نشریه علوم کاربردی و محاسباتی در مکانیک
سال سی و چهارم شماره 2 (تابستان 1401)

In the present study, the effect of material degradation in hygrothermal environment on the bending of laminated composite plates is investigated. Heat and humidity are environmental factors that affect the mechanical properties of polymers and therefore, behavior of laminated composites changes. For investigating these changes, a laminated composite is modeled through the Kirchhoff hypothesis and classical plate theory for thin plates, and the bending governing equations are derived. The resulted equation is solved for a simply supported laminated plate and exact solution is obtained for numerical analysis. The environmental effects on the mechanical properties are modeled using the available experimental results in the literature. Finally, the effects of laminate dimensions, temperature, relative humidity, fiber volume fraction, void volume fraction, lay-up on the maximum deflection of laminate is investigated in details. Results show that variation of temperature and relative humidity severely reduce the mechanical properties and affect the behavior of laminated plates.

In this paper the boundary element method is used to calculate the added mass matrix of an airship. Here, the governing equations are desecrated on the triangular computational cells on the surface of the airship geometry. The computational grid cells are generated on the surface of the body using the Gambit software and inserted to the BEM Fortran code. First, in order to validate the numerical code, the added mass of a sphere and ellipsoid with two different fineness ratio (a/b=2, 3.85) is obtained and the results are compared with the analytical results. The BEM results are in a very good agreement with the analytical results. Then the BEM code is used to calculate the envelope added mass matrix with NPL and GNVR body profile which are two common body profiles in airships. Finally, the simulation is conducted for the whole airship with fins and gondola and the added mass matrix is obtained for two envelope profiles.

Flow-induced instabilities are one of the major challenges in the design of aerospace structures. Numerous passive and active control methods have been used to reduce the flow-induced oscillations of square cross-section cylinder as the basic geometry for structures with sharp corners. The suction and blowing flow control method are one of the most effective approaches for controlling the flow and consequently reducing the vibrations resulting from the aerodynamic forces, which so far are not considered for an elastically-mounted square cylinder which fluctuates freely in the transverse direction. Therefore, in this paper, suction and blowing flow control methods have been used separately to suppress flow-induced oscillations. In the suction-based method, a slut is placed on the front surface of the cylinder and in the blowing-based method another slot is inserted on the back surface of the cylinder. In the present study, the effect of suction and blowing velocities as well as the effect of suction and blowing slut lengths on the efficiency of the flow control approach was evaluated. According to the flow-structure interaction simulations, it is observed that the applied flow control method has been able to reduce flow-induced vibrations appropriately.

In this paper, turbulent flow in an asymmetric two-dimensional diffuser is investigated. In many applications, it is important to know whether the boundary layer separates from the surface or inside a particular object, it is also important to know exactly where the flow separation occurs. Combining turbulence data with artificial intelligence is currently an active research topic for studying turbulence. This research makes it possible to replace traditional turbulent models with artificial neural networks (ANN). In this study, to predict flow separation in an asymmetric two-dimensional diffuser, three turbulence models, standard k-, standard k-and SST k-, and intelligent neural network model with reverse pressure gradient were investigated. Fluent software was used to solve the Navier-Stokes-Reynolds equations. Three types of networking are designed and at the end, the second type is used to analyze the flow. 21, 29, 39 and 49 cm distances from the edge of the diffuser were analyzed and compared with experimental data. x and y/H are considered as the input point and U/U0 is the velocity at that point as the output of the neural network model. RMSE, MBE, t-test statistical indices have been calculated and reported for the desired points, The ANN had a better prediction of separation than the other three standard models, and the standard k- had a lower prediction than the other models. This research shows the perspective of chaotic modeling with machine learning methods, especially neural networks.

Biomass is important as a renewable source of energy worldwide. The role of mixing and segregation of particles in the process of gasification of the fluidized bed is important. better mixing of these particles the better the quality of synthesized gases emitted from biomass gasification process. This study investigates the three-phase mixing process of rice husk (biomass), sand (bed material) and air in a bubbling fluidized bed using the finite volume and computational fluid dynamics tool with Eulerian multiphase flow approach. effect of the restitution coefficient between the particles and the wall boundary conditions for the solid phase in the process of mixing biomass and bed material has been studied. In this study, the effect of free slip, partial slip and no-slip for particles in contact with the wall has been investigated. In the case of partial slip the velocity of rice husk and sand higher than other two cases. Therefore, as the velocity of particles in the bed increases, the uniform mixing and distribution of particles in the bed increases and segregation of particles decreases. study of pressure drop in the fluidized bed shows that in free slip conditions, the pressure drop is 8.09% and 14.2% less than partial slip and no-slip, respectively. Also, three types of rice husks with different restitution coefficients have been studied. As a result of this study, with decreasing the restitution coefficient between particles, the velocity of rice husk and sand particles increases by about 9% and the pressure drop decreases by about 22%.

Currently, real-time force control of actuators is one of the most important issues found in different branches of industry. In order to achieve the best performance of a given electromagnetic actuator, first of all, the parameters of the dynamic model of the actuator should be identified. In this research, an experimental platform is designed and manufactured to conduct experiments and identify the parameters of the electromagnetic actuator. The process of generating a reference signal for identification is performed in a real-time manner by the STM32F746ZG board. The ARM-Cortex M7 microcontroller on the board has provided us with the ability to produce any type of signal with the desired frequency, amplitude and bias. In this research, a harmonic chirp signal is generated to study the behavior of the actuator at different frequency intervals. The amplitude of inertial force generated by the actuator is measured by a Kistler Type 9255B dynamometer. Finally, by analyzing the system response, the accurate dynamic model for the system is successfully estimated.