نشریه روش های عددی در مهندسی
سال سی‌ام شماره 1 (تابستان 1390)

In updated Lagrangian simulation of machining, chip separation from the workpiece is done by deleting the elements of predefined critical values in front of the tool tip. In this paper, a systematic evaluation of three progressive damage models is carried out to identify the most suitable fracture criterion in simulation of chip separation. The three models considered are the Johnson–Cook (J-C), the modified Cockcroft–Latham (C-L), and the Wilkins models. In addition, a new algorithm is presented to calculate the coefficients of damage models in the range of very high strain, strain rate, temperature and pressure of machining processes and in presence of the combined effects of two different tensile and shear failure mechanisms. In this respect, the results obtained by few Arbitrary Lagrangian-Eulerian (ALE) simulations are used as sources to study the accumulation of damage. The steady state orthogonal cutting of AISI 1045 steel was considered to take benefit of evaluation of the models performances with available experimental data in "Assessment of Machining Models" (AMM) effort. Calibration of damage models in real condition of chip separation is the most important advantage of the new method. According to the obtained results, the Johnson–Cook damage model is the most capable chip separation criteria.

In this paper, numerical simulation of cavitating flow over hydrofoils is presented by the aid of Preconditioned Artificial compressibility Method for solving the multi-phase N-S equations. Dominant equations include conservation of mass, momentum and a liquid phase volume fraction transfer equation. Equation of volume fraction transfer is obtained on the basis of homogeneous equilibrium flow concept in modeling of multi-phase flows. Mass transfer between phases is simulated by the Merkle model. To accelerate the convergence rate, the discrete equations are preconditioned. Third order Roe-based flux difference splitting and second order central differencing method respectively is utilized for convection and viscous term discretization. Effects of turbulence are simulated in terms of an eddy viscosity coefficient added to molecular coefficient of viscosity via Spalart-Allmaras model. To demonstrate the capabilities of the scheme, several single and two-phase test case problems are computed and the results are compared with experimental and numerical data. Computed results present the appropriate accuracy of algorithm. Results of single phase flow over NACA0012 hydrofoil at renolds number, 2.8e6 & 0, 6 angle of attack, are compared with experimental data. The capability of code for simulation of cavitating flows at various cavitation numbers and angle of attacks are presented via simulation of two phase flow over non-truncated & truncated modified NACA0009 hydrofoil at renolds number, 2.0 e6 & 0, 2.5 angle of attack & σ = 1.0, 0.9, 0.8, 0.75, 0.6, 0.5, 0.4, 0.3. Then results are compared with experimental and numerical data. The results are in good agreement with the available data and other published computations.

In this paper, post-buckling behavior of cold-formed, thin-walled structures containing thickness-tapered plate with initial imperfection is investigated. A computer program has been developed using the nonlinear Finite Strip Method for postbuckling analysis of plates and plate assemblies under compression and bending. Axial and flexural stiffness of lipped channels, Z-shaped and T-shaped sections containing thickness-tapered and thickness constant plates are calculated for different geometries. Stress redistributions of those sections are also determined. Results for stress redistributions show that sectional geometries and applied strains have important effects on stress distributions.

This paper is concerned with the phenomenon of disc brake squeal. Brake squeal is a high frequency noise created by the car brake systems. The noise does not disturb the performance of the brake system but mainly affects the passenger’s comfort. That is why nowadays it is one of the main factors in determining the quality of the brake system. First, the reasons expressed in the literature for the source and mechanisms of generating brake squeal are presented. Next, the instability causeb by close modes is shown as a realistic basis for the onset of brake squeal. In other words, modes which are close to each other in the frequency range and have similar characteristics may merge as the friction contribution increases and creates the squeal noise. A finite element model of the Samand brake system was constructed in a commercial finite element software and then solved in several steps. Due to the complexity of the problem and presence of large number of degrees of freedom in the model, the solution is carried out by use of parallel computing. Finally, the behavior of the model is analyzed with respect to the variation of important parameters such as coefficient of friction, brake force, stiffness of the brake system and its material characteristics. The effect of slots on the pads is also investigated. It is shown that the slots can have an important role in the squeal noise suppression.

In this study, a new computational scheme called the scaled boundary finite element method (SBFEM) is employed to analyze confined seepage flow. This technique combines the advantages of both finite element and boundary element methods, i. e., only the boundary is discretized, no fundamental solution is required, unbounded domains and singularity points are modeled rigorously, and finally anisotropic materials and non-homogenous materials satisfying similarity can be modeled without additional computational efforts. In this paper, after presenting formulation of the method for solving confined seepage problems, selected problems using this method are analyzed and the results are compared with the results of other numerical methods. High accuracy and efficiency of this method is demonstrated.

Free convection of Ag-water nanofluid in a square cavity with two or three pairs of hot and cold discrete elements on its side walls is simulated and the effects of number and arrangement of thermal elements and volume fraction of nanoparticles on the fluid flow and heat transfer are studied. Volume fraction of nanoparticles ranges from 0 to 0.2. Several different arrangements of the thermal elements are considered in a manner that for each case, numbers of vortexes formed inside the cavity are different. The obtained results show that by increasing the Rayleigh number, the number of vortexes, and the volume fraction of the nanoparticles, the rate of heat transfer is increased. Also it is observed that when the number of formed vortexes inside the cavity increases, the effect of increasing the volume fraction of the nanoparticles on the heat transfer rate is enhanced. When six vortexes are formed in the cavity at Ra=106, by increasing the volume fraction of nanoparticles from 0 to 0.2, the average Nusselt number increases about 60% with respect to the base fluid, while for the case of four vortexes, the increasing is about 35%. Moreover it is found that at all the considered Rayleigh numbers, the average Nusselt number is more sensitive to the nanoparticles volume fraction than to the number of formed vortexes.

The applicability of the differential quadrature method (DQM) and incremental differential quadrature method (IDQM) in solving the unsteady free convection flow over a sphere is investigated in this paper. The rules of DQ method are used in both Spatial and temporal domains. Also, it is shown that splitting the total temporal domain greatly enhances the performance of method. It is worth mentioning that this is the first attempt in using these methods for modeling of transient convective fluid flow. Two advantages of IDQM over the conventional methods are shown through the results of this study, which are: (1) unconditional stablity & (2) minimum computational effort required. For this purpose, the convergence study is performed and for the cases that a solution is available, comparison is done.