Scientia Iranica
Volume:28 Issue: 4, Jul-Aug 2021

In this paper, the effect of the combustion and turbulence sub-grid scale (SGS) model on the simulation of pool fire turbulence field has been studied in open source CFD software, OpenFOAM. Two combustion models of Eddy Dissipation Model (EDM) and infinite fast chemistry, with the one-equation and Smagorinsky SGS model, is evaluated for a large-scale pool fire. In general, fast kinetic-based combustion models predict excessive heat release rate. The mean squared of the velocity fluctuations is over-predicted. In this simulation, the turbulence models have no significant effect on the results. In fact, the effect of the combustion model is dominant. The EDM combustion model is more compatible when used with the one-equation SGS model and improves the results compared to other cases. In addition, the infinite fast chemistry combustion model is not a suitable model for fire simulation.

The purpose of this study is to provide an efficient Multi-Objective Multidisciplinary Robust Design Optimization (MOMRDO) framework. To this end, Bi-Level Integrated System Synthesis (BLISS) framework is implemented as a fast Multi-disciplinary Design Optimization (MDO) framework. Progressive Latin Hypercube Sampling (PLHS) is developed as a Design of Experiment (DOE) of the Uncertainty Analysis (UA). This systematic approach leads to a fast, adaptive and efficient framework for Robust Design Optimization (RDO) of complex systems. The accuracy and performance of the proposed algorithm have been evaluated with various tests. Finally, the RDO of a hydrazine monopropellant thruster is defined as a case study. The results show that the proposed method is a fast and efficient method for the multi-objective optimization design of complex systems, and this approach can be used for other engineering applications as well.

Numerical and analytical solutions of Stokes theory of couple stress fluid under the effects of constant, space, and variable viscosity in the inclined channel are discussed here. The considered couple stress fluid is described mathematically with the definition of the stress tensor. The dimensional form of the boundary value problem is transformed into dimensionless form by defining dimensionless quantities and then solved with help of the perturbation technique. The analytical expressions of velocity and temperature of all cases based on the viscosity of the couple stress fluid are presented. For the validity of the perturbation solution, the Pseudo-Spectral collocation method is employed for each case of the viscosity model including constant, space, and Vogel’s models, respectively. The solution of the perturbation method and Pseudo-Spectral methods are shown together in the graphs. The effects of couple stress parameters on velocity and temperature distributions are also elaborated with physical reasoning in the results and discussion part. It is observed that velocity and temperature of fluid escalate via the pressure gradient parameter and Brinkman number while decelerating via couple stress parameter.

In this research, nonlinear buckling and post-buckling behaviours of composite plates with the ‎circular/elliptical cut-out are investigated using particle semi-energy (PSE) method. The semi-‎energy is based on the solution of compatibility equation via an Airy force and out-of-plane ‎displacement functions. The‏ ‏unknown parameters of these functions are determined by ‎minimizing the potential energy. The integrals of potential energy are replaced with ‎summations at perforated plate particle (node). The cut-out is modelled easily using these ‎nodes. The advantages of this method are modelling cut-out by nodes easily and proposing ‎just one of the displacement fields (i.e. out-of-plane). Based on the results, there is a good ‎agreement (1.25%) between the post-buckling loads derived from PSE of this paper and ‎experimental test of other literature. The accuracy of the finite element method (FEM) is 7.5% ‎with respect to experimental test. The influences of rotating elliptical cut-out and replacing it ‎with two circular cut-outs via same areas on post-buckling load are investigated‎

One of the most well-known strategies to eliminate or reduce the longitudinal instabilities in planing hull, is to reduce the trim of the craft. In the current study, porpoising is controlled through creating a transverse step, and the combination of adding a wedge to the stern and transverse step in the vessel. Usually, performance of stepped boats is not suitable in pre-planing regime. However, through the proposed method, stepped model performance can be improved prior to the planing regime. The investigated craft is a 2.56 m long monohull high speed model with speed range of 1,3,5,7 and 9 m/s. The obtained results indicate that best performance is acquired by the step and wedge model at the beginning of the planing regime. From 3 to 7 m/s, drag of stepped and wedged models has the lowest value and above 7 m/s and at 9 m/s, the stepped model has the lowest resistance. Among the investigated methods, using combined step and wedge indicates largest reduction in trim angle (At speeds of 3 to 9 m/s). It can therefore be concluded that model equipped by combination of wedge and step improves the poor performance of the stepped models prior to the planing regime.

Polymer composites have a wide share among engineering materials. It is important that the material properties are known before being used in industrial applications. Damage behavior needs to be determined in order to safely forming of laminated composites. Propagation characteristics of existing cracks for determining damage are among the current research topics of the researchers. In this study, the fracture toughness of the composite structure was investigated by performing compact tensile and compact compression tests for hybrid fiber reinforced polypropylene composite laminates which have three types of composition having various thicknesses and fiber contents, woven and/or chopped glass fiber reinforcement. The critical energy release rates of fiber and matrix in both tensile and compressive fracture cases were determined in pre-cracked specimens under plane-strain loading conditions. The damage mechanisms of the composite materials used in the present study were described as fiber breakage/buckling of longitudinal and matrix crack/crushing of transverse. As a result of the longitudinal tension, the damage progressed gradually as translaminar fiber breaking in materials containing continuous fibers. In the transverse tension process, fiber-matrix separation caused intralaminar deformation in the materials. The highest fracture critical energy release rate was found in the material with the maximal fiber layer.

Low cutting forces can significantly reduce damage risk on sensitive tissues adjacent to the bone. Applying an ultrasound tool in bone cutting is an interest among surgeons due to its better control in an incision, low cutting force, and reduced postoperative complications. In this study, by applying a full factorial design of experiments, the effects of changes in cutting tool geometry, ultrasonic power, bone-cutting direction, and tool speed on the cutting forces of cortical bone are assessed simultaneously. The analyses of variance and regression are run on experimental data, and the influence of each factor and interactions of the elements on the cutting forces are discussed. The adjusted coefficient of determination (R2adj.) of the statistical models is 91.49% and 91.15% in the main cutting force and cutting resistant force, respectively. Both the blade geometry and ultrasonic power, together with their interactions, are the most influential factors in cutting forces with 82.2% and 86.6% contribution therein, respectively. Creating teeth in the cutting edge improves the cutting process and reduces the cutting force by about 40%. The ultrasonic-powered toothed edge blade with a 1 mm pitch, low vertical velocity, and high longitudinal speed is recommended for high efficiency and low cutting force.

As the first endeavor, a combination of fast Fourier transform and p-version of finite element method is proposed for electro-thermo-elastic analysis of a thick hollow cylinder under asymmetric thermal loadings. Especially in shells of revolution, the proposed FFT-pFE method is accompanied by a significant decrease in the computational costs. Due to the problem periodicity in such structures, the fast Fourier transform technique is used to discretize the governing equations into a set of harmonics in circumferential direction. Each harmonic is then partitioned using higher order finite elements. Hierarchical finite elements based on Legendre polynomial interpolation functions are utilized to discretize 2D governing equations of a functionally graded piezoelectric (FGP) cylinder. 3D governing equations of a FGP hollow cylinder are then discretized by using the higher-order Lagrangian finite elements. The effects of FFT grid-size as well as the order of the interpolation functions are investigated on convergence behavior of the proposed mixed FFT-pFE method. The piezoelectric material properties, with the exception of the Poisson’s ratio, are considered to vary along the radius of the cylinder and pursue the power function. The governing equations are derived using the principle of virtual displacements. For a 3D FGP hollow cylinder, the influence of ...

In this paper, an attempt has been made to optimize the welding parameters. FSWed sections strength and quality is affected by materials transfer, work hardening and transformations. These properties depends strongly on the materials transfer, which is under the control of welding parameters. The soundness of friction stir welded sections usually studied by NDT techniques. However, it could be characterized by physical properties such as electrical conductivity. As the higher electrical conductivity, means lower defects and higher welding quality. For this purpose, the Taguchi L9 orthogonal design of experiment was used to optimize the welding parameters. The optimum process parameters and their effectiveness on the electrical conductivity of welded sections were analyzed by S/N ratio and ANOVA tests. The results indicated that the tilt angle and tool shape are the most influential parameters to catch the maximum conductivity in welded joints. The optimum tool shape and tilt angle are cylindrical and 3º. The optimum conditions for welding speed and rotational speed were obtained as following; 100 mm/min and 900 rpm in stir zone, 250 mm/min and 900 rpm in advancing side (AS) and 100 mm/min and 450 rpm in Retreating side (RS), respectively.

In this study, a new material was produced using Hot Isostatic Pressing (HIP) method, upon which Co and Ni in different ratios were added into a CuSn-based (85/15) alloy. HIP method has very important advantages in that it allows pressure and temperature to be applied simultaneously during the process. In the study, constant sintering temperature of 800 °C, a constant sintering time of 15 min, and two different sintering pressures of 20 and 30 MPa were used. The sintering process was performed under a vacuum after the initial burning process. The produced samples were subjected to various metallographic processes as well as SEM and EDS analyses. Afterwards, wear test was carried out on the samples. The study investigated the effects of Ni and Co additions and the sintering pressure on the wear behavior. It was found that as the amount of Co and the sintering pressure increased, the wear resistance increased.

This paper aims to study the impact analysis of a composite sandwich panel with a flexible foam core subjected to low-velocity impact loading by using a Finite element (FE) model in ABAQUS/CAE software. Impact damage remains a major concern for all structural components; that create internal damage and reduced the structural strength of the structure. Very few multiple-mass impact studies have been done on the composite sandwich panel. In the present work, the formulation was based on first-order shear deformation theory is used to develop the model. Impacts were done over the top of the face sheet with different velocities and impact masses. The numerical model is verified by the literature experimental one. Good agreements in terms of contact-force histories and deformation of the sandwich panel. Once results are validated for a single impact, furthermore, the study has extended to multi-mass impact analysis with varying velocities of the impactor. Comparison of various parameters such as contact force, deformation, and Von-Mises stress results are reported. Comparisons of responses are shown for cylindrical sandwich panel with flexible core were studied and reported.