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1
Kribes, N., N. Ouelaa, M. A. Yallese e S. Belhadi. "Analyse de l'impact des paramètres de coupe et des vibrations sur la rugosité des pièces usinées en tournage à partir de la méthode de régression linéaire multiple". Matériaux & Techniques 95, n. 3 (2007): 197–203. http://dx.doi.org/10.1051/mattech:2008004.
2
Mortimer, B. "A Spider’s Vibration Landscape: Adaptations to Promote Vibrational Information Transfer in Orb Webs". Integrative and Comparative Biology 59, n. 6 (20 maggio 2019): 1636–45. http://dx.doi.org/10.1093/icb/icz043.
Abstract (sommario):
Abstract Spider orb webs are used not only for catching prey, but also for transmitting vibrational information to the spider. Vibrational information propagates from biological sources, such as potential prey or mates, but also abiotic sources, such as wind. Like other animals, the spider must cope with physical constraints acting on the propagation of vibrational information along surfaces and through materials—including loss of energy, distortion, and filtering. The spider mitigates these physical constraints by making its orb web from up to five different types of silks, closely controlling silk use and properties during web building. In particular, control of web geometry, silk tension, and silk stiffness allows spiders to adjust how vibrations spread throughout the web, as well as their amplitude and speed of propagation, which directly influences energy loss, distortion, and filtering. Turning to how spiders use this information, spiders use lyriform organs distributed across their eight legs as vibration sensors. Spiders can adjust coupling to the silk fibers and use posture to modify vibrational information as it moves from the web to the sensors. Spiders do not sense all vibrations equally—they are least sensitive to low frequencies (<30 Hz) and most sensitive to high frequencies (ca. 1 kHz). This sensitivity pattern cannot be explained purely by the frequency range of biological inputs. The role of physical and evolutionary constraints is discussed to explain spider vibration sensitivity and a role of vibration sensors to detect objects on the web as a form of echolocation is also discussed.
3
Shaikh, Zubair, Sudarshan Gajre, Kishor Deshmukh e Jotiprasad Shete. "Developing a Robust Process for Design Margin Calculation Through Modal Scaling and Harmonic Analysis of Engine Mounted After Treatment System". Indian Journal of Signal Processing 4, n. 1 (28 febbraio 2024): 1–6. http://dx.doi.org/10.54105/ijsp.c4352.04010224.
Abstract (sommario):
The last few years have seen an increase in the complexity of emission standards. This has caused OEMs to start using Exhaust Gas Processors (EGP) or Exhaust After Treatment Systems (EATS)in complex integration. These systems are usually mounted on vehicle chassis or engine body with the help of mounting straps or brackets. The arrangement of the system leads to road loads and/or engine vibrations being transferred and causing damage to its components. New BS VI engines need some AT (After treatment) components to be mounted directly on the engine and others to chassis. The components that are directly mounted on engine are called close couple AT system which are subjected to engine harmonic vibrations which falls under forced vibration criteria. Most of the AT system are subjected to random vibrations and industry has a well-defined procedure to address the problem, but for harmonic vibrations there is no specific approach. In order to optimize the structural durability of close couple AT system against HCF (high cycle fatigue) fatigue harmonic vibration, there is a need for well-defined test analysis correlation procedure. The objective of this work is defining and documenting a robust process for design margin through calculation modal scaling and harmonic analysis of close couple AT system through test analysis correlation activity. Analytical, numerical and testing data were compared and conclusions are drawn. More case studies can be added to this work in order to validate the test analysis correlation activity and boost the degree of confidence. Future study may include recording additional failure modes in addition to the harmonic HCF failure mode.
4
Romdhon, Abdul ghofar, Mohammad Ilham, Rini puji Astutik e Denny Irawan. "Penanganan Lonjakan Vibrasi pada Rotor Elektrik Turbin di PLTU Gresik". Journal of Applied Smart Electrical Network and Systems 1, n. 02 (31 dicembre 2020): 47–54. http://dx.doi.org/10.52158/jasens.v1i02.116.
Abstract (sommario):
This analysis will discuss how to handle vibrations in the Turbine Rotor. The measuring instrument used is Vibration Analysis test with Prov. 2140 type which measured amplitude, time and frequency domain of vibration signal. The results obtained in this study, firstly, the measurement vibration of rotor at PT PJB Gresik found the highest amplitude of vibration was 59,6 μm at 3000 rpm. In this condition, the rotor is in very good condition as per standard vibration in ISO 7919-2 stated 80 μm at 3000 rpm. However in the next measurement, there is an dramatically increase of amplitude in each vibration measurement. The top amplitude of vibration reached at 115 μm at 3000 rpm and shown a symtom of damage on the rotor as a result of vibration. In solving the problem this time we use the method Root couse analysis (RCA). The results of this research found that there was a short turn to turn on the rotor windings and the closed slot liner holes that caused electric vibrations and needed to be repaired to eliminate vibration disturbances. After repairing the vibration, it decreased which initially 115 μm to 33.5 μm at 3000 Rpm, it is still on the range of the permitted safe zone of ISO standard 7919−2.
5
Ren, Fushen, Baojin Wang e Suli Chen. "Nonlinear Modeling and Qualitative Analysis of Coupled Vibrations in a Drill String". International Journal of Bifurcation and Chaos 28, n. 10 (settembre 2018): 1850119. http://dx.doi.org/10.1142/s0218127418501195.
Abstract (sommario):
A coupled model for axial/torsional/lateral vibrations of the drill string is presented, in which the nonlinear dynamics and qualitative analysis method are employed to find out the key factors and sensitive zone for coupled vibration. The drill string is simplified as an equivalent shell under axial rotation. After dimensionless processing, the mathematical model for coupled axial/torsional/lateral vibrations of the drill string is obtained. The Runge–Kutta–Fehlberg method is employed for the numerical simulation, and the rules that govern the changing of the torsional and axial excitation are revealed. And the stability domains of the explicit Runge–Kutta method are analyzed. Furthermore, the suggestions for field applications are also presented. It is demonstrated by simulation results that the lateral/axial/torsional vibrations exist simultaneously and couple with each other. The system will obtain a stable period motion with an axial excitation zone before the coupled vibration in the three directions, and continue to increase the axial excitation to cause the coupled vibration easily. The torsional excitation of the drill string mainly contributes to the coupled vibration in the three directions when in a specific rotation speed zone. The system is more likely to obtain a periodic motion through adjusting the torsional excitation out of this zone.
6
Mazur, Krzysztof, e Marek Pawełczyk. "Active Noise Control with a Single Nonlinear Control Filter for a Vibrating Plate with Multiple Actuators". Archives of Acoustics 38, n. 4 (1 dicembre 2013): 537–45. http://dx.doi.org/10.2478/aoa-2013-0063.
Abstract (sommario):
Abstract Vibrating plates can be used in Active Noise Control (ANC) applications as active barriers or as secondary sources replacing classical loudspeakers. The system with vibrating plates, especially when nonlinear MFC actuators are used, is nonlinear. The nonlinearity in the system reduces performance of classical feedforward ANC with linear control filters systems, because they cannot cope with harmonics generated by the nonlinearity. The performance of the ANC system can be improved by using nonlinear control filters, such as Artificial Neural Networks or Volterra filters. However, when multiple actuators are mounted on a single plate, which is a common practice to provide effective control of more vibration modes, each actuator should be driven by a dedicated nonlinear control filter. This significantly increases computational complexity of the control algorithm, because adaptation of nonlinear control filters is much more computationally demanding than adaptation of linear FIR filters. This paper presents an ANC system with multiple actuators, which are driven with a single nonlinear filter. To avoid destructive interference of vibrations generated by different actuators the control signal is filtered by appropriate separate linear filters. The control system is experimentally verified and obtained results are reported.
7
Aghazadeh, Reza. "Free Vibration Analysis of Shear Deformable Small-Scale Tubes". Academic Perspective Procedia 3, n. 1 (25 ottobre 2020): 418–27. http://dx.doi.org/10.33793/acperpro.03.01.86.
Abstract (sommario):
This study presents an approach for investigating free vibration problem of small-scale tubes based on modified couple stress theory in conjunction with higher order shear deformation tube model. The size effect is captured through utilization of a length scale parameter involved in modified couple stress theory. A newly developed refined tube model is employed to satisfy friction-free conditions on inner and outer surfaces of micro-tubes. Hamilton&rsquo;s principle is used as a variational technique for derivation of governing system of equations. For axial vibrations, an analytical procedure is conducted, while for transverse vibrations differential quadrature method is used as a numerical technique. The correctness of numerical results are verified through comparisons made with results which are available in the literature for limiting cases. The analyses reveal the effects of size and transverse shear deformation on the natural frequencies of micro-tubes.
8
Ansari, R., M. A. Ashrafi, T. Pourashraf e M. Hemmatnezhad. "Vibration Analysis of a Postbuckled Microscale FG Beam Based on Modified Couple Stress Theory". Shock and Vibration 2014 (2014): 1–20. http://dx.doi.org/10.1155/2014/654640.
Abstract (sommario):
On the basis of modified couple stress theory, the postbuckling behavior of the Euler-Bernoulli microscale FG beams is investigated by means of an exact solution method. The modified couple stress theory as a nonclassical continuum theory is capable of interpreting the size dependencies which become more significant at micro/nanoscales. The Von-Karman type nonlinear strain-displacement relationships are employed. The thermal effects are also incorporated into formulation. The governing equation of motion and the corresponding boundary conditions are derived using Hamilton’s principle. The material properties are assumed to be graded in the thickness direction according to the power-law distribution. A closed-form solution is obtained for the postbuckling deformation which is beyond the critical buckling load. To study the vibrations taking place in the vicinity of a buckled equilibrium position, the linear vibration problem is exactly solved around the first three buckled configurations. The natural frequencies of the lowest vibration modes around each of the first three buckled configurations are obtained. The influences of power-law exponent, boundary condition, length scale parameter, and thermal environment changes on the static deflection and free vibration frequencies are studied. A comparison is also made between the present results and those obtained via the classical beam theories.
9
Jin, Hao, Weining Liu e Shunhua Zhou. "Optimization of Vibration Reduction Ability of Ladder Tracks by FEM Coupled with ACO". Shock and Vibration 2015 (2015): 1–6. http://dx.doi.org/10.1155/2015/484827.
Abstract (sommario):
Ladder track, which has drawn increased attention in scientific communities, is an effective method for reducing vibrations from underground railways. In order to optimize the vibration reduction ability of ladder track, a new method, that is, the finite element method (FEM) coupled with ant colony optimization (ACO), has been proposed in this paper. We describe how to build the FEM model verified by the vibration tests in the Track Vibration Abatement and Control Laboratory and how to couple the FEM with ACO. The density and elasticity modulus of the sleeper pad are optimized using this method. After optimization, the vibration acceleration level of the supporting platform in the 1–200 Hz range was reduced from 102.8 dB to 94.4 dB. The optimized density of the sleeper pad is 620 kg/m3, and the optimized elasticity modulus of the sleeper pad is 6.25 × 106 N/m2.
10
Brennan, M. J., M. J. Day e R. J. Randall. "An Experimental Investigation into the Semi-Active and Active Control of Longitudinal Vibrations in a Large Tie-Rod Structure". Journal of Vibration and Acoustics 120, n. 1 (1 gennaio 1998): 1–12. http://dx.doi.org/10.1115/1.2893806.
Abstract (sommario):
An experimental study into the use of one semi-active and two active control devices employed to attenuate the transmission of longitudinal vibrations on a large tie-rod structure is described. A tie-rod structure similar to that found in marine machinery installations was assembled in the laboratory. This type of structure was chosen because it is difficilt to apply standard passive techniques due to the static stiffness requirement. A tunable pneumatic vibration absorber was used as the semi-active device, and an inertial electrodynamic exciter and a magnetostrictive actuator were used as the active devices. The way in which these devices couple into and modify the dynamic behaviour of the tie-rod structure is discussed, and experimental results are presented showing the effectiveness of the control measures in attenuating longitudinal vibrations. Significant reductions in transmitted vibrations were achieved by all the devices and the merits of each method are discussed.
11
Loureiro, Jakeline, Francisco Augusto Aparecido Gomes e Paulo Rogerio Novak. "Numerical study of the vibrational absorption considering the periodic foundation effect in a small structure". CONTRIBUCIONES A LAS CIENCIAS SOCIALES 16, n. 11 (10 novembre 2023): 25869–88. http://dx.doi.org/10.55905/revconv.16n.11-065.
Abstract (sommario):
The growth of urban areas has led buildings to come closer and closer to road traffic routes, exposing civil buildings to traffic vibrations, causing discomfort for users and damage to structures. Although there are numerical studies on traffic vibrations, effective vibrational isolation techniques are little explored in this research. A promising approach is the use of periodic structures. Although used in several areas of engineering, periodic structures still have limited application in civil engineering, especially to isolate vibrations caused by vehicles rolling on pavement in small buildings. In this context, this research developed three numerical finite element models for a small structure, which represent residential and/or commercial buildings with a number of floors equal to or less than three, in reinforced concrete. The first model involved a periodic block-type structure foundation, while the two comparative models included periodic raft-type foundations and block-type concrete foundations. The objective was to analyze the vibrational absorption of different foundations for forced vibrations arising from road traffic in the 1-50Hz range. In order to compare them and observe how beneficial the use of periodic foundation is, in the context of the study. The methodology used consisted of creating structural models using finite elements, applying boundary conditions to couple the foundation layers and the structure, establishing continuity. The study looked for modal responses, and in the frequency domain, resulting from excitation in the foundation, using the Ansys® software (2023) for all simulations. The results revealed that periodic foundations are capable of reducing amplitude peaks at frequencies above 30 Hz, which is beneficial for attenuating vibrations in this range. With an appropriate design, adjusting the geometric and physical parameters of the materials, it is possible to obtain effective vibrational isolation for structures, minimizing vibrations arising from ground waves in buildings. This suggests that the use of periodic structures would be promising in isolating vibrations caused by traffic in small structures.
12
Brake, M. R., e J. A. Wickert. "Optimizing Vibration Isolation of Flex Circuits in Hard Disk Drives". Journal of Vibration and Acoustics 127, n. 2 (3 giugno 2004): 165–72. http://dx.doi.org/10.1115/1.1891813.
Abstract (sommario):
A “flex circuit” is a laminate of polyimide substrate, adhesive, and copper conductors that is used to connect the stationary electronic components in a computer hard disk drive to the rotating arm that positions read/write heads above the disks. The flex circuit’s transverse and longitudinal vibrations couple with the arm, and those motions, although seemingly small, degrade performance during seek operations from one data track to another. The flex circuit and arm mechanism is defined by a number of geometric parameters, and some latitude is available at the design stage for choosing dimensions and angles so as to minimize vibration transmission from the flex circuit to the arm. In this paper, the results of parameter, optimization, and experimental studies are discussed with a view toward improving isolation of the arm from vibration of the flex circuit in one or several modes. Particularly for the mechanism’s odd modes, the flex circuit’s free length and the relative attachment angle between the arm’s centerline and the circuit can each be chosen to significantly reduce vibration transmission. A genetic algorithm was applied to minimize a metric of vibration coupling in several vibration modes, and, in the case study examined, vibration isolation was improved by over 80%.
13
Yalçın, Barış Can, e Haluk Erol. "Semiactive Vibration Control for Horizontal Axis Washing Machine". Shock and Vibration 2015 (2015): 1–10. http://dx.doi.org/10.1155/2015/692570.
Abstract (sommario):
A semiactive vibration control method is developed to cope with the dynamic stability problem of a horizontal axis washing machine. This method is based on adjusting the maximum force values produced by the semiactive suspension elements considering a washing machine’s vibration data (three axis angular position and three axis angular acceleration values in time). Before actuation signals are received by the step motors of the friction dampers, vibration data are evaluated, and then, the step motors start to narrow or expand the radius of bracelets located on the dampers. This changes the damping properties of the damper in the suspension system, and thus, the semiactive suspension system absorbs unwanted vibrations and contributes to the dynamic stability of the washing machine. To evaluate the vibration data, the angular position and angular acceleration values in three axes are defined in a function, and the maximum forces produced by semiactive suspension elements are calculated according to the gradient of this function. The relation between the dynamic stability and the walking stability is also investigated. A motion (gyroscope and accelerometer) sensor is installed on the top-front panel of the washing machine because a mathematical model of a horizontal axis washing machine suggests that the walking behavior starts around this location under some assumptions, and therefore, calculating the vibrations occurring there is crucial. Semiactive damping elements are located under the left and right sides of the tub. The proposed method is tested during the spinning cycle of washing machine operation, increasing gradually from 200 rpm to 900 rpm, which produces the most challenging vibration patterns for dynamic stability. Moreover, the sound power levels produced by the washing machine are measured to evaluate the noise performance of the washing machine while the semiactive suspension system is controlled. The effectiveness of the proposed control method is shown through experimental results.
14
Jiang, Yu, Gun Jin Yun, Li Zhao e Junyong Tao. "Experimental Design and Validation of an Accelerated Random Vibration Fatigue Testing Methodology". Shock and Vibration 2015 (2015): 1–13. http://dx.doi.org/10.1155/2015/147871.
Abstract (sommario):
Novel accelerated random vibration fatigue test methodology and strategy are proposed, which can generate a design of the experimental test plan significantly reducing the test time and the sample size. Based on theoretical analysis and fatigue damage model, several groups of random vibration fatigue tests were designed and conducted with the aim of investigating effects of both Gaussian and non-Gaussian random excitation on the vibration fatigue. First, stress responses at a weak point of a notched specimen structure were measured under different base random excitations. According to the measured stress responses, the structural fatigue lives corresponding to the different vibrational excitations were predicted by using the WAFO simulation technique. Second, a couple of destructive vibration fatigue tests were carried out to validate the accuracy of the WAFO fatigue life prediction method. After applying the proposed experimental and numerical simulation methods, various factors that affect the vibration fatigue life of structures were systematically studied, including root mean squares of acceleration, power spectral density, power spectral bandwidth, and kurtosis. The feasibility of WAFO for non-Gaussian vibration fatigue life prediction and the use of non-Gaussian vibration excitation for accelerated fatigue testing were experimentally verified.
15
Mohamadi, Bijan, S. Ali Eftekhari e Davood Toghraie. "Numerical investigation of nonlinear vibration analysis for triple-walled carbon nanotubes conveying viscous fluid". International Journal of Numerical Methods for Heat & Fluid Flow 30, n. 4 (30 gennaio 2019): 1689–723. http://dx.doi.org/10.1108/hff-10-2018-0600.
Abstract (sommario):
Purpose The purpose of this paper is to investigate nonlinear vibrations of triple-walled carbon nanotubes buried within Pasternak foundation carrying viscous fluids. Design/methodology/approach Considering the geometry of nanotubes, the governing equations were initially derived using Timoshenko and modified couple stress theories and by taking into account Von-Karman expressions. Then, by determining boundary conditions, type of fluid motion, Knudsen number and, ultimately, fluid viscosity, the principal equation was solved using differential quadrature method, and linear and nonlinear nanotube frequencies were calculated. Findings The results indicated that natural frequency is decreased as the fluid velocity and aspect ratio increase. Moreover, as the aspect ratio is increased, the results converge for simple and fixed support boundary conditions, and the ratio of nonlinear to linear frequencies approaches. Natural frequency of vibrations and critical velocity increase as Pasternak coefficient and characteristic length increase. As indicated by the results, by assuming a non-uniform velocity for the fluid and a slip boundary condition at Kn = 0.05, reductions of 10.714 and 28.714% were observed in the critical velocity, respectively. Moreover, the ratio of nonlinear to linear base frequencies decreases as the Winkler and Pasternak coefficients, maximum deflection of the first wall and characteristic length are increased in couple stress theory. Originality/value This paper is a numerical investigation of nonlinear vibration analysis for triple-walled carbon nanotubes conveying viscous fluid.
16
Takeda, Hayato, Eikai Murakami, Motonobu Tomoda, Osamu Matsuda, Kentaro Fujita e Oliver B. Wright. "Tapered rainbow metabeam for wideband multimode acoustic blocking based on quadruple-mode resonators". Applied Physics Letters 121, n. 13 (26 settembre 2022): 131701. http://dx.doi.org/10.1063/5.0098371.
Abstract (sommario):
We construct a rainbow metamaterial for multimode sound blocking over a broad range of sub-kHz frequencies in the form of a tapered rectangular cross section beam of machined cells based on elements that can, on average, simultaneously attenuate the majority of the possible elastic-wave polarizations. Using aluminum, we construct a five-cell structure containing sub-wavelength planar resonators with interconnected ribs, which couple to compressional, in-plane shear, flexural, and torsional vibrations. Backed up by numerical simulations, we verify that this tapered structure can, on average, strongly attenuate acoustic modes over the frequency range of the combined metamaterial bandgaps, that is over a frequency range representing ∼50% around ∼0.7 kHz. Applications include vibration isolation.
17
Abouelregal, Ahmed E., S. S. Askar e Marin Marin. "An Axially Compressed Moving Nanobeam Based on the Nonlocal Couple Stress Theory and the Thermoelastic DPL Model". Mathematics 11, n. 9 (4 maggio 2023): 2155. http://dx.doi.org/10.3390/math11092155.
Abstract (sommario):
This article introduces a new model that can be used to describe elastic thermal vibrations caused by changes in temperature in elastic nanobeams in response to transverse external excitations. Using the idea of nonlocal elasticity and the dual-phase lagging thermoelastic model (DPL), the coupled equations of motion and heat transfer were derived to explain small-scale effects. Additionally, modified couple stress theory (MCST) and Euler–Bernoulli (EB) beam assumptions were considered. The proposed theory was verified by considering the thermodynamic response of nanobeams moving horizontally at a constant speed while one end is subjected to a periodic thermal load. The system of governing equations has been solved numerically with the help of Laplace transforms and one of the tested evolutionary algorithms. The effects of changing the nonlocal modulus, the magnitude of the external force, and the length scale parameter on the system fields were investigated. It is also shown how the behavior of the thermal nanobeam changes depending on the phase delay factors in addition to the horizontal velocity of the beam. To determine this model’s accuracy, its results were compared with the results of the classical continuity model and thermoelastic concepts. The numerical results show that when the nanobeam moves, the length scale can change the studied thermal and mechanical vibration wave patterns and physical fields. Additionally, during thermally stimulated vibrations, thermodynamic effects that have implications for the dynamic design and performance improvement of nanostructures must be considered.
18
Nourbakhsh, H., R. Mohammadzadeh, M. Rafiee e R. Rafiee. "Nonlinear Effects on Resonance Behaviour of Beams in Micro Scale". Applied Mechanics and Materials 110-116 (ottobre 2011): 4178–86. http://dx.doi.org/10.4028/www.scientific.net/amm.110-116.4178.
Abstract (sommario):
Nonlinear free and forced oscillation of microscale simply supported beams is investigated in this paper. Introducing a material length scale parameter, the nonlinear model is conducted within the context of non-classical continuum mechanics. By using a combination of the modified couple stress theory and Hamilton’s principle the nonlinear equation of motion is derived. The nonlinear frequencies of a beam with initial lateral displacement are discussed. Equations have been solved using an exact method for free vibration and multiple times scales (MTS) method for forced vibration and some analytical relations have been obtained for natural frequency of oscillations. The results have been compared with previous work and good agreement has been obtained. Also forced vibrations of system in primary resonance have been studied and the effects of different parameters on the frequency-response have been investigated. It is shown that the size effect is significant when the ratio of characteristic thickness to internal material length scale parameter is approximately equal to one, but is diminishing with the increase of the ratio. Our results also indicate that the nonlinearity has a great effect on the vibration behavior of microscale beams.
19
Jang, S.-J., J. W. Kim e Y. J. Choi. "Triangular relationship between vibration modes of an elastically supported rigid body with a plane of symmetry". Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 226, n. 5 (29 settembre 2011): 1254–62. http://dx.doi.org/10.1177/0954406211422145.
Abstract (sommario):
The geometrical properties of vibration modes of a single rigid body with one plane of symmetry are presented. When in-plane vibration modes are represented by the axes normal to the plane of symmetry, three intersecting points of those axes and the plane of symmetry constitute two triangles whose orthocentres are coincident with the mass centre and planar couple point, while the induced wrenches of three out-of-plane modes are found to form two triangles whose orthocentres are lying on the mass centre and the perpendicular translation point. Examining these triangles reveals that the triangular areas are proportional to the distributions of the mass and stiffness in the vibrating system and the shapes of the triangles are related to the natural frequencies. A numerical example is provided to verify the proposed findings.
20
Tadi Beni, Yaghoub, Fahimeh Mehralian e Mehran Karimi Zeverdejani. "Free vibration of anisotropic single-walled carbon nanotube based on couple stress theory for different chirality". Journal of Low Frequency Noise, Vibration and Active Control 36, n. 3 (29 marzo 2017): 277–93. http://dx.doi.org/10.1177/0263092317700153.
Abstract (sommario):
In the present work, using the couple stress theory, a new model is provided for vibrating behavior of anisotropic carbon nanotubes. Carbon nanotubes have many applications, and careful analysis of their behavior is important. So far, using the isotropic models, several studies have been conducted on carbon nanotube vibration. According to the arrangement of carbon atoms on the nanotube walls, their properties will be different in various directions. Therefore, the behavior of carbon nanotubes must be considered as anisotropic materials. In this article, initially, using the Hamilton's principle, motion equations, and boundary conditions of carbon nanotubes are extracted based on couple stress theory. Afterwards, the equations are solved using the analytical solution method. In the results section, the effect of different parameters, particularly the anisotropic effect, on the carbon nanotube natural frequency is investigated.
21
Brunetti, Jacopo, Walter D'Ambrogio e Annalisa Fregolent. "Analysis of the Vibrations of Operators’ Seats in Agricultural Machinery Using Dynamic Substructuring". Applied Sciences 11, n. 11 (21 maggio 2021): 4749. http://dx.doi.org/10.3390/app11114749.
Abstract (sommario):
The vibrations produced by an agricultural machine are transmitted to the seat of the tractor operator and must comply with the limitations imposed by international and national regulations. An agricultural machine is generally composed of a tractor that can be linked to different machines required to perform a large number of agricultural tasks. In this paper, substructuring techniques are proposed to investigate the dynamics of the agricultural machine and to evaluate the resulting vibration exposure to the tractor driver in different configurations of the machine. These techniques allow one to couple reduced-order models or experimental models of the component subsystems to obtain the response of the whole system. In the results, the vibration exposure of the tractor operator is evaluated for different configurations of the agricultural machine, by observing the frequency response function (inertance and transmissibility) and the transient response to a given excitation. In conclusion, these techniques allow one to investigate a large number of different configurations and a wide range of operating conditions with a light computational burden and without asking the manufacturers to share sensitive design details.
22
Alam, Md Mahbub. "Effects of Mass and Damping on Flow-Induced Vibration of a Cylinder Interacting with the Wake of Another Cylinder at High Reduced Velocities". Energies 14, n. 16 (20 agosto 2021): 5148. http://dx.doi.org/10.3390/en14165148.
Abstract (sommario):
Flow-induced vibration is a canonical issue in various engineering fields, leading to fatigue or immediate damage to structures. This paper numerically investigates flow-induced vibrations of a cylinder interacting with the wake of another cylinder at a Reynolds number Re = 150. It sheds light on the effects of mass ratio m*, damping ratio, and mass-damping ratio m*ζ on vibration amplitude ratio A/D at different reduced velocities Ur and cylinder spacing ratios L/D = 1.5 and 3.0. A couple of interesting observations are made. The m* has a greater influence on A/D than ζ although both m* and ζ cause reductions in A/D. The m* effect on A/D is strong for m* = 2–16 but weak for m* > 16. As opposed to a single isolated cylinder case, the mass-damping m*ζ is not found to be a unique parameter for a cylinder oscillating in a wake. The vortices in the wake decay rapidly at small ζ. Alternate reattachment of the gap shear layers on the wake cylinder fuels the vibration of the wake cylinder for L/D = 1.5 while the impingement and switch of the gap vortices do the same for L/D = 3.0.
23
Bambill, Diana V., Graciela I. Guerrero e Daniel H. Felix. "Natural vibrations of micro beams with nonrigid supports". Journal of Vibration and Control 23, n. 19 (29 gennaio 2016): 3233–46. http://dx.doi.org/10.1177/1077546315627727.
Abstract (sommario):
The present study aims to provide some new information for the design of micro systems. It deals with free vibrations of Bernoulli–Euler micro beams with nonrigid supports. The study is based on the formulation of the modified couple stress theory. This theory is a nonclassical continuum theory that allows one to capture the small-scale size effects in the vibrational behavior of micro structures. More realistic boundary conditions are represented with elastic edge conditions. The effect of Poisson’s ratio on the micro beam characteristics is also analyzed. The present results revealed that the characterization of real boundary conditions is much more important for micro beams than for macro beams, and this is an assessment that cannot be ignored.
24
Mahmood, Mahmood S., Ameen A. Nassar e Haider M. Mohammad. "Study of Performance of Incorporating Pneumatic Suspension System with the Hydraulic Actuator for Quarter Car and Using Controllers with Genetic Algorithm". Instrumentation Mesure Métrologie 21, n. 4 (31 agosto 2022): 151–58. http://dx.doi.org/10.18280/i2m.210405.
Abstract (sommario):
Suspension systems are one of the main parts of the vehicle that provide the passenger comfort and stability, while it is difficult for conventional passive suspension systems to cope with the vibrations to which the vehicle is exposed. Air suspension systems have a dynamic character that allows good handling of the road and a comfortable ride, but in a certain area for this reason the stiffness of the air suspension must be flexibly changed. The air suspension has been developed with the inclusion of a hydraulic actuator to create an additional force that withstands the incoming vibration from the road. The pneumatic suspension system parameters, such as vertical acceleration, road holding, and vertical displacement, are improved continuously based on the controllers that have been used for nonlinear pneumatic suspension systems, fractional order proportional integral derivative (FOPID), and fuzzy logic control (FLC). The genetic algorithm is utilized to tune the controller's parameters to the nonlinear active pneumatic system's 3-DOF. A model's simulation outcomes with controllers improved the suspension performance. The proposed active pneumatic system and pneumatic suspension systems are compared when a vehicle is traveling at a speed of 72 km/h on an ISO level B road to test the ability and efficiency of the system to suppress body vibration to enhance safety and provide a comfortable ride on rough roads. According to simulation results, the improved suspension substantially lowers vertical vibrations and enhances road adaptability.
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Chen, Xiong, Ming Qiu, Jie Song, Longxu Ma e Zhenqiang Liao. "Dual Nozzle Weapon Power Couple Vibration Controller With Delayed Rear Nozzle". Journal of Physics: Conference Series 2125, n. 1 (1 novembre 2021): 012034. http://dx.doi.org/10.1088/1742-6596/2125/1/012034.
Abstract (sommario):
Abstract Aiming at the problem that the firing accuracy of barrel weapon is affected by the violent vibration during continuous firing, a double-nozzle vibration controller using the energy of gunpowder gas in the chamber is proposed. The synchronous external injection of the double nozzles of the controller is realized by the delayed ejection of the rear nozzles, so as to generate a power couple to balance the recoil flipping torque of the barrel weapon to achieve the stable firing effect of reducing the bore vibration. A double-nozzle vibration controller with a delayed rear nozzle for a chain gun is designed. The rigid-flexible coupling dynamic model of a chain gun with a double-nozzles vibration controller was established considering the two-phase flow of propellant gas in the barrel and airway. The numerical simulation of the muzzle vibration characteristics of the original weapon and a chain gun equipped with a double-nozzles vibration controller is carried out respectively, and the effectiveness of the double-nozzles dynamic couple vibration controller for the continuous firing vibration control of the barrel weapon is verified.
26
Oveissi, Soheil, Davood Toghraie, S. Ali Eftekhari e Ali J. Chamkha. "Instabilities of SWCNT conveying laminar, incompressible and viscous fluid flow". International Journal of Numerical Methods for Heat & Fluid Flow 30, n. 4 (11 febbraio 2019): 1773–94. http://dx.doi.org/10.1108/hff-10-2018-0563.
Abstract (sommario):
Purpose This study aims to study the transverse vibration and instabilities of the fluid-conveying single-walled carbon nanotubes (CNTs). To this purpose, the Euler–Bernoulli beam model is used. Also, the surface effects, small-size effects of the both fluid and structure and two different elastic mediums viscoelastic and Pasternak elastic are investigated. Design/methodology/approach To consider the nano-scale for the CNT, the strain-inertia gradient theory is used and to solve the governing equation of motion for the system, the Galerkin’s method is used. The effect of the flow velocity, aspect ratio, characteristic lengths of the mentioned theory, effects of Knudsen number and effects of the Winkler, the Pasternak elastic and the viscoelastic medium on the frequencies and stabilities of the system are studied. The effects of the above parameters on the vibrational behavior are investigated both separately and simultaneously. Findings The results show that the critical flow velocity value is increased as the aspect ratio, characteristic lengths, Winkler modulus, shear and damping factors increase. Also, the critical flow velocity is increased by considering the surface effects. In addition, the consequence of increase in the nano-flow-size effects (Knudsen number) is decreasing the critical flow velocity. Moreover, it can be observed that the effect of the shear factor on increasing the critical flow velocity is different from the rest of parameters. Originality/value Use of Timoshenko and modified couple stress theories and taking into account Von-Karman expressions for investigating the nonlinear vibrations of triple-walled CNTs buried within Pasternak foundation.
27
Hong, Liu, Yongzhi Qu, Yuegang Tan, Mingyao Liu e Zude Zhou. "Vibration Based Diagnosis for Planetary Gearboxes Using an Analytical Model". Shock and Vibration 2016 (2016): 1–11. http://dx.doi.org/10.1155/2016/2620518.
Abstract (sommario):
The application of conventional vibration based diagnostic techniques to planetary gearboxes is a challenge because of the complexity of frequency components in the measured spectrum, which is the result of relative motions between the rotary planets and the fixed accelerometer. In practice, since the fault signatures are usually contaminated by noises and vibrations from other mechanical components of gearboxes, the diagnostic efficacy may further deteriorate. Thus, it is essential to develop a novel vibration based scheme to diagnose gear failures for planetary gearboxes. Following a brief literature review, the paper begins with the introduction of an analytical model of planetary gear-sets developed by the authors in previous works, which can predict the distinct behaviors of fault introduced sidebands. This analytical model is easy to implement because the only prerequisite information is the basic geometry of the planetary gear-set. Afterwards, an automated diagnostic scheme is proposed to cope with the challenges associated with the characteristic configuration of planetary gearboxes. The proposed vibration based scheme integrates the analytical model, a denoising algorithm, and frequency domain indicators into one synergistic system for the detection and identification of damaged gear teeth in planetary gearboxes. Its performance is validated with the dynamic simulations and the experimental data from a planetary gearbox test rig.
28
Estabragh, Ehsan Raeisi, e Gholam Hossein Baradaran. "Large Amplitude Free Vibration Analysis of Nanobeams Based on Modified Couple Stress Theory". International Journal of Structural Stability and Dynamics 21, n. 09 (19 maggio 2021): 2150129. http://dx.doi.org/10.1142/s0219455421501297.
Abstract (sommario):
In this study, the large amplitude free vibration of nanobeams based on the modified couple stress theory was developed by using Total Lagrangian finite element formulation. In this study, Timoshenko beam theory has been used in free vibration analysis of nanobeams. Minimal kinematic assumptions have been used to model nanobeams. With this model, free vibration of nanobeams with small to large amplitude and with arbitrary boundary conditions can be analyzed. The numerical results obtained for free vibration based on the modified couple stress theory with small amplitude and the results obtained for free vibration with large amplitude without considering the modified couple stress theory are in good agreement with the similar results reported in previous research. Effects of the dimensionless length scale parameter, slenderness ratio, vibration amplitude and different boundary conditions on the nonlinear frequency ratio of nanobeams have been investigated. The results show the importance of considering nonlinear and size effects in the free vibration analysis of nanobeams with large amplitude.
29
Liu, Jia, e Xuesong Jin. "Research on the Vibration Insulation of High-Speed Train Bogies in Mid and High Frequency". Shock and Vibration 2018 (2018): 1–13. http://dx.doi.org/10.1155/2018/6759105.
Abstract (sommario):
According to a large amount of the test data, the mid and high frequency vibrations of high-speed bogies are very notable, especially in the 565~616 Hz range, which are just the passing frequencies corresponding to the 22nd to 24th polygonal wear of the wheel. In order to investigate the main cause of wheel higher-order polygon formation, a 3D flexible model of a Chinese high-speed train bogie is developed using the explicit finite element method. The results show that the couple vibration of bogie and wheelset may lead to the high-order wears of wheel. In order to reduce the coupled resonance of the wheelset and the bogie frame, the effects of the stiffness and damping of the primary suspensions, wheelset axle radius, and bogie frame strength on the vibration transmissibility are discussed carefully. The numerical results show that the resonance peaks in high frequency range can be reduced by reducing the stiffness of axle box rotary arm joint, reducing the wheelset axle radius or strengthening the bogie frame location. The related results may provide a reference for structure improvement of the existing bogies and structure design of the new high-speed bogies.
30
Bisegna, Paolo, e Giovanni Caruso. "A Continuous Model for the Dynamical Analysis of Mistuned Bladed Rotors". International Journal of Rotating Machinery 2012 (2012): 1–10. http://dx.doi.org/10.1155/2012/378565.
Abstract (sommario):
Ideal bladed rotors are rotationally symmetric, as a consequence they exhibit couples of degenerate eigenmodes at coinciding frequencies. When even small imperfections are present destroying the periodicity of the structure (disorder or mistuning), each couple of degenerate eigenfrequencies splits into two distinct values (frequency split) and the corresponding modal shapes exhibit vibration amplitude peaks concentrated around few blades (localization phenomenon). In this paper a continuous model describing the in-plane vibrations of a mistuned bladed rotor is derived via the homogenization theory. Imperfections are accounted for as deviations of the mass and/or stiffness of some blades from the design value; a perturbation approach is adopted in order to investigate the frequency split and localization phenomena arising in the imperfect structure. Numerical simulations show the effectiveness of the proposed model, requiring much lower computational effort than classical finite element schemes.
31
Mirjavadi, Seyed Sajad, Behzad Mohasel Afshari, Navvab Shafiei, Samira Rabby e Mohammad Kazemi. "Effect of temperature and porosity on the vibration behavior of two-dimensional functionally graded micro-scale Timoshenko beam". Journal of Vibration and Control 24, n. 18 (26 luglio 2017): 4211–25. http://dx.doi.org/10.1177/1077546317721871.
Abstract (sommario):
This work is aimed to present analysis on the thermal vibrational behavior of two-dimensional functionally graded porous microbeams based on Timoshenko beam theory. According to the power law function, the material composition and so the material properties are varying along thickness and axis of the microbeam. The governing equations are derived on the basis of the couple stress theory and the generalized differential quadrature method is used to solve the equations. The temperature gradient is considered to be uniform and nonuniform across the thickness of the microbeam. The results are presented to show the effect of temperature change, porosity, functionally graded and axially functionally graded power indexes and also micro-scale parameter on the vibration of the microbeam.
32
Elahinia, Mohammad H., Jeong-Hoi Koo e Honghao Tan. "Improving Robustness of Tuned Vibration Absorbers Using Shape Memory Alloys". Shock and Vibration 12, n. 5 (2005): 349–61. http://dx.doi.org/10.1155/2005/168260.
Abstract (sommario):
A conventional passive tuned vibration absorber (TVA) is effective when it is precisely tuned to the frequency of a vibration mode; otherwise, it may amplify the vibrations of the primary system. In many applications, the frequency often changes over time. For example, adding or subtracting external mass on the existing primary system results in changes in the system’s natural frequency. The frequency changes of the primary system can significantly degrade the performance of TVA. To cope with this problem, many alternative TVAs (such as semiactive, adaptive, and active TVAs) have been studied. As another alternative, this paper investigates the use of Shape Memory Alloys (SMAs) in passive TVAs in order to improve the robustness of the TVAs subject to mass change in the primary system. The proposed SMA-TVA employs SMA wires, which exhibit variable stiffness, as the spring element of the TVA. This allows us to tune effective stiffness of the TVA to adapt to the changes in the primary system's natural frequency. The simulation model, presented in this paper, contains the dynamics of the TVA along with the SMA wire model that includes phase transformation, heat transfer, and the constitutive relations. Additionally, a PID controller is included for regulating the applied voltage to the SMA wires in order to maintain the desired stiffness. The robustness analysis is then performed on both the SMA-TVA and the equivalent passive TVA. For our robustness analysis, the mass of the primary system is varied by ± 30% of its nominal mass. The simulation results show that the SMA-TVA is more robust than the equivalent passive TVA in reducing peak vibrations in the primary system subject to change of its mass.
33
Friskney, Brett, Panagiotis Alevras, Sourabh Londhe, Stephanos Theodossiades e Donald Michael McFarland. "A Nonlinear Energy Sink Design to Attenuate the Torsional Oscillations of Lightly Loaded Gear Pairs". Applied Sciences 12, n. 13 (4 luglio 2022): 6778. http://dx.doi.org/10.3390/app12136778.
Abstract (sommario):
Nonlinear energy sinks (NES) have recently attracted significant interest for the suppression of unwanted vibrations in a variety of mechanical systems. The key advantage in employing this (vibration absorber) approach is the broadband nature of the interactions with a primary system for which vibration energy dissipation is required. Thus, the effectiveness of the NES is decoupled from the need of tuning to specific frequencies. Nevertheless, NES for rotational fluctuations of powertrains have received limited attention in the literature. In this work, a design for a rotational NES to mitigate speed fluctuations in gear trains is presented and tested experimentally. The development of the proposed system is underpinned by previous optimisation studies conducted by the authors, where a disk was utilised as an inerter NES. A set of beams couple the inerter with the wheel gear of a spur gear pair with a nonlinear restoring torque, which is designed to approach the desired essential nonlinearity within realistic practical tolerances. Static and dynamic identification is conducted to confirm the desired characteristics. Despite uncertainties in the prototype testing, the approach is found to reduce the speed fluctuations on the gear pair output shaft, with appropriate predictability established for the model and the design procedure.
34
Bhattacharya, Sujash, e Debabrata Das. "Modified couple stress-based free vibration behavior of pre-twisted tapered BFGM rotating micro beam considering spin-softening and Coriolis effects". Proceedings of the Institution of Mechanical Engineers, Part L: Journal of Materials: Design and Applications 234, n. 1 (31 agosto 2019): 21–47. http://dx.doi.org/10.1177/1464420719870822.
Abstract (sommario):
An improved mathematical model of pre-twisted tapered rotating micro beams made of bidirectional functionally graded material (BFGM) is presented to study its free vibration behavior. The effects of spin-softening and Coriolis acceleration are incorporated, and modified couple stress theory is employed to address the size effect. The mathematical formulation is based on first-order shear deformation theory and is developed in a global non-inertial frame incorporating appropriate transformations between the global inertial frame and the local non-inertial frame. Two different but interrelated steps are employed, where the first step determines the centrifugally deformed configuration using minimum potential energy principle, and the second step determines the free vibration behavior through tangent stiffness of the deformed rotating beam using Hamilton's principle. The direct use of tangent stiffness considers the centrifugal stiffening effect through von Kármán non-linearity and bypasses the need of strain energy functional for the vibrating beam. The governing equations are transformed to an eigenvalue problem through state-space approach and solved following Ritz method. The effects of spin-softening, Coriolis acceleration, and pre-twist angle are shown and discussed. The effects of different parameters such as size-dependent parameter, aspect ratio, material gradation indices, operating temperature, FGM constituent, taperness parameters, and slender parameter are discussed.
35
Shojaeefard, Mohammad Hassan, Hamed Saeidi Googarchin, Mohammad Mahinzare e Seyed Ahmad Eftekhari. "Magnetic field effect on free vibration of smart rotary functionally graded nano/microplates: A comparative study on modified couple stress theory and nonlocal elasticity theory". Journal of Intelligent Material Systems and Structures 29, n. 11 (27 aprile 2018): 2492–507. http://dx.doi.org/10.1177/1045389x18770875.
Abstract (sommario):
In this article, free vibration behavior of a rotating nano/microcircular plate constructed from functionally graded magneto-elastic material is simulated with the first-order shear deformation theory. For the sake of comparison, the nonlocal elasticity theory and the modified couple stress theory are employed to implement the small size effect in the natural frequencies behavior of the nano/microcircular plate. The governing equations of motion for functionally graded magneto-elastic material nano/microcircular plates are derived based on Hamilton’s principle; comparing the obtained results with those in the literature, they are in a good agreement. Finally, the governing equations are solved using the differential quadrature method. It is shown that the vibrational characteristics of functionally graded magneto-elastic material nano/microcircular plates are significantly affected by non-dimensional angular velocity, size dependency of the Eringen’s and the modified couple stress theories, and power law index for clamped and hinged boundary conditions. Results show that a critical point occurs by increasing the angular velocity and the effect of several parameters are changed after this point.
36
Yang, Liang, Ming Qiu, Zhenqiang Liao, Jie Song, Zijian Li e Wenjun Huang. "Research on Vibration Control of Paired Inclined Nozzles Dynamic Coupled Tubes". Journal of Physics: Conference Series 2528, n. 1 (1 luglio 2023): 012040. http://dx.doi.org/10.1088/1742-6596/2528/1/012040.
Abstract (sommario):
Abstract The barrel vibrates violently, which will lead to a serious drop in shooting accuracy. To solve this issue, a barrel vibration control method of the paired oblique nozzle dynamic couple is proposed. A pair of inclined nozzle devices are designed on the barrel to fully use the gunpowder gas energy in the chamber during the shooting process. A dynamic couple is generated to balance the turning moment of the barrel weapon. Simultaneously, the recoil force is reduced by exporting the gunpowder gas in the chamber. Therefore, the vibration of the barrel is reduced. Firstly, the internal ballistic two-phase flow model including the gas transient flow model in the vibration control device is modelled based on the internal ballistic theory of two-phase flow. Secondly, the numerical simulation of the weapon launching process is carried out. Thirdly, the rigid-flexible coupling firing dynamics modelling and simulation research is conducted on a 30mm chain gun equipped with a paired oblique nozzle dynamic couple vibration control device. At last, the effects of the device on the continuous firing vibration control of barrel weapons are analyzed. The results show that the vibration reduction efficiency of the inclined nozzle is better than that of the vertical nozzle and the horizontal nozzle. When the angle of the inclined nozzle is 30°, the barrel shows the highest vibration reduction efficiency. The vibration reduction efficiency of each vibration characteristic is 39.2%, 17.1%, 44.8%, and 48.9%, respectively.
37
Chen, Yong, Penghui Xia e Xin Liu. "Axial Impact Analysis of Torsion Impactor Based on Water Strike Effect". Academic Journal of Science and Technology 7, n. 2 (27 settembre 2023): 151–60. http://dx.doi.org/10.54097/ajst.v7i2.12259.
Abstract (sommario):
The stick-slip vibration phenomenon that occurs during the drilling process not only reduces the drilling speed, but also affects the performance of the drill pipe and the service life of the drill bit. In response to the problem of stick-slip vibration, a torsional impactor has been developed. The tool, through its internal throttle action, will produce a sudden change in the mass flow of fluid in the central tube and thus produce a water strike phenomenon, and the change in the axial force of the torsional impactor caused by the water strike effect can cope with the stick-slip vibration that occurs during drilling as well as increase the drilling efficiency. In this paper, the axial impact capacity of the tool is investigated based on its water impact effect. CFD simulations were used to determine the axial impact capacity of the torsional impactor at different drilling fluid flow rates, and the maximum equivalent force of the central tube under the water impact effect was analyzed and strength checks were performed. The research results show that: two axial vibrations occur in the center tube within half a working cycle; As the drilling fluid flow rate increased from 24L/s to 31L/s, the axial impact force of the torsion impactor increased from 32506N to 43189N; the maximum equivalent force of the center tube is 106.59 MPa, which meets the impact strength requirements. Finally, it was verified through field tests that the water impact effect generated inside the torsional impactor can effectively solve the stick-slip vibration problem and improve the rock-breaking efficiency under different drilling fluid flow rates.
38
Neuman, Tomáš, Javier Aizpurua e Ruben Esteban. "Quantum theory of surface-enhanced resonant Raman scattering (SERRS) of molecules in strongly coupled plasmon–exciton systems". Nanophotonics 9, n. 2 (25 febbraio 2020): 295–308. http://dx.doi.org/10.1515/nanoph-2019-0336.
Abstract (sommario):
AbstractLocalised surface plasmons can couple strongly with the electronic transitions of a molecule, inducing new hybridised states of light and matter, the plasmon–exciton polaritons. Furthermore, molecules support vibrational degrees of freedom that interact with the electronic levels, giving rise to inelastic resonant Raman scattering under coherent laser illumination. Here we show the influence of strong plasmon–exciton coupling on resonant Raman processes that populate the vibrational states of the molecule and that lead to the characteristic surface-enhanced Raman scattering spectra. We develop analytical expressions that give insight into these processes for the case of moderate illumination intensity, weak electron–vibration coupling and no dephasing. These expressions help us to elucidate the twofold role of plasmon–exciton polaritons to pump the system efficiently and to enhance the Raman emission. Our results show a close analogy with the optomechanical process described for off-resonant Raman scattering but with a difference in the resonant reservoir. We also use full numerical calculations to study the effects reaching beyond these approximations and discuss the interplay between the fluorescence background and the Raman lines. Our results allow for better understanding and exploitation of the strong coupling regime in vibrational pumping and in the surface-enhanced resonant Raman scattering signal.
39
Yayli, Mustafa Özgür. "Torsional vibrations of restrained nanotubes using modified couple stress theory". Microsystem Technologies 24, n. 8 (22 gennaio 2018): 3425–35. http://dx.doi.org/10.1007/s00542-018-3735-3.
40
Mazur, Krzysztof, e Marek Pawełczyk. "Hammerstein Nonlinear Active Noise Control with the Filtered-Error LMS Algorithm". Archives of Acoustics 38, n. 2 (1 giugno 2013): 197–203. http://dx.doi.org/10.2478/aoa-2013-0023.
Abstract (sommario):
Abstract Active Noise Control (ANC) of noise transmitted through a vibrating plate causes many problems not observed in classical ANC using loudspeakers. They are mainly due to vibrations of a not ideally clamped plate and use of nonlinear actuators, like MFC patches. In case of noise transmission though a plate, nonlinerities exist in both primary and secondary paths. Existence of nonlinerities in the system may degrade performance of a linear feedforward control system usually used for ANC. The performance degradation is especially visible for simple deterministic noise, such as tonal noise, where very high reduction is expected. Linear feedforward systems in such cases are unable to cope with higher harmonics generated by the nonlinearities. Moreover, nonlinearities, if not properly tackled with, may cause divergence of an adaptive control system. In this paper a feedforward ANC system reducing sound transmitted through a vibrating plate is presented. The ANC system uses nonlinear control filters to suppress negative effects of nonlinearies in the system. Filtered-error LMS algorithm, found more suitable than usually used Filtered-reference LMS algorithm, is employed for updating parameters of the nonlinear filters. The control system is experimentally verified and obtained results are discussed.
41
Mazur, Olga, e Jan Awrejcewicz. "Ritz Method in Vibration Analysis for Embedded Single-Layered Graphene Sheets Subjected to In-Plane Magnetic Field". Symmetry 12, n. 4 (2 aprile 2020): 515. http://dx.doi.org/10.3390/sym12040515.
Abstract (sommario):
Vibrations of single-layered graphene sheets subjected to a longitudinal magnetic field are considered. The Winkler-type and Pasternak-type foundation models are employed to reproduce the surrounding elastic medium. The governing equation is based on the modified couple stress theory and Kirchhoff–Love hypotheses. The effect of the magnetic field is taken into account due to the Lorentz force deriving from Maxwell’s equations. The developed approach is based on applying the Ritz method. The proposed method is tested by a comparison with results from the existing literature. The numerical calculations are performed for different boundary conditions, including the mixed ones. The influence of the material length scale parameter, the elastic foundation parameters, the magnetic parameter and the boundary conditions on vibration frequencies is studied. It is observed that an increase of the magnetic parameter, as well as the elastic foundation parameters, brings results closer to the classical plate theory results. Furthermore, the current study can be applied to the design of microplates and nanoplates and their optimal usage.
42
Sundukov, A. Ye, e Ye V. Shakhmatov. "Series of diagnostic indicators of gearbox teeth wear in aircraft gas turbine engines". VESTNIK of Samara University. Aerospace and Mechanical Engineering 21, n. 4 (18 gennaio 2023): 109–17. http://dx.doi.org/10.18287/2541-7533-2022-21-4-109-117.
Abstract (sommario):
Aircraft gas turbine engine gearboxes are intended for providing optimum rotational speeds for propellers and fans. Wear of the tooth flanks is their key and most dangerous defect. The defect generates vibrations leading to fatigue failure of engine components. Vibration-based diagnostics is the most effective tool of non-destructive testing of the technical condition of rotating machines. This review of the known diagnostic indicators of the defect in question shows the need for its significant expansion. Previously performed researches made it possible to suggest a series of diagnostic indicators of tooth wear for the sun gear satellites couple in the differential reducer of a gas turbine engine. It is shown that the mathematical models of the dependence of the levels of diagnostic indicators on the wear value have both linear and power form. It was found that diagnostic indicators described by power dependences are the closest ones to the model of wear development. It is noted that when selecting diagnostic indicators for operating conditions, the optimal ones should be recognized as those based on the parameters of the current frequency.
43
Ambattu, Lizebona A., e Leslie Yeo. "Sonomechanobiology: High frequency cell mechanostimulation". Journal of the Acoustical Society of America 154, n. 4_supplement (1 ottobre 2023): A51. http://dx.doi.org/10.1121/10.0022765.
Abstract (sommario):
It is well known that cells respond in many different ways to various forms of mechanical cues. To date, however, mechanostimulation has typically been carried out statically or at relatively low frequencies (several Hz), characteristic of the frequencies associated with the motion experienced by cells in their local environment, for example, in the human body (e.g., walking and running). Where higher frequency vibrational mechanotransduction pathways have been investigated, these have primarily been limited to kHz order, and it has generally been suggested that there is no significant advantage in utilising higher frequencies. In a similar manner to observations of new and often nonlinear discoveries when we couple high frequency (10–30 MHz) vibration in the form of surface and hybrid acoustic waves into fluids as well as crystalline materials, we however observe unique and novel phenomena when similar MHz-order vibrational stimuli are transmitted into cells. These include modulation of various ion and piezo channels, and transient, yet reversible, permeabilization of the cell membrane, which have implications for efficient intracellular cytosol delivery, exosome biogenesis, cytoskeletal reorganization and stem cell differentiation, at the same time maintaining very high levels (>95%) in cellular viability.
44
Lin, F., J. S. Peng, S. F. Xue, L. Yang e J. Yang. "Nonlinear free vibration of size-dependent microbeams with nonlinear elasticity under various boundary conditions". Journal of Mechanics 37 (2021): 380–403. http://dx.doi.org/10.1093/jom/ufab009.
Abstract (sommario):
Abstract In this study, nonlinear couple stress–strain constitutive relationships in the modified couple stress theory (MCST) are derived on the basis of previous classical stress–strain constitutive relationships of nonlinear elasticity materials. Hamilton's principle is employed to obtain higher-order nonlinear governing equations within the framework of the updated MCST, von Kármán geometric nonlinearity and Bernoulli–Euler beam theory. These mathematical formulations are solved numerically by the differential quadrature method together with an iterative algorithm to determine the nonlinear dynamic features of microbeams with four groups of boundary conditions. A detailed parametric study is conducted to analyze the influences of nonlinear elasticity properties on the nonlinear free vibration characteristics of the microbeams. Results show that these microbeams exhibiting nonlinear couple constitutive relationships have lower frequencies than their approximately simplified linear couple constitutive relationships. In addition, the frequencies of microbeams with nonlinear elasticity properties decrease as the vibration amplitude increases.
45
Santos, J. V. Araújo dos, e J. N. Reddy. "Vibration of Timoshenko Beams Using Non-classical Elasticity Theories". Shock and Vibration 19, n. 3 (2012): 251–56. http://dx.doi.org/10.1155/2012/307806.
Abstract (sommario):
This paper presents a comparison among classical elasticity, nonlocal elasticity, and modified couple stress theories for free vibration analysis of Timoshenko beams. A study of the influence of rotary inertia and nonlocal parameters on fundamental and higher natural frequencies is carried out. The nonlocal natural frequencies are found to be lower than the classical ones, while the natural frequencies estimated by the modified couple stress theory are higher. The modified couple stress theory results depend on the beam cross-sectional size while those of the nonlocal theory do not. Convergence of both non-classical theories to the classical theory is observed as the beam global dimension increases.
46
Jousse, Fabien, Daniel P. Vercauteren e Scott M. Auerbach. "How Does Benzene in NaY Zeolite Couple to the Framework Vibrations?" Journal of Physical Chemistry B 104, n. 37 (settembre 2000): 8768–78. http://dx.doi.org/10.1021/jp9942872.
47
Eskandari Shahraki, Majid, Mahmoud Shariati, Mohsen Heydari Beni e Jafar Eskandari Jam. "Bending, buckling and Vibrations Analysis of the graphene nanoplate using the modified couple stress theory". Mechanics 27, n. 5 (12 ottobre 2021): 376–84. http://dx.doi.org/10.5755/j02.mech.25298.
Abstract (sommario):
In this paper using the modified couple stress theory, to study the bending, buckling and vibration characteristics of the rectangular Mindlin's nanoplates with graphene material was investigated. With the aim of considering the effects of small scales, the modified couple stress theory, which has only one parameter of length scale and also was presented by Yang in 2002, was used. In the modified couple stress theory; the strain energy density is a function of the components of the strain tensor, curvature tensor, stress tensor and the symmetric part of the couple stress tensor. After obtaining the strain energy, external work, and buckling equation and placing them in the Hamilton's equation, the basic and auxiliary equations of the nanoplates were obtained. Then, by applying boundary and force conditions in the governing equations, the bending, buckling and vibration of the rectangular graphene nanoplates with thickness h and simply-supported conditions were explored. Also, the solution method was the Navier's solution.
48
Abbaspour, Fatemeh, e Hadi Arvin. "Vibration and thermal buckling analyses of three-layered centrosymmetric piezoelectric microplates based on the modified consistent couple stress theory". Journal of Vibration and Control 26, n. 15-16 (30 aprile 2020): 1253–65. http://dx.doi.org/10.1177/1077546320924273.
Abstract (sommario):
In this study, free and forced vibration investigations and thermal buckling analysis of three-layered centrosymmetric piezoelectric microplates are examined. To model the size effects, the size-dependent consistent couple stress theory is used. To be compatible with the modified coupled stress theory, a modification is proposed to apply to the consistent couple stress theory. Resorting to the Navier’s approach, the governing equations are treated in the case of simply supported boundary conditions to extract the free and forced vibration outcomes and the thermal buckling numerical results. The verifications demonstrate the effectiveness of the proposed modification. The effects of the material length scale parameter and the flexoelectricity coefficient on the findings are investigated. Moreover, the closed- and open-circuit condition impacts on the free and forced vibration and the thermal buckling analyses are studied.
49
Becker, Fabian B., Martin A. Sehr e Stephan Rinderknecht. "Vibration isolation for parameter-varying rotor systems using piezoelectric actuators and gain-scheduled control". Journal of Intelligent Material Systems and Structures 28, n. 16 (1 febbraio 2017): 2286–97. http://dx.doi.org/10.1177/1045389x17689933.
Abstract (sommario):
This paper deals with the active vibration isolation for a rotor subject to gyroscopic oscillations, where gain-scheduled [Formula: see text]-control is used to steer an active, piezoelectric bearing. Rotating machines are often exposed to gyroscopic effects, which occur due to bending deformations of rotors and subsequent tilting of eccentric mass elements. Gyroscopic moments observed at rotors are proportional to the rotational speed and couple radial degrees of freedom. This relationship with the operating conditions renders the system dynamics well-suited for the use of linear parameter-varying models and controllers, relying on the rotational speed as an uncertain parameter. In this paper, we design linear gain-scheduled [Formula: see text]-controllers guaranteeing both robust stability and performance within a given range of operating conditions. The paper is based on a rotor test rig with two unbalance-induced resonance frequencies in its operating range. The rotor has two protruding discs, one of which is centered between one active and one passive bearing support. The active support consists of two piezoelectric stack actuators and two collocated piezoelectric load washers. Closed-loop performance is assessed via isolation of unbalance-induced vibrations using both simulation and supporting experimental data.
50
Huang, Chunlin, Jianshe Peng, Lin Fan e Yang Liu. "Forced Vibration Analysis of Bimodular Microbeams Based on the Modified Couple Stress Theory". Journal of Physics: Conference Series 2437, n. 1 (1 gennaio 2023): 012075. http://dx.doi.org/10.1088/1742-6596/2437/1/012075.
Abstract (sommario):
Abstract The forced vibration model of bimodular microbeams is studied in this paper based on the modified couple stress theory. The effects of the bimodular characteristic and the size effect are considered in this model. The forced vibration governing equation, boundary conditions, and initial conditions are obtained by Hamilton’s principle. The influence of the bimodular ratio and the material length scale parameters on the time history response are investigated based on the analytical method. Results show that the larger the two parameters, the higher the frequency and the smaller amplitude.