Noise & Vibration Worldwide

Under low-frequency excitation, the human subject is highly sensitive to Whole Body Vibrations (WBV). In the present paper, a biodynamic human model is seated posture without backrest support and also with backrest support at different angles (i.e., 0°, 15° and 30°) is formulated to analyse the influences of the frequency and the magnitude of the vibration, backseat support and the angles of inclination of the backseat support on Seat To Head Transmissibility (STHT) of the biodynamic human subject in seating position exposed to WBV. The model parameters such as damping, mass and stiffness of the mathematical model considered in this paper are derived from an alternate methodology which is based on anthropometric data. The STHT is computed analytically with the help of MATLAB software for all the considered cases. The effect of vibration and excitation frequencies on STHT is analysed. The results of STHT evaluated from this work are justified by comparing the same with the mean STHT characteristics reported in past studies and the results of the present analysis come out to be in good agreement with past published research.

A modified harmonic balance method has been presented and adopted for the nonlinear vibration problem of beams on an elastic foundation. By this method, a nonlinear algebraic equation along with a set of linear algebraic equations are required to be solved, which reduces computation effort. The results determined by the present method are compared with the corresponding results obtained by the existing method. Besides, the effect of various parameters on nonlinear vibrational behavior is examined.

To evaluate the isolation performance of the negative-stiffness structure (NSS) used by the tuned-mass-damper (NSS-TMD) and the air pistons (NSS-AP) on improving the ride quality of the electrical automobile (EA), an EA’s dynamics model is built under the excitation of the road surface roughness and the in-wheel-motor. Based on the root mean square value of the driver’s seat acceleration response used to assess the driver’s ride quality, two models of the seat suspension added by NSS-AP and NSS-TMD are then simulated to compare the performance between NSS-TMD and NSS-AP in enhancing the ride quality of the EA. The study indicates that both NSS-TMD and NSS-AP added to the seat suspension improve the driver’s ride quality better than the seat suspension without the NSS. Particularly, the root mean square value of the driver’s seat acceleration with the NSS-AP is smaller than that of NSS-TMS by 17.2%. Additionally, when the EA is traveling on the road surfaces of ISO level A, level B, and level C with a high velocity of over 70 km/h, the root mean square value of the driver’s seat acceleration with the NSS-AP is also slowly increased and slower than that of the NSS-TMD. Moreover, the root mean square value of the driver’s seat acceleration with the NSS-AP is also reduced in comparison with the NSS-TMD under the change of the total mass of the in-wheel-motor and the rotor’s eccentricity. Thereby, the NSS-AP improves the EA’s ride quality better than the NSS-TMD; and the NSS-AP should be used on the seat suspension of the EA to further enhance the ride quality.

Clearance between the disk and shaft can lead to the aggravation of the system fault. To solve this problem, a disk-shaft dynamic model with the clearance-eccentric coupling faults is established by the finite element method. Based upon the model, the dynamic characteristics of the system with different influence factors such as clearance and rotating speed are acquired by comprehensive analysis. Meanwhile, the accuracy of the dynamic model is verified by experiment investigations. The results show that frequency components in the spectrum include the shaft’s rotating frequency and high frequency multiplication components. And the sawtooth phenomenon from the trajectory diagram of disk center can be observed. With the increase of rotating speed, the disk-shaft contact stress and strain energy first decrease and then increase, while the speed difference of disk to shaft and vibration amplitude increase, and the number of high frequency multiplication components in the spectrum decreases gradually. Furthermore, with the increase of clearance, the stable values of the disk-shaft contact stress and strain energy decrease, while the vibration amplitude, the number of high frequency multiplication components and speed difference increase gradually, and the trajectory shape of disk center changes from closed circle to hollow ring.

This paper investigates metamaterial functionally graded plates with quasi-zero stiffness resonators. This way, the governing equations of free vibrations and the mode shapes are obtained using the assumed mode method. The free vibrations analysis of the metamaterial functionally graded plates is then performed using finite element analysis. The objective of the current paper is to present an FG metamaterial plate structure to attenuate its mode shapes. Various resonators’ arrangements on the FG plate evaluate the best arrangements. This paper shows that the proposed metamaterial attenuates the corresponding shape modes for the first nine natural frequencies.

To investigate the motion characteristics and vibration characteristics of elastic composite cylindrical roller bearings (ECCRBs), a simulation model of the ECCRB is established in ABAQUS software. The influences of filling degrees and working conditions on motion characteristics of the ECCRB are compared, and the modal characteristics and harmonic response of the ECCRB are analyzed. Calculation results show that when the filling degree increases from 0% to 60%, there is a nonlinear relationship between the filling degree and the slip rate of cage, the natural frequency of each order decreases, and the vibration displacement of ECCRB increases under the excitation load; increasing the rotation speed and decreasing the radial load reasonably is beneficial to the motion stability of the ECCRB. At the same time, with the increase of the excitation load, the vibration displacement of the ECCRB increases. The analysis results can present some theoretical basis for the structural optimization of the ECCRB.

The influence of fluid on the lock gate structure in a dam-reservoir system subjected to sinusoidal excitation is investigated. The gate’s material is considered homogeneous, isotropic, prismatic, and elastic, and the gate is analysed using Mindlin’s plate theory. The fluid is considered non-viscous, incompressible, and has an irrotational flow field. The method of separation of variables with the Fourier half range cosine series is used to solve the fluid domain’s Laplace equation. The fluid’s infinite length is curtailed near the gate, controlling the calculations without affecting the results too much. Both the domains are interacted with each other by transferring the fluid’s pressure to the gate and the gate’s acceleration to fluid. At the fluid’s free surface, undisturbed and linearised, conditions are considered. The Newmark-beta time integration approach is used to solve the forced vibration equations using developed FORTRAN computer code. A study has been performed to assess the dynamic pressure variation due to fluid. The present results may be valuable if the lock gate is subjected to any terrible natural phenomena.

This study deals with piezoelectric energy harvesters carrying the magnet at the free end while a magnifier connected them to the base. The harvester consists of a cantilever beam with Functionally Graded (FG) porous foam core and two piezoelectric faces while taking into account the von-Karman strains and the magnetic interaction of two magnets. The governing equation has been developed using Hamilton’s principle and reduced-order via the Galerkin method. Frequency response of vibrations and voltage derived using harmonic balance method and the adjusted model has been confirmed by parametric studies of the lumped parameter model. A parametric study is also performed to expose the effects of porosity coefficient and pattern, magnifier ratios, and excitation level on the responses. Results show that by correct selection of the magnifier parameters, the proposed harvester can provide a higher output over a wider frequency band. Also, the core porosity increases the flexibility of the beam and raised the voltage by a factor of 1.8.