نشریه علوم کاربردی و محاسباتی در مکانیک
سال سی‌ام شماره 2 (بهار و تابستان 1398)

In this research, the twist and the longitudinal bow defects were studied by finite element analysis in the asymmetrical channel sections. Effects of the geometrical properties including the strip thickness, the web width, and the flange width were investigated on the above effects. Some experiments were performed on an industrial roll-forming machine to verify the accuracy of the finite element model. The results showed that the twist angle decreases with the increase of both strip thickness and web width. However, the twist angle increases with the increase of flanges width. Also the variations of the longitudinal bow height are similar to those of the average residual longitudinal strain of both flange edges.

Nanometric machining process is an advanced method for producing brittle silicon workpiece with nano-level surface finish. With the aid of molecular dynamics simulation, valuable details of machining mechanism could be obtained. Choosing the appropriate potential function is the main parameter in determining the results of this simulation. In this paper, the combination of the three potential functions of Morse, Tersoff, and Stillinger-Weber is used to define interatomic interactions. The machining mechanism, workpiece temperature, cutting forces, systems’ energy as well as subsurface damages were studied to compare these potential functions. The results exhibit that using the combination of the Morse and Tersoff potential function would change the machining mechanism to brittle mode and reduce the system energy by as much as 7.3%. It is also found that the interaction between tool and workpiece has a greater influence on the determination of the workpiece temperature and machining forces.

In in this paper, cyclic behavior of SS316L cubic shells under pure torsional load was experimentally and numerically studied. Experimental tests were carried out by a servo-hydraulic NSTRON 8802 machine under torsional load-control condition. In this loading condition and based on experimental results, due to the existence of larger shear stress along the shell thickness, increasing of torsional torque amplitude caused the enhancement of ratcheting angle and reduction of shells’s life. Also, the effect of cutout and its size on ratcheting behavior of cubic shell were investigated , According to experimental results, it was seen that the sensitivity of ratcheting angle to cutout position near the applied load was high and the shell’s life decreases in this condition. Numerical analysis was done by Abaqus software and using the nonlinear isotropic/kinematic hardening model. There is a good agreement with that of experimental results.

In this paper, nonlinear vibration of the functionally graded rectangular plates made of piezoelectric BaTiO3 and magnetostrictive CoFe2O4, whit simply supported boundary condition has been investigated. It is assumed that the composition is varied from the bottom surfaces to top surface, i.e., the top surface of the plate is piezoelectric-rich, whereas the bottom surface is magnetostrictive-rich. In addition, material properties are graded along the thickness according to volume fraction power-law distribution. Based on the Reddy’s third-order share deformation plate theory, the governing equations of motion, whereas Maxwell equations for electrostatics and magnetostatics are used to model the electric and magnetic behavior. Then, the nonlinear partial differential equations of motion are transformed into five coupled nonlinear ordinary differential equations by using the Galerkin method. Afterward, the obtained coupled ordinary differential equations are reduced to a single nonlinear differential equation which include nonlinear inertia and stiffness terms with quadratic and cubic nonlinear terms. A perturbation method is used to solve the equation of motion analytically. The results for natural frequency are compared with the available results for isotropic, laminated and piezo-laminated plates and good agreement is found between the results of present study with the results of previously published papers. In the forced vibration, primary, super-harmonic resonances are studied and the frequency response equation has been obtained. Because of the importance of the primary resonance, the stability of the steady-state motion is investigated for the primary resonance, The applied external force is assumed to be harmonic in time with a constant amplitude.

Employing the Isogeometric Analysis method for solution of nonlinear compressible elastic materials, generally known as hyperelasticity, is the subject of this article. For this purpose, the matrix of coefficients is derived and by the linearization of governing equations the discretized equilibrium equations are obtained and a solution algorithm is presented. To study the performance and accuracy of the method in compressible hyperelastic problems, the obtained results are compared with those of finite elements. The presented approach, besides providing a good flexibility in geometrical modeling, results in a smaller system of equations and consequently reducing the computational cost. Furthermore, despite having large deformations, the need for remeshings is alleviated. Also, the effects of the number of load increments, as well as, the number of Gauss integration points on the convergence of the solution are studied.

In this paper the Multi Relaxation Time Lattice Boltzmann Method in conjunction with the Large Eddy Simulation model was used to study the particle deposition in a room  with various diameters (10nm-10µm)and the effect of buoyancy, drag and Brownian forces to particle deposition on the different walls of the room has been investigated.  The sub-grid scale turbulence effects were simulated through a shear-improved Smagorinsky model. To simulate the particle deposition in the room, the particle injection process was initiated with 144 particles injected uniformly at the inlet with the same velocity as the airflow at every 0.05s; particle injection was stopped after 30s. Therefore, a total of 86400 particles were injected into the room. The present simulation results for the airflow showed good agreement with the experimental data and the earlier numerical results. The simulated results for particle dispersion and deposition showed that the numbers of deposited particles on the walls increases by augmentation of the time. When the particle injection started the concentration in the inlet jet region is more than other zones and that increases in the region far from the inlet by time. Present results will be interesting for designing air condition systems in the office and hospitals rooms.

Recycling of waste rubbers is developing due to environmental concerns and continuous increasing raw materials price. The EPDM (ethylene-propylene-diene rubber) rubber is the rubber base of the non tire automotive rubber articles and their recycling is necessary for resources saving and the environment protection. A mechanical recycling technique, a twin screw extruder with the aid of a de-vulcanizing agent, TMTD (tetramethylthiuram disulfide) was used to de-vulcanize waste rubber powder from discarded EPDM automotive parts. The de-vulcanized rubbers, subsequently, re-vulcanized in a semi-efficient (SEV) curing system and correspondent curing and mechanical properties including hardness, tensile strength and elongation at break were measured and the results were compared and discussed. The results showed that the waste rubber de-vulcanized with used technique efficiently. The direct relationship was observed between increasing de-vulcanization percent and also the crosslink density reduction of the waste cured rubbers with improving the curing and mechanical properties of re-vulcanized compounds. The optimum de-vulcanization operating conditions were obtained by a design of experiment software at rotor speed of 180 rpm at a constant operative temperature, 220 . The main challenge for using the outcomes of this study in commercial scale was the difference between waste rubbers composition because they provided from various sources.

Sheets are widely used in various branches of modern technology industries such as automotive, marine, aerospace, optics, nuclear industries and structural engineering. One of the most important problems in design is their weakness against impact. Various impacts are applied by external objects during construction, operation or maintenance of the structure. For this reason, the reinforcement and increased strength of the sheets against the impact is the subject of many studies of researchers. This study was conducted for three levels of impact energy (using Drop weight). The sheets are of AL3105, with dimensions of 220 * 230 mm and 1 millimeter thick, 2 millimeters thick, and are connected by bolts. The sheets are completely free on the fixture The screws are made of a bolt with Standard din933. In the experimental method, the picker acceleration has been measured by the accelerometer sensor and the permanent deformation of the sheet is measured at the end of the impact. The parameters to be evaluated include the impact acceleration on the sheet, the permanent deformation and the energy absorption of the sheets. Abaqus finite element software has been used for numerical modeling. Comparing the results of experimental and numerical methods shows that these two research methods have a good agreement. The results also show that the absorption of energy in single-layer sheets is greater than double-layered sheets. Also the acceleration in double-layered sheets are more than single-layer sheets.

Orbit valves are used dehydration processes of gas. Failure of valves impose cost of repair and maintenance and its experimental tests are more expensive and in many cases are not applicable. Therefore, in this work a three dimensional model of an orbit valve class 900 is created and exported to a CFD solver. Results are exported to a structural analyzer to determine the exerted forces and stresses. Analysis are considered in six position of valve ball. Results show that ball position of 45° is the critical position and probability of failure in this situation is very high. Therefore, results of 45° are valuable to design of parts and choosing appropriate material inside parts.

In the present study, 2D numerical simulation of flow around a circular cylinder and the effect of plasma actuators to control the flow around it have been investigated. Plasma actuators which have been used include single plasma actuator and Linear Plasma Synthetic Jet Actuator (L-PSJA). In order to numerically simulate the actuators, the linearized force model has been used. In the present work, accuracy of the linearized force model to analysis the plasma actuators behavior and the effect of their position on the point of separation and elimination of the vortices have been investigated. The results show that the simulation of actuators operates qualitatively successful in flow separation using linearized force model (despite of its simplicity). Using of single plasma actuators at angle of ±45 and ±90 degree is the best position of the plasma actuators. The position of the actuators at angel of ±90 degree is recommended, if the lower power consumption of the plasma and at the same time the most influence on the flow is to be considered. Using L-PSJ actuators at angel of ±45 degree is not recommended, due to low influence on the flow and higher power consumption.

This study aims to investigate the influence of the plate uncertainty elastic modulus on free vibration response and buckling behavior. To this purpose, elastic modulus of plate is modeled as a random variable with a normal distribution. Spatial autocorrelation function is used for random fields. In this method, the correlation is dependent on the distance, as the points be far away from each other, the correlation is also reduced. Then, applying the powerful finite element method stochastic finite element relations were calculated using Monte Carlo simulation. To this purpose, a four-node Kirchhoff’s element was used with twelve degrees of freedom. For the analysis, random variable is simulated 5,000 times. At last, by numerical tests, the effects of uncertainty on elastic modulus are investigated on the natural frequencies and buckling loads of plate. The results of these tests show that the effect of uncertainty in elastic modulus of the plate has a different effect on the response of vibration and buckling of plate. So that these changes have low effect on free vibration responses of plate. But buckling loads are highly dependent on the elasticity coefficient.