نشریه یافته های نوین کاربردی و محاسباتی در سیستم های مکانیکی
سال سوم شماره 1 (بهار 1402)

In this study, the effect of using louvered strip inserts in heat exchangers on flow and transfer characteristics is numerically investigated. The continuity, momentum, and energy equations have been solved using a finite volume method. The wall of the tube is heated with a uniform heat flux boundary condition. This paper uses a louvered strip insert arrangement (forward) with a Reynolds number of 10,000. The effects of louvered strip slant angle of  and pitch of 50 mm were used for Al2O3 nanoparticles with different volume fractions in the range of 1% to 4% and different nanoparticle diameters in the range of 20 nm to 50 nm, mixed in a base fluid (water) is used. The comparison of numerical analysis results with existing equations has shown a good convergence. The numerical results reveal that the Nusselt number has increased with decreasing the nanoparticle diameter. The results indicate a slight change in the skin friction coefficient when nanoparticle diameters of Al2O3 nanofluid are varied. The Nusselt number increases with increasing nanoparticle volume fraction of Al2O3 /water nanofluid, while it is found that pure water has the lowest Nusselt number value. Also, the nanofluid has reduced the wall's temperature more than the base fluids (water), which indicates the advantage of using nanofluids in improving the system's thermal performance.

In this research, an analysis of the stress and stress intensity factor in a cracked plate under thermal and mechanical loading is done. For this purpose, using MATLAB coding, a plate with a center crack was modeled by the isogeometric method (IGA) based on the Bezier extraction operator. In this method, NURBS basis functions are generated as a linear combination of Bernstein polynomials using the Bezier extraction operator. Using this operator Bezier elements with Co continuity (similar to elements of the finite element method) were produced and Bernstein polynomials are defined on these elements. In order to model the crack, the extended isogeometric method (XIGA) was used. In this method, the control points that exist along the crack and at the tip of the crack are identified and extracted using the proper level set functions. Therefore, there is no need to re-meshing or modify the elements. By enriching the extracted control points with appropriate enrichment functions and applying boundary conditions, the analysis process was carried out and the strains and stresses were calculated. Finally, the value of the first mode stress intensity factor was obtained based on the interaction integral method. To check the accuracy of the obtained results, a similar analysis was performed using the finite element method and the results obtained from both methods were compared. These studies showed that the considered isogeometric method provides more accurate solutions with a much smaller number of elements and computational costs.

Hydrochloric acid is used in many industries. One of its applications is for boilers’ acid cleaning and well acidizing in the oil and gas industry. For the reduction of HCl corrosion on metal parts and installations, corrosion inhibitors are used. In this research, the effect of Imidazole-Based corrosion inhibitor PL-464 and the corrosion behavior of X65 steel in Hydrochloric Acid (HCl) is considered. Polarization and Electrochemical Impedance Spectroscopy (EIS) experiments without and with 50, 100, and 150 ppm of PL-464 corrosion inhibitor at 25, 40, and 60ºc in hydrochloric acid solution are done. The result of these experiments showed that PL-464 inhibits corrosion by surface adsorption mechanisms. As temperature increases, corrosion potential moves toward positive amounts, and inhibition efficiency decreases. Also, corrosion decreases as inhibitor concentration is increased. Weight loss experiment at 25, 60ºc without and with 50, 150 ppm inhibitor is done, which corrosion weight loss percent is decreased as inhibitor concentration is increased. SEM and EDAX analysis showed that the steel surface in solution without inhibitor is damaged and Fe picks are shorter with respect to steel in solution with inhibitor. The results are attributed to the adsorption of inhibitors onto the steel surfaces which protects the steel surface from dissolving in acid solution.

Using nano additives in lubricants is one of the most effective ways to control friction and wear, which is significant for energy conservation, emission reduction, and environmental protection. With scientific and technological development, great advances have been made in nano lubricant additives in scientific research and industrial applications. This review summarizes the categories of nano lubricant additives and illustrates the tribological properties of these additives. Based on the component elements of nanomaterials, nano lubricant additives are discussed in three types, nanometal-based, nanocarbon-based, and nanocomposite-based additives in the review systematically. Moreover, the review summarizes the lubrication mechanisms of nano lubricant additives, including tribofilm formation, micro-bearing effect, self-repair performance, and synergistic effect. At last, the challenges and prospects of nano lubricant additives are proposed, which guide the design and synthesis of novel additives with significant lubrication and antiwear properties in the future.

Wearable mechanisms and robots are designed to improve human performance and body shape, and their design aims to help humans interact better with the environment. By using this human-connected mechanism, it is possible to help disabled people in more appropriate performance of movement activities such as walking, sitting and standing up, as well as in lifting objects that they are normally unable to lift. Improving a person's performance can include less fatigue in performing activities, protection against physical injuries resulting from heavy work, a person's capacity to carry more load, or a higher speed in performing movements. The upper body exoskeleton robotic mechanism (UBER) is designed as an easy-to-wear, flexible and adjustable mechanism to prevent common injuries, musculoskeletal, spinal and joint diseases. The purpose of developing this mobility aid robot for a skilled worker is to perform specialized tasks such as assembly operations in a production line in a relatively long period of time, with less fatigue and also to use the tools he needs easily. The stress and strain analysis performed with a load of 5 kilograms shows that the arm, in addition to bearing the weight of the user's hand, can also move a load of up to 3 kilograms. Considering the range of motion of the designed robot and the number of degrees of freedom, using this robot in the long term will maintain the skeletal health of the skilled worker, thus increasing production efficiency by reducing labor health costs.

Due to the progress of technical and engineering sciences and the more complex equipment and machinery in recent years, the maintenance and repair technology based on condition monitoring and defect estimation, under different titles such as performance-based logistic (PBL) and condition-based maintenance (CBM) is considered. These methods are used to prevent human and financial losses and to increase the production rate. This thesis presents an intelligent troubleshooting system to diagnose centrifugal pump-bearing faults. As a result, to design this intelligent troubleshooting system, a test set including shaft, bearings and real support conditions was designed and implemented in the laboratory. In this setup, three bearings with Normal wear and fault conditions (defect on the outer race) were examined, and vibration data were obtained. Then, the vibration data in extraction time and statistical features were calculated. After that, these features were used as classifier input data for intelligent troubleshooting. To identify the defect, the independent component analysis method was used. Also, the accuracy of fault detection was improved by using the particle batch optimization method. Finally, it was found that the statistical feature of Percentile can detect bearing defects by combining independent component analysis and particle swarm optimization methods.