1,720,969 research outputs found
Nonlinear vibration absorbers applied on footbridges
No full textThis paper deals with the performance of linear and nonlinear dynamic vibration absorbers (DVAs) to suppress footbridges vertical vibrations. The walking pedestrian vertical force is modeled as a moving time-dependent force and mass. The partial differential equations govern the dynamics of the system; such equations are reduced to a set of ordinary differential equations by means of the Bubnov–Galerkin method with an accurate multimode expansion of the displacement field. The optimal vibration absorber parameters are determined using two objective functions: maximum footbridge deflection and the transferred energy from the footbridge to the DVA. The most suitable nonlinear DVA is proposed for the investigated footbridge. The results show that the DVAs with quadratic nonlinearity are the most performant DVAs
Nonlinear vibration of the bevel gear with teeth profile modification
No full textThe prediction of gear vibration and noise has always been a major concern in gear design. Noise and vibration are inevitable problems that are involved in transmission systems; they have intensified when some nonlinear phenomena such as jump phenomenon, tooth separation and period-doubling bifurcation appear in the system. Tip and/or root modifications are well-known solutions that improve dynamic performance of gears. The present work investigates the complex, nonlinear dynamic behavior of three bevel gear models: (1) model with pure involute profile, (2) model with statically optimized tooth profile, and (3) model with dynamically optimized tooth profile. Tooth profile modification is employed in models by means of genetic algorithm in order to extract the best amount and length of modifications. The dynamic responses obtained from dynamic analyzer were compared qualitatively and quantitatively. By augmenting tooth profile modification, the average value of the dynamic responses is decreased intensely for both statically and dynamically optimized gear pairs. Dynamic load factor is calculated and compared with the involute tooth profile model and the two optimized gear sets. Employing teeth optimization leads to elimination of period- (Formula presented.) in both optimized simulations
Vibration reduction of footbridges subjected to walking, running, and jumping pedestrian
No full textIn this paper, the performance of vibration absorbers in reducing the vertical deflections of the footbridges subjected to human activities is studied. The vertical component of the pedestrian force during walking, running, and jumping is simulated as a moving time-dependent force model. The optimal parameters for the attached vibration absorbers are defined to minimize the deflection of the footbridge. The effectiveness of each vibration absorber is reviewed for different types of excitations. Results show reductions of 91%, 95%, and 96% in terms of the amplitude of vibration for the footbridge with the optimized tuned mass damper subjected to walking, running, and jumping, respectively, in comparison with a bare footbridge. The performance of the tuned mass dampers optimized numerically in the present study is compared with the tuned mass dampers possessing parameters achieved analytically. The damped footbridge with the numerically optimized tuned mass damper under walking, running, and jumping pedestrian experienced a deflection reduction of 9%, 34%, and 37%, respectively, concerning the tuned mass damperwith analytical parameters
A novel nonlinear variable damping device and its application for the systems with uncertain parameters
No full textThis paper deals with the performance of a novel nonlinear viscous dashpot with variable damping. The new proposed dashpot can be utilized in devices for instance dynamic vibration absorbers (DVAs). When the vibration absorber is tuned to the bridge's fundamental frequency, it represents a robust effect in controlling the vibrations of the bridge; however, a DVA is very sensitive to frequency detuning. The proposed nonlinear dashpot can be applied in a passive vibration absorber and upgrades it to a nonlinear variable damping one. Since the parameter of such DVA can be adjusted, it is the so-called nonlinear adjustable DVA. The mentioned dashpot, provides a quadratic nonlinearity for the damping element. The proposed dashpot in this study possesses a simple mechanism, which can handle large range of flow rates of fluid, smoothly without turbulence, in the oil channel. To investigate the effectiveness of an adjustable vibration absorber, a semi-active DVA with variable damping, and stiffness elements is applied on a footbridge; where, the footbridge is experienced variations of the fundamental frequency over time, and is subjected to a walking pedestrian. For the case study in the present study, a vibration reduction of 31% in comparison with the attached traditional passive DVA with constant parameters was achieved. The results show that, by using the proposed nonlinear dashpot, presented in this study, into an attached DVA, the footbridge will experience about 10% more deflection reduction concerning a classical linear DVA
Spiral Bevel Gears Nonlinear Vibration Having Radial and Axial Misalignments Effects
Full text linkIn gear transmissions, vibration causes noise and malfunction. In actual applications, misalignments contribute to intensifying the destructive effect of vibrations. In this paper, the nonlinear dynamics of a spiral bevel gear pair, with small helix angle, considering different misalignments, are deeply investigated. Axial misalignment, radial misalignment, and the combination of these two types are considered in this study. The governing equation is numerically solved through an implicit Runge-Kutta scheme. Since the main goal of this study is the analysis of the dynamic scenario, the mesh stiffness of the gear pair is obtained from the literature. The dynamical system is nonlinear and time-varying; it is analyzed through time responses, phase portraits, Poincare maps, and bifurcation diagrams. Results show that, among the considered three cases with different types of misalignments, the spiral bevel gear with axial misalignment is the worst destructive case; aperiodic, subharmonic, and multiperiod responses are observable for this case. It is interesting that the chaotic responses for the case, having both types of misalignments, are less likely for the case with axial misalignment, only
Application of linear and nonlinear vibration absorbers for the nonlinear beam under moving load
Full text linkRecently, a large amount of studies have been related to nonlinear systems with multi-degrees of freedom as well as continuous systems. The purpose of this paper is to optimize passive vibration absorbers in linear and nonlinear states for an Euler-Bernoulli beam with a nonlinear vibratory behavior under concentrated moving load. The goal parameter in the optimization is maximum deflection of the beam. The large deformation for beam modeling is considered, i.e. the relation between strains and deflections is nonlinear. The force magnitude and beam length are two effective factors for the beam deflection. Vibration absorber with linear damping and linear or nonlinear stiffness is also considered in this manuscript. The results show that, for normal forces and short beams, linear and nonlinear models have similar behaviors, while surveying nonlinear behavior is necessary by increasing the force and length of the beam, i.e. large deflections. Moreover, the difference between linear and nonlinear beam models for regular force magnitudes and beam lengths is negligible. For higher loads and longer beams, beam model nonlinearity can be important. Results demonstrate that,in the presented numerical values (train bridge application) for cubic nonlinear vibration absorber, there are two optimal locations for vibration absorber installation: one inclined from the middle of the beam to the direction of moving loads and the second which is more interestingly inclined from the middle of the beam to moving loads in the opposite direction. Moreover, depending on the model's numerical parameters, for short beams, linear vibration absorber is more effective, while for long beams, cubic nonlinear beam behaves better than the linear one
Nonlinear dynamic behavior of spiral bevel gear by considering the torsional shaft stiffness
No full textSpiral bevel gears (SBGs) play a crucial role in developing silent power transmissions for non-parallel shaft applications, offering advantages such as improved motor allocation flexibility and space reduction. While SBGs have been recognized for reducing vibration magnitude in high-speed gearboxes compared to straight bevel gears, complete vibration suppression remains elusive, leading to potential challenges such as teeth contact loss and complex dynamic scenarios. To construct the dynamical model of SBG, time-dependent mesh stiffness and non-smooth nonlinearity caused by backlash is considered. The employed dynamical system is a three-degree-of-freedom model, integrating rotational shaft stiffness, to investigate the dynamic behavior of SBGs. Through the utilization of various analysis tools such as bifurcation diagram, Fourier spectrum, 3D-phase diagram, Poincaré map, and amplitude-frequency diagram are generated, revealing the presence of periodic, quasiperiodic, and chaotic responses in specific regimes. This research provides an in-deep understanding of the dynamic behavior of SBG system, contributing to the characterization and prediction of nonlinear phenomena, which is vital for the optimization and design of gear mechanisms across various engineering applications.Spiral bevel gears (SBGs) play a crucial role in developing silent power transmissions for non-parallel shaft applications, offering advantages such as improved motor allocation flexibility and space reduction. While SBGs have been recognized for reducing vibration magnitude in high-speed gearboxes compared to straight bevel gears, complete vibration suppression remains elusive, leading to potential challenges such as teeth contact loss and complex dynamic scenarios. To construct the dynamical model of SBG, time-dependent mesh stiffness and non-smooth nonlinearity caused by backlash is considered. The employed dynamical system is a three-degree-of-freedom model, integrating rotational shaft stiffness, to investigate the dynamic behavior of SBGs. Through the utilization of various analysis tools such as bifurcation diagram, Fourier spectrum, 3D-phase diagram, Poincaré map, and amplitude-frequency diagram are generated, revealing the presence of periodic, quasiperiodic, and chaotic responses in specific regimes. This research provides an in-deep understanding of the dynamic behavior of SBG system, contributing to the characterization and prediction of nonlinear phenomena, which is vital for the optimization and design of gear mechanisms across various engineering applications
Vibration Control of Light Bridges Under Moving Loads Using Nonlinear Semi-Active Absorbers
Full text linkThe dynamic response of light bridges to moving loads presents significant challenges in controlling vibrations that can impact on the structural integrity and the user comfort. This study investigates the effectiveness of nonlinear semi-active absorbers in mitigating these vibrations on light bridges that are particularly susceptible to human-induced vibrations, due to their inherent low damping and flexibility, especially under near-resonance conditions. Traditional passive vibration control methods, such as dynamic vibration absorbers (DVAs), may not be entirely adequate for mitigating vibrations, as they require adjustments in damping and stiffness when operating conditions change over time. Therefore, suitable strategies are needed to dynamically adapt DVA parameters and ensure optimal performance. This paper explores the effectiveness of linear and nonlinear DVAs in reducing vertical vibrations of lightweight beams subjected to moving loads. Using the Bubnov-Galerkin method, the governing partial differential equations are reduced to a set of ordinary differential equations and a novel nonlinear DVA with a variable damping dashpot is investigated, showing better performances compared to traditional constant-parameter DVAs. The nonlinear viscous damping device enables real-time adjustments, making the DVA semi-active and more effective. A footbridge case study demonstrates significant vibration reductions using optimized nonlinear DVAs for lightweight bridges, showing broader frequency effectiveness than linear ones. The quadratic nonlinear DVA is the most efficient, achieving a 92% deflection reduction in the 1.5-2.5 Hz range, and under running and jumping reduces deflection by 42%
NONLINEAR DYNAMICS OF SPIRAL BEVEL GEAR FOR HELICOPTER TRANSMISSION IN THE PRESENCE OF AXIAL AND RADIAL MISALIGNMENTS
No full textSpiral bevel gears (SBGs) play a significant role in mechanical transmissions systems when power is transferred from non-parallel shafts at high speed. SBGs are capable of bearing high levels of torque/power in a silent way, due to their high contact ratio. Nevertheless, their complex geometry necessitates understanding all geometric characteristics that determine the transmission efficiency and lifetime. In gear transmissions, vibration causes noise, malfunction, and imbalance in the stress distribution, thereby decreasing the lifetime of the gearbox. Due to manufacturing imperfections and flexibility of components, the system might experience misalignments that intensify or exert a destructive effect on the gear vibration. The main purpose of this study is to investigate the nonlinear dynamics of an SBG pair in the presence of two types of misalignments, namely, axial and radial. Investigating the mesh stiffness is significant to understand the dynamic behavior of gear systems; indeed, obtaining the mesh stiffness is needed to simulate the dynamic model of the geartrain. The loaded tooth contact analysis (LTCA) is employed to determine the static transmission error (STE) and mesh stiffness (MS) of a gear pair. To conduct LTCA, three main approaches could be utilized: finite element method (FEM), experimental, and analytical approaches. Based on the aforementioned methods, different software packages for LTCA have been produced and developed during the previous decade. One of the most powerful and reliable software regarding gear stress analysis is Transmission3D-Calyx, a FEM-based software, which is used in this study. Due to the backlash and MS fluctuation, the governing equations of motion are nonlinear and time-dependent. These equations are numerically solved through an implicit Runge–Kutta approach. To illustrate the dynamic scenario, results are analyzed by means of root mean square, phase portraits, Poincaré maps, and bifurcation diagrams
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