جستجوی مقالات مرتبط با کلیدواژه « المان محدود » در نشریات گروه « برق »

In this paper, a novel structure of a axial flux switching machines for use in wind speed turbines at low speeds has been proposed, which in addition to the previous advantages, has a simple and economical design for the production of this type of machines. In this proposed machine, the magnets are placed on the surface of stator, and the three-phase winding is located in the space between the magnets. After designing according to the criteria like increasing electromotive force, reducing the cogging torque and reducing the total harmonic distortion, using the design of experiments and the surface response method combined with the finite element software, the appropriate dimensions are selected and the machine is optimized. To test the design accuracy, a prototype model is also made.

In this paper, in order to improve the cogging torque in the radial flux magnetic gear with integer gear ratio, the axial pole skew technique has been used. This design reduces cogging torque by shaping the distribution of the magnetic field in the air gap of inner rotor in the axial and radial directions. In order to compare the proposed method, the optimal design of radial shaping in inner high speed rotor is also investigated. The introduced methods have been optimized using genetic algorithm in order to obtain the maximum torque density and the minimum cogging torque. The results are compared using 3-D finite element method and the superiority of the axial shaping method is shown in it.

Recently, the most common tool to compensate for various organ defects is tissue transplantation with several problems involved. These problems have led to the rapid growth of tissue engineering with a designed tissue approach or organ substitute in the last decade. For this purpose, it is important to determine the tissue mechanical properties. In this study, to obtain the cartilage structural parameters, isotropic Pro-Hyper-Viscoelastic Mooney-Rivlin and Neo-Hooke are used. These model coefficients are obtained by reverse engineering methods and using a coupled finite element-optimization algorithm utilized unconfined stress relaxation tests with root-mean-square error (RMSE)) less than 0.036, 0.033 for Neo-Hooke and Mooney-Rivlin respectively. Using Neo-Hooke and Mooney-Rivlin models, the modulus of elasticity was 0.47 MPa and 0.44 MPa, and the shear modulus was 0.188 MPa and 0.184 MPa, respectively. The predicted tissue mechanical response obtained by the finite element model showed that the Mooney-Rivlin model is more consistent with the stress relaxation experiments than Neo-Hooke one. The results showed that during the stress relaxation test, by applying a compressing load on the sample, initially the fluid pressurization in the matrix pores has the most contribution in the load-bearing (total stress). When time elapses, the fluid contribution in the load-bearing decreases, and the solid matrix contribution increases.

In this paper the design and three dimensions (3D) simulation of a photonic crystal (PC) pressure sensor is presented. The device is based on a 2D PC slab of PbMoO4. The simulations are based on finite element method (FEM) and finite-difference time-domain (FDTD) method and are done using CST STUDIO SUITE software. The sensitivity of the proposed sensor is calculated by considering the deformation and also refractive index variation factors. The numerical results show that when a pressure is applied, both factors cause to a reduction in the resonant wavelength of the transmission spectrum. It has been shown that the relationship between the applied pressure and the shift in the resonant wavelength of the cavity is linear. Based on the simulation results, the quality factor of the resonant peak of the transmission spectrum and the sensitivity of the proposed sensor are  -2.858 nm/GPa and 1040 , respectively.

The majority of the power transformers failures are caused by the thermal stresses under abnormal operating conditions, such as harmonic loads. Therefore, it is of great interest to determine the temperature distribution inside the power transformers. In this paper, a new thermal equivalent circuit is presented by which the temperature in different regions of the transformer is estimated under harmonic loads. Also, the three-dimensional Finite Element (FE) Model of the power transformer is developed to calculate the power losses in each part of the transformer that are considered as the heat sources in the proposed equivalent circuit. The computed hotspot and average oil temperatures are compared with those obtained from IEEE Std C57.91 method, thereby the accuracy of the proposed method for calculating the temperature rise due to harmonic loads, is investigated. Finally, derating of the power transformer is discussed under harmonic loads.

Electromagnetic Compatibility (EMC) analysis around High Voltage (HV) cables is one of the important research problems, which several standards are published. In this paper, field simulation of HV cable space based on finite element method (FEM) is proposed to identify cable shielding effectiveness for a permitted distance of HV cable and communication cable proximity. FEM simulation method is performed for four situations including shielded cable or simple cable (cable with or without shield) for each type of HV and communication cable in losses environment. As authors are aware there is no research report for the amount of proximity distance for HV cable and communication cable in losses spaces in spite of partial approach in cabling route. Finally, simulation result is evaluated by comparison with ICNIRP standard constraints.FEM simulation results are validated by FDM based simulation software(CST); Also electromagnetic field measurement for one-core medium voltage voltage labratory. Both of them illustrates the authentication of FEM modeling of and simulation results of the investigation.

Severe saturation of the magnetic core is the most influential factor in ferroresonance that leads to distorted currents and voltages. , modeling the nonlinear behavior of the magnetic core is the most important challenge in ferroresonance study. In this paper, finite element method in conjunction with the inverse Jiles-Atherton (JA) hysteresis model of the steel core, is employed for modeling of a single-phase transformer accurately. Then, ferroresonance is studied by inserting different capacitors in series with the unloaded transformer, and the corresponding variation of copper losses and iron losses are obtained and discussed. Ferroresonance affects the shape of the hysteresis loop that necessitates the retuning of the parameters of the JA hysteresis model. The numerical results agree well with the experimental ones.

Today, piezoelectric micro-beams are widely used in atomic and friction force microscopies, thermal scanning microscopy, and biomass measurement due to their flexible structure, sensitivity to molecular and atomic forces, and very fast response. Due to the small displacements of these micro-beams, their complete vibrating analysis and studying their behavior can play a key role in their measurement precision and optimal design. For this reason, first the numerical Runge-Kutta method (based on the discontinuous beam model) as well as the finite element method was employed to solve the differential equation governing the piezoelectric micro-beams motion by considering geometrical discontinuities. Then, the sensitivity analysis was conducted to determine the effects of each micro-beams geometric parameter on the main parameters of the vibratory motion. The sensitivity analysis was conducted using Sobol method which is based on the output data variance. According to the obtained results, both the discontinuous cantilever model and the finite element model exhibited acceptable accuracy in calculating the natural frequency as well as the resonance amplitude of this type of micro-beams. Also, the results obtained from the sensitivity analysis showed that the first mode of the vibratory MC motion was the most suitable mode for nanoparticle surface topography.

With respect to the height to width ratio, the concrete shear walls are divided into two categories of cantilever and short shear walls. Cantilever shear walls with the aspect ratio greater than 2 demonstrate flexural behavior while short shear walls with the aspect ratio smaller than to 2 exhibit shear behavior. In this study the behavior of short reinforced concrete shear walls are investigated using the nonlinear finite element software ATENA 3D. The failure mode and the ultimate and residual shear resistance of the short shear walls, as well as the affecting parameters such as the magnitude of the axial force, the compression strength of concrete and yield strength of reinforcements are studied. It is resulted that the magnitude of axial forces has significance effect on the ductile behavior of short shear walls.

In this Article, no-load magnetic flux density and Back-EMF of the redial flux Air-Cored permanent magnet electrical machine (RFAMP) is provided with meddle stator using the subdomain analysis. First, Analytical relationships of no-load magnetic flux density and Back-EMF of this machine are presented with maxwell equations and, then, these relationships are validated by finite element numerical results in Maxwell 16.02 software. This comparison shows that the difference between analytical relations and finite element results is 3% about. In this article, to calculate the Back-EMF resulting from the permanent magnet, all the components of winding conductor density distribution are used. It should be noted that in the investigations relating to this case, only the first radial component of the magnetic flux density is used. It is also shown that magnet width coefficient plays an essential role in the non- sinusoidal of the no-load magnetic flux density in the stator nominal radius and reduction of the number of pairs of poles in the magnetic saturation of yokes and induced voltage reduction. It is also shown that increasing the length of the air gap can have the greatest role in zero harmonic distortion of Back-EMF.

As the need for seismic designing of the earthquake resistant structures increases, numerous laboratory and numerical studies are being done to estimate the nonlinear response of these structures. With respect to the height to width ratio, the concrete shear walls are divided into two categories of cantilever and short shear walls. Cantilever shear walls with the aspect ratio greater than 2 demonstrate flexural behavior while short shear walls with the aspect ratio smaller than to 2 exhibit shear behavior. In this study the behavior of short reinforced concrete shear walls are investigated using the nonlinear finite element software ATENA 3D. The failure mode and the ultimate and residual shear resistance of the short shear walls, as well as the affecting parameters such as concentration of longitudinal and transverse bars at the edges of the wall, change of the horizontal and vertical bars spacing and the use of diagonal bars are studied. It is revealed that unlike the cantilever walls, the concentration of the bars at the edges have no influence on the increasing of ductility.

In this article, a radial magnetic flux density and flux-linkage of the radial flux Air-Cored permanent magnet electrical machine (RFAMP) is provided with double-sided rotor which can be calculated analytically using the sub-domain analysis. First, Analytical relationships of on load magnetic flux density and flux-linkage of this machine are presented with poisson equations and, then, these relationships are validated by finite element of numerical results in Maxwell 16.02 software. Comparisons show that the difference between fundamental components of radial magnetic flux density and flux-linkage of analytical relations and that of finite element results is less than 3%. Also, It is shown that in this machine type, even harmonics appear and the radial components of the magnetic flux density is not symmetrical, unit half cycle and Lack of attention to this subject in the design of the machine can cause inner or outer yoke magnetic saturation. In this article, to calculate the flux linkage resulting from the armature reaction, all the components of winding conductor density distribution are utilized and in the calculation of the flux linkage, all radial components of the magnetic flux density are used. In some relevant references, only the first radial component of the magnetic flux density and the second component of winding conductor are used and the other are ignored. In comparison with some related references the linkage flux and RFAPM machine inductance have been increased about 21%, that the number is significant in the study of magnetic saturation yokes. It is worth noting that the study of the comparative results has only been up to 17th harmonics and that the higher harmonics can adapt better to have the finite element results.

Dynamic stress intensity factor determination on crack tip under impact loading is widely investigated. The history of impact loading in analytical researches is considered to be step function but experimental tests show that in impact loading, a small time is needed to the loading rise from zero to ultimate amount. This interval time is called rise time. In this research, Firstly, Dynamic stress intensity factor for a semi- infinite crack on a plate under impact loading is determined analytically but the history of loading is considered as a ramp function. Then a comparison between the analytical solution in this paper and the last results and also with finite element is done. Finally, the experimental method for changing the rise time on impact loading is presented and the effect of it in dynamic stress intensity factor is researched.