فهرست مطالب یونس شکاری

In this study evaluated stress distribution at the adhesively-bonded single-lap joints under tensile loading with isotropic adherends using a three-parameter viscoelastic foundation model. In this model, assumed shear stress is constant and peel stress is different along thickness of adhesive layer. In this study, the adhesive layer is modeled as a three-parameter viscoelastic foundation using the Zener model and the governing differential equations are derived using equilibrium equations and constitutive equations in Laplace’s domain. Then simultaneously solving them, the Gaver-Stehfest inverse Laplace transform method is used to obtain the equations in the time domain. At the end, results obtained of this model compare with the results of finite element that there are good agreement between them. Maximum reduction of shear stress occurs at 0.5mm last end of the overlap of Brass adherend and Maximum reduction of Pell stress occurs at 0.5mm last end of the overlap of Aluminum adherend. Reduction of stress with pass time after about 11 days near to zero and it stable.

Energy harvesting is the process of converting different kinds of energy, such as solar, thermal, kinetic energy of fluid, etc., to a usable form of energy. Different kinds of transduction mechanisms are used for energy harvesting. The piezoelectric mechanism has received considerable interest because of its advantages, such as ease of application and working over a wide range of frequencies. Simulation and investigation of energy harvesting from a piezoelectric plate, which is mounted on an elastic beam and located behind a cylinder through flow-induced vibrations, is the subject of the present research. First, the results of the lift and drag coefficients in the fluid flow around a stationary cylinder at Reynolds 200 are compared and validated with the previous studies. After that, by placing an elastic beam and a piezoelectric behind the cylinder, flow around the cylinder, and the fluid-solids interactions are investigated. Due to the vortex shedding phenomenon, which happens in the fluid flow past the cylinder, the elastic piezoelectric beam deforms periodically, and thus, the mechanical energy of the flow is converted into electrical energy. In this problem, the beam effect on both the drag/lift reduction and the amount of voltage extracted from the piezoelectric layer were investigated, and the optimal mode obtained was selected based on the extraction of more energy. In this regard, the process of finding the most optimal energy harvesting mode for the location of the elastic beam, the length of the beam, and the fixed point of the elastic beam in different geometries are carried out. The results of the optimal investigations are as the length of the elastic beam of 2D, the distance of the beam from the back of the cylinder 2.5D, and the state in which the beam is fixed from the right side, where D is the diameter of the cylinder.

: In the present research, the problem of mixed convection flow of a non-Newtonian nanofluid in a lid-driven cavity is simulated using a two-phase mixture model. Nanofluid of water-copper in this problem shows a shear-thinning behavior. To study the effects of non-Newtonian fluid with power-law model on the amount of heat transfer, various power-law indices are considered. After applying the governing equations and related models in the computational code, its validation is done by simulating the problem with Newtonian and non-Newtonian fluid behavior and comparing the results with those of other researchers. Afterwards, simulation of the problem is accomplished for the Richardson numbers of 0.001-1 and power-law indices of 0.2-1 while the volume fraction of nanoparticles alters from 0 to 0.09. The obtained results show that the increase in Richardson number decreases the amount of heat transfer. For all Richardson number decrease in the power law index leads to a decrease in the average Nusselt number. Variation of volume fraction from 0 to 0.09 at the power law index of 0.2 leads to an approximate increase of 15.75% and 17.32% in the average Nusselt number for Ri=0.001 and 1, respectively.

In this paper, gas-liquid two-phase flow in the annulus of a real well during under-balanced drilling operations is simulated numerically. Oil and gas flow from the reservoir in to the annulus is considered due to under-balanced drilling condition. A numerical code based on one-dimensional form of steady-state single pressure two-fluid model in the Eulerian frame of reference is developed and its results are validated using experimental data from two real wells. The results of numerical simulation show better accuracy in comparison with other researches. Given the importance of prediction and control of the bottom-hole pressure and the amount of oil and gas production during the drilling operations, the effects of controlling parameters such as liquid and gas injection flow rate and choke pressure are discussed. Also, the effects of different controlling parameters on the characteristics of two-phase flow pattern, including liquid and gas void fractions, liquid and gas velocities and pressure distribution along with the annulus are discussed. According to the results, the effects of choke pressure and injected liquid flow rate on the production of the oil from the reservoir are independent of the values of each other and are dependent on the injected gas flow rate.

In the present research, the high-order DG-ADER method is used to solve governing equations of two-phase drift flux model. The drift flux model is suitable for studying two-phase flows where the phases are strongly coupled. This model is composed of three differential equations including two continuity equations for two phases and a mixture momentum equation. The mixture model uses also an algebraic relation to link the velocity of the phases. The high-order DG-ADER numerical method, which is a new scheme to get high order accuracy of results, is used to solve the governing equations. The DG-ADER is a nonlinear method in which the reconstruction process is performed using WENO method and the time evolution part is achieved by discontinues Galerkine approach. The results are compared with those reported by other researchers. Three problems including two two-phase shock tubes and a pure rarefaction test problem are solved using this method. The results show that DG-ADER method can solve the two-phase flow problems with a very good accuracy even on a coarse grid. The drawback of this method is presenting numerical fluctuations with limited domain at the position of shock waves.

Two-phase flows are of great importance in the oil, gas and nuclear power plant industries. In this paper drift-flux model was used for mathematical modeling of two-phase flows and then its hyperbolic analysis was performed. For numerical solution of hyperbolic equations, primitive (PRI) centered (CE) or PRICE-C scheme, which is a conservative scheme along the central path was used. The scheme does not need calculation of whole eigenstucture for solving the system of governing equations; therefore, the speed of solution is high. Shock-tube, pure rarefaction and transonic rarefaction problems were solved using this method. The results indicate that the PRICE-C scheme has high ability in capturing the discontinuities in the flow field and can predict the flow behavior successfully.

In this paper; reduced order modeling (ROM) of unsteady two-phase flows is performed based upon two-fluid models and a proper-orthogonal decomposition (POD) method. The four-equation two-phase flow model is used as a mathematical model to describe physics of the problem. After presenting the governing equations, direct numerical solution of the problem is introduced using AUSMDV* method. Then, the POD method is introduced as a mathematical tool to reduce computational time of the transient problems. In the present research, an equation free/Galerkine free POD method is used for ROM of the unsteady two-phase flows. In this approach, the singular value decomposition (SVD) method is used to compute the base vectors of the reduced space. A shock tube and water-air separation two-phase problems are solved using the present ROM method. Results show that this approach can reduce computational time of unsteady simulations about 35%. Reduction of the computational time directly depends on the size of the computational gird. The results also indicate that application of POD method on the fine grids is more efficient than on the coarse grids.

Two-fluid models are the most accurate and complex models for analysis of two-phase flows. There are two different two-fluid models for analyzing compressible isothermal two-phase flows which are Single Pressure Model (SPM) and Two-Pressure Model (TPM). In spite of capabilities of these models in capturing two-phase flow behavior، it is not possible to express them in conservative form due to existence of non-conservative term in momentum equation of phases. Therefore، the classical Rankine-Hugoniot condition across discontinuities in the flow filed is not applicable for these equations and there would be difficulty in using classical numerical methods for solving these equations. In this paper a new path-conservative method is used to overcome this difficulty. In this method، one can apply general Rankine-Hugoniot condition along a path connecting left and right states of the discontinuity. After expressing path-conservative form of the employed central numerical methods which are Lax-Fridriches، Lax-Wendroff and Rusanove، water faucet and large relative velocity shock tube problems are solved by using these schemes. Grid independence was achieved using different grid sizes. For water faucet problem، comparison of numerical results with analytical solution show good agreement and for shock tube problem، the results indicate that this method is highly capable in capturing discontinuities in two-phase flow.