Sharif Digital Repository

Supercavitation is known as the way of viscous drag reduction for the projectiles, moving in the liquid phase. In recent works, there is distinct investigation between cavitation flow and momentum transfer far away from the cavity surface. In fact such methodologies consider cavitation flow statically, rather than taking dynamic effects of overall flow into account. However, it seems that there is strong connection between overall flow and what takes place in the sheet cavity where a constant pressure distribution is assumed. Thereby, in order to configure the system conditions which may be cause of cavity perturbation and so system oscillation, we need to use proper methodologies in which... 

In this paper, the large amplitude tree vibration of a doubly clamped microbeam is considered. The effects of shear deformation and rotary inertia on the large amplitude vibration of the microbeam are investigated. To this end, first Hamilton's principle is used in deriving the partial differential equation of the microbeam response under the mentioned conditions. Then, implementing the Galerkin's method the partial differential equation is converted to an ordinary nonlinear differential equation. Finally, the method of multiple scales is used to determine a second order perturbation solution for the obtained ODE. The results show that nonlinearity acts in the direction of increasing the... 

In reply to the comment of Lu and An on our publication paper [Phys. Rev. E 70, 016304 (2004)], we show that the consideration of water vapor exchange at the bubble interface is essential for obtaining our results and the adiabatic model is too simple to produce the differences. Moreover, in spite of smallness of the compressional viscosity term at the collapse, the illustrated differences are reasonable due to the strong nonlinearity of the bubble dynamics at the collapse and its sensitivity to even small perturbations. We emphasize on the correctness of our calculation results and our simulation programs are now available on the web. © 2005 The American Physical Society  

The response of infinite beams supported by nonlinear viscoelastic foundations subjected to harmonic moving loads is studied. A straightforward solution technique applicable in the frequency domain is presented in this paper. The governing equations are solved using a perturbation method in conjunction with complex Fourier transformation. A closed-formed solution is presented in an integral form based on the presented Green's function and the theorem of residues is used for the calculation of integrals. The solution is directed to compute the deflection and bending moment distribution along the length of the beam. A parametric study is carried out and influences of the load speed and... 

The resulting motion in waves can be considered as a superposition of the motion of the body in still water and the forces on the restrained body. In this study the effect of added mass fluctuation on vertical vibration of TLP in the case of vibration in still water for both free and forced vibration subjected to axial load at the top of the leg is presented. This effect is more important when the amplitude of vibration is large. Also this is important in fatigue life study of tethers. The structural model used here is very simple. Perturbation method is used to formulate and solve the problem. First and second order perturbations arc used to solve the free and forced vibration respectively  

The GV-MSA, the BMCSL-MSA and the Pitzer models were used to correlate the individual, the mean ionic activity coefficients and the osmotic coefficients of symmetric and asymmetric electrolyte solutions. In order to compare the results obtained from the GV-MSA with those obtained from the Pitzer and the BMCSL-MSA models, the same experimental data and the same minimization procedure were used and the new sets of parameters for the BMCSL-MSA and the Pitzer models were also reported. The values for the osmotic coefficients of electrolyte solutions were calculated directly using the values of the mean ionic activity coefficients obtained from the models studied in this work. The results for the... 

In this paper, the large amplitude free vibration of a cantilever Timoshenko beam is considered. To this end, first Hamilton's principle is used in deriving the partial differential equation of the beam response under the mentioned conditions. Then, implementing the Galerkin's method the partial differential equation is converted to an ordinary nonlinear differential equation. Finally, the method of multiple scales is used to determine a second order perturbation solution for the obtained ODE. The results show that nonlinearity acts in the direction of increasing the natural frequency of the thick-cantilevered beam  

A nonlinear fluid–structure interaction (FSI) model is presented for nonlinear vibration analysis of sandwich cylindrical shells subjected to an external compressible flow by considering the curvature nonlinearity in impermeability condition and bending. The sandwich shells are made of two face sheets and a central core of advanced materials including functionally graded (FG), metal foam, and anisogrid lattice composite. Based on the Kirchhoff–love hypotheses with the geometric nonlinearities in the normal strain and curvature of mid-surface, one decoupled nonlinear integral–differential equation is obtained for axisymmetric bending vibration of sandwich cylindrical shells. For the first... 

In this paper, a modified partial derivative method is developed to predict the linear and nonlinear dynamic coefficients of tilting-pad journal bearings with journal and pad perturbation. To this end, Reynolds equation and its boundary conditions along with equilibrium equations of the pad are used. Finite difference, partial derivative method, and perturbation technique have been employed simultaneously for solving these equations. The accuracy of the results is investigated by comparing the linear dynamic coefficients of three types of tilting-pad journal bearings with those published the literature. It is shown that the nonlinear dynamic coefficients depend on Sommerfeld number,... 

Deep learning architectures employ various regularization terms to handle different types of priors. Non-smooth regularization terms have shown promising performance in the deep learning architectures and a learning framework has recently been proposed to train autoencoders with such regularization terms. While this framework efficiently manages the non-smooth term during training through proximal operators, it is limited to autoencoders and suffers from low convergence speed due to several optimization sub-problems that must be solved in a row. In this paper, we address these issues by extending the framework to general feed-forward neural networks and introducing variable extrapolation... 

Analytical frequency analysis of a nonlinear viscoelastic microcantilever is performed based on strain gradient theory. The Kelvin–Voigt scheme is utilized to model the viscoelasticity effect. Due to the microcantilever shortening effect via Euler–Bernoulli inextensibility condition, geometric, inertia, stiffness, and inherent damping nonlinearities are considered. The equation of motion is derived from Hamilton’s principle, and discretized using Galerkin method. The multiple timescale perturbation method is performed to solve the time response equation. Implying steady-state condition, the nonlinear relation between detuning parameter and amplitude of the vibration of a nonlinear... 

This letter deals with a novel variant of antithetic integral feedback controller (AIFC) motifs which can feature robust perfect adaptation, a pervasive (desired) ability in natural (synthetic) biomolecular circuits, when coupled with a wide class of process networks to be regulated. Using the separation of time-scales in the proposed kind of AIFC, here we find a reduced-order controller that captures the governing slow part of the original solutions under suitable assumptions. Inspired by Rössler systems, we then make use of such a simpler controller to show that the antithetic circuit can exhibit chaotic behaviors with strange attractors, where the bifurcation from a homeostatic state to... 

Based on the first-order shear deformation (FSD) model and nonlocal elasticity theory, the simultaneous effects of shear and small scale on the nonlinear vibration behavior of functionally graded carbon nanotube-reinforced composite (FG-CNTRC) beams are investigated for the first time. To this end, the governing equations of bending and stretching with von Kármán geometric nonlinearity are decoupled into one fourth-order partial differential equation in terms of transverse deflection. A closed-form solution of the nonlinear natural frequency, which can be used in conceptual design and optimization algorithms of FG- CNTRC beams with different boundary conditions, is developed using a hybrid...