نشریه مهندسی مکانیک ایران
سال بیست و ششم شماره 4 (پیاپی 77، زمستان 1403)

In this article, the analysis of free and forced vibrations of a microplate based on the Kirchhoff gradient strain theory with clamped boundary conditions is presented using the finite element formulation with  continuity. Due to the presence of higher-order derivatives,  continuous interpolation functions are employed to provide a standard formulation. Subsequently, the stiffness and mass matrices of the microplate element are extracted using the Hamiltonian principle, and the formulation is applied to a four-noded quadrilateral element with 36 degrees of freedom. The natural frequencies of the desired microplate are obtained using the finite element method and compared with analytical results. Additionally, by refining the element dimensions (mesh refinement), the accuracy of this method is compared by examining the obtained frequencies with the finite element method and the desired analytical results. Furthermore, the natural frequencies for microplates with different boundary conditions are provided, and the influence of the  ratio on the natural frequencies of microplates with various boundary conditions is investigated.Subsequently, vibration diagrams for the microplate with specified initial conditions and applied forces are presented. The effects of boundary conditions and the  ratio on various microplate parameters are examined and discussed.

In this study, the performance of different cooling methods including natural air circulation cooling, forced air circulation in the presence of a heat sink, forced air circulation with paraffin as phase change material, forced air circulation with paraffin and metal foam and forced air circulation with paraffin, foam and fin on cooling of lithium-ion batteries of electric vehicles have been investigated using numerical simulation. The results showed that when the battery temperature in the state of cooling with pure paraffin exceeds the allowed temperature of 55 degrees Celsius, for paraffin with metal foam and paraffin with metal foam and fins, the maximum temperature is 39.3 and 1.36 degrees Celsius, respectively. is Therefore, metal foam and finned metal foam reduce the temperature by 29% and 34% respectively in the same period of time compared to pure paraffin, and even after 21 complete cycles with the change of production heat rate, the maximum temperature does not exceed the allowed temperature. At a relatively high temperature, the use of phasing materials along with conductivity amplifiers makes the hybrid cooling system more efficient than the forced displacement-heat well cooling system; In such a way that the allowed time span increases more than 11 times.

Heavy turbofan engines with high thrust values have a special place among air engines. Between the components of gas turbine engines, the turbine part is very sensitive and important due to the high temperature and long-distance operation of its components. In the present study, based on the results of the cycle design, the conceptual design of the turbine of the considered turbofan engine has been done by using the defined software and algorithms. The pressure ratio of the designed turbines in the conceptual design and numerical simulation section differed only by 0.7 and 0.5%. However, the efficiency of the high pressure turbine differed by about 5.6% between the conceptual design and the numerical simulation due to not considering the cooling in the numerical simulation.

In this paper, based on a refined quasi-3D beam theory and using the isogeometric method, the free vibration behavior of composite beams reinforced by graphene platelets is studied. The quasi-3D beam theory takes into account both shear deformation and thickness stretching effects. The beam under consideration is assumed to be a laminated beam where the volume fraction of graphene may be different in each layer which leads to a functionally graded structure. The equivalent modulus of the beams is obtained by means of the Halpin-Tsai model. Besides, the equivalent mass density and Poisson's ratio are evaluated using the conventional rule of mixture. The results demonstrate that the isogeometric analysis (IGA) based on the refined quasi-3D beam theory can precisely predict the natural frequencies of the composite beams reinforced by graphene platelets with low computational cost. Moreover, a set of new results are presented for different parameters related to the beam material and geometrical characteristics of the functionally graded graphene platelet-reinforced composite (FG-GPLRC) beams.

Nowadays, ozone therapy has been proposed as a non-invasive and efficient method to treat many diseases. Excess amounts of this gas are harmful to the lungs and eyes and can have adverse effects on the treatment process. Therefore, it is important to monitor the amount of ozone gas used. In this article, in order to accurately measure and control the amount of this gas, the design and construction of the nanobiomechanical ozone gas sensor has been discussed. In this sensor, zinc oxide active material is used on a glass substrate and aluminum shoulder electrodes. The results of the characterization and measurement of this sensor show that this sensor has the best performance at a temperature of 120 degrees Celsius in the amount of 5 ppm of ozone gas with an efficiency of 84%. Also, the response and recovery time of this sensor has been measured as 15 and 120 seconds, respectively. The remarkable thing about the built sensor is the ability to measure ozone gas up to the minimum value of 1 ppm. Also, it has good selectivity to oxygen and acetone gases in equal amounts, so the response of the sensor to 5 ppm of oxygen and acetone gas is 21% and 31%, respectively. Also, the results showed that the proper design of the sensor packaging, looking at its mechanical aspects, does not make significant changes to the sensor performance.

In this article, the use of vibration absorbers to dampen the vibrations created by the helicopter engine has been described. During their flight mission, helicopters are affected by many vibrations, which can be considered as one of the most important sources of vibrations in helicopters, which cause different and intense dynamic environments such as the effects of vibrations with sinusoidal input and step and triangle to the helicopter, in between, the vibration environment with sinusoidal input has the main contribution in destroying and weakening the overall performance of the helicopter and the possible failure of the flight mission. By using the design of the damper system of the article, which is actually a combination of active absorbers with LQR PID algorithm and passive, which, at low frequencies, the active control function and its combination with the elastomeric base absorber is 20% more optimal than the passive absorber and 10 % is more optimal than the active absorber and since the helicopter engine is subjected to various vibrations with a high vibration amplitude during its flight mission, the designed system significantly reduces the generated vibrations and up to 96% of these vibrations in It will dampen the average performance of the engine and in different working conditions.