Effects of mistuning on dynamic behavior of nonlinear cyclic systems with lump masses and cubic nonlinearity

Mistuning in cyclic symmetric systems increases severely the forced response of system and splits the modes. This paper concerns with nonlinear behavior of mistuned cyclic systems. A nonlinear, mistuned model based on the method of multiple scales is proposed and formulated in which nonlinearity and mistuning parameter is assumed to be in of low order. Next, two mistuned systems were considered and solved by the multiple scale technique. Numerical results demonstrate that mistuning can lead to repeating and scattering of jump phenomena during the excitation frequency whereas in tuned cyclic system it occurs simultaneously (synchronously).Peer ReviewedPostprint (published version

Bearings coefficients effects on chaotic and bifurcation behavior of flexible rotor systems subjected to rub-impact

This study investigates the influence of end-support conditions on the chaotic and bifurcation behavior of a rotating flexible shaft-disk system. The system is modeled as a continuous shaft with a rigid disk in its mid span whilst supported by multi-coefficients bearings. Both Coriolis and centrifugal effects due to shaft flexibility are included. The partial differential equations of motion are extracted using the Rayleigh beam theory and the assumed mode method is used to discretize them in order to be solved numerically. The analytical tools used in this work include time series, phase plane portrait, power spectrum, Poincaré map, bifurcation diagrams, and Lyapunov exponents. The main objective of the present study is to investigate the effects of end-supports stiffness and damping coefficients on the chaotic vibration behavior of a rotating system. Periodic, sub-harmonic, quasi-periodic, and chaotic states have been observed for each case. As demonstrated, inclusion of the bearing effects can primarily change the speed ratios at which rub-impact occurs. The principal and cross-coupling stiffness and damping coefficients have quite different effects in the chaotic behavior of the system

Numerical prediction of developing flow in gas pipelines

Paper presented at the 5th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 1-4 July, 2007.In this paper the numerical modeling of the dynamic behavior of compressible gas flow is investigated in pipelines. The numerical simulation is performed by solving the coupled conservation form of the governing equations for twodimensional, laminar, viscous, supersonic flow in developing region under different thermal boundary conditions. The numerical procedure is a finite-volume based finite-element method applied on unstructured grids. The convection terms are discretized by well-defined Roe Method and diffusion terms by a Galerkin finite element formulation. The temporal terms are evaluated based on an explicit fourth order Runge-Kutta scheme. The results indicate that heating the gas flow leads to an increase in pressure loss. In the other words, cooling the gas flow leads to decrease the pressure drop or power consumption of booster pressure station. Furthermore, change in the gas viscosity has considerable effects on the flow quantities such as pressure loss and friction factor

A Similarity Solution with Two-Equation Turbulence Model for Computation of Turbulent Film Condensation on a Vertical Surface

In this paper, we presented a similarity solution for turbulent film condensation of stationary vapor on an isothermal vertical flat plate. In this method, some similarity transformations are employed and the set of governing partial differential equations (PDE) of conservation together with transport equations of turbulent kinetic energy and dissipation rate are transformed into a set of ordinary differential equations (ODE). Calculated data for the flow field, velocity profile, wall shear stress, condensate film thickness, turbulent kinetic energy, rate of dissipation, and heat transfer properties are discussed. The effect of Prandtl (Pr) number was also investigated in a wide range of variations. The obtained results showed that at high Prandtl numbers, the velocity profile becomes more uniform across the condensation film and therefore, the kinetic energy of turbulence is reduced. Furthermore, the effect of change in Pr is negligible at high Pr numbers and consequently, the flow parameters have no significant change in this range. The friction coefficient changes linearly through the condensation film and the slope of friction lines diminishes slightly by the Pr number. The rate of turbulent kinetic energy increases linearly from the wall up to about 20% of condensate film, then rises asymptotically and converges to a constant value near the liquid-vapor interface. Also, the rate of turbulent dissipation grows linearly up to 40% of condensate film thickness and then increases slightly while it oscillates

MicroRNA-129-1 acts as tumour suppressor and induces cell cycle arrest of GBM cancer cells through targeting IGF2BP3 and MAPK1

Background MicroRNA-129-1 (miR-129-1) seems to behave as a tumour suppressor since its decreased expression is associated with different tumours such as glioblastoma multiforme (GBM). GBM is the most common form of brain tumours originating from glial cells. The impact of miR-129-1 downregulation on GBM pathogenesis has yet to be elucidated. Methods MiR-129-1 was overexpressed in GBM cells, and its effect on proliferation was investigated by cell cycle assay. MiR-129-1 predicted targets (CDK6, IGF1, HDAC2, IGF2BP3 and MAPK1) were also evaluated by western blot and luciferase assay. Results Restoration of miR-129-1 reduced cell proliferation and induced G1 accumulation, significantly. Several functional assays confirmed IGF2BP3, MAPK1 and CDK6 as targets of miR-129-1. Despite the fact that IGF1 expression can be suppressed by miR-129-1, through 30-untranslated region complementary sequence, we could not find any association between IGF1 expression and GBM. MiR-129-1 expression inversely correlates with CDK6, IGF2BP3 and MAPK1 in primary clinical samples. Conclusion This is the first study to propose miR129-1 as a negative regulator of IGF2BP3 and MAPK1 and also a cell cycle arrest inducer in GBM cells. Our data suggests miR-129-1 as a potential tumour suppressor and presents a rationale for the use of miR-129-1 as a novel strategy to improve treatment response in GBM

Study of temperature-curvature relationships in Bi-stable composite laminates

The interest in bi-stable structures comes from their ability that these structures can have two different stable equilibrium configurations to define a discrete set of stable shapes. The geometrical changes occur with no need to continuously consume power, and mechanical hinges to preserve the structure in each stable shape. It is known that asymmetric composite laminates can have bi-stable response to different kind of loadings. In this research, the non-linear temperature-curvature relationship for the asymmetric composite laminates is studied using Rayleigh–Ritz technique. Attention is focused on studying the effect of material temperature dependency and resin layers; especially in the bifurcation point by use of analytical method. To this end, the well-known analytical theories are extended and used to consider the temperature dependency of material. The results obtained from the theory are then compared with the finite element simulations results and a good correlation is obtained. Finally, an experimental investigation is carried out and several specimens with [90/0] T, [70/–20]T and [70/20]T compositions were manufactured. In order to study the effect of resin layers, optical microscopy is utilized and the exact thickness of different layers in the manufactured specimens is determined. The thermal responses of the manufactured plates were measured and used to validate the results obtained from the analytical theory and finite element simulations

Dynamic Analysis of Small Pigs in Space Pipelines

This paper deals with the dynamics of small pipeline inspection gauges (pigs) in space pipelines. First, the differential equations for dynamic analysis of the small pig, whose length is short, are developed. The flow field can significantly influence the pig's trajectory. In this research, the effect of the flow field on the pig's trajectory was ignored. The path of the pig or centerline of the pipeline is assumed to be a curve in 3D space. Next, the differential equations of motion are combined and reduced to only one nonlinear differential equation with respect to the parameter of the space curve. The fourth-order Runge-Kutta method is then used for solving the equation. The driving force is assumed to be time-dependent, but the coefficient of friction is assumed to be constant for the sake of simplicity. The simulation results show that the derived equations are effective for estimating the position and velocity of the pig and forces acting on it at all time instants of its motion