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1 - Analysis of Time–Varying Mesh Stiffness for the Planetary Gear System with Analytical and Finite Element Methods
Ali Shahabi Amir Hosein KazemianIn dynamic model of planetary gears, one of the key design parameters and one of the main sources of vibration is time–varying mesh stiffness of meshing gears. According to previous researches, the finite element method and analytical method are two techniques to أکثرIn dynamic model of planetary gears, one of the key design parameters and one of the main sources of vibration is time–varying mesh stiffness of meshing gears. According to previous researches, the finite element method and analytical method are two techniques to estimate the mesh stiffness of meshing gears. In this work, in an innovation the periodically time–varying mesh stiffness of meshing gears is examined by both of finite element and analytical methods. The planetary gear set is modeled as a set of lumped masses and springs. Each element such as sun gear, carrier, ring gear and planets possesses three degrees of freedom and is considered as rigid body. The influence of effective parameters on the mesh stiffness of meshing gears and also numerical results of natural frequencies and vibration modes of the system are obtained. Based on the results, the influence of the higher pressure angles on the mesh stiffness of meshing gears is perceptible. By using the proposed mesh stiffness of meshing gears, for the system with numbers of odd and even equally and unequally spaced planets, natural frequencies and vibration modes are validated with a high accuracy. تفاصيل المقالة -
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2 - Vibration Behavior of the Planetary Gear System by Considering the Fixed Output
Ali Shahabi Amir Hossein KazemianThis work studies on analytical model of the single–stage spur planetary gear in form of lumped–parameter model. It includes key nonlinear factors of planetary gear vibration such as mesh stiffness and backlash of meshing gears. The planetary gear set is mod أکثرThis work studies on analytical model of the single–stage spur planetary gear in form of lumped–parameter model. It includes key nonlinear factors of planetary gear vibration such as mesh stiffness and backlash of meshing gears. The planetary gear set is modeled as a set of lumped masses and springs and dynamic model of the planetary gear set is presented. Nonlinear equations of motion are presented for each component and each component has three degrees of freedom in planar motion. We have numerically evaluated a set of linear and nonlinear equations to obtain natural frequencies and analysis of vibration behavior of the system under nonlinear factors and fixed output. In previous researches, natural frequencies of planetary gears were evaluated from two points of view: the first one considered fixed output for planetary gears and the second one consists of free rotational output. In this research, the influence of the output flexibility is evaluated on natural frequencies of the planetary gear. Meanwhile, by considering the fixed output, vibration behavior of the nonlinear system is investigated. Results show that the most important effect of the output flexibility is on the principal natural frequency. Because of chaotic phenomenon, vibration behavior of components in translational directions is different. تفاصيل المقالة -
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3 - Mass and Stiffness Matrices and Frequencies of Simple Beam Elements Based on Real Shape Functions
Pedram Abouzari Karen Khanlari Reza EsmaeilabadiIn this research, we investigate and compare the natural frequencies of simple beams and their mass and stiffness matrices of the two methods: classic shape functions and real shape functions. To this end, we solve the beam motion Equation and apply boundary conditions. أکثرIn this research, we investigate and compare the natural frequencies of simple beams and their mass and stiffness matrices of the two methods: classic shape functions and real shape functions. To this end, we solve the beam motion Equation and apply boundary conditions. This article shows that the coefficients of the real shape functions, and consequently, the real shape functions, become harmonic and hyperbolic and also, they are dependent on the natural frequency value of the element. As a result, the real mass and the real stiffness matrix of each element are also dependent on the element frequency. The frequency values obtained from these two methods are compared with the exact frequency values of two simple beam types with different support conditions. In this way, we determine which method leads to more accurate and acceptable frequencies for these beams. Based on the obtained results, the percentage of frequency error obtained by the classical method is relatively high in the sample beams. Hence, the natural frequency value of the beams studied using exact shape functions shows a small error compared to the classical method in terms of the exact frequency value of these beams. It is of note that the frequency error obtained from the classical method is greater in the elements with a higher natural frequency. Overall, obtaining the exact natural frequency of an element will result in accurate dynamic responses and more appropriate analyses and designs. تفاصيل المقالة -
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4 - Effect of Adding a Styrene-Butadiene Rubber Damper to A Sled Sample and Extraction of Its Equivalent Stiffness and Damping
Mohammad Reza Najafi Saied Mahjoub MoghadasProtection of sled systems from destructive vibrations is inevitably under attraction due to the importance of sled testing in the aerospace industry. A pair of SBR dampers were used between the slipper and the sled body to reduce vertical vibrations, so a design of the أکثرProtection of sled systems from destructive vibrations is inevitably under attraction due to the importance of sled testing in the aerospace industry. A pair of SBR dampers were used between the slipper and the sled body to reduce vertical vibrations, so a design of the sled model was studied. Both equivalent stiffness and equivalent damping of the sled system were obtained to reduce the transmission of vibrations from slippers to the body. A combination of analytical, numerical and experimental test methods was utilized and the results were validated. The stiffness values of 370500 and 391000 N⁄m were obtained from numerical and experimental measurements, respectively. Finally, by designing the sled model, first and second natural frequencies of 12.49 and 19.56 Hz and mode shapes of the sled system were obtained. The results show that the dampers used in the sled have an important role in reducing the transmission of vibrations to the sled body by withstanding the tension and pressure on the slippers. تفاصيل المقالة -
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5 - Investigation of the Effects of Dimensional Inaccuracies on the First Natural Frequency of Cellular Lattice Structures
Amir Hosein Samimi Mohammad Reza Karamooz-Ravari Reza DehghaniLattice structures have attracted a great deal of attention for being used in different industries due to unique properties such as high strength-to-weight ratio and high damping coefficient. These metamaterials might suffer from dimensional inaccuracies, i.e., variable أکثرLattice structures have attracted a great deal of attention for being used in different industries due to unique properties such as high strength-to-weight ratio and high damping coefficient. These metamaterials might suffer from dimensional inaccuracies, i.e., variable strut’s diameter, wavy struts, micropores, and deviation from the designed cross-sectional area, which arise from the fabrication process. These inaccuracies can drastically affect their mechanical response. In this paper, the effects of different dimensional inaccuracies, including variable struts’ diameter, wavy struts, and material concentration at nodes, on the frequency response of different cellular lattice structures are studied. To do so, a finite element model is constructed using Timoshenko beam elements, and the natural frequencies are obtained for four different lattices. The obtained results show that, by increasing the average diameter, the natural frequency increases drastically, whereas by increasing the amount of variation in the struts’ diameter and waviness the natural frequency decreases by a small amount. It is also observed that the lattice structures whose main deformation mechanism is axial loading are more sensitive to the change of average struts’ diameter. In addition, the natural frequency increases as the concentration of material in the vicinity of the nodes increases. The effect of material concentration inaccuracy is more pronounced for the first lattice for which the number of struts meeting at one node is the smallest. تفاصيل المقالة -
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6 - Investigation of Pressure Distribution on Slippers of a Monorail Sled with Vibration Damper
Mohammad Reza Najafi Saied Mahjoub MoghadasIn this paper, the pressure distribution on the slippers of a mono-rail sled with vibration damping is investigated. Due to the many applications of sled testing in the aerospace industry, the study of system vibrations is highly noticeable. In this research, first, by أکثرIn this paper, the pressure distribution on the slippers of a mono-rail sled with vibration damping is investigated. Due to the many applications of sled testing in the aerospace industry, the study of system vibrations is highly noticeable. In this research, first, by mathematical modelling of the sled, the governing Equations are extracted and natural frequencies and vibration modes are obtained from the analytical method using the mass and stiffness matrix of the system. Then, using numerical simulation and validation methods with experimental results performed in wind tunnels, the modal analysis of the designed sled sample is performed. A difference of less than eight percent in both numerical and analytical methods proves the accuracy of the results. The results show that the role of the slipper in the vibrations created in the sled is very important due to the large torsional and transverse oscillations in different positions, and the highest static pressure occurs in the inner layer of the slipper. تفاصيل المقالة -
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7 - Numerical and Experimental Investigation of Natural Frequency and Damping Coefficient of Flexible Cellular Lattice Structures
Amir Hosein Samimi M. R. Karamooz-Ravari Reza DehghaniCellular lattice structures encompass a class of metamaterials characterized by the arrangement of interconnected struts and/or plates, offering an adaptable microstructure that enables a broad range of property control. These structures have garnered significant attent أکثرCellular lattice structures encompass a class of metamaterials characterized by the arrangement of interconnected struts and/or plates, offering an adaptable microstructure that enables a broad range of property control. These structures have garnered significant attention for their distinctive properties and have found widespread application across industries such as aerospace, medical, pharmaceutical, automotive, defense and safety. This study seeks to explore the impact of geometric parameters on the natural frequency and damping coefficient of cellular lattice structures. Samples featuring BCC and OCTET architectures with varying porosities were initially produced using fused deposition modeling (FDM). Subsequently, both experimental and numerical analyses were conducted to assess the first natural frequency and damping coefficient of these materials. Comparison of the numerically obtained results with experimental data revealed a strong agreement. The findings indicate that, for both BCC and OCTET lattices, an increase in porosity is associated with a decrease in both natural frequency and damping coefficient. تفاصيل المقالة -
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8 - Free Vibration Analysis of Nonlinear Circular Plates Resting on Winkler and Pasternak Foundations
M.G Sobamowo S.A SalawuDynamic behaviour of nonlinear free vibration of circular plate resting on two-parameters foundation is studied. The governing ordinary differential equation is solved analytically using hybrid Laplace Adomian decomposition method. The analytical solutions obtained are أکثرDynamic behaviour of nonlinear free vibration of circular plate resting on two-parameters foundation is studied. The governing ordinary differential equation is solved analytically using hybrid Laplace Adomian decomposition method. The analytical solutions obtained are verified with existing results in literature. The analytical solutions are used to determine the influence of elastic foundation, radial and circumferential stress on natural frequency of the plate. Also, the radial and circumferential stress determined. From the results, it is observed that, increase in elastic foundation parameter increases the natural frequency of the plate. It is recorded that the modal radial and circumferential stress affect the extrema mode of the plate. It is hoped that the present study will contribute to the existing knowledge in the field of vibration analysis of engineering structures. تفاصيل المقالة -
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9 - Coupled Axial-Radial Vibration of Single-Walled Carbon Nanotubes Via Doublet Mechanics
Z Azimzadeh A Fatahi-VajariThis paper investigates the coupled axial-radial (CAR) vibration of single-walled carbon nanotubes (SWCNTs) based on doublet mechanics (DM) with a scale parameter. Two coupled forth order partial differential equations that govern the CAR vibration of SWCNTs are derived أکثرThis paper investigates the coupled axial-radial (CAR) vibration of single-walled carbon nanotubes (SWCNTs) based on doublet mechanics (DM) with a scale parameter. Two coupled forth order partial differential equations that govern the CAR vibration of SWCNTs are derived. It is the first time that DM is used to model the CAR vibration of SWCNTs. To obtain the natural frequency and dynamic response of the CAR vibration, the equations of motion are solved and the relation between natural frequencies and scale parameter is derived. It is found that there are two frequencies in the frequency spectrum and these CAR vibrational frequencies are complicated due to coupling between two vibration modes. The advantage of these analytical formulas is that they are explicitly dependent to scale parameter and chirality effect. The influence of changing some geometrical and mechanical parameters of SWCNT on its CAR frequencies has been investigated, too. It is shown that the chirality and scale parameter play significant role in the CAR vibration response of SWCNTs. The scale parameter decreases the higher band CAR frequency compared to the predictions of the classical continuum models. However, with increase in tube radius and length, the effect of the scale parameter on the natural frequencies decreases. The lower band CAR frequency is nearly independent to scale effect and tube diameter. The CAR frequencies of SWCNTs decrease as the length of the tube increases. This decreasing is higher for higher band CAR frequency. To show the accuracy and ability of this method, the results obtained herein are compared with the existing theoretical and experimental results and good agreement is observed. تفاصيل المقالة -
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10 - Free Vibration Analysis of Composite Grid Stiffened Cylindrical Shells Using A Generalized Higher Order Theory
H Mohammad Panahiha A Davar M Heydari Beni J Eskandari JamThe present study analyzes the free vibration of multi-layered composite cylindrical shells and perforated composite cylindrical shells via a modified version of Reddy’s third-order shear deformation theory (TSDT) under simple support conditions. An advantage of t أکثرThe present study analyzes the free vibration of multi-layered composite cylindrical shells and perforated composite cylindrical shells via a modified version of Reddy’s third-order shear deformation theory (TSDT) under simple support conditions. An advantage of the proposed theory over other high-order theories is the inclusion of the shell section trapezoidal form coefficient term in the displacement field and strain equations to improve the accuracy of results. The non-uniform stiffness and mass distributions across reinforcement ribs and the empty or filled bays between the ribs in perforated shells were addressed via a proper distribution function. For integrated perforated cylindrical shells, the results were validated by comparison to other studies and the numerical results obtained via ABAQUS. The proposed theory was in good consistency with numerical results and the results of previous studies. It should be noted that the proposed theory was more accurate than TSDT. تفاصيل المقالة -
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11 - Free Torsional Vibration Analysis of Hollow and Solid Non-Uniform Rotating Shafts Using Distributed and Lumped Modeling Technique
A Saghafi M .A AziziIn this paper, the torsional free vibration of solid and hollow rotating shafts with non-uniform tapered elements are investigated. To this end, the exact solution and also transfer matrix for the free torsional vibration of a hollow tapered shaft element with uniform t أکثرIn this paper, the torsional free vibration of solid and hollow rotating shafts with non-uniform tapered elements are investigated. To this end, the exact solution and also transfer matrix for the free torsional vibration of a hollow tapered shaft element with uniform thickness and also solid element are firstly obtained. Then, the natural frequencies are determined based on distributed and lumped modeling technique (DLMT). This technique is similar to transfer matrix method (TMM) but the exact solution is employed to obtain the transfer matrixes of the distributed element, therefore, there is no approximation and the natural frequencies and mode shapes are the exact values. To confirm the reliability of the presented method, the simulation results are compared with the results obtained from the other methods such as finite element method. It is shown that the proposed method provides highly accurate results and it can be simply applied to the complex torsional systems. تفاصيل المقالة -
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12 - Analysis of Coupled Nonlinear Radial-Axial Vibration of Single-Walled Carbon Nanotubes Using Numerical Methods
A Fatahi-Vajari Z AzimzadehThis paper investigates the nonlinear coupled radial-axial vibration of single-walled carbon nanotubes (SWCNTs) based on numerical methods. Two coupled partial differential equations that govern the nonlinear coupled radial-axial vibration for such nanotube are derived أکثرThis paper investigates the nonlinear coupled radial-axial vibration of single-walled carbon nanotubes (SWCNTs) based on numerical methods. Two coupled partial differential equations that govern the nonlinear coupled radial-axial vibration for such nanotube are derived using nonlocal doublet mechanics (DM) theory. To obtain the nonlinear natural frequencies in coupled radial-axial vibration mode, these equations are solved using Homotopy perturbation method (HPM). It is found that the coupled radial-axial vibrational frequencies are complicated due to coupling between two vibration modes. The influences of some commonly used boundary conditions, changes in vibration modes and variations of the nanotubes geometrical parameters on the nonlinear coupled radial-axial vibration characteristics of SWCNTs are discussed. It was shown that boundary conditions and maximum vibration velocity play significant roles in the nonlinear coupled radial-axial vibration response of SWCNTs. It was shown that unlike the linear one, the nonlinear natural frequencies are dependent to maximum vibration velocity. Increasing the maximum vibration velocity increases the natural frequency of vibration compared to the prediction of the linear model. However, with increase in tube length, the effect of the maximum vibration velocity on the natural frequencies decreases. It was also shown that the amount and variation of nonlinear natural frequencies are more apparent in higher vibration modes and two clamped boundary conditions. To show the accuracy and capability of this method, the results obtained herein are compared with the fourth order Runge-Kuta numerical results and also with the other available results and good agreement is observed. It is notable that the results generated herein are new and can be served as a benchmark for future works. تفاصيل المقالة -
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13 - Comparison of Various Shell Theories for Vibrating Functionally Graded Cylindrical Shells
M JavadinejadThe classical shell theory, first-order shear deformation theory, and third-order shear deformation theory are employed to study the natural frequencies of functionally graded cylindrical shells. The governing equations of motion describing the vibration behavior of fun أکثرThe classical shell theory, first-order shear deformation theory, and third-order shear deformation theory are employed to study the natural frequencies of functionally graded cylindrical shells. The governing equations of motion describing the vibration behavior of functionally graded cylindrical shells are derived by Hamilton’s principle. Resulting equations are solved using the Navier-type solution method for a functionally graded cylindrical shell with simply supported edges. The effects of transverse shear deformation, geometric size, and configurations of the constituent materials on the natural frequencies of the shell are investigated. Validity of present formulation was checked by comparing the numerical results with the Love’s shell theory. تفاصيل المقالة -
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14 - Improving Power Density of Piezoelectric Vibration-Based Energy Scavengers
R Hosseini O Zargar M HamediVibration energy harvesting with piezoelectric materials currently generate up to 300 microwatts per cm2, using it to be mooted as an appropriate method of energy harvesting for powering low-power electronics. One of the important problems in bimorph piezoelectric energ أکثرVibration energy harvesting with piezoelectric materials currently generate up to 300 microwatts per cm2, using it to be mooted as an appropriate method of energy harvesting for powering low-power electronics. One of the important problems in bimorph piezoelectric energy harvesting is the generation of the highest power with the lowest weight. In this paper the effect of the shape and geometry of a bimorph piezoelectric cantilever beam harvester on the electromechanical efficiency of the system is studied. An analytic model has been presented using Rayleigh cantilever beam approximations for piezoelectric harvesters with tapered bimorph piezoelectric cantilever beam. In order to study the effect of a cantilever beam length and geometry on the generated voltage, finite element simulation has been performed using ABAQUS. Design optimization has been used to obtain the maximum output power and tapered beams are observed to lead to more uniform distribution of strain in the piezoelectric layer, thus increasing efficiency. تفاصيل المقالة -
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15 - Calculation of Natural Frequencies of Bi-Layered Rotating Functionally Graded Cylindrical Shells
I Fakhari GolpayeganiIn this paper, an exact analytical solution for free vibration of rotating bi-layered cylindrical shell composed of two independent functionally graded layers was presented. The thicknesses of the shell layers were assumed to be equal and constant. The material properti أکثرIn this paper, an exact analytical solution for free vibration of rotating bi-layered cylindrical shell composed of two independent functionally graded layers was presented. The thicknesses of the shell layers were assumed to be equal and constant. The material properties of the constituents of bi-layered FGM cylindrical shell were graded in the thickness direction of the layers of the shell according to a volume fraction power-law distribution. In order to derive the equations of motion, the Sanders’ thin shell theory and Rayleigh-Ritz method were used. Also the results were extracted by considering Coriolis, centrifugal and initial hoop tension effects. Effects of rotating speed, geometrical parameters, and material distribution in the two functionally graded layers of the shell, circumferential and longitudinal wave number on the forward and backward natural frequencies were investigated. A comparison of the results was made with those available in the literature for the validity and accuracy of the present methodology. تفاصيل المقالة -
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16 - Investigation of Vibrational Behavior of Perfect and Defective Carbon Nanotubes Using Non–Linear Mass–Spring Model
A.A Shariati A.R Golkarian M JabbarzadehIn the present study, the effects of arrangement and distribution of multifarious types of defects on fundamental frequency of carbon nanotubes are investigated with respect to different chirality and boundary conditions. Interatomic interactions between each pair of ca أکثرIn the present study, the effects of arrangement and distribution of multifarious types of defects on fundamental frequency of carbon nanotubes are investigated with respect to different chirality and boundary conditions. Interatomic interactions between each pair of carbon atoms are modeled using two types of non–linear spring–like elements. To obtain more information about the influences of defects; the effects of location, number and distribution (gathered or scattered defects) of two most common types of defects (vacancy and Stone–Wales defects) are examined on vibrational behavior of carbon nanotubes. Obtained results are in good agreement with the results reported in other literature. The results show that, gathered vacancy defects cause to a reduction in natural frequency of nanotubes, especially in the case of fix–fix boundary condition. It is also observed that the effect of defects depends on chirality intensively. In addition, the influence of the first vacancy defect is significantly more than the first Stone–Wales defect. تفاصيل المقالة -
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17 - Analysis of Nonlinear Vibrations for Multi-walled Carbon Nanotubes Embedded in an Elastic Medium
A Ghorbanpour Arani H Rabbani S Amir Z Khoddami Maraghi M Mohammadimehr E HaghparastNonlinear free vibration analysis of double-walled carbon nanotubes (DWCNTs) embedded in an elastic medium is studied in this paper based on classical (local) Euler-Bernoulli beam theory. Using the averaging method, the nonlinear free vibration responses of DWCNTs are o أکثرNonlinear free vibration analysis of double-walled carbon nanotubes (DWCNTs) embedded in an elastic medium is studied in this paper based on classical (local) Euler-Bernoulli beam theory. Using the averaging method, the nonlinear free vibration responses of DWCNTs are obtained. The result is compared with the obtained results from the harmonic balance method for single-walled carbon nanotubes (SWCNTs) and DWCNTs. The effects of the surrounding elastic medium, van der waals (vdW) forces and aspect ratio of SWCNTs and DWCNTs on the vibration amplitude are discussed. The error percentage of the nonlinear free vibration frequencies between two theories decreases with increasing the spring constant of elastic medium. Results are also shown that if the value of the spring constant is lower than (), the nonlinear free vibration frequencies are increased. In this case, the effect of the spring constant on frequency responses is significant, while if the value of the spring constant is higher than (), the curve of frequency responses has a constant value near to 1 and therefore the effect of the spring constant on frequency responses is negligible. تفاصيل المقالة -
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18 - Vibration Analysis of FG Nanoplate Based on Third-Order Shear Deformation Theory (TSDT) and Nonlocal Elasticity
M.M Najafizadeh M Raki P YousefiIn present study, the third-order shear deformation theory has been developed to investigate vibration analysis of FG Nano-plates based on Eringen nonlocal elasticity theory. The materials distribution regarding to the thickness of Nano-plate has been considered based o أکثرIn present study, the third-order shear deformation theory has been developed to investigate vibration analysis of FG Nano-plates based on Eringen nonlocal elasticity theory. The materials distribution regarding to the thickness of Nano-plate has been considered based on two different models of power function and exponential function. All equations governing on the vibration of FG Nano-plate have been derived from Hamilton’s principle. It has been also obtained the analytical solution for natural frequencies and corresponding mode shapes of simply supported FG Nano-plates. In addition, the general form of stiffness and mass matrix elements has been expressed based on this theory. The effect of different parameters such as power and exponential indexes of targeted function , nonlocal parameter of Nano-plate, aspect ratio and thickness to length ratio of Nano-plate on non-dimensional natural frequencies of free vibration responses have been investigated. The obtained analytical results show an excellent agreement with other available solutions of previous studies. The formulation and analytical results obtained from proposed method can be used as a benchmark for further studies to develop this area of research. تفاصيل المقالة -
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19 - Analyzing Frequency of Conical (∆ shaped) Tanks
F SaljughiA finite element analysis is presented for sloshing and impulsive motion of liquid-filled conical tanks during lateral anti-symmetric excitation. The performed analyses led to the development of a number of charts which can be used to identify the natural frequency, the أکثرA finite element analysis is presented for sloshing and impulsive motion of liquid-filled conical tanks during lateral anti-symmetric excitation. The performed analyses led to the development of a number of charts which can be used to identify the natural frequency, the mode shapes of conical tanks for both fundamental and the cos(θ)-modes of vibration. Conical tank geometry was described with several parameters namely, bottom radius( Rb) total height of liquid (h), angle of inclination of the tanks(θi), as variables. Numerical result of the free vibration was obtained for the cases of conical tanks with θi=0 and compared with existing experiments and other predicated results, showing a good agreement between the experiment and numerical results. تفاصيل المقالة -
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20 - Lateral Vibrations of Single-Layered Graphene Sheets Using Doublet Mechanics
A Fatahi-Vajari A. ImamThis paper investigates the lateral vibration of single-layered graphene sheets based on a new theory called doublet mechanics with a length scale parameter. After a brief reviewing of doublet mechanics fundamentals, a sixth order partial differential equation that gove أکثرThis paper investigates the lateral vibration of single-layered graphene sheets based on a new theory called doublet mechanics with a length scale parameter. After a brief reviewing of doublet mechanics fundamentals, a sixth order partial differential equation that governs the lateral vibration of single-layered graphene sheets is derived. Using doublet mechanics, the relation between natural frequency and length scale parameter is obtained in the lateral mode of vibration for single-layered graphene. It is shown that length scale parameter plays a significant role in the lateral vibration behavior of single-layered graphene sheets. Such effect decreases the natural frequency compared to the predictions of the classical continuum mechanics models. However with increasing the length of the plate, the effect of scale parameter on the natural frequency decreases. For validating the results of this method, the results obtained herein are compared with the existing nonlocal and molecular dynamics results and good agreement with the latter is observed. تفاصيل المقالة -
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21 - Microtremor analysis to evaluate BMKG region III building, Bali, Indonesia
Muh Sarkowi Rahmat Wibowo Ida Bagus Yogi Mahmud Yusuf Yohana BokaBali Island has experienced more than 6 significant earthquakes (magnitude > 6) since 1815, which caused extensive damage to buildings and casualties. The microtremor data analysis in the building of Indonesian meteorology, climatology and geophysics agency (BMKG) Re أکثرBali Island has experienced more than 6 significant earthquakes (magnitude > 6) since 1815, which caused extensive damage to buildings and casualties. The microtremor data analysis in the building of Indonesian meteorology, climatology and geophysics agency (BMKG) Region III Denpasar aims to reduce the risk of building damage and casualties due to the earthquake. The analysis was conducted by measuring microtremor and processing the data to obtain the natural frequency of the soil (f0s HVSR) and building (f0b HVSR), resonance, soil (Kg), and building vulnerability index (Kb) so that the safety of the building can be known in the event of an earthquake. The processing and analyzing results the characteristics of microtremor data get the f0b has a greater value than the f0s value so that the building is relatively safe from resonance. The resonance value of the building with the ground has an (R) value of 6.67% - 13.3%, with an average resonance value of 8.89% which is included in the medium resonance. The location of the building is in an area with a Kg of 8.20 – 10.81, which is included in the category of low to moderate soil vulnerability index, and the Kb has a value of 0.4827x10-6 – 7.9771x10-6, with the first floor having an index highest vulnerability. The f0s, f0b, R, Kg, and Kb show that the building is in the safe category in the event of an earthquake. تفاصيل المقالة -
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22 - بررسی اثر دما بر روی رفتار ارتعاشی کاور کلاچ خودروی سواری
کاظم رضاکاشی زاده سارا علی پناه کیویدر مقاله حاضر، هدف اصلی تعیین فرکانس های طبیعی و نیز شکل مودهای کاور کلاچ خودروی سواری پژو 405 بوده و در نهایت بررسی میزان اثر دما بر روی رفتار ارتعاشی خودرو در مقایسه با حالت عملکردی آن می باشد. بدین منظور از نرم افزار ورک بنچ انسیس برای شبیه سازی المان محدود کاور کلاچ أکثردر مقاله حاضر، هدف اصلی تعیین فرکانس های طبیعی و نیز شکل مودهای کاور کلاچ خودروی سواری پژو 405 بوده و در نهایت بررسی میزان اثر دما بر روی رفتار ارتعاشی خودرو در مقایسه با حالت عملکردی آن می باشد. بدین منظور از نرم افزار ورک بنچ انسیس برای شبیه سازی المان محدود کاور کلاچ خودرو استفاده شده است. دوازده فرکانس طبیعی اول به همراه شکل مود متناظر با آن در دمای محیط بدست آمده است. سپس به منظور بررسی اثر دما بر روی رفتار ارتعاشی کاور کلاچ، دوازده فرکانس طبیعی سیستم در دماهای کاری مختلف (تا 300 درجه) بدست آمده و با یکدیگر مقایسه شده است. تفاصيل المقالة -
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23 - مروری بر روش های شناسایی آسیب بر اساس پارامترهای مودال
احسان جمشیدی بهرام جمشیدی فاطمه تقی خاکی علیرضا ارغوانیکی از روشهای متداول شناسایی آسیب در سازه ها و تعیین محل و شدت آسیب در آنها بررسی تغییرات پارامترهای مودال سازه قبل و بعد از بروز آسیب است. در این روند که اغلب بر پایه روشهای بهینه سازی هستند، یک تابع هدف بر پایه فرکانسهای طبیعی و یا شکلمودهای سازه و یا هر دو به کا أکثریکی از روشهای متداول شناسایی آسیب در سازه ها و تعیین محل و شدت آسیب در آنها بررسی تغییرات پارامترهای مودال سازه قبل و بعد از بروز آسیب است. در این روند که اغلب بر پایه روشهای بهینه سازی هستند، یک تابع هدف بر پایه فرکانسهای طبیعی و یا شکلمودهای سازه و یا هر دو به کار برده میشود.در این مقاله سعی میشود مروری اجمالی بر تحقیقات پیشین در خصوص شناسایی آسیب براساس پارامترهای مودال و توابع هدف متداول در مرحله بهینهسازی در فرایند شناسایی آسیب انجام گیرد. به این منظور، روش های شناسایی آسیب براساس فرکانس طبیعی، شکل مود، انحنای شکل مود و هردو، شکل مود و فرکانس طبیعی مرور میشوند. در ادامه با توجه به اهمیت بالای توابع هدف در فرایند شناسایی آسیب، توابع هدف بر پایه معیار اطمینان مودال، ماتریس انعطاف پذیری و فرکانسهای طبیعی و شکلهای مود مقایسه میشوند. تفاصيل المقالة -
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24 - اثر محل و شدت ترک بر پارامترهای مودال تیر یکسرگیردار
احسان جمشیدی بهرام جمشیدی فاطمه تقی خاکی علیرضا ارغوانیکی از روشهای متداول شناسایی آسیب در سازه ها بررسی تغییرات پارامترهای مودال سازه قبل و بعد از بروز آسیب است. در این روند که اغلب بر پایه روشهای بهینه سازی هستند، یک تابع هدف بر پایه فرکانسهای طبیعی و یا شکلمودهای سازه و یا هر دو به کار برده میشود. موفقیت در یافتن أکثریکی از روشهای متداول شناسایی آسیب در سازه ها بررسی تغییرات پارامترهای مودال سازه قبل و بعد از بروز آسیب است. در این روند که اغلب بر پایه روشهای بهینه سازی هستند، یک تابع هدف بر پایه فرکانسهای طبیعی و یا شکلمودهای سازه و یا هر دو به کار برده میشود. موفقیت در یافتن محل و شدت آسیب در این روشها شدیدا تابع حساسیت تابع هدف به آسیب خواهد بود. از آنجا که تابع هدف خود تابعی از فرکانسهای طبیعی و یا شکلمودهای سازه و یا هر دو است، لازم است حساسیت پارامترهای مودال به محل و شدت آسیب مورد بررسی قرار گیرد. به این منظور در این مقاله یک تیر یکسرگیردار به صورت عددی شبیه سازی شده است. با تغییر محل و شدت ترک، اثر آنها بر فرکانسهای طبیعی و شکل مودها مطالعه میشود. نتایج نشان میدهد که با افزایش شدت ترک فرکانس های طبیعی کاهش مییابند. از طرف دیگر با جابجا شدن ترک از سر گیردار به سمت انتهای آزاد، تغییرات فرکانس طبیعی از الگویی خاصی پیروی نکرده و برای یک ترک با عمق ثابت کاهش فرکانسهای طبیعی نسبت به حالت تیر سالم وابسته به موقعیت ترک بر روی تیر میباشد. همچنین مشاهده میشود هرچه ترک به سر گیر دار تیر نزدیک تر باشد، فرکانس طبیعی بیشتر کاهش مییابد. نتایج نشان میدهد که حساسیت شکل مودها نسبت به بروز ترک در تیر پایین است. بنابراین توصیه میشود در توابع هدف از فرکانسهای طبیعی و یا فرکانسهای طبیعی و شکل مودها به صورت توامان استفاده گردد. تفاصيل المقالة -
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25 - مطالعه مقایسهای توابع هدف معمول برپایه پارامترهای مودال در شناسایی آسیب سازهای
احسان جمشیدی بهرام جمشیدی فاطمه تقی خاکی علیرضا ارغوانانتخاب تابع هدف مناسب برای تعیین محل آسیب و تخمین شدت آن در سازه امری ضروری میباشد. برای این منظور توابع هدف وابسته به پارامترهای مودال سازه از قبیل شکل مود و فرکانس طبیعی با توابع هدف دیگر که قادر به پیشبینی محل آسیب میباشند ترکیب میشوند. سپس به کمک روشهای بهینه أکثرانتخاب تابع هدف مناسب برای تعیین محل آسیب و تخمین شدت آن در سازه امری ضروری میباشد. برای این منظور توابع هدف وابسته به پارامترهای مودال سازه از قبیل شکل مود و فرکانس طبیعی با توابع هدف دیگر که قادر به پیشبینی محل آسیب میباشند ترکیب میشوند. سپس به کمک روشهای بهینه سازی محل و شدت آسیب به دست میآید. در این مقاله با استفاده از روش المان محدود ابتدا یک تیر یک سرگیر دار در نرم افزار MATLAB شبیه سازی شده و سپس الگوریتم ژنتیک تک و چندهدفه با استفاده از توابع هدف مختلف به دست آمده از پارامترهای مودال برای تعیین میزان و محل ترک بکار گرفته میشود. به منظور مقایسه توابع هدف مختلف اثر ناکاملی درجات آزادی اندازه گیری شده، محدوده فرکانسی اندازه گیری و همچنین نویز محیطی بر نتایج شناسایی آسیب مورد مطالعه قرار می گیرد. تفاصيل المقالة -
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26 - تشخیص انکیلوز بودن دندان با استفاده از فرکانس طبیعی
زاوش امینی احسان جمشیدی فائزه اسلامی پورچکیده در این مقاله فرکانسهای دندان در حالت طبیعی و انکیلوز(فک جوش) بررسی و مقایسه میگردد. در درمان ارتودنسی اصل درمان بر مبنای جابجایی و چرخش دندانها است عدم تشخیص انکیلوز بودن دندان درمان ارتودنسی را طولانی و کم اثر مینماید حال آنکه در عکسهای سی تی اسکن تشخیص انکیلو أکثرچکیده در این مقاله فرکانسهای دندان در حالت طبیعی و انکیلوز(فک جوش) بررسی و مقایسه میگردد. در درمان ارتودنسی اصل درمان بر مبنای جابجایی و چرخش دندانها است عدم تشخیص انکیلوز بودن دندان درمان ارتودنسی را طولانی و کم اثر مینماید حال آنکه در عکسهای سی تی اسکن تشخیص انکیلوز بودن دندان با دشواری صورت می-گیرد. در این پژوهش ابتدا عکسهای بدست آمده از سی تی اسکن توسط نرمافزار میمیکس به مدل سه بعدی تبدیل گردید سپس در نرمافزار ماجیک نقاط اضافی موجود در مدل حذف گردیده و مدل برای تحلیل آماده میگردد مدل دندان به نرمافزار سالیدورک انتقال یافته و برای آن لیگامان و فک متناظر با آن ساخته شد سپس مدل به نرمافزار آباکوس که از روش المان محدود برای تحلیل استفاده میکند وارد گردید، چگالی و مدول یانگ برای هریک از قسمتهای دندان، فک و لیگامان تعریف شد همچنین برهم کنش بین اعضاء مشخص گردید برای فک و دندان بتنهایی فرکانس طبیعی بدست آمد که از فرکانس مجموعه فک، دندان و لیگامنت بالاتر میباشد برای مجموعه فک، دندان و لیگامان در حالت عادی و انکیلوز فرکانس طبیعی بدست آمد که فرکانس طبیعی در حالت انکیلوز بسیار بالاتر از فرکانس طبیعی در حالت عادی میباشد و از این روش میتوان برای تشخیص انکیلوز بودن دندان استفاده نمود. تفاصيل المقالة -
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27 - بررسی و تحلیلی بر ارتعاشات برج توربین های بادی و کنترل ارتعاش آن با استفاده از جاذب
اسداله خراسانی مهدی شریف نیاشرایط امروز جهان در حوزه سوخت های فسیلی ایجاب می کند انرژی بادی و توربین های بادی ساحلی و فراساحلی بیش از پیش مورد توجه همگان باشد، لذا به دلیل بهرهگیری بیشتر از این انرژی پاک باید طول پره و برج توربین باد نیز افزایش پیدا کند، در نتیجه مطالعات ارتعاشات توربینها بیش از أکثرشرایط امروز جهان در حوزه سوخت های فسیلی ایجاب می کند انرژی بادی و توربین های بادی ساحلی و فراساحلی بیش از پیش مورد توجه همگان باشد، لذا به دلیل بهرهگیری بیشتر از این انرژی پاک باید طول پره و برج توربین باد نیز افزایش پیدا کند، در نتیجه مطالعات ارتعاشات توربینها بیش از گذشته مورد توجه قرار گرفته است. در این پژوهش کنترل سازهای یک توربین باد بواسطه میراگر مورد بررسی قرار گرفته که هدف نیز کاهش ارتعاشات سازه در بخش های مختلف توربین، تغییر فرکانس و دور شدن از محدوده خطر میباشد. یکی از روشهای جذب ارتعاش در سازه ها استفاده از مواد جاذب در بدنه میباشد. در این تحقیق سعی شده توربین باد از لحاظ ارتعاشی مورد بررسی قرار گیرد و ارتعاشات آن کاهش یابد. بدین منظور فرکانس طبیعی آن بوسیله نرم افزار آباکوس استخراج شده و سپس جهت جلوگیری از ارتعاش توربین از یک سیستم جاذب استفاده و مجددا فرکانس توربین مورد بررسی قرار گرفته و در دو حالت با یکدیگر مقایسه و اعتبار سنجی شده است. همچنین با تحریک جابجایی در پایه توربین، جابجایی در دو نقطه از پره و هد توربین در دو حالت با جاذب و بدون جاذب مورد بررسی قرار گرفته که نتایج خوبی حاصل گردیده و ارتعاش کاهش یافته است. تفاصيل المقالة -
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28 - توسعه مدل آیروالاستیسیته پره کامپوزیتی و تحلیل اثر چرخش و افزایش طول بر فرکانسهای طبیعی
رضا اثباتی لواسانی شاهرخ شمسدر این پژوهش معادلات آیروالاستیسیته خطی پره توربین بادی با روش گسسته سازی المان محدود جهت درنظر گرفتن اثر چرخش و افزایش طول بر فرکانسهای طبیعی استخراج شده است. پره یک تیر یکسر گیردار اویلر-برنولی کامپوزیتی در نظر گرفته شده و با روش المان محدود مدل شده است. با بکارگیری أکثردر این پژوهش معادلات آیروالاستیسیته خطی پره توربین بادی با روش گسسته سازی المان محدود جهت درنظر گرفتن اثر چرخش و افزایش طول بر فرکانسهای طبیعی استخراج شده است. پره یک تیر یکسر گیردار اویلر-برنولی کامپوزیتی در نظر گرفته شده و با روش المان محدود مدل شده است. با بکارگیری روش همیلتونین معادلات حرکت را بدست آمده است. ماتریسهای المان محدود با تعیین جابجایی گرهها و فرض رابطه خطی در جابجایی محوری و تابع هرمیشن در جهات عرضی و پیچشی محاسبه میشوند. اعتبار سنجی معادلات به صورت عددی بر روی پره با شبیه سازی سیستم معادلات و بررسی فرکانسهای طبیعی و شکل مدها انجام شده است. همچنین اثر افزایش طول پره و چرخش پره در پره کوتاه و بلند کامپوزیتی بررسی شده است. بررسی فرکانسهای طبیعی نشان میدهد فرکانسهای اول و دوم پرههای بلند تحت تاثیر افزایش طول و چرخش هستند. اما در فرکانسهای بالا و همچنین در پره کوتاه اثر افزایش طول و چرخش کمتر از یک درصد است. تفاصيل المقالة -
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29 - تشخیص آسیب در خطوط انتقال گاز بر اساس تغییرات فرکانس طبیعی به کمک شبکه های عصبی مصنوعی
علی اصغر بینائیان احسان جمشیدی علیرضا ارغوانهدف از این مقاله معرفی یک رویکرد جدید برای عیب یابی خطوط لوله انتقال گاز با استفاده از امواج مکانیکی است. در این مقاله تلاش شده است با استفاده از خصوصیات فرکانس طبیعی و تغییر آن، روشی جهت پیدا کردن عیوب ارائه گردد. با توجه به ارتباط جرم و سفتی در تعیین فرکانس طبیعی، به أکثرهدف از این مقاله معرفی یک رویکرد جدید برای عیب یابی خطوط لوله انتقال گاز با استفاده از امواج مکانیکی است. در این مقاله تلاش شده است با استفاده از خصوصیات فرکانس طبیعی و تغییر آن، روشی جهت پیدا کردن عیوب ارائه گردد. با توجه به ارتباط جرم و سفتی در تعیین فرکانس طبیعی، به جای ایجاد عیب (کاهش سفتی) از افزایش جرم استفاده شده است. روش ارائه شده شامل مدل سازی لوله 2 اینچی به طول2 متر در نرم افزار آباکوس و بررسی فرکانسهای طبیعی لوله در حالت سالم و دارای عیب ( ایجاد ترک ) است . سپس نسبت به تعیین جرم معادل برای مدل سازی عیوب اقدام شده است و در ادامه لوله فوق تحت آنالیز مودال تجربی قرار گرفت و با ایجاد عیوب مصنوعی ( افزودن جرم )، حالتهای مختلف آن آزمایش گردید. سپس از اطلاعات به دست آمده درآموزش شبکه عصبی پرسپترون در محیط نرم افزار متلب استفاده شده است و خروجی برنامه مکان عیب و شدت آن (مقدار جرم ) می باشد. تفاصيل المقالة -
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30 - تاثیر عیوب ریخته گری بر پارامترهای مودال بلوک سیلندر خودرو
امیر حسین عموزاده مرتضی محمدظاهری احسان جمشیدیدر این مقاله،به تاثیر عیوب ریخته گری بر فرکانس طبیعی بلوک سیلندر خودرو توجه شده است . لذا برای این منظور بلوک سیلندر خودرو توسط نرم افزارSalid work،مدل سه بعدی شده است و سپس با نرم افزار المان محدود Ansys Workbench مدل المان محدود رسم شده و فرکانس طبیعی بلوک سیلندر در م أکثردر این مقاله،به تاثیر عیوب ریخته گری بر فرکانس طبیعی بلوک سیلندر خودرو توجه شده است . لذا برای این منظور بلوک سیلندر خودرو توسط نرم افزارSalid work،مدل سه بعدی شده است و سپس با نرم افزار المان محدود Ansys Workbench مدل المان محدود رسم شده و فرکانس طبیعی بلوک سیلندر در مدل FEM بدست آمده است. با استفاده از آزمایش مودال، فرکانس طبیعی بلوک سیلندر گرفته شده است. با تایید شدن مدل FEM توسط نتایج آزمایش مودال،شبیه سازی عیوب در مدل FEM به صورت تک به تک صورت گرفته و فرکانس طبیعی بلوک سیلندر برای تک تک عیوب به دست آمده است.با محاسبه اختلاف فرکانس طبیعی مدل سالم با مدل معیوب،تاثیر تک تک عیوب بر فرکانس طبیعی قطعه به طور قابل ملاحظه ای مشاهده شده است. تفاصيل المقالة -
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31 - تحلیل ارتعاش آزاد عرضی کابل با استفاده از روش جدا سازی ادمین
رضا احراری محمد شادکامی محمد حسین ابوالبشریدر این مقاله روش جداسازی ادمین به منظور بررسی ارتعاش آزاد یک کابل دو تکه به کار گرفته شده است. هر قسمت از کابل به صورت مجزا توسط این روش تحلیل شده است. با اعمال شرایط پیوستگی و شرایط مرزی، فرکانس های طبیعی و شکل مدهای مربوطه به سادگی و به صورت هم زمان به دست می آید. با أکثردر این مقاله روش جداسازی ادمین به منظور بررسی ارتعاش آزاد یک کابل دو تکه به کار گرفته شده است. هر قسمت از کابل به صورت مجزا توسط این روش تحلیل شده است. با اعمال شرایط پیوستگی و شرایط مرزی، فرکانس های طبیعی و شکل مدهای مربوطه به سادگی و به صورت هم زمان به دست می آید. با ارائه چند مثال برای شرایط مرزی مختلف، این مقادیر محاسبه شده اند. نتایج به دست آمده از راه حل های تحلیلی و عددی ذکر شده در مقاله با دقت خوبی نتایج حاصله از این روش را تایید می نمایند و مشخص می کنند که روش ادمین یک روش موثر و قابل اطمینان بوده و نسبت به سایر تحلیل های ارتعاشی کارآمدتر و ساده تر می باشد. در بخش پایانی، تاثیر میزان پارامترهای جرم و سختی فنر در شرایط مرزی بر میزان و نحوه تغییرات فرکانس های طبیعی بررسی شده و یک راهکار موثر برای برخورد با این گونه شرایط مرزی پیشنهاد شده است. تفاصيل المقالة -
حرية الوصول المقاله
32 - Modal Identification Of A Tested Steel Frame Using Linear Arx Model Structure
Yavuz KayaThis study contains the identification of modal dynamic properties of a 3-story large-scale steel test frame structure through shaking table measurements. Shaking table test is carried out to estimate the modal properties of the test frame such as natural frequencies, d أکثرThis study contains the identification of modal dynamic properties of a 3-story large-scale steel test frame structure through shaking table measurements. Shaking table test is carried out to estimate the modal properties of the test frame such as natural frequencies, damping ratios and mode shapes. Among many different model structures, ARX (Auto Recursive Exogenous) model structure is used for modal identification of the frame structure system. The unknown parameters in the obtained ARX model structure are estimated by Least-Square method by minimizing the AIC criteria with the help of a program coded in advanced computing software MATLAB®. The adopted model structure is then tested out in time domain to verify the validity of the model with the selected model parameters. Then the modal characteristics of test frame and the story stiffness are estimated using the white noise shakings. An attempt is done to determine the change of modal characteristics and the story stiffness of test frame according to the velocity, which the test frame structure experienced during the shaking schedule and also during the input shaking of El Centro 1940 NS. Results shows that there is an increase in damping ratio and a decrease in both story stiffness and natural frequency for all modes when the damage forms at cementitious device and the test frame structure itself during the shaking schedule. تفاصيل المقالة -
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33 - Damage Detection in Truss Structures Using Grasshopper Optimization Algorithm
Pouria Foroutanrad Behnam AdhamiStructural engineers' goal has constantly been identifying, restoring, repairing, or replacing damaged members. As a result, one of the most crucial and necessary steps in the upkeep and restoration of structures is identifying damaged members. Damage detection tec أکثرStructural engineers' goal has constantly been identifying, restoring, repairing, or replacing damaged members. As a result, one of the most crucial and necessary steps in the upkeep and restoration of structures is identifying damaged members. Damage detection techniques from structural dynamic response measurements can often be used to detect and locate damage. This paper proposes a structural damage identification method based on changing natural frequency, finite element modeling, and the Grasshopper Optimization Algorithm (GOA). This algorithm mathematically models and mimics the behavior of grasshopper swarms in nature for solving optimization problems. As numerical examples, the 13-bar and a 31-bar planar truss are considered to examine the suggested methodology's precision. According to the findings, the recommended method is workable for systems with few members and minor damage. However, the accuracy of the diagnosed damage in structures with medium-sized members and considerable damages was poor, making it more likely to converge to local optimum points conditions. تفاصيل المقالة -
حرية الوصول المقاله
34 - A new method for determination of natural frequency in bending vibration mode of single-walled carbon nanotubes
علیرضا فتاحی واجاریThis paper investigates the bending vibration of single-walled carbon nanotubes based on a new theory called doublet mechanics with a scale parameter. A sixth order partial differential equation that governs the bending vibration for such nanotubes is derived. Euler-Ber أکثرThis paper investigates the bending vibration of single-walled carbon nanotubes based on a new theory called doublet mechanics with a scale parameter. A sixth order partial differential equation that governs the bending vibration for such nanotubes is derived. Euler-Bernoulli beam model is used in this paper. Using doublet mechanics, the relation between natural frequency and scale parameter is derived in the bending vibration mode. It is proven that scale parameter plays significant role in the vibration behavior of such nanotubes in lateral direction. Such effect decreases the natural frequency compared to the predictions of the classical continuum mechanics models. However, with increasing the tube length, the scale effect on the natural frequency decreases. To validate this method, the results obtained herein are compared with the existing nonlocal and molecular dynamics results and good agreement is observed. It is the first time that DM is used to model the bending vibration of carbon nanotube. تفاصيل المقالة -
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35 - Free Vibration of Annular Plate Reinforced with Multi-walled Carbon Nanotubes Resting on an Elastic Foundation Using Refined Theory
مسعود رضایی حمید محسنی منفرد سید علیرضا مهاجرانیIn this paper, an attempt is made for solution of free vibration analysis of annular plate reinforced with carbon nanotubes for Uniformly Distribution (UD), resting on an elastic foundation using a refined theory presented. In this theory, a parabolic distribution of sh أکثرIn this paper, an attempt is made for solution of free vibration analysis of annular plate reinforced with carbon nanotubes for Uniformly Distribution (UD), resting on an elastic foundation using a refined theory presented. In this theory, a parabolic distribution of shear stress and strain in the thickness direction and satisfies the boundary conditions of zero shear stress on the upper and lower crust cut without using a correction factor to be considered. The equations of motion are obtained using Hamilton's principle. And then these equations are solved by GDQ method .Factors affecting the frequency such large radius to small radius, the ratio of thickness to the radius of the annular plate, the length of the radius is obtained. To check the compatibility equations and solving method is used, a comparison between the present work has been done with papers تفاصيل المقالة -
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36 - Design and Production of a Pneumatic Moving Exciter for Determination of Vibration Behavior of Structures in Variable Frequencies
فیروز بختیارینژاد میثم میرزایی مهدی وهابی امیر ابوالفضل صورتگرDetermination and analysis of vibration behavior of structures for at least first few natural frequencies and mode shapes needs several sensors to be connected at different non node points and exciting the structure at one point. Other method for determination of first أکثرDetermination and analysis of vibration behavior of structures for at least first few natural frequencies and mode shapes needs several sensors to be connected at different non node points and exciting the structure at one point. Other method for determination of first few mode shapes is to excite several points of the structure at once and sensing the response from one point. Both methods need several force or accelerometer sensors. Excitation of the structure can be done by impulse from a hammer, electromagnetic, pneumatic, and acoustic or laser exciters. Other method for determination of mode shapes with only one accelerometer sensor and one force transducer is possible by a moving exciter with predetermined velocity. Force excitation can be from electromagnetic, hydraulic or pneumatic system. Pneumatic type of excitation which is clean and is sensitive to small changes is used to design a moving non touching exciter for structures. This type of exciter is useful for determination of vibration behavior of sensitive and fragile structures which hammer or touching electromagnetic system cannot be used. This paper presents a design and production of a pneumatic moving exciter of a structure. Excitation force can be impulse, step, ramp or harmonic with different speeds of moving excitation point. The system was used to excite a beam and results are verified with theoretical results. تفاصيل المقالة -
حرية الوصول المقاله
37 - Severe Impact on the Behavior of Energy Absorbing Cylindrical Base in Frontal Impact
عبدالمجید کنی اکبر علی بیگلوIn this paper, the vibration characteristics of multi-layer shell that internal and external surfaces with a layer of piezoelectric sensor and actuator is investigated. The backrest shell laminated with simple analytical method to evaluate and the results were compared أکثرIn this paper, the vibration characteristics of multi-layer shell that internal and external surfaces with a layer of piezoelectric sensor and actuator is investigated. The backrest shell laminated with simple analytical method to evaluate and the results were compared with results obtained by other researchers. The numerical solution methods (GDQ) for shells with piezoelectric layers and plain bearings, compared with analytical solution and then a variety of boundary conditions is studied. Using the equations of motion, the fundamental equations and relations Krnsh- displacement, State-space equations derived the equations using approximate separate layer, State-space equations with constant coefficients will become. These equations can be solved using natural frequencies in the backrest shell simple to obtain. If the abutments are not simple, solving equations differentials State-space analysis is not possible and should be used numerical methods. A fourth difference method numerical method common with the small number of sample points can be exact to achieve. By dq, State-space differential equations are solved and the non-traction conditions by applying high and low levels, can be found at the natural frequency. The direct and inverse piezoelectric effect, piezoelectric layer and composite layer thickness ratio of the radius of the middle of a thick crust on the vibrational behavior is studied تفاصيل المقالة -
حرية الوصول المقاله
38 - Identification of Crack Location and Depth in a Structure by GMDH- type Neural Networks and ANFIS
منصور درویزه نادر نریمانزاده علی ملیحی دیزگاه مهدی جوادزاده رضا انصاریThe Existence of crack in a structure leads to local flexibility and changes the stiffness and dynamic behavior of the structure. The dynamic behavior of the cracked structure depends on the depth and the location of the crack. Hence, the changes in the dynamic behavior أکثرThe Existence of crack in a structure leads to local flexibility and changes the stiffness and dynamic behavior of the structure. The dynamic behavior of the cracked structure depends on the depth and the location of the crack. Hence, the changes in the dynamic behavior in the structure due to the crack can be used for identifying the location and depth of the crack. In this study the first three natural eigenfrequencies of a cantilever beam having a transverse open crack have been computed for 10 different depths and 30 different locations by the finite element method. These natural eigenfrequencies have been used as input data for GMDH-type neural networks and adaptive neuro-fuzzy inference system, ANFIS, for crack location and depth modeling. تفاصيل المقالة
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