• 한국전산구조공학회논문집
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• 제20권2호
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• pp.127-136
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• 2007

본 논문에서는 비동질 반무한 평면에 대한 비례경계유한요소법의 식을 유도하고 수치예제를 해석하였다. 비례경계유한 요소법은 편미분 방정식을 경계방향으로는 유한요소와 같은 근사를 통해서 약화시키고 방사방향으로는 정확해를 사용하는 반 해석적인 방법으로, 방사방향으로 멱함수를 따라 탄성계수가 변화되는 반무한 평면에 대해서 관계식을 가상일의 원리에 근거하여 새로이 유도하였다. 이 과정에서 반무한평면의 거동이 Euler-Cauchy방정식을 따름을 보이고, 기존의 동질 반무한평면의 해석시 도입되던 로그모드가 비동질 반무한 평면의 해석에는 유효하지 않음을 보였다. 수치예제를 통하여 유도된 식이 타당한 거동을 보임을 증명하고 이 접근법이 실제 공학적 문제의 해결에 있어서 유용함을 보였다.

• 충청수학회지
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• 제31권4호
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• pp.363-368
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• 2018

The aim of this work is to derive a partial differential equation that explains the movement of vortex lines on a vortex trajectory surface in a three dimensional incompressible inviscid flow.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2000년도 유체기계 연구개발 발표회 논문집
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• pp.110-115
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• 2000

The mean streamline analysis using the empirical loss correlations has been developed for performance prediction of industrial mixed-flow fan impellers in the present study. New simple, but effective, models for the additional Euler input work characteristic and an internal recirculation loss due to internal flow reversal under the low flowrate conditions are proposed in this paper. Comparison of overall performance predictions with six sets of test data of mixed-flow fans is accomplished to demonstrate the accuracy of the proposed models. Predicted performance curves by the present set of loss models agree fairly well with experimental data for a variety of mixed-flow fan impellers over the entire operating conditions. The prediction method presented herein can be used efficiently in the conceptual design phase of mixed-flow fan impellers.

• 한국소음진동공학회논문집
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• 제21권6호
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• pp.553-561
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• 2011

A theoretical approach is carried out to predict the quality factors of flexible modes of a microcantilever on a squeeze-film. The frequency response function of an inertially-excited microcantilever beam is derived using an Euler-Bernoulli beam theory. The external force due to squeeze-film phenomenon is developed from the Reynolds equation. Slip boundary conditions are employed at the interfaces between the fluid and the structure to consider the gas rarefaction effect, and pressure boundary condition at both ends of fluid analysis region is enhanced to increase the exactness of predicted quality factors. To the end, an approximate equation is derived for the first bending mode of the microcantilever. Using the approximate equation, the quality factors of the second and third bending modes are calculated and compared with experimental results of previously reported work. The comparison shows the feasibility of the current approach.

• Journal of applied mathematics & informatics
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• 제41권2호
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• pp.295-309
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• 2023

The Richards' equation attracts the attention of several scientific researchers due to its importance in the hydrogeology field especially porous soil. This work presents a numerical method to solve the two dimensional Richards' equation. The pressure form and the mixed form of Richards' equation are solved numerically using a bivariate diamond finite volumes scheme. Euler explicit scheme is used for the time discretization. Different test cases are done to validate the accuracy and the efficiency of our numerical model and to compare the possible numerical strategies. We started with a first simple test case of Richards' pressure form where the hydraulic capacity and the hydraulic conductivity are taken constant and then a second test case where the hydrodynamics parameters are linear variables. Finally, a third test case where the soil parameters are taken according the Van Gunchten empirical model is presented.

• 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.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2007년도 추계 학술대회논문집
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• pp.157-161
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• 2007

The prediction of the safe separation of the external stores carried on military aircraft is an important task in the aerodynamic design area having the objective to define the operational, release envelopes. The major concern of this study is only safe jettison problem with ejections. This work consists of concept and some results for external store configurations. A Computational Fluid Dynamics technique is applied to calculate the aerodynamic forces. The FLUENT with an implicit Euler solver is used for the present simulations. The computational results are validated against the experimental data.

• Steel and Composite Structures
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• 제32권5호
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• pp.643-655
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• 2019

Perforation and cutouts of structures are compulsory in some modern applications such as in heat exchangers, nuclear power plants, filtration and microeletromicanical system (MEMS). This perforation complicates dynamic analyses of these structures. Thus, this work tends to introduce semi-analytical model capable of investigating the dynamic performance of perforated beam structure under free and forced conditions, for the first time. Closed forms for the equivalent geometrical and material characteristics of the regular square perforated beam regular square, are presented. The governing dynamical equation of motion is derived based on Euler-Bernoulli kinematic displacement. Closed forms for resonant frequencies, corresponding Eigen-mode functions and forced vibration time responses are derived. The proposed analytical procedure is proved and compared with both analytical and numerical analyses and good agreement is noticed. Parametric studies are conducted to illustrate effects of filling ratio and the number of holes on the free vibration characteristic, and forced vibration response of perforated beams. The obtained results are supportive in mechanical design of large devices and small systems (MEMS) based on perforated structure.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2013년도 춘계학술대회 논문집
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• pp.528-532
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• 2013

본 연구에서는, 해석적 모델로 불규칙하게 분포된 질량을 가진 열탄성 댐핑을 포함하는 마이크로빔 구조물을 연구하였다. 마이크로 스케일의 기계적 공명체(mechanical resonator)에 대한 열탄성 댐핑의 중요성은 높은 Q-factor를 설계하는데 고려된다. 본 연구에서의 빔 모델은 Euler-Bernoulli 빔 이론을 기조로 한다. 빔의 고유 진동수를 결정하기 위하여, 에너지 기법이 적용되었다. 또한, 열탄성 댐핑 효과는 열전도 방정식을 사용할으로써 고려되었고, Q-factor가 결정될 수 있었다. 운동방정식의 유도에는 체계적인 무차원화를 수행하였다. 임의의 집중된 질량을 포함하는 열탄성 댐핑을 가진 마이크로빔에 대해 모델의 결과값을 입증하였고 mode shape과 Q-factor를 제시하였다.

• Journal of applied mathematics & informatics
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• 제42권1호
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• pp.85-92
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• 2024

In this work we give the necessary and sufficient conditions for f-biharmonic curves in three-dimensional generalized symmetric spaces.