Applied Mechanics and Materials Vol. 394

Abstract: Two-dimensional numerical simulations are performed to analyze the turbulent flow over a circular cylinder close to a moving plane. This flow receives interference from the plane boundary layer, being this effect identified by recirculation zones close to the wall and slight difference in pressure distribution around cylinder. URANS equations and SST modeling are employed to calculate velocity and pressure field. The simulation was performed by a finite element projection scheme. Four distances between the cylinder and the plane are analyzed by the SST model. The SST results showed the generation and development of vortex shedding. Lift and drag coefficients show the flow oscillatory pattern. All results are similar with other numerical results at the literature.

Abstract: In this paper, the physical model of the cantilever beam with a surface crack is established to study the free vibration of the cracked beam from three aspects that are theoretical analysis, FEM analysis, and experiment. At the same time, the relation between the crack parameter and the vibration characteristics, which are natural frequencies and the modes of each order, is obtained through analysis. The theoretical analysis is on the basis of the mode analysis theory and applied mechanics. The crack is regarded as a flexible hinge. Utilizing the external boundary conditions and internal boundary conditions at the crack, the free vibration characteristics are obtained combining with the vibration mechanics. With the ANSYS software, a finite element model of the cracked beam is established by the beam element. During the process of calculation, it calculates the natural frequencies and the modes of cracked beam with different parameters of crack. The results obtained from the experiment are in agreement with the results obtained from the theoretical and the FEM analysis. So the accuracy of the theoretical analysis and the numerical simulation is verified by the experiment. At last, the effects of the crack location and depth on the natural frequencies and modes of each order are shown, and it could provide the theoretical, numerical and experimental basis for the identification of cracked materials and the relevant study.

Abstract: Large Eddy Simulation (LES) based on the least square meshless method was proposed in the present paper to simulate the classical turbulent flow around a stationary 2D circular cylinder. The subgrid scale model of Smagorinsky-Lily was employed to close the Navier-Stokes equations filtered by Favre filter. The Reynolds number is 3900 which means that the flow is subcritical and the wake is fully turbulent but the cylinder boundary is still laminar. Results obtained in this paper were evaluated by comparison with published experimental results and other numerical results. The results obtained in the present work show better agreement with the experimental values than other two-dimensional LES results .

Abstract: Auxetic materials are solids that possess negative Poissons ratio. Although rare, such materials do occur naturally and also have been artificially produced. Due to their unique properties, auxetic materials have been extensively investigated for load bearing applications including in biomedical engineering and aircraft structures. This paper considers the effect of Poissons ratio on the stress concentration factors on rods with hyperbolic groove and large thin plates with circular holes and rigid inclusions. Results reveal that the use of auxetic materials is useful for reducing stress concentration in the maximum circumferential stress of the rods with grooves, and in plates with circular holes and rigid inclusions. However, the use of auxetic materials increases the stress concentration in the axial direction of the rod. Therefore a procedure to accurately select and/or design materials with precise negative Poissons ratio for optimal design is suggested for future work.

Abstract: The dynamics of chain drives is a complex issue due to the polygonal effect and the multiple successive impacts that take place. The combined effect of these phenomena leads to discontinuities in the systems velocities giving rise to transversal and longitudinal vibrations on the chain spans. To investigate the pretension effect on the drive dynamics, a tensioner is applied to a generalized chain drives multibody model developed and implemented in a computational code by the authors. In this model, the clearance revolute joints formulation is used to handle the dry contact between all drive components. The pretension changes the characteristics of the contact pairs by enforcing a continuous contact with only a small number of contact losses. When no pretension is used, the contact is characterized by a sequence of short duration contacts. The strands of the pretensioned chain vibrate with higher frequency but smaller amplitude in comparison to the non-pretensioned system.

Abstract: In this paper, the periodic behavior of iced cable in the case of the in-plane fundamental parametric resonance-principal resonance, out-of-plane principal parametric resonance-principal resonance, and in 1:2 internal resonances is investigated. The sufficient condition for the existence of the periodic solutions about the system is obtained through using Melnikov function and Poincare mapping, then the stability of periodic solution is investigated by using blow-up transformations and the average method. Numerical simulations are performed to verify the analytical predictions and get three groups of diagrams.

Abstract: The reanalysis approach consists in determining the effect of already established modifications. This study presents the dynamic reanalysis method to describe the dynamic response of modified system by combining the theoretically calculated receptances of the original system and the information on the modified substructure. The proposed formulation includes dynamic reanalysis where there are and are not additional dofs due to structural modification without any numerical iteration. A numerical example is given to illustrate the applications of the proposed method. And the numerical results raise the application limit of the proposed method.

Abstract: The physical parameters obtained from modal tests do not satisfy the eigenvalue function due to modeling and measurement errors, and unexpected damage. The desired dynamic response can be obtained by identifying the most appropriate changes required to obtain the desired dynamic behaviour. The purpose of this study is to present the analytical equations on the updated stiffness and mass matrices in the satisfaction of eigenfunction including residual force vector term. Minimizing the cost functions of the difference between analytical and desired physical parameter matrices, the variations in parameter matrices are straightforwardly derived without using any multipliers. The validity of the proposed methods is evaluated in an application.

Abstract: Laminar natural convection heat transfer inside water-filled, tilted square and shallow cavities heated at one side and cooled at the opposite side, is studied numerically. A computational code based on the SIMPLE-C algorithm is used to solve the system of the mass, momentum and energy transfer governing equations. Simulations are performed using the Rayleigh number based on the length of the heated and cooled sides, the height-to-width aspect ratio of the enclosure, and the positive tilting angle with respect to the gravity vector (which corresponds to configurations with the heated wall facing upwards), as independent variables. It is found that the heat transfer performance has a peak at an optimal tilting angle which increases as the Rayleigh number is decreased and the aspect ratio is increased. On the basis of the results obtained, a set of dimensionless correlations is developed.

Abstract: The flow and heat transfer characteristics were numerically studied in wave, dimple and wave-dimple microchannels for thermal managements on the chip of Intel i7-996X with heat flux of 0.56 W/mm².The results show that, in microchannles heat sink, the dimple structure could reduce the flow resistances and the wavy wall could enhance heat transfer. According to the both advantages, two types of microchannel heat sink both with dimples and wavy walls were designed, and the flow and heat transfer characteristics were numerically studied. It is proved that the wave-dimple microchannels heat sink holds the characteristics of enhancing heat transfer with low pressure drop, which implies it has great potential of development and application prospect.