Modares Mechanical Engineering
Year:2021 | Volume:21 | Issue:11|Papers Count:7

Composite structures under impact loading are prone to a variety of damage mechanisms such as delamination, fiber breakage, or matrix cracking. It is proven that the impact-induced damage mechanisms of composite materials are dependent on scaling (in-plane and out-ofplane) and layup configurations. The present study has investigated the effect of scaling and layup configurations on the failure mechanisms of composite materials under low-velocity impact force using acoustic emission, C-scan, and CT-scan tools. For this purpose, four samples with quasi-isotropic configurations of [45m/0m/90m/-45m]ns were manufactured, then they were loaded and acoustic signals were recorded. The three IS (m=1, n=2), PS (m=2, n=2), and SS (m=1, n=4) samples were investigated based on D62624/D6264M ASTM standard test and the R (m=1, n=2) sample had half of the in-plane dimension of them. The variables m and n vary according to the design plan. The obtained acoustic emission data were analyzed using the sentry function, then C-Scan and CT-scan were utilized for damages’ size and location. It was proven that scaling and layup configuration affect the type and intensity of damage mechanisms as well as mechanical behavior of the laminated composites. Overall, the samples with thinner laminas have a smaller damaged area. Furthermore, damages mostly happen in the lower half but near the symmetric line of the samples. Besides, the acoustic emission method is shown as an indicator of scaling and layup configuration effects in glass/epoxy composite materials under low-velocity impact.

Numerical simulation of Eulerian fluid Lagrangian solid interaction incorporating H2-O2 mixture gas detonation plate forming by employing conservative element and solution element immersed boundary method in LS-DYNA software is proposed in this paper. The detonation mechanism includes 7 species and 16 reactions. The chemical reaction mechanism and detonation wave propagation of Eulerian solver and dynamic plastic response of mild steel thin plate of Lagrangian solver are discussed thoroughly. The Johnson-Cook phenomenological material model with failure criterion is used to provide accurate predictions of dynamic response and failure state of detonation loaded steel plates taking into account material strain-rate sensitivity and non-linearities. The 2D numerical model is validated by comparing the simulation results with experimental data for thickness strain. The simulated pressure-time history of combustion cylinder, von Mises stress and deflection pattern of plate are also represented. Furthermore, a series of numerical simulation is carried out to determine the effect of the magnitude of internal detonation pressure on plate, taking into account different combustion cylinder longitudinal capacities, pre-detonation pressures and ignition point locations. Results show that an increase of pre-detonation pressure is conducive to increase the value of maximum detonation pressure while decreasing the combustion duration. Moreover, combustion cylinder with higher longitudinal capacity is more powerful to deform the plate.

In this paper, the performance of a typical 190 W photovoltaic cell, located in the Research Institute of Petroleum Industry, Tehran, Iran, has been studied and evaluated from the energy and exergy point of view. A computer code has been developed for modeling and determining the electrical characteristics of the system such as open-circuit voltage, short circuit current, system resistances, maximum power point properties, and characteristic curves. The operational and electrical parameters of the system and the environmental conditions such as solar radiation, wind speed, and ambient temperature have been experimentally measured and logged on one typical day of May. For the validation of the model, the results obtained from the model have been compared with the data reported by the manufacturer as well as the experimental data. The results show that the energy efficiency varies from 11. 22 to 13. 94 percent during the study period (7: 30 AM to 5: 30 PM) and its average is equal to 13. 19 percent. The exergy efficiency also varies from 14. 77 to 16. 66 percent during the study period and its average is 15. 62 percent.

The purpose of this study is to generate two-phase flow patterns and to obtain a flow pattern map for two phases as water and air in a vertical pipe which is made of transparent Plexiglas. The pipe specification is 50 mm diameter and 390 cm length. In this attempt the average velocity of the Taylor bubble will be calculate. In order to facilitate this research work, a two phase flow was designed, built and adjusted at Tarbiat Modares University Two-phase flow laboratory. Three flow patterns as bubbly, slug and churn flow are generated and examined for 320 runs of different superficial velocities of air and water. A seven-layer distributor with the ability to change the number of bubbles produced is used to create a bubbly flow pattern at the air inlet. The effect of the superficial velocities of each phase on the flow pattern was evaluated and a flow pattern map was presented for 320 different data. By processing the images obtained from the high-speed camera, the average Taylor bubble velocity was calculated for different flow conditions with uncertainty in calculating the velocity. Also, for 5 different velocities of the liquid phase, a diagram of the average velocity of Taylor velocity with increasing gas velocity was drawn and compared with the Nicklin correlation which can be found in the literature.

Thermoacoustic engine is an energy conversion device that uses the energy carrying capacity of sound waves to generate sound power from thermal energy. Although it is not difficult to build thermoacoustic engines due to having no moving parts, many researchers have always tried to reduce the temperature difference required to run thermoacoustic engines, so that these devices can be used in most industries. To investigate the onset conditions of the system, temperature changes in the stack section of a standing wave Thermoacoustic engine were investigated. Numerical analysis of temperature changes along the stack, was performed using the Rott's thermoacoustic equations. The temperature was calculated instantaneously along the stack, and this process continued until the thermal equilibrium was established in the system. In addition, integrating numerical solution equations with the circuit analogy method, made it possible to calculate the startup time of spontaneous oscillations. A standing wave with an open end was designed and built to validate the temperature curves obtained at different moments. This thermoacoustic engine was able to display the temperature instantaneously along the stack with parallel plates structure. The data obtained from the experimental tests and the temperature changes diagram resulting from the numerical solution method, showed a good agreement with each other for the onset process in the system.

Deriving the accurate dynamic model of robots is pivotal for robot design, control, calibration, and fault detection. To derive an accurate dynamic model of robots, all the terms affecting the robot's dynamics are necessary to be considered, and the dynamic parameters of the robot must be identified with appropriate physical insight. In this paper, first, the kinematics of the ARAS-Diamond spherical parallel robot, which has been developed for vitreoretinal ophthalmic surgery, are investigated, then by presenting a formulation based on the principle of virtual work, a linear form of robot dynamics is derived, and the obtained results are validated in SimMechanics environment. Furthermore, other terms affecting the robot dynamics are modeled, and by using the linear regression form of the robot dynamics with the required physical bounds on the parameters, the identification process is accomplished adopting the least-squares method with appropriate physical consistency. Finally, by using the criteria of the normalized root mean squared error (NRMSE) and using different trajectories, the accuracy of the identified dynamic parameters is evaluated. The experimental validation results demonstrate a good fitness for the actuator torques (about 75 percent), and a positive mass matrix in the entire workspace, which allows us to design the common model-based controllers such as the computer torque method, for precise control of the robot in vitreoretinal ophthalmic surgery.