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In this article, the free vibration of a functionally graded Euler–Bernoulli beam with a tip nanoparticle and a nonlinear/linear spring constraint is presented for the first time using strain gradient theory. It is assumed that there is a nonlinear/linear spring and a nanoparticle at one end of the beam while the other is clamped. The influence of different parameters, such as the material length scale parameter, the mass of the nanoparticle, and the nonlinear/linear spring constant on the natural frequencies, is discussed in detail. The presented benchmark tables can be used as an excellent database to verify approximate or analytical solutions in future works. The presented results can be useful for those designing micro/nano electromechanical devices. [ABSTRACT FROM AUTHOR]

Free vibration and wave analysis of thick rectangular graphene are studied by employing the wave propagation method. To consider small-scale effects and thickness of a plate in nanoscales, equations of motions are represented by the Eringen nonlocal theory coupled with the Mindlin plate theory of thick plates. To solve the governing equations of motion with the wave propagation technique, propagation and reflection matrices are derived. These matrices are combined to obtain exact natural frequencies of graphene sheets for all six possible boundary conditions. To check the accuracy and reliability of the method, natural frequencies are compared with the results of the literature, and excellent agreement is observed. Additionally, wave analysis of the graphene sheet is performed and different types of waves in the graphene sheet are captured. Deriving the dispersion relation of the graphene sheet, bifurcation frequencies (cut-off and escape frequencies) are analytically found. Finally, the effects of graphene sheet thickness and nonlocal parameter on the natural frequencies and bifurcation frequencies are investigated. It is observed that natural frequencies are highly dependent on the graphene sheet's thickness and nonlocal parameter. More importantly, the number and order of bifurcation frequencies depend on these two parameters as well. Our findings are valuable for the sustainable design and fabrication of graphene-based sensors, in which structural health monitoring of embedded graphene sheets is of great importance. [ABSTRACT FROM AUTHOR]

Friction stir processing is one of the solid-state processes which can be used to modify the structure and properties of alloys. In addition, it has become one of the most promising techniques for the preparation of the surface layer composites. To pursue cost savings and a time-efficient design, the mathematical model and optimization of the process can represent a valid choice for engineers. Friction stir processing was employed to generate an Al 6061/Al2O3-TiB2 hybrid composite layer, and mechanical properties such as the hardness and wear behavior were also measured. The relationship between the hardness and wear behavior, process parameters of friction stir processing were evaluated using an artificial neural network and response surface methodology. The rotational speed (1500–1800 rpm), traverse speeds (25, 50, 100 mm/min), and the number of passes (1–4) with constant axial force (2.61 kN) were used as the input, while the hardness and weight loss values were the output. Experimentally, the results showed that the process parameters have significant effect on hardness and wear behavior of Al 6061/Al2O3-TiB2. In addition, the developed artificial neural network and response surface methodology models can be employed as alternative methods to compute the hardness and weight loss for given process parameters. The results of both models showed that the estimated values for the hardness and wear behavior of the processed zone had an error less than 0.60%, which indicated reliability, and an evaluation of the estimated values of both models and the experimental values confirmed that the artificial neural network is a better model than response surface methodology. [ABSTRACT FROM AUTHOR]

In recent years, electricity generation by employing wind turbines has been increased significantly due to technology advancement and environmental concern. In the present study, meteorological data have been employed to compute the Weibull distribution function as well as wind power and energy density. The wind data measured at 10-min intervals at three heights of 10, 30, and 40 m above the ground. Monthly, seasonal, and annual wind speed variations are analyzed, and the performance of the selected wind turbines is evaluated. The results show that the highest wind power potential occurs in July at Lotak and in August at Shandol. The estimated annual power and energy densities demonstrated that both investigated sites are suitable for large-scale power generation. Finally, the levelized cost of energy (LCOE) is employed to evaluate the economic feasibility of electricity generation from wind power energy. It was demonstrated that the minimum cost of energy achieved by Dongfang DF100-2500 model with LCOE of 0.0830 and 0.0786 USD/kWh in Lotak and Shandol, respectively. [ABSTRACT FROM AUTHOR]

According to the present literature review, the axial vibration of the axially functionally graded (FG) tapered nanorod with attached nonlinear spring has not been addressed so far. In this study, the axial vibration of the FG tapered nanorod is studied based on Eringen's nonlocal theory, in which one end of the nanorod is clamped and the other end is attached to a nonlinear spring and a nanoparticle. The influence of different parameters such as the nonlinear spring constant, mass of the nanoparticle, and the nonlocal parameter on the natural frequencies is presented in detail. The solutions via Tables can be utilized as a reliable reference for evaluating the validity of future researches. The presented nonlocal solutions can be helpful for those who are interested in designing micro/nano electromechanical systems. [ABSTRACT FROM AUTHOR]

Reflection, propagation and energy analysis are crucially important in designing structures, especially plates. A thick plate is considered based on first order shear deformation theory. Wave Propagation Method (WPM) is employed to exactly derive resonant frequencies and wave power reflection from different classical boundary conditions. Firstly, the frequency results are compared with other literature to validate the exact proposed wave solution in the present work. Then, wave analysis and benchmark results for natural frequencies are presented for six different combinations of boundary conditions. The results indicate that the wave power reflection of thick rectangular plates is quite complicated and an incident wave of a specific type gives rise to other types of waves except for simply supported boundary conditions where the reflected wave power does not depend on the system parameters. [ABSTRACT FROM AUTHOR]

In this paper, the wave propagation method and the differential constitutive law consequent (not equivalent) to the Eringen strain-driven integral nonlocal elasticity model are utilized to analyze the free vibration, wave power transmission and reflection in multi-cracked nanorods. This aim is pursued by deriving the propagation, reflection and transmission matrices and comparing the natural frequencies obtained by these matrices with the available results in the literature. Then, the nonlocal, crack-severity, and crack location effects on the natural frequencies are presented for two combinations of the boundary conditions. Finally, the paper presents the effects that the reflected and transmitted power of a wave incident on a crack location receive from the nonlocal and crack-severity parameters. The results obtained via the reflection and transmission matrices will provide valuable insights into the subject of wave power reflection and transmission analysis in nanoscale structures for the future. The computer coding of the proposed method is much easier than the classical vibration analysis methods which makes it more appropriate in implementation. [ABSTRACT FROM AUTHOR]

In this paper, the wave propagation method and the nonlocal elasticity theory are utilized to analyze the vibration, wave power transmission and reflection in multi-cracked Euler-Bernoulli nanobeams. This aim is pursued by deriving the propagation, reflection and transmission matrices and comparing the natural frequencies obtained by these matrices with the available results in the literature. Then, the nonlocal and crack-severity effects on the natural frequencies are presented for some combinations of the boundary conditions. Finally, the effects of nonlocal and crack-severity parameters on the reflected and transmitted power of a wave incident upon a crack location are studied in details for cracked nanobeams. The results obtained via the reflection and transmission matrices will provide valuable insights into the subject of wave power reflection and transmission analysis in nanoscale structures for the future. The computer coding of the proposed method is much easier than the classical vibration analysis methods for similar analyses which makes it more appropriate in implementation. [ABSTRACT FROM AUTHOR]

In this paper, the wave propagation technique is developed for analyzing the wave power reflection in circular annular nanoplates. Firstly, the propagation and reflection matrices are derived for circular annular nanoplates. Then, the obtained natural frequencies by these matrices are compared with the available literature. A set of natural frequency results is provided in a practical range of small scale for all nine possible combinations of classical boundary conditions. Finally, the effect of small scale on the reflected power of an incident wave upon different boundary conditions is investigated in details for circular annular nanoplates. The obtained hints via these matrices are valuable for future works correlated with wave power reflection and transmission in nanoscale structures. [ABSTRACT FROM AUTHOR]

Thermal energy for water and space heating can be trapped using flat plate solar collectors (FPSC). Several techniques, such as using a polymer as the collector material, nanofluid as the heat transfer fluid, and phase change material (PCM), have been proposed to enhance the thermal performance of the FPSC. The present paper concentrates on utilizing solar trackers (dual and single axis) as an enhancement device to improve the performance of the FPSC. For the single-axis trackers, various tracking orientations such as East-West (EW), North-South (NS), Inclined East-West (IEW), and Vertical-axis (V) are taken into consideration. The considered locations are in the latitude range from 20 to 70°N, hence spread across the African, Asian, European, and North American continents. Unlike prior literature, the more accurate Perez diffuse model with the hourly weather data are utilized in this study. The system performance is assessed and ranked in terms of useful energy from the collector and economic indicators, unlike the previous studies with no economic feasibility analysis as the key practical point for decision making. The study aims to provide a comprehensive outlook for engineers, designers, installers, and policymakers in the adoption of FPSC incorporated with various dual and single-axis trackers in the northern hemisphere. [ABSTRACT FROM AUTHOR]

In this paper, the effect of latitude on the performance of different solar trackers is examined. The hourly solar radiation data of different locations around Europe and Africa measured on a horizontal surface is collected and utilized. Widely validated Perez anisotropic model is used to predict the diffuse component of the solar radiation on an inclined surface. Different solar trackers namely, Full/dual-axis, East–West (EW), North–South (NS), Inclined East–West (IEW), and Vertical-axis (V) trackers are considered in calculating the available solar potential of the locations. The performance of the solar trackers in terms of the energy gain is ranked according to the area location latitudes. The results show that the tracking performance is highly dependent on the locations, thus changes with the latitude. The percentage variation among the implemented one-axis tracking options relative to dual-axis trackers ranges from 0.42% to 23.4%. Overall, the increase in the energy gain of dual-axis trackers compared to the optimal fixed panel for the locations varies from 17.72% to 31.23%, thus emphasizes the importance of solar trackers. Finally, the study is expected to aid designers in the selection and installation of appropriate solar trackers in the regions. [ABSTRACT FROM AUTHOR]

Wave propagation is one of the famous approaches for analyzing the vibration of solid structures. Literature reviews show that most bodies analyzed with this approach are one-dimensional waveguide structures. In this paper, the free vibration of annular circular and sectorial membranes are analyzed using the wave propagation approach. Firstly, the propagation and reflection matrices are derived. Then, a concise and systematic approach for obtaining the natural frequencies is presented which can be a reference for future studies. The solution obtained by this method is exactly the same as those derived by the classical method. [ABSTRACT FROM AUTHOR]

It is well known that anode and cathode pressures and cell temperature are the effective parameters in performance of Direct Methanol Fuel Cell (DMFC). In the present study, the genetic algorithm as one of the most powerful optimization tools is applied to determine operating conditions which result in the maximum power density of a DMFC. A quasi-two-dimensional, isothermal model is presented to determine maximum power of a DMFC. For validation of this model, the results of the model are compared to experimental results and shown to be in good agreement with them. [ABSTRACT FROM AUTHOR]

Crohn's disease (CD) is associated with bone loss and increased fracture risk. TX-Analyzer™ is a new fractal-based technique to evaluate bone microarchitecture based on conventional radiographs. The aim of the present study was to evaluate the TX-Analyzer™ of the thoracic and lumbar spine in CD patients and healthy controls (CO) and to correlate the parameters to standard imaging techniques. 39 CD patients and 39 age- and sex-matched CO were analyzed. Demographic parameters were comparable between CD and CO. Bone structure value (BSV), bone variance value (BVV) and bone entropy value (BEV) were measured at the vertebral bodies of T7 to L4 out of lateral radiographs. Bone mineral density (BMD) and trabecular bone score (TBS) by dual energy X-ray absorptiometry (DXA) were compared to TX parameters. BSV and BVV of the thoracic spine of CD were higher compared to controls, with no difference in BEV. Patients were further divided into subgroups according to the presence of a history of glucocorticoid treatment, disease duration > 15 years and bowel resection. BEV was significantly lower in CD patients with these prevalent risk factors, with no differences in BMD at all sites. Additionally, TBS was reduced in patients with a history of glucocorticoid treatment. Despite a not severely pronounced bone loss in this population, impaired bone quality in CD patients with well-known risk factors for systemic bone loss was assessed by TX-Analyzer™. [ABSTRACT FROM AUTHOR]