finite element method

Semiconductor quantum structures are one of the advanced sources in light production, and applying impurities to them causes changes in their electronic and electro-optical properties, so investigating their properties is of particular importance. The title of a new research subject with many applications has attracted the attention of scientists and industrialists. In this study, the electronic properties of a spherical quantum dot made of gallium arsenide and two spherical quantum dots made of indium arsenide inside the gallium arsenide quantum sphere have been investigated. First Schrödinger's equation was investigated in the mentioned structures by using finite element method and effective mass approximation. The obtained results such as eigenfunctions and energy eigenvalues and other physical properties have been compared with the results obtained from previous similar works. Then, the effect of impurities on the electronic properties by using the self-consistent Poisson-Schrödinger equation, has been obtained and compared with the results of solving the Schrödinger equation in boundaries conditions. The software used in this review is Comsol. The obtained results indicate that the effect of impurity and the radii of the internal nanostructures on the electronic properties of the nanostructure are significant. As a result, by changing the mentioned parameters, it is possible to calculate the energy difference between the first excited state and the ground state. Results show that according to energy difference, it is possible to design infrared detectors with a relatively wide range.

The bottom of floats and flying boat should be strong against impact loads such as low velocity impact despite being light weight. In this article, we will investigate the dynamic behavior of the structure of meta-sandwich panels with different cores under low velocity impact loading using analytical and numerical methods. Four different core samples including honeycomb, auxetic, square and triangular made of polylactic acid under impact, a hemispherical steel projectile with a radius of 15 mm with fixed boundary conditions have been investigated. The interaction between the impactor and the meta-sandwich panel has been modeled using a two-degree-of-freedom mass and spring system using finite element software such as ANSYS Workbench. The maximum impact contact force is also analytically and numerically compared with each other and the results show a good match between these two methods. Considering the importance of the effective parameters in the dynamic response of the sandwich panel structure, the effect of some parameters, including the velocity and mass of the impactor, on the maximum contact force, the maximum displacement and the maximum Von Mises stress were numerically investigated and evaluated. The results show that impactor velocity effects are a more important factor in increasing and decreasing contact force, displacement, Von Mises stress and impact time compared to impactor mass. In the end, by comparing the different cores presented in this article, the auxetic core is introduced as the best core among other cores.

In addition to aerodynamic pressures, the wing of a flying boat is also subjected to combined hydrodynamic forces from the ski side (caused by landing and takeoff on the sea). In the asymmetric seating mode, the bending moment applied to the wing spars is one of the most important loading modes in the design of the wing spar structure. In the composite wing, the most critical part is the connection of the flange to the spar. In the finite element modeling of the real composite wing, which consists of a number of spars, ribs and other members, the connection of the flange to the web is done in a simple way without modeling the details of the connection.In this research, the finite element analysis of the wing spars of a flying boat with cross section I with different geometries under different types of loading (according to the standard) for different functional modes is performed. then, based on the results of the numerical analysis, general and simple design rules and guidelines are presented regarding how to connect the flange to the web of these spars.At the end, in order to validate the results of the finite element, an experimental sample has been built and tested, and the comparison of the results shows a very good match.

In this article, the production of high-quality thin-layer graphene using the liquid-phase exfoliation method has been investigated. The step probe was designed using COMSOL Multiphysics. The diameter of the reaction vessel and the distance of the probe tip from the bottom of the vessel were studied in relation to graphene production. The diameters of the containers used were 60 mm, 75 mm, and 85 mm, while the distance of the probe tip from the bottom of the container varied from 20 mm to 50 mm. Initially, the effect of acoustic pressure in each container was simulated. The highest acoustic pressure difference obtained in the simulation was 7.74×10⁷ Pa for a container with a 60 mm diameter and a probe-to-bottom distance of 50 mm. The results of ultraviolet-visible spectroscopy of the samples indicated the presence of a higher amount of graphene, with a peak at 266 nm. Using the Beer-Lambert law, the concentration of the produced graphene was estimated to be approximately 0.13 g/L. SEM and TEM analyses confirmed the production of few-layer graphene with good quality. Finally, Raman spectroscopy was used for complementary characterization of the samples. The I₂D/I_G ratio was found to be approximately 1.02, confirming the successful production of few-layer graphene in this study.

Inductively coupled plasma (ICP) is widely used in applications such as material processing and microelectronic device fabrication. However, their electromagnetic properties have not been fully investigated. Therefore, we performed time-dependent (2D) finite element simulations in this study. We have made profiles of magnetic field, electron density, and temperature distribution for argon gas by applying variable power of 750 W, 950 W, 1100 W and 1200 W. In a comparative study, the effect of input power change on plasma parameters was investigated and the relevant results were shown. It was shown that with increasing power, the electron density and temperature in the working chamber increase. In the following, with a constant power of 1200 watts as an optimized power, the effect of changing the position of the coils and reducing the thickness of the dielectric layer on the magnetic field flux, electron density and temperature was investigated and we showed that by changing the position of the coils, the magnetic field flux, the electron density and the temperature of the reactor do not change. However, with the decrease in the thickness of the dielectric layer, the magnetic field flux, the electron density, and the temperature decrease to an insignificant amount.

The double-spherical harmonics method (DPN) is a common approximation in the study of the neutron transport equation in reactor physics problems. Inside a reactor near points where strong discontinuities in material properties occur, such as bare boundaries or areas near strong absorbers, there is usually greater anisotropy in the angular distribution of neutron flux. A more appropriate description of the angular flux behavior at such points requires the use of methods such as DPN, which utilize separate expansions for different directions of neutron motion instead of using a single expansion for all directions, as in the PN method. In this paper, the multigroup, one-dimensional neutron transport equation in the Cartesian coordinate system is solved using the DP1 approximation. To do this, first the multigroup DP1 equations and the corresponding boundary conditions are derived, then they are written in the form of multigroup neutron diffusion equations, which are here called the simplified-DP1 or SDP1 equations. The finite element method is then used to numerically solve the SDP1 equations. The results of the proposed method are discussed for several different test problems in comparison with the P3 method.

Cancer is a significant public health problem worldwide and one of the leading causes of death worldwide. Breast cancer and fibroids are common among women, and if they are diagnosed on time, recovery and treatment will increase significantly.
In this article, breast cysts are diagnosed based on the surface temperature characteristic of breast tissue. For this purpose, the temperature characteristics of a breast with a cyst have been evaluated. Heat transfer inside the breast is modeled by Penne’s bio-heat equation and solved by the finite element method. In this study, due to the difference in the dielectric properties of healthy and tumor breast tissue, the temperature distribution on the surface of the breast with a cyst of different sizes was determined. For this purpose, parameters such as temperature and SAR levels were examined and evaluated. The results show that with a similar amount of total energy for electromagnetic waves, the temperature level of the tissue exposed to the waves remains constant regardless of the input power combination. Also, results show that as the size of the tumor increases, the effect of radiation on breast tissue increases, and therefore the malignant area can be distinguished from the healthy area of breast tissue. The results show the difference in the surface temperature characteristics of the normal breast and breast with a cyst of various sizes, which can be a criterion in diagnosing the complication of breast cysts compared to normal breasts.

In designing the fuel rod, having a reliable prediction of fuel performance is of high importance in order to comply with safety principles. Various computer codes have been provided for this purpose. Each of these codes uses different mechanical models, numerical and analytical methods. Accordingly, the purpose of the present work is to develop Fortran computer software for mechanical and thermal analysis of fuel rods using numerical methods, especially applying the principle of virtual work in mechanical analysis of fuel rods in steady-state conditions. The finite element method is used to solve the equations. The mechanical analysis includes phenomena such as swelling and fuel density and clad creep. Through these phenomena and simultaneous performance of mechanical and thermal analysis, fuel-clad interaction, stress and strain rate in fuel and clad, fuel center temperature, oxide layer thickness, fuel, and clad temperature distribution during operation is obtained by the code. The results of the code are compared with the results of the analytical method which are available in other research works. Finally, for the VVER1000 reactor, mechanical and thermal analysis of the fuel rod was performed over a 1600-day interval. According to the simulation, the fuel-clad interaction occurs after 1250 days.

A Magnetic Anomaly Detector (MAD) is a passive system that is used to detect vague ferromagnetic objects in the environment by detecting anomalies in the Earth's magnetic field. Detection of magnetic anomalies is an important issue in some projects, from geological surveillance to military identification. MAD sensors detect local disturbances in the magnetic field of earth, which can be used to detect the presence of hidden or immersive objects, such as submarines, land mines or naval mines and estimate their location. It is impossible to detect the acoustically quiet submarines by detectors, so it is necessary to use magnetic anomaly detection systems. In this study, the existing systems were examined and then the mechanical structure of an airborne MAD system was redesigned. In next step, the stress distribution of the designed system was analyzed. The stress analysis was performed by finite element method (FEM) using ABAQUS software. The results showed that according to the stress distribution, the maximum value of the stress for the set of parts is 88.7 MPa at acceleration 0.2 g, which is actually much less than the yield stress of the used material. As a result, there is no permanent deformation in any of the components of the system.

In this paper, we have studied the electronic structure of few two dimensional semiconducting nano-systems by suing three numerical methods meshless, finite element and finite difference. These methods .have been used to solve the two dimensional stationary Schrodinger equation w and the results have been compared. In order to solve the applied problems in the computational semiconducting quantum electronics, it is usually needed to solve the two dimensional stationary Schrodinger equation which have special numerical complexities. Evaluation of the energy eigenvalues is a challenging problem in this field of study. Here, by applying the methods on five applied examples we have shown that the eigenvalues converge to the exact values from lower bound in the finite difference method and converge to the exact values from upper bound in the finite element method. Therefore, in general applied problems under research, that we have not analytic eigenvalues and solutions, we are confidently able to find the upper and lower bounds of the eigenvalues. Finally, we have shown that in the mentioned examples, the meshless method has maximum accuracy among the investigated methods.

Computer modeling for the design of inductors for different applications in the induction heating process often seems to be necessary to save costs caused by the trial and error. In this paper, the effects of the number of loops in the induction heating process with the numerical solution of the Maxwell equations have been investigated using finite element method (FEM) and the COMSOL MULTIPHYSICS software package in three dimensions. Therefore, considering the effect of the number of coil turns on the amount and pattern of heat produced in the workpiece for special applications in the industry and technology is critical. This is because the number of coil turns is one of the important parameters in the design of induction heating systems. At first, a single turn coil is simulated in a three-dimensional model; then multi-turn coils with the turns number 2, 3, and 4 have been considered. The voltage of 200 V with the frequency of 1 KHz has been used, as applied to the coil, to serve as the source of electromagnetic fields. The results of numerical calculations show that the number of coil turns can have a significant effect on quantities such as distribution and intensity of magnetic flux density, eddy currents density in the workpiece, and the volume of heat produced in the coil and workpiece.

The distribution of the magnetized magnitudes of the flowing nuclear spins has a key role to evaluate the radiofrequency pulses used in the magnetic resonance angiography (MRA). In this study, a finite difference method is used to solve Bloch equations for the flowing nuclear spins during and after a 90° rectangular selective pulse which is important for optimization of the pulse sequence. The results of the simulation indicate that the magnitudes are deformed due to the flowing nuclear spins, while their velocity is increased. The maximum variations are created on the transverse magnitudes namely, Mx and My. The symmetry on these profiles disappear by increasing the velocity. In contrast, no variation on the longitudinal magnitude namely Mz is observed, except a shift on the velocity direction. The sensitivity of these profiles at low velocities for the rectangular selective pulse is more than that of the sinc type, which probably it may be used for characterizing the capillary space. In general, one may obtain the distribution of magnitudes for pulses with various flip angles, as well as, the combination of different pulses. The results may be employed to improve mapping indices in the MRA as well as assessment pulse sequences on the flowing nuclear spins.

In this work, eigen modes and eigen frequencies of the body (sound board and sound box) of the setar, a persian stringed musical instrument, are studied. Eigen modes of the sound board and the whole body, neglecting the holes, are calculated independently and analyzed comparatively. This scheme of separate modal analyses for different parts of the setar will lead to the understanding of their individual roles in the overall output sound. In categorizing and assessment of sound quality of musical instruments, the study of characteristics of frequency response function (ERF) is important. In case of stringed musical instruments like setar, of the defining parameters are the first peak of FRF and its location. This first peak usually coincides with first air eigen frequency which in the present research occurs at about 377 Hz. Thus, all the other eigen modes like 588 Hz and 740 Hz, construct the rest of the FRF. Also, the effects of such as sound board thickness, wood material properties shape of sound box and other structural features of setar on two value of eigon frequencies can assessed. Furthermore, analysis of the aero-acoustic pressure contours and the eigen modes of the setar structure (sound board and box) and air allows the nature (air, structure or coupled air-structure) of a acoustic mode to be determined.

In this paper, a theoretical approach is proposed, in which spatial distribution of the strength of interplate coupling between two faces of strike-slip faults is investigated in detail through the inverse analysis of synthesized geodetic data. Synthesized (or available) geodetic data representing free surface movements is implemented to determine the solution of undertaken inverse problem that computes slippage vectors’ rates. Analytical approaches for treatment of faults in crustal deformation analysis involve some limitations. One important limitation of these methods is idealization of uniform dislocation on a rectangular fault plane in a uniform medium or half space. In fact, the real source is more complex than that supposed in these models and thus only the first-order aspects of the source characteristics can be evaluated from a uniform dislocation model. Isotropic and homogeneous material properties are the main assumptions of these methods. The Finite Element Method (FEM) on the other hand, allows easy treatment of complex boundary shape (interface zone) and internal variations of material properties. The FEM can simulate source geometry flexibly, and is also able to regard geological regimes and various layered structures. The standard equations of inverse problems offer a straightforward way for finding slippage vectors at two faces of the considered fault. One of the new aspects of the current study is evaluation of Green’s Operator Matrix (GOM) by means of FEM. This concept enables us to overcome all limitations of traditional inverse methods. In other words, the Green’s functions are not only functions of interface’s geometry, but are also functions of some other parameters like far-field boundary conditions, and geological structures (various material properties) which are not regarded in the traditional analytical inversion analysis. To implement fault sliding in a continuum-based FEM program, Split Node Technique (SNT) as a simple and efficient method is applied. This method does not increase the number of Degree Of Freedom (DOF) and the global stiffness matrix of system remains unchanged, which is the major advantage of this method. Furthermore, no net forces or moments are induced on the finite element mesh. This method is a direct approach and does not need any iteration, which is a common feature of other methods (e.g., contact problem techniques, or interface/joint elements). The initial idea of SNT for simple one-dimensional element is developed to 2D and 3D domains in the present research. How to find the Green’s functions by the FEM? By applying unit slippage vectors in each DOF of the interface nodes, we can determine corresponding component of the GOM. As other common inversion problems, singularity of coefficient matrix is the main problem. This problem particularly emerges if the number of DOFs is too large. The numerical procedure does not fail algorithmically, however it returns a set of slippage vectors that are wrong, even though direct substitution back into the original equations results in acceptable free-surface deformations. Singular Value Decomposition (SVD) diagnoses precisely what the problem is. In some cases, SVD will not only diagnose the problem, it will also solve it. The approach in current research is based on kinematic modeling of seismological problem. In other words, we only investigate fault movement, not causes of the occurred movement. In this research, both forward and inverse steps are considered to completely solve the problem. The forward step is performed by applying the slip along the fault’s faces and determining the displacement at the ground surface. This step is done using the FEM, whose results are compared with the analytical ones to verify the forward step. In the inverse solution on the other hand, our goal is to reach fault slip field using of surface displacement obtained from the first step as input data. Here, using this technique, 2D and 3D models of different types of strike-slip faults are presented in elastic mode for splitting purposes. The final step is to verify the inverse solution obtained for all models, from which the coupled zones of the considered faults are determined with acceptable accuracies.

Many earthquakes occur in Iran every year and some of these earthquakes cause loss of life and property. Consequently earthquake is one of challenging topics not only in Iran but also in other active tectonic regions in the world. Investigating the mechanism of earthquake as a natural disaster is the first and important step. To study earthquakes، different information such as geometry and behavior of active faults، as well as the mechanical properties of the earth’s upper most layers، are required. Geometric and rheology properties of earth’s layers as well as details of the contemporary strain، temperature and stress have increased significantly over the past decade. Furthermore thanks to availability of Global Navigation Systems (GNSS)، like GPS، modern space geodesy data processing and new tools like PS-InSAR that provide unforeseen spatial coverage of precise observations of the Earth’s surface deformations. The only processing approach that composes all geometrical and physical complexities is Finite Element Modeling (FEM). The first step in using FEM is to examine its capabilities. In this paper deformation field of a dip slip (normal and reverse) and a strike slip fault (left lateral) in linear homogenous isotropic elastic medium by means of 2D and 3D Finite Element Method (FEM) has been investigated. By means of FEM، the complexity of mechanism of a fault related disaster for determination of precise Green operator and solution of a reverse problem for extraction of fault slip rate can be modeled. As a sample، we apply contact elements and develop a frictionless fault surface and then deformation field of dip and strike slip faults for one meter of slip for each side of fault surface. Fault top lines for dip and strike slip faults are assumed to be on the ground. The dimensions of semi infinite medium for dip and strike slip faults are respectively 1000*500 and 1000*3000*120 km and these dimensions relative to fault’s dimensions are large. FEM deformation field are compared to Okada analytical model (an analytical model). The comparison shows that there is a good agreement between FEM and the analytical model. Our procedure can be summarized as follows: 1- 2D geometrical modeling of 90، 70 and 25 degree dip slip faults and 3D vertical strike slip fault. 2- Meshing of medium and assign material properties (linear homogenous isotropic elastic). 3- Apply boundary conditions by horizontal and vertical displacement vectors. 4- Determination of horizontal and vertical displacement vectors on the ground by means of FEM. 5- Comparison of analytical (Okada model) and FEM results and computation of Root Mean Square (RMS) as an efficiency test of results.