operational modal analysis and achieving acceptable results, proper test planning has great importance. Initially,in this article, test planning steps will be described for the studied WT's successful operation modal test. Then the modal analysis results will be revealed, and finally, the dynamic behavior of the WT will be discussed based on the modal results.

In this paper, the in-plane and out of plane free vibration of the Kirchhoff nano ultra-thin film are studied. To reveal the altering natures of natural frequencies in nano ultra-thin film, the film is modeled according to the general nonlocal theory. The film governing equations as well as the characteristics eigenvalues equations are derived depending on two different nonlocal parameters.The existence of these different nonlocal parameters causes the model is able to predict both increase and reduction of stiffness in nano ultra-thin film. Here, the differential quadrature method (DQM) is applied for obtaining the natural frequencies of in-plane and out of plane. An intensive parametric study is carried out the nonlocal on the natural frequencies of nano ultra-thin film. The results reveal that the effect of nonlocal parameters on the frequency parameter is more prominent at the higher aspect ratios. Also, the effects of different boundary conditions are considered.

The high level of transmitted noise and vibrations of a helicopter flight to the aircrew body can cause discomfort and perhaps affect their performance and physical condition. This paper presents an active seat suspension system with intelligent active force control (AFC) using an artificial neural network (ANN), iterative learning (IL) algorithm, and fuzzy logic (FL) to reduce vibration on the helicopter seat. Therefore, three control schemes are considered for this application, namely AFCANN, AFCIL, and AFCFL. Computer simulations have been performed using MATLAB software to verify the proposed control schemes. The pilot head displacement, acceleration, and also seat acceleration transmissibility are selected as target variables. The simulation results illustrate that the usage of proposed control schemes leads to effective control of target variables, especially active force control using fuzzy logic (AFCFL), which is showing superior performance and accuracy between other intelligent adaptive force control schemes.In future work, this controller will be assessed by experimental tests.