فصلنامه مدل سازی در مهندسی
پیاپی 43 (زمستان 1394)

In this paper, the propagation of ultrasonic guided wave in the isotropic single-layer and multi-layer plate with the assumption that layers are fully connected to each other and top and bottom surfaces of plate are free stress, are investigated and the dispersion curves, including diagrams of frequency spectrum, phase velocity and group velocity for single-layer and multi-layer can be extracted. The next, using the obtained dispersion curves how to excitation a specific mode at a probe frequency for single-layer plate and multi-layer plate using the phased array technique to be paid and graphs of emission angle versus frequency for single-layer plate and multi-layer plate are plotted and results are compared with each other.

Domed roofs are the masterwork of mechanical engineering because of building heat load reduction in Iran. Received ‎solar radiation on a domed and flat roof has been compared with each other experimentally and numerically in this ‎research. Data measurements have been done on 15th day of each month from sunrise to sunset with one hour intervals. ‎A 1/10 scaled model of a mosque in Yazd has been used for experimental investigation. Data obtained on 13 point on ‎this model. The dome has three circuits named A, B and C, with a horizontal angle of 30o, 50o and 90o respectively. ‎Four points on every circuit in the four main directions are considered. Results show that the total received solar ‎radiation (per unite area of dome base) for flat roof is higher than domed roof. The maximum solar radiation received ‎on the East and South direction for warm and cold seasons respectively for domed roof. The minimum solar radiation ‎received on the North direction during a year. The maximum solar radiation on the East direction is received in the ‎early morning, while the West has its maximum in the late afternoon. In addition the maximum received solar ‎radiation for the flat roof and the South direction of the dome occur at approximately noon, while the maximum ‎received solar radiation tends to be happened before noon for the North direction.‎

In this paper, the effect of radii ratio and material exponent parameters on the pattern of yielding initiation for a rotating hollow FGM cylinder is analytically investigated. The analysis is based on small deformation theory in plane-strain state and Tresca criterion has been used for yielding investigating. Assuming power-law functions for Young's modulus, density and yield stress, equilibrium equation has been analytically solved. Comparing with homogeneous cylinder and also the special case of zero exponents of density and yield stress, the presented analysis has been validated. Then the effect of radii ratio and exponent parameters on the order of stress components and yielding initiation is investigated. The results show that density and yield stress variation may have considerable effect on yielding of rotating FGM cylinder. To best knowledge of authors, the effect of density and yield stress variation and radii ratio on the yielding initiation pattern of rotating hollow FGM cylinder was not studied in the previously published researches.

The surface stress effects on electro-thermo-mechanical linear vibration of triple-walled boron nitride nano tube embedded in an elastic medium conveying fluid flow using nonlocal Euler-Bernoulli beam theory for clamped-clamped boundary condition are investigated. The kinematic energy of fluid and nano tube, strain energy, the external work done due to the van der Waals forces, elastic medium, viscosity of fluid for nano tube, centripetal force of fluid for the inner layer of nano tube are obtained. Using energy method and applying Hamilton’s principle, the governing equations of motion for triple-walled boron nitride nano tube under surface stress effects are derived. To solve these equations, the differential quadrature method is used. Their research results show that the dimensionless natural frequency decreases with an increase in fluid velocity. Also the buckling phenomenon is occurred, when the dimensionless natural frequency is equal to zero, which the system loses its stability due to the divergence. It can be seen that the stability range increases with increasing the thickness and length to diameter due to surface stresses. This study may be useful to accurately measure the vibration characteristics of nanotubes conveying fluid flow and to design nanofluidic devices for detecting blood Glucose.

In this paper, steady heat transfer in multi-layer composite pin fins has been investigated. The appropriate analytical solution for heat conduction in pin fins under the all common thermal boundary conditions has been introduced. The efficiency of pin fins in different boundary conditions of fin's tip has been compared. Placement angle of fibers in each layer as well as a composite material, consisting of fiber and matrix, can be changed layer by layer. In each layer the effects of layer's arrangement based on composite material and fiber's angle has been investigated in details. The impact of environmental and geometric parameters affecting the efficiency of the fin such as heat transfer coefficient, the conductivity of the material used as a filler and fiber, length to diameter ratio of fin thoroughly studied, and the related charts are plotted.

Having knowledge about the personality of social network members can improve the social network services. This knowledge also can be applied to improve the interactions of social network members. The personality characteristics of social network members can be estimated via personality questionnaires. However, usually people are not interested in filling these questionnaires because it may violate their privacy. So, their personality characteristics should be estimated implicitly. In previous researches some methods have been presented to estimate the personality of social network members implicitly. However, these methods require the users’ profile and contextual information that is not accessible in most of the cases. In this paper, a model is presented which can estimate the extraversion degree of social network members implicitly using information extracted from the graph structure around each member. To develop this model, first, a dataset of social network members are collected. Then, by applying genetic programming and M5 regression on this dataset, some relations are extracted to estimate the extraversion degree of each member. The results of our model show high accuracy. In addition, the model extracted by genetic programming has higher accuracy and lower computational complexity compared to M5 regression.

In today's world, using the renewable energies is the most important solution for the survival of human society. This necessity has taken on a more serious in 1970's decade when the lake of fossil fuels happened. Three categories: lack of energy resources, population growth and widespread use of energy in all of human society requires us to use new energies. One of the applications of solar energy is the usage in heating and cooling systems. This paper estimates the demand for hot water and taking in to account the geographical designed and economic parameter to simulate an appropriate model of solar water heaters and after the economic analysis of the issue, such as energy saving and cash flow analysis by SAM software, we review the incentive and their impact on the profitability of the project. Research continues to determine the optical angles of the collector position, and we can see that the angles 32 and 170 degrees are the best angles to position the collector in the desired location.

In this paper, a novel MESFET with an undoped region (DS-UR) and drain side-double recessed 4H-SiC metal semiconductor field effect transistor (MESFET) is presented. The key idea in this work is to modify the charge concentration and electric field distribution to improving breakdown voltage (VBR) and the maximum output power density (Pmax). The charge distribution plays an important role in determining device characteristics. Two-dimensional and two-carrier device simulation demonstrate that the VBR and Pmax are improved about 57% and 50% compared to source side-double recessed 4H-SiC MESFET (SS) structure, respectively which are important for high power applications.

Nowadays the use of switching converter systems are increasing. One of these converters is resonant converter which is more efficient than other converters. In this paper, the parallel resonant converter (PRC) is used. Because of environmental conditions, there is probably a variation in the resonance tank parameters values in resonant circuits. These variations occur due to variation in the resonance circuit impedance. The output voltage is strongly dependent on variation of the output load and the resonance tank parameters. Changing the resonance parameters will directly affect the output voltage. By using the mathematical relations, values of the resonance tank frequency and proper switching frequency are obtained. With partial changes in obtained frequency, output voltage is fixed. The main advantages of this design are recognizing proper resonance tank parameters, resonance frequency and switching frequency which depends on each circuit with unknown values. In proper searching method, there is more accurate regulation of obtained switching frequency. Other advantages include simple control algorithm which can be assembled with simple processor system. Experimental and simulation results presented in this paper show the benefits of proposed method.

Dynamic compaction (DC) technique with tamping is one of the soil improvement methods. Nowadays, there is a considerable interest in DC due to its advantages among the methods of soil improvement. In the present study, fuzzy logic and Sugeno inference system have been used to evaluate the influence of parameters involved in dynamic compaction over the depth of improvement. Input variables are used for loose granular soils and include tamper weight, height of tamping, tamper radius, print spacing, number of drops and soil layer geotechnical properties and four improvement depth of relative degree as output variables. Input and output data are extracted from the reliable scientific literature. Following development of the fuzzy model, the results of this study has been validated with the results of valid Dynamic Compaction operation in the world. Then as a case study with using the prepared model, Dynamic Compaction Operation in Shahid Rajaee Port in Iran has been analyzed. The results indicate that the effect of tamper weight is greater than the height of tamping and print spacing is in third importance grade. The interaction between tamper weight and dropping height plays the greatest role in the design procedures. Studies show that the optimal tamper radius for most compaction patterns with medium to high applied energies is equal 1.5 to 2 meters, the optimal dropping numbers are equal 25 and optimal print spacing is equal 6 to 7 meters so using this pattern leads to obtain maximum improvement depth.