Journal of Theoretical and Applied Vibration and Acoustics
Volume:6 Issue: 2, Summer & Autumn 2020

In this paper, a nonlinear 5-D hyperchaotic Rikitake dynamic system has been taken into consideration. The hyperchaotic behavior of the model was proved, and the response of the system has been shown. Besides, in the case of existing parametric uncertainties in the system, it shows even more complex behavior. An adaptive control strategy to have stable behavior is synchronized for an uncertain hyperchaotic system with an identical 5-D system. The stability of the control law has been identified by using the Lyapunov stability theory. The numerical simulations are presented for the hyperchaotic Rikitake system with unknown parameters and a system with time-varying parameters to indicate the effectiveness of the proposed algorithm for a class of complex systems. Moreover, since there are often lags between the signals gained by the system and the signals that the controller receives, the control input with the time delay parameter is implemented in the model. Also, the results show the gradual transformation from an unstable system into a stable one.

In this study, energy harvesting from two-dimensional vortex-induced vibrations of a circular cylinder is investigated. To do so, the vibratory behavior of the flexibly mounted circular cylinders is described using the nonlinear wake-oscillator model. Then, the effect of changing the flow velocity on the dynamic behavior of the cylinder is numerically obtained and validated by experimental results.  The effect of changing the main parameters of the system on its electrical and vibratory behavior is investigated by employing the nonlinear electromechanical equations of motion. Unlike most previous studies that only tend to maximize the harvested energy, structural failure due to large deformation is considered in this study. For this reason, the so-called Perfection Rate (PR) parameter is introduced. By using this parameter, the application of the energy harvester is characterized, in which the energy harvesting system works efficiently, regarding its vibration amplitude, which should be small enough. Furthermore, the proper load resistance range for the VIV-based energy harvesting system in the post-synchronization regime is obtained and it is demonstrated that the energy harvesting system with a small electromechanical coupling coefficient can effectively work in this regime

An exact closed-form solution was introduced to analyze axisymmetric free damped vibration of circular magnetorheological fluid (MRF) sandwich plate. Hamilton principle, as well as the classical thin plate theory were used to extract three fully coupled governing equations of motion and the corresponding boundary conditions. Shear modulus of the MRF was tunable by changing a magnetic field which was perpendicular to the mid-plane of the plate. Using two new functions named as phase and anti-phase in-plane displacement functions (PIDF and AIDF), transverse displacement of the sandwich plate was firstly decoupled and finally, in-plane displacements of the top and bottom layers were extracted to obtain the frequency equation for clamped, simply supported and free boundary conditions. Accuracy and stability of results were assessed according to a finite element analysis. The role of various parameters on variations of natural frequencies and loss factors was investigated. Considering obtained results, it was found that despite the insensitivity of natural frequencies to the intensity of the magnetic field and the MRF thickness variations, the loss factors showed high sensitivity to these parameters. Also, the slope of the plate has a significant role in the dissipated energy of the sandwich circular plate. These findings can be applied by engineers and researchers in designing magnetically controlled devices such as brakes or clutches and heavy motor dampers.

Underwater three-dimensional imaging can be performed using several sonar sensors and interferometric methods. The problem with employng multiple sensors is the increased cost of hardware and synchronization issues. However, uncertainty reduces by using this method. An alternative way to reduce hardware is to utilize multipath circuits in the underwater environment. In this environment, multipath circuits are created by the impact of sound waves on the seafloor and sea surface. Seafloor reflections create direct-direct, direct-indirect, indirect-direct, and indirect-indirect circuits. In this paper, both methods of using and not using multipath circuits for three-dimensional imaging are presented in detail. Moreover, both approaches of using or not using virtual sources and cube target imaging will be carried out using the MATLAB software package. The type of sonar presented in this paper is an inverse synthetic aperture sonar. The results are comparable with those of the commercial systems. However, not all practical conditions are considered in this study in contrast with the commercial systems. Our contribution is the study of a novel method in three-dimensional imaging using virtual sources. This method has not been applied for this purpose before

In this paper, the effects of higher-order terms in aerodynamic force model have been investigated on the response of galloping piezoelectric energy harvesters. The system comprised a PZT beam with a bluff body and was exposed to a fluid force. First, the dimensionless governing electromechanical equations were provided. To model the aerodynamic force, the 3rd and 7th order galloping models have been employed by adopting the quasi-steady assumption. Then, the dynamic response based on the 3rd and 7th order aerodynamic force models has been studied using a numerical integration method. Besides, an approximateanalytical solution based on the multiple scales method (MSM) has been provided. Next, the mechanical and electrical responses of the system are obtained using the MSM solutions. Finally, the optimum electrical power and the corresponding dimensionless load resistance have been obtained. The results reveal that considering higher-order terms in aerodynamic force expansion is necessary for accurate characterization of the mechanical and electrical responses.

This paper investigates the main problem of combustion instability in turbofan engines which is usually the unbalanced fuel pump causing turbulences in the fuel flow as well as vibrations in the fuel pipes of the system.At first, the equations of frequencies are derived analytically in the direct and knee joint pipes to verify the results of the Abaqus software. The results show an acceptable accuracy of the Abaqus software to solve the problem of the fluid coupling structure. The results show that the vibration frequency of this part of the fuel transfer system (2.5 to 18 Hz in different modes) is very low compared to the entire engine operational frequency (around 140 Hz). The maximum transverse displacement (range) is relatively significant (up to 16 mm), which is noticeable with respect to the overall dimensions of the system. However, this amplitude would decrease by two clamped-ended with two fastened belts. In the following part, optimization of the system parameters was done using the Design-expert Software and NSGA II code. The basic parameters studied in this paper are radius, thickness, and length of the pipe with different spans, as well as the turbulence inflow. Optimal mode is achieved with laminar velocity contours. In conclusion, the outflow disturbance has been decreased, which consequently reduces the turbulence of the fuel that can improve combustion stability

This paper covers the application of the Fuzzy-PID controller to stabilize the three-axis gimbal payload orientation with respect to the inertial frame in the presence of platform motion. In this way, the effect of external disturbances induced by the operating environment is greatly reduced, thereby increasing the accuracy of ultimate operation. Three independent controllers are employed to maintain the triple angles of the three-axis gimbal payload at a desired orientation. The Fuzzy-PID controller benefits the typical PID control structure in which the control gains are adaptively computed by a fuzzy inference system. The particle swarm optimization algorithm is also used to calculate the optimal values of input-output scale factors. A co-simulation platform is considered by coupling the PSO-optimized Fuzzy-PID controllers modeled in Matlab/Simulink to the mechanical gimbal model designed in Solidworks and exported to Simulink by using Simscape toolbox, aiming at the calculation of control torque needed for stabilization of gimbal payload. The effectiveness of the proposed controller is examined by simulation of the designed system for various commanded angles in the presence of different disturbances, including sinusoidal disturbances with diverse frequencies and random vibrations. According to the adopted collaborative simulations, it is shown that the utilized control system performs very well in the tracking of the desired angles and also the rejection of the applied perturbations.

In this work, a multi-objective optimization process based on the genetic algorithm is employed to damp the vibrations of a piezo actuating composite beam. A new mathematical model for the control effort is proposed and optimized with two objective functions. Conflicting objectives are considered as the displacement of the beam and the second derivative of the control voltage. The coefficients of the proposed control voltage model are regarded as the design variables for this optimization process. The corresponding Pareto front represents non-dominated optimum solutions with different choices to designers. The time behaviors of displacement, velocity and acceleration as well as the related control effort at the midpoint of the beam for three optimum design points are illustrated. The simulation of the time responses of a selected optimum point exhibits the advantage of the planned optimum strategy with regard to those stated in some research such as the cases used in the maximum principle for the same structure.

The present article proposes the idea of multi-frequency excitation to harvest energy from low-frequency ambient vibrations. A nonlinear piezomagnetoelastic set-up, operating in the monostable mode, is considered. Due to nonlinearities being present in the system, a multi-frequency excitation gives rise to complicated phenomena such as combination and simultaneous resonances. We propose the idea of multi-frequency excitation and employing secondary resonances such as combination and simultaneous resonances occurring in nonlinear systems. Nonlinear differential equations governing the harvester dynamics are obtained based on the Hamilton extended principle and solved using the direct harmonic balance method. Numerical results are presented for an actual energy harvester subjected to a dual-frequency excitation. It is ascertained that multi-frequency excitation and exploiting combination and simultaneous resonance result in a significant enhancement in the harvester output voltage and power. It is also found that simultaneous resonance is more effective in improving the harvester performance than combination resonances

This paper addresses the vehicle's CG (center of gravity) height control enhancement for the new road vehicle Series Active Variable Geometry Suspension (SAVGS) concept using the PID control technique. Thus, the study utilizes a nonlinear full-car model that represents accurately the dynamics and geometry of a high-performance car with the new double-wishbone active suspension concept. The proposed controller is installed on the nonlinear full-car model, and its performance is examined by the parameters, CG Height and Pitch. In this study, PID is tuned by a Genetic Algorithm and thus a robust control system is designed. Finally, the system's robustness is examined through four different simulation configurations such as different speeds and different road conditions. The vehicle is supposed to be moving with 20 km/h and 100 km/h horizontal speed and also it is going through Road Classes types C and D. Figures show that this suspension system successfully controls vehicle CG height around a desirable height (0.5m) and does not make harmful impacts on vehicle pitch angle.

This paper presents a new method for identifying damage in bridge girders based on modal flexibility deflections. By utilizing modal inertia forces for spatial load distribution vector, a new approach for obtaining modal flexibility deflections is presented. By flexibility deflections due to the modal inertia forces, a new two-stage damage identification method is pro-posed for beam-like structures. In damage severity estimations, the concepts of static beam deflections are utilized. The abilities of the proposed method are demonstrated using experimental modal data of the two full-scale bridge girders. Four damage scenarios of a steel plate girder from I-40 Bridge over the Rio Grande river and the surface damages in a pre-stressed concrete box girder removed from Provincial Highway Bridge over the Qu'Appelle river are considered and discussed. The influence of uniform load surface and the number of vibration modes on damage patterns are studied. The results show that the localization resolution declines between 15%-30% when applying the uniform load surface method, and the two first vibration modes are very influential on the damage patterns. In most cases, the predictions based on the flexibility deflections due to the modal inertia forces are found to closely (above 90%) match to the actual damage of the bridge girders. Finally, the performance of the pro-posed method in the presence of modelling errors and noisy data is investigated. The results indicate that the proposed method is efficient in damage identification of beam-like structures.

Usually, payloads are carried on long routes with different road surface conditions and road obstacles by commercial vehicles from factory to destination. These road conditions cause truck and its cargo exposed to shock and vibration of different amplitudes and frequencies that may impose catastrophic damages to delicate sensitive payloads. The aim of this paper is to present 3-D model of a secondary suspension system, including double-ended magnetorheological dampers in cargo vehicles to protect sensitive cargo against induced excitations due to various road surface roughness. First, a double-ended magnetorheological damper was modeled, fabricated, and dynamically tested. Harmonic tests at different frequencies were performed using a UTM test machine and applying different electric currents to the damper. Considering these tests results, the parameters of modified Bouc-Wen model for the damper are identified. Using the updated model for the damper, 3-D model of secondary suspension system with four magnetorheological dampers in the four corners of the cargo holder pallet is provided. The impact of the secondary suspension against the loads imposed by three types of road surface profiles, namely harmonic long wave, the bumpy surface, and surface with random roughness, is investigated. Furthermore, the effect of various uneven cargo mass arrangements on the magnitude of the dynamic loads of the payload are investigated. The results show that with increasing electric current at different road profiles, the vertical displacement amplitude has an average decrease of 40% in peak and 30% decrease in RMS and at the same time the isolation region has acceptable characteristics.