Archive of Mechanical Engineering

For a deeper understanding of the inner ear dynamics, a Finite-Element model of the human cochlea is developed. To describe the unsteady, viscous creeping flow of the liquid, a pressure-displacement-based Finite-Element formulation is used. This allows one to efficiently compute the basilar membrane vibrations resulting from the fluid-structure interaction leading to hearing nerve stimulation. The results show the formation of a travelingwave on the basilar membrane propagating with decreasing velocity towards the peaking at a frequency dependent position. This tonotopic behavior allows the brain to distinguish between sounds of different frequencies. Additionally, not only the middle ear, but also the transfer behavior of the cochlea contributes to the frequency dependence of the auditory threshold. Furthermore, the fluid velocity and pressure fields show the effect of viscous damping forces and allow us to deeper understand the formation of the pressure difference, responsible to excite the basilar membrane.

Embedded delamination growth stability was analysed with the help of the FEM combined with a specially developed procedure for node relocation to obtain a smooth variation of the SERR components along the delamination contour. The procedure consisted in the replacement of the actual material with the very compliant fictitious one and the displacement of the delamination front nodes by the previously determined distance in a local coordinate system. Due to this loading, the new delamination front was created. Subsequently, the original material was restored. Evolution under inplane compression of three initially circular delaminations of diameters d = 30, 40 and 50 mm embedded in thin laminates of two different stacking sequences, i.e., 0^o₄//0^o₂₄ and 0^o₄//90^o₂₀/0^o₄ were considered. It was found that the growth history and the magnitude of the load that triggers unstable delamination growth depended mainly on the combined effects of the initial delamination size, delamination contour, out of plane post-buckling geometry of the disbonded layers, reinforcement arrangement, and magnitude and variation of the SERR components along the delamination contour. To present the combined effect of these features, an original concept of the effective resistance curve, G_Reff , was introduced.

System identification is an approach for parameter detection and mathematical model determination using response signals of a dynamic system. Two degrees of freedom (2DOF) pendulum controlled by a QUBE-servo motor is a great experiment device to work with; though it is not easy to control this system due to its complex structure and multi-dimensional outputs. Hence, system identification is required for this system to analyze and evaluate its dynamic behaviors. This paper presents a methodology for identifying a 2DOF pendulum and its dynamic behaviors including noise from an encoder cable. Firstly, all parameters from both mechanical and electrical sides of the QUBE-servo motor are analyzed. Secondly, a mathematical model and identified parameters for the 2DOF pendulum are illustrated. Finally, disturbances from encoder cable of the QUBE-servo motor which introduce an unwanted oscillation or self-vibration in this system are introduced. The effect of itself on output response signals of the 2DOF QUBE-pendulum is also discussed. All identified parameters are checked and verified by a comparison between a theoretical simulation and experimental results. It is found that the disturbance from encoder cable of the 2DOF QUBE-pendulum is not negligible and should be carefully considered as a certain factor affecting response of system.

In this paper, a comprehensive study is carried out on the dynamic behaviour of Euler–Bernoulli and Timoshenko beams resting on Winkler type variable elastic foundation. The material properties of the beam and the stiffness of the foundation are considered to be varying along the length direction. The free vibration problem is formulated using Rayleigh-Ritz method and Hamilton’s principle is applied to generate the governing equations. The results are presented as non-dimensional natural frequencies for different material gradation models and different foundation stiffness variation models. Two distinct boundary conditions viz., clamped-clamped and simply supported-simply supported are considered in the analysis. The results are validated with existing literature and excellent agreement is observed between the results.

A compliant beam subjected to large deformation is governed by a multifaceted nonlinear differential equation. In the context of theoretical mechanics, solution for such equations plays an important role. Since it is hard to find closed-form solutions for this nonlinear problem and attempt at direct solution results in linearising the model. This paper investigates the aforementioned problem via the multi-step differential transformation method (MsDTM), which is well-known approximate analytical solutions. The nonlinear governing equation is established based on a large radius of curvature that gives rise to curvature-moment nonlinearity. Based on established boundary conditions, solutions are sort to address the free vibration and static response of the deforming flexible beam. The geometrically linear and nonlinear theory approaches are related. The efficacy of the MsDTM is verified by a couple of physically related parameters for this investigation. The findings demonstrate that this approach is highly efficient and easy to determine the solution of such problems. In new engineering subjects, it is forecast that MsDTM will find wide use.

A numerical solution is presented to investigate the influence of the geometry and the amplitude of the transverse ridge on the characteristics of elastohydrodynamic lubrication for point contact problem under steady state condition. Several shapes of ridges with different amplitudes are used in the stationary case, such as flattop ridge, cosine wave ridge and sharp ridge of triangular shape. Results of film thickness and pressure distributions of the aforementioned ridge feature are presented at different locations through an elastohydrodynamically lubricated contact zone for different amplitude of the ridge. Simulations were performed using the Newton-Raphson iteration technique to solve the Reynolds equation. The numerical results reveal that, to predict optimum solution for lubricated contact problem with artificial surface roughness, the geometrical characteristics of the ridge should have profiles with smooth transitions such as those of a cosine wave shape with relatively low amplitude to reduce pressure spike and therefore cause the reduction in the film thickness. The position of the location of the ridge across the contact zone and the amplitude of the ridge play an important role in the formation of lubricant film thickness and therefore determine the pressure distribution through the contact zone.