Showing 7 results for Safikhani
Mohsen Safikhani Nasim, Ehsan Etemadi,
Volume 17, Issue 4 (6-2017)
Abstract
In this paper, the behavior of a new type of auxetic composite (composite with negative Poisson’s ratio) consisted of polyester fibers and ABS tubes as reinforcement as well as polyurethane foam as matrix was investigated by finite element method. Furthermore, the effect of negative Poisson’s ratio and mechanical properties of auxetic composite under quasi-static pressure were analyzed and the results were compared with the published experimental works. Good agreements were found between the results. Considering stress-strain diagram, it is concluded that this type of composite can operate as a damping material due to the specific properties such as high shear strength, indentation strength toughness. So, the foresaid properties make them a great choice with high potential application in various industries. Also, the ways to get the effective parameters to achieve more negative Poisson’s ratio were investigated. The parameters include the foam density as well as material, diameter and distances between ABS tubes. The results show that with decreasing foam density and decreasing distances between ABS tubes, the negative Poisson’s ratio increases at first to reach the critical value and then decreases.
Amin Yousefpour, Mohammad Safikhani, Mohammad Reza Hairi Yazdi, Arash Bahrami,
Volume 18, Issue 7 (11-2018)
Abstract
Nonlinearities give rise to secondary resonances such as superharmonic and subharmonic resonances. The superharmonic resonance can activate large-amplitude responses when the excitation frequency is a fraction of the fundamental frequency of the system. These low frequency excitations are very beneficial for energy harvesting systems. This paper presents an analytical investigation of vibrational energy harvesters with superharmonic excitation in a pietzomagnetoelastic configuration. A piezomagnetoelastic power generator is assumed to operate in the monostable and bistable modes. Nonlinear differential equations governing the oscillations of the system is solved using the method of multiple scales. System responses to the superharmonic resonance including the cantilever tip displacement and the output voltage are determined. It is found that employing the superharmonic resonance can increase the amount of harvested energy in the system. The root mean square value of the output voltage is obtained for several cases in both monostable and bistable modes. The power generated in monostable and bistable modes is then compared through numerical simulations. It is observed that the bistable mode is more convenient for harvesting energy. In addition, a Rung-Kutta numerical scheme is used to solve the differential equations. It is shown that the perturbation solution is in a close agreement with the numerical solution.
Mohammad Safikhani Mahmoudi, Amin Yousefpour, Arash Bahrami,
Volume 18, Issue 7 (11-2018)
Abstract
In the present research, higher resonance frequencies are employed to improve the performance of the atomic force microscopy in the non-contact mode. Conventional models already used in the literature to study AFM microcantilever dynamics such as point-mass approach are not only incapable of modeling higher vibrational modes but also fail to predict microcantilever complicated dynamics with a sufficient accuracy. In this paper, the Hamilton’s extended principle is used to obtain equations governing the nonlinear oscillations of the AFM probe. Euler-Bernoulli beam assumptions and small deflection theory are assumed. The resulting partial differential equation is often converted to a set of ordinary differential equations and then this set is solved either numerically or based on perturbation methods. In the present research, however, the partial differential equation is attacked directly by a special perturbation technique. The accuracy of the present method is then verified by a combination of the Galerkin discretization scheme and a Rung - Kutta numerical solution. Finally, different behaviors of the AFM probe including static behavior, linear mode shapes and frequency response curves are investigated through several numerical simulations. It is found out that higher vibrational modes have smaller frequency shift. It is also found out that higher modes are faster in gathering surface information and also more sensitive to the excitation.
S.a. Mostafavi, H. Safikhani, J. Zamani,
Volume 19, Issue 12 (December 2019)
Abstract
Air pollution is one of the consequences of industrial development that its severity is increasing day to day, due to the population growth and expanding urbanization, development of transport and fuel consumption increases. Awareness of air quality and trends of pollutants changes in different locations in a city can play an important and effective role in urban health management and macro policymaking. The first practical step in reducing the level of pollutants is the adequate knowledge of the pollutants details, including the type, amount and frequency of events throughout the year to determine the type of pollution and its source. In this paper, the results of hourly, daily, monthly and annual analysis of the various pollutants have been studied and scrutinized using the experimental data obtained from air quality measurement stations in the city of Saveh. In the end, In addition to the general solutions and suggestions for reducing the air pollution level in Saveh city, two precise solutions include the construction of an underpass and construction of a high way have been presented which the geometry and detailed features of each one has been mentioned in the article.
M. Sharjerdi, H. Safikhani,
Volume 19, Issue 12 (December 2019)
Abstract
In this article, technical-economical investigation of heating and cooling loads in faculty of engineering of Arak university, Iran has been investigated. The tradiational and modern conditioner systems such as CAV, VAV, fan coil systems (all three systems are tested with direct fired absorption chiller and screw chiller), VRF system, split system and evaporative cooling system (in total 9 different systems) are designed for this faculty and are compared technically-economically. In this article, the costs of water, electricity and gas, purchase of systems and equipment, maintenance and repair of equipment of the examined systems are calculated and are compared with each other and then this work is done in different cooling loads, so that the results are not limited to the technical faculty of Arak university and can be used for all existing systems throughout the country. In the end, it is shown, that the evaporative cooling system has the lowest current and initial cost among the other systems. however, since this systems do not have the ability to determination of the amount of humidity and ideal temperature for the desired space can not be considered as an ideal and standard system. Also it is shown, that the current and initial costs of compression chiller are less than of absorption chiller and VAV systems have the better performance than CAV and fan coil systems, and the VRF system, after the evaporative cooling system, has the lowest current and initial cost among the examined systems, especially the split system. Due to the intelligent and optimal control of this system, it can be selected as an ideal system.
H. Safikhani, M. Loloee ,
Volume 20, Issue 3 (March 2020)
Abstract
In this paper, multi-objective optimization of the cooling and heating systems at the faculty of engineering of Arak University is investigated to increasing comfort and reducing the cost of energy. In the first step, the faculty building with 4 floors, 11800 square meters of infrastructure and 122 classrooms and rooms is modeled and the comfort and cost of the faculty are calculated. In the next step, a database of 2,000 faculties with different design variables was created and analyzed. Between the formed databases, buildings with the best objective functions are selected and presented in a Pareto front. Design variables are the 11 geometrical and non-geometrical factors affecting the comfort and cost of the faculty. The objective functions are the comfort, cost, and energy consumption. The results indicate that both absorption and compression systems have the ability to achieve acceptable levels of comfort, but the amount of energy consumed in the absorption chiller is higher than the energy consumption of the compression system, which indicates the necessity of using absorption systems in conditions of waste heat. Also, the results indicate that the absorption system, despite the higher energy consumption than the compression system, has lower energy consumption costs due to the difference between electricity and gas tariffs in Iran country and should be corrected.
Seyed Alireza Mostafavi, Hamed Safikhani, Ali Karimi, Siavash Salahfard,
Volume 21, Issue 3 (March 2021)
Abstract
Arak is ranked 71st in the worldchr('39')s most polluted cities. Arakchr('39')s air is more polluted than the Iranian capital in terms of pollutants. The influx of large amounts of pollution into the city shows that a high percentage of pollution is concentrated in a small town, and this volume of pollution is very dangerous for both humans and the environment. In order to reduce air pollution in the city, the Iranian government in 2007 approved a plan called the comprehensive plan to reduce air pollution in Arak. In this comprehensive plan, the construction of a highway called Amirkabir (58 meters) has been approved, which connects the east and west of Arak. In this article, numerically and experimentally, the effect of constructing this highway on the reduction of air pollution in Arak city has been investigated. In the results section, the details of changes in air pollution in Arak city before and after the construction of this highway have been compared. The results show that a 2.75 percent decrease is observed for Nox pollutants, 4 percent decrease is observed for Co, and a change is obtained for So2. As a result, the implementation of this project at a very high cost will not have a significant impact on improving air pollution in the city of Arak.
