Journal of Theoretical and Applied Vibration and AcousticsJournal of Theoretical and Applied Vibration and Acoustics
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Feed provided by Journal of Theoretical and Applied Vibration and Acoustics. Click to visit.Artificial neural network to predict the health risk caused by whole body vibration of mining trucks
http://tava.isav.ir/article_24749_4331.html
Drivers of mining trucks are exposed to whole-body vibrations (WBV) and shocks during the various working cycles. These exposures have an adversely influence on the health, comfort and also working efficiency of drivers. Determination and prediction of the vibrational health risk of the mining haul trucks at thevarious operational conditions is the main goal of this study. To this aim, three haul roads with low, medium and poor qualities are considered based on the ISO 8608 standard. Accordingly, the vibration of a mining truck in different speeds, weights and distribution qualities of the materials in the dump body are evaluated for each haul road quality using the Trucksim software. An artificial neural network (ANN) is used to predict the vibrational health risk. The obtained results indicate that the haul road qualities, the truck speeds and the accumulation sides of material in the truck dump body have significant effects on the root mean square (RMS) of vertical vibrations. However, there is no significant relation between the material’s weight and the RMS values. Also, the application of ANN revealed that there is a good correlation between the predicted and simulated RMS values. The performance of the proposed neural network to predict the moderate and high health risk are 88.11% and 93.93% respectivelySat, 31 Dec 2016 20:30:00 +0100Optimal characteristics determination of engine mounting system using TRA mode decoupling with ...
http://tava.isav.ir/article_29616_0.html
It is possible to improve vehicle vibration by tuning the parameters of engine mounting system. By optimization of mount characteristics or finding the optimal position of mounts, vibration of the engine and transmitted force from the engine to the chassis can be reduced. This paper examines the optimization of 6-degree-of-freedom engine mounting system based on torque roll axis (TRA) mode decoupling, so that TRA direction coincides with one of the natural modes of vibration. This is achieved by determination of optimal location and stiffness of mounts. In order to find feasible results, physical constraints are taken into account in optimization process. A detailed procedure of optimization problem is explained. Finally, by comparing the frequency and time responses of the optimal design with the original configuration, it is concluded that TRA decoupling is a proper objective function in engine mounting optimization and can greatly improve the vibration behavior of the engine. Achieving decoupled system, the optimal configuration has a better chance of placing dominant natural frequency below the operation range. Also, the forces transmitted through the mounts are reduced noticeably in the optimal design.Sun, 24 Sep 2017 20:30:00 +0100Automatic formulation of falling multiple flexible-link robotic manipulators using 3×3 ...
http://tava.isav.ir/article_24846_4331.html
In this paper, the effect of normal impact on the mathematical modeling of flexible multiple links is investigated. The response of such a system can be fully determined by two distinct solution procedures. Highly nonlinear differential equations are exploited to model the falling phase of the system prior to normal impact; and algebraic equations are used to model the normal collision of this open-chain robotic system. To avoid employing the Lagrangian method which suffers from too many differentiations, the governing equations of such complicated system are acquired via the Gibbs-Appell (G-A) methodology. The main contribution of the present work is the use of an automatic algorithm according to 3×3 rotational matrices to obtain the system’s motion equations more efficiently. Accordingly, all mathematical formulations are completed by the use of 3×3 matrices and 3×1 vectors only. The dynamic responses of this system are greatly reliant on the step sizes. Therefore, as well as solving the obtained differential equations by using several ODE solvers, a computer program according to the Runge-Kutta method was also developed. Finally, the computational counts of both algorithms i.e., 3×3 rotational matrices and 4×4 transformation matrices are compared to prove the efficiency of the former in deriving the motion equations.Sat, 31 Dec 2016 20:30:00 +0100An analytical approach for the nonlinear forced vibration of clamped-clamped buckled beam
http://tava.isav.ir/article_29617_0.html
Analytical solutions are attractive for parametric studies and consideration of the problems physics. In addition, analytical solutions can be employed as a reference framework for verification of numerical results. In this paperHomotopy analysis method and Homotopy Pade technique which are approximate analytical methods, are used to obtain nonlinear forced vibration response of Euler-Bernoulli clamped-clamped buckled beam subjected to an axial force and transverse harmonic load for the first time. Analytical solutions for nonlinear frequency are derived via Homotopy analysis method, Homotopy Pade technique and Runge Kutta method and the results are compared with experimental results of literature. Also the time response of the beam is obtained for free and forced vibration via analytical and numerical methods. In addition, the frequency response is drawn. Comparison of analytical results with numerical results and literature results reveals that Homotopy analysis method and Homotopy Padetechnique have excellent accuracy for wide range of nonlinear parameters and predict system behavior precisely.Sun, 24 Dec 2017 20:30:00 +0100Application of the method of multiple scales for nonlinear vibration analysis of mechanical ...
http://tava.isav.ir/article_25123_4331.html
In this study, the method of multiple scales is used to perform a nonlinear vibration analysis of a mechanical system in two cases; with dry and lubricated clearance joints. In the dry contact case, the Lankarani-Nikravesh model is used to represent the contact force between the joined bodies. The surface elasticity is modeled as a nonlinear spring-damper element. Primary resonance is discussed and the effect of the clearance size and coefficient of restitution on the frequency response is presented. Then, a frequency analysis is done using the Fast Fourier Transform. A comparison between the Lankarani-Nikravesh and Hunt-Crossly contact force models is made. The results obtained numerically and analytically had an acceptable agreement. It is observed that decreasing the clearance size changes the frequency response in the primary resonance analysis. Furthermore, Hunt-Crossly contact force model showed a slightly more dissipative effect on the response. In the lubricated joint case, a linear spring and a nonlinear damper based on the Reynolds equation veloped for Sommerfeld’s boundary conditions are used to model the lubricant behavior. It is shown that only the fluid stiffness has influence on the amplitude of the steady state response and the fluid does not make any effect on the response frequencies after the transient response vanishes. The steady state response frequency for both dry and lubricated cases depends on the linear natural frequency corresponding to the pendulum oscillation. In the primary resonance analysis, increasing the dynamic lubricant viscosity decreases the amplitude in the vicinity of the linear natural frequency as expected.Sat, 31 Dec 2016 20:30:00 +0100Isogeometric analysis: vibration analysis, Fourier and wavelet spectra
http://tava.isav.ir/article_29802_0.html
This paper presents the Fourier and wavelet characterization of vibration problem. To determine the natural frequencies, modal damping and mass participation factors of bars, a rod element is established by means ofisogeometric formulation. The non-uniform rational Bezier splines (NURBS) is presented to characterize the geometry and the deformation field in isogeometric analysis (IGA). Non-proportional damping has been used to measure the real-state energy dissipation in vibration. Therefore, the stiffness, damping and mass matrices are derived by the NURBS basis functions. The efficiency and accuracy of the present isogeometric analysis is demonstrated by using classical finite element method (FEM) models and closed-form analytical solutions. The frequency content, modal excitation energy and damping are measured as basis values. Results show that the present isogeometric formulation can determine the modal frequencies and inherent damping in anaccurate way. Damping as an inherent characteristics of viscoelastic materials is treated in a realistic way in IGA method using non-proportional form. Based on results, k-refinement technique has enhanced the accuracy convergence with respect to other refinement methods. In addition, the half-power bandwidth method givesmodal damping for the IGA solution with appropriate accuracy with respect to FEM. Accuracy difference between quadratic and cubic NURBS is significant in IGA h-refinementWed, 27 Dec 2017 20:30:00 +0100Exact analytical approach for free longitudinal vibration of nanorods based on nonlocal ...
http://tava.isav.ir/article_25746_4331.html
In this paper, free longitudinal vibration of nanorods is investigated from the wave viewpoint. The Eringen’s nonlocal elasticity theory is used for nanorods modelling. Wave propagation in a medium has a similar formulation as vibrations and thus, it can be used to describe the vibration behavior. Boundaries reflect the propagating waves after incident. Firstly, the governing quation of nanorods longitudinal vibration based on the Eringen’s nonlocal elasticity theory is derived. Secondly, the propagation matrix for nanorod waveguide is derived and then the reflection atrix for spring boundary condition is calculated. The relations between amplitudes of propagation and reflection waves in the waveguide dominant are then combined in a matrix form format to set up a laconic efficient method for free axial vibration analysis of nanorods. The exact analytical solution for arbitrary boundary conditions natural frequencies is derived. To validate this approach, the exact solutions of special boundary conditions cases (clamped-clamped and clamped-free) are used. At the end, the effect of nonlocal parameter on the natural frequencies and boundary stiffness for arbitrary boundary condition is discussedSat, 31 Dec 2016 20:30:00 +0100A magnetorheological fluid damper for robust vibration control of flexible rotor-bearing ...
http://tava.isav.ir/article_26137_4331.html
Squeeze Film Dampers (SFD) are commonly used for passive vibration control of rotor-bearing systems. The Magnetorheological (MR) and Electrorheological (ER) fluids in SFDs give a varying damping characteristic to the bearing that can provide active control schemes for the rotor-bearing system. A common way to model an MR bearing is implementing the Bingham plastic model. Adding this model to the finite element (F.E.) model of the rotor enables analyzing the rotor bearing behavior. In this work, considering uncertainties, three types of controllers are designed for a rotor-bearing system and the efficiency of using these controllers in attenuating the vibration amplitude of the system is studied. As a result, employing these controllers reveals a remarkable improvement in reducing the vibration amplitude of the shaft midpoint near the critical velocity.Sat, 31 Dec 2016 20:30:00 +0100An integrated strategy for vehicle active suspension and anti-lock braking systems
http://tava.isav.ir/article_26281_4331.html
In this paper, a decentralized integrated control structure is developed based on a quarter car vehicle model including longitudinal and vertical dynamics. In this structure, the anti-lock braking system (ABS) is designed to decrease the stopping distance by regulating the longitudinal slip for improved safety during hard braking while the active suspension system (ASS) decreases the sprung mass acceleration to improve the ride comfort on irregular roads. During hard braking, it is preferred for conventional ASS to control the variations of tire deflection to improve the braking performance. How ever, in a new strategy, it is shown that if the ABS controller follows the optimal longitudinal slip varied with the vehicle speed and tire normal force instead of a constant value, the dependency of ASS and ABS is decreased. In this way, the ABS performance has high quality performance even in the presence of passive suspension. Application of ASS causes more reduction in the body vibration to provide more ride comfort during braking. As a conclusion, when the ASS is integrated with the proposed strategy of ABS, the overall ride and safety performances are simultaneously improved during hard braking on a good road spectrum.Sat, 31 Dec 2016 20:30:00 +0100