• 한국농공학회지
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• 제33권4호
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• pp.73-83
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• 1991

A numerical simulation of a 2-dimensional tidal flow in a shallow sea was performed using the frequency domain finite element method. In this study, to overcome the inherent problems of a time domain model which requires high eddy viscosity and small time steps to insure numerical stability, the harmonic function incorporated with the linearized function of governing equations was applied. Calculations were carried out using the developed tidal model(TIDE) in a rectangular channel of lOm(depth) X 4km (width) X 25km(length) under the condition of tidal waves entering the channel closed at one end for both with and without bottom friction damping. The predicted velocities and water levels at different points of the channel were in close agreement with less than 1 % error between the numerical and analytical solutions. The results showed that the characteristics of the tidal flow were greatly affected by the magnitude of tidal elevation forcing, and not by on surface friction, wind, or the linear bottom friction when the value was less than 0.01. For the optimum size of grid to obtain a consistent solution, the ratio between the length of the maximum grid and the tidal wave length should be less than 0.0018. It was concluded that the finite element tidal model(TIDE) developed in this study could handle the numerical simulation of tidal flows for more complex geometrical conditions.

• Journal of the Korean Wood Science and Technology
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• 제44권2호
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• pp.204-217
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• 2016

Modified poplar has emerged as a potential raw material for furniture production. Lack of specific modified poplar strength information; however, restricts applications in the furniture industry especially as related to strength in corner-joints. Optimization of strength in L-shaped corner dowel modified poplar joints under compression loads utilizing finite element analysis (FEA) by Taguchi method with the focus of this study. Four experiment factors (i.e., Structure Style, Tenon Length, Tenon Diameter, and Tenon Gap), each at three levels, were conducted by adopting a $L_9-3^4$ Taguchi orthodoxy array (OA) to determine the optimal combination of factors and levels for the von Mises stress utilizing ANSYS software. Results of Signal-to-Noise ratio (S/N) analysis and the analysis of variance (ANOVA) revealed the optimal L-shaped corner dowel joint in modified poplar is $45^{\circ}$ Bevel Butt in structure style, 24 mm in tenon length, 6 mm in tenon diameter, and 20 mm in tenon gap. Tenon length and tenon gap are determined to be significant design factors for affecting von Mises Stress. Confirmation tests with optimal levels and experimental test indicated the predicted optimal condition is comparable to the actual experimental optimal condition.

• 한국광학회지
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• 제13권3호
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• pp.266-271
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• 2002

구면수차와 Stiles-Crawford 효과를 기준으로 4개의 굴절비구면을 가지는 모형안을 최적화 기법으로 설계하였다. 구속조건으로는 측정된 안구의 곡률반경 , 중심두께, 비구면도, 구면수차를 사용하였다. 또한 동공에서의 Stiles-Crawford 효과를 고려하여 최적화하였다 최적화의 결과로 얻은 모형안의 근축영역값들은 유효초점거리 20.8169mm, 상측정점초점거리 15.4820mm, 물측정점초점거리 -13.8528mm, 상거리 15.7150mm이다. 본 논문의 모형안은 한국인 정시 75안을 대상으로 측정되어진 자료를 바탕으로 국내에서 처음으로 제작된 정밀모형안이다.

• Structural Engineering and Mechanics
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• 제42권6호
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• pp.849-866
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• 2012

Single span historic bridges often contain non-prismatic members identified with a varying depth along their span lengths. Commonly, the symmetric parabolic height variations having the constant haunch length ratio of 0.5 have been selected to lower the stresses at the high bending moment points and to maintain the deflections within the acceptable limits. Due to their non-prismatic geometrical configuration, their assessment, particularly the computation of fixed-end horizontal forces (FEFs) and fixed-end moments (FEMs) becomes a complex problem. Therefore, this study aimed to investigate the behavior of non-prismatic beams with symmetrical parabolic haunches (NBSPH) having the constant haunch length ratio of 0.5 using finite element analyses (FEA). FEFs and FEMs due to vertical loadings as well as the stiffness coefficients and the carry-over factors were computed through a comprehensive parametric study using FEA. It was demonstrated that the conventional methods using frame elements can lead to significant errors, and the deviations can reach to unacceptable levels for these types of structures. Despite the robustness of FEA, the generation of FEFs and FEMs using the nodal outputs of the detailed finite element mesh still remains an intricate task. Therefore, this study advances to propose effective formulas and dimensionless estimation coefficients to predict the FEFs, FEMs, stiffness coefficients and carry-over factors with reasonable accuracy for the analysis and re-evaluation of the NBSPH. Using the proposed approach, the fixed-end reactions due to vertical loads, and also the stiffness coefficients and the carry-over factors of the NBSPH can be determined without necessitating the detailed FEA.

• 한국CDE학회논문집
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• 제21권4호
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• pp.426-432
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• 2016

Designing a morphologically well-fitted hip implant to a patient anatomy is desirable to improve surgical outcomes since a commercial ready-made hip implant may not well conform to the patient joint. In this study, biomechanical stability of patient-specific hip implants with two different stem lengths was compared and discussed using a 3D finite element analysis (FEA). The FEA results in this study showed that an increase in stem length brings about more the peaked von-Mises stress (PVMS) in the prosthesis and less in the femur. However the decrease in von-Mises stress in the femur causes stress shielding phenomenon that usually leads to considerable bone resorption. Although, in biomechanical stability point of view, this work recommends the use of smaller stems, the length of stem must be determined by considering both the von-Mises stress and the stress-shielding phenomenon.

• 소성∙가공
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• 제13권3호
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• pp.248-252
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• 2004

The mechanical properties of polycrystalline thin-films, critical for Micro-Electro-Mechanical Systems (MEMS) components, are known to have the size effect and the scatter in the length scale of microns by the numbers of intensive investigation by experiments and simulations. So, the consideration of the microstructure is essential to cover these length scale effects. The lattice based stochastic model for the microstructure evolution is used to simulate the actual microstructure, and the fast and reliable algorithm is described in this paper. The kinetics parameters, which are the key parameters for the microstructure evolution based on the nucleation and growth mechanism, are extracted from the given micrograph of a polycrystalline material by an inverse method. And the method is verified by the comparison of the quantitative measures, the number of grains and the grain size distribution, for the actual and simulated microstructures. Finite element mesh is then generated on this lattice based microstructure by the developed code. And the statistical finite element analysis is accomplished for selected microstructure.

• Structural Engineering and Mechanics
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• 제28권2호
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• pp.239-257
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• 2008

Double-sided punched metal plate timber fasteners present projections on both sides, which offer improved joint fire resistance and better joint aesthetics. In this paper, 3-D nonlinear finite element models were developed to simulate double-sided nail plate fastener timber joints. The models, incorporating orthotropic elasticity, Hill's yield criterion and elasto-plasticity and contact algorithms, are capable of simulating complex contact between the tooth and the timber and between the base plate and the timber in a fastener. Using validated models, parametric studies of the double-sided nail plate joints was undertaken to cover the tooth length and the tooth width. Optimal configuration was assumed to have been attained when increase in nail plate tooth width did not result in a raise in joint capacity, in conjunction with the optimum tooth length. This paper presents the first attempt to model and optimise tooth profile of double-sided nail plate fastener timber joints, which offers rational designs of such fasteners.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1999년도 추계학술대회 논문집 학회본부 B
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• pp.533-536
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• 1999

We consider digital implementation problems of continuous-time controllers. In general, digital controllers use fixed point representation of number and of finite word length(FWL). Under these conditions, this paper investigates the closed-loop stability caused by three design constraints; (i) finite precision representation of the controller parameters, (ii) realization forms such as direct form, cascade form, and parallel form, and (iii) sampling time. We calculate the coefficient stability margins of both predesigned controllers and controller to be implemented. This method can be applied to determine the word length, realization structure, and sampling time so that remains the stability.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2001년도 춘계학술대회 논문집(한국공작기계학회)
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• pp.22-27
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• 2001

Cochlea is well known to have the ability to analyze a wide frequency and this ability seems to be caused to the Basilar Membrane(BM) configuration. However, the relationship between the Cochlea frequency-position map is not clear. In this paper, the three-dimensional BM Model was made using the Finite Element method. Then, an attempt was made to examine the influence of the BM configuration on the Cochlea frequency-position map. Theoretical consideration reveals that the wide frequency-position of Cochlea is achieved by not only the BM configuration change along the length of the Cochlea but also the change of the Young's module of the BM along the length of the Cochlea.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2003년도 춘계학술대회 논문집
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• pp.694-697
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• 2003

Materials with specific micro-structural shape can exhibit negative Poisson's ratio. These materials can be widely used in structural applications because of their high resilience and resistance to impact. Specially, in the field of artificial implant's material, they have many potential applications. In this study, we investigated the Poisson's ratio and the ratio(E$_{e}$/E) of the elastic modulus of rotational particle structures based on structural design variables using finite element method. As the ratio of fibril's length to particle's diameter increased and the ratio of fibril's diameter to fibril's length decreased fixing the fibril's angle with 45 degree. the negative Poisson effect of rotational particle structures increased. The ratio of elastic modulus of these structures decreased with Poisson's ratio. The results show the reasonable values as compared with the previous analytical results.s.