Explore the vast range of titles available.

In working processes, mechanical systems are often affected by both internal and external forces, which are the cause of the forced vibrations of the structures. They can be destroyed if the amplitude of vibration reaches a high enough value. One of the most popular ways to reduce these forced vibrations is to attach tuned mass damper (TMD) devices, which are commonly added at the maximum displacement point of the structures. This paper presents the computed results of the free vibration and the vibration response of the space frame system under an external random load, which is described as a stationary process with white noise. Static and dynamic equations are formed through the finite element method. In addition, this work also establishes artificial neural networks (ANNs) in order to predict the vibration response of the first frequencies of the structure. Numerical studies show that the data set of the TMD device strongly affects the first frequencies of the mechanical system, and the proposed artificial intelligence (AI) model can predict exactly the vibration response of the first frequencies of the structure. For the forced vibration problem, we can find optimal parameters of the TMD device and thus obtain minimum displacements of the structure. The results of this work can be used as a reference when applying this type of structure to TMD devices.

Purpose This study devotes to analyze the stochastic vibration response of multilayer functionally graded graphene platelets reinforced composite (FG-GPLRC) truncated conical shell subjected to moving loads. Two moving random load paths including meridional and circumferential moving random loads are taken into account. This research can provide the thoeretical reference for predicting the stochastic vibration response of multilayer FG-GPLRC truncated conical shell subjected to moving random loads. Methods The theoretical model is constructed by untilizing the differential quadrature finite element method (DQFEM) in conjunction with pseudo excitation method (PEM) and Newmark-β method based on first-order shear deformation shell theory (FSDST). The penalty function method is selected to simulate the various boundary conditions. The effective material property parameters of FG-GPLRC are determined according to Halpin-Tsai micromechanics and the rules of mixture models and five dispersion patterns of GPL are considered. Results The convergence, accuracy, stability and reliability of the proposed theoretical model are verified gradually by using some representative numerical examples. The stochastic vibration response analysis of multilayer FG-GPLRC truncated conical shell subjected to moving random loads is carried out by investigating the effects of model parameters including weight fractions, dispersion patterns of GPL, boundary conditions, thicknesses, semi-vertex angles and radii on the stochastic response systematically.

This paper studies the fatigue life of underwater vehicle pressure-resistant shell structures under random diving load. Firstly, the random load sequence that conforms to the Gumbel distribution is given. Secondly, the mathematical relationship between diving depth and maximum stress is given based on the approximate model method. Then, 500 random load sequences based on the Monte Carlo sampling method are obtained. The calculation model of the stress intensity factor and fatigue crack propagation model is given, and the life of fatigue cracks under the random load sequence is calculated using the method of numerical integration calculation of cycle by cycle. Finally, the probability distribution of lives of fatigue crack propagation under random load sequences is analyzed. The results show that, under each initial crack size, the fatigue crack growth life of the pressure-resistant shell follows the normal distribution and has a high level of significance.

The integration of renewable energy systems into the existing power grid has become a global necessity. While there are numerous advantages to this integration, it also presents challenges such as oscillations in system frequency and tie-line power. These issues can lead to instability and undesirable situations within the power system. To ensure a consistent and reliable supply of high-quality electrical power to consumers, a control system is essential. In recent years, cascaded controllers, known for their increased flexibility and degree of freedom compared to non-cascaded controllers, have gained popularity in the literature. In this study, we aim to examine the performance of cascaded fractional and integer order TI-TD and PI-PD controllers in comparison with non-cascaded PID and TID controllers for a challenging stability and robustness assessment. Our focus is on a two-area PV-reheat thermal power system. By conducting comprehensive tests, we aim to gain insights into the effectiveness of these controller types within this context. To ensure optimal controller responses, the designed controllers are optimized using the Mayfly algorithm, with a focus on minimizing the integral of the time-weighted absolute error performance index. The performance tests conducted in this study cover various aspects, including time domain analysis, robustness, random load changes, the impact of progressive nonlinearities, and cyber-attack (C-A) scenarios. The power system under examination incorporates several nonlinear components, namely governor dead band, generation rate constraints, boiler dynamics, and time delay. Additionally, two C-A models, namely resonance attack (ResA) and random attack, are applied to the controller systems. Unlike conventional robustness and C-A tests found in existing literature, this study goes further by measuring the response of the proposed controller to high parameter changes (uncertainty) and conducting a quantitative analysis of its resilience against C-A scenarios. The aim is to assess the controller’s ability to withstand significant variations in system parameters and its effectiveness in dealing with cyber-attacks. The simulation results demonstrate the superior performance of the optimized and cascaded controllers, particularly the TI-TD controller. These controllers exhibit improved performance compared to other controllers reported in the literature. The findings validate the effectiveness of the proposed controllers and highlight their advantages in terms of system stability, response time, and overall control quality.

A novel method is proposed to investigate the pattern of variation in the residual strength and reliability of wind turbine gear. First, the interaction between loads and the effect of the loading sequence is considered based on the fatigue damage accumulation theory, and a residual strength degradation model with few parameters is established. Experimental data from two materials are used to verify the predictive performance of the proposed model. Secondly, the modeling and simulation of the wind turbine gear is conducted to analyze the types of fatigue failures and obtain their fatigue life curves. Due to the randomness of the load on the gear, the rain flow counting method and the Goodman method are employed. Thirdly, considering the seasonal variation of load, the decreasing trend of gear fatigue strength under multistage random load is calculated. Finally, the dynamic failure rate and reliability of gear fatigue failure under multistage random loads are analyzed. The results demonstrate that the randomness of residual strength increases with increasing service time. The seasonality of load causes fluctuations in the reliability of gear, providing a new idea for evaluating the reliability of the wind turbine gear.

PurposeEngineering components/structures are usually subjected to complex and variable loads, which result in random multiaxial stress/strain states. However, fatigue analysis methods under constant loads cannot be directly applied to fatigue life prediction analysis under random loads. Therefore, the purpose of this study is how to effectively evaluate fatigue life under multiaxial random loading.Design/methodology/approachFirst, the average phase difference is characterized as the ratio of the number of shear strain cycles to the number of normal strain cycles, and the new non-proportional additional hardening factor is proposed. Then, the determined random typical load spectrum is processed into a simple variable amplitude load spectrum, and the damage in each plane is calculated according to the multiaxial fatigue life prediction model and Miner theory. Meanwhile, the cumulative damage can be calculated separately by projection method. Finally, the maximum projected cumulative damage plane is defined as the critical plane of multiaxial random fatigue.FindingsThe fatigue life prediction capability of the method is verified based on test data of TC4 titanium alloy under random multiaxial loading. Most of the predicting results are within double scatter bands.Originality/valueThe objective of this study is to provide a reference for the determination of critical plane and non-proportional additional hardening factor under multiaxial random loading, and to promote the development of multiaxial fatigue from experimental studies to practical engineering applications.

This study develops a rapid algorithm coupled with the finite element method to predict the fatigue crack propagation process and select the enhancement factor for the equivalent random load spectrum of accelerated fatigue tests. The proposed algorithm is validated by several fatigue tests of an aluminum alloy under the accelerated random load spectra. In the validation process, two kinds of panels with different geometries and sizes are used to calculate the stress intensity factor, critical crack length, and crack propagation life. The simulated and experimental findings indicate that when the aluminum alloy is in a low plasticity state, the crack propagation life exhibits a linear relationship with the acceleration factor. When the aluminum alloy is in a high plasticity state, this study proposes an empirical formula to calculate the equivalent stress intensity factor and crack propagation life. The normalized empirical formula is independent of the geometry and size of different samples, although the fracture processes are different in the two kinds of panels used in our study. Overall, the numerical method proposed in this paper can be applied to predict the fatigue crack propagation life for the random spectrum of large samples based on the results of the simulated accelerated crack propagation process and the accelerated fatigue tests of small samples to reduce the cost and time of the testing.

The defect-induced excitations causing the bearing to vibrate have significant contribution in vibration generated from rolling element bearings. Therefore, in this work an investigation has been made to estimate the excitations caused by localized defects on different elements of a bearing, viz., inner race, rolling element and outer race, subjected to load. The applied load on a radially loaded bearing is often not of pure static nature but has a dynamic component associated with it. The dynamic load on bearing has been considered to be composed of a static and a dynamic component. The dynamic component has been considered to be either harmonic or random in nature. The spectra of excitations have been obtained to correlate with the significant spectral components of respective response. The amplitudes of harmonic and variance of random loading have been varied to investigate the effects of dynamic loading on excitation spectra. Numerical results have been obtained for NJ305 bearing with normal clearance. For harmonic load, a new spectral component has been noticed in frequency spectrum of excitation for the defects on outer race and rolling element, whereas there is no new component for inner race defect. In the case of random loading, noise in the spectrum has been noticed. The rise in noise level and coefficients of spectral components also perceived with the increase in variance of random load. The rise in noise level with increment in dispersion of random loading is significant so that few spectral components have been masked under the noise for non-stationary defect, whereas for stationary defect the spectral components are clearly detected in spite of rise in noise level. The numerical procedure explained can be extended for different kinds of loading which may be due to the defects in mating components supported by shaft and bearing system.

In this paper, based on the finite element software, the residual stress of the structure weld is obtained through simulation analysis. The influence of stress concentration is considered by using the mean square stress concentration factor; and the S-N curve equation of the structure is derived. then, the stress power spectrum density of dangerous parts is obtained by random response analysis; Then, the vibration mode of the welded structure is obtained by random response analysis, and the acceleration power spectral density of the structure is input, and then the stress power spectrum density of the dangerous part is obtained Finally, the appropriate stress probability density distribution model is selected to predict the fatigue life with S-N curve equation and Miner damage accumulation theory. The results show that the fatigue life predicted by this method is very close to that of rain flow counting method.

An aircraft in practice serves under extreme flight conditions that will have a substantial impact on its flight safety. Understanding dynamics of airfoil structure of an aircraft subjected to severe load conditions is thus extremely valuable and necessary. In this study, we will explore the complicated dynamical behaviors of a conceptual airfoil excited by an external harmonic force and an extreme random load. Importantly, such an extreme random load is portrayed by a non-Gaussian Lévy noise with a heavy-tailed feature. Bistable behaviors of the deterministic airfoil system are performed firstly from amplitude–frequency response and basin of attraction. Then, the effects of the extreme random load on the airfoil system are thoroughly investigated. Interestingly, within the bistable regime, the extreme random load can lead to stochastic transition and stochastic resonance. Due to its heavy-tailed nature, the Lévy noise would increase the possibility of a highly unexpected stochastic transition behavior between desirable low-amplitude and catastrophic high-amplitude oscillations compared with the Gaussian scenario. Such vibration patterns might damage or destroy the airfoil structure, which will put an aircraft in great danger. All the findings would be helpful in ensuring the flight safety and enhancing the strength and reliability of airfoil structure operating at extreme flight conditions.