نشریه علوم کاربردی و محاسباتی در مکانیک
سال سی و دوم شماره 1 (پاییز و زمستان 1399)

Using renewable energies including wind and solar have become an important subject among investigators. Therefore, numerous studies have been performed to optimize wind turbines at the vicinity of areas which are capable of producing renewable energy. In this research, the feasibility of using  four-bladed Darrieus wind turbine on a one-way highway has been studied numerically. The Fluent commercial software is used  in the simulation conducted. The results of simulation indicate a good agreement with the experimental data. In this research, the turbine performance has been evaluated at different tip speed ratios and according to the results, the maximum power coefficient at the tip speed ratio of 0.644 is 0.00299 with a corresponding power output of 61.81 watt.

In this paper Parabolic Dish Solar Concentrator (PDSC) are studied numerically and experimentally. In addition to designing, manufacturing and testing the collector, the system is also modeled in COMSOL software. Experiments and modeling have been performed using two helical tubular absorbers and a fin-shaped plate at the focal point, with three different discharges in two closed and open cycles. Comparison of experimental and simulation results shows a good agreement and the error rate is between 1 and 4درصد. The results show that the first type adsorbent has better efficiency compared to the second type adsorbent and also increases the collector efficiency with increasing flow rate.

In this experimental study the effect of using phase change materials (PCM) in the thermal storage tank on the performance of a solar dryer was investigated. The experiments were carried out for three levels of PCM 1.54, 2.45 and 3.6 kg and two levels of fluid flow rate of 0.2 and 0.4 l/min. The results showed that with increasing the fluid flow, the thermal efficiency of the collector from 62.4% to 20.2% for 0.4 l/min. The thermal energy for fluid flow of 0.2 and 0.4 lit/min obtained about 13.31 to 13.63 MJ and 14.45 to 14.92 MJ, respectively. The results also showed that the overall efficiency of the dryer increased with increasing PCM and it changes from 32.92% to 35.55% for the fluid flow rate of 0.2 l/min and 32.19% to 36.02% for 0.4 l/min. Considering the specific energy used for drying of the samples and drying efficiency the fluid flow with 0.2 l/min and PCM with 3.6 kg is a proper choice for drying of apple slices. The payback period was obtained about 20 months.

The heat generation during laser-induced thermotherapy can damage healthy tissue. Therefore, it is necessary to predict the temperature distribution and the possibility of tissue damage due to temperature rise. In this study, temperature changes and thermal stresses caused by laser on a healthy and cancerous tissue of human skin are modeled using a numerical method based on the finite element technique. It should be noted that the laser beams are assumed to be Gaussian and the attenuation of the laser light in the skin layers is based on Beer-Lambert's law, and the deformation in all parts of the element is expressed by equilibrium equations. The numerical results include the effects of laser intensity, radiation radius and wavelength as well as the role of blood perfusion on the temperature and von Mises stress distributions. Laser thermal damage to cancerous tissue is also investigated based on Arrhenius' theory. The present results can provide as preliminary information to physicians and provide a detailed account of events during the treatment.

Detection and analysis of circulating tumor cells can provide important information to prevent the spread of cancer, which annually kills millions of people worldwide. So the researchers are trying to find a way to separate these cancer cells for detecting them. In this study, the OpenFOAM code was used to simulate the sheathless focusing and separation of White Blood Cells from Prostate cancer cells using standing and traveling surface acoustic waves in two stages. In the first stage, cells are focused in the center of the channel utilizing standing waves. Then, with the aid of traveling waves, the white blood cells are pushed to the opposite side and the two cells are separated by 100% efficiency.

In this study, the numerical analysis was studied about mixed convection of sodium alginate (non Newtonian Pseudoplastic fluid) with Nano particle in a two dimensional rectangular channel containing several blocks. The temperature of inlet fluid to the rectangular channel were kept in steady state and fixed temperature that is less than wall temperature. To solve the Continuity, momentum and energy equations, numerical analysis and finite volume method with SIMPLE technique is used. In this study the effect of height and numbers of blocks, volume fraction of nano particle, Richardson number and Reynolds number is investigated on Nusselt number and skin friction coefficient. The results show that increasing of aluminum solid particles in sodium alginate will increase the heat transfer rate and skin friction coefficient in channel length. Also by increasing Reynolds number there is an increase in convection rate through the channel. In addition to the conclusions, increasing the block height from H/3 to H/2 enhance the average Nusselt number by 10% and skin friction coefficient by 13%. It is observed that increasing of Richardson number decreases the Nusselt number and skin friction coefficient. Also changing block number from 3 to 5 decrease Nusselt number about 3.5%.

In this study, a stress updating method is formulated in a semi-implicit way for the von Mises plasticity model with the Chaboche nonlinear isotropic hardening and the Armstrong-Frederick kinematic hardening in the regime of the small deformations. For this purpose, the exponential map integration method is utilized. Then, in order to investigate the correctness, accuracy and convergence of the new proposed method, the numerous numerical tests are carried out and their results are compared with previously accepted methods. The results show considerable increasing in accuracy of the presented method and the second-order convergence rate of the method. On the other hand, in this research, the derived relationships have been presented in a way that it is possible to extract data from any desired point during the plastic step; finally, it is studied that selecting the data of which point of the elastoplastic loading step leads to the most accurate results.

In this paper, the propagation of ultrasonic waves generated by a laser pulse in thermoelastic regime up to the evaporation threshold of the material is modeled in two-dimensions by using the Code-Aster finite element solver. While in previous studies, this problem is solved in one step, in the new approach, we use different meshes and different increment times for modeling each of the thermal and mechanical parts of the problem. This new approach results in significant reduction in computation time. The propagation of ultrasonic waves generated by laser powers of up to 10 mJ with 17 ns pulse duration are modeled as a function of time. Computation time for separate thermal and mechanical analyses on the computer used for this purpose was 1 hour and 55 minutes; while combined analysis of the problem on the same computer takes at least 11 hours and 29 minutes. The resulting longitudinal and transverse waves, as well as the thermal behaviour of the material are then analysed and the results are compared with experimental and numerical data available in the literature. Very good agreement is observed between our simulation results and experimental and numerical results available in the literature which indicates that the laser ultrasonics process is accurately modeled by using the new approach and new finite element solver.

In this study, heat transfer of nanofluid in a channel with an externally–applied magnetic field and a porous obstacle is simulated and discussed. To simulate the flow field inside the obstacle, the Darcy–Brinkman–Forchheimer model is implemented in the LBM method. Thereafter, effects of influencing parameters on the heat transfer rate are analyzed utilizing the experimental design method. The results show that the nanoparticles type has the greatest effect on the heat transfer with the contribution ratio of 62.79%. The second and the third parameters are the obstacle size and the Reynolds number, with the contribution ratios of 20.71% and 7.58%, respectively. The contribution ratios of the Hartmann number and the nanoparticles fraction are estimated about 3%. However, it is found that in this problem, the influences of the porosity, type, and the Darcy number of the obstacle on the mean Nusselt number are almost negligible.

In the present paper, the mixing in electroosmotic flow is studied numerically and simulated in the presence of a magnetic field with three different locations. The flow geometry was included a two-dimensional duct between two parallel plates, and the flow was assumed to be incompressible, steady and laminar. The governing equations of the problem, including modified momentum equations (Navier-Stokes) for the fluid flow field, the equations of external and internal electric potential fields, the equations of distribution of the positive and negative ions (Nernst-Planck), the magnetic field equation, and the concentration equation for species have been solved using the finite volume numerical method. The obtained numerical results were validated against the analytical solutions of an EOF with uniform microchannel walls zeta potentials. The numerical results show that in the presence of a magnetic field, so the final mixing efficiency reaches to 93.3 %. However, this is while the magnetic field has been applied before the electric double layer.

In present study, the performance of a Heller-type natural draft dry cooling tower in the Fars Combined Cycle Power Plant is investigated under different environmental conditions (ambient temperature and wind velocity), based on a new theoretical method. The data collected from the control center of this power plant confirms the accuracy of the theoretical method; Therefore, a new mathematical model is created for predicting the performance of this cooling tower. This model is only applicable for wind velocities less than critical velocity, which is usually large and uncommon in operational conditions. Using this model for the described Heller cooling tower, it is shown that in high ambient temperatures, as the wind velocity increases, the heat transfer rate in the cooling tower decreases with a lower slope. The results of using the new theoretical method for calculating the performance of three aligned cooling towers in the power plant, along with the measured data, showed that when the wind direction is perpendicular to the towers, the efficiency of each tower is lower than the single tower in the same condition. When the wind is in line with the towers' direction, the efficiency of the rear towers will increase from the tower in the wind attack line.

This investigation for all specimens the concrete with self-contact is used. The specimen has expanded metal sheets layers. The behavior of sheets is analyzed for specimens.  For experimental method the acceleration parameter are measured with the acceleration sensor. Drop hammer test machine had been used for experimental tests. For numerical method the ABAQUS software is used. Abaqus is used for dynamic test loading and it is suitable for dynamic loading. For the specimens with two and free fixed of area are investigated on experimentally. For the specimens with thin thickness the free fixed is used. The specimens without expanded metal sheet are collapsed under impact loading. The specimens with expanded metal sheet have a strong resistance for impact loading. The displacement of the specimens without expanded metal sheet is more than of the specimens with expanded metal sheet. Expanded metal sheets are simulated in the specimens with experimentally and numerically loading.

Gas leakage from transmission pipelines waste a large amount of gas and interrupt the gas flow. In addition, it could cause significant loss of life and environmental damage. If the leaks in the pipelines are not restrained, in this way the National Gas Company will pay huge economics losses annually. The subject of this study is numerical simulation of gas leakage from high pressure buried pipelines (up to 1050 psi or 7240 kPa) in the soil and develops correlations for estimating gas leakage from these pipelines. Leakage hole was considered on the upper side of the pipe surface. The working fluid is compressible and the flow are turbulent and steady. Also the soil surrounding the tube was modeled as a homogeneous porous zone. The information required to simulate this problem was provided with the help of the industrial consultant. In this study, parameters affecting on the volume of gas leakage were investigated. The results show that the leakages from damaged cross-sections on high pressure buried pipelines, unlike unburied pipes, happen at low velocities and there is no evidence of choked flow. Finally, the accurate correlations were provided to estimate the leakage from the feed and transmission pipelines that minimum R equal 0.9981.