• Structural Engineering and Mechanics
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• 제70권6호
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• pp.737-750
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• 2019

This paper investigates the static and dynamic behaviors of imperfect single walled carbon nanotube (SWCNT) modeled as a beam structure by using energy-equivalent model (EEM), for the first time. Based on EEM Young's modulus and Poisson's ratio for zigzag (n, 0), and armchair (n, n) carbon nanotubes (CNTs) are presented as functions of orientation and force constants. Nonlinear Euler-Bernoulli assumptions are proposed considering mid-plane stretching to exhibit a large deformation and a small strain. To simulate the interaction of CNTs with the surrounding elastic medium, nonlinear elastic foundation with cubic nonlinearity and shearing layer are employed. The equation governed the motion of curved CNTs is a nonlinear integropartial-differential equation. It is derived in terms of only the lateral displacement. The nonlinear integro-differential equation that governs the buckling of CNT is numerically solved using the differential integral quadrature method (DIQM) and Newton's method. The linear vibration problem around the static configurations is discretized using DIQM and then is solved as a linear eigenvalue problem. Numerical results are depicted to illustrate the influence of chirality angle and imperfection amplitude on static response, buckling load and dynamic behaviors of armchair and zigzag CNTs. Both, clamped-clamped (C-C) and simply supported (SS-SS) boundary conditions are examined. This model is helpful especially in mechanical design of NEMS manufactured from CNTs.

• Steel and Composite Structures
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• 제50권1호
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• pp.25-43
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• 2024

In this article, a mathematical model is developed to predict the dynamic behavior of bio-inspired composite beam with helicoidal orientation scheme under variable axial load using a unified higher order shear deformation beam theory. The geometrical kinematic relations of displacements are portrayed with higher parabolic shear deformation beam theory. Constitutive equation of composite beam is proposed based on plane stress problem. The variable axial load is distributed through the axial direction by constant, linear, and parabolic functions. The equations of motion and associated boundary conditions are derived in detail by Hamilton's principle. Using the differential quadrature method (DQM), the governing equations, which are integro-differential equations are discretized in spatial direction, then they are transformed into linear eigenvalue problems. The proposed model is verified with previous works available in literatures. Parametric analyses are developed to present the influence of axial load type, orthotropic ratio, slenderness ratio, lamination scheme, and boundary conditions on the natural frequencies of composite beam structures. The present enhanced model can be used especially in designing spacecrafts, naval, automotive, helicopter, the wind turbine, musical instruments, and civil structures subjected to the variable axial loads.

• Advances in aircraft and spacecraft science
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• 제11권1호
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• pp.55-81
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• 2024

This paper presents the exact solutions and closed forms for of nonlinear stability and vibration behaviors of straight and curved beams with nonlinear viscoelastic boundary conditions, for the first time. The mathematical formulations of the beam are expressed based on Euler-Bernoulli beam theory with the von Karman nonlinearity to include the mid-plane stretching. The classical boundary conditions are replaced by nonlinear viscoelastic boundary conditions on both sides, that are presented by three elements (i.e., linear spring, nonlinear spring, and nonlinear damper). The nonlinear integro-differential equation of buckling problem subjected to nonlinear nonhomogeneous boundary conditions is derived and exactly solved to compute nonlinear static response and critical buckling load. The vibration problem is converted to nonlinear eigenvalue problem and solved analytically to calculate the natural frequencies and to predict the corresponding mode shapes. Parametric studies are carried out to depict the effects of nonlinear boundary conditions and amplitude of initial curvature on nonlinear static response and vibration behaviors of curved beam. Numerical results show that the nonlinear boundary conditions have significant effects on the critical buckling load, nonlinear buckling response and natural frequencies of the curved beam. The proposed model can be exploited in analysis of macrosystem (airfoil, flappers and wings) and microsystem (MEMS, nanosensor and nanoactuators).

• Asian-Australasian Journal of Animal Sciences
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• 제24권10호
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• pp.1377-1385
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• 2011

This study was conducted to determine the nutritive value of live yeast culture (RumiSacc, Saccharomyces cerevisiae) and to investigate its effects on milk yield, milk composition and some blood parameters in lactating cows. Six multiparous Holstein cows were allocated to two groups of three cows and assigned randomly to one of two diets in a cross-over experiment. Daily 50 g RumiSacc was top dressed at the p.m. feeding for the treatment group. RumiSacc supplied a high protein and energy with high organic matter digestibility values (83.35%) determined by in vitro enzymatic analysis. Yeast culture supplementation significantly increased milk yield, tended to increase fat yield, protein yield and lactose yield of milk. Methylated fatty acid level of 18:3 (n-3) in milk fat was increased by yeast culture supplementation. The concentrations of methionine, phenyalanine, tyrosine, tryptophan and taurine were significantly increased with dietary inclusion of yeast culture. Live yeast culture supplementation did not affect other performance characteristics, milk quality characteristics and blood parameters. As a conclusion live yeast culture (RumiSacc, Saccharomyces cerevisiae) had high nutritive value and positive effects on milk production and some milk quality characteristics in lactating cows under field conditions.

• 전자공학회논문지D
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• 제36D권8호
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• pp.45-53
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• 1999

접지된 유전체층 위의 유한한 개수의 도체스트립에 의한 전자기 산란문제를 TM편파의 경우에 대하여 송수신 누설파 안테나와 격자결합기의 관점에서 고려하였다. 도체스트립에 유기된 전류를 미지수로 하는 적미분 방정식을 유도하고 모멘트법을 이용하여 풀었다. 도체스트립에 걸쳐서 특정한 전원(전류) 분포를 갖는 비균일한 누설파 구조를 구성하기 위하여 누설파 구조를 따라 인접하는 스트립들 사이의 거리의 스트립의 폭이 함께 변화되었다. 도체스트립의 전류분포 및 표면파 전력에 대한 해석결과들로부터 적절히 구성된 비균일한 누설파 구조의 수신 누설파 안테나 및 적자결합기 관점에서의 최대 결합효율이 균일한 구조에서의 80%에 비해 15%정도 개선된 95%가 됨을 관찰하였다.

• 한국전산구조공학회논문집
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• 제27권2호
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• pp.87-94
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• 2014

페리다이나믹 이론은 재료파괴 및 균열진전 해석에 적합하다. 그러나 적분 방정식을 풀기위해 많은 비국부 상호작용을 해석해야만 하기 때문에 일반적으로 사용되는 국부 모델들에 비해 비효율적이다. 따라서 효율적이면서 정확한 해석 모델을 구성하기 위해 페리다이나믹 모델과 다른 국부 모델을 연성하는 연성 해석법의 개발이 필요하다. 연성 방법론 개발을 위해서는 불연속성 혹은 응력 집중이 발생될 것으로 예상되는 영역에는 페리다이나믹 모델을 구성하고 상대적으로 변형 거동이 복잡하지 않은 영역은 국부 모델을 구성하는 방법이 많이 사용된다. 본 연구에서는 최근에 개발된 힘-기반 연성 방법론을 소개한다. 이 방법론에서는 블랜딩 함수를 활용하여 연성 영역을 사이에 두고 페리다이나믹 모델과 탄성체 모델을 연성한다. 수치예제를 통해 연성 모델이 집중하중 해석 혹은 정적파괴 해석 문제를 효율적이고 엄밀하게 해석할 수 있음을 확인하였다. 이와 같은 문제들은 일반적인 탄성체 모델을 사용해서는 엄밀한 해석이 어렵다. 반면에 페리다이나믹 모델은 엄밀한 해석이 가능하지만 계산 시간과 비용이 매우 많이 요구된다는 문제점이 있다.

• 대한조선학회논문집
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• 제50권4호
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• pp.224-231
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• 2013

The concept of the natural frequency is useful for understanding the characters of oscillating systems. However, when a circular cylinder floating horizontally on the water surface is heaving, due to the hydrodynamic forces, the system is not governed by the equation like that of the harmonic one. In this paper, in order to shed some lights on the more correct use of the concept of the natural frequency, a problem of the heaving circular cylinder is analyzed in the time domain. The equation of motion, an integro-differential equation, was derived following the fashion of Cummins (1962), and its coefficients including the retardation function were obtained using the numerical solution of Lee (2012). The equation was solved numerically, and the experiment was also carried out in the CNU flume. Using our numerical and experimental results, the natural frequency was defined as its average value given by the motion data excluding those of the initial stage. Our results were then compared with those of the existing investigations such as Maskell and Ursell (1970), Ito (1977) and Yeung (1982) as well as the newly obtained results of Lee (2012). Comparison showed that the natural frequency obtained here agrees well with that of Lee (2012), which was found through the frequency domain analysis. It was also shown that the approximation of heaving motion by a damped harmonic oscillation, which was regarded as suitable by most previous investigators, is not physically suitable for the reason that can be clearly shown through comparing the shape of MCFRs(Modulus of Complex Frequency Response). Furthermore, we found that although the previous approximations yield the damping ratio significantly different from our result the magnitude of natural frequency is not much different from our result.

• 대한조선학회논문집
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• 제31권3호
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• pp.47-58
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• 1994

본 논문에서는 천수역에 위치한 선박의 선형(線形) 조종성 계수를 추정하기 위한 이론적인 해석법에 대한 연구가 수행되었다. 세장체 이론을 사용하여 선체 주위의 유동을 모델화하였으며, 이로부터 물체 근처의 내부 유체 영역에서의 횡방향 유속에 대한 적 미분 방정식을 유도하였다. 이의 수치해법에 관하여 자세히 기술하였고, 특정 경우에 대한 이론해와 계산 결과를 비교하여 그 타당성을 검증하였다. 이 적 미분 방정식의 해를 이용하여 선체의 선형(線形) 조종성 계수를 추정할 수 있다. Mariner. Series 60, Wigley 선형에 대한 계산을 수행하였으며, 기존의 실험 결과와 비교하여 보았다. 조종 운동을 하고 있는 선체 주위의 복잡한 유동을 모델화하는 과정중에 포함된 여러 가지 가정에도 불구하고, 계산 결과는 실험 결과와 정성적, 정량적으로 잘 일치하며, 선박의 초기 설계 단계시 수심에 따른 기본적인 조종성 변화를 추정할 수 있을 것으로 생각된다.

• 대한한의학방제학회지
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• 제29권4호
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• pp.229-237
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• 2021

Objectives: This study aimed to analyze the effectiveness of Sogunjung-tang on neuropathic pain. Methods: This study was conducted on 50 cases of patients with neuropathic pain who were treated in LUA clinic from Jun 2021, to Oct 2021. All patients were treated with Sogunjung-tang, and in some cases, acupuncture or moxibustion was also performed. We measured the efficacy of treatment with a numerical rating scale (NRS), frequency, and duration of pain before treatment, after 1 week, and 3 weeks. Results: Both average pain NRS and worst pain NRS significantly decreased 1 week and 3 weeks after treatment compared to pre-treatment. The frequency and duration of pain did not differ after 1 week of treatment but showed a significant difference after 3 weeks. Conclusions: This study suggests that herbal medicine treatment with Sogunjung-tang reduces pain intensity, frequency, and duration in patients with neuropathic pain.

• Nuclear Engineering and Technology
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• 제54권6호
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• pp.2077-2083
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• 2022

In the unlikely event of core disruptive accident in sodium cooled fast reactors, the reactor containment building would be bottled up with sodium and fission product aerosols. The behavior of these aerosols is crucial to estimate the in-containment source term as a part of nuclear reactor safety analysis. In this work, the evolution of sodium aerosol characteristics (mass concentration and size) is simulated using HAARM-S code. The code is based on the method of moments to solve the integro-differential equation. The code is updated to FORTRAN-77 and run in Microsoft FORTRAN PowerStation 4.0 (on Desktop). The sodium aerosol characteristics simulated by HAARM-S code are compared with the measured values at Aerosol Test Facility. The maximum deviation between measured and simulated mass concentrations is 30% at initial period (up to 60 min) and around 50% in the later period. In addition, the influence of humidity on aerosol size growth for two different aerosol mass concentrations is studied. The measured and simulated growth factors of aerosol size (ratio of saturated size to initial size) are found to be matched at reasonable extent. Since sodium is highly reactive with atmospheric constituents, the aerosol growth factor depends on the hygroscopic growth, chemical transformation and density variations besides coagulation. Further, there is a scope for the improvement of the code to estimate the aerosol dynamics in confined environment.