• Structural Engineering and Mechanics
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• 제62권5호
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• pp.587-593
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• 2017

The objective of this analytical study is to calculate the elasto-plastic stresses of Functionally Graded (FG) hyperbolic disc subjected to uniform temperature. The material properties (elastic modulus, thermal expansion coefficient and yield strength) and the geometry (thickness) of the disc are assumed to vary radially with a power law function, but Poisson's ratio does not vary. FG disc material is assumed to be non-work hardening. Radial and tangential stresses are obtained for various thickness profile, temperature and material properties. The results indicate that thickness profile and volume fractions of constituent materials play very important role on the thermal stresses of the FG hyperbolic discs. It is seen that thermal stresses in a disc with variable thickness are lower than those with constant thickness at the same temperature. As a result of this, variations in the thickness profile increase the operation temperature. Moreover, thickness variation in the discs provides a significant weight reduction. A disc with lower rigidity at the inner surface according to the outer surface should be selected to obtain almost homogenous stress distribution and to increase resistance to temperature. So, discs, which have more rigid region at the outer surface, are more useful in terms of resistance to temperature.

• Structural Engineering and Mechanics
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• 제57권4호
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• pp.617-639
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• 2016

In this work, an analytical formulation based on both hyperbolic shear deformation theory and stress function, is presented to study the nonlinear post-buckling response of symmetric functionally graded plates supported by elastic foundations and subjected to in-plane compressive, thermal and thermo-mechanical loads. Elastic properties of material are based on sigmoid power law and varying across the thickness of the plate (S-FGM). In the present formulation, Von Karman nonlinearity and initial geometrical imperfection of plate are also taken into account. By utilizing Galerkin procedure, closed-form expressions of buckling loads and post-buckling equilibrium paths for simply supported plates are obtained. The effects of different parameters such as material and geometrical characteristics, temperature, boundary conditions, foundation stiffness and imperfection on the mechanical and thermal buckling and post-buckling loading capacity of the S-FGM plates are investigated.

• Advances in nano research
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• 제10권3호
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• pp.281-293
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• 2021

This paper presents a new nonlocal Hyperbolic Shear Deformation Beam Theory (HSDBT) for the free vibration of porous Functionally Graded (FG) nanobeams. A new displacement field containing integrals is proposed which involves only three variables. The present model incorporates the length scale parameter (nonlocal parameter) which can capture the small scale effect and its account for shear deformation by a hyperbolic variation of all displacements through the thickness without using the shear correction factor. It has been observed that during the manufacture of Functionally Graded Materials (FGMs), micro-voids and porosities can occur inside the material. Thus, in this work, the investigation of the free vibration analysis of FG beams taking into account the influence of these imperfections is established. Four different porosity types are considered for FG nanobeam. Material characteristics of the FG beam are supposed to vary continuously within thickness direction according to a power-law scheme which is modified to approximate material characteristics for considering the influence of porosities. Based on the nonlocal differential constitutive relations of Eringen, the equations of motion of the nanobeam are derived using Hamilton's principle. The effects of nonlocal parameter, aspect ratio, and the porosity types on the dynamic responses of the nanobeam are discussed.

• Geomechanics and Engineering
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• 제11권2호
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• pp.289-307
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• 2016

A simple hyperbolic shear deformation theory taking into account transverse shear deformation effects is proposed for the free flexural vibration analysis of thick functionally graded plates resting on elastic foundations. By considering further supposition, the present formulation introduces only four unknowns and its governing equations are therefore reduced. Hamilton's principle is employed to obtain equations of motion and Navier-type analytical solutions for simply-supported plates are compared with the available solutions in literature to check the accuracy of the proposed theory. Numerical results are computed to examine the effects of the power-law index and side-to-thickness ratio on the natural frequencies.

• Coupled systems mechanics
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• 제9권3호
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• pp.265-280
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• 2020

In this paper, a new refined hyperbolic shear deformation beam theory for the free vibration analysis of functionally graded beam is presented. The theory accounts for hyperbolic distribution of the transverse shear strains and satisfies the zero traction boundary conditions on the surfaces of the functionally graded beam without using shear correction factors. In addition, the effect of different micromechanical models on the free vibration response of these beams is studied. Various micromechanical models are used to evaluate the mechanical characteristics of the FG beams whose properties vary continuously across the thickness according to a simple power law. Based on the present theory, the equations of motion are derived from the Hamilton's principle. Navier type solution method was used to obtain frequencies, and the numerical results are compared with those available in the literature. A detailed parametric study is presented to show the effect of different micromechanical models on the free vibration response of a simply supported FG beams.

• 한국지반환경공학회 논문집
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• 제6권1호
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• pp.53-62
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• 2005

본 연구에서는 수도권매립지의 신선한 쓰레기 매립층의 장기침하거동 특성을 규명하기 위해 매립시점부터 설치, 관리되어 온 180여개의 침하판을 대상으로 약 12년간에 걸쳐서 측정된 침하계측 결과에 대한 분석을 수행하였다. 국내 매립지의 침하계측자료와 외국매립지 침하자료들을 분석한 결과 외국 매립지의 압축률보다 다소 작게 측정되고 있으나, 상당히 근접하는 압축률을 보이고 있으며, 기존 장기침하 예측 모델을 적용하여 예측된 장기침하량 분석 결과 쌍곡선 모델, Gibson and Lo의 모델은 상당히 근접한 예측 결과를 나타내었으며, Bjarngard and Edgers 침하모델과 Power Creep Law 모델의 경우 침하계측 기간 동안은 침하자료와 잘 일치되는 경향을 보이나 장기침하량을 예측할 경우 다른 침하모델들에 비해 과다 예측됨을 알 수 있었다. 이외의 다른 예측식(Sowers, 대수함수)은 본 현장에는 적합하지 않은 것으로 사료된다.

• 에너지공학
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• 제8권4호
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• pp.540-545
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• 1999

고전적인 Fourier 열전도 방정식은 극저온하에서 또는 아주 짧은 시간동안의 가열시 타당성이 없는 것으로 고려되었다. 이러한 조건하에서는 열전도파의 성질이 지배적이기 때문에 , 수정된 Fourier 법칙에 근거한 쌍곡선형 열전도 방정식이 도입되었다. 열전도에 대한 Fourier 모델과 쌍곡선형 열전도모델이 적분변환법과 함께 Green 함수방법을 이용하여 분되었다. 한쪽 표면에서 주기적인 표면가열을 하는 유한한 평판의 열유속 분포 및 온도분포의 해를 제시하였고 각가의 모델로부터 얻어진 결과를 서로 비교검토하였다. 쌍곡선형 열전도 방정식에서 유도된 열전도파는 매개물을 통해 전파되어 맞은편쪽의 단열표면에서 가열 표면쪽으로 반사하였으나 , 고전적인 Fourier 모델에 의한 열은 열적교란이 매개물의 전체에 걸쳐서 전달된 후 즉각적으로 무한한 속도로 열전파가 발생함을 보여주었다.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1998년도 춘계학술대회논문집
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• pp.76-79
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• 1998

High temperature plastic deformation behavior of Al 6061 alloy was characterized by hot torsion test. The Al 6061 alloy deformed continuously in the temperature range of 400∼550$^{\circ}C$, and strain rate range of 0.05∼5/sec. The softening mechanism of Al 6061 alloy was dynamic recrystallization and identified by hyperbolic sine law and zener-Hollmon parameter. The evolution of grain size and deformation resistance were calculated by the relationships of deformation variables.

• International Journal of Control, Automation, and Systems
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• 제3권4호
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• pp.601-611
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• 2005

In this paper, an active vibration control of a tensioned, elastic, axially moving string is investigated. The dynamics of the translating string are described with a non-linear partial differential equation coupled with an ordinary differential equation. A right boundary control to suppress the transverse vibrations of the translating continuum is proposed. The control law is derived via the Lyapunov second method. The exponential stability of the closed-loop system is verified. The effectiveness of the proposed control law is simulated.

• International Journal of Naval Architecture and Ocean Engineering
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• 제11권1호
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• pp.584-596
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• 2019

This paper presents a Modified Adaptive Complementary Sliding Mode Control (MACSMC) system for the longitudinal motion control of the Fully-Submerged Hydrofoil Craft (FSHC) in the presence of time varying disturbance and uncertain perturbations. The nonlinear disturbance observer is designed with less conservatism that only boundedness of the derivative of the disturbance is required. Then, a complementary sliding mode control system combined with adaptive law is designed to reduce the bound of stabilization error with fast convergence. In particularly, the modified complementary sliding mode surface which contains the estimation of the disturbance can reduce the switching gain and retain the normal performance of the system. Moreover, a hyperbolic tangent function contained in the control law is utilized to attenuate the chattering of the actuator. The global asymptotic stability of the closed-loop system is demonstrated utilizing the Lyapunov stability theory. Ultimately, the simulation results show the effectiveness of the proposed approach.