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Search Results: 1 - 10 of 713 matches for " FEM "
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Hemispherical DRA Antennas Mounted on or Embedded in Circular Cylindrical Surface forProducing Omnidirectional Radiation Pattern  [PDF]
Saber H. Zainud-Deen, Noha A. El-Shalaby, Kamal H. Awadalla
Int'l J. of Communications, Network and System Sciences (IJCNS) , 2011, DOI: 10.4236/ijcns.2011.49072
Abstract: The radiation characteristics of hemispherical DRA elements mounted on or embedded in a hollow circular cylindrical ground structure are investigated. The performance of the DRA array which operates at about 1.8 Ghz, is studied. Factors influencing the array performance, such as the number of elements and element spacing are explained. The perforated dielectric technique is used to design the array from a single dielectric sheet. The overall profile of the antenna can be significantly reduced. The radiation patterns with respect to the number of DRA elements are depicted.
Analysis of Power Transformer Insulation Design Using FEM
Tathagat Chakraborty,Akik Biswas,Sudha R.
International Journal of Soft Computing & Engineering , 2012,
Abstract: A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core and thus a varying magnetic field through the secondary winding. This varying magnetic field induces a varying electromotive force (EMF), or "voltage", in the secondary winding. This effect is called inductive coupling. If a load is connected to the secondary, current will flow in the secondary winding, and electrical energy will be transferred from the primary circuit through the transformer to the load. In an ideal transformer, the induced voltage in the secondary winding (Vs) is in proportion to the primary voltage (Vp) and is given by the ratio of the number of turns in the secondary (Ns) to the number of turns in the primary (Np) as follows: By appropriate selection of the ratio of turns, a transformer thus enables an alternating current (AC) voltage to be "stepped up" by making Ns greater than Np, or "stepped down" by making Ns less than Np. In the vast majority of transformers, the windings are coils wound around a ferromagnetic core, air-core transformers being a notable exception. Transformers range in size from a thumbnail-sized coupling transformer hidden inside a stage microphone to huge units weighing hundreds of tons used to interconnect portions of power grids. All operate on the same basic principles, although the range of designs is wide. While new technologies have eliminated the need for transformers in some electronic circuits, transformers are still found in nearly all electronic devices designed for household ("mains") voltage. Transformers are essential for high-voltage electric power transmission, which makes long-distance transmission economically practical. Finite element modeling (FEM) is a useful and commonly used tool in the solution of electromagnetic problems that arise in the design of power transformers. With approximately 30% of all transformer failures being due to insulation breakdown (due to excessive electrostatic stress), electrostatic FEM techniques are providing engineers with a valuable means of more accurately quantifying the electric stress in their designs. The validity of FEM, in general, always depends on having sound modeling assumptions and techniques. In addition, this problem introduced further complications that required carefully considered assumptions and treatments.
Reduction of Cogging Torque in Permanent Magnet Flux-Switching Machines  [PDF]
Yu Wang, Jianxin Shen, Zongxi Fang, Weizhong Fei
Journal of Electromagnetic Analysis and Applications (JEMAA) , 2009, DOI: 10.4236/jemaa.2009.11003
Abstract: Permanent magnet flux-switching machine (PMFSM) is a relatively new structure. Available literatures mainly focused on its general design procedure and performance analysis. In this paper, Finite Element Method (FEM) is taken to ana-lyze various design techniques to reduce the cogging torque in a prototype 12/10-pole PMFSM.
Extended Finite Element Modeling: Basic Review and Programming  [PDF]
Yazid Abdelaziz, K. Bendahane, A. Baraka
Engineering (ENG) , 2011, DOI: 10.4236/eng.2011.37085
Abstract: In this work, we have exposed a recent method for modeling crack growth without re-meshing. The main advantage of this method is its capability in modeling discontinuities independently, so the mesh is prepared without any considering the existence of discontinuities. The paper covers the formulation and implementation of XFEM, and discusses various aspects of the approach (enrichments functions, level set representation, numerical integration…). Numerical experiments show the effectiveness and robustness of the XFEM implementation.
Evaluation of Screw Reinforcement on Bearing Performance of Wood Depending on Screw Position  [PDF]
Satoru Murakami, Akihisa Kitamori, Kiho Jung, Ivon B. Hassel, Kohei Komatsu
Open Journal of Civil Engineering (OJCE) , 2012, DOI: 10.4236/ojce.2012.23021
Abstract: In this study, the reinforcement of wood by screws for partial compression perpendicular to the grain was studied. For the estimation of stiffness and strength, the reinforcement effect of screws depending on their position under the loading plate was evaluated by taking into account the internal displacement distribution of the wood. The finite element analysis (FEA) was used to investigate the internal displacement distribution of the wood. Then an approximate function that can be applied to various internal displacement distributions under loading plate was proposed. From the shear resistance mechanism between the screw and wood by taking their relative displacement distribution into consideration, the equations to estimate the initial stiffness and yield strength of the bearing performance of the wood reinforced by screws were derived. Then partial compression test was carried out for wood reinforced by screws with setting screw thread at various positions. The values obtained by the equations corresponded with the tendency of the experimental results. It was found that the screw reinforcement is more effective when its thread is positioned as much as distant from the contact surface.
Finite Element Method Study on the Squats Growth Simulation  [PDF]
Daren Peng, Rhys Jones
Applied Mathematics (AM) , 2013, DOI: 10.4236/am.2013.45A004

A simplified finite element analysis on the squats growth simulation and the effect different contact stresses has been presented. This analysis is based on the element removal study to simulate squat growth in a rail track under cyclic loading. The major principal stress (maximum principal stress failure theory) has been used as failure criteria. Evolution strategies are derived from the biological process of evolution, to find squats growth path solution to a complex rail/ wheel contact problem.

Finite Element Modeling of Seismic Response of Field Fabricated Liquefied Natural Gas (LNG) Spherical Storage Vessels  [PDF]
Oludele Adeyefa, Oluleke Oluwole
Engineering (ENG) , 2013, DOI: 10.4236/eng.2013.56065
Abstract: All real physical structures behave dynamically when subjected to loads or displacements. This research paper, therefore, presents seismic response of field fabricated liquefied natural gas spherical storage vessels using finite element analysis. The seismic analysis procedure used represents a practical approach in quantifying the response of spherical storage vessel with its content when it is subjected to seismic loading. In the finite element method approach, six degrees of freedom per node is used for legs/column of the spherical storage tanks. Lumped mass procedure is employed to determine system mass matrix of the structure. Computer programme code is developed for the resulting matrix equation form finite element analysis of the structure using FORTRAN 90 programming language. The modeling of the seismic load utilizes the ground acceleration curve of a site. From the results of the modal analysis, the system is uncoupled thereby gives way to the application of Newmark’s method. Newmark’s method as one of the widely used time-step approach for the seismic response is applied. The developed programme coding is validated with analytical results (P > 0.5). It shows that the approach in this research work can be successfully used in determine the stability of large spherical storage vessels against seismic loadings when base acceleration spectral of the site are known. This approach gives better results than the static-force approach which gives conservative results. While the approach used in this research treats seismic loads as time event, static-force approach assumed that the full ground force due to seismic motion is applied instantaneously.
Comparative Study of the Shielding Properties of Slotted Enclosure with Inner or Outer Excitations Using FEM  [PDF]
Baolin Nie, Pingan Du
Open Journal of Applied Sciences (OJAppS) , 2013, DOI: 10.4236/ojapps.2013.32B009
Abstract: Finite element method (FEM) is employed in this paper to conduct the comparative study of the shielding properties of enclosure with outer and inner excitations. Plane wave is adopted for the outer excitation case while coaxial cable is utilized to model the inner excitation source. Moreover, the resonance phenomena of slotted enclosure under different excitation are studied in detail. Finally, some conclusions with regard to the relationships and distinctions between the inner and outer excitations for the same enclosure are proposed.
Electromagnetic Study of MW-Class HTS Wind Turbine Generators  [PDF]
Yongchun Liang
Energy and Power Engineering (EPE) , 2013, DOI: 10.4236/epe.2013.54B072
Abstract: High temperature superconductor (HTS) technology enables a significant reduction in the size and weight of MW-class generators for direct-drive wind turbine systems and reduce the cost of clean energy relative to conventional copper an permanent-magnet-based generators and gearbox. Using MAXWELL, we studied MW class superconducting synchronous machines. By comparison the weight, we concluded that HTS wind turbine with rotor iron is the heaviest and HTS wind turbine without rotor iron and stator teeth is the lightest. By comparison the flux density, HTS wind turbine without rotor iron is the least and HTS wind turbine without rotor iron and stator teeth is the largest. By comparison the cost, HTS wind turbine with rotor iron is the highest and the other two is almost the same. HTS wind turbine without rotor iron and stator teeth is the best type.
Supersonic Flutter of a Spherical Shell Partially Filled with Fluid  [PDF]
Mohamed Menaa, Aouni A. Lakis
American Journal of Computational Mathematics (AJCM) , 2014, DOI: 10.4236/ajcm.2014.43014

In the present study, a hybrid ?nite element method is applied to investigate the dynamic behavior of a spherical shell partially filled with fluid and subjected to external supersonic airflow. The structural formulation is a combination of linear spherical shell theory and the classic finite element method. In this hybrid method, the nodal displacements are derived from exact solution of spherical shell theory rather than approximated by polynomial functions. Therefore, the number of elements is a function of the complexity of the structure and it is not necessary to take a large number of elements to get rapid convergence. Linearized first-order potential (piston) theory with the curvature correction term is coupled with the structural model to account for aerodynamic loading. It is assumed that the fluid is incompressible and has no free surface effect. Fluid is considered as a velocity potential at each node of the shell element where its motion is expressed in terms of nodal elastic displacements at the ?uid-structure interface. Numerical simulation is done and vibration frequencies are obtained. The results are validated using numerical and theoretical data available in literature. The investigation is carried out for spherical shells with different boundary conditions, geometries, filling ratios, flow parameters, and radius to thickness ratios. Results show that the spherical shell loses its stability through coupled-mode flutter. This proposed hybrid finite element method can be used efficiently for analyzing the flutter of spherical shells employed in aerospace structures at less computational cost than other commercial FEM software.

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