• 한국산학기술학회논문지
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• 제21권3호
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• pp.380-389
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• 2020

포화지방산 함량이 높은 우지와 불포화지방산 함량이 높은 식물성 유지인 해바라기유를 혼합한 혼합오일의 바이오디젤 전환특성을 규명하고 연료특성을 분석하였다. 다변량분산분석을 이용하여 도출한 기여율로 각 실험변수 (메탄올/유지 몰비, 오일혼합비) 가 바이오디젤 전환에 미치는 영향을 규명하였다. 또한, 바이오디젤의 고점도 문제를 해결하기 위해 가열과 초음파 조사의 방법을 적용하여 동점도 감소효과를 검증하였다. 연료별 온도 도와 동점도간의 상관관계식을 통해 동점도 감소를 위한 연료별 최적 온도를 도출하였다. 그 결과, 바이오디젤 전환율은 오일 혼합비 TASU7, 메탄올/유지 몰비 10에서 가장 우수한 것으로 나타났고 지방산 조성에 따라 연료특성에 차이가 있었다. 또한, 우지, 해바라기유 오일 혼합 바이오디젤의 연료특성 분석 결과 바이오디젤의 품질기준을 만족하는 것으로 나타났다. 바이오디젤의 고점도를 해결하기 위한 동점도 실험 결과 가열 방법의 동점도 감소 효과가 초음파 조사 방법에 비해 우수한 것으로 나타나 간단한 가열장치로 바이오디젤의 고점도를 해결할 수 있음을 확인하였다.

• Smart Structures and Systems
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• 제25권2호
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• pp.219-228
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• 2020

This work presents a modified continuum model to explore and investigate static and vibration behaviors of perforated piezoelectric NEMS structure. The perforated nanostructure is modeled as a thin perforated nanobeam element with Euler-Bernoulli kinematic assumptions. A size scale effect is considered by included a nonlocal constitutive equation of Eringen in differential form. Modifications of geometrical parameters of perforated nanobeams are presented in simplified forms. To satisfy the Maxwell's equation, the distribution of electric potential for the piezoelectric nanobeam model is assumed to be varied as a combination of a cosine and linear functions. Hamilton's principle is exploited to develop mathematical governing equations. Modified numerical finite model is adopted to solve the equation of motion and equilibrium equation. The proposed model is validated with previous respectable work. Numerical investigations are presented to illustrate effects of the number of perforated holes, perforation size, nonlocal parameter, boundary conditions, and external electric voltage on the electro-mechanical behaviors of piezoelectric nanobeams.

• 오토저널
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• 제14권3호
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• pp.43-56
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• 1992

This task is to derive the Hamiltonian equations of motion for BMW 323i vehicle. The kinematic relationships are defined. The cut constraint equations are derived. The cut constraint equations are stabilized. The stabilized constraint equations are used to derive the relationships between the independent and dependent coordinates. The Hamiltonian equations of motion are reduced only in terms of the independent generalized coordinates.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2009년도 춘계학술대회 논문집
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• pp.1592-1597
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• 2009

Ratcheting is a cyclic accumulation of strain under a cyclic loading. It is a kind of mechanisms which generate cracks in rail steels. Though some experimental and numerical study has been performed, modeling of ratcheting is still a challenging problem. In this study, an elastic-plastic constitutive equation considering non-linear kinematic hardening and isotropic hardening was applied. Under the tangential stress of the contact stresses, a cyclic stress-strain relation was obtained by using the model. Strain under repeated cycles was accumulated.

• 한국해양공학회지
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• 제10권2호
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• pp.136-145
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• 1996

The theory is based on two thermodynamic equations for the air mass in the air column and bydrodynamic equation for the relation between the response of the air in the water column and the incident wave. The numerical model is experimented in a two dimensional water tank and the caisson model with sloped front wall is tested in the large towing tank.

• 대한기계학회논문집A
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• 제21권1호
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• pp.12-21
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• 1997

A model for analysis of the crushing mechanism of thin-walled rectangular tube is presented. The crushing modes of rectangular tubes may be characterized as either compact or noncompact and the model presented only considers compact modes. The unloading process in the crushing are categorized into three different stages where the distinction is based on the ratio of outward to inward fold length. Using the kinematic relations and the energy conservation principle, the instantaneous crush load is derived. An approximate equation that considers the rolling behavior is also given so that the crush load history may be established. The equation is experimentally proved.

• 대한기계학회논문집A
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• 제28권12호
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• pp.1845-1855
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• 2004

This paper presents the forward kinematics of the Casing Oscillator that is a construction machine. The Structure of the Casing Oscillator is similar to those of 4 degree-of-freedom mechanisms with a redundancy. With analytical (geometrical) methods, the solutions of the forward position kinematics problem are significantly found by both solving an 8$^{th}$ -order polynomial equation in one unknown variable and using one over-constraint geometrical equation which can be derived under the condition of a redundancy. The proposed forward kinematics has closed-form solutions and allows Auto-Balancing control of the moving platform in real time. Numerical examples are presented and the results are verified by an inverse kinematics analysis.

• 대한기계학회논문집A
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• 제21권8호
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• pp.1311-1321
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• 1997

In multibody dynamics, differential and algebraic equations which can satisfy both equation of motion and kinematic constraint equation should be solved. To solve these equations, coordinate partitioning method and constraint stabilization method are commonly used. In the coordinate partitioning method, the coordinates are divided into independent and dependent and coordinates. The most typical coordinate partitioning method are LU decomposition, QR decomposition, and SVD (singular value decomposition). The objective of this research is to find an efficient coordinate partitioning method in the dynamic analysis of flexible multibody systems. Comparing two coordinate partitioning methods, i.e. LU and QR decomposition in the flexible multibody systems, a new hybrid coordinate partitioning method is suggested for the flexible multibody analysis.

• 한국해양공학회지
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• 제17권4호
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• pp.1-7
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• 2003

A virtual reality technology for multipurpose numerical simulation is developed to reproduce and investigate a variety of ocean environmental problems in a 3D Numerical Wave Tank(NWT). The governing equations for solving incompressible fluid motion are Navier-Stokes equation and continuity equation. The Marker-Density function technique is adopted to implement the fully nonlinear freesurface kinematic condition. The marine environmental situations, i.e., waves, currents, etc., are reproduced by use of multi-segmented wavemakers on the basis of the so-called ″snake-principle″. In this paper, some numerical reproduction techniques for regular, and irregular waves, multi-directional waves, Bull's-eye wave. wave-current, and solitary wave are presented, and a model test in motion with large amplitude of roll angle is conducted in the developed 3D-NWT, using a overlaid grid system.

• 한국농공학회:학술대회논문집
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• 한국농공학회 2001년도 학술발표회 발표논문집
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• pp.45-50
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• 2001

The purpose of this study was to estimate of soil loss form hillslope using WEPP(Water Erosion Prediction Project) model. WEPP model was developed for predicting soil erosion and deposition, fundamentally based on soil erosion prediction technology. The model for predicting sediment yields from single storms was applied to a tested watershed. Surface runoff is calculated by kinematic wave equation and infiltration is based on the Green and Ampt equation. Governing equations for sediment continuity, detachment, deposition, shear stress in rills, and transport capacity are presented. Tested watershed has an area of 0.6ha, where the runoff and sediment data were collected. The relative error between predicted and measured runoff was $-16.6{\sim}2.2%$, peak runoff was $-15.6{\sim}2.2%$ and soil loss was $-23.9{\sim}356.5%$.