نشریه علوم کاربردی و محاسباتی در مکانیک
سال سی و پنجم شماره 2 (تابستان 1402)

Goals such as not harming healthy tissues and other organs when using medicine and identifying cancerous tissues as soon as possible have led to the entry of nanoscience into the field of medicine. In this regard, a research was conducted considering various tools and methods, and the most desirable of these methods was the nanomanipulation method based on the atomic force microscope due to its many applications in the study of cell tissues in different environments. Therefore, in this article, in order to find the optimal amount of force and critical time in nanomanipulation of cancer tissue, with the aim of exploring the surface and obtaining information about gastric cancer tissue with the least damage, 2D simulation of nanomanipulation has been carried out. The important factor investigated in this research is friction, which is one of the factors that resist movement and has a direct effect on force and critical time. Therefore, with the development of simple friction models, considering Carlson-Batista, Lemaitre-Carlson and FKT friction models, force-time diagrams have been drawn and critical force and time values have been calculated. The lowest value of the force was equal to 0.453 nN and the lowest value of the critical time was equal to 45 ms, which was obtained from the simulation with the FKT friction model. Also, by comparing these values with past researches, a decrease in force and critical time compared to the LuGre friction model has been seen.

In this paper, the effect of using four different types of inserts in cavity receiver tube of solar power tower to improve heat transfer and reduce non-uniform temperature distribution is investigated. Numerical simulation is performed in three dimensions and the effect of inserts configurations, position inside receiver tube, pitch and thickness of insert and the effect of non-uniform heat fluxon the Nusselt number, friction factor and temperature of outer surface of receiver tube are investigated. The flow is incompressible, steadystate, turbulent and the Reynolds number is in the range of 8000 to 20000. Numerical simulation results for four types of inserts: twisted-tape, wavy-tape, helical-tape and louvered-tape show that wavy-tape compared to the other three types, has the higher Nusselt number and the lower average temperature of receiver tubesurface. The Nusselt number of the wavy-tape is increased by 1.8%, 2% and 3.2% relative to the louvered-tape, twisted-tape and helical-tape, respectively and 10% relative to the receiver tube without insert. By increasing the insert thickness and decreasing the insert pitch, the Nusselt number increases and average temperature of receiver tubesurface decreases. Investigating the insert position in three cases: close to the non-uniform heat flux wall, the middle of the tube and close to the insulation wall show that by increasing the distance of insert from non-uniform heat flux wall, the mixing of hot and cold fluids flow is better and the temperature distribution is more uniform.Therefore, the best position to place insert is the farthest distance from the non-uniform heat flux wall.

Solar radiation, the basic parameter required for solar energy programs, is not measured in all parts of the world due to technical and financial limitations, and it is necessary to determine with the accurate estimation methods. In this research, a model was developed to estimate the daily horizontal scattered solar radiation with the hybrid methods of Support Vector Regression, Gray Wolf Optimization and Harmony Search Algorithm. To determine the validity of the model, daily measured solar radiation data of different cities in the sunny part of Iran (Bandar Abbas, Kerman, Sanandaj, Semnan and Zahedan) were used. The input parameters of the models are the mean temperature, relative humidity, sunshine hour, evaporation and wind velocity. The comparison of the solar radiation of the hybrid model with the measured values shows the desired results based on statistical analysis, and the hybrid model is an efficient and accurate method compared to other models, especially experimental models. The average absolute bias error obtained, root mean square error and correlation coefficient for Zahedan station are respectively equal to 14.77 MJ⁄m^2, 26.85 MJ⁄m^2, and 0.68 for the experimental equation and the obtained values of the regression vector machine - Harmony respectively It was similar to 13.85MJ⁄m^2, 9.58 MJ⁄m^2 and 0.71. The research results showed that the regression-harmony vector machine model is an efficient method that is much more accurate than other models.

 In this paper, the effect of using trefoil and segmental baffles on heat transfer and pressure drop towards the shell of shell and tube heat exchangers is studied. Baffles are used in shell and tube heat exchangers to increase heat transfer coefficient, pipe support, flow pattern determination, structural strength and vibration prevention. Using the genetic algorithm under the same conditions, the heat transfer and pressure drop functions of the baffles are optimized as single-objective and multi-objective. The heat exchanger with the trefoil baffles is simulated by Aansys fluent software. The results show that in trefoil baffles, increasing the heat transfer coefficient will be accompanied by a greater pressure drop. The heat transfer capacity of the trefoil baffle has increased by 19.944% in the square arrangement and 16.25% in the triangle arrangement compared to the segmental baffle in the maximum state obtained from the single-objective genetic algorithm, while the pressure drop for the square arrangement of the tube bundle is 3.2 times and for the triangle arrangement tube bundle has increased 2.075 times compared to the segmental baffle. The jet fluid flow created in the trefoil perforated increase the heat transfer performance and the corrosion products and chemical sediments are reduced, which also improves the corrosion conditions of the shell and tube heat exchanger with the trefoil perforated plate.

The natural frequencies and mode shapes of bone are widely used in the diagnosis of bone fracture healing, bone remodeling, osteoporosis diagnosis, and implant-bone interaction. These characteristics can be estimated using numerical analysis and finite element modeling and measured and validated by modal testing of laboratory samples. Bone heterogeneity in finite element models affects its natural frequency. In this research, the effect of bone heterogeneity and density-elasticity relationships on the natural frequency of bone and the accuracy of their estimation have been investigated. A cow tibia bone was prepared and subjected to modal test. The experimental results of the modal test were compared with the results of the 3D finite element model created from the bone CT scan images. Inhomogeneity based on the proposed density-elasticity relationships was applied element by element (continuous) and regionally based on a tolerance (discrete) in the model. Comparing the results of heterogeneous models with experimental results shows that there is very little difference between the natural frequencies of discrete and continuous heterogeneous models. So, for the first five frequencies, a discrete heterogeneous model with 20 regions can predict the natural frequencies with an error of less than 2% with less cost and shorter time.

One of the industrial parts that requires very high manufacturing accuracy is industrial molds and especially cutting molds. In these molds, the clearance of the dies is equal to 0.1 of the thickness of the sheet, so the accuracy of making these molds is very important. Today, the wirecut process is widely used in making these molds. In the process, due to the lack of contact between the tool and the work piece, there is no mechanical tension and the produced parts have high precision. Nevertheless, in order to achieve the high precision required in the production of cutting molds, various methods are used. In this research, using the response surface method, the dimensional accuracy value has been investigated based on three parameters of wire speed, wire tension and generator power for Mo40 steel workpiece. Based on this method, at first, the importance of each parameter on dimensional accuracy was determined. Then, by deriving the equation according to the conducted tests, the optimal value of dimensional accuracy was extracted based on the mentioned parameters. The results showed that for tension values of 1.3485 kg, wire speed of 10 cm/s and power of 46.7677%, the accuracy value reaches its maximum value. Finally, these values were experimentally tested and a 0.2% error was recorded. Therefore, by using the method of the response procedure, the amount of dimensional accuracy can be used in the wirecut process of industrial steel molds.