Scientia Iranica
Volume:30 Issue: 1, Jan-Feb 2023

This study investigates the mechanical properties, microstructure, and fracture behavior of friction stir welded (FSWed) AA7075 joints considering the influence of process parameters and tool geometry. FSWed joints are produced with a conical pin and conical threaded pin type tools using tool rotational speeds of 1400 and 2000 rpm and welding speeds of 20 and 40 mm/min. The FSWed joint showed higher values of the tensile strength (188 MPa), percentage elongation (5.7%), and microhardness (137 HV) with the conical threaded pin type tool. However, the conical pin type tool produced a minimum surface roughness of 9.59 μm. A comparatively lower tensile strength observed for the FSWed joint with conical pin type tool could be attributed to their coarser, elongated, and heterogeneous grain distribution and porosity defects in the welding zone. No significant difference has been observed in the microhardness with the conical pin and conical threaded pin type tools. The fracture of the FSWed joint predominantly occurred in the heat-affected zone during the tensile test. The FSWed joint produced with a conical threaded pin showed better mechanical properties, favorable microstructure, and ductile type fracture behavior at a welding speed of 40 mm/min and tool rotation of 2000 rpm.

The problem of position tracking in teleoperation systems containing latencies and dynamical uncertainties is addressed in this work. In many applications, such as telesurgery, safe interaction with the external environment is a factor which may undermine the synchronization of the positions. For nondestructive contact with the environment, in addition to an errorless steady-state position tracking, the closed-loop system requires to have a response with the least possible overshoot. To this end, a state-feedback controller based upon L1 theory is proposed in this work. The compensator is synthesized utilizing the linear matrix inequality (LMI) technology, and the asymptotic stability of the system is verified employing Lyapunov-Krasovskii functional. Another advantage of the proposed control scheme is that it is robust to asymmetric randomly varying time delays in the communication channels. The L1-based controller is finally compared to the well-known sliding mode controller via simulation, and is proved to outperform it from maximum error point of view, while preserving low steady-state error. The proposed controller is also illustrated to be effective even in the presence of model uncertainties.

In this paper, the behavior of blood flow in passing through several consecutive and relatively close clogs inside the vessel has been investigated using modeling of blood vessels in the vessel. The clogs used are dual-channel and single-channel currents, which are naturally very close. Consecutive clogs with equal intervals and with different clogs of 3% (30%, 50% and 70%) are considered. The vessel wall is considered rigid. The inflow to the clogged area is in the form of a real pulse, the same as the pulse of blood flow in a vein. As a result, the rate of change of current intensity and Reynolds numbers is close to reality. For this purpose, the Navier–Stokes equations have been solved numerically in the unstable state together with the continuity equation in the capillary coordinate system by numerical method. These changes are more severe at distances of 17 mm for two channels and 25 mm for single channels, which have their maximum blood flow rate. Examination of the flow lines shows that due to the low Reynolds number, the return and eddy currents behind the clogs are limited.

This study presents the flow of Hibiscus Sabdariffa Roselle (Sobo), Soymilk (Soya), and Pap (Ogi) through a modeled intestine. The study employed experimental and Computational Fluid Dynamics (CFD) techniques, while AUTODESK INVENTOR 2020 version was used to draw the 3-D computational model of the human intestine. ANSYS FLUENT 16.0 was utilized as a CFD solver. Analyses of the results show that fluid velocity, pressure, density, and viscosity significantly influence the flow behavior of nutrients in the intestinal walls. The density and viscosity of the investigated fluids are in the range of 800-1024 kg/m3 and 0.316-1.095 Pas, respectively, while the maximum and the minimum viscosity were observed with Ogi and Sobo, respectively. The highest drop in the velocity along the whole length of the intestinal model was noticed between 0.8 and 1.5 m, which corresponds to the pulsating section of the model. The maximum and minimum Reynolds numbers were recorded with Sobo and Ogi samples, respectively. For effective flow and to avoid complications when taking the food supplements, especially for someone under medication, a flow velocity of 0.005 m/s is recommended. The presence of villi in the intestinal wall augmented heat transfer.

The mechanical stir casting effect on Al7075 based lightweight alloy established with Al2O3 and SiC has been studied with varied stirrer time and speed. Hybrid metal matrix improved wear resistance of composite material Al7075 (SiC+Al2O3). Experimental designs are formulated using Taguchi’s DoE. Considered 4 level 4 parameters, L16 OA is selected. Grey Relational Analysis (GRA) and Principle component analysis (PCA) coupled has been employed to calculate matrix composition. POD test (Pin-on-Disc) was used to measure the wear resistance of the casted pins. Further, mechanical characterization tests like tensile, hardness, impact, density and porosity were also accomplished. Optimum parameters are found, SiC of 6%, Al2O3 of 4%, Stirrer time of 15 min and stirrer speed of 600rpm, which gives low wear loss of 0.0034g, superior micro hardness 154.22 BHN, the tensile strength of 443.61 Mpa and Impact energy is 3J. From the ANOVA results, Stirrer speed is the most influential parameter with 49.40%. SEM-EDX analysis characterized the worn surfaces.

The heat transfer from circular cylinders in turbulent cross flows plays a significant role in industrial operations. The objective of this paper is to evaluate the heat transfer from a cylinder with circular cross section and four flexible fins in turbulent flows numerically. The governing equations of thermal fluid are discretized by finite element method (FEM) while the equations of motion of deformable structure of fins are discretized by finite element method (FEM). The k-ω SST model is used to simulate the flow. The results are validated by comparing the heat transfer rate from the circular cylinder with that of other investigators’ experimental and numerical studies. In addition, the fluid-structure interaction (FSI) results are validated against a benchmark example. The flexible fins are glued to the circular cylinder by two different angles (θ=0° and θ=45°). In both cases, the thermal enhancement, as well as the flow-induced vibrations of the fins, are investigated for various non-dimensional flexural rigidity. It is found that attached fins in both angles and the flexural rigidity are significantly affect Nusselt number. Moreover, it is found that the very flexible fins can increase the Nusselt number by 26%.

In the present study, the performance of a cylinder-based piezoelectric wind energy harvester attached to an elastic beam is numerically simulated. The wind flow perpendicular to beam axis causes an oscillatory aerodynamic force exerted on the beam tip. The beam and the piezoelectric layer are modeled as elastic continuous bodies, and the continuum governing equations of the solid and piezoelectric layers are extracted. Moreover, the induced lift force by the vortex shedding downstream of the cylinder is estimated by the modified van der Pol wake oscillator equation. The cantilever mode shapes and the Galerkin method is applied to solve the three transient and coupled equations of elastic deflection, electrical resistance and fluid force. Besides to verify the accuracy of the modified van der Pol equation, a moving object computational fluid dynamics (CFD) simulation is also conducted. The effect of oscillator length, cylinder diameter, resistance load, structure and piezoelectric thickness as well as the wind speed on the produced power is investigated. According to the obtained results, by increasing of the cylinder diameter from 0.05 m by 100, 200 and 300 %, the output power is increased by 219, 801 and 1502 % at the wind speed of 5 m/s.