مجله مکانیک سازه ها و شاره ها
سال سیزدهم شماره 1 (فروردین و اردیبهشت 1402)

Thermoplastic composite sheets have attracted increasing attention in various industries due to their high Specific strength and energy absorption capacity. In the upcoming research, the behavior of composite sheets with polyamide6 thermoplastic matrix and continuous glass fibers (PA6/GF) has been investigated under quasi-static penetration and drop weight test. Since the polyamide matrix is significantly sensitive to the effects of strain rate, the required mechanical properties at different strain rates were extracted by the Hopkinson test. Based on this test, the strength of the studied composite has grown by 47% at the same strain rate as the drop weight compared to the quasi-static penetration test. As a result of the impact, failure modes such as fiber breakage, separation of fibers from the matrix, vertical and horizontal cracks concerning to the direction of the fibers have been observed. Also, numerical simulation was performed with LS-DYNA software and the effects of strain rate extracted from Hopkinson's test were applied in numerical simulation, which brought the accuracy of the simulation to 9.6% in calculating the maximum force. Based on the results of numerical simulation, in thicknesses less than 2.5mm, the SAE of the composite sheet is constant; Also, the maximum energy absorption in 4-layer composites were related to the laminate [902/02] with 18J of energy absorption.

The satellite system is subjected to shock during launch and separation. The shock causes damage to various parts, including the electronic system. In this article, the electronic board of the satellite guidance system has been analytically examined. This board is located on 5 legs that are connected to the body. The purpose of this study is to design the legs so that the least amount of shock is introduced to the electronic board. The electronic board is assumed to be a plate. Effective parameters in shock transmission, including geometrical parameters and the leg angle with the horizon surface, have been studied. The influence of the leg angle with the horizontal surface on the stiffness of the system has been investigated using analytical relations. Finite element simulation has been used to validate the equivalent stiffness. The results of this study show that changing the base angle causes the transmissibility of acceleration to change according to the excitation frequency. Acceleration transmissibility depends on the ratio ω/ω_n . For this reason, different parameters should be selected according to the excitation frequency range. If different parameters are not selected properly, the output acceleration will be higher than the input acceleration.

Heat sinks have always played a crucial role in cooling electrical equipment. In this research, in a new approach, paraffin is used as a phase change material according to the suitable phase change temperature range with multi-wall carbon tube nanoparticles homogeneously in a heat sink. AnasysFluent software with finite volume method and PISO algorithm was used to model and solve the governing equations. The melting process of the PCM is numerically investigated in a three-dimensional space by applying three heat fluxes of 10,000, 20,000, and 30,000 watts per square meter, using the enthalpy-porosity method. According to the obtained results during the phase-change process, the addition of nanoparticles with volumetric percentages of 4, 6, and 8% leads to better performance in reducing the phase-change temperature. After the completion of the phase change process, increasing the volume percentage of nanoparticles does not always have a positive effect, and among the proposed options, nanoparticles with a volume fraction of 4% showed the best performance.This improvement is due to the increased conductive heat transfer in the PCM, resulting from reduced viscosity. Overall, adding 8% nanoparticles increases the total melting time by 15% compared to the pure PCM.

Structure optimization in aerospace industries is of particular importance due to the need for light structures to reduce costs and increase flight performance. The main components of an airplane wing consist of spars, ribs and skin. At first, in this research a wing structure with two I-shaped spars, 6 ribs and a shell with specific geometric characteristics is modeled. By choosing aluminum alloy as the material of the structure and using the finite element method, the wing structure has been subjected to static loading and the maximum amount of stress and displacement of the wing box area has been obtained. Then, according to the results of the analysis and the optimization capability, the wing structure has been divided into three parts in order to optimize the thickness of the components along the length of the wing. By defining the thickness of the wing box components in all three parts as factors and stress and weight as the answers to the optimization problem through the method of designing experiments, which in this problem is the static analysis of the structure, the thickness of the components of the wing box area according to the goal of the lowest weight and the highest stress Optimization is allowed. The obtained results indicate that after the optimization, the weight of the wing box has decreased by 46.5%.

Considering the widespread use of hydraulic pilot valves, including orifices with fixed and moving parallel surfaces in the structure of two-stage pressure control valves, it is necessary to evaluate and analyze their performance in order to optimize and control. In this article, the effect of slope, length and curvature of the valve seat on pressure distribution and oil flow rate passing through the pilot valve chamber, flow coefficient, force coefficient and force on the moving part of the valve were investigated using numerical and experimental methods. In all working conditions, the difference between the results obtained from the experimental measurements of the flow coefficient and the force on the moving part of the pilot valve with the numerical results was determined to be less than 6%. Investigation results showed that reducing the slope and length of the seat, the force on the moving part of the valve is increased. Meanwhile, creating a curve in the inlet port of the valve causes 36% reduction in the force on the moving part of the valve and 70% increase in its flow coefficient. The force on the moving component of the valves including orifices with fixed and moving parallel surfaces was determined to be 20% lower on average than the valve with a vertical seat.

In the transportation industry, the vehicles aerodynamics is important because it affects on fuel consumption and stability of cars. In this numerical research by using Ansys Fluent software, the aerodynamic performance of the Iranian car Tara was investigated by creating an air duct with different dimensions and geometries in the modification of front aerodynamics and the modification of rear aerodynamics. The purpose of these changes was to establish air flow between areas of the body that have a high pressure difference, which in both aerodynamic developments reduced drag force and lift force. Also, the effect of creating side curvature on the body was also studied. The results showed that design and direction of the air flow from the sides to the back of the car is very important in aerodynamics forces, however, drag force was reduced in all cases. Finally, the best methods were combined simultaneously on the car. In the most optimal model, through the combination of the the front aerodynamic modifications and rear aerodynamic modifications the drag coefficient and lift coefficient reduced 16.3% and 4.1% respectively as the drag coefficients reduced from 0.332 to 0.278.

Transformers are one of the most significant and sensitive tools in the electrical grid. Their life and optimal operations are very imperative. The hot-spot temperature of this equipment plays a crucial role in the life of the transformer. Increasing hot spot temperature reduces the oil quality and aging of the insulation, ultimately, the life of the transformer. There are several ways to reduce the hot-spot temperature. One of these techniques is the passive cooling system via heat pipe, which has played an effective role in reducing the hot-spot temperature. However, using heat pipes in the space inside the transformer causes problems, including disruption of its electrical performance. Therefore, in this research, the thermal effects of the heat pipe inside and outside the oil tank on the thermal performance of the transformer are investigated experimentally, and finally the obtained results are compared. The results showed that by installing the heat pipe outside the transformer on the radiators, the temperature reduction of the hot spot reached 12 degrees Celsius, which reduces the corresponding aging rate to 0.17.

This research aims to improve the aerodynamics performance of a NACA 23012 airfoil equipped with a High lift device by changing one of its most important geometric parameters. In this research, Navier-Stokes equations are solved in turbulent and incompressible flow conditions using Fluent software. After the airfoil and flap modeling process, at different flap angles (10 to 30 degrees), unstructured meshing was produced in Gambit software and the improvement of aerodynamics performance due to change in the geometric parameter of the slot lip was investigated. The flow is assumed to be steady, turbulent, and incompressible, and the algorithm for solving the equations is also selected as pressure-based. The flow Reynolds range is 3.6×106 and the turbulence model used is realizable k-epsilon. A comparison of the results and aerodynamics characteristics of the airfoil equipped with a flap after making a change in the geometric parameter shows that with the significant improvement of the aerodynamics coefficients (on average, an increase of 9% in the lift coefficient and also an increase of 6% in the drag coefficient), the landing distance of the airplane will be reduced. Also, the investigation of the pressure and velocity gradients at different stages shows that the change is effective and better distributed compared to the reference article.

Increasing the propagation speed of the flame due to centrifugal force can lead to reducing the length of the combustion chamber and increasing the thrust-to-weight ratio in air gas turbine engines. The effect of centrifugal force on the propagation of the premixed flame has been investigated. For this purpose, the large eddy simulation of premixed combustion of the air-propane mixture in two straight and curved ducts with a step in the outer wall as a flame holder was performed using OpenFoam software and compared with the experimental data. The ducts have an inlet and outlet, and the averaged temperature and the wrinkling (the ratio of laminar to turbulent flame speed) were investigated for two different inlet velocities. It was observed that the curved duct inducing centrifugal force to the fuel and air mixture causes better mixing and wrinkling, increases the area of the flame, and as a result, the speed of flame propagation was improved. Also, the curved duct can withstand increasing the inlet velocity to higher values. To study the effect of fluid circulation, a new duct geometry for more mixture circulation was designed and analyzed. The comparison of temperature and wrinkling parameters in the outlet section for two initial curve ducts (C2) and the new one (C3) showed that the increase in the rotation due to the increase in centrifugal force improved the average temperature and wrinkling parameters in the outlet.

In this research, the combined displacement inside a closed square enclosure was investigated. The geometry of this chamber is considered as a quadrilateral with the same dimensions, which is tilted and the upper and lower sides are insulated, and the left side is hot and the right side is cold. The effect of changing the angle of the chamber wall in some specific angles (θ), changes in the volume ratio of nanoparticles in Reynolds numbers 10 and 100 and in Richardson numbers 0.1 and 1 in the range of laminar flow are investigated in two dimensions. The base fluid is water and the nanofluid mixture is considered homogeneous. To solve Navirastox and discrete energy equations, the equations were solved numerically. Discretized equations were solved by coding in Fortran software. The results are presented in the form of Nusselt number distribution, temperature contour, flow contour and velocity vector in different solutions. The results showed that increasing the volume fraction of nanoparticles in the base fluid increases the Reynolds number and the dimensionless Nusselt number. An increase in the Richardson number, especially at high Reynolds numbers, leads to a noticeable increase in the Nusselt number. Also, the highest amount of heat transfer is related to the angle of 90 degrees.

The use of gold metal in astronautics, electronics and medical sciences has led to its consideration. Therefore, structural studies and changes have been made to improve the properties or establish special atomic arrangements in nanoscience for this particular metal. Atomic force microscopy(AFM) is one of the most widely used tools for these purposes. Therefore, in this paper, the displacement of gold nanoparticles during manipulation using the atomic force microscopy, which is one of the objectives of the second phase, in the environmental conditions of water, plasma and methanol, has been investigated. For this purpose, the process is first modeled in two dimensions and the intermolecular forces of van der Waals, the double layer force and the hydration force are considered. Then, the displacement diagrams are drawn considering the forces between the molecule and the studied environments. Finally, according to the simulation results in different environments, the highest displacement of gold nanoparticles in the second phase of manipulation was in water and the lowest in plasma.

Arthritis of the knee is one of the leading health problems in people, and most knee surgeries have been for this reason. This disease occurs mostly in old age, spreads slowly, and affects the knee joint components. Since arthritis over time causes the destruction of the articular cartilage in the knee, therefore, the destruction of this joint is discussed and investigated according to the applied stresses. By entering CT scan and MRI images into Mimix software, 3D models of the knee are extracted and by using a dedicated software developed for the analysis of radiographic images based on the programming in the MATLAB GUI environment, the 3D CT scan files are matched to the radiographic images. The final 3D model has been created using Solidwork software, and by running numerical simulations in Abaqus software, the stresses on the cartilages have been calculated for healthy and arthritic knees. The results showed that the amount of stress in the middle side of the joint is always higher than on the lateral side, and this difference will be greater in the arthritic joint than in the healthy joint.