Yasin Yilmaz

Buckling Analyses of Axially Functionally Graded Nonuniform Columns with Elastic Restraint Using a Localized Differential Quadrature Method

A localized differential quadrature method (LDQM) is introduced for buckling analysis of axially functionally graded nonuniform columns with elastic restraints. Weighting coefficients of differential quadrature discretization are obtained making use of neighboring points in forward and backward type schemes for the reference grids near the beginning and end boundaries of the physical domain, respectively, and central type scheme for the reference grids inside the physical domain. Boundary conditions are directly implemented into weighting coefficient matrices, and there is no need to use fictitious points near the boundaries. Compatibility equations are not required because the governing differential equation is discretized only once for each reference grid using neighboring points and variation of flexural rigidity is taken to be continuous in the axial direction. A large case of columns having different variations of cross-sectional profile and modulus of elasticity in the axial direction are considered. The results for nondimensional critical buckling loads are compared to the analytical and numerical results available in the literature. Some new results are also given. Comparison of the results shows the potential of the LDQM for solving such generalized eigenvalue problems governed by fourth-order variable coefficient differential equations with high accuracy and less computational effort.

An investigation of the effect of counterweight configuration on main bearing load and crankshaft bending stress

In this study, effects of counterweight mass and position on main bearing load and crankshaft bending stress of an in-line six-cylinder diesel engine is investigated using Multibody System Simulation Program, ADAMS. In the analysis, rigid, beam and 3D solid crankshaft models are used. Main bearing load results of rigid, beam and 3D solid models are compared and beam model is used in counterweight configuration analyses. Twelve-counterweight configurations with a zero degree counterweight angle and eight-counterweight configurations with 30^o counterweight angle, each for 0%, 50% and 100% counterweight balancing rates, are considered. It is found that maximum main bearing load and web bending stress increase with increasing balancing rate, and average main bearing load decreases with increasing balancing rate. Both configurations show the same trend. The load from gas pressure rather than inertia forces is the parameter with the most important influence on design of the crankshaft. Results of bearing loads and web bending stresses are tabulated.

Vibration behavior of a radially functionally graded annular disc with variable geometry

Abstract In this study, the free vibration behavior of an annular disc made of functionally graded material (FGM) with variable geometry is investigated. The elasticity modulus, density, and thickness of the disc are assumed to vary through the radial direction according to the power law so that the effects of their indexes on the natural frequency of the disc are investigated. The Poisson’s ratio is assumed as a constant. The natural frequencies of the disc are calculated for various boundary conditions by using classical plate theory, and the various types of mode shapes, which are described by the number of nodal diameters and nodal circles, are also discussed. Moreover, the effects of the ratio of the inner radius to the outer radius on the natural frequency are also considered. It is found that in order to increase the natural frequency, the elasticity modulus and thickness should be increased at the inner surface, whereas density should be increased at the outer surface. The natural frequency can also be increased by increasing the ratio of inner radius to outer radius. The results obtained are compared with the results of a finite-element-based commercial program, ANSYS®, and found to be consistent with each other.

An Investigation of the Effect of Weatherstrip Seals on Vehicle Vibration and Acoustics Using an Alternative Modeling Technique

In this study, the effect of weatherstrip seals on panel vibrations and structure borne noise is studied. First, a test structure is built to model vehicles body and door; hammer impact tests are carried out to determine frequency shifts in door vibration modes with the inclusion of rubber seals. Then, a finite element model of the test structure is built. Rubber seals are modeled as spring elements, and a modal analysis is carried out. Finite element results are compared to experimental ones to check the validity of the model used. Following a parametric study to determine stiffness of linear springs, the full vehicle is modeled using finite elements, and the effect of rubber weatherstrip seals on sound pressure level (SPL) inside the passenger compartment is studied. Frequency response curves are plotted.

A Combining Method for solution of nonlinear boundary value problems

Abstract Modeling-based simulation techniques and numerical methods such as Differential Quadrature Method and Integral Quadrature Method are widely used for solution of ordinary differential equations. However simulation techniques do not allow to impose boundary conditions, and both Differential Quadrature Method and Integral Quadrature Method have some deficiencies in applying multiple boundary conditions at the same location. Moreover they are not convenient for the solution of non-linear Ordinary Differential Equations without using any linearization process such as Newton–Raphson technique and Frechet derivative which requires an iterative procedure increasing the time needed for solution. In this study, modeling-based simulation technique is combined with Differential Quadrature Method and/or Integral Quadrature Method to eliminate the aforementioned deficiencies. The proposed method is applied to four different nonlinear boundary value problems including a coupled nonlinear system, second and fourth order nonlinear boundary value problems and a stiff nonlinear ordinary differential equation. The numerical results obtained using Combining Method are compared with existing exact results and/or results of other methods. Comparison of the results show the potential of Combining Method for solution of nonlinear boundary value problems with high efficiency and accuracy, and less computational work.