2021-09-21T18:11:31Z
http://tava.isav.ir/?_action=export&rf=summon&issue=3419
Journal of Theoretical and Applied Vibration and Acoustics
2423-4761
2423-4761
2016
2
1
Free in-plane vibration of heterogeneous nanoplates using Ritz method
Shirko
Faroughi
Seyed Mohammad Hossein
Goushegir
In this paper, the Ritz method has been employed to analyze the free in-plane vibration of heterogeneous (non-uniform) rectangular nanoplates corresponding to Eringen’s nonlocal elasticity theory. The non-uniformity is taken into account using combinations of linear and quadratic forms in the thickness, material density and Young’s modulus. Two-dimensional boundary characteristic orthogonal polynomials are applied in the Ritz method in order to examine the nonlocal effect, aspect ratio, length of nanoplate and non-uniformity parameters on the vibrational behaviors of the nanoplate. Results are verified with the available published data and good agreements are observed. The outcomes confirm apparent dependency of in-plane frequency of nanoplate on the small scale effect, non-uniformity, aspect ratio and boundary conditions. For instance, frequency parameter decreases by increasing the nonlocal parameter in all vibration modes; the frequency parameters increase with length and aspect ratio of nanoplates. Furthermore, the effect of nonlocal parameters on the frequency parameter is more prominent at the higher aspect ratios. Finally, the effect of nonlocal parameter on the in-plane modes is also presented in this analysis.
In-plane vibration
Rectangular heterogeneous nanoplate
Nonlocal elasticity theory
Ritz method
2016
01
01
1
20
http://tava.isav.ir/article_15342_13964456d67a2be70d2e712d68470b24.pdf
Journal of Theoretical and Applied Vibration and Acoustics
2423-4761
2423-4761
2016
2
1
Numerical solution of unsteady flow on airfoils with vibrating local flexible membrane
Alireza
Naderi
Mohammad
Mojtahedpoor
Unsteady flow separation on the airfoils with local flexible membrane (LFM) has been investigated in transient and laminar flows by the finite volume element method. A unique feature of the present method compared with the common computational fluid dynamic softwares, especially ANSYS CFX, is the modification using the physical influence scheme in convection fluxes at cell surfaces. In contrary to the common softwares which use mathematical methods for discretization, this method considers the physical effects on approximation and discretization and thus increases the accuracy of solution and decreases the diffusion errors significantly. We have focused on the effects of deformation of the membrane on aerodynamic characteristics. For this purpose, first, we have solved the flow on NACA0012 airfoil in Reynolds number of 5000 and investigated the effects of local flexible membrane on aerodynamic coefficients in laminar flow. Then, we have solved the flow over LH37 airfoil in Reynolds number of 1.1×106 and studied the effects of flexible membrane on aerodynamic characteristics in transient flow. To calculate the Reynolds stress in turbulence equations, transient γ-Reθ model has been used. According to the results, airfoil with local flexible membrane prevents flow separation, eliminates laminar separation bubble (LSB) and delays the stall.
Finite volume element
Fluid solid interaction
Local flexible membrane
Low rReynolds number
2016
01
01
21
34
http://tava.isav.ir/article_18559_48c63d74efbc2aa5aa2accda665a849f.pdf
Journal of Theoretical and Applied Vibration and Acoustics
2423-4761
2423-4761
2016
2
1
A finite element model for extension and shear modes of piezo-laminated beams based on von Karman's nonlinear displacement-strain relation
Ahmad Ali
Tahmasebi Moradi
Saeed
Ziaei-Rad
Reza
Tikani
Hamid Reza
Mirdamadi
Piezoelectric actuators and sensors have been broadly used for design of smart structures over the last two decades. Different theoretical assumptions have been considered in order to model these structures by the researchers. In this paper, an enhanced piezolaminated sandwich beam finite element model is presented. The facing layers follow the Euler-Bernoulli assumption while the core layers are modeled with the third-order shear deformation theory (TSDT). To refine the model, the displacement-strain relationships are developed by using von Karman's nonlinear displacement-strain relation. It will be shown that this assumption generates some additional terms on the electric fields and also introduces some electromechanical potential and non-conservative work terms for the extension piezoelectric sub-layers. A variational formulation of the problem is presented. In order to develop an electromechanically coupled finite element model of the extension/shear piezolaminated beam, the electric DoFs as well as the mechanical DoFs are considered. For computing the natural frequencies, the governing equation is linearized around a static equilibrium position. Comparing natural frequencies, the effect of nonlinear terms is studied for some examples
Piezolaminated sandwich beam
Finite element model
von Karman's relation
Third-order shear deformation theory
2016
01
01
35
64
http://tava.isav.ir/article_19079_1d303d79b66f028d059b6d4dc72e63c3.pdf
Journal of Theoretical and Applied Vibration and Acoustics
2423-4761
2423-4761
2016
2
1
Finite element model updating of bolted lap joints implementing identification of joint affected region parameters
Saeed
Shokrollahi
Farhad
Adel
In this research, the new concept of ‘bolted joint affected region (BJAR)’ is introduced to simulate dynamical behavior of bolted lap joints. Such regions are modeled via special elements called contact zone element (CZE) which unify the neighboring contact surfaces of substructures. These elements are different from the thin layer interface elements that form an individual layer between the two substructures. The CZEs have no specified elastic characteristics. They are thus different from the adjoining solid elements and the constitutive relation for them is prescribed in normal and shear components. The unknown parameters of the model can be identified throughout model updating with modal test data. The structure’s frequency response function (FRF) is measured by excitation with an impact hammer and the measured responses are compared with model predictions including the CZEs’ parameters. The difference between the measured and predicted frequencies is minimized as the objective function. The optimized thickness and density are considered in addition to the elastic properties of BJAR. The competency of the proposed procedure is verified with modeling an actual structure containing a single lap bolted joint coupling two identical structural steel beams. The results showed proper conformity with model predictions. This model can be incorporated into the commercial finite element codes to simulate bolted joints for large and complex structures considering its accuracy and computationally efficient manner
Bolted joint affected region
Model updating
Contact zone element
identification
2016
01
01
65
78
http://tava.isav.ir/article_19385_13616cec3334ea2edfab34400113c5e4.pdf
Journal of Theoretical and Applied Vibration and Acoustics
2423-4761
2423-4761
2016
2
1
A one-dimensional model for variations of longitudinal wave velocity under different thermal conditions
Ramin
Shabani
Farhang
Honarvar
Ultrasonic testing is a versatile and important nondestructive testing method. In many industrial applications, ultrasonic testing is carried out at relatively high temperatures. Since the ultrasonic wave velocity is a function of the workpiece temperature, it is necessary to have a good understanding of how the wave velocity and test piece temperature are related. In this paper, variations of longitudinal wave velocity in the presence of a uniform temperature distribution or a thermal gradient is studied using one-dimensional theoretical and numerical models. The numerical model is based on finite element analysis. A linear temperature gradient is assumed and the length of the workpiece and the temperature of the hot side are considered as varying parameters. The workpiece is made of st37 steel, its length is varied in the range of 0.04-0.08 m and the temperature of the hot side is changed from 400 K to 1000 K. The results of the theoretical model are compared with those obtained from the finite element model (FEM) and very good agreement is observed.
Longitudinal ultrasonic wave
Thermal gradient
Theoretical method
finite element method
2016
01
01
79
90
http://tava.isav.ir/article_19717_e504a059c22c21722e4688aacd09095a.pdf
Journal of Theoretical and Applied Vibration and Acoustics
2423-4761
2423-4761
2016
2
1
Nonlinear dynamic analysis of a four-bar mechanism having revolute joint with clearance
Sajjad
Boorghan Farahan
Mohammad Reza
Ghazavi
Sasan
Rahmanian
In general, joints are assumed without clearance in the dynamic analysis of multi-body echanical systems. When joint clearance is considered, the mechanism obtains two uncontrollable degrees of freedom and hence the dynamic response considerably changes. The joints’ clearances are the main sources of vibrations and noise due to the impact of the coupling parts in the joints. Therefore, the system responses lead to chaotic and unpredictable behaviors instead of being periodic and regular. In this paper, nonlinear dynamic behavior of a four-bar linkage with clearance at the joint between the coupler and the rocker is studied. The system response is performed by using a nonlinear continuous contact force model proposed by Lankarani and Nikravesh [1] and the friction effect is considered by a modified Coulomb friction law [2]. By using the Poincaré portrait, it is proven that either strange attractors or chaos exist in the system response. Numerical simulations display both periodic and chaotic motions in the system behavior. Therefore, bifurcation analysis is carried out with a change in the size of the clearance corresponding to different values of crank rotational velocities. Fast Fourier Transformation is applied to analyze the frequency spectrum of the system response.
Four-bar linkage
Clearance
Poincaré portrait
Bifurcation
chaos
2016
01
01
91
106
http://tava.isav.ir/article_19881_e87e176ea8ad08e808321243143c6199.pdf