• 대한전자공학회논문지SP
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• 제46권1호
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• pp.79-86
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• 2009

본 논문에서는 자연지진음과 인공지진음 특성 분석을 위해 스펙트럼 기울기 파라미터 추출을 위한 알고리즘을 제안하였다. 신뢰성을 높이기 위해 다양한 지역에서 실험을 실시하였고 제안한 알고리즘을 이용하여 실험 데이터로부터 자연지진음과 인공지진음의 기울기 지수를 추출함으로써 특성을 분석하였다. 실험 및 분석결과 자연지진음이 인공지진음보다 스펙트럼에서 고주파 감쇠가 크고 저주파대역에 집중되어 있어 자연지진음의 기울기 지수가 인공지진음의 기울기 지수보다 높은 것으로 나타났다.

• Computers and Concrete
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• 제26권1호
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• pp.31-52
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• 2020

This paper investigates the size dependent effect on the vibration analysis of a porous nanocomposite viscoelastic plate reinforced by functionally graded-single walled carbon nanotubes (FG-SWCNTs) by considering nonlocal strain gradient theory. Therefore, using energy method and Hamilton's principle, the equations of motion are derived. In this article, the effects of nonlocal parameter, aspect ratio, strain gradient parameter, volume fraction of carbon nanotubes (CNTs), damping coefficient, porosity coefficient, and temperature change on the natural frequency are perused. The innovation of this paper is to compare the effectiveness of each mentioned parameters individually on the free vibrations of this plate and to represent the appropriate value for each parameter to achieve an ideal nanocomposite plate that minimizes vibration. The results are verified with those referenced in the paper. The results illustrate that the effect of damping coefficient on the increase of natural frequency is significantly higher than the other parameters effect, and the effects of the strain gradient parameter and nonlocal parameter on the natural frequency increase are less than damping coefficient effect, respectively. Furthermore, the results indicate that the natural frequency decreases with a rise in the nonlocal parameter, aspect ratio and temperature change. Also, the natural frequency increases with a rise in the strain gradient parameter and CNTs volume fraction. This study can be used for optimizing the industrial and medical designs, such as automotive industry, aerospace engineering and water purification system, by considering ideal properties for the nanocomposite plate.

• 한국산림과학회지
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• 제71권1호
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• pp.50-54
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• 1985

경사면(傾斜面)에 생육(生育)하는 굴참나무, 물참나무, 갈참나무, 떡갈나무 천연림(天然林)의 입목경사도(立木傾斜度)에 미치는 여러 인자(因子)의 영향을 측정(測定) 분석(分析)하였다. 입목경사도(立木傾斜度)에 영향을 미치고 있는 인자(因子)는 수종간(樹種間)의 차(差), 입목경사도(立木傾斜度), 방위(方位)였으며, 입목밀도(立木密度)와 수고(樹高)는 입목경사도(立木傾斜度)와는 상관(相關)이 없었다. 인자(因子) 중 수종간(樹種間)의 차(差)가 입목경사도(立木傾斜度)에 가장 크게 영향을 미쳤으며 다음이 사면경사도(斜面傾斜度)였다. 특히 수종(樹種) 중에서는 물참나무가 모든 사면경사도(斜面傾斜度)에서 가장 기울어지는 양상을 나타내었다.

• Structural Engineering and Mechanics
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• 제15권6호
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• pp.705-716
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• 2003

Gradient elastic flexural beams are dynamically analysed by analytic means. The governing equation of flexural beam motion is obtained by combining the Bernoulli-Euler beam theory and the simple gradient elasticity theory due to Aifantis. All possible boundary conditions (classical and non-classical or gradient type) are obtained with the aid of a variational statement. A wave propagation analysis reveals the existence of wave dispersion in gradient elastic beams. Free vibrations of gradient elastic beams are analysed and natural frequencies and modal shapes are obtained. Forced vibrations of these beams are also analysed with the aid of the Laplace transform with respect to time and their response to loads with any time variation is obtained. Numerical examples are presented for both free and forced vibrations of a simply supported and a cantilever beam, respectively, in order to assess the gradient effect on the natural frequencies, modal shapes and beam response.

• Structural Engineering and Mechanics
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• 제48권3호
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• pp.415-434
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• 2013

This work is concerned with transverse vibrations of axially traveling nanobeams including strain gradient and thermal effects. The strain gradient elasticity theory and the temperature field are taken into consideration. A new higher-order differential equation of motion is derived from the variational principle and the corresponding higher-order non-classical boundary conditions including simple, clamped, cantilevered supports and their higher-order "offspring" are established. Effects of strain gradient nanoscale parameter, temperature change, shape parameter and axial traction on the natural frequencies are presented and discussed through some numerical examples. It is concluded that the factors mentioned above significantly influence the dynamic behaviors of an axially traveling nanobeam. In particular, the strain gradient effect tends to induce higher vibration frequencies as compared to an axially traveling macro beams based on the classical vibration theory without strain gradient effect.

• 충청수학회지
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• 제33권2호
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• pp.219-226
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• 2020

In this paper, we consider gradient Ricci solitons and gradient Yamabe solitons in the warped product spaces. Also we study warped product space with harmonic curvature related to gradient Ricci solitons and gradient Yamabe solitons. Consequently some theorems are generalized and we derive differential equations for a warped product space to be a gradient Ricci soliton.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2004년도 춘계학술발표회
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• pp.580-585
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• 2004

The purpose of this study is the stability evaluation of soil slope according to inclination of upper natural slope. Upper natural slope breeds loss of slope by inflow in slope of surface water by rainfal1 and f1uctuation of amount of materials in slope through method of cutting slope according to degree of inclination. Basis of standard inclination does not consider of inclination of upper natural slope and is presented uniformly. Therefore, in this study, analyzed stability of inclination of upper natural slope through limit equilibrium analysis. Result is same as following. First, safety factor through limit equilibrium analysis is almost direct decrease when gradient of soil slope is 1:1.2, 1:1.5. However, when gradient of soil slope is 1:1.0, 1:0.7, if sinclination of upper natural slope are $20^{\circ}$, it shows tendency that decrease of safety factor becomes low rapidly. Second, when when gradient of soil slope is fixed, inclination of upper natural slope increase tendency(maximum 3.0 times) that decrease of safety factor.

• International Journal of Control, Automation, and Systems
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• 제3권2호
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• pp.244-251
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• 2005

In this paper, we study the problem of stabilizing a general nonlinear control system by means of gradient descent control method which is a dynamic feedback control law. In this method, the general nonlinear control system can be considered as an affine nonlinear control systems. Then by using Sontag's formula we investigate the stability (asymptotic) of the general nonlinear control system.

• 대한수학회논문집
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• 제35권1호
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• pp.261-268
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• 2020

In this paper, we study gradient Yamabe solitons in the warped product manifolds and classify the warped product manifolds with gradient Yamabe solitons. Moreover we investigate the admitness of gradient Yamabe solitons and geometric structures for some model spaces.

• Steel and Composite Structures
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• 제26권4호
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• pp.421-437
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• 2018

Free vibration analysis of a three-layered microbeam including an elastic micro-core and two piezo-magnetic face-sheets resting on Pasternak's foundation are studied in this paper. Strain gradient theory is used for size-dependent modeling of microbeam. In addition, three-unknown shear and normal deformations theory is employed for description of displacement field. Hamilton's principle is used for derivation of the governing equations of motion in electro-magneto-mechanical loads. Three micro-length-scale parameters based on strain gradient theory are employed for prediction of vibrational characteristics of structure in micro-scale. The results show that increase of three micro-length-scale parameters leads to significant increase of three natural frequencies especially for increase of second micro-length-scale parameter. This result is according to this fact that stiffness of a micro-scale structure is increased with increase of micro-length-scale parameters.