International Journal of Advanced Design and Manufacturing Technology
Volume:16 Issue: 2, Jun 2023

In this paper, free vibration of laminated composite cylindrical shells reinforced with circumferential rings, are investigated with experimental, analytical and finite element methods and natural frequencies are obtained. The analysis is carried out for clamp-free and clamp-clamp boundary conditions and the results are compared with each other. To solve the problem, the equilibrium Equations of motions are written according to the classical shells theory and after simplification, the structural stiffness and mass matrices and the frequency Equation are derived using Galerkin method. The results obtained in this paper, are compared with the results available in the literatures, and the results of experimental and finite element methods and good agreement is observed.

This paper explores the optimal position and minimum stiffness of two intermediate supports to maximize the fundamental natural frequency of a vibrating cantilever Timoshenko beam with tip mass using Finite Element Method (FEM) and a multi-objective genetic algorithm (GA). After validating the results by comparison to previous works, the effects of the mass ratio and the position and stiffness of intermediate elastic support on the fundamental frequency are investigated. The numerical results demonstrated that as mass ratio increases, the optimal position moves toward the tip mass, and minimum stiffness increases. In many practical applications, it is not possible to place intermediate support in the optimal position; therefore, the minimum stiffness does not exist. In order to overcome this issue, a tolerance zone is considered, and  design curves are proposed. The simultaneous optimization of the first and second natural frequencies of the beam with two intermediate supports was carried out using the genetic algorithm (GA) and the multi-objective GA. It was found that the optimization of the first and second natural frequencies did not require the two supports to have the same and high stiffness. The stiffness and optimal positions of the two supports differ at different mass ratios. Moreover, to optimize the first natural frequency, the second support should be stiffer, while the optimization of the second natural frequency requires the higher stiffness of the first support.

In this research, the impact behavior of nanocomposite sandwich panels with epoxy/fiberglass/nanosilica face sheet were assessed by the finite element method. In the first step, the mechanical properties of the nanoparticle-containing composite should be obtained. A unit cell of fabric was designed in Catia software and placed within the designed polymeric matrix. The mechanical properties of this unit cell were defined as a new matrix and the nanoparticles were randomly dispersed in the new matrix using a Python code. The elastic properties of the modeled nanocomposite were obtained using Abaqus software via applying periodic boundary conditions based on the mean volumetric stress. In the next step, the sandwich structure was subjected to impact loads at various speeds and contact force-time diagrams were plotted using Abaqus software. The modeled results were compared with the known experimental data which showed a high accuracy in predicting the mechanical properties and impact behavior of the nanocomposite sandwich structures.

This 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.

Vibration analysis of rotating disks is one of the most important problems in turbomachines. In this study, a new method has been presented which analyzed the radial vibration of a turbo-pump rotating disk carrying two annular concentrated masses located on the disk and at its end. Natural frequencies have been calculated in different rotating speeds; then results have been compared with each other. The effects of concentrated masses position and intensity on natural frequencies have been investigated. The results show that concentrated masses always have been decreased the value of first natural frequency, but in the case of second and third natural frequencies, depending on the mass concentration magnitude and its position, the magnitude of natural frequency has been increased or decreased. The vibration of the rotating disk without considering the concentrated mass, was examined. Then the resulting solution was generalized for two connected disks in internal concentrated mass location. The effect of concentrated masses, one on the disk body and the other on the outside of the disk, is considered as boundary conditions in the two disk Equations. The results show that increasing in angular velocity of rotating disk reduces the natural frequency. Concentrated masses always reduce the first natural frequency. At the second and third natural frequencies, concentrated masses may increase or decrease the natural frequency, which depends on the value and position of concentrated mass. Concentrated mass has the most impact when it is in a position that has the most radial displacement.

In this paper, control of shimmy vibration of aircraft nose landing gear is presented. In this regard, the NARMA-L2 neural controller and a robust controller using a fuzzy method are designed and compared. The efficiency of these controllers was measured by comparing the results obtained from CTM and PID controllers. Using the NARMA-L2 neural controller, maximum effort and settling time are improved whereas using fuzzy controller overshoot of the vibration response improvement in the closed-loop system was observed. According to these results, a large part of the design requirements can be solved by the implemented controllers.

Due to the increasing application of Functionally Graded Materials (FGM) shells, it seems necessary to investigate their behaviour under different loads. Therefore, in this paper, the dynamic response of functionally graded materials cylindrical shells under explosive load has been investigated with analytical and simulation methods. LS-DYNA software is used in the simulation method. In analytical solution, vibration of composite circular cylindrical shells is investigated based on the first-order deformation shell theory. The boundary conditions are assumed to be fully simply supported. The dynamic response of composite shells is studied under blast loading. The modal technique is used to develop the analytical solution of composite shell. The solution for the shell under the giving loading condition can be found using the convolution integral. Material properties are assumed to be graded in the thickness direction according to Reddy function. A FGM cylindrical shell is made up of a mixture of ceramic and metal. Results show that the effect of explosion is such that it has the greatest effect on the inner layer and with increasing thickness to the outside of the shell this effect decreases and when the maximum deflection occurs, the dynamic velocity is zero. Also, it was observed that with increasing length, the radial deflection increases due to increasing the distance from the support to the center of the shell.

Joints are considered the weakest part of an engineering structure and failure usually occurs in this region, firstly. One of the main factors in the rupture of adhesive joints is the normal stresses between the layers created by the presence of an out-of-center load and bending moment. The present research work has focused on the influence of parameters including the adhesive zone length, adhesive and adherend layer thickness on reducing the amount of normal interlayer stress in a single-lap adhesive joint. Optimization of parameters have been done using BA and PSO optimization algorithm. The distribution of normal and shear stresses are based on two-dimensional elasticity theory that includes the complete stress-strain and strain-displacement relations for the adhesive and adherends. The results obtained from current research revealed that by optimization of mentioned parameters, the value of peeling stress is significantly reduced. Although increasing in Young’s modulus of adhesive layer leads to an increase in normal stress of the joint, it creates a more uniform stress distribution at the edges. The outcomes also revealed that increasing the length of the joint zone and the thickness of adherends can improve the interlayer normal stress in the adhesive joint.

This work involves an experimental study of the thermophysical properties of hybrid nanofluids of TiO2 and graphene in a binary mixture of water and ethylene glycol. Hybrid nanofluid samples with different volume fractions (0.05-2.5%) were prepared by dispersing equal volumes of TiO2 and graphene nanoparticles in a binary mixture of water and ethylene glycol in the ratio of 50-50% by volume. The thermal conductivity, surface tension, and dynamic viscosity of the hybrid nanofluids were measured at temperatures ranging from 253 K to 303 K. The experimental results showed that the low concentration samples exhibited shear thinning non-Newtonian behavior, while the high concentration samples exhibited shear thickening non-Newtonian behavior. The measurements showed that the thermal conductivity of the nanofluids increases by up to 41.93% with increasing nanoparticle concentration and temperature. The surface tension improves by 43.61%, 39.77%, and 51.98% at concentrations of 2.5%, 2%, and 2% by volume at temperatures of 258.15 K, 268.15 K, and 283.15 K, respectively. In terms of aircraft deicing fluid performance, the addition of TiO2 and graphene nanoparticles at less than 0.5% by volume contributes to the improvement of aircraft deicing fluid performance.

Offshore fixed metal platforms have unique characteristics in specific location such as shallow waters, and oil platform may be physically connected to seabed. Offshore platforms in the sea are affected by complex and destructive forces caused by wind, waves, marine currents, earthquakes and even large displacement vortex forces. The purpose of refurbishing metal fixed platforms is to somehow equalize the capacity of the structure with its seismic requirements. In some cases, they increase the capacity of the structure to meet seismic requirements. In this research, dynamic vibration absorbers or dampers, such as passive dampers, fluid system adjusted for damping vibrations and reduced structural response against wave and earthquake hydrodynamic loads will be used as an efficient control method. The purpose of this research is to improve the performance of the liquid platform vibration damping of the metal platform. The results show that equipping offshore platforms with liquid damping systems has a good performance on the safety and dynamic behaviour of the platforms and has a significant effect on the displacement response and acceleration of the platform under study at its highest deck level. Also, as the water depth in the tank increases, the damping value for the rectangular and cylindrical tanks decreases and the rectangular tank creates more control and damping force than the cylindrical tank.