1,721,010 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
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
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
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
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
The synergistic effect of texture and surface roughness on electrophoretic deposited bioactive glass coating
No full textTo improve the biocompatibility of AISI 316L, bioactive glass (BG) coating of SiO2–CaO–P2O5 which helps bonding with bone implants was used by an electrophoretic deposition method. Before coating deposition, the samples were treated by shot peening, known as an efficient process for metal grain refinement and fatigue properties. The stainless steel 316L was investigated in terms of microstructure, texture, and roughness. This research covers the effects of chosen shot peening parameter on the BG-coating properties on the obtained results. Shot peening was carried using two different sets of parameters as conventional shot peening, and severe shot peening. Wettability, roughness, microstructure, coating thickness, and corrosion behavior of coated sample were investigated in terms of potentiodynamic polarization and electrochemical impedance spectroscopy in simulated body fluid (SBF) solutions at 37°C. The results indicated that the coating thickness decreased from 35.5 ± 10 μm for coated not peened (CNP) to 20 ± 5 and 17 ± 2 μm for coated conventionally shot-peened (CCSP) and coated severely shot-peened (CSSP), respectively. As well as, the water contact angle of CSSP sample was equal to 15.71° which is much lower than CNP (20.7°). The protection ability of the tested samples in the SBF was improved in the following order: CCSP < CNP < CSSP
Effect of shot peening on electrophoretic deposition of bioactive glass coating on AISI 316L stainless steel
No full textBioactive glass coating of SiO2–CaO–P2O5 was synthesized and deposited on shot peened stainless steel AISI 316L substrates through electrophoretic deposition. Shot peening is known to enhance the fatigue properties of the substrate material; however, the present study aims to investigate how this prior shot peening can affect on the electrophoretic coating properties and performance. Shot peening was carried using two different sets of parameters as conventional shot peening (Almen intensity: 15A and coverage:100%), and severe shot peening (Almen intensity: 7C and coverage:1500%). The coated samples were studied regarding deposition thickness, microstructure, macrotexture and surface roughness, as well as wettability with contact angle tests. Corrosion behavior was also investigated using potentiodynamic polarization and electrochemical impedance spectroscopy in simulated body fluid solutions at 37 °C. The results confirmed that the coating thickness decreased from 55.3 μm for CNP to 27 μm and 9.5 μm for CCSP and CSSP respectively. Shot peening applied before electrophoretic deposition modulated the wettability and corrosion resistance of the coated samples through variation of roughness and the extent of grain refinement. As well as, the water contact angle of CSSP sample was equal to 15.64° which is much lower than CNP (55.3°). Also, the amount of coated samples’ corrosion rate changed by this order CCSP (1.91 × 10−2)>CNP (1.31 × 10−2)>CSSP (1.07 × 10−2). The high surface energy on shot peened samples caused the smaller BG grain size deposited on surfaces. The amount of BG grain size of each sample is as follow CNP 2.12 ± 1.6 μm, CCSP 1.34 ± 0.8 μm and CSSP 0.81 ± 0.3 μm
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