فهرست مطالب

Theoretical and Applied Vibration and Acoustics - Volume:3 Issue: 1, 2017
  • Volume:3 Issue: 1, 2017
  • تاریخ انتشار: 1396/03/11
  • تعداد عناوین: 6
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  • Mohammad Javad Rahimdel, Mehdi Mirzaei *, Javad Sattarvand, Behzad Ghodrati, Hosein Mirzaei Nasirabad Page 1
    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% respectively
    Keywords: Mining trucks, Health risk, Whole body vibration, Artificial neural network
  • Ali Shafei * Page 15
    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.
    Keywords: Recursive formulation, Gibbs-Appell, Flight phase, Impact phase, 3×3 rotational matrices
  • Saeed Ebrahimi *, Esmaeil Salahshoor, Mohsen Maasoomi Page 42
    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.
    Keywords: Lubricated joints, Clearance, Method of multiple scales, Primary resonance, Fast Fourier Transform
  • Mohammad Reza Hairi Yazdi *, Mansour Nikkhah-Bahrami, Masih Loghmani Page 62
    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 discussed
    Keywords: Nanorod vibration, Wave propagation, Arbitrary boundary, Nonlocal elasticity theory, Small-scale effect
  • Ali Kamalie Egoli *, Abdolreza Ohadi, Milad Kazemi Mehrabadi Page 78
    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.
    Keywords: Rotor dynamics, Squeeze Film Damper, Magnetorheological fluid, Sliding Mode, Fuzzy Controllers
  • Sajjad Aghasizade, Mehdi Mirzaei * Page 98
    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.
    Keywords: Active suspension system, Anti-lock braking system, Integrated vehicle control, Optimal control, Prediction