Article
Engineering, Mechanical
Sai Vishal, Ashwad Raaj, Chandan Bose, J. Venkatramani, Grigorios Dimitriadis
Summary: The present study investigates the bifurcation characteristics of a pitch-plunge aeroelastic system with coupled non-smooth nonlinearities in both structural and aerodynamic aspects. The study shows that the freeplay gap plays a key role in combining the effects of structural and aerodynamic nonlinearities. Interesting discontinuity-induced bifurcation scenarios arise at high values of the freeplay gap, which can significantly impact the safety of the aeroelastic system.
NONLINEAR DYNAMICS
(2022)
Article
Mechanics
R. Vasconcellos, A. Bouma, F. Marques, A. Abdelkefi, M. R. Hajj
Summary: This study investigates the effects of freeplay, multi-segmented, and impact nonlinearities in the pitch and control surface degrees of freedom on the nonlinear responses of a three-degree of freedom aeroelastic system. The results show the presence of grazing/sliding bifurcations and complex responses due to nonlinear coupling of the system's frequencies, including sudden transitions between harmonic and chaotic responses.
INTERNATIONAL JOURNAL OF NON-LINEAR MECHANICS
(2022)
Article
Engineering, Aerospace
Yayun Shi, Shun He, Gaowei Cui, Gang Chen, Yan Liu
Summary: This study investigates the quenching of limit cycle oscillation (LCO) in a supercritical airfoil (NLR 7301) considering freeplay in transonic viscous flow. Computational Fluid Dynamics (CFD) based on Navier-Stokes equations is used to calculate transonic aerodynamic forces. A loosely coupled scheme with steady CFD and an efficient graphic method is developed to obtain the aerodynamic preload. The LCO quenching is observed based on nonlinear dynamic aeroelastic response obtained using a time marching approach.
CHINESE JOURNAL OF AERONAUTICS
(2023)
Article
Mechanics
Sai Vishal, Ashwad Raaj, Chandan Bose, J. Venkatramani
Summary: This study investigates the synchronization characteristics of a pitch-plunge aeroelastic system under the influence of coupled structural free-play and dynamic stall-induced aerodynamic non-linearities. The results show that free-play nonlinearity plays a dominant role in the dynamical transition when attached flow is present. The onset of dynamic stall is found to be crucial in bifurcation scenarios at high flow speed regimes.
INTERNATIONAL JOURNAL OF NON-LINEAR MECHANICS
(2021)
Article
Acoustics
Peihan Wang, Zhigang Wu, Chao Yang
Summary: The frequency-time domain method is a powerful tool but limited to steady-state solutions. A modified frequency-time domain method is proposed to investigate nonlinear dynamic behaviors with initial conditions. The feasibility is validated through numerical results and compared with the Runge-Kutta algorithm. The sensitivity of parameters and calculation methods of convolution integral contributes to strategies for accuracy.
JOURNAL OF SOUND AND VIBRATION
(2023)
Article
Chemistry, Multidisciplinary
Liuyue Bai, Zhigang Wu, Chao Yang
Summary: This study provides novel perspectives on the nonlinear aeroelastic characteristics of all-movable fins with freeplay nonlinearities. An unsteady aerodynamic model based on the second-order piston theory considering thickness effects is employed. A discrete scanning method using the describing function method is established for systems with multiple freeplay nonlinearities to solve limit-cycle oscillations (LCOs) and avoid solution loss. The influence of support stiffness and freeplay size ratio on the system's dynamical response is analyzed.
APPLIED SCIENCES-BASEL
(2023)
Article
Engineering, Mechanical
Larissa Drews Wayhs-Lopes, Earl H. Dowell, Douglas D. Bueno
Summary: Control surface nonlinearities can cause limit cycle oscillations (LCO). Harmonic Balance-based methods (HB) and Equivalent Linearization Technique (ELT) are proposed to predict LCO. This paper presents a new approach that combines eigenvalue analysis and describing functions. Numerical simulations demonstrate the improved accuracy of the new method and its effectiveness in predicting LCOs in systems with freeplay and friction nonlinearities.
JOURNAL OF FLUIDS AND STRUCTURES
(2023)
Article
Mathematics, Applied
Bo Yu
Summary: This work investigates a piezoelectric energy harvester under the combined influence of fluid flow and harmonic excitation. A lumped parameter model incorporating fluid-structure interaction is proposed to analyze the impact of both fluid flow and harmonic excitation on the harvester. The study presents the calculation of periodic displacement, voltage, and velocity oscillations using the implicit mapping method, and determines the stabilities and bifurcations of periodic oscillations based on the eigenvalues of the mapping structures.
Article
Engineering, Mechanical
Janos Lelkes, Tamas Kalmar-Nagy
Summary: The study analyzes the stability and bifurcations of equilibria in a two degrees-of-freedom aeroelastic system, highlighting the transition to stall flutter and the application of a linear tuned vibration absorber. The effect of absorber parameters on equilibrium stability is investigated, showing that the onset of rapid bifurcation can be shifted to higher wind speed or oscillations can be eliminated completely with the absorber.
NONLINEAR DYNAMICS
(2021)
Article
Engineering, Mechanical
K. Boulbrachene, M. Breuer
Summary: This paper investigates the effect of vertical wind gusts on airfoils for Micro-Air Vehicles in a relevant parameter range through numerical simulations. A simplified substitute model is used, considering a rigid but elastically mounted airfoil with two degrees of freedom. The problem is solved using a partitioned fluid-structure interaction coupling scheme based on large-eddy simulation (LES) and a rigid-body solver. The results show that the airfoil-gust interaction leads to sustained heave and pitch oscillations of bounded amplitudes (LCO) in most cases, while the strongest gust cases induce pitch-induced diverging flutter. The energy analysis further reveals differences between these two scenarios.
JOURNAL OF FLUIDS AND STRUCTURES
(2023)
Article
Neurosciences
Nanxi Lai, Zhisheng Li, Cenglin Xu, Yi Wang, Zhong Chen
Summary: In this review, the authors briefly describe the electrographic characteristics of high-frequency oscillations (HFOs), interictal spikes (ISs), and slow wave activities (SWAs) in the interictal state, and discuss their various roles in epilepsy. They summarize representative evidence from experimental and clinical epilepsy to address their critical roles in seizure generation and epileptogenesis, indicating their potential as electrophysiological biomarkers of epilepsy. Importantly, they propose perspectives for further research in the field.
NEUROBIOLOGY OF DISEASE
(2023)
Article
Chemistry, Multidisciplinary
Xiangyu Wang, Zhigang Wu, Chao Yang
Summary: This study introduces a state space iterating scheme to efficiently find limit cycle solutions using time integrations, visually depicts system behaviors through a combination of modified Poincare and Lorenz maps, and verifies its ability to find LCOs in aeroelastic systems.
APPLIED SCIENCES-BASEL
(2021)
Article
Engineering, Mechanical
Xiaomin An, Bin Deng, Jiayue Feng, Youwen Qu
Summary: The study reveals that the curvature of the panel has a significant impact on its critical flutter dynamic pressure. When subjected to impinging shockwaves, both the curvature of the panel and incident shock strength influence the occurrence of flutter and post-flutter oscillations.
JOURNAL OF FLUIDS AND STRUCTURES
(2021)
Article
Astronomy & Astrophysics
S. A. Belov, D. Riashchikov, D. Y. Kolotkov, S. Vasheghani Farahani, N. E. Molevich, V. V. Bezrukovs
Summary: Research shows that the propagation of non-linear torsional Alfven waves in magnetic flux tubes can induce collective and radially uniform density perturbations. This finding could serve as an additional observational signature of Alfven waves in the upper layers of the solar atmosphere.
MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY
(2023)
Article
Physics, Particles & Fields
Gabriel M. Salla
Summary: In this paper, we study the interactions between neutrinos and dark matter by analyzing the potential generated by the galactic dark matter background. We compute this potential in a model-independent way and find that only ultra light scalar dark matter could be relevant to oscillation experiments under certain assumptions.
EUROPEAN PHYSICAL JOURNAL C
(2023)