• Journal of international Conference on Electrical Machines and Systems
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• 제3권3호
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• pp.256-263
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• 2014

Torque ripple is a very essential index for evaluating the effectiveness of a switched reluctance motor (SRM). Many common design strategies for reducing torque ripples of a SRM are changing the excitation trigger angle of stator windings, delaying the cut-off time of winding excitation, adjusting the ratio of arc angle between stator and rotor, and changing the geometric shape of rotor. However, the output torque or the efficiency of the SRM may drop as the above design strategies are solely adopted. In this paper, a hybrid design model which is obtained by the Taguchi Method for optimally designing a SRM with lower torque ripple and higher efficiency is presented. A 12S/8P motor is taken as a study case, and the 3D finite element method (FEM) is applied to analyze the characteristics of the motor and optimize the design process. The results have shown that the proposed method can achieve the design goal of obtaining a high-performance SRM for light electric vehicle applications.

• 대한토목학회논문집
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• 제26권3A호
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• pp.439-445
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• 2006

터널과 같이 구조물의 크기가 매질의 영역에 비하여 상대적으로 작은 경우와 같은 무한영역의 문제는 유한요소법을 적용하여 해석할 수 있으나 해석의 정밀도를 높이기 위해서는 해석영역을 크게 선정하게 되어 계산량이 증가하고, 인위적인 경계조건에 의한 오차의 영향을 피할 수 없다. 이를 개선하기 위해 관심영역은 유한요소로 모델링하고 무한영역은 무한요소로 모델링하는 혼합법을 적용하면 보다 효과적이다. 본 연구에서는 다양한 감쇠함수를 적용한 등매개변수형 무한요소를 제안하였고 매개변수해석을 통하여 터널해석에 적합한 감쇠함수의 특성치를 제시하였다. 또한 이를 적용한 3차원 혼합모델이 터널 해석에 유효함을 입증하였다.

• Structural Engineering and Mechanics
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• 제34권4호
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• pp.525-539
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• 2010

Polymer matrix composites are widely used in many engineering applications as they can be customized to meet a desired performance while not only maintaining low cost but also reducing weight. Polymers can experience viscoelastic-viscoplastic response when subjected to external loadings. Various reinforcements and fillers are added to polymers which bring out more complexity in analyzing the timedependent response. This study formulates an integrated micromechanical model and finite element (FE) analysis for predicting effective viscoelastic-viscoplastic response of polymer based hybrid composites. The studied hybrid system consists of unidirectional short-fiber reinforcements and a matrix system which is composed of solid spherical particle fillers dispersed in a homogeneous polymer constituent. The goal is to predict effective performance of hybrid systems having different compositions and properties of the fiber, particle, and matrix constituents. A combined Schapery's viscoelastic integral model and Valanis's endochronic viscoplastic model is used for the polymer constituent. The particle and fiber constituents are assumed linear elastic. A previously developed micromechanical model of particle reinforced composite is first used to obtain effective mechanical properties of the matrix systems. The effective properties of the matrix are then integrated to a unit-cell model of short-fiber reinforced composites, which is generated using the FE. The effective properties of the matrix are implemented using a user material subroutine in the FE framework. Limited experimental data and analytical solutions available in the literatures are used for comparisons.

• 한국소음진동공학회논문집
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• 제17권2호
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• pp.105-113
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• 2007

In this study, three-dimensional rotordynamic analyses have been conducted using equivalent beam, hybrid and full three-dimensional models. The present computational method is based on the general finite element method with rotating gyroscopic effects of the rotor system. General purpose commercial finite element code, SAMCEF which includes practical rotordynamics module with various types of rotor analysis tools and bearing elements is applied. For the purpose of numerical verification, comparison study for a benchmark rotor model with support bearings is performed first. Detailed finite element models based on three different modeling concepts are constructed and then computational analyses are conducted for the realistic and complex three-dimensional rotor system. The results for rotor stability and mass unbalance response are presented and compared with the experimental vibration test data conducted herein.

• 한국해양공학회지
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• 제24권6호
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• pp.16-22
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• 2010

In this paper, the diffraction problems for fixed offshore structures are solved using a hybrid scheme. In this hybrid scheme, potential-based solutions and the Navier-Stokes-based finite volume method (FVM) with a volume-of-fluid (VOF) method are combined. We introduce a buffer zone for efficient wave-making and damping. In this buffer zone, the near field solution from FVM-VOF is gradually changed to Stokes' 2nd order wave solutions. Three different models, including the truncated cylinder, sphere, and wigleyIII model, are numerically investigated in regular waves with a wave steepness of 1/30. The efficiency and accuracy of the hybrid scheme are numerically validated from results using different domain sizes and buffer zones. The wave exciting forces from the FVM-VOF simulations are compared with experiments and potential-based solutions from the higher-order boundary element method (HOBEM). This comparison shows good agreement between the hybrid scheme and potential-based solutions.

• Nuclear Engineering and Technology
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• 제39권4호
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• pp.337-348
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• 2007

A fuzzy neural network model is presented to predict residual stress for dissimilar metal welding under various welding conditions. The fuzzy neural network model, which consists of a fuzzy inference system and a neuronal training system, is optimized by a hybrid learning method that combines a genetic algorithm to optimize the membership function parameters and a least squares method to solve the consequent parameters. The data of finite element analysis are divided into four data groups, which are split according to two end-section constraints and two prediction paths. Four fuzzy neural network models were therefore applied to the numerical data obtained from the finite element analysis for the two end-section constraints and the two prediction paths. The fuzzy neural network models were trained with the aid of a data set prepared for training (training data), optimized by means of an optimization data set and verified by means of a test data set that was different (independent) from the training data and the optimization data. The accuracy of fuzzy neural network models is known to be sufficiently accurate for use in an integrity evaluation by predicting the residual stress of dissimilar metal welding zones.

• Ocean Systems Engineering
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• 제8권4호
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• pp.381-407
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• 2018

This paper presents a hybrid numerical approach, which combines a two-phase Navier-Stokes model (NS) and the fully nonlinear potential theory (FNPT), for modelling wave-structure interaction. The former governs the computational domain near the structure, where the viscous and turbulent effects are significant, and is solved by OpenFOAM/InterDyMFoam which utilising the finite volume method (FVM) with a Volume of Fluid (VOF) for the phase identification. The latter covers the rest of the domain, where the fluid may be considered as incompressible, inviscid and irrotational, and solved by using the Quasi Arbitrary Lagrangian-Eulerian finite element method (QALE-FEM). These two models are weakly coupled using a zonal (spatially hierarchical) approach. Considering the inconsistence of the solutions at the boundaries between two different sub-domains governed by two fundamentally different models, a relaxation (transitional) zone is introduced, where the velocity, pressure and surface elevations are taken as the weighted summation of the solutions by two models. In order to tackle the challenges associated and maximise the computational efficiency, further developments of the QALE-FEM have been made. These include the derivation of an arbitrary Lagrangian-Eulerian FNPT and application of a robust gradient calculation scheme for estimating the velocity. The present hybrid model is applied to the numerical simulation of a fixed horizontal cylinder subjected to a unidirectional wave with or without following current. The convergence property, the optimisation of the relaxation zone, the accuracy and the computational efficiency are discussed. Although the idea of the weakly coupling using the zonal approach is not new, the present hybrid model is the first one to couple the QALE-FEM with OpenFOAM solver and/or to be applied to numerical simulate the wave-structure interaction with presence of current.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• 제11B권2호
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• pp.15-21
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• 2001

This paper presents an improved characteristic analysis methodology for a 5-phase hybrid stepping motor. The basic approach is based on the use of equivalent magnetic circuit taking into account the localized saturation throughout the hybrid stepping motor. The finite element method(FEM) is used to generate the magnetic circuit parameters for the complex stator and rotor teeth and airgap considering the saturation effects in tooth and poles. In addition, the neural network is used to map a change of parameters and predicts their approximation. Therefore, the proposed method efficiently improves the accuracy of analysis by using the parameter characterizing localized saturation effects and reduces the computational time by using the neural network. An improved circuit model of 5-phase hybrid stepping motor is presented and its application is provided to demonstrate the effectiveness of the proposed method.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1999년도 춘계 학술대회논문집
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• pp.90-97
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• 1999

An implicit turbulent flow solver is developed for 2-D unstructured hybrid meshes. Spatial discretization is accomplished by a cell-centered finite volume formulation using an upwind flux differencing. Time is advanced by an implicit backward Euler time stepping scheme. Flow turbulence effects are modeled by the Spalart-Allmaras one equation model, which is coupled with wall function. The numerical method is applied for flows on a flat plate, the NACA 0012 airfoil, and the Douglas 3 element airfoil. The results are compared with experimental data.

• Earthquakes and Structures
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• 제24권6호
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• pp.393-404
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• 2023

This paper presents the application of hybrid-simulation-based adapter elements for the non-linear two-scale analysis of reinforced concrete frames with masonry infills under seismic-like demands. The approach provides communication and distribution of the computations carried out by two or more remote or locally distributed numerical models connected through the OpenFresco Framework. The modeling consists of a global analysis formed by macro-elements to represent frames and walls, and to reduce global degrees of freedom, portions of the structure that require advanced analysis are substituted by experimental elements and dimensional couplings acting as interfaces with their respective sub-assemblies. The local sub-assemblies are modeled by solid finite elements where the non-linear behavior of concrete matrix and masonry infill adopt a continuum damage representation and the reinforcement steel a discrete one, the conditions at interfaces between concrete and masonry are considered through a contact model. The methodology is illustrated through the analysis of a frame-wall system subjected to lateral loads comparing the results of using macro-elements, finite element model and experimental observations. Finally, to further assess and validate the methodology proposed, the paper presents the pushover analysis of two more complex structures applying both modeling scales to obtain their corresponding capacity curves.