Abstract in English:Abstract The components of flexible rotors are subjected to uncertainties. The main sources of uncertainties include the variation of mechanical properties. This contribution aims at analyzing the dynamics of flexible rotors under uncertain parameters modeled as fuzzy and fuzzy random variables. The uncertainty analysis encompasses the modeling of uncertain parameters and the numerical simulation of the corresponding flexible rotor model by using an approach based on fuzzy dynamic analysis. The numerical simulation is accomplished by mapping the fuzzy parameters of the deterministic flexible rotor model. Thereby, the flexible rotor is modeled by using both the Fuzzy Finite Element Method and the Fuzzy Stochastic Finite Element Method. Numerical simulations illustrate the methodology conveyed in terms of orbits and frequency response functions subject to uncertain parameters.
Abstract in English:Abstract Concrete barriers prevent vehicles from entering the opposite lane and going off the road. An important factor in the design of concrete barriers is impact load, which a vehicle exerts upon collision with a concrete barrier. This study suggests that a height of 813 mm, a base width of 600 mm, and a top width of 240 mm are optimum dimensions for a concrete barrier. These dimensions ensure the stability of concrete barriers during vehicle collisions. An analytical and experimental model is used to analyze the concrete barrier design. The LS-DYNA software is utilized to create the analytical models because it can effectively simulate vehicle impact on concrete barriers. Field tests are conducted with a vehicle, whereas laboratory tests are conducted with machines that simulate collisions. Full-scale tests allow the actual simulation of vehicle collisions with concrete barriers. In the vehicle tests, a collision angle of 25°, collision speeds of 100 km per hour, and a vehicle weighing more than 2 t are considered in the reviewed studies. Laboratory tests are performed to test bridge concrete barriers in static condition.
Abstract in English:Abstract An analysis has been performed to study the problem of the flow of incompressible Newtonian fluid between two parallel plates where the upper plate is impermeable and can move up or down and the lower one is fixed and has a porous surface. The governing equations for this problem are reduced to an ordinary form and is solved using Homotopy Analysis Method (HAM) and numerically by fourth order Runge-Kutta technique. Also, Velocity fields have been computed and shown graphically for various values of physical parameters. As an important outcome, HAM is able to solve a large class of nonlinear problems effectively, more easily and accurately; and thus it has been widely applicable in engineering and physics.
Abstract in English:Abstract The phenomena of reflection and refraction of plane waves incident obliquely at a plane interface between uniform elastic solid half-space and porous solid containing liquid filled bound pores and two-phase fluid in connected pores has been analyzed. The amplitude ratios of the reflected and refracted waves to that of the incident wave are calculated as a non- singular system of linear algebraic equations. These amplitude ratios are used further to derive the expressions for the partition of incident energy among the reflected and refracted waves. Partition of incident energy among the reflected and refracted waves is studied for incidence of P and SV waves. The conservation of the energy across the interface is verified. The effect of gas saturation, wave frequency, capillary pressure and bound liquid film on the amplitude ratios and energy partitions are studied in the numerical example.
Abstract in English:Abstract To investigate the thermal buckling of curved carbon nanotubes (CCNTs) embedded in an elastic medium, nonlocal elasticity theory is employed in combination with the theory of thin curved beams. Differential quadrature (DQ) method is implemented to discretize the resulted governing equations. Solving these equations enables us to estimate the critical temperature and the critical axial buckling load for CCNTs surrounded by an elastic medium and under the effect of a uniform temperature change. The elastic interaction between the nanotube and its surrounding medium is modeled as a Winkler-Pasternak elastic foundation. The fast convergence of the DQ method is demonstrated and also its accuracy is verified by comparing the results with available solutions in the literature. The effects of various parameters such as different boundary conditions, nonlocal parameter, Winkler and Pasternak elastic modulus, temperature and nanotube curvature on the critical buckling temperature and load are successfully studied. The results reveal that the critical buckling load depends significantly on the curvature of the CCNT.
Abstract in English:Abstract This paper is concerned with the nonlinear free vibration of a heated micro/nano beam modeled after the nonlocal continuum elasticity theory and Euler-Bernoulli beam theory. The governing partial differential equations are derived from the Hamilton variational principle and von Kármán geometric nonlinearity, in which the effects of the nonlocality and ambient temperature are inclusive. These equations are converted into ordinary forms by employing the Kantorovich method. The solutions of nonlinear free vibration are then sought through the use of shooting method in spatial domain. Numerical results show that the proposed treatment provides excellent accuracy and convergence characteristics. The influences of the aspect ratio, nonlocal parameter and temperature rise parameter on the dimensionless radian frequency are carefully investigated. It is concluded that the nonlocal and temperature rise parameters lead to reductions of the nonlinear vibration frequency, while the influence of the nonlocal effect decreases with an increase in the aspect ratio.
Abstract in English:Abstract An in-depth study has been carried out for the dispersion of Love waves in an isotropic elastic layer sandwiched between orthotropic and prestressed inhomogeneous elastic half-spaces. The inhomogeneities in density and rigidity of the lower half-space are space dependent and an arbitrary function of depth. Simple mathematical techniques are used to obtain dispersion relation for Love wave propagation in an isotropic layer. An extensive analysis is carried out through numerical computation to explore the effect of inhomogeneity and initial stress the lower half on the phase velocity of the Love waves. The numerical analysis of dispersion equation manifests that the phase velocity of the Love wave increases with the increase of stress parameter. The results further indicate that the inhomogeneity of the half space affect the wave velocity significantly. These results can be useful to study geophysical prospecting and understanding the cause and estimation of damage due to earthquakes.
Abstract in English:Abstract This research was an experimental and numerical investigation of the cylindrical expanded Sheets under impact loading. Two types of absorbers with different cell angles were examined (i.e. α = 0 and α = 90). The experiments were performed using the drop hammer setup, and the numerical simulations were conducted by ABAQUS. In this study, the type of collapse, force-displacement diagrams, the crushing length, and the absorbed energy were investigated. The experimental and numerical results were compared, and it was observed that they were in good agreement. Results showed that the absorbers with the cell angle of α = 0 had a symmetric collapse and a high energy absorption capacity. Also, various heights of fall were considered for the impact mass to examine the type of collapse in the models. The crushing amounts of the models were also compared in different heights. Multi-walled expanded metal tubes were studied, and the effect of being multi-walled in collapse was examined.
Abstract in English:Abstract At conceptual phases of designing a vehicle, engineers need simplified models to examine the structural and functional characteristics and apply custom modifications for achieving the best vehicle design. Using detailed finite-element (FE) model of the vehicle at early steps can be very conducive; however, the drawbacks of being excessively time-consuming and expensive are encountered. This leads engineers to utilize trade-off simplified models of body-in-white (BIW), composed of only the most decisive structural elements that do not employ extensive prior knowledge of the vehicle dimensions and constitutive materials. However, the extent and type of simplification remain ambiguous. In fact during the procedure of simplification, one will be in the quandary over which kind of approach and what body elements should be regarded for simplification to optimize costs and time, while providing acceptable accuracy. Although different approaches for optimization of timeframe and achieving optimal designs of the BIW are proposed in the literature, a comparison between different simplification methods and accordingly introducing the best models, which is the main focus of this research, have not yet been done. In this paper, an industrial sedan vehicle has been simplified through four different simplified FE models, each of which examines the validity of the extent of simplification from different points of views. Bending and torsional stiffness are obtained for all models considering boundary conditions similar to experimental tests. The acquired values are then compared to that of target values from experimental tests for validation of the FE-modeling. Finally, the results are examined and taking efficacy and accuracy into account, the best trade-off simplified model is presented.
Abstract in English:Abstract A solution procedure using the Green's function based finite element method (FEM) is presented for two-dimensional nonlinear steady-state seepage analysis with the presence of free surface in isotropic dams. In the present algorithm, an iteration strategy is designed to convert the over-specified free surface problem to a regular partial differential equation problem. Then, at each iteration step, the Green's function for isotropic linear seepage partial differential equation is employed to construct the element interior water head field, while the conventional shape functions are used for the independent element frame water head field. Then these two independent fields are connected by a double-variable hybrid functional to produce the final solving equation system. By means of the physical definition of Green's function, all two-dimensional element domain integrals in the present algorithm can reduce to one-dimensional element boundary integrals, so that versatile multi-node element is constructed to simplify mesh reconstruction during iteration. Finally, numerical results from the present Green's function based FEM with isotropic Green's function kernels are compared with other numerical results to verify and demonstrate the performance of the present method.