• 한국농공학회논문집
• /
• 제54권2호
• /
• pp.115-125
• /
• 2012

Application of the Object-oriented Programming (OOP) method to the Finite Element Model (FEM) program has various strengths including the features of encapsulation, polymorphism and inheritance. However, this technique should be based upon a premise that the independency of the object method and data to be used is guaranteed. By attempting to apply the OOP to the FEM, existing researches go against the independency of the OOP which is an essential feature of the method. The reason is this: existing researches apply the OOP to modules in accordance with analysis procedures, although the data to be used is classified as an element unit in the FEM. Therefore, the required independency cannot be maintained as whole stiffness matrices and boundary conditions are combined together. Also, solutions are sought from analysis module after data is regrouped at the pre-processor, and their results are analyzed during the post-processor. As this is similar to a batch processing, it cannot use data at analysis, and recalculation should be done from the beginning if any condition is changed after the analysis is complete, which are limitations of the existing researches. This research implemented the Object-orientation of elements so that the three features of the OOP (i.e. encapsulation, polymorphism and inheritance) can be guaranteed and their independency maintained as a result. For this purpose, a model called 'Object-oriented Finite element Model ensuring the Independency of Elements (OFMIE)', which enables the analysis of targets through mutual data exchanges within instance, was developed. In conclusion, the required independency was achieved in the instance of the objected elements and the analysis results of previous conditions could be used for the analysis after changes. The number of repetitive calculations was reduced by 75 per cent through this gradual analysis processes.

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

• Geomechanics and Engineering
• /
• 제9권4호
• /
• pp.415-426
• /
• 2015

Researches have been done to discover ways to strengthen peat soil deposits. In this model study, fibrous peat that is the most compressible types of peat has been reinforced with precast peat columns stabilized with ordinary Portland cement and polypropylene fibres. Rowe cell consolidation tests as well as plate load tests (PLTs) were conducted on various types of test samples to evaluate the strength and deformation of untreated peat and peat reinforced by various types of columns. PLTs were conducted in a specially designed and fabricated circular steel test tank. The compression index ($C_c$) and recompression index ($C_r$) of fibrous peat samples reduced considerably upon use of precast columns. Also, PLT results confirmed the results obtained from Rowe cell tests. Use of polypropylene fibres added to cement further decreased ($C_c$) and ($C_r$) and increased load bearing capacity of untreated peat. Finite element method (FEM) using Plaxis 3D was carried out to evaluate the stress distributions along various types of tested samples and also, to compare the deformations obtained from FEM analysis with the actual maximum deformations found from PLTs. FEM results indicate that most of the induced stresses are taken on the upper portion of tested samples and reach their maximum values below the loading plate. Also, a close agreement was found between actual deformation values obtained from PLTs and values resulted from FEM analysis for various types of tested samples.

• 대한기계학회논문집 C: 기술과 교육
• /
• 제5권2호
• /
• pp.81-87
• /
• 2017

315Fr 컴프레서용 모터가 진동 기준을 초과하는 문제가 발생하였고 이를 해결하기 위한 FEM해석과 모드실험을 수행하였다. 먼저 자유단 조건하의 해석과 실험을 수행하여 해석을 위한 조건을 확인하였다. 해석을 위한 Mesh, 재질, 경계 조건을 검토하였다. 여기서 얻은 결과를 바탕으로 볼트가 고정된 상태의 FEM 해석과 모드 실험을 수행하여 진동의 원인을 확인하였다. 모드실험 결과 121.7Hz에 Rolling 모드가 있음을 확인하였고 해석을 통해서도 동일한 결과를 얻을 수 있었다. 이 결과를 바탕으로 진동 기준을 초과하는 원인은 120Hz에 존재하는 Rolling 운동과 2X, 2fl 가진 주파수의 공진에 의한 것임을 알게 되었다. 여기서 얻은 결과를 바탕으로 추후 시리즈 설계에 있어서는 시험 모델 제작이나 실험 없이 해석만으로 문제점을 예측하고 해결할 수 있는 기술을 보유하게 되었다.

• 한국지반공학회:학술대회논문집
• /
• 한국지반공학회 1994년도 가을 학술발표회 논문집
• /
• pp.235-246
• /
• 1994

At pre-construction design stage, most of the design data are based on the site investigation results or property estimation which often does not provide satisfactory output for the tunnel analysis. Nonlinear FEM tunnel analysis was cariied out by Hoek-Brown model which is principly semi-empirical design method based on insitu rock descriptions, rock test results as well as field measurement data. The results of the analytical methods from Hoek-Brown model and Mohr-Coulomb model are compared with the sige measurement data from two-NATM tunnel construction sites. It was found that the Hoek-Brown model can be satisfactorily adopted as a feed back analysis technique in order to examin the safety of NATM tunnel at any construction stage.

• Structural Engineering and Mechanics
• /
• 제53권4호
• /
• pp.661-679
• /
• 2015

In this article, nonlinear finite element solutions of bending responses of functionally graded spherical panels are presented. The material properties of functionally graded material are graded in thickness direction according to a power-law distribution of volume fractions. A general nonlinear mathematical shallow shell model has been developed based on higher order shear deformation theory by taking the geometric nonlinearity in Green-Lagrange sense. The model is discretised using finite element steps and the governing equations are obtained through variational principle. The nonlinear responses are evaluated through a direct iterative method. The model is validated by comparing the responses with the available published literatures. The efficacy of present model has also been established by demonstrating a simulation based nonlinear model developed in ANSYS environment. The effects of power-law indices, support conditions and different geometrical parameters on bending behaviour of functionally graded shells are obtained and discussed in detail.

• Structural Engineering and Mechanics
• /
• 제64권1호
• /
• pp.23-31
• /
• 2017

In the study, dynamic behavior of laminated orthotropic beams on elastic foundation is investigated. Consistent model presented here combines the finite element solution of the system with SAP2000 software and the calculation of soil parameters with MATLAB software using Modified Vlasov Model type elastic foundation. For this purpose, a computing tool is coded in MATLAB which employs Open Application Programming Interface (OAPI) feature of SAP2000 to provide two-way data flow during execution. Firstly, an example is taken from the literature to demonstrate the accuracy of the consistent FEM-Vlasov Model. Subsequently, the effects of boundary conditions, subsoil depth, elasticity modulus of subsoil, slenderness ratio, velocity of moving load and lamination scheme on the behavior of laminated orthotropic beams on elastic foundation are investigated on a new numerical example. It can be concluded that it is really convenient to use OAPI feature of SAP2000 to model this complex behavior of laminated orthotropic beams on elastic foundation under moving load.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
• /
• 제2B권4호
• /
• pp.156-161
• /
• 2002

This paper proposes an optimized universal motor for improving its performance using the finite element method (FEM) with the (1＋1) Evolution Strategy (ES) algorithm. To do this, various design parameters are modified, such as air gap length, shape of motor slot, pole shoe, pole width, and rotor shaft diameter. Two parameters (arc length of stator pole and thickness of pole shoe) are chosen and optimized using the program, and the optimized model is built and tested with a performance measuring system. The measured values of the model are compared with those of the initial and the optimized model to prove the algorithm. As a result, the final model improves its performance compared with those of the initial model.

• 소성∙가공
• /
• 제11권6호
• /
• pp.538-546
• /
• 2002

Hot deformation behavior of Udiment720Li was characterized by compression tests in the temperature range of 10$25^{\circ}C$ to 115$0^{\circ}C$ and the strain rate range of $0.0005 s^{-1};to;5 s^{-1}$. The combination of dynamic material model (DMM) and Ziegler's instability criterion was applied to predict an optimum condition and unstable regions for hot forming. A dynamic recrystallization model coupled with FEM results was used to interpret the evolution of microstructures. In order to verify the reliability of the present coupled model, isothermal forging was performed in the temperature range 1050~115$0^{\circ}C$ at strain rates of $0.05 s^{-1};and;0.005 s^{-1}$. The present model was successfully applied to the hot forming process of Udimet720Li.

• Nuclear Engineering and Technology
• /
• 제53권8호
• /
• pp.2696-2707
• /
• 2021

The purpose of this study is to investigate the efficiency of various structural modeling schemes for evaluating seismic performances and fragility of the reactor containment building (RCB) structure in the advanced power reactor 1400 (APR1400) nuclear power plant (NPP). Four structural modeling schemes, i.e. lumped-mass stick model (LMSM), solid-based finite element model (Solid FEM), multi-layer shell model (MLSM), and beam-truss model (BTM), are developed to simulate the seismic behaviors of the containment structure. A full three-dimensional finite element model (full 3D FEM) is additionally constructed to verify the previous numerical models. A set of input ground motions with response spectra matching to the US NRC 1.60 design spectrum is generated to perform linear and nonlinear time-history analyses. Floor response spectra (FRS) and floor displacements are obtained at the different elevations of the structure since they are critical outputs for evaluating the seismic vulnerability of RCB and secondary components. The results show that the difference in seismic responses between linear and nonlinear analyses gets larger as an earthquake intensity increases. It is observed that the linear analysis underestimates floor displacements while it overestimates floor accelerations. Moreover, a systematic assessment of the capability and efficiency of each structural model is presented thoroughly. MLSM can be an alternative approach to a full 3D FEM, which is complicated in modeling and extremely time-consuming in dynamic analyses. Specifically, BTM is recommended as the optimal model for evaluating the nonlinear seismic performance of NPP structures. Thereafter, linear and nonlinear BTM are employed in a series of time-history analyses to develop fragility curves of RCB for different damage states. It is shown that the linear analysis underestimates the probability of damage of RCB at a given earthquake intensity when compared to the nonlinear analysis. The nonlinear analysis approach is highly suggested for assessing the vulnerability of NPP structures.