• Advances in aircraft and spacecraft science
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• 제10권1호
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• pp.19-49
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• 2023

The present study proposes a theoretical and numerical investigation on the dynamic response behaviour of a functional graded (FG) ceramic-metal tapered rotor shaft system, by the differential quadrature finite elements method (DQFEM) to identify the natural frequencies for modelling and analysis of the structure with suitable validations. The purpose of this paper is to explore the influence of heat gradients on the natural frequency of rotation of FG shafts via three-dimensional solid elements, as well as a theoretical examination using the Timoshenko beam mode, which took into account the gyroscopic effect and rotational inertia. The functionally graded material's distribution is described by two distribution laws: the power law and the exponential law. To simulate varied thermal conditions, radial temperature distributions are obtained using the nonlinear temperature distribution (NLTD) and exponential temperature distribution (ETD) approaches. This work deals with the results of the effect on the fundamental frequencies of different material's laws gradation and temperature gradients distributions. Attempts are conducted to identify adequate explanations for the behaviours based on material characteristics. The effect of taper angle and material distribution on the dynamic behaviour of the FG conical rotor system is discussed.

• 대한기계학회논문집
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• 제6권3호
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• pp.247-255
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• 1982

The heat diffusion equation for an annular fin is analyzed by Laplace transformation. The fin has a uniform thickness, with its end insulated, and three different temperature profiles at the base such as step change, harmonic and exponential functions. The exact solutions for the temperature and heat flux of the fins are obtained with the infinite series. The series solutions converge rapidly for large values of dimensionless time, but slowly for small values. Therefore some approximate solutions are presented here to fine the temperature distribution and heat flux for small values of dimensionless time. Furthermore a simple approximate heat flux, .OMEGA.=1.13c.tau.$^{1}$2/ is found in the range of .tau. .leg. o.1/c for the exponential function at the base.

• International Journal of Contents
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• 제5권2호
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• pp.16-19
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• 2009

In this paper, we concern about the distribution characteristics of surface temperature by the increment of time, diffusivity and heat flux on irradiating of a laser. The penetration depth corresponding to the induced constant heat flux or irradiated laser, is simulated by a computer algorithm. The distribution of temperature versus penetration depth for the variation of time and diffusivity is characterized at the constant heat flux and on irradiating of a laser. The temperature of constant heat flux at the fixed diffusivity or time, is decreased by the pattern of exponential function as the time t or diffusivity a is increased (a=10, 100, 1000). The temperature of constant heat flux is not changed but exponentially fixed with the increasing diffusivity and the fixed time. On the other hand, the temperature of laser at the fixed diffusivity or time is decreased linearly. Our results show that the characteristics of the simulated surface temperature in a semi-infinite solid are similar to the graphs on theoretical consideration.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2004년도 하계학술대회 논문집 C
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• pp.1817-1819
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• 2004

From the plasma application point of view, electron temperature and density are one of the most important parameters for plasma process. But it is only available to control plasma by adjusting external factors like gas pressure and input power. In this paper, pulse-modulated plasma is generated by modulating 13.56GHz RF power with 1, 5, 10kHz pulse. And Langmuir probe technique is used to study the distribution of electron temperature and density. When modulated pulse is off, electron temperature decreases gradually in form of exponential decay. The value t of exponential decay slope is 33.619, 13.834, 10.803 in 1kHz. 5kHz. 10kHz. This implies that this method can be used to control electron temperature and density.

• 한국산림과학회지
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• 제86권1호
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• pp.17-24
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• 1997

지구(地球)의 잠재자연식생분포(潛在自然植生分布)를 추정(推定)하기 위한 첫단계로서 자연식생분포(自然植生分布)와 밀접(密接)한 관계가 있는 기온(氣溫)과 강수량(降水量)에 대한 최적구면보간방법(最適球面補間方法)을 개발하기 위해, Light Climatic Dataset로 명명(命名)한 전세계에 분포(分布)된 1,060점의 측후소(測候所)의 실측자료(實測資料)를 보간용(補間用)과 검정용(檢定用)으로 무작위(無作爲) 2등분(等分)하고, 검정용(檢定用) 측후소(測候所)에 있어서 관측치(觀測値)와 보간용(補間用)에 의한 추정치(推定値)와의 오차(誤差)를 보간방법(補間方法)과 파라메타가 틀린 조합(組合)에 대해 상호비교(相互比較)하였다. 보간용(補間用)에 의한 추정치(推定値)는, 측후소(測候所)의 선택법(選擇法)으로 전점(全点), 정점(定点), 안반경(安半徑)의 3가지 방법, 거리에 대한 하중(荷重)으로 n승 반비례(反比例), 부(負)의 지수함수(指數函數)의 2가지 방법, 방위(方位)에 관한 하중(荷重)으로 타원하중법(楕圓荷重法), 각각에대해 상호조합(相互組合)하여 산출(算出)되었다. 그 결과, 측후소(測候所)의 선택법(選擇法)은 정반경법(定半徑法), 거리(距離)에 관한 하중식(荷重式)은 부(負)의 지수함수(指數函數), 방위(方位)에 관한 하중법(荷重法)은 타원하중법(楕圓荷重法)을 조합(組合)하는 것이 기온(氣溫)과 강수량(降水量)의 보간(補間)에 적합(適合)하였으며, 그에 관한 파라메타 값은 기온(氣溫)에 있어서 정반경(定半徑) $30^{\circ}$, -0.78의 지수함수(指數函數), 타원하중(楕圓荷重) 0.4로, 강수량(降水量)에 있어서는 각각 $35^{\circ}$, -0.53, 1.2로 나타났다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회B
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• pp.2254-2255
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• 2008

Thermoforming is one of the most versatile and economical process to produce polymer products. The drawback of thermoforming is difficult to control thickness of final products. Temperature distribution affects the thickness distribution of final products, but temperature difference between surface and center of sheet is difficult to decrease because of low thermal conductivity of ABS material. In order to decrease temperature difference between surface and center, heating profile must be expressed as exponential function form. In this study, Finite Difference Method was used to find out the coefficients of optimal heating profiles. Through investigation, the optimal results using Finite Difference Method show that temperature difference between surface and center of sheet can be remarkably minimized with satisfying Temperature of Forming Window.

• 전기학회논문지
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• 제68권1호
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• pp.52-60
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• 2019

In this paper, four types of insulation coils were fabricated by adding various kinds of glycols to improve the flexibility and adhesion of insulating coils in varnish dispersed with PAI / Nano Silica_15wt%. The applied voltage and frequency were 1.5 kV / 20 kHz for accelerated life evaluation. Through the 6th temperature stress level, the cause of the insulation breakdown of the coil was ignored and only the breakdown time was measured. The Arrhenius model was chosen based on the theoretical relationship between chemical reaction rate and temperature for estimating the insulation life of the coil due to accelerated thermal stress. Three types of distributions (Weibull, Lognormal, Exponential) were selected as the relationship between thermal stress model and distribution. The average insulation lifetime was estimated under the temperature stress of four types of insulation coils through the relationship between one kind of model and three kinds of distributions.

• Journal of Information Display
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• 제12권1호
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• pp.23-27
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• 2011

The correlation between the temporal and spatial variations of the elastic constant and temperature change was examined for a light guide plate (LGP) adopted in the edge-lit light-emitting-diode backlight for mobile applications, using the micro- Brillouin light scattering method. The velocity of sound and the elastic constant $C_{11}$ of an LGP made from bisphenol-A polycarbonate (PC) were investigated as functions of temperature, time, and position on the LGP. The temporal variation of $C_{11}$ exhibited an exponential decay, while the spatial variation of $C_{11}$ reflected the temperature distribution on the LGP. The glass transition temperature of the PC LGP was found to be located at $155^{\circ}C$. The result showed that systematic transformation between the elastic property and the temperature is possible and that the temperature distribution on the bulk LGP can be accurately probed via the present experiment method, without using any special temperature measurement equipment.

• Food Science and Biotechnology
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• 제15권5호
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• pp.773-777
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• 2006

Growth of Bacillus cereus was assessed during the storage of seasoned soybean sprouts at 0,5, 10, and $15^{\circ}C$. No lag time in its growth curve was observed and thus the specific growth rate of B. cereus in the exponential growth phase was estimated for bootstrapped microbial count data. The distribution of the specific growth rate could be explained by the BetaGeneral distribution function, and temperature dependence was described by the Ratkowsky square root model. The temperature dependence of the growth could be successfully incorporated into the differential equation of microbial growth to predict the B. cereus count on the seasoned soybean sprouts under fluctuating temperature conditions. Safe shelf lives with different probabilities to reach $10^5\;CFU/g$ were presented at four different temperatures, considering the variation in initial contamination and specific growth rate by the Monte Carlo method and 2-step bootstrapping, respectively. Safe shelf lives defined as the time with a probability of less than 0.1% of reaching the critical limit, were 13.4, 5.2, 3.6, and 2.8 days at 0, 5, 10, and $15^{\circ}C$, respectively.

• 한국자기공명학회논문지
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• 제17권1호
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• pp.19-23
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• 2013

The temperature dependences of the NMR spectrum and the spin-lattice relaxation times in $KH_2PO_4$ were investigated via single-crystal NMR and MAS NMR. The stretched-exponential relaxation that occurred because of the distribution of correlation times was indicative of the degree of the distribution of the double-well potential on the hydrogen bond. The behaviors responsible for the strong temperature dependences of the $^1H$ and $^{31}P$ spin-lattice relaxation times in the rotating frame $T_{1{\rho}}$ in $KH_2PO_4$ are likely related to the reorientational motion of the hydrogen-bond geometry and the $PO_4$ tetrahedral distortion.