http://yetl.yabesh.ir/yetl1/handle/yetl/19042 Mon, 14 Sep 2026 17:50:00 GMT 2026-09-14T17:50:00Z https://localhost:443/yetl1/bitstream/id/184283/ http://yetl.yabesh.ir/yetl1/handle/yetl/19042 http://yetl.yabesh.ir/yetl1/handle/yetl/4316929 Low-Frequency Bandgap Characteristics of a Graphene-Inspired Two-Dimensional Twisted Bilayer Composite Phononic Crystal Qi, Nakun; Li, Qi; Li, Rui; Hou, Qingyun Abstract. This article presents a two-dimensional composite phononic crystal with a graphene-inspired twisted bilayer configuration. The structure consists of tungsten-rubber core–shell scatterers embedded in an elastic matrix and arranged in a honeycomb lattice. A minimal unit cell was constructed, and finite-element calculations were performed to investigate the low-frequency bandgap characteristics of the structure. By systematically varying the geometric parameter q, the independent dimensions of the core and coating, and the twist angle θ, the effects of geometric scaling and twisting on the first two low-frequency bandgaps were analyzed. The results show that the low-frequency bandgap characteristics exhibit a pronounced nonmonotonic dependence on q, while independent scaling of the core and coating dictates the bandgap frequency position and width, respectively. Under the representative geometric condition of q=2.5, twisting significantly modifies the bandgap structure by broadening the low-frequency bandgap range, particularly the second bandgap, and shifting the first bandgap toward lower frequencies. In addition, the twist angle provides an additional geometric degree-of-freedom for tuning both bandgap width and frequency position. Finite-structure wave propagation simulations and frequency-response analysis further confirm that elastic-wave transmission is effectively suppressed within the predicted bandgap ranges, in good agreement with the band structure calculations. These results show that the proposed twisted bilayer model provides an effective strategy for designing low-frequency phononic crystals and regulating low-frequency elastic-wave propagation. Thu, 01 Jan 2026 00:00:00 GMT http://yetl.yabesh.ir/yetl1/handle/yetl/4316929 2026-01-01T00:00:00Z http://yetl.yabesh.ir/yetl1/handle/yetl/4316922 Dynamic Modeling and Vibration Characteristics of Rolling Bearings With Asymmetric Edge-Wear Evolution of Raceway Defects Wang, Tiantian; Li, Jiahang; Xie, Jingsong; Zhu, Yan; Chen, Dawei; Niu, Buzhao; Guan, Jirui; Guo, Zhibin; Yang, Buyao Abstract. Rolling bearings undergo progressive degradation during service, where localized raceway defects evolve from initial pitting to extended wear, often exhibiting asymmetric defect-edge geometries and shoulder formation. Such geometric evolution plays a critical role in failure development but is inadequately represented in conventional dynamic models based on rectangular or idealized defect assumptions, limiting their ability to explain failure-induced vibration responses observed in practice. This study develops a physics-based dynamic model to investigate the failure mechanisms associated with asymmetric edge-wear evolution of raceway defects. The model explicitly incorporates evolving edge profiles and shoulder geometries through piecewise displacement excitation functions, enabling a mechanistic description of rolling-element motion and transient contact interactions across different defect regions. A direct relationship is thereby established between defect morphology, transient contact forces, and vibration responses. The proposed model is validated using finite element simulations of contact forces and experimental vibration measurements under defective conditions. Results show that neglecting defect-edge evolution leads to systematic overestimation of impact severity in rectangular defect models, whereas edge steepness and shoulder height dominate transient impact intensity and vibration persistence. These findings explain why defects of identical length can produce markedly different vibration amplitudes. By clarifying the role of defect geometry in failure-related dynamics, this work provides a mechanism-oriented interpretation of bearing vibration behavior and offers quantitative parameters for vibration-based fault diagnosis, defect localization, and prognosis, contributing to improved bearing health monitoring and reliability assessment. Thu, 01 Jan 2026 00:00:00 GMT http://yetl.yabesh.ir/yetl1/handle/yetl/4316922 2026-01-01T00:00:00Z http://yetl.yabesh.ir/yetl1/handle/yetl/4316916 Nonminimum-Phase-Based Loop Shaping for Multimode Active Damping Control: Application to Piezoelectric Nanopositioning System Natu, Aditya; HosseinNia, Hassan Abstract. Piezoelectric nanopositioning systems, typically guided by flexure mechanisms, are limited by lightly damped resonances, which constrain achievable closed-loop bandwidth. Active damping controllers (ADCs) are widely employed to suppress the dominant first mode and increase bandwidth; however, their effectiveness degrades significantly in the presence of delay, and dominant higher-order modes often remain insufficiently attenuated, further restricting precision. This article proposes a simple loop-shaping methodology that incorporates a constant-gain nonminimum-phase (NMP) filter in series with a linear damping controller. The NMP filter is tuned using two open-loop crossover frequencies to enforce sufficiently large and approximately symmetric phase margins, thereby mitigating delay-induced degradation in closed-loop damping performance. The methodology is further extended to a parallel damping control structure that enables simultaneous suppression of both the first dominant and higher-order modes. Experimental validation on a piezoelectric nanopositioner demonstrates the effectiveness of the proposed strategy, achieving up to 13.7 dB attenuation of higher-order resonances under significant delay. In combination with a standard proportional-integral (PI) motion controller and a nonminimum-phase resonant controller (NRC) targeting the first mode, the overall control architecture extends the closed-loop bandwidth to 760 Hz, surpassing the system’s first resonance frequency without compromising low-frequency dynamics. Thu, 01 Jan 2026 00:00:00 GMT http://yetl.yabesh.ir/yetl1/handle/yetl/4316916 2026-01-01T00:00:00Z http://yetl.yabesh.ir/yetl1/handle/yetl/4316910 A Deterministic Algorithm for Finding the Entire Roots or Extrema of Finitely Smooth Transcendental Univariates Arising in Mechanical Vibrations With Application to Nonlinear Eigenvalue Problems Tari, Hafez Abstract. Vibration and control problems often lead to solving intricate transcendental univariates. However, finding the entire solution set to such functions is an open problem. Existing methods employ (i) approximations to convert the problem into a simpler, or generally a proxy, function amenable to the entire solution set, and then (ii) refinements to remove the approximation error. However, the former could be hampered by the degree of the nonlinearity of the problem, and the latter could miss solutions if converged to the same solution for distinct approximate ones. In this article, a deterministic algorithm is proposed for finding the entire solution set to any finitely smooth univariate for a given interval. The algorithm, utilizing no proxy functions, sweeps the solutions to the univariate through the application of the proposed Principle of Next Solution and a localized solver, the restrained Newton’s method. The next solution is the endpoint of the solutions to the cascade of higher order derivatives of the function. This is useful for parametric studies and eigenvalue problems in vibrations and control, where solutions within particular ranges are of interest. The algorithm also solves the global optimization problem for transcendental univariates. It finds the entire extrema of the problem, among which it extracts the global optimizer. The algorithm is naturally parallelizable, allowing the independent processing of subdivisions of the input interval, thus speeding up the computations. Examples from nonlinear eigenvalue problems to a suite of univariate global optimization test problems are presented to demonstrate the superb performance of the proposed algorithm. Thu, 01 Jan 2026 00:00:00 GMT http://yetl.yabesh.ir/yetl1/handle/yetl/4316910 2026-01-01T00:00:00Z