ضریب شکل

In the current study, transportation of the microparticles deposition through a channel has been investigated where elliptical obstacle with constant cross sectional area but different shape factors was assumed in the channel. Numerical simulation was conducted using lattice Boltzmann method, and Lagrange method was used for particle tracking. A two-dimensional and nine-velocity model was used as the network model. A curved boundary condition was applied for the obstacle boundaries. In the designed model, particles at standard condition were injected at the inlet of the channel. Gravity force, drag force, Brownian force and Soffman lift force were applied in the motion equation of the particles. The effect of shape factor as a geometrical parameter, which was defined as the ratio of the diameters of elliptical obstacle, and the flow parameters such as Reynolds’ number was examined on the particle deposition and particle scattering. Results were examined at eight different shape factors and five different Reynolds numbers .Results revealed that the change in the shape factor varies the effect of the obstacle in the flowing stream, and also changes the flow regime. This variation was obtained at different Reynolds numbers. Furthermore, changes of the shape factor associated with variations in the flow regime and deposition mechanisms, changes the forces exerted on the particles. Generally, the effect of the mentioned parameters can be interpreted based on the number of the precipitated particles.

The Griffith crack, a central crack in an infinite plane under uniform loading, is converted to a subsurface one by moving close to a loaded edge of the plane. Subsurface cracks initiate under rolling contact fatigue conditions. In this paper, first, finite element model of the Griffith crack has been developed and validated by calculating stress intensity factors (SIFs) under uniform tension and shear loadings. Then, by moving the crack close to a parallel edge of the plane, mixed mode SIFs of the subsurface crack have been determined for a wide range of the cracks depths. Non-symmetrical geometry with respect to the crack edge causes coupling between fracture modes and so, considerable shear and tension fracture modes under tension and shear loadings, respectively. The ratio of SIF for the coupling mode to the direct mode is creased up to 69% for the length to depth ratio of 20. Also, by fitting third-degree polynomials to the mixed mode SIFs, four geometry correction factors have been obtained for SIFs of subsurface cracks under uniform loadings. These approximate equations can be used easily and efficiently by engineers. Also, the relations can be utilized as a primary estimation for non-uniform loadings, especially when the crack length as well as the load variation along it is small.

In this paper, multi-stage optimum design of composite pressure vessels is presented. The design variables for composite vessels include the head shape, the winding angle, the layer thickness, the number of layers, and the stacking sequence. A parameter called modified shape factor is introduced as an objective function. This parameter takes into account the effects of the internal pressure and volume, the vessel weight, and the composite material properties. The proposed algorithm uses genetic algorithm and finite element analysis to optimize the design parameters. As a few examples, this procedure is implemented on geodesic and ellipsoidal heads. The results show that for the given vessel conditions, the geodesic head shape with helical winding angle of nine degrees has the better performance