• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.2797-2802
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• 2007

It has been confirmed that implementation of the no-slip boundary conditions for the lattice-Boltzmann method play an important role in the overall accuracy of the numerical solutions as well as the stability of the solution procedure. We in this paper propose a new algorithm, i.e. the method of the dynamic boundary condition for no-slip boundary condition. The distribution functions on the wall along each of the links across the physical boundary are assumed to be composed of equilibrium and nonequilibrium parts which inherit the idea of Guo's extrapolation method. In the proposed algorithm, we apply a dynamic equation to reflect the computational slip velocity error occurred on the actual wall boundary to the correction; the calculated slip velocity error dynamically corrects the fictitious velocity on the wall nodes which are subsequently employed to the computation of equilibrium distribution functions on the wall nodes. Along with the dynamic selfcorrecting process, the calculation efficiently approaches the steady state. Numerical results show that the dynamic boundary method is featured with high accuracy and simplicity.

• Advances in nano research
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• 제14권3호
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• pp.285-294
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• 2023

The dynamic and sensing performances of nanomechanical resonators with their different boundary conditions are studied based on surface elasticity-based modeling and simulation. Specifically, the effect of surface stress is included in Euler-Bernoulli beam model for different boundary conditions. It is shown that the surface effect on the intrinsic elastic property of nanowire is independent of boundary conditions, while these boundary conditions affect the frequency behavior of nanowire resonator. The detection sensitivity of nanowire resonator is remarkably found to depend on the boundary conditions such that double-clamping boundary condition results in the higher mass sensitivity of the resonator in comparison with simple-support or cantilever boundary condition. Furthermore, we show that the frequency shift of nanowire resonator due to mass adsorption is determined by its length, whereas the frequency shift is almost independent of its thickness. This study enables a design principle providing an insight into how the dynamic and sensing performances of nanomechanical resonator is determined and tuned.

• 대한토목학회논문집
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• 제28권6B호
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• pp.691-696
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• 2008

본 연구에서는 자유수면 흐름에 적용할 수 있는 연직방향에 대해 좌표변환된 3차원 동수압 모형을 제시하였다. 제시한 모형은 자유수면과 동수압의 해석을 위하여, 2중 예측-수정(double predictor-corrector)방법을 적용하였다. 본 연구에서는 정확한 동역학적 경계조건(자유수면에서의 압력은 0인 조건)을 적용하는 방법을 검토하였고, 이 경계조건은 기존에 개발된 모형에 미소한 수정을 통하여 적용 가능함을 보여주었다. 본 연구에서 제시한 모형과 기존 모형의 계산결과를 비교하였을 때 동역학적 경계조건의 정확한 적용이 매우 중요함을 알 수 있다.

• Tribology and Lubricants
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• 제14권3호
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• pp.39-45
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• 1998

Reynolds equation, which describes behavior of fluid film in journal bearings, basically satisfies mass conservation. But, boundary conditions usually used with this equation, e.g. half Sommerfeld or Reynolds boundary conditions, cannot fulfill this natural law of conservation. In the case of connecting rod bearing, where applied load is dynamic and its magnitude is relatively large, such unrealistic boundary conditions have serious influence on calculation results, especially on lubricant flow rate or power disspation which are important parameters in thermal analysis. In this paper, mass-conserving boundary condition was applied in the finite element analysis of connecting rod bearings. Lubricant flow rate and power dissipation rate were calculated together with journal center locus, minimum film thickness and maxmium film pressure. These computation results were compared with those of the case of Reynolds boundary condition. Balance between inlet and outlet flow rate was well achieved in the case of mass-conserving boundary condition.

• Geomechanics and Engineering
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• 제28권2호
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• pp.107-116
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• 2022

The steady state of unsaturated soil takes a long time to achieve. The soil seepage behaviours and hydraulic properties depend highly on the wetting/drying rate. It is observed that the soil-water characteristic curve (SWCC) is dependent on the wetting/drying rate, which is known as the dynamic effect. The dynamic effect apparently influences the scanning curves and will substantially affect the seepage behavior. However, the previous models commonly ignore the dynamic effect and cannot quantitatively describe the hysteresis scanning loops under dynamic conditions. In this study, a dynamic hysteresis model for SWCC is proposed considering the dynamic change of contact angle and the moving of the contact line. The drying contact angle under dynamic condition is smaller than that under static condition, while the wetting contact angle under dynamic condition is larger than that under static condition. The dynamic contact angle is expressed as a function of the saturation rate according to the Laplace equation. The model is given by a differential equation, in which the slope of the scanning curve is related to the slope of the boundary curve by means of contact angle. Empirical models can simulate the boundary curves. Given the two boundary curves, the scanning curve can be well predicted. In this model, only two parameters are introduced to describe the dynamic effect. They can be easily obtained from the experiment, which facilitates the calibration of the model. The proposed model is verified by the experimental data recorded in the literature and is proved to be more convenient and effective.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 1998년도 제27회 춘계학술대회
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• pp.212-217
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• 1998

Reynolds equation, which describes behavior of fluid film in journal bearing, basically satisfies mass conservation. But, boundary conditions usually used with this equation, e.g. half Sommerfeld or Reynolds boundary conditions, cannot fulfill this natural law of conservation. In the case of connecting rod bearing, where applied load is dynamic and its magnitude is relatively large, such unrealistic boundary conditions have serious influence on calculation results, especially on lubricant flow rate or power dissipation which are important parameters in thermal analysis. Another important factor in the analysis of connecting rod bearing is elastic deformation of bearing support structure which is relatively flexible. In this paper, EHL analysis of connecting rod beating is performed using mass-conserving boundary condition. Elastic deformation of bearing support structure and application of mass-conserving boundary condition have significant effects on the performances of connecting rod bearing.

• Coupled systems mechanics
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• 제12권4호
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• pp.365-389
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• 2023

Dynamic analysis of a typical concrete gravity dam-reservoir system is formulated by FE-(FE-TE) approach (i.e., Finite Element-(Finite Element-Truncation Element)). In this technique, dam and reservoir are discretized by plane solid and fluid finite elements. Moreover, the H-W (i.e., Hagstrom-Warburton) high-order condition imposed at the reservoir truncation boundary. This task is formulated by employing a truncation element at that boundary. It is emphasized that reservoir far-field is excluded from the discretized model. The formulation is initially reviewed which was originally proposed in a previous study. Thereafter, the response of Pine Flat dam-reservoir system is studied due to horizontal and vertical ground motions for two types of reservoir bottom conditions of full reflective and absorptive. It should be emphasized that study is carried out under high order of H-W condition applied on the truncation boundary. The initial part of study is focused on the time harmonic analysis. In this part, it is possible to compare the transfer functions against corresponding responses obtained by FE-(FE-HE) approach (referred to as exact method). Subsequently, the transient analysis is carried out. In that part, it is only possible to compare the results for low and high normalized reservoir length cases. Therefore, the sensitivity of results is controlled due to normalized reservoir length values.

• 한국방재학회 논문집
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• 제10권1호
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• pp.103-109
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• 2010

본 연구에서는 자유수면 흐름에 적용할 수 있는 연직방향에 대해 좌표변환된 3차원 동수압 모형을 제시하였다. 제시한 모형은 자유수면과 동수압의 해석을 위하여, 2중 예측-수정(double predictor-corrector)방법을 적용하였다. 본 연구에서는 정확한 동역학적 경계조건(자유수면에서의 압력은 0인 조건)을 적용하는 방법을 검토하였고, 제시한 모형을 이용한 수치모의 결과를 해석해와 비교하여 본 연구에서 제시한 모형의 우수성을 검증하였다.

• 대한기계학회논문집
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• 제15권1호
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• pp.61-68
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• 1991

본 연구에서는 스프링힌지, 클램프, 단순지지, 탄성지반, 다수의 병진 및 회 전스프링 그리고 중간지지점의 조합으로 구성되어 있는 보에 대하여 우선 Hamilton원 리에 의하여 정확한 보의 특성방정식을 유도하고 모든 경계조건을 만족하는 직교다항 식을 구한 후, 스프링, 댐퍼로 구성된 여러개의 질량이 일정한 속도로 이동할 경우에 대하여 Galerkin방법과 수치적분 방법을 사용하여 동적응답을 구하였다. 또한 구속 조건 및 경계조건이 변함에 따라 동적응답에 미치는 영향을 연구하였다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 1997년도 추계학술대회논문집; 한국과학기술회관; 6 Nov. 1997
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• pp.160-165
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• 1997

Structural boundary condition is very important as a part of a structural system because it determines the dynamic characteristics of the structure. It is often to experience that experimental measurements of structural dynamic characteristics are somewhat different from the analytical predictions in which idealized boundary conditions are usually assumed. However, real structural boundary conditions are not so ideal; not perfectly clamped, for instance. Thus this paper introduces a new method to determine the non-ideal structural boundary conditions in the frequency domain. In this method, structural boundary conditions are modeled by both extensional (vertical) and torsional elastic springs. The effective springs are then determined from experimental FRFs (frequency response functions) by using the spectral element method (SEM). For a cantilevered beam experiments are conducted to determine the real boundary conditions in terms of effective springs. Dynamic characteristics (analytically predicted) based on identified boundary conditions are found to be much closer to experimental measurements when compared with those based on ideal boundary conditions.